Age-related loss of muscle mass and function, sarcopenia, has a major impact on the quality of life in the elderly. Among the proposed causes of sarcopenia are mitochondrial dysfunction and accumulated oxidative damage during aging. Dietary restriction (DR), a robust dietary intervention that extends lifespan and modulates age-related pathology in a variety of species has been shown to protect from sarcopenia in rodents. Although the mechanism(s) by which DR modulates aging are still not defined, one potential mechanism is through modulation of oxidative stress and mitochondrial dysfunction. To directly test the protective effect of DR against oxidative stress induced muscle atrophy in vivo, we subjected mice lacking a key antioxidant enzyme, CuZnSOD (Sod1) to DR (40% of ad libitum fed diet). We have previously shown that the Sod1−/− mice exhibit an acceleration of sarcopenia associated with high oxidative stress, mitochondrial dysfunction, and severe neuromuscular innervation defects. Despite the dramatic atrophy phenotype in the Sod1−/− mice, DR led to a reversal or attenuation of reduced muscle function, loss of innervation and muscle atrophy in these mice. DR improves mitochondrial function as evidenced by enhanced Ca2+ regulation and reduction of mitochondrial reactive oxygen species (ROS). Furthermore, we show upregulation of SIRT3 and MnSOD in DR animals, consistent with reduced mitochondrial oxidative stress and reduced oxidative damage in muscle tissue measured as F2- isoprostanes. Collectively, our results demonstrate that DR is a powerful mediator of mitochondrial function, mitochondrial ROS production, and oxidative damage, providing a solid protection against oxidative stress induced neuromuscular defects and muscle atrophy in vivo even under conditions of high oxidative stress.
A spectral analysis approach was developed for detailed study of time-resolved, dynamic changes in vascular smooth muscle cell (VSMC) elasticity and adhesion to identify differences in VSMC from young and aged monkeys. Atomic force microscopy (AFM) was used to measure Young's modulus of elasticity and adhesion as assessed by fibronectin (FN) or anti-beta 1 integrin interaction with the VSMC surface. Measurements demonstrated that VSMC cells from old versus young monkeys had elevated elasticity (21.6 kPa vs 3.5 kPa or a 612% elevation in elastic modulus) and adhesion (86 pN vs 43 pN or a 200% increase in unbinding force). Spectral analysis identified three major frequency components in the temporal oscillation patterns for elasticity (ranging from 1.7×10-3 to 1.9×10-2 Hz in old and 8.4×10-4 to 1.5×10-2 in young) and showed that the amplitude of oscillation was larger (p<0.05) in old than in young at all frequencies. It was also observed that patterns of oscillation in the adhesion data were similar to the elasticity waveforms. Cell stiffness was reduced and the oscillations were inhibited by treatment with cytochalasin D, ML7 or blebbistatin indicating involvement of actin-myosin driven processes. In conclusion, these data demonstrate the efficacy of time-resolved analysis of AFM cell elasticity and adhesion measurements and that it provides a uniquely sensitive method to detect real-time functional differences in biomechanical and adhesive properties of cells. The oscillatory behavior suggests mechanisms governing elasticity and adhesion are coupled and affected differentially during aging which may link these events to changes in vascular stiffness.
Fibronectin; integrins; vascular smooth muscle cell contractile function; Young's modulus; cytoskeleton; mechanotransduction; extracellular matrix adhesion; force measurement; atomic force microscopy
Genome-Wide Association studies (GWAS) offer an unbiased means to understand the genetic basis of traits by identifying single nucleotide polymorphisms (SNPs) linked to causal variants of complex phenotypes. GWAS have identified a host of susceptibility SNPs associated with many important human diseases, including diseases associated with aging. In an effort to understand the genetics of broad resistance to age-associated diseases (i.e. ‘wellness’), we performed a meta-analysis of human GWAS. Toward that end, we compiled 372 GWAS that identified 1,775 susceptibility SNPs to 105 unique diseases and used these SNPs to create a genomic landscape of disease susceptibility. This map was constructed by partitioning the genome into 200 kb ‘bins’ and mapping the 1,775 susceptibility SNPs to bins based on their genomic location. Investigation of these data revealed significant heterogeneity of disease association within the genome, with 92% of bins devoid of disease-associated SNPs. In contrast, 10 bins (0.06%) were significantly (p<0.05) enriched for susceptibility to multiple diseases, 5 of which formed two highly significant peaks of disease association (p<0.0001). These peaks mapped to the Major Histocompatibility (MHC) locus on 6p21 and the INK4/ARF (CDKN2a/b) tumor suppressor locus on 9p21.3. Provocatively, all 10 significantly enriched bins contained genes linked to either inflammation or cellular senescence pathways, and SNPs near regulators of senescence were particularly associated with disease of aging (e.g. cancer, atherosclerosis, type 2 diabetes, glaucoma). This analysis suggests that germline genetic heterogeneity in the regulation of immunity and cellular senescence influences the human health span.
p16INK4a; p14ARF; ANRIL; TERT; longevity
CD4 T cells, and especially T follicular helper cells, are critical for the generation of a robust humoral response to an infection or vaccination. Importantly, immunosenescence affects CD4 T cell function and the accumulation of intrinsic defects decreases the cognate helper functions of these cells. However, much less is known about the contribution of the aged microenvironment to this impaired CD4 T cell response. In the current study, we have employed a preclinical model to determine whether the aged environment contributes to the defects in CD4 T cell functions with aging. Using an adoptive transfer model in mice, we demonstrate for the first time that the aged microenvironment negatively impacts at least three steps of the CD4 T cell response to antigenic stimulation. First, the recruitment of CD4 T cells to the spleen is reduced in aged compared to young hosts, which correlates with dysregulated chemokine expression in the aged organ. Second, the priming of CD4 T cells by DCs is reduced in aged compared to young mice. Finally, naïve CD4 T cells show a reduced transition to a T follicular helper cell phenotype in the aged environment, which impairs the subsequent generation of germinal centers. These studies have provided new insights into how aging impacts the immune system and how these changes influence the development of immunity to infections or vaccinations.
CD4 T cells; dendritic cells; homeostatic chemokines; secondary lymphoid organs; immune defects; T follicular helper cells
Serum dehydroepiandrosterone (DHEA) concentrations decrease ~80% between ages 25 and 75 yr. Aging also results in an increase in arterial stiffness, which is an independent predictor of cardiovascular disease (CVD) risk and mortality. Therefore, it is conceivable that DHEA replacement in older adults could reduce arterial stiffness. We sought to determine if DHEA replacement therapy in older adults reduces carotid augmentation index (AI) and carotid-femoral pulse wave velocity (PWV) as indices of arterial stiffness.
A randomized, double-blind trial was conducted to study the effects of 50 mg/d DHEA replacement on AI (n=92) and PWV (n=51) in women and men aged 65–75 yr. Inflammatory cytokines and sex hormones were measured in fasting serum.
AI decreased in the DHEA group but not in the placebo group (difference between groups, −6±2 AI units, p=0.002). PWV also decreased (difference between groups, −3.5±1.0 m/sec, p=0.001); however, after adjusting for baseline values, the between-group comparison became non-significant (p=0.20). The reductions in AI and PWV were accompanied by decreases in inflammatory cytokines (TNFα and IL-6, p<0.05) and correlated with increases in serum DHEAS (r = −0.31 and −0.37, respectively, p<0.05). The reductions in AI also correlated with free testosterone index (r = −0.23, p=0.03).
DHEA replacement in elderly men and women improves indices of arterial stiffness. Arterial stiffness increases with age and is an independent risk factor for CVD. Therefore the improvements observed in the present study suggest that DHEA replacement might partly reverse arterial aging and reduce CVD risk.
vasculature; augmentation index; aging
Age-related loss of muscle mass and strength (sarcopenia) leads to a decline in physical function and frailty in the elderly. Among the many proposed underlying causes of sarcopenia, mitochondrial dysfunction is inherent in a variety of aged tissues. The intent of this study was to examine the effect of aging on key groups of regulatory proteins involved in mitochondrial biogenesis and how this relates to physical performance in two groups of sedentary elderly participants, classified as high- and low-functioning based on the Short Physical Performance Battery test. Muscle mass was decreased by 38% and 30% in low-functioning elderly (LFE) participants when compared to young and high-functioning elderly (HFE) participants, respectively, and positively correlated to physical performance. Mitochondrial respiration in permeabilized muscle fibers was reduced (41%) in the LFE group when compared to the young, and this was associated with a 30% decline in COX activity. Levels of key metabolic regulators, SIRT3 and PGC-1α were significantly reduced (50%) in both groups of elderly participants when compared to young. Similarly, the fusion protein OPA1 was lower in muscle from elderly subjects, however no changes were detected in Mfn2, Drp1 or Fis1 among the groups. In contrast, protein import machinery (PIM) components Tom22 and cHsp70 were increased in the LFE group when compared to the young. This study suggests that aging in skeletal muscle is associated with impaired mitochondrial function and altered biogenesis pathways, and that this may contribute to muscle atrophy and the decline in muscle performance observed in the elderly population.
aging; sarcopenia; mitochondria; skeletal muscle; PGC-1α
Reactive oxygen species (ROS) modulate aging and aging-related diseases. Dietary composition is critical in modulating lifespan. However, how ROS modulate dietary effects on lifespan remains poorly understood. Superoxide dismutase 1 (SOD1) is a major cytosolic enzyme responsible for scavenging superoxides. Here we investigated the role of SOD1 in lifespan modulation by diet in Drosophila. We found that a high sugar-low protein (HS-LP) diet or low-calorie diet with low-sugar content, representing protein restriction, increased lifespan but not resistance to acute oxidative stress in wild-type flies, relative to a standard base diet. A low sugar-high protein diet had an opposite effect. Our genetic analysis indicated that SOD1 overexpression or dfoxo deletion did not alter lifespan patterns of flies responding to diets. However, sod1 reduction blunted lifespan extension by the HS-LP diet but not the low-calorie diet. HS-LP and low-calorie diets both reduced target-of-rapamycin (TOR) signaling and only the HS-LP diet increased oxidative damage. sod1 knockdown did not affect phosphorylation of S6 kinase, suggesting that SOD1 acts in parallel with or downstream of TOR signaling. Surprisingly rapamycin decreased lifespan in sod1 mutant but not wild-type males fed the standard, HS-LP and low calorie diets, whereas antioxidant N-acetylcysteine only increased lifespan in sod1 mutant males fed the HS-LP diet, when compared to diet-matched controls. Our findings suggest that SOD1 is required for lifespan extension by protein restriction only when dietary sugar is high, and support the context-dependent role of ROS in aging and caution the use of rapamycin and antioxidants in aging interventions.
The variation of individual lifespans, even in highly inbred cohorts of animals and under strictly controlled environmental conditions, is substantial and not well understood. This variation in part could be due to epigenetic variation, which later affects the animal’s physiology and ultimately longevity. Identification of the physiological properties that impact health and lifespan is crucial for longevity research and the development of anti-aging therapies. Here we measured individual circadian and metabolic characteristics in a cohort of inbred F1 hybrid mice and correlated these parameters to their lifespans. We found that mice with innate circadian periods close to 24 hours (revealed during 30 days of housing in total darkness) enjoyed nearly 20% longer lifespans than their littermates, which had shorter or longer innate circadian periods. These findings show that maintenance of a 24 hour intrinsic circadian period is a positive predictor of longevity. Our data suggest that circadian period may be used to predict individual longevity and that processes that control innate circadian period affect aging.
The p16INK4a tumor suppressor gene is a mediator of cellular senescence and has been suggested to be a biomarker of ‘molecular’ age in several tissues including T-cells. To determine the association of both active and suppressed HIV infection with T-cell aging, T-cell p16INK4a expression was compared between 60 HIV+ suppressed subjects, 23 HIV+ untreated subjects, and 18 contemporaneously collected HIV-negative controls, as well as 148 HIV-negative historical samples. Expression did not correlate with chronologic age in untreated HIV+ patients, consistent with an effect of active HIV replication on p16INK4a expression. In patients on cART with suppressed viral loads, however, p16INK4a levels were similar to uninfected controls and correlated with chronologic age, with a trend toward an inverse correlation with CD4 count. These data show that p16INK4a is a reliable biomarker of T cell aging in HIV+ patients with suppressed viral loads and suggest that poor CD4 cell recovery on cART may be associated with increased T-cell expression of p16INK4a, a marker of cellular senescence.
Circadian clocks generate daily rhythms in molecular, cellular, and physiological functions providing temporal dimension to organismal homeostasis. Recent evidence suggests two-way relationship between circadian clocks and aging. While disruption of the circadian clock leads to premature aging in animals, there is also age-related dampening of output rhythms such as sleep/wake cycles and hormonal fluctuations. Decay in the oscillations of several clock genes was recently reported in aged fruit flies, but mechanisms underlying these age-related changes are not understood. We report that the circadian light-sensitive protein CRYPTOCHROME (CRY), is significantly reduced at both mRNA and protein levels in heads of old Drosophila melanogaster. Restoration of CRY using the binary GAL4/UAS system in old flies significantly enhanced the mRNA oscillatory amplitude of several genes involved in the clock mechanism. Flies with CRY overexpressed in all clock cells maintained strong rest/activity rhythms in constant darkness late in life when rhythms were disrupted in most control flies. WE also observed a remarkable extension of healthspan in flies with elevated CRY. Conversely, CRY deficient mutants showed accelerated functional decline and accumulated greater oxidative damage. Interestingly, overexpression of CRY in central clock neurons alone was not sufficient to restore rest/activity rhythms or extend healthspan. Together, these data suggest novel anti-aging functions of CRY and indicate that peripheral clocks play an active role in delaying behavioral and physiological aging.
cryptochrome; circadian clock; aging; healthspan; Drosophila
The severity and mortality rates of acute pancreatitis (AP) are significantly elevated in the elderly population. However, due to a lack of appropriate animal models, the underlying mechanisms for this age-dependent vulnerability remain largely unknown. The purpose of this study was to characterize a murine model of AP, which displays age-associated severity, and to use this model to identify pathophysiologies that are distinctive of the aged with AP. AP was induced in young (4–5 months), middle-aged (12–13 months), and aged (23–25 months) C57BL/6 mice by repeated injection of caerulein, a homologue of the gastrointestinal hormone cholecystokinin. Approximately 10% of aged mice died during AP while young and middle-aged mice showed no mortality. Although both young and aged mice exhibited early signs of edema and inflammation in the pancreas, kidney, and lung, young mice showed signs of recovery within 24 h while aged mice exhibited increasingly severe tissue damage and cell death. There was a significant age-dependent increase in pancreatic neutrophil activation and systemic inflammation as assessed by pancreatic myeloperoxidase (MPO) and plasma interleukin-6 (IL-6) concentration, respectively. Importantly, aged but not young mice with AP showed significantly elevated thrombosis in the lung and kidney as well as a marked increase in plasma concentration of plasminogen activator inhibitor-1 (PAI-1), a primary inhibitor of the fibrinolytic system. These results demonstrate that aging is associated with increased severity of AP characterized by augmented and prolonged pancreatic inflammation and the presence of multiple extra-pancreatic sequelae including thrombosis.
Aging; Acute Pancreatitis; Systemic Inflammation; Multiple Organ Dysfunction Syndrome; Coagulation
Oxidative damage affects protein structure and function. Progressive accumulation of oxidized proteins is considered a putative mechanism of aging; however, empirical evidence supporting their role in aging is inconsistent. This inconsistency may reflect a failure to distinguish damage to particular cellular compartments. We found significant reduction of protein carbonyl in the insoluble, but not the soluble, fraction of liver tissues of long-lived compared to short-lived animals. Of cellular components analyzed, only nuclear protein carbonyl level was uniformly reduced in long-lived compared with short-lived animals. This observation suggests that attenuated accumulation of protein carbonyls in the nucleus, where they can affect multiple aspects of gene expression and DNA repair, might contribute to the longevity in mammalian species.
naked-mole rat; marmoset; bats; protein carbonylation; dietary restriction; oxidative stress
Aging is characterized by a progressive loss of muscle mass and impaired contractility (e.g., decline in force, velocity, and power). Although the slowing of contraction speed in aging muscle is well described, the underlying molecular mechanisms responsible for the decrement in speed are unknown. Myosin heavy chain (MHC) isoforms are the primary molecules determining contractile velocity; however, the contraction speed of single fibers within a given MHC isoform type is variable. Recent evidence proposes that the decline in shortening velocity (Vo) with aging is associated with a decrease in the relative content of essential myosin light chain 3f (MLC3f) isoform. In the current study, we first evaluated the relative content of MLC3f isoform and Vo in adult and old rats. We then used recombinant adenovirus (rAd) gene transfer technology to increase MLC3f protein content in the MHC type II semimembranosus muscle (SM). We hypothesized that (i) aging would decrease the relative MLC3f content and Vo in type II fibers, and (ii) increasing the MLC3f content would restore the age-induced decline in Vo. We found that there was an age-related decrement in relative MLC3f content and Vo in MHC type II fibers. Increasing MLC3f content, as indicated by greater % MLC3f and MLC3f/MLC2f ratio, provided significant protection against age-induced decline in Vo without influencing fiber diameter, force generation, MHC isoform distribution, or causing cellular damage. To the best of our knowledge, these are the first data to demonstrate positive effects of MLC3f against slowing of contractile function in aged skeletal muscle.
contraction velocity; MLC3f; isometric muscle contraction; myofibrillar proteins; sarcopenia; gene delivery
The naked mole-rat (NMR, Heterocephalus glaber) is a long-lived mammal in which spontaneous cancer has not been observed. In order to investigate possible mechanisms for cancer resistance in this species, we studied the properties of skin fibroblasts from the NMR following transduction with oncogenes that cause cells of other mammalian species to form malignant tumors. NMR fibroblasts were transduced with a retrovirus encoding SV40 large T antigen and oncogenic RasG12V. Following transplantation of transduced cells into immunodeficient mice, cells rapidly entered crisis, as evidenced by the presence of anaphase bridges, giant cells with enlarged nuclei, multinucleated cells, and cells with large number of chromosomes or abnormal chromatin material. In contrast, similarly transduced mouse and rat fibroblasts formed tumors that grew rapidly without crisis. Crisis was also observed after >40 population doublings in SV40 TAg/Ras-expressing NMR cells in culture. Crisis in culture was prevented by additional infection of the cells with a retrovirus encoding hTERT (telomerase reverse transcriptase). SV40 TAg/Ras/hTERT-expressing NMR cells formed tumors that grew rapidly in immunodeficient mice without evidence of crisis. Crisis could also be induced in SV40 TAg/Ras-expressing NMR cells by loss of anchorage, but after hTERT transduction cells were able to proliferate normally following loss of anchorage. Thus, rapid crisis is a response of oncogene-expressing NMR cells to growth in an in vivo environment, which requires anchorage independence, and hTERT permits cells to avoid crisis and to achieve malignant tumor growth. The unique reaction of NMR cells to oncogene expression may form part of the cancer resistance of this species.
Naked mole-rat; longevity; cancer resistance; oncogenes; crisis; DNAdamage
In many tissues, mammalian aging is associated with a decline in the replicative and functional capacity of somatic stem cells and other self-renewing compartments. Understanding the basis of this decline is a major goal of aging research. In particular, therapeutic approaches to ameliorate or reverse the age-associated loss of stem function could be of use in clinical geriatrics. Such approaches include attempts to protect stem cells from age-promoting damage, to ‘rejuvenate’ stem cells through the use of pharmacologic agents that mitigate aging-induced alterations in signaling, and to replace lost stem cells through regenerative medicine approaches. Some headway has been made in each of these arenas over the last 18 months including advances in the production of donor-specific totipotent stem cells through induced pluripotency (iPS), gains in our understanding of how tumor suppressor signaling is controlled in self-renewing compartments to regulate aging, and further demonstration of extracellular ‘milieu’ factors that perturb stem cell function with age. This period has also been marked by the recent award of the Nobel Prize in Physiology or Medicine for elucidation of telomeres and telomerase, a topic of critical importance to stem cell aging.
aging; induced pluripotency; senescence; telomere
Heat shock response (HSR) that protects cells from proteotoxic stresses is downregulated in aging, as well as upon replicative senescence of cells in culture. Here we demonstrate that HSR is suppressed in fibroblasts from the patients with segmental progerioid Werner Syndrome, which undergo premature senescence. Similar suppression of HSR was seen in normal fibroblasts, which underwent senescence in response to DNA damaging treatments. The major DNA-damage-induced signaling (DDS) pathways p53–p21 and p38-NF-kB-SASP contributed to the HSR suppression. The HSR suppression was associated with inhibition of both activity and transcription of the heat shock transcription factor Hsf1. This inhibition in large part resulted from the downregulation of SIRT1, which in turn was because of decrease in the expression of the translation regulator HuR. Importantly, we uncovered a positive feedback regulation, where suppression of Hsf1 further activates the p38–NF-κB-SASP pathway, which in turn promotes senescence. Overexpression of Hsf1 inhibited the p38–NFκB-SASP pathway and partially relieved senescence. Therefore, downregulation of Hsf1 plays an important role in the development or in the maintenance of DNA damage signaling-induced cell senescence.
heat shock response; Hsp70; HuR; inflammation; p38; p53; SIRT1
Rapamycin increases lifespan in mice, but whether this represents merely inhibition of lethal neoplastic diseases, or an overall slowing in multiple aspects of aging is currently unclear. We report here that many forms of age-dependent change, including alterations in heart, liver, adrenal glands, endometrium, and tendon, as well as age-dependent decline in spontaneous activity, occur more slowly in rapamycin-treated mice, suggesting strongly that rapamycin retards multiple aspects of aging in mice, in addition to any beneficial effects it may have on neoplastic disease. We also note, however, that mice treated with rapamycin starting at 9 months of age have significantly higher incidence of testicular degeneration and cataracts; harmful effects of this kind will guide further studies on timing, dosage, and tissue-specific actions of rapamycin relevant to the development of clinically useful inhibitors of TOR action.
interventions; longevity pathology; TOR
Cellular senescence suppresses cancer by arresting the proliferation of cells at risk for malignant transformation. Recently, senescent cells were shown to secrete numerous cytokines, growth factors and proteases that can alter the tissue microenvironment and may promote age-related pathology. To identify small molecules that suppress the senescence-associated secretory phenotype (SASP), we developed a screening protocol using normal human fibroblasts and a library of compounds that are approved for human use. Among the promising library constituents was the glucocorticoid corticosterone. Both corticosterone and the related glucocorticoid cortisol decreased the production and secretion of selected SASP components, including several pro-inflammatory cytokines. Importantly, the glucocorticoids suppressed the SASP without reverting the tumor suppressive growth arrest, and were efficacious whether cells were induced to senesce by ionizing radiation or strong mitogenic signals delivered by oncogenic RAS or MAP kinase kinase 6 overexpression. Suppression of the prototypical SASP component IL-6 required the glucocorticoid receptor, which, in the presence of ligand, inhibited IL-1α signaling and NF-κB transactivation activity. Accordingly, co-treatments combining glucocorticoids with the glucocorticoid antagonist RU-486 or recombinant IL-1α efficiently reestablished NF-κB transcriptional activity and IL-6 secretion. Our findings demonstrate feasibility of screening for compounds that inhibit the effects of senescent cells. They further show that glucocorticoids inhibit selected components of the SASP, and suggest that corticosterone and cortisol, two FDA-approved drugs, might exert their effects in part by suppressing senescence-associated inflammation.
aging; cancer; inflammation; IL-6; IL-8; MMP-3
The accumulation of epigenetic changes was proposed to contribute to the age-related increase in the risk for most common diseases. In this study on 230 monozygotic twin pairs (MZ pairs), aged 18 to 89 years old, we investigated the occurrence of epigenetic changes over the adult lifespan. Using mass spectrometry, we investigated variation in global (LINE1) DNA methylation and in DNA methylation at INS, KCNQ1OT1, IGF2, GNASAS, ABCA1, LEP, and CRH, candidate loci for common diseases. Except for KCNQ1OT1, inter-individual variation in locus specific DNA methylation was larger in old individuals than in young individuals, ranging from 1.2 fold larger at ABCA1 (p = 0.010) to 1.6 fold larger at INS (p = 3.7 * 10−07). Similarly, there was more within-MZ-pair discordance in old as compared with young MZ pairs, except for GNASAS, ranging from an 8 % increase in discordance each decade at CRH (p = 8.9 * 10−06) to a 16 % increase each decade at LEP (p = 2.0 * 10−08). Still, old MZ pairs with strikingly similar DNA methylation were also observed at these loci. After 10 year follow-up in elderly twins, the variation in DNA methylation showed a similar pattern of change as observed cross-sectionally. The age-related increase in methylation variation was generally due to unique environmental factors, except for CRH, for which familial factors may play a more important role. In conclusion, sustained epigenetic differences arise from early adulthood to old age and contribute to an increasing discordance of MZ twins during ageing.
Epigenetics; Aging; MZ twin design; Full adult lifespan; DNA methylation; Stochastic variation
Accumulation of DNA damage is implicated in aging. This is supported by the fact that inherited defects in DNA repair can cause accelerated aging of tissues. However, clear-cut evidence for DNA damage accumulation in old age is lacking. Numerous studies report measurement of DNA damage in nuclear and mitochondrial DNA from tissues of young and old organisms, with variable outcomes. Variability results from genetic differences between specimens or the instability of some DNA lesions. To control these variables and test the hypothesis that elderly organisms have more oxidative DNA damage than young organisms, we measured 8,5′-cyclopurine-2′-deoxynucleosides (cPu), which are relatively stable, in tissues of young and old wild-type and congenic progeroid mice. We found that cPu accumulate spontaneously in the nuclear DNA of wild-type mice with age and to a greater extent in DNA repair-deficient progeroid mice, with a similar tissue-specific pattern (liver>kidney>brain). These data, generated under conditions where genetic and environmental variables are controlled, provide strong evidence that DNA repair mechanisms are inadequate to clear endogenous lesions over the lifespan of mammals. The similar, although exaggerated, results obtained from progeroid, DNA repair-deficient mice and old normal mice support the conclusion that DNA damage accumulates with, and likely contributes to aging.
ageing; progeria; DNA damage; nucleotide excision repair; oxidative DNA lesion
Chemokine-dependent migration of T lymphocytes assures recirculation of naïve T cells to secondary lymphoid organs, and tissue specific trafficking of memory-effector T cells. Previous studies carried out in rodents, have demonstrated age-associated modulation of the expression of chemokine receptors such as CXCR4 and CCR5, however, little is known about the molecular mechanisms that regulate receptor expression and turnover in T cells, during advancing age in humans. Our recent results demonstrating increased chemotactic migration in response to CXCL12 in CD4+ T cells obtained from the elderly, as compared to those from young donors, led us to hypothesize that increase in surface expression, due to altered endocytic regulation of CXCR4 on T cells during aging, might be directly responsible for increased migration towards CXCL12. Studies presented here demonstrate a significant increase in the surface expression of CXCR4 in CD4+ T cells from elderly human donors, relative to those from the young. Additionally, CXCL12-mediated endocytosis of CXCR4 was differentially regulated during aging, which could be attributed to alterations in the ubiquitination of CXCR4. Thus, altered ubiquitination of CXCR4 may contribute to the increased surface expression and enhanced T cell migration to chemotactic stimuli in the elderly.
Previous work has shown that primary skin-derived fibroblasts from long-lived pituitary dwarf mutants resist the lethal effects of many forms of oxidative and non-oxidative stress. We hypothesized that increased autophagy may protect fibroblasts of Pit-1dw/dw (Snell dwarf) mice from multiple forms of stress. We found dwarf-derived fibroblasts had higher levels of autophagy, using LC3 and p62 as markers, in responses to amino acid deprivation, hydrogen peroxide, and paraquat. Fibroblasts from dwarf mice also showed diminished phosphorylation of mTOR, S6K and 4EBP1, consistent with the higher levels of autophagy in these cells after stress. Similar results were also observed in fibroblasts from mutant mice lacking growth hormone receptor (GHRKO mice) after amino acid withdrawal. Our results suggested that increased autophagy, regulated by TOR-dependent processes, may contribute to stress resistance in fibroblasts from long-lived mutant mice.
Autophagy; Snell dwarf; GHRKO; Aging; Oxidative Stress; Amino Acid Deprivation
We undertook genetic and non-genetic approaches to investigate the relationship between telomere maintenance and osteoblast differentiation, as well as to uncover a possible link between a known mediator of cellular aging and senile bone loss. Using mouse models of disrupted telomere maintenance molecules, including mutants in the Werner helicase (Wrn−/−), telomerase (Terc−/−) and Wrn−/− Terc−/− double mutants predisposed to accelerated bone loss, we measured telomere dysfunction-induced foci (TIFs) and markers of osteoblast differentiation in mesenchymal progenitor cells (MPCs). We found that telomere maintenance is directly and significantly related to osteoblast differentiation, with dysfunctional telomeres associated with impaired differentiation independent of proliferation state. Telomere-mediated defects in osteoblast differentiation are associated with increased p53/p21 expression and concomitant reduction in RUNX2. Conversely, MPCs from p53−/− mice do not have substantial telomere dysfunction and spontaneously differentiate into osteoblasts. These results suggest critical telomere dysfunction may be a prominent mechanism for age-related osteoporosis and limits MPC differentiation into bone-forming cells via the p53/p21 pathway.
Telomere; telomere dysfunction; aging; osteoporosis; mesenchymal stem cells
Cellular senescence is a defense mechanism in response to molecular damage which accumulates with aging. Correspondingly, the number of senescent cells has been reported to be greater in older than in younger subjects and furthermore associates with age-related pathologies. Inter-individual differences exist in the rate at which a person ages (biological age). Here, we studied whether younger biological age is related to fewer senescent cells in middle- aged individuals with the propensity for longevity, using p16INK4a as a marker for cellular senescence. We observed that a younger biological age associates with lower levels of p16INK4a positive cells in human skin.
p16INK4a; biological age; familial longevity; cellular senescence
Caloric restriction (CR) retards aging in laboratory rodents. No information is available on the effects of long-term CR on physiologic markers of aging and longevity in humans. Heart rate variability (HRV) is a marker for cardiac autonomic functioning. The progressive decline in HRV with aging and the association of higher HRV with better health outcomes are well established. Heart rate variability assessment is a reliable tool by which the effects of CR on autonomic function can be assessed. Time- and frequency-domain analyses compared 24-h HRV in 22 CR individuals aged 35–82 years and 20 age-matched controls eating Western diets (WD). The CR group was significantly leaner than the WD group. Heart rate was significantly lower, and virtually, all HRV values were significantly higher in the CR group than in the WD group (P < 0.002). Heart rate variability in the CR individuals was comparable with published norms for healthy individuals 20 years younger. In addition, when differences in HRAUTHOR: Please define HR. and HRV between CR and WD were compared with previously published changes in HRV induced in healthy adults given atenolol, percent differences in each measure were generally similar in direction and magnitude and suggested declines in sympathetic and increases in parasympathetic modulation of HR and increased circadian variability associated with CR. These findings provide evidence that CR has direct systemic effects that counter the expected age-associated changes in autonomic function so that HRV indexes in CR individuals are similar to those of individuals 20 years younger eating WDs.
calorie restriction; heart rate variability; autonomic function; parasympathetic function; aging; cardiovascular health