bims-senagi Biomed News
on Senescence and aging
Issue of 2021‒01‒10
37 papers selected by
Maria Grazia Vizioli
Mayo Clinic


  1. J Gerontol A Biol Sci Med Sci. 2021 Jan 06. pii: glab002. [Epub ahead of print]
    Saccon TD, Nagpal R, Yadav H, Cavalcante MB, Nunes ADC, Schneider A, Gesing A, Hughes B, Yousefzadeh M, Tchkonia T, Kirkland JL, Niedernhofer LJ, Robbins PD, Masternak MM.
      Cellular senescence contributes to age-related disorders including physical dysfunction, disabilities and mortality caused by tissue inflammation and damage. Senescent cells accumulate in multiple tissues with aging and at etiological sites of multiple chronic disorders. The senolytic drug combination, Dasatinib plus Quercetin (D+Q), is known to reduce senescent cell abundance in aged mice. However, the effects of long-term D+Q treatment on intestinal senescent cell and inflammatory burden and microbiome composition in aged mice remain unknown. Here, we examine the effect of D+Q on senescence (p16 Ink4a and p21 Cip1) and inflammation (Cxcl1, Il1β, Il6, Mcp1, and Tnfα) markers in small (ileum) and large (caecum and colon) intestine in aged mice (n=10) compared to age-matched placebo-treated mice (n=10). Additionally, we examine microbial composition along the intestinal tract in these mice. D+Q-treated mice show significantly lower senescent cell (p16 and p21 expression) and inflammatory (Cxcl1, Il1β, Il6, Mcp1 and Tnfα expression) burden in small and large intestine compared with control mice. Further, we find specific microbial signatures in ileal, cecal, colonic and fecal regions that are distinctly modulated by D+Q, with modulation being most prominent in small intestine. Further analyses reveal specific correlation of senescence and inflammation markers with specific microbial signatures. Together, these data demonstrate that the senolytic treatment reduces intestinal senescence and inflammation while altering specific microbiota signatures and suggest that the optimized senolytic regimens might improve health via reducing intestinal senescence, inflammation and microbial dysbiosis in older subjects.
    Keywords:  biology of aging; cellular senescence; longevity; microbiome; microbiota
    DOI:  https://doi.org/10.1093/gerona/glab002
  2. Aging Cell. 2021 Jan 03. e13285
    Squarzoni S, Schena E, Sabatelli P, Mattioli E, Capanni C, Cenni V, D'Apice MR, Andrenacci D, Sarli G, Pellegrino V, Festa A, Baruffaldi F, Storci G, Bonafè M, Barboni C, Sanapo M, Zaghini A, Lattanzi G.
      Hutchinson-Gilford progeria syndrome (HGPS) causes premature aging in children, with adipose tissue, skin and bone deterioration, and cardiovascular impairment. In HGPS cells and mouse models, high levels of interleukin-6, an inflammatory cytokine linked to aging processes, have been detected. Here, we show that inhibition of interleukin-6 activity by tocilizumab, a neutralizing antibody raised against interleukin-6 receptors, counteracts progeroid features in both HGPS fibroblasts and LmnaG609G / G609G progeroid mice. Tocilizumab treatment limits the accumulation of progerin, the toxic protein produced in HGPS cells, rescues nuclear envelope and chromatin abnormalities, and attenuates the hyperactivated DNA damage response. In vivo administration of tocilizumab reduces aortic lesions and adipose tissue dystrophy, delays the onset of lipodystrophy and kyphosis, avoids motor impairment, and preserves a good quality of life in progeroid mice. This work identifies tocilizumab as a valuable tool in HGPS therapy and, speculatively, in the treatment of a variety of aging-related disorders.
    Keywords:  accelerated aging; ageing; anti-aging; cellular senescence; cytokines; inflammation; laminopathies; nuclear lamina
    DOI:  https://doi.org/10.1111/acel.13285
  3. Front Aging Neurosci. 2020 ;12 507140
    Yu AQ, Wang J, Zhou XJ, Chen KY, Cao Y, Wang ZX, Mao ZB.
      Cellular senescence is implicated in several lines of aging-related disorders. However, the potential molecular mechanisms by which cellular senescence modulates age-related pathologies remain largely unexplored. Herein, we report that the density of sympathetic fibers (SFs) is significantly elevated in naturally aged mouse tissues and human colon adenoma tissues compared to the SFs densities in the corresponding young mouse tissues and human non-lesion colon tissues. A dorsal root ganglion (DRG)-human diploid fibroblast coculture assay revealed that senescent cells promote the outgrowth of SFs, indicating that the senescent cells induce recruitment of SFs in vitro. Additionally, subcutaneous transplantation of 2BS fibroblasts in nude mice shows that transplanted senescent 2BS fibroblasts promote SFs infiltration. Intra-articular senolytic molecular injection can reduce SFs density and inhibit SFs infiltration caused by senescent cells in osteoarthritis (OA), suggesting senescent cells promote the infiltration of SFs in vivo in aged tissues. Notably, the elevated level of SFs contributes to impaired cognitive function in naturally aged mice, which can be reversed by treatment with propranolol hydrochloride, a non-selective β receptor blocker that inhibits sympathetic nerve activity (SNA) by blocking non-selective β receptors. Additionally, 6-hydroxydopamine (6-OHDA)-induced sympathectomy improved hepatic sympathetic overactivity mediated hepatic steatosis in high fat diet (HFD)-fed APOE knockout mice (APOE-/- mice) by reducing hepatic SNA. Taken together, this study concludes that senescent cell-secreted netrin-1 mediated SFs outgrowth and infiltration, which contributes to aging-related disorders, suggesting that clearing senescent cells or inhibiting SNA is a promising therapeutic strategy for improving sympathetic nervous system (SNS) hyperactivity-induced aging-related pathologies.
    Keywords:  aged tissues; aging-related disorders; netrin-1; senescent cells; sympathetic fibers
    DOI:  https://doi.org/10.3389/fnagi.2020.507140
  4. Int J Mol Med. 2020 Nov 25.
    Sun X, Wang Z, Cong X, Lv Y, Li Z, Rong L, Yang T, Yu D.
      The mitochondria have been proven to be involved in processes of aging; however, the mechansims through which mitoepigenetics affect the cytological behaviors of cardiomyocytes during the aging process are not yet fully understood. In the present study, two senescence models were constructed, replicative senescence (RS) and stress‑induced premature senescence (SIPS), using human heart mesenchymal stem cells (HMSCs). First, the differences in age‑related gene expression levels and telomere length were compared between the HMSCs in the RS and SIPS models by PCR. Subsequently, protein expression and the mitochondrial DNA (mtDNA) methylation status of cytochrome c oxidase subunit II (COX2) was measured by western blot analysis and bisulfite genomic sequencing (BSP). Finally, the value of the DNA methyltransferase (Dnmt) inhibitor, 5‑aza‑2'‑deoxycytidine (AdC), in delaying the senescence of HMSCs was evaluated. It was found that the p16, p27 and p53 mRNA expression levels increased in the senescent cells, whereas p21 mRNA expression did not. It was also found that telomere shortening only occurred in the RS model, but not in the SIPS model. Along with the senescence of HMSCs, COX2 gene methylation increased and its protein expression level significantly decreased. It was demonstrated that AdC inhibited COX2 methylation and downregulated COX2 expression. The addition of exogenous COX2 or the administration of AdC promoted cell proliferation and delayed cell aging. On the whole, the present study demonstrates that COX2 methylation and downregulation are biomarkers of HMSC senescence. Thus, COX2 may have potential for use as a therapeutic target of cardiovascular diseases and this warrants further investigation.
    DOI:  https://doi.org/10.3892/ijmm.2020.4799
  5. Sci Transl Med. 2021 Jan 06. pii: eabd2655. [Epub ahead of print]13(575):
    Wang W, Zheng Y, Sun S, Li W, Song M, Ji Q, Wu Z, Liu Z, Fan Y, Liu F, Li J, Esteban CR, Wang S, Zhou Q, Belmonte JCI, Zhang W, Qu J, Tang F, Liu GH.
      Understanding the genetic and epigenetic bases of cellular senescence is instrumental in developing interventions to slow aging. We performed genome-wide CRISPR-Cas9-based screens using two types of human mesenchymal precursor cells (hMPCs) exhibiting accelerated senescence. The hMPCs were derived from human embryonic stem cells carrying the pathogenic mutations that cause the accelerated aging diseases Werner syndrome and Hutchinson-Gilford progeria syndrome. Genes whose deficiency alleviated cellular senescence were identified, including KAT7, a histone acetyltransferase, which ranked as a top hit in both progeroid hMPC models. Inactivation of KAT7 decreased histone H3 lysine 14 acetylation, repressed p15INK4b transcription, and alleviated hMPC senescence. Moreover, lentiviral vectors encoding Cas9/sg-Kat7, given intravenously, alleviated hepatocyte senescence and liver aging and extended life span in physiologically aged mice as well as progeroid Zmpste24-/- mice that exhibit a premature aging phenotype. CRISPR-Cas9-based genetic screening is a robust method for systematically uncovering senescence genes such as KAT7, which may represent a therapeutic target for developing aging interventions.
    DOI:  https://doi.org/10.1126/scitranslmed.abd2655
  6. J Biol Chem. 2020 Nov 24. pii: S0021-9258(20)00035-6. [Epub ahead of print]296 100049
    Nagano T, Iwasaki T, Onishi K, Awai Y, Terachi A, Kuwaba S, Asano S, Katasho R, Nagai K, Nakashima A, Kikkawa U, Kamada S.
      Although senescent cells display various morphological changes including vacuole formation, it is still unclear how these processes are regulated. We have recently identified the gene, lymphocyte antigen 6 complex, locus D (LY6D), to be upregulated specifically in senescent cells. LY6D is a glycosylphosphatidylinositol-anchored cell-surface protein whose function remains unknown. Here, we analyzed the functional relationship between LY6D and the senescence processes. We found that overexpression of LY6D induced vacuole formation and knockdown of LY6D suppressed the senescence-associated vacuole formation. The LY6D-induced vacuoles were derived from macropinocytosis, a distinct form of endocytosis. Furthermore, Src family kinases and Ras were found to be recruited to membrane lipid rafts in an LY6D-dependent manner, and inhibition of their activity impaired the LY6D-induced macropinocytosis. Finally, reduction of senescent-cell survival induced by glutamine deprivation was recovered by albumin supplementation to the culture media in an LY6D-dependent manner. Because macropinocytosis acts as an amino acid supply route, these results suggest that LY6D-mediated macropinocytosis contributes to senescent-cell survival through the incorporation of extracellular nutrients.
    Keywords:  LY6D; Ras protein; cellular senescence/endocytosis; lipid raft; macropinocytosis; vacuole
    DOI:  https://doi.org/10.1074/jbc.RA120.013500
  7. Aging (Albany NY). 2021 Jan 06. 12
    Yoon KJ, Ahn A, Park SH, Kwak SH, Kwak SE, Lee W, Yang YR, Kim M, Shin HM, Kim HR, Moon HY.
      Although several evidence has suggested the impact of exercise on the prevention of aging phenotypes, few studies have been conducted on the mechanism by which exercise alters the immune-cell profile, thereby improving metabolism in senile obesity. In this study, we confirmed that 4-week treadmill exercise sufficiently improved metabolic function, including increased lean mass and decreased fat mass, in 88-week-old mice. The expression level of the senescence marker p16 in the white adipose tissue (WAT) was decreased after 4-weeks of exercise. Exercise induced changes in the profiles of immune-cell subsets, including natural killer (NK) cells, central memory CD8+ T cells, eosinophils, and neutrophils, in the stromal vascular fraction of WAT. In addition, it has been shown through transcriptome analysis of WAT that exercise can activate pathways involved in the interaction between WAT and immune cells, in particular NK cells, in aged mice. These results suggest that exercise has a profound effect on changes in immune-cell distribution and senescent-cell scavenging in WAT of aged mice, eventually affecting overall energy metabolism toward a more youthful state.
    Keywords:  NK cell; aging; exercise; immunosenescence; metabolism
    DOI:  https://doi.org/10.18632/aging.202312
  8. Cells. 2021 Jan 06. pii: E79. [Epub ahead of print]10(1):
    Rottenberg H, Hoek JB.
      The activity of the mitochondrial permeability transition pore, mPTP, a highly regulated multi-component mega-channel, is enhanced in aging and in aging-driven degenerative diseases. mPTP activity accelerates aging by releasing large amounts of cell-damaging reactive oxygen species, Ca2+ and NAD+. The various pathways that control the channel activity, directly or indirectly, can therefore either inhibit or accelerate aging or retard or enhance the progression of aging-driven degenerative diseases and determine lifespan and healthspan. Autophagy, a catabolic process that removes and digests damaged proteins and organelles, protects the cell against aging and disease. However, the protective effect of autophagy depends on mTORC2/SKG1 inhibition of mPTP. Autophagy is inhibited in aging cells. Mitophagy, a specialized form of autophagy, which retards aging by removing mitochondrial fragments with activated mPTP, is also inhibited in aging cells, and this inhibition leads to increased mPTP activation, which is a major contributor to neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. The increased activity of mPTP in aging turns autophagy/mitophagy into a destructive process leading to cell aging and death. Several drugs and lifestyle modifications that enhance healthspan and lifespan enhance autophagy and inhibit the activation of mPTP. Therefore, elucidating the intricate connections between pathways that activate and inhibit mPTP, in the context of aging and degenerative diseases, could enhance the discovery of new drugs and lifestyle modifications that slow aging and degenerative disease.
    Keywords:  Parkinson’s disease; aging; aging-driven degenerative disease; autophagy; longevity; mitochondrial permeability transition; mitophagy; reactive oxygen species
    DOI:  https://doi.org/10.3390/cells10010079
  9. Aging Cell. 2021 Jan 02. e13295
    Webb LMC, Fra-Bido S, Innocentin S, Matheson LS, Attaf N, Bignon A, Novarino J, Fazilleau N, Linterman MA.
      Ageing profoundly changes our immune system and is thought to be a driving factor in the morbidity and mortality associated with infectious disease in older people. We have previously shown that the impaired immunity to vaccination that occurs in aged individuals is partly attributed to the effect of age on T follicular helper (Tfh) cell formation. In this study, we examined how age intrinsically affects Tfh cell formation in both mice and humans. We show increased formation of Tfh precursors (pre-Tfh) but no associated increase in germinal centre (GC)-Tfh cells in aged mice, suggesting age-driven promotion of only early Tfh cell differentiation. Mechanistically, we show that ageing alters TCR signalling which drives expression of the Notch-associated transcription factor, RBPJ. Genetic or chemical modulation of RBPJ or Notch rescues this age-associated early Tfh cell differentiation, and increased intrinsic Notch activity recapitulates this phenomenon in younger mice. Our data offer mechanistic insight into the age-induced changes in T-cell activation that affects the differentiation and ultimately the function of effector T cells.
    Keywords:  CXCR5; Notch; RBPJ; T follicular helper cells; age
    DOI:  https://doi.org/10.1111/acel.13295
  10. Int J Mol Sci. 2021 Jan 02. pii: E406. [Epub ahead of print]22(1):
    Song J, Bae YS.
      Senescent cells secrete pro-inflammatory factors, and a hallmark feature of senescence is senescence-associated secretory phenotype (SASP). The aim of this study is to investigate the protein kinase CK2 (CK2) effects on SASP factors expression in cellular senescence and organism aging. Here CK2 down-regulation induced the expression of SASP factors, including interleukin (IL)-1β, IL-6, and matrix metalloproteinase (MMP) 3, through the activation of nuclear factor-κB (NF-κB) signaling in MCF-7 and HCT116 cells. CK2 down-regulation-mediated SIRT1 inactivation promoted the degradation of inhibitors of NF-κB (IκB) by activating the AKT-IκB kinase (IKK) axis and increased the acetylation of lysine 310 on RelA/p65, an important site for the activity of NF-κB. kin-10 (the ortholog of CK2β) knockdown increased zmp-1, -2, and -3 (the orthologs of MMP) expression in nematodes, but AKT inhibitor triciribine and SIRT activator resveratrol significantly abrogated the increased expression of these genes. Finally, antisense inhibitors of miR-186, miR-216b, miR-337-3p, and miR-760 suppressed CK2α down-regulation, activation of the AKT-IKK-NF-κB axis, RelA/p65 acetylation, and expression of SASP genes in cells treated with lipopolysaccharide. Therefore, this study indicated that CK2 down-regulation induces the expression of SASP factors through NF-κB activation, which is mediated by both activation of the SIRT1-AKT-IKK axis and RelA/p65 acetylation, suggesting that the mixture of the four miRNA inhibitors can be used as anti-inflammatory agents.
    Keywords:  AKT; NF-κB; SASP factors; SIRT1; anti-inflammatory agent; miRNA; protein kinase CK2
    DOI:  https://doi.org/10.3390/ijms22010406
  11. Clin Transl Oncol. 2021 Jan 03.
    Zhang C, Gu X, Pan M, Yuan Q, Cheng H.
      PURPOSE: An in-depth understanding of the mechanism of thyroid cancer progression will help identify patients with thyroid cancer with a high risk of recurrence and metastasis. Although studies have pointed out that the senescence of thyroid tumor cells may stimulate TAMs and cause a series of changes. However, the role of TAMs in aging thyroid cancer cells is still unknown. The aim of this study was to investigate the function of TAMs in aging thyroid cancer cells.METHODS: We conducted in vitro model studies based on the K1 cell line to induce tumor cell senescence and study its effect on the differentiation of macrophages, flow cytometry was used to confirm polarization of macrophages, transwell assay was used to confirm changes of invasion and migration of tumor cells.
    RESULT: Our data indicate that aging thyroid tumor cell lines trigger the polarization of M2-like macrophages, accompanied by increased expression of CCL17, CCL18, IL-18, and TGFβ1. This event is caused by the activation of the NFκB pathway upregulation of CXCL2 and CXCL3 is related. Further studies have shown that differentiated M2-like macrophages promote tumor cell migration (but have no effect on cell proliferation).
    CONCLUSION: Our study indicating that the interaction between tumor and TAMs also occurs in the advanced stages of thyroid tumors and will lead to faster tumors progress.
    Keywords:  Cell migration; Cell senescence; Nfκb signal pathway; TAMs; Thyroid carcinoma
    DOI:  https://doi.org/10.1007/s12094-020-02516-2
  12. Cancer Manag Res. 2020 ;12 13553-13566
    Liao C, Xiao Y, Liu L.
      Cellular senescence is traditionally considered as stable cell cycle arrest state with other phenotypic alterations including the production of an array of cytokines and growth factors. Cancer cells undergo senescence in response to chemotherapeutic agents, radiotherapy and molecular targeted therapy. This form of senescence is termed therapy-induced senescence (TIS) and represents a desirable target in cancer therapy. Recent studies have shown that cellular senescence is a highly heterogeneous and dynamic process. Apart from being cleared by the immune system, the senescent cancer cells may survive for a long time and escape from senescence state. Notably, these cells even have the potential to regain stem-like state with high aggressiveness that eventually facilitates cancer recurrence. Furthermore, the senescence-associated secretory phenotype (SASP) of senescent cells is not always the same, and could establish immunosuppression and a protumor microenvironment. Given these detrimental effects, senescence-inducing chemotherapy followed by senotherapy (the "one-two punch" approach), has emerged. This combined therapy could mitigate unnecessary side effects of the persistent senescent cells, reduce the toxicity of pro-senescence therapy and prolong the survival of cancer patients, and it has a potential future in the precise treatment of cancer. Herein, we review the complex effects of therapy-induced senescence in cancer and highlight the great promise of two-step strategies in anticancer therapies.
    Keywords:  SASP; cancer therapy; cellular senescence; reversibility; senotherapy
    DOI:  https://doi.org/10.2147/CMAR.S285083
  13. Front Pharmacol. 2020 ;11 593832
    Li X, Yang K, Gao S, Zhao J, Liu G, Chen Y, Lin H, Zhao W, Hu Z, Xu N.
      Background: Macrophages can selectively recognize and eliminate senescent cells, but this function is impaired with age, resulting in excessive accumulation of senescent cells in the skin, which ultimately causes skin aging. Therefore, enhancing the immune surveillance ability of macrophages to clear senescent keratinocytes and fibroblasts from aging skin may be an effective skin rejuvenation strategy. Methods: In this study, a macrophage and senescent skin cell co-culture model was established whereby THP-1-derived macrophages and tert-butyl hydroxide-induced senescent skin cells (HaCaT and HFF-1) were grown in the same culture. Senescent skin cells were detected by the SPiDER-βgal assay, and the expression of secretory phenotype factors related to senescence was assayed by qPCR. The effect of carnosine on the number of SA-β-gal positive skin cells in the macrophage-senescent skin cell co-culture was evaluated and compared with that in the senescent skin cell monoculture. Results: Carnosine promoted macrophage-mediated elimination of senescent skin cells in the co-culture. Through the AKT2 signaling pathway, carnosine upregulated the expression of CD36 and receptors for advanced glycation end products and elevated the phagocytic capacity of the macrophages, thereby promoting the ability of the macrophages to eliminate the senescent skin cells. Conclusions: Carnosine could boost the immune surveillance ability of macrophages to clear senescent keratinocytes and fibroblasts in the macrophage-senescent skin cell co-culture by activating the AKT2 signaling pathway, suggesting the possibility of using carnosine as an agent to reverse skin aging.
    Keywords:  Akt2; carnosine; co-culture; macrophages; senescent cell; skin aging
    DOI:  https://doi.org/10.3389/fphar.2020.593832
  14. Stem Cell Res Ther. 2021 Jan 07. 12(1): 45
    Yi L, Ju Y, He Y, Yin X, Xu Y, Weng T.
      BACKGROUND: Age-related bone loss plays a vital role in the development of osteoporosis and osteoporotic fracture. Bone marrow stromal cell (BMSC) senescence is highly associated with osteoporosis and limits the application of BMSCs in regenerative medicine. Hypoxia is an essential component for maintaining the normal physiology of BMSCs. We have reported that activation of hypoxia-induced factor by deletion of von Hippel-Lindau gene in osteochondral progenitor cells protected mice from aging-induced bone loss. However, whether pharmacologically manipulation of hypoxic niche would attenuate age-related bone loss and dysfunction of BMSCs is not well understood.METHODS: Twelve-month-old Sprague-Dawley rats were used as an aged model and were intraperitoneally injected with Desferal® (20, 60 mg/kg weight or vehicle), three times a week for a continuous 8-week period. Two-month-old young rats were set as a reference. After 8 weeks, micro-CT and HE staining were performed to determine the effect of Desferal® on bone loss. In order to investigate the effects of Desferal® on BMSC senescence, 12-month-old rats were treated with high-dose Desferal® (60 mg/kg weight) daily for 10 days. BMSCs were isolated and evaluated using CCK-8 assay, colony-forming cell assay, cell differentiation assay, laser confocal for reactive oxygen species (ROS) level, senescence-associated β-galactosidase (SA-β-gal) staining, and molecular expression test for stemness/senescence-associated genes.
    RESULTS: Micro-CT and HE staining showed that high-dose Desferal® significantly prevented bone loss in aged rats. Compared with vehicle group, the ex vivo experiments showed that short-term Desferal® administration could promote the potential of BMSC growth (proliferation and colony formation ability) and improve the rebalance of osteogenic and adipogenic differentiation, as well as rejuvenate senescent BMSCs (ROS level and SA-β-gal staining) and revise the expression of stemness/senescence-associated genes. The potential of BMSCs from 12M-H-Desferal® group at least partly revised to the level close to 2-month-old group.
    CONCLUSIONS: The current study suggested that Desferal®, an iron-chelating agent, could alleviate age-related bone loss in middle-aged rats. Meanwhile, we found that short-term intraperitoneal injection of Desferal® partly rejuvenate BMSCs from aged rats. Overall, we demonstrated a novel role of Desferal® in rejuvenating aged BMSCs and preventing age-related bone loss.
    Keywords:  Aging; Bone loss; Bone marrow stromal cells; Desferal®; Hypoxia
    DOI:  https://doi.org/10.1186/s13287-020-02112-9
  15. NPJ Aging Mech Dis. 2020 Jan 07. 6(1): 1
    Okur MN, Mao B, Kimura R, Haraczy S, Fitzgerald T, Edwards-Hollingsworth K, Tian J, Osmani W, Croteau DL, Kelley MW, Bohr VA.
      Age-related hearing loss (ARHL) is one of the most common disorders affecting elderly individuals. There is an urgent need for effective preventive measures for ARHL because none are currently available. Cockayne syndrome (CS) is a premature aging disease that presents with progressive hearing loss at a young age, but is otherwise similar to ARHL. There are two human genetic complementation groups of CS, A and B. While the clinical phenotypes in patients are similar, the proteins have very diverse functions, and insight into their convergence is of great interest. Here, we use mouse models for CS (CSA-/- and CSBm/m) that recapitulate the hearing loss in human CS patients. We previously showed that NAD+, a key metabolite with various essential functions, is reduced in CS and associated with multiple CS phenotypes. In this study, we report that NAD+ levels are reduced in the cochlea of CSBm/m mice and that short-term treatment (10 days) with the NAD+ precursor nicotinamide riboside (NR), prevents hearing loss, restores outer hair cell loss, and improves cochlear health in CSBm/m mice. Similar, but more modest effects were observed in CSA-/- mice. Remarkably, we observed a reduction in synaptic ribbon counts in the presynaptic zones of inner hair cells in both CSA-/- and CSBm/m mice, pointing to a converging mechanism for cochlear defects in CS. Ribbon synapses facilitate rapid and sustained synaptic transmission over long periods of time. Ribeye, a core protein of synaptic ribbons, possesses an NAD(H) binding pocket which regulates its activity. Intriguingly, NAD+ supplementation rescues reduced synaptic ribbon formation in both CSA-/- and CSBm/m mutant cochleae. These findings provide valuable insight into the mechanism of CS- and ARHL-associated hearing loss, and suggest a possible intervention.
    DOI:  https://doi.org/10.1038/s41514-019-0040-z
  16. Biometals. 2021 Jan 03.
    Wong CP, Magnusson KR, Sharpton TJ, Ho E.
      Age-related T cell dysfunction contributes to immunosenescence and chronic inflammation. Aging is also associated with a progressive decline in zinc status. Zinc is an essential micronutrient critical for immune function. A significant portion of the older populations are at risk for marginal zinc deficiency. The combined impact of dietary zinc deficiency and age on immune dysfunction has not been well explored despite the common occurrence together in the elderly population. We hypothesize that age-related zinc loss contributes to T cell dysfunction and chronic inflammation in the elderly and is exacerbated by inadequate dietary intake and improved with zinc supplementation. Using an aging mouse model, the effects of marginal zinc deficiency and zinc supplementation on Th1/Th17/proinflammatory cytokine profiles and CD4+ T cell naïve/memory phenotypes were examined. In the first study, young (2 months) and old (24 months) C57BL/6 mice were fed a zinc adequate (ZA) or marginally zinc deficient (MZD) diets for 6 weeks. In the second study, mice were fed a ZA or zinc supplemented (ZS) diet for 6 weeks. MZD old mice had significant increase in LPS-induced IL6 compared to ZA old mice. In contrast, ZS old mice had significantly reduced plasma MCP1 levels, reduced T cell activation-induced IFNγ, IL17, and TNFα response, as well as increased naïve CD4+ T-cell subset compared to ZA old mice. Our data suggest that zinc deficiency is an important contributing factor in immune aging, and improving zinc status can in part reverse immune dysfunction and reduce chronic inflammation associated with aging.
    Keywords:  Aging; Immune dysfunction; Inflammation; T cells; Zinc
    DOI:  https://doi.org/10.1007/s10534-020-00279-5
  17. Int J Biol Sci. 2021 ;17(1): 151-162
    Huang Y, Wu B, Shen D, Chen J, Yu Z, Chen C.
      As a systemic syndrome characterized by age-associated degenerative skeletal muscle atrophy, sarcopenia leads to a risk of adverse outcomes in the elderly. Age-related iron accumulation is found in the muscles of sarcopenia animal models and patients, but the role of iron in sarcopenia remains poorly understood. It has been recently found that iron overload in several diseases is involved in ferroptosis, an iron- dependent form of programmed cell death. However, whether this excess iron can result in ferroptosis in muscles is still unclear. In our present study, we found that ferric citrate induced ferroptosis in C2C12 cells, as well as impaired their differentiation from myoblasts to myotubes. Due to the decreased muscle mass and fiber size, 40-week-old senescence accelerated mouse prone 8 (SAMP8) mice were used as a sarcopenia model, in whose muscles the iron content and markers of ferroptosis were found to increase, compared to 8-week- old SAMP8 controls. Moreover, our results showed that iron overload upregulated the expression of P53, which subsequently repressed the protein level of Slc7a11 (solute carrier family 7, member 11), a known ferroptosis-related gene. The downregulation of Slc7a11 then induced the ferroptosis of muscle cells through the accumulation of lipid peroxidation products, which may be one of the causes of sarcopenia. The findings in this study indicate that iron plays a key role in triggering P53- Slc7a11-mediated ferroptosis in muscles, and suggest that targeting iron accumulation and ferroptosis might be a therapeutic strategy for treating sarcopenia.
    Keywords:  C2C12; Ferroptosis; Iron overload; SAMP8; Sarcopenia
    DOI:  https://doi.org/10.7150/ijbs.53126
  18. Free Radic Biol Med. 2021 Jan 05. pii: S0891-5849(20)32118-3. [Epub ahead of print]
    White TL, Deshpande N, Kumar V, Gauthier AG, Jurkunas UV.
      Fuchs endothelial corneal dystrophy (FECD) is an age-related disease whereby progressive loss of corneal endothelial cells (CEnCs) leads to loss of vision. There is currently a lack of therapeutic interventions as the etiology of the disease is complex, with both genetic and environmental factors. In this study, we have provided further insights into the pathogenesis of the disease, showing a causal relationship between senescence and endothelial-mesenchymal transition (EMT) using in vitro and in vivo models. Ultraviolet A (UVA) light induced EMT and senescence in CEnCs. Senescent cells were arrested in G2/M phase of the cell cycle and responsible for the resulting profibrotic phenotype. Inhibiting ATR signaling and subsequently preventing G2/M arrest attenuated EMT. In vivo, UVA irradiation induced cell cycle re-entry in post mitotic CEnCs, resulting in senescence and fibrosis at 1- and 2-weeks post-UVA. Selectively eliminating senescent cells using the senolytic cocktail of dasatinib and quercetin attenuated UVA induced fibrosis, highlighting the potential for a new therapeutic intervention for FECD.
    Keywords:  Fuchs endothelial corneal dystrophy; cell cycle; endothelial-mesenchymal transition; fibrosis; senescence
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2020.12.445
  19. Mol Biol Rep. 2021 Jan 03.
    Kanoi R, Loachan P, Das S, Rao BSS.
      Chronic oxidative stress has been associated with several human ailments including the condition of aging. Extensive studies have shown the causal relationship between oxidative stress, aging, and cellular senescence. In this regard, forestalling or preventing senescence could delay the aging process as well as act as an intervention against premature aging. Hence, in the present study, we investigated the anti-senescence potential of Mangiferin (MGN) against Hydrogen peroxide (H2O2) induced premature senescence using human dermal fibroblast cells. Early passage human dermal fibroblasts cells were exposed to H2O2 (10 μM) for 15 days. In order to assess the anti-senescence property of MGN, cells were preconditioned with MGN (10 μM / 50 μM; 2 h) followed by addition of H2O2 (10 μM). H2O2 mediated induction of premature senescence was accompanied by elevated ROS, lowering of mitochondrial mass and membrane potential, changes in ATP content along with G0/G1 arrest and SA-β-gal expression. While, conditioning the cells with MGN lowered oxidative burden, stabilized mitochondrial membrane potential / mass and protected the cells against cell cycle arrest, ultimately rendering protection against premature senescence. The present findings showed that MGN might act as a potential cytoprotective nutraceutical that can prolong the onset of chronic oxidative stress mediated premature senescence.
    Keywords:  G0/G1 arrest; Oxidative stress; Polyphenols; Senescence
    DOI:  https://doi.org/10.1007/s11033-020-06074-2
  20. Biomed Pharmacother. 2021 Jan 05. pii: S0753-3322(20)31384-6. [Epub ahead of print]135 111191
    Wang Y, Wang Y, Yang M, Ma X.
      Chronic kidney disease (CKD) is an increasing major public health problem worldwide. And CKD shares numerous phenotypic similarities with kidney as well as systemic ageing. Cellular senescence is mainly characterized by a stable cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Herein, the regulations and the internal mechanisms of cellular senescence will be discussed. Meanwhile, efforts are made to give a comprehensive overview of the recent advances of the implication of cellular senescence in CKD. To date, numerous studies have focused on the effects of ageing risk factors in kidney and thereby trying to interrupt the kidney ageing processes with senolytics. Interestingly, some of them showed enormous clinical application potentials. Therefore, senotherapeutics can be applied as novel potential strategies for the treatment of CKD.
    Keywords:  Cellular senescence; Chronic kidney disease; SASP; SCAPs; Senolytics
    DOI:  https://doi.org/10.1016/j.biopha.2020.111191
  21. Cancer Cell Int. 2021 Jan 07. 21(1): 26
    Niu J, Gao RQ, Cui MT, Zhang CG, Li ST, Cheng S, Ding W.
      BACKGROUND: TCAB1, a.k.a. WRAP53β or WDR79, is an important molecule for the maintenance of Cajal bodies and critically involved in telomere elongation and DNA repair. Upregulation of TCAB1 were discovered in a variety types of cancers. However, the function of TCAB1 in tumor cell senescence remains absent.METHODS: The TCAB1 knockdown cell lines were constructed. The expression levels of TCAB1, p21, p16 and p53 were detected by qRT-PCR and western blotting. Staining of senescence-associated β-galactosidase was used to detect senescent cells. The ubiquitination of the p21 was analysed by immunoprecipitation and in vivo ubiquitination assay. TCGA databases were employed to perform in silico analyses for the mRNA expression of TCAB1, p21, p16 and p53.
    RESULTS: Here, we discovered that knockdown of TCAB1 induced rapid progression of cellular senescence in A549, H1299 and HeLa cells. In exploiting the mechanism underlining the role of TCAB1 on senescence, we found a significant increase of p21 at the protein levels upon TCAB1 depletion, whereas the p21 mRNA expression was not altered. We verified that TCAB1 knockdown was able to shunt p21 from proteasomal degradation by regulating the ubiquitination of p21. In rescue assays, it was demonstrated that decreasing the expression of p21 or increasing the expression of TCAB1 were able to attenuate the cellular senescence process induced by TCAB1 silencing.
    CONCLUSIONS: This study revealed the importance of TCAB1 for its biological functions in the regulation of cell senescence. Our results will be helpful to understand the mechanisms of senescence in cancer cells, which could provide clues for designing novel strategies for developing effective treatment regimens.
    Keywords:  Cancer; Cellular senescence; Proteasomal degradation; TCAB1; p21
    DOI:  https://doi.org/10.1186/s12935-020-01745-3
  22. Immun Ageing. 2021 Jan 05. 18(1): 2
    Ragonnaud E, Biragyn A.
      Extrinsic factors, such as lifestyle and diet, are shown to be essential in the control of human healthy aging, and thus, longevity. They do so by targeting at least in part the gut microbiome, a collection of commensal microorganisms (microbiota), which colonize the intestinal tract starting after birth, and is established by the age of three. The composition and abundance of individual microbiota appears to continue to change until adulthood, presumably reflecting lifestyle and geographic, racial, and individual differences. Although most of these changes appear to be harmless, a major shift in their composition in the gut (dysbiosis) can trigger harmful local and systemic inflammation. Recent reports indicate that dysbiosis is increased in aging and that the gut microbiota of elderly people is enriched in pro-inflammatory commensals at the expense of beneficial microbes. The clinical consequence of this change remains confusing due to contradictory reports and a high degree of variability of human microbiota and methodologies used. Here, we present the authors' thoughts that underscore dysbiosis as a primary cause of aging-associated morbidities, and thus, premature death of elderly people. We provide evidence that the dysbiosis triggers a chain of pathological and inflammatory events. Examples include alteration of levels of microbiota-affected metabolites, impaired function and integrity of the gastrointestinal tract, and increased gut leakiness. All of these enhance systemic inflammation, which when associated with aging is termed inflammaging, and result in consequent aging-associated pathologies.
    Keywords:  Aging; B cells; Commensals; IgA
    DOI:  https://doi.org/10.1186/s12979-020-00213-w
  23. Int J Mol Sci. 2021 Jan 02. pii: E401. [Epub ahead of print]22(1):
    Saul D, Kosinsky RL.
      Aging represents the multifactorial decline in physiological function of every living organism. Over the past decades, several hallmarks of aging have been defined, including epigenetic deregulation. Indeed, multiple epigenetic events were found altered across different species during aging. Epigenetic changes directly contributing to aging and aging-related diseases include the accumulation of histone variants, changes in chromatin accessibility, loss of histones and heterochromatin, aberrant histone modifications, and deregulated expression/activity of miRNAs. As a consequence, cellular processes are affected, which results in the development or progression of several human pathologies, including cancer, diabetes, osteoporosis, and neurodegenerative disorders. In this review, we focus on epigenetic mechanisms underlying aging-related processes in various species and describe how these deregulations contribute to human diseases.
    Keywords:  CDKN2A; aging; aging-associated diseases; diabetes; epigenetics; gene expression; histone modifications; histones; osteoporosis; sarcopenia
    DOI:  https://doi.org/10.3390/ijms22010401
  24. Aging Med (Milton). 2020 Dec;3(4): 266-275
    Wang C, Chen B, Feng Q, Nie C, Li T.
      As percentages of elderly people rise in many societies, age-related diseases have become more prevalent than ever. Research interests have been shifting to delaying age-related diseases by delaying or reversing aging itself. We use metformin as an entry point to talk about the important molecular and genetic longevity-regulating mechanisms that have been extensively studied with it. Then we review a number of observational studies, animal studies, and clinical trials to reflect the clinical potentials of the mechanisms in lifespan extension, cardiovascular diseases, tumors, and neurodegeneration. Finally, we highlight remaining concerns that are related to metformin and future anti-aging research.
    Keywords:  aging; clinical pharmacology; longevity; metformin
    DOI:  https://doi.org/10.1002/agm2.12135
  25. Aging (Albany NY). 2020 Dec 19. 12
    Long P, He M, Yan W, Chen W, Wei D, Wang S, Zhang Z, Ge W, Chen T.
      During the process of aging, the retina exhibits chronic oxidative stress (OS) damage. Our preliminary experiment showed that acetaldehyde dehydrogenase 2 (ALDH2) could alleviate retinal damage caused by OS. This study aimed to explore whether ALDH2 could inhibit mice retinal cell apoptosis and enhance the function of unfolded protein response in endoplasmic reticulum (UPRER) through reducing OS in aging process. Retinal function and structure in vivo and in vitro were examined in aged ALDH2+ overexpression mice and ALDH2 agonist Alda1-treated aged mice. Levels of ALDH2, endoplasmic reticulum stress (ERS), apoptosis and inflammatory cytokines were evaluated. Higher expression of ALDH2 was observed at the outer nuclear layer (ONL) and the inner nuclear layer (INL) in aged ALDH2+ overexpression and aged Alda1-treated mice. Moreover, aged ALDH2+ overexpression mice and aged Alda1-treated mice exhibited better retinal function and structure. Increased expression of glucose-regulated protein 78 (GRP78) and ERS-related protein phosphorylated eukaryotic initiation factor 2 (peIF2α) and decreased expression of apoptosis-related protein, including C/EBP homologous protein (CHOP), caspase12 and caspase9, and retinal inflammatory cytokines were detected in the retina of aged ALDH2+ overexpression mice and aged Alda1-treated mice. The expression of ALDH2 in the retina was decreased in aging process. ALDH2 could reduce retinal oxidative stress and apoptosis, strengthen UPRER during the aging process to improve retinal function and structure.
    Keywords:  ALDH2; UPRER; aged mice; oxidative stress; retina
    DOI:  https://doi.org/10.18632/aging.202325
  26. Nat Commun. 2021 01 04. 12(1): 49
    Pérez-Jiménez MM, Monje-Moreno JM, Brokate-Llanos AM, Venegas-Calerón M, Sánchez-García A, Sansigre P, Valladares A, Esteban-García S, Suárez-Pereira I, Vitorica J, Ríos JJ, Artal-Sanz M, Carrión ÁM, Muñoz MJ.
      Aging and fertility are two interconnected processes. From invertebrates to mammals, absence of the germline increases longevity. Here we show that loss of function of sul-2, the Caenorhabditis elegans steroid sulfatase (STS), raises the pool of sulfated steroid hormones, increases longevity and ameliorates protein aggregation diseases. This increased longevity requires factors involved in germline-mediated longevity (daf-16, daf-12, kri-1, tcer-1 and daf-36 genes) although sul-2 mutations do not affect fertility. Interestingly, sul-2 is only expressed in sensory neurons, suggesting a regulation of sulfated hormones state by environmental cues. Treatment with the specific STS inhibitor STX64, as well as with testosterone-derived sulfated hormones reproduces the longevity phenotype of sul-2 mutants. Remarkably, those treatments ameliorate protein aggregation diseases in C. elegans, and STX64 also Alzheimer's disease in a mammalian model. These results open the possibility of reallocating steroid sulfatase inhibitors or derivates for the treatment of aging and aging related diseases.
    DOI:  https://doi.org/10.1038/s41467-020-20269-y
  27. Curr Biol. 2021 Jan 05. pii: S0960-9822(20)31838-8. [Epub ahead of print]
    Reyes GX, Kolodziejczak A, Devakumar LJPS, Kubota T, Kolodner RD, Putnam CD, Hombauer H.
      Mismatch repair (MMR) safeguards genome stability through recognition and excision of DNA replication errors.1-4 How eukaryotic MMR targets the newly replicated strand in vivo has not been established. MMR reactions reconstituted in vitro are directed to the strand containing a preexisting nick or gap,5-8 suggesting that strand discontinuities could act as discrimination signals. Another candidate is the proliferating cell nuclear antigen (PCNA) that is loaded at replication forks and is required for the activation of Mlh1-Pms1 endonuclease.7-9 Here, we discovered that overexpression of DNA ligase I (Cdc9) in Saccharomyces cerevisiae causes elevated mutation rates and increased chromatin-bound PCNA levels and accumulation of Pms1 foci that are MMR intermediates, suggesting that premature ligation of replication-associated nicks interferes with MMR. We showed that yeast Pms1 expression is mainly restricted to S phase, in agreement with the temporal coupling between MMR and DNA replication.10 Restricting Pms1 expression to the G2/M phase caused a mutator phenotype that was exacerbated in the absence of the exonuclease Exo1. This mutator phenotype was largely suppressed by increasing the lifetime of replication-associated DNA nicks, either by reducing or delaying Cdc9 ligase activity in vivo. Therefore, Cdc9 dictates a window of time for MMR determined by transient DNA nicks that direct the Mlh1-Pms1 in a strand-specific manner. Because DNA nicks occur on both newly synthesized leading and lagging strands,11 these results establish a general mechanism for targeting MMR to the newly synthesized DNA, thus preventing the accumulation of mutations that underlie the development of human cancer.
    Keywords:  Cdc9; DNA ligase I; DNA ligase I overexpression; DNA replication fidelity; DNA replication-associated nicks; MMR; MMR strand discrimination signal; ligation Okazaki fragments; mismatch repair; mutation accumulation
    DOI:  https://doi.org/10.1016/j.cub.2020.12.018
  28. Cell Death Dis. 2021 Jan 04. 12(1): 13
    Guo Q, Chen X, Chen J, Zheng G, Xie C, Wu H, Miao Z, Lin Y, Wang X, Gao W, Zheng X, Pan Z, Zhou Y, Wu Y, Zhang X.
      Damaged deoxyribonucleic acid (DNA) is a primary pathologic factor for osteoarthritis (OA); however, the mechanism by which DNA damage drives OA is unclear. Previous research demonstrated that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) participates in DNA damage response. As a result, the current study aimed at exploring the role STING, which is the major effector in the cGAS-STING signaling casacde, in OA progress in vitro, as well as in vivo. In this study, the expression of STING was evaluated in the human and mouse OA tissues, and in chondrocytes exposed to interleukin-1 beta (IL-1β). The influences of STING on the metabolism of the extracellular matrix (ECM), apoptosis, and senescence, were assessed in STING overexpressing and knocking-down chondrocytes. Moreover, the NF-κB-signaling casacde and its role in the regulatory effects of STING on ECM metabolism, apoptosis, and senescence were explored. The STING knockdown lentivirus was intra-articularly injected to evaluate its therapeutic impact on OA in mice in vivo. The results showed that the expression of STING was remarkably elevated in the human and mouse OA tissues and in chondrocytes exposed to IL-1β. Overexpression of STING promoted the expression of MMP13, as well as ADAMTS5, but suppressed the expression of Aggrecan, as well as Collagen II; it also enhanced apoptosis and senescence in chondrocytes exposed to and those untreated with IL-1β. The mechanistic study showed that STING activated NF-κB signaling cascade, whereas the blockage of NF-κB signaling attenuated STING-induced apoptosis and senescence, and ameliorated STING-induced ECM metabolism imbalance. In in vivo study, it was demonstrated that STING knockdown alleviated destabilization of the medial meniscus-induced OA development in mice. In conclusion, STING promotes OA by activating the NF-κB signaling cascade, whereas suppression of STING may provide a novel approach for OA therapy.
    DOI:  https://doi.org/10.1038/s41419-020-03341-9
  29. Cells. 2021 Jan 03. pii: E63. [Epub ahead of print]10(1):
    Kwon JH, Kim M, Um S, Lee HJ, Bae YK, Choi SJ, Hwang HH, Oh W, Jin HJ.
      In order to provide a sufficient number of cells for clinical use, mesenchymal stem cells (MSCs) must be cultured for long-term expansion, which inevitably triggers cellular senescence. Although the small size of MSCs is known as a critical determinant of their fate, the main regulators of stem cell senescence and the underlying signaling have not been addressed. Umbilical cord blood-derived MSCs (UCB-MSCs) were obtained using size-isolation methods and then cultured with control or small cells to investigate the major factors that modulate MSC senescence. Cytokine array data suggested that the secretion of interukin-8 (IL-8) or growth-regulated oncogene-alpha (GROa) by senescent cells was markedly inhibited during incubation of small cells along with suppression of cognate receptor (C-X-C motif chemokine receptor2, CXCR2) via blockade of the autocrine/paracrine positive loop. Moreover, signaling via toll-like receptor 2 (TLR2) and TLR5, both pattern recognition receptors, drove cellular senescence of MSCs, but was inhibited in small cells. The activation of TLRs (2 and 5) through ligand treatment induced a senescent phenotype in small cells. Collectively, our data suggest that small cell from UCB-MSCs exhibit delayed cellular senescence by inhibiting the process of TLR signaling-mediated senescence-associated secretory phenotype (SASP) activation.
    Keywords:  C-X-C motif chemokine receptor 2; cell-based therapy; growth-regulated oncogene-alpha; interukin-8; mesenchymal stem cell senescence; senescence-associated secretory phenotype; small cell; toll-like receptor 2; toll-like receptor 5
    DOI:  https://doi.org/10.3390/cells10010063
  30. Cell Rep. 2021 Jan 05. pii: S2211-1247(20)31554-0. [Epub ahead of print]34(1): 108565
    Sharma S, Anand R, Zhang X, Francia S, Michelini F, Galbiati A, Williams H, Ronato DA, Masson JY, Rothenberg E, Cejka P, d'Adda di Fagagna F.
      The MRE11-RAD50-NBS1 (MRN) complex supports the synthesis of damage-induced long non-coding RNA (dilncRNA) by RNA polymerase II (RNAPII) from DNA double-strand breaks (DSBs) by an unknown mechanism. Here, we show that recombinant human MRN and native RNAPII are sufficient to reconstitute a minimal functional transcriptional apparatus at DSBs. MRN recruits and stabilizes RNAPII at DSBs. Unexpectedly, transcription is promoted independently from MRN nuclease activities. Rather, transcription depends on the ability of MRN to melt DNA ends, as shown by the use of MRN mutants and specific allosteric inhibitors. Single-molecule FRET assays with wild-type and mutant MRN show a tight correlation between the ability to melt DNA ends and to promote transcription. The addition of RPA enhances MRN-mediated transcription, and unpaired DNA ends allow MRN-independent transcription by RNAPII. These results support a model in which MRN generates single-strand DNA ends that favor the initiation of transcription by RNAPII.
    Keywords:  DNA damage; DNA double-strand breaks; DNA melting; DNA-damage induced transcription; MRE11-RAD50-NBS1 complex; RNA polymerase II; damage-induced long non-coding RNA; dilncRNA; in vitro transcription; single-molecule FRET
    DOI:  https://doi.org/10.1016/j.celrep.2020.108565
  31. Cell Rep. 2021 Jan 05. pii: S2211-1247(20)31575-8. [Epub ahead of print]34(1): 108586
    Sun H, Huang Y, Mei S, Xu F, Liu X, Zhao F, Yin L, Zhang D, Wei L, Wu C, Ma S, Wang J, Cen S, Liang C, Hu S, Guo F.
      The cyclic GMP-AMP (cGAMP) synthase (cGAS) is a key DNA sensor that initiates STING-dependent signaling to produce type I interferons through synthesizing the secondary messenger 2'3'-cGAMP. In this study, we confirm previous studies showing that cGAS is located both in the cytoplasm and in the nucleus. Nuclear accumulation is observed when leptomycin B is used to block the exportin, CRM1 protein. As a result, leptomycin B impairs the production of interferons in response to DNA stimulation. We further identify a functional nuclear export signal (NES) in cGAS, 169LEKLKL174. Mutating this NES leads to the sequestration of cGAS within the nucleus and the loss of interferon response to cytosolic DNA treatment, and it further determines the key amino acid to L172. Collectively, our data demonstrate that the cytosolic DNA-sensing function of cGAS depends on its presence within the cytoplasm, which is warranted by a functional NES.
    Keywords:  DNA sensor; cGAS; innate immune system; nuclear export signal
    DOI:  https://doi.org/10.1016/j.celrep.2020.108586
  32. J Mol Histol. 2021 Jan 03.
    Wang Z, Shi D, Zhang N, Yuan T, Tao H.
      Studies have shown that miR-217 can induce cell senescence, but its mechanism of action in vascular endothelial cell senescence is less reported. Therefore, this study aimed to investigate how miR-217 plays a role in endothelial cell senescence. Human umbilical vein endothelial cells (HUVECs) were used to replicate the aging model, and the population doubling levels (PDLs) during cell passage were counted. Senescence-associated β-galactosidase (SA-β-gal) staining, Real-time quantitative PCR (RT-qPCR), MTT assay, Transwell, and tube formation were used to detect the effects of miR-217 on young and senescent HUVECs. Targetscan7.2 and luciferase assay predicted and verified the relationship between miR-217 and the target gene, and the expression of silent information regulator 1 (SIRT1) and p53 was detected by RT-qPCR and western blot. In addition, SA-β-gal staining detected the effects of miR-217 inhibitor and SIRT1 on senescent HUVECs. MiR-217 was upregulated in senescent endothelial cells. Overexpression of miR-217 promoted the increase of SA-β-gal positive cells, and inhibited proliferation, migration and angiogenesis during endothelial cell growth. Furthermore, SIRT1 was a target gene of miR-217. Simultaneous silencing of SIRT1 reversed the effect of miR-217 inhibitor on the reduction of SA-β-gal positive-staining cells. Our data suggest that overexpression of miR-217 promoted vascular endothelial cell senescence by targeting the SIRT1/p53 signaling pathway, which may provide a new basis for studying the mechanism of action in vascular endothelial cell senescence.
    Keywords:  Endothelial cell; SIRT1; Senescent; miR-217; p53
    DOI:  https://doi.org/10.1007/s10735-020-09945-x
  33. Cell Death Dis. 2021 Jan 04. 12(1): 27
    Trayssac M, Clarke CJ, Stith JL, Snider JM, Newen N, Gault CR, Hannun YA, Obeid LM.
      Senescence is an antiproliferative mechanism that can suppress tumor development and can be induced by oncogenes such as genes of the Ras family. Although studies have implicated bioactive sphingolipids (SL) in senescence, the specific mechanisms remain unclear. Here, using MCF10A mammary epithelial cells, we demonstrate that oncogenic K-Ras (Kirsten rat sarcoma viral oncogene homolog) is sufficient to induce cell transformation as well as cell senescence-as revealed by increases in the percentage of cells in the G1 phase of the cell cycle, p21WAF1/Cip1/CDKN1A (p21) expression, and senescence-associated β-galactosidase activity (SA-β-gal). Furthermore, oncogenic K-Ras altered SL metabolism, with an increase of long-chain (LC) C18, C20 ceramides (Cer), and very-long-chain (VLC) C22:1, C24 Cer, and an increase of sphingosine kinase 1 (SK1) expression. Since Cer and sphingosine-1-phosphate have been shown to exert opposite effects on cellular senescence, we hypothesized that targeting SK1 could enhance oncogenic K-Ras-induced senescence. Indeed, SK1 downregulation or inhibition enhanced p21 expression and SA-β-gal in cells expressing oncogenic K-Ras and impeded cell growth. Moreover, SK1 knockdown further increased LC and VLC Cer species (C18, C20, C22:1, C24, C24:1, C26:1), especially the ones increased by oncogenic K-Ras. Fumonisin B1 (FB1), an inhibitor of ceramide synthases (CerS), reduced p21 expression induced by oncogenic K-Ras both with and without SK1 knockdown. Functionally, FB1 reversed the growth defect induced by oncogenic K-Ras, confirming the importance of Cer generation in the senescent phenotype. More specifically, downregulation of CerS2 by siRNA blocked the increase of VLC Cer (C24, C24:1, and C26:1) induced by SK1 knockdown and phenocopied the effects of FB1 on p21 expression. Taken together, these data show that targeting SK1 is a potential therapeutic strategy in cancer, enhancing oncogene-induced senescence through an increase of VLC Cer downstream of CerS2.
    DOI:  https://doi.org/10.1038/s41419-020-03281-4
  34. Genome Biol. 2021 Jan 05. 22(1): 17
    Shafik AM, Zhang F, Guo Z, Dai Q, Pajdzik K, Li Y, Kang Y, Yao B, Wu H, He C, Allen EG, Duan R, Jin P.
      BACKGROUND: N6-methyladenosine (m6A) modification is known to impact many aspects of RNA metabolism, including mRNA stability and translation, and is highly prevalent in the brain.RESULTS: We show that m6A modification displays temporal and spatial dynamics during neurodevelopment and aging. Genes that are temporally differentially methylated are more prone to have mRNA expression changes and affect many pathways associated with nervous system development. Furthermore, m6A shows a distinct tissue-specific methylation profile, which is most pronounced in the hypothalamus. Tissue-specific methylation is associated with an increase in mRNA expression and is associated with tissue-specific developmental processes. During the aging process, we observe significantly more m6A sites as age increases, in both mouse and human. We show a high level of overlap between mouse and human; however, humans at both young and old ages consistently show more m6A sites compared to mice. Differential m6A sites are found to be enriched in alternative untranslated regions of genes that affect aging-related pathways. These m6A sites are associated with a strong negative effect on mRNA expression. We also show that many Alzheimer-related transcripts exhibit decreased m6A methylation in a mouse model of Alzheimer's disease, which is correlated with reduced protein levels.
    CONCLUSIONS: Our results suggest that m6A exerts a critical function in both early and late brain development in a spatio-temporal fashion. Furthermore, m6A controls protein levels of key genes involved in Alzheimer's disease-associated pathways, suggesting that m6A plays an important role in aging and neurodegenerative disease.
    Keywords:  Aging; Alternative 3′UTR; Alzheimer’s; Epitranscriptomics; Neurodevelopment; Regulation of mRNA levels; Regulation of protein levels; m6A
    DOI:  https://doi.org/10.1186/s13059-020-02249-z
  35. Nat Commun. 2021 01 04. 12(1): 4
    Chow RD, Majety M, Chen S.
      Age is a major risk factor for severe coronavirus disease-2019 (COVID-19). Here, we interrogate the transcriptional features and cellular landscape of the aging human lung. By intersecting these age-associated changes with experimental data on SARS-CoV-2, we identify several factors that may contribute to the heightened severity of COVID-19 in older populations. The aging lung is transcriptionally characterized by increased cell adhesion and stress responses, with reduced mitochondria and cellular replication. Deconvolution analysis reveals that the proportions of alveolar type 2 cells, proliferating basal cells, goblet cells, and proliferating natural killer/T cells decrease with age, whereas alveolar fibroblasts, pericytes, airway smooth muscle cells, endothelial cells and IGSF21+ dendritic cells increase with age. Several age-associated genes directly interact with the SARS-CoV-2 proteome. Age-associated genes are also dysregulated by SARS-CoV-2 infection in vitro and in patients with severe COVID-19. These analyses illuminate avenues for further studies on the relationship between age and COVID-19.
    DOI:  https://doi.org/10.1038/s41467-020-20323-9
  36. J Cell Biol. 2021 Feb 01. pii: e201911025. [Epub ahead of print]220(2):
    Ma S, Rong Z, Liu C, Qin X, Zhang X, Chen Q.
      DNA double-strand breaks (DSBs) are mainly repaired by c-NHEJ and HR pathways. The enhanced DSB mobility after DNA damage is critical for efficient DSB repair. Although microtubule dynamics have been shown to regulate DSB mobility, the reverse effect of DSBs to microtubule dynamics remains elusive. Here, we uncovered a novel DSB-induced microtubule dynamics stress response (DMSR), which promotes DSB mobility and facilitates c-NHEJ repair. DMSR is accompanied by interphase centrosome maturation, which occurs in a DNA-PK-AKT-dependent manner. Depletion of PCM proteins attenuates DMSR and the mobility of DSBs, resulting in delayed c-NHEJ. Remarkably, DMSR occurs only in G1 or G0 cells and lasts around 6 h. Both inhibition of DNA-PK and depletion of 53BP1 abolish DMSR. Taken together, our study reveals a positive DNA repair mechanism in G1 or G0 cells in which DSBs actively promote microtubule dynamics and facilitate the c-NHEJ process.
    DOI:  https://doi.org/10.1083/jcb.201911025
  37. Mol Cell. 2020 Dec 30. pii: S1097-2765(20)30902-3. [Epub ahead of print]
    Genois MM, Gagné JP, Yasuhara T, Jackson J, Saxena S, Langelier MF, Ahel I, Bedford MT, Pascal JM, Vindigni A, Poirier GG, Zou L.
      DNA replication forks use multiple mechanisms to deal with replication stress, but how the choice of mechanisms is made is still poorly understood. Here, we show that CARM1 associates with replication forks and reduces fork speed independently of its methyltransferase activity. The speeding of replication forks in CARM1-deficient cells requires RECQ1, which resolves reversed forks, and RAD18, which promotes translesion synthesis. Loss of CARM1 reduces fork reversal and increases single-stranded DNA (ssDNA) gaps but allows cells to tolerate higher replication stress. Mechanistically, CARM1 interacts with PARP1 and promotes PARylation at replication forks. In vitro, CARM1 stimulates PARP1 activity by enhancing its DNA binding and acts jointly with HPF1 to activate PARP1. Thus, by stimulating PARP1, CARM1 slows replication forks and promotes the use of fork reversal in the stress response, revealing that CARM1 and PARP1 function as a regulatory module at forks to control fork speed and the choice of stress response mechanisms.
    Keywords:  CARM1; PARP1; PARylation; PrimPol; RECQ1; fork reversal; fork speed; replication fork; replication stress; translesion synthesis
    DOI:  https://doi.org/10.1016/j.molcel.2020.12.010