Nuclear DNA Damage as a Direct Cause of Aging

Exploring DNA Damage and Repair Mechanisms: A Review with Computational Insights

DNA damage is a critical factor contributing to genetic alterations, directly affecting human health, including developing diseases such as cancer and age-related disorders. DNA repair mechanisms play a pivotal role in safeguarding genetic integrity and preventing the onset of these ailments. Over the past decade, substantial progress and pivotal discoveries have been achieved in DNA damage and repair. This comprehensive review paper consolidates research efforts, focusing on DNA repair mechanisms, computational research methods, and associated databases. Our work is a valuable resource for scientists and researchers engaged in computational DNA research, offering the latest insights into DNA-related proteins, diseases, and cutting-edge methodologies. The review addresses key questions, including the major types of DNA damage, common DNA repair mechanisms, the availability of reliable databases for DNA damage and associated diseases, and the predominant computational research methods for enzymes involved in DNA damage and repair.

Causal Associations Between Gut Microbiota, Gut Microbiota-Derived Metabolites, and Alzheimer's Disease: A Multivariable Mendelian Randomization Study

Background

Multiple studies have demonstrated that the gut microbiome is closely related to the onset of Alzheimer's disease, but the causal relationship between the gut microbiome and AD, as well as potential mediating factors, have not been fully explored.

Objective

Our aim is to validate the causal relationship between the gut microbiome and the onset of AD and determine the key mechanism by which the gut microbiome mediates AD through blood metabolites using Mendelian randomization (MR) analysis methods.

Methods

We first conducted bidirectional and mediating MR analyses using gut microbiota, blood amino acid metabolites, and AD-related single nucleotide polymorphisms as research data. In the analysis process, the inverse variance-weighted average method was mainly used as the primary method, with other methods serving as supplementary evidence.

Results

Ultimately, we found that six types of gut bacteria and two blood amino acid metabolites have a causal effect on AD. Subsequent mediation analysis proved that decreased glutamine concentration mediates the negative causal effect of Holdemanella bacteria on AD (mediation ratio of 14.5%), and increased serum alanine concentration mediates the positive causal effect of Parabacteroide bacteria on AD (mediation ratio of 9.4%).

Conclusions

Our study demonstrates the causality of Holdemanella and Parabacteroides bacteria in the onset of AD and suggests that the reduced glutamine and increased alanine serums concentration may be key nodes in mediating this effect.

miR-302d Targeting of CDKN1A Regulates DNA Damage and Steroid Hormone Secretion in Bovine Cumulus Cells

(1) Background: DNA damage in cumulus cells hinders oocyte maturation and affects steroid hormone secretion. It is crucial to identify the key factors that regulate cellular DNA damage and steroid hormone secretion. (2) Methods: Treatment of bovine cumulus cells with bleomycin to induce DNA damage. The effects of DNA damage on cell biology were determined by detecting changes in DNA damage degree, cell cycle, viability, apoptosis, and steroid hormones. It was verified that mir-302d targeted regulation of CDKN1A expression, and then affected DNA damage and steroid hormone secretion in cumulus cells. (3) Results: Bleomycin induced increased DNA damage, decreased G1-phase cells, increased S-phase cells, inhibited proliferation, promoted apoptosis, affected E2 and P4 secretion, increased CDKN1A expression, and decreased miR-302d expression. Knockdown of CDKN1A reduced DNA damage, increased G1-phase cells, decreased G2-phase cells, promoted proliferation, inhibited apoptosis, increased E2 and P4 secretion, and increased the expression of BRCA1, MRE11, ATM, CDK1, CDK2, CCNE2, STAR, CYP11A1, and HSD3B1. The expression of RAD51, CCND1, p53, and FAS was decreased. Overexpression of CDKN1A resulted in the opposite results. miR-302d targets CDKN1A expression to regulate DNA damage and then affects the cell cycle, proliferation, apoptosis, steroid hormone secretion, and the expression of related genes. (4) Conclusions: miR-302d and CDKN1A were candidate molecular markers for the diagnosis of DNA damage in bovine cumulus cells.

Signaling pathways in hair aging

Hair follicle (HF) homeostasis is regulated by various signaling pathways. Disruption of such homeostasis leads to HF disorders, such as alopecia, pigment loss, and hair aging, which is causing severe health problems and aesthetic concerns. Among these disorders, hair aging is characterized by hair graying, hair loss, hair follicle miniaturization (HFM), and structural changes to the hair shaft. Hair aging occurs under physiological conditions, while premature hair aging is often associated with certain pathological conditions. Numerous investigations have been made to determine the mechanisms and explore treatments to prevent hair aging. The most well-known hypotheses about hair aging include oxidative stress, hormonal disorders, inflammation, as well as DNA damage and repair defects. Ultimately, these factors pose threats to HF cells, especially stem cells such as hair follicle stem cells, melanocyte stem cells, and mesenchymal stem cells, which hamper hair regeneration and pigmentation. Here, we summarize previous studies investigating the above mechanisms and the existing therapeutic methods for hair aging. We also provide insights into hair aging research and discuss the limitations and outlook.

In Response to Precision Medicine: Current Subcellular Targeting Strategies for Cancer Therapy

Emerging as a potent anticancer treatment, subcellular targeted cancer therapy has drawn increasing attention, bringing great opportunities for clinical application. Here, two targeting strategies for four main subcellular organelles (mitochondria, lysosome, endoplasmic reticulum, and nucleus), including molecule- and nanomaterial (inorganic nanoparticles, micelles, organic polymers, and others)-based targeted delivery or therapeutic strategies, are summarized. Phototherapy, chemotherapy, radiotherapy, immunotherapy, and "all-in-one" combination therapy are among the strategies covered in detail. Such materials are constructed based on the specific properties and relevant mechanisms of organelles, enabling the elimination of tumors by inducing dysfunction in the corresponding organelles or destroying specific structures. The challenges faced by organelle-targeting cancer therapies are also summarized. Looking forward, a paradigm for organelle-targeting therapy with enhanced therapeutic efficacy compared to current clinical approaches is envisioned.

Response to Ovarian Stimulation for Urgent Fertility Preservation before Gonadotoxic Treatment in BRCA-Pathogenic-Variant-Positive Breast Cancer Patients

BRCA 1/2 pathogenic variants increase the risk of developing early and aggressive breast cancers (BC). For these patients, fertility potential can be directly affected by oncologic treatments. In addition, evidence indicates that BRCA-mutated women had a significant reduction in their ovarian reserve. In order to improve their chances of conception after the completion of cancer treatments, fertility preservation should be proposed before the administration of gonadotoxic drugs, ideally by oocyte vitrification after controlled ovarian hyperstimulation (COH). The present investigation aims to assess the ovarian response to COH in BRCA 1/2-pathogenic-variant carriers diagnosed with BC. Patient characteristics and COH outcomes were compared between BRCA-positive (n = 54) and BRCA-negative (n = 254) patients. The number of oocytes recovered did not differ between the two groups. However, the oocyte maturation rate and the number of mature oocytes obtained (7 (4.5-11.5) vs. 9 (5-14) oocytes, p = 0.05) were significantly lower in the BRCA-mutated patients. Although individualized COH protocols should be discussed, BRCA-mutated patients would benefit from FP before BC occurs, in order to cope with the potential accelerated decline of their ovarian reserve, optimize the success rate of FP by repeating COH cycles, and to preserve the feasibility of PGT-M by collecting a large amount of eggs.

Dietary Supplementation of Silybum marianum Seeds Improved Growth Performance and Upregulated Associated Gene Expression of Muscovy Ducklings (Cairina moschata)

The effect of feeding on diets supplemented with Silybum marianum L. dry seeds (SMS) on growth performance, mortality percentage, biochemical parameters, the expression profile of related genes, and genotoxic effect in Muscovy ducklings was evaluated during a brooding period of 4 weeks. Two hundred and forty one-day-old Muscovy ducks were randomly assigned to four treatment groups (60 ducklings/group), the first group fed on basal diet with no additives (control), and the second (4 g kg-1), third (8 g kg-1), and fourth (12 g kg-1) groups fed the basal diet supplemented with 0, 4, 8, and 12 g kg-1 diet SMS, respectively. A substantial improvement in live body weight (LBW), body weight gain (BWG), and growth rate (GR), and a decrease in feed conversion ratios (FCR) and mortality rate were shown in ducks fed a diet supplemented with either 8 g kg-1 or 12 g kg-1 SMS compared to the other groups. Relevant improvements in liver function, oxidative stress markers, purinergic cell energy, and brain appetite were recorded on ducklings fed diets supplemented with SMS. Moreover, diets which included 8 or 12 g kg-1 SMS positively upregulated the expression of growth hormone gene (GH) and antioxidant genes (SOD1, SOD2, and CAT). These results are consistent with the increase in liver activity SOD and CAT enzymes, resulting in less DNA fragmentation. Consequently, all the aforementioned improvements in biochemical parameters and gene expression profiling may explain the superiority of the treated ducklings compared with the control group. Conclusively, the SMS could be used as a natural feed additive to promote health status and improve the growth performance of small grower ducks during the brooding period.

P16INK4A—More Than a Senescence Marker

Aging is a biological feature that is characterized by gradual degeneration of function in cells, tissues, organs, or an intact organism due to the accumulation of environmental factors and stresses with time. Several factors have been attributed to aging such as oxidative stress and augmented production or exposure to reactive oxygen species, inflammatory cytokines production, telomere shortening, DNA damage, and, importantly, the deposit of senescent cells. These are irreversibly mitotically inactive, yet metabolically active cells. The reason underlying their senescence lies within the extrinsic and the intrinsic arms. The extrinsic arm is mainly characterized by the expression and the secretory profile known as the senescence-associated secretory phenotype (SASP). The intrinsic arm results from the impact of several genes meant to regulate the cell cycle, such as tumor suppressor genes. P16^INK4A is a tumor suppressor and cell cycle regulator that has been linked to aging and senescence. Extensive research has revealed that p16 expression is significantly increased in senescent cells, as well as during natural aging or age-related pathologies. Based on this fact, p16 is considered as a specific biomarker for detecting senescent cells and aging. Other studies have found that p16 is not only a senescence marker, but also a protein with many functions outside of senescence and aging. In this paper, we discuss and shed light on several studies that show the different functions of p16 and provide insights in its role in several biological processes besides senescence and aging.

Crosstalk between Lipid Rafts and Aging: New Frontiers for Delaying Aging

With the rapid aging in the global population, delay of aging has become a hot research topic. Lipid rafts (LRs) are microdomains in the plasma membrane that contain sphingolipids and cholesterol. Emerging evidence indicates an interesting interplay between LRs and aging. LRs and their components are altered with aging. Further, the aging process is strongly influenced by LRs. In recent years, LRs and their component signaling molecules have been recognized to affect aging by interfering with its hallmarks. Therefore, targeting LRs is a promising strategy to delay aging.

Dynamic Spatiotemporal Expression Pattern of the Senescence-Associated Factor p16Ink4a in Development and Aging

A plethora of factors have been attributed to underly aging, including oxidative stress, telomere shortening and cellular senescence. Several studies have shown a significant role of the cyclin-dependent kinase inhibitor p16ink4a in senescence and aging. However, its expression in development has been less well documented. Therefore, to further clarify a potential role of p16 in development and aging, we conducted a developmental expression study of p16, as well as of p19ARF and p21, and investigated their expression on the RNA level in brain, heart, liver, and kidney of mice at embryonic, postnatal, adult, and old ages. P16 expression was further assessed on the protein level by immunohistochemistry. Expression of p16 was highly dynamic in all organs in embryonic and postnatal stages and increased dramatically in old mice. Expression of p19 and p21 was less variable and increased to a moderate extent at old age. In addition, we observed a predominant expression of p16 mRNA and protein in liver endothelial cells versus non-endothelial cells of old mice, which suggests a functional role specifically in liver endothelium of old subjects. Thus, p16 dynamic spatiotemporal expression might implicate p16 in developmental and physiological processes in addition to its well-known function in the build-up of senescence.

Modeling Neuroregeneration and Neurorepair in an Aging Context: The Power of a Teleost Model

Aging increases the risk for neurodegenerative disease and brain trauma, both leading to irreversible and multifaceted deficits that impose a clear societal and economic burden onto the growing world population. Despite tremendous research efforts, there are still no treatments available that can fully restore brain function, which would imply neuroregeneration. In the adult mammalian brain, neuroregeneration is naturally limited, even more so in an aging context. In view of the significant influence of aging on (late-onset) neurological disease, it is a critical factor in future research. This review discusses the use of a non-standard gerontology model, the teleost brain, for studying the impact of aging on neurorepair. Teleost fish share a vertebrate physiology with mammals, including mammalian-like aging, but in contrast to mammals have a high capacity for regeneration. Moreover, access to large mutagenesis screens empowers these teleost species to fill the gap between established invertebrate and rodent models. As such, we here highlight opportunities to decode the factor age in relation to neurorepair, and we propose the use of teleost fish, and in particular killifish, to fuel new research in the neuro-gerontology field.

Genetic variations in DNA-repair genes (XRCC1, 3, and 7) and the susceptibility to hepatocellular carcinoma in a cohort of Egyptians

Chronic hepatitis C (CHC) is a worldwide etiology of chronic hepatic insult particularly in Egypt. DNA-repair systems are responsible for maintaining genomic integrity by countering threats posed by DNA lesions. Deficiency in the repair capacity due to genetic alterations in DNA-repair genes can lead to genomic instability and increased risk of cancer development. The present work aimed at studying the possible association between XRCC1-G28152A (rs25487), XRCC3-C18067T (rs861539), and XRCC7-G6721T (rs7003908) single nucleotide polymorphisms (SNPs) and the susceptibility to hepatocellular carcinoma (HCC) in Egyptian population. The study was conducted on 100 newly diagnosed HCC patients and 100 age- and sex-matched healthy controls. Laboratory workup revealed that all HCC patients have chronic hepatitis C viral infection. Genotyping of the studied SNPs was performed by real-time PCR. The heteromutant genotype of XRCC1 (GA) conferred an almost two-fold increased risk of HCC (OR ,  2.35; 95% CI, 1.33-4.04). Regarding XRCC7, the heteromutant (TG) genotype conferred a two-fold increased risk of HCC (OR ,  2.17; 95% CI, 1.23-3.82). Coinheritance of the polymorphic genotypes of XRCC1 and 7 was significantly higher in HCC cases than controls and was associated with an 11-fold increased risk of HCC (OR , 11.66; 95% CI,  2.77-49.13). The frequency of XRCC3 polymorphic genotypes in HCC patients was close to that of the controls.

Astaxanthin protects oxidative stress mediated DNA damage and enhances longevity in Saccharomyces cerevisiae

Reactive oxygen species (ROS) have long been found to play an important role in oxidative mediated DNA damage. Fortunately, cells possess an antioxidant system that can neutralize ROS. However, oxidative stress occurs when antioxidants are overwhelmed by ROS or impaired antioxidant pathways. This study was carried out to find the protective effect of astaxanthin on the yeast DNA repair-deficient mutant cells under hydrogen peroxide stress. The results showed that astaxanthin enhances the percent cell growth of rad1∆, rad51∆, apn1∆, apn2∆ and ogg1∆ cells. Further, the spot test and colony-forming unit count results confirmed that astaxanthin protects DNA repair mutant cells from oxidative stress. The DNA binding property of astaxanthin studied by in silico and in vitro methods indicated that astaxanthin binds to the DNA in the major and minor groove, and that might protect DNA against oxidative stress induced by Fenton's reagent. The intracellular ROS, 8-OHdG level and the DNA fragmentation as measured by comet tail was reduced by astaxanthin under oxidative stress. Similarly, reduced nuclear fragmentation and chromatin condensation results suggest that astaxanthin might reduce apoptosis. Finally, we show that astaxanthin decreases the accumulation of mutation rate and enhances the longevity of DNA repair-deficient mutants' cells during a chronological lifespan.

The role of transposable elements activity in aging and their possible involvement in laminopathic diseases

Eukaryotic genomes contain a large number of transposable elements, part of which are still active and able to transpose in the host genome. Mobile element activation is repressed to avoid deleterious effects, such as gene mutations or chromosome rearrangements. Control of transposable elements includes a variety of mechanisms comprising silencing pathways, which are based on the production of small non-coding RNAs. Silencing can occur either through transposable element RNA degradation or through the targeting of DNA sequences by heterochromatin formation and consequent transcriptional inhibition. Since the important role of the heterochromatin silencing, the gradual loss of heterochromatin marks in constitutive heterochromatin regions during the aging process promotes derepression of transposable elements, which is considered a cause of the progressive increase in genomic instability and of the activation of inflammatory responses. This review provides an overview of the effects of heterochromatin loss on the activity of transposable elements during the aging process and the possible impact on genome function. In this context, we discuss the possible role of the nuclear lamina, a major player in heterochromatin dynamics, in the regulation of transposable element activity and potential implications in laminopathic diseases.

IL-6 deficiency attenuates p53 protein accumulation in aged male mouse hippocampus

Our earlier studies demonstrated slower age-related memory decline in IL-6-deficient than in control mice. Therefore, in the present study we evaluated the effect of IL-6 deficiency and aging on expression of p53, connected with accumulation of age-related cellular damages, in hippocampus of 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and wild type control (WT) mice. The accumulation of p53 protein in hippocampus of aged IL-6KO mice was significantly lower than in aged WT ones, while p53 mRNA level was significantly higher in IL-6-deficient mice, what indicates that the effect was independent on p53 transcription. Presence of few apoptotic cells in hippocampal dentate gyrus and lack of changes in levels of pro-apoptotic Bax, antiapoptotic Bcl-2, as well as in p21 protein in aged animals of both genotypes, points to low transcriptional activity of p53, especially in aged WT mice. Because the amount of p53 protein did not correlate with the level of Mdm2 protein, its main negative regulator, other than Mdm2-dependent mechanism was involved in p53 build-up. Significantly higher mRNA levels of autophagy-associated genes: Pten, Tsc2, and Dram1 in IL-6KO mice, in conjunction with significantly lower amount of Bcl-2 protein in 4-month-old IL-6KO mice, suggests that lack of IL-6/STAT3/Bcl-2 signaling could account for better autophagy performance in these mice, preventing excessive accumulation of proteins. Taken together, attenuated p53 protein build-up, absence of enhanced apoptosis, and transcriptional up-regulation of autophagy-associated genes imply that IL-6 deficiency may protect hippocampus from age-related accumulation of cellular damages.

Aging Neurovascular Unit and Potential Role of DNA Damage and Repair in Combating Vascular and Neurodegenerative Disorders

Progressive neurological deterioration poses enormous burden on the aging population with ischemic stroke and neurodegenerative disease patients, such as Alzheimers’ disease and Parkinson’s disease. The past two decades have witnessed remarkable advances in the research of neurovascular unit dysfunction, which is emerging as an important pathological feature that underlies these neurological disorders. Dysfunction of the unit allows penetration of blood-derived toxic proteins or leukocytes into the brain and contributes to white matter injury, disturbed neurovascular coupling and neuroinflammation, which all eventually lead to cognitive dysfunction. Recent evidences suggest that aging-related oxidative stress, accumulated DNA damage and impaired DNA repair capacities compromises the genome integrity not only in neurons, but also in other cell types of the neurovascular unit, such as endothelial cells, astrocytes and pericytes. Combating DNA damage or enhancing DNA repair capacities in the neurovascular unit represents a promising therapeutic strategy for vascular and neurodegenerative disorders. In this review, we focus on aging related mechanisms that underlie DNA damage and repair in the neurovascular unit and introduce several novel strategies that target the genome integrity in the neurovascular unit to combat the vascular and neurodegenerative disorders in the aging brain.

Depletion of the RNA binding protein HNRNPD impairs homologous recombination by inhibiting DNA-end resection and inducing R-loop accumulation

DNA double strand break (DSB) repair through homologous recombination (HR) is crucial to maintain genome stability. DSB resection generates a single strand DNA intermediate, which is crucial for the HR process. We used a synthetic DNA structure, mimicking a resection intermediate, as a bait to identify proteins involved in this process. Among these, LC/MS analysis identified the RNA binding protein, HNRNPD. We found that HNRNPD binds chromatin, although this binding occurred independently of DNA damage. However, upon damage, HNRNPD re-localized to γH2Ax foci and its silencing impaired CHK1 S345 phosphorylation and the DNA end resection process. Indeed, HNRNPD silencing reduced: the ssDNA fraction upon camptothecin treatment; AsiSI-induced DSB resection; and RPA32 S4/8 phosphorylation. CRISPR/Cas9-mediated HNRNPD knockout impaired in vitro DNA resection and sensitized cells to camptothecin and olaparib treatment. We found that HNRNPD interacts with the heterogeneous nuclear ribonucleoprotein SAF-A previously associated with DNA damage repair. HNRNPD depletion resulted in an increased amount of RNA:DNA hybrids upon DNA damage. Both the expression of RNase H1 and RNA pol II inhibition recovered the ability to phosphorylate RPA32 S4/8 in HNRNPD knockout cells upon DNA damage, suggesting that RNA:DNA hybrid resolution likely rescues the defective DNA damage response of HNRNPD-depleted cells.

Effect of eluates from zirconia-modified glass ionomer cements on DNA double-stranded breaks in human gingival fibroblast cells

OBJECTIVE

To formulate novel glass ionomer cements (GICs) containing zirconia (nanoparticles (NPs) and micro-particles (MPs)) and investigate the genotoxic effect of their eluates on DNA double-strand breaks of human gingival fibroblasts (HGFs) in vitro using a γ-H2AX fluorescent assay.

METHODS

GIC (control, C), 10%ZrO₂NPsGIC (T1) and 10%ZrO₂MPsGIC (T2) were prepared per the manufacturer's instructions (hand-mixed, P/L=3.4:1w/w%). Dulbecco's modified Eagle's medium (DMEM) was used as the culture medium for HGFs and for eluate preparation. Eluates were collected from all specimens (n=5/g, 5×2mm) after 24h and used for XTT to obtain the EC₅₀ using Graph Pad Prism4. A γ-H2AX immunofluorescence assay was performed to detect DSBs in HGFs. The mean foci per cells and percentage of free foci cells were statistically compared (one-way ANOVA with Tamhane's post hoc and Chi-square respectively) (p<0.05).

RESULTS

(1) EC₅₀ ranged from 31 to 36%. 5% and 20% eluate concentrations were selected for the genotoxicity test. (2) Cells exposed to eluates from T1 had lower mean foci per cell than cells in T2 and C eluates (p<0.05). Only cells in T1 at 5% had lower mean foci cell than medium (p<0.05). (3) T1 and C at both concentration showed a higher, but not significant, percentage of free foci cells than negative control (medium). At 20% eluate concentration T2 had a lower percentage of free foci cells than C (p<0.05).

SIGNIFICANCE

Nano-zirconia GIC and micro-zirconia GIC were formulated. GIC and both zirconia modified GICs had no genotoxic effect on HGFs in vitro. Further studies related to physical properties should be performed to determine the future clinical applications for these novel nanomaterials.

Age-associated increase of thyroid hormone receptor β gene promoter methylation coexists with decreased gene expression

PURPOSE

It is not established if healthy aging of the thyroid axis is associated with alterations other than changes in hormone secretion.

METHODS

The expression of thyroid hormone receptor β gene (THRB) was analyzed in peripheral blood mononuclear cells (PBMC) obtained from young, elderly, and long-lived individuals. The interaction between the 3'UTR of TRβ1 mRNA and selected miRNAs was measured using pmirGLO reporter vector. Methylation of the THRB CpG island was analyzed using methylation-sensitive restriction/RT-PCR and bisulfite sequencing methods.

RESULTS

Old age was associated with a significantly lower amount of total TRβ mRNA (p = 0.033) and of TRβ1 mRNA (p = 0.02). Older age was also associated with significantly higher methylation of the THRB promoter (restriction/RT-PCR: p = 0.0023, bisulfite sequencing: p = 0.0004). Higher methylation corresponded to a lower expression of the THRB mRNA, but this correlation did not reach the level of significance. miR-26a interacted with two sites in the 3'UTR of the TRβ1 mRNA leading to the decrease of the reporter protein activity (p < 0.0001 and p = 0.0005), and miR-496 interacted with one of the two putative binding sites which also decreased the reporter protein activity (p < 0.0001). Analysis of the expression of miR-21, miR-26a, miR-146a, miR-181a, miR-221, and miR-496 showed that the expression of miR-26a was significantly decreased in old subjects (p = 0.017), while the levels of other miRNAs were unaffected.

CONCLUSIONS

Age-related decrease of THRB expression in PBMC of elderly and long-lived humans might be, in part, a result of the increased methylation of its promoter, but is unrelated to the activity of the miRNAs analyzed here.

DNA damage and neurodegenerative phenotypes in aged Ciz1 null mice

Cell-cycle dysfunction and faulty DNA repair are closely intertwined pathobiological processes that may contribute to several neurodegenerative disorders. CDKN1A interacting zinc finger protein 1 (CIZ1) plays a critical role in DNA replication and cell-cycle progression at the G1/S checkpoint. Germline or somatic variants in CIZ1 have been linked to several neural and extra-neural diseases. Recently, we showed that germline knockout of Ciz1 is associated with motor and hematological abnormalities in young adult mice. However, the effects of CIZ1 deficiency in much older mice may be more relevant to understanding age-related declines in cognitive and motor functioning and age-related neurologic disorders such as isolated dystonia and Alzheimer disease. Mouse embryonic fibroblasts from Ciz1^-/- mice showed abnormal sensitivity to the effects of γ-irradiation with persistent DNA breaks, aberrant cell-cycle progression, and apoptosis. Aged (18-month-old) Ciz1^-/- mice exhibited marked deficits in motor and cognitive functioning, and, in brain tissues, overt DNA damage, NF-κB upregulation, oxidative stress, vascular dysfunction, inflammation, and cell death. These findings indicate that the deleterious effects of CIZ1 deficiency become more pronounced with aging and suggest that defects of cell-cycle control and associated DNA repair pathways in postmitotic neurons could contribute to global neurologic decline in elderly human populations. Accordingly, the G1/S cell-cycle checkpoint and associated DNA repair pathways may be targets for the prevention and treatment of age-related neurodegenerative processes.

The activated DNA double-strand break repair pathway in cumulus cells from aging patients may be used as a convincing predictor of poor outcomes after in vitro fertilization-embryo transfer treatment

Women with advanced maternal age exhibit low anti-Müllerian hormone (AMH) levels and an altered follicular environment, which is associated with poor oocyte quality and embryonic developmental potential. However, the underlying mechanism is poorly understood. The present study aimed to assesswhether aging patients exhibit an activated DNA double-strandbreak (DSB) repair pathway in cumulus cells and thus, an association with poor outcomes after in vitro fertilization-embryo transfer (IVF-ET) treatment. Cumulus cells from young (≤29 y) and aging (≥37 y) human female patients were collected after oocyte retrieval. Our results indicated that aging patients showed a higher rate of γ-H2AX-positive cells than in young patients (24.33±4.55 vs.12.40±2.31, P<0.05). We also found that the mRNA expression levels of BRCA1, ATM, MRE11 and RAD51 were significantly elevated in aging cumulus cells. Accordingly, significantly increased protein levels of phospho-H2AX, BRCA1, ATM, MRE11 and RAD51 could be observed in aging cumulus cells. Moreover, aging cumulus cells showed a more frequent occurrence of early apoptosis than young cumulus cells. This study found that increases in DSBs and the activation of the repair pathway are potential indicators that may be used to predictoutcomes after IVF-ET treatment.

Streptococcus pneumoniae's Virulence and Host Immunity: Aging, Diagnostics, and Prevention

Streptococcus pneumoniae is an infectious pathogen responsible for millions of deaths worldwide. Diseases caused by this bacterium are classified as pneumococcal diseases. This pathogen colonizes the nasopharynx of its host asymptomatically, but overtime can migrate to sterile tissues and organs and cause infections. Pneumonia is currently the most common pneumococcal disease. Pneumococcal pneumonia is a global health concern and vastly affects children under the age of five as well as the elderly and individuals with pre-existing health conditions. S. pneumoniae has a large selection of virulence factors that promote adherence, invasion of host tissues, and allows it to escape host immune defenses. A clear understanding of S. pneumoniae's virulence factors, host immune responses, and examining the current techniques available for diagnosis, treatment, and disease prevention will allow for better regulation of the pathogen and its diseases. In terms of disease prevention, other considerations must include the effects of age on responses to vaccines and vaccine efficacy. Ongoing work aims to improve on current vaccination paradigms by including the use of serotype-independent vaccines, such as protein and whole cell vaccines. Extending our knowledge of the biology of, and associated host immune response to S. pneumoniae is paramount for our improvement of pneumococcal disease diagnosis, treatment, and improvement of patient outlook.

Genomic Approach to Understand the Association of DNA Repair with Longevity and Healthy Aging Using Genomic Databases of Oldest-Old Population

Aged population is increasing worldwide due to the aging process that is inevitable. Accordingly, longevity and healthy aging have been spotlighted to promote social contribution of aged population. Many studies in the past few decades have reported the process of aging and longevity, emphasizing the importance of maintaining genomic stability in exceptionally long-lived population. Underlying reason of longevity remains unclear due to its complexity involving multiple factors. With advances in sequencing technology and human genome-associated approaches, studies based on population-based genomic studies are increasing. In this review, we summarize recent longevity and healthy aging studies of human population focusing on DNA repair as a major factor in maintaining genome integrity. To keep pace with recent growth in genomic research, aging- and longevity-associated genomic databases are also briefly introduced. To suggest novel approaches to investigate longevity-associated genetic variants related to DNA repair using genomic databases, gene set analysis was conducted, focusing on DNA repair- and longevity-associated genes. Their biological networks were additionally analyzed to grasp major factors containing genetic variants of human longevity and healthy aging in DNA repair mechanisms. In summary, this review emphasizes DNA repair activity in human longevity and suggests approach to conduct DNA repair-associated genomic study on human healthy aging.

Alu siRNA to increase Alu element methylation and prevent DNA damage

Global DNA hypomethylation promoting genomic instability leads to cancer and deterioration of human health with age.

AIM

To invent a biotechnology that can reprogram this process.

METHODS

We used Alu siRNA to direct Alu interspersed repetitive sequences methylation in human cells. We evaluated the correlation between DNA damage and Alu methylation levels.

RESULTS

We observed an inverse correlation between Alu element methylation and endogenous DNA damage in white blood cells. Cells transfected with Alu siRNA exhibited high Alu methylation levels, increased proliferation, reduced endogenous DNA damage and improved resistance to DNA damaging agents.

CONCLUSION

Alu methylation stabilizes the genome by preventing accumulation of DNA damage. Alu siRNA could be useful for evaluating reprograming of the global hypomethylation phenotype in cancer and aging cells.

Control of DNA integrity in skeletal muscle under physiological and pathological conditions

Skeletal muscle is a highly oxygen-consuming tissue that ensures body support and movement, as well as nutrient and temperature regulation. DNA damage induced by reactive oxygen species is present in muscles and tends to accumulate with age. Here, we present a summary of data obtained on DNA damage and its implication in muscle homeostasis, myogenic differentiation and neuromuscular disorders. Controlled and transient DNA damage appears to be essential for muscular homeostasis and differentiation while uncontrolled and chronic DNA damage negatively affects muscle health.

The Emerging Role of GLP-1 Receptors in DNA Repair: Implications in Neurological Disorders

Glucagon-like peptide-1 (GLP-1) is originally found as a metabolic hormone (incretin) that is able to regulate blood-glucose levels via promoting synthesis and secretion of insulin. GLP-1 and many analogues are approved for treatment of type II diabetes. Accumulating results imply that GLP-1 performs multiple functions in various tissues and organs beyond regulation of blood-glucose. The neuroprotective function of GLP-1 has been extensively explored during the past two decades. Three of our previous studies have shown that apurinic/apyrimidinic endonuclease 1 (APE1) is the only protein of the base excision repair (BER) pathway able to be regulated by oxidative stress or exogenous stimulations in rat primary cortical neurons. In this article, we review the role of APE1 in neurodegenerative diseases and its relationship to neuroprotective mechanisms of the activated GLP-1 receptor (GLP-1R) in neurodegenerative disorders. The purpose of this article is to provide new insight, from the aspect of DNA damage and repair, for studying potential treatments in neurodegenerative diseases.

Simple and fast quantification of DNA damage by real-time PCR, and its application to nuclear and mitochondrial DNA from multiple tissues of aging zebrafish

We describe a real-time (rt) PCR-based method of quantifying DNA damage, adapted from the long-run rtPCR method of DNA damage quantification (LORD-Q) developed by Lehle et al. (Nucleic Acids Res 42(6):e41, 2014). We show that semi-long run rtPCR, which generates amplicons half the length of those generated in LORD-Q, provides equivalent sensitivity for detecting low lesion frequencies, and better sensitivity for detecting high frequencies. The smaller amplicon size greatly facilitates PCR optimization and allows greater flexibility in the use of detection dyes, and a modified data analysis method simplifies the calculation of lesion frequency. The method was used to measure DNA damage in the nuclear and mitochondrial genomes of different tissues in zebrafish of different ages. We find that nuclear DNA damage generally increases with age, and that the amount of mitochondrial DNA damage varies substantially between tissues, increasing with age in liver and brain but not in heart or skeletal muscle, the latter having the highest levels of damage irrespective of age.

Latitudinal and age-specific patterns of larval mortality in the damselfly Lestes sponsa: Senescence before maturity?

Latitudinal differences in life history traits driven by differences in seasonal time constraints have been widely documented. Yet, latitudinal patterns in (age-specific) mortality rates have been poorly studied. Here, we studied latitudinal differences in pre-adult age-specific mortality patterns in the strictly univoltine damselfly Lestes sponsa. We compared individuals from three latitudes reared from the egg stage in the laboratory at temperatures and photoperiods simulating those at the latitude of origin (main experiment) and under common-garden conditions at a fixed temperature and photoperiod (supplementary experiment). Results from the main experiment showed that the high-latitude population exhibited higher mortality rates than the central and southern populations, likely reflecting a cost of their faster development. Age-specific mortality patterns, also indicated higher ageing rates in the high-latitude compared to the low-latitude population, which likely had a genetic basis. The strong within-population variation in hatching dates in the low-latitude population caused variation in mortality rates; individuals that hatched later showed higher mortality rates presumably due to their shorter development times compared to larvae that hatched earlier. In both experiments, larvae from all three latitudes showed accelerated mortality rates with age, which is consistent with a pattern of senescence before adulthood.

Interacting effects of early dietary conditions and reproductive effort on the oxidative costs of reproduction

The hypothesis that oxidative damage accumulation can mediate the trade-off between reproduction and lifespan has recently been questioned. However, in captive conditions, studies reporting no evidence in support of this hypothesis have usually provided easy access to food which may have mitigated the cost of reproduction. Here, I test the hypothesis that greater investment in reproduction should lead to oxidative damage accumulation and telomere loss in domestic zebra finches Taeniopygia guttata. Moreover, since the change or fluctuation in diet composition between early and late postnatal period can impair the ability to produce antioxidant defences in zebra finches, I also tested if early nutritional conditions (constant vs fluctuating early diet) influenced the magnitude of any subsequent costs of reproduction (e.g., oxidative damage and/or telomere shortening). In comparison to pairs with reduced broods, the birds that had to feed enlarged broods showed a higher level of oxidative DNA damage (8-OHdG), but brood size had no effect on telomeres. Fluctuating early diet composition reduced the capacity to maintain the activity of endogenous antioxidants (GPx), particularly when reproductive costs were increased (enlarged brood). The decline in GPx in birds feeding enlarged broods was accompanied by a change in bill colouration. This suggests that birds with lower endogenous antioxidant defences might have strategically increased the mobilization of antioxidants previously stored in other tissues (i.e., bill and liver) and thus, preventing an excessive accumulation of damage during reproduction.

Variation and Evolution of the Meiotic Requirement for Crossing Over in Mammals

The segregation of homologous chromosomes at the first meiotic division is dependent on the presence of at least one well-positioned crossover per chromosome. In some mammalian species, however, the genomic distribution of crossovers is consistent with a more stringent baseline requirement of one crossover per chromosome arm. Given that the meiotic requirement for crossing over defines the minimum frequency of recombination necessary for the production of viable gametes, determining the chromosomal scale of this constraint is essential for defining crossover profiles predisposed to aneuploidy and understanding the parameters that shape patterns of recombination rate evolution across species. Here, I use cytogenetic methods for in situ imaging of crossovers in karyotypically diverse house mice (Mus musculus domesticus) and voles (genus Microtus) to test how chromosome number and configuration constrain the distribution of crossovers in a genome. I show that the global distribution of crossovers in house mice is thresholded by a minimum of one crossover per chromosome arm, whereas the crossover landscape in voles is defined by a more relaxed requirement of one crossover per chromosome. I extend these findings in an evolutionary metaanalysis of published recombination and karyotype data for 112 mammalian species and demonstrate that the physical scale of the genomic crossover distribution has undergone multiple independent shifts from one crossover per chromosome arm to one per chromosome during mammalian evolution. Together, these results indicate that the chromosomal scale constraint on crossover rates is itself a trait that evolves among species, a finding that casts light on an important source of crossover rate variation in mammals.

Activation of GLP-1 Receptor Enhances Neuronal Base Excision Repair via PI3K-AKT-Induced Expression of Apurinic/Apyrimidinic Endonuclease 1

Glucagon-like peptide-1 (GLP-1) is an intestinal-secreted incretin that increases cellular glucose up-take to decrease blood sugar. Recent studies, however, suggest that the function of GLP-1 is not only to decrease blood sugar, but also acts as a neurotrophic factor that plays a role in neuronal survival, neurite outgrowth, and protects synaptic plasticity and memory formation from effects of β-amyloid. Oxidative DNA damage occurs during normal neuron-activity and in many neurological diseases. Our study describes how GLP-1 affected the ability of neurons to ameliorate oxidative DNA damage. We show that activation of GLP-1 receptor (GLP-1R) protect cortical neurons from menadione induced oxidative DNA damage via a signaling pathway involving enhanced DNA repair. GLP-1 stimulates DNA repair by activating the cyclic AMP response element binding protein (CREB) which, consequently, induces the expression of apurinic/apyrimidinic endonuclease 1 (APE1), a key enzyme in the base excision DNA repair (BER) pathway. In this study, APE1 expression was down-regulated as a consequence phosphatidylinositol-3 kinase (PI3K) suppression by the inhibitor LY294002, but not by the suppression of MEK activity. Ischemic stroke is typically caused by overwhelming oxidative-stress in brain cells. Administration of exentin-4, an analogue of GLP-1, efficiently enhanced DNA repair in brain cells of ischemic stroke rats. Our study suggests that a new function of GLP-1 is to elevate DNA repair by inducing the expression of the DNA repair protein APE1.

Age-associated de-repression of retrotransposons in the Drosophila fat body, its potential cause and consequence

Eukaryotic genomes contain transposable elements (TE) that can move into new locations upon activation. Since uncontrolled transposition of TEs, including the retrotransposons and DNA transposons, can lead to DNA breaks and genomic instability, multiple mechanisms, including heterochromatin‐mediated repression, have evolved to repress TE activation. Studies in model organisms have shown that TEs become activated upon aging as a result of age‐associated deregulation of heterochromatin. Considering that different organisms or cell types may undergo distinct heterochromatin changes upon aging, it is important to identify pathways that lead to TE activation in specific tissues and cell types. Through deep sequencing of isolated RNAs, we report an increased expression of many retrotransposons in the old Drosophila fat body, an organ equivalent to the mammalian liver and adipose tissue. This de‐repression correlates with an increased number of DNA damage foci and decreased level of Drosophila lamin‐B in the old fat body cells. Depletion of the Drosophila lamin‐B in the young or larval fat body results in a reduction of heterochromatin and a corresponding increase in retrotransposon expression and DNA damage. Further manipulations of lamin‐B and retrotransposon expression suggest a role of the nuclear lamina in maintaining the genome integrity of the Drosophila fat body by repressing retrotransposons.

NAD+ as the Link Between Oxidative Stress, Inflammation, Caloric Restriction, Exercise, DNA Repair, Longevity, and Health Span

Oxidative stress and decreased DNA damage repair in vertebrates increase with age also due to lowered cellular NAD+. NAD+ depletion may play a major role in the aging process at the cellular level by limiting (1) energy production, (2) DNA repair, and (3) genomic signaling. In this study, we hypothesize that it is not NAD+ as a cofactor in redox reactions and coenzyme in metabolic processes that has the ultimate role in aging, but rather the role of NAD+ in cellular signaling when used as substrate for sirtuins (SIRT1-7 in mammals) and PARPs [Poly(ADP-ribose) polymerases]. Both sirtuins and PARPs influence many transcription factors and can affect gene expression. As a signaling molecule, NAD+ is consumed in the reaction donating ADP-ribose and releasing nicotinamide (NAM) as a by-product. It seems that aging at the cellular level is associated with a decline of NAD+ and that NAD+ restoration can reverse phenotypes of aging by inducing cellular repair and stress resistance. Adequate intracellular NAD+ concentrations may be an important longevity assurance factor, while lowered cellular NAD+ concentration may negatively influence the life span.

Whole-Body Induced Cell Turnover: A Proposed Intervention for Age-Related Damage and Associated Pathology

In both biomedicine in general and biomedical gerontology in particular, cell replacement therapy is traditionally proposed as an intervention for cell loss. This article presents a proposed intervention-whole-body induced cell turnover (WICT)-for use in biomedical gerontology that combines cell replacement therapy with a second therapeutic component (targeted cell ablation) so as to broaden the therapeutic utility of cell therapies and increase the categories of age-related damage that are amenable to cell-based interventions. In particular, WICT may allow cell therapies to serve as an intervention for accumulated cellular and intracellular damage, such as telomere depletion, genomic DNA and mitochondrial DNA damage and mutations, replicative senescence, functionally deleterious age-related changes in gene expression, accumulated cellular and intracellular aggregates, and functionally deleterious posttranslationally modified gene products. WICT consists of the gradual ablation and subsequent replacement of a patient's entire set of constituent cells gradually over the course of their adult life span through the quantitative and qualitative coordination of targeted cell ablation with exogenous cell administration. The aim is to remove age-associated cellular and intracellular damage present in the patient's endogenous cells. In this study, we outline the underlying techniques and technologies by which WICT can be mediated, describe the mechanisms by which it can serve to negate or prevent age-related cellular and intracellular damage, explicate the unique therapeutic components and utilities that distinguish it as a distinct type of cell-based intervention for use in biomedical gerontology, and address potential complications associated with the therapy.

Potential risk of esophageal squamous cell carcinoma due to nucleotide excision repair XPA and XPC gene variants and their interaction among themselves and with environmental factors

The association of nucleotide excision repair (NER) gene polymorphisms with esophageal squamous cell carcinoma (ESCC) is inconclusive. The aim of the current study was to assess the association of repair gene xeroderma pigmentosum A (XPA) (rs-1800975) and xeroderma pigmentosum C (XPC) (rs-2228000) polymorphisms with ESCC risk as well as modifying effects of environmental factors. The genotyping was done in 450 confirmed ESCC cases and equal number of individually matched controls by the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) and direct sequencing methods. Conditional logistic regression models were used to assess the genotypic associations and interactions. A high ESCC risk was found in subjects who carried the homozygous minor allele of XPA (odds ratio (OR) = 3.57; 95 % confidence interval (CI) = 1.76-7.23), and the risk was higher when analysis was limited to participants who were ever smokers (OR = 4.22; 95 % CI = 2.01-8.88), lived in adobe houses (OR = 8.42; 95 % CI = 3.74-18.95), consumed large volumes of salt tea (OR = 7.42; 95 % CI = 3.30-16.69), or had a positive family history of cancer (FHC) (OR = 9.47; 95 % CI = 4.67-19.20). In case of XPC, a homozygous minor allele also showed strong association with ESCC risk (OR = 4.43; 95 % CI = 2.41-8.16). We again observed a very strong effect of the above environmental factors in elevating the risk of ESCC. Further, the variant genotypes of both genes in combination showed an increased risk towards ESCC (OR = 7.01; 95 % CI = 3.14-15.64) and such association was synergistically significant. Salt tea consumption showed an interaction with genotypes of XPA and XPC. However, an interaction with FHC was significant in the case of XPA genotype only. XPA and XPC genotypes are associated with an increased risk of ESCC, and such association was reasonably modulated by different exposures.

Potent Chemopreventive/Antioxidant Activity Detected in Common Spices of the Apiaceae Family

Spices are used worldwide, particularly in the Asian and Middle Eastern countries, and considered protective against degenerative diseases, including cancer. Here, we report the efficacy of aqueous and non-aqueous extracts of 11 Apiaceae spices for free radical-scavenging activity and to inhibit cytochrome P450s in two separate reactions involving: 1) 4-hydroxy-17ß-estradiol (4E2), DNA, and CuCl2 and 2) 17ß-estradiol, rat liver microsomes, cofactors, DNA and CuCl2. Oxidative DNA adducts resulting from redox cycling of 4E2 were analyzed by (32)P-postlabeling. Aqueous (5 mg/ml) and non-aqueous extracts (6 mg/ml) substantially inhibited (83-98%) formation of DNA adducts in the microsomal reaction. However, in nonmicrosomal reaction, only aqueous extracts showed the inhibitory activity (83-96%). Adduct inhibition was also observed at five-fold lower concentrations of aqueous extracts of cumin (60%) and caraway (90%), and 10-fold lower concentrations of carrot seeds (76%) and ajowan (90%). These results suggests the presence of 2 groups of phytochemicals: polar compounds that have free radical-scavenging activity and lipophilic compounds that selectively inhibit P450 activity associated with estrogen metabolism. Because most of these Apiaceae spices are used widely with no known toxicity, the phytochemicals from the Apiaceae spices used in foods may be potentially protective against estrogen-mediated breast cancer.

BRCA Mutations, DNA Repair Deficiency, and Ovarian Aging

Oocyte aging has a significant impact on reproductive outcomes both quantitatively and qualitatively. However, the molecular mechanisms underlying the age-related decline in reproductive success have not been fully addressed. BRCA is known to be involved in homologous DNA recombination and plays an essential role in double-strand DNA break repair. Given the growing body of laboratory and clinical evidence, we performed a systematic review on the current understanding of the role of DNA repair in human reproduction. We find that BRCA mutations negatively affect ovarian reserve based on convincing evidence from in vitro and in vivo results and prospective studies. Because decline in the function of the intact gene occurs at an earlier age, women with BRCA1 mutations exhibit accelerated ovarian aging, unlike those with BRCA2 mutations. However, because of the still robust function of the intact allele in younger women and because of the masking of most severe cases by prophylactic oophorectomy or cancer, it is less likely one would see an effect of BRCA mutations on fertility until later in reproductive age. The impact of BRCA2 mutations on reproductive function may be less visible because of the delayed decline in the function of normal BRCA2 allele. BRCA1 function and ataxia-telangiectasia-mutated (ATM)-mediated DNA repair may also be important in the pathogenesis of age-induced increase in aneuploidy. BRCA1 is required for meiotic spindle assembly, and cohesion function between sister chromatids is also regulated by ATM family member proteins. Taken together, these findings strongly suggest the implication of BRCA and DNA repair malfunction in ovarian aging.

A new hypothesis of aging

INTRODUCTION AND AIMS

There are over 300 hypotheses of aging, but none of them has enough predictive power to explain most experiments and observations on this process. On the basis of a critical analysis of the most relevant data on aging, especially on the factors that influences its rhythm, we present a new hypothesis, as well as the way the hypothesis' predictions explain some of the phylogenetic implications of the aging process.

METHODS

The hypothesis starts from a new, biochemical view on evolution and the behavior of living matter. According to this view, life is a fabric of chemical reactions that sustain each other. Reactants and energy support are needed for these reactions to take place in a cell. Given this, aging stems from a leftward shift of the global equilibrium of some biochemical reactions involved in cell differentiation and repair, which take place at a high level during the organism's growth period. In time, for species with evident aging, some reactions lose their specificity, which affects cell division and differentiation. This, in turn, influences cell energy metabolism.

RESULTS

Cell and tissue degeneration appears when, while some specific reactions are absent, non-specific reactions such as those of cell proliferation receive additional energy support.

CONCLUSIONS

This hypothesis explains phylogenetic differences related to lifespan and longevity, and body-size differences between species and within the same species.

Molecular consequences of psychological stress in human aging

Psychological stress has often been described as a feeling of being overwhelmed by the necessity of constant adjustment to an individual's changing environment. Stress affects people of all ages, but the lives of the elderly may particularly be affected. Major changes can cause anxiety leading to feelings of insecurity and/or loss of self-esteem and depression. The cellular mechanisms underlying psychological stress are poorly understood. This review focuses on the physical and molecular consequences of psychological stress linked to aging processes and, in particular, how molecular changes induced by psychological stress can compromise healthy aging.

Circadian gene variants in cancer

Humans as diurnal beings are active during the day and rest at night. This daily oscillation of behavior and physiology is driven by an endogenous circadian clock not environmental cues. In modern societies, changes in lifestyle have led to a frequent disruption of the endogenous circadian homeostasis leading to increased risk of various diseases including cancer. The clock is operated by the feedback loops of circadian genes and controls daily physiology by coupling cell proliferation and metabolism, DNA damage repair, and apoptosis in peripheral tissues with physical activity, energy homeostasis, immune and neuroendocrine functions at the organismal level. Recent studies have revealed that defects in circadian genes due to targeted gene ablation in animal models or single nucleotide polymorphism, deletion, deregulation and/or epigenetic silencing in humans are closely associated with increased risk of cancer. In addition, disruption of circadian rhythm can disrupt the molecular clock in peripheral tissues in the absence of circadian gene mutations. Circadian disruption has recently been recognized as an independent cancer risk factor. Further study of the mechanism of clock-controlled tumor suppression will have a significant impact on human health by improving the efficiencies of cancer prevention and treatment.

Adult Stem Cells and Diseases of Aging

Preservation of adult stem cells pools is critical for maintaining tissue homeostasis into old age. Exhaustion of adult stem cell pools as a result of deranged metabolic signaling, premature senescence as a response to oncogenic insults to the somatic genome, and other causes contribute to tissue degeneration with age. Both progeria, an extreme example of early-onset aging, and heritable longevity have provided avenues to study regulation of the aging program and its impact on adult stem cell compartments. In this review, we discuss recent findings concerning the effects of aging on stem cells, contributions of stem cells to age-related pathologies, examples of signaling pathways at work in these processes, and lessons about cellular aging gleaned from the development and refinement of cellular reprogramming technologies. We highlight emerging therapeutic approaches to manipulation of key signaling pathways corrupting or exhausting adult stem cells, as well as other approaches targeted at maintaining robust stem cell pools to extend not only lifespan but healthspan.