Considerations on temperature, longevity and aging

Cold and longevity: Can cold exposure counteract aging?

Aging is a multifaceted biological process characterized by a progressive decline in physiological functions and heightened vulnerability to diseases, shaped by genetic, environmental, and lifestyle factors. Among these, cold exposure has garnered interest for its potential anti-aging benefits. This review examines the impact of cold exposure on aging, focusing on key physiological processes such as inflammation, oxidative stress, metabolic regulation, and cardiovascular health. Cold exposure has been shown to reduce chronic inflammation, enhance antioxidant defenses, and improve metabolic health by activating brown adipose tissue. Furthermore, findings from hibernating mammals and model organisms suggest a connection between lower environmental temperatures and increased longevity. However, the potential long-term health risks of extended cold exposure, particularly in older adults, remain a significant concern. Epidemiological studies reveal increased rates of mortality and morbidity in populations living in cold climates, emphasizing the complexity of the relationship between cold exposure and aging. This review underscores the need for further research to elucidate the long-term effects of cold exposure on aging and to establish guidelines for leveraging its benefits while mitigating cold-induced risks.

Resting Body Temperature and Long-Term Survival in Older Adults at a Mental Health Center: Cross-Sectional and Longitudinal Data

Background/Objectives: Elevated body temperature is a well-established biomarker of infection, increased disease risk, and adverse health outcomes. However, the relationship between resting body temperature and long-term survival in older individuals is complex. Emerging evidence suggests that higher basal body temperature is associated with reduced survival and accelerated aging in non-obese older adults. This study aimed to compare body temperatures across different age groups in hospitalized older adults. Methods: Data were retrospectively collected from 367 physically healthy residents of a mental health center. Longitudinal data from 142 individuals (68 men and 74 women), aged 45 to 70 years and monitored continuously over 25 years, were compared with cross-sectional data from 225 individuals (113 men and 112 women) who underwent periodic clinical examinations with temperature measurements. The cross-sectional sample was stratified into four survival categories. Resting oral temperatures were measured under clinical conditions to ensure protocol consistency. Age-related changes in both sexes were evaluated using standard regression analysis, Student's t-tests, ANOVA, and Generalized Linear Models. Results: Longitudinal analysis revealed an increase in body temperature with age among women, while cross-sectional analysis showed that long-lived residents generally had lower body temperatures compared to their shorter-lived counterparts. Conclusions: These findings support the hypothesis that lower lifetime steady-state body temperature is associated with greater longevity in physically healthy older adults. However, further research is needed to determine whether the lower body temperature observed in long-lived individuals is linked to specific health advantages, such as enhanced immune function, absence of detrimental factors or diseases, or a reduced metabolic rate potentially influenced by caloric restriction.

The ion channel TRPM8 is a direct target of the immunosuppressant rapamycin in primary sensory neurons

BACKGROUND AND PURPOSE

The mechanistic target of rapamycin (mTOR) signalling pathway is a key regulator of cell growth and metabolism. Its deregulation is implicated in several diseases. The macrolide rapamycin, a specific inhibitor of mTOR, has immunosuppressive, anti-inflammatory and antiproliferative properties. Recently, we identified tacrolimus, another macrolide immunosuppressant, as a novel activator of TRPM8 ion channels, involved in cold temperature sensing, thermoregulation, tearing and cold pain. We hypothesized that rapamycin may also have agonist activity on TRPM8 channels.

EXPERIMENTAL APPROACH

Using calcium imaging and electrophysiology in transfected HEK293 cells and wildtype or Trpm8 KO mouse DRG neurons, we characterized rapamycin's effects on TRPM8 channels. We also examined the effects of rapamycin on tearing in mice.

KEY RESULTS

Micromolar concentrations of rapamycin activated rat and mouse TRPM8 channels directly and potentiated cold-evoked responses, effects also observed in human TRPM8 channels. In cultured mouse DRG neurons, rapamycin increased intracellular calcium levels almost exclusively in cold-sensitive neurons. Responses were markedly decreased in Trpm8 KO mice or by TRPM8 channel antagonists. Cutaneous cold thermoreceptor endings were also activated by rapamycin. Topical application of rapamycin to the eye surface evokes tearing in mice by a TRPM8-dependent mechanism.

CONCLUSION AND IMPLICATIONS

These results identify TRPM8 cationic channels in sensory neurons as novel molecular targets of the immunosuppressant rapamycin. These findings may help explain some of its therapeutic effects after topical application to the skin and the eye surface. Moreover, rapamycin could be used as an experimental tool in the clinic to explore cold thermoreceptors.

Exposure to ambient temperature and heat index in relation to DNA methylation age: A population-based study in Taiwan

BACKGROUND

Climate change caused an increase in ambient temperature in the past decades. Exposure to high ambient temperature could result in biological aging, but relevant studies in a warm environment were lacking. We aimed to study the exposure effects of ambient temperature and heat index (HI) in relation to age acceleration in Taiwan, a subtropical island in Asia.

METHODS

The study included 2,084 participants from Taiwan Biobank. Daily temperature and relative humidity data were collected from weather monitoring stations. Individual residential exposure was estimated by ordinary kriging. Moving averages of ambient temperature and HI from 1 to 180 days prior to enrollment were calculated to estimate the exposure effects in multiple time periods. Age acceleration was defined as the difference between DNA methylation age and chronological age. DNA methylation age was calculated by the Horvath's, Hannum's, Weidner's, ELOVL2, FHL2, phenotypic (Pheno), Skin & blood, and GrimAge2 (Grim2) DNA methylation age algorithms. Multivariable linear regression models, generalized additive models (GAMs), and distributed lag non-linear models (DLNMs) were conducted to estimate the effects of ambient temperature and HI exposures in relation to age acceleration.

RESULTS

Exposure to high ambient temperature and HI were associated with increased age acceleration, and the associations were stronger in prolonged exposure. The heat stress days with maximum HI in caution (80-90°F), extreme caution (90-103°F), danger (103-124°F), and extreme danger (>124°F) were also associated with increased age acceleration, especially in the extreme danger days. Each extreme danger day was associated with 571.38 (95 % CI: 42.63-1100.13), 528.02 (95 % CI: 36.16-1019.87), 43.9 (95 % CI: 0.28-87.52), 16.82 (95 % CI: 2.36-31.28) and 15.52 (95 % CI: 2.17-28.88) days increase in the Horvath's, Hannum's, Weidner's, Pheno, and Skin & blood age acceleration, respectively.

CONCLUSION

High ambient temperature and HI may accelerate biological aging.

Are size and mitochondrial power of cells inter-determined?

Mitochondria are the central hub of ATP production in most eukaryotic cells. Cellular power (energy per unit time), which is primarily generated in these organelles, is crucial to our understanding of cell function in health and disease. We investigated the relation between a mitochondrion's power (metabolic rate) and host cell size by combining metabolic theory with the analysis of two recent databases, one covering 109 protists and the other 63 species including protists, metazoans, microalgae, and vascular plants. We uncovered an interesting statistical regularity: in well-fed protists, relatively elevated values of mitochondrion power cluster around the smallest cell sizes and the medium-large cell sizes. In contrast, in starved protists and metazoans, the relation between mitochondrion power and cell size is inconclusive, and in microalgae and plants, mitochondrion power seems to increase from smaller cells to larger ones (where this investigation includes plant cells of volume up to ca. 2.18 × 105 μm3). Using these results, estimates are provided of the number of active ATP synthase molecules and basal uncouplers.

The forgotten art of cold therapeutic properties in cancer: A comprehensive historical guide

Cold therapy has been used for centuries, from Julius Caesar to Mohandas Gandhi, as a potent therapeutic approach. However, it has been largely forgotten in modern medicine. This review explores the history of cold therapy and its potential application as a therapeutic strategy against various diseases, including cancer. We examine the different techniques of cold exposure and the use of other therapeutical approaches, such as cryoablation, cryotherapy, cryoimmunotherapy, cryothalectomy, and delivery of cryogen agents. While clinical trials using cold therapy for cancer treatment are still limited, recent research shows promising results in experimental animal cancer models. This area of research is becoming increasingly significant and warrants further investigation.

Behavioural changes in slime moulds over time

Changes in behaviour over the lifetime of single-cell organisms have primarily been investigated in response to environmental stressors. However, growing evidence suggests that unicellular organisms undergo behavioural changes throughout their lifetime independently of the external environment. Here we studied how behavioural performances across different tasks vary with age in the acellular slime mould Physarum polycephalum. We tested slime moulds aged from 1 week to 100 weeks. First, we showed that migration speed decreases with age in favourable and adverse environments. Second, we showed that decision making and learning abilities do not deteriorate with age. Third, we revealed that old slime moulds can recover temporarily their behavioural performances if they go throughout a dormant stage or if they fuse with a young congener. Last, we observed the response of slime mould facing a choice between cues released by clone mates of different age. We found that both old and young slime moulds are attracted preferentially toward cues left by young slime moulds. Although many studies have studied behaviour in unicellular organisms, few have taken the step of looking for changes in behaviour over the lifetime of individuals. This study extends our knowledge of the behavioural plasticity of single-celled organisms and establishes slime moulds as a promising model to investigate the effect of ageing on behaviour at the cellular level. This article is part of a discussion meeting issue 'Collective behaviour through time'.

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.

Study on the Correlation between Life Expectancy and the Ecological Environment around the Cities along the Belt and Road

The impact of building the Belt and Road on the ecological environment and the health of the related cities along this belt deserves more attention. Currently, there are few relevant pieces of research in this area, and the problem of a time lag between the ecological environment and health (e.g., life expectancy, LE) has not been explored. This paper investigates the aforementioned problem based on five ecological indicators, i.e., normalized difference vegetation index, leaf area index, gross primary production (GPP), land surface temperature (LST), and wet, which were obtained from MODIS satellite remote-sensing products in 2010, 2015, and 2020. The research steps are as follows: firstly, a comprehensive ecological index (CEI) of the areas along the Belt and Road was calculated based on the principle of component analysis; secondly, the changes in the trends of the five ecological indicators and the CEI in the research area in the past 11 years were calculated by using the trend degree analysis method; then, the distributions of the cold and hot spots of each index in the research area were calculated via cold and hot spot analysis; finally, the time lag relationship between LE and the ecological environment was explored by using the proposed spatiotemporal lag spatial crosscorrelation analysis. The experimental results show that ① there is a positive correlation between LE and ecological environment quality in the study area; ② the ecological environment has a lagging impact on LE, and the impact of ecological indicators in 2010 on LE in 2020 is greater than that in 2015; ③ among the ecological indicators, GPP has the highest impact on LE, while LST and Wet have a negative correlation with LE.

One-day thermal regime extends the lifespan in Caenorhabditis elegans

Environmental factors, including temperature, can modulate an animal's lifespan. However, their underlying mechanisms remain largely undefined. We observed a profound effect of temperature on the aging of Caenorhabditis elegans (C. elegans) by performing proteomic analysis at different time points (young adult, middle age, and old age) and temperature conditions (20 °C and 25 °C). Importantly, although at the higher temperature, animals had short life spans, the shift from 20 °C to 25 °C for one day during early adulthood was beneficial for protein homeostasis since; it decreased protein synthesis and increased degradation. Consistent with our findings, animals who lived longer in the 25 °C shift were also more resistant to high temperatures along with oxidative and UV stresses. Furthermore, the lifespan extension by the 25 °C shift was mediated by three important transcription factors, namely FOXO/DAF-16, HSF-1, and HIF-1. We revealed an unexpected and complicated mechanism underlying the effects of temperature on aging, which could potentially aid in developing strategies to treat age-related diseases. Our data are available in ProteomeXchange with the identifier PXD024916.

Genetic Disruption of KLF1 K74 SUMOylation in Hematopoietic System Promotes Healthy Longevity in Mice

The quest for rejuvenation and prolonged lifespan through transfusion of young blood has been studied for decades with the hope of unlocking the mystery of the key substance(s) that exists in the circulating blood of juvenile organisms. However, a pivotal mediator has yet been identified. Here, atypical findings are presented that are observed in a knockin mouse model carrying a lysine to arginine substitution at residue 74 of Krüppel-like factor 1 (KLF1/EKLF), the SUMOylation-deficient Klf1^K74R/K74R mouse, that displayed significant improvement in geriatric disorders and lifespan extension. Klf1^K74R/K74R mice exhibit a marked delay in age-related physical performance decline and disease progression as evidenced by physiological and pathological examinations. Furthermore, the KLF1(K74R) knockin affects a subset of lymphoid lineage cells; the abundance of tumor infiltrating effector CD8⁺ T cells and NKT cells is increased resulting in antitumor immune enhancement in response to tumor cell administration. Significantly, infusion of hematopoietic stem cells (HSCs) from Klf1^K74R/K74R mice extends the lifespan of the wild-type mice. The Klf1^K74R/K74R mice appear to be an ideal animal model system for further understanding of the molecular/cellular basis of aging and development of new strategies for antiaging and prevention/treatment of age-related diseases thus extending the healthspan as well as lifespan.

Molecular mechanisms of exceptional lifespan increase of Drosophila melanogaster with different genotypes after combinations of pro-longevity interventions

Aging is one of the global challenges of our time. The search for new anti-aging interventions is also an issue of great actuality. We report on the success of Drosophila melanogaster lifespan extension under the combined influence of dietary restriction, co-administration of berberine, fucoxanthin, and rapamycin, photodeprivation, and low-temperature conditions up to 185 days in w¹¹¹⁸ strain and up to 213 days in long-lived E(z)/w mutants. The trade-off was found between longevity and locomotion. The transcriptome analysis showed an impact of epigenetic alterations, lipid metabolism, cellular respiration, nutrient sensing, immune response, and autophagy in the registered effect.

The lifespan of fruit flies can be extended up to 213 days under specialized conditions.

Spatial heterogeneity of human lifespan in relation to living environment and socio-economic polarization: a case study in the Beijing-Tianjin-Hebei region, China

The spatial heterogeneity and influence factors of public lifespan have been reported worldwide at the national level or typical longevous areas. However, few sub-national studies considering the living environment and socio-economic level together have been explored in the imbalanced developed region with a huge population base and deteriorated air quality. In this paper, spatial heterogeneity of lifespan integrating environment and socio-economic influence factors was investigated in the Beijing-Tianjin-Hebei (BTH) region of China using geographically weighted regression (GWR). Five indicators were constructed to determine the lifespan based on the three national censuses (1990-2010) in the BTH region. The results showed that the areas with higher CH (centenarians per 100,000 inhabitants) and centenarity index (CI) exhibited changing distribution in the BTH region, whereas those with lower CH and CI and extreme value of the ultra-octogenarian index (UOI) and LI (> 90/ > 65) maintained a relatively stable feature through time. But as lifespan indicators increase overall, the differences between the counties/districts widen. Furthermore, remarkable spatial heterogeneity was detected for the associations between the significant environmental and socio-economic variables and lifespan indicators. Although the natural geographic condition (altitude) still exhibited a negative influence on the longevity of the population, the socio-economic factors (GDP_pc and income level) showed a more dominant influence on the extension of the elderly and longevity population. Correspondingly, the widened unbalance of population lifespan (UOI, LI, CH) was considered closely related to the socio-economic polarization, and the adverse effects of air pollution on life expectancy at birth (LEB) have also emerged. To further improve the overall lifespan level and narrow the lifespan gap in the BTH region, future work on cleaner air and more balanced development is still needed.

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.

Distinct and additive effects of calorie restriction and rapamycin in aging skeletal muscle

Preserving skeletal muscle function is essential to maintain life quality at high age. Calorie restriction (CR) potently extends health and lifespan, but is largely unachievable in humans, making “CR mimetics” of great interest. CR targets nutrient-sensing pathways centering on mTORC1. The mTORC1 inhibitor, rapamycin, is considered a potential CR mimetic and is proven to counteract age-related muscle loss. Therefore, we tested whether rapamycin acts via similar mechanisms as CR to slow muscle aging. Here we show that long-term CR and rapamycin unexpectedly display distinct gene expression profiles in geriatric mouse skeletal muscle, despite both benefiting aging muscles. Furthermore, CR improves muscle integrity in mice with nutrient-insensitive, sustained muscle mTORC1 activity and rapamycin provides additive benefits to CR in naturally aging mouse muscles. We conclude that rapamycin and CR exert distinct, compounding effects in aging skeletal muscle, thus opening the possibility of parallel interventions to counteract muscle aging.

The anti-aging intervention calorie restriction (CR) is thought to act via the nutrient-sensing multiprotein complex mTORC1. Here the authors show that the mTORC1-inhibitor rapamycin and CR use largely distinct mechanisms to slow mouse muscle aging.

Hibernation slows epigenetic ageing in yellow-bellied marmots

Species that hibernate generally live longer than would be expected based solely on their body size. Hibernation is characterized by long periods of metabolic suppression (torpor) interspersed by short periods of increased metabolism (arousal). The torpor–arousal cycles occur multiple times during hibernation, and it has been suggested that processes controlling the transition between torpor and arousal states cause ageing suppression. Metabolic rate is also a known correlate of longevity; we thus proposed the ‘hibernation–ageing hypothesis’ whereby ageing is suspended during hibernation. We tested this hypothesis in a well-studied population of yellow-bellied marmots (Marmota flaviventer), which spend 7–8 months per year hibernating. We used two approaches to estimate epigenetic age: the epigenetic clock and the epigenetic pacemaker. Variation in epigenetic age of 149 samples collected throughout the life of 73 females was modelled using generalized additive mixed models (GAMM), where season (cyclic cubic spline) and chronological age (cubic spline) were fixed effects. As expected, the GAMM using epigenetic ages calculated from the epigenetic pacemaker was better able to detect nonlinear patterns in epigenetic ageing over time. We observed a logarithmic curve of epigenetic age with time, where the epigenetic age increased at a higher rate until females reached sexual maturity (two years old). With respect to circannual patterns, the epigenetic age increased during the active season and essentially stalled during the hibernation period. Taken together, our results are consistent with the hibernation–ageing hypothesis and may explain the enhanced longevity in hibernators.

Species that hibernate generally have longer lifespans than expected based on their body size. The authors show epigenetic ageing patterns from a natural population of hibernating yellow-bellied marmots consistent with the hypothesis that ageing is suspended during hibernation.

Body temperature is a more important modulator of lifespan than metabolic rate in two small mammals

The relationships between metabolic rate, body temperature (T_b), body composition and ageing are complex, and not fully resolved. In particular, T_b and metabolic rate often change in parallel, making disentangling their effects difficult. Here we show that in both sexes of mice and hamsters exposure to a temperature of 32.5 °C leads to a reduced lifespan, coincident with lowered metabolic rate and elevated T_b with no change in body composition. We exploit the unique situation that when small mammals are exposed to hot ambient temperatures their T_b goes up, at the same time that their metabolic rate goes down, allowing us to experimentally separate the impacts of T_b and metabolic rate on lifespan. The impact of ambient temperature on lifespan can be reversed by exposing the animals to elevated heat loss by forced convection, which reverses the effect on T_b but does not affect metabolic rate, demonstrating the causal effect of T_b on lifespan under laboratory conditions for these models. The impact of manipulations such as calorie restriction that increase lifespan may be mediated via effects on T_b, and measuring T_b may be a useful screening tool for putative therapeutics to extend the human lifespan.

Sex-specific aging in animals: Perspective and future directions

Sex differences in aging occur in many animal species, and they include sex differences in lifespan, in the onset and progression of age-associated decline, and in physiological and molecular markers of aging. Sex differences in aging vary greatly across the animal kingdom. For example, there are species with longer-lived females, species where males live longer, and species lacking sex differences in lifespan. The underlying causes of sex differences in aging remain mostly unknown. Currently, we do not understand the molecular drivers of sex differences in aging, or whether they are related to the accepted hallmarks or pillars of aging or linked to other well-characterized processes. In particular, understanding the role of sex-determination mechanisms and sex differences in aging is relatively understudied. Here, we take a comparative, interdisciplinary approach to explore various hypotheses about how sex differences in aging arise. We discuss genomic, morphological, and environmental differences between the sexes and how these relate to sex differences in aging. Finally, we present some suggestions for future research in this area and provide recommendations for promising experimental designs.

Association between body temperature and leukocyte telomere length in Korean middle-aged and older adults

OBJECTIVES

Data on associations between body temperature (BT) and leukocyte telomere length (LTL), which has been widely used as a biomarker of cellular senescence in recent epidemiological studies, are limited. Therefore, this study aimed to explore the associations between a normal BT range (35.0-37.5°C) and LTL via 6-year longitudinal observations of 2,004 male and female adults aged 50 or older.

METHODS

BT was obtained by measuring the tympanic temperature, and relative LTL was determined by real-time polymerase chain reaction. Robust regression analysis was used to evaluate the association between the baseline and follow-up LTL values and their differences.

RESULTS

A significant inverse association was found between BT and LTL at baseline. The regression coefficient estimate was -0.03 (95% confidence interval, -0.07 to -0.001; p<0.05). This association was stronger in participants with a body mass index >25 kg/m² and males (p<0.01). However, there were no associations between BT and LTL at follow-up or BT and 6-year longitudinal differences in LTL.

CONCLUSIONS

These findings suggest that having a high BT between 35°C and 37.5°C (95°F and 99°F) may be detrimental for obese individuals in terms of biological aging.

Sexual dimorphic impact of adult-onset somatopause on life span and age-induced osteoarthritis

Osteoarthritis (OA), the most prevalent joint disease, is a major cause of disability worldwide. Growth hormone (GH) has been suggested to play significant roles in maintaining articular chondrocyte function and ultimately articular cartilage (AC) homeostasis. In humans, the age-associated decline in GH levels was hypothesized to play a role in the etiology of OA. We studied the impact of adult-onset isolated GH deficiency (AOiGHD) on the life span and skeletal integrity including the AC, in 23- to 30-month-old male and female mice on C57/BL6 genetic background. Reductions in GH during adulthood were associated with extended life span and reductions in body temperature in female mice only. However, end-of-life pathology revealed high levels of lymphomas in both sexes, independent of GH status. Skeletal characterization revealed increases in OA severity in AOiGHD mice, evidenced by AC degradation in both femur and tibia, and significantly increased osteophyte formation in AOiGHD females. AOiGHD males showed significant increases in the thickness of the synovial lining cell layer that was associated with increased markers of inflammation (IL-6, iNOS). Furthermore, male AOiGHD showed significant increases in matrix metalloproteinase-13 (MMP-13), p16, and β-galactosidase immunoreactivity in the AC as compared to controls, indicating increased cell senescence. In conclusion, while the life span of AOiGHD females increased, their health span was compromised by high-grade lymphomas and the development of severe OA. In contrast, AOiGHD males, which did not show extended life span, showed an overall low grade of lymphomas but exhibited significantly decreased health span, evidenced by increased OA severity.

Changes in Antioxidative, Oxidoreductive and Detoxification Enzymes during Development of Aphids and Temperature Increase

Temperature, being the main factor that has an influence on insects, causes changes in their development, reproduction, winter survival, life cycles, migration timing, and population dynamics. The effects of stress caused by a temperature increase on insects may depend on many factors, such as the frequency, amplitude, duration of the stress, sex, or the developmental stage of the insect. The aim of the study was to determine the differences in the enzymatic activity of nymphs and adult aphids Aphis pomi, Macrosiphum rosae and Cinara cupressi, and changes in their response to a temperature increase from 20 to 28 °C. The activity of enzymatic markers (superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), β-glucosidase, polyphenol oxidase (PPO) and peroxidase (POD)) in aphid tissues was analysed for three constant temperatures. The results of our research showed that the enzymatic activity of aphids (measured as the activity of antioxidant, detoxifying and oxidoreductive enzymes) was mainly determined by the type of morph. We observed a strong positive correlation between the activity of the detoxifying and oxidoreductive enzymes and aphids' development, and a negative correlation between the activity of the antioxidant enzymes and aphids' development. Moreover, the study showed that an increase in temperature caused changes in enzyme activity (especially SOD, CAT and β-glucosidase), which was highest at 28 °C, in both nymphs and adults. Additionally, a strong positive correlation between metabolic activity (heat flow measured by microcalorimeter) and longevity was observed, which confirmed the relationship between these characteristics of aphids. The antioxidant enzyme system is more efficient in aphid nymphs, and during aphid development the activity of antioxidant enzymes decreases. The antioxidant enzyme system in aphids appears to deliver effective protection for nymphs and adults under stressful conditions, such as high temperatures.

Translational control of gene expression by eIF2 modulates proteostasis and extends lifespan

Although the stress response in eukaryotes depends on early events triggered in cells by environmental insults, long-term processes such as aging are also affected. The loss of cellular proteostasis greatly impacts aging, which is regulated by the balancing of protein synthesis and degradation systems. As translation is the input event in proteostasis, we decided to study the role of translational activity on cell lifespan. Our hypothesis was that a reduction on translational activity or specific changes in translation may increase cellular longevity.

Using mutant strains of Schizosaccharomyces pombe and various stress conditions, we showed that translational reduction caused by phosphorylation of eukaryotic translation initiation factor 2 (eIF2) during the exponential growth phase enhances chronological lifespan (CLS). Furthermore, through next-generation sequence analysis, we found eIF2α phosphorylation-dependent translational activation of some specific genes, especially those involved in autophagy. This fact, together with the observed regulation of autophagy, points to a conserved mechanism involving general and specific control of translation and autophagy as mediators of the role of eIF2α phosphorylation in aging.

Analysis of longevity in Chordata identifies species with exceptional longevity among taxa and points to the evolution of longer lifespans

Animals have a considerable variation in their longevity. This fundamental life-history trait is shaped by both intrinsic and extrinsic mortality pressures, influenced by multiple parameters including ecological variables and mode-of-life traits. Here, we examined the distribution of maximum age at multiple taxonomic ranks (class, order and family) in Chordata, and identified species with exceptional longevity within various taxa. We used a curated dataset of maximum longevity of animals from AnAge database, containing a total of 2542 chordates following our filtering criteria. We determined shapes of maximum age distributions at class, order and family taxonomic ranks, and calculated skewness values for each distribution, in R programming environment. We identified species with exceptional longevity compared to other species belonging to the same taxa, based on our definition of outliers. We collected data on ecological variables and mode-of-life traits which might possibly contribute, at least in part, to the exceptional lifespans of certain chordates. We found that 23, 12 and 4 species have exceptional longevity when we grouped chordates by their class, order and family, respectively. Almost all distributions of maximum age among taxa were positively skewed (towards increased longevity), possibly showing the emergence of longer lifespans in contrast to shorter lifespans, through the course of evolution. However, potential biases in the collection of data should be taken into account. Most of the identified species in the current study have not been previously studied in the context of animal longevity. Our analyses point that certain chordates may have evolved to have longer lifespans compared to other species belonging to the same taxa, and that among taxa, outliers in terms of maximum age have always longer lifespans, not shorter. Future research is required to understand how and why increased longevity have arose in certain species.

Thermal and nutritional environments during development exert different effects on adult reproductive success in Drosophila melanogaster

Environments experienced during development have long-lasting consequences for adult performance and fitness. The "environmental matching" hypothesis predicts that individuals perform best when adult and developmental environments match whereas the "silver spoon" hypothesis expects that fitness is higher in individuals developed under favorable environments regardless of adult environments. Temperature and nutrition are the two most influential determinants of environmental quality, but it remains to be elucidated which of these hypotheses better explains the long-term effects of thermal and nutritional histories on adult fitness traits. Here we compared how the temperature and nutrition of larval environment would affect adult survivorship and reproductive success in the fruit fly, Drosophila melanogaster. The aspect of nutrition focused on in this study was the dietary protein-to-carbohydrate (P:C) ratio. The impact of low developmental and adult temperature was to improve adult survivorship. High P:C diet had a negative effect on adult survivorship when ingested during the adult stage, but had a positive effect when ingested during development. No matter whether adult and developmental environments matched or not, females raised in warm and protein-enriched environments produced more eggs than those raised in cool and protein-limiting environments, suggesting the presence of a significant silver spoon effect of larval temperature and nutrition. The effect of larval temperature on adult egg production was weak but persisted across the early adult stage whereas that of larval nutrition was initially strong but diminished rapidly after day 5 posteclosion. Egg production after day 5 was strongly influenced by the P:C ratio of the adult diet, indicating that the diet contributing mainly to reproduction had shifted from larval to adult diet. Our results highlight the importance of thermal and nutritional histories in shaping organismal performance and fitness and also demonstrate how the silver spoon effects of these aspects of environmental histories differ fundamentally in their nature, strength, and persistence.

A Multicellular Network Mechanism for Temperature-Robust Food Sensing

Responsiveness to external cues is a hallmark of biological systems. In complex environments, it is crucial for organisms to remain responsive to specific inputs even as other internal or external factors fluctuate. Here, we show how the nematode Caenorhabditis elegans can discriminate between different food levels to modulate its lifespan despite temperature perturbations. This end-to-end robustness from environment to physiology is mediated by food-sensing neurons that communicate via transforming growth factor β (TGF-β) and serotonin signals to form a multicellular gene network. Specific regulations in this network change sign with temperature to maintain similar food responsiveness in the lifespan output. In contrast to robustness of stereotyped outputs, our findings uncover a more complex robustness process involving the higher order function of discrimination in food responsiveness. This process involves rewiring a multicellular network to compensate for temperature and provides a basis for understanding gene-environment interactions. Together, our findings unveil sensory computations that integrate environmental cues to govern physiology.

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C. elegans’ ability to modulate lifespan in response to food is robust to temperature

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Robustness requires TGF-β and serotonin signaling in a neuronal network

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Specific regulations in the neuronal network change sign with temperature

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Temperature-dependent regulations compensate for temperature

Temperature Sensation: From Molecular Thermosensors to Neural Circuits and Coding Principles

Temperature is a universal cue and regulates many essential processes ranging from enzymatic reactions to species migration. Due to the profound impact of temperature on physiology and behavior, animals and humans have evolved sophisticated mechanisms to detect temperature changes. Studies from animal models, such as mouse, Drosophila, and C. elegans, have revealed many exciting principles of thermosensation. For example, conserved molecular thermosensors, including thermosensitive channels and receptors, act as the initial detectors of temperature changes across taxa. Additionally, thermosensory neurons and circuits in different species appear to adopt similar logic to transduce and process temperature information. Here, we present the current understanding of thermosensation at the molecular and cellular levels. We also discuss the fundamental coding strategies of thermosensation at the circuit level. A thorough understanding of thermosensation not only provides key insights into sensory biology but also builds a foundation for developing better treatments for various sensory disorders.

Physiological and cognitive consequences of a daily 26 h photoperiod in a primate: exploring the underlying mechanisms of the circadian resonance theory

The biological clock expresses circadian rhythms, whose endogenous period (tau) is close to 24 h. Daily resetting of the circadian clock to the 24 h natural photoperiod might induce marginal costs that would accumulate over time and forward affect fitness. It was proposed as the circadian resonance theory. For the first time, we aimed to evaluate these physiological and cognitive costs that would partially explain the mechanisms of the circadian resonance hypothesis. We evaluated the potential costs of imposing a 26 h photoperiodic regimen compared to the classical 24 h entrainment measuring several physiological and cognitive parameters (body temperature, energetic expenditure, oxidative stress, cognitive performances) in males of a non-human primate (Microcebus murinus), a nocturnal species whose endogenous period is about 23.5 h. We found significant higher resting body temperature and energy expenditure and lower cognitive performances when the photoperiodic cycle length was 26 h. Together these results suggest that a great deviation of external cycles from tau leads to daily greater energetic expenditure, and lower cognitive capacities. To our knowledge, this study is the first to highlight potential mechanisms of circadian resonance theory.

Effects of Temperature on Lifespan of Drosophila melanogaster from Different Genetic Backgrounds: Links between Metabolic Rate and Longevity

Despite many studies of the aging process, questions about key factors ensuring longevity have not yet found clear answers. Temperature seems to be one of the most important factors regulating lifespan. However, the genetic background may also play a key role in determining longevity. The aim of this study was to investigate the relationship between the temperature, genetic background (fruit fly origin), and metabolic rate on lifespan. Experiments were performed with the use of the wild type Drosophila melanogaster fruit flies originating from Australia, Canada, and Benin and the reference OregonR strain. The metabolic rate of D. melanogaster was measured at 20 °C, 25 °C, and 28 °C in an isothermal calorimeter. We found a strong negative relationship between the total heat flow and longevity. A high metabolic rate leads to increased aging in males and females in all strains. Furthermore, our results showed that temperature has a significant effect on fecundity and body weight. We also showed the usefulness of the isothermal calorimetry method to study the effect of environmental stress conditions on the metabolic activity of insects. This may be particularly important for the forecasting of impact of global warming on metabolic activity and lifespan of various insects.

Combined effects of temperature and macronutrient balance on life-history traits in Drosophila melanogaster: implications for life-history trade-offs and fundamental niche

Temperature and nutrition are amongst the most influential environmental determinants of Darwinian fitness in ectotherms. Since the ongoing climate warming is known to alter nutritional environments encountered by ectotherms, a precise understanding of the integrated effects of these two factors on ectotherm performance is essential for improving the accuracy of predictions regarding how ectotherms will respond to climate warming. Here we employed response surface methodology to examine how multiple life-history traits were expressed across a grid of environmental conditions representing full combinations of six ambient temperatures (13, 18, 23, 28, 31, 33 °C) and eight dietary protein:carbohydrate ratios (P:C = 1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, 8:1) in Drosophila melanogaster. Different life-history traits were maximized in different regions in the two-dimensional temperature-nutrient space. The optimal temperature and P:C ratio identified for adult lifespan (13 °C and 1:16) were lower than those for early-life female fecundity (28 °C and 4:1). Similar divergence in thermal and nutritional optima was found between body mass at adult emergence (18 °C and P:C 1:1) and the rate of pre-adult development (28 °C and P:C 4:1). Pre-adult survival was maximized over a broad range of temperature (18-28 °C) and P:C ratio (1:8-8:1). These results indicate that the occurrence of life-history trade-offs is regulated by both temperature and dietary P:C ratio. The estimated measure of fitness was maximized at 23 °C and P:C 2:1. Based on the shape of the response surface constructed for this estimated fitness, we characterized the fundamental thermal and nutritional niche for D. melanogaster with unprecedented detail.

Redox signalling and ageing: insights from Drosophila

Ageing and age-related diseases are major challenges for the social, economic and healthcare systems of our society. Amongst many theories, reactive oxygen species (ROS) have been implicated as a driver of the ageing process. As by-products of aerobic metabolism, ROS are able to randomly oxidise macromolecules, causing intracellular damage that accumulates over time and ultimately leads to dysfunction and cell death. However, the genetic overexpression of enzymes involved in the detoxification of ROS or treatment with antioxidants did not generally extend lifespan, prompting a re-evaluation of the causal role for ROS in ageing. More recently, ROS have emerged as key players in normal cellular signalling by oxidising redox-sensitive cysteine residues within proteins. Therefore, while high levels of ROS may be harmful and induce oxidative stress, low levels of ROS may actually be beneficial as mediators of redox signalling. In this context, enhancing ROS production in model organisms can extend lifespan, with biological effects dependent on the site, levels, and specific species of ROS. In this review, we examine the role of ROS in ageing, with a particular focus on the importance of the fruit fly Drosophila as a powerful model system to study redox processes in vivo.

Greater loss of mitochondrial function with ageing is associated with earlier onset of sarcopenia in C. elegans

Sarcopenia, the age-related decline of muscle, is a significant and growing public health burden. C. elegans, a model organism for investigating the mechanisms of ageing, also displays sarcopenia, but the underlying mechanism(s) remain elusive. Here, we use C. elegans natural scaling of lifespan in response to temperature to examine the relationship between mitochondrial content, mitochondrial function, and sarcopenia. Mitochondrial content and maximal mitochondrial ATP production rates (MAPR) display an inverse relationship to lifespan, while onset of MAPR decline displays a direct relationship. Muscle mitochondrial structure, sarcomere structure, and movement decline also display a direct relationship with longevity. Notably, the decline in mitochondrial network structure occurs earlier than sarcomere decline, and correlates more strongly with loss of movement, and scales with lifespan. These results suggest that mitochondrial function is critical in the ageing process and more robustly explains the onset and progression of sarcopenia than loss of sarcomere structure.

Early Biological Aging and Fetal Exposure to High and Low Ambient Temperature: A Birth Cohort Study

BACKGROUND

Although studies have provided estimates of premature mortality to either heat or cold in adult populations, and fetal exposure to ambient temperature may be associated with life expectancy, the effects of temperature on aging in early life have not yet been studied. Telomere length (TL) is a marker of biological aging, and a short TL at birth may predict lifespan and disease susceptibility later in life.

OBJECTIVES

We studied to what extent prenatal ambient temperature exposure is associated with newborn TL.

METHODS

In the ENVIRONAGE (ENVIRonmental influence ON early AGEing) birth cohort in Flanders, Belgium, we measured cord blood and placental TL in 1,103 mother-newborn pairs (singletons with ≥36wk of gestation) using a quantitative real-time polymerase chain reaction (qPCR) method. We associated newborn TL with average weekly exposure to ambient temperature using distributed lag nonlinear models (DLNMs) while controlling for potential confounders. Double-threshold DLNMs were used to estimate cold and heat thresholds and the linear associations between temperature and TL below the cold threshold and above the heat threshold.

RESULTS

Prenatal temperature exposure above the heat threshold (19.5°C) was associated with shorter cord blood TL. The association with a 1°C increase in temperature was strongest at week 36 of gestation and resulted in a 3.29% [95% confidence interval (CI): -4.67, -1.88] shorter cord blood TL. Consistently, prenatal temperature exposure below the cold threshold (5.0°C) was associated with longer cord blood TL. The association with a 1°C decrease in temperature was strongest at week 10 of gestation with 0.72% (95% CI: 0.46, 0.97) longer cord blood TL.

DISCUSSION

Our study supports potential effects of prenatal temperature exposure on longevity and disease susceptibility later in life. Future climate scenarios might jeopardize the potential molecular longevity of future generations from birth onward. https://doi.org/10.1289/EHP5153.

MDT-15/MED15 permits longevity at low temperature via enhancing lipidostasis and proteostasis

Low temperatures delay aging and promote longevity in many organisms. However, the metabolic and homeostatic aspects of low-temperature–induced longevity remain poorly understood. Here, we show that lipid homeostasis regulated by Caenorhabditis elegans Mediator 15 (MDT-15 or MED15), a transcriptional coregulator, is essential for low-temperature–induced longevity and proteostasis. We find that inhibition of mdt-15 prevents animals from living long at low temperatures. We show that MDT-15 up-regulates fat-7, a fatty acid desaturase that converts saturated fatty acids (SFAs) to unsaturated fatty acids (UFAs), at low temperatures. We then demonstrate that maintaining a high UFA/SFA ratio is essential for proteostasis at low temperatures. We show that dietary supplementation with a monounsaturated fatty acid, oleic acid (OA), substantially mitigates the short life span and proteotoxicity in mdt-15(-) animals at low temperatures. Thus, lipidostasis regulated by MDT-15 appears to be a limiting factor for proteostasis and longevity at low temperatures. Our findings highlight the crucial roles of lipid regulation in maintaining normal organismal physiology under different environmental conditions.

Low temperatures delay aging and promote longevity in many organisms. This study shows that at low ambient temperatures, Mediator 15, a transcriptional coregulator, allows the nematode Caenorhabditis elegans to live longer by increasing the levels of unsaturated lipids, helping to maintain protein homeostasis.

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.

Interactions among morphotype, nutrition, and temperature impact fitness of an invasive fly

Invasive animals depend on finding a balanced nutritional intake to colonize, survive, and reproduce in new environments. This can be especially challenging during situations of fluctuating cold temperatures and food scarcity, but phenotypic plasticity may offer an adaptive advantage during these periods. We examined how lifespan, fecundity, pre‐oviposition periods, and body nutrient contents were affected by dietary protein and carbohydrate (P:C) ratios at variable low temperatures in two morphs (winter morphs WM and summer morphs SM) of an invasive fly, Drosophila suzukii. The experimental conditions simulated early spring after overwintering and autumn, crucial periods for survival. At lower temperatures, post‐overwintering WM lived longer on carbohydrate‐only diets and had higher fecundity on low‐protein diets, but there was no difference in lifespan or fecundity among diets for SM. As temperatures increased, low‐protein diets resulted in higher fecundity without compromising lifespan, while high‐protein diets reduced lifespan and fecundity for both WM and SM. Both SM and WM receiving high‐protein diets had lower sugar, lipid, and glycogen (but similar protein) body contents compared to flies receiving low‐protein and carbohydrate‐only diets. This suggests that flies spend energy excreting excess dietary protein, thereby affecting lifespan and fecundity. Despite having to recover from nutrient depletion after an overwintering period, WM exhibited longer lifespan and higher fecundity than SM in favorable diets and temperatures. WM exposed to favorable low‐protein diet had higher body sugar, lipid, and protein body contents than SM, which is possibly linked to better performance. Although protein is essential for oogenesis, WM and SM flies receiving low‐protein diets did not have shorter pre‐oviposition periods compared to flies on carbohydrate‐only diets. Finding adequate carbohydrate sources to compensate protein intake is essential for the successful persistence of D. suzukii WM and SM populations during suboptimal temperatures.

Congeneric variability in lifespan extension and onset of senescence suggest active regulation of aging in response to low temperature

Lifespan extension under low temperature is well conserved across both endothermic and exothermic taxa, but the mechanism underlying this change in aging is poorly understood. Low temperature is thought to decrease metabolic rate, thus slowing the accumulation of cellular damage from reactive oxygen species, although recent evidence suggests involvement of specific cold-sensing biochemical pathways. We tested the effect of low temperature on aging in 11 strains of Brachionus rotifers, with the hypothesis that if the mechanism of lifespan extension is purely thermodynamic, all strains should have a similar increase in lifespan. We found differences in change in median lifespan ranging from a 6% decrease to a 100% increase, as well as differences in maximum and relative lifespan extension and in mortality rate. Low temperature delays reproductive senescence in most strains, suggesting an extension of healthspan, even in strains with little to no change in lifespan. The combination of low temperature and caloric restriction in one strain resulted in an additive lifespan increase, indicating these interventions may work via non- or partially-overlapping pathways. The known low temperature sensor TRPA1 is present in the rotifer genome, but chemical TRPA1 agonists did not affect lifespan, suggesting that this gene may be involved in low temperature sensation but not in chemoreception in rotifers. The congeneric variability in response to low temperature suggests that the mechanism of low temperature lifespan extension is an active genetic process rather than a passive thermodynamic one and is dependent upon genotype.

Variation in adult stress resistance does not explain vulnerability to climate change in copper butterflies

Ongoing climate change is a major threat to biodiversity. However, although many species clearly suffer from ongoing climate change, others benefit from it, for example, by showing range expansions. However, which specific features determine a species' vulnerability to climate change? Phenotypic plasticity, which has been described as the first line of defence against environmental change, may be of utmost importance here. Against this background, we here compare plasticity in stress tolerance in 3 copper butterfly species, which differ arguably in their vulnerability to climate change. Specifically, we investigated heat, cold and desiccation resistance after acclimatization to different temperatures in the adult stage. We demonstrate that acclimation at a higher temperature increased heat but decreased cold tolerance and desiccation resistance. Contrary to our predictions, species did not show pronounced variation in stress resistance, though plastic capacities in temperature stress resistance did vary across species. Overall, our results seemed to reflect population-rather than species-specific patterns. We conclude that the geographical origin of the populations used should be considered even in comparative studies. However, our results suggest that, in the 3 species studied here, vulnerability to climate change is not in the first place determined by stress resistance in the adult stage. As entomological studies focus all too often on adults only, we argue that more research effort should be dedicated to other developmental stages when trying to understand insect responses to environmental change.

Relationship between lifespan indicators and elemental background values: A case study in Guangdong Province, China

There was a significant difference in the distribution of centenarians at county-level in Guangdong Province, China. To carry out an integrated analysis on elemental background values and their relation to lifespan level, samples of environmental media such as drinking water, staple rice and soil were collected in ten counties (non-longevity and longevity areas) in Guangdong Province. Meanwhile, lifespan indicators were calculated based on census data in 2010: the percentage of population aged 80 to 90years (octogenarian index, 80-90%, OI%), the percentage of population aged 90 to 100years (longevity index, 90-100%, LI%), centenarians per one hundred thousand inhabitants (CH). Grey relational analysis (GRA) and stepwise multiple linear regression analysis (SMLR) were conducted. The major results show that the contents of Se, Mo, Ni, K and Zn in drinking water and rice and the content of Se in soil in longevity areas are significantly higher than those in non-longevity areas. Significantly positive correlation between elemental background values (Se, K, Mo, Ni and Zn) and three lifespan indicators shows an increasing trend in the order of OI, LI and CH. However, element Al in rice and soil shows a negative correlation with CH. In addition, the influence degree of elemental background values on LI and CH can be ranked as Se>Mo>K>Zn>Ni. The explanatory power of elemental background values (Se, K, Mo, Ni and Zn) to difference in LI/CH in longevity and non-longevity areas can be ranked: drinking water>rice>soil. The elemental background values (Se, K, Mo, Ni and Zn) have a positive impact on human lifespan, especially for those who live longer than 90years old.

Progeny of old parents have increased social space in Drosophila melanogaster

We report the effects of aging and parental age in Drosophila melanogaster on two types of responses to social cues: the choice of preferred social spacing in an undisturbed group and the response to the Drosophila stress odorant (dSO) emitted by stressed flies. The patterns of changes during aging were notably different for these two social responses. Flies were initially closer in space and then became further apart. However, the pattern of change in response to dSO followed a more typical decline in performance, similarly to changes in locomotion. Interestingly, the increased social space of old parents, as well as their reduced performance in avoiding dSO, was passed on to their progeny, such that young adults adopted the behavioural characteristic of their old parents. While the response to social cues was inherited, the changes in locomotion were not. We were able to scale the changes in the social space of parents and their progeny by accelerating or decelerating the physiological process of aging by increasing temperatures and exposure to oxidative stress, or via caloric restriction, respectively. Finally, when we aged only one parent, only the male progeny of old fathers and the progeny of very old mothers were more distant.

Individual differences in normal body temperature: longitudinal big data analysis of patient records

OBJECTIVE

To estimate individual level body temperature and to correlate it with other measures of physiology and health.

DESIGN

Observational cohort study.

SETTING

Outpatient clinics of a large academic hospital, 2009-14.

PARTICIPANTS

35 488 patients who neither received a diagnosis for infections nor were prescribed antibiotics, in whom temperature was expected to be within normal limits.

MAIN OUTCOME MEASURES

Baseline temperatures at individual level, estimated using random effects regression and controlling for ambient conditions at the time of measurement, body site, and time factors. Baseline temperatures were correlated with demographics, medical comorbidities, vital signs, and subsequent one year mortality.

RESULTS

In a diverse cohort of 35 488 patients (mean age 52.9 years, 64% women, 41% non-white race) with 243 506 temperature measurements, mean temperature was 36.6°C (95% range 35.7-37.3°C, 99% range 35.3-37.7°C). Several demographic factors were linked to individual level temperature, with older people the coolest (-0.021°C for every decade, P<0.001) and African-American women the hottest (versus white men: 0.052°C, P<0.001). Several comorbidities were linked to lower temperature (eg, hypothyroidism: -0.013°C, P=0.01) or higher temperature (eg, cancer: 0.020, P<0.001), as were physiological measurements (eg, body mass index: 0.002 per m/kg², P<0.001). Overall, measured factors collectively explained only 8.2% of individual temperature variation. Despite this, unexplained temperature variation was a significant predictor of subsequent mortality: controlling for all measured factors, an increase of 0.149°C (1 SD of individual temperature in the data) was linked to 8.4% higher one year mortality (P=0.014).

CONCLUSIONS

Individuals' baseline temperatures showed meaningful variation that was not due solely to measurement error or environmental factors. Baseline temperatures correlated with demographics, comorbid conditions, and physiology, but these factors explained only a small part of individual temperature variation. Unexplained variation in baseline temperature, however, strongly predicted mortality.

Genetic interaction with temperature is an important determinant of nematode longevity

As in other poikilotherms, longevity in C. elegans varies inversely with temperature; worms are longer-lived at lower temperatures. While this observation may seem intuitive based on thermodynamics, the molecular and genetic basis for this phenomenon is not well understood. Several recent reports have argued that lifespan changes across temperatures are genetically controlled by temperature-specific gene regulation. Here, we provide data that both corroborate those studies and suggest that temperature-specific longevity is more the rule than the exception. By measuring the lifespans of worms with single modifications reported to be important for longevity at 15, 20, or 25 °C, we find that the effect of each modification on lifespan is highly dependent on temperature. Our results suggest that genetics play a major role in temperature-associated longevity and are consistent with the hypothesis that while aging in C. elegans is slowed by decreasing temperature, the major cause(s) of death may also be modified, leading to different genes and pathways becoming more or less important at different temperatures. These differential mechanisms of age-related death are not unlike what is observed in humans, where environmental conditions lead to development of different diseases of aging.

The 4E-BP growth pathway regulates the effect of ambient temperature on Drosophila metabolism and lifespan

Changes in body temperature can profoundly affect survival. The dramatic longevity-enhancing effect of cold has long been known in organisms ranging from invertebrates to mammals, yet the underlying mechanisms have only recently begun to be uncovered. In the nematode Caenorhabditis elegans, this process is regulated by a thermosensitive membrane TRP channel and the DAF-16/FOXO transcription factor, but in more complex organisms the underpinnings of cold-induced longevity remain largely mysterious. We report that, in Drosophila melanogaster, variation in ambient temperature triggers metabolic changes in protein translation, mitochondrial protein synthesis, and posttranslational regulation of the translation repressor, 4E-BP (eukaryotic translation initiation factor 4E-binding protein). We show that 4E-BP determines Drosophila lifespan in the context of temperature changes, revealing a genetic mechanism for cold-induced longevity in this model organism. Our results suggest that the 4E-BP pathway, chiefly thought of as a nutrient sensor, may represent a master metabolic switch responding to diverse environmental factors.

Basal body temperature as a biomarker of healthy aging

Scattered evidence indicates that a lower basal body temperature may be associated with prolonged health span, yet few studies have directly evaluated this relationship. We examined cross-sectional and longitudinal associations between early morning oral temperature (95.0-98.6 °F) and usual gait speed, endurance walk performance, fatigability, and grip strength in 762 non-frail men (52 %) and women aged 65-89 years participating in the Baltimore Longitudinal Study of Aging. Since excessive adiposity (body mass index ≥35 kg/m² or waist-to-height ratio ≥0.62) may alter temperature set point, associations were also examined within adiposity strata. Overall, controlling for age, race, sex, height, exercise, and adiposity, lower temperature was associated with faster gait speed, less time to walk 400 m quickly, and lower perceived exertion following 5-min of walking at 0.67 m/s (all p ≤ 0.02). In the non-adipose (N = 662), these associations were more robust (all p ≤ 0.006). Direction of association was reversed in the adipose (N = 100), but none attained significance (all p > 0.22). Over 2.2 years, basal temperature was not associated with functional change in the overall population or non-adipose. Among the adipose, lower baseline temperature was associated with greater decline in endurance walking performance (p = 0.006). In longitudinal analyses predicting future functional performance, low temperature in the non-adipose was associated with faster gait speed (p = 0.021) and less time to walk 400 m quickly (p = 0.003), whereas in the adipose, lower temperature was associated with slower gait speed (p = 0.05) and more time to walk 400 m (p = 0.008). In older adults, lower basal body temperature appears to be associated with healthy aging in the absence of excessive adiposity.

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.

Life in the cold: links between mammalian hibernation and longevity

The biological process of aging is the primary determinant of lifespan, but the factors that influence the rate of aging are not yet clearly understood and remain a challenging question. Mammals are characterized by >100-fold differences in maximal lifespan, influenced by relative variances in body mass and metabolic rate. Recent discoveries have identified long-lived mammalian species that deviate from the expected longevity quotient. A commonality among many long-lived species is the capacity to undergo metabolic rate depression, effectively re-programming normal metabolism in response to extreme environmental stress and enter states of torpor or hibernation. This stress tolerant phenotype often involves a reduction in overall metabolic rate to just 1-5% of the normal basal rate as well as activation of cytoprotective responses. At the cellular level, major energy savings are achieved via coordinated suppression of many ATP-expensive cell functions; e.g. global rates of protein synthesis are strongly reduced via inhibition of the insulin signaling axis. At the same time, various studies have shown activation of stress survival signaling during hibernation including up-regulation of protein chaperones, increased antioxidant defenses, and transcriptional activation of pro-survival signaling such as the FOXO and p53 pathways. Many similarities and parallels exist between hibernation phenotypes and different long-lived models, e.g. signal transduction pathways found to be commonly regulated during hibernation are also known to induce lifespan extension in animals such as Drosophila melanogaster and Caenorhabditis elegans. In this review, we highlight some of the molecular mechanisms that promote longevity in classic aging models C. elegans, Drosophila, and mice, while providing a comparative analysis to how they are regulated during mammalian hibernation.

The effects of graded levels of calorie restriction: II. Impact of short term calorie and protein restriction on circulating hormone levels, glucose homeostasis and oxidative stress in male C57BL/6 mice

Limiting food intake attenuates many of the deleterious effects of aging, impacting upon healthspan and leading to an increased lifespan. Whether it is the overall restriction of calories (calorie restriction: CR) or the incidental reduction in macronutrients such as protein (protein restriction: PR) that mediate these effects is unclear. The impact of 3 month CR or PR, (10 to 40%), on C57BL/6 mice was compared to controls fed ad libitum. Reductions in circulating leptin, tumor necrosis factor-α and insulin-like growth factor-1 (IGF-1) were relative to the level of CR and individually associated with morphological changes but remained unchanged following PR. Glucose tolerance and insulin sensitivity were improved following CR but not affected by PR. There was no indication that CR had an effect on oxidative damage, however CR lowered antioxidant activity. No biomarkers of oxidative stress were altered by PR. CR significantly reduced levels of major urinary proteins suggesting lowered investment in reproduction. Results here support the idea that reduced adipokine levels, improved insulin/IGF-1 signaling and reduced reproductive investment play important roles in the beneficial effects of CR while, in the short-term, attenuation of oxidative damage is not applicable. None of the positive effects were replicated with PR.