Are mice calorically restricted in nature?

In the land of not-unhappiness: On the state-of-the-art of targeting aging and age-related diseases by biomedical research

The concept of the Land of Not-Unhappiness refers to the potential achievement of eliminating the pathologies of the aging process. To inform of how close we are to settling in the land, we summarize and review the achievements of research on anti-aging interventions over the last hundred years with a specific focus on strategies that slow down metabolism, compensate for aging-related losses, and target a broad range of age-related diseases. We critically evaluate the existing interventions labeled as "anti-aging," such as calorie restriction, exercise, stem cell administration, and senolytics, to provide a down-to-earth evaluation of their current applicability in counteracting aging. Throughout the text, we have maintained a light tone to make it accessible to non-experts in biogerontology, and provide a broad overview for those considering conducting studies, research, or seeking to understand the scientific basis of anti-aging medicine.

Does diet influence aging? Evidence from animal studies

Nutrition profoundly influences the risk for many age-related diseases. Whether nutrition influences human aging biology directly is less clear. Studies in different animal species indicate that reducing food intake ("caloric restriction" [CR]) can increase lifespan and delay the onset of diseases and the biological hallmarks of aging. Obesity has been described as "accelerated aging" and therefore the lifespan and health benefits generated by CR in both aging and obesity may occur via similar mechanisms. Beyond calorie intake, studies based on nutritional geometry have shown that protein intake and the interaction between dietary protein and carbohydrates influence age-related health and lifespan. Studies where animals are calorically restricted by providing free access to diluted diets have had less impact on lifespan than those studies where animals are given a reduced aliquot of food each day and are fasting between meals. This has drawn attention to the role of fasting in health and aging, and exploration of the health effects of various fasting regimes. Although definitive human clinical trials of nutrition and aging would need to be unfeasibly long and unrealistically controlled, there is good evidence from animal experiments that some nutritional interventions based on CR, manipulating dietary macronutrients, and fasting can influence aging biology and lifespan.

Effects of the Density of Invasive Lantana camara Plants on the Biodiversity of Large and Small Mammals in the Groenkloof Nature Reserve (GNR) in South Africa

Multi-scale approaches have been used to determine scales at which mammal species are responding to habitat destruction due to invasion, but the impacts of weeds on mammals have not been extensively studied, especially in Africa. Inside the Groenkloof Nature Reserve (GNR), we assessed how mammals are affected by an invasive weed Lantana camara. A series of models were applied to determine the differences in species abundance as well as richness, separated for large and small mammals. When diversity indices were used, an Analysis of Variance (ANOVA) revealed no statistically significant difference between treatments (F₅ = 0.233, p = 0.945) for large mammals. The results of a Generalised Linear Mixed Model (GLMM) showed that vegetation type (Wald χ²₂ = 120.156; p < 0.01) and foraging guilds (Wald χ²₃ = 76.771; p < 0.01) were significant predictors of large mammal species richness. However, for small mammals, the results of a GLMM showed that only treatment type (Wald χ²₅ = 10.62; p = 0.050) was a significant predictor of the number of small mammals trapped. In addition, the ANOVA revealed statistically significant differences in species diversity between treatments (F₅ = 0.934; p < 0.001) and by season (F₁ = 9.122 p = 0.003) for small mammals. The presence of L. camara coupled with other predictors was associated with differences in large mammal abundances and diversity, and differences in how these large mammals were distributed across the landscape. Furthermore, the highest species diversity was found in the spring for small mammals. Therefore, for all the mammals studied, the presence of L. camara negatively affected species abundance, richness, and diversity, as well as how these species were distributed across the invaded and cleared areas.

Rodent diet aids and the fallacy of caloric restriction

Understanding the molecular mechanisms of normal aging is a prerequisite to significantly improving human health span. Caloric restriction (CR) can delay aging and has served as a yardstick to evaluate interventions extending life span. However, mice given unlimited access to food suffer severe obesity. Health gains from CR depend on control mice being sufficiently overweight and less obese mouse strains benefit far less from CR. Pharmacologic interventions that increase life span, including resveratrol, rapamycin, nicotinamide mononucleotide and metformin, also reduce body weight. In primates, CR does not delay aging unless the control group is eating enough to suffer from obesity-related disease. Human survival is optimal at a body mass index achievable without CR, and the above interventions are merely diet aids that shouldn't slow aging in healthy weight individuals. CR in humans of optimal weight can safely be declared useless, since there is overwhelming evidence that hunger, underweight and starvation reduce fitness, survival, and quality of life. Against an obese control, CR does, however, truly delay aging through a mechanism laid out in the following tumor suppression theory of aging.

Effects of ad libitum free-choice access to freshly squeezed domestic white asparagus juice on intestinal microbiota composition and universal biomarkers of immuno-metabolic homeostasis and general health in middle-aged female and male C57BL/6 mice

BACKGROUND AND PURPOSE

Asparagus contains different bioactive and volatile components including pyrazines, sulphur-containing compounds, and polyphenols. Asparagus juice is a new low-calorie LAB-containing natural juice product, the usage of which is expanding. Pyrazines and sulphur-containing compounds are degraded by bacteria on one hand, but on the other hand, dietary polyphenols prevent human colorectal diseases as modulators of the composition and/or activity of gut microbiota. However, the utility of these asparagus compounds for reversal of age-associated microbial dysbiosis and the immunometabolic disorders that dysbiosis incites body inflammatory reactions was not much explored so far. Hence, using middle-aged mice, we conducted the current study to verify the effect of freshly squeezed domestic white asparagus juice on the biomarkers reflecting immuno-metabolic pathways linking age-related dysbiosis and metabolic events.

MATERIALS AND METHODS

Thirty-two conventional Harlan Laboratories C57BL/6 mice aged between 11-12 months were randomly divided into two groups (n=16). Mice in control group 1 received sterile tap water. Animals in group 2 had 60 days ad libitum free-choice access to sterile tap water supplemented with 5% (v/v) freshly squeezed domestic white asparagus juice. Clinical signs of general health, hydration, and inflammation were monitored daily. Caecal content samples were analysed by qPCR for microbial composition. Histology of relevant organs was carried out on day 60 after sacrificing the mice. Universal markers of metabolic- and liver function were determined in serum samples. Caecal SCFAs contents were measured using HPLC.

RESULTS

Overall, no significant differences in general health or clinical signs of inflammation between the two groups were observed. The liver to body weight ratio in asparagus juice-drank mice was lowered. The qPCR quantification showed that asparagus juice significantly decreased the caecal Clostridium coccoides group while causing an enhancement in Clostridium leptum, Firmicutes, and bifidobacterial groups as well as total caecal bacterial count. Asparagus juice significantly elevated the caecal contents of SCFAs. Enhanced SCFAs (acetate, butyrate, and propionate) in mice receiving asparagus juice, however, did coincide with altered lipid levels in plasma or changes in the abundance of relevant bacteria for acetate-, butyrate-, and propionate production.

DISCUSSION

To the best of our knowledge, this is the first study aiming at evaluating the effect of freshly squeezed German domestic white asparagus juice on universal markers of metabolic- and liver function in middle-aged mice and the role of gut microbiota in this regard. The effectiveness of asparagus juice to improve metabolism in middle-aged mice was associated with alterations in intestinal microbiota but maybe also due to uptake of higher amounts of SCFAs. Hence, the key signal pathways corresponding to improved immune-metabolic homeostasis will be an important research scheme in the future.

Beyond calorie restriction: aging as a biological target for nutrient therapies

Arguably, the most important discovery in the biology of aging to date was that simply reducing food intake extended life and improved many aspects of health in a diversity of animal species. The conventional wisdom that emerged from first 50 years of rodent food restriction studies included (1) that the longevity impact of restriction was greater the longer restriction was imposed, and (2) that restricting calories rather than any specific macronutrient was critical to its health and longevity benefits. However these assumptions began to crumble as more and more restriction research was performed on other species besides laboratory rodents. Recent investigations of flies, rodents, monkeys, and increasingly humans, has begun to parse how calorie restriction, protein restriction, intermittent fasting, and the temporal pattern of eating all impact the health benefits of food restriction. Fly research continues to inform, as it has repeatedly shown that genotype, age, sex, duration, and tempo restriction all affect the health impact. Ultimately, optimizing human diets will require a personalized approach using omics approaches.

Metabolic and behavioral adaptations of greater white-toothed shrews to urban conditions

The global trend of urbanization is creating novel challenges for many animal species. Studies investigating behavioral differences between rural and urban populations often report a general increase in risk-taking behaviors in urban populations. According to the most common energy management model (the performance model), behaviors that increase access to resources, such as aggression and boldness, and behaviors that consume net energy, like locomotion and stress responses, are both positively correlated to resting metabolic rate (RMR). Thus, we expect urban populations to not only exhibit a higher level of risk-taking behavior but also a higher RMR. However, these interactions remain poorly investigated. Our main goal was to analyze the relationship between RMR and risk-taking behaviors in the greater white-toothed shrew (Crocidura russula) in rural versus urban populations. Trapped shrews were brought to captivity where we measured RMR, boldness, and exploration rate three times in each individual. Our findings revealed that urban shrews were indeed bolder and more exploratory, but contrary to our expectations, their RMR was lower than that of rural shrews. This is likely explained by differences in the environmental conditions of these two habitats, such as higher ambient temperatures and/or lower prey availability in cities. When looking at each population separately, this relationship remained similar: urban shrews with a higher RMR were less bold, and rural shrews with a higher RMR showed a lower exploration rate. We conclude that the energetic strategy of C. russula is dependent on the environmental and observational context and cannot be explained by the performance model.

Deletion of Nrf2 shortens lifespan in C57BL6/J male mice but does not alter the health and survival benefits of caloric restriction

Caloric restriction (CR) is the leading non-pharmaceutical dietary intervention to improve health- and lifespan in most model organisms. A wide array of cellular pathways is induced in response to CR and CR-mimetics, including the transcriptional activator Nuclear factor erythroid-2-related factor 2 (Nrf2), which is essential in the upregulation of multiple stress-responsive and mitochondrial enzymes. Nrf2 is necessary in tumor protection but is not essential for the lifespan extending properties of CR in outbred mice. Here, we sought to study Nrf2-knockout (KO) mice and littermate controls in male C57BL6/J, an inbred mouse strain. Deletion of Nrf2 resulted in shortened lifespan compared to littermate controls only under ad libitum conditions. CR-mediated lifespan extension and physical performance improvements did not require Nrf2. Metabolic and protein homeostasis and activation of tissue-specific cytoprotective proteins were dependent on Nrf2 expression. These results highlight an important contribution of Nrf2 for normal lifespan and stress response.

The hidden costs of dietary restriction: Implications for its evolutionary and mechanistic origins

Dietary restriction (DR) extends life span across taxa. Despite considerable research, universal mechanisms of DR have not been identified, limiting its translational potential. Guided by the conviction that DR evolved as an adaptive, pro-longevity physiological response to food scarcity, biomedical science has interpreted DR as an activator of pro-longevity molecular pathways. Current evolutionary theory predicts that organisms invest in their soma during DR, and thus when resource availability improves, should outcompete rich-fed controls in survival and/or reproduction. Testing this prediction in Drosophila melanogaster (N > 66,000 across 11 genotypes), our experiments revealed substantial, unexpected mortality costs when flies returned to a rich diet following DR. The physiological effects of DR should therefore not be interpreted as intrinsically pro-longevity, acting via somatic maintenance. We suggest DR could alternatively be considered an escape from costs incurred under nutrient-rich conditions, in addition to costs associated with DR.

The effect of dietary restriction on reproduction: a meta-analytic perspective

BACKGROUND

Dietary restriction (DR), a reduction in the amount of food or particular nutrients eaten, is the most consistent environmental manipulation to extend lifespan and protect against age related diseases. Current evolutionary theory explains this effect as a shift in the resolution of the trade-off between lifespan and reproduction. However, recent studies have questioned the role of reproduction in mediating the effect of DR on longevity and no study has quantitatively investigated the effect of DR on reproduction across species.

RESULTS

Here we report a comprehensive comparative meta-analysis of the effect of DR on reproduction. In general, DR reduced reproduction across taxa, but several factors moderated this effect. The effect of DR on reproduction was greater in well-studied model species (yeast, nematode worms, fruit flies and rodents) than non-model species. This mirrors recent results for longevity and, for reproduction, seems to result from a faster rate of decline with decreasing resources in model species. Our results also suggested that not all reproductive traits are affected equally by DR. High and moderate cost reproductive traits suffered a significant reduction with DR, but low cost traits, such as ejaculate production, did not. Although the effect of DR on reproduction was stronger in females than males, this sex difference reduced to near zero when accounting for other co-factors such as the costliness of the reproductive trait. Thus, sex differences in the effect of DR on longevity may be due to a failure to expose males to as complete a range of the costs of reproduction as females.

CONCLUSIONS

We suggest that to better understand the generality of the effect of DR, future studies should attempt to address the cause of the apparent model species bias and ensure that individuals are exposed to as many of the costs of reproduction as possible. Furthermore, our meta-analytic approach reveals a general shortage of DR studies that record reproduction, particularly in males, as well as a lack of direct side-by-side comparisons of the effect of DR on males and females.

Effect of calorie restriction on spontaneous physical activity and body mass in mice divergently selected for basal metabolic rate (BMR)

Spontaneous physical activity (SPA) represents an important component of daily energy expenditures in animals and humans. Intra-specific variation in SPA may be related to the susceptibility to metabolic disease or obesity. In particular, reduced SPA under conditions of limited food availability may conserve energy and prevent loss of body and fat mass ('thrifty genotype hypothesis'). However, both SPA and its changes during food restriction show wide inter-individual variations. We studied the effect of 30% caloric restriction (CR) on SPA in laboratory mice divergently selected for high (H-BMR) and low (L-BMR) basal metabolic rate. Selection increased SPA in the H-BMR line but did not change it in the L-BMR mice. This effect reflected changes in SPA intensity but not SPA duration. CR increased SPA intensity more strongly in the L-BMR line than in the H-BMR line and significantly modified the temporal variation of SPA. However, the initial between-line differences in SPA were not affected by CR. Loss of body mass during CR did not differ between both lines. Our results show that the H-BMR mice can maintain their genetically determined high SPA under conditions of reduced food intake without sacrificing their body mass. We hypothesize that this pattern may reflect the higher flexibility in the energy budget in the H-BMR line, as we showed previously that mice from this line reduced their BMR during CR. These energy savings may allow for the maintenance of elevated SPA in spite of reduced food intake. We conclude that the effect of CR on SPA is in large part determined by the initial level of BMR, whose variation may account for the lack of universal pattern of behavioural responses to CR.

Behavioural changes are a major contributing factor in the reduction of sarcopenia in caloric-restricted ageing mice

BACKGROUND

In rodent models, caloric restriction (CR) with maintenance of adequate micronutrient supply has been reported to increase lifespan and to reduce age-induced muscle loss (sarcopenia) during ageing. In the present study, we further investigated effects of CR on the onset and severity of sarcopenia in ageing male C57BL/6 J mice. The aim of this study was to investigate whether CR induces changes in behaviour of the animals that could contribute to the pronounced health-promoting effects of CR in rodents. In addition, we aimed to investigate in more detail the effects of CR on the onset and severity of sarcopenia.

METHODS

The mice received either an ad libitum diet (control) or a diet matching 70 E% of the control diet (C). Daily activity, body composition (dual energy X-ray absorptiometry), grip strength, insulin sensitivity, and general agility and balance were determined at different ages. Mice were killed at 4, 12, 24, and 28 months. Skeletal muscles of the hind limb were dissected, and the muscle extensor digitorum longus muscle was used for force-frequency measurements. The musculus tibialis was used for real-time quantitative PCR analysis.

RESULTS

From the age of 12 months, CR animals were nearly half the weight of the control animals, which was mainly related to a lower fat mass. In the control group, the hind limb muscles showed a decline in mass at 24 or 28 months of age, which was not present in the CR group. Moreover, insulin sensitivity (oral glucose tolerance test) was higher in this group and the in vivo and ex vivo grip strength did not differ between the two groups. In the hours before food was provided, CR animals were far more active than control animals, while total daily activity was not increased. Moreover, agility test indicated that CR animals were better climbers and showed more climbing behaviours.

CONCLUSIONS

Our study confirms earlier findings that in CR animals less sarcopenia is present. The mice on the CR diet, however, showed specific behavioural changes characterized by higher bursts of activity within a short time frame before consumption of a 70 E% daily meal. We hypothesize that the positive effects of CR on muscle maintenance in rodents are not merely a direct consequence of a lower energy intake but also related to a more active behaviour in a specific time frame. The burst of activity just before immediate start of eating, might lead to a highly effective use of the restricted protein sources available.

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

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

Why do the well-fed appear to die young? A new evolutionary hypothesis for the effect of dietary restriction on lifespan

Dietary restriction (DR) famously extends lifespan and reduces fecundity across a diverse range of species. A prominent hypothesis suggests that these life-history responses evolved as a survival-enhancing strategy whereby resources are redirected from reproduction to somatic maintenance, enabling organisms to weather periods of resource scarcity. We argue that this hypothesis is inconsistent with recent evidence and at odds with the ecology of natural populations. We consider a wealth of molecular, medical, and evolutionary research, and conclude that the lifespan extension effect of DR is likely to be a laboratory artifact: in contrast with captivity, most animals living in natural environments may fail to achieve lifespan extension under DR. What, then, is the evolutionary significance of the suite of responses that extend lifespan in the laboratory? We suggest that these responses represent a highly conserved nutrient recycling mechanism that enables organisms to maximize immediate reproductive output under conditions of resource scarcity.

Measuring energy metabolism in the mouse - theoretical, practical, and analytical considerations

The mouse is one of the most important model organisms for understanding human genetic function and disease. This includes characterization of the factors that influence energy expenditure and dysregulation of energy balance leading to obesity and its sequelae. Measuring energy metabolism in the mouse presents a challenge because the animals are small, and in this respect it presents similar challenges to measuring energy demands in many other species of small mammal. This paper considers some theoretical, practical, and analytical considerations to be considered when measuring energy expenditure in mice. Theoretically total daily energy expenditure is comprised of several different components: basal or resting expenditure, physical activity, thermoregulation, and the thermic effect of food. Energy expenditure in mice is normally measured using open flow indirect calorimetry apparatus. Two types of system are available – one of which involves a single small Spartan chamber linked to a single analyzer, which is ideal for measuring the individual components of energy demand. The other type of system involves a large chamber which mimics the home cage environment and is generally configured with several chambers/analyzer. These latter systems are ideal for measuring total daily energy expenditure but at present do not allow accurate decomposition of the total expenditure into its components. The greatest analytical challenge for mouse expenditure data is how to account for body size differences between individuals. This has been a matter of some discussion for at least 120 years. The statistically most appropriate approach is to use analysis of covariance with individual aspects of body composition as independent predictors.

Major urinary protein 5, a scent communication protein, is regulated by dietary restriction and subsequent re-feeding in mice

Major urinary proteins (Mups) are important for rodent scent communication and sexual behaviour. Recent evidence suggests that Mup1 may be regulated by fasting and re-feeding (RF). However, other Mup isoforms are poorly investigated, and data on the impact of long-term dietary restriction (DR) and ad libitum RF on Mup expression are missing. We investigated the effects of long-term 25 per cent DR and subsequent RF on Mup expression in male C57BL6 mice. DR significantly decreased Mup gene expression, hepatic and urinary protein levels compared with ad libitum (AL) fed control mice, with the greatest downregulation found for Mup5 expression. The decline in Mup expression was inverted by six months of RF. Because of inhibitory glucocorticoid response elements in the genomic sequence of the Mup5 gene, the observed inverse correlation of nuclear glucocorticoid receptor levels with Mup expression in response to DR and subsequent RF is a possible regulatory mechanism. Additionally, gene-expression-inhibiting histone deacetylation (H3K9) occurred in the region of the Mup5 gene in response to DR. We assume that Mup may act as a molecular switch linking nutritional status to sexual behaviour of mice, and thereby regulating male fertility and reproduction in response to food supply.

Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study

Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14 years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.

Comparative and meta-analytic insights into life extension via dietary restriction

Dietary restriction (DR) extends the lifespan of a wide range of species, although the universality of this effect has never been quantitatively examined. Here, we report the first comprehensive comparative meta-analysis of DR across studies and species. Overall, DR significantly increased lifespan, but this effect is modulated by several factors. In general, DR has less effect in extending lifespan in males and also in non-model organisms. Surprisingly, the proportion of protein intake was more important for life extension via DR than the degree of caloric restriction. Furthermore, we show that reduction in both age-dependent and age-independent mortality rates drives life extension by DR among the well-studied laboratory model species (yeast, nematode worms, fruit flies and rodents). Our results suggest that convergent adaptation to laboratory conditions better explains the observed DR-longevity relationship than evolutionary conservation although alternative explanations are possible.

Dietary restriction in rats and mice: a meta-analysis and review of the evidence for genotype-dependent effects on lifespan

Laboratory survival experiments have shown that dietary restriction (DR) can increase median and maximum lifespan. This paper provides a meta-analysis of laboratory experiments that have evaluated the effects of DR on lifespan in rats and mice (1934-present). In rats, DR increased median lifespan by 14-45% in half of all experiments, but in mice the effects of DR have been much weaker (4-27%). The least favorable effects of DR on lifespan have been observed among inbred rather than non-inbred mouse strains. In fact, some inbred mouse strains do not necessarily live longer with DR, including DBA/2 male mice and several strains from the ILSXISS recombinant inbred panel. Shortening of lifespan with DR has also been observed and confirmed for ILSXISS strain 114. Importantly, all rodent studies may be biased by the effects of laboratory breeding, since one study has shown that median lifespan is not improved by DR in wild-derived mice. These findings suggest that the set of genetic backgrounds studied in rodent DR experiments should be diversified. This will broaden the scope of genotypes studied in aging research, but may also be critical for translation of findings from rodents to historically outbred and genetically heterogeneous primate species.

Effect of dietary restriction on immune response of laboratory mice divergently selected for basal metabolic rate

To study whether dietary restriction (DR; 70% of ad lib. feeding)-elicited immunosuppression results from the trade-off between the costs of mounting an immune response and the metabolic costs of maintenance, we subjected mice from two divergent lines selected for high basal metabolic rate (H-BMR) and low BMR (L-BMR) to 4 wk of DR and then challenged them with keyhole limpet hemocyanin (KLH) antigen. Those line types differ genetically with respect to BMR and to the mass of metabolically expensive internal organs, which are larger in H-BMR mice. In mice of both line types, DR resulted in a significant reduction of body mass, an immune response, and the downsizing of spleen, lymph nodes, thymus, heart, and kidneys but not small intestines. DR resulted in a greater reduction of the spleen and lymph nodes in mice of the H-BMR line type, whereas the thymus was more affected in L-BMR line type. In contrast, immunization resulted in an increase of liver mass in DR mice of both line types. A comparison of the results of current and earlier studies on the same mouse line types suggests that metabolic trade-offs involving the costs of an immune response are more apparent when animals are forced to increase energy demands (e.g., by cold exposure) compared to when energy demands are decreased through DR. Our findings also suggest that divelrgent selection on BMR resulted in between-line-type differences in T-cell- and B-cell-mediated types of an immune response. More generally, our results indicate that production of a wide repertoire of antibodies is not correlated with high BMR.

An evolutionary review of human telomere biology: the thrifty telomere hypothesis and notes on potential adaptive paternal effects

Telomeres, repetitive DNA sequences found at the ends of linear chromosomes, play a role in regulating cellular proliferation, and shorten with increasing age in proliferating human tissues. The rate of age-related shortening of telomeres is highest early in life and decreases with age. Shortened telomeres are thought to limit the proliferation of cells and are associated with increased morbidity and mortality. Although natural selection is widely assumed to operate against long telomeres because they entail increased cancer risk, the evidence for this is mixed. Instead, here it is proposed that telomere length is primarily limited by energetic constraints. Cell proliferation is energetically expensive, so shorter telomeres should lead to a thrifty phenotype. Shorter telomeres are proposed to restrain adaptive immunity as an energy saving mechanism. Such a limited immune system, however, might also result in chronic infections, inflammatory stress, premature aging, and death--a more "disposable soma." With an increased reproductive lifespan, the fitness costs of premature aging are higher and longer telomeres will be favored by selection. Telomeres exhibit a paternal effect whereby the offspring of older fathers have longer telomeres due to increased telomere lengths of sperm with age. This paternal effect is proposed to be an adaptive signal of the expected age of male reproduction in the environment offspring are born into. The offspring of lineages of older fathers will tend to have longer, and thereby less thrifty, telomeres, better preparing them for an environment with higher expected ages at reproduction.

Calorie restriction: what recent results suggest for the future of ageing research

BACKGROUND

Calorie Restriction (CR) research has expanded rapidly over the past few decades and CR remains the most highly reproducible, environmental intervention to improve health and extend lifespan in animal studies. Although many model organisms have consistently demonstrated positive responses to CR, it remains to be shown whether CR will extend lifespan in humans. Additionally, the current environment of excess caloric consumption and high incidence of overweight/obesity illustrate the improbable nature of the long-term adoption of a CR lifestyle by a significant proportion of the human population. Thus, the search for substances that can reproduce the beneficial physiologic responses of CR without a requisite calorie intake reduction, termed CR mimetics (CRMs), has gained momentum.

MATERIAL AND METHODS

Recent articles describing health and lifespan results of CR in nonhuman primates and short-term human studies are discussed. Additional consideration is given to the rapidly expanding search for CRMs.

RESULTS

The first results from a long-term, randomized, controlled CR study in nonhuman primates showing statistically significant benefits on longevity have now been reported. Additionally, positive results from short-term, randomized, controlled CR studies in humans are suggestive of potential health and longevity gains, while test of proposed CRMs (including rapamycin, resveratrol, 2-deoxyglucose and metformin) have shown both positive and mixed results in rodents.

CONCLUSION

Whether current positive results will translate into longevity gains for humans remains an open question. However, the apparent health benefits that have been observed with CR suggest that regardless of longevity gains, the promotion of healthy ageing and disease prevention may be attainable.

Thermoregulation in mice exhibits genetic variability early in senescence

Aging leads to a loss of thermoregulation that can be readily monitored in laboratory mice. However, it is unclear from previous studies-we provide a tabular summary of 15 articles-whether significant loss occurs by midlife ( approximately 15 months of age). In this study, we examined 34 females from 22 LSXSS strains starting at 4 and 8 months of age (17 mice per age group). We used transponders inserted just under the loose skin of the pelt and calibrated against rectal body temperature to measure temperatures quickly without restraint. We found that the mean body temperatures measured 5 months later (9 and 13 months of age) had dropped significantly below normal in both groups: 0.6 masculineC lower in the younger cohort and 1.0 masculineC lower in the older cohort. These drops were not associated with weight loss or signs of pathology. Notably, the loss of thermoregulation between 8 and 13 months of age also exhibited genetic variation that was highly significant (P = 0.004). Such variation is potentially a powerful tool for determining the cause of thermoregulatory loss with age and whether this loss predicts senescence changes later in life, including the force of mortality.

Demographic analysis reveals gradual senescence in the flatworm Macrostomum lignano

Free-living flatworms ("Turbellaria") are appropriate model organisms to gain better insight into the role of stem cells in ageing and rejuvenation. Ageing research in flatworms is, however, still scarce. This is partly due to culture difficulties and the lack of a complete set of demographic data, including parameters such as median lifespan and age-specific mortality rate. In this paper, we report on the first flatworm survival analysis. We used the species Macrostomum lignano, which is an emerging model for studying the reciprocal influence between stem cells, ageing and rejuvenation. This species has a median lifespan of 205 +/- 13 days (average +/- standard deviation [SD]) and a 90th percentile lifespan of 373 +/- 32 days. The maximum lifespan, however, is more than 745 days, and the average survival curve is characterised by a long tail because a small number of individuals lives twice as long as 90% of the population. Similar to earlier observations in a wide range of animals, in M. lignano the age-specific mortality rate increases exponentially, but levels off at the oldest ages. To compare the senescence of M. lignano with that of other ageing models, we determined the mortality rate doubling time, which is 0.20 +/- 0.02 years. As a result, we can conclude that M. lignano shows gradual senescence at a rate similar to the vertebrate ageing models Rattus norvegicus and Mus musculus. We argue that M. lignano is a suitable model for ageing and rejuvenation research, and especially for the role of stem cells in these processes, due to its accessible stem cell system and regeneration capacity, and the possibility of combining stem cell studies with demographic analyses.

A structural basis for cellular senescence

Replicative senescence (RS) that limits the proliferating potential of normal eukaryotic cells occurs either by a cell-division counting mechanism linked to telomere erosion or prematurely through induction by cell stressors such as oncogene hyper-activation. However, there is evidence that RS also occurs by a stochastic process that is independent of number of cell divisions or cellular stress and yet it leads to a highly-stable, non-reversible post-mitotic state that may be long-lasting and that such a process is widely represented among higher eukaryotes. Here I present and discuss evidence that the interactions between DNA and the nuclear substructure, commonly known as the nuclear matrix, define a higher-order structure within the cell nucleus that following thermodynamic constraints, stochastically evolves towards maximum stability, thus becoming limiting for mitosis to occur. It is suggested that this process is responsible for ultimate replicative senescence and yet it is compatible with long-term cell survival.

Detoxification reactions: relevance to aging

It is widely (although not universally) accepted that organismal aging is the result of two opposing forces: (i) processes that destabilize the organism and increase the probability of death, and (ii) longevity assurance mechanisms that prevent, repair, or contain damage. Processes of the first group are often chemical and physico-chemical in nature, and are either inevitable or only under marginal biological control. In contrast, protective mechanisms are genetically determined and are subject to natural selection. Life span is therefore largely dependent on the investment into protective mechanisms which evolve to optimize reproductive fitness. Recent data indicate that toxicants, both environmental and generated endogenously by metabolism, are major contributors to macromolecular damage and physiological dysregulation that contribute to aging; electrophilic carbonyl compounds derived from lipid peroxidation appear to be particularly important. As a consequence, detoxification mechanisms, including the removal of electrophiles by glutathione transferase-catalyzed conjugation, are major longevity assurance mechanisms. The expression of multiple detoxification enzymes, each with a significant but relatively modest effect on longevity, is coordinately regulated by signaling pathways such as insulin/insulin-like signaling, explaining the large effect of such pathways on life span. The major aging-related toxicants and their cognate detoxification systems are discussed in this review.

Aging and survival: the genetics of life span extension by dietary restriction

Reducing food intake to induce undernutrition but not malnutrition extends the life spans of multiple species, ranging from single-celled organisms to mammals. This increase in longevity by dietary restriction (DR) is coupled to profound beneficial effects on age-related pathology. Historically, much of the work on DR has been undertaken using rodent models, and 70 years of research has revealed much about the physiological changes DR induces. However, little is known about the genetic pathways that regulate the DR response and whether or not they are conserved between species. Elucidating these pathways may facilitate the design of targeted pharmaceutical treatments for a range of age-related pathologies. Here, we discuss how recent work in nonmammalian model organisms has revealed new insight into the genetics of DR and how the discovery of DR-specific transcription factors will advance our understanding of this phenomenon.

Wild-derived mouse stocks: an underappreciated tool for aging research

Virtually all biomedical research makes use of a relatively small pool of laboratory-adapted, inbred, isogenic stocks of mice. Although the advantages of these models are many, there are a number of disadvantages as well. When studying a multifaceted process such as aging, the problems associated with using laboratory stocks are greatly inflated. On the other hand, wild-derived mouse stocks, loosely defined here as either wild-caught individuals or the recent progeny of wild-caught individuals, have much to offer to biogerontology research. Hence, the aims of this review are threefold: (1) to (re)acquaint readers with the pros and cons of using a typical inbred laboratory mouse model for aging research; (2) to reintroduce the notion of using wild-derived mouse stocks in aging research as championed by Austad, Miller and others for more than a decade, and (3) to provide an overview of recent advances in biogerontology using wild-derived mouse stocks.

Longevity-fertility trade-offs in the tephritid fruit fly, Anastrepha ludens, across dietary-restriction gradients

Although it is widely known that dietary restriction (DR) not only extends the longevity of a wide range of species but also reduces their reproductive output, the interrelationship of DR, longevity extension and reproduction is not well understood in any organism. Here we address the question: 'Under what nutritional conditions do the longevity-enhancing effects resulting from food restriction either counteract, complement or reinforce the mortality costs of reproduction? To answer this question we designed a fine-grained DR study involving 4800 individuals of the tephritid fruit fly, Anastrepha ludens, in which we measured sex-specific survival and daily reproduction in females in each of 20 different treatments (sugar : yeast ratios) plus 4 starvation controls. The database generated from this 3-year study consisted of approximately 100 000 life-days for each sex and 750 000 eggs distributed over the reproductive lives of 2400 females. The fertility and longevity-extending responses were used to create contour maps (X-Y grid) that show the demographic responses (Z-axis) across dietary gradients that range from complete starvation to both ad libitum sugar-only and ad libitum standard diet (3 : 1 sugar : yeast). The topographic perspectives reveal demographic equivalencies along nutritional gradients, differences in the graded responses of males and females, egg production costs that are sensitive to the interaction of food amounts and constituents, and orthogonal contours (equivalencies in longevity or reproduction) representing demographic thresholds related to both caloric content and sugar : yeast ratios. In general, the finding that lifespan and reproductive maxima occur at much different nutritional coordinates poses a major challenge for the use of food restriction (or a mimetic) in humans to improve health and extend longevity in humans.

Sleep is increased by weight gain and decreased by weight loss in mice

OBJECTIVE

To determine whether weight loss could reverse excessive sleep in high-fat diet-induced obesity.

DESIGN

Three groups of mice participated in the study. A weight gain/loss group was fed with high-fat food for 6 weeks (weight gain), and regular food again for 4 weeks (weight loss). A control group and a weight gain only group were fed with regular food and high-fat food, respectively, for 10 weeks after the baseline.

PARTICIPANTS

Adult male C57BL/6 mice.

MEASUREMENTS

The amounts of wake, rapid eye movement sleep (REMS) and non-REM sleep (NREMS) were determined at week 0 (baseline), week 6, and week 10.

RESULTS

The weight gain/loss group displayed a significant decrease in wakefulness and increases in NREMS and episodes of NREMS during 6 weeks of weight gain, which were reversed during subsequent 4 weeks of weight loss. The weight gain only group displayed significant decrease in wakefulness and increase of NREMS and REMS at both week 6 and week 10. The control group did not show significant sleep alterations during the experiment.

CONCLUSION

These observations indicate that sleep alterations induced by weight gain are reversed by weight loss in obese animals. These data may shed light on the mechanisms underlying the well-established association between obesity and sleepiness in humans and may lead to new therapeutic strategies for these 2 increasingly prevalent problems in the modern societies.

Age structure changes and extraordinary lifespan in wild medfly populations

The main purpose of this study was to test the hypotheses that major changes in age structure occur in wild populations of the Mediterranean fruit fly (medfly) and that a substantial fraction of individuals survive to middle age and beyond (> 3-4 weeks). We thus brought reference life tables and deconvolution models to bear on medfly mortality data gathered from a 3-year study of field-captured individuals that were monitored in the laboratory. The average time-to-death of captured females differed between sampling dates by 23.9, 22.7, and 37.0 days in the 2003, 2004, and 2005 field seasons, respectively. These shifts in average times-to-death provided evidence of changes in population age structure. Estimates indicated that middle-aged medflies (> 30 days) were common in the population. A surprise in the study was the extraordinary longevity observed in field-captured medflies. For example, 19 captured females but no reference females survived in the laboratory for 140 days or more, and 6 captured but no reference males survived in the laboratory for 170 days or more. This paper advances the study of aging in the wild by introducing a new method for estimating age structure in insect populations, demonstrating that major changes in age structure occur in field populations of insects, showing that middle-aged individuals are common in the wild, and revealing the extraordinary lifespans of wild-caught individuals due to their early life experience in the field.

Dietary restriction by bacterial deprivation increases life span in wild-derived nematodes

Dietary restriction is known to promote longevity in a variety of eukaryotic organisms. Most studies of dietary restriction have been performed on animals bred for many generations under conditions that differ substantially from their natural environment, raising the possibility that some apparent beneficial effects of dietary restriction are due to adaptation to laboratory conditions. To address this question in an invertebrate model, we determined the effect of dietary restriction by bacterial deprivation on life span in five different wild-derived Caenorhabditis elegans strains and two strains of the related species Caenorhabditis remanei. Longevity was enhanced in each of the wild-derived C. elegans strains, in most cases to a degree similar to that observed in N2, the standard laboratory strain. Both strains of C. remanei were substantially longer lived any of the C. elegans isolates, produced larger brood sizes, and retained the ability to produce offspring for a longer period of time. Dietary restriction failed to increase mean life span in one C. remanei isolate, but significantly increased the maximum life span of both C. remanei strains. Thus, we find no evidence that adaptation to laboratory conditions has significantly altered the aging process in C. elegans under either standard or food-restricted conditions.

Divergent metabolic adaptations to intestinal parasitic nematode infection in mice susceptible or resistant to obesity

BACKGROUND & AIMS

Diet-induced obesity results from increased ingestion of energy-dense food and sedentary lifestyle in genetically susceptible individuals. An environmental factor that may have shaped our energy homeostasis throughout evolution is parasitic nematode infection.

METHODS

To test the hypothesis that a metabolically "thrifty phenotype" is advantageous during intestinal nematode infection, we compared the responses to Heligmosomoides polygyrus infection between 2 mouse strains: obesity-prone C57Bl/6J vs obesity-resistant SWR/J. Metabolic phenotyping was performed using indirect calorimetry, dual energy x-ray absorptiometry, and magnetic resonance imaging scanning. Gene expression was assessed by quantitative reverse-transcription polymerase chain reaction and immunohistochemistry.

RESULTS

Body weight was maintained in both strains during nematode infection via different mechanisms. There was no apparent change in energy expenditure between the strains; however, SWR/J mice exhibited a marked hyperphagia (calorie intake 60% higher than C57Bl/6J) to maintain body weight. The importance of hyperphagia was confirmed by severe weight loss in a group of infected SWR/J mice whose food intake was restricted to that of naïve mice. Furthermore, SWR/J mice expelled nematodes more rapidly than C57Bl/6J mice, an effect related to a T helper cell 2 immune response.

CONCLUSIONS

C57Bl/6J mice are more energy efficient during parasitic nematode infection, which may explain their ability to tolerate the infection. SWR/J mice, on the other hand, require an increase in food intake to maintain energy stores during nematode infection. In addition, a strong T helper cell 2-mediated immune response that facilitates a prompt clearance of nematode infection in SWR/J mice may have evolved to conserve energy in this strain.

Physiological deterioration associated with breeding in female mice: a model for the study of senescence and aging

Longevity is a complex and dynamic process influenced by a diversity of factors. Amongst other, gestation and lactation contribute to organismal decline because they represent a great energetic investment in mammals. Here we compared the rate of senescence onset observed in primary fibroblast obtained from the lungs of retired female breeder mice (12 months old), with the senescence arrival observed in fibroblasts derived from age-matched nulliparous mice. Two-month-old animals were also used as controls of young, fully-developed adults. Cell proliferation, DNA synthesis, and expression of senescence-associated beta-galactosidase activity were evaluated as senescent parameters. In order to test differences in energetic competence at a systemic level, mitochondrial respiration was also evaluated in mitochondria isolated from the livers of the same animals used for the primary cultures. Our data indicated that the cells derived from female mice subjected to the physiological stress of breeding onset into replicative senescence prior than the cells from female mice age-matched without that particular stress. Thus validating the use of retired breeders as a model to study aging and senescence at the cellular level.

Social stress, immune functions and disease in rodents

The link between social factors, stress and health has been the focus of many interdisciplinary studies mostly because: (i) animals, including humans, often live in societies; (ii) positive and negative social relationships affect disease and well being; (iii) physiological alterations, which parallel social interactions also modulate immune and neuroendocrine functions. This review will focus on studies conducted on laboratory and wild rodents where social factors such as dyadic interactions, individual housing and differential group housing were investigated. The results obtained allow one to conclude that social factors in rodents are causally linked with immune disorders/disease susceptibility. In particular, lower lymphocyte proliferation and antigen-specific-IgG, granulocytosis and lymphopenia, as well as higher tumor induction and progression, are reliably associated with negative social events. Finally, due to the increasing utilization of social stress-based animal models the reliability of the concept of "social stress" and its evolutionary context are re-evaluated.

Does caloric restriction extend life in wild mice?

To investigate whether mice genetically unaltered by many generations of laboratory selection exhibit similar hormonal and demographic responses to caloric restriction (CR) as laboratory rodents, we performed CR on cohorts of genetically heterogeneous male mice which were grandoffspring of wild-caught ancestors. Although hormonal changes, specifically an increase in corticosterone and decrease in testosterone, mimicked those seen in laboratory-adapted rodents, we found no difference in mean longevity between ad libitum (AL) and CR dietary groups, although a maximum likelihood fitted Gompertz mortality model indicated a significantly shallower slope and higher intercept for the CR group. This result was due to higher mortality in CR animals early in life, but lower mortality late in life. A subset of animals may have exhibited the standard demographic response to CR in that the longest-lived 8.1% of our animals were all from the CR group. Despite the lack of a robust mean longevity difference between groups, we did note a strong anticancer effect of CR as seen in laboratory rodents. Three plausible interpretations of our results are the following: (1) animals not selected under laboratory conditions do not show the typical CR effect; (2) because wild-derived animals eat less when fed AL, our restriction regime was too severe to see the CR effect; or (3) there is genetic variation for the CR effect in wild populations; variants that respond to CR with extended life are inadvertently selected for under conditions of laboratory domestication.

Transgenic mice with a reduced core body temperature have an increased life span

Reduction of core body temperature has been proposed to contribute to the increased life span and the antiaging effects conferred by calorie restriction (CR). Validation of this hypothesis has been difficult in homeotherms, primarily due to a lack of experimental models. We report that transgenic mice engineered to overexpress the uncoupling protein 2 in hypocretin neurons (Hcrt-UCP2) have elevated hypothalamic temperature. The effects of local temperature elevation on the central thermostat resulted in a 0.3 degrees to 0.5 degrees C reduction of the core body temperature. Fed ad libitum, Hcrt-UCP2 transgenic mice had the same caloric intake as their wild-type littermates but had increased energy efficiency and a greater median life span (12% increase in males; 20% increase in females). Thus, modest, sustained reduction of core body temperature prolonged life span independent of altered diet or CR.

Behavioral, physical, and demographic changes in Drosophila populations through dietary restriction

Dietary restriction (DR) is a valuable experimental tool for studying the aging process. Primary advancement of research in this area has relied on rodent models, but attention has recently turned toward Drosophila melanogaster. However, little is known about the baseline effects of DR on wild-type Drosophila and continued experimentation requires such information. The findings described here survey the effects of DR on inbred, wild-type populations of Canton-S fruit flies and demonstrate a robust effect of diet on longevity. Over a circumscribed range of dietary conditions, healthy lifespan varies by as much as 121% for wild-type Drosophila females. Significant differences are also observed for male flies, but the magnitude of the DR effect is less robust. Mortality analyses of the survivorship data reveal that this variation in lifespan can be attributed to a modulation of the rate parameter for the mortality function - a change in the demographic rate of aging. Since the feeding of fruit flies is less easily controlled than that of rodents, this research also addresses the validity of applying a DR model to Drosophila populations. Feeding and body weight data for flies given the various dietary conditions surveyed indicate that Drosophila on higher-calorie diets consume a similar volume of food to those on a low-calorie diet, resulting in different levels of calorie intake. Fertility and activity levels demonstrate that the diets surveyed are comparable, and that increasing the calorie content of laboratory food up to twice the normal concentration is not pathologic for experimental fly populations.

Food restriction, evolution and ageing

The food restriction model for life extension is nearing "three-score and 10" years of age and remains in good shape, preserving much of the mystique of its youth. Although originally described for laboratory rodents, recent work shows that food restriction also appears to slow ageing processes in a range of other animal species, raising the question of whether this response represents some generalised evolutionary adaptation, perhaps a strategy to cope with periods of famine. If the food restriction response does have an adaptive basis, this would suggest that specific gene regulatory processes have evolved to shape the organism's physiological response to food restriction. It will then be important to investigate how these are organised and whether the same or different factors are at play in the various species in which food restriction extends life span.

Female oxytocin gene-knockout mice, in a semi-natural environment, display exaggerated aggressive behavior

Compared to results from a generation of neuropharmacological work, the phenotype of mice lacking the oxytocin (OT) peptide gene was remarkably normal. An important component of the current experiments was to assay OT-knockout (OTKO) and wild-type (WT) littermate control mice living under controlled stressful conditions designed to mimic more closely the environment for which the mouse genome evolved. Furthermore, our experimental group was comprised of an all-female population, in contrast to previous studies which have focused on all-male populations. Our data indicated that aggressive behaviors initiated by OTKO during a food deprivation feeding challenge were considerably more intense and diverse than aggressive behaviors initiated by WT. From the measures of continuous social interaction in the intruder paradigm, it emerged that OTKO mice were more offensively aggressive (attacking rumps and tails) than WT. In a test of parental behaviors, OTKO mice were 100% infanticidal while WT were 16% infanticidal and 50% maternal. Finally, 'alpha females' (always OTKO) were identified in each experiment. They were the most aggressive, the first to feed and the most dominant at nesting behaviors. Semi-natural environments are excellent testing environments for elucidating behavioral differences between transgenic mice and their WT littermates which may not be ordinarily discernible. Future studies of mouse group behavior should include examining female groupings in addition to the more usual all-male groups.

Sex and death: what is the connection?

A cost of reproduction, where lifespan and fecundity are negatively correlated, is of widespread occurrence. Mutations in insulin/IGF signaling (IIS) pathways and dietary restriction (DR) can extend lifespan in model organisms but do not always reduce fecundity, suggesting that the link between lifespan and fecundity is not inevitable. Understanding the molecular basis of the cost of reproduction will be informed by elucidation of the mechanisms by which DR and IIS affect these two traits.

The role of NGF uptake in selective vulnerability to cell death in ageing sympathetic neurons

We have examined the hypothesis that differences in nerve growth factor (NGF) uptake and transport determine vulnerability to age-related neurodegeneration. Neurons projecting to cerebral blood vessels (CV) in aged rats are more vulnerable to age-related degeneration than those projecting to the iris. Uptake of NGF was therefore examined in sympathetic neurons projecting from the superior cervical ganglion (SCG) to CV and iris in young and old rats by treating the peripheral processes of these neurons with different doses of I125-NGF. Total uptake of I125-NGF was reduced in old CV-projecting, but not iris-projecting, neurons. Numbers of radiolabelled neurons projecting to each target were counted in sectioned ganglia. The data showed age-related reductions in numbers of labelled neurons projecting to CV, but no change in numbers of neurons projecting to the iris. Calculation of uptake of I125-NGF per neuron unexpectedly showed no major age-related differences in either of the two neuron populations. However, uptake per neuron was considerably lower for young and old CV-projecting, compared to iris-projecting, SCG neurons. We hypothesized that variations in NGF uptake might affect neuronal survival in old age. Counts of SCG neurons using a physical disector following retrograde tracing with Fluorogold confirmed the selective vulnerability of CV-projecting neurons by showing a significant 37% loss of these neurons in the period between 15 and 24 months. In contrast, there was no significant loss of iris-projecting neurons. We conclude that vulnerability to, or protection from, age-related neurodegeneration and neuronal cell death are associated with life-long low, or high, levels of NGF uptake, respectively.

Stochastic dietary restriction using a Markov-chain feeding protocol elicits complex, life history response in medflies

Lifespan in individually housed medflies (virgins of both sexes) and daily reproduction for females were studied following one of 12 dietary restriction (DR) treatments in which the availability of high-quality food (yeast-sugar mixture) for each fly was based on a Markov chain feeding scheme--a stochastic dietary regime which specifies that the future dietary state depends only on the present dietary state and not on the path by which the present state was achieved. The stochastic treatments consisted of a combination of one of four values of a 'discovery' parameter and one of three values of a 'persistence' parameter. The results supported the hypotheses that: (i) longevity is extended in most medfly cohorts subject to stochastic DR; and (ii) longevity is more affected by the patch discovery than the patch persistence parameter. One of the main conclusions of the study is that, in combination with the results of earlier dietary restriction studies on the medfly, the results reinforce the concept that the details of the dietary restriction protocols have a profound impact on the sign and magnitude of the longevity extension relative to ad libitum cohorts and that a deeper understanding of the effect of food restriction on longevity is not possible without an understanding of its effect on reproduction.

Metabolic consequences of overfeeding in humans

PURPOSE OF REVIEW

Overfeeding leads to obesity and metabolic disorders, including impaired glucose homeostasis, lipid disorders, and hepatic steatosis. The consequences of standardized overfeeding on body weight have shown, however, considerable interindividual variability, which suggests that it also leads to adaptative changes in energy expenditure, in some individuals at least. The present review is mainly focused on the recent developments regarding the effects of overfeeding on energy expenditure.

RECENT FINDINGS

Individuals who gain the less body weight during overfeeding are those who experience a greater increase in total energy expenditure. This increase in energy expenditure has been attributed to stimulation of nonexercise physical activity. Recent developments regarding adaptative increases in physical activity are critically reviewed. Overfeeding also alters the pathways used for carbohydrate storage after a glucose load, by increasing de-novo lipogenesis in the liver and adipose tissue at the expense of glycogen storage. The sympathetic nervous system is a good candidate for energy expenditure increase during overfeeding. The increases in energy expenditure observed during acute stimulation of the sympathetic nervous system were however found to be unaltered by short-term overfeeding.

SUMMARY

The mechanisms by which some individuals protect themselves against body weight gain remain poorly understood. Nonvoluntary physical activity may allow one to increase energy expenditure during overfeeding, and may therefore constitute a regulatory factor in body weight control. The biological determinant of spontaneous, nonvoluntary physical activity, however, remains to be investigated.

Aerobic Performance of Wild‐Derived House Mice Does Not Change with Cold Exposure or Intestinal Parasite Infection

Aerobic performance is affected by numerous endogenous and exogenous factors. We investigated the effects of ambient temperature and parasite infection on resting metabolism and maximal exercise-induced oxygen consumption in wild-derived house mice (Mus musculus). We also collected preliminary data for effects of lactation on these measures of aerobic performance. Mice were experimentally infected with a naturally occurring intestinal nematode (Heligmosomoides polygyrus) and then exposed to cold temperatures for 10 d or allowed to mate and reproduce. Wild-derived house mice did not change their resting metabolism with H. polygyrus infection or cold exposure, which is in stark contrast to similar studies with laboratory mice. Preliminary data also showed no effect of lactation on aerobic performance. Similarly, maximal exercise-induced oxygen consumption and hematocrit and hemoglobin were unaffected by all experimental treatments. We conclude that resting metabolism, maximal oxygen consumption, and hematology of wild-derived house mice are unaffected by exogenous (temperature) and endogenous (H. polygyrus) demands and, therefore, wild-derived mice respond to these demands without incurring potential costs associated with changes in aerobic performance.