FGF23
Fibroblast growth factor 23 precursor (FGF-23) (Phosphatonin) (Tumor-derived hypophosphatemia-inducing factor) [Contains: Fibroblast growth factor 23 N-terminal peptide; Fibroblast growth factor 23 C-terminal peptide] [HYPF] [UNQ3027/PRO9828]
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During the evolution of skeletons, terrestrial vertebrates acquired strong bones made of calcium-phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate ions, they created the bone when and where they wanted simply by providing a cue for precipitation. To secure this strategy, they acquired a novel endocrine system to strictly control the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion, thereby maintaining phosphate homeostasis. The FGF23-Klotho endocrine system, when disrupted in mice, results in hyperphosphatemia and vascular calcification. Besides, mice lacking Klotho or FGF23 suffer from complex aging-like phenotypes, which are alleviated by placing them on a low-phosphate diet, indicating that phosphate is primarily responsible for the accelerated aging. Phosphate acquires the ability to induce cell damage and inflammation when precipitated with calcium. In the blood, calcium-phosphate crystals are adsorbed by serum protein fetuin-A and prevented from growing into large precipitates. Consequently, nanoparticles that comprised calcium-phosphate crystals and fetuin-A, termed calciprotein particles (CPPs), are generated and dispersed as colloids. CPPs increase in the blood with an increase in serum phosphate and age. Circulating CPP levels correlate positively with vascular stiffness and chronic non-infectious inflammation, raising the possibility that CPPs may be an endogenous pro-aging factor. Terrestrial vertebrates with the bone made of calcium-phosphate may be destined to age due to calcium-phosphate in the blood.
Keywords
- Aging
- Calciprotein particles (CPPs)
- Fibroblast growth factor-23 (FGF23)
- Inflammation
- Klotho
- Phosphate
- Vascular calcification
αKlotho is a hormone and co-receptor for fibroblast growth factor 23 (FGF23), a hormone that downregulates active vitamin D synthesis and promotes phosphate excretion. Low αKlotho and high FGF23 occur in chronic kidney disease (CKD). We aimed to assess the relationships of αKlotho and FGF23 with mobility disability in community-dwelling older adults. We estimated associations of plasma-soluble αKlotho and serum FGF23 concentrations with mobility disability over 6 years. Additional analyses was stratified by CKD. Participants included 2751 adults (25.0% with CKD), aged 71 to 80 years, from the 1998 to 1999 Health, Aging, and Body Composition Study visit. Walking disability and stair climb disability were defined as self-reported "a lot of difficulty" or an inability to walk a quarter mile and climb 10 stairs, respectively. Median (interquartile range [IQR]) serum FGF23 and plasma soluble αKlotho concentrations were 46.6 (36.7, 60.2) pg/mL and 630.4 (478.4, 816.0) pg/mL, respectively. After adjustment, higher αKlotho concentrations were associated with lower walking disability rates (Rate Ratio [RR] highest vs. lowest tertile = 0.74; 95% confidence interval l [CI] = 0.62, 0.89; [i]P[/i] = 0.003). Higher FGF23 concentrations were associated with higher walking disability rates (RR highest vs. lowest tertile = 1.24; 95%CI = 1.03, 1.50; [i]P[/i] = 0.005). Overall, higher αKlotho combined with lower FGF23 was associated with the lowest walking disability rates ([i]P[/i] for interaction = 0.023). Stair climb disability findings were inconsistent. No interactions with CKD were statistically significant ([i]P[/i] for interaction > 0.10). Higher plasma soluble αKlotho and lower serum FGF23 concentrations were associated with lower walking disability rates in community-dwelling older adults, particularly those without CKD.
Keywords
- aging
- chronic kidney disease
- fibroblast growth factor 23
- mobility disability
- αKlotho
To clarify the regulation of astragalus on the aging BMSCs model and the effect of astragalus on Vitamin D (VD)-FGF23-Klotho axis. siRNA was used to interfere the expression of VDR gene in aging BMSCs. Serum containing astragalus in different concentrations was added to the cultured cells. The expression of osteocalcin and alkaline phosphatase were detected by alizarin red staining and ELISA. Cell vitality was detected by flow cytometry, CCK-8 test, and [i]β[/i]-galactosidase staining. The expression of FGF23, Klotho, CYP27B1, and CYP24A1 was detected by qRT-PCR and western blot. The results showed that after reducing VDR gene expression, the aging BMSCs model showed decreased activity and osteogenic ability, increased expression of FGF23, Klotho and CYP24A1, and decreased expression of CYP27B1. After adding serum-containing astragalus, the activity of cells and the osteogenic ability was increased; the expression levels of FGF23, Klotho and CYP24A1 were decreased, the expression levels of CYP27B1 were increased, and the trend was more obvious with the increase of astragalus concentration. This study confirmed that astragalus could inhibit the aging of BMSCs and improve the osteogenesis ability by regulating the VD-FGF23-Klotho pathway. This study provided a certain research basis for the therapeutic of traditional Chinese medicine (TCM) on primary osteoporosis.
Keywords
- Astragalus
- BMSCs
- VD-FGF23-Klotho axis
- aging
- osteogenesis differentiation
The polysaccharide of Polygonatum sibiricum (PSP)is one of the main active ingredients of Polygonatum Polygonatum in Liliaceae. It has anti-tumor, anti-aging, immune regulation, and anti-oxidative effects. Recent studies have shown that the Klotho gene and fibroblast growth factor-23 (FGF-23) have a common receptor, which is closely related to aging and highly expressed in kidney and meninges. Our study aimed to investigate the anti-aging effect of PSP on D-galactose-induced rats and its mechanism. D-galactose (120 mg Kg ) and PSP (100 mg Kg ) was used to intervene in rats, respectively. Then The changes of indexes of the natural aging-like model rats before and after PSP intervention were observed. We found that PSP could significantly improve the learning and memory abilities of rats and reverse the pathological changes of kidney tissues in rats. At the same time, PSP up-regulated the expression of Klotho mRNA and Klotho protein in the renal cortex, down-regulated the expression of FOXO3a mRNA and p-FOXO3a protein in renal tissue, and inhibited the expression of FGF-23 protein in the femur. Our studies suggest that PSP may play a role by regulating the Klotho-FGF23 endocrine axis, alleviating oxidative stress, and balancing calcium and phosphorus metabolism.
MeSH Terms
- Aging
- Animals
- Calcium
- Dietary Carbohydrates
- Fibroblast Growth Factors
- Galactose
- Glucuronidase
- Male
- Oxidative Stress
- Phosphorus
- Phytochemicals
- Polygonatum
- Polysaccharides
- Protective Agents
- Rats
- Rats, Sprague-Dawley
Observations in transgenic α-Klotho (Kl) mice (KlTg) defined the antiaging role of soluble Klotho (sKL130). A genetic translocation that elevates sKL levels in humans is paradoxically associated with increased circulating fibroblast growth factor 23 (FGF23) levels and the potential of both membrane KL (mKL135) and sKL130 to act as coreceptors for FGF23 activation of fibroblast growth factor receptors (FGFRs). Neither FGF23 expression nor the contributions of FGF23, mKL135, and sKL130 codependent and independent functions have been investigated in KlTg mice. In the current study, we examined the effects of Kl overexpression on FGF23 levels and functions in KlTg mice. We found that mKL135 but not sKL130 stimulated FGF23 expression in osteoblasts, leading to elevated Fgf23 bone expression and circulating levels in KlTg mice. Elevated FGF23 suppressed 1,25(OH)2D and parathyroid hormone levels but did not cause hypophosphatemic rickets in KlTg mice. KlTg mice developed low aldosterone-associated hypertension but not left ventricular hypertrophy. Mechanistically, we found that mKL135 and sKL130 are essential cofactors for FGF23-mediated ERK activation but that they inhibited FGF23 stimulation of PLC-γ and PI3K/AKT signaling. Thus, increased longevity in KlTg mice occurs in the presence of excess FGF23 that interacts with mKL and sKL to bias FGFR pathways.
MeSH Terms
- Aldosterone
- Animals
- Bone and Bones
- Cardiovascular Diseases
- Disease Models, Animal
- Female
- Fibroblast Growth Factors
- Gene Knockout Techniques
- Glucuronidase
- Kidney
- Longevity
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Osteoblasts
- Protein Isoforms
- Transcriptome
Keywords
- Bone Biology
- Cardiovascular disease
Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone that is increased in azotemic cats with chronic kidney disease (CKD) and predictive of the onset of azotemia in older cats. The introduction of symmetric dimethylarginine (SDMA) as a biomarker of glomerular filtration rate has led to the identification of cats in which SDMA is increased, but plasma creatinine concentrations remains within reference range. There is currently little understanding of the metabolic changes present in such cats. To examine the relationship between plasma FGF23 and SDMA concentrations in non-azotemic geriatric cats. Records of a cross section of client-owned cats (n = 143) without azotemic CKD. Clinicopathological information was obtained from cats (≥ 9 years) from records of 2 first opinion practices. The relationship between plasma SDMA and FGF23 concentrations was examined using Spearman's correlation and variables compared using the Mann-Whitney U test. Cats with increased SDMA concentrations had significantly higher plasma FGF23 (P < .001) and creatinine (P < .001) concentrations compared to cats with SDMA concentrations within reference range. A weak positive relationship was demonstrated between plasma FGF23 and SDMA concentrations (r = .35, P < .001) and between plasma FGF23 and creatinine (r = .23, P = .005) concentrations. More cats with increased SDMA concentrations had higher FGF23 concentrations than those with SDMA concentrations within the reference range, suggesting the presence of an alteration in phosphate homeostasis. Further studies are warranted to identify influencing factors and to explore the utility of FGF23 concentration to inform management of cats with early stage CKD.
MeSH Terms
- Aging
- Animals
- Arginine
- Biomarkers
- Cats
- Cross-Sectional Studies
- Female
- Fibroblast Growth Factors
- Male
- Reference Values
- Retrospective Moral Judgment
Keywords
- azotemia
- feline
- phosphate
- renal
The nature of muscle-bone crosstalk has been historically considered to be only mechanical, where the muscle is the load applier while bone provides the attachment sites. However, this dogma has been challenged with the emerging notion that bone and muscle act as secretory endocrine organs affect the function of each other. Biochemical crosstalk occurs through myokines such as myostatin, irisin, interleukin (IL)-6, IL-7, IL-15, insulin-like growth factor-1, fibroblast growth factor (FGF)-2, and β-aminoisobutyric acid and through bone-derived factors including FGF23, prostaglandin E , transforming growth factor β, osteocalcin, and sclerostin. Aside from the biochemical and mechanical interaction, additional factors including aging, circadian rhythm, nervous system network, nutrition intake, and exosomes also have effects on bone-muscle crosstalk. Here, we summarize the current research progress in the area, which may be conductive to identify potential novel therapies for the osteoporosis and sarcopenia, especially when they develop in parallel.
MeSH Terms
- Aging
- Bone and Bones
- Circadian Rhythm
- Humans
- Muscle Proteins
- Muscle, Skeletal
- Nervous System Physiological Phenomena
- Osteocalcin
- Protein Binding
- Signal Transduction
Keywords
- bone
- crosstalk
- muscle
- myokines
- osteoporosis
- sarcopenia
Children with Hutchinson-Gilford progeria syndrome (HGPS), a rare premature aging disease, exhibit extraskeletal calcifications detected by radiographic analysis and on physical examination. The aim of this study was to describe the natural history and pathophysiology of these abnormal calcifications in HGPS, and to determine whether medications and/or supplements tested in clinical trials alter their development. Children from two successive clinical trials administering 1) lonafarnib (n = 26) and 2) lonafarnib pravastatin zoledronic acid (n = 37) were studied at baseline (pre-therapy), one year on therapy, and at end-of-therapy (3.3-4.3 years after the baseline visit). Calcium supplementation (oral calcium carbonate) was administered during the first year of the second trial and was subsequently discontinued. Information on calcifications was obtained from physical examinations, radiographs, and serum and urinary biochemical measures. The mineral content of two skin-derived calcifications was determined by x-ray diffraction. Extraskeletal calcifications were detected radiographically in 12/39 (31%) patients at baseline. The odds of exhibiting calcifications increased with age (p = 0.045). The odds were unaffected by receipt of lonafarnib, pravastatin, and zoledronate therapies. However, administration of calcium carbonate supplementation, in conjunction with all three therapeutic agents, significantly increased the odds of developing calcifications (p = 0.009), with the odds plateauing after the supplement's discontinuation. Composition analysis of calcinosis cutis showed hydroxyapatite similar to bone. Although serum calcium, phosphorus, and parathyroid hormone (PTH) were within normal limits at baseline and on-therapy, PTH increased significantly after lonafarnib initiation (p < 0.001). Both the urinary calcium/creatinine ratio and tubular reabsorption of phosphate (TRP) were elevated at baseline in 22/39 (56%) and 31/37 (84%) evaluable patients, respectively, with no significant changes while on-therapy. The mean calcium × phosphorus product (Ca × Pi) was within normal limits, but plasma magnesium decreased over both clinical trials. Fibroblast growth factor 23 (FGF23) was lower compared to age-matched controls (p = 0.03). Extraskeletal calcifications increased with age in children with HGPS and were composed of hydroxyapatite. The urinary calcium/creatinine ratio and TRP were elevated for age while FGF23 was decreased. Magnesium decreased and PTH increased after lonafarnib therapy which may alter the ability to mobilize calcium. These findings demonstrate that children with HGPS with normal renal function and an unremarkable Ca × Pi develop extraskeletal calcifications by an unidentified mechanism that may involve decreased plasma magnesium and FGF23. Calcium carbonate accelerated their development and is, therefore, not recommended for routine supplementation in these children.
MeSH Terms
- Calcinosis
- Calcium
- Child
- Child, Preschool
- Creatinine
- Female
- Humans
- In Vitro Techniques
- Lamin Type A
- Male
- Parathyroid Hormone
- Piperidines
- Pravastatin
- Progeria
- Pyridines
- Zoledronic Acid
Keywords
- Aging
- Extraskeletal calcifications
- HGPS
- Lamin
- Laminopathy
- Magnesium
- Parathyroid hormone
- Progeria
Body weight (BW) at different ages are of increasing importance in dairy cattle breeding schemes, because of their strong correlation with energy efficiency traits, and their impact on cow health, longevity and farm economy. In total, 15,921 dairy cattle from 56 large-scale test-herds with BW records were genotyped for 45,613 single nucleotide polymorphisms (SNPs). This dataset was used for genome-wide association studies (GWAS), in order to localize potential candidate genes for direct and maternal genetic effects on BW recorded at birth (BW0), at 2 to 3 months of age (BW23), and at 13 to 14 months of age (BW1314). The first 20 principal components (PC) of the genomic relationship matrix ([Formula: see text]) grouped the genotyped cattle into three clusters. In the statistical models used for GWAS, correction for population structure was done by including polygenic effects with various genetic similarity matrices, such as the pedigree-based relationship matrix ([Formula: see text]), the [Formula: see text]-matrix, the reduced [Formula: see text]-matrix LOCO (i.e. exclusion of the chromosome on which the candidate SNP is located), and LOCO plus chromosome-wide PC. Inflation factors for direct genetic effects using [Formula: see text] and LOCO were larger than 1.17. For [Formula: see text] and LOCO plus chromosome-wide PC, inflation factors were very close to 1.0. According to Bonferroni correction, ten, two and seven significant SNPs were detected for the direct genetic effect on BW0, BW23, and BW1314, respectively. Seventy-six candidate genes contributed to direct genetic effects on BW with four involved in growth and developmental processes: FGF6, FGF23, TNNT3, and OMD. For maternal genetic effects on BW0, only three significant SNPs (according to Bonferroni correction), and four potential candidate genes, were identified. The most significant SNP on chromosome 19 explained only 0.14% of the maternal de-regressed proof variance for BW0. For correction of population structure in GWAS, we suggest a statistical model that considers LOCO plus chromosome-wide PC. Regarding direct genetic effects, several SNPs had a significant effect on BW at different ages, and only two SNPs on chromosome 5 had a significant effect on all three BW traits. Thus, different potential candidate genes regulate BW at different ages. Maternal genetic effects followed an infinitesimal model.
MeSH Terms
- Aging
- Animals
- Body Weight
- Cattle
- Extracellular Matrix Proteins
- Female
- Fibroblast Growth Factors
- Genome-Wide Association Study
- Male
- Polymorphism, Single Nucleotide
- Proteoglycans
- Quantitative Trait Loci
- Troponin T
Fibrous dysplasia (FD) is a mosaic disease in which bone is replaced with fibro-osseous tissue. Lesions expand during childhood, reaching final burden by age 15 years. In vitro data suggest that disease activity decreases in adulthood; however, there is no clinical data to support this concept. Bone turnover markers (BTMs) have been used as markers of disease activity in FD; however, the natural history of BTM changes, the effects of antiresorptive treatment, and their association to clinical outcomes have not been described. The goals of this study are to describe 1) the natural history of FD disease activity and its association with pain; 2) the impact of bisphosphonates on the natural history of BTMs; and 3) the effect of bisphosphonates on progression of FD burden during childhood. Disease burden scores and alkaline phosphatase, osteocalcin, NTx, FGF23, and RANKL levels from 178 subjects in an FD/MAS natural history study were reviewed, including 73 subjects treated with bisphosphonates. BTMs, RANKL, and FGF23 demonstrated a sustained reduction with age. Bisphosphonate treatment did not significantly impact this age-dependent decrease in BTMs. Pain was more prevalent and severe in adults compared with children and was not associated with BTMs. In children, the progression of disease burden was not affected by bisphosphonates. In conclusion, FD is associated with an age-dependent decline in bone turnover and other markers of disease activity. Pain, in contrast, is more frequent and severe in adults with FD and is not related to bone turnover. Bisphosphonate treatment does not significantly impact the age-dependent decrease in bone turnover, nor does it prevent the progression of FD disease burden in children. These findings, in association with the established adverse effects of antiresorptives, should be considered when evaluating use and response to bisphosphonates in patients being treated for FD and in any study using BTMs as surrogate endpoints. © 2019 American Society for Bone and Mineral Research.
MeSH Terms
- Adolescent
- Adult
- Age Factors
- Aged
- Aged, 80 and over
- Aging
- Biomarkers
- Bone Remodeling
- Child
- Child, Preschool
- Diphosphonates
- Female
- Fibrous Dysplasia of Bone
- Humans
- Male
- Middle Aged
- Pain
- Prevalence
Keywords
- ANTIRESORPTIVES
- BIOCHEMICAL MARKERS OF BONE TURNOVER
- FIBROUS DYSPLASIA
- MCCUNE-ALBRIGHT SYNDROME
Three fibroblast growth factor(FGF) members, FGF19, FGF21, and FGF23, function as endocrine factors that regulate various metabolic processes. The unique feature of these endo- crine FGFs is the fact that they require Klotho proteins to bind to their cognate FGF recep- tors. Defects in Klotho or FGF23 result in disturbed mineral metabolism and accelerated aging. The aging phenotypes can be alleviated by correcting phosphate imbalance, leading us to hypothesize that phosphate accelerates aging. In contrast, overexpression of FGF21 extends life span in mice. Thus, the FGF-Klotho endocrine axes have emerged as key regula- tors of the aging process and are regarded as potential therapeutic targets for the treatment of age-related disorders.
MeSH Terms
- Aging
- Animals
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Longevity
- Mice
The Klotho proteins, αKlotho and βKlotho, are essential components of endocrine fibroblast growth factor (FGF) receptor complexes, as they are required for the high-affinity binding of FGF19, FGF21 and FGF23 to their cognate FGF receptors (FGFRs). Collectively, these proteins form a unique endocrine system that governs multiple metabolic processes in mammals. FGF19 is a satiety hormone that is secreted from the intestine on ingestion of food and binds the βKlotho-FGFR4 complex in hepatocytes to promote metabolic responses to feeding. By contrast, under fasting conditions, the liver secretes the starvation hormone FGF21, which induces metabolic responses to fasting and stress responses through the activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system following binding to the βKlotho-FGFR1c complex in adipocytes and the suprachiasmatic nucleus, respectively. Finally, FGF23 is secreted by osteocytes in response to phosphate intake and binds to αKlotho-FGFR complexes, which are expressed most abundantly in renal tubules, to regulate mineral metabolism. Growing evidence suggests that the FGF-Klotho endocrine system also has a crucial role in the pathophysiology of ageing-related disorders, including diabetes, cancer, arteriosclerosis and chronic kidney disease. Therefore, targeting the FGF-Klotho endocrine axes might have therapeutic benefit in multiple systems; investigation of the crystal structures of FGF-Klotho-FGFR complexes is paving the way for the development of drugs that can regulate these axes.
MeSH Terms
- Aging
- Animals
- Biomarkers
- Birds
- Cardiovascular Diseases
- Endocrine System Diseases
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Hypothalamo-Hypophyseal System
- Kidney Diseases
- Mammals
- Phosphates
- Pituitary-Adrenal System
Over the last two decades, it has become increasingly apparent that Wnt signaling plays a critical role in development and adult tissue homeostasis in multiple organs and in the pathogenesis of many diseases. In particular, a crucial role for Wnt signaling in bone development and bone tissue homeostasis has been well recognized. Numerous genome-wide association studies confirmed the importance of Wnt signaling in controlling bone mass. Moreover, ample evidence suggests that Wnt signaling is essential for kidney, intestine, and adipose tissue development and homeostasis. Recent emerging evidence demonstrates that Wnt signaling may play a fundamental role in the aging process of those organs. New discoveries show that bone is not only the major reservoir for calcium and phosphate storage, but also the largest organ with multiple functions, including mineral and energy metabolism. The interactions among bone, kidney, intestine, and adipose tissue are controlled and regulated by several endocrine signals, including FGF23, klotho, sclerostin, osteocalcin, vitamin D, and leptin. Since the aging process is characterized by structural and functional decline in almost all tissues and organs, understanding the Wnt signaling-related interactions among bone, kidney, intestine, and adipose tissue in aging may shed light on the pathogenesis of age-related diseases.
MeSH Terms
- Adipose Tissue
- Aging
- Animals
- Bone Development
- Bone and Bones
- Humans
- Intestinal Mucosa
- Kidney
- Wnt Signaling Pathway
Keywords
- FGF23-klotho
- Wnt/β-catenin signaling
- aging
- bone
- sclerostin
Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel. Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers. A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified. Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.
MeSH Terms
- Aged
- Aging
- Amyloid beta-Peptides
- Amyloid beta-Protein Precursor
- Animals
- Apoptosis
- Biomarkers
- Fibronectins
- Frailty
- Genetic Association Studies
- Growth Differentiation Factor 15
- Humans
- Insulin-Like Growth Factor I
- Interleukin-1 Receptor-Like 1 Protein
- Membrane Glycoproteins
- MicroRNAs
- Signal Transduction
Keywords
- Age-related diseases
- Biomarker panel
- Frailty
- Hallmark of aging pathways
The [i]klotho[/i] gene encodes a type I single-pass transmembrane protein that contains a large extracellular domain, a membrane spanning segment, and a short intracellular domain. Klotho protein exists in several forms including the full-length membrane form (mKl) and a soluble circulating form [soluble klotho (sKl)]. mKl complexes with fibroblast growth factor receptors to form coreceptors for FGF23, which allows it to participate in FGF23-mediated signal transduction and regulation of phosphate and calcium homeostasis. sKl is present in the blood, urine, and cerebrospinal fluid where it performs a multitude of functions including regulation of ion channels/transporters and growth factor signaling. How sKl exerts these pleiotropic functions is poorly understood. One hurdle in understanding sKl's mechanism of action as a "hormone" has been the inability to identify a receptor that mediates its effects. In the body, the kidneys are a major source of sKl and sKl levels decline during renal disease. sKl deficiency in chronic kidney disease makes the heart susceptible to stress-induced injury. Here, we summarize the current knowledge of mKl's mechanism of action, the mechanistic basis of sKl's protective, FGF23-independent effects on the heart, and provide new insights into the mechanism of action of sKl focusing on recent findings that sKl binds sialogangliosides in membrane lipid rafts to regulate growth factor signaling.
Keywords
- FGF23
- IGF-1
- TRPC6
- aging
- heart disease
- klotho
- lipid rafts
- sialidase
α-Klotho is well described as an anti-aging protein, with critical roles in kidney function as a transmembrane co-receptor for FGF23, and as a soluble factor in serum. α-Klotho is also expressed in the choroid plexus, where it is released into the cerebrospinal fluid. Nonetheless, α-Klotho is also expressed in the brain parenchyma. Accumulating evidence indicates that this pool of α-Klotho, which we define as brain α-Klotho, may play important roles as a neuroprotective factor and in promoting myelination, thereby supporting healthy brain aging. Here we summarize what is known about brain α-Klotho before focusing on the outstanding scientific questions related to its function. We believe there is a need for in vitro studies designed to distinguish between brain α-Klotho and other pools of α-Klotho, and for a greater understanding of the basic function of soluble α-Klotho. The mechanism by which the human KL-VS variant affects cognition also requires further elucidation. To help address these questions we suggest some experimental approaches that other laboratories might consider. In short, we hope to stimulate fresh ideas and encourage new research approaches that will allow the importance of α-Klotho for the aging brain to become clear.
MeSH Terms
- Aging
- Animals
- Brain
- Central Nervous System
- Cognition
- Fibroblast Growth Factors
- Glucuronidase
- Humans
Keywords
- Aging
- CNS
- Cognition
- KLOTHO
- Signaling
{{medline-entry |title=Fibroblast Growth Factor 23 and the Risk of Infection-Related Hospitalization in Older Adults. |pubmed-url=https://pubmed.ncbi.nlm.nih.gov/28122946 |abstract=Within monocytes, 1,25-dihydroxyvitamin D [1,25(OH) D] is important for production of cathelicidins, which in turn, are critical for antibacterial action. Fibroblast growth factor 23 (FGF23) decreases 1,25(OH) D production and thus, could increase infection risk. We examined this possibility in 3141 community-dwelling adults ages ≥65 years old at baseline in the Cardiovascular Health Study using Cox proportional hazards models to examine the association between FGF23 concentrations and first infection-related hospitalizations and determine whether associations differed by the presence of CKD (eGFR<60 ml/min per 1.73 m [[i]n[/i]=832] or urine albumin-to-creatinine ratio >30 mg/g [[i]n[/i]=577]). Mean±SD age of participants was 78±5 years old, 60% of participants were women, and the median plasma FGF23 concentration was 70 (interquartile range, 53-99) relative units per milliliter. In fully adjusted models, higher FGF23 concentrations associated with higher risk of first infection-related hospitalization (hazard ratio [HR], 1.11; 95% confidence interval [95% CI], 1.03 to 1.20 per doubling of FGF23) during a median follow-up of 8.6 years. In participants with or without CKD (defined by eGFR), FGF23 concentration associated with first infection-related hospitalization with HRs of 1.24 (95% CI, 1.08 to 1.42) and 1.06 (95% CI, 0.97 to 1.17) per doubling of FGF23, respectively ([i]P[/i]=0.13 for interaction). Associations did not differ between groups when stratified by urine albumin-to-creatinine ratio. In sensitivity analyses, the addition of serum calcium, phosphorus, 25-hydroxyvitamin D, intact parathyroid hormone, and 24,25-dihydroxyvitamin D did not meaningfully change the estimates. In conclusion, in community-dwelling older adults, higher plasma FGF23 concentrations independently associated with the risk of first infection-related hospitalization. |mesh-terms=* Aged
- Bacterial Infections
- Female
- Fibroblast Growth Factors
- Hospitalization
- Humans
- Longitudinal Studies
- Male
- Prospective Studies
- Risk Factors
|keywords=* aging
- chronic kidney disease
- clinical epidemiology
- infection
- mineral metabolism
|full-text-url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5373449 }}
To investigate the effect of testosterone treatment on biomarkers calprotectin, fibroblast growth factor 23 (FGF23), soluble Klotho, phosphate, calcium, parathyroid hormone, creatinine and estimated glomerular filtration rate. Randomized, double-blinded, placebo-controlled study. Odense Androgen Study-the effect of Testim and training in hypogonadal men. Men aged 60-78 years old with a low normal concentration of free of bioavailable testosterone <7.3 nmol/L and waist circumference >94 cm recruited from 2008 to 2009 (N = 48) by advertisement. Participants were randomized to receive 5-10 g gel/50-100 mg testosterone (Testim , Ipsen, France) or 5-10 g gel/placebo. The plasma levels of calprotectin and phosphate were significantly reduced in the group receiving testosterone therapy (gel) compared to the placebo group (p < 0.05). Testosterone treatment did not have any significant effect on plasma levels of FGF23 or soluble Klotho. The reduction in phosphate levels was inversely associated with bioavailable testosterone. Compared to the placebo group, 6 months of testosterone therapy (gel) reduced calprotectin and phosphate levels suggesting decreased inflammation and decreased cardiovascular risk.
MeSH Terms
- Aged
- Aging
- Androgens
- Double-Blind Method
- Female
- Follow-Up Studies
- Humans
- Leukocyte L1 Antigen Complex
- Male
- Middle Aged
- Phosphates
- Prognosis
- Risk Factors
- Testosterone
Keywords
- Biomarkers
- Calprotectin
- FGF23
- Klotho
- Phosphate
- Testosterone therapy
Previous studies showed that circulating fibroblast growth factor-23 (FGF23) is a new biomarker linked to cardiovascular and kidney diseases. Here, we explored the association between serum FGF23 and aging-related cardiovascular-renal parameters in a healthy Chinese population. A total of 314 healthy participants aged 36-87 years were enrolled. Cardiovascular structure and function were assessed by the left ventricular ejection fraction, the ratio of early diastolic peak flow velocity to late diastolic peak flow velocity at the mitral leaflet tips, carotid intima-media thickness, the diameter of the bilateral common carotid artery, blood systolic peak and end diastolic velocities, which were measured by M-mode ultrasonography. Glomerular filtration rate was evaluated using the Chronic Kidney Disease Epidemiology Collaboration equation and Chronic Kidney Disease Epidemiology Collaboration equation for Asians. Serum FGF23, 1, 25-dihydroxy vitamin D and parathyroid hormone were measured by enzyme-linked immunosorbent assay. For all participants, intima-media thickness/diameter of the bilateral common carotid artery gradually decreased with the progression from low to high FGF23 concentration (P < 0.05). After adjusting for all possible confounders, FGF23 remained significantly associated with intima-media thickness/diameter of the bilateral common carotid artery (P = 0.016). In women, serum FGF23 was significantly associated with serum creatinine, cystatin C and estimated glomerular filtration rate in the Spearman correlation analysis. FGF23 remained significantly associated with serum creatinine (P = 0.046) and estimated glomerular filtration rate (P = 0.034) after full adjustment. However, no such relationship was apparent in men. Serum FGF23 was correlated with aging-related cardiovascular-renal parameters even in healthy people. Measurement of serum FGF23 can provide valuable information to predict cardiovascular-renal function in healthy people, especially in older female adults. Geriatr Gerontol Int 2017; 17: 1221-1231.
MeSH Terms
- Adult
- Aged
- Aged, 80 and over
- Aging
- Biomarkers
- Cardiovascular System
- Carotid Intima-Media Thickness
- China
- Female
- Fibroblast Growth Factors
- Glomerular Filtration Rate
- Healthy Volunteers
- Heart Function Tests
- Humans
- Kidney Function Tests
- Male
- Middle Aged
- Reference Values
Keywords
- age
- cardiovascular
- fibroblast growth factor-23
- parameters
- renal
The functions of Klotho (KL) are multifaceted and include the regulation of aging and mineral metabolism. It was originally identified as the gene responsible for premature aging-like symptoms in mice and was subsequently shown to function as a coreceptor in the fibroblast growth factor (FGF) 23 signaling pathway. The discovery of KL as a partner for FGF23 led to significant advances in understanding of the molecular mechanisms underlying phosphate and vitamin D metabolism, and simultaneously clarified the pathogenic roles of the FGF23 signaling pathway in human diseases. These novel insights led to the development of new strategies to combat disorders associated with the dysregulated metabolism of phosphate and vitamin D, and clinical trials on the blockade of FGF23 signaling in X-linked hypophosphatemic rickets are ongoing. Molecular and functional insights on KL and FGF23 have been discussed in this review and were extended to how dysregulation of the FGF23/KL axis causes human disorders associated with abnormal mineral metabolism.
MeSH Terms
- Animals
- Calcium
- Fibroblast Growth Factors
- Gene Expression
- Glucuronidase
- Homeostasis
- Humans
- Metabolic Diseases
- Minerals
- Mutation
- Phosphates
- Receptors, Fibroblast Growth Factor
- Renal Insufficiency, Chronic
- Signal Transduction
- Vitamin D
Keywords
- Aging
- FGF23
- Klotho
- Phosphate
- Vitamin D
Skin atrophy and delayed wound healing are observed in aged humans; however, the molecular mechanism are still elusive. The aim of this study was to analyze the molecular mechanisms of delayed wound healing by aging using α-Klotho-deficient (kl/kl) mice, which have phenotypes similar to those of aged humans. The kl/kl mice showed delayed wound healing and impaired granulation formation compared with those in wild-type (WT) mice. The skin graft experiments revealed that delayed wound healing depends on humoral factors, but not on kl/kl skin tissue. The mRNA expression levels of cytokines related to acute inflammation including IL-1β, IL-6 and TNF-α were higher in wound lesions of kl/kl mice compared with the levels in WT mice by RT-PCR analysis. LPS-induced TNF-α production model using spleen cells revealed that TNF-α production was significantly increased in the presence of FGF23. Thus, higher levels of FGF23 in kl/kl mouse may have a role to increase TNF-α production in would lesion independently of α-Klotho protein, and impair granulation formation and delay wound healing.
MeSH Terms
- Aging
- Animals
- Cytokines
- Disease Models, Animal
- Female
- Glucuronidase
- Humans
- Male
- Mice
- Mice, Knockout
- Mice, Transgenic
- Skin
- Species Specificity
- Treatment Outcome
- Wound Healing
Keywords
- FGF23
- Klotho
- TNF-α
- Wound healing
Klotho is required for the inhibitory effect of FGF23 on 1,25(OH)2D3 formation and Klotho-hypomorphic mice (kl/kl) suffer from severe tissue calcification due to excessive 1,25(OH)2D3 formation with subsequent increase of Ca2 and phosphate concentrations and stimulation of osteogenic signaling. The excessive tissue calcification dramatically accelerates aging and leads to premature death of the animals. Osteogenic signaling in those mice is disrupted by treatment with NH4Cl, which prevents tissue calcification and early death of kl/kl mice. The present study explored whether the beneficial effects of NH4Cl treatment could be mimicked by NH4NO3 treatment. The kl/kl mice had free access to tap water either without or with addition of NH4NO3 (0.28 M) starting with the mating of the parental generation. Calcification of trachea, lung, kidney, stomach, heart and vessels was visualized by histology with von Kossa staining. Plasma phosphate concentration was determined utilizing photometry, blood gas and electrolytes utilizing a blood Gas and Chemistry Analysis System and plasma 1,25(OH)2D3 concentration with ELISA. In untreated kl/kl mice plasma 1,25(OH)2D3 and phosphate concentrations were elevated, and the mice suffered from marked calcification of all tissues analyzed. Untreated kl/kl mice further suffered from respiratory acidosis due to marked lung emphysema. NH4NO3-treatment decreased both, blood pCO2 and HCO3-, decreased calcification of trachea, lung, kidney, stomach, heart and vessels and increased the life span of kl/kl mice more than 1.7-fold (♂) or 1.6-fold (♀) without significantly affecting extracellular pH or plasma concentrations of 1,25(OH)2D3, Ca2 , phosphate, Na , and K . NH4NO3-treatment turns respiratory acidosis into metabolic acidosis and mitigates calcification thus leading to a substantial extension of kl/kl mice survival.
MeSH Terms
- Animals
- Calcinosis
- Female
- Glucuronidase
- Longevity
- Male
- Mice
- Mice, Knockout
- Nitrates
- Treatment Outcome
Circulating level of phosphate is altered by age and diet, and is also controlled by several hormones such as parathyroid hormone(PTH), 1,25-dihydroxyvitamin D[1,25(OH)2D]and fibroblast growth factor 23(FGF23). The main function of PTH and 1,25(OH)2D is maintaining calcium homeostasis, while FGF23 plays a central role in phosphate metabolism. PTH suppresses phosphate reabsorption in the proximal tubules to increase the renal phosphate wasting, while 1,25(OH)2D facilitates the intestinal phosphate absorption. FGF23 increases the renal phosphate wasting and reduces the production of 1,25(OH)2D. Of note, these hormones mutually regulate one another. The production of FGF23 is also regulated by various local factors. The mechanism for sensing the phosphate availability still remains unknown, and further investigation is required.
MeSH Terms
- Aging
- Animals
- Calcitriol
- Calcium
- Diet
- Fibroblast Growth Factors
- Homeostasis
- Humans
- Intestinal Absorption
- Kidney Tubules
- Parathyroid Hormone
- Phosphates
Klotho-deficient mice have accelerated aging phenotypes, whereas overexpression of Klotho in mice extends lifespan. Klotho is an anti-aging single-pass membrane protein predominantly produced in the kidney, with shedding of the amino-terminal extracellular domain into the systemic circulation. Circulating levels of soluble Klotho decrease with age, and the klotho gene is associated with increased risk of age-related diseases. The three forms of Klotho protein have distinct functions. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors, functions as an obligatory co-receptor for FGF23, which is involved in aging and the development of chronic diseases via regulation of P i and vitamin D metabolism. Secreted Klotho functions as a humoral factor with pleiotropic activities including regulation of oxidative stress, growth factor signaling, and ion homeostasis. Secreted Klotho is also involved in organ protection. The intracellular form of Klotho suppresses inflammation-mediated cellular senescence and mineral metabolism. Herein we provide a brief overview of the structure and function and recent research about Klotho.
Keywords
- Age-related diseases
- Aging
- Klotho
Although the Klotho gene has been recognized as an aging-suppressor gene, the significance of its soluble product, soluble αKlotho (sKlotho), in aging remains to be elucidated. To address this issue, we conducted a single-centered cross-sectional study in a region with a high prevalence of aging. We compared sKlotho levels with the patient characteristics from medical records and laboratory measurements, including fibroblast growth factor 23 (FGF23), intact parathyroid hormone, activated vitamin D3 and factors associated with mineral bone metabolism, in 52 outpatients with a mean age of 78.2 years. Serum sKlotho levels significantly decreased with age, but were not associated with the stage of chronic kidney disease (CKD). Serum FGF23 levels increased as CKD stages advanced, but were not associated with aging. Univariate analyses revealed that sKlotho levels positively correlated with glomerular filtration rate, and negatively with age and serum levels of FGF23 and phosphorus. In a multivariable linear regression analysis, sKlotho significantly correlated with aging and lower FGF23 levels. Only osteoporosis affected sKlotho and FGF23 levels among the various complications and patient status including medication. In summary, serum sKlotho levels inversely correlated with age and FGF23, and were significantly reduced in patients with osteoporosis. sKlotho may serve as a biomarker of aging independent of renal function.
MeSH Terms
- Aged
- Aged, 80 and over
- Aging
- Biomarkers
- Female
- Glucuronidase
- Humans
- Male
- Solubility
Keywords
- Aging
- Chronic kidney disease
- FGF23
- Klotho
- Osteoporosis
- Soluble αKlotho
Klotho, a protein expressed mainly in the kidney, is required for the inhibitory effect of FGF23 on renal 1,25(OH)2D3 formation. Klotho counteracts vascular calcification and diverse age-related disorders. Klotho-hypomorphic mice (kl/kl) suffer from severe vascular calcification and rapid aging. The calcification is at least in part caused by excessive 1,25(OH)2D3, Ca(2 ), and phosphate concentrations in blood, which trigger osteogenic signaling including upregulation of alkaline phosphatase (Alpl). As precipitation of calcium and phosphate is fostered by alkaline pH, extracellular acidosis could counteract tissue calcification. In order to induce acidosis, acetazolamide was added to drinking water (0.8 g/l) of kl/kl and wild-type mice. As a result, acetazolamide treatment of kl/kl mice partially reversed the growth deficit, tripled the life span, almost completely reversed the calcifications in trachea, lung, kidney, stomach, intestine, and vascular tissues, the excessive aortic alkaline phosphatase mRNA levels and the plasma concentrations of osteoprotegerin, osteopontin as well as fetuin-A, without significantly decreasing FGF23, 1,25(OH)2D3, Ca(2 ), and phosphate plasma concentrations. In primary human aortic smooth muscle cells, acidotic environment prevented phosphate-induced alkaline phosphatase mRNA expression. The present study reveals a completely novel effect of acetazolamide, i.e., interference with osteoinductive signaling and tissue calcification in kl/kl mice. Klotho deficient (kl/kl) mice suffer from hyperphosphatemia with dramatic tissue calcification. Acetazolamide (ACM) treatment partially reversed the growth deficit of kl/kl mice. In kl/kl mice, ACM reversed tissue calcification despite continued hyperphosphatemia. ACM tripled the life span of kl/kl mice. In human aortic smooth muscle cells, low extracellular pH prevented osteogenic signaling.
MeSH Terms
- Acetazolamide
- Acidosis
- Aging
- Alkaline Phosphatase
- Animals
- Calcitriol
- Calcium
- Carbonic Anhydrase Inhibitors
- Cells, Cultured
- Glucuronidase
- Humans
- Hyperphosphatemia
- Mice
- Mice, Knockout
- Osteogenesis
- Phosphates
- Signal Transduction
- Vascular Calcification
Keywords
- 1,25(OH)2D3
- Acetazolamide
- Acidosis
- Calcification
- Calcium
- Phosphate
Ectopic calcification (EC), which is the pathological deposition of calcium and phosphate in extra-skeletal tissues, may be associated with hypercalcaemic and hyperphosphataemic disorders, or it may occur in the absence of metabolic abnormalities. In addition, EC may be inherited as part of several monogenic disorders and studies of these have provided valuable insights into the metabolic pathways regulating mineral metabolism. For example, studies of tumoural calcinosis, a disorder characterised by hyperphosphataemia and progressive EC, have revealed mutations of fibroblast growth factor 23 (FGF23), polypeptide N-acetyl galactosaminyltransferase 3 (GALNT3) and klotho (KL), which are all part of a phosphate-regulating pathway. However, such studies in humans are limited by the lack of available large families with EC, and to facilitate such studies we assessed the progeny of mice treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) for EC. This identified two mutants with autosomal recessive forms of EC, and reduced lifespan, designated Ecalc1 and Ecalc2. Genetic mapping localized the Ecalc1 and Ecalc2 loci to a 11.0 Mb region on chromosome 5 that contained the klotho gene (Kl), and DNA sequence analysis identified nonsense (Gln203Stop) and missense (Ile604Asn) Kl mutations in Ecalc1 and Ecalc2 mice, respectively. The Gln203Stop mutation, located in KL1 domain, was severely hypomorphic and led to a 17-fold reduction of renal Kl expression. The Ile604Asn mutation, located in KL2 domain, was predicted to impair klotho protein stability and in vitro expression studies in COS-7 cells revealed endoplasmic reticulum retention of the Ile604Asn mutant. Further phenotype studies undertaken in Ecalc1 (kl203X/203X) mice demonstrated elevations in plasma concentrations of phosphate, FGF23 and 1,25-dihydroxyvitamin D. Thus, two allelic variants of Kl that develop EC and represent mouse models for tumoural calcinosis have been established.
MeSH Terms
- Alleles
- Amino Acid Sequence
- Animals
- COS Cells
- Calcinosis
- Chlorocebus aethiops
- Codon, Nonsense
- Disease Models, Animal
- Endoplasmic Reticulum
- Ethylnitrosourea
- Fibroblast Growth Factors
- Genetic Loci
- Genotype
- Glucuronidase
- Humans
- Kidney
- Longevity
- Male
- Mice
- Mice, Inbred C57BL
- Molecular Sequence Data
- Mutation, Missense
- N-Acetylgalactosaminyltransferases
- Phenotype
- Phosphates
- Polymorphism, Single Nucleotide
- Sequence Alignment
- Vitamin D
The Klotho protein deficiency is known to participate in premature aging. As an aging suppressor, Klotho is an important molecule in aging processes and its overexpression results in longevity. Due to many reasons, the insulin/insulin-like growth factor-1 (IGF-1) has been considered as a key pathway in aging research. The Klotho gene is closely related to this pathway. The Klotho gene encodes a transmembrane protein that after cleavage is also found as a secreted protein. Importantly, its overexpression suppresses insulin/IGF-1 signaling and thus extends the lifespan. In addition, Klotho participates in the regulation of several other intracellular signaling pathways, including regulation of FGF23 signaling, cAMP, PKC, transforming growth factor-β (TGF-β), p53/p21, and Wnt signaling. The aim of this review is to summarize current literature that shows the involvement of Klotho in the regulation of several intracellular pathways. The results of our review clearly indicate that Klotho participates in several intracellular signaling pathways, and by regulating them, Klotho is involved in aging and longevity.
MeSH Terms
- Aging, Premature
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Insulin
- Insulin-Like Growth Factor I
- Longevity
- Transforming Growth Factor beta
- Wnt Signaling Pathway
Tumour-associated osteomalacia is a paraneoplastic syndrome caused by renal phosphate wasting, leading to severe hypophosphataemia. Excess of circulating fibroblast growth factor 23 (FGF23) is the likely cause, acting via the FGF23/α-Klotho coreceptor, a critical regulator of phosphate metabolism. The other possible effects of that complex in humans are still under investigation. We present a case of an 84-year-old Belgian man, presenting prostate cancer with bone metastases. From June 2010 to March 2013, he presented three episodes of disease progression. From January 2012, the patient developed a progressively marked dorsal kyphosis with significant hypophosphataemia. The calculated TRP (tubular reabsorption of phosphate) was decreased and the FGF23 increased. Mid-March 2013, the patient died after a profound unconsciousness due to hypoglycaemia with hypothermia. We hypothesised that the two paraneoplastic manifestations of this patient (tumour-associated osteomalacia and refractory hypoglycaemia) were due to one cause chain with two main nodes-FGF23 and its coreceptor Klotho..
MeSH Terms
- Aged, 80 and over
- Aging
- Biomarkers, Tumor
- Blood Glucose
- Fatal Outcome
- Glucuronidase
- Humans
- Hypoglycemia
- Hypophosphatemia
- Male
- Osteomalacia
- Paraneoplastic Syndromes
- Prostatic Neoplasms
Taking good care of elderly is a major challenge of our society, and thus identification of potential drug targets to reduce age-associated disease burden is desirable. α-klotho(-/-) (α-kl) is a short-lived mouse model that displays multiple phenotypes resembling human aging-related syndromes. Such ageing phenotype of α-kl(-/-) mice is associated with activation of a proteolytic enzyme, Calpain-1. We hypothesized that uncontrolled activation of calpain-1 might be causing age-related phenotypes in α-kl-deficient mice. We found that daily administration of BDA-410, a calpain-1 inhibitor, strikingly ameliorated multiple aging-related phenotypes. Treated mice showed recovery of reproductive ability, increased body weight, reduced organ atrophy, and suppression of ectopic calcifications, bone mineral density reduction, pulmonary emphysema and senile atrophy of skin. We also observed ectopic expression of FGF23 in calcified arteries of α-kl(-/-) mice, which might account for the clinically observed association of increased FGF23 level with increased risk of cardiovascular mortality. These findings allow us to propose that modulation of calpain-1 activity is a potential therapeutic option for delaying age-associated organ pathology, particularly caused by the dysregulation of mineral ion homeostasis.
MeSH Terms
- Aging
- Animals
- Calpain
- Drug Evaluation, Preclinical
- Female
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Male
- Mice, Knockout
- Phenotype
- Renal Insufficiency, Chronic
- Sulfonamides
- Vascular Calcification
α-klotho (α-kl) was first identified as an aging gene and was later shown to be a regulator of mineral homeostasis. α-kl (- / -) mice display multiple aging related phenotypes including atherosclerosis, cardiovascular/soft tissue calcifications, pulmonary emphysema, osteopenia, and senile atrophy of skin ; such age-related organ pathologies are associated with biochemical changes in blood, including severe hyperphosphatemia, elevated serum FGF23 and1,25 (OH) 2 Vitamin D levels. Of significance, advanced stage patients suffering chronic kidney disease (CKD) develop multiple complications quite resembling phenotypes observed in α-kl (- / -) mice, and high serum phosphate, the major cause of abnormalities of α-kl (- / -) mice, has been reported to be closely associated with high levels of cardiovascular disease morbidity and mortality in patients with CKD, particularly in patients with end-stage renal disease. In addition, the expressions of α-kl mRNA and α-Kl protein were severely reduced in these patients. These results suggest the involvement of α-Kl and FGF23 in the pathogeneses of not only aging-associated syndromes but also the complications of CKD. Here, the unveiling of the molecular functions of α-Klotho and FGF23 has recently given new insight into the field of mineral homeostasis and the pathogeneses of aging-associated syndromes and the complications of CKD.
MeSH Terms
- Aging
- Animals
- Bone Density
- Bone and Bones
- Cardiovascular Diseases
- Fibroblast Growth Factors
- Glucuronidase
- Homeostasis
- Humans
- Renal Insufficiency, Chronic
Despite renal replacement therapy mortality among chronic kidney disease patients is 10-1000-fold higher than in age-matched controls. Klotho is a kidney protein with anti-ageing hormonal properties that is also a co-receptor for the FGF23 fosfatonin. There is a bidirectional relationship between Klotho and inflammation. Thus, inflammation decreases renal Klotho and Klotho has anti-inflammatory properties. Mice with genetic defects in Klotho suffer from accelerated aging and early death. Decreasing the phosphate load improves the phenotype and prolongs survival in these mice. Unraveling the Klotho-phosphate-inflammation interaction may open new avenues for research that may improve the outcomes of kidney patients as well as provide new tools to retard aging in the general population.
MeSH Terms
- Aging
- Animals
- Diet
- Glucuronidase
- Humans
- Inflammation
- Mice
- Renal Insufficiency, Chronic
The Klotho gene was identified as an 'aging suppressor' in mice. Overexpression of the Klotho gene extends lifespan and defective Klotho results in rapid aging and early death. Both the membrane and secreted forms of Klotho have biological activity that include regulatory effects on general metabolism and a more specific effect on mineral metabolism that correlates with its effect on aging. Klotho serves as a co-receptor for fibroblast growth factor (FGF), but it also functions as a humoral factor that regulates cell survival and proliferation, vitamin D metabolism, and calcium and phosphate homeostasis and may serve as a potential tumor suppressor. Moreover, Klotho protects against several pathogenic processes in a FGF23-independent manner. These processes include cancer metastasis, vascular calcification, and renal fibrosis. This review covers the recent advances in Klotho research and discusses novel Klotho-dependent mechanisms that are clinically relevant in aging and age-related diseases.
MeSH Terms
- Aging
- Animals
- Calcium
- Cell Proliferation
- Cell Survival
- Fibroblast Growth Factors
- Glucuronidase
- Homeostasis
- Humans
- Kidney Diseases
- Membrane Proteins
- Mice
- Neoplasm Metastasis
- Neoplasms
- Phosphates
- Signal Transduction
- Vascular Calcification
FGF23 is a bone-derived hormone that regulates mineral metabolism by inhibiting renal tubular phosphate reabsorption and suppressing circulating 1,25(OH)2D and PTH levels. These effects are mediated by FGF-receptor binding and activation in the presence of its coreceptor Klotho, which is expressed in the distal tubules of the kidney. Recently, expression of Klotho in skeletal tissues has been reported, indicating a direct, yet unclear, extrarenal effect of FGF23 on cells involved with bone development and remodeling. In the present study, we found that bone marrow stromal cells harvested from Klotho null mice developed fewer osteoblastic but more adipocytic colonies than cells from wild-type mice. The underlying mechanism was explored by experiments on mouse C3H10T1/2 cells. We found that Klotho was weakly expressed and that FGF23 dose-dependently affected the lineage fate determination. The effects of FGF23 on cell differentiation can be diminished by SU 5402, a specific tyrosine kinase inhibitor for FGF receptors. Our results indicate that FGF23 directly affects the differentiation of bone marrow stromal cells.
MeSH Terms
- Adipocytes
- Aging
- Animals
- Bone and Bones
- Cell Differentiation
- Cell Lineage
- Cell Proliferation
- Dose-Response Relationship, Drug
- Fibroblast Growth Factors
- Gene Expression Regulation
- Glucuronidase
- Kidney Tubules
- Mesenchymal Stem Cells
- Mice
- Mice, Inbred C3H
- Osteoblasts
- Osteoporosis
- Phosphates
- Protein Binding
- Recombinant Proteins
Through alternative splicing, Klotho protein exists both as a secreted and a membrane form whose extracellular domain could be shed from the cell surface by secretases and released into the circulation to act as endocrine factor. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23) to modulate FGF23 signal transduction, soluble Klotho is a multifunction protein present in the biological fluids including blood, urine and cerebrospinal fluid and plays important roles in antiaging, energy metabolism, inhibition of Wnt signaling, antioxidation, modulation of ion transport, control of parathyroid hormone and 1,25(OH)2VD3 production, and antagonism of renin-angiotensin-aldosterone system. Emerging evidence from clinical and basic studies reveal that chronic kidney disease is a state of endocrine and renal Klotho deficiency, which may serve as an early biomarker and a pathogenic contributor to chronic progression and complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. Supplementation of exogenous Klotho and/or upregulation of endogenous Klotho production by using rennin angiotensin system inhibitors, HMG CoA reductase inhibitors, vitamin D analogues, peroxisome proliferator-activated receptors-gamma agonists, or anti-oxidants may confer renoprotection from oxidation and suppression of renal fibrosis, and also on prevention or alleviation of complications in chronic kidney disease. Therefore, Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.
MeSH Terms
- Aging
- Animals
- Calcinosis
- Calcium
- Cardiomyopathies
- Chronic Kidney Disease-Mineral and Bone Disorder
- Disease Models, Animal
- Disease Progression
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Hyperparathyroidism, Secondary
- Membrane Proteins
- Nephrosclerosis
- Parathyroid Hormone
- Phosphates
- Renal Insufficiency, Chronic
- Renin-Angiotensin System
- Signal Transduction
- Solubility
- Uremia
- Vitamin D
Endocrine fibroblast growth factors (FGFs) have been recognized as hormones that regulate a variety of metabolic processes. FGF19 is secreted from intestine upon feeding and acts on liver to suppress bile acid synthesis. FGF21 is secreted from liver upon fasting and acts on adipose tissue to promote lipolysis and responses to fasting. FGF23 is secreted from bone and acts on kidney to inhibit phosphate reabsorption and vitamin D synthesis. One critical feature of endocrine FGFs is that they require the Klotho gene family of transmembrane proteins as coreceptors to bind their cognate FGF receptors and exert their biological activities. This chapter overviews function of Klotho family proteins as obligate coreceptors for endocrine FGFs and discusses potential link between Klothos and age-related diseases.
MeSH Terms
- Aging
- Animals
- Glucuronidase
- Homeostasis
- Humans
- Membrane Proteins
- Phosphates
- Receptors, Cytoplasmic and Nuclear
Isoforms of the mammalian klotho protein serve as membrane co-receptors that regulate renal phosphate and calcium reabsorption. Phosphaturic effects of klotho are mediated in cooperation with fibroblast growth factor receptor-1 and its FGF23 ligand. The vitamin D receptor and its 1,25-dihydroxyvitamin D(3) ligand are also crucial for calcium and phosphate regulation at the kidney and participate in a feedback loop with FGF23 signaling. Herein we characterize vitamin D receptor-mediated regulation of klotho mRNA expression, including the identification of vitamin D responsive elements (VDREs) in the vicinity of both the mouse and human klotho genes. In keeping with other recent studies of vitamin D-regulated genes, multiple VDREs control klotho expression, with the most active elements located at some distance (-31 to -46 kb) from the klotho transcriptional start site. We therefore postulate that the mammalian klotho gene is up-regulated by liganded VDR via multiple remote VDREs. The phosphatemic actions of 1,25-dihydroxyvitamin D(3) are thus opposed via the combined phosphaturic effects of FGF23 and klotho, both of which are upregulated by the liganded vitamin D receptor.
MeSH Terms
- Aging
- Animals
- Cell Line
- Gene Expression Regulation
- Glucuronidase
- Humans
- Kidney
- Ligands
- Mice
- RNA, Messenger
- Receptors, Calcitriol
- Vitamin D
- Vitamin D Response Element
The absence of Klotho (KL) from mice causes the development of disorders associated with human aging and decreased longevity, whereas increased expression prolongs lifespan. With age, KL protein levels decrease, and keeping levels consistent may promote healthier aging and be disease-modifying. Using the KL promoter to drive expression of luciferase, we conducted a high-throughput screen to identify compounds that activate KL transcription. Hits were identified as compounds that elevated luciferase expression at least 30%. Following validation for dose-dependent activation and lack of cytotoxicity, hit compounds were evaluated further in vitro by incubation with opossum kidney and Z310 rat choroid plexus cells, which express KL endogenously. All compounds elevated KL protein compared with control. To determine whether increased protein resulted in an in vitro functional change, we assayed FGF23 (fibroblast growth factor 23) signalling. Compounds G-I augmented ERK (extracellular-signal-regulated kinase) phosphorylation in FGFR (fibroblast growth factor receptor)-transfected cells, whereas co-transfection with KL siRNA (small interfering RNA) blocked the effect. These compounds will be useful tools to allow insight into the mechanisms of KL regulation. Further optimization will provide pharmacological tools for in vivo studies of KL.
MeSH Terms
- Aging
- Animals
- Cell Line
- Cloning, Molecular
- Drug Screening Assays, Antitumor
- Fibroblast Growth Factors
- Gene Expression Regulation
- Glucuronidase
- Kidney
- Mice
- Opossums
- Rats
Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events. Vascular calcification refers to the deposition of calcium phosphate mineral, most often hydroxyapatite, in arteries. Extensive calcification of the vascular system is a key characteristic of aging. In this article, we outline the mechanisms governing vascular calcification and highlight its association with cellular senescence. This review discusses the molecular mechanisms of cellular senescence and its affect on calcification of vascular cells, the relevance of phosphate regulation and the function of FGF23 and Klotho proteins. The association of vascular calcification and cellular senescence with the rare human aging disorder Hutchison-Gilford Progeria Syndrome (HGPS) is highlighted and the mouse models used to try to determine the underlying pathways are discussed. By understanding the pathways involved in these processes novel drug targets may be elucidated in an effort to reduce the effects of cellular aging as a risk factor in cardiovascular disease.
MeSH Terms
- Aging
- Animals
- Calcinosis
- Cellular Senescence
- Durapatite
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Models, Animal
- Phosphates
- Vascular Diseases
Klotho exerts anti-aging properties in mammals in two different ways. While membrane-bound Klotho, which is primarily expressed in the kidney, acts as an obligate co-receptor of FGF23 to regulate phosphate homeostasis, secreted Klotho, resulting from the shedding of the KL1-KL2 ectodomain into the bloodstream, inhibits Insulin/IGF1 signalling. However, the underlying molecular mechanisms are not fully understood. Here, we investigated the biological role of Klotho in Caenorhabditis elegans. Two redundant homologues of the klotho gene exist in C. elegans and encode predicted proteins homologous to the glucosidase-like KL1 domain of mammalian Klotho. We have used a genetic approach to investigate the functional activity of Klotho in C. elegans. Here, we report that whereas Klotho requires EGL-15 (FGFR) and EGL-17 to promote longevity and oxidative stress resistance, it is not involved in the regulation of fluid homeostasis, controlled by LET-756. Besides revealing a new post-developmental role for EGL-17, our data suggest that the KL1 form of Klotho is involved in FGF23-independent FGF signalling. We also report a genetic interaction between Klotho and the DAF-2 (Ins/IGF1R)/DAF-16 (FOXO) pathway. While the regulation of longevity requires functional DAF-2/DAF-16 signalling, the control of oxidative stress resistance involves a DAF-2- independent, DAF-16-dependent pathway, suggesting that Klotho may target either DAF-2 or DAF-16, depending of environmental conditions. Thus, the predictive KL1 form of Klotho appears to crosstalk with both FGF and Insulin/IGF1/FOXO pathways to exert anti-aging properties in C. elegans.
MeSH Terms
- Aging
- Amino Acid Sequence
- Animals
- Caenorhabditis elegans
- Caenorhabditis elegans Proteins
- Fibroblast Growth Factors
- Glucuronidase
- Insulin
- Insulin-Like Growth Factor I
- Intercellular Signaling Peptides and Proteins
- Longevity
- Models, Animal
- Molecular Sequence Data
- Receptor, Insulin
- Receptors, Fibroblast Growth Factor
- Signal Transduction
- Stress, Physiological
- Water-Electrolyte Balance
The aim of this study was to observe the effect of sirolimus (SRL) on calcineurin inhibitor (CNI)-induced nephrotoxicity in the aging process by using renal expression of KLOTHO, an antiaging gene. METHODS.: Mice were treated with vehicle (VH; 1 mL/kg/day of olive oil), cyclosporine A (CsA; 30 mg/kg/day), or tacrolimus (FK; 1 mg/kg/day) with or without SRL (0.3 mg/kg/day) for 2 weeks. KLOTHO expression was evaluated by using reverse-transcriptase polymerase chain reaction, immunoblotting, and immunohistochemistry. Oxidative stress was evaluated by using immunohistochemistry and urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG). The calcium metabolism was evaluated by using renal ectopic calcification, serum intact parathyroid hormone level, and renal fibroblast factor 23 (FGF23) expression. Treatment with CsA or FK alone significantly decreased KLOTHO expression and increased urinary 8-OHdG excretion compared with VH treatment but SRL treatment did not. Treatment SRL CsA or SRL FK further decreased KLOTHO expression and increased urinary 8-OHdG excretion compared with treatment of CsA or FK alone. There was a strong correlation between KLOTHO expression and urinary 8-OHdG excretion (r=-0.893; P<0.001). Treatment of CsA or FK alone increased renal ectopic calcification and serum intact parathyroid hormone level and decreased renal FGF23 expression compared with VH treatment (P<0.05) but SRL treatment did not. Treatment with SRL CNI aggravated these parameters compared with CNI alone. SRL accelerates the CNI-induced oxidative process by down-regulating the renal antioxidant KLOTHO expression in the kidney.
MeSH Terms
- Aging
- Animals
- Calcineurin Inhibitors
- Colforsin
- Cyclosporine
- DNA Primers
- Gene Expression Regulation
- Glucuronidase
- Immunosuppressive Agents
- Kidney
- Mice
- Nephritis, Interstitial
- Oxidative Stress
- RNA
- RNA, Messenger
- Reverse Transcriptase Polymerase Chain Reaction
- Sirolimus
- Tacrolimus
Klotho is an anti-aging protein predominantly expressed in the kidney, parathyroid glands, and choroid plexus of the brain. It is a single-pass transmembrane protein with a large extracellular domain. The extracellular domain of Klotho is cleaved and released into extracellular fluid, including blood, urine, and cerebrospinal fluid. The membrane-bound full-length Klotho and secreted extracellular domain of Klotho have distinct functions. Membrane Klotho interacts with fibroblast growth factor (FGF) receptors to form high-affinity receptors for FGF23. Secreted Klotho functions as a humoral factor that regulates several ion channels and transporters, and other processes, including insulin and insulin-like growth factor signaling. This mini-review focuses on the mechanisms of regulation of cell-surface abundance of ion channels by secreted Klotho and the importance of these effects of Klotho in physiology and pathological conditions.
MeSH Terms
- Aging
- Animals
- Cell Membrane
- Insulin
- Ion Channels
- Ions
- Kidney
- Mice
- Receptors, Fibroblast Growth Factor
- Signal Transduction
The nuclear vitamin D receptor (VDR) binds 1,25-dihydroxyvitamin D3 (1,25D), its high affinity renal endocrine ligand, to signal intestinal calcium and phosphate absorption plus bone remodeling, generating a mineralized skeleton free of rickets/osteomalacia with a reduced risk of osteoporotic fractures. 1,25D/VDR signaling regulates the expression of TRPV6, BGP, SPP1, LRP5, RANKL and OPG, while achieving feedback control of mineral ions to prevent age-related ectopic calcification by governing CYP24A1, PTH, FGF23, PHEX, and klotho transcription. Vitamin D also elicits numerous intracrine actions when circulating 25-hydroxyvitamin D3, the metabolite reflecting vitamin D status, is converted to 1,25D locally by extrarenal CYP27B1, and binds VDR to promote immunoregulation, antimicrobial defense, xenobiotic detoxification, anti-inflammatory/anticancer actions and cardiovascular benefits. VDR also affects Wnt signaling through direct interaction with beta-catenin, ligand-dependently blunting beta-catenin mediated transcription in colon cancer cells to attenuate growth, while potentiating beta-catenin signaling via VDR ligand-independent mechanisms in osteoblasts and keratinocytes to function osteogenically and as a pro-hair cycling receptor, respectively. Finally, VDR also drives the mammalian hair cycle in conjunction with the hairless corepressor by repressing SOSTDC1, S100A8/S100A9, and PTHrP. Hair provides a shield against UV-induced skin damage and cancer in terrestrial mammals, illuminating another function of VDR that facilitates healthful aging.
MeSH Terms
- Aging
- Animals
- Calcium
- Cell Nucleus
- Gene Expression Regulation
- Humans
- Keratinocytes
- Mice
- Models, Biological
- Osteopontin
- Phosphates
- Receptors, Calcitriol
- Signal Transduction
- Wnt Proteins
- beta Catenin
Phosphate homeostasis is maintained primarily by a bone-kidney endocrine axis. When phosphate is in excess, fibroblast growth factor-23 (FGF23) is secreted from bone and acts on kidney to promote phosphate excretion into urine. FGF23 also reduces serum vitamin D levels to suppress phosphate absorption from intestine. Thus, FGF23 functions as a hormone that induces negative phosphate balance. One critical feature of FGF23 is that it requires Klotho, a single-pass transmembrane protein expressed in renal tubules, as an obligate co-receptor to bind and activate cognate FGF receptors. Importantly, defects in either FGF23 or Klotho not only cause phosphate retention but also a premature-aging syndrome in mice, which can be rescued by resolving hyperphosphatemia. In addition, changes in extracellular and intracellular phosphate concentration affect glucose metabolism, insulin sensitivity, and oxidative stress in vivo and in vitro, which potentially affect aging processes. These findings suggest an unexpected link between inorganic phosphate and aging in mammals.
MeSH Terms
- Aging
- Aging, Premature
- Animals
- Bone and Bones
- Fibroblast Growth Factors
- Homeostasis
- Hyperphosphatemia
- Kidney
- Mice
- Oxidative Stress
- Phosphates
- Receptors, Fibroblast Growth Factor
- Risk Factors
- Vitamin D
FGF19, FGF21, and FGF23 form a unique subfamily of fibroblast growth factors. Because they contain intra-molecular disulfide bonds and show reduced affinity toward heparan sulfate located in the extracellular space, it is thought that, in contrast to other FGFs, they function as endocrine hormones. FGF23 and its co-receptor alphaKlotho are involved in the control of aging, but it is not known if the same holds true for FGF19, which can also signal through alphaKlotho. However, considerable evidence supports a role for FGF19 in controlling various aspects of metabolism. We have recently fully characterized FGF19/FGFR/co-factor interactions and signaling, and in the current manuscript discuss the contribution of the FGF19/FGFR4 axis to bile acid and glucose regulation.
MeSH Terms
- Animals
- Bile Acids and Salts
- Blood Glucose
- Fibroblast Growth Factors
- Homeostasis
- Humans
- Mice
- Receptor, Fibroblast Growth Factor, Type 4
Keywords
- FGF19
- FGF21
- FGF23
- aging
- diabetes
- fibroblast growth factors
- insulin
- metabolic diseases
Fibroblast growth factor 23 (FGF23) is a phosphaturic factor and a suppressor of 1alpha-hydroxylase activity in the kidney. Although its importance in chronic kidney disease (CKD) has been demonstrated in adults, there is little information in pediatric patients. The aims of this study were: 1) to determine reference values for FGF23 serum levels according to glomerular filtration rate (GFR) (measured by the reference standard, inulin clearance), gender, and age; and 2) to evaluate the effects of different etiologies and treatments on FGF23 serum levels in a prospective single-center cohort of 227 CKD children (119 boys). Age, body weight, height, and GFR (mean /- sd) values were: 11.3 /- 4.1 yr, 37 /- 16 kg, 140 /- 20 cm, and 98 /- 34 ml/min per 1.73 m(2), respectively. Calcium, phosphate, PTH, 25 hydroxyvitamin D, 1,25 dihydroxyvitamin D, C-terminal FGF23, and intact FGF23 (mean /- sd) levels were: 2.43 /- 0.11 mmol/liter, 1.41 /- 0.22 mmol/liter, 41 /- 23 pg/ml, 24 /- 10 ng/ml, 152 /- 72 pmol/liter, 76 /- 134 relative units/ml, and 44 /- 37 pg/ml, respectively. There was a wide range of FGF23 serum levels, but FGF23 levels increased when GFR decreased. FGF23 serum levels were not modified by gender, but they increased with age. In univariate analysis, corticosteroid therapy seemed to be associated with increased FGF23 serum levels. A multivariate linear regression analysis found a significant impact of GFR, body mass index, and solid organ transplantation on FGF23 serum levels. Age, GFR, body mass index, and solid organ transplantation seem to influence FGF23 serum levels in a pediatric population. The impact of corticosteroids on FGF23 metabolism should be further investigated; further longitudinal studies will also help to better define the prognostic impact of FGF23 serum levels in pediatric CKD in terms of disease progression, cardiovascular morbidities, and bone disabilities.
MeSH Terms
- Adolescent
- Adrenal Cortex Hormones
- Aging
- Body Height
- Body Weight
- Child
- Child, Preschool
- Circadian Rhythm
- Cohort Studies
- Cross-Sectional Studies
- Female
- Fibroblast Growth Factors
- Glomerular Filtration Rate
- Hormones
- Humans
- Inulin
- Kidney Failure, Chronic
- Kidney Transplantation
- Kidney Tubules
- Male
- Prospective Studies
- Reference Values
- Sex Characteristics
- Vitamins
- Water-Electrolyte Balance
- Young Adult
The klotho gene was identified as an "aging-suppressor" gene in mice that accelerates aging when disrupted and extends life span when overexpressed. It encodes a single-pass transmembrane protein and is expressed primarily in renal tubules. The extracellular domain of Klotho protein is secreted into blood and urine by ectodomain shedding. The two forms of Klotho protein, membrane Klotho and secreted Klotho, exert distinct functions. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors and functions as an obligate co-receptor for FGF23, a bone-derived hormone that induces phosphate excretion into urine. Mice lacking Klotho or FGF23 not only exhibit phosphate retention but also display a premature-aging syndrome, revealing an unexpected link between phosphate metabolism and aging. Secreted Klotho functions as a humoral factor that regulates activity of multiple glycoproteins on the cell surface, including ion channels and growth factor receptors such as insulin/insulin-like growth factor-1 receptors. Potential contribution of these multiple activities of Klotho protein to aging processes is discussed.
MeSH Terms
- Aging
- Animals
- Bone and Bones
- Calcium Channels
- Fibroblast Growth Factors
- Glucuronidase
- Homeostasis
- Humans
- Insulin Resistance
- Kidney
- Longevity
- Mice
- Oxidative Stress
- Phosphates
- Receptors, Fibroblast Growth Factor
- TRPV Cation Channels
- Vitamin D
Since the discovery of alphaklotho-mutant mice, it has been questioned whether the responsible gene, alphaklotho, makes any effect on 'intrinsic aging' process. So far we found that alphaKlotho regulates transcellular calcium transport by mediating Na,K-ATPase activity and dominates mineral-regulating hormones such as PTH, vitamin D and FGF23. A new concept is now emerged that alphaklotho integrates mineral homeostasis. Findings of human cases with mineral disorders revealed impairment of alphaklotho expression as a pathological cause. Mineral metabolic system contributes to health and thus its disruption should result in acceleration of aging and disease.
MeSH Terms
- Aging
- Animals
- Glucuronidase
- Mice
- Mice, Mutant Strains
- Minerals
The kidney is a key player of phosphate balance, it determines serum phosphate levels by coupling phosphate reabsorption in the renal proximal tubule, calcitriol synthesis and consequently intestinal -phosphate absorption. The identification of fibroblast growth factor 23 (FGF23) as a hormone regulating phosphate and calcitriol metabolism has unveiled the mechanisms that coordinate these renal proximal tubule functions. A bone-kidney axis has emerged that controls bone mineralization. Animal model studies have improved our understanding of phosphate homeostasis and revealed the role of the Klotho protein, which is mandatory to FGF23 action. In this review, we detail FGF23 and Klotho implication in physiology and in genetic or acquired disorders. Phosphate ion is involved in vascular and soft tissue calcification and is important for cell proliferation. Disorders of FGF23-klotho axis alter life span and are involved in senescence.
MeSH Terms
- Aging
- Animals
- Calcification, Physiologic
- Calcitriol
- Cell Division
- Fibroblast Growth Factors
- Glucuronidase
- Homeostasis
- Humans
- Hyperphosphatemia
- Hypophosphatemia
- Intestinal Absorption
- Kidney Tubules, Proximal
- Longevity
- Mice
- Mice, Knockout
- Phosphates
Fibroblast growth factor (FGF) 23 is an endocrine hormone regulating the phosphate and vitamin D metabolism in the normal physiology. Recent studies have revealed that Klotho plays an essential role in FGF23 signaling. Klotho-deficient mice exhibit premature aging-like phenotypes, and therefore, this molecule has provided insights into the molecular mechanism of aging. However, it is suggested that the phenotype of the Klotho-deficient mice results from the disturbance in the phosphate and vitamin D metabolism. The importance of the FGF23/Klotho system thus is evident, but additional questions arose from this new concept.
MeSH Terms
- Aging
- Amino Acid Sequence
- Animals
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Mice
- Molecular Sequence Data
- Phosphates
- Signal Transduction
- Vitamin D
Recent studies using genetically modified mice, such as FGF23-/- and Klotho-/- mice that exhibit altered mineral homeostasis due to a high vitamin D activity showed features of premature aging that include retarded growth, osteoporosis, atherosclerosis, ectopic calcification, immunological deficiency, skin and general organ atrophy, hypogonadism and short lifespan. The phenotype reversed by normalizing vitamin D and/or mineral homeostasis. Thus, hypervitaminosis D due to an increased 1alpha-hydroxylase activity seems to be a cause of the premature aging. In several studies, we have described that a complete or partial lack of vitamin D action (VDR-/- mice and CYP27B1-/-) show almost similar phenotype as FGF23-/- or Klotho-/- mice. VDR mutant mice have growth retardation, osteoporosis, kyphosis, skin thickening and wrinkling, alopecia, ectopic calcification, progressive loss of hearing and balance as well as short lifespan. CYP27B1-/- mice do not show alopecia nor balance deficit, which might be apoVDR-dependent or calcidiol-dependent. The features are typical to premature aging. The phenotype is resistant to a normalization of the mineral homeostasis by a rescue diet containing high calcium and phosphate. Taken together, aging shows a U-shaped dependency on hormonal forms of vitamin D suggesting that there is an optimal concentration of vitamin D in delaying aging phenomena. Our recent study shows that calcidiol is an active hormone. Since serum calcidiol but not calcitriol is fluctuating in physiological situations, calcidiol might determine the biological output of vitamin D action. Due to its high serum concentration and better uptake of calcidiol-DBP by the target cells through the cubilin-megalin system, calcidiol seems to be an important circulating hormone. Therefore, serum calcidiol might be associated with an increased risk of aging-related chronic diseases more directly than calcitriol. Aging and cancer seem to be tightly associated phenomena. Accumulation of damage on DNA and telomeres cause both aging and cancer, moreover the signalling pathways seem to converge on tumour suppressor protein, p53, which seems to be regulated by vitamin D. Also, the insulin-like growth factor signalling pathway (IGF-1, IGFBPs, IGFR) and fibroblast growth factor-23 (FGF-23) regulate growth, aging and cancer. Vitamin D can regulate these signalling pathways, too. Also NF-kappaB and telomerase reverse transcriptase (TERT) might be molecular mechanisms mediating vitamin D action in aging and cancer. Calcidiol serum concentrations show a U-shaped risk of prostate cancer suggesting an optimal serum concentration of 40-60 nmol/L for the lowest cancer risk. Therefore, it is necessary to study several common aging-associated diseases such as osteoporosis, hypertension and diabetes known to be vitamin D-dependent before any recommendations of an optimal serum concentration of calcidiol are given.
MeSH Terms
- Aging
- Aging, Premature
- Animals
- Calcifediol
- Calcitriol
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Neoplasms
- Nutrition Disorders
- Vitamin D
- Vitamin D Deficiency
X-linked hypophosphatemia (XLH), characterized by renal phosphate wasting, is the most common cause of vitamin D-resistant rickets. It has been postulated that some phosphaturic factor plays a causative role in XLH and its murine homolog, the Hyp mouse. Fibroblast growth factor 23 (FGF23) is a physiological phosphaturic factor; its circulatory level is known to be high in most patients with XLH and Hyp mice, suggesting its pathophysiological role in this disease. To test this hypothesis, we treated Hyp mice with anti-FGF23 antibodies to inhibit endogenous FGF23 action. A single injection of the antibodies corrected the hypophosphatemia and inappropriately normal serum 1,25-dihydroxyvitamin D. These effects were accompanied by increased expressions of type IIa sodium-phosphate cotransporter and 25-hydroxyvitamin-D-1alpha-hydroxylase and a suppressed expression of 24-hydroxylase in the kidney. Repeated injections during the growth period ameliorated the rachitic bone phenotypes typically observed in Hyp mice, such as impaired longitudinal elongation, defective mineralization, and abnormal cartilage development. Thus, these results indicate that excess actions of FGF23 underlie hypophosphatemic rickets in Hyp mice and suggest a novel therapeutic potential of the FGF23 antibodies for XLH.
MeSH Terms
- Aging
- Animals
- Antibodies
- Body Weight
- Familial Hypophosphatemic Rickets
- Female
- Fibroblast Growth Factors
- Genetic Diseases, X-Linked
- Growth Plate
- Immunohistochemistry
- Injections, Subcutaneous
- Male
- Mice
- Osteomalacia
- Tibia
- Time Factors
- Vitamin D
The klotho gene encodes a single-pass transmembrane protein that forms a complex with multiple fibroblast growth factor (FGF) receptors and functions as an obligatory co-receptor for FGF23, a bone-derived hormone that induces negative phosphate balance. Defects in either Klotho or Fgf23 gene expression cause not only phosphate retention but also a premature-aging syndrome in mice, unveiling a potential link between phosphate metabolism and aging. In addition, the extracellular domain of Klotho protein is clipped on the cell surface and secreted into blood stream, potentially functioning as an endocrine factor. The secreted Klotho protein has a putative sialidase activity that modifies glycans on the cell surface, which may explain the ability of secreted Klotho protein to regulate activity of multiple ion channels and growth factors including insulin, IGF-1, and Wnt. Secreted Klotho protein also protects cells and tissues from oxidative stress through a mechanism yet to be identified. Thus, the transmembrane and secreted forms of Klotho protein have distinct functions, which may collectively affect aging processes in mammals.
MeSH Terms
- Aging
- Animals
- Calcium Channels
- Fibroblast Growth Factors
- Glucuronidase
- Humans
- Mice
- Models, Biological
- Mutation
- Vitamin D
Treatment of X-linked hypophosphatemic rickets improves bone mineralization and bone deformities, but its effect on skeletal growth is highly variable. Genetic variants in the promoter region of the vitamin D receptor (VDR) gene may explain the response to treatment because this receptor mediates vitamin D action. We studied the VDR promoter haplotype structure in a large cohort of 91 patients with hypophosphatemic rickets including 62 patients receiving 1alpha-hydroxyvitamin D3 derivatives and phosphates from early childhood on. Treatment improved bone deformities and final height, but 39% of treated patients still had short stature at the end of growth (-2 sd score or below). Height was closely associated with VDR promoter Hap1 genotype. Hap1(-) patients (35% of the cohort) had severe growth defects. This disadvantageous association of Hap1(-) status with height was visible before treatment, under treatment, and on to adulthood. Gender and age at initiation of treatment could not account for the Hap1 effect. No association with growth was found with a polymorphism of the PTH receptor gene otherwise found to be associated with adult height. Compared with Hap1( ) patients, those who were Hap1(-) had a higher urinary calcium response to 1alpha-hydroxyvitamin D3 and had significantly lower circulating FGF23 levels (C-terminal assay), taking into account their phosphate and 1alpha-hydroxyvitamin D3 intakes. The present work identifies the VDR promoter genotype as a key predictor of growth under treatment with 1alpha-hydroxyvitamin D3 derivatives in patients with hypophosphatemic rickets, including those with established PHEX alterations. The VDR promoter genotype appears to provide valuable information for adjusting treatment and for deciding upon the utility of early GH therapy.
MeSH Terms
- Adolescent
- Adult
- Aging
- Calcitriol
- Child
- Child, Preschool
- Cohort Studies
- DNA
- Familial Hypophosphatemic Rickets
- Female
- Fibroblast Growth Factors
- Genetic Diseases, X-Linked
- Genotype
- Haplotypes
- Humans
- Male
- Middle Aged
- Organophosphates
- Predictive Value of Tests
- Promoter Regions, Genetic
- Receptor, Parathyroid Hormone, Type 1
- Receptors, Calcitriol
- Reverse Transcriptase Polymerase Chain Reaction
- Sex Characteristics
- Young Adult
The kidney plays a critical role in the calcium (Ca) homeostasis. With advancing age, the kidney function, including glomerular filtration rate and tubular electrolyte reabsorption, is deteriorating without any kidney disease. Disturbed Ca metabolism may be associated with premature aging process, in which various cellular function is impaired by intracellular Ca burden due to increased Ca efflux from bone. Fibroblast growth factor (FGF) 23, a novel phosphate (P) -regulating factor, is involved in disorders of mineral bone metabolism. Recent studies suggest that FGF23 plays a certain role in premature aging process through altered P and vitamin D metabolism.
MeSH Terms
- Aging
- Animals
- Bone and Bones
- Calcium
- Fibroblast Growth Factors
- Homeostasis
- Humans
- Kidney
- Phosphorus
- Vitamin D
The klotho gene functions as an aging-suppressor gene that extends life span when overexpressed and accelerates aging-like phenotypes when disrupted in mice. The klotho gene encodes a single-pass transmembrane protein that binds to multiple fibroblast growth factor (FGF) receptors and functions as a co-receptor for FGF23, a bone-derived hormone that suppresses phosphate reabsorption and vitamin D biosynthesis in the kidney. In addition, the extracellular domain of Klotho protein is shed and secreted, potentially functioning as a humoral factor. The secreted Klotho protein can regulate multiple growth factor signaling pathways, including insulin/IGF-1 and Wnt, and the activity of multiple ion channels. Klotho protein also protects cells and tissues from oxidative stress, yet the precise mechanism underlying these activities remains to be determined. Thus, understanding of Klotho protein function is expected to provide new insights into the molecular basis for aging, phosphate/vitamin D metabolism, cancer and stem cell biology.
MeSH Terms
- Aging
- Animals
- Atrophy
- Bone Density
- Calcinosis
- Cognition Disorders
- Female
- Fibroblast Growth Factors
- Glucuronidase
- Hearing Loss
- Hypogonadism
- Insulin
- Insulin-Like Growth Factor I
- Ion Channels
- Male
- Mice
- Mice, Transgenic
- Nitric Oxide
- Osteoporosis
- Oxidative Stress
- Pulmonary Emphysema
- Signal Transduction
- Skin
- Spinal Cord Diseases
- Wnt Proteins
Klotho gene mutation leads to a syndrome strangely resembling chronic kidney disease patients undergoing dialysis with multiple accelerated age-related disorders, including hypoactivity, sterility, skin thinning, muscle atrophy, osteoporosis, vascular calcifications, soft-tissue calcifications, defective hearing, thymus atrophy, pulmonary emphysema, ataxia, and abnormalities of the pituitary gland, as well as hypoglycemia, hyperphosphatemia, and paradoxically high-plasma calcitriol levels. Conversely, mice overexpressing klotho show an extended existence and a slow aging process through a mechanism that may involve the induction of a state of insulin and oxidant stress resistance. Two molecules are produced by the klotho gene, a membrane bound form and a circulating form. However, their precise biological roles and molecular functions have been only partly deciphered. Klotho can act as a circulating factor or hormone, which binds to a not yet identified high-affinity receptor and inhibits the intracellular insulin/insulin-like growth factor-1 (IGF-1) signaling cascade; klotho can function as a novel beta-glucuronidase, which deglycosylates steroid beta-glucuronides and the calcium channel transient receptor potential vallinoid-5 (TRPV5); as a cofactor essential for the stimulation of fibroblast growth factor (FGF) receptor by FGF23. The two last functions have propelled klotho to the group of key factors regulating mineral and vitamin D metabolism, and have also stimulated the interest of the nephrology community. The purpose of this review is to provide a nephrology-oriented overview of klotho and its potential implications in normal and altered renal function states.
MeSH Terms
- Aging
- Animals
- Bone and Bones
- Glucuronidase
- Humans
- Kidney
- Minerals
- RNA, Messenger
- Vitamin D
It has been known that phosphate homeostasis is mainly regulated by parathyroid hormone and vitamin D. Fibroblast growth factor 23 (FGF23) has been identified as a novel factor that regulates vitamin D and phosphate metabolism. Genetic defect of FGF23 in mice revealed not only abnormal vitamin D and phosphate metabolism, but also premature aging-like phenotype that is quite similar to Klotho mice. Regulation of vitamin D and phosphate metabolism is closely related to aging processes as well as bone and mineral metabolism.
MeSH Terms
- Aging
- Aging, Premature
- Animals
- Bone and Bones
- Fibroblast Growth Factors
- Forkhead Transcription Factors
- Glucuronidase
- Humans
- Insulin-Like Growth Factor I
- Mice
- Phosphates
- Phosphorus, Dietary
- Signal Transduction
- Vitamin D
klotho mutant mice were originally described as a short-lived mouse model with premature aging-like disorders. The klotho gene responsible for these phenotypes encodes a type I membrane protein with a considerable similarity to beta-glycosidase. klotho is predominantly expressed in tissues functioning in the regulation of calcium homeostasis. Suggested functions of Klotho are (i) a fundamental regulator of calcium homeostasis, namely, a cofactor for the fibroblast growth factor (FGF) receptor 1c in FGF23 signaling and a regulator of parathyroid hormone secretion; (ii) a hormone that interferes with the intracellular signaling of insulin and insulin-like growth factor-1; and (iii) a beta-glucuronidase that activates the transient receptor potential ion channel TRPV5 by trimming its sugar moiety. How can we reconcile these pleiotropic functions of Klotho? Is there any common mechanism? Further in vivo studies, and biochemical as well as physiological analyses, are required for a better understanding of the molecular aspects of Klotho.
MeSH Terms
- Aging
- Aging, Premature
- Animals
- Calcium
- Fibroblast Growth Factors
- Glucuronidase
- Homeostasis
- Insulin Antagonists
- Mice
- Mutation
- Phenotype
- Signal Transduction
A girl with autosomal dominant hypophosphatemic rickets, presented with clinical, radiological and laboratory signs of rickets at the age of 11 months. She showed a good response to the treatment with low doses of oral phosphate and calcitriol. Surprisingly, she lost her renal phosphate wasting at the age of 8 years, indicating that the disturbed phosphate metabolism can be compensated by hormonal or other factors.
MeSH Terms
- Administration, Oral
- Aging
- Calcitriol
- Calcium Channel Agonists
- Child
- Female
- Fibroblast Growth Factors
- Genes, Dominant
- Humans
- Hypophosphatemia, Familial
- Kidney
- Mutation
- Pedigree
- Phosphates