Tying it all together: telomeres, sexual size dimorphism and the gender gap in life expectancy

Pleiotropic effects of melanin pigmentation: haemoparasite infection intensity but not telomere length is associated with plumage morph in black sparrowhawks

There is increasing recognition of the potential pleiotropic effects of melanin pigmentation, particularly on immunity, with reports of variation in haemoparasite infection intensity and immune responses between the morphs of colour-polymorphic bird species. In a population of the black sparrowhawk (Accipiter melanoleucus) in western South Africa, light morphs have a higher haemoparasite infection intensity, but no physiological effects of this are apparent. Here, we investigate the possible effects of haemoparasite infection on telomere length in this species and explore whether relative telomere length is associated with either plumage morph or sex. Using quantitative polymerase chain reaction analysis, we confirmed that dark morphs had a lower haemoparasite infection intensity than light morphs. However, we found no differences in telomere length associated with either the haemoparasite infection status or morph in adults, although males have longer telomeres than females. While differences in haemoparasite intensity between morphs are consistent with pleiotropic effects of melanin pigmentation in the black sparrowhawk, we found no evidence that telomere length was associated with haemoparasite infection. Further work is needed to investigate the implications of possible pleiotropic effects of plumage morph and their potential role in the maintenance of colour polymorphism in this species.

Lifespan and telomere length variation across populations of wild-derived African killifish

Telomeres and telomerase prevent the continuous erosion of chromosome-ends caused by lifelong cell division. Shortened telomeres are associated with age-related pathologies. While short telomere length is positively correlated with increased lethality at the individual level, in comparisons across species short telomeres are associated with long (and not short) lifespans. Here, we tested this contradiction between individual and evolutionary patterns in telomere length using African annual killifish. We analysed lifespan and telomere length in a set of captive strains derived from well-defined wild populations of Nothobranchius furzeri and its sister species, N. kadleci, from sites along a strong gradient of aridity which ultimately determines maximum natural lifespan. Overall, males were shorter-lived than females, and also had shorter telomeres. Male lifespan (measured in controlled laboratory conditions) was positively associated with the amount of annual rainfall in the site of strain origin. However, fish from wetter climates had shorter telomeres. In addition, individual fish which grew largest over the juvenile period possessed shorter telomeres at the onset of adulthood. This demonstrates that individual condition and environmentally-driven selection indeed modulate the relationship between telomere length and lifespan in opposite directions, validating the existence of inverse trends within a single taxon. Intraindividual heterogeneity of telomere length (capable to detect very short telomeres) was not associated with mean telomere length, suggesting that the shortest telomeres are controlled by regulatory pathways other than those that determine mean telomere length. The substantial variation in telomere length between strains from different environments identifies killifish as a powerful system in understanding the adaptive value of telomere length.

Gender Differences in Perceived Stress and Its Relationship to Telomere Length in Costa Rican Adults

Introduction

Stress is associated with disease and reduced leukocyte telomere length (LTL). The objective of this research is to determine if self-perceived stress is associated with telomere length in Costa Rican adults and the gender differences in this association. Findings may help explain how some populations in apparent socioeconomic disadvantage and with limited access to specialized medical services have a remarkably high life expectancy.

Methodology

Data come from the pre-retirement cohort of the Costa Rican Longevity and Healthy Aging Study (CRELES), a population based survey conducted in the households to 2,327 adults aged 53 to 66 years. The DNA to measure LTL was extracted from blood cells in laboratories of the University of Costa Rica whereas the Blackburn laboratory at the University of California performed the telomere length measurement applying the quantitative polymerase chain reaction (Q-PCR). The relationship between telomere length and perceived stress was measured using least-squares multiple regression. Perceived stress was measured by a set of questions about family, job, finances and, health reasons to be stressed. Models included the control variables: (1) age and sex of the participant, (2) whether he or she resides in the Nicoya area, a “blue zone” known for its high longevity, and (3) the aforementioned sociodemographic, health and lifestyles characteristics.

Results

Stress perception and LTL are significantly different by sex. Women perceived higher stress levels than men in almost all aspects studied, except work. Women have significantly longer telomeres. Shorter telomeres are significantly associated with caregiving stress in men and with parental health concerns in women. Counter-intuitive telomere lengthenings were observed among women who feel stressed about caring for family members; and among men who feel stressed due to their family relationships as well as concerns about their own health.

Discussion

Results confirm that people with self-perceived stress due to caregiving or health issues have shorter telomeres. The relationship between stress and telomere length differs between men and women. Gender relations exert a strong modifier effect on the relationship between stress and LTL: gender is related to perceived stress, telomere length, and apparently also to the way stress and LTL are related.

Genetic, Environmental and Lifestyle Determinants of Accelerated Telomere Attrition as Contributors to Risk and Severity of Multiple Sclerosis

Telomeres are protective structures at the ends of linear chromosomes. Shortened telomere lengths (TL) are an indicator of premature biological aging and have been associated with a wide spectrum of disorders, including multiple sclerosis (MS). MS is a chronic inflammatory, demyelinating and neurodegenerative disease of the central nervous system. The exact cause of MS is still unclear. Here, we provide an overview of genetic, environmental and lifestyle factors that have been described to influence TL and to contribute to susceptibility to MS and possibly disease severity. We show that several early-life factors are linked to both reduced TL and higher risk of MS, e.g., adolescent obesity, lack of physical activity, smoking and vitamin D deficiency. This suggests that the mechanisms underlying the disease are connected to cellular aging and senescence promoted by increased inflammation and oxidative stress. Additional prospective research is needed to clearly define the extent to which lifestyle changes can slow down disease progression and prevent accelerated telomere loss in individual patients. It is also important to further elucidate the interactions between shared determinants of TL and MS. In future, cell type-specific studies and advanced TL measurement methods could help to better understand how telomeres may be causally involved in disease processes and to uncover novel opportunities for improved biomarkers and therapeutic interventions in MS.

Telomeres, species differences, and unusual telomeres in vertebrates: presenting challenges and opportunities to understanding telomere dynamics

There has been increasing interest in the use of telomeres as biomarkers of stress, cellular ageing and life-histories. However, the telomere landscape is a diverse feature, with noticeable differences between species, a fact which is highlighted by the unusual telomeres of various vertebrate organisms. We broadly review differences in telomere dynamics among vertebrates, and emphasize the need to understand more about telomere processes and trends across species. As part of these species differences, we review unusual telomeres in vertebrates. This includes mega-telomeres, which are present across a diverse set of organisms, but also focusing on the unusual telomeres traits of marsupials and monotremes, which have seen little to no prior discussion, yet uniquely stand out from other unusual telomere features discovered thus far. Due to the presence of at least two unique telomere features in the marsupial family Dasyuridae, as well as to the presence of physiological strategies semelparity and torpor, which have implications for telomere life-histories in these species, we suggest that this family has a very large potential to uncover novel information on telomere evolution and dynamics.

No sex differences in adult telomere length across vertebrates: a meta-analysis

In many mammalian species, females live on average longer than males. In humans, women have consistently longer telomeres than men, and this has led to speculation that sex differences in telomere length (TL) could play a role in sex differences in longevity. To address the generality and drivers of patterns of sex differences in TL across vertebrates, we performed meta-analyses across 51 species. We tested two main evolutionary hypotheses proposed to explain sex differences in TL, namely the heterogametic sex disadvantage and the sexual selection hypotheses. We found no support for consistent sex differences in TL between males and females among mammal, bird, fish and reptile species. This absence of sex differences in TL across different classes of vertebrates does not support the heterogametic sex disadvantage hypothesis. Likewise, the absence of any negative effect of sexual size dimorphism on male TL suggests that sexual selection is not likely to mediate the magnitude of sex differences in TL across vertebrates. Finally, the comparative analyses we conducted did not detect any association between sex differences in TL and sex differences in longevity, which does not support the idea that sex differences in TL could explain the observed sex differences in longevity.

Sex Differences in Telomere Length Are Not Mediated by Sex Steroid Hormones or Body Size in Early Adolescence

Telomere length is a biomarker of cell aging that is hypothesized to contribute to women’s greater longevity. Although most previous studies have found no sex difference in telomere length at birth, it is well established that females have longer average telomere length than males during adulthood. Proposed biological mechanisms underlying sex differences in adult telomere length include differences in sex steroid hormones and body size, which emerge during the pubertal transition. The purpose of this study was to examine the total effect of sex on telomere length during early adolescence and to examine estradiol, total testosterone, and body surface area (BSA; a measure of body size) as potential mediators of sex differences in telomere length. Data were from a population-based sample of 126 female and 109 male Hispanic adolescents aged 8 to 14 years from the Early Life Exposures in Mexico to ENvironmental Toxicants (ELEMENT) study. Relative telomere length (T/S ratio) was measured by the quantitative polymerase chain reaction method; sex steroid hormones were measured using an automated chemiluminescent immunoassay, and BSA was calculated using measured height and weight. Adjusting for age and pubertal status, we found that girls had significantly longer telomeres than boys (β = .13; P < .01), but there were no significant indirect effects of sex on telomere length through any of the proposed mediators. We conclude that sex differences in telomere length are evident during early adolescence but are not explained by cross-sectional differences in sex steroid hormones or body size.

Bovine telomere dynamics and the association between telomere length and productive lifespan

Average telomere length (TL) in blood cells has been shown to decline with age in a range of vertebrate species, and there is evidence that TL is a heritable trait associated with late-life health and mortality in humans. In non-human mammals, few studies to date have examined lifelong telomere dynamics and no study has estimated the heritability of TL, despite these being important steps towards assessing the potential of TL as a biomarker of productive lifespan and health in livestock species. Here we measured relative leukocyte TL (RLTL) in 1,328 samples from 308 Holstein Friesian dairy cows and in 284 samples from 38 female calves. We found that RLTL declines after birth but remains relatively stable in adult life. We also calculated the first heritability estimates of RLTL in a livestock species which were 0.38 (SE = 0.03) and 0.32 (SE = 0.08) for the cow and the calf dataset, respectively. RLTL measured at the ages of one and five years were positively correlated with productive lifespan (p < 0.05). We conclude that bovine RLTL is a heritable trait, and its association with productive lifespan may be used in breeding programmes aiming to enhance cow longevity.

Sex differences in the 1-year risk of dying following all-cause and cause-specific hospital admission after age 50 in comparison with a general and non-hospitalised population: a register-based cohort study of the Danish population

OBJECTIVES

We examine the mortality of men and women within the first year after all-cause and cause-specific hospital admission to investigate whether the sex differences in mortality after hospitalisation are higher than in the corresponding general and non-hospitalised population.

DESIGN

This is a population-based, longitudinal study with nationwide coverage. The study population was identified by linking the National Patient Register with the Central Population Register using a 5% random sample of the Danish population.

SETTING

The population born between 1898 and 1961, who was alive and residing in Denmark after 1977, was followed up between 1977 and 2011 with respect to hospital admissions and mortality while aged 50-79.

PRIMARY OUTCOME MEASURES

The absolute sex differences in the 1-year risk of dying after all-cause and cause-specific hospital admission. The hospitalised population sex differentials were then compared with the sex differences in a general and a non-hospitalised population, randomly matched by age, sex and hospitalisation status.

RESULTS

The risk of dying was consistently higher for hospitalised men and women. At all ages, the absolute sex differences in mortality were largest in the hospitalised population, were smaller in the general population and were smallest in the non-hospitalised population. This pattern was consistent across all-cause admissions, and with respect to admissions for neoplasms, circulatory diseases and respiratory diseases. For all-cause hospital admissions, absolute sex differences in the 1-year risk of dying resulted in 43.8 excess male deaths per 1,000 individuals within the age range 50-79, while the levels were lower in the general and the non-hospitalised population, at levels of 13.5 and 6.6, respectively.

CONCLUSIONS

This study indicates a larger male disadvantage in mortality following hospitalisation, pointing towards an association between the health status of a population and the magnitude of the female advantage in mortality.

Telomere length as a potential biomarker of coronary artery disease

Coronary artery disease (CAD) is a multifactorial disease whose prevalence remains unabated especially in developing countries. Both lifestyle factors and genetic predisposition contribute to this disorder. Though notable achievements have been made in the medical, interventional and surgical management of CAD, the need for its prevention is more important. Among other modalities, this calls for defining evidence-based new biomarkers, which on their own or in combination with other known biomarkers may predict the risk of CAD to enable institution of appropriate preventive strategies. In the present communication, we have discussed the usefulness of shortening of telomeres as a potential biomarker of CAD. Clinical research evidence in favour of telomere shortening in CAD is well documented in different ethnic populations of the world. Establishing a well-standardized and accurate method of evaluating telomere length is essential before its routine use in preventive cardiology.

Somatic growth and telomere dynamics in vertebrates: relationships, mechanisms and consequences

Much telomere loss takes place during the period of most rapid growth when cell proliferation and potentially energy expenditure are high. Fast growth is linked to reduced longevity. Therefore, the effects of somatic cell proliferation on telomere loss and cell senescence might play a significant role in driving the growth-lifespan trade-off. While different species will have evolved a growth strategy that maximizes lifetime fitness, environmental conditions encountered during periods of growth will influence individual optima. In this review, we first discuss the routes by which altered cellular conditions could influence telomere loss in vertebrates, with a focus on oxidative stress in both in vitro and in vivo studies. We discuss the relationship between body growth and telomere length, and evaluate the empirical evidence that this relationship is generally negative. We further discuss the potentially conflicting hypotheses that arise when other factors are taken into account, and the further work that needs to be undertaken to disentangle confounding variables.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Gender and survival in essential thrombocythemia: A two-center study of 1,494 patients

Based on suggestive information from recent epidemiologic data and earlier retrospective studies, we revisited the effect of gender on survival in 1,494 patients with essential thrombocythemia (ET). The primary study population included 904 patients from the Mayo Clinic (median age 58 years; 65% females); risk distribution, according to the international prognostic score for ET (IPSET), was 23% high, 42% intermediate and 35% low. Multivariable analysis that included IPSET-relevant risk factors identified male sex (HR 1.6, 95% CI 1.3-2.0), age ≥60 years (HR 4.3, 95% CI 3.4-5.4) and leukocyte count ≥11 × 10(9)/L (HR 1.5, 95% CI 1.3-1.9) as independent predictors of shortened survival. These findings were confirmed by analysis of a separate cohort of 590 ET patients (65% females) from the University of Florence, Italy, with corresponding HRs (95% CI) of 1.6 (1.1-2.5), 4.6 (2.2-9.5) and 1.8 (1.1-2.8). The independent prognostic effect of gender was further corroborated by a separate multivariable analysis against IPSET risk categories; HR (95% CI) for the Mayo Clinic/Florence cohorts were 1.5/1.6 (1.2/1.1-1.8/2.5) for male sex, 6.8/7.5 (5.0/3.1-9.3/18.3) for IPSET high risk and 2.8/4.1 (2.1/1.8-3.8/9.5) for IPSET intermediate risk. Furthermore, the survival disadvantage in men was most apparent in IPSET high risk category and in patients older than 60 years. In both patient cohorts, thrombosis history garnered significance in univariate, but not in multivariable analysis. The observations from the current study suggest that women with ET live longer than their male counterparts and that gender might supersede thrombosis history as a risk variable for overall survival.

Sex differences in leucocyte telomere length in a free-living mammal

Mounting evidence suggests that average telomere length reflects previous stress and predicts subsequent survival across vertebrate species. In humans, leucocyte telomere length (LTL) is consistently shorter during adulthood in males than in females, although the causes of this sex difference and its generality to other mammals remain unknown. Here, we measured LTL in a cross‐sectional sample of free‐living Soay sheep and found shorter telomeres in males than in females in later adulthood (>3 years of age), but not in early life. This observation was not related to sex differences in growth or parasite burden, but we did find evidence for reduced LTL associated with increased horn growth in early life in males. Variation in LTL was independent of variation in the proportions of different leucocyte cell types, which are known to differ in telomere length. Our results provide the first evidence of sex differences in LTL from a wild mammal, but longitudinal studies are now required to determine whether telomere attrition rates or selective disappearance are responsible for these observed differences.

see also the Perspective by Dantzer and Garratt

Understanding the links between month of birth, body height, and longevity: why some studies reveal that shorter people live longer – further evidence of seasonal programming from the Polish population

There is a lack of agreement in the literature as to whether adult height depends on month of birth and whether height affects lifespan. Additionally, the relationship between stature and longevity involves conflicting findings and the results remain mixed due to several confounders, such as: year of birth, somatotype, relative body weight, genetic inheritance, diet, diseases, etc. Here, we hypothesize that the season of birth effect can also be involved in shaping the mysterious link between body height and longevity. To assess the links between month of birth, adult height, and longevity in the Polish population, data on 848,860 individuals, of whom 483,512 were men (57%) and 365,348 were women (43%), born in the years 1896-1988 and died in the years 2004-2008, were collected from the ‘PESEL’ database and signalments in the censuses obtained from identity card offices throughout Poland. ANOVA and the LSD test were performed. A significant relationship between month of birth and lifespan was found. Individuals born in autumn and winter months lived significantly longer than those who were born in the middle of the year (May). The amplitudes of lifespan were 16 months in men and 14 months in women. As expected, subjects of both sexes born in autumn and winter months were significantly shorter than their peers born around the middle of the year. In conclusion, the results of the study not only corroborate the theory of seasonal programming of longevity and support the idea that some undetermined factors from early stages of ontogeny and associated with season of birth have long-term effects on phenotype in later life in terms of adult height and longevity, but also bear out the hypothesis that month of birth can be another important confounding factor with respect to the relationship between adult height and longevity.

Life history evolution, reproduction, and the origins of sex-dependent aging and longevity

Males and females in many species differ in how they age and how long they live. These differences have motivated much research, concerning both their evolution and the underlying mechanisms that cause them. We review how differences in male and female life histories have evolved to shape patterns of aging and some of the mechanisms and pathways involved. We pay particular attention to three areas where considerable potential for synergy between mechanistic and evolutionary research exists: (1) the role of estrogens, androgens, the growth hormone/insulin-like growth factor 1 pathway, and the mechanistic target of rapamycin signaling pathway in sex-dependent growth and reproduction; (2) sexual conflict over mating rate and fertility, and how mate presence or mating can become an avenue for males and females to directly affect each other's life span; and (3) the link between dietary restriction and aging, and the emerging understanding that only the restriction of certain nutrients is involved and that this is linked to reproduction. We suggest that ideas about life histories, sex-dependent selection, and sexual conflict can inform and be informed by the ever more refined and complex understanding of the mechanisms that cause aging.

The relationship between adult stature and longevity: tall men are unlikely to outlive their short peers – evidence from a study of all adult deaths in Poland in the years 2004–2008

Early epidemiological studies demonstrated that short stature is associated with cardiovascular disease (CVD), diabetes, lower energy intake or food deprivation during growth, poor health, and increased all-cause mortality. Nevertheless, the links between adult height and longevity become tenuous if certain confounders (e.g. BMI, SES, educational attainment, etc.) are allowed for. Furthermore, numerous studies have found that like excess weight, tallness is costly in terms of longevity in late ontogeny, and shorter people tend to outlive their taller peers, especially if they are slim and maintain a healthy diet and lifestyle. Therefore, there is currently a lack of agreement in the literature as to whether and how body height and lifespan are linked. The objective of this study was to explore the relationship between adult stature and longevity on the basis of a large sample from a population-based cohort study. Data on declared height and exact dates of birth and death were available from 480,493 men and 364,666 women who died in the years 2004-2008 in Poland. To control for secular changes, the sample was divided into fifteen birth cohorts and each group was subsequently split into five height categories using pentiles, separately for both sexes. The analysis has revealed an inverse relationship between height and lifespan in men and women. However, after controlling for secular changes in height, the relationship turned out to be very weak and linear in men, and inverted U-shaped in women. In general, taller individuals had lower age at death compared to shorter ones, and this relationship was more pronounced and consistent in men. To sum up, these findings do not comport with the traditional belief that taller individuals live longer. The role of several possible biological mechanisms pertinent to enhanced longevity in smaller individuals was emphasized, and these biological factors were discussed.

Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon

A larger body size confers many benefits, such as increased reproductive success, ability to evade predators and increased competitive ability and social status. However, individuals rarely maximize their growth rates, suggesting that this carries costs. One such cost could be faster attrition of the telomeres that cap the ends of eukaryotic chromosomes and play an important role in chromosome protection. A relatively short telomere length is indicative of poor biological state, including poorer tissue and organ performance, reduced potential longevity and increased disease susceptibility. Telomere loss during growth may also be accelerated by environmental factors, but these have rarely been subjected to experimental manipulation in the natural environment. Using a wild system involving experimental manipulations of juvenile Atlantic salmon Salmo salar in Scottish streams, we found that telomere length in juvenile fish was influenced by parental traits and by direct environmental effects. We found that faster‐growing fish had shorter telomeres and there was a greater cost (in terms of reduced telomere length) if the growth occurred in a harsher environment. We also found a positive association between offspring telomere length and the growth history of their fathers (but not mothers), represented by the number of years fathers had spent at sea. This suggests that there may be long‐term consequences of growth conditions and parental life history for individual longevity.

Contemporary views on human aging and longevity

Aging is currently stimulating intense interest of both researchers and the general public. In developed countries, the average life expectancy has increased by roughly 30 years within the last century, and human senescence has been delayed by around a decade. Although aging is arguably the most familiar aspect of human biology, its proximate and ultimate causes have not been elucidated fully and understood yet. Nowadays there are two main approaches to the ultimate causes of aging. These are deterministic and stochastic models. The proximate theories constitute a distinct group of explanations. They focus on mechanistic causes of aging. In this view, there is no reason to believe that there is only one biological mechanism responsible for aging. The aging process is highly complex and results from an accumulation of random molecular damage. Currently, the disposable soma theory (DST), proposed by Thomas Kirkwood, is the most influential and coherent line of reasoning in biogerontology. This model does not postulate any particular mechanism underpinning somatic defense. Therefore, it is compatible with various models, including mechanistic and evolutionary explanations. Recently, however, an interesting theory of hyper-function of mTOR as a more direct cause of aging has been formulated by Mikhail Blagosklonny, offering an entirely different approach to numerous problems and paradoxes in current biogerontology. In this view, aging is quasi-programmed, which means that it is an aimless continuation of developmental growth. This mTOR-centric model allows the prediction of completely new relationships. The aim of this article is to present and compare the views of both parties in the dispute, based on the results of some recent experimental studies, and the contemporary knowledge of selected major aspects of human aging and longevity

How Much Should We Weigh for a Long and Healthy Life Span? The Need to Reconcile Caloric Restriction versus Longevity with Body Mass Index versus Mortality Data

Total caloric restriction (CR) without malnutrition is a well-established experimental approach to extend life span in laboratory animals. Although CR in humans is capable of shifting several endocrinological parameters, it is not clear where the minimum inflection point of the U-shaped curve linking body mass index (BMI) with all-cause mortality lies. The exact trend of this curve, when used for planning preventive strategies for public health is of extreme importance. Normal BMI ranges from 18.5 to 24.9; many epidemiological studies show an inverse relationship between mortality and BMI inside the normal BMI range. Other studies show that the lowest mortality in the entire range of BMI is obtained in the overweight range (25-29.9). Reconciling the extension of life span in laboratory animals by experimental CR with the BMI-mortality curve of human epidemiology is not trivial. In fact, one interpretation is that the CR data are identifying a known: "excess fat is deleterious for health"; although a second interpretation may be that: "additional leanness from a normal body weight may add health and life span delaying the process of aging." This short review hope to start a discussion aimed at finding the widest consensus on which weight range should be considered the "healthiest" for our species, contributing in this way to the picture of what is the correct life style for a long and healthy life span.

Gender and cataract--the role of estrogen

There is evidence from epidemiologic data that cataract is more common in women than men. This is not solely due to a higher rate of cataract extraction in women, as is the case in the western world, but several population-based studies show that females have a higher prevalence of lens opacities, especially cortical. There is no firm evidence that lifestyle-related factors are the cause of this gender discrepancy. Focus has therefore been directed towards the role of estrogen in cataract formation. Although data on endogenous and exogenous estrogen involvement in cataractogenesis are conflicting, some studies have indicated that hormone therapy may decrease the risk of cataract and thus be protective. It has been hypothesized that the decrease in estrogen at menopause cause increased risk of cataract in women, i.e. not strictly the concentration of estrogen, but more the withdrawal effect. Estrogens are known to exert several anti-aging effects that may explain the longer lifespan in women, including metabolically beneficial effects, neuroprotection, preservation of telomeres and anti-oxidative properties. Since oxidative stress is considered important in cataractogenesis, studies have investigated the effects of estrogens on lens epithelial cells in culture or in animal models. Several investigators have found protection by physiological concentrations of 17β-estradiol against oxidative stress induced by H2O2 in cultured lens epithelial cells. Although both main types of estrogen receptors, ERα and ERβ, have been demonstrated in lens epithelium, most studies so far indicate that the estrogen-mediated protection in the lens is exerted through non-genomic, i.e. receptor-independent mechanisms, possibly through phosphorylation of extracellular signal-regulated kinase (ERK1/ERK2), a member of the mitogen-activated protein kinase (MAPK)-signaling pathway. Further studies are needed, both epidemiologic as to the role of hormone therapies, and laboratory studies regarding molecular estrogen-mediated mechanisms, in order to comprehend the role of estrogens on cataract formation.

The telomeric sync model of speciation: species-wide telomere erosion triggers cycles of transposon-mediated genomic rearrangements, which underlie the saltatory appearance of nonadaptive characters

Charles Darwin knew that the fossil record is not overwhelmingly supportive of genetic and phenotypic gradualism; therefore, he developed the core of his theory on the basis of breeding experiments. Here, I present evidence for the existence of a cell biological mechanism that strongly points to the almost forgotten European concept of saltatory evolution of nonadaptive characters, which is in perfect agreement with the gaps in the fossil record. The standard model of chromosomal evolution has always been handicapped by a paradox, namely, how speciation can occur by spontaneous chromosomal rearrangements that are known to decrease the fertility of heterozygotes in a population. However, the hallmark of almost all closely related species is a differing chromosome complement and therefore chromosomal rearrangements seem to be crucial for speciation. Telomeres, the caps of eukaryotic chromosomes, erode in somatic tissues during life, but have been thought to remain stable in the germline of a species. Recently, a large human study spanning three healthy generations clearly found a cumulative telomere effect, which is indicative of transgenerational telomere erosion in the human species. The telomeric sync model of speciation presented here is based on telomere erosion between generations, which leads to identical fusions of chromosomes and triggers a transposon-mediated genomic repatterning in the germline of many individuals of a species. The phenotypic outcome of the telomere-triggered transposon activity is the saltatory appearance of nonadaptive characters simultaneously in many individuals. Transgenerational telomere erosion is therefore the material basis of aging at the species level.

A test of biological and behavioral explanations for gender differences in telomere length: the multi-ethnic study of atherosclerosis

The purpose of this study was to examine biological and behavioral explanations for gender differences in leukocyte telomere length (LTL), a biomarker of cell aging that has been hypothesized to contribute to women's greater longevity. Data are from a subsample (n = 851) of the Multi-Ethnic Study of Atherosclerosis, a population-based study of women and men aged 45 to 84. Mediation models were used to examine study hypotheses. We found that women had longer LTL than men, but the gender difference was smaller at older ages. Gender differences in smoking and processed meat consumption partially mediated gender differences in telomere length, whereas gender differences in estradiol, total testosterone, oxidative stress, and body mass index did not. Neither behavioral nor biological factors explained why the gender difference in LTL was smaller at older ages. Longitudinal studies are needed to assess gender differences in the rate of change in LTL over time; to identify the biological, behavioral, and psychosocial factors that contribute to these differences throughout the life course; and to determine whether gender differences in LTL explain the gender gap in longevity.

Do you know the sex of your cells?

Do you know the sex of your cells? Not a question that is frequently heard around the lab bench, yet thanks to recent research is probably one that should be asked. It is self-evident that cervical epithelial cells would be derived from female tissue and prostate cells from a male subject (exemplified by HeLa and LnCaP, respectively), yet beyond these obvious examples, it would be true to say that the sex of cell lines derived from non-reproductive tissue, such as lung, intestine, kidney, for example, is given minimal if any thought. After all, what possible impact could the presence of a Y chromosome have on the biochemistry and cell biology of tissues such as the exocrine pancreatic acini? Intriguingly, recent evidence has suggested that far from being irrelevant, genes expressed on the sex chromosomes can have a marked impact on the biology of such diverse tissues as neurons and renal cells. It is also policy of AJP-Cell Physiology that the source of all cells utilized (species, sex, etc.) should be clearly indicated when submitting an article for publication, an instruction that is rarely followed (http://www.the-aps.org/mm/Publications/Info-For-Authors/Composition). In this review we discuss recent data arguing that the sex of cells being used in experiments can impact the cell's biology, and we provide a table outlining the sex of cell lines that have appeared in AJP-Cell Physiology over the past decade.

Medaka fish exhibits longevity gender gap, a natural drop in estrogen and telomere shortening during aging: a unique model for studying sex-dependent longevity

Introduction

Females having a longer telomere and lifespan than males have been documented in many animals. Such linkage however has never been reported in fish. Progressive shortening of telomere length is an important aging mechanism. Mounting in vitro evidence has shown that telomere shortening beyond a critical length triggered replicative senescence or cell death. Estrogen has been postulated as a key factor contributing to maintenance of telomere and sex-dependent longevity in animals. This postulation remains unproven due to the lack of a suitable animal system for testing. Here, we introduce a teleost model, the Japanese medaka Oryzias latipes, which shows promise for research into the molecular mechanism(s) controlling sex difference in aging.

Results

Using the medaka, we demonstrate for the first time in teleost that (i) sex differences (female > male) in telomere length and longevity also exist in fish, and (ii) a natural, ‘menopause’-like decline of plasma estrogen was evident in females during aging. Estrogen levels significantly correlated with telomerase activity as well as telomere length in female organs (not in males), suggesting estrogen could modulate telomere length via telomerase activation in a sex -specific manner. A hypothetical in vivo ‘critical’ terminal restriction fragment (TRF, representing telomere) length of approximately 4 kb was deduced in medaka liver for prediction of organismal mortality, which is highly comparable with that for human cells. An age conversion model was also established to enable age translation between medaka (in months) and human (in years). These novel tools are useful for future research on comparative biology of aging using medaka.

Conclusion

The striking similarity in estrogen profile between aging female O. latipes and women enables studying the influence of “postmenopausal” decline of estrogen on telomere and longevity without the need of invasive ovariectomy. Medaka fish is advantageous for studying the direct effect of increased estrogen on telomere length and longevity without the breast cancer complications reported in rodents. The findings strongly support the notion that O. latipes is a unique non-mammalian model for validation of estrogenic influence on telomere and longevity in vertebrates. This laboratory model fish is of potential significance for deciphering the ostensibly conserved mechanism(s) of sex-associated longevity in vertebrates.

Gender and longevity: why do men die earlier than women? Comparative and experimental evidence

Sex differences in lifespan exist world-wide, with women outliving men by more than a decade in some countries. The gender gap is not a uniquely human phenomenon; most sexually reproducing species examined show sex differences in patterns of ageing, yet a comprehensive explanation does not exist. Here, we discuss how ageing responds to natural selection on traits that arise as a consequence of sexuality. Sexual dimorphisms in vertebrates are mediated by sex-steroids, such as androgens and oestrogens, and we examine their regulation of biological processes that can affect ageing and lifespan. The sexes can respond differently to dietary restriction and altered activity of nutrient-sensing pathways, with females showing a greater plasticity for life extension. We suggest that the cross-regulation of steroid hormone and nutrient-sensing signalling pathways is a promising process for further study in understanding the biological basis for the gender gap.

How height is related to our health and longevity: a review

Most people believe that being taller and heavier is a sign of higher social status and privilege; however, an objective evaluation of the advantages and disadvantages of increased body size (excluding obesity) indicated that shorter, smaller bodies have numerous advantages in terms of health and longevity. With healthful nutrition and lifestyles, and good medical care, shorter people are less likely to suffer from age-related chronic diseases and more likely to reach advanced ages. A variety of biological factors explain the inherent benefits of smaller bodies. These include reduced cell replication, much lower DNA damage and reduced cancer incidence. Other beneficial factors include higher sex hormone binding globulin, higher insulin-like growth factor binding protein-1, lower insulin and lower insulin-like growth factor-1. We discuss recommendations for how taller people can minimize their risks. Future public health practices should focus on healthful nutrition, without promoting continued secular growth in height and weight.

Sex differences in telomeres and lifespan

Males and females often age at different rates resulting in longevity 'gender gaps', where one sex outlives the other. Why the sexes have different lifespans is an age-old question, still fiercely debated today. One cellular process related to lifespan, which is known to differ according to sex, is the rate at which the protective telomere chromosome caps are lost. In humans, men have shorter lifespans and greater telomere shortening. This has led to speculation in the medical literature that sex-specific telomere shortening is one cause of sex-specific mortality. However, telomere shortening may be a cause for and/or a consequence of the processes that govern survival, and to infer general principles from single-taxon studies may be misleading. Here, we review recent work on telomeres in a variety of animal taxa, including those with reverse sexual lifespan dimorphism (i.e., where males live longer), to establish whether sex-specific survival is generally associated with sex differences in telomere dynamics. By doing this, we attempt to tease apart the potential underlying causes for sex differences in telomere lengths in humans and highlight targets for future research across all taxa.

Are men aging as oaks and women as reeds? A behavioral hypothesis to explain the gender paradox of French centenarians

Since the 1990s, several studies involving French centenarians have shown a gender paradox in old age. Even if women are more numerous in old age and live longer than men, men are in better physical and cognitive health, are higher functioning, and have superior vision. If better health should lead to a longer life, why are men not living longer than women? This paper proposes a hypothesis based on the differences in the generational habitus between men and women who were born at the beginning of the 20th century. The concept of generational habitus combines the generation theory of Mannheim with the habitus concept of Bourdieu based on the observation that there exists a way of being, thinking, and doing for each generation. We hypothesized that this habitus still influences many gender-linked behaviours in old age. Men, as "oaks," seem able to delay the afflictions of old age until a breaking point, while women, as "reeds," seem able to survive despite an accumulation of health deficits.

The association of telomere length and cancer: a meta-analysis

BACKGROUND

Telomeres shorten with each cell division and are essential for chromosomal stability. Short telomeres in surrogate tissues (e.g., blood cells) are associated with increased cancer risk in several case-control studies, but findings are inconsistent in prospective studies.

METHODS

We systematically reviewed studies published prior to August 30, 2010, on the association between telomere length (TL) in surrogate tissues and cancer. There were 27 reports on 13 cancers and/or incident cancer investigating this association. The majority, 16, were retrospective case--control studies, 11 were prospective studies. Meta-analyses were conducted to determine ORs and 95% CIs for these studies.

RESULTS

Studies on bladder, esophageal, gastric, head and neck, ovarian, renal, and overall incident cancer found associations between short telomeres and these cancers. Non-Hodgkin lymphoma, breast, lung, and colorectal cancer reports were inconsistent. Single studies on endometrial, prostate, and skin cancers were null. In a random-effects meta-analysis, short TL was significantly associated with cancer in retrospective studies (pooled OR for the shortest TL quartile compared with the longest: 2.9, 95% CI: 1.75-4.8, P < 0.0001). The pooled OR for prospective studies was 1.16 (95% CI: 0.87-1.54, P = 0.32). All studies combined yielded a pooled OR of 1.96 (95% CI: 1.37-2.81, P = 0.0001) for the association of short TL and cancer.

CONCLUSION AND IMPACT

There is suggestive evidence that short surrogate tissue TL is associated with cancer; the strongest evidence exists for bladder, esophageal, gastric, and renal cancers. Additional prospective studies with consistent methodology are needed to confirm this hypothesis.

Sex differences in sand lizard telomere inheritance: paternal epigenetic effects increases telomere heritability and offspring survival

Background

To date, the only estimate of the heritability of telomere length in wild populations comes from humans. Thus, there is a need for analysis of natural populations with respect to how telomeres evolve.

Methodology/Principal Findings

Here, we show that telomere length is heritable in free-ranging sand lizards, Lacerta agilis. More importantly, heritability estimates analysed within, and contrasted between, the sexes are markedly different; son-sire heritability is much higher relative to daughter-dam heritability. We assess the effect of paternal age on Telomere Length (TL) and show that in this species, paternal age at conception is the best predictor of TL in sons. Neither paternal age per se at blood sampling for telomere screening, nor corresponding age in sons impact TL in sons. Processes maintaining telomere length are also associated with negative fitness effects, most notably by increasing the risk of cancer and show variation across different categories of individuals (e.g. males vs. females). We therefore tested whether TL influences offspring survival in their first year of life. Indeed such effects were present and independent of sex-biased offspring mortality and offspring malformations.

Conclusions/Significance

TL show differences in sex-specific heritability with implications for differences between the sexes with respect to ongoing telomere selection. Paternal age influences the length of telomeres in sons and longer telomeres enhance offspring survival.

Sexual differences in telomere selection in the wild

Telomere length is restored primarily through the action of the reverse transcriptase telomerase, which may contribute to a prolonged lifespan in some but not all species and may result in longer telomeres in one sex than the other. To what extent this is an effect of proximate mechanisms (e.g. higher stress in males, higher oestradiol/oestrogen levels in females), or is an evolved adaptation (stronger selection for telomere length in one sex), usually remains unknown. Sand lizard (Lacerta agilis) females have longer telomeres than males and better maintain telomere length through life than males do. We also show that telomere length more strongly contributes to life span and lifetime reproductive success in females than males and that telomere length is under sexually diversifying selection in the wild. Finally, we performed a selection analysis with number of recruited offspring into the adult population as a response variable with telomere length, life span and body size as predictor variables. This showed significant differences in selection pressures between the sexes with strong ongoing selection in females, with these three predictors explaining 63% of the variation in recruitment. Thus, the sexually dimorphic telomere dynamics with longer telomeres in females is a result of past and ongoing selection in sand lizards. Finally, we compared the results from our selection analyses based on Telometric-derived data to the results based on data generated by the software ImageJ. ImageJ resulted in shorter average telomere length, but this difference had virtually no qualitative effect on the patterns of ongoing selection.

The role of estrogen deficiency in skin ageing and wound healing

The links between hormonal signalling and lifespan have been well documented in a range of model organisms. For example, in C. elegans or D. melanogaster, lifespan can be modulated by ablating germline cells, or manipulating reproductive history or pregnenolone signalling. In mammalian systems, however, hormonal contribution to longevity is less well understood. With increasing age human steroid hormone profiles change substantially, particularly following menopause in women. This article reviews recent links between steroid sex hormones and ageing, with special emphasis on the skin and wound repair. Estrogen, which substantially decreases with advancing age in both males and females, protects against multiple aspects of cellular ageing in rodent models, including oxidative damage, telomere shortening and cellular senescence. Estrogen's effects are particularly pronounced in the skin where cutaneous changes post-menopause are well documented, and can be partially reversed by classical Hormone Replacement Therapy (HRT). Our research shows that while chronological ageing has clear effects on skin wound healing, falling estrogen levels are the principle mediator of these effects. Thus, both HRT and topical estrogen replacement substantially accelerate healing in elderly humans, but are associated with unwanted deleterious effects, particularly cancer promotion. In fact, much current research effort is being invested in exploring the therapeutic potential of estrogen signalling manipulation to reverse age-associated pathology in peripheral tissues. In the case of the skin the differential targeting of estrogen receptors to promote healing in aged subjects is a real therapeutic possibility.

A role for cell sex in stem cell-mediated skeletal muscle regeneration: female cells have higher muscle regeneration efficiency

We have shown that muscle-derived stem cells (MDSCs) transplanted into dystrophic (mdx) mice efficiently regenerate skeletal muscle. However, MDSC populations exhibit heterogeneity in marker profiles and variability in regeneration abilities. We show here that cell sex is a variable that considerably influences MDSCs' regeneration abilities. We found that the female MDSCs (F-MDSCs) regenerated skeletal muscle more efficiently. Despite using additional isolation techniques and cell cloning, we could not obtain a male subfraction with a regeneration capacity similar to that of their female counterparts. Rather than being directly hormonal or caused by host immune response, this difference in MDSCs' regeneration potential may arise from innate sex-related differences in the cells' stress responses. In comparison with F-MDSCs, male MDSCs have increased differentiation after exposure to oxidative stress induced by hydrogen peroxide, which may lead to in vivo donor cell depletion, and a proliferative advantage for F-MDSCs that eventually increases muscle regeneration. These findings should persuade researchers to report cell sex, which is a largely unexplored variable, and consider the implications of relying on cells of one sex.

Arterial baroreflex function does not influence telomere length in kidney of rats

AIM

To investigate the relationship between arterial baroreflex (ABR) function and telomere length in kidney of rats.

METHODS

Stroke-prone spontaneously hypertensive rats (SHR-SP) and sinoaortic denervated rats (SAD) were used as models with depressed arterial baroreflex. In the first experiments, SHR-SP rats were examined at the age of 24 weeks for both sexes and 40 weeks for female rats. In the second experiments, SAD rats were studied 4 and 35 weeks after SAD operation. Blood pressure was continuously recorded for 4 h in a conscious state. After the determination of baroreflex sensitivity (BRS), the terminal restriction fragment (TRF) of rat kidney was analyzed using Southern blot.

RESULTS

The TRF length was found shorter in: a) male SHR-SP compared with age-matched female SHR-SP; b) female SHR-SP 40 weeks of age compared with 24 weeks of age; c) in rats 35 weeks after operation compared with rats 4 weeks post operation in both sham-operated and SAD rats.

CONCLUSION

In SHR-SP, the TRF length did not correlate with BRS. In addition, SAD did not affect TRF length at either 4 or 35 weeks post-surgery. It may be concluded that baroreflex function does not influence the terminal restriction fragment (TRF) length in rats.

Women's Mental Health Research: The Emergence of a Biomedical Field

This review surveys the field of women's mental health, with particular emphasis on its evolution into a distinct area of biomedical research. The field employs a biomedical disease model but it also emphasizes social and cultural influences on health outcomes. In recent years, its scope has expanded beyond studies of disorders occurring in women at times of reproductive transitions and it now encompasses a broader study of sex and gender differences. Historical and conceptual influences on the field are discussed. The review also surveys gender differences in the prevalence and clinical manifestations of mental disorders. Epidemiological findings have provided a rich resource for theory development, but without research tools to test theories adequately, findings of gender differences have begged the question of their biological, social, and cultural origins. Clinical depression is used to exemplify the usefulness of a sex/gender perspective in understanding mental illness; and major theories proposed to account for gender differences are critically evaluated. The National Institutes of Health (NIH) is the primary federal funding source for biomedical women's mental health research. The review surveys areas of emphasis in women's mental health research at the NIH as well as some collaborative activities that represent efforts to translate research findings into the public health and services arenas. As new analytic methods become available, it is anticipated that a more fundamental understanding of the biological and behavioral mechanisms underlying sex and gender differences in mental illness will emerge. Nonetheless, it is also likely that integration of findings predicated on different conceptual models of the nature and causes of mental illness will remain a challenge. These issues are discussed with reference to their impact on the field of women's mental health research.

Maternal inheritance, sexual conflict and the maladapted male

Females differ from males in transmitting not only nuclear genes but also cytoplasmic genetic elements (CGEs), including DNA in mitochondria, chloroplasts and microorganisms that are present in the cell. Until recently, evolutionary research has adopted a nucleocentric approach in which organelles have been viewed as subservient energy suppliers. In this article, we propose that a more equitable view of nuclear genes and organelle genomes will lead to a better understanding of the dynamics of sexual selection and the constraints on male adaptation. Maternal inheritance of CGEs intensifies sexually-antagonistic coevolution and provides a parsimonious explanation for the relatively high frequency in males of such apparently maladaptive traits as infertility, homosexuality and baldness.

An alternative hypothesis to the obesity epidemic: Obesity is due to increased maternal body size, birth size, growth rate, and height

A new hypothesis for dealing with the obesity epidemic is based on changing several factors normally considered desirable by the medical community. These factors include reductions in pre-pregnancy maternal weight, modest reduction of infant birthweight, slower childhood and adolescent growth and reduced caloric intake from infancy through adulthood. The underlining roots for the obesity epidemic involve raised levels of insulin, insulin-like growth factor-1 and cell proliferation which are subject to human control. The implication of this hypothesis is that current measures are inadequate unless a much more comprehensive response is implemented to deal with the obesity epidemic.