Living fast, dying when? The link between aging and energetics

Telomeres and the Rate of Living: Linking Biological Clocks of Senescence

AbstractTwo prominent theories of aging, one based on telomere dynamics and the other on mass-specific energy flux, propose biological time clocks of senescence. The relationship between these two theories, and the biological clocks proposed by each, remains unclear. Here, we examine the relationships between telomere shortening rate, mass-specific metabolic rate, and lifespan among vertebrates (mammals, birds, fishes). Results show that telomere shortening rate increases linearly with mass-specific metabolic rate and decreases nonlinearly with increasing body mass in the same way as mass-specific metabolic rate. Results also show that both telomere shortening rate and mass-specific metabolic rate are similarly related to lifespan and that both strongly predict differences in lifespan, although the slopes of the relationships are less than linear. On average, then, telomeres shorten a fixed amount per unit of mass-specific energy flux. So the mitotic clock of telomere shortening and the energetics-based clock described by metabolic rate can be viewed as alternative measures of the same biological clock. These two processes may be linked, we speculate, through the process of cell division.

Biological thermodynamics: Ervin Bauer and the unification of life sciences and physics

Biological systems operate toward the maximization of their self-maintenance and adaptability. This is achieved through the establishment of robust self-maintaining configurations acting as attractors resistant to external and internal perturbations. Ervin Bauer (1890-1938) was the first who formulated this essential thermodynamic constraint in the operation of biological systems, which he defined as the stable non-equilibrium state. The latter appears as the basic attractor relative to which biological organization is established. The stable non-equilibrium state represents a generalized cell energy status corresponding to efficient spatiotemporal organization of the fluxes of matter and energy and constantly reproducing the conditions of self-maintenance of metabolism and controlling the rates of major metabolic fluxes that follow thermodynamically and kinetically defined computational principles. This state is realized in the autopoietic structures having closed loops of causation based on the operation of biological codes. The principle of thermodynamic buffering determines the conditions for optimization of the fluxes of load and consumption in metabolism establishing the conditions of metabolic stable non-equilibrium. In developing and evolving biological systems, the principle of stable non-equilibrium is transformed into the principle of increasing external work, which is grounded in the hyper-restorative non-equilibrium dynamics. Bauer's concept of the stable non-equilibrium state puts thermodynamics into the frames of the internal biological causality governing self-maintenance and development of living systems. It can be defined as a relational theory of biological thermodynamics since the standard to which it refers represents the actual biological function rather than the abstract state of thermodynamic equilibrium.

Energetic budget of diploid and triploid eastern oysters during a summer die-off

Triploid oysters are widely used in off-bottom aquaculture of eastern oysters, Crassostrea virginica. However, farmers of the Gulf of Mexico (GoM) and Atlantic coast estuaries have observed unresolved, late-spring die-offs of triploid oysters, threatening the sustainability of triploid aquaculture. To investigate this, the physiological processes underlying oyster growth (e.g., feeding, respiration) and mortality of one-year-old diploid and triploid oysters were compared in early summer following an uptick in mortality. It was predicted that higher triploid mortality was the result of energetic imbalances (increased metabolic demands and decreased feeding behavior). Oyster clearance rates, percentage of time valves were open, absorption efficiency, oxygen consumption rates (basal and routine), ammonia excretion rate were measured in the laboratory and scope for growth was calculated. In addition, their condition index, gametogenic stage, Perkinsus marinus infection level, and mortality were measured. Mortality of triploids in the laboratory was greater than for diploids, mirroring mortality observed in a related field study. The physiological parameters measured, however, could not explain triploid mortality. Scope for growth, condition index, and clearance rates of triploids were greater than for diploids, suggesting sufficient energy reserves, while all other measurements where similar between the ploidies. It remains to be determined whether mortality could be caused from disruption of energy homeostasis at the cellular level.

Memories that last: Dynamics of memory T cells throughout the body

Memory T cells form an essential part of immunological memory, which can last for years or even a lifetime. Much experimental work has shown that the individual cells that make up the memory T-cell pool are in fact relatively short-lived. Memory T cells isolated from the blood of humans, or the lymph nodes and spleen of mice, live about 5-10 fold shorter than naive T cells, and much shorter than the immunological memory they convey. The commonly accepted view is, therefore, that long-term T-cell memory is maintained dynamically rather than by long-lived cells. This view is largely based on memory T cells in the circulation, identified using rather broad phenotypic markers, and on research in mice living in overly clean conditions. We wondered to what extent there may be heterogeneity in the dynamics and lifespans of memory T cells. We here review what is currently known about the dynamics of memory T cells in different memory subsets, locations in the body and conditions of microbial exposure, and discuss how this may be related to immunometabolism and how this knowledge can be used in various clinical settings.

Mitochondria Need Their Sleep: Redox, Bioenergetics, and Temperature Regulation of Circadian Rhythms and the Role of Cysteine-Mediated Redox Signaling, Uncoupling Proteins, and Substrate Cycles

Although circadian biorhythms of mitochondria and cells are highly conserved and crucial for the well-being of complex animals, there is a paucity of studies on the reciprocal interactions between oxidative stress, redox modifications, metabolism, thermoregulation, and other major oscillatory physiological processes. To address this limitation, we hypothesize that circadian/ultradian interaction of the redoxome, bioenergetics, and temperature signaling strongly determine the differential activities of the sleep–wake cycling of mammalians and birds. Posttranslational modifications of proteins by reversible cysteine oxoforms, S-glutathionylation and S-nitrosylation are shown to play a major role in regulating mitochondrial reactive oxygen species production, protein activity, respiration, and metabolomics. Nuclear DNA repair and cellular protein synthesis are maximized during the wake phase, whereas the redoxome is restored and mitochondrial remodeling is maximized during sleep. Hence, our analysis reveals that wakefulness is more protective and restorative to the nucleus (nucleorestorative), whereas sleep is more protective and restorative to mitochondria (mitorestorative). The “redox–bioenergetics–temperature and differential mitochondrial–nuclear regulatory hypothesis” adds to the understanding of mitochondrial respiratory uncoupling, substrate cycling control and hibernation. Similarly, this hypothesis explains how the oscillatory redox–bioenergetics–temperature–regulated sleep–wake states, when perturbed by mitochondrial interactome disturbances, influence the pathogenesis of aging, cancer, spaceflight health effects, sudden infant death syndrome, and diseases of the metabolism and nervous system.

Survival and growth of triploid eastern oysters, Crassostrea virginica, produced from wild diploids collected from low-salinity areas

Triploid Eastern oysters have been reported to suffer greater mortalities than diploids when exposed to low-salinity (<5) conditions in the U.S. Gulf of Mexico and Atlantic estuaries. As such, the effect of broodstock parentage was investigated on the low-salinity tolerance of triploid progeny produced by mating diploid females (collected from three Louisiana estuaries differing in salinity regimes) with male tetraploids at two hatcheries. Diploid crosses were also produced using the wild broodstocks to verify expected differences in low-salinity tolerance among diploid progeny and between ploidy levels. All progeny were deployed at low and moderate-salinity (averages of 9.3 and 19.4) field sites to monitor monthly growth and mortality. Sex ratio, gametogenic stage, gonad-to-body ratio, condition index, and Perkinsus marinus infection were also measured periodically at both field sites Although high triploid mortality at the low-salinity site prevented complete analysis, results indicated that diploid parentage had little effect on triploid survival at low salinity. Broodstock parentage affected diploid mortality and growth, although results did not match with predictions made based on historical salinity at broodstock collection sites. Ploidy level had the largest effect on triploid survival and growth followed by the hatchery site where the oysters were produced.

The 13C-bicarbonate technique as a tool for measurement of energy expenditure in overweight dogs undergoing body weight reduction and the effect of different dietary composition

Changes in body size and composition, i.e., body weight (BW) gain or loss, affect the daily energy expenditure (EE). To ensure an appropriate BW reduction and to find an efficient strategy to reduce and maintain a target BW, regular evaluations and adjustments of energy allowance are important. This study aimed to provide a detailed knowledge about the possible changes in resting EE using the oral 13C-bicarbonate technique (o13CBT) as a research tool in 16 overweight pet dogs undergoing BW reduction. Dietary composition (i.e., in % of dry matter [DM] being a high protein [33.3], low fat [9.6], and high crude fiber [18.0] diet [LFHFibre], and a high protein [37.9], high fat [52.0], carbohydrate-free diet [HFat]) during 16 wk of energy restriction were evaluated regarding effects on resting EE, rate of BW reduction, body composition, and plasma concentrations of metabolic hormones involved in energy metabolism and appetite regulation. The mean BW loss was higher (P < 0.05) for the dogs fed the LFHFibre diet (1.1%/wk) than that for dogs fed the HFat diet (0.8%/wk), but the total BW reduction of 14.6% and 12.0% of initial BW did not differ significantly (P > 0.05). Resting EE was lower (P < 0.02) after the BW reduction; 414 kJ (99 kcal)/kg BW0.75/d at the start (week 0) and 326 kJ (78 kcal)/kg BW0.75/d at the end (week 16) of the study. The BW reduction in both groups (P > 0.05) consisted of both fat mass (FM) and fat-free mass (FFM). Energy expenditure, calculated in relation to amount of FFM, was not significantly (P > 0.05) affected by BW reduction. Dietary composition did not significantly affect (P > 0.05) plasma concentrations of insulin, leptin, and ghrelin, and no effect (P > 0.05) of BW reduction was observed on hormone concentrations. In conclusion, the o13CBT proved to be a useful research method for studying short-term EE in overweight dogs. Even though all dogs lost BW, most dogs were still overweight at the end of the study. Due to a high individual variation among dogs, a longer experimental period with a larger sample size would be desirable.

Not just a cousin of the naked mole-rat: Damaraland mole-rats offer unique insights into biomedicine

Evolutionary medicine has been a fast-growing field of biological research in the past decade. One of the strengths of evolutionary medicine is to use non-traditional model organisms which often exhibit unusual characteristics shaped by natural selection. Studying these unusual traits could provide valuable insight to understand biomedical questions, since natural selection likely discovers solutions to those complex biological problems. Because of many unusual traits, the naked mole-rat (NMR) has attracted attention from different research areas such as aging, cancer, and hypoxia- and hypercapnia-related disorders. However, such uniqueness of NMR physiology may sometimes make the translational study to human research difficult. Damaraland mole-rat (DMR) shares multiple characteristics in common with NMR, but shows higher degree of similarity with human in some aspects of their physiology. Research on DMR could therefore offer alternative insights and might bridge the gap between experimental findings from NMR to human biomedical research. In this review, we discuss studies of DMR as an extension of the current set of model organisms to help better understand different aspects of human biology and disease. We hope to encourage researchers to consider studying DMR together with NMR. By studying these two similar but evolutionarily distinct species, we can harvest the power of convergent evolution and avoid the potential biased conclusions based on life-history of a single species.

Thyroid function and age-related decline in kidney function in older Chinese adults: a cross-sectional study

Background

Thyroid function may be a factor affecting kidney function in the general population. Kidney and thyroid function vary with age; therefore, the association between thyroid function and decreased kidney function in older adults may be different from that in younger adults and remains controversial. This study aimed to estimate the association between normal-range thyroid function and age-related decline in kidney function in older Chinese adults.

Methods

A total of 15,653 adults, of whom 23.2% (N = 3624) were older adults (age≧65 years), were collected at the Health Management Center of the First Affiliated Hospital of Nanjing Medical University from January 2018 to January 2020. Basic demographic information was collected by a physician-administered questionnaire. The estimated glomerular filtration rate (eGFR) was calculated using the CKD-EPI formula. Trends in thyroid function with age were shown by means of free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) in subgroups every ten years. The association between kidney function and thyroid function was estimated by multiple linear regression using β value and by multivariable logistic regression models using odds ratios (OR) after adjusting for age, gender, body mass index, and serum urine acid.

Results

In the older population, TSH tended to increase with age and FT3 tended to decrease, whereas FT4 was relatively stable. eGFR decreased significantly with increasing TSH (β = -0.081) and decreasing FT3 (β = 0.083) concentrations. Compared with those in the lowest quartile of FT3 (3.10–4.47 pmol/L), the prevalence of eGFR < 75 ml/min/1.73m² decreased significantly by 22.0% for those with FT3 of 4.47–4.81 pmol/L, 27.6% for those with FT3 of 4.82–5.20 pmol/L, and 34.9% for those with FT3 of 5.21–6.8 pmol/L in older individuals (P for trend < .001). The OR was 1.315 (P: 0.025) in subjects with high-normal TSH, using low-normal TSH as a reference. The prevalence of reduced kidney function was not significantly associated with FT4 within the reference range. Similar results were found in association between the prevalence of eGFR < 60 ml/min/1.73m² and thyroid function.

Conclusions

This study demonstrated a significant association between kidney function and thyroid function, particularly FT3, in the older population. Clinicians may need to pay more attention to the assessment and follow-up of kidney function in older individuals with low-normal FT3 and high-normal TSH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02904-z.

Senescence as a trade-off between successful land colonisation and longevity: critical review and analysis of a hypothesis

BACKGROUND

Most common terrestrial animal clades exhibit senescence, suggesting strong adaptive value of this trait. However, there is little support for senescence correlated with specific adaptations. Nevertheless, insects, mammals, and birds, which are the most common terrestrial animal clades that show symptoms of senescence, evolved from clades that predominantly did not show symptoms of senescence. Thus, we aimed to examine senescence in the context of the ecology and life histories of the main clades of animals, including humans, and to formulate hypotheses to explain the causes and origin of senescence in the major clades of terrestrial animals.

METHODOLOGY

We reviewed literature from 1950 to 2020 concerning life expectancy, the existence of senescence, and the adaptive characteristics of the major groups of animals. We then proposed a relationship between senescence and environmental factors, considering the biology of these groups of animals. We constructed a model showing the phylogenetic relationships between animal clades in the context of the major stages of evolution, distinguishing between senescent and biologically 'immortal' clades of animals. Finally, we synthesised current data on senescence with the most important concepts and theories explaining the origin and mechanisms of senescence. Although this categorisation into different senescent phenotypes may be simplistic, we used this to propose a framework for understanding senescence.

RESULTS

We found that terrestrial mammals, insects, and birds show senescence, even though they likely evolved from non-senescent ancestors. Moreover, secondarily aquatic animals show lower rate of senescence than their terrestrial counterparts. Based on the possible life histories of these groups and the analysis of the most important factors affecting the transition from a non-senescent to senescent phenotype, we conclude that aging has evolved, not as a direct effect, but as a correlated response of selection on developmental strategies, and that this occurred separately within each clade. Adoption of specific life history strategies could thus have far-reaching effects in terms of senescence and lifespan.

CONCLUSIONS

Our analysis strongly suggests that senescence may have emerged as a side effect of the evolution of adaptive features that allowed the colonisation of land. Senescence in mammals may be a compromise between land colonisation and longevity. This hypothesis, is supported by palaeobiological and ecological evidence. We hope that the development of new research methodologies and the availability of more data could be used to test this hypothesis and shed greater light on the evolution of senescence.

Long-Lived Species of Bivalves Exhibit Low MT-DNA Substitution Rates

Bivalves represent valuable taxonomic group for aging studies given their wide variation in longevity (from 1–2 to >500 years). It is well known that aging is associated to the maintenance of Reactive Oxygen Species homeostasis and that mitochondria phenotype and genotype dysfunctions accumulation is a hallmark of these processes. Previous studies have shown that mitochondrial DNA mutation rates are linked to lifespan in vertebrate species, but no study has explored this in invertebrates. To this end, we performed a Bayesian Phylogenetic Covariance model of evolution analysis using 12 mitochondrial protein-coding genes of 76 bivalve species. Three life history traits (maximum longevity, generation time and mean temperature tolerance) were tested against 1) synonymous substitution rates (dS), 2) conservative amino acid replacement rates (Kc) and 3) ratios of radical over conservative amino acid replacement rates (Kr/Kc). Our results confirm the already known correlation between longevity and generation time and show, for the first time in an invertebrate class, a significant negative correlation between dS and longevity. This correlation was not as strong when generation time and mean temperature tolerance variations were also considered in our model (marginal correlation), suggesting a confounding effect of these traits on the relationship between longevity and mtDNA substitution rate. By confirming the negative correlation between dS and longevity previously documented in birds and mammals, our results provide support for a general pattern in substitution rates.

Effects of dietary restriction on metabolic and cognitive health

Life expectancy in most developed countries has been rising over the past century. In the UK alone, there are about 12 million people over 65 years old and centenarians have increased by 85% in the past 15 years. As a result of the ageing population, which is due mainly to improvements in medical treatments, public health, improved housing and lifestyle choices, there is an associated increase in the prevalence of pathological conditions, such as metabolic disorders, type 2 diabetes, cardiovascular and neurodegenerative diseases, many types of cancer and others. Statistics suggest that nearly 54% of elderly people in the UK live with at least two chronic conditions, revealing the urgency for identifying interventions that can prevent and/or treat such disorders. Non-pharmacological, dietary interventions such as energetic restriction (ER) and methionine restriction (MR) have revealed promising outcomes in increasing longevity and preventing and/or reversing the development of ageing-associated disorders. In this review, we discuss the evidence and mechanisms that are involved in these processes. Fibroblast growth factor 1 and hydrogen sulphide are important molecules involved in the effects of ER and MR in the extension of life span. Their role is also associated with the prevention of metabolic and cognitive disorders, highlighting these interventions as promising modulators for improvement of health span.

Aging, Life History, and Human Evolution

Aging occurs in all sexually reproducing organisms. That is, physical degradation over time occurs from conception until death. While the life span of a species is often viewed as a benchmark of aging, the pace and intensity of physical degradation over time varies owing to environmental influences, genetics, allocation of energetic investment, and phylogenetic history. Significant variation in aging within mammals, primates, and great apes, including humans, is therefore common across species. The evolution of aging in the hominin lineage is poorly known; however, clues can be derived from the fossil record. Ongoing advances continue to shed light on the interactions between life-history variables such as reproductive effort and aging. This review presents our current understanding of the evolution of aging in humans, drawing on population variation, comparative research, trade-offs, and sex differences, as well as tissue-specific patterns of physical degradation. Implications for contemporary health challenges and the future of human evolutionary anthropology research are also discussed.

Predictive and reactive changes in antioxidant defence system in a heterothermic rodent

Living in a seasonal environment requires periodic changes in animal physiology, morphology and behaviour. Winter phenotype of small mammals living in Temperate and Boreal Zones may differ considerably from summer one in multiple traits that enhance energy conservation or diminish energy loss. However, there is a considerable variation in the development of winter phenotype among individuals in a population and some, representing the non-responding phenotype (non-responders), are insensitive to shortening days and maintain summer phenotype throughout a year. Differences in energy management associated with the development of different winter phenotypes should be accompanied by changes in antioxidant defence capacity, leading to effective protection against oxidative stress resulting from increased heat production in winter. To test it, we analysed correlation of winter phenotypes of Siberian hamsters (Phodopus sungorus) with facultative non-shivering thermogenesis capacity (NST) and oxidative status. We found that in both phenotypes acclimation to winter-like conditions increased NST capacity and improved antioxidant defence resulting in lower oxidative stress (OS) than in summer, and females had always lower OS than males. Although NST capacity did not correlate with the intensity of OS, shortly after NST induction responders had lower OS than non-responders suggesting more effective mechanisms protecting from detrimental effects of reactive oxygen metabolites generated during rewarming from torpor. We suggest that seasonal increase in antioxidant defence is programmed endogenously to predictively prevent oxidative stress in winter. At the same time reactive upregulation of antioxidant defence protects against reactive oxygen species generated during NST itself. It suggests that evolution of winter phenotype with potentially harmful characteristics was counterbalanced by the development of protective mechanisms allowing for the maintenance of phenotypic adjustments to seasonally changing environment.

Survival of the cheapest: how proteome cost minimization drives evolution

Darwin's theory of evolution emphasized that positive selection of functional proficiency provides the fitness that ultimately determines the structure of life, a view that has dominated biochemical thinking of enzymes as perfectly optimized for their specific functions. The 20th-century modern synthesis, structural biology, and the central dogma explained the machinery of evolution, and nearly neutral theory explained how selection competes with random fixation dynamics that produce molecular clocks essential e.g. for dating evolutionary histories. However, quantitative proteomics revealed that selection pressures not relating to optimal function play much larger roles than previously thought, acting perhaps most importantly via protein expression levels. This paper first summarizes recent progress in the 21st century toward recovering this universal selection pressure. Then, the paper argues that proteome cost minimization is the dominant, underlying 'non-function' selection pressure controlling most of the evolution of already functionally adapted living systems. A theory of proteome cost minimization is described and argued to have consequences for understanding evolutionary trade-offs, aging, cancer, and neurodegenerative protein-misfolding diseases.

Association of Hypothyroidism and Mortality in the Elderly Population: A Systematic Review and Meta-Analysis

CONTEXT

The evidence of whether hypothyroidism increases mortality in the elderly population is currently inconsistent and conflicting.

OBJECTIVE

The objective of this meta-analysis is to determine the impact of hypothyroidism on mortality in the elderly population.

DATA SOURCES

PubMed, Embase, Cochrane Library, Scopus, and Web of Science databases were searched from inception until May 10, 2019.

STUDY SELECTION

Studies evaluating the association between hypothyroidism and all-cause and/or cardiovascular mortality in the elderly population (ages ≥ 60 years) were eligible.

DATA EXTRACTION

Two reviewers independently extracted data and assessed the quality of the studies. Relative risk (RR) was retrieved for synthesis. A random-effects model for meta-analyses was used.

DATA SYNTHESIS

A total of 27 cohort studies with 1 114 638 participants met the inclusion criteria. Overall, patients with hypothyroidism experienced a higher risk of all-cause mortality than those with euthyroidism (pooled RR = 1.26, 95% CI: 1.15-1.37); meanwhile, no significant difference in cardiovascular mortality was found between patients with hypothyroidism and those with euthyroidism (pooled RR = 1.10, 95% CI: 0.84-1.43). Subgroup analyses revealed that overt hypothyroidism (pooled RR = 1.10, 95% CI: 1.01-1.20) rather than subclinical hypothyroidism (pooled RR = 1.14, 95% CI: 0.92-1.41) was associated with increased all-cause mortality. The heterogeneity primarily originated from different study designs (prospective and retrospective) and geographic locations (Europe, North America, Asia, and Oceania).

CONCLUSIONS

Based on the current evidence, hypothyroidism is significantly associated with increased all-cause mortality instead of cardiovascular mortality among the elderly. We observed considerable heterogeneity, so caution is needed when interpreting the results. Further prospective, large-scale, high-quality studies are warranted to confirm these findings.

Age-related differences in physiology and survival of northern red-backed voles (Myodes rutilus) in captivity

Age-related deterioration of physiological functions is one of the most evident manifestations of ageing. In wild populations of some species, including murid rodents, lifespans are substantially modified by environmental signals that affect an individual's response to such challenges as unfavourable climatic conditions, parasitic load etc. But the real impact of ageing on natural mortality of most species remains obscure. To clarify how age affects the responsiveness of organisms to environmental challenges, we performed longitudinal laboratory observations of wild-derived northern red-backed voles (Myodes rutilus). We fixed individual longevity and measured metabolic indexes (basal and maximal metabolic rates), ability to maintain body temperature under acute cooling, plasma corticosterone, indexes of acquired and innate immunity in the same individuals of 3-4, 6-7 and 9-10 months old. The maximum estimated lifespan was about 2 years 8 months, which is considerably older than in nature, but less than 30% of individuals passed the one-year milestone. Regardless of the intense mortality, in the first year of life, animals did not demonstrate any age-related deterioration in physiological functions, except leucocyte number. No consistency in any individual physiological index was found. As the individual longevity of red-backed voles varied between years of captivity, we suggest that the welfare and lifespan of wild animals in captivity may be affected by the environmental conditions in the period preceding removal of the animal from the wild.

Age-Related Resistance to Thyroid Hormone Action

The age-related resistance to thyroid hormones (THs) explains the paucity of symptoms and signs of hyperthyroidism in older adults and may partly explain the myriad of symptoms and signs of hypothyroidism in biochemically euthyroid older people. This review considers the available data on the mechanisms underlying TH resistance with aging and compares these physiologic changes with the changes observed in congenital TH resistance syndromes. Aging is associated with alterations in TH economy along with a host of changes in the responsiveness of various tissues to THs. The age-related resistance to THs can be attributed to decreased TH transport to tissues, decreased nuclear receptor occupancy, decreased activation of thyroxine to triiodothyronine, and alterations in TH responsive gene expression. Although an increase in serum TH levels is expected in syndromes of TH resistance, unchanged serum TH levels in the euthyroid elderly is the result of increased sensitivity to TH negative feedback with increased suppression of thyroid-stimulating hormone, decreased thyroidal sensitivity to thyroid-stimulating hormone, and decreased TH production and secretion. The current clinical evidence suggests that the age-related TH resistance is mostly an adaptive response of the aging organism. It is tempting to speculate that similar changes can occur prematurely in a group of younger people who present with signs and symptoms of hypothyroidism despite normal serum thyroid function tests.

Structural-functional modifications of the liver to chronic radioactive exposure in pygmy wood mouse (Apodemus uralensis) within the East-Urals Radioactive Trace

The hepatic parameters (contents of glycogen, total lipids, nuclear and cytoplasmic proteins, DNA and RNA, fructose-6-phosphate, water, lipid peroxidation products, as well as activities of succinate dehydrogenase and glucose phosphate isomerase), radiometric data, and the relative population abundance of the pygmy wood mouse (Apodemus uralensis Pall., 1811) inhabiting natural (Middle Urals, Southern Urals, and Trans-Urals) areas and radioactivity territory (the EURT zone after of the Kyshtym accident in the South Urals in 1957) were analysed. Structural-functional modifications of the liver in A. uralensis from the EURT area are presented, taking into account irradiation power by dose-forming radionuclides (external and internal exposure to ¹³⁷Cs and ⁹⁰Sr), population size, and reproductive status (sexually immature and sexually mature yearlings, representing different ontogenetic patterns). The sexually immature mice from the EURT area can be considered to be the more sensitive (reactive) intrapopulation group to synergistic factors, such as radiation burden and population overabundance. The extent of structural-functional hepatic modification under current conditions of radionuclide exposure, in addition to the 60 year long effect of radioactive contamination in the EURT, can exceed the level of natural (geographic) variation observed in this species in the Urals region, which points to a long term evolutionary-ecological process.

Thyroid hormones mediate metabolic rate and oxidative, anti-oxidative balance at different temperatures in Mongolian gerbils (Meriones unguiculatus)

Oxidative damage is a potential physiological cost of thermoregulation during seasonal adjustments to air temperature (T_a) in small mammals. Here, we hypothesized that T_a affects serum thyroid hormone levels and these hormones can mediate the changes in metabolic rate and oxidative damage. Mongolian gerbils (Meriones unguiculatus) were acclimated at different T_as (5 °C, 23 °C and 37 °C) for 3 weeks. Serum tri-iodothyronine (T3) levels increased at 5 °C but decreased at 37 °C compared to the control (23 °C). Protein carbonyls increased in liver at 37 °C compared with control, however, lipid damage (malonaldehyde, MDA) in both serum and liver was unrelated to T_a. After the effects of different T_as on thyroid hormone levels and oxidative damage markers were determined, we further investigate whether thyroid hormones mediated metabolic rate and oxidative damage. Another set of gerbils received 0.0036% L-thyroxin (hyperthyroid), 0.04% Methylimazol (hypothyroid) or water (control). Hypothyroid group showed a 34% reduction in resting metabolic rate (RMR) also 42% and 26% increases in MDA and liver protein carbonyl respectively, whereas hyperthyroid group had higher RMR, liver mass and superoxide dismutase (SOD) compared to control. Serum T3 or T3/T4 levels were correlated positively with RMR, liver mass, and SOD, but negatively with MDA and uncoupling protein 2 (UCP2). We concluded that high T_a induced hypothyroidism, decreased RMR and increased oxidative damage, whereas low T_a induced hyperthyroidism, increased RMR and unchanged oxidative damage. These data supported our hypothesis that thyroid hormones can be a cue to mediate metabolic rate and different aspects of oxidative and antioxidant activities at different T_as.

Cellular metabolic rates and oxidative stress profiles in primary fibroblast cells isolated from virgin females, reproductively experienced females, and male Sprague-Dawley rats

Life-history theory posits that differences in reproductive strategies may dictate lifespans of organisms. Animals that have higher investments in reproduction in terms of litter size and frequency of litters tend to have shorter lifespans. The accumulation of oxidative stress damage has been proposed to be a cost of reproduction and a mediator of life-histories among animals, however, the implications of reproduction on oxidative stress still remain unclear. We tested physiological consequences of reproduction on metabolism and oxidative stress of Sprague-Dawley Rats (Rattus norvegicus) with various reproductive experiences at the cell level. We grew primary dermal fibroblasts from Sprague-Dawley rats which have the potential of having large litters frequently. Cells were isolated from virgin females, primiparous females, multiparous females, and reproductively-experienced males. We measured basal oxygen consumption (OCR), proton leak, ATP production, spare respiratory capacity, coupling efficiency and glycolysis using a Seahorse XF96 oxygen flux analyzer. Additionally, we measured rates of RS (reactive species) production, reduced glutathione (GSH), mitochondrial content, and lipid peroxidation (LPO) damage to quantify oxidative stress. There were no significant differences in any OCR or glycolytic parameters across any of our groups. However, reproductively-experienced females had significantly lower rates of LPO damage as compared with virgin females and males, as well as nonsignificant decreases in GSH concentration. Decreases in LPO damage and GSH indicate that reproductively-experienced females potentially use their endogenous antioxidant system to combat delirious effects of increased metabolism during reproduction. Our results suggest that reproduction may, in fact, have a protective effect in females.

The effects of graded levels of calorie restriction: XI. Evaluation of the main hypotheses underpinning the life extension effects of CR using the hepatic transcriptome

Calorie restriction (CR) may extend longevity by modulating the mechanisms involved in aging. Different hypotheses have been proposed for its main mode of action. We quantified hepatic transcripts of male C57BL/6 mice exposed to graded levels of CR (0% to 40% CR) for three months, and evaluated the responses relative to these various hypotheses. Of the four main signaling pathways implied to be linked to the impact of CR on lifespan (insulin/insulin like growth factor 1 (IGF-1), nuclear factor-kappa beta (NF-ĸB), mechanistic target of rapamycin (mTOR) and sirtuins (SIRTs)), all the pathways except SIRT were altered in a manner consistent with increased lifespan. However, the expression levels of SIRT4 and SIRT7 were decreased with increasing levels of CR. Changes consistent with altered fuel utilization under CR may reduce reactive oxygen species production, which was paralleled by reduced protection. Downregulated major urinary protein (MUP) transcription suggested reduced reproductive investment. Graded CR had a positive effect on autophagy and xenobiotic metabolism, and was protective with respect to cancer signaling. CR had no significant effect on fibroblast growth factor-21 (FGF21) transcription but affected transcription in the hydrogen sulfide production pathway. Responses to CR were consistent with several different hypotheses, and the benefits of CR on lifespan likely reflect the combined impact on multiple aging related processes.

Metabolic Slowing and Reduced Oxidative Damage with Sustained Caloric Restriction Support the Rate of Living and Oxidative Damage Theories of Aging

Calorie restriction (CR) is a dietary intervention with potential benefits for healthspan improvement and lifespan extension. In 53 (34 CR and 19 control) non-obese adults, we tested the hypothesis that energy expenditure (EE) and its endocrine mediators are reduced with a CR diet over 2 years. Approximately 15% CR was achieved over 2 years, resulting in an average 8.7 kg weight loss, whereas controls gained 1.8 kg. In the CR group, EE measured over 24 hr or during sleep was approximately 80-120 kcal/day lower than expected on the basis of weight loss, indicating sustained metabolic adaptation over 2 years. This metabolic adaptation was accompanied by significantly reduced thyroid axis activity and reactive oxygen species (F2-isoprostane) production. Findings from this 2-year CR trial in healthy, non-obese humans provide new evidence of persistent metabolic slowing accompanied by reduced oxidative stress, which supports the rate of living and oxidative damage theories of mammalian aging.

OASIS 2: online application for survival analysis 2 with features for the analysis of maximal lifespan and healthspan in aging research

Online application for survival analysis (OASIS) has served as a popular and convenient platform for the statistical analysis of various survival data, particularly in the field of aging research. With the recent advances in the fields of aging research that deal with complex survival data, we noticed a need for updates to the current version of OASIS. Here, we report OASIS 2 (http://sbi.postech.ac.kr/oasis2), which provides extended statistical tools for survival data and an enhanced user interface. In particular, OASIS 2 enables the statistical comparison of maximal lifespans, which is potentially useful for determining key factors that limit the lifespan of a population. Furthermore, OASIS 2 provides statistical and graphical tools that compare values in different conditions and times. That feature is useful for comparing age-associated changes in physiological activities, which can be used as indicators of “healthspan.” We believe that OASIS 2 will serve as a standard platform for survival analysis with advanced and user-friendly statistical tools for experimental biologists in the field of aging research.

Association of Thyroid Function With Life Expectancy With and Without Cardiovascular Disease: The Rotterdam Study

IMPORTANCE

Variations in thyroid function within reference ranges are associated with an increased risk of cardiovascular disease (CVD) and mortality. However, the impact of thyroid function on life expectancy (LE) and the number of years lived with and without CVD remains unknown.

OBJECTIVE

To investigate the association of thyroid function with total LE and LE with and without CVD among euthyroid individuals.

DESIGN, SETTING, AND PARTICIPANTS

The Rotterdam Study, a population-based, prospective cohort study. We included participants without known thyroid disease and with thyrotropin and free thyroxine (FT4) levels within the reference ranges.

MAIN OUTCOMES AND MEASURES

Multistate life tables were used to calculate total LE and LE with and without CVD among thyrotropin and FT4 tertiles. Life expectancy estimates in men and women aged 50 years and older were obtained using prevalence, incidence rates, and hazard ratios for 3 transitions (healthy to CVD, healthy to death, and CVD to death), adjusting for sociodemographic and cardiovascular risk factors.

RESULTS

The mean (SD) age of the 7785 participants was 64.7 (9.8) years, and 52.5% were women. Over a median follow-up of 8.1 (interquartile range, 2.7-9.9) years, we observed 789 incident CVD events and 1357 deaths. Compared with those in the lowest tertile, men and women in the highest thyrotropin tertile lived 2.0 (95% CI, 1.0 to 2.8) and 1.4 (95% CI, 0.2 to 2.4) years longer, respectively, of which, 1.5 (95% CI, 0.2 to 2.6) and 0.9 (95% CI, -0.2 to 2.0) years longer without CVD. Compared with those in the lowest tertile, the difference in life expectancy for men and women in the highest FT4 tertile was -3.2 (95% CI, -5.0 to -1.4) and -3.5 (95% CI, -5.6 to -1.5) years, respectively, of which, -3.1 (95% CI, -4.9 to -1.4) and -2.5 (95% CI, -4.4 to -0.7) years without CVD.

CONCLUSIONS AND RELEVANCE

At the age of 50 years, participants with low-normal thyroid function live up to 3.5 years longer overall and up to 3.1 years longer without CVD than participants with high-normal thyroid function. These findings provide supporting evidence for a reevaluation of the current reference ranges of thyroid function and can help inform preventive and clinical care.

The effects of graded levels of calorie restriction: VIII. Impact of short term calorie and protein restriction on basal metabolic rate in the C57BL/6 mouse

Under calorie restriction (CR) animals need to lower energy demands. Whether this involves a reduction in cellular metabolism is an issue of contention. We exposed C57BL/6 mice to graded CR for 3 months, measured BMR and dissected out 20 body compartments. From a separate age-matched group (n=57), we built 7 predictive models for BMR. Unadjusted BMR declined with severity of restriction. Comparison of measured and predicted BMR from the simple models suggested suppression occurred. The extent of 'suppression' was greater with increased CR severity. However, when models based on individual organ sizes as predictors were used, the discrepancy between the prediction and the observed BMR disappeared. This suggested 'metabolic suppression' was an artefact of not having a detailed enough model to predict the expected changes in metabolism. Our data have wide implications because they indicate that inferred 'metabolic' impacts of genetic and other manipulations may reflect effects on organ morphology.

Senescence is not inevitable

Senescence, the physiological deterioration resulting in an increase in mortality and decline in fertility with age, is widespread in the animal kingdom and has often been regarded as an inescapable feature of all organisms. This essay briefly describes the history of the evolutionary theoretical ideas on senescence. The canonical evolutionary theories suggest that increasing mortality and decreasing fertility should be ubiquitous. However, increasing empirical data demonstrates that senescence may not be as universal a feature of life as once thought and that a diversity of demographic trajectories exists. These empirical observations support theoretical work indicating that a wide range of mortality and fertility trajectories is indeed possible, including senescence, negligible senescence and even negative senescence (improvement). Although many mysteries remain in the field of biogerontology, it is clear that senescence is not inevitable.

Reproduction, ageing, and longevity in two species of laboratory rodents with different life histories

Social subterranean rodents of the Bathyergidae family are known to have extended longevity and some signs of negligible senescence, although the manifestation of these traits depends on the reproductive status of individuals. Such enormous life history peculiarities are usually explained by the specificity of a subterranean way of life. If so, all subterranean rodents, regardless of their taxonomic position, are expected to have higher maximum lifespans and shorter senescence periods than the related above-ground species. In this study we compared the mortality rates and age-related reproductive activity and physical conditions in two sympatric rodents of the Cricetidae family: subterranean mole voles and above-ground dwarf hamsters. Mole voles have a maximum lifespan that is as high as two times the maximum lifespan of the dwarf hamsters; however, only a few mole voles outlasted the maximum lifespan of dwarf hamsters. Dwarf hamsters were generally more fecund than mole voles, which manifests both in a higher number of litters and larger litter sizes. Neither species demonstrated a significant age-related decline in litter size or muscle strength, although there were negative trends for dwarf hamsters. We conclude that some evidence of extended longevity and slow ageing do occur in mole voles, but due to the relatively short "subterranean" phylogenetic history of the species, this evidence is not as pronounced as in the social species of Bathyergidae family.

Energy excess is the main cause of accelerated aging of mammals

The analysis of cases of unusually high longevity of naked mole rats and an alternative explanation of the phenomenon of calorie restriction effects in monkeys allowed for postulating that any factor preventing an excess of energy consumed, leads to increased lifespan, both in evolutionary and an individual lifetime scale. It is postulated that in mammals the most destructive processes resulting in shortening of life are not restricted to the phenomena explained by the hyperfunction theory of Mikhail Blagosklonny. Hyperfunction, understood as unnecessary or even adverse syntheses of cell components, can be to some extent prevented by lowered intake of nutrients when body growth ceases. We postulate also the contribution of glyco/lipotoxicity to aging, resulting from the excess of energy. Besides two other factors seem to participate in aging. One of them is lack of telomerase activity in some somatic cells. The second factor concerns epigenetic phenomena. Excessive activity of epigenetic maintenance system probably turns off some crucial organismal functions. Another epigenetic factor playing important role could be the micro RNA system deciding on expression of numerous age-related diseases. However, low extrinsic mortality from predation is a conditio sine qua non of the expression of all longevity phenotypes in animals. Among all long-lived animals, naked mole rats are unique in the elimination of neoplasia, which is accompanied by delayed functional symptoms of senescence. The question whether simultaneous disappearance of neoplasia and delayed senescence is accidental or not remains open.

Oxidative Damage Does Not Occur in Striped Hamsters Raising Natural and Experimentally Increased Litter Size

Life-history theory assumes that animals can balance the allocation of limited energy or resources to the competing demands of growth, reproduction and somatic maintenance, while consequently maximizing their fitness. However, somatic damage caused by oxidative stress in reproductive female animals is species-specific or is tissue dependent. In the present study, several markers of oxidative stress (hydrogen peroxide, H₂O₂ and malonadialdehyde, MDA) and antioxidant (catalase, CAT and total antioxidant capacity, T-AOC) were examined in striped hamsters during different stages of reproduction with experimentally manipulated litter size. Energy intake, resting metabolic rate (RMR), and mRNA expression of uncoupling protein 1 (UCP₁) in brown adipose tissue (BAT) and UCP₃ in skeletal muscle were also examined. H₂O₂ and MDA levels did not change in BAT and liver, although they significantly decreased in skeletal muscle in the lactating hamsters compared to the non-reproductive group. However, H₂O₂ levels in the brain were significantly higher in lactating hamsters than non-reproductive controls. Experimentally increasing litter size did not cause oxidative stress in BAT, liver and skeletal muscle, but significantly elevated H₂O₂ levels in the brain. CAT activity of liver decreased, but CAT and T-AOC activity of BAT, skeletal muscle and the brain did not change in lactating hamsters compared to non-reproductive controls. Both antioxidants did not change with the experimentally increasing litter size. RMR significantly increased, but BAT UCP₁ mRNA expression decreased with the experimentally increased litter size, suggesting that it was against simple positive links between metabolic rate, UCP₁ expression and free radicals levels. It may suggest that the cost of reproduction has negligible effect on oxidative stress or even attenuates oxidative stress in some active tissues in an extensive range of animal species. But the increasing reproductive effort may cause oxidative stress in the brain, indicating that oxidative stress in response to reproduction is tissue dependent. These findings provide partial support for the life-history theory.

Caloric restriction in lean and obese strains of laboratory rat: effects on body composition, metabolism, growth and overall health

NEW FINDINGS

What is the central question of this study? How do lean and obese rats respond physiologically to caloric restriction? What is the main finding and its importance? Obese rats show marked benefits compared with lean animals. Reduced body fat is associated with improved longevity with caloric restriction (CR) in rodents. Little is known regarding effects of CR in genetically lean versus obese strains. Long-Evans (LE) and Brown Norway (BN) rats make an ideal comparison for a CR study because the percentage body fat of young adult LE rats is double that of BN rats. Male LE and BN rats were either fed ad libitum (AL) or were calorically restricted to 80 or 90% of their AL weight. The percentages of fat, lean and fluid mass were measured non-invasively at 2- to 4-week intervals. Metabolic rate and respiratory quotient were measured after 3, 6, 9 and 12 months of CR. Overall health was scored monthly. The percentage of fat of the LE strain decreased with CR, whereas the percentage of fat of the BN strain remained above the AL group for several months. The percentage of lean mass increased above the AL for both strains subjected to CR. The percentage of fluid was unaffected by CR. The average metabolic rate over 22 h of the BN rats subjected to CR was reduced, whereas that of LE rats was increased slightly above the AL group. The respiratory quotient of BN rats was decreased with CR. Overall health of the CR LE group was significantly improved compared with that of the AL group, whereas health of the CR BN rats was impaired compared with the AL group. Overall, the lean BN and obese LE strains differ markedly in fat utilization and metabolic response to prolonged CR. There appears to be little benefit of CR in the lean strain.

Reproduction, aging and mortality rate in social subterranean mole voles (Ellobius talpinus Pall.)

Eusocial subterranean rodents of the Bathyergidae family have enormous longevity. The long lifespan of these species is associated with negligible senescence, that is, an absence of the signs of age-related deterioration in physical condition. The question arises as to whether these features are unique to eusocial Bathyergids or typical of other social subterranean rodents as well. In the present study, we analysed data from observations of a social subterranean Microtinae rodent, the northern mole vole (Ellobius talpinus Pall.), which, like mole-rats, has reproductive skew. Among the individuals captured in the wild and maintained in captivity, females that reproduced lived significantly longer than non-breeding females. We did not find any changes in muscle strength with age in any of the demographic groups studied. Faecal glucocorticoid concentrations before death were significantly higher in non-breeding females than in breeding females and males. Increased adrenocortical activity may be one mechanism responsible for the decreased lifespan of non-reproducing individuals of social subterranean rodents. We conclude that the patterns of aging, although different in some respects, are generally common for social subterranean rodents of different taxonomic groups.

Physical activity after surgically obtained weight loss: study with a SenseWear armband in subjects undergoing biliopancreatic diversion

BACKGROUND

This study aimed to understand the role of the extra load of body mass in limiting physical activity and in preventing an active lifestyle in severely obese patients.

MATERIALS AND METHODS

The study was carried out in a University Hospital setting, and investigates severely obese patients, having undergone biliopancreatic diversion (BPD) for obesity and control subjects with a body weight closely similar to that of the BPD subjects; energy intake was evaluated by alimentary interview and energy expenditure was assessed with the Body Media SenseWear® Pro armband (SWA).

RESULTS

SWA metabolic efficiency (MET) was negatively associated with body mass index values (ρ = -0.464, p < 0.01), and the SWA overall energy expenditure was very similar to the energy alimentary intake in the obese patients and in the control subjects. Among the controls, the MET mean value was higher (p < 0.05) than that observed both in obese and in BPD subjects (1.392 ± 0.211 vs. 1.149 ± 0.181 and 1.252 ± 0.284, respectively); furthermore, in comparison with the obese and the BPD groups, among the control individuals a greater number of active persons (27% vs. 0 and 7%, respectively) and a lower number of sedentary persons (27% vs. 70 and 43%, respectively) was found (p < 0.01).

CONCLUSIONS

These preliminary results suggest the reliability of SWA data in assessing energy expenditure and tend to rule out the hypothesis that in severely obese patients the extra load of body mass by itself is a main factor limiting physical activity and leading to a sedentary lifestyle.

Using doubly-labeled water to measure energy expenditure in an important small ectotherm Drosophila melanogaster

Energy expenditure is a key variable in the study of ageing, and the fruit fly Drosophila melanogaster is a model organism that has been used to make step changes in our understanding of the ageing process. Standard methods for measurement of energy expenditure involve placing individuals in metabolic chambers where their oxygen consumption and CO₂ production can be quantified. These measurements require separating individuals from any social context, and may only poorly reflect the environment in which the animals normally live. The doubly-labeled water (DLW) method is an isotope-based technique for measuring energy expenditure which overcomes these problems. However, technical challenges mean that the smallest animals this method has been previously applied to weighed 50–200 mg. We overcame these technical challenges to measure energy demands in Drosophila weighing 0.78 mg. Mass-specific energy expenditure varied between 43 and 65 mW·g⁻¹. These estimates are considerably higher than estimates using indirect calorimetry of Drosophila in small metabolic chambers (around 18 mW·g⁻¹). The methodology we have established extends downwards by three orders of magnitude the size of animals that can be measured using DLW. This approach may be of considerable value in future ageing research attempting to understand the genetic and genomic basis of ageing.

Thyroid status and renal function in older persons in the general population

BACKGROUND

Prevalence estimates of thyroid dysfunction and chronic kidney disease both increase with age. The aim of this study was to investigate the cross-sectional association between low thyroid function and renal function in subjects aged 85 years and to assess whether a low thyroid function at age 85 years is associated with an accelerated decline in renal function during follow-up.

METHODS

We included 558 participants from the Leiden 85-plus Study. At baseline (age 85 y), TSH, free T4 (fT4), and free T3 levels were measured. Thyroid function groups were created using clinical cutoff values of TSH and fT4. Serum creatinine concentrations were determined at baseline and annually during a 5-year follow-up period. Estimated glomerular filtration rates (eGFRs) were calculated by means of the Modification of Diet in Renal Disease Study equation.

RESULTS

At baseline, subjects with higher levels of TSH and lower levels of fT4 and free T3 had lower renal function. Participants with hypothyroidism [mean 53.7 (2.0) mL/min per 1.73 m(2))] and subclinical hypothyroidism [55.7 (2.1) mL/min per 1.73 m(2)] had lower mean eGFRs (SE) than participants with normal thyroid function [59.5 (0.7) mL/min per 1.73 m(2)]; the highest eGFR was observed in participants with hyperthyroidism [eGFR 61.5 (3.1) mL/min per 1.73 m(2)] (P for trend = .004). There was no association between thyroid hormone levels at baseline and the change in renal function during follow-up.

CONCLUSIONS

Although low thyroid function was associated with lower renal function at age 85 years, an association between a low thyroid function and change in renal function over time was absent. Our findings question the causal relevance of the thyroid status for the deterioration of renal function in the oldest old.

Mitohormesis: Promoting Health and Lifespan by Increased Levels of Reactive Oxygen Species (ROS)

Increasing evidence indicates that reactive oxygen species (ROS), consisting of superoxide, hydrogen peroxide, and multiple others, do not only cause oxidative stress, but rather may function as signaling molecules that promote health by preventing or delaying a number of chronic diseases, and ultimately extend lifespan. While high levels of ROS are generally accepted to cause cellular damage and to promote aging, low levels of these may rather improve systemic defense mechanisms by inducing an adaptive response. This concept has been named mitochondrial hormesis or mitohormesis. We here evaluate and summarize more than 500 publications from current literature regarding such ROS-mediated low-dose signaling events, including calorie restriction, hypoxia, temperature stress, and physical activity, as well as signaling events downstream of insulin/IGF-1 receptors, AMP-dependent kinase (AMPK), target-of-rapamycin (TOR), and lastly sirtuins to culminate in control of proteostasis, unfolded protein response (UPR), stem cell maintenance and stress resistance. Additionally, consequences of interfering with such ROS signals by pharmacological or natural compounds are being discussed, concluding that particularly antioxidants are useless or even harmful.

High basal metabolic rate does not elevate oxidative stress during reproduction in laboratory mice

Increased oxidative stress (OS) has been suggested as a physiological cost of reproduction. However, previous studies reported ambiguous results, with some even showing a reduction of oxidative damage during reproduction. We tested whether the link between reproduction and OS is mediated by basal metabolic rate (BMR), which has been hypothesized to affect both the rate of radical oxygen species production and antioxidative capacity. We studied the effect of reproduction on OS in females of laboratory mice divergently selected for high (H-BMR) and low (L-BMR) BMR, previously shown to differ with respect to parental investment. Non-reproducing L-BMR females showed higher oxidative damage to lipids (quantified as the level of malondialdehyde in internal organ tissues) and DNA (quantified as the level of 8-oxodG in blood serum) than H-BMR females. Reproduction did not affect oxidative damage to lipids in either line; however, it reduced damage to DNA in L-BMR females. Reproduction increased catalase activity in liver (significantly stronger in L-BMR females) and decreased it in kidneys. We conclude that the effect of reproduction on OS depends on the initial variation in BMR and varies between studied internal organs and markers of OS.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Age, sex, and telomere dynamics in a long-lived seabird with male-biased parental care

The examination of telomere dynamics is a recent technique in ecology for assessing physiological state and age-related traits from individuals of unknown age. Telomeres shorten with age in most species and are expected to reflect physiological state, reproductive investment, and chronological age. Loss of telomere length is used as an indicator of biological aging, as this detrimental deterioration is associated with lowered survival. Lifespan dimorphism and more rapid senescence in the larger, shorter-lived sex are predicted in species with sexual size dimorphism, however, little is known about the effects of behavioral dimorphism on senescence and life history traits in species with sexual monomorphism. Here we compare telomere dynamics of thick-billed murres (Urialomvia), a species with male-biased parental care, in two ways: 1) cross-sectionally in birds of known-age (0-28 years) from one colony and 2) longitudinally in birds from four colonies. Telomere dynamics are compared using three measures: the telomere restriction fragment (TRF), a lower window of TRF (TOE), and qPCR. All showed age-related shortening of telomeres, but the TRF measure also indicated that adult female murres have shorter telomere length than adult males, consistent with sex-specific patterns of ageing. Adult males had longer telomeres than adult females on all colonies examined, but chick telomere length did not differ by sex. Additionally, inter-annual telomere changes may be related to environmental conditions; birds from a potentially low quality colony lost telomeres, while those at more hospitable colonies maintained telomere length. We conclude that sex-specific patterns of telomere loss exist in the sexually monomorphic thick-billed murre but are likely to occur between fledging and recruitment. Longer telomeres in males may be related to their homogamous sex chromosomes (ZZ) or to selection for longer life in the care-giving sex. Environmental conditions appeared to be the primary drivers of annual changes in adult birds.