Telomere Length and the Cancer-Atherosclerosis Trade-Off

Telomeres and aging: on and off the planet!

Improving human healthspan in our rapidly aging population has never been more imperative. Telomeres, protective "caps" at the ends of linear chromosomes, are essential for maintaining genome stability of eukaryotic genomes. Due to their physical location and the "end-replication problem" first envisioned by Dr. Alexey Olovnikov, telomeres shorten with cell division, the implications of which are remarkably profound. Telomeres are hallmarks and molecular drivers of aging, as well as fundamental integrating components of the cumulative effects of genetic, lifestyle, and environmental factors that erode telomere length over time. Ongoing telomere attrition and the resulting limit to replicative potential imposed by cellular senescence serves a powerful tumor suppressor function, and also underlies aging and a spectrum of age-related degenerative pathologies, including reduced fertility, dementias, cardiovascular disease and cancer. However, very little data exists regarding the extraordinary stressors and exposures associated with long-duration space exploration and eventual habitation of other planets, nor how such missions will influence telomeres, reproduction, health, disease risk, and aging. Here, we briefly review our current understanding, which has advanced significantly in recent years as a result of the NASA Twins Study, the most comprehensive evaluation of human health effects associated with spaceflight ever conducted. Thus, the Twins Study is at the forefront of personalized space medicine approaches for astronauts and sets the stage for subsequent missions. We also extrapolate from current understanding to future missions, highlighting potential biological and biochemical strategies that may enable human survival, and consider the prospect of longevity in the extreme environment of space.

Identification of M2 Macrophage-Related Key Genes in Advanced Atherosclerotic Plaques by Network-Based Analysis

ABSTRACT

Atherosclerotic plaque accounts for major adverse cardiovascular events because of its vulnerability. The classically activated macrophage (M1) and alternatively activated macrophage (M2) are implicated in the progression and regression of plaque, respectively. However, the therapeutic targets related to M2 macrophages still remain largely elusive. In this study, cell-type identification by estimating relative subsets of RNA transcripts and weighted gene coexpression network analysis algorithms were used to establish a weighted gene coexpression network for identifying M2 macrophage-related hub genes using GSE43292 data set. The results showed that genes were classified into 7 modules, with the blue module (Cor = 0.67, P = 3e-05) being the one that was most related to M2 macrophage infiltration in advanced plaques, and then 99 hub genes were identified from blue module. Meanwhile, 1289 differentially expressed genes were produced in GSE43292 data set. Subsequently, the intersection genes of hub genes and differentially expressed genes, including AKTIP , ASPN , FAM26E , RAB23 , PLS3 , and PLSCR4 , were obtained by Venn diagrams and named as key genes. Further validation using data sets GSE100927 and GSE41571 showed that 6 key genes all downregulated in advanced and vulnerable plaques compared with early and stable plaque samples (|Log2 (fold change)| > 0.5, P < 0.05 or 0.001), respectively. Receiver operator characteristic curve analysis indicated that the 6 key genes might have potential diagnostic value. The validation of key genes in the model in vitro and in vivo also demonstrated decreased mRNA expressions of AKTIP , ASPN , FAM26E , RAB23 , PLS3 , and PLSCR4 ( P < 0.05 or 0.001). Collectively, we identified AKTIP, ASPN, FAM26E, RAB23, PLS3, and PLSCR4 as M2 macrophage-related key genes during atherosclerotic progression, proposing potential intervention targets for advanced atherosclerotic plaques.

Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant

NASA envisions a future where humans establish a thriving colony on the Moon by 2050. Plants will be essential for this endeavor, but little is known about their adaptation to extraterrestrial bodies. The capacity to grow plants in lunar regolith would represent a major step towards this goal by minimizing the reliance on resources transported from Earth. Recent studies reveal that Arabidopsis thaliana can germinate and grow on genuine lunar regolith as well as on lunar regolith simulant. However, plants arrest in vegetative development and activate a variety of stress response pathways, most notably the oxidative stress response. Telomeres are hotspots for oxidative damage in the genome and a marker of fitness in many organisms. Here we examine A. thaliana growth on a lunar regolith simulant and the impact of this resource on plant physiology and on telomere dynamics, telomerase enzyme activity and genome oxidation. We report that plants successfully set seed and generate a viable second plant generation if the lunar regolith simulant is pre-washed with an antioxidant cocktail. However, plants sustain a higher degree of genome oxidation and decreased biomass relative to conventional Earth soil cultivation. Moreover, telomerase activity substantially declines and telomeres shorten in plants grown in lunar regolith simulant, implying that genome integrity may not be sustainable over the long-term. Overcoming these challenges will be an important goal in ensuring success on the lunar frontier.

Identifying Potential Causal Effects of Telomere Length on Health Outcomes: A Phenome-Wide Investigation and Mendelian Randomization Study

BACKGROUND

Telomere length has been linked to various health outcomes. To comprehensively investigate the causal effects of telomere length throughout the human disease spectrum, we conducted a phenome-wide Mendelian randomization study (MR-PheWAS) and a systematic review of MR studies.

METHODS

We conducted a PheWAS to screen for associations between telomere length and 1 035 phenotypes in the UK Biobank (n = 408 354). The exposure of interest was the genetic risk score (GRS) of telomere length. Observed associations passing multiple testing corrections were assessed for causality by 2-sample MR analysis. A systematic review of MR studies on telomere length was performed to harmonize the published evidence and complement our findings.

RESULTS

Of the 1 035 phenotypes tested, PheWAS identified 29 and 78 associations of telomere length GRS at a Bonferroni- and false discovery rate-corrected threshold; 24 and 66 distinct health outcomes were causal in the following principal MR analysis. The replication MR using data from the FinnGen study provided evidence of causal effects of genetically instrumented telomere length on 28 out of 66 outcomes, including decreased risks of 5 diseases in respiratory diseases, digestive diseases, and myocardial infarction, and increased risks of 23 diseases, mainly comprised neoplasms, diseases of the genitourinary system, and essential hypertension. A systematic review of 53 MR studies found evidence to support 16 out of the 66 outcomes.

CONCLUSIONS

This large-scale MR-PheWAS identified a wide range of health outcomes that were possibly affected by telomere length, and suggested that susceptibility to telomere length may vary across disease categories.

Arabidopsis telomerase takes off by uncoupling enzyme activity from telomere length maintenance in space

Spaceflight-induced changes in astronaut telomeres have garnered significant attention in recent years. While plants represent an essential component of future long-duration space travel, the impacts of spaceflight on plant telomeres and telomerase have not been examined. Here we report on the telomere dynamics of Arabidopsis thaliana grown aboard the International Space Station. We observe no changes in telomere length in space-flown Arabidopsis seedlings, despite a dramatic increase in telomerase activity (up to 150-fold in roots), as well as elevated genome oxidation. Ground-based follow up studies provide further evidence that telomerase is induced by different environmental stressors, but its activity is uncoupled from telomere length. Supporting this conclusion, genetically engineered super-telomerase lines with enhanced telomerase activity maintain wildtype telomere length. Finally, genome oxidation is inversely correlated with telomerase activity levels. We propose a redox protective capacity for Arabidopsis telomerase that may promote survivability in harsh environments.

Inbreeding effects on telomeres in hatchling sand lizards (Lacerta agilis): An optimal family affair?

Telomeres are nucleotide-protein caps, predominantly at the ends of Metazoan linear chromosomes, showing complex dynamics with regard to their lengthening and shortening through life. Their complexity has entertained the idea that net telomere length and attrition could be valuable biomarkers of phenotypic and genetic quality of their bearer. Intuitively, those individuals could be more heterozygous and, hence, less inbred. However, some inbred taxa have longer, not shorter, telomeres. To understand the role of inbreeding in this complex scenario we need large samples across a range of genotypes with known maternity and paternity in telomere-screened organisms under natural conditions. We assessed the effects of parental and hatchling inbreeding on telomere length in >1300 offspring from >500 sires and dams in a population of sand lizards (Lacerta agilis). Maternal and paternal ID and their interactions predict hatchling telomere length at substantial effect sizes (R²  > .50). Deviation from mean maternal heterozygosity statistically predicts shorter offspring telomeres but this only when sibship is controlled for by paternal ID, and then is still limited (R²  = .06). Raw maternal heterozygosity scores, ignoring absolute deviation from the mean, explained 0.07% of the variance in hatchling telomere length. In conclusion, inbreeding is not a driver of telomere dynamics in the sand lizard (Lacerta agilis) study system.

The bullwhip effect, T-cell telomeres, and SARS-CoV-2

Both myeloid cells, which contribute to innate immunity, and lymphoid cells, which dominate adaptive immunity, partake in defending against SARS-CoV-2. In response to the virus, the otherwise slow haematopoietic production supply chain quickly unleashes its preconfigured myeloid element, which largely resists a bullwhip-like effect. By contrast, the lymphoid element risks a bullwhip-like effect when it produces T cells and B cells that are specifically designed to clear the virus. As T-cell production is telomere-length dependent and telomeres shorten with age, older adults are at higher risk of a T-cell shortfall when contracting SARS-CoV-2 than are younger adults. A poorly calibrated adaptive immune response, stemming from a bullwhip-like effect, compounded by a T-cell deficit, might thus contribute to the propensity of people with inherently short T-cell telomeres to develop severe COVID-19. The immune systems of these individuals might also generate an inadequate T-cell response to anti-SARS-CoV-2 vaccination.

Methylmercury chronic exposure affects the expression of DNA single-strand break repair genes, induces oxidative stress, and chromosomal abnormalities in young dyslipidemic APOE knockout mice

Mercury (Hg) is one of the most toxic environmental pollutants, especially when methylated, forming methylmercury (MeHg). MeHg affects DNA repair, increases oxidative stress, and predisposes to cancer. MeHg neurotoxicity is well-known, but recently MeHg-associated cardiovascular effects were recognized. This study evaluated circulating lipids, oxidative stress, and genotoxicity after MeHg-chronic exposure (20 mg/L in drinking water) in C57BL/6J wild-type and APOE knockout (ko) mice, the latter, being spontaneously dyslipidemic. Experimental mice were assigned to four groups: non-intoxicated and MeHg-intoxicated wild-type mice and non-intoxicated and MeHg-intoxicated APOE ko mice. Plasma levels of triglycerides, total cholesterol (TC), HDL, and LDL were analyzed. Liver lipid peroxidation and splenic gene expression of xeroderma pigmentosum complementation groups A, C, D, and G (XPA, XPC, XPD, and XPG), X-ray repair cross-complementing protein 1 (XRCC1), and telomerase reverse transcriptase (TERT) were measured. Fur Hg levels confirmed chronic MeHg intoxication. MeHg exposure raises TC levels both in wild-type and APOE ko mice. HDL and LDL-cholesterol levels were increased only in the MeHg-challenged APOE ko mice. MeHg increased liver lipid peroxidation, regardless of the genetic background. Unintoxicated APOE ko mice showed higher expression of TERT than all other groups. APOE deficiency increases XPA expression, regardless of MeHg intoxication. Furthermore, MeHg-intoxicated mice had more cytogenetic abnormalities, effect which was independent of APOE deficiency. More studies are needed to dissect the interactions between circulating lipids, MeHg intoxication, and DNA-repair pathways even at young age, interactions that likely play critical roles in cell senescence and the risk for chronic disorders later in life.

Ad Astra - telomeres in space!

PURPOSE

My journey to the stars began as I - along with the whole world - stood still and watched Neil Armstrong take those first small steps on the Moon. Fast forward 50 years and NASA astronauts Scott Kelly and Christina Koch each spend nearly a year in space aboard the International Space Station (ISS), a remarkable multinational collaborative project and floating U.S. National Laboratory that has supported continuous human presence in low Earth orbit for the past 20 years. Marking a new era of human space exploration, the first commercial rocket, SpaceX Falcon 9, recently launched NASA astronauts Doug Hurley and Bob Behnken in the Crew Dragon spacecraft Endeavor to the ISS and returned safely to Earth. NASA and its commercial partners are rapidly advancing innovative space technologies, and with the recently announced Artemis team of astronauts, plans to send the first woman and next man back to the moon and establish sustainable exploration by the end of the decade. Humankind will then be poised to take the next giant leap - pioneering human exploration of Mars.

CONCLUSIONS

Historically, fewer than 600 individuals have participated in spaceflight, the vast majority of whom have been middle aged males (35-55 years) on short duration missions (less than 20 days). Thus, as the number and diversity of space travelers increase, a better understanding of how long-duration spaceflight affects human health is essential to maintaining individual astronaut performance during, and improving disease and aging trajectories following, future exploration missions. Here, I review findings from our NASA Twins Study and Telomeres investigations, highlighting potential mechanistic roles of chronic space radiation exposure in changes in telomere length and persistent DNA damage responses associated with long-duration spaceflight. Importantly, similar trends were observed in prostate cancer patients undergoing intensity-modulated radiation therapy (IMRT), additional support specifically for the role of radiation exposure. Individual differences in response were also observed in both cohorts, underscoring the importance of developing personalized approaches for evaluating human health effects and long-term outcomes associated with radiation exposures, whether on Earth or living in the extreme environment of space.

Telomere Dynamics and Telomerase in the Biology of Hair Follicles and their Stem Cells as a Model for Aging Research

In this review, we propose that telomere length dynamics play an important but underinvestigated role in the biology of the hair follicle (HF), a prototypic, cyclically remodeled miniorgan that shows an intriguing aging pattern in humans. Whereas the HF pigmentary unit ages quickly, its epithelial stem cell (ESC) component and regenerative capacity are surprisingly aging resistant. Telomerase-deficient mice with short telomeres display an aging phenotype of hair graying and hair loss that is attributed to impaired HF ESC mobilization. Yet, it remains unclear whether the function of telomerase and telomeres in murine HF biology translate to the human system. Therefore, we propose new directions for future telomere research of the human HF. Such research may guide the development of novel treatments for selected disorders of human hair growth or pigmentation (e.g., chemotherapy-induced alopecia, telogen effluvium, androgenetic alopecia, cicatricial alopecia, graying). It might also increase the understanding of the global role of telomeres in aging-related human disease.

Telomere Length Dynamics and Chromosomal Instability for Predicting Individual Radiosensitivity and Risk via Machine Learning

The ability to predict a cancer patient's response to radiotherapy and risk of developing adverse late health effects would greatly improve personalized treatment regimens and individual outcomes. Telomeres represent a compelling biomarker of individual radiosensitivity and risk, as exposure can result in dysfunctional telomere pathologies that coincidentally overlap with many radiation-induced late effects, ranging from degenerative conditions like fibrosis and cardiovascular disease to proliferative pathologies like cancer. Here, telomere length was longitudinally assessed in a cohort of fifteen prostate cancer patients undergoing Intensity Modulated Radiation Therapy (IMRT) utilizing Telomere Fluorescence in situ Hybridization (Telo-FISH). To evaluate genome instability and enhance predictions for individual patient risk of secondary malignancy, chromosome aberrations were assessed utilizing directional Genomic Hybridization (dGH) for high-resolution inversion detection. We present the first implementation of individual telomere length data in a machine learning model, XGBoost, trained on pre-radiotherapy (baseline) and in vitro exposed (4 Gy γ-rays) telomere length measurements, to predict post radiotherapy telomeric outcomes, which together with chromosomal instability provide insight into individual radiosensitivity and risk for radiation-induced late effects.

Advanced paternal age and risk of cancer in offspring

Many risk factors of cancer have been established, but the contribution of paternal age in this regard remains largely unexplored. To further understand the etiology of cancer, we investigated the relationship between paternal age and cancer incidence using PLCO cohort. Cox proportional hazards models were performed to assess the association between paternal age and the risk of cancers. During follow-up time (median 11.5 years), 18,753 primary cancers occurred. Paternal age was associated with reduced risk of cancers of the female genitalia (HR, 0.79; 95%CI, 0.66-0.94; P = 0.008) as well as cancers of the respiratory and intrathoracic organs (HR, 0.78; 95%CI, 0.63-0.97; P = 0.026). The association was stronger for lung cancer (HR, 0.67; 95%CI, 0.52-0.86; P = 0.002). The subgroup analysis suggested that age, gender, smoking and BMI were related to the decreased cancer incidence of the respiratory and intrathoracic organs, lung and the female genitalia. Positive linear associations were observed between paternal age and cancer incidence of the female genitalia, respiratory and intrathoracic organs and the lungs. These findings indicate that advanced paternal age is an independent protective factor against various cancers in offspring.

Temporal Telomere and DNA Damage Responses in the Space Radiation Environment

Telomeres, repetitive terminal features of chromosomes essential for maintaining genome integrity, shorten with cell division, lifestyle factors and stresses, and environmental exposures, and so they provide a robust biomarker of health, aging, and age-related diseases. We assessed telomere length dynamics (changes over time) in three unrelated astronauts before, during, and after 1-year or 6-month missions aboard the International Space Station (ISS). Similar to our results for National Aeronautics and Space Administration's (NASA's) One-Year Mission twin astronaut (Garrett-Bakelman et al., 2019), significantly longer telomeres were observed during spaceflight for two 6-month mission astronauts. Furthermore, telomere length shortened rapidly after return to Earth for all three crewmembers and, overall, telomere length tended to be shorter after spaceflight than before spaceflight. Consistent with chronic exposure to the space radiation environment, signatures of persistent DNA damage responses were also detected, including mitochondrial and oxidative stress, inflammation, and telomeric and chromosomal aberrations, which together provide potential mechanistic insight into spaceflight-specific telomere elongation.

Telomere Length Dynamics and DNA Damage Responses Associated with Long-Duration Spaceflight

Telomere length dynamics and DNA damage responses were assessed before, during, and after one-year or shorter duration missions aboard the International Space Station (ISS) in a comparatively large cohort of astronauts (n = 11). Although generally healthy individuals, astronauts tended to have significantly shorter telomeres and lower telomerase activity than age- and sex-matched ground controls before and after spaceflight. Although telomeres were longer during spaceflight irrespective of mission duration, telomere length shortened rapidly upon return to Earth, and overall astronauts had shorter telomeres after spaceflight than they did before; inter-individual differences were identified. During spaceflight, all crewmembers experienced oxidative stress, which positively correlated with telomere length dynamics. Significantly increased frequencies of chromosomal inversions were observed during and after spaceflight; changes in cell populations were also detected. We propose a telomeric adaptive response to chronic oxidative damage in extreme environments, whereby the telomerase-independent Alternative Lengthening of Telomeres (ALT) pathway is transiently activated in normal somatic cells.

Genetics and geography of leukocyte telomere length in sub-Saharan Africans

Leukocyte telomere length (LTL) might be causal in cardiovascular disease and major cancers. To elucidate the roles of genetics and geography in LTL variability across humans, we compared LTL measured in 1295 sub-Saharan Africans (SSAs) with 559 African-Americans (AAms) and 2464 European-Americans (EAms). LTL differed significantly across SSAs (P = 0.003), with the San from Botswana (with the oldest genomic ancestry) having the longest LTL and populations from Ethiopia having the shortest LTL. SSAs had significantly longer LTL than AAms [P = 6.5(e-16)] whose LTL was significantly longer than EAms [P = 2.5(e-7)]. Genetic variation in SSAs explained 52% of LTL variance versus 27% in AAms and 34% in EAms. Adjustment for genetic variation removed the LTL differences among SSAs. LTL genetic variation among SSAs, with the longest LTL in the San, supports the hypothesis that longer LTL was ancestral in humans. Identifying factors driving LTL variation in Africa may have important ramifications for LTL-associated diseases.

Are long telomeres better than short? Relative contributions of genetically predicted telomere length to neoplastic and non-neoplastic disease risk and population health burden

Background

Mendelian Randomization (MR) studies exploiting single nucleotide polymorphisms (SNPs) predictive of leukocyte telomere length (LTL) have suggested that shorter genetically determined telomere length (gTL) is associated with increased risks of degenerative diseases, including cardiovascular and Alzheimer’s diseases, while longer gTL is associated with increased cancer risks. These varying directions of disease risk have long begged the question: when it comes to telomeres, is it better to be long or short? We propose to operationalize and answer this question by considering the relative impact of long gTL vs. short gTL on disease incidence and burden in a population.

Methods and findings

We used odds ratios (OR) of disease associated with gTL from a recently published MR meta-analysis to approximate the relative contributions of gTL to the incidence and burden of neoplastic and non-neoplastic disease in a European population. We obtained incidence data of the 9 cancers associated with long gTL and 4 non-neoplastic diseases associated with short gTL from the Institute of Health Metrics (IHME). Incidence rates of individual cancers from SEER, a database of United States cancer records, were used to weight the ORs in order to align with the available IHME data. These data were used to estimate the excess incidences due to long vs. short gTL, expressed as per 100,000 persons per standard deviation (SD) change in gTL. To estimate the population disease burden, we used the Disability Adjusted Life Years (DALY) metric from the IHME, a measure of overall disease burden that accounts for both mortality and morbidity, and similarly calculated the excess DALY associated with long vs. short gTL.

Results

Our analysis shows that, despite the markedly larger ORs of neoplastic disease, the large incidence of degenerative diseases causes the excess incidence attributable to gTL to balance that of neoplastic diseases. Long gTL is associated with an excess incidence of 94.04 cases/100,000 persons/SD (45.49–168.84, 95%CI) from the 9 cancer, while short gTL is associated with an excess incidence of 121.49 cases/100,000 persons/SD (48.40–228.58, 95%CI) from the 4 non-neoplastic diseases. When considering disease burden using the DALY metric, long gTL is associated with an excess 1255.25 DALYs/100,000 persons/SD (662.71–2163.83, 95%CI) due to the 9 cancers, while short gTL is associated with an excess 1007.75 DALYs/100,000 persons/SD (411.63–1847.34, 95%CI) due to 4 non-neoplastic diseases.

Conclusions

Our results show that genetically determined long and short telomere length are associated with disease risk and burden of approximately equal magnitude. These results provide quantitative estimates of the relative impact of genetically-predicted short vs. long TL in a human population, and provide evidence in support of the cancer-aging paradox, wherein human telomere length is balanced by opposing evolutionary forces acting to minimize both neoplastic and non-neoplastic diseases. Importantly, our results indicate that odds ratios alone can be misleading in different clinical scenarios, and disease risk should be assessed from both an individual and population level in order to draw appropriate conclusions about the risk factor’s role in human health.

Comparing the Role of the p53 Gene and Telomerase Enzyme in 'Accelerated Aging Due to Cancer': A Literature Review

Aging is defined as progressive physiological alterations in an organism that lead to senescence. In response to stress, when proliferative-competent cells undergo permanent, irreversible growth arrest (like replicative dividing limit, oncogene activation, oxidative stress, or deoxyribonucleic acid (DNA) damage), it is termed as cellular senescence. Biomarkers p53, telomerase, and other inflammatory cytokines have a vital link with senescence, and directed use of these markers might be useful in manipulating cancer and the aging process. We included studies related to topics ' accelerated aging due to cancer', telomerase's relation to Aging and Cancer, p53's relation to Aging and Cancer, Atherosclerosis and Cancer from Search databases like PubMed and Google Scholar. We relied on peer-reviewed articles and included literature from the last 10 years written in the English language. Degenerative diseases in humans are usually linked to atherosclerosis, and atherosclerosis is associated with short leukocyte telomere length. Cancer itself and its treatment are linked with accelerated aging by causing progressive shortening of telomeres during cell replication, resulting in cell death. Gene p53 is known to have a dual effect that works as a tumor suppressor and has pro-aging side effects. In experimental studies, when p53 overcomes multiple regulatory mechanisms controlling its activity, then only the pro-aging side effects of p53 manifested. This might be a potential key for treating cancer without causing the side-effects of aging. In this review, we aim to explain and summarize the interdependent nature of p53, telomeres, and other conventional mechanisms of aging and cancer like inflammation, oxidative stress, uncontrolled proliferation, angiogenesis, micro ribonucleic acids (RNAs), and apoptosis, with a more synergistic approach that can help in developing new therapeutics and play a potential role in shaping modern human lifespan and revolutionize cancer treatment.

Telomere length varies substantially between blood cell types in a reptile

Telomeres are repeat sequences of non-coding DNA-protein molecules that cap or intersperse metazoan chromosomes. Interest in telomeres has increased exponentially in recent years, to now include their ongoing dynamics and evolution within natural populations where individuals vary in telomere attributes. Phylogenetic analyses show profound differences in telomere length across non-model taxa. However, telomeres may also differ in length within individuals and between tissues. The latter becomes a potential source of error when researchers use different tissues for extracting DNA for telomere analysis and scientific inference. A commonly used tissue type for assessing telomere length is blood, a tissue that itself varies in terms of nuclear content among taxa, in particular to what degree their thrombocytes and red blood cells (RBCs) contain nuclei or not. Specifically, when RBCs lack nuclei, leucocytes become the main source of telomeric DNA. RBCs and leucocytes differ in lifespan and how long they have been exposed to 'senescence' and erosion effects. We report on a study in which cells in whole blood from individual Australian painted dragon lizards (Ctenophorus pictus) were identified using flow cytometry and their telomere length simultaneously measured. Lymphocyte telomeres were on average 270% longer than RBC telomeres, and in azurophils (a reptilian monocyte), telomeres were more than 388% longer than those in RBCs. If this variation in telomere length among different blood cell types is a widespread phenomenon, and DNA for comparative telomere analyses are sourced from whole blood, evolutionary inference of telomere traits among taxa may be seriously complicated by the blood cell type comprising the main source of DNA.

Telomeres and COVID-19

The medical, public health, and scientific communities are grappling with monumental imperatives to contain COVID-19, develop effective vaccines, identify efficacious treatments for the infection and its complications, and find biomarkers that detect patients at risk of severe disease. The focus of this communication is on a potential biomarker, short telomere length (TL), that might serve to identify patients more likely to die from the SARS-CoV-2 infection, regardless of age. The common thread linking these patients is lymphopenia, which largely reflects a decline in the numbers of CD4/CD8 T cells but not B cells. These findings are consistent with data that lymphocyte TL dynamics impose a limit on T-cell proliferation. They suggest that T-cell lymphopoiesis might stall in individuals with short TL who are infected with SARS-CoV-2.

Retrotransposons shuttling genetic and epigenetic information from the nuclear to the mitochondrial compartment: Do they play a pathogenetic role in scleroderma?

Endogenous retroelements are a class of ancient defective viral insertions contained in the genome of host cells, where they account for up to 40% of all DNA. Centuries of co-existence in host genome have led to the development of immunotolerance to endogenous retroelements, most of which are defective and unable to replicate or transcribe functional proteins. However, given their capacity to move across the nuclear and mitochondrial genome and recombine, they could mix phenotypes and give rise to infections that may trigger innate and adaptive immune responses by sensing receptors capable of recognising foreign nucleic acids and proteins. It has recently been suggested that they play a role in the pathogenesis of autoimmune diseases on the grounds of their partial reactivation or the epigenetic control of host gene transcription. A number of studies have confirmed their contribution to the development of rheumatoid arthritis, multiple sclerosis and systemic lupus erythematosus, but there is still a lack of data concerning systemic sclerosis (SSc). Their role in the pathogenesis of SSc can be hypothesised on the basis of mitochondrial and nuclear chromatinic damage, and hyper-activation of the immune pathway involved in antiviral defense. SSc is characterised by genetic and immunological evidence of a viral infection but, as no viral agent has yet been isolated from SSc patients, the hypothesis that partial reactivation of endogenous retroviruses may trigger the disease cannot be excluded and deserves further investigation.

Telomere regulation: lessons learnt from mice and men, potential opportunities in horses

Telomeres are genetically conserved nucleoprotein complexes located at the ends of chromosomes that preserve genomic stability. In large mammals, somatic cell telomeres shorten with age, owing to the end replication problem and lack of telomere-lengthening events (e.g. telomerase and ALT activity). Therefore, telomere length reflects cellular replicative reserve and mitotic potential. Environmental insults can accelerate telomere attrition in response to cell division and DNA damage. As such, telomere shortening is considered one of the major hallmarks of ageing. Much effort has been dedicated to understanding the environmental perturbations that accelerate telomere attrition and therapeutic strategies to preserve or extend telomeres. As telomere dynamics seem to reflect cumulative cellular stress, telomere length could serve as a biomarker of animal welfare. The assessment of telomere dynamics (i.e. rate of shortening) in conjunction with telomere-regulating genes and telomerase activity in racehorses could monitor long-term animal health, yet it could also provide some unique opportunities to address particular limitations with the use of other animal models in telomere research. Considering the ongoing efforts to optimise the health and welfare of equine athletes, the purpose of this review is to discuss the potential utility of assessing telomere length in Thoroughbred racehorses. A brief review of telomere biology in large and small mammals will be provided, followed by discussion on the biological implications of telomere length and environmental (e.g. lifestyle) factors that accelerate or attenuate telomere attrition. Finally, the utility of quantifying telomere dynamics in horses will be offered with directions for future research.

Genetic Pathways of Aging and Their Relevance in the Dog as a Natural Model of Human Aging

Aging research has experienced a burst of scientific efforts in the last decades as the growing ratio of elderly people has begun to pose an increased burden on the healthcare and pension systems of developed countries. Although many breakthroughs have been reported in understanding the cellular mechanisms of aging, the intrinsic and extrinsic factors that contribute to senescence on higher biological levels are still barely understood. The dog, Canis familiaris, has already served as a valuable model of human physiology and disease. The possible role the dog could play in aging research is still an open question, although utilization of dogs may hold great promises as they naturally develop age-related cognitive decline, with behavioral and histological characteristics very similar to those of humans. In this regard, family dogs may possess unmatched potentials as models for investigations on the complex interactions between environmental, behavioral, and genetic factors that determine the course of aging. In this review, we summarize the known genetic pathways in aging and their relevance in dogs, putting emphasis on the yet barely described nature of certain aging pathways in canines. Reasons for highlighting the dog as a future aging and gerontology model are also discussed, ranging from its unique evolutionary path shared with humans, its social skills, and the fact that family dogs live together with their owners, and are being exposed to the same environmental effects.

Identification of a blood-based 12-gene signature that predicts the severity of coronary artery stenosis: An integrative approach based on gene network construction, Support Vector Machine algorithm, and multi-cohort validation

BACKGROUND AND AIMS

We aimed to identify a blood-based gene expression score (GES) to predict the severity of coronary artery stenosis in patients with known or suspected coronary artery disease (CAD) by integrative use of gene network construction, Support Vector Machine (SVM) algorithm, and multi-cohort validation.

METHODS

In the discovery phase, a public blood-based microarray dataset of 110 patients with known CAD was analyzed by weighted gene coexpression network analysis and protein-protein interaction network analysis to identify candidate hub genes. In the training set with 151 CAD patients, bioinformatically identified hub genes were experimentally verified by real-time polymerase chain reaction, and statistically filtered with the SVM algorithm to develop a GES. Internal and external validation of GES was performed in patients with suspected CAD from two validation cohorts (n = 209 and 206).

RESULTS

The discovery phase screened 15 network-centric hub genes significantly correlated with the Duke CAD Severity Index. In the training cohort, 12 of 15 hub genes were filtered to construct a blood-based GES12, which showed good discrimination for higher modified Gensini scores (AUC: 0.798 and 0.812), higher Sullivan Extent scores (AUC: 0.776 and 0.778), and the presence of obstructive CAD (AUC: 0.834 and 0.792) in two validation cohorts. A nomogram comprising GES12, smoking status, hypertension status, low density lipoprotein cholesterol level, and body mass index further improved performance, with respect to discrimination, risk classification, and clinical utility, for prediction of coronary stenosis severity.

CONCLUSIONS

GES12 is useful in predicting the severity of coronary artery stenosis in patients with known or suspected CAD.

Epigenome-wide association study of leukocyte telomere length

Telomere length is associated with age-related diseases and is highly heritable. It is unclear, however, to what extent epigenetic modifications are associated with leukocyte telomere length (LTL). In this study, we conducted a large-scale epigenome-wide association study (EWAS) of LTL using seven large cohorts (n=5,713) - the Framingham Heart Study, the Jackson Heart Study, the Women's Health Initiative, the Bogalusa Heart Study, the Lothian Birth Cohorts of 1921 and 1936, and the Longitudinal Study of Aging Danish Twins. Our stratified analysis suggests that EWAS findings for women of African ancestry may be distinct from those of three other groups: males of African ancestry, and males and females of European ancestry. Using a meta-analysis framework, we identified DNA methylation (DNAm) levels at 823 CpG sites to be significantly associated (P<1E-7) with LTL after adjusting for age, sex, ethnicity, and imputed white blood cell counts. Functional enrichment analyses revealed that these CpG sites are near genes that play a role in circadian rhythm, blood coagulation, and wound healing. Weighted correlation network analysis identified four co-methylation modules associated with LTL, age, and blood cell counts. Overall, this study reveals highly significant relationships between two hallmarks of aging: telomere biology and epigenetic changes.

Helicobacter pylori infection, serum pepsinogens as markers of atrophic gastritis, and leukocyte telomere length: a population-based study

Background

Persistent infections that induce prolonged inflammation might negatively affect the leukocyte telomere length (LTL); however, the role in LTL of Helicobacter pylori (H. pylori) infection, which persistently colonizes the stomach, remains unknown.

The study objective was to examine associations of sero-prevalence of H. pylori immunoglobulin G (IgG) antibody and serum pepsinogens (PGs), as markers of atrophic gastritis, with LTL.

A cross-sectional study was performed among 934 Arab residents of East Jerusalem, aged 27–78 years, randomly selected from Israel’s national population registry. Sera were tested for H. pylori IgG and PG levels by ELISA. LTL was measured by southern blots. Multiple linear regression models were fitted to adjust for sociodemographic and lifestyle factors.

Results

LTL decreased significantly with age (p < 0.001) and was shorter in men than women (p = 0.032). The mean LTL was longer in H. pylori sero-positive persons than negative ones: mean difference 0.13 kb (95% CI 0.02, 0.24), p = 0.016. Participants with atrophic gastritis (PGI < 30 μg/L or a PGI: PGII < 3.0) had shorter LTL than did those without: mean difference − 0.18 (95% CI − 0.32, − 0.04). The difference was of larger magnitude between persons who had past H. pylori infection (sero-negative to H. pylori IgG antibody) and atrophic gastritis, compared to those who were H. pylori sero-negative and did not have atrophic gastritis: mean difference − 0.32 kb (95% CI − 0.55, − 0.10). This association remained significant after adjustment for age, sex, and religiosity: beta coefficient − 0.21 kb (95% CI − 0.41, − 0.001), p = 0.049. The results were similar after further adjustment for lifestyle factors. In bivariate analysis, mean LTL was longer in physically active persons than non-active ones, and shorter in persons with than without obesity; however, these differences were diminished and were not significant in the multivariable model.

Conclusions

H. pylori IgG sero-positivity per se was not related to reduced LTL. However, persons with past H. pylori infection (i.e., lacking H. pylori IgG serum antibody) and with serological evidence of atrophic gastritis, had a significantly shorter LTL than did those without atrophic gastritis.

Electronic supplementary material

The online version of this article (10.1186/s40246-019-0217-3) contains supplementary material, which is available to authorized users.

Genetic and epigenetic regulation of human aging and longevity

Here we summarize the latest data on genetic and epigenetic contributions to human aging and longevity. Whereas environmental and lifestyle factors are important at younger ages, the contribution of genetics appears more important in reaching extreme old age. Genome-wide studies have implicated ~57 gene loci in lifespan. Epigenomic changes during aging profoundly affect cellular function and stress resistance. Dysregulation of transcriptional and chromatin networks is likely a crucial component of aging. Large-scale bioinformatic analyses have revealed involvement of numerous interaction networks. As the young well-differentiated cell replicates into eventual senescence there is drift in the highly regulated chromatin marks towards an entropic middle-ground between repressed and active, such that genes that were previously inactive "leak". There is a breakdown in chromatin connectivity such that topologically associated domains and their insulators weaken, and well-defined blocks of constitutive heterochromatin give way to generalized, senescence-associated heterochromatin, foci. Together, these phenomena contribute to aging.

Exposure to Environmental Pollutants and Their Association with Biomarkers of Aging: A Multipollutant Approach

Mitochondrial DNA (mtDNA) content and telomere length are putative aging biomarkers and are sensitive to environmental stressors, including pollutants. Our objective was to identify, from a set of environmental exposures, which exposure is associated with leukocyte mtDNA content and telomere length in adults. This study includes 175 adults from 50 to 65 years old from the cross-sectional Flemish Environment and Health study, of whom leukocyte telomere length and mtDNA content were determined using qPCR. The levels of exposure of seven metals, 11 organohalogens, and four perfluorinated compounds (PFHxS, PFNA, PFOA, PFOS) were measured. We performed sparse partial least-squares regression analyses followed by ordinary least-squares regression to assess the multipollutant associations. While accounting for possible confounders and coexposures, we identified that urinary cadmium (6.52%, 95% confidence interval, 1.06, 12.28), serum hexachlorobenzene (2.89%, 018, 5.68), and perfluorooctanesulfonic acid (11.38%, 5.97, 17.08) exposure were positively associated ( p < 0.05) with mtDNA content, while urinary copper (-9.88%, -14.82, -4.66) and serum perfluorohexanesulfonic acid (-4.75%, -8.79, -0.54) exposure were inversely associated with mtDNA content. Urinary antimony (2.69%, 0.45, 4.99) and mercury (1.91%, 0.42, 3.43) exposure were positively associated with leukocyte telomere length, while urinary copper (-3.52%, -6.60, -0.34) and serum perfluorooctanesulfonic acid (-3.64%, -6.60, -0.60) showed an inverse association. Our findings support the hypothesis that environmental pollutants interact with molecular hallmarks of aging.

The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight

To understand the health impact of long-duration spaceflight, one identical twin astronaut was monitored before, during, and after a 1-year mission onboard the International Space Station; his twin served as a genetically matched ground control. Longitudinal assessments identified spaceflight-specific changes, including decreased body mass, telomere elongation, genome instability, carotid artery distension and increased intima-media thickness, altered ocular structure, transcriptional and metabolic changes, DNA methylation changes in immune and oxidative stress-related pathways, gastrointestinal microbiota alterations, and some cognitive decline postflight. Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within 6 months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted. These multiomic, molecular, physiological, and behavioral datasets provide a valuable roadmap of the putative health risks for future human spaceflight.

Telomere length and age-dependent telomere attrition: the blood-and-muscle model

Short telomere length (TL) is associated with atherosclerotic cardiovascular disease (ACVD) and other age-related diseases. It is unclear whether these associations originate from having inherently short TL or a faster TL attrition before or during disease development. We proposed the blood-and-muscle model to assess TL dynamics throughout life course. Our objective was to measure TL in leukocytes (LTL) and in skeletal muscle (MTL), which served as a proxy of TL at birth. The delta (MTL–LTL) represented life-long telomere attrition. Blood draws and skeletal muscle biopsies were performed on 35 Lebanese individuals undergoing surgery. Following DNA extraction, LTL and MTL were measured by Southern blot. In every individual aged between 30 and 85 years, MTL was longer than LTL. With age, MTL and LTL decreased, but the delta (MTL–LTL) increased by 14 bp/year. We validated the blood-and-muscle model that allowed us to identify TL, TL at birth, and lifelong TL attrition in a cross-sectional study. This model can be used in larger cross-sectional studies to evaluate the association of telomere dynamics with age-related diseases onset and progression.

All's well that ends well: why large species have short telomeres

Among mammal species, almost all life-history traits are strongly size dependent. This size dependence even occurs at a molecular level. For example, both telomere length and telomerase expression show a size-dependent threshold. With some exceptions, species smaller than approximately 2 kg express telomerase, while species larger than that do not. Among species greater than approximately 5 kg, telomeres tend to be short-less than 25 kb-while among smaller species, some species have short and some have long telomeres. Here, we present a model to explore the role of body size-dependent trade-offs in shaping this threshold. We assume that selection favours short telomeres as a mechanism to protect against cancer. At the same time, selection favours long telomeres as a protective mechanism against DNA damage and replicative senescence. The relative importance of these two selective forces will depend on underlying intrinsic mortality and risk of cancer, both of which are size-dependent. Results from this model suggest that a cost-benefit model for the evolution of telomere length could explain phylogenetic patterns observed within the Class Mammalia. In addition, the model suggests a general conceptual framework to think about the role that body size plays in the evolution of tumour suppressor mechanisms.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Reflections on telomere dynamics and ageing-related diseases in humans

Epidemiological studies have principally relied on measurements of telomere length (TL) in leucocytes, which reflects TL in other somatic cells. Leucocyte TL (LTL) displays vast variation across individuals—a phenomenon already observed in newborns. It is highly heritable, longer in females than males and in individuals of African ancestry than European ancestry. LTL is also longer in offspring conceived by older men. The traditional view regards LTL as a passive biomarker of human ageing. However, new evidence suggests that a dynamic interplay between selective evolutionary forces and TL might result in trade-offs for specific health outcomes. From a biological perspective, an active role of TL in ageing-related human diseases could occur because short telomeres increase the risk of a category of diseases related to restricted cell proliferation and tissue degeneration, including cardiovascular disease, whereas long telomeres increase the risk of another category of diseases related to increased proliferative growth, including major cancers. To understand the role of telomere biology in ageing-related diseases, it is essential to expand telomere research to newborns and children and seek further insight into the underlying causes of the variation in TL due to ancestry and geographical location.

This article is part of the theme issue ‘Understanding diversity in telomere dynamics’.

Characterization in humans of in vitro leucocyte maximal telomerase activity capacity and association with stress

The goal of this study was to develop and validate a measure of maximal telomerase activity capacity (mTAC) for use in human studies of telomere biology, and to determine its association with measures of stress and stress responsivity. The study was conducted in a population of 28 healthy young women and men who were assessed serially across two separate days, at multiple time points, and in response to a standardized laboratory stressor. Venous blood was collected at each of these multiple assessments, and an in vitro mitogen challenge (phytohaemagglutinin supplemented with interleukin-2) was used to stimulate telomerase activity in leucocytes. After first establishing the optimal post-stimulation time course to characterize mTAC, we determined the within-subject stability and the between-subject variability of mTAC. The major findings of our study are as follows: (i) the optimal time point to quantify human leucocyte mTAC appears to be at 72 h after mitogen stimulation; (ii) mTAC exhibits substantial within-subject stability (correlations were in the range of r 0.68-0.82) and between-subject variability, with a high intra-class coefficient (0.70), indicating greater between-subject relative to within-subject variability; (iii) mTAC is not influenced by situational factors including time of day, cortisol, acute stress exposure and immune cell distribution in the pre-stimulation blood sample; and (iv) a significant proportion of the between-subject variability in mTAC is associated with measures of stress and stress responsivity (mTAC is lower in subjects reporting higher levels of perceived (chronic) stress and exhibiting higher psychophysiological stress reactivity). Based collectively on these findings, it appears that mTAC, as proposed and operationalized, empirically meets the key criteria to represent a potentially useful individual difference measure of telomerase activity capacity of human leucocytes.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Evolution of telomere maintenance and tumour suppressor mechanisms across mammals

Mammalian species differ dramatically in telomere biology. Species larger than 5-10 kg repress somatic telomerase activity and have shorter telomeres, leading to replicative senescence. It has been proposed that evolution of replicative senescence in large-bodied species is an anti-tumour mechanism counteracting increased risk of cancer due to increased cell numbers. By contrast, small-bodied species express high telomerase activity and have longer telomeres. To counteract cancer risk due to longer lifespan, long-lived small-bodied species evolved additional telomere-independent tumour suppressor mechanisms. Here, we tested the connection between telomere biology and tumorigenesis by analysing the propensity of fibroblasts from 18 rodent species to form tumours. We found a negative correlation between species lifespan and anchorage-independent growth. Small-bodied species required inactivation of Rb and/or p53 and expression of oncogenic H-Ras to form tumours. Large-bodied species displayed a continuum of phenotypes requiring additional genetic 'hits' for malignant transformation. Based on these data we refine the model of the evolution of tumour suppressor mechanisms and telomeres. We propose that two different strategies evolved in small and large species because small-bodied species cannot tolerate small tumours that form prior to activation of the telomere barrier, and must instead use telomere-independent strategies that act earlier, at the hyperplasia stage.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Paternal Age and Transgenerational Telomere Length Maintenance: A Simulation Model

Telomere length (TL) in offspring is positively correlated with paternal age at the time of the offspring conception. The paternal-age-at-conception (PAC) effect on TL is puzzling, and its biological implication at the population level is unknown. Using a probabilistic model of transgenerational TL and population dynamics, we simulated the effect of PAC on TL in individuals over the course of 1,000 years. Findings suggest a key role for an isometric PAC midpoint (PACmp) in modulating TL across generations, such that offspring conceived by males younger than the isometric PACmp have comparatively short telomeres, while offspring conceived by males older than the isometric PACmp have comparatively long telomeres. We further show that when cancer incidence escalates, the average PAC drops below the isometric PACmp and transgenerational adaptation to cancer ensues through TL shortening. We propose that PAC serves to maintain an optimal TL across generations.

A Tale of Two Concepts: Harmonizing the Free Radical and Antagonistic Pleiotropy Theories of Aging

SIGNIFICANCE

The two foremost concepts of aging are the mechanistic free radical theory (FRT) of how we age and the evolutionary antagonistic pleiotropy theory (APT) of why we age. Both date from the late 1950s. The FRT holds that reactive oxygen species (ROS) are the principal contributors to the lifelong cumulative damage suffered by cells, whereas the APT is generally understood as positing that genes that are good for young organisms can take over a population even if they are bad for the old organisms. Recent Advances: Here, we provide a common ground for the two theories by showing how aging can result from the inherent chemical reactivity of many biomolecules, not just ROS, which imposes a fundamental constraint on biological evolution. Chemically reactive metabolites spontaneously modify slowly renewable macromolecules in a continuous way over time; the resulting buildup of damage wrought by the genes coding for enzymes that generate such small molecules eventually masquerades as late-acting pleiotropic effects. In aerobic organisms, ROS are major agents of this damage but they are far from alone.

CRITICAL ISSUES

Being related to two sides of the same phenomenon, these theories should be compatible. However, the interface between them is obscured by the FRT mistaking a subset of damaging processes for the whole, and the APT mistaking a cumulative quantitative process for a qualitative switch.

FUTURE DIRECTIONS

The manifestations of ROS-mediated cumulative chemical damage at the population level may include the often-observed negative correlation between fitness and the rate of its decline with increasing age, further linking FRT and APT. Antioxid. Redox Signal. 29, 1003-1017.

Leukocyte telomere length, T cell composition and DNA methylation age

Both leukocyte telomere length (LTL) and DNA methylation age are strongly associated with chronological age. One measure of DNA methylation age─ the extrinsic epigenetic age acceleration (EEAA)─ is highly predictive of all-cause mortality. We examined the relation between LTL and EEAA. LTL was measured by Southern blots and leukocyte DNA methylation was determined using Illumina Infinium HumanMethylation450 BeadChip in participants in the Women's Health Initiative (WHI; n=804), the Framingham Heart Study (FHS; n=909) and the Bogalusa Heart study (BHS; n=826). EEAA was computed using 71 DNA methylation sites, further weighted by proportions of naïve CD8⁺ T cells, memory CD8⁺ T cells, and plasmablasts. Shorter LTL was associated with increased EEAA in participants from the WHI (r=-0.16, p=3.1x10^-6). This finding was replicated in the FHS (r=-0.09, p=6.5x10^-3) and the BHS (r=-0.07, p=3.8x 10^-2). LTL was also inversely related to proportions of memory CD8⁺ T cells (p=4.04x10^-16) and positively related to proportions of naive CD8⁺ T cells (p=3.57x10^-14). These findings suggest that for a given age, an individual whose blood contains comparatively more memory CD8⁺ T cells and less naive CD8⁺ T cells would display a relatively shorter LTL and an older DNA methylation age, which jointly explain the striking ability of EEAA to predict mortality.

Maternal human telomerase reverse transcriptase variants are associated with preterm labor and preterm premature rupture of membranes

Objective

Premature aging and short telomere lengths of fetal tissues are associated with spontaneous preterm labor (PTL) and preterm premature rupture of membranes (pPROM). Maintenance of telomere length is performed by the enzyme telomerase. Human telomerase reverse transcriptase (hTERT) is a subunit of telomerase, and its dysfunction affects telomere shortening. This study assessed whether maternal or fetal genetic variations in the hTERT gene are associated with PTL or pPROM.

Methods

A case (PTL or pPROM) control (term birth) genetic association study was conducted in 654 non-Hispanic white mothers (438 term, 162 PTL, 54 pPROM) and 502 non-Hispanic white newborns (346 term, 116 PTB, 40 pPROM). Maternal and fetal DNA samples were genotyped for 23 single nucleotide polymorphisms (SNPs) within the hTERT gene. Allele frequencies were compared between cases and controls, stratified by PTL and pPROM. Maternal and fetal data were analyzed separately.

Results

Allelic differences in one SNP of hTERT (rs2853690) were significantly associated with both PTL (adjusted OR 2.24, 95%CI 1.64–3.06, p = 2.32e-05) and with pPROM (adjusted OR 7.54, 95%CI 3.96–14.33, p = 2.39e-07) in maternal DNA. There was no significant association between the hTERT SNPs analyzed and PTL or pPROM in the fetal samples.

Conclusion

hTERT polymorphisms in fetal DNA do not associate with PTL or pPROM risk; however, maternal genetic variations in hTERT may play a contributory role in risk of PTL and PPROM.

Beginning at the ends: telomeres and human disease

Studies of rare and common illnesses have led to remarkable progress in the understanding of the role of telomeres (nucleoprotein complexes at chromosome ends essential for chromosomal integrity) in human disease. Telomere biology disorders encompass a growing spectrum of conditions caused by rare pathogenic germline variants in genes encoding essential aspects of telomere function. Dyskeratosis congenita, a disorder at the severe end of this spectrum, typically presents in childhood with the classic triad of abnormal skin pigmentation, nail dystrophy, and oral leukoplakia, accompanied by a very high risk of bone marrow failure, cancer, pulmonary fibrosis, and other medical problems. In contrast, the less severe end of the telomere biology disorder spectrum consists of middle-age or older adults with just one feature typically seen in dyskeratosis congenita, such as pulmonary fibrosis or bone marrow failure. In the common disease realm, large-scale molecular epidemiology studies have discovered novel associations between illnesses, such as cancer, heart disease, and mental health, and both telomere length and common genetic variants in telomere biology genes. This review highlights recent findings of telomere biology in human disease from both the rare and common disease perspectives. Multi-disciplinary collaborations between clinicians, basic scientists, and epidemiologist are essential as we seek to incorporate new telomere biology discoveries to improve health outcomes.

Reconstructing the molecular life history of gliomas

At the time of their clinical manifestation, the heterogeneous group of adult and pediatric gliomas carries a wide range of diverse somatic genomic alterations, ranging from somatic single-nucleotide variants to structural chromosomal rearrangements. Somatic abnormalities may have functional consequences, such as a decrease, increase or change in mRNA transcripts, and cells pay a penalty for maintaining them. These abnormalities, therefore, must provide cells with a competitive advantage to become engrained into the glioma genome. Here, we propose a model of gliomagenesis consisting of the following five consecutive phases that glioma cells have traversed prior to clinical manifestation: (I) initial growth; (II) oncogene-induced senescence; (III) stressed growth; (IV) replicative senescence/crisis; (V) immortal growth. We have integrated the findings from a large number of studies in biology and (neuro)oncology and relate somatic alterations and other results discussed in these papers to each of these five phases. Understanding the story that each glioma tells at presentation may ultimately facilitate the design of novel, more effective therapeutic approaches.

Stress, Telomeres, and Psychopathology: Toward a Deeper Understanding of a Triad of Early Aging

Telomeres play an important part in aging and show relationships to lifetime adversity, particularly childhood adversity. Meta-analyses demonstrate reliable associations between psychopathology (primarily depression) and shorter telomere length, but the nature of this relationship has not been fully understood. Here, we review and evaluate the evidence for impaired telomere biology as a consequence of psychopathology or as a contributing factor, and the important mediating roles of chronic psychological stress and impaired allostasis. There is evidence for a triadic relationship among stress, telomere shortening, and psychiatric disorders that is positively reinforcing and unfolds across the life course and, possibly, across generations. We review the role of genetics and biobehavioral responses that may contribute to shorter telomere length, as well as the neurobiological impact of impaired levels of telomerase. These complex interrelationships are important to elucidate because they have implications for mental and physical comorbidity and, potentially, for the prevention and treatment of depression.

Telomere Homeostasis: Interplay with Magnesium

Telomere biology, a key component of the hallmarks of ageing, offers insight into dysregulation of normative ageing processes that accompany age-related diseases such as cancer. Telomere homeostasis is tightly linked to cellular metabolism, and in particular with mitochondrial physiology, which is also diminished during cellular senescence and normative physiological ageing. Inherent in the biochemistry of these processes is the role of magnesium, one of the main cellular ions and an essential cofactor in all reactions that use ATP. Magnesium plays an important role in many of the processes involved in regulating telomere structure, integrity and function. This review explores the mechanisms that maintain telomere structure and function, their influence on circadian rhythms and their impact on health and age-related disease. The pervasive role of magnesium in telomere homeostasis is also highlighted.

Telomere length and fetal programming: A review of recent scientific advances

We sought to synthesize a comprehensive literature review comprising recent research linking fetal programming to fetal telomere length. We also explored the potential effects fetal telomere length shortening has on fetal phenotypes. Utilizing the PubMed database as our primary search engine, we retrieved and reviewed 165 articles of published research. The inclusion criteria limited the articles to those that appeared within the last ten years, were pertinent to humans, and without restriction to language of publication. Our results showed that socio-demographic factors like age, sex, genetic inheritance, and acquired disease impact telomere length. Further, we found several maternal characteristics to be associated with fetal telomere length shortening, and these include maternal chemical exposure (eg, tobacco smoke), maternal stress during pregnancy, maternal nutritional and sleeping disorders during pregnancy as well as maternal disease status. Due to paucity of data, our review could not synthesize evidence directly linking fetal phenotypes to telomere length shortening. Although the research summarized in this review shows some association between determinants of intrauterine programming and fetal telomere length, there is still significant work that needs to be done to delineate the direct relationship of telomere attrition with specific fetal phenotypes.

Telomeres, Aging and Exercise: Guilty by Association?

Telomeres are repetitive tandem DNA sequences that cap chromosomal ends protecting genomic DNA from enzymatic degradation. Telomeres progressively shorten with cellular replication and are therefore assumed to correlate with biological and chronological age. An expanding body of evidence suggests (i) a predictable inverse association between telomere length, aging and age-related diseases and (ii) a positive association between physical activity and telomere length. Both hypotheses have garnered tremendous research attention and broad consensus; however, the evidence for each proposition is inconsistent and equivocal at best. Telomere length does not meet the basic criteria for an aging biomarker and at least 50% of key studies fail to find associations with physical activity. In this review, we address the evidence in support and refutation of the putative associations between telomere length, aging and physical activity. We finish with a brief review of plausible mechanisms and potential future research directions.

Association of Accelerometer-Measured Physical Activity With Leukocyte Telomere Length Among Older Women

Background

Previous studies on physical activity and telomere length have relied largely upon self-reported physical activity data, and few studies have examined older adults. The association of objectively measured physical activity with leukocyte telomere length (LTL) is currently unknown.

Methods

In this study, we examined cross-sectional associations between accelerometer-measured total, light, and moderate-to-vigorous physical activity (MVPA) and LTL, measured using Southern blot. The sample included 1,405 older (64-95 years old) white and African American women from the Women's Health Initiative. Multiple linear regression models adjusting for potential confounders were used to determine the association between accelerometer-measured physical activity and LTL.

Results

Overall, the mean (standard deviation) of total, light, and moderate-to-vigorous activity was 5.5 (1.6), 4.7 (1.3), and 0.8 (0.5) h/d, respectively. Adjusting for accelerometer wear time, age, race/ethnicity, education, marital status, smoking, alcohol, body mass index, a history of chronic diseases, and hormone therapy use, LTL was 80 (95% confidence interval: 9, 150) base pairs longer among women with ≥2.5 compared with <2.5 h/wk of MVPA. Light activity was not significantly associated with LTL. For total activity, the most physically active women had significantly longer LTL than the least active women after adjustment for demographic and lifestyle characteristics; however, findings were not significant after further adjustment for health-related factors.

Conclusions

Older women meeting current recommendations of ≥2.5 h/wk of MVPA, as assessed by accelerometer, had longer LTL. Additional studies using accelerometers in large, diverse cohorts of older women are needed to confirm and extend these findings.

Enhancing GTEx by bridging the gaps between genotype, gene expression, and disease

Genetic variants have been associated with myriad molecular phenotypes that provide new insight into the range of mechanisms underlying genetic traits and diseases. Identifying any particular genetic variant's cascade of effects, from molecule to individual, requires assaying multiple layers of molecular complexity. We introduce the Enhancing GTEx (eGTEx) project that extends the GTEx project to combine gene expression with additional intermediate molecular measurements on the same tissues to provide a resource for studying how genetic differences cascade through molecular phenotypes to impact human health.

Leukocyte telomere length and cardiovascular disease in African Americans: The Jackson Heart Study

BACKGROUND AND AIMS

In European descent populations, shorter leukocyte telomere length (LTL) has been associated with subclinical atherosclerosis, cardiovascular disease (CVD), and mortality, while longer LTL has been associated with greater left ventricular hypertrophy. We evaluated the relationship of LTL with subclinical cardiovascular disease indices and incident clinical events and mortality in African Americans (AAs).

METHODS

Analyses were restricted to 2518 participants of the Jackson Heart Study (JHS) with LTL measured by Southern blot in baseline blood samples.

RESULTS

Adjusting for established CVD risk factors, longer LTL was significantly associated with lower prevalence of coronary artery calcification (CAC) (odds ratio (OR) = 0.810) per 1 kb increase in LTL; (95% confidence interval [CI] 0.656, 0.9998), p=0.0498). Longer LTL was also associated with higher ankle brachial index (ABI) (β = 0.023; (95% CI 0.004, 0.042), p=0.017) when comparing the highest to the lowest LTL quartile. There were no significant associations between LTL and abdominal aortic calcification, carotid intima-media thickness, or left ventricular mass. After a median follow-up of 9 years, longer LTL was associated with lower risk of incident ischemic stroke (hazard ratio (HR) 0.69 (95% CI 0.48, 0.99), p=0.044) and total mortality (HR 0.81 (95% CI 0.67, 0.97), p=0.026) in age and sex adjusted models, but these associations were no longer significant in fully adjusted models.

CONCLUSIONS

Among a community-based cohort of AAs, longer LTL was nominally associated with lower odds of CAC and increased ABI, indicative of decreased prevalence of subclinical atherosclerosis and peripheral arterial disease. These findings do not offer strong support for LTL as an independent biomarker of CVD risk in AAs.