Naked mole-rats maintain healthy skeletal muscle and Complex IV mitochondrial enzyme function into old age

This project was funded by Newcastle University Centre for Brain Ageing and Vitality (supported by the Biotechnology and Biological Sciences Research Council, Engineering and Physical Sciences Research Council, Economic and Social Research Council and Medical Research Council [G0700718]), the UK NIHR Biomedical Research Centre in Age and Age Related Diseases award to the Newcastle upon Tyne Hospitals NHS Foundation Trust, MRC Centre for Neuromuscular Disease [G000608-1], The Wellcome Trust Centre for Mitochondrial Research [096919/Z/11/Z]

Aspects of the energetics and renal physiology of some African arid-adapted rodents

Bibliography: leaves 358-363.The following aspects of physiological adaptation and resource usage were examined in several species of arid-adapted African rodents: The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in the North East African pigmy gerbil, gerbillus ppusillus; This gerbil did not strictly maintain homoeothermy and like most arid-adapted rodents had a reduced basal metabolic rate. When G. pusillus was maintained on an ad lib. food and water diet, its daily energy expenditure was similar to that predicted by mass. This increased to 116% of the expected allometric value when deprived of water. On a diet of air-dried millet seeds, increased kidney concentrating ability, reduced pulmocutaneous evaporation and a reduction in faecal water loss, were sufficient to impart virtual independence of exogenous water and the maintenance of a positive water balance. If food was restricted, G. pusillus utilized torpor to precisely balance energy expenditure with that available and so maintained a constant body mass. During torpor, assimilation efficiency was significantly reduced. The cost of maintaining coenothermia for the full duration of food processing would be prohibitive and it was estimated that it would have utilised approximately 50% of the daily energy available. The cost of employing torpor (0.5kJ.day-1) on the other hand was insignificant in comparison with the savings accrued by the use of torpor (32.25kJ. day -1). Parsimony of water loss with food restriction enabled the maintenance of a positive water balance during this period. The importance of micro-habitat in thermoregulation was investigated in Gerbillurus paeba, inhabiting the thermally stable confines of a plugged burrow, and in Aethomys namaquensis, a crevice dwelling rock rat. The rock rat, living in an environment characterized by large diet ranges, precisely controlled body temperature. It did this by compensating for its reduced basal metabolic rate, with a low rate of thermal conductance. Gerbillurus paeba tolerated a labile body temperature and used a high rate of thermal conductance to remove metabolic heat, for the high humidities it encountered in its milieu would impede the use of evaporative cooling. Daily energy expenditure of both Namib rodents. Was monitored when they were maintained on a low fibre food source (golden millet) and then when this was replaced with a high fibre food source (high-bulk bran). Aethomys namaquensis showed a DEE similar to that predicted by mass and this remained constant, irrespective of the food source or the presence or absence of water. The DEE of G. paeba was more variable. When water was freely available DEE was higher than that predicted by mass and was similar to that predicted for an insectivore of similar body mass. This might reflect its propensity towards an insectivorous diet. When water-stressed on a high fibre diet, DEE of G. paeba declined by half, suggesting that G. paeba employed torpor when conditions were stressful and when the quality of resources was reduced. On a low fibre diet, both species were able to maintain a positive water balance when deprived of water, showing similar reductions in water loss to that of G. pusillus. Low assimilation efficiency and the concomitant increase in faecal water loss precluded the maintenance of a positive water balance when they were fed a high fibre food source. Despite increased urine concentrations and reduced evaporative water loss both species succumbed to chronic water-deprivation. Daily water turnovers and urine concentrating ability was monitored in 17 species of African rodents from arid areas. In general, rodents belonging to the Cricetidae exhibited lower water turnovers and voided smaller volumes of urine at significantly greater concentrations than the murids. All these cricetid rodents were found to produce a crystalline precipitate of allantoin in their urine when water stressed. The quantities of crystalline allantoin excreted were far greater than that expected from purine catabolism and accounted for 30% of the total nitrogenous wastes of the cricetids when deprived of water. It was thought that the substantial quantities of allantoin excreted were responsible for the lower water turnover rates in the cricetids. It is suggested, therefore, when water is limiting, there is a shift in the nitrogen pathway from urea to allantoin, so conferring an eco-physiological advantage to these long term residents of the arid regions of Africa

DNA methylation clocks as a predictor for ageing and age estimation in naked mole-rats, Heterocephalus glaber.

The naked mole-rat, Heterocephalus glaber (NMR), the longest-lived rodent, is of significance and interest in the study of biomarkers for ageing. Recent breakthroughs in this field have revealed 'epigenetic clocks' that are based on the temporal accumulation of DNA methylation at specific genomic sites. Here, we validate the hypothesis of an epigenetic clock in NMRs based on changes in methylation of targeted CpG sites. We initially analysed 51 CpGs in NMR livers spanning an age range of 39-1,144 weeks and found 23 to be significantly associated with age (p<0.05). We then built a predictor of age using these sites. To test the accuracy of this model, we analysed an additional set of liver samples, and were successfully able to predict their age with a root mean squared error of 166 weeks. We also profiled skin samples with the same age range, finding a striking correlation between their predicted age versus their actual age (R=0.93), but which was lower when compared to the liver, suggesting that skin ages slower than the liver in NMRs. Our model will enable the prediction of age in wild-caught and captive NMRs of unknown age, and will be invaluable for further mechanistic studies of mammalian ageing

The First International Mini-Symposium on Methionine Restriction and Lifespan

It has been 20 years since the Orentreich Foundation for the Advancement of Science, under the leadership Dr. Norman Orentreich, first reported that low methionine (Met) ingestion by rats extends lifespan (Orentreich et al., 1993). Since then, several studies have replicated the effects of dietary methionine restricted (MR) in delaying age-related diseases (Richie et al., 1994; Miller et al., 2005; Ables et al., 2012; Sanchez-Roman and Barja, 2013). We report the abstracts from the First International Mini-Symposium on Methionine Restriction and Lifespan held in Tarrytown, NY, September 2013. The goals were (1) to gather researchers with an interest in MR and lifespan, (2) to exchange knowledge, (3) to generate ideas for future investigations, and (4) to strengthen relationships within this community. The presentations highlighted the importance of research on cysteine, growth hormone (GH), and ATF4 in the paradigm of aging. In addition, the effects of dietary restriction or MR in the kidneys, liver, bones, and the adipose tissue were discussed. The symposium also emphasized the value of other species, e.g., the naked mole rat, Brandt's bat, and Drosophila, in aging research. Overall, the symposium consolidated scientists with similar research interests and provided opportunities to conduct future collaborative studies (Figure 3)

Seasonal and daily variation in blood and urine concentrations of free-ranging Angolan free-tailed bats (Mops condylurus) in hot roosts in southern Africa

Urine and plasma concentrations and haematocrits were measured in free-ranging Angolan free-tailed bats (Mops condylurus) inhabiting thermally-challenging roosts in the Komatipoort region of South Africa. Samples were collected in both autumn and summer, from bats caught emerging from roosts before feeding (pre-feed- ing), and those returning after foraging (post-prandial). Post-prandial bats exhibited higher body fluid concentrations, but lower haematocrits, than individuals caught prior to feeding, reflecting raised excretory mineral and nitrogenous loads and replenishment of body water pools during nocturnal foraging. Pre-feeding concentrations of both urine (2637 ± 506 mOsm/kg; n = 16) and plasma (331.5 ± 25.9mOsm/kg; n = 24) were significantly higher in summer than autumn (urine: 2157 ± 454mOsm/kg; n = 8; plasma: 294.5 ± 35.2 mOsm/kg; n = 18) reflecting the greater dehydration stresses within hotter roost microclimates, and a moderate kidney concentrating ability in this species. Haematocrits of pre-feeding animals were not, however, influenced by season and in both instances exceeded 53%, indicative of the higher oxygen carrying capacity needed for sustained flight in volant insectivores and also the defense of the rheologica! properties of blood. The ability of Mops condylurus to withstand a thermally-challenging roost milieu reflects, in part, its tolerance to dehydration, rather than the maintenance of water balance through exceptional renal concentrating ability

Appetite and Energy Intake Responses to Acute Energy Deficits in Females versus Males.

Purpose: To explore whether compensatory responses to acute energy deficits induced by exercise or diet differ by sex. Methods: In experiment one, twelve healthy women completed three 9 h trials (control, exercise-induced (Ex-Def) and food restriction induced energy deficit (Food-Def)) with identical energy deficits being imposed in the Ex-Def (90 min run, ~70% of VO2 max) and Food-Def trials. In experiment two, 10 men and 10 women completed two 7 h trials (control and exercise). Sixty min of running (~70% of VO2 max) was performed at the beginning of the exercise trial. Participants rested throughout the remainder of the exercise trial and during the control trial. Appetite ratings, plasma concentrations of gut hormones and ad libitum energy intake were assessed during main trials. Results: In experiment one, an energy deficit of ~3500 kJ induced via food restriction increased appetite and food intake. These changes corresponded with heightened concentrations of plasma acylated ghrelin and lower peptide YY3-36. None of these compensatory responses were apparent when an equivalent energy deficit was induced by exercise. In experiment two, appetite ratings and plasma acylated ghrelin concentrations were lower in exercise than control but energy intake did not differ between trials. The appetite, acylated ghrelin and energy intake response to exercise did not differ between men and women. Conclusions: Women exhibit compensatory appetite, gut hormone and food intake responses to acute energy restriction but not in response to an acute bout of exercise. Additionally, men and women appear to exhibit similar acylated ghrelin and PYY3-36 responses to exercise-induced energy deficits. These findings advance understanding regarding the interaction between exercise and energy homeostasis in women

Survival tactics within thermally-challenging roosts: heat tolerance and cold sensitivity in the Angolan free-tailed bat, Mops condylurus

We studied roost microclimates, thermal preferences and temperature-related variation in body temperatures and flight abilities of M. condylurus from three roosts in man-made structures in South Africa. Roosts were characterized by marked spatio-temporal variability in ambient temperature and relative humidity on a daily and seasonal basis. Microclimates were thermally challenging, being very hot (&gt;40°C) for several hours daily in summer and autumn, and cold (&lt;10°C) for much of the night in winter Thermal preference tests revealed that the bats actively selected temperature zones (35°- 42°C) in which basal metabolic rate could be maintained, and above the minimum necessary for sustained flight. This presumably allowed them to minimize energy costs of thermoregulation without compromising reproductive activity or their ability to avoid predators. Bats displayed pronounced heat tolerance and hyperthermia in response to prolonged experimental exposure to high temperatures (40°C). They also exhibited cold-sensitivity, characterized by hypothermia and entry into torpor, when exposed to ambient temperatures below the thermal neutral zone. This response to low ambient temperatures would conserve energy in cold periods when the high energetic costs of foraging may not be met owing to reduced insect availability. We hypothesize that this broad roosting tolerance has energetic, ecological and evolutionary benefits that outweigh attendant disadvantages, which are largely compensated for by an unusual physiology

Proteomic profiling of mitochondria: what does it tell us about the ageing brain?

Mitochondrial dysfunction is evident in numerous neurodegenerative and age-related disorders. It has also been linked to cellular ageing, however our current understanding of the mitochondrial changes that occur are unclear. Functional studies have made some progress reporting reduced respiration, dynamic structural modifications and loss of membrane potential, though there are conflicts within these findings. Proteomic analyses, together with functional studies, are required in order to profile the mitochondrial changes that occur with age and can contribute to unravelling the complexity of the ageing phenotype. The emergence of improved protein separation techniques, combined with mass spectrometry analyses has allowed the identification of age and cell-type specific mitochondrial changes in energy metabolism, antioxidants, fusion and fission machinery, chaperones, membrane proteins and biosynthesis pathways. Here, we identify and review recent data from the analyses of mitochondria from rodent brains. It is expected that knowledge gained from understanding age-related mitochondrial changes of the brain should lead to improved biomarkers of normal ageing and also age-related disease progression

Digital dissection of the masticatory muscles of the naked mole-rat, Heterocephalus glaber (Mammalia, Rodentia)

The naked mole-rat, Heterocephalus glaber, of the family Bathyergidae is a subterranean rodent that feeds on underground roots and tubers and digs extensive tunnel systems with its incisors. It is a highly unusual mammal with regard to its social structure, longevity, pain insensitivity and cancer resistance, all of which have made it the subject of a great deal of research in recent years. Yet, much of the basic anatomy of this species remains undocumented. In this paper, we describe the morphology of the jaw-closing musculature of the naked mole-rat, as revealed by contrast-enhanced micro-computed tomography. This technique uses an iodine stain to enable the imaging of soft tissues with microCT. The iodine-enhanced scans were used to create 3D reconstructions of the naked mole-rat masticatory muscles from which muscle masses were calculated. The jaw-closing musculature of Heterocephalus glaber is relatively very large compared to other rodents and is dominated by the superficial masseter, the deep masseter and the temporalis. The temporalis in particular is large for a rodent, covering the entirety of the braincase and much of the rear part of the orbit. The morphology of the masseter complex described here differs from two other published descriptions of bathyergid masticatory muscles, but is more similar to the arrangement seen in other rodent families. The zygomaticomandibularis (ZM) muscle does not protrude through the infraorbital foramen on to the rostrum and thus the naked mole-rat should be considered protrogomorphous rather than hystricomorphous, and the morphology is consistent with secondarily lost hystricomorphy as has been previously suggested for Bathyergidae. Overall, the morphology of the masticatory musculature indicates a species with a high bite force and a wide gape–both important adaptations for a life dominated by digging with the incisors

Preliminary fMRI findings concerning the influence of 5-HTP on food selection

Objective: This functional magnetic resonance imaging study was designed to observe how physiological brain states can alter food preferences. A primary goal was to observe food-sensitive regions and moreover examine whether 5-HTP intake would activate areas which have been associated with appetite suppression, anorexia, satiety, and weight loss. Methods and Procedure: Fourteen healthy male and female participants took part in the study, of which half of them received the supplement 5-HTP and the rest vitamin C (control) on an empty stomach. During the scanning session, they passively observed food (high calories, proteins, carbohydrates) and nonfood movie stimuli. Results: Within the 5-HTP group, a comparison of food and nonfood stimuli showed significant responses that included the limbic system, the basal ganglia, and the prefrontal, temporal, and parietal cortices. For the vitamin C group, activity was mainly located in temporal and occipital regions. Compared to the vitamin C group, the 5-HTP group in response to food showed increased activation on the VMPFC, the DLPFC, limbic, and temporal regions. For the 5-HTP group, activity in response to food high in protein content compared to food high in calories and carbohydrates was located in the limbic system and the right caudomedial OFC, whereas for the vitamin C group, activity was mainly located at the inferior parietal lobes, the anterior cingulate gyri, and the left ventrolateral OFC. Greater responses to carbohydrates and high calorie stimuli in the vitamin C group were located at the right temporal gyrus, the occipital gyrus, the right VLPFC, whereas for the 5-HTP group, activity was observed at the left VMPFC, the parahippocampal gyrus bilaterally, the occipital lobe, and middle temporal gyri. Discussion: In line with the hypotheses, 5-HTP triggered cortical responses associated with healthy body weight as well as cerebral preferences for protein-rich stimuli. The brain’s activity is altered by macronutrients rich or deprived in the body. By reading the organisms physiological states and combining them with memory experiences, it constructs behavioral strategies steering an individual toward or in opposition to a particular food