Thermoregulation in mice exhibits genetic variability early in senescence

Skeletal Muscle Uncoupling Proteins in Mice Models of Obesity

Obesity and accompanying type 2 diabetes are among major and increasing worldwide problems that occur fundamentally due to excessive energy intake during its expenditure. Endotherms continuously consume a certain amount of energy to maintain core body temperature via thermogenic processes, mainly in brown adipose tissue and skeletal muscle. Skeletal muscle glucose utilization and heat production are significant and directly linked to body glucose homeostasis at rest, and especially during physical activity. However, this glucose balance is impaired in diabetic and obese states in humans and mice, and manifests as glucose resistance and altered muscle cell metabolism. Uncoupling proteins have a significant role in converting electrochemical energy into thermal energy without ATP generation. Different homologs of uncoupling proteins were identified, and their roles were linked to antioxidative activity and boosting glucose and lipid metabolism. From this perspective, uncoupling proteins were studied in correlation to the pathogenesis of diabetes and obesity and their possible treatments. Mice were extensively used as model organisms to study the physiology and pathophysiology of energy homeostasis. However, we should be aware of interstrain differences in mice models of obesity regarding thermogenesis and insulin resistance in skeletal muscles. Therefore, in this review, we gathered up-to-date knowledge on skeletal muscle uncoupling proteins and their effect on insulin sensitivity in mouse models of obesity and diabetes.

Impact of the Age of Cecal Material Transfer Donors on Alzheimer’s Disease Pathology in 5xFAD Mice

Alzheimer’s disease is a progressive neurodegenerative disorder affecting around 30 million patients worldwide. The predominant sporadic variant remains enigmatic as the underlying cause has still not been identified. Since efficient therapeutic treatments are still lacking, the microbiome and its manipulation have been considered as a new, innovative approach. 5xFAD Alzheimer’s disease model mice were subjected to one-time fecal material transfer after antibiotics-treatment using two types of inoculation: material derived from the caecum of age-matched (young) wild type mice or from middle aged, 1 year old (old) wild type mice. Mice were profiled after transfer for physiological parameters, microbiome, behavioral tasks, and amyloid deposition. A single time transfer of cecal material from the older donor group established an aged phenotype in the recipient animals as indicated by elevated cultivatable fecal Enterobacteriaceae and Lactobacillaceae representative bacteria, a decreased Firmicutes amount as assessed by qPCR, and by increased levels of serum LPS binding protein. While behavioral deficits were not accelerated, single brain regions (prefrontal cortex and dentate gyrus) showed higher plaque load after transfer of material from older animals. We could demonstrate that the age of the donor of cecal material might affect early pathological hallmarks of Alzheimer’s disease. This could be relevant when considering new microbiome-based therapies for this devastating disorder.

Age-Related Changes in the Thermoregulatory Properties in Bank Voles From a Selection Experiment

As with many physiological performance traits, the capacity of endotherms to thermoregulate declines with age. Aging compromises both the capacity to conserve or dissipate heat and the thermogenesis, which is fueled by aerobic metabolism. The rate of metabolism, however, not only determines thermogenic capacity but can also affect the process of aging. Therefore, we hypothesized that selection for an increased aerobic exercise metabolism, which has presumably been a crucial factor in the evolution of endothermic physiology in the mammalian and avian lineages, affects not only the thermoregulatory traits but also the age-related changes of these traits. Here, we test this hypothesis on bank voles (Myodes glareolus) from an experimental evolution model system: four lines selected for high swim-induced aerobic metabolism (A lines), which have also increased the basal, average daily, and maximum cold-induced metabolic rates, and four unselected control (C) lines. We measured the resting metabolic rate (RMR), evaporative water loss (EWL), and body temperature in 72 young adult (4 months) and 65 old (22 months) voles at seven ambient temperatures (13-32°C). The RMR was 6% higher in the A than in the C lines, but, regardless of the selection group or temperature, it did not change with age. However, EWL was 12% higher in the old voles. An increased EWL/RMR ratio implies either a compromised efficiency of oxygen extraction in the lungs or increased skin permeability. This effect was more profound in the A lines, which may indicate their increased vulnerability to aging. Body temperature did not differ between the selection and age groups below 32°C, but at 32°C it was markedly higher in the old A-line voles than in those from other groups. As expected, the thermogenic capacity, measured as the maximum cold-induced oxygen consumption, was decreased by about 13% in the old voles from both selection groups, but the performance of old A-line voles was the same as that of the young C-line ones. Thus, the selection for high aerobic exercise metabolism attenuated the adverse effects of aging on cold tolerance, but this advantage has been traded off by a compromised coping with hot conditions by aged voles.

Gonadal hormones influence core body temperature during calorie restriction

During calorie restriction (CR), endotherms adjust several physiological processes including the decrease of core body temperature (T_b) and reduction of energy expenditure. We recently found that CR-induced hypothermia is regulated in a sex-dependent manner in mice with lowered central insulin-like growth factor receptor signaling. Here, we describe the contribution of sex hormones to CR-induced hypothermia in wild type C57BL6 mice by measuring T_b of female and male mice following bilateral gonadectomy and hormonal replacement. Specifically, we evaluated the effects of progesterone (P4), 17-ß estradiol (E2), a combination of both (P4 + E2) in females and of 5-α dihydrotestosterone (5-α DHT) in males. Gonadectomy resulted in an earlier and stronger CR-induced hypothermia in both sexes. These effects were fully antagonized in females by E2 replacement, but not by P4, which had only minor and partial effects when used alone and did not prevent the action of E2 during CR when both hormones were given in combination. 5-α-DHT had only minor and transient effects on preventing the reduction of T_b during CR on gonadectomized male mice. These findings indicate that gonadal hormones contribute to sex-specific regulation of T_b and energy expenditure when nutrient availability is scarce. Abbreviations: AL: ad libitum; ANOVA: analysis of variance; CR: calorie restriction; E2: 17-ß estradiol; GNX: gonadectomy or gonadectomized; IGF-1R: insulin-like growth factor 1 receptor; POA: preoptic area; P4: progesterone; RM: repeated measures; SD: standard deviation; SEM: standard error of mean; T_b: core body temperature; WT: wildtype; 5-α DHT: 5-α dihydrotestosterone.

Circadian rhythms of body temperature and locomotor activity in aging BALB/c mice: early and late life span predictors

Impairment of one or more parameters of circadian rhythms (CR) of body temperature (BT) and locomotor activity (LMA) are considered among the hallmarks of mammalian aging. These alterations are frequently used as markers for imminent death in laboratory mice. However, there are still contradictory data for particular strains and it is also uncertain which changes might predict senescence changes later in life, including the force of mortality. In the present paper we use telemetry to study LMA and CR of BT during aging of BALB/c mice. At our knowledge this is the first time that CR of BT and LMA are investigated in this strain in a range of age covering the whole lifespan, from young adult up to very old age. CR of BT was analyzed with a cosine model using a cross sectional approach and follow-up measurements. The results show that BT, LMA, amplitude, goodness-of-fit (GoF) to circadian cycle of temperature decrease with different shapes during chronological age. Moreover, we found that the % change of amplitude and BT in early life (5-19 months) can predict the remaining lifespan of the mice. Later in life (22-32 months), best predictors are single measurements of LMA and GoF. The results of this study also offer potential measures to rapidly identifying freely unrestrained mice with the worst longitudinal outcome and against which existing or novel biomarkers and treatments may be assessed.

Markers for heightened monitoring, imminent death, and euthanasia in aged inbred mice

The goal of this study was to identify objective criteria that would reliably predict spontaneous death in aged inbred mice. We evaluated male and female AKR/J mice, which die at a relatively young age due to the development of lymphoma, as well as male C57BL/6J and BALB/cByJ mice. Mice were implanted subcutaneously with an identification chip that also allowed remote measurement of body temperature. Temperatures and body weights were measured weekly until spontaneous death occurred or until euthanasia was performed for humane reasons. In AKR/J mice, hypothermia and weight loss began about 4 wk prior to death and increased gradually during that antemortem interval. In C57BL/6J and BALB/cByJ mice, these declines began earlier and were more prolonged prior to death. However, C57BL/6J and BALB/cByJ mice developed a relatively precipitous hypothermia during the 2 wk prior to death. For all 3 strains, the derived composite score of temperature × weight, expressed as a percentage of stable values for each mouse, was similarly informative. These changes in individual and composite measures can signal the need for closer observation or euthanasia of individual mice. Validated markers of clinical decline or imminent death can allow the use of endpoints that reduce terminal distress, do not significantly affect longevity or survival data, and permit timely collection of biologic samples.

Is older colder or colder older? The association of age with body temperature in 18,630 individuals

In animal studies, caloric restriction resulting in increased longevity is associated with a reduction in body temperature, which is strain specific and likely under genetic control. Small studies in humans have suggested that temperatures may be lower among elderly populations, usually attributed to loss of thermoregulation. We analyzed cross-sectional data from 18,630 white adults aged 20-98 years (mean 58.3 years) who underwent oral temperature measurement as part of a standardized health appraisal at a large U.S. health maintenance organization. Overall, women had higher mean temperatures (97.5 ± 1.2°F) than men (97.2 ± 1.1°F; p < .0001). Mean temperature decreased with age, with a difference of 0.3°F between oldest and youngest groups after controlling for sex, body mass index, and white blood cell count. The results are consistent with low body temperature as a biomarker for longevity. Prospective studies are needed to confirm whether this represents a survival advantage associated with lifetime low steady state temperature.