Increased Growth and Life-span with Lowered Ambient Temperature in the Annual Fish, Cynolebias adloffi

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.

Caloric restriction extends lifespan in a clonal plant

When subjected to dietary caloric restriction (CR), individual animals often outlive well-fed conspecifics. Here, we address whether CR also extends lifespan in plants. Whereas caloric intake in animals comes from ingestion, in plants it derives from photosynthesis. Thus, factors that reduce photosynthesis, such as reduced light intensity, can induce CR. In two lab experiments investigating the aquatic macrophyte Lemna minor, we tracked hundreds of individuals longitudinally, with light intensity-and hence, CR-manipulated using neutral-density filters. In both experiments, CR dramatically increased lifespan through a process of temporal scaling. Moreover, the magnitude of lifespan extension accorded with the assumptions that (a) light intensity positively relates to photosynthesis following Michaelis-Menten kinetics, and (b) photosynthesis negatively relates to lifespan via a power law. Our results emphasize that CR-mediated lifespan extension applies to autotrophs as well as heterotrophs, and suggest that variation in light intensity has quantitatively predictable effects on plant aging trajectories.

Cold temperature extends longevity and prevents disease-related protein aggregation through PA28γ-induced proteasomes

Aging is a primary risk factor for neurodegenerative disorders that involve protein aggregation. Because lowering body temperature is one of the most effective mechanisms to extend longevity in both poikilotherms and homeotherms, a better understanding of cold-induced changes can lead to converging modifiers of pathological protein aggregation. Here, we find that cold temperature (15 °C) selectively induces the trypsin-like activity of the proteasome in Caenorhabditis elegans through PSME-3, the worm orthologue of human PA28γ/PSME3. This proteasome activator is required for cold-induced longevity and ameliorates age-related deficits in protein degradation. Moreover, cold-induced PA28γ/PSME-3 diminishes protein aggregation in C. elegans models of age-related diseases such as Huntington's and amyotrophic lateral sclerosis. Notably, exposure of human cells to moderate cold temperature (36 °C) also activates trypsin-like activity through PA28γ/PSME3, reducing disease-related protein aggregation and neurodegeneration. Together, our findings reveal a beneficial role of cold temperature that crosses evolutionary boundaries with potential implications for multi-disease prevention.

Exceptional longevity in northern peripheral populations of Wels catfish (Siluris glanis)

Studies of life-history variation across a species range are crucial for ecological understanding and successful conservation. Here, we examined the growth and age of Wels catfish (Silurus glanis) in Sweden, which represent the northernmost populations in Europe. A total of 1183 individuals were captured, marked and released between 2006 and 2020. Mark-recapture data from 162 individuals (size range: 13–195 cm) were used to estimate von Bertalanffy growth curve parameters which revealed very slow growth rates compared to catfish within the core distribution area (central Europe). The fitted von Bertalanffy growth curve predicted a 150 cm catfish to be around 40 years old, while the largest recaptured individual (length 195 cm) was estimated to be 70 (95% CI 50–112) years old. This was substantially older than the previously documented maximum age of a catfish. The weight at length relationships in these northern peripheral populations were similar to those documented for catfish in central Europe indicating that resources did not constrain growth. This indicates that the slow growth and exceptional high age in the northern catfish populations are the result of lower temperatures and/or local adaptations.

Daily temperature cycles prolong lifespan and have sex-specific effects on peripheral clock gene expression in Drosophila melanogaster

Circadian rhythms optimize health by coordinating the timing of physiological processes to match predictable daily environmental challenges. The circadian rhythm of body temperature is thought to be an important modulator of molecular clocks in peripheral tissues, but how daily temperature cycles affect physiological function is unclear. Here, we examined the effect of constant temperature (Tcon, 25°C) and cycling temperature (Tcyc, 28°C:22°C during light:dark) paradigms on lifespan of Drosophila melanogaster, and the expression of clock genes, heat shock protein 83 (Hsp83), Frost (Fst) and senescence marker protein-30 (smp-30). Male and female D. melanogaster housed at Tcyc had longer median lifespans than those housed at Tcon. Tcyc induced robust Hsp83 rhythms and rescued the age-related decrease in smp-30 expression that was observed in flies at Tcon, potentially indicating an increased capacity to cope with age-related cellular stress. Ageing under Tcon led to a decrease in the amplitude of expression of all clock genes in the bodies of male flies, except for cyc, which was non-rhythmic, and for per and cry in female flies. Strikingly, housing under Tcyc conditions rescued the age-related decrease in amplitude of all clock genes, and generated rhythmicity in cyc expression, in the male flies, but not the female flies. The results suggest that ambient temperature rhythms modulate D. melanogaster lifespan, and that the amplitude of clock gene expression in peripheral body clocks may be a potential link between temperature rhythms and longevity in male D. melanogaster. Longevity due to Tcyc appeared predominantly independent of clock gene amplitude in female D. melanogaster.

The gill-oxygen limitation theory (GOLT) and its critics

The gill-oxygen limitation theory (GOLT) provides mechanisms for key aspects of the biology (food conversion efficiency, growth and its response to temperature, the timing of maturation, and others) of water-breathing ectotherms (WBEs). The GOLT's basic tenet is that the surface area of the gills or other respiratory surfaces of WBE cannot, as two-dimensional structures, supply them with sufficient oxygen to keep up with the growth of their three-dimensional bodies. Thus, a lower relative oxygen supply induces sexual maturation, and later a slowing and cessation of growth, along with an increase of physiological processes relying on glycolytic enzymes and a declining role of oxidative enzymes. Because the "dimensional tension" underlying this argument is widely misunderstood, emphasis is given to a detailed refutation of objections to the GOLT. This theory still needs to be put on a solid quantitative basis, which will occur after the misconceptions surrounding it are put to rest.

Resumption of donor-origin spermatogenesis in senescent goldfish Carassius auratus (Linnaeus, 1758) following spermatogonial cell therapy

Stem cell research has come into prominence because of its applications in assisted reproductive technology and the treatment of deadly diseases. In teleost fishes, spermatogonial stem cells have been effectively used to produce surrogate gametes and progeny through germ cell transplantation technique. The present study is the first report of an innovative application of stem cell therapy in fish species for revitalising the reproductive competence of senescent individuals. Senescent male goldfish, Carassius auratus, approximately 10 years of age were procured from a fish-breeding farm and were reared locally in the lab for an additional two years. The senescence of the individuals was then evaluated and confirmed using histological analysis, gonadal index assessment, and germ-cell specific vasa gene expression. Analyses revealed absence of spermatogonial cells and other germ cells in the testes of the senescent fish (n = 5). Spermatogonial cells from sexually immature C. auratus male donor were isolated using discontinuous percoll gradients, labelled with the fluorescent dye PKH-26, and transplanted into the gonads of senescent C. auratus males through urogenital papilla. Six months after the transplant, spermatozoa were collected through applying gentle manual pressure on the abdomen and were observed under a microscope. All C. auratus males with the transplant had produced spermatozoa from the transplanted cells. This was confirmed by the retention of PKH-26 in the spermatozoa and diagnostic SSR locus. Gravid C. auratus females were artificially inseminated with the spermatozoa of those senescent males and natural spawning was allowed. As a result viable progeny were produced. These observation suggests that the reproductive competence of senescent male fishes can be revitalised through spermatogonial stem cell therapy to produce functional gametes.

The effect of population density on growth and survival of a Neotropical annual killifish

We used a field experiment to test the effects of population density on the growth rate and survival of Austrolebias bellottii, a Neotropical annual killifish. Effects differed between the sexes: males at high densities achieved a smaller final size and experienced higher mortality while no such effects were observed in females. This sex-specific effect could be an indirect consequence of mate competition.

Prostaglandin signals from adult germ stem cells delay somatic aging of Caenorhabditis elegans

A moderate reduction of body temperature can induce a remarkable lifespan extension. Here we examine the link between cold temperature, germ line fitness and organismal longevity. We show that low temperature reduces age-associated exhaustion of germ stem cells (GSCs) in Caenorhabditis elegans, a process modulated by thermosensory neurons. Notably, robust self-renewal of adult GSCs delays reproductive aging and is required for extended lifespan at cold temperatures. These cells release prostaglandin E2 (PGE2) to induce cbs-1 expression in the intestine, increasing somatic production of hydrogen sulfide (H₂S), a gaseous signaling molecule that prolongs lifespan. Whereas loss of adult GSCs reduces intestinal cbs-1 expression and cold-induced longevity, application of exogenous PGE2 rescues these phenotypes. Importantly, tissue-specific intestinal overexpression of cbs-1 mimics cold-temperature conditions and extends longevity even at warm temperatures. Thus, our results indicate that GSCs communicate with somatic tissues to coordinate extended reproductive capacity with longevity.

The role of the gut microbiome during host ageing

Gut microbial communities participate in key aspects of host biology, including development, nutrient absorption, immunity and disease. During host ageing, intestinal microbes undergo dramatic changes in composition and function and can shift from commensal to pathogenic. However, whether they play a causal role in host ageing and life span has remained an open question for a long time. Recent work in model organisms has revealed for the first time that gut microbes can modulate ageing, opening new questions and opportunities to uncover novel ageing-modulating mechanisms and to design anti-ageing interventions by targeting the gut microbiota.

Insulin-like growth factor 1 receptor regulates hypothermia during calorie restriction

When food resources are scarce, endothermic animals can lower core body temperature (T_b). This phenomenon is believed to be part of an adaptive mechanism that may have evolved to conserve energy until more food becomes available. Here, we found in the mouse that the insulin-like growth factor 1 receptor (IGF-1R) controls this response in the central nervous system. Pharmacological or genetic inhibition of IGF-1R enhanced the reduction of temperature and of energy expenditure during calorie restriction. Full blockade of IGF-1R affected female and male mice similarly. In contrast, genetic IGF-1R dosage was effective only in females, where it also induced transient and estrus-specific hypothermia in animals fed ad libitum. These effects were regulated in the brain, as only central, not peripheral, pharmacological activation of IGF-1R prevented hypothermia during calorie restriction. Targeted IGF-1R knockout selectively in forebrain neurons revealed that IGF signaling also modulates calorie restriction-dependent T_b regulation in regions rostral of the canonical hypothalamic nuclei involved in controlling body temperature. In aggregate, these data identify central IGF-1R as a mediator of the integration of nutrient and temperature homeostasis. They also show that calorie restriction, IGF-1R signaling, and body temperature, three of the main regulators of metabolism, aging, and longevity, are components of the same pathway.

The short-lived African turquoise killifish: an emerging experimental model for ageing

Human ageing is a fundamental biological process that leads to functional decay, increased risk for various diseases and, ultimately, death. Some of the basic biological mechanisms underlying human ageing are shared with other organisms; thus, animal models have been invaluable in providing key mechanistic and molecular insights into the common bases of biological ageing. In this Review, we briefly summarise the major applications of the most commonly used model organisms adopted in ageing research and highlight their relevance in understanding human ageing. We compare the strengths and limitations of different model organisms and discuss in detail an emerging ageing model, the short-lived African turquoise killifish. We review the recent progress made in using the turquoise killifish to study the biology of ageing and discuss potential future applications of this promising animal model.

The effects of graded levels of calorie restriction: III. Impact of short term calorie and protein restriction on mean daily body temperature and torpor use in the C57BL/6 mouse

A commonly observed response in mammals to calorie restriction (CR) is reduced body temperature (T_b). We explored how the T_b of male C57BL/6 mice responded to graded CR (10 to 40%), compared to the response to equivalent levels of protein restriction (PR) over 3 months. Under CR there was a dynamic change in daily T_b over the first 30–35 days, which stabilized thereafter until day 70 after which a further decline was noted. The time to reach stability was dependent on restriction level. Body mass negatively correlated with T_b under ad libitum feeding and positively correlated under CR. The average T_b over the last 20 days was significantly related to the levels of body fat, structural tissue, leptin and insulin-like growth factor-1. Some mice, particularly those under higher levels of CR, showed periods of daily torpor later in the restriction period. None of the changes in T_b under CR were recapitulated by equivalent levels of PR. We conclude that changes in T_b under CR are a response only to the shortfall in calorie intake. The linear relationship between average T_b and the level of restriction supports the idea that T_b changes are an integral aspect of the lifespan effect.

Effect of temperature on replicative aging of the budding yeast Saccharomyces cerevisiae

The use of the budding yeast Saccharomyces cerevisiae in gerontological studies was based on the assumption that the reproduction limit of a single cell (replicative aging) is a consequence of accumulation of a hypothetical universal "senescence factor" within the mother cell. However, some evidence suggests that molecules or structures proposed as the "aging factor", such as rDNA circles, oxidatively damaged proteins (with carbonyl groups) or mitochondria, have little effect on replicative lifespan of yeast cells. Our results also suggest that protein aggregates associated with Hsp104, treated as a marker of yeast aging, do not seem to affect the numeric value of replicative lifespan of yeast. What these results indicate, however, is the need for finding a different way of expressing age and longevity of yeast cells instead of the commonly used number of daughters produced over units of time, as in the case of other organisms. In this paper, we show that the temperature has a stronger influence on the time of life (the total lifespan) than on the reproductive potential of yeast cells.

Late-onset temperature reduction can retard the aging process in aged fish via a combined action of an anti-oxidant system and the insulin/insulin-like growth factor 1 signaling pathway

Two different mechanisms are considered to be related to aging. Cumulative molecular damage caused by reactive oxygen species (ROS), the by-products of oxidative phosphorylation, is one of these mechanisms (ROS concept). Deregulated nutrient sensing by the insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) pathway is the second mechanism (IIS concept). Temperature reduction (TR) is known to modulate aging and prolong life span in a variety of organisms, but the mechanisms remain poorly defined. Here we first demonstrate that late-onset TR from 26 °C to 22 °C extends mean life span and maximum life span by approximately 5.2 and 3 weeks, respectively, in the annual fish Nothobranchius guentheri. We then show that TR is able to decrease the accumulation of the histological aging markers senescence-associated β-galactosidase (SA-β-Gal) in the epithelium and lipofuscin (LF) in the liver and to reduce protein oxidation and lipid peroxidation levels in the muscle. We also show that TR can enhance the activities of catalase, glutathione peroxidase, and superoxide dismutase, and stimulate the synthesis of SirT1 and FOXO3A/FOXO1A, both of which are the downstream regulators of the IIS pathway. Taken together, our findings suggest that late-onset TR, a simple non-intrusion intervention, can retard the aging process in aged fish, resulting in their life span extension, via a synergistic action of an anti-oxidant system and the IIS pathway. This also suggests that combined assessment of the ROS and IIS concepts will contribute to providing a more comprehensive view of the anti-aging process.

Being cool: how body temperature influences ageing and longevity

Temperature is a basic and essential property of any physical system, including living systems. Even modest variations in temperature can have profound effects on organisms, and it has long been thought that as metabolism increases at higher temperatures so should rates of ageing. Here, we review the literature on how temperature affects longevity, ageing and life history traits. From poikilotherms to homeotherms, there is a clear trend for lower temperature being associated with longer lifespans both in wild populations and in laboratory conditions. Many life-extending manipulations in rodents, such as caloric restriction, also decrease core body temperature. Nonetheless, an inverse relationship between temperature and lifespan can be obscured or reversed, especially when the range of body temperatures is small as in homeotherms. An example is observed in humans: women appear to have a slightly higher body temperature and yet live longer than men. The mechanisms involved in the relationship between temperature and longevity also appear to be less direct than once thought with neuroendocrine processes possibly mediating complex physiological responses to temperature changes. Lastly, we discuss species differences in longevity in mammals and how this relates to body temperature and argue that the low temperature of the long-lived naked mole-rat possibly contributes to its exceptional longevity.

Mixing times towards demographic equilibrium in insect populations with temperature variable age structures

In this study, we use entropy related mixing rate modules to measure the effects of temperature on insect population stability and demographic breakdown. The uncertainty in the age of the mother of a randomly chosen newborn, and how it is moved after a finite act of time steps, is modeled using a stochastic transformation of the Leslie matrix. Age classes are represented as a cycle graph and its transitions towards the stable age distribution are brought forth as an exact Markov chain. The dynamics of divergence, from a non equilibrium state towards equilibrium, are evaluated using the Kolmogorov-Sinai entropy. Moreover, Kullback-Leibler distance is applied as information-theoretic measure to estimate exact mixing times of age transitions probabilities towards equilibrium. Using empirically data, we show that on the initial conditions and simulated projection's trough time, that population entropy can effectively be applied to detect demographic variability towards equilibrium under different temperature conditions. Changes in entropy are correlated with the fluctuations of the insect population decay rates (i.e. demographic stability towards equilibrium). Moreover, shorter mixing times are directly linked to lower entropy rates and vice versa. This may be linked to the properties of the insect model system, which in contrast to warm blooded animals has the ability to greatly change its metabolic and demographic rates. Moreover, population entropy and the related distance measures that are applied, provide a means to measure these rates. The current results and model projections provide clear biological evidence why dynamic population entropy may be useful to measure population stability.

Ambient temperature reduction extends lifespan via activating cellular degradation activity in an annual fish (Nothobranchius rachovii)

Ambient temperature reduction (ATR) can extend the lifespan of organisms, but the underlying mechanism is poorly understood. In this study, cellular degradation activity was evaluated in the muscle of an annual fish (Nothobranchius rachovii) reared under high (30 °C), moderate (25 °C), and low (20 °C) ambient temperatures. The results showed the following: (i) the activity of the 20S proteasome and the expression of polyubiquitin aggregates increased with ATR, whereas 20S proteasome expression did not change; (ii) the expression of microtubule-associated protein 1 light chain 3-II (LC3-II) increased with ATR; (iii) the expression of lysosome-associated membrane protein type 2a (Lamp 2a) increased with ATR, whereas the expression of the 70-kD heat shock cognate protein (Hsc 70) decreased with ATR; (iv) lysosome activity increased with ATR, whereas the expression of lysosome-associated membrane protein type 1 (Lamp 1) did not change with ATR; and (v) the expression of molecular target of rapamycin (mTOR) and phosphorylated mTOR (p-mTOR) as well as the p-mTOR/mTOR ratio did not change with ATR. These findings indicate that ATR activates cellular degradation activity, constituting part of the mechanism underlying the longevity-promoting effects of ATR in N. rachovii.

Links between thermoregulation and aging in endotherms and ectotherms

While the link between thermoregulation and aging is generally accepted, much further research, reflection, and debate is required to elucidate the physiological and molecular pathways that generate the observed thermal-induced changes in lifespan. Our aim in this review is to present, discuss, and scrutinize the thermoregulatory mechanisms that are implicated in the aging process in endotherms and ectotherms. Our analysis demonstrates that low body temperature benefits lifespan in both endothermic and ectothermic organisms. Research in endotherms has delved deeper into the physiological and molecular mechanisms linking body temperature and longevity. While research in ectotherms has been steadily increasing during the past decades, further mechanistic work is required in order to fully elucidate the underlying phenomena. What is abundantly clear is that both endotherms and ectotherms have a specific temperature zone at which they function optimally. This zone is defended through both physiological and behavioral means and plays a major role on organismal senescence. That low body temperature may be beneficial for lifespan is contrary to conventional medical theory where reduced body temperature is usually considered as a sign of underlying pathology. Regardless, this phenomenon has been targeted by scientists with the expectation that advancements may compress morbidity, as well as lower disease and mortality risk. The available evidence suggests that lowered body temperature may prolong life span, yet finding the key to temperature regulation remains the problem. While we are still far from a complete understanding of the mechanisms linking body temperature and longevity, we are getting closer.

Life history variation in Barents Sea fish: implications for sensitivity to fishing in a changing environment

Under exploitation and environmental change, it is essential to assess the sensitivity and vulnerability of marine ecosystems to such stress. A species’ response to stress depends on its life history. Sensitivity to harvesting is related to the life history “fast–slow” continuum, where “slow” species (i.e., large, long lived, and late maturing) are expected to be more sensitive to fishing than “fast” ones. We analyze life history traits variation for all common fish species in the Barents Sea and rank fishes along fast–slow gradients obtained by ordination analyses. In addition, we integrate species’ fast–slow ranks with ecosystem survey data for the period 2004–2009, to assess life history variation at the community level in space and time. Arctic fishes were smaller, had shorter life spans, earlier maturation, larger offspring, and lower fecundity than boreal ones. Arctic fishes could thus be considered faster than the boreal species, even when body size was corrected for. Phylogenetically related species possessed similar life histories. Early in the study period, we found a strong spatial gradient, where members of fish assemblages in the southwestern Barents Sea displayed slower life histories than in the northeast. However, in later, warmer years, the gradient weakened caused by a northward movement of boreal species. As a consequence, the northeast experienced increasing proportions of slower fish species. This study is a step toward integrating life history traits in ecosystem-based areal management. On the basis of life history traits, we assess the fish sensitivity to fishing, at the species and community level. We show that climate warming promotes a borealization of fish assemblages in the northeast, associated with slower life histories in that area. The biology of Arctic species is still poorly known, and boreal species that now establish in the Arctic are fishery sensitive, which calls for cautious ecosystem management of these areas.

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.

A cool way to live long

In this issue, Xiao et al. challenge the notion that cold temperatures promote longevity solely through thermodynamic effects. They show that low temperatures activate a cold-sensitive cation channel, TRPA-1, which triggers a complex signaling pathway in both neurons and nonneuronal cells to extend the lifespan of Caenorhabditis elegans.

Role of the hypothalamus in mediating protective effects of dietary restriction during aging

Dietary restriction (DR) can extend lifespan and reduce disease burden across a wide range of animals and yeast but the mechanisms mediating these remarkably protective effects remain to be elucidated despite extensive efforts. Although it has generally been assumed that protective effects of DR are cell-autonomous, there is considerable evidence that many whole-body responses to nutritional state, including DR, are regulated by nutrient-sensing neurons. In this review, we explore the hypothesis that nutrient sensing neurons in the ventromedial hypothalamus hierarchically regulate the protective responses of dietary restriction. We describe multiple peripheral responses that are hierarchically regulated by the hypothalamus and we present evidence for non-cell autonomous signaling of dietary restriction gathered from a diverse range of models including invertebrates, mammalian cell culture, and rodent studies.

Growth of Critically Endangered annual fish Austrolebias wolterstorffi (Cyprinodontiformes: Rivulidae) at different temperatures

Given the importance of knowledge of the biology of endangered species for the planning of conservation and management efforts, the aim of this study was to investigate the influence of temperature on the growth of Austrolebias wolterstorffi (Ahl, 1924). To clarify the thermal influence on the growth of the species, temperatures of 16, 20, 24 , and 28°C were tested in triplicate. The present study showed that a water temperature of 28°C is detrimental to the growth of the species. Among the other tested temperatures, it was found that the optimum temperature for growth decreases as an individual ages and is slightly lower for females. It was demonstrated here that males reach a higher weight and length, and grow faster than females, reaching sexual maturity earlier. To optimize the growth of this species in captivity, the ideal temperature of the water during the initial life period is 24°C, until after puberty when the temperature should decrease to about 21°C.

Effect of temperature on growth of the threatened annual fish Austrolebias nigrofasciatus Costa & Cheffe 2001

This study evaluated the effect of temperature on growth of Austrolebias nigrofasciatus, an endemic and threatened annual killifish species of the Patos-Mirim lagoon system in Southern Brazil. In order to verify the effect of temperature on initial growth of A. nigrofasciatus, eggs stored in the laboratory were hatched and juveniles reared for eight weeks at 16 and 22 ºC. The standard length of newly hatched fishes was 4.67 ± 0.25 mm and after eight weeks they reached 23.68 ± 3.73 and 22.68 ± 5.36 mm, respectively at 16 and 22 ºC. However, initial growth of fish reared at 22 ºC was faster and they reached sexual dimorphism at an earlier age compared to those reared at 16 ºC. Final length of females reared at 22 ºC was 23.00 ± 2.83 mm, they were significantly larger than those reared at 16 ºC (17.91 ± 2.47 mm). Males were significantly larger than the females at 16 ºC, but there was no difference for growth between sexes of fish reared at 22 ºC. The sex ratios were 1:0.6 and 1:1.1 (M:F) at 16 ºC and 22 ºC, respectively, suggesting temperature determination of phenotypic sex. Considering the results, it appears that juveniles to be developed in captivity should be kept at 22 ºC during the first six weeks of life, thus ensuring a higher growth rate until puberty.

Sex- and age-specific differences in core body temperature of C57Bl/6 mice

Gender-specific differences in longevity are reported across species and are mediated by mechanisms not entirely understood. In C57Bl/6 mice, commonly used in aging research, males typically outlive females. Since in these animals modest but prolonged reduction of core body (Tc) increased life span, we hypothesized that differential Tc may contribute to sex-specific longevity. Here, we compared the circadian profiles of Tc and locomotor activity (LMA) of male and female C57Bl/6 mice. Since Tc and LMA normally change with age, measurements were carried out in young (3 months) as well as in old (24 months) mice. In young females, Tc was influenced by estrous but was overall higher than in males. This difference was larger in old animals after age eliminated the variations associated with estrous. Although temperature homeostasis is regulated centrally by the sexually dimorphic hypothalamic preoptic area, these differences were uniquely dependent on the gonads. In fact, bilateral gonadectomy abolished the effects of estrous and increased resting Tc in males eliminating all sex-specific differences in Tc and LMA. These effects were only partially mimicked by hormonal replacement as Tc was affected by progesterone and to a lesser extent by estrogen but not by testosterone. Thus, gonadal-dependent modulation of Tc may be one of the physiological parameters contributing to gender-specific differences in longevity.

Life cycle truncation in a trematode: does higher temperature indicate shorter host longevity?

The typical three-host life cycle of most trematodes creates transmission challenges for which a variety of adaptations have evolved to increase the probability of transmission. Some species can abbreviate their life cycle via progenesis, the precocious maturation of the parasite in the second intermediate host resulting in the production of eggs through self-fertilisation without requiring a definitive host. Adoption of the progenetic life cycle may be a conditional strategy in response to different environmental cues related to low probability of transmission to the definitive host. Using high water temperature and/or limited diet as experimental stressors, we tested the effect of body condition and life span of the fish second intermediate host on facultative truncation of the typical three-host life cycle by progenesis in Stegodexamene anguillae. The results suggest that environmental cues, such as temperature and encystment site, may signal transmission opportunities to the parasite so that it may adjust its developmental strategy accordingly. Indeed, a greater proportion of worms became progenetic at higher temperatures, and progenesis was more common among worms encysted in the gonads or body cavity of their fish hosts than among those in other host tissues. These findings highlight the often unrecognised plasticity in parasite developmental and transmission strategies.

Caloric restriction and longevity: effects of reduced body temperature

Caloric restriction (CR) causes a reduction in body temperature (T(b)) which is suggested to contribute to changes that increase lifespan. Moreover, low T(b) has been shown to improve health and longevity independent of CR. In this review we examine the connections between CR, T(b) and mechanisms that influence longevity and ageing. Recent findings regarding the overlapping mechanisms of CR and T(b) that benefit longevity are discussed, including changes in body composition, hormone regulation, and gene expression, as well as reductions in low-level inflammation and reactive oxygen species-induced molecular damage. This information is summarized in a model describing how CR and low T(b), both synergistically and independently, increase lifespan. Moreover, the nascent notion that the rate of ageing may be pre-programmed in response to environmental influences at critical periods of early development is also considered. Based on current evidence, it is concluded that low T(b) plays an integral role in mediating the effects of CR on health and longevity, and that low T(b) may exert independent biological changes that increase lifespan. Our understanding of the overlap between CR- and T(b)-mediated longevity remains incomplete and should be explored in future research.

Caloric restriction: from soup to nuts

Caloric restriction (CR), reduced protein, methionine, or tryptophan diets; and reduced insulin and/or IGFI intracellular signaling can extend mean and/or maximum lifespan and delay deleterious age-related physiological changes in animals. Mice and flies can shift readily between the control and CR physiological states, even at older ages. Many health benefits are induced by even brief periods of CR in flies, rodents, monkeys, and humans. In humans and nonhuman primates, CR produces most of the physiologic, hematologic, hormonal, and biochemical changes it produces in other animals. In primates, CR provides protection from type 2 diabetes, cardiovascular and cerebral vascular diseases, immunological decline, malignancy, hepatotoxicity, liver fibrosis and failure, sarcopenia, inflammation, and DNA damage. It also enhances muscle mitochondrial biogenesis, affords neuroprotection; and extends mean and maximum lifespan. CR rapidly induces antineoplastic effects in mice. Most claims of lifespan extension in rodents by drugs or nutrients are confounded by CR effects. Transcription factors and co-activators involved in the regulation of mitochondrial biogenesis and energy metabolism, including SirT1, PGC-1alpha, AMPK and TOR may be involved in the lifespan effects of CR. Paradoxically, low body weight in middle aged and elderly humans is associated with increased mortality. Thus, enhancement of human longevity may require pharmaceutical interventions.

Hypothalamic and dietary control of temperature-mediated longevity

Temperature is an important modulator of longevity and aging in both poikilotherms and homeotherm animals. In homeotherms, temperature homeostasis is regulated primarily in the preoptic area (POA) of the hypothalamus. This region receives and integrates peripheral, central and environmental signals and maintains a nearly constant core body temperature (T(core)) by regulating the autonomic and hormonal control of heat production and heat dissipation. Temperature sensitive neurons found in the POA are considered key elements of the neuronal circuitry modulating these effects. Nutrient homeostasis is also a hypothalamically regulated modulator of aging as well as one of the signals that can influence T(core) in homeotherms. Investigating the mechanisms of the regulation of nutrient and temperature homeostasis in the hypothalamus is important to understanding how these two elements of energy homeostasis influence longevity and aging as well as how aging can affect hypothalamic homeostatic mechanisms.

Ambient temperature influences aging in an annual fish (Nothobranchius rachovii)

Extending lifespan by lowering ambient temperature in the habitat has been shown in a variety of organisms. Its mechanism, however, remains elusive. In this study, we examined the survivorship and the aging process of the annual fish (Nothobranchius rachovii) reared under high (30 degrees C), moderate (25 degrees C) and low (20 degrees C) ambient temperatures. The results showed that low ambient temperatures prolong survivorship, whereas high ambient temperatures shorten survivorship. At low ambient temperature, expression of senescence-associated beta-galactosidase, lipofuscin, reactive oxygen species, lipid peroxidation, protein oxidation, mitochondrial density and ADP/ATP ratio were reduced compared with those reared at high and moderate temperatures, whereas catalase activity, Mn-superoxide dismutase activities, mitochondrial membrane potential and the levels of ATP, ADP, Sirt1 and Forkhead box O expression were elevated. The expression levels of Hsp70 and CIRP showed no significant difference under any of the ambient temperatures tested. We concluded that cellular metabolism, energy utilization and gene expression are altered at lower ambient temperature, which is associated with the extension of lifespan of the annual fish.

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.

Temperature affects longevity and age-related locomotor and cognitive decay in the short-lived fish Nothobranchius furzeri

Temperature variations are known to modulate aging and life-history traits in poikilotherms as different as worms, flies and fish. In invertebrates, temperature affects lifespan by modulating the slope of age-dependent acceleration in death rate, which is thought to reflect the rate of age-related damage accumulation. Here, we studied the effects of temperature on aging kinetics, aging-related behavioural deficits, and age-associated histological markers of senescence in the short-lived fish Nothobranchius furzeri. This species shows a maximum captive lifespan of only 3 months, which is tied with acceleration in growth and expression of aging biomarkers. These biological peculiarities make it a very convenient animal model for testing the effects of experimental manipulations on life-history traits in vertebrates. Here, we show that (i) lowering temperature from 25 degrees C to 22 degrees C increases both median and maximum lifespan; (ii) life extension is due to reduction in the slope of the age-dependent acceleration in death rate; (iii) lowering temperature from 25 degrees C to 22 degrees C retards the onset of age-related locomotor and learning deficits; and (iv) lowering temperature from 25 degrees C to 22 degrees C reduces the accumulation of the age-related marker lipofuscin. We conclude that lowering water temperature is a simple experimental manipulation which retards the rate of age-related damage accumulation in this short-lived species.

Lower body temperature as a potential mechanism of life extension in homeotherms

Although best known for his studies on the anti-aging effects of dietary restriction, Dr Roy Walford began his career by studying the anti-aging effects of lowering body temperature. As a tribute to his long and productive career, we review these pioneering studies and the singular influence these have had on our own thinking about the potential for lower body temperature to extend the life span of homeotherms. We show our results from a study of six classical inbred strains of mice that depict marked strain variation in the body temperature response to dietary restriction. In addition, we show a genome scan from a recombinant inbred strain panel in which we identified a significant quantitative trait locus on murine chromosome 9 and a provisional locus on chromosome 17 that specify variation in the response of body temperature to dietary restriction. These discoveries suggest that we can now extend the studies of Dr Walford to critically test whether lower body temperature can prolong the life span of mammals.

Comparative aspects of zebrafish (Danio rerio) as a model for aging research

The zebrafish has emerged over the past decade as a major model system for the study of development due to its invertebrate-like advantages coupled with its vertebrate biology. These features also make it a potentially valuable organism for gerontological research. The main advantages of zebrafish include its economical husbandry, small yet accessible size, high reproductive capacity, genetic tractability, and a large and growing biological database. Although zebrafish life span is longer than rodents, it shares the feasibility of large-scale mutational analysis with the extremely short-lived invertebrate models. This review compares zebrafish with the more widely used model organisms used for aging research, including yeast, worms, flies, mice, and humans.

A call to fins! Zebrafish as a gerontological model

Among the wide variety of model organisms commonly used for studies on aging, such as worms, flies and rodents, a wide research gap exists between the invertebrate and vertebrate model systems. In developmental biology, a similar gap has been filled by the zebrafish (Danio rerio). We propose that the zebrafish is uniquely suited to serve as a bridge model for gerontology. With high fecundity and economical husbandry requirements, large populations of zebrafish may be generated quickly and cheaply, facilitating large-scale approaches including demographic studies and mutagenesis screens. A variety of mutants identified in such screens have led to modelling of human disease, including cardiac disorders and cancer. While zebrafish longevity is at least 50% longer than in commonly used mouse strains, as an ectothermic fish species, its life span may be readily modulated by caloric intake, ambient temperature and reproductive activity. These features, coupled with a growing abundance of biological resources, including an ongoing genome sequencing project, make the zebrafish a compelling model organism for studies on aging.

Life spans and senescent phenotypes in two strains of Zebrafish (Danio rerio)

Zebrafish have become a widely used model organism in developmental biology research. In order to initiate an experimental foundation for aging studies, we have determined some basic gerontological parameters for populations of outbred zebrafish, and the golden sparse strain. Outbred zebrafish manifested a mean life span of about 42 months, with the longest living individual surviving for 66 months. The golden sparse populations had a mean life span of 36 months and a maximum longevity of 58 months. Skeletal length at death increased with age, suggestive of indeterminate growth. A common age-related phenotype was spinal curvature. Radiographic analysis excluded bony changes as the cause of the spinal curvature, suggesting muscle abnormalities as a primary mechanism. These data and a growing abundance of related biological resources suggest that the zebrafish may be a compelling model organism for studies on aging.

Growth of the annual fish Cynopoecilus melanotaenia (Regan, 1912) based in a temporary water body population in Rio Grande do Sul State, Brazil (Cyprinodontiformes, Rivulidae)

The growth of the annual fish Cynopoecilus melanotaenia was studied in its natural environment, in order to obtain information about its biology. A total of 797 specimens of C. melanotaenia were collected on a monthly basis between April 1994 and March 1995 in a temporary water body, located in Rio Grande do Sul State, Brazil. The growth curve in total length suggests, to both sexes, a fast initial growth. Males present a smaller growth rate than females, but they attain a higher average maximum length than the females.

Age-dependent proteins in eyes of annual killifishes Pterolebias longipinnis detected by 2-dimensional electrophoresis

1. Eye proteins of Pterolebias longipinnis have been analyzed by 2-dimensional isoelectric focusing SDS-polyacrylamide gel electrophoresis during aging from adolescence until normal death. 2. The protein pattern on the gels changed gradually with progressing age. 3. In senescent eyes, three protein spots appeared for a time and 36 disappeared from the pattern. 4. The isoelectric points of the proteins in the presence of urea and the molecular weights in an unreducing buffer are presented.

Age-related differences in the response of hepatic oxygen consumption to thermal stress in the male garden lizard

The main aim of the present study is to compare the thermal adaptation capacity of young, middle-aged and old lizards with respect to hepatic oxygen consumption. Cold exposure (1 h at 0-4 degrees C) caused a decline in endogenous oxygen consumption in young but did not evoke significant changes in middle-aged and old lizards. On the other hand, with 5 mM succinate the rate of respiration increased marginally only in cold-exposed old lizards. This suggests that the metabolic response to cold is age-dependent in these lizards. Exposure of homogenates at 40 +/- 1 degree C for 15 min led to a rise in the hepatic oxygen consumption of young but not in that of either middle-aged or old lizards. There were no changes in the rate of oxygen consumption upon exposure for a similar period at 45 +/- 1 degree C of liver homogenates from lizards of three different age groups. However, exposure at 51 +/- 1 degree C resulted in a higher degree of decline in the rate of hepatic oxygen consumption in middle-aged and old than in young lizards. Thus, the young lizards appear to be better-adapted to hyperthermic stress than the middle-aged and old.

Aging changes in lymphopoietic and myelopoietic organs of the annual cyprinodont fish, Nothobranchius guentheri

The thymus of aging annual, cyprinodont fish, Nothobranchius guentheri and Cynolebias adloffi begins to undergo senescent changes at approximately four months. At this time, the histopathology reveals increased amounts of connective tissue, epithelial cysts and myoid cells, but decreased numbers of thymocytes. At 12 months, of the 50 fish observed at 10 stages from day 15 and 1, 2, 4, 6, 8, 9, 10, 11, 12 months the maximum time of senescence, there was an increased incidence of tumors in the oral cavity, connective tissue, kidney and liver in all 5 fish. At least in the kidney, the malignant transformation was classified as nodular-type histiocytic lymphoma. It is of interest that development of these tumors occurs during peak senescent changes in the thymus, supporting the view that as fish age, accompanied by atrophy of the thymus, the immune system is less vigorous and there is an increase in the incidence of cancer.

The effect of age on body energy content of the annual cyprinodont fish, Nothobranchius guentheri

Bomb calorimetry measurements were made on dried whole body samples of N. guentheri in an attempt to detect the effect of age induced protein crosslinking. The results show a clear decrease in body energy with increasing age. However, this decrease was larger than expected and was probably due to a slight decrease in body fat component with increasing age rather than crosslinking alone.