ATF6
Cyclic AMP-dependent transcription factor ATF-6 alpha (cAMP-dependent transcription factor ATF-6 alpha) (Activating transcription factor 6 alpha) (ATF6-alpha) [Contains: Processed cyclic AMP-dependent transcription factor ATF-6 alpha]
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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
Proteostasis collapse, the diminished ability to maintain protein homeostasis, has been established as a hallmark of nematode aging. However, whether proteostasis collapse occurs in humans has remained unclear. Here, we demonstrate that proteostasis decline is intrinsic to human senescence. Using transcriptome-wide characterization of gene expression, splicing, and translation, we found a significant deterioration in the transcriptional activation of the heat shock response in stressed senescent cells. Furthermore, phosphorylated HSF1 nuclear localization and distribution were impaired in senescence. Interestingly, alternative splicing regulation was also dampened. Surprisingly, we found a decoupling between different unfolded protein response (UPR) branches in stressed senescent cells. While young cells initiated UPR-related translational and transcriptional regulatory responses, senescent cells showed enhanced translational regulation and endoplasmic reticulum (ER) stress sensing; however, they were unable to trigger UPR-related transcriptional responses. This was accompanied by diminished ATF6 nuclear localization in stressed senescent cells. Finally, we found that proteasome function was impaired following heat stress in senescent cells, and did not recover upon return to normal temperature. Together, our data unraveled a deterioration in the ability to mount dynamic stress transcriptional programs upon human senescence with broad implications on proteostasis control and connected proteostasis decline to human aging.
Keywords
- UPR
- chaperones
- heat shock response
- protein homeostasis
- senescence
The enteric nervous system degenerates gradually with age, and α-synuclein (α-syn) is a suitable marker of enteric nervous system degeneration, which is intimately related with endoplasmic reticulum stress and unfolded protein response (UPR ). Saponins from Panax japonicus (SPJ) have obvious protective effects on neurons in several degenerative disease models. Here, the study was designed to investigate whether SPJ could reverse the neuron degeneration through regulating the UPR in the colon myenteric plexus of aging rats. Aging rats had been treated with SPJ for 6 months since they were aged 18 months. Then, the colon samples were collected and neuron morphology in the myenteric plexus was observed. Immunohistochemistry staining was used to detect the expressions of NeuN, α-syn, GRP78 and three different UPR branches. Double immunofluorescence was used to determine the co-localization of α-syn and NeuN, GRP78 and NeuN. Neurons degenerated in the colon myenteric plexus of aging rats, but co-localization of α-syn and NeuN increased. In addition, both the expressions of GRP78 and three UPR branch signaling pathway proteins decreased in the colon myenteric plexus of aging rats. Treatment of SPJ almost alleviated the above effects in aging rats, except for ATF6. SPJ could reverse the neuron loss caused by accumulation of α-syn in the myenteric plexus of colon in aging rats, which is potentially associated with increased GRP78 and most URP changes. Geriatr Gerontol Int 2020; ••: ••-••.
Keywords
- aging
- myenteric plexus
- saponins from Panax japonicus
- unfolded protein response of endoplasmic reticulum
- α-synuclein
Endoplasmic reticulum (ER) stress is associated with several aging-related diseases; however, the mechanism underlying age-related deterioration of oocyte quality is unclear. Here, we used post-ovulatory, in vivo aged mouse oocytes as a model. Super-ovulated oocytes harvested from the oviduct at 14 h and 20 h post-hCG injection were designated as 'fresh' and 'aged', respectively. Embryo development following IVF was compared between fresh, aged and ER stress-induced oocytes. Expression of the ER stress marker GRP78 was examined at each stage. To evaluate the effect of salubrinal, an ER stress suppressor, on embryo development following IVF, expression levels of GRP78 and phospho-eukaryotic initiation factor 2 alpha were compared between aged and salubrinal-treated aged oocytes. Embryo transfer of salubrinal-treated aged oocytes was performed to examine the safety of salubrinal. Similar to aged oocytes, ER stress-induced oocytes showed lower fertilization rates and poor embryo development. Following IVF, expression of GRP78 decreased with embryo development. GRP78 expression was significantly higher in aged oocytes than in fresh oocytes. Salubrinal lowered GRP78 levels and improved embryo development. No adverse effect of salubrinal treatment was found on the birth weight of pups or on organogenesis in mice. The limitation of this study was that protein kinase-like ER kinase was the only ER stress pathway examined; the role of IRE1 and ATF6 pathways was not considered. Nevertheless, salubrinal can significantly improve embryo development in in vivo aged oocytes undergoing ER stress. Hence, regulation of ER stress might represent a promising therapeutic strategy to overcome poor oocyte quality.
Keywords
- ER stress
- GRP78
- PERK
- eIF2α
- endoplasmic reticulum
- mouse oocyte
- oocyte aging
- salubrinal
The endoplasmic reticulum (ER) contains stress sensors which recognize the accumulation of unfolded proteins within the lumen of ER, and subsequently these transducers stimulate the unfolded protein response (UPR). The ER sensors include the IRE1, PERK, and ATF6 transducers which activate the UPR in an attempt to restore the quality of protein folding and thus maintain cellular homeostasis. If there is excessive stress, UPR signaling generates alarmins, e.g., chemokines and cytokines, which activate not only tissue-resident immune cells but also recruit myeloid and lymphoid cells into the affected tissues. ER stress is a crucial inducer of inflammation in many pathological conditions. A chronic low-grade inflammation and cellular senescence have been associated with the aging process and many age-related diseases, such as Alzheimer's disease. Currently, it is known that immune cells can exhibit great plasticity, i.e., they are able to display both pro-inflammatory and anti-inflammatory phenotypes in a context-dependent manner. The microenvironment encountered in chronic inflammatory conditions triggers a compensatory immunosuppression which defends tissues from excessive inflammation. Recent studies have revealed that chronic ER stress augments the suppressive phenotypes of immune cells, e.g., in tumors and other inflammatory disorders. The activation of immunosuppressive network, including myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg), has been involved in the aging process and Alzheimer's disease. We will examine in detail whether the ER stress-related changes found in aging tissues and Alzheimer's disease are associated with the activation of immunosuppressive network, as has been observed in tumors and many chronic inflammatory diseases.
Keywords
- Ageing
- Immunometabolism
- Immunosenescence
- Immunosuppression
- Inflammaging
- Neurodegeneration
Immunosenescence in monocytes has been shown to be associated with several biochemical and functional changes, including development of senescence-associated secretory phenotype (SASP), which may be inhibited by klotho protein. To date, it was believed that SASP activation is associated with accumulating DNA damage. However, some literature data suggest that endoplasmic reticulum and Golgi stress pathways may be involved in SASP development. Thus, the aim of this study was to investigate the role of klotho protein in the regulation of immunosenescence-associated Golgi apparatus and ER stress response induced by bacterial antigens in monocytes. We provide evidence that initiation of immunosenescent-like phenotype in monocytes is accompanied by activation of CREB34L and TFE3 Golgi stress response and ATF6 and IRE1 endoplasmic reticulum stress response, while klotho overexpression prevents these changes. Further, these changes are followed by upregulated secretion of proinflammatory cytokines, which final modification takes place exclusively in the Golgi apparatus. In conclusion, we provide for the first time evidence of klotho involvement in the crosstalk on the line ER-Golgi, which may, in turn, affect activation of SASP. This data may be useful for a novel potential target for therapy in age-related and chronic inflammatory conditions.
Keywords
- ER stress response
- Golgi apparatus/complex stress response
- SASP
- immunosenescence
- klotho
- monocytes
Amyotrophic lateral sclerosis (ALS) is a multisystemic neurodegenerative disorder. Given that peripheral blood mononuclear cells (PBMCs) serve as a "window to the central nervous system" we aimed to answer whether endoplasmic reticulum (ER) stress in ALS-PBMCs is related to disease aggressiveness. We studied ER stress in the PBMCs of 49 patients with ALS and 31 age- and sex-matched healthy controls. The expression of a main ER stress marker, activating transcription factor 6 (ATF6), was significantly higher in ALS compared to controls, but did not correlate with age, disease severity, disease duration and disease progression rate. When ATF6 expression levels were plotted against relative D50 (rD50)-derived disease phases derived from the D50 ALS model, two distinct clusters of patients were observed: cluster 1, with progressively increasing ATF6 expression levels and cluster 2, which demonstrated stable ATF6 expression over the disease course. Individuals in the two clusters did not significantly differ in terms of ALS Functional Rating Scale-Revised (ALSFRS-R), disease aggressiveness, disease duration and subtype. However, patients with the increasing ATF6 level were significantly younger, indicating that aging processes might be related to ER stress in ALS. Our data suggest that the reaction to ER stress during disease course may be compromised in older patients with ALS.
Keywords
- activating transcription factor 6
- aging
- endoplasmic reticulum stress
- peripheral blood mononuclear cells
- progression
- 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
Aging is associated with changes in several metabolic pathways affecting liver function including the adaptive unfolded protein response (UPR). On the other hand, exercise training has been shown to exert beneficial effects on metabolism in the liver and exercise training has been reported to affect hepatic UPR. PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in skeletal muscle and liver. Therefore, the aim of the present study was to examine the impact of PGC-1α in aging and lifelong exercise training-induced hepatic UPR in mice. Liver was obtained from young (3months old), aged (15months old) and lifelong exercise trained aged wild-type (WT) and whole-body PGC-1α knockout (KO) mice. Hepatic BiP, IRE1α and cleaved ATF6 protein content increased, whereas PERK protein content was reduced with aging indicating both increased and decreased capacity of specific UPR pathways and increased activity of the ATF6 pathway in the liver with aging. Lifelong exercise training prevented the age-associated change in BiP and IRE1α protein, but not cleaved ATF6 protein and resulted in further decreased PERK protein. Taken together, the present study provides evidence that the capacity and activity of the three UPR pathways are differentially regulated in the liver with aging and lifelong exercise training. In addition, PGC-1α does not seem to regulate the activity of hepatic UPR in response to exercise training, but to influence the capacity of the liver to induce UPR in a pathway specific manner.
MeSH Terms
- Age Factors
- Aging
- Animals
- Apoptosis
- Autophagy
- Energy Metabolism
- Female
- Gene Expression Regulation
- Genotype
- Liver
- Mice, Knockout
- Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
- Phenotype
- Physical Conditioning, Animal
- Protein Carbonylation
- Signal Transduction
- Unfolded Protein Response
Keywords
- Aging
- ER stress
- Exercise
- Liver
- PGC-1α
- UPR
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
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
The aging process is characterized by progressive accumulation of damaged biomolecules in the endoplasmic reticulum, as result of increased oxidative stress accompanying cellular senescence. In agreement, we hypothesized that WI-38 human cellular models of replicative senescence and stress-induced premature senescence (SIPS) induced by hydrogen peroxide (H2O2-SIPS) or copper sulfate (CuSO4-SIPS) would present endoplasmic reticulum chaperoning mechanisms impairment and unfolded protein response activation. Results show that in replicative senescence and CuSO4-SIPS, immunoglobulin binding protein, calnexin, protein disulfide isomerase, and ER oxireductin-1 levels adjust to restore proteostasis and inositol-requiring enzyme-1 (IRE1)-, activating transcription factor 6 (ATF6)-, and pancreatic ER kinase (PERK)-mediated unfolded protein response are activated. However, H2O2-SIPS does not exhibit IRE1 and ATF6 pathways activation but a PERK-mediated upregulation of CCAAT/enhancer-binding protein homologous protein, showing that CuSO4-SIPS mimics better the endoplasmic reticulum molecular events of replicative senescence than H2O2-SIPS. Moreover, unfolded protein response activation is required for both SIPS models induction, because PERK and IRE1 inhibitors decreased senescence-associated beta-galactosidase appearance. In CuSO4-SIPS, the decrease in senescence levels is associated with PERK-driven, but IRE1 independent, cell cycle arrest while in H2O2-SIPS cell proliferation is PERK independent. These results add a step further on the molecular mechanisms that regulate senescence induction; moreover, they validate CuSO4-SIPS model as a useful tool to study cellular stress responses during aging, hoping to postpone age-related health decline.
MeSH Terms
- Activating Transcription Factor 6
- Cell Proliferation
- Cell Survival
- Cells, Cultured
- Cellular Senescence
- DNA-Binding Proteins
- Endoplasmic Reticulum Stress
- Endoribonucleases
- Eukaryotic Initiation Factor-2
- Humans
- Protein-Serine-Threonine Kinases
- Regulatory Factor X Transcription Factors
- Signal Transduction
- Transcription Factors
- eIF-2 Kinase
Keywords
- Copper
- ER stress
- Human fibroblasts
- Replicative senescence
- SIPS
Age-related macular degeneration (AMD) can be classified into two main categories: the atrophic, dry form and the exudative, wet form. The crucial difference between dry and wet AMD is the development of choroidal neovascularization in wet AMD. One fundamental cause of the neovascularization is the increased expression of VEGF (vascular endothelial growth factor) in retinal pigment epithelial cells. Progression of AMD is linked to augmentation of cellular stress, for example, oxidative stress, proteotoxic stress, inflammation and hypoxia. All these conditions can trigger stress in endoplasmic reticulum (ER), which maintains protein quality control in cells. ER stress induces the unfolded protein response (UPR) via IRE1 (inositol-requiring protein-1), PERK (protein kinase RNA-like ER kinase) and ATF6 (activating transcription factor-6) transducers. UPR signaling is a double-edged sword, that is, it can restore cellular homeostasis as far as possible, but ultimately may lead to chronic, overwhelming stress that can cause apoptotic cell death. Interestingly, ER stress is a well-known inducer of angiogenesis in cancer. Moreover, stress conditions associated with the progress of AMD can induce the expression of VEGF. We discuss the role of ER stress in the regulation of neovascularization and the conversion of dry AMD to its wet, detrimental counterpart.
MeSH Terms
- Activating Transcription Factor 6
- Aging
- Apoptosis
- Endoplasmic Reticulum
- Humans
- Macular Degeneration
- Neovascularization, Pathologic
- Oxidative Stress
- Retinal Pigment Epithelium
- Signal Transduction
- Unfolded Protein Response
- Vascular Endothelial Growth Factors
An ability to mount a stress resistance under pressure is a major host defence mechanism and has been a fundamental force during evolution. However, the adaptation capacity clearly declines during aging and this loss of stress resistance accelerates the aging process exposing the organism to degenerative diseases. The effect of stress on organisms seems to be a dose-dependent response, i.e. mild stress induces a stress tolerance and extends the lifespan whereas excessive stress accentuates the aging process. This paradox is known as hormesis in aging research. It is essential to distinguish the intensity of cellular stress and thus mount an appropriate host defence. The endoplasmic reticulum (ER) contains three branches of stress transducers, i.e. IRE1, PERK, and ATF6 pathways, all of which recognize stress-related disturbances in the function of ER. These transducers trigger a complex signaling network which activates an unfolded protein response (UPR). Interestingly, ER stress transducers can distinguish the intensity of ER stress and induce a dose-dependent UPR, either adaptive response to stress or apoptotic cell death. The efficiency of the stress recognition system and UPR signaling declines during aging. We will discuss the role of ER stress in hormetic regulation of aging process and longevity.
MeSH Terms
- Aging
- Animals
- Endoplasmic Reticulum
- Humans
- Stress, Physiological
- Unfolded Protein Response