bims-senagi Biomed News
on Senescence and aging
Issue of 2020‒12‒20
twenty-nine papers selected by
Maria Grazia Vizioli
Mayo Clinic

  1. Nat Metab. 2020 12;2(12): 1482-1497
      White and beige adipocytes in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) are maintained by proliferation and differentiation of adipose progenitor cells (APCs). Here we use mice with tissue-specific telomerase reverse transcriptase (TERT) gene knockout (KO), which undergo premature telomere shortening and proliferative senescence in APCs, to investigate the effect of over-nutrition on APC exhaustion and metabolic dysfunction. We find that TERT KO in the Pdgfra+ cell lineage results in adipocyte hypertrophy, inflammation and fibrosis in SAT, while TERT KO in the Pdgfrb+ lineage leads to adipocyte hypertrophy in both SAT and VAT. Systemic insulin resistance is observed in both KO models and is aggravated by a high-fat diet. Analysis of human biopsies demonstrates that telomere shortening in SAT is associated with metabolic disease progression after bariatric surgery. Our data indicate that over-nutrition can promote APC senescence and provide a mechanistic link between ageing, obesity and diabetes.
  2. Nat Rev Mol Cell Biol. 2020 Dec 16.
      Cellular senescence, first described in vitro in 1961, has become a focus for biotech companies that target it to ameliorate a variety of human conditions. Eminently characterized by a permanent proliferation arrest, cellular senescence occurs in response to endogenous and exogenous stresses, including telomere dysfunction, oncogene activation and persistent DNA damage. Cellular senescence can also be a controlled programme occurring in diverse biological processes, including embryonic development. Senescent cell extrinsic activities, broadly related to the activation of a senescence-associated secretory phenotype, amplify the impact of cell-intrinsic proliferative arrest and contribute to impaired tissue regeneration, chronic age-associated diseases and organismal ageing. This Review discusses the mechanisms and modulators of cellular senescence establishment and induction of a senescence-associated secretory phenotype, and provides an overview of cellular senescence as an emerging opportunity to intervene through senolytic and senomorphic therapies in ageing and ageing-associated diseases.
  3. Front Cell Dev Biol. 2020 ;8 599376
      Oxidative stress is one of the main causes of aging. The process of physiological aging is always accompanied by increased levels of endogenous oxidative stress. Exogenous oxidants have contributed to premature cellular senescence. As a deacetylase located in mitochondrial matrix, Sirt3 plays critical roles in mitochondrial energy metabolism, oxidative stress regulation, and cellular senescence. However, it remains unknown whether Sirt3 exerts the analogous role in cellular senescence caused by two different oxidation pathways. In this study, the function of Sirt3 was investigated in age-related natural senescence and H2O2-induced premature senescence of rat bone marrow mesenchymal stem cells (MSCs). Our results showed that Sirt3 expression was significantly decreased in both senescent MSCs, which was concerned with reduced cellular reactive oxygen species (ROS) and aggravated DNA injury. Sirt3 repletion could partly reverse the senescence-associated phenotypic features in natural and premature senescent MSCs. Moreover, Sirt3 replenishment led to the reduction in the levels of cellular ROS by enhancing the expression and activity of superoxide dismutase 2 (SOD2), thus maintaining the balance of intracellular oxidation and antioxidation and ameliorating oxidative stress damage. Altogether, Sirt3 inhibits MSC natural senescence and H2O2-induced premature senescence through alleviating ROS-induced injury and upregulating SOD2 expression and activity. Our research indicates that Sirt3 might contribute to uncovering the novel mechanisms underlying MSC senescence and provide new insights to aging and oxidative stress-related diseases.
    Keywords:  Sirt3; cellular senescence; mesenchymal stem cells; oxidative stress; superoxide dismutase 2
  4. Elife. 2020 12 15. pii: e60827. [Epub ahead of print]9
      Aging-associated diseases, including cardiac dysfunction, are increasingly common in the population. However, the mechanisms of physiologic aging in general, and cardiac aging in particular, remain poorly understood. Age-related heart impairment is lacking a clinically effective treatment. Using the model of naturally aging mice and rats, we show direct evidence of increased proton leak in the aged heart mitochondria. Moreover, our data suggested ANT1 as the most likely site of mediating increased mitochondrial proton permeability in old cardiomyocytes. Most importantly, the tetra-peptide SS-31 prevents age-related excess proton entry, decreases the mitochondrial flash activity and mitochondrial permeability transition pore opening, rejuvenates mitochondrial function by direct association with ANT1 and the mitochondrial ATP synthasome, and leads to substantial reversal of diastolic dysfunction. Our results uncover the excessive proton leak as a novel mechanism of age-related cardiac dysfunction and elucidate how SS-31 can reverse this clinically important complication of cardiac aging.
    Keywords:  SS-31; aging; cardiomyocyte; cell biology; mitochondria; mouse; proton leak; rat
  5. Front Cell Dev Biol. 2020 ;8 593283
      Aging is an inevitable and complex natural phenomenon due to the increase in age. Cellular senescence means a non-proliferative but viable cellular physiological state. It is the basis of aging, and it exists in the body at any time point. Idiopathic pulmonary fibrosis (IPF) is an interstitial fibrous lung disease with unknown etiology, characterized by irreversible destruction of lung structure and function. Aging is one of the most critical risk factors for IPF, and extensive epidemiological data confirms IPF as an aging-related disease. Senescent fibroblasts in IPF show abnormal activation, telomere shortening, metabolic reprogramming, mitochondrial dysfunction, apoptosis resistance, autophagy deficiency, and senescence-associated secretory phenotypes (SASP). These characteristics of senescent fibroblasts establish a close link between cellular senescence and IPF. The treatment of senescence-related molecules and pathways is continually emerging, and using senolytics eliminating senescent fibroblasts is also actively tried as a new therapy for IPF. In this review, we discuss the roles of aging and cellular senescence in IPF. In particular, we summarize the signaling pathways through which senescent fibroblasts influence the occurrence and development of IPF. On this basis, we further talk about the current treatment ideas, hoping this paper can be used as a helpful reference for future researches.
    Keywords:  aging; cellular senescence; fibroblast; idiopathic pulmonary fibrosis; senolytics
  6. J Invest Dermatol. 2020 Dec 14. pii: S0022-202X(20)32367-8. [Epub ahead of print]
      During aging, skin accumulates senescent cells. Transient presence of senescent cells, followed by their clearance by the immune system is important in tissue repair and homeostasis. Persistence of senescent cells that evaded clearance contributes to the age-related deterioration of the skin. The senescence associated secretory phenotype (SASP) these cells contains immunomodulatory molecules which facilitate clearance, but also promote chronic damage. We here investigated the epilipidome - the oxidative modifications of phospholipids - of senescent dermal fibroblasts, as these molecules are among the bioactive lipids which were recently identified as SASP factors. Using replicative- and stress- induced senescence protocols we identified lysophosphatidylcholines as universally elevated in senescent fibroblasts, while other oxidized lipids displayed a pattern that was characteristic for the used senescence protocol. When we tested the lysophosphatidylcholines for SASP activity, we found that they elicit chemokine release in non-senescent FB but also interfere with TLR2/6/CD36 signaling and phagocytic capacity in macrophages. Using MALDI-FTICR-mass spectrometric imaging we localized two lysoPC species in aged skin. This suggests that the lysophospholipids may facilitate immune evasion and low grade chronic inflammation in skin aging.
  7. Front Oncol. 2020 ;10 589908
      Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. The lack of effective targeted drugs has become a challenge on treating HCC patients. Cellular senescence is closely linked to the occurrence, development, and therapy of tumor. Induction of cellular senescence and further activation of immune surveillance provides a new strategy to develop HCC targeted drugs, that is, senescence-induced therapy for HCC. Precancerous hepatocytes or HCC cells can be induced into senescent cells, subsequently producing senescence-associated secretory phenotype (SASP) factors. SASP factors recruit and activate various types of immune cells, including T cells, NK cells, macrophages, and their subtypes, which carry out the role of immune surveillance and elimination of senescent cells, ultimately preventing the occurrence of HCC or inhibiting the progression of HCC. Specific interventions in several checkpoints of senescence-mediated therapy will make positive contributions to suppress tumorigenesis and progression of HCC, for instance, by applying small molecular compounds to induce cellular senescence or selecting cytokines/chemokines to activate immunosurveillance, supplementing adoptive immunocytes to remove senescent cells, and screening chemical drugs to induce apoptosis of senescent cells or accelerate clearance of senescent cells. These interventional checkpoints become potential chemotherapeutic targets in senescence-induced therapy for HCC. In this review, we focus on the frontiers of senescence-induced therapy and discuss senescent characteristics of hepatocytes during hepatocarcinogenesis as well as the roles and mechanisms of senescent cell induction and clearance, and cellular senescence-related immunosurveillance during the formation and progression of HCC.
    Keywords:  cellular senescence; hepatocellular carcinoma; hepatocellular senescence; immunosurveillance; senescence-associated secretory phenotype; senescence-induced therapy
  8. Food Funct. 2020 Dec 18.
      Quercetin is one of the most abundant dietary flavonoid compounds, and its mechanism for combating age-related neurodegenerative diseases is unclear. In this study, quercetin (35 and 70 mg kg-1, orally administered for 4 weeks) was administered to 7-month-old aging mice (senescence-accelerated mouse prone 8 mice). As a result, it was found that quercetin could improve spatial learning and memory impairment displayed by aging mice in the Morris water maze. The results of immunoblotting reflected the protein expressions of the longevity factor (sirtuin1), inflammasomes (NLRP3 and ASC), synaptic marker (PSD95) and neurotrophic factors (BDNF and NGF) in the hippocampus of the brain. It indicated that the intervention of quercetin could increase the expression of sirtuin1 and prevent neuroinflammation, which was evident from the decrease in the protein levels of the astrocyte marker (GFAP) and inflammatory factors (cleaved-caspase 1, IL-1β and IL-18). In addition, quercetin could reduce the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) in the hippocampus of aging mice. Current data indicated that quercetin might improve neuroinflammation in aging mice by regulating the Sirtuin1/NLRP3 pathway.
  9. Aging Cell. 2020 Dec 18. e13288
      Morphological change is an explicit characteristic of cell senescence, but the underlying mechanisms remains to be addressed. Here, we demonstrated, after a survey of various actin-binding proteins, that the post-translational up-regulation of cofilin-1 was essential for the reduced rate of actin depolymerization morphological enlargement in senescent cells. Additionally, up-regulated cofilin-1 mainly existed in the serine-3 phosphorylated form, according to the 2D gel immunoblotting assay. The up-regulation of cofilin-1 was also detected in aged mammalian tissues. The over-expression of wild-type cofilin-1 and constitutively phosphorylated cofilin-1 promoted cell senescence with an increased cell size. Additionally, senescent phenotypes were also reduced by knockdown of total cofilin-1, which led to a decrease in phosphorylated cofilin-1. The senescence induced by the over-expression of cofilin-1 was dependent on p27Kip1 , but not on the p53 and p16INK4 expressions. The knockdown of p27Kip1 alleviated cell senescence induced by oxidative stress or replicative stress. We also found that the over-expression of cofilin-1 induced the expression of p27Kip1 through transcriptional suppression of the transcriptional enhancer factors domain 1 (TEAD1) transcription factor. The TEAD1 transcription factor played a transrepressive role in the p27Kip1  gene promoter, as determined by the promoter deletion reporter gene assay. Interestingly, the down-regulation of TEAD1 was accompanied by the up-regulation of cofilin-1 in senescence. The knockdown and restoration of TEAD1 in young cells and old cells could induce and inhibit p27Kip1 and senescent phenotypes, respectively. Taken together, the current data suggest that cofilin-1/TEAD1/p27Kip1 signaling is involved in senescence-related morphological change and growth arrest.
    Keywords:  TEAD1; cofilin-1; growth arrest; morphology; p27Kip1; senescence
  10. Aging Cell. 2020 Dec 13. e13282
      Spermatogenesis-associated protein 4 (SPATA4) is conserved across multiple species. However, the function of this gene remains largely unknown. In this study, we generated Spata4 transgenic mice to explore tissue-specific function of SPATA4. Spata4 overexpression mice displayed increased subcutaneous fat tissue compared with wild-type littermates at an old age, while this difference was not observed in younger mice. Aging-induced ectopic fat distribution, inflammation, and insulin resistance were also significantly attenuated by SPATA4. In vitro, SPATA4 promoted preadipocyte differentiation through activation of the ERK1/2 and C/EBPβ pathway and increased the expression of adipokines. These data suggest SPATA4 can regulate lipid accumulation in a tissue-specific manner and improve aging-induced dysmetabolic syndromes. Clarifying the mechanism of SPATA4 functioning in lipid metabolism might provide novel therapeutic targets for disease interventions.
    Keywords:  SPATA4; adipocyte differentiation; aging; fat redistribution
  11. Sci Rep. 2020 Dec 17. 10(1): 22127
      LINE-1 hypomethylation of cell-free DNA has been described as an epigenetic biomarker of human aging. However, in the past, insufficient differentiation between cellular and cell-free DNA may have confounded analyses of genome-wide methylation levels in aging cells. Here we present a new methodological strategy to properly and unambiguously extract DNA methylation patterns of repetitive, as well as single genetic loci from pure cell-free DNA from peripheral blood. Since this nucleic acid fraction originates mainly in apoptotic, senescent and cancerous cells, this approach allows efficient analysis of aged and cancerous cell-specific DNA methylation patterns for diagnostic and prognostic purposes. Using this methodology, we observe a significant age-associated erosion of LINE-1 methylation in cfDNA suggesting that the threshold of hypomethylation sufficient for relevant LINE-1 activation and consequential harmful retrotransposition might be reached at higher age. We speculate that this process might contribute to making aging the main risk factor for many cancers.
  12. Biology (Basel). 2020 Dec 09. pii: E455. [Epub ahead of print]9(12):
      Cellular senescence is viewed as a mechanism to prevent malignant transformation, but when it is chronic, as occurs in age-related diseases, it may have adverse effects on cancer. Therefore, targeting senescent cells is a novel therapeutic strategy against senescence-associated diseases. In addition to its role in cancer protection, cellular senescence is also considered a mechanism to control virus replication. Both interferon treatment and some viral infections can trigger cellular senescence as a way to restrict virus replication. However, activation of the cellular senescence program is linked to the alteration of different pathways, which can be exploited by some viruses to improve their replication. It is, therefore, important to understand the potential impact of senolytic agents on viral propagation. Here we focus on the relationship between virus and cellular senescence and the reported effects of senolytic compounds on virus replication.
    Keywords:  senescence; senolytics; virosenolytics; virus
  13. Curr Opin Pharmacol. 2020 Dec 13. pii: S1471-4892(20)30131-4. [Epub ahead of print]56 68-73
      Increasing evidence suggests that there is acceleration of normal lung ageing in chronic obstructive pulmonary disease (COPD), with the accumulation of senescent cells in the lung, which release an array of inflammatory proteins, which drive further senescence and disease progression. This suggests that drugs that target cellular senescence (senotherapies) may treat the underlying disease process in COPD and reduce disease progression and mortality. Several existing or future drugs may inhibit the development of cellular senescence, which is driven by chronic oxidative stress (senostatics), whereas other drugs selectively remove senescent cells (senolytics). Clinical studies of senotherapies have commenced in several age-related diseases, and these approaches appear to be safe and feasible, although no clinical studies in COPD patients have yet been reported.
    Keywords:  Ageing; Cellular senescence; Mechanistic target of rapamycin; Micro-RNA; Mitochondria; Senolytic; Sirtuin
  14. Front Physiol. 2020 ;11 593630
      Senescent cells with replicative arrest can be generated during genotoxic, oxidative, and oncogenic stress. Long-term retention of senescent cells in the body, which is attributed to highly expressed BCL-family proteins, chronically damages tissues mainly through a senescence-associated secretory phenotype (SASP). It has been documented that accumulation of senescent cells contributes to chronic diseases and aging-related diseases. Despite the fact that no unique marker is available to identify senescent cells, increased p16INK4a expression has long been used as an in vitro and in vivo marker of senescent cells. We reviewed five existing p16INK4a reporter mouse models to detect, isolate, and deplete senescent cells. Senescent cells express high levels of anti-apoptotic and pro-apoptotic genes compared to normal cells. Thus, disrupting the balance between anti-apoptotic and pro-apoptotic gene expression, such as ABT-263 and ABT-737, can activate the apoptotic signaling pathway and remove senescent cells. Mitochondrial abnormalities in senescent cells were also discussed, for example mitochondrial DNA mutation accumulation, dysfunctional mitophagy, and mitochondrial unfolded protein response (mtUPR). The mitochondrial-targeted tamoxifen, MitoTam, can efficiently remove senescent cells due to its inhibition of respiratory complex I and low expression of adenine nucleotide translocase-2 (ANT2) in senescent cells. Therefore, senescent cells can be removed by various strategies, which delays chronic and aging-related diseases and enhances lifespan and healthy conditions in the body.
    Keywords:  aging; apoptosis; p16INK4a; senescence; senolytics
  15. Front Cell Dev Biol. 2020 ;8 588050
      Retinal pigment epithelium (RPE) cellular senescence is an important etiology of age-related macular degeneration (AMD). Aging interventions based on the application of stem cells to delay cellular senescence have shown good prospects in the treatment of age-related diseases. This study aimed to investigate the potential of the embryonic stem cells (ESCs) to reverse the senescence of RPE cells and to elucidate its regulatory mechanism. The hydrogen peroxide (H2O2)-mediated premature and natural passage-mediated replicative senescent RPE cells were directly cocultured with ESCs. The results showed that the proliferative capacity of premature and replicative senescent RPE cells was increased, while the positive rate of senescence-associated galactosidase (SA-β-GAL) staining and levels of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were decreased. The positive regulatory factors of cellular senescence (p53, p21WAF1/CIP1, p16INK4a) were downregulated, while the negative regulatory factors of cellular senescence (Cyclin A2, Cyclin B1, Cyclin D1) were upregulated. Furthermore, replicative senescent RPE cells entered the S and G2/M phases from the G0/G1 phase. TGFβ (TGFB1, SMAD3, ID1, ID3) and PI3K (PIK3CG, PDK1, PLK1) pathway-related genes were upregulated in premature and replicative senescent RPE cells after ESCs application, respectively. We further treated ESCs-cocultured premature and replicative senescent RPE cells with SB531542 and LY294002 to inhibit the TGFβ and PI3K pathways, respectively, and found that p53, p21WAF1/CIP1 and p16INK4a were upregulated, while Cyclin A2, Cyclin B1, Cyclin D1, TGFβ, and PI3K pathway-related genes were downregulated, accompanied by decreased proliferation and cell cycle transition and increased positive rates of SA-β-GAL staining and levels of ROS and MMP. In conclusion, we demonstrated that ESCs can effectively reverse the senescence of premature and replicative senescent RPE cells by a direct coculture way, which may be achieved by upregulating the TGFβ and PI3K pathways, respectively, providing a basis for establishing a new therapeutic option for AMD.
    Keywords:  age-related macular degeneration; embryonic stem cell; regulatory mechanism; retinal pigment epithelium cell; reversing cellular senescence
  16. Immunol Lett. 2020 Dec 10. pii: S0165-2478(20)30425-9. [Epub ahead of print]
      Ageing is a global burden. Increasing age is associated with increased incidence of infections and cancer and decreased vaccine efficacy. This increased morbidity observed with age, is believed to be due in part to a decline in adaptive immunity, termed immunosenescence. However not all aspects of immunity decrease with age as ageing presents with systemic low grade chronic inflammation, characterised by elevated concentrations of mediators such as IL-6, TNFα and C Reactive protein (CRP). Inflammation is a strong predictor of morbidity and mortality, and chronic inflammation is known to be detrimental to a functioning immune system. Although the source of the inflammation is much discussed, the key cells which are believed to facilitate the inflammageing phenomenon are the monocytes and macrophages. In this review we detail how macrophages and monocytes phenotype and function change with age. The impact of ageing on macrophages includes decreased phagocytosis and immune resolution, increased in senescent-associated markers, increase inflammatory cytokine production, and reduced autophagy and decrease in TLR expression. With monocytes there is an increase in circulating CD16+ monocytes, decreased type I IFN production, and decreased efferocytosis. In conclusion, we believe that monocytes and macrophages contribute to immunosenescence and inflammageing and as a result have an important role in defective immunity with age.
    Keywords:  Immunosenescence; Monocytes; ageing; inflammageing; macrophages
  17. Biomedicines. 2020 Dec 15. pii: E615. [Epub ahead of print]8(12):
      According to the World Health Organization, the population of over 60 will double in the next 30 years in the developed countries, which will enforce a further raise of the retirement age and increase the burden on the healthcare system. Therefore, there is an acute issue of maintaining health and prolonging active working longevity, as well as implementation of early monitoring and prevention of premature aging and age-related disorders to avoid early disability. Traditional indicators of biological age are not always informative and often require extensive and expensive analysis. The study of blood factors is a simple and easily accessible way to assess individual health and supplement the traditional indicators of a person's biological age with new objective criteria. With age, the processes of growth and development, tissue regeneration and repair decline; they are gradually replaced by enhanced catabolism, inflammatory cell activity, and insulin resistance. The number of senescent cells supporting the inflammatory loop rises; cellular clearance by autophagy and mitophagy slows down, resulting in mitochondrial and cellular damage and dysfunction. Monitoring of circulated blood factors not only reflects these processes, but also allows suggesting medical intervention to prevent or decelerate the development of age-related diseases. We review the age-related blood factors discussed in recent publications, as well as approaches to slowing aging for healthy and active longevity.
    Keywords:  aging; aging biomarkers; biological age; blood factors; inflammation; metabolic disorders; senescence
  18. Aging (Albany NY). 2020 12 09. 12
      The accumulation of senescent adipose-derived mesenchymal stem cells (AMSCs) in subcutaneous white adipose tissue (WAT) is the main cause for the deterioration of WAT and the subsequent age-related disorders in obesity. The number of AMSCs staining positively for senescence-associated-β-galactosidase (SA-β-Gal) increased significantly after incubation with postprandial triglyceride-rich lipoproteins (TRL), accompanied by an impaired cell proliferation capacity and increased expression of inflammatory factors. Besides, the expression of anti-aging protein, silent mating-type information regulation 2 homolog 1 (SIRT1), was downregulated significantly, while those of acetylated p53 (Ac-p53), total p53, and p21 proteins were upregulated significantly during postprandial TRL-induced premature senescence of AMSCs. Furthermore, the production of intracellular reactive oxygen species (ROS) in the TRL group increased significantly, while pretreatment with the ROS scavenger N-acetyl-L-cysteine effectively attenuated the premature senescence of AMSCs by decreasing ROS production and upregulating SIRT1 level. Thus, postprandial TRL induced premature senescence of AMSCs through the SIRT1/p53/Ac-p53/p21 axis, partly through increased oxidative stress.
    Keywords:  SIRT1; adipose-derived mesenchymal stem cells; oxidative stress; premature senescence; triglyceride-rich lipoproteins
  19. Aging Cell. 2020 Dec 13. e13281
      Astrocytes are highly specialised cells, responsible for CNS homeostasis and neuronal activity. Lack of human in vitro systems able to recapitulate the functional changes affecting astrocytes during ageing represents a major limitation to studying mechanisms and potential therapies aiming to preserve neuronal health. Here, we show that induced astrocytes from fibroblasts donors in their childhood or adulthood display age-related transcriptional differences and functionally diverge in a spectrum of age-associated features, such as altered nuclear compartmentalisation, nucleocytoplasmic shuttling properties, oxidative stress response and DNA damage response. Remarkably, we also show an age-related differential response of induced neural progenitor cells derived astrocytes (iNPC-As) in their ability to support neurons in co-culture upon pro-inflammatory stimuli. These results show that iNPC-As are a renewable, readily available resource of human glia that retain the age-related features of the donor fibroblasts, making them a unique and valuable model to interrogate human astrocyte function over time in human CNS health and disease.
    Keywords:  ageing; astrocytes; direct reprogramming; in vitro model; neurodegeneration; neuroinflammation; neuron-astrocyte crosstalk; nuclear abnormalities; nucleocytoplasmic transport; oxidative stress
  20. J Nutr Biochem. 2020 Dec 13. pii: S0955-2863(20)30600-8. [Epub ahead of print] 108568
      Resveratrol has been found to improve ethanol-induced diabetes. Although pancreatic β-cell senescence-induced β-cell mass loss plays a critical role in the progression of diabetes, the exact mechanisms by which resveratrol improves ethanol-triggered β-cell senescence and its role in ethanol-induced diabetes remains unknown. Male Sprague-Dawley rats were fed either control or ethanol liquid diets containing 2.4 g/kg•bw ethanol with or without 100 mg/kg•bw resveratrol for 22 weeks. Resveratrol decreased the ethanol-induced augmentation in senescence-associated β-galactosidase (SA-β-gal)-positive area and attenuated reduction in β-cell mass, which were based on elevated levels of SIRT1 and proliferation marker Ki67 and reduced levels of senescence-associated markers (p-p38MAPK and p16INK4a). Similarly, resveratrol rescued the reduction in NAD+/NADH ratio and SIRT1 and inhibited the upregulation of p-p38MAPK and p16INK4a in ethanol-treated INS-1 cells. Furthermore, supplementation with NAD+ inducer nicotinamide mononucleotide, SIRT1 activator SRT1720 or p38MAPK inhibitor SB203580 effectively reversed ethanol-induced β-cell senescence, while supplementation with SIRT1 inhibitor Ex527 or NAD+ inhibitor FK866 abrogated resveratrol-mediated anti-senescence effects in INS-1 cells. Together, our results indicate that resveratrol improves ethanol-triggered β-cell senescence and consequently recovers β-cell mass loss by inhibiting p38MAPK/p16 pathway through an NAD+/SIRT1 dependent pathway.
    Keywords:  Diabetes; Ethanol; NAD(+)/SIRT1 pathway; Resveratrol; p38MAPK/p16 pathway; β-cell senescence
  21. Mech Ageing Dev. 2020 Dec 14. pii: S0047-6374(20)30213-X. [Epub ahead of print] 111417
      Nucleus pulposus cell (NPC) is the major cell type maintaining the physiological function of intervertebral discs by producing extracellular matrix (ECM). NPC apoptosis and senescence together contribute to NPC loss, finally leading to intervertebral disc degeneration (IDD). Herein, miR-623 showed to be downregulated within IDD tissue samples according to both bioinformatics and experimental analyses. In LPS-injured NPCs, miR-623 overexpression promoted LPS-suppressed cell proliferation; moreover, miR-623 overexpression inhibited cell apoptosis and senescence, increased ECM secretion, and reduced levels of inflammatory factors. In contrast to miR-623, CXCL12 expression was significantly upregulated in IDD tissues; miR-623 directly bound CXCL12 to inhibit its expression. In LPS-stimulated NPCs, CXCL12 silencing also LPS-induced changes in cell proliferation, cell senescence, ECM secretion, and inflammatory factor levels. More importantly, CXCL12 overexpression aggravated LPS-induced changes and significantly reversed the protective effects of miR-623 overexpression. In conclusion, the miR-623/CXCL12 axis could affect NPC apoptosis and senescence, ECM deposition, and inflammatory factor levels under LPS stimulation in vitro. The p65 signaling might be involved.
    Keywords:  CXCL12; apoptosis; intervertebral disc degeneration (IDD); miR-623; nucleus pulposus cell (NPC); senescence
  22. Mol Ther. 2020 Dec 09. pii: S1525-0016(20)30666-3. [Epub ahead of print]
      Contrasting myelin damage through the generation of new myelinating oligodendrocytes represents a promising approach to promote functional recovery after stroke. Here, we asked whether activation of microglia and monocyte-derived macrophages affects the regenerative process sustained by GPR17-expressing oligodendrocyte precursor cells (OPCs), a subpopulation of OPCs specifically reacting to ischemic injury. GPR17-iCreERT2:CAG-eGFP reporter mice were employed to trace the fate of GPR17-expressing (GFP+) OPCs after permanent middle cerebral artery occlusion. By microglia/macrophages pharmacological depletion studies, we show that innate immune cells favour GFP+ OPCs reaction and limit myelin damage early after injury, while they lose their pro-resolving capacity and acquire a dystrophic "senescent-like" phenotype at later stages. Intracerebral infusion of regenerative microglia-derived extracellular vesicles (EVs) restores protective microglia/macrophages functions, limiting their senescence during the post-stroke phase, and enhances the maturation of GFP+ OPCs at lesion borders, resulting in ameliorated neurological functionality. In vitro experiments show that EV-carried transmembrane TNFα mediates the pro-differentiating effects on OPCs, with future implications for regenerative therapies.
    Keywords:  Cerebral ischemia; Extracellular vesicles; GPR17 receptor; Microglia; Oligodendrocyte precursor cells
  23. J Cell Mol Med. 2020 Dec 12.
      Yes-associated protein (YAP), a major effector of the Hippo signalling pathway, is widely implicated in vascular pathophysiology processes. Here, we identify a new role of YAP in the regulation of vascular senescence. The inhibition or deficiency and overexpression of YAP were performed in human umbilical vein endothelial cells (HUVECs) and isolated vascular tissues. Cellular and vascular senescence was assessed by analysis of the senescence-associated β-galactosidase (SA-β-gal) and expression of senescence markers P16, P21, P53, TERT and TRF1. We found that YAP was highly expressed in old vascular tissues, inhibition and knockdown of YAP decreased senescence, while overexpression of YAP increased the senescence in both HUVECs and vascular tissues. In addition, autophagic flux blockage and mTOR pathway activation were observed during YAP-induced HUVECs and vascular senescence, which could be relieved by the inhibition and knockdown of YAP. Moreover, YAP-promoted cellular and vascular senescence could be relieved by mTOR inhibition. Collectively, our findings indicate that YAP may serve as a potential therapeutic target for ageing-associated cardiovascular disease.
    Keywords:  YAP; autophagy; mTOR; vascular senescence
  24. Mutat Res. 2020 Oct - Dec;786:pii: S1383-5742(20)30062-4. [Epub ahead of print]786 108342
      Micronuclei (MNi) are among the most widely studied biomarkers of DNA damage and chromosomal instability in humans. They originate from chromosome fragments or intact chromosomes that are not included in daughter nuclei during mitosis. The main reasons for their formation are a lack of functional centromere in the chromosome fragments or whole chromosomes or defects in one or more of the proteins of the mitotic system that, consequently, fails to segregate chromosomes properly. Assays have been developed to measure MNi in peripheral blood lymphocytes, red blood cells as well as various types of epithelial cells such as buccal, nasal, urothelial and cervical cells. Some of the assays have been further developed into micronucleus (MN) cytome assays to include additional nuclear anomalies, cell death and nuclear division biomarkers. In addition, the use of molecular probes has been adopted widely for the purpose of understanding the mechanistic origin of MNi. MN assays in humans are used for the purpose of investigating the genotoxic effects of adverse environmental, life-style and occupational factors, genetic susceptibility to DNA damage, and for determining risk of accelerated aging and diseases affected by genomic instability such as developmental defects and cancer. The emerging new knowledge showing that chromosomes trapped in MNi can undergo a high rate of fragmentation and become massively re-arranged have highlighted the possibility that MN formation is not only a biomarker of induced DNA damage but also a mechanism that drives hypermutation. Furthermore, another line of recent research showed that DNA and chromatin leaking from disrupted MNi triggers the innate immune cGAS-STING mechanism that promotes inflammation which can cause a wide-range of age-related diseases if left unresolved. For these reasons, MN assays in humans have become an increasingly important biomarker of disease initiation and progression across all life-stages.
    Keywords:  Aneuploidy; DNA damage; Human; Inflammation; Micronuclei; Micronucleus
  25. FASEB J. 2021 Jan;35(1): e21204
      Cellular senescence is a state of permanent growth arrest that can ultimately contribute to aging. Senescence can be induced by various stressors and is associated with a myriad of cellular functions and phenotypic markers. Alternative splicing is emerging as a critical contributor to senescence and aging. However, it is unclear how the composition and function of the spliceosome are involved in senescence. Here, using replicative and oxidative stress-induced senescence models in primary human fibroblasts, we report a common shift in the expression of 58 spliceosomal genes at the pre-senescence stage, prior to the detection of senescence-associated β-galactosidase (SA-β-gal) activity. Spliceosomal perturbation, induced by pharmacologic and genetic inhibition of splicesomal genes, triggered cells to enter senescence, suggesting a key role as a gatekeeper. Association analysis of transcription factors based on the 58 splicesomal genes revealed Sp1 as a key regulator of senescence entry. Indeed, Sp1 depletion suppressed the expression of downstream spliceosomal genes (HNRNPA3, SRSF7, and SRSF4) and effectively induced senescence. These results indicate that spliceosomal gene sets, rather than a single spliceosomal gene, regulate the early transition into senescence prior to SA-β-gal expression. Furthermore, our study provides a spliceosome signature that may be used as an early senescence marker.
    Keywords:  Sp1; oxidative stress; replicative senescence; splicing factors; splicing variant; transcriptome
  26. Commun Biol. 2020 Dec 15. 3(1): 774
      Human mesenchymal stem cells (hMSCs) promote endogenous tissue regeneration and have become a promising candidate for cell therapy. However, in vitro culture expansion of hMSCs induces a rapid decline of stem cell properties through replicative senescence. Here, we characterize metabolic profiles of hMSCs during expansion. We show that alterations of cellular nicotinamide adenine dinucleotide (NAD + /NADH) redox balance and activity of the Sirtuin (Sirt) family enzymes regulate cellular senescence of hMSCs. Treatment with NAD + precursor nicotinamide increases the intracellular NAD + level and re-balances the NAD + /NADH ratio, with enhanced Sirt-1 activity in hMSCs at high passage, partially restores mitochondrial fitness and rejuvenates senescent hMSCs. By contrast, human fibroblasts exhibit limited senescence as their cellular NAD + /NADH balance is comparatively stable during expansion. These results indicate a potential metabolic and redox connection to replicative senescence in adult stem cells and identify NAD + as a metabolic regulator that distinguishes stem cells from mature cells. This study also suggests potential strategies to maintain cellular homeostasis of hMSCs in clinical applications.
  27. Sci Adv. 2020 Dec;pii: eabc5629. [Epub ahead of print]6(51):
      Circadian gene expression driven by transcription activators CLOCK and BMAL1 is intimately associated with dynamic chromatin remodeling. However, how cellular metabolism directs circadian chromatin remodeling is virtually unexplored. We report that the S-adenosylhomocysteine (SAH) hydrolyzing enzyme adenosylhomocysteinase (AHCY) cyclically associates to CLOCK-BMAL1 at chromatin sites and promotes circadian transcriptional activity. SAH is a potent feedback inhibitor of S-adenosylmethionine (SAM)-dependent methyltransferases, and timely hydrolysis of SAH by AHCY is critical to sustain methylation reactions. We show that AHCY is essential for cyclic H3K4 trimethylation, genome-wide recruitment of BMAL1 to chromatin, and subsequent circadian transcription. Depletion or targeted pharmacological inhibition of AHCY in mammalian cells markedly decreases the amplitude of circadian gene expression. In mice, pharmacological inhibition of AHCY in the hypothalamus alters circadian locomotor activity and rhythmic transcription within the suprachiasmatic nucleus. These results reveal a previously unappreciated connection between cellular metabolism, chromatin dynamics, and circadian regulation.
  28. Nature. 2020 Dec 16.
      Altered expression of mitochondrial DNA (mtDNA) occurs in ageing and a range of human pathologies (for example, inborn errors of metabolism, neurodegeneration and cancer). Here we describe first-in-class specific inhibitors of mitochondrial transcription (IMTs) that target the human mitochondrial RNA polymerase (POLRMT), which is essential for biogenesis of the oxidative phosphorylation (OXPHOS) system1-6. The IMTs efficiently impair mtDNA transcription in a reconstituted recombinant system and cause a dose-dependent inhibition of mtDNA expression and OXPHOS in cell lines. To verify the cellular target, we performed exome sequencing of mutagenized cells and identified a cluster of amino acid substitutions in POLRMT that cause resistance to IMTs. We obtained a cryo-electron microscopy (cryo-EM) structure of POLRMT bound to an IMT, which further defined the allosteric binding site near the active centre cleft of POLRMT. The growth of cancer cells and the persistence of therapy-resistant cancer stem cells has previously been reported to depend on OXPHOS7-17, and we therefore investigated whether IMTs have anti-tumour effects. Four weeks of oral treatment with an IMT is well-tolerated in mice and does not cause OXPHOS dysfunction or toxicity in normal tissues, despite inducing a strong anti-tumour response in xenografts of human cancer cells. In summary, IMTs provide a potent and specific chemical biology tool to study the role of mtDNA expression in physiology and disease.
  29. Nucleic Acids Res. 2020 Dec 16. pii: gkaa1202. [Epub ahead of print]
      DNA double-strand breaks drive genomic instability. However, it remains unknown how these processes may affect the biomechanical properties of the nucleus and what role nuclear mechanics play in DNA damage and repair efficiency. Here, we have used Atomic Force Microscopy to investigate nuclear mechanical changes, arising from externally induced DNA damage. We found that nuclear stiffness is significantly reduced after cisplatin treatment, as a consequence of DNA damage signalling. This softening was linked to global chromatin decondensation, which improves molecular diffusion within the organelle. We propose that this can increase recruitment for repair factors. Interestingly, we also found that reduction of nuclear tension, through cytoskeletal relaxation, has a protective role to the cell and reduces accumulation of DNA damage. Overall, these changes protect against further genomic instability and promote DNA repair. We propose that these processes may underpin the development of drug resistance.