Determining the influence of telomere dysfunction and DNA damage on stem and progenitor cell aging: what markers can we use?

Aging of intestinal stem cells

The intestine is one of the organs that relies on stem cell function for maintaining tissue homeostasis. Recent findings on intestinal aging show that intestinal architecture, such as villus length, crypt size, and cell composition changes in the aged crypts. The correspondent decline in the regenerative capacity of the intestine is mainly due to a decline in intestinal stem cell function upon aging, as the underlying mechanisms of aging intestinal stem cells are beginning to unravel. This review summarizes our current knowledge on stem cell-intrinsic mechanisms of aging of intestinal stem cells and their connection to extrinsic factors, such as niche cells and microbiota and will introduce recent approaches to attenuate or even revert the aging of intestinal stem cells.

Effects of Cardiovascular, Resistance and Combined Exercise Training on Cardiovascular, Performance and Blood Redox Parameters in Coronary Artery Disease Patients: An 8-Month Training-Detraining Randomized Intervention

It is well-documented that chronic/regular exercise improves the cardiovascular function, decreases oxidative stress and enhances the antioxidant capacity in coronary artery disease (CAD) patients. However, there is insufficient evidence regarding the chronic effects of different types of training and detraining on cardiovascular function and the levels of oxidative stress and antioxidant status in these patients. Therefore, the present study aimed at investigating the effects of cardiovascular, resistance and combined exercise training followed by a three-month detraining period, on cardiovascular function, physical performance and blood redox status parameters in CAD patients. Sixty coronary artery disease patients were randomly assigned to either a cardiovascular training (CVT, N = 15), resistance training (RT, N = 11), combined cardiovascular and resistance training (CT, N = 16) or a control (C, N = 15) group. The training groups participated in an 8-month supervised training program (training three days/week) followed by a 3-month detraining period, while the control group participated only in measurements. Body composition, blood pressure, performance-related variables (aerobic capacity (VO_2max), muscle strength, flexibility) and blood redox status-related parameters (thiobarbituric acid reactive substances (TBARS), total antioxidant capacity (TAC), reduced glutathione (GSH), oxidized glutathione (GSSG), catalase activity (CAT), protein carbonyls (PC)) were assessed at the beginning of the study, after 4 and 8 months of training as well as following 1, 2 and 3 months of detraining (DT). CVT induced the most remarkable and pronounced alterations in blood pressure (~9% reduction in systolic blood pressure and ~5% in diastolic blood pressure) and redox status since it had a positive effect on all redox-related variables (ranging from 16 to 137%). RT and CT training affected positively some of the assessed (TAC, CAT and PC) redox-related variables. Performance-related variables retained the positive response of the training, whereas most of the redox status parameters, for all training groups, restored near to the pre-exercise values at the end of the DT period. These results indicate that exercise training has a significant effect on redox status of CAD. Three months of detraining is enough to abolish the exercise-induced beneficial effects on redox status, indicating that for a better antioxidant status, exercise must be a lifetime commitment.

Analysis of Aged Dysfunctional Intestinal Stem Cells

Aging is a multifactorial process. Organ maintenance and tissue regeneration are impaired upon aging mainly due to loss of stem cell function in organs that depend on stem cell in the adult. Intestine is such an organ, and upon aging intestinal regeneration is impaired due to decline of intestinal stem cell function. To determine the aging status of intestine and intestinal stem cells, histological analyses; analyses of the level of proliferation markers in tissue by immunofluorescence and/or quantitative RT-PCR; and gene expression analysis for stemness related genes in isolated crypts, intestinal stem cells (ISC), and Paneth cells can be used. To analyze the level of regeneration in intestine and thus determine a decline in ISC function, techniques like in vitro organoid cultures and lineage tracing with BrdU, lineage tracing using transgenic mice and histological analyses of tissue regeneration after 3 and 5 days after two rounds of 10 Gy of radiation (a 10 + 10 Gy IR experiment) can be applied. In this chapter we will focus on protocols for lineage tracing, the 10 + 10 gy IR experiment and for organoid cultures from young and aged mouse intestine.Lineage tracing experiments in intestine can be done in many ways. In this chapter we describe a protocol for lineage tracing upon BrdU incorporation and lineage tracing using the Lgr5^eGFPCreERT2 Rosa26^YFP transgenic mouse. For BrdU based-lineage tracing BrdU is administrated via intraperitoneal injections into mice. Animals will be analyzed 3 days (72 h) after BrdU administration. For experiments involving Lgr5^eGFPCreERT2 Rosa26^YFP mice, mice will be analyzed after tamoxifen injection that activates Cre in Lgr5 positive (ISC) cells, which will result in permanent YFP expression. This allows for tracing of YFP positive cells in the intestine. The time point for the analysis of the intestinal tissue will depend in this case on the underlying scientific question that will be addressed. For 10 + 10 Gy experiments, animals will be irradiated with a radiation dose of 10 Gy on 2 consecutive days. The intestinal tissue will be analyzed 3 and 5 days after the second dose of radiation. Quantitative analyses of crypt depth and determination of the rate of crypt fission upon histochemistry will provide an estimation on the in vivo regenerative potential of ISCs. For serial organoid culture experiments, crypts will be harvested from mouse intestine, initially plated at concentrations ranging from 500 to 1000 crypts per well in Matrigel and grown in conditional medium or ISC medium. ISC Medium is changed every 2 days. After 1 week in culture, the organoids will be disrupted via a syringe and replated in fresh Matrigel. As the ability to form multilobed organoids is considered to be a direct stem cell function, the frequency of organoid formation in serial replating experiments can serve as a quantitative measurement of ISC function. For example, we demonstrated a reduced frequency of organoid formation as well as a reduction in number of lobes formed per organoid after 4-5 replatings of intestinal organoids from aged compared to young mice. These three techniques are thus, in combination, able to quantify the regeneration potential of intestinal stem cells and thus determine the extent to which intestinal stem cell regenerative function is reduced upon aging.

Design, synthesis of 4,5-diazafluorene derivatives and their anticancer activity via targeting telomeric DNA G-quadruplex

In our work, 19 novel 4,5-diazafluorene derivatives (11a-d, 12a-d, 13a-d, 14a-c, 15c, 16a-c) bearing a 1,3-disubstituted pyrazol/thioxothiazolidinone or thioxothiazolidinone-oxadiazole moieties were designed, synthesized, preliminarily explored for their antitumor activities and in vitro mechanism. All compounds showed different values of antiproliferative activity against A549, AGS, HepG2 and MCF-7 cell lines through CCK-8. Especially, the compound 14c exhibited the strongest activity and best selectivity against A549 cells with an IC₅₀ 1.13 μM and an SI value of 7.01 relative to MRC-5 cells, which was better than cisplatin (SI = 1.80) as a positive control. Experimental results at extracellular level demonstrated that compounds 14a-c could strongly interact with the G-quadruplex(es) formed in a 26 nt telomeric G-rich DNA, in particular, the 14c exhibits quite strong binding affinity with an association equilibrium constant (K_A) of 7.04(±0.16) × 10⁷ M^-1 and more than 1000-fold specificity to G4-DNA over ds-DNA and Mut-DNA at the compound/G4-DNA ratio of 1:1. Further trap assay ascertained that compounds 14a-c owned strong inhibitory ability of telomerase activity in A549 cells, suggesting that these compounds have great possibility to target telomeric G-quadruplexes and consequently indirectly inhibit the telomerase activity. In addition, it is worthy of note that the remarkable inhibitory effects of 14a-c on the mobility of tested cancer cells were observed by wound healing assays. Furthermore, molecular docking and UV-Vis spectral results unclose the rationale for the interaction of compounds with such G-quadruplex(es). These results indicate that the growth and metastasis inhibition of cancer cells mediated by these 4,5-diazafluorene derivatives possibly result from their interaction with telomeric G-quadruplexes, suggesting that 4,5-diazafluorene derivatives, especially 14c, possess potential as anticancer drugs.

Sex-dependent telomere shortening, telomerase activity and oxidative damage in marine medaka Oryzias melastigma during aging

Marine medaka Oryzias melastigma at 4months (young), 8months (middle-aged) and 12months old (senior) were employed to determine age-associated change of sex ratios, sex hormones, telomere length (TL), telomerase activity (TA), telomerase transcription (omTERT) and oxidative damage in the liver. Overall, O. melastigma exhibited gradual senescence, sex differences in longevity (F>M), TL (F>M) and oxidative damage (F<M) during aging. In females, the plasma E2 level was positively correlated with TL (TRF>5kb), TA and omTERT expression (p≤0.01), and negatively correlated with liver DNA oxidation (p≤0.05). The results suggest high levels of E2 in female O. melastigma may retard TL shortening by enhancing TA via TERT transcription and/or reducing oxidative DNA damage. The findings support TL shortening as a biomarker of aging and further development of accelerated TL shortening, abnormal suppression of TA and excessive oxidative DNA damage as early molecular endpoints, indicative of advanced/premature aging in marine medaka/fish.

Canonical Wnt Signaling Ameliorates Aging of Intestinal Stem Cells

Although intestinal homeostasis is maintained by intestinal stem cells (ISCs), regeneration is impaired upon aging. Here, we first uncover changes in intestinal architecture, cell number, and cell composition upon aging. Second, we identify a decline in the regenerative capacity of ISCs upon aging because of a decline in canonical Wnt signaling in ISCs. Changes in expression of Wnts are found in stem cells themselves and in their niche, including Paneth cells and mesenchyme. Third, reactivating canonical Wnt signaling enhances the function of both murine and human ISCs and, thus, ameliorates aging-associated phenotypes of ISCs in an organoid assay. Our data demonstrate a role for impaired Wnt signaling in physiological aging of ISCs and further identify potential therapeutic avenues to improve ISC regenerative potential upon aging.

Association between telomere length and complete blood count in US adults

INTRODUCTION

Telomere length (TL) is related to age-related health outcomes, but little is known about the relationship between TL and complete blood count (CBC) parameters. We aimed to determine the relationship between TL and CBC in a sample of healthy US adults.

MATERIAL AND METHODS

Participants in the National Health and Nutrition Examination Survey (NHANES) recruited between 1999 and 2002 who had essential data on total CBC and TL were studied. We computed age- and race-adjusted mean values for total CBC using analysis of covariance (ANCOVA). All statistical analyses accounted for the survey design and sample weights by using SPSS Complex Samples v22.0 (IBM Corp, Armonk, NY).

RESULTS

Of the 8892 eligible participants, 47.8% (n = 4123) were men. The mean age was 41.8 years overall, 41.0 years in men and 42.6 in women (p = 0.238). The sex-stratified ANCOVA showed no significant difference in the total CBC across TL quartiles (all p > 0.05) in both sexes. In the adjusted model, there was a significant negative relationship with monocyte count (β = -0.051, 95% CI: -0.422; -0.142), mean cell hemoglobin (β = -0.051, 95% CI: -0.038; -0.011) and red cell distribution width (β = -0.031, 95% CI: -0.054; -0.003), while there was a significant positive relationship with basophil ratio (β = 0.046, 95% CI: 0.049-0.171).

CONCLUSIONS

These results support the possibility that telomere attrition may be a marker for reduced proliferative reserve in hematopoietic progenitor cells.

The Association Between Psychiatric Disorders and Telomere Length: A Meta-Analysis Involving 14,827 Persons

OBJECTIVE

This study examined the relationship between leukocyte telomere length (LTL), a marker of cell aging, and psychiatric disorders in adults compared with controls using meta-analytic methods.

METHODS

Data were abstracted from studies examining the relationship between LTL and adult psychiatric disorders. In addition to an overall estimate of effect size, subgroup analyses and meta-regression were performed to examine whether covariates (including psychiatric diagnoses) moderated the estimate.

RESULTS

A significant overall effect size showing LTL shortening was found across all psychiatric disorders (Hedge g = -0.50, p < .001). Subgroup analyses did not demonstrate significant differences in effect size based on individual covariates (psychiatric disorder, sex, age, or assay method). The meta-regression indicated that although type of disorder and, likely, age moderate the overall effect size, the heterogeneity between studies could not be explained by a model that included these variables as well as sex and assay method. Although not significantly different, posttraumatic stress disorder, anxiety disorders, and depressive disorders had comparatively larger effect sizes (-1.27, -0.53, and -0.55), and psychotic and bipolar disorders had comparatively smaller ones (-0.23 and -0.26).

CONCLUSIONS

We observed a robust effect size of LTL shortening for psychiatric disorders as a whole compared with controls. The results were less straightforward regarding relative differences in the strength of this association by specific disorder. Future studies should focus on mechanisms explaining accelerated cell aging with psychiatric illness, defining directions (if any) of causality and elucidating possible differences in this association between disorders.

DAMPs and influenza virus infection in ageing

Influenza A virus (IAV) is a serious global health problem worldwide due to frequent and severe outbreaks. IAV causes significant morbidity and mortality in the elderly population, due to the ineffectiveness of the vaccine and the alteration of T cell immunity with ageing. The cellular and molecular link between ageing and virus infection is unclear and it is possible that damage associated molecular patterns (DAMPs) may play a role in the raised severity and susceptibility of virus infections in the elderly. DAMPs which are released from damaged cells following activation, injury or cell death can activate the immune response through the stimulation of the inflammasome through several types of receptors found on the plasma membrane, inside endosomes after endocytosis as well as in the cytosol. In this review, the detriment in the immune system during ageing and the links between influenza virus infection and ageing will be discussed. In addition, the role of DAMPs such as HMGB1 and S100/Annexin in ageing, and the enhanced morbidity and mortality to severe influenza infection in ageing will be highlighted.

Psychiatric disorders and leukocyte telomere length: Underlying mechanisms linking mental illness with cellular aging

Many psychiatric illnesses are associated with early mortality and with an increased risk of developing physical diseases that are more typically seen in the elderly. Moreover, certain psychiatric illnesses may be associated with accelerated cellular aging, evidenced by shortened leukocyte telomere length (LTL), which could underlie this association. Shortened LTL reflects a cell's mitotic history and cumulative exposure to inflammation and oxidation as well as the availability of telomerase, a telomere-lengthening enzyme. Critically short telomeres can cause cells to undergo senescence, apoptosis or genomic instability, and shorter LTL correlates with poorer health and predicts mortality. Emerging data suggest that LTL may be reduced in certain psychiatric illnesses, perhaps in proportion to exposure to the psychiatric illnesses, although conflicting data exist. Telomerase has been less well characterized in psychiatric illnesses, but a role in depression and in antidepressant and neurotrophic effects has been suggested by preclinical and clinical studies. In this article, studies on LTL and telomerase activity in psychiatric illnesses are critically reviewed, potential mediators are discussed, and future directions are suggested. A deeper understanding of cellular aging in psychiatric illnesses could lead to re-conceptualizing them as systemic illnesses with manifestations inside and outside the brain and could identify new treatment targets.

Effects of combined physical exercise training on DNA damage and repair capacity: role of oxidative stress changes

Regular physical exercise has been shown to be one of the most important lifestyle influences on improving functional performance, decreasing morbidity and all causes of mortality among older people. However, it is known that acute physical exercise may induce an increase in oxidative stress and oxidative damage in several structures, including DNA. Considering this, the purpose of this study was to identify the effects of 16 weeks of combined physical exercise in DNA damage and repair capacity in lymphocytes. In addition, we aimed to investigate the role of oxidative stress involved in those changes. Fifty-seven healthy men (40 to 74 years) were enrolled in this study. The sample was divided into two groups: the experimental group (EG), composed of 31 individuals, submitted to 16 weeks of combined physical exercise training; and the control group (CG), composed of 26 individuals, who did not undergo any specifically orientated physical activity. We observed an improvement of overall physical performance in the EG, after the physical exercise training. A significant decrease in DNA strand breaks and FPG-sensitive sites was found after the physical exercise training, with no significant changes in 8-oxoguanine DNA glycosylase enzyme activity. An increase was observed in antioxidant activity, and a decrease was found in lipid peroxidation levels after physical exercise training. These results suggest that physical exercise training induces protective effects against DNA damage in lymphocytes possibly related to the increase in antioxidant capacity.

Study of the association of total and differential white blood cell counts with geriatric conditions, cardio-vascular diseases, seric IL-6 levels and telomere length

BACKGROUND/OBJECTIVES

Geriatric patients are highly susceptible to infections. While reduced lymphocyte count has been associated with age, other studies found no change in WBC counts with age. Increased circulating white blood cell (WBC) count has been associated with cardiovascular (CV) diseases and frailty but there are discrepancies. Frailty, geriatric conditions, cardiovascular diseases and WBC count have also been associated with low grade inflammation. Association between geriatric conditions and WBC has been scarcely studied. The aim of the study is to assess the association between WBC and geriatric conditions, CV diseases, and seric IL-6 levels.

DESIGN, SETTING, PARTICIPANTS, MEASUREMENTS

We recruited 100 subjects in the general population and hospitalized for chronic medical conditions (age, 23-96years). We collected information on clinical status (medical history, comorbidities, treatments and geriatric syndromes), biological parameters (hematological tests, cytomegalovirus serology) and cytokine production (basal IL-6). Using stepwise backward multivariate analyses, we defined which set of clinical and biological variables could be predictive of increased total and differential WBC counts.

RESULTS

We found that low-grade inflammation is independently associated with total WBC, monocyte and neutrophil counts, but not geriatric conditions. CV diseases were the only significant associated factor for high monocyte count.

CONCLUSION

In this study, we observed that differential and total WBC counts do not seem to be associated with geriatric conditions but with CV diseases, low-grade inflammation and telomere length.

Social isolation shortens telomeres in African Grey parrots (Psittacus erithacus erithacus)

Telomeres, the caps of eukaryotic chromosomes, control chromosome stability and cellular senescence, but aging and exposure to chronic stress are suspected to cause attrition of telomere length. We investigated the effect of social isolation on telomere length in the highly social and intelligent African Grey parrot (Psittacus erithacus erithacus). Our study population consisted of single-housed (n = 26) and pair-housed (n = 19) captive individuals between 0.75 to 45 years of age. Relative telomere length of erythrocyte DNA was measured by quantitative real-time PCR. We found that telomere length declined with age (p<0.001), and socially isolated parrots had significantly shorter telomeres compared to pair-housed birds (p<0.001) - even among birds of similar ages. Our findings provide the first evidence that social isolation affects telomere length, which supports the hypothesis that telomeres provide a biomarker indicating exposure to chronic stress.

Telomere length in elderly Caucasians weakly correlates with blood cell counts

Background. Age-related decrease in bone marrow erythropoietic capacity is often accompanied by the telomere length shortening in peripheral white blood cells. However, limited and conflicting data hamper the conclusive opinion regarding this relationship. Therefore, the aim of this study was to assess an association between telomere length and peripheral blood cell count parameters in the Polish elderly population. Material and Methods. The substudy included 1573 of 4981 subjects aged 65 years or over, participants of the population-based PolSenior study. High-molecular-weight DNA was isolated from blood mononuclear cells. Telomere length (TL) was measured by QRT-PCR as abundance of telomere template versus a single gene copy encoding acidic ribosomal phosphoprotein P0. Results. Only white blood count (WBC) was significantly different in TL tertile subgroups in all subjects (P = 0.02) and in men (P = 0.01), but not in women. Merely in men significant but weak positive correlations were found between TL and WBC (r = 0.11, P < 0.05) and RBC (r = 0.08, P < 0.05). The multiple regression analysis models confirmed a weak, independent contribution of TL to both RBC and WBC. Conclusions. In the elderly, telomere shortening limits hematopoiesis capacity to a very limited extent.

Adipogenic differentiation is impaired in replicative senescent human subcutaneous adipose-derived stromal/progenitor cells

We demonstrate that adipose-derived stromal/progenitor cells isolated from abdominal subcutaneous fat pads of adult donors successively enter replicative senescence after long-term cultivation. This is characterized by enlarged cell size, flattened morphology, and upregulated senescence-associated β-galactosidase activity. Moreover, the senescence- associated cyclin-dependent kinase inhibitors p16(Ink4A) and p21(Cip1) were induced correlating with activation of the G1/S cell cycle inhibitor retinoblastoma protein and terminal proliferation arrest. The number of cells in the adipose-derived stromal/progenitor cell population with high adipogenic capacity declined inversely with the increase of senescent cells. Adipogenic hormone cocktail induced expression of the adipogenic key regulators peroxisome proliferator-activated receptor-γ2 and CCAAT/enhancer-binding protein α was significantly reduced in senescent adipose-derived stromal/ progenitor cells. Furthermore, the expression of the adipogenic differentiation genes fatty acid binding protein-4, adiponectin, and leptin and the formation of fat droplets were impaired. We conclude cellular senescence contributes to dysfunctions in adipose-derived stromal/progenitor cell replication, adipogenesis, triglyceride storage, and adipokine secretion.

Human bone marrow hematopoietic stem cells are increased in frequency and myeloid-biased with age

In the human hematopoietic system, aging is associated with decreased bone marrow cellularity, decreased adaptive immune system function, and increased incidence of anemia and other hematological disorders and malignancies. Recent studies in mice suggest that changes within the hematopoietic stem cell (HSC) population during aging contribute significantly to the manifestation of these age-associated hematopoietic pathologies. Though the mouse HSC population has been shown to change both quantitatively and functionally with age, changes in the human HSC and progenitor cell populations during aging have been incompletely characterized. To elucidate the properties of an aged human hematopoietic system that may predispose to age-associated hematopoietic dysfunction, we evaluated immunophenotypic HSC and other hematopoietic progenitor populations from healthy, hematologically normal young and elderly human bone marrow samples. We found that aged immunophenotypic human HSC increase in frequency, are less quiescent, and exhibit myeloid-biased differentiation potential compared with young HSC. Gene expression profiling revealed that aged immunophenotypic human HSC transcriptionally up-regulate genes associated with cell cycle, myeloid lineage specification, and myeloid malignancies. These age-associated alterations in the frequency, developmental potential, and gene expression profile of human HSC are similar to those changes observed in mouse HSC, suggesting that hematopoietic aging is an evolutionarily conserved process.

Telomere biology in hematopoiesis and stem cell transplantation

Telomeres are long (TTAGGG)(n) nucleotide repeats and an associated protein complex located at the end of the chromosomes. They shorten with every cell division and, thus are markers for cellular aging, senescence, and replicative capacity. Telomere dysfunction is linked to several bone marrow disorders, including dyskeratosis congenita, aplastic anemia, myelodysplastic syndrome, and hematopoietic malignancies. Hematopoietic stem cell transplantation (HSCT) provides an opportunity in which to study telomere dynamics in a high cell proliferative environment. Rapid telomere shortening of donor cells occurs in the recipient shortly after HSCT; the degree of telomere attrition does not appear to differ by graft source. As expected, telomeres are longer in recipients of grafts with longer telomeres (e.g., cord blood). Telomere attrition may play a role in, or be a marker of, long term outcome after HSCT, but these data are limited. In this review, we discuss telomere biology in normal and abnormal hematopoiesis, including HSCT.

Aging and amyloid beta-induced oxidative DNA damage and mitochondrial dysfunction in Alzheimer's disease: implications for early intervention and therapeutics

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease affecting thousands of people in the world and effective treatment is still not available. Over two decades of intense research using AD postmortem brains, transgenic mouse and cell models of amyloid precursor protein and tau revealed that amyloid beta (Aβ) and hyperphosphorylated tau are synergistically involved in triggering disease progression. Accumulating evidence also revealed that aging and amyloid beta-induced oxidative DNA damage and mitochondrial dysfunction initiate and contributes to the development and progression of the disease. The purpose of this article is to summarize the latest progress in aging and AD, with a special emphasis on the mitochondria, oxidative DNA damage including methods of its measurement. It also discusses the therapeutic approaches against oxidative DNA damage and treatment strategies in AD.

p53 governs telomere regulation feedback too, via TRF2

p53 takes critical part in a number of positive and negative feedback loops to regulate carcinogenesis, aging and other biological processes. Uncapped or dysfunctional telomeres are an endogenous DNA damage that activates ATM kinase (ataxia telangiectasia mutated) and then p53 to induce cellular senescence or apoptosis. Our recent study shows that p53, a downstream effector of the telomere damage signaling, also functions upstream of the telomere-capping protein complex by inhibiting one of its components, TRF2 (telomeric repeat binding factor 2). Since TRF2 inhibition leads to ATM activation, a novel positive feedback loop exists to amplify uncapped telomere-induced, p53-mediated cellular responses. Siah1 (seven in absentia homolog 1), a p53-inducible E3 ubiquitin ligase, plays a key role in this feedback regulation by targeting TRF2 for ubiquitination and proteasomal degradation. Biological significance and therapeutic implications of this study are discussed.

Telomere, DNA damage, and oxidative stress in stem cell aging

"Stem cell aging" is a novel concept that developed together with the advances of stem cell biology, especially the sophisticated prospectively isolation and characterization of multipotent somatic tissue stem cells. Although being immortal in principle, stem cells can also undergo aging processes and potentially contribute to organismal aging. The impact of an age-dependent decline of stem cell function weighs differently in organs with high or low rates of cell turnover. Nonetheless, most of the organ systems undergo age-dependent loss of homeostasis and functionality, and emerging evidence showed that this has to do with the aging of resident stem cells in the organ systems. The mechanisms of stem cell aging and its real contribution to human aging remain to be defined. Many antitumor mechanisms protect potential malignant transformation of stem cell by inducing apoptosis or senescence but simultaneously provoke stem cell aging. In this review, we try to discuss several concept of stem cell aging and summarize recent progression on the molecular mechanisms of stem cell aging.

Positive feedback between p53 and TRF2 during telomere-damage signalling and cellular senescence

The telomere-capping complex shelterin protects functional telomeres and prevents the initiation of unwanted DNA-damage-response pathways. At the end of cellular replicative lifespan, uncapped telomeres lose this protective mechanism and DNA-damage signalling pathways are triggered that activate p53 and thereby induce replicative senescence. Here, we identify a signalling pathway involving p53, Siah1 (a p53-inducible E3 ubiquitin ligase) and TRF2 (telomere repeat binding factor 2; a component of the shelterin complex). Endogenous Siah1 and TRF2 were upregulated and downregulated, respectively, during replicative senescence with activated p53. Experimental manipulation of p53 expression demonstrated that p53 induces Siah1 and represses TRF2 protein levels. The p53-dependent ubiquitylation and proteasomal degradation of TRF2 are attributed to the E3 ligase activity of Siah1. Knockdown of Siah1 stabilized TRF2 and delayed the onset of cellular replicative senescence, suggesting a role for Siah1 and TRF2 in p53-regulated senescence. This study reveals that p53, a downstream effector of telomere-initiated damage signalling, also functions upstream of the shelterin complex.

Haematopoietic stem and progenitor cells in rheumatoid arthritis

RA is the prototypic chronic inflammatory disease, characterized by progressive articular cartilage and bone destruction. The systemic nature of RA is evidenced by the increased risk of atherosclerosis and lymphoproliferative disorders. Components of both the innate and adaptive immune system are implicated in the pathophysiology of the articular and extra-articular manifestations of the disease. A fundamental process in the onset of RA is the breakdown in self-tolerance. Accelerated ageing of immune cells (immunosenescence) appears to be a major mechanism favouring the disruption of tolerance. Telomere erosion, a hallmark of immunosenescence, is present in lymphoid (naïve and memory T cells) and myeloid (granulocytes) cells in RA. The premature ageing process also involves the haematopoietic stem and progenitor cells (CD34(+) HSPC), thus extending the RA immunopathogenesis to include early events in the shaping of the immune system. This review summarizes current concepts of HSPC ageing and its impact on immune regeneration, highlighting the phenotypic and functional similarities between elderly and RA HSPC.

Emerging biomarkers in breast cancer care

Currently, decision-making for breast cancer treatment in the clinical setting is mainly based on clinical data, histomorphological features of the tumor tissue and a few cancer biomarkers such as steroid hormone receptor status (estrogen and progesterone receptors) and oncoprotein HER2 status. Although various therapeutic options were introduced into the clinic in recent decades, with the objective of improving surgery, radiotherapy, biochemotherapy and chemotherapy, varying response of individual patients to certain types of therapy and therapy resistance is still a challenge in breast cancer care. Therefore, since breast cancer treatment should be based on individual features of the patient and her tumor, tailored therapy should be an option by integrating cancer biomarkers to define patients at risk and to reliably predict their course of the disease and/or response to cancer therapy. Recently, candidate-marker approaches and genome-wide transcriptomic and epigenetic screening of different breast cancer tissues and bodily fluids resulted in new promising biomarker panels, allowing breast cancer prognosis, prediction of therapy response and monitoring of therapy efficacy. These biomarkers are now subject of validation in prospective clinical trials.

Lifestyle impacts on the aging-associated expression of biomarkers of DNA damage and telomere dysfunction in human blood

Cellular aging is characterized by telomere shortening, which can lead to uncapping of chromosome ends (telomere dysfunction) and activation of DNA damage responses. There is some evidence that DNA damage accumulates during human aging and that lifestyle factors contribute to the accumulation of DNA damage. Recent studies have identified a set of serum markers that are induced by telomere dysfunction and DNA damage, and these markers showed an increased expression in blood during human aging. Here, we investigated the influence of lifestyle factors (such as exercise, smoking, body mass) on the aging-associated expression of serum markers of DNA damage (CRAMP, EF-1alpha, stathmin, n-acetyl-glucosaminidase and chitinase) in comparison with other described markers of cellular aging (p16(INK4a) upregulation and telomere shortening) in human peripheral blood. The study shows that lifestyle factors have an age-independent impact on the expression level of biomarkers of DNA damage. Smoking and increased body mass indices were associated with elevated levels of biomarkers of DNA damage independent of the age of the individuals. In contrast, exercise was associated with an age-independent reduction in the expression of biomarkers of DNA damage in human blood. The expression of biomarkers of DNA damage correlated positively with p16(INK4a) expression and negatively with telomere length in peripheral blood T-lymphocytes. Together, these data provide experimental evidence that both aging and lifestyle impact on the accumulation of DNA damage during human aging.

CHK2-independent induction of telomere dysfunction checkpoints in stem and progenitor cells

Telomere shortening limits the proliferation of primary human fibroblasts by the induction of senescence, which is mediated by ataxia telangiectasia mutated-dependent activation of p53. Here, we show that CHK2 deletion impairs the induction of senescence in mouse and human fibroblasts. By contrast, CHK2 deletion did not improve the stem-cell function, organ maintenance and lifespan of telomere dysfunctional mice and did not prevent the induction of p53/p21, apoptosis and cell-cycle arrest in telomere dysfunctional progenitor cells. Together, these results indicate that CHK2 mediates the induction of senescence in fibroblasts, but is dispensable for the induction of telomere dysfunction checkpoints at the stem and progenitor cell level in vivo.

Dietary reference values of individual micronutrients and nutriomes for genome damage prevention: current status and a road map to the future

Damage to the genome is recognized as a fundamental cause of developmental and degenerative diseases. Several micronutrients play an important role in protecting against DNA damage events generated through endogenous and exogenous factors by acting as cofactors or substrates for enzymes that detoxify genotoxins as well as enzymes involved in DNA repair, methylation, and synthesis. In addition, it is evident that either micronutrient deficiency or micronutrient excess can modify genome stability and that these effects may also depend on nutrient-nutrient and nutrient-gene interaction, which is affected by genotype. These observations have led to the emerging science of genome health nutrigenomics, which is based on the principle that DNA damage is a fundamental cause of disease that can be diagnosed and nutritionally prevented on an individual, genetic subgroup, or population basis. In this article, the following topics are discussed: 1) biomarkers used to study genome damage in humans and their validation, 2) evidence for the association of genome damage with developmental and degenerative disease, 3) current knowledge of micronutrients required for the maintenance of genome stability in humans, 4) the effect of nutrient-nutrient and nutrient-genotype interaction on DNA damage, and 5) strategies to determine dietary reference values of single micronutrients and micronutrient combinations (nutriomes) on the basis of DNA damage prevention. This article also identifies important knowledge gaps and future research directions required to shed light on these issues. The ultimate goal is to match the nutriome to the genome to optimize genome maintenance and to prevent pathologic amounts of DNA damage.

Senescence and life span

Senescence is a general cellular process that occurs as a response to stress and damage. It forms an alternative response of cells to damage that might otherwise cause programmed cell death. Whereas telomere shortening leading to telomere dysfunction was the first described cause of senescence, it is now known that senescence can result from many sources of damage. Senescent cells are found in tissues in vivo, but the cause of senescence in these cells is mostly unknown. In many cases, senescence may be the result of the action of activated oncogenes in cells. By preventing activated oncogenes from initiating a clone of neoplastic cells, senescence acts as a protective mechanism against cancer development. Until recently, the fate of senescent cells in vivo was unknown, but new evidence indicates that they are cleared by components of the innate immune system. In this way, senescence and apoptosis act as parallel pathways by which severely damaged cells are eliminated from the body. Some senescent cells persist in tissues, in some cases increasing in frequency as a function of age. It is hypothesized that these persistent senescent cells have adverse effects on tissue function. If so, senescence may be an example of antagonistic pleiotropy, providing an anticancer mechanism in early life but having adverse effects on tissue function in late life. Much more research is needed to address the broader question of the overall impact of senescence on life span.

Aging and replicative senescence have related effects on human stem and progenitor cells

The regenerative potential diminishes with age and this has been ascribed to functional impairments of adult stem cells. Cells in culture undergo senescence after a certain number of cell divisions whereby the cells enlarge and finally stop proliferation. This observation of replicative senescence has been extrapolated to somatic stem cells in vivo and might reflect the aging process of the whole organism. In this study we have analyzed the effect of aging on gene expression profiles of human mesenchymal stromal cells (MSC) and human hematopoietic progenitor cells (HPC). MSC were isolated from bone marrow of donors between 21 and 92 years old. 67 genes were age-induced and 60 were age-repressed. HPC were isolated from cord blood or from mobilized peripheral blood of donors between 27 and 73 years and 432 genes were age-induced and 495 were age-repressed. The overlap of age-associated differential gene expression in HPC and MSC was moderate. However, it was striking that several age-related gene expression changes in both MSC and HPC were also differentially expressed upon replicative senescence of MSC in vitro. Especially genes involved in genomic integrity and regulation of transcription were age-repressed. Although telomerase activity and telomere length varied in HPC particularly from older donors, an age-dependent decline was not significant arguing against telomere exhaustion as being causal for the aging phenotype. These studies have demonstrated that aging causes gene expression changes in human MSC and HPC that vary between the two different cell types. Changes upon aging of MSC and HPC are related to those of replicative senescence of MSC in vitro and this indicates that our stem and progenitor cells undergo a similar process also in vivo.

Sod2 haploinsufficiency does not accelerate aging of telomere dysfunctional mice

Telomere shortening represents a causal factor of cellular senescence. At the same time, several lines of evidence indicate a pivotal role of oxidative DNA damage for the aging process in vivo. A causal connection between the two observations was suggested by experiments showing accelerated telomere shorting under conditions of oxidative stress in cultured cells, but has never been studied in vivo. We therefore have analysed whether an increase in mitochondrial derived oxidative stress in response to heterozygous deletion of superoxide dismutase (Sod2^+/-) would exacerbate aging phenotypes in telomere dysfunctional (mTerc^-/-) mice. Heterozygous deletion of Sod2 resulted in reduced SOD2 protein levels and increased oxidative stress in aging telomere dysfunctional mice, but this did not lead to an increase in basal levels of oxidative nuclear DNA damage, an accumulation of nuclear DNA breaks, or an increased rate of telomere shortening in the mice. Moreover, heterozygous deletion of Sod2 did not accelerate the depletion of stem cells and the impairment in organ maintenance in aging mTerc^-/- mice. In agreement with these observations, Sod2 haploinsufficiency did not lead to a further reduction in lifespan of mTerc^-/- mice. Together, these results indicate that a decrease in SOD2-dependent antioxidant defence does not exacerbate aging in the context of telomere dysfunction.

[Delirium in the elderly]

Delirium is a common, serious medical and often life-threatening condition in elderly in-patients. Delirium can develop primarily or secondarily related to other medical conditions and lead to hospital admission. The pathogenesis is still not fully known and is usually addressed as multifactorial. Alterations in neurotransmitters have a key role in this process. The incidence varies by setting up to 90%. Delirium is associated with increased short- and long-term mortality, iatrogenic complications, functional decline, and future development of cognitive impairment or dementia. Delirium is also associated with longer hospital stays, higher hospital and total health system costs, and an increasing rate of nursing home admissions. A structured diagnostic and therapeutic process is recommended. Delirium should become a quality indicator for hospital medicine; however, many research questions still exist.