Genetically heterogeneous mice exhibit a female survival advantage that is age- and site-specific: Results from a large multi-site study

Assessing the existence of the male-female health-survival paradox in the past: Dental caries in medieval London

OBJECTIVES

This study seeks to identify signals of the male-female health-survival paradox in medieval London.

MATERIALS AND METHODS

This study uses skeletal data on age, sex, dental caries (n = 592) and antemortem tooth loss (n = 819) from adult individuals from medieval London cemeteries (c. 1200-1540 CE). The association between age and dental caries was assessed using binary logistic regression. The associations among age, time period (pre- vs. post-Black Death), oral biomarker (dental caries or antemortem tooth loss), and sex were tested using hierarchical log-linear analysis.

RESULTS

The analyses reveal significantly higher odds of dental caries with increasing adult ages, more older adults after the Black Death, different age distributions of dental caries between the sexes, and a greater decrease in the prevalence of dental caries for females after the Black Death. These results appear not to be an artifact of trends in AMTL. However, this study does not yield evidence suggesting that females experienced both a survival advantage and a decline in oral health at late adult ages after the Black Death relative to males.

CONCLUSIONS

These results do not provide evidence of the existence of a male-female health-survival paradox, but they do corroborate existing evidence of improvements in health in general in the aftermath of the Black Death. The decreased prevalence of dental caries after the Black Death may reflect dietary improvements or the effects of selective mortality during the epidemic.

Targeting multiple hallmarks of mammalian aging with combinations of interventions

Aging is currently viewed as a result of multiple biological processes that manifest themselves independently, reinforce each other and in their totality lead to the aged phenotype. Genetic and pharmaceutical approaches targeting specific underlying causes of aging have been used to extend the lifespan and healthspan of model organisms ranging from yeast to mammals. However, most interventions display only a modest benefit. This outcome is to be expected if we consider that even if one aging process is successfully treated, other aging pathways may remain intact. Hence solving the problem of aging may require targeting not one but many of its underlying causes at once. Here we review the challenges and successes of combination therapies aimed at increasing the lifespan of mammals and propose novel directions for their development. We conclude that both additive and synergistic effects on mammalian lifespan can be achieved by combining interventions that target the same or different hallmarks of aging. However, the number of studies in which multiple hallmarks were targeted simultaneously is surprisingly limited. We argue that this approach is as promising as it is understudied.

Quantifying the Impact of Co-Housing on Murine Aging Studies

Analysis of preclinical lifespan studies often assume that outcome data from co-housed animals are independent. In practice, treatments, such as controlled feeding or putative life-extending compounds, are applied to whole housing units, and as a result the outcomes are potentially correlated within housing units. We consider intra-class (here, intra-cage) correlation in three published and two unpublished lifespan studies of aged mice encompassing more than 20 thousand observations. We show that the independence assumption underlying common analytic techniques does not hold in these data, particularly for traits associated with frailty. We describe and demonstrate various analytical tools available to accommodate this study design and highlight a limitation of standard variance components models (i.e., linear mixed models) which are the usual statistical tool for handling correlated errors. Through simulations, we examine the statistical biases resulting from intra-cage correlations with similar magnitudes as observed in these case studies and discuss implications for power and reproducibility.

Dynamics of single-nuclei transcriptomic profiling of adipose tissue from diverse anatomical locations during mouse aging process

Adipose tissue plays critical roles in an individual's aging process. In this research, we use single-nucleus RNA sequencing to create highly detailed transcriptional maps of subcutaneous adipose tissue and visceral adipose tissue in young and aged mice. We comprehensively identify the various cell types within the white adipose tissue of mice, our study has elucidated seven distinct cell types within this tissue. Further analyses focus on adipocytes, fibro-adipogenic progenitors, and immune cells, revealing age-related declines in the synthetic metabolic activity of adipocytes, diminished immune regulation, and reduced maturation or proliferation of fibroblasts in undifferentiated adipocytes. We confirm the presence of distinct subpopulations of adipocytes, highlighting decreases in adipogenesis subgroups due to aging. Additionally, we uncover a reduction in immune cell subpopulations, driven by age-associated immune system dysregulation. Furthermore, pseudo-time analyses indicate that Adipocyte1 represents the 'nascent' phase of adipocyte development, while Adipocyte2 represents the 'mature' phase. We use cell-cell interaction to explore the age-dependent complexities of the interactions between FAPs and adipocytes, and observed increased expression of the inflammation-related Retn-Tlr4 interaction in older mice, while the anti-inflammatory Angpt1-Tek interaction was only detected in young mice. These transcriptional profiles serve as a valuable resource for understanding the functional genomics underlying metabolic disorders associated with aging in human adipose tissue.

Castration reduces mortality and increases resilience in male mice: what is next?

This commentary concerns our recent report that prepubertal castration rescued the shorter lifespan of males, using the first mouse line that robustly shows the same shorter longevity with a similar age-variable mortality disadvantage as human males. This model provides a unique opportunity for research to uncover the basis for this clinically important sex difference in aging. Researchers can now identify the hormones involved, the duration of exposure required, and, most important, the cellular and molecular targets, with the ultimate goal of developing therapeutic interventions to enhance health and reduce mortality without castration-compromising reproductive function.

Deciphering the Timing and Impact of Life-extending Drugs: A Novel Analytic Approach that Differentiates Early, Midlife, and Senescence Phase Efficacies

Evidence that life-extending interventions are not uniformly effective across the lifespan calls for an analytic tool that can estimate age-specific treatment effects on mortality hazards. Here we report such a tool, applying it to mouse data from 42 agents tested in the NIA Interventions Testing Program. This tool identified agents that either reduced (22) or increased (16) mortality hazards or did both (6), all with marked variation in the duration of efficacy and magnitude of effect size. Only 7 reduced mortality hazards after the 90% mortality, when the burden of senescence is greatest. Sex differences were apparent in all parameters. This new analytic tool complements the commonly used log-rank test. It detects more potential life-extending candidates (22 versus 10) and indicates when during the life course they are effective. It also uncovers adverse effects. Most importantly, it identifies agents that specifically reduce mortality hazards during the senescent phase of life.

Maternal Obesity Programs the Premature Aging of Rat Offspring Liver Mitochondrial Electron Transport Chain Genes in a Sex-Dependent Manner

We investigated whether maternal obesity affects the hepatic mitochondrial electron transport chain (ETC), sirtuins, and antioxidant enzymes in young (110 postnatal days (PND)) and old (650PND) male and female offspring in a sex- and age-related manner. Female Wistar rats ate a control (C) or high-fat (MO) diet from weaning, through pregnancy and lactation. After weaning, the offspring ate the C diet and were euthanized at 110 and 650PND. The livers were collected for RNA-seq and immunohistochemistry. Male offspring livers had more differentially expressed genes (DEGs) down-regulated by both MO and natural aging than females. C-650PND vs. C-110PND and MO-110PND vs. C-110PND comparisons revealed 1477 DEGs in common for males (premature aging by MO) and 35 DEGs for females. Analysis to identify KEGG pathways enriched from genes in common showed changes in 511 and 3 KEGG pathways in the male and female livers, respectively. Mitochondrial function pathways showed ETC-related gene down-regulation. All ETC complexes, sirtuin2, sirtuin3, sod-1, and catalase, exhibited gene down-regulation and decreased protein expression at young and old ages in MO males vs. C males; meanwhile, MO females down-regulated only at 650PND. Conclusions: MO accelerates the age-associated down-regulation of ETC pathway gene expression in male offspring livers, thereby causing sex-dependent oxidative stress, premature aging, and metabolic dysfunction.

Prepubertal castration eliminates sex differences in lifespan and growth trajectories in genetically heterogeneous mice

Sex differences in aging and longevity have been widely observed, with females consistently outliving males across human populations. However, the mechanisms driving these disparities remain poorly understood. In this study, we explored the influence of post-pubertal testicular effects on sex differences in aging by prepubertally castrating genetically heterogeneous (UM-HET3) mice, a unique mouse model that emulates human sex differences in age-related mortality. Prepubertal castration eliminated the longevity disparity between sexes by reducing the elevated early- to mid-life mortality rate observed in males and extending their median lifespan to match that of females. Additionally, castration extended the duration of body weight growth and attenuated the inverse correlation between early-age body weight and lifespan in males, aligning their growth trajectories with those of females. Our findings suggest that post-pubertal testicular actions in genetically diverse mice are primarily responsible for sex differences in longevity as well as growth trajectories. These findings offer a foundation for further investigation into the fundamental mechanisms driving sex-specific aging patterns and the development of potential pro-longevity interventions.

The Stria Vascularis in Mice and Humans Is an Early Site of Age-Related Cochlear Degeneration, Macrophage Dysfunction, and Inflammation

Age-related hearing loss, or presbyacusis, is a common degenerative disorder affecting communication and quality of life for millions of older adults. Multiple pathophysiologic manifestations, along with many cellular and molecular alterations, have been linked to presbyacusis; however, the initial events and causal factors have not been clearly established. Comparisons of the transcriptome in the lateral wall (LW) with other cochlear regions in a mouse model (of both sexes) of "normal" age-related hearing loss revealed that early pathophysiological alterations in the stria vascularis (SV) are associated with increased macrophage activation and a molecular signature indicative of inflammaging, a common form of immune dysfunction. Structure-function correlation analyses in mice across the lifespan showed that the age-dependent increase in macrophage activation in the stria vascularis is associated with a decline in auditory sensitivity. High-resolution imaging analysis of macrophage activation in middle-aged and aged mouse and human cochleas, along with transcriptomic analysis of age-dependent changes in mouse cochlear macrophage gene expression, support the hypothesis that aberrant macrophage activity is an important contributor to age-dependent strial dysfunction, cochlear pathology, and hearing loss. Thus, this study highlights the SV as a primary site of age-related cochlear degeneration and aberrant macrophage activity and dysregulation of the immune system as early indicators of age-related cochlear pathology and hearing loss. Importantly, novel new imaging methods described here now provide a means to analyze human temporal bones in a way that had not previously been feasible and thereby represent a significant new tool for otopathological evaluation.SIGNIFICANCE STATEMENT Age-related hearing loss is a common neurodegenerative disorder affecting communication and quality of life. Current interventions (primarily hearing aids and cochlear implants) offer imperfect and often unsuccessful therapeutic outcomes. Identification of early pathology and causal factors is crucial for the development of new treatments and early diagnostic tests. Here, we find that the SV, a nonsensory component of the cochlea, is an early site of structural and functional pathology in mice and humans that is characterized by aberrant immune cell activity. We also establish a new technique for evaluating cochleas from human temporal bones, an important but understudied area of research because of a lack of well-preserved human specimens and difficult tissue preparation and processing approaches.

Developmental Programming-Aging Interactions Have Sex-Specific and Developmental Stage of Exposure Outcomes on Life Course Circulating Corticosterone and Dehydroepiandrosterone (DHEA) Concentrations in Rats Exposed to Maternal Protein-Restricted Diets

The steroids corticosterone and dehydroepiandrosterone (DHEA) perform multiple life course functions. Rodent life-course circulating corticosterone and DHEA trajectories are unknown. We studied life course basal corticosterone and DHEA in offspring of rats fed protein-restricted (10% protein, R) or control (20% protein, C), pregnancy diet first letter, and/or lactation second letter, producing four offspring groups-CC, RR, CR, and RC. We hypothesize that 1. maternal diet programs are sexually dimorphic, offspring life course steroid concentrations, and 2. an aging-related steroid will fall. Both changes differ with the plastic developmental period offspring experienced R, fetal life or postnatally, pre-weaning. Corticosterone was measured by radioimmunoassay and DHEA by ELISA. Steroid trajectories were evaluated by quadratic analysis. Female corticosterone was higher than male in all groups. Male and female corticosterone were highest in RR, peaked at 450 days, and fell thereafter. DHEA declined with aging in all-male groups. DHEA: corticosterone fell in three male groups but increased in all-female groups with age. In conclusion, life course and sexually dimorphic steroid developmental programming-aging interactions may explain differences in steroid studies at different life stages and between colonies experiencing different early-life programming. These data support our hypotheses of sex and programming influences and aging-related fall in rat life course serum steroids. Life course studies should address developmental programming-aging interactions.

Sex- and age-dependent genetics of longevity in a heterogeneous mouse population

DNA variants that modulate life span provide insight into determinants of health, disease, and aging. Through analyses in the UM-HET3 mice of the Interventions Testing Program (ITP), we detected a sex-independent quantitative trait locus (QTL) on chromosome 12 and identified sex-specific QTLs, some of which we detected only in older mice. Similar relations between life history and longevity were uncovered in mice and humans, underscoring the importance of early access to nutrients and early growth. We identified common age- and sex-specific genetic effects on gene expression that we integrated with model organism and human data to create a hypothesis-building interactive resource of prioritized longevity and body weight genes. Finally, we validated Hipk1, Ddost, Hspg2, Fgd6, and Pdk1 as conserved longevity genes using Caenorhabditis elegans life-span experiments.

Research Centers Collaborative Network Workshop on Sex and Gender Differences in Aging

Aging affects men and women differently; however, the impact of sex and gender on the aging process is not well understood. Moreover, these 2 concepts are often conflated, which further contributes to a lack of clarity on this important issue. In an effort to better understand the relevance of sex and gender in aging research, the Research Centers Collaborative Network sponsored a 1.5-day conference on sex and gender differences in aging that brought together key thought leaders from the 6 National Institute on Aging center programs. The meeting included sessions on comparing males and females, pathophysiological differences, sex/gender in clinical care, and gender and health in the social context. Presenters from a wide array of disciplines identified opportunities for multidisciplinary research to address current gaps in the field and highlighted the need for a more systematic approach to understanding the how and why of sex/gender differences, as well as the health implications of these differences and the sex/gender biases that affect clinical treatment and outcomes. This article summarizes the proceedings of the workshop and provides several recommendations to move the field forward, such as better data collection tools to assess the intersection of sex and gender in epidemiological research; a life course perspective with attention to fetal/developmental origins and key life stages; innovative animal models to distinguish contributions from sex hormones versus sex chromosomes; and integration of sex/gender into teaching and clinical practice. Ultimately, successful implementation of these recommendations will require thoughtful investigations across the translational spectrum and increased collaborations among those with expertise in sex and gender differences.

Sex and genetic background define the metabolic, physiologic, and molecular response to protein restriction

Low-protein diets promote metabolic health in humans and rodents. Despite evidence that sex and genetic background are key factors in the response to diet, most protein intake studies examine only a single strain and sex of mice. Using multiple strains and both sexes of mice, we find that improvements in metabolic health in response to reduced dietary protein strongly depend on sex and strain. While some phenotypes were conserved across strains and sexes, including increased glucose tolerance and energy expenditure, we observed high variability in adiposity, insulin sensitivity, and circulating hormones. Using a multi-omics approach, we identified mega-clusters of differentially expressed hepatic genes, metabolites, and lipids associated with each phenotype, providing molecular insight into the differential response to protein restriction. Our results highlight the importance of sex and genetic background in the response to dietary protein level, and the potential importance of a personalized medicine approach to dietary interventions.

Fasting blood glucose as a predictor of mortality: Lost in translation

Aging leads to profound changes in glucose homeostasis, weight, and adiposity, which are considered good predictors of health and survival in humans. Direct evidence that these age-associated metabolic alterations are recapitulated in animal models is lacking, impeding progress to develop and test interventions that delay the onset of metabolic dysfunction and promote healthy aging and longevity. We compared longitudinal trajectories, rates of change, and mortality risks of fasting blood glucose, body weight, and fat mass in mice, nonhuman primates, and humans throughout their lifespans and found similar trajectories of body weight and fat in the three species. In contrast, fasting blood glucose decreased late in life in mice but increased over the lifespan of nonhuman primates and humans. Higher glucose was associated with lower mortality in mice but higher mortality in nonhuman primates and humans, providing a cautionary tale for translating age-associated metabolic changes from mice to humans.

Evaluating the beneficial effects of dietary restrictions: A framework for precision nutrigeroscience

Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.

Rodent studies of developmental programming and ageing mechanisms: Special issue: In utero and early life programming of ageing and disease

Compelling evidence exists indicating that developmental programming influences ageing. Programming alters life-course phenotype in multiple organs, predisposing to diseases such as diabetes, obesity and cardiovascular disease that shorten lifespan. This review describes studies in rodents, the most commonly studied species, addressing interactions of programming challenges with ageing. We first consider ageing and programming of insulin function that has been clearly shown to decrease with age. It is important to evaluate ageing in pancreatic islets isolated from other systems. Studies discussed show premature pancreatic islet ageing resulting from both maternal under- and overnutrition. New ways to determine programming of adipose tissue and effects on fat storage are explored. Oxidative stress is a major factor that regulates ageing in tissues. Oxidative stress is discussed in relation to reproductive and cardiovascular ageing. Premature ageing is associated with both low and high glucocorticoid function. Both over and undernutrition have offspring sex-specific programming effects on life-course glucocorticoid concentrations. Evidence is provided that maternal age at conception affects offspring endocrine and metabolism ageing. Finally, the importance of matching foetal nutrition and energy availability with composition and energy content in the post-weaning diet is demonstrated. This mismatch can lead to a greatly shortened lifespan. General principles are discussed throughout. For example, sexual dimorphism of age-related outcomes can be marked. Accelerated ageing occurs early in life. Improving knowledge on programming ageing interactions will improve health span as well as lifespan. Finally, there are considerable similarities in outcomes programmed by maternal undernutrition and overnutrition.

Gene-by-environment modulation of lifespan and weight gain in the murine BXD family

How lifespan and body weight vary as a function of diet and genetic differences is not well understood. Here we quantify the impact of differences in diet on lifespan in a genetically diverse family of female mice, split into matched isogenic cohorts fed a low-fat chow diet (CD, n = 663) or a high-fat diet (HFD, n = 685). We further generate key metabolic data in a parallel cohort euthanized at four time points. HFD feeding shortens lifespan by 12%: equivalent to a decade in humans. Initial body weight and early weight gains account for longevity differences of roughly 4-6 days per gram. At 500 days, animals on a HFD typically gain four times as much weight as control, but variation in weight gain does not correlate with lifespan. Classic serum metabolites, often regarded as health biomarkers, are not necessarily strong predictors of longevity. Our data indicate that responses to a HFD are substantially modulated by gene-by-environment interactions, highlighting the importance of genetic variation in making accurate individualized dietary recommendations.

Sexual dimorphism in liver cell cycle and senescence signalling pathways in young and old rats

At the molecular level, cellular ageing involves changes in multiple gene pathways. Cellular senescence is both an important initiator and a consequence of natural ageing. Senescence results in changes in multiple cellular mechanisms that result in a natural decrease in cell cycle activity. Liver senescence changes impair hepatic function. Given the well-established sexual dimorphism in ageing, we hypothesized that the natural hepatic ageing process is driven by sex-dependent gene mechanisms. We studied our well-characterized normal, chow-fed rat ageing model, lifespan ∼850 days, in which we have reported ageing of metabolism, reproduction and endocrine function. We performed liver RNA-seq on males and females at 110 and 650 days to determine changes in the cell cycle and cellular senescence signalling pathways. We found that natural liver ageing shows sexual dimorphism in these pathways. RNA-seq revealed more male (3967) than female (283) differentially expressed genes between 110 and 650 days. Cell cycle pathway signalling changes in males showed decreased protein and expression of key genes (Cdk2, Cdk4, Cycd and PCNA) and increased expression ofp57 at 650 vs 110 days. In females, protein and gene expression of cell growth regulators, e.g. p15 and p21, which inhibit cell cycle G1 progression, were increased. The cell senescence pathway also showed sexual dimorphism. Igfbp3, mTOR and p62 gene and protein expression decreased in males while those ofTgfb3 increased in females. Understanding the involvement of cell cycling and cellular senescence pathways in natural ageing will advance evaluation of mechanisms associated with altered ageing and frailty trajectories. KEY POINTS: In rats RNA-seq analysis showed sexual dimorphism in gene expression across the life-course between 110 and 650 days of life. Fourteen times more liver transcriptome and six times more pathway changes were observed in males compared with females. Significant changes were observed in several signalling pathways during ageing. Bioinformatic analysis were focused on changes in genes and protein products related to cell cycle and cellular senescence pathways. Males showed decreased protein product and expression of the key genes Cdk2 and Cdk4 responsible for cell cycle progression while females increased protein product and expression of p21 and p15, key genes responsible for cell cycle arrest. In conclusion, normative rat hepatic ageing involves changes in cellular pathways that control cell cycle arrest but through changes in different genes in males and females. These findings identify mechanisms that underlie the well-established sexual dimorphism in ageing.

San Antonio Nathan Shock Center: your one-stop shop for aging research

With evolving cores, enrichment and training programs, and supported research projects, the San Antonio (SA) Nathan Shock Center has for 26 years provided critical support to investigators locally, nationally, and abroad. With its existing and growing intellectual capital, the SA Nathan Shock Center provides to local and external investigators an enhanced platform to conduct horizontally integrated (lifespan, healthspan, pathology, pharmacology) transformative research in the biology of aging, and serves as a springboard for advanced educational and training activities in aging research. The SA Nathan Shock Center consists of six cores: Administrative/Program Enrichment Core, Research Development Core, Aging Animal Models and Longevity Assessment Core, Pathology Core, Analytical Pharmacology and Drug Evaluation Core, and Integrated Physiology of Aging Core. The overarching goal of the SA Nathan Shock Center is to advance knowledge in the basic biology of aging and to identify molecular and cellular mechanisms that will facilitate the development of pharmacologic interventions and other strategies to extend healthy lifespan. In pursuit of this goal, we provide an innovative "one-stop shop" venue to accelerate transformative research in the biology of aging through our integrated research cores. Moreover, we aim to foster and promote career development of early-stage investigators in aging biology through our research development programs, to serve as a resource and partner to investigators from other Shock Centers, and to disseminate scientific knowledge and enhanced awareness about aging research. Overall, the SA Nathan Shock Center aims to be a leader in research that advances our understanding of the biology of aging and development of approaches to improve longevity and healthy aging.

The nonhuman primate hypothalamo-pituitary-adrenal axis is an orchestrator of programming-aging interactions: role of nutrition

Developmental programming alters life-course multi-organ function and significantly affects life-course health. Recently, interest has developed in how programming may influence the rate of aging. This review describes interactions of nutrition and programming-aging interactions in hypothalamo-pituitary-adrenal (HPA) development and function from fetal development to old age. A full picture of these interactions requires data on levels of HPA activity relating to the hypothalamic, adrenal cortical, circulating blood, and peripheral cortisol metabolism. Data are provided from studies on our baboon, nonhuman primate model both across the normal life course and in offspring of maternal baboons who were moderately undernourished by a global 30% diet reduction during pregnancy and lactation. Sex differences in offspring outcomes in response to similar challenges are described. The data clearly show programming of increased HPA axis activity by moderate maternal undernutrition. Increased postnatal circulating cortisol concentrations are related to accelerated aging of the brain and cardiovascular systems. Future studies should address peripheral cortisol production and the influence of aging advantage in females. These data support the view that the HPA is an orchestrator of interactions of programming-aging mechanisms.

Aging Endocrine and Metabolic Phenotypes Are Programmed by Mother’s Age at Conception in a Sex-Dependent Fashion in the Rat

Programming of offspring life-course health by maternal nutrition and stress are well studied. At postnatal day 850, we evaluated male and female steroid levels and metabolism in aged offspring of primigravid sister rats bred at 70, 90, 150, or 300 days’ life. At 850 days life, male offspring corticosterone was similar regardless of maternal age. Female corticosterone was highest in offspring of 70- and 300-day mothers. Serum dehydroepiandrosterone:corticosterone was lowest in both sexes of offspring of 70- and 300-day mothers. Male and female fat depots were smaller in offspring of 150- than 70- and 90-day mothers. Insulin, glucose, and homeostatic model assessment were similar in all male offspring but higher in female offspring of 70-day mothers than other ages. We conclude, maternal age affects offspring aging in an offspring sex-dependent manner and merits consideration in designing and interpreting programming studies.

A toolbox for the longitudinal assessment of healthspan in aging mice

The number of people aged over 65 is expected to double in the next 30 years. For many, living longer will mean spending more years with the burdens of chronic diseases such as Alzheimer's disease, cardiovascular disease, and diabetes. Although researchers have made rapid progress in developing geroprotective interventions that target mechanisms of aging and delay or prevent the onset of multiple concurrent age-related diseases, a lack of standardized techniques to assess healthspan in preclinical murine studies has resulted in reduced reproducibility and slow progress. To overcome this, major centers in Europe and the United States skilled in healthspan analysis came together to agree on a toolbox of techniques that can be used to consistently assess the healthspan of mice. Here, we describe the agreed toolbox, which contains protocols for echocardiography, novel object recognition, grip strength, rotarod, glucose tolerance test (GTT) and insulin tolerance test (ITT), body composition, and energy expenditure. The protocols can be performed longitudinally in the same mouse over a period of 4-6 weeks to test how candidate geroprotectors affect cardiac, cognitive, neuromuscular, and metabolic health.

A 2D analysis of correlations between the parameters of the Gompertz-Makeham model (or law?) of relationships between aging, mortality, and longevity

When mortality (μ), aging rate (γ) and age (t) are treated according to the Gompertz model μ(t) = μ₀e^γt (GM), any mean age corresponds to a manifold of paired reciprocally changing μ₀ and γ. Therefore, any noisiness of data used to derive GM parameters makes them negatively correlated. Besides this artifactual factor of the Strehler-Mildvan correlation (SMC), other factors emerge when the age-independent mortality C modifies survival according to the Gompertz-Makeham model μ(t) = C+μ₀e^γt (GMM), or body resources are partitioned between survival and protection from aging [the compensation effect of mortality (CEM)]. Theoretical curves in (γ, logμ₀) coordinates show how μ₀ decreases when γ increases upon a constant mean age. Within a species-specific range of γ, such "isoage" curves look as nearly parallel straight lines. The slopes of lines constructed by applying GM to survival curves modeled according to GMM upon changes in C are greater than the isoage slopes. When CEM is modeled, the slopes are still greater. Based on these observations, CEM is shown to contribute to SMC associated with sex differences in lifespan, with the effects of several life-extending drugs, and with recent trends in survival/mortality patterns in high-life-expectancy countries; whereas changes in C underlie differences between even high-life-expectancy countries, not only between high- and low-life-expectancy countries. Such interpretations make sense only if GM is not merely a statistical model, but rather reflects biological realities. Therefore, GM is discussed as derivable by applying certain constraints to a natural law termed the generalized Gompertz-Makeham law.

Genetically heterogeneous mice exhibit a female survival advantage that is age- and site-specific: Results from a large multi-site study

The female survival advantage is a robust characteristic of human longevity. However, underlying mechanisms are not understood, and rodent models exhibiting a female advantage are lacking. Here, we report that the genetically heterogeneous (UM-HET3) mice used by the National Institute on Aging Interventions Testing Program (ITP) are such a model. Analysis of age-specific survival of 3,690 control ITP mice revealed a female survival advantage paralleling that of humans. As in humans, the female advantage in mice was greatest in early adulthood, peaking around 350 days of age and diminishing progressively thereafter. This persistent finding was observed at three geographically distinct sites and in six separate cohorts over a 10-year period. Because males weigh more than females and bodyweight is often inversely related to lifespan, we examined sex differences in the relationship between bodyweight and survival. Although present in both sexes, the inverse relationship between bodyweight and longevity was much stronger in males, indicating that male mortality is more influenced by bodyweight than is female mortality. In addition, male survival varied more across site and cohort than female survival, suggesting greater resistance of females to environmental modulators of survival. Notably, at 24 months the relationship between bodyweight and longevity shifted from negative to positive in both sexes, similar to the human condition in advanced age. These results indicate that the UM-HET3 mouse models the human female survival advantage and provide evidence for greater resilience of females to modulators of survival.