ATF4
Cyclic AMP-dependent transcription factor ATF-4 (cAMP-dependent transcription factor ATF-4) (Activating transcription factor 4) (Cyclic AMP-responsive element-binding protein 2) (CREB-2) (cAMP-responsive element-binding protein 2) (Tax-responsive enhancer element-binding protein 67) (TaxREB67) [CREB2] [TXREB]
Publications[править]
Vascular calcification is common among aging populations and mediated by vascular smooth muscle cells (VSMCs). The endoplasmic reticulum (ER) is involved in protein folding and ER stress has been implicated in bone mineralization. The role of ER stress in VSMC-mediated calcification is less clear. Approach and Results: mRNA expression of the ER stress markers PERK (PKR (protein kinase RNA)-like ER kinase), ATF (activating transcription factor) 4, ATF6, and Grp78 was detectable in human vessels with levels of PERK decreased in calcified plaques compared to healthy vessels. Protein deposition of Grp78/Grp94 was increased in the matrix of calcified arteries. Induction of ER stress accelerated human primary VSMC-mediated calcification, elevated expression of some osteogenic markers (Runx2, Osterix, ALP, BSP, and OPG), and decreased expression of SMC markers. ER stress potentiated extracellular vesicle (EV) release via SMPD3. EVs from ER stress-treated VSMCs showed increased Grp78 levels and calcification. Electron microscopy confirmed the presence of Grp78/Grp94 in EVs. siRNA knock-down of Grp78 decreased calcification. Warfarin-induced Grp78 and ATF4 expression in rat aortas and VSMCs and increased calcification in an ER stress-dependent manner via increased EV release. ER stress induces vascular calcification by increasing release of Grp78-loaded EVs. Our results reveal a novel mechanism of action of warfarin, involving increased EV release via the PERK-ATF4 pathway, contributing to calcification. This study is the first to show that warfarin induces ER stress and to link ER stress to cargo loading of EVs.
Keywords
- aging
- arteries
- endoplasmic reticulum
- vascular calcification
- warfarin
Resveratrol is one of the most well-known drugs used in the treatment of aging. However, the potential mechanisms of resveratrol on intestinal aging have not yet been fully investigated. Herein, we aimed to further explore the pharmacological mechanisms of resveratrol as a therapy for intestinal aging. We performed network construction and enrichment analysis [i]via[/i] network pharmacology. Then a further animal experimental validation containing 20 female C57BL/6J (wild type, WT) and 16 female [i]ATF4 [/i] (knock down, KD) naturally aging mice and oral supplementary resveratrol (44 mg/kg/day) for 30 days were conducted. The expression of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), linear alkylethoxylate (AE), and malondialdehyde (MDA) were measured by ELISA, the observation of pathological changes and apoptosis in intestinal tissue were performed by HE, PAS, and TUNEL staining, the ATF4/Chop/Bcl-2/Bax signaling pathway-related proteins and mRNAs expression were measured by western blotting and real-time PCR. The network pharmacology showed 132 targets of resveratrol on aging. The enrichment analysis showed resveratrol antiaging involved mainly included protein heterodimerization activity, apoptosis, etc. Then ATF4/Chop/Bcl-2/Bax signaling pathway in biological process of apoptosis was selected to verify the potential mechanisms. Animal studies showed resveratrol upregulated the relative expression of SOD, GSH-Px, CAT, AE, whereas it downregulated the relative expression of MDA in intestine compared with the control group. There was also higher relative expression of SOD, GSH-Px, CAT, AE, and lower relative expression of MDA in KD mice than that in WT mice. Moreover, there was higher relative expression of SOD, GSH-Px, CAT, AE, and lower relative expression of MDA in KD mice than that in WT mice after resveratrol treatment. Decreased ATF4, Chop, Bax but increased Bcl-2 proteins and mRNAs expression were determined after resveratrol treatment compared with the control group; lower ATF4, Chop, Bax but higher Bcl-2 proteins and mRNAs expression were found in KD mice than that in WT mice. Additionally, lower relative proteins and mRNAs expression of ATF4, Chop, Bax and higher relative expression of Bcl-2 in KD mice than that in WT mice after resveratrol treatment. These findings demonstrated that resveratrol substantially inhibited intestinal aging [i]via[/i] downregulating ATF4/Chop/Bcl-2/Bax signaling pathway.
Keywords
- aging
- animal experiment
- apoptosis
- mechanisms
- network pharmacology
- resveratrol
Activation of the unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondrial apoptotic pathway serves as a central regulator for maintaining cell function and survival, and is associated with ageing and spermatogenesis. However, changes in UPR activation and mitochondrial apoptotic pathway in the testis during ageing remain unclear. In this study, we hypothesized that UPR activation declines and the mitochondrial apoptotic pathway is activated in the testis during ageing, and these changes are associated with a decline in testicular function. To test this theory, we utilized 6-, 12-, 18-, and 22-month-old Sprague Dawley rats to evaluate the changes in testicular and epididymal weights and indexes, sperm quality, histology, UPR activation, and mitochondrial apoptotic pathway in testicular tissues. The results showed that there was a progressive decline in testicular and epididymal weights and indexes, sperm count, and sperm viability during ageing. Correspondingly, seminiferous tubule diameters and epithelium heights progressively decreased with ageing. Western blot analysis and immunofluorescence staining results revealed that the expression of UPR-related proteins (GRP78, p-PERK, p-eif2α, ATF4, p-IRE1α, ATF6α, and XBP1) progressively decreased in the testis with ageing. In contrast, the expression of ER stress-related pro-apoptotic proteins CHOP, Caspase 12, and p-JNK progressively increased with advancing age. TUNEL staining further confirmed that testicular germ cell apoptosis was significantly increased from month 6 to 22 in rats. Additionally, the relative expression levels of cytochrome c and its downstream molecules including Capsase 9 and Caspase 3 were significantly increased in the testis during ageing. Collectively, our results suggest that impaired UPR activation and increased germ cell apoptosis partly mediated by the UPR and mitochondrial apoptotic pathway might correlate with an age-related decline in testicular function.
MeSH Terms
- Aging
- Animals
- Apoptosis
- Caspase 12
- Endoplasmic Reticulum Stress
- JNK Mitogen-Activated Protein Kinases
- Male
- Metabolic Networks and Pathways
- Mitochondria
- Organ Size
- Rats, Sprague-Dawley
- Signal Transduction
- Sperm Count
- Spermatozoa
- Testis
- Unfolded Protein Response
Keywords
- Ageing
- Apoptosis
- Endoplasmic reticulum
- Mitochondria
- Testis
- Unfolded protein response
Acidosis of the tumor microenvironment is a characteristic of solid tumors such as malignant melanoma. Main causes of the extracellular acidification are metabolic alterations in cancer cells. While numerous studies showed that acidosis promotes tumor invasiveness, metastasis, and neoangiogenesis resulting in malignant progression, contrary data reported that acidosis induces cell apoptosis, inhibits cell proliferation, and mediates cell autophagy. Here, we show that low pH (pH 6.7) induces senescent/quiescent phenotype in melanoma cells after long-time treatment defined by induction of SA-ß-galactosidase, upregulation of p21, G /G cell cycle arrest, and reduction of proliferation. Moreover, we revealed that extracellular acidosis triggers the inhibition of eIF2α and subsequently the activation of ATF4 expression, a key component of the integrated stress response (ISR), indicating an acid-mediated translation reprogramming. Interestingly, we also demonstrated that acidosis represses microphthalmia-associated transcription factor (MITF) and activates the expression of the receptor tyrosine kinase AXL. This MITF /AXL phenotype is correlated with drug resistance and therapeutic outcome in melanoma. Our results suggest that acidosis is an important microenvironmental factor triggering phenotypic plasticity and promoting tumor progression.
MeSH Terms
- Acidosis
- Cell Cycle Checkpoints
- Cell Line, Tumor
- Cell Proliferation
- Cellular Senescence
- Drug Resistance, Neoplasm
- Etoposide
- Extracellular Space
- Humans
- Hydrogen-Ion Concentration
- Melanoma
- Phenotype
Keywords
- dormancy
- extracellular acidosis
- melanoma
- senescence
- slow-cycling phenotype
- tumor microenvironment
Spongiform encephalopathy is an intriguing yet poorly understood neuropathology characterized by vacuoles, demyelination, and gliosis. It is observed in patients with prion disease, primary mitochondrial disease, HIV-1 infection of the brain, and some inherited disorders, but the underlying mechanism of disease remains unclear. The brains of mice lacking the MGRN1 E3 ubiquitin ligase develop vacuoles by 9 months of age. MGRN1-dependent ubiquitination has been reported to regulate mitofusin 1 and GP78, suggesting MGRN1 may have a direct effect on mitochondrial homeostasis. Here, we demonstrate that some MGRN1 localizes to mitochondria, most likely due to N-myristoylation, and mitochondria in cells from Mgrn1 null mutant mice display fragmentation and depolarization without recruitment of the parkin E3 ubiquitin ligase. The late onset of pathology in the brains of Mgrn1 null mutant mice suggests that a further, age-dependent effect on mitochondrial homeostasis may be required to trigger vacuolation. Parkin protein and mRNA levels showed a significant decline in the brains of Mgrn1 null mutant mice by 12 months of age. To test whether loss of parkin triggers vacuolation through a synergistic effect, we generated Mgrn1; parkin double mutant mice. By 1 month of age, their brains demonstrated more severe mitochondrial dysfunction than Mgrn1 null mutants, but there was no effect on the age-of-onset of spongiform neurodegeneration. Expression of the ATF4 transcription factor, a key regulator of the mitochondrial stress response, also declined in the brains of aged Mgrn1 null mutant mice. Together, the data presented here indicate that loss of MGRN1 has early, direct effects on mitochondrial homeostasis and late, indirect effects on the ability of cells to respond to mitochondrial stress.
MeSH Terms
- Aging
- Animals
- Brain
- Cells, Cultured
- Gene Expression
- Homeostasis
- Humans
- Mice
- Mice, Knockout
- Mitochondria
- Neurodegenerative Diseases
- Ubiquitin-Protein Ligases
- Vacuoles
In aging, the capacity of subcutaneous adipose tissue (SAT) to store lipids decreases and this results in metabolically unfavorable fat redistribution. Triggers of this age-related SAT dysfunction may include cellular senescence or endoplasmic reticulum (ER) stress. Therefore, we compared lipogenic capacity of SAT between young and older women and investigated its relation to senescence and ER stress markers. Samples of SAT and corresponding SAT-derived primary preadipocytes were obtained from two groups of women differing in age (36 vs. 72 years, n = 15 each) but matched for fat mass. mRNA levels of selected genes (lipogenesis: ACACA, FASN, SCD1, DGAT2, ELOVL6; senescence: p16, p21, NOX4, GDF15; ER stress-ATF4, XBP1s, PERK, HSPA5, GADD34, HYOU1, CHOP, EDEM1, DNAJC3) were assessed by qPCR, protein levels of GDF15 by ELISA, and mitochondrial function by the Seahorse Analyzer. Compared to the young, SAT and in vitro differentiated adipocytes from older women exhibited reduced mRNA expression of lipogenic enzymes. Out of analyzed senescence and ER stress markers, the only gene, whose expression correlated negatively with the expression of lipogenic enzymes in both SAT and adipocytes, was GDF15, a marker of not only senescence but also mitochondrial dysfunction. In line with this, inhibition of mitochondrial ATP synthase in adipocytes strongly upregulated GDF15 while reduced expression of lipogenic enzymes. Moreover, adipocytes from older women had a tendency for diminished mitochondrial capacity. Thus, a reduced lipogenic capacity of adipocytes in aged SAT appears to be linked to mitochondrial dysfunction rather than to ER stress or accumulation of senescent cells.
MeSH Terms
- Adipocytes
- Adult
- Aged
- Aging
- Biomarkers
- Cell Differentiation
- Cellular Senescence
- Endoplasmic Reticulum Stress
- Female
- Growth Differentiation Factor 15
- Humans
- Lipogenesis
- Mitochondria
- Subcutaneous Fat
Keywords
- Aging
- Lipogenesis
- Mitochondrial dysfunction
- Senescence
- Stress of endoplasmic reticulum
- Subcutaneous adipose tissue
Aging has been related with a decline in the ability to handle protein folding, which leads to endoplasmic reticulum stress and alterations in unfolded protein response (UPR). Importantly, physical activity could activate the UPR and attenuate or prevent age-induced endoplasmic reticulum (ER) dysfunction. The current study evaluated the effects of a resistance exercise on UPR and mitochondrial functions in peripheral blood mononuclear cells (PBMCs) from elderly subjects. Thirty healthy women and men (age, 72.8, [i]s [/i] = 2.2 years) were randomized to a training group, which performed an 8-week resistance training programme, or a control group, which followed their daily routines. The phosphorylation of PERK and IRE1, as well as ATF4, and XBP1 protein expression, significantly increased following the training, while expression of BiP, AFT6 and CHOP remain without changes. Additionally, the intervention also induced an increase in PGC-1α and Mfn1 protein levels, while no changes were found in Drp1 expression. Finally, the resistance protocol was not able to activate PINK1/Parkin and Bnip3/Nix pathways. The results obtained seem to indicate that 8-week resistance exercise activates the UPR, stimulates mitochondrial biogenesis, maintains mitochondrial dynamics and prevents mitophagy activation by unfolded proteins in PBMCs from elderly subjects.
MeSH Terms
- Aged
- Aging
- Endoplasmic Reticulum Stress
- Female
- Humans
- Male
- Mitophagy
- Muscle Strength
- Resistance Training
- Signal Transduction
- Unfolded Protein Response
Keywords
- Aging
- endoplasmic reticulum stress
- mitophagy
- physical activity
- strength
- unfolded protein response
To study the protective effects of Wuzi Yanzong recipe on testis germ cell apoptosis in natural ageing rats through endoplasmic reticulum stress (ERS), 16-month-old male SPF grade SD rats were randomly divided into three groups: ageing model group, and low and high-dose Wuzi Yanzong recipe groups (WZ, 1 and 4 g·kg⁻¹), with 10 rats in each group. In addition, 2-month-old SD male rats were used as adult control group. The ageing model group and the adult control group were fed with normal diet for 4 months. WZ groups were given the medicated feed for 4 months. After fasting for 12 hours, the rats were put to death. Then, the testes were immediately collected. The change of testicular tissue morphology was observed by HE staining. The expression levels of ER stress-related proteins GRP78, p-PERK, p-eif2[i]α[/i], ATF4, p-IRE1, XBP1, ATF6 and apoptosis-related proteins CHOP, caspase12 and p-JNK in testes were detected by Western blot. Compared with the ageing model group, Wuzi Yanzong recipe alleviated the morphological changes of testicular tissue. Western blot results showed that Wuzi Yanzong recipe significantly increased the expression levels of endoplasmic reticulum stress-related proteins GRP78, p-PERK, p-eif2[i]α[/i], ATF4, p-IRE1, XBP1, ATF6 and significantly decreased the expression levels of endoplasmic reticulum-induced apoptosis-related proteins CHOP, caspase 12 and p-JNK. In conclusion, Wuzi Yanzong recipe can alleviate the ageing-related apoptosis of testicular germ cells in natural ageing rats by regulating endoplasmic reticulum stress.
MeSH Terms
- Aging
- Animals
- Apoptosis
- Drugs, Chinese Herbal
- Endoplasmic Reticulum Stress
- Germ Cells
- Male
- Rats
- Rats, Sprague-Dawley
- Testis
Keywords
- Wuzi Yanzong recipe
- ageing
- apoptosis
- endoplasmic reticulum stress
- testis
It has been demonstrated that excessively activated endoplasmic reticulum stress (ERS) is closely associated with ageing-related diseases and male reproductive dysfunction. Wuzi Yanzong recipe (WZ) is a classical Traditional Chinese Medicine prescription for treatment of male reproductive system diseases. However, it remains unknown whether WZ improves testicular dysfunction with ageing via ERS. In this study, we investigated the protective effects and its mechanism of WZ on testicular dysfunction in ageing rats. The results showed that treatment with WZ for 4 months significantly increased the testicular weight and index, sperm count and viability, and the levels of testosterone and decreased the levels of estradiol. In addition, WZ significantly activated the onset of ERS and prevented germ cell apoptosis by upregulating the expression levels of ERS-responsive proteins GRP78, phospho-PERK, phospho-eIF2α, ATF4, phospho-IRE-1α, XBP1 and ATF6α, and downregulating the expression levels of pro-apoptotic proteins p-JNK, Caspase12 and CHOP in testicular germ cell of ageing rats. Besides, WZ significantly decreased the numbers of TUNEL-positive cells. Taken together, WZ effectively improves ageing-related testicular dysfunction through inhibition of germ cell apoptosis via ERS.
MeSH Terms
- Aging
- Animals
- Apoptosis
- Drugs, Chinese Herbal
- Endoplasmic Reticulum Stress
- Male
- Protective Agents
- Rats
- Rats, Sprague-Dawley
- Spermatozoa
- Testis
Keywords
- Wuzi Yanzong recipe
- ageing
- apoptosis
- endoplasmic reticulum stress
- testis
Age-related macular degeneration (AMD) is a multi-factorial disease that is the leading cause of irreversible and severe vision loss in the developed countries. It has been suggested that the pathogenesis of dry AMD involves impaired protein degradation in retinal pigment epithelial cells (RPE). RPE cells are constantly exposed to oxidative stress that may lead to the accumulation of damaged cellular proteins, DNA and lipids and evoke tissue deterioration during the aging process. The ubiquitin-proteasome pathway and the lysosomal/autophagosomal pathway are the two major proteolytic systems in eukaryotic cells. NRF-2 (nuclear factor-erythroid 2-related factor-2) and PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1 alpha) are master transcription factors in the regulation of cellular detoxification. We investigated the role of NRF-2 and PGC-1α in the regulation of RPE cell structure and function by using global double knockout (dKO) mice. The NRF-2/PGC-1α dKO mice exhibited significant age-dependent RPE degeneration, accumulation of the oxidative stress marker, 4-HNE (4-hydroxynonenal), the endoplasmic reticulum stress markers GRP78 (glucose-regulated protein 78) and ATF4 (activating transcription factor 4), and damaged mitochondria. Moreover, levels of protein ubiquitination and autophagy markers p62/SQSTM1 (sequestosome 1), Beclin-1 and LC3B (microtubule associated protein 1 light chain 3 beta) were significantly increased together with the Iba-1 (ionized calcium binding adaptor molecule 1) mononuclear phagocyte marker and an enlargement of RPE size. These histopathological changes of RPE were accompanied by photoreceptor dysmorphology and vision loss as revealed by electroretinography. Consequently, these novel findings suggest that the NRF-2/PGC-1α dKO mouse is a valuable model for investigating the role of proteasomal and autophagy clearance in the RPE and in the development of dry AMD.
MeSH Terms
- Animals
- Autophagy
- Biomarkers
- Disease Models, Animal
- Electroretinography
- Endoplasmic Reticulum Stress
- Genetic Association Studies
- Genetic Predisposition to Disease
- Immunohistochemistry
- Lysosomes
- Macular Degeneration
- Mice
- Mice, Knockout
- Mitochondria
- Molecular Imaging
- Mutation
- NF-E2-Related Factor 2
- Oxidative Stress
- Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
- Phenotype
- Photoreceptor Cells
- Protein Aggregation, Pathological
- Reactive Oxygen Species
- Retinal Pigment Epithelium
Keywords
- Aging
- Autophagy
- Degeneration
- Oxidative stress
- Proteasome
- Protein aggregation
Flavokawain B (FKB), a natural kava chalcone, displays potent antitumor activity in various types of cancer. The mechanism of action, however, remains unclear. Here, we evaluated the efficacy of FKB in the treatment of human glioblastoma multiforme (GBM) as well as the molecular basis for its inhibitory effects in cancer. Approximately 60% of GBM cells became senescent after treatment with FKB as assessed in the senescence-associated (SA)-GLB1/SA-β-galactosidase assay. The cellular process of autophagy potentially contributed to the establishment of senescence. Transmission electron microscopy revealed the formation of autophagic vesicles under FKB treatment, and MAP1LC3B (microtubule associated protein 1 light chain 3 beta)-II was increased. Transfection of ATG5 or ATG7 small interfering RNAs (siRNAs) inhibited FKB-induced autophagy in U251 cells. Western blot revealed that molecular components of the endoplasmic reticulum stress pathway were activated, including ATF4 (activating transcription factor 4) and [[DDIT3]] (DNA damage inducible transcript 3), while levels of TRIB3 (tribbles pseudokinase 3) increased. In addition, based on the phosphorylation status, the AKT-MTOR-RPS6KB1 pathway was inhibited, which induced autophagy in GBM cells. Inhibition of autophagy by autophagy inhibitors 3-methyladenine and chloroquine or knockdown of ATG5 or ATG7 caused FKB-treated U251 cells to switch from senescence to apoptosis. Finally, knockdown of ATG5 or treatment with chloroquine in combination with FKB, significantly inhibited tumor growth in vivo. Our results demonstrated that FKB induced protective autophagy through the ATF4-[[DDIT3]]-TRIB3-AKT-MTOR-RPS6KB1 signaling pathway in GBM cells, indicating that the combination treatment of FKB with autophagy inhibitors may potentially be an effective therapeutic strategy for GBM. 3-MA: 3-methyladenine; 4-PBA: 4-phenylbutyrate; AKT: AKT serine/threonine kinase; ATF4: activating transcription factor 4; ATG: autophagy related; CASP3: caspase 3; CCK-8: cell counting kit-8; CDKN1A: cyclin-dependent kinase inhibitor 1A; CQ: chloroquine; [[DDIT3]]: DNA damage inducible transcript 3; DMEM: Dulbecco's modified Eagle's medium; EIF2A: eukaryotic translation initiation factor 2A; EIF2AK3: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; FKB: flavokawain B; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GBM: glioblastoma multiforme; GFP: green fluorescent protein; HSPA5: heat shock protein family A (Hsp70) member 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PARP1: poly(ADP-ribose) polymerase; 1RPS6KB1: ribosomal protein S6 kinase B1; SA-GLB1: senescence-associated galactosidase beta 1; siRNA: short interfering RNA; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TRIB3: tribbles pseudokinase 3; TUNEL: deoxynucleotidyl transferase-mediated dUTP nick-end labeling.
MeSH Terms
- Animals
- Antineoplastic Agents, Phytogenic
- Autophagy
- Autophagy-Related Protein 5
- Autophagy-Related Protein 7
- Cell Proliferation
- Cells, Cultured
- Endoplasmic Reticulum Stress
- Flavonoids
- Gene Expression Regulation, Neoplastic
- Glioma
- Humans
- Male
- Mice
- Mice, Nude
- Xenograft Model Antitumor Assays
Keywords
- Apoptosis
- ER stress
- autophagy
- flavokawain B
- senescence
The growth factor receptor bound protein GRB10 is an imprinted gene product and a key negative regulator of the insulin, IGF1 and mTORC1 signaling pathways. GRB10 is highly expressed in mouse fetal liver but almost completely silenced in adult mice, suggesting a potential detrimental role of this protein in adult liver function. Here we show that the [i]Grb10[/i] gene could be reactivated in adult mouse liver by acute endoplasmic reticulum stress (ER stress) such as tunicamycin or a short-term high-fat diet (HFD) challenge, concurrently with increased unfolded protein response (UPR) and hepatosteatosis. Lipogenic gene expression and acute ER stress-induced hepatosteatosis were significantly suppressed in the liver of the liver-specific GRB10 knockout mice, uncovering a key role of [i]Grb10[/i] reactivation in acute ER stress-induced hepatic lipid dysregulation. Mechanically, acute ER stress induces [i]Grb10[/i] reactivation via an ATF4-mediated increase in [i]Grb10[/i] gene transcription. Our study demonstrates for the first time that the silenced [i]Grb10[/i] gene can be reactivated by acute ER stress and its reactivation plays an important role in the early development of hepatic steatosis.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Diet, High-Fat
- Endoplasmic Reticulum Stress
- Fatty Acids
- Fatty Liver
- Feeding Behavior
- GRB10 Adaptor Protein
- Gene Deletion
- Gene Expression Regulation
- Gene Silencing
- Lipid Metabolism
- Liver
- Mice, Inbred C57BL
- Mice, Knockout
- Organ Specificity
- Tunicamycin
Keywords
- ER stress
- Grb10
- UPR
- hepatic steatosis
- lipid metabolism
With upcoming age, the capability to fight against harmful stimuli decreases and the organism becomes more susceptible to infections and diseases. Here, the objective was to demonstrate the effect of dietary resveratrol in aged mice in potentiating brain defenses against LipoPolySaccharide (LPS). Acute LPS injection induced a strong proinflammatory effect in 24-months-old C57/BL6 mice hippocampi, increasing InterLeukin (Il)-6, Tumor Necrosis Factor-alpha (Tnf-α), Il-1β, and C-X-C motif chemokine (Cxcl10) gene expression levels. Resveratrol induced higher expression in those cytokines regarding to LPS. Oxidative Stress (OS) markers showed not significant changes after LPS or resveratrol, although for resveratrol treated groups a slight increment in most of the parameters studies was observed, reaching signification for NF-kB protein levels and iNOS expression. However, Endoplasmic Reticulum (ER) stress markers demonstrated significant changes in resveratrol-treated mice after LPS treatment, specifically in eIF2α, BIP, and ATF4. Moreover, as described, resveratrol is able to inhibit the mechanistic Target of Rapamycin (mTOR) pathway and this effect could be linked to (eIF2α) phosphorylation and the increase in the expression of the previously mentioned proinflammatory genes as a response to LPS treatment in aged animals. In conclusion, resveratrol treatment induced a different cellular response in aged animals when they encountered acute inflammatory stimuli.
MeSH Terms
- Age Factors
- Aging
- Animals
- Anti-Inflammatory Agents
- Cytokines
- Disease Models, Animal
- Endoplasmic Reticulum Stress
- Eukaryotic Initiation Factor-2B
- Gene Expression Regulation
- Hippocampus
- Inflammation
- Inflammation Mediators
- Lipopolysaccharides
- Male
- Mice, Inbred C57BL
- NF-kappa B
- Nitric Oxide Synthase Type II
- Oxidative Stress
- Phosphorylation
- Resveratrol
- Signal Transduction
- TOR Serine-Threonine Kinases
Keywords
- Aging
- Cytokines
- Inflammation
- eukaryotic Initiation Factor 2 (eIF2)
- iNOS
- mTOR
FGF21 is a multifunctional metabolic and stress hormone which is normally expressed in liver but cellular stress, e.g. mitochondrial or endoplasmic reticulum (ER) stress, can induce its expression and subsequent secretion from several mammalian tissues. The stress kinases of the integrated stress response (ISR) pathway stimulate the expression of FGF21 through the activation of ATF4 transcription factor, thus enhancing cellular stress resistance. The metabolic and stress-inducible transactivation mechanisms of FGF21 gene are mostly mediated through separate pathways. FGF21 is an interorgan regulator which can alleviate many age-related metabolic and stress disorders, e.g. through the activation of AMPK signaling. FGF21 signaling is also involved in circadian and torpor regulation. Given that circulating FGF21 can attenuate organelle stress, e.g. mitochondrial and ER stresses, it resembles a stress-induced cell non-autonomous regulation of proteostasis and longevity present in model organisms. The overexpression of FGF21 can even extend the lifespan of mice, probably by improving the healthspan. We will clarify the positive and negative signaling mechanisms which control the stress-related expression of FGF21 through the ISR pathway. Moreover, we will examine the role of FGF21 as an interorgan coordinator of survival functions in metabolic and stress disorders. We conclude that FGF21 can be viewed as a cell non-autonomous enhancer of longevity in mammals.
MeSH Terms
- Animals
- Endoplasmic Reticulum Stress
- Fibroblast Growth Factors
- Gene Expression Regulation
- Liver
- Longevity
- Mice
- Mitochondria
- Signal Transduction
Keywords
- AMPK
- Cell non-autonomous
- FGF21
- Healthspan
- Klotho
- Lifespan
- PERK
Here, we discuss recent work focused on the role of activating transcription factor 4 (ATF4) in skeletal muscle atrophy. Muscle atrophy involves and requires widespread changes in skeletal muscle gene expression; however, the transcriptional regulatory proteins responsible for those changes are not yet well defined. Recent work indicates that some forms of muscle atrophy require ATF4, a stress-inducible bZIP transcription factor subunit that helps to mediate a broad range of stress responses in mammalian cells. ATF4 expression in skeletal muscle fibers is sufficient to induce muscle fiber atrophy and required for muscle atrophy during several stress conditions, including aging, fasting, and limb immobilization. By helping to activate specific genes in muscle fibers, ATF4 contributes to the expression of numerous mRNAs, including at least two mRNAs (Gadd45a and p21) that encode mediators of muscle fiber atrophy. Gadd45a promotes muscle fiber atrophy by activating the protein kinase MEKK4. p21 promotes atrophy by reducing expression of spermine oxidase, a metabolic enzyme that helps to maintain muscle fiber size under nonstressed conditions. In skeletal muscle fibers, ATF4 is critical component of a complex and incompletely understood molecular signaling network that causes muscle atrophy during aging, fasting, and immobilization.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Fasting
- Humans
- Immobilization
- Muscle Fibers, Skeletal
- Muscle, Skeletal
- Muscular Atrophy
- Signal Transduction
Reduced amino acid availability attenuates mRNA translation in cells and helps to extend lifespan in model organisms. The amino acid deprivation-activated kinase GCN2 mediates this response in part by phosphorylating eIF2α. In addition, the cap-dependent translational inhibitor 4E-BP is transcriptionally induced to extend lifespan in Drosophila melanogaster, but through an unclear mechanism. Here, we show that GCN2 and its downstream transcription factor, ATF4, mediate 4E-BP induction, and GCN2 is required for lifespan extension in response to dietary restriction of amino acids. The 4E-BP intron contains ATF4-binding sites that not only respond to stress but also show inherent ATF4 activity during normal development. Analysis of the newly synthesized proteome through metabolic labeling combined with click chemistry shows that certain stress-responsive proteins are resistant to inhibition by 4E-BP, and gcn2 mutant flies have reduced levels of stress-responsive protein synthesis. These results indicate that GCN2 and ATF4 are important regulators of 4E-BP transcription during normal development and aging.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Amino Acids
- Animals
- Binding Sites
- Cell Line
- Click Chemistry
- Diet, Protein-Restricted
- Drosophila Proteins
- Drosophila melanogaster
- Endoplasmic Reticulum Stress
- Genotype
- Intracellular Signaling Peptides and Proteins
- Introns
- Longevity
- Mutation
- Peptide Initiation Factors
- Phenotype
- Protein Kinases
- Proteome
- Proteomics
- RNA Interference
- Signal Transduction
- Time Factors
- Transcription Factors
- Transcription, Genetic
- Transfection
- Up-Regulation
- eIF-2 Kinase
During normal aging, the number of dopaminergic (DA) neurons in the substantia nigra progressively diminishes, although massive DA neuronal loss is a hallmark sign of Parkinson's disease. Unfortunately, there is little known about the molecular events involved in age-related DA neuronal loss. In this study, we found that (1) the level of parkin was decreased in the cerebellum, brain stem, substantia nigra, and striatum of aged mice, (2) diaminodiphenyl sulfone (DDS) restored the level of parkin, (3) DDS prevented age-dependent DA neuronal loss, and (4) DDS protected SH-SY5Y cells from 1-methyl-4-phenylpyridinium and hydrogen peroxide. Furthermore, pretreatment and/or post-treatment of DDS in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease model attenuated DA neuronal loss and restored motor behavior. DDS transcriptionally activated parkin via protein kinase RNA-like endoplasmic reticulum kinase-activating transcription factor 4 signaling and DDS not only failed to induce parkin expression but also failed to rescue SH-SY5Y cells from 1-methyl-4-phenylpyridinium in the absence of ATF4. Herein, we demonstrated for the first time that DDS increased parkin level and served as a neuroprotective agent for age-dependent DA neuronal loss. Thus, DDS may be a potential therapeutic agent for age-related neurodegeneration.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Anti-Inflammatory Agents
- Brain
- Cells, Cultured
- Dapsone
- Disease Models, Animal
- Dopaminergic Neurons
- Endoplasmic Reticulum Stress
- Female
- Male
- Mice, Inbred C57BL
- Neuroprotective Agents
- Parkinson Disease
- Signal Transduction
- Substantia Nigra
- Ubiquitin-Protein Ligases
- eIF-2 Kinase
Keywords
- Diaminodiphenyl sulfone
- Dopaminergic neuron
- ER stress
- PERK-ATF4 signaling
- Parkin
- Parkinson's disease
In mammals, circadian rhythms in physiological function are generated by a molecular oscillator driven by transcriptional-translational feedback loop consisting of negative and positive regulators. Disruption of this circadian clock machinery is thought to increase the risk of cancer development, but the potential contributions of each component of circadian clock to oncogenesis have been little explored. Here we reported that negative and positive transcriptional regulators of circadian feedback loop had different roles in oncogene-induced neoplastic transformation. Mouse embryonic fibroblasts prepared from animals deficient in negative circadian clock regulators, Period2 (Per2) or Cryptochrome1/2 (Cry1/2), were prone to transformation induced by co-expression of H-ras(V12) and SV40 large T antigen (SV40LT). In contrast, mouse embryonic fibroblasts prepared from mice deficient in positive circadian clock regulators, Bmal1 or Clock, showed resistance to oncogene-induced transformation. In Per2 mutant and Cry1/2-null cells, the introduction of oncogenes induced expression of ATF4, a potent repressor of cell senescence-associated proteins p16INK4a and p19ARF. Elevated levels of ATF4 were sufficient to suppress expression of these proteins and drive oncogenic transformation. Conversely, in Bmal1-null and Clock mutant cells, the expression of ATF4 was not induced by oncogene introduction, which allowed constitutive expression of p16INK4a and p19ARF triggering cellular senescence. Although genetic ablation of either negative or positive transcriptional regulators of the circadian clock leads to disrupted rhythms in physiological functions, our findings define their different contributions to neoplastic cellular transformation.
MeSH Terms
- ARNTL Transcription Factors
- Activating Transcription Factor 4
- Animals
- CLOCK Proteins
- Cell Movement
- Cell Transformation, Neoplastic
- Cellular Senescence
- Circadian Clocks
- Cryptochromes
- Mice
- Mice, Inbred ICR
- Mice, Inbred NOD
- Mice, Knockout
- Mice, Mutant Strains
- Mice, SCID
- Mutant Proteins
- Oncogenes
- Period Circadian Proteins
Keywords
- cellular senescence
- circadian rhythm
- clock gene
- oncogene
- tumor cell biology
Human differentiated embryo chondrocyte expressed gene 1 (DEC1) is frequently used as a marker of senescence in vivo. Fibroblast growth factor 21 (FGF21), a novel endocrine-like member of the FGF superfamily, is highly expressed in the liver, and FGF21-transgenic mice have extended lifespans. Thus, we hypothesized that FGF21 may play a role in the DEC1-mediated aging process. In this study, DEC1 knockout (KO) mice were used to characterize the mechanism by which FGF21 protects mice from aging. Aging is strongly diminished in DEC1 KO mice, which is reflected by decreased lipid levels and oxidative stress, leading to an amelioration of liver function and structure. The expression of FGF21 decreased with aging in wild-type (WT) mice, whereas ATF4, Phospho-ERK and Phospho-p38 expression was maintained and was accompanied by a compensatory rise of FGF21 mRNA and protein expression in DEC1 KO mice. Over-expression of DEC1 markedly abolished the hepatic expression of FGF21, and siRNA-mediated inhibition of endogenous DEC1 increased the expression of FGF21. DEC1 further diminished the expression of ATF4 in HepG2 cells over-expressing DEC1. The induction of FGF21 and ATF4 at the mRNA and protein levels during the course of aging supports the view that DEC1 KO mice are able to restore the age-related imbalance of metabolism. Collectively, the data obtained in this study suggest that DEC1 is a novel negative regulator of hepatic FGF21 expression.
MeSH Terms
- Aging
- Animals
- Basic Helix-Loop-Helix Transcription Factors
- Cell Line
- Fibroblast Growth Factors
- Gene Expression Regulation, Developmental
- Hepatocytes
- Homeodomain Proteins
- Liver
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
Keywords
- Aging
- DEC1
- FGF21
- Hepatic homeostasis
- Liver
An unfolded protein response (UPR) in addition to oxidative stress and the inflammatory response is known to be activated in age-related ocular disorders, such as macular degeneration, diabetic retinopathy, glaucoma, and cataracts. Therefore, we aimed to investigate whether healthy aged retinas display UPR hallmarks, in order to establish a baseline for the activated UPR markers for age-related ocular diseases. Using western blotting, we determined that the hallmarks of the UPR PERK arm, phosphorylated (p) eIF2a, ATF4, and GADD34, were significantly altered in aged vs. young rat retinas. The cleaved pATF6 (50) and CHOP proteins were dramatically upregulated in the aged rodent retinas, indicating the activation of the ATF6 UPR arm. The UPR activation was associated with a drop in rhodopsin expression and in the NRF2 and HO1 levels, suggesting a decline in the anti-oxidant defense in aged retinas. Moreover, we observed down-regulation of anti-inflammatory IL-10 and IL-13 and upregulation of pro-inflammatory RANTES in the healthy aged retinas, as measured using the Bio-plex assay. Our results suggest that cellular homeostasis in normal aged retinas is compromised, resulting in the concomitant activation of the UPR, oxidative stress, and inflammatory signaling. This knowledge brings us closer to understanding the cellular mechanisms of the age-related retinopathies and ocular disorders characterized by an ongoing UPR, and highlight the UPR signaling molecules that should be validated as potential therapeutic targets.
MeSH Terms
- Aging
- Animals
- Biomarkers
- Inflammation
- Mice, Inbred C57BL
- Oxidative Stress
- Rats, Inbred F344
- Retina
- Rhodopsin
- Unfolded Protein Response
Keywords
- AMD
- Aging
- Retina
- Unfolded protein response
Aging reduces skeletal muscle mass and strength, but the underlying molecular mechanisms remain elusive. Here, we used mouse models to investigate molecular mechanisms of age-related skeletal muscle weakness and atrophy as well as new potential interventions for these conditions. We identified two small molecules that significantly reduce age-related deficits in skeletal muscle strength, quality, and mass: ursolic acid (a pentacyclic triterpenoid found in apples) and tomatidine (a steroidal alkaloid derived from green tomatoes). Because small molecule inhibitors can sometimes provide mechanistic insight into disease processes, we used ursolic acid and tomatidine to investigate the pathogenesis of age-related muscle weakness and atrophy. We found that ursolic acid and tomatidine generate hundreds of small positive and negative changes in mRNA levels in aged skeletal muscle, and the mRNA expression signatures of the two compounds are remarkably similar. Interestingly, a subset of the mRNAs repressed by ursolic acid and tomatidine in aged muscle are positively regulated by activating transcription factor 4 (ATF4). Based on this finding, we investigated ATF4 as a potential mediator of age-related muscle weakness and atrophy. We found that a targeted reduction in skeletal muscle ATF4 expression reduces age-related deficits in skeletal muscle strength, quality, and mass, similar to ursolic acid and tomatidine. These results elucidate ATF4 as a critical mediator of age-related muscle weakness and atrophy. In addition, these results identify ursolic acid and tomatidine as potential agents and/or lead compounds for reducing ATF4 activity, weakness, and atrophy in aged skeletal muscle.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Gene Expression
- Male
- Mice
- Mice, Inbred C57BL
- Muscle, Skeletal
- RNA, Messenger
- Sarcopenia
- Tomatine
- Triterpenes
Keywords
- ATF4
- aging
- muscle atrophy
- protein synthesis
- sarcopenia
- skeletal muscle
- skeletal muscle atrophy
- skeletal muscle metabolism
- tomatidine
- ursolic acid
In our studies investigating the role of autophagy in systemic metabolism, we found that mitochondrial dysfunction due to autophagy deficiency in insulin target tissues, such as skeletal muscle or liver, leads to the induction of fibroblast growth factor (FGF)21 as a mitokine and protection against obesity and insulin resistance. In the following studies, we observed that metformin, one of the most widely used antidiabetic medications, induces mitochondrial stress and induces FGF21 through a PERK-eIF2α-ATF4 pathway, which may contribute to the antidiabetic effect of metformin. Amino acid deprivation also induced ATF4 and FGF21, while the role of mitochondrial dysfunction in this condition is not yet clear. These results suggest the possibility that mitochondrial stress inducing an integrated stress response can induce a mitokine response and affect systemic metabolism in a non-cell-autonomous manner, in addition to the well-recognized cell-autonomous role of mitochondrial function in metabolism.
MeSH Terms
- Animals
- Autophagy
- Biomarkers
- Energy Metabolism
- Fibroblast Growth Factors
- Humans
- Hypoglycemic Agents
- Metformin
- Mitochondria
- Mitochondrial Diseases
- Models, Biological
- Stress, Physiological
Keywords
- FGF21
- longevity
- metabolism
- mitochondrial stress
- mitokine
Neurodegeneration is the characteristic pathology in the brains of Alzheimer's disease (AD). However, the nature and molecular mechanism leading to the degeneration are not clarified. Given that only the neurons filled with neurofibrillary tangles survive to the end stage of the disease and the major component of the tangles is the hyperphosphorylated tau proteins, it is conceivable that tau hyperphosphorylation must play a crucial role in AD neurodegeneration. We have demonstrated that tau hyperphosphorylation renders the cells more resistant to the acute apoptosis. The molecular mechanisms involve substrate competition of tau and β-catenin for glycogen synthase kinase 3β (GSK-3β); activation of Akt; preservation of Bcl-2 and suppression of Bax, cytosolic cytochrome-c, and caspase-3 activity; and upregulation of unfolded protein response (UPR), i.e., up-regulating phosphorylation of PERK, eIF2 and IRE1 with an increased cleavage of ATF6 and ATF4. On the other hand, tau hyperphosphorylation promotes its intracellular accumulation and disrupts axonal transport; hyperphosphorylated tau also impairs cholinergic function and inhibits proteasome activity. These findings indicate that tau hyperphosphorylation and its intracellular accumulation play dual role in the evolution of AD. We speculate that transient tau phosphorylation helps cells abort from an acute apoptosis, while persistent tau hyperphosphorylation/accumulation may trigger cell senescence that eventually causes a chronic neurodegeneration. Therefore, the nature of "AD neurodegeneration" may represent a new type of tau-regulated chronic neuron death; and the stage of cell senescence may provide a broad window for the intervention of AD.
MeSH Terms
- Alzheimer Disease
- Animals
- Apoptosis
- Cellular Senescence
- Disease Models, Animal
- Endoplasmic Reticulum Stress
- Humans
- Mitochondria
- Neurofibrillary Tangles
- Neurogenesis
- Neuroglia
- Phosphorylation
- Proto-Oncogene Proteins c-akt
- Tumor Suppressor Protein p53
- tau Proteins
Keywords
- Alzheimer's disease
- Apoptosis
- Hyperphosphorylation
- Neurodegeneration
- Senescence
- Tau
Premature senescence is an important event during diabetic nephropathy (DN) progression. Here, we investigated the role of endoplasmic reticulum (ER) stress-regulated activation of transcription factor 4 (ATF4)/p16 signaling in the premature senescence of renal tubular epithelial cells (RTECs) during DN development. In the renal tissues of Type 2 DN patients, we detected an increased number of senescent cells; elevated deposition of advanced glycation end products (AGEs); upregulated expression of ER stress marker, glucose-regulated protein 78; as well as overexpression of ATF4 and p16. Similarly, these phenomena were also observed in cultured mouse RTECs following AGE treatment. Interestingly, AGE-induced p16 expression and premature senescence were successfully attenuated by ER stress inhibitor and ATF4 gene silencing. Moreover, AGE-induced premature senescence was mimicked by ER stress inducers and ATF4 overexpression, while suppressed by p16 gene silencing. In addition, ER stress inducers can augment ATF4 expression. Therefore, our results demonstrate that the ER stress-regulated ATF4/p16 pathway is involved in the premature senescence of RTECs during DN progression.
MeSH Terms
- Activating Transcription Factor 4
- Aged
- Aging, Premature
- Animals
- Cadherins
- Cells, Cultured
- Cellular Senescence
- Cyclin-Dependent Kinase Inhibitor p16
- Diabetic Nephropathies
- Endoplasmic Reticulum
- Endoplasmic Reticulum Stress
- Epithelial Cells
- Female
- Glycation End Products, Advanced
- Heat-Shock Proteins
- Humans
- Kidney Tubules
- Male
- Mice
- Mice, Inbred C57BL
- Middle Aged
- Neoplasm Proteins
- RNA Interference
- RNA, Small Interfering
Keywords
- activating transcription factor 4
- advanced glycation end products
- endoplasmic reticulum stress
- p16
- premature senescence
ATF4, a DNA-binding factor that modulates responses to amino acid availability and ribosomal function, has been shown to be altered in both liver and fibroblasts from two strains of long-lived mice, i.e. Snell dwarf and PAPP-A knockout mice. New data now show elevated ATF4 levels, and elevation of ATF4-dependent proteins and mRNAs, in liver of mice treated with acarbose or rapamycin, calorically restricted mice, methionine-restricted mice, and mice subjected to litter crowding. Elevation of ATF4, at least in liver, thus seems to be a shared feature of diets, drugs, genes, and developmental alterations that extend maximum lifespan in mice.
MeSH Terms
- Activating Transcription Factor 3
- Activating Transcription Factor 4
- Aging
- Animals
- Caloric Restriction
- Disease Models, Animal
- Female
- Liver
- Male
- Mice
- Mice, Knockout
- Transcription Factor CHOP
Keywords
- acarbose
- caloric restriction
- longevity
- methionine restriction
- rapamycin
Endoplasmic reticulum (ER) stress results from an imbalance between the abundance of synthesized proteins and the folding capacity of the ER. In response, the unfolded protein response (UPR) attempts to restore ER function by attenuating protein synthesis and inducing chaperone expression. Resistance exercise (RE) stimulates protein synthesis; however, a postexercise accumulation of unfolded proteins may activate the UPR. Aging may impair protein folding, and the accumulation of oxidized and misfolded proteins may stimulate the UPR at rest in aged muscle. Eighteen younger (n = 9; 21 ± 3 yr) and older (n = 9; 70 ± 4 yr) untrained men completed a single, unilateral bout of RE using the knee extensors (four sets of 10 repetitions at 75% of one repetition maximum on the leg press and leg extension) to determine whether the UPR is increased in resting, aged muscle and whether RE stimulates the UPR. Muscle biopsies were taken from the nonexercised and exercised vastus lateralis at 3, 24, and 48 h postexercise. Age did not affect any of the proteins and transcripts related to the UPR. Glucose-regulated protein 78 (GRP78) and protein kinase R-like ER protein kinase (PERK) proteins were increased at 48 h postexercise, whereas inositol-requiring enzyme 1 alpha (IRE1α) was elevated at 24 h and 48 h. Despite elevated protein, GRP78 and PERK mRNA was unchanged; however, IRE1α mRNA was increased at 24 h postexercise. Activating transcription factor 6 (ATF6) mRNA increased at 24 h and 48 h, whereas ATF4, CCAAT/enhancer-binding protein homologous protein (CHOP), and growth arrest and DNA damage protein 34 mRNA were unchanged. These data suggest that RE activates specific pathways of the UPR (ATF6/IRE1α), whereas PERK/eukaryotic initiation factor 2 alpha/CHOP does not. In conclusion, acute RE results in UPR activation, irrespective of age.
MeSH Terms
- Activating Transcription Factor 4
- Activating Transcription Factor 6
- Adolescent
- Age Factors
- Aged
- Endoplasmic Reticulum
- Endoplasmic Reticulum Stress
- Endoribonucleases
- Heat-Shock Proteins
- Humans
- Male
- Muscle Contraction
- Protein-Serine-Threonine Kinases
- Quadriceps Muscle
- RNA, Messenger
- Resistance Training
- Signal Transduction
- Time Factors
- Transcription Factor CHOP
- Unfolded Protein Response
- Young Adult
- eIF-2 Kinase
Keywords
- aging
- endoplasmic reticulum
- resistance exercise
- skeletal muscle
- unfolded protein response
Methionine restriction (MR) decreases body weight and adiposity and improves glucose homeostasis in rodents. Similar to caloric restriction, MR extends lifespan, but is accompanied by increased food intake and energy expenditure. Most studies have examined MR in young animals; therefore, the aim of this study was to investigate the ability of MR to reverse age-induced obesity and insulin resistance in adult animals. Male C57BL/6J mice aged 2 and 12 months old were fed MR (0.172% methionine) or control diet (0.86% methionine) for 8 weeks or 48 h. Food intake and whole-body physiology were assessed and serum/tissues analyzed biochemically. Methionine restriction in 12-month-old mice completely reversed age-induced alterations in body weight, adiposity, physical activity, and glucose tolerance to the levels measured in healthy 2-month-old control-fed mice. This was despite a significant increase in food intake in 12-month-old MR-fed mice. Methionine restriction decreased hepatic lipogenic gene expression and caused a remodeling of lipid metabolism in white adipose tissue, alongside increased insulin-induced phosphorylation of the insulin receptor (IR) and Akt in peripheral tissues. Mice restricted of methionine exhibited increased circulating and hepatic gene expression levels of FGF21, phosphorylation of eIF2a, and expression of ATF4, with a concomitant decrease in IRE1α phosphorylation. Short-term 48-h MR treatment increased hepatic FGF21 expression/secretion and insulin signaling and improved whole-body glucose homeostasis without affecting body weight. Our findings suggest that MR feeding can reverse the negative effects of aging on body mass, adiposity, and insulin resistance through an FGF21 mechanism. These findings implicate MR dietary intervention as a viable therapy for age-induced metabolic syndrome in adult humans.
MeSH Terms
- Animals
- Energy Metabolism
- Fibroblast Growth Factors
- Gene Expression
- Glucose
- Insulin Resistance
- Lipid Metabolism
- Male
- Methionine
- Mice
- Mice, Inbred C57BL
- Obesity
- Phenotype
Keywords
- activating transcription factor 4
- aging
- fibroblast growth factor 21
- lipid
- metabolism
- unfolded protein response
It has been 20 years since the Orentreich Foundation for the Advancement of Science, under the leadership Dr. Norman Orentreich, first reported that low methionine (Met) ingestion by rats extends lifespan (Orentreich et al., 1993). Since then, several studies have replicated the effects of dietary methionine restricted (MR) in delaying age-related diseases (Richie et al., 1994; Miller et al., 2005; Ables et al., 2012; Sanchez-Roman and Barja, 2013). We report the abstracts from the First International Mini-Symposium on Methionine Restriction and Lifespan held in Tarrytown, NY, September 2013. The goals were (1) to gather researchers with an interest in MR and lifespan, (2) to exchange knowledge, (3) to generate ideas for future investigations, and (4) to strengthen relationships within this community. The presentations highlighted the importance of research on cysteine, growth hormone (GH), and ATF4 in the paradigm of aging. In addition, the effects of dietary restriction or MR in the kidneys, liver, bones, and the adipose tissue were discussed. The symposium also emphasized the value of other species, e.g., the naked mole rat, Brandt's bat, and Drosophila, in aging research. Overall, the symposium consolidated scientists with similar research interests and provided opportunities to conduct future collaborative studies (Figure 3).
Keywords
- aging and longevity
- animal models
- lifespan
- methionine restriction
Work in yeast has shown that longevity extension induced by nutrient deprivation, altered ribosomal function, or diminished target of rapamycin action requires the activity of GCN4. We hypothesized that increased activity of ATF4, the mammalian equivalent of yeast GCN4, might be characteristic of mutations that extend mouse life span. Fibroblasts from the skin of two such mutants (Snell dwarf and PAPP-A knockout) were found to have higher levels of ATF4 protein and expression of several ATF4 target genes in responses to amino acid withdrawal, cadmium, hydrogen peroxide, and tunicamycin. ATF4 pathways were also elevated in liver of both kinds of long-lived mutant mice. Thus, a connection between ATF4 pathways and longevity may have deep evolutionary roots, and further studies of ATF4 mechanisms may provide insights into the links between cellular stress resistance, protein translation control, and aging.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Calcium Channels
- Cell Culture Techniques
- Cell Cycle Proteins
- Female
- Fibroblasts
- Liver
- Mice
- Mice, Knockout
- Pregnancy-Associated Plasma Protein-A
- RNA, Messenger
- Skin
- Stress, Physiological
- TRPV Cation Channels
- Transcription Factor CHOP
Keywords
- ATF4
- Cell stress resistance
- Life span.
- Slow aging
Evidence from model organisms suggests that the insulin/IGF-1 signaling pathway has an important, evolutionarily conserved influence over rate of aging and thus longevity. In humans, the FOXO3 gene is the only widely replicated insulin/IGF-1 signaling pathway gene associated with longevity across multiple populations. Therefore, we conducted a nested case-control study of other insulin/IGF-1 signaling genes and longevity, utilizing a large, homogeneous, long-lived population of American men of Japanese ancestry, well characterized for aging phenotypes. Genotyping was performed of single nucleotide polymorphisms, tagging most of the genetic variation across several genes in the insulin/IGF-1 signaling pathway or related gene networks that may be influenced by FOXO3, namely, ATF4, CBL, CDKN2, EXO1, and JUN. Two initial, marginal associations with longevity did not remain significant after correction for multiple comparisons, nor were they correlated with aging-related phenotypes.
MeSH Terms
- Activating Transcription Factor 4
- Aged, 80 and over
- Aging
- Asian Americans
- Case-Control Studies
- Cohort Studies
- DNA Repair Enzymes
- Exodeoxyribonucleases
- Forkhead Box Protein O3
- Forkhead Transcription Factors
- Gene Frequency
- Genes, jun
- Genes, p16
- Genetic Variation
- Genotype
- Humans
- Insulin
- Insulin Resistance
- Insulin-Like Growth Factor I
- Japan
- Longevity
- Longitudinal Studies
- Male
- Polymorphism, Genetic
- Polymorphism, Single Nucleotide
- Proto-Oncogene Proteins c-cbl
- Signal Transduction
Keywords
- Human.
- Insulin signaling genes
- Longevity
- Molecular genetics
A decline in relative levels and phosphorylation of many of the eukaryotic initiation factors (eIFs) including S6, the 40S ribosomal subunit protein in many of the rat tissues during chronological aging is accompanied by elevated levels of eIF2alpha kinases, such as PKR and PERK, but not their activity. Concomitant with increased eIF2alpha phosphorylation, young tissues displayed a higher level of eIF2B to tolerate the toxic effect of eIF2alpha phosphorylation on translation, ATF4, a b-zip transcriptional factor that is produced as part of the gene expression programme in response to eIF2alpha phosphorylation, and BiP, an endoplasmic reticulum (ER) molecular chaperone and regulator of ER stress sensors. Decline in eIF2alpha phosphorylation in aged tissues is associated with a higher level of GADD34, a subunit of eIF2alpha phosphatase, and proapoptotic proteins like CHOP/GADD153 and phospho JNK, suggesting that young tissues possess an efficient ER stress adaptive mechanism that declines with aging.
MeSH Terms
- Activating Transcription Factor 4
- Aging
- Animals
- Apoptosis
- Eukaryotic Initiation Factor-2
- Heat-Shock Proteins
- Molecular Chaperones
- Phosphorylation
- Rats
- Signal Transduction