bims-senagi Biomed News
on Senescence and aging
Issue of 2021‒01‒24
twenty-five papers selected by
Maria Grazia Vizioli
Mayo Clinic

  1. Aging Cell. 2021 Jan 20. e13296
      Cellular senescence is characterized by an irreversible cell cycle arrest and a pro-inflammatory senescence-associated secretory phenotype (SASP), which is a major contributor to aging and age-related diseases. Clearance of senescent cells has been shown to improve brain function in mouse models of neurodegenerative diseases. However, it is still unknown whether senescent cell clearance alleviates cognitive dysfunction during the aging process. To investigate this, we first conducted single-nuclei and single-cell RNA-seq in the hippocampus from young and aged mice. We observed an age-dependent increase in p16Ink4a senescent cells, which was more pronounced in microglia and oligodendrocyte progenitor cells and characterized by a SASP. We then aged INK-ATTAC mice, in which p16Ink4a -positive senescent cells can be genetically eliminated upon treatment with the drug AP20187 and treated them either with AP20187 or with the senolytic cocktail Dasatinib and Quercetin. We observed that both strategies resulted in a decrease in p16Ink4a exclusively in the microglial population, resulting in reduced microglial activation and reduced expression of SASP factors. Importantly, both approaches significantly improved cognitive function in aged mice. Our data provide proof-of-concept for senolytic interventions' being a potential therapeutic avenue for alleviating age-associated cognitive impairment.
    Keywords:  SASP; aging; brain; cognition; memory; neurodegeneration; senescence; senolytic; telomeres
  2. Nature. 2021 Jan 20.
      Ageing is characterized by the development of persistent pro-inflammatory responses that contribute to atherosclerosis, metabolic syndrome, cancer and frailty1-3. The ageing brain is also vulnerable to inflammation, as demonstrated by the high prevalence of age-associated cognitive decline and Alzheimer's disease4-6. Systemically, circulating pro-inflammatory factors can promote cognitive decline7,8, and in the brain, microglia lose the ability to clear misfolded proteins that are associated with neurodegeneration9,10. However, the underlying mechanisms that initiate and sustain maladaptive inflammation with ageing are not well defined. Here we show that in ageing mice myeloid cell bioenergetics are suppressed in response to increased signalling by the lipid messenger prostaglandin E2 (PGE2), a major modulator of inflammation11. In ageing macrophages and microglia, PGE2 signalling through its EP2 receptor promotes the sequestration of glucose into glycogen, reducing glucose flux and mitochondrial respiration. This energy-deficient state, which drives maladaptive pro-inflammatory responses, is further augmented by a dependence of aged myeloid cells on glucose as a principal fuel source. In aged mice, inhibition of myeloid EP2 signalling rejuvenates cellular bioenergetics, systemic and brain inflammatory states, hippocampal synaptic plasticity and spatial memory. Moreover, blockade of peripheral myeloid EP2 signalling is sufficient to restore cognition in aged mice. Our study suggests that cognitive ageing is not a static or irrevocable condition but can be reversed by reprogramming myeloid glucose metabolism to restore youthful immune functions.
  3. Aging Cell. 2021 Jan 17. e13307
      Lycorine, a natural compound isolated from the traditional Chinese medicinal herb Lycoris radiata, exhibits multiple pharmacological effects, such as anti-inflammatory, antiviral, and anticancer effects. Accumulating evidence also indicates that lycorine might hold the potential to treat age-associated Alzheimer's disease. However, whether lycorine is involved in delaying the onset of cellular senescence and its underlying mechanisms has not been determined. Here, we demonstrate that the salt of lycorine, lycorine hydrochloride, significantly suppressed stress-induced premature cellular senescence (SIPS) by ~2-fold, as determined by senescence-associated beta-galactosidase (SA-β-gal) staining and the expression of p16 and p21. In addition, pretreating cells with lycorine hydrochloride significantly inhibited the expression of CXCL1 and IL1α, two factors of the senescence-associated secreted phenotype (SASP) in SIPS cells. Further experiments revealed that lycorine hydrochloride promoted both the homologous recombination (HR) and nonhomologous end joining (NHEJ) pathways of DNA double-strand break (DSB) repair. Mechanistic studies suggested that lycorine hydrochloride treatment promoted the transcription of SIRT1 and SIRT6, critical longevity genes positively regulating both HR and NHEJ repair pathways, thereby stimulating DSB repair and stabilizing genomes. Inhibiting SIRT1 enzymatic activity abrogated the protective effect of lycorine hydrochloride on delaying the onset of SIPS, repairing DSBs, and restoring genome integrity. In summary, our work indicates that lycorine hydrochloride might hold therapeutic potential for treating age-associated diseases or promoting healthy aging by stabilizing genomes.
    Keywords:  Lycorine hydrochloride; SIRT1; SIRT6; cellular senescence; genome integrity; homologous recombination; nonhomologous end joining
  4. J Neuroinflammation. 2021 Jan 22. 18(1): 32
      Age-related macular degeneration (AMD), a degenerative disease in the central macula area of the neuroretina and the supporting retinal pigment epithelium, is the most common cause of vision loss in the elderly. Although advances have been made, treatment to prevent the progressive degeneration is lacking. Besides the association of innate immune pathway genes with AMD susceptibility, environmental stress- and cellular senescence-induced alterations in pathways such as metabolic functions and inflammatory responses are also implicated in the pathophysiology of AMD. Cellular senescence is an adaptive cell process in response to noxious stimuli in both mitotic and postmitotic cells, activated by tumor suppressor proteins and prosecuted via an inflammatory secretome. In addition to physiological roles in embryogenesis and tissue regeneration, cellular senescence is augmented with age and contributes to a variety of age-related chronic conditions. Accumulation of senescent cells accompanied by an impairment in the immune-mediated elimination mechanisms results in increased frequency of senescent cells, termed "chronic" senescence. Age-associated senescent cells exhibit abnormal metabolism, increased generation of reactive oxygen species, and a heightened senescence-associated secretory phenotype that nurture a proinflammatory milieu detrimental to neighboring cells. Senescent changes in various retinal and choroidal tissue cells including the retinal pigment epithelium, microglia, neurons, and endothelial cells, contemporaneous with systemic immune aging in both innate and adaptive cells, have emerged as important contributors to the onset and development of AMD. The repertoire of senotherapeutic strategies such as senolytics, senomorphics, cell cycle regulation, and restoring cell homeostasis targeted both at tissue and systemic levels is expanding with the potential to treat a spectrum of age-related diseases, including AMD.
    Keywords:  Cellular senescence; Immune aging; Macular degeneration; Microglia; Neuron; Retinal pigment epithelium; SASP
  5. Cells. 2021 Jan 14. pii: E153. [Epub ahead of print]10(1):
      Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature aging disease caused by a mutation in LMNA. A G608G mutation in exon 11 of LMNA is responsible for most HGPS cases, generating a truncated protein called "progerin". Progerin is permanently farnesylated and accumulates in HGPS cells, causing multiple cellular defects such as nuclear dysmorphism, a thickened lamina, loss of heterochromatin, premature senescence, and clustering of Nuclear Pore Complexes (NPC). To identify the mechanism of NPC clustering in HGPS cells, we evaluated post-mitotic NPC assembly in control and HGPS cells and found no defects. Next, we examined the occurrence of NPC clustering in control and HGPS cells during replicative senescence. We reported that NPC clustering occurs solely in the dysmorphic nuclei of control and HGPS cells. Hence, NPC clustering occurred at a higher frequency in HGPS cells compared to control cells at early passages; however, in late cultures with similar senescence index, NPCs clustering occurred at a similar rate in both control and HGPS. Our results show that progerin does not disrupt post-mitotic reassembly of NPCs. However, NPCs frequently cluster in dysmorphic nuclei with a high progerin content. Additionally, nuclear envelope defects that arise during replicative senescence cause NPC clustering in senescent cells with dysmorphic nuclei.
    Keywords:  mitosis; nuclear envelope; nuclear pore; nucleus; progeria; progerin; replicative senescence
  6. Mol Cell. 2021 Jan 12. pii: S1097-2765(20)30958-8. [Epub ahead of print]
      Micronuclei are aberrant nuclear compartments that can form as a result of chromosome mis-segregation. Frequent loss of micronuclear envelope integrity exposes DNA to the cytoplasm, leading to chromosome fragmentation and immune activation. Here, we use micronuclei purification to show that the endoplasmic reticulum (ER)-associated nuclease TREX1 inhibits cGAS activation at micronuclei by degrading micronuclear DNA upon micronuclear envelope rupture. We demonstrate that the ER accesses ruptured micronuclei and plays a critical role in enabling TREX1 nucleolytic attack. TREX1 mutations, previously implicated in immune disease, untether TREX1 from the ER, disrupt TREX1 localization to micronuclei, diminish micronuclear DNA damage, and enhance cGAS activation. These results establish ER-directed resection of micronuclear DNA by TREX1 as a critical regulator of cytosolic DNA sensing in chromosomally unstable cells and provide a mechanistic basis for the importance of TREX1 ER tethering in preventing autoimmunity.
    Keywords:  APE1; BAF; STING; TREX1; cGAS; chromosome instability; chromothripsis; endoplasmic reticulum; micronuclei; nuclear envelope
  7. Cell Rep. 2021 Jan 19. pii: S2211-1247(20)31649-1. [Epub ahead of print]34(3): 108660
      Aging is characterized by loss of proteostasis and mitochondrial homeostasis. Here, we provide bioinformatic evidence of dysregulation of mitochondrial and proteostasis pathways in muscle aging and diseases. Moreover, we show accumulation of amyloid-like deposits and mitochondrial dysfunction during natural aging in the body wall muscle of C. elegans, in human primary myotubes, and in mouse skeletal muscle, partially phenocopying inclusion body myositis (IBM). Importantly, NAD+ homeostasis is critical to control age-associated muscle amyloidosis. Treatment of either aged N2 worms, a nematode model of amyloid-beta muscle proteotoxicity, human aged myotubes, or old mice with the NAD+ boosters nicotinamide riboside (NR) and olaparib (AZD) increases mitochondrial function and muscle homeostasis while attenuating amyloid accumulation. Hence, our data reveal that age-related amyloidosis is a contributing factor to mitochondrial dysfunction and that both are features of the aging muscle that can be ameliorated by NAD+ metabolism-enhancing approaches, warranting further clinical studies.
    Keywords:  NAD(+); aging; amyloid-beta; amyloidosis; inclusion body myositis; mitochondria; nicotinamide riboside; olaparib; proteostasis; skeletal muscle
  8. Int Immunopharmacol. 2021 Jan 15. pii: S1567-5769(20)32133-0. [Epub ahead of print]92 107044
      BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a disease associated with accelerated aging that threatens the lives of people worldwide and imposes heavy social and economic burdens. Cellular senescence is commonly observed in COPD and contributes to aging-related diseases.PURPOSE: To identify the possible molecular pathways modulating cellular senescence in COPD.
    METHODS: MiR-494-3p expression levels in COPD tissues, small airway epithelial cells (SAECs) and BEAS-2B cells were detected by qRT-PCR. After transfection with miR-494-3p mimic or inhibitor in COPD SAECs, miR-494-3p modulation of senescence markers and senescence-associated secretory phenotype (SASP) proteins was detected. A luciferase assay was employed to verify the direct binding of SIRT3 and miR-494-3p. VX745 and c-myc siRNA were used to investigate the regulation of p38MAPK and c-myc by miR-494-3p.
    RESULTS: As a result of oxidative stress, MiR-494-3p was increased via the p38MAPK-c-myc signaling pathway in the lung tissues and cells of patients with COPD, and the increase in miR-494-3p was accompanied by increases in senescence markers (p27, p21 and p16) and SASP proteins (IL-1β, TNF-α, MMP2 and MMP9). MiR-494-3p was directly bound to SIRT3 in SAECs and was involved in cellular senescence. The upregulation of miR-494-3p decreased SIRT3 expression while increasing p27 expression in SAECs. Inhibition of miR-494-3p in SAECs from COPD patients reduced cell cycle arrest and the expression of SASP proteins (IL-1β, TNF-α, MMP2 and MMP9).
    CONCLUSION: MiR-494-3p expression can be induced by oxidative stress via the p38MAPK-c-myc signaling pathway, and miR-494-3p can directly bind to SIRT3 to reduce its expression, leading to increased cellular senescence and thereby contributing to COPD progression.
  9. Biochem Biophys Res Commun. 2021 Jan 16. pii: S0006-291X(21)00026-7. [Epub ahead of print]541 43-49
      Oxidative stress is one of the major causes of cellular senescence in mammalian cells. The excess amount of reactive oxygen species generated by oxygen metabolism is pathogenic and facilitates tissue aging. Lung tissue is more susceptible to oxidative stress than other organs because it is directly exposed to environmental stresses. The aging of lung tissues increases the risk of chronic diseases. Senescent cells accumulate in tissues during aging and contribute to aging-associated morbidity; however, the roles of cellular senescence in lung aging and diseases have not yet been elucidated in detail. To clarify the physiological role of oxidative stress-induced cellular senescence in aging-associated declines in pulmonary function, we herein investigated the effects of the antioxidant N-acetyl-L-cysteine (NAC) on lung cellular senescence and aging in mice. The administration of NAC to 1-year-old mice reduced the expression of senescence-associated genes in lung tissue. Pulmonary function and lung morphology were partly restored in mice administered NAC. Collectively, these results suggest that oxidative stress is a major inducer of cellular senescence in vivo and that the control of oxidative stress may prevent lung aging and diseases.
    Keywords:  Aging; Arf; Lung; NAC; Senescence
  10. EMBO J. 2021 Jan 18. e104296
      The IκB kinase (IKK)-NF-κB pathway is activated as part of the DNA damage response and controls both inflammation and resistance to apoptosis. How these distinct functions are achieved remained unknown. We demonstrate here that DNA double-strand breaks elicit two subsequent phases of NF-κB activation in vivo and in vitro, which are mechanistically and functionally distinct. RNA-sequencing reveals that the first-phase controls anti-apoptotic gene expression, while the second drives expression of senescence-associated secretory phenotype (SASP) genes. The rapidly activated first phase is driven by the ATM-PARP1-TRAF6-IKK cascade, which triggers proteasomal destruction of inhibitory IκBα, and is terminated through IκBα re-expression from the NFKBIA gene. The second phase, which is activated days later in senescent cells, is on the other hand independent of IKK and the proteasome. An altered phosphorylation status of NF-κB family member p65/RelA, in part mediated by GSK3β, results in transcriptional silencing of NFKBIA and IKK-independent, constitutive activation of NF-κB in senescence. Collectively, our study reveals a novel physiological mechanism of NF-κB activation with important implications for genotoxic cancer treatment.
    Keywords:  DNA damage response; IκBα; NF-κB; SASP; senescence
  11. Exp Gerontol. 2021 Jan 13. pii: S0531-5565(21)00016-4. [Epub ahead of print] 111241
      Considerable researches implicate that the circadian clock regulates the responsive rhythms of organs and sets the orderly aging process of cells indirectly. It influences an array of diverse biological process including intestinal flora, peripheral inflammatory responses, and redox homeostasis. People with sleep disoders and other kinds of circadian disruptions are prone to have vascular aging earlier. Meanwhile, those people are always faced with chronic vascular inflammation. It has not been elucidated that the specific mechanism of the interaction between the circadian system and early vascular aging. To explore the biphasic relationship between vascular aging and the circadian system, we summarize what is linking circadian clock with early vascular aging through four major prospect: inflammatory process, oxidative stress response, intestinal flora, and cellular senescence. Meanwhile, we discuss the hypothesis that the deterioration of circadian rhythms may exacerbate the process of early vascular aging, leading to the cardiovascular diseases. It will help us to provide new ideas for understanding the process of vascular aging and exploring the possible ways to design personalized chronotherapies.
    Keywords:  Arterial stiffness; Cellular senescence; Circadian clock; Inflammation response; Vascular aging
  12. RNA Biol. 2021 Jan 21. 1-5
      With advancing age, human muscle loses strength and function, but the molecular causes of these losses are unknown. Skeletal muscle shows an age-dependent decline in the levels of different proteins, but whether such decline is associated with reduced translation has not been studied. To address this gap of knowledge, we used the technique of ribosome profiling to study translation in muscle from middle-aged and old individuals. Using ribosome occupancy as a measure of translation status, several mRNAs showed differential translation with age. Older age was associated with lower translation of myosin and titin isoforms and more broadly with the translation of proteins involved in oxidative phosphorylation encoded by the mitochondrial genome. Based on our findings, we propose that mitochondrial proteins are less translated in old skeletal muscle.
    Keywords:  Ageing; ribosome profiling; skeletal muscle; translation regulation
  13. FEBS J. 2021 Jan 18.
      Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by progressive memory loss and motor impairment. Aging is a major risk factor for neurodegenerative diseases. Neurodegenerative diseases and aging often develop in an irreversible manner and cause a significant socioeconomic burden. When considering their pathogenesis, many studies usually focus on mitochondrial dysfunction and DNA damage. More recently, neuroinflammation, autophagy dysregulation and SIRT1 inactivation were shown to be involved in the pathogenesis of neurodegenerative diseases and aging. In addition, studies uncovered the role of poly (ADP-ribose)-polymerase-1 (PARP1) in neurodegenerative diseases and aging. PARP1 links to a cluster of stress signals, including those originated by inflammation and autophagy dysregulation. In this review, we summarized the recent research progresses on PARP1 in neurodegenerative diseases and aging, with an emphasis on the relationship among PARP1, neuroinflammation, mitochondria and autophagy. We discussed the possibilities of treating neurodegenerative diseases and aging through targeting PARP1.
    Keywords:  Aging; DNA damage; Neurodegenerative diseases; Neuroinflammation; PARP1
  14. Aging Cell. 2021 Jan 23. e13302
      Dietary restriction (DR) and rapamycin extend healthspan and life span across multiple species. We have recently shown that DR in progeroid DNA repair-deficient mice dramatically extended healthspan and trippled life span. Here, we show that rapamycin, while significantly lowering mTOR signaling, failed to improve life span nor healthspan of DNA repair-deficient Ercc1∆/- mice, contrary to DR tested in parallel. Rapamycin interventions focusing on dosage, gender, and timing all were unable to alter life span. Even genetically modifying mTOR signaling failed to increase life span of DNA repair-deficient mice. The absence of effects by rapamycin on P53 in brain and transcription stress in liver is in sharp contrast with results obtained by DR, and appoints reducing DNA damage and transcription stress as an important mode of action of DR, lacking by rapamycin. Together, this indicates that mTOR inhibition does not mediate the beneficial effects of DR in progeroid mice, revealing that DR and rapamycin strongly differ in their modes of action.
    Keywords:  DNA damage repair; aging; dietary restriction; rapamycin; transcription stress
  15. Cartilage. 2021 Jan 20. 1947603520988768
      OBJECTIVE: Advanced glycation end-product (AGE) accumulation is implicated in osteoarthritis (OA) pathogenesis in aging and diabetic populations. Here, we develop a representative nonenzymatic glycation-induced OA cartilage explant culture model and investigate the effectiveness of resveratrol, curcumin, and eugenol in inhibiting AGEs and the structural and biological hallmarks of cartilage degeneration.DESIGN: Bovine cartilage explants were treated with AGE-bovine serum albumin, threose, and ribose to determine the optimal conditions that induce physiological levels of AGEs while maintaining chondrocyte viability. AGE crosslinks, tissue stiffness, cell viability, metabolism and senescence, nitrite release and loss of glycosaminoglycans were assessed. Explants were cotreated with resveratrol, curcumin, or eugenol to evaluate their anti-AGE properties. Blind docking analysis was conducted to estimate binding energies of drugs with collagen II.
    RESULTS: Treatment with 100 mM ribose significantly increased AGE crosslink formation and tissue stiffness, resulting in reduced chondrocyte metabolism and enhanced senescence. Blind docking analysis revealed stronger binding energies of both resveratrol and curcumin than ribose, with glycation sites along a human collagen II fragment, indicating their increased likelihood of competitively inhibiting ribose activity. Resveratrol and curcumin, but not eugenol, successfully inhibited AGE crosslink formation and its associated downstream biological response.
    CONCLUSIONS: We establish a cartilage explant model of OA that recapitulates several aspects of aged human cartilage. We find that resveratrol and curcumin are effective anti-AGE therapeutics with the potential to decelerate age-related and diabetes-induced OA. This in vitro nonenzymatic glycation-induced model provides a tool for screening OA drugs, to simultaneously evaluate AGE-induced biological and mechanical changes.
    Keywords:  advanced glycation end-product (AGE); cartilage; curcumin; eugenol; osteoarthritis; resveratrol
  16. Aging Cell. 2021 Jan 22. e13309
      Aging-associated declines in innate and adaptive immune responses are well documented and pose a risk for the growing aging population, which is predicted to comprise greater than 40 percent of the world's population by 2050. Efforts have been made to improve immunity in aged populations; however, safe and effective protocols to accomplish this goal have not been universally established. Aging-associated chronic inflammation is postulated to compromise immunity in aged mice and humans. Interleukin-37 (IL-37) is a potent anti-inflammatory cytokine, and we present data demonstrating that IL-37 gene expression levels in human monocytes significantly decline with age. Furthermore, we demonstrate that transgenic expression of interleukin-37 (IL-37) in aged mice reduces or prevents aging-associated chronic inflammation, splenomegaly, and accumulation of myeloid cells (macrophages and dendritic cells) in the bone marrow and spleen. Additionally, we show that IL-37 expression decreases the surface expression of programmed cell death protein 1 (PD-1) and augments cytokine production from aged T-cells. Improved T-cell function coincided with a youthful restoration of Pdcd1, Lat, and Stat4 gene expression levels in CD4+ T-cells and Lat in CD8+ T-cells when aged mice were treated with recombinant IL-37 (rIL-37) but not control immunoglobin (Control Ig). Importantly, IL-37-mediated rejuvenation of aged endogenous T-cells was also observed in aged chimeric antigen receptor (CAR) T-cells, where improved function significantly extended the survival of mice transplanted with leukemia cells. Collectively, these data demonstrate the potency of IL-37 in boosting the function of aged T-cells and highlight its therapeutic potential to overcome aging-associated immunosenescence.
    Keywords:  CAR T-cells; PD-1; T-cells; aging; cytokines; inflammation; leukemia; signaling
  17. Rejuvenation Res. 2021 Jan 21.
      Aging is strongly correlated with several non-communicable disorders such as diabetes, obesity, cardiovascular disease, and neurodegenerative conditions. Glucosamine (2-amino-2-deoxy-D-glucose, GlcN) is a naturally occurring amino sugar and is reported to act as a caloric restriction mimetic (CRM). In young and D-galactose-induced accelerated rat aging models, we tested a persistent oral dietary dose of GlcN and evaluated various aging biomarkers in erythrocytes and plasma. A significant increase in the reactive oxygen species (ROS) was observed in GlcN treated young and accelerated senescent rat model. Increased value of Ferric Reducing Antioxidant Potential (FRAP), Superoxide Dismutase (SOD), Catalase (CAT), and Plasma membrane reduced system (PMRS) was observed. We suggest that GlcN induces a mitohormetic impact by a transient increase in ROS. Our findings indicate that GlcN may be a successful CRM.
  18. Mol Cell. 2021 Jan 08. pii: S1097-2765(20)30951-5. [Epub ahead of print]
      Alternative lengthening of telomeres (ALT) is mediated by break-induced replication (BIR), but how BIR is regulated at telomeres is poorly understood. Here, we show that telomeric BIR is a self-perpetuating process. By tethering PML-IV to telomeres, we induced telomere clustering in ALT-associated PML bodies (APBs) and a POLD3-dependent ATR response at telomeres, showing that BIR generates replication stress. Ablation of BLM helicase activity in APBs abolishes telomere synthesis but causes multiple chromosome bridges between telomeres, revealing a function of BLM in processing inter-telomere BIR intermediates. Interestingly, the accumulation of BLM in APBs requires its own helicase activity and POLD3, suggesting that BIR triggers a feedforward loop to further recruit BLM. Enhancing BIR induces PIAS4-mediated TRF2 SUMOylation, and PIAS4 loss deprives APBs of repair proteins and compromises ALT telomere synthesis. Thus, a BLM-driven and PIAS4-mediated feedforward loop operates in APBs to perpetuate BIR, providing a critical mechanism to extend ALT telomeres.
    Keywords:  ALT; APB; BIR; BLM; PIAS4; PML; SUMO; phase separation; replication stress; telomere
  19. Aging Cell. 2021 Jan 20. e13297
      The progressively increasing frailty, morbidity and mortality of aging organisms coincides with, and may be causally related to, their waning ability to adapt to environmental perturbations. Transcriptional responses to challenges, such as oxidative stress or pathogens, diminish with age. This effect is manifest in the declining function of the stress responsive transcription factor Nrf2. Protective gene expression programs that are controlled by the Drosophila Nrf2 homolog, CncC, support homeostasis and longevity. Age-associated chromatin changes make these genes inaccessible to CncC binding and render them inert to signal-dependent transcriptional activation in old animals. In a previous paper, we have reported that overexpression of the CncC dimerization partner Maf-S counteracts this degenerative effect and preserves organism fitness. Building on this work, we show here that Maf-S overexpression prevents loss of chromatin accessibility and maintains gene responsiveness. Moreover, the same outcome, along with an extension of lifespan, can be achieved by inducing CncC target gene expression pharmacologically throughout adult life. Thus, pharmacological or dietary interventions that can preserve stress responsive gene expression may be feasible anti-aging strategies.
    Keywords:  Nrf2; aging; chromatin; drosophila; oxidative stress; transcription
  20. Cells. 2021 Jan 16. pii: E174. [Epub ahead of print]10(1):
      According to the WHO, 38 million individuals were living with human immunodeficiency virus (HIV), 25.4 million of which were using antiretroviral therapy (ART) at the end of 2019. Despite ART-mediated suppression of viral replication, ART is not a cure and is associated with viral persistence, residual inflammation, and metabolic disturbances. Indeed, due to the presence of viral reservoirs, lifelong ART therapy is required to control viremia and prevent disease progression into acquired immune deficiency syndrome (AIDS). Successful ART treatment allows people living with HIV (PLHIV) to achieve a similar life expectancy to uninfected individuals. However, recent studies have illustrated the presence of increased comorbidities, such as accelerated, premature immune aging, in ART-controlled PLHIV compared to uninfected individuals. Studies suggest that both HIV-infection and ART-treatment lead to mitochondrial dysfunction, ultimately resulting in cellular exhaustion, senescence, and apoptosis. Since mitochondria are essential cellular organelles for energy homeostasis and cellular metabolism, their compromise leads to decreased oxidative phosphorylation (OXPHOS), ATP synthesis, gluconeogenesis, and beta-oxidation, abnormal cell homeostasis, increased oxidative stress, depolarization of the mitochondrial membrane potential, and upregulation of mitochondrial DNA mutations and cellular apoptosis. The progressive mitochondrial damage induced by HIV-infection and ART-treatment likely contributes to accelerated aging, senescence, and cellular dysfunction in PLHIV. This review discusses the connections between mitochondrial compromise and cellular dysfunction associated with HIV- and ART-induced toxicities, providing new insights into how HIV and current ART directly impact mitochondrial functions and contribute to cellular senescence and aging in PLHIV. Identifying this nexus and potential mechanisms may be beneficial in developing improved therapeutics for treating PLHIV.
    Keywords:  ART; HIV; ROS; cellular dysfunction; mitochondria; mtDNA
  21. Cell Cycle. 2021 Jan 21. 1-9
      A key to longevity assurance is the nutrient-sensing mTOR pathway. Inhibition of mTOR extends lifespan in a variety of organisms. However, the downstream effectors of the mTOR pathway for lifespan regulation are elusive. In a recent report, we described the role of Maf1 as a critical lifespan regulator downstream of the mTOR pathway in fission yeast. Maf1 is the master negative regulator of RNA polymerase III-directed transcription (e.g. tRNAs and 5S rRNAs) and is regulated by mTOR-mediated phosphorylation. We demonstrated that Maf1 is required for lifespan extension under calorie restriction or when mTOR is inhibited. We also showed that Maf1 prevents DNA damage at tRNA genes, which appears to contribute to lifespan maintenance by Maf1. Here we highlight these observations and present additional results to discuss the role of the mTOR-Maf1-Pol III axis in promoting genomic integrity in the face of DNA replication-transcription conflicts in order to maintain normal lifespan.
    Keywords:  Maf1; RNA polymerase III; aging; genomic integrity; mTOR; replication fork
  22. Nat Commun. 2021 01 20. 12(1): 470
      Healthy aging can be promoted by enhanced metabolic fitness and physical capacity. Mitochondria are chief metabolic organelles with strong implications in aging that also coordinate broad physiological functions, in part, using peptides that are encoded within their independent genome. However, mitochondrial-encoded factors that actively regulate aging are unknown. Here, we report that mitochondrial-encoded MOTS-c can significantly enhance physical performance in young (2 mo.), middle-age (12 mo.), and old (22 mo.) mice. MOTS-c can regulate (i) nuclear genes, including those related to metabolism and proteostasis, (ii) skeletal muscle metabolism, and (iii) myoblast adaptation to metabolic stress. We provide evidence that late-life (23.5 mo.) initiated intermittent MOTS-c treatment (3x/week) can increase physical capacity and healthspan in mice. In humans, exercise induces endogenous MOTS-c expression in skeletal muscle and in circulation. Our data indicate that aging is regulated by genes encoded in both of our co-evolved mitochondrial and nuclear genomes.
  23. Aging Cell. 2021 Jan 19. e13303
      Intramyocellular lipid (IMCL) utilization is impaired in older individuals, and IMCL accumulation is associated with insulin resistance. We hypothesized that increasing muscle total carnitine content in older men would increase fat oxidation and IMCL utilization during exercise, and improve insulin sensitivity. Fourteen healthy older men (69 ± 1 year, BMI 26.5 ± 0.8 kg/m2 ) performed 1 h of cycling at 50% VO2 max and, on a separate occasion, underwent a 60 mU/m2 /min euglycaemic hyperinsulinaemic clamp before and after 25 weeks of daily ingestion of a 220 ml insulinogenic beverage (44.4 g carbohydrate, 13.8 g protein) containing 4.5 g placebo (n = 7) or L-carnitine L-tartrate (n = 7). During supplementation, participants performed twice-weekly cycling for 1 h at 50% VO2 max. Placebo ingestion had no effect on muscle carnitine content or total fat oxidation during exercise at 50% VO2 max. L-carnitine supplementation resulted in a 20% increase in muscle total carnitine content (20.1 ± 1.2 to 23.9 ± 1.7 mmol/kg/dm; p < 0.01) and a 20% increase in total fat oxidation (181.1 ± 15.0 to 220.4 ± 19.6 J/kg lbm/min; p < 0.01), predominantly due to increased IMCL utilization. These changes were associated with increased expression of genes involved in fat metabolism (ACAT1, DGKD & PLIN2; p < 0.05). There was no change in resting insulin-stimulated whole-body or skeletal muscle glucose disposal after supplementation. This is the first study to demonstrate that a carnitine-mediated increase in fat oxidation is achievable in older individuals. This warrants further investigation given reduced lipid turnover is associated with poor metabolic health in older adults.
    Keywords:  carnitine; fat oxidation; insulin resistance; intramyocellular lipid; older adults; skeletal muscle
  24. Int J Mol Sci. 2021 Jan 14. pii: E782. [Epub ahead of print]22(2):
      Post-transcriptional gene regulation is an important step in the regulation of eukaryotic gene expression. Subcellular compartmentalization of RNA species plays a crucial role in the control of mRNA turnover, spatial restriction of protein synthesis, and the formation of macromolecular complexes. Although long noncoding RNAs (lncRNAs) are one of the key regulators of post-transcriptional gene expression, it is not heavily studied whether localization of lncRNAs in subcellular organelles has functional consequences. Here, we report on mitochondrial lncRNAs whose expression fluctuates in the process of cellular senescence. One of the mitochondrial lncRNAs, RPPH1 RNA, is overexpressed and accumulates in mitochondria of senescent fibroblasts, possibly modulated by the RNA-binding protein AUF1. In addition, RPPH1 RNA overexpression promotes spontaneous replicative cellular senescence in proliferating fibroblasts. Using MS2 aptamer-based RNA affinity purification strategy, we identified putative target mRNAs of RPPH1 RNA and revealed that partial complementarity of RPPH1 RNA to its target mRNAs prevents those mRNAs decay in proliferating fibroblasts. Altogether, our results demonstrate the role of mitochondrial noncoding RNA in the regulation of mRNA stability and cellular senescence.
    Keywords:  RNA-binding protein; cellular senescence; mitochondrial long noncoding RNA; posttranscriptional gene regulation
  25. FASEB J. 2021 Feb;35(2): e21340
      The purpose of this study is to determine whether moderate aerobic exercise training improves high-fat diet-induced alterations in mitochondrial function and structure in the skeletal muscle. Male 4-week-old C57BL/6 mice were randomly divided into four groups: control (CON), control plus exercise (CON + EX), high-fat diet (HFD), and high-fat diet plus exercise (HFD + EX). After obesity was induced by 20 weeks of 60% HFD, treadmill exercise training was performed at 13-16 m/min, 40-50 min/day, and 6 days/week for 12 weeks. Mitochondrial structure, function, and dynamics, and mitophagy were analyzed in the skeletal muscle fibers from the red gastrocnemius. Exercise training increased mitochondrial number and area and reduced high-fat diet-induced obesity and hyperglycemia. In addition, exercise training attenuated mitochondrial dysfunction in the permeabilized myofibers, indicating that HFD-induced decrease of mitochondrial O2 respiration and Ca2+ retention capacity and increase of mitochondrial H2 O2 emission were attenuated in the HFD + EX group compared to the HFD group. Exercise also ameliorated HFD-induced imbalance of mitochondrial fusion and fission, demonstrating that HFD-induced decrease in fusion protein levels was elevated, and increase in fission protein levels was reduced in the HFD + EX groups compared with the HFD group. Moreover, dysregulation of mitophagy induced by HFD was mitigated in the HFD + EX group, indicating a decrease in PINK1 protein level. Our findings demonstrated that moderate aerobic exercise training mitigated obesity-induced insulin resistance by improving mitochondrial function, and reversed obesity-induced mitochondrial structural damage by improving mitochondrial dynamics and mitophagy, suggesting that moderate aerobic exercise training may play a therapeutic role in protecting the skeletal muscle against mitochondrial impairments and insulin resistance induced by obesity.
    Keywords:  aerobic exercise; insulin resistance; mitochondrial dynamics; mitochondrial function; skeletal muscle