An organism-wide atlas of hormonal signaling based on the mouse lemur single-cell transcriptome.

Hormones mediate long-range cell communication and play vital roles in physiology, metabolism, and health. Traditionally, endocrinologists have focused on one hormone or organ system at a time. Yet, hormone signaling by its very nature connects cells of different organs and involves crosstalk of different hormones. Here, we leverage the organism-wide single cell transcriptional atlas of a non-human primate, the mouse lemur (Microcebus murinus), to systematically map source and target cells for 84 classes of hormones. This work uncovers previously-uncharacterized sites of hormone regulation, and shows that the hormonal signaling network is densely connected, decentralized, and rich in feedback loops. Evolutionary comparisons of hormonal genes and their expression patterns show that mouse lemur better models human hormonal signaling than mouse, at both the genomic and transcriptomic levels, and reveal primate-specific rewiring of hormone-producing/target cells. This work complements the scale and resolution of classical endocrine studies and sheds light on primate hormone regulation.

Molecular Liver Fingerprint Reflects the Seasonal Physiology of the Grey Mouse Lemur (Microcebus murinus) during Winter.

Grey mouse lemurs (Microcebus murinus) are primates that respond to environmental energetic constraints through strong physiological seasonality. They notably fatten during early winter (EW), and mobilize their lipid reserves while developing glucose intolerance during late winter (LW), when food availability is low. To decipher how the hepatic mechanisms may support such metabolic flexibility, we analyzed the liver proteome of adult captive male mouse lemurs, whose seasonal regulations are comparable to their wild counterparts. We highlight profound hepatic changes that reflect fat accretion in EW at the whole-body level, without triggering an ectopic storage of fat in the liver, however. Moreover, molecular regulations are consistent with the decrease in liver glucose utilization in LW, and therefore with reduced tolerance to glucose. However, no major regulation was seen in insulin signaling/resistance pathways. Fat mobilization in LW appeared possibly linked to the reactivation of the reproductive system while enhanced liver detoxification may reflect an anticipation to return to summer levels of food intake. Overall, these results show that the physiology of mouse lemurs during winter relies on solid molecular foundations in liver processes to adapt fuel partitioning while opposing the development of a pathological state despite large lipid fluxes.

Profiling torpor-responsive microRNAs in muscles of the hibernating primate Microcebus murinus.

When food scarcity is coupled with decreased temperatures, gray mouse lemurs (Microcebus murinus) depress their metabolic rates and retreat into bouts of either daily torpor or multi-day hibernation, without dramatically dropping body temperatures like other 'traditional hibernators'. Rapid and reversible mechanisms are required to coordinate the simultaneous suppression of energetically expensive processes and activation of pro-survival pathways critical for successful torpor-arousal cycling. MicroRNAs, a class of endogenous non-coding small RNAs, are effective post-transcriptional regulators that modulate all aspects of cellular function. The present study hypothesizes that miRNAs are intimately involved in facilitating the molecular reorganization events necessary for lemur skeletal muscle torpor. Small RNA-Sequencing was used to compare miRNA profiles from skeletal muscles of torpid and control primates. We characterized 234 conserved miRNAs, of which 20 were differentially expressed during torpor, relative to control. Examples included downregulation of key muscle-specific (myomiR) members, miR-1 and miR-133, suggesting a switch to muscle-specific energy-saving strategies. In silico target mapping and logistic regression-based gene set analysis indicated the inhibition of energy costly pathways such as oxidative phosphorylation and muscle proliferation. The suppression of these metabolic pathways was balanced with a lack of miRNA inhibition of various signaling pathways, such as MAPK, mTOR, focal adhesion, and ErbB. This study identifies unique miRNA signatures and 'biomarkers of torpor' that provide us with primate-specific insights on torpor at high body temperatures that can be exploited for human biomedical concerns.

Metabolic and genomic adaptations to winter fattening in a primate species, the grey mouse lemur (Microcebus murinus).

AIM: To understand the mechanisms underlying the development of metabolic changes leading to obesity remains a major world health issue. Among such mechanisms, seasonality is quite underestimated although it corresponds to the manifestation of extreme metabolic flexibility in response to a changing environment. Nevertheless, the changes induced by such flexibility are far to be understood, especially at the level of insulin signaling, genomic stability or inflammation. METHODS: Here, we investigated the metabolic regulations displayed by a seasonal primate species, the grey mouse lemur (Microcebus murinus) that exhibits pronounced changes in body mass during the 6-month winter season: a fattening period followed by a spontaneous fat loss, without ever reaching pathological stages. RESULTS: Such body weight modulations result from a combination of behavioral (food intake) and physiological (endocrine changes, switch between carb and lipid oxidation) adjustments that spontaneously operate during winter. Conversely to classical models of obesity, insulin sensitivity is paradoxically preserved during the obesogenic phase. Fat loss is associated with increased metabolic activity, especially in brown adipose tissue, and induced increased oxidative stress associated with telomere length dynamic. Furthermore, liver gene expression analysis revealed regulations in metabolic homeostasis (beta-oxidation, insulin signaling, cholesterol and lipid metabolism) but not for genes involved in inflammatory process (for example, Ifng, Tnf, Nfkb1). CONCLUSION: Altogether, these results show that mouse lemurs undergo deep physiological and genomic seasonal changes, without ever reaching a pathological stage. Further investigation is needed to decipher the underlying mechanisms, which may well be highly relevant for human therapeutic strategies.

Induction of Antioxidant and Heat Shock Protein Responses During Torpor in the Gray Mouse Lemur, Microcebus murinus.

A natural tolerance of various environmental stresses is typically supported by various cytoprotective mechanisms that protect macromolecules and promote extended viability. Among these are antioxidant defenses that help to limit damage from reactive oxygen species and chaperones that help to minimize protein misfolding or unfolding under stress conditions. To understand the molecular mechanisms that act to protect cells during primate torpor, the present study characterizes antioxidant and heat shock protein (HSP) responses in various organs of control (aroused) and torpid gray mouse lemurs, Microcebus murinus. Protein expression of HSP70 and HSP90α was elevated to 1.26 and 1.49 fold, respectively, in brown adipose tissue during torpor as compared with control animals, whereas HSP60 in liver of torpid animals was 1.15 fold of that in control (P<0.05). Among antioxidant enzymes, protein levels of thioredoxin 1 were elevated to 2.19 fold in white adipose tissue during torpor, whereas Cu-Zn superoxide dismutase 1 levels rose to 1.1 fold in skeletal muscle (P<0.05). Additionally, total antioxidant capacity was increased to 1.6 fold in liver during torpor (P<0.05), while remaining unchanged in the five other tissues. Overall, our data suggest that antioxidant and HSP responses are modified in a tissue-specific manner during daily torpor in gray mouse lemurs. Furthermore, our data also show that cytoprotective strategies employed during primate torpor are distinct from the strategies in rodent hibernation as reported in previous studies.

Regulation of the PI3K/AKT Pathway and Fuel Utilization During Primate Torpor in the Gray Mouse Lemur, Microcebus murinus.

Gray mouse lemurs (Microcebus murinus) from Madagascar present an excellent model for studies of torpor regulation in a primate species. In the present study, we analyzed the response of the insulin signaling pathway as well as controls on carbohydrate sparing in six different tissues of torpid versus aroused gray mouse lemurs. We found that the relative level of phospho-insulin receptor substrate (IRS-1) was significantly increased in muscle, whereas the level of phospho-insulin receptor (IR) was decreased in white adipose tissue (WAT) of torpid animals, both suggesting an inhibition of insulin/insulin-like growth factor-1 (IGF-1) signaling during torpor in these tissues. By contrast, the level of phospho-IR was increased in the liver. Interestingly, muscle, WAT, and liver occupy central roles in whole body homeostasis and each displays regulatory controls operating at the plasma membrane. Changes in other tissues included an increase in phospho-glycogen synthase kinase 3α (GSK3α) and decrease in phospho-ribosomal protein S6 (RPS6) in the heart, and a decrease in phospho-mammalian target of rapamycin (mTOR) in the kidney. Pyruvate dehydrogenase (PDH) that gates carbohydrate entry into mitochondria is inhibited via phosphorylation by pyruvate dehydrogenase kinase (e.g., PDK4). In the skeletal muscle, the protein expression of PDK4 and phosphorylated PDH at Ser 300 was increased, suggesting inhibition during torpor. In contrast, there were no changes in levels of PDH expression and phosphorylation in other tissues comparing torpid and aroused animals. Information gained from these studies highlight the molecular controls that help to regulate metabolic rate depression and balance energetics during primate torpor.

Cytokine and Antioxidant Regulation in the Intestine of the Gray Mouse Lemur (Microcebus murinus) During Torpor.

During food shortages, the gray mouse lemur (Microcebus murinus) of Madagascar experiences daily torpor thereby reducing energy expenditures. The present study aimed to understand the impacts of torpor on the immune system and antioxidant response in the gut of these animals. This interaction may be of critical importance given the trade-off between the energetically costly immune response and the need to defend against pathogen entry during hypometabolism. The protein levels of cytokines and antioxidants were measured in the small intestine (duodenum, jejunum, and ileum) and large intestine of aroused and torpid lemurs. While there was a significant decrease of some pro-inflammatory cytokines (IL-6 and TNF-α) in the duodenum and jejunum during torpor as compared to aroused animals, there was no change in anti-inflammatory cytokines. We observed decreased levels of cytokines (IL-12p70 and M-CSF), and several chemokines (MCP-1 and MIP-2) but an increase in MIP-1α in the jejunum of the torpid animals. In addition, we evaluated antioxidant response by examining the protein levels of antioxidant enzymes and total antioxidant capacity provided by metabolites such as glutathione (and others). Our results indicated that levels of antioxidant enzymes did not change between torpor and aroused states, although antioxidant capacity was significantly higher in the ileum during torpor. These data suggest a suppression of the immune response, likely as an energy conservation measure, and a limited role of antioxidant defenses in supporting torpor in lemur intestine.

Regulation of Torpor in the Gray Mouse Lemur: Transcriptional and Translational Controls and Role of AMPK Signaling.

The gray mouse lemur (Microcebus murinus) is one of few primate species that is able to enter daily torpor or prolonged hibernation in response to environmental stresses. With an emerging significance to human health research, lemurs present an optimal model for exploring molecular adaptations that regulate primate hypometabolism. A fundamental challenge is how to effectively regulate energy expensive cellular processes (e.g., transcription and translation) during transitions to/from torpor without disrupting cellular homeostasis. One such regulatory mechanism is reversible posttranslational modification of selected protein targets that offers fine cellular control without the energetic burden. This study investigates the role of phosphorylation and/or acetylation in regulating key factors involved in energy homeostasis (AMP-activated protein kinase, or AMPK, signaling pathway), mRNA translation (eukaryotic initiation factor 2α or eIF2α, eukaryotic initiation factor 4E or eIF4E, and initiation factor 4E binding protein or 4EBP), and gene transcription (histone H3) in six tissues of torpid and aroused gray mouse lemurs. Our results indicated selective tissue-specific changes of these regulatory proteins. The relative level of Thr172-phosphorylated AMPKα was significantly elevated in the heart but reduced in brown adipose tissue during daily torpor, as compared to the aroused lemurs, implicating the regulation of AMPK activity during daily torpor in these tissues. Interestingly, the levels of the phosphorylated eIFs were largely unaltered between aroused and torpid animals. Phosphorylation and acetylation of histone H3 were examined as a marker for transcriptional regulation. Compared to the aroused lemurs, level of Ser10-phosphorylated histone H3 decreased significantly in white adipose tissue during torpor, suggesting global suppression of gene transcription. However, a significant increase in acetyl-histone H3 in the heart of torpid lemurs indicated a possible stimulation of transcriptional activity of this tissue. Overall, our study demonstrates that AMPK signaling and posttranslational regulation of selected proteins may play crucial roles in the control of transcription/translation during daily torpor in mouse lemurs.

Modulation of Gene Expression in Key Survival Pathways During Daily Torpor in the Gray Mouse Lemur, Microcebus murinus.

A variety of mammals employ torpor as an energy-saving strategy in environments of marginal or severe stress either on a daily basis during their inactive period or on a seasonal basis during prolonged multi-day hibernation. Recently, a few Madagascar lemur species have been identified as the only primates that exhibit torpor; one of these is the gray mouse lemur (Microcebus murinus). To explore the regulatory mechanisms that underlie daily torpor in a primate, we analyzed the expression of 28 selected genes that represent crucial survival pathways known to be involved in squirrel and bat hibernation. Array-based real-time PCR was used to compare gene expression in control (aroused) versus torpid lemurs in five tissues including the liver, kidney, skeletal muscle, heart, and brown adipose tissue. Significant differences in gene expression during torpor were revealed among genes involved in glycolysis, fatty acid metabolism, antioxidant defense, apoptosis, hypoxia signaling, and protein protection. The results showed upregulation of select genes primarily in liver and brown adipose tissue. For instance, both tissues showed elevated gene expression of peroxisome proliferator activated receptor gamma (ppargc), ferritin (fth1), and protein chaperones during torpor. Overall, the data show that the expression of only a few genes changed during lemur daily torpor, as compared with the broader expression changes reported for hibernation in ground squirrels. These results provide an indication that the alterations in gene expression required for torpor in lemurs are not as extensive as those needed for winter hibernation in squirrel models. However, identification of crucial genes with altered expression that support lemur torpor provides key targets to be explored and manipulated toward a goal of translational applications of inducible torpor as a treatment option in human biomedicine.

Primate Torpor: Regulation of Stress-activated Protein Kinases During Daily Torpor in the Gray Mouse Lemur, Microcebus murinus.

Very few selected species of primates are known to be capable of entering torpor. This exciting discovery means that the ability to enter a natural state of dormancy is an ancestral trait among primates and, in phylogenetic terms, is very close to the human lineage. To explore the regulatory mechanisms that underlie primate torpor, we analyzed signal transduction cascades to discover those involved in coordinating tissue responses during torpor. The responses of mitogen-activated protein kinase (MAPK) family members to primate torpor were compared in six organs of control (aroused) versus torpid gray mouse lemurs, Microcebus murinus. The proteins examined include extracellular signal-regulated kinases (ERKs), c-jun NH2-terminal kinases (JNKs), MAPK kinase (MEK), and p38, in addition to stress-related proteins p53 and heat shock protein 27 (HSP27). The activation of specific MAPK signal transduction pathways may provide a mechanism to regulate the expression of torpor-responsive genes or the regulation of selected downstream cellular processes. In response to torpor, each MAPK subfamily responded differently during torpor and each showed organ-specific patterns of response. For example, skeletal muscle displayed elevated relative phosphorylation of ERK1/2 during torpor. Interestingly, adipose tissues showed the highest degree of MAPK activation. Brown adipose tissue displayed an activation of ERK1/2 and p38, whereas white adipose tissue showed activation of ERK1/2, p38, MEK, and JNK during torpor. Importantly, both adipose tissues possess specialized functions that are critical for torpor, with brown adipose required for non-shivering thermogenesis and white adipose utilized as the primary source of lipid fuel for torpor. Overall, these data indicate crucial roles of MAPKs in the regulation of primate organs during torpor.

First evidence for functional vomeronasal 2 receptor genes in primates.

Two classes of vomeronasal receptor genes, V1R and V2R, occur in vertebrates. Whereas, V1R loci are found in a wide variety of mammals, including primates, intact V2R genes have thus far only been described in rodents and marsupials. In primates, the V2R repertoire has been considered degenerate. Here, we identify for the first time two intact V2R loci in a strepsirrhine primate, the grey mouse lemur (Microcebus murinus), and demonstrate their expression in the vomeronasal organ. Putatively functional orthologues are present in two other strepsirrhines, whereas, both loci are pseudogenes in a range of anthropoid species. The functional significance of the loci is unknown, but positive selection on one of them is consistent with an adaptive role in pheromone detection. Finally, conservation of V2R loci in strepsirrhines is notable, given their high diversity and role in MUP and MHC detection in rodents.

Characterization of blood biochemical markers during aging in the Grey Mouse Lemur (Microcebus murinus): impact of gender and season.

BACKGROUND: Hematologic and biochemical data are needed to characterize the health status of animal populations over time to determine the habitat quality and captivity conditions. Blood components and the chemical entities that they transport change predominantly with sex and age. The aim of this study was to utilize blood chemistry monitoring to establish the reference levels in a small prosimian primate, the Grey Mouse Lemur (Microcebus murinus). METHOD: In the captive colony, mouse lemurs may live 10-12 years, and three age groups for both males and females were studied: young (1-3 years), middle-aged (4-5 years) and old (6-10 years). Blood biochemical markers were measured using the VetScan Comprehensive Diagnostic Profile. Because many life history traits of this primate are highly dependent on the photoperiod (body mass and reproduction), the effect of season was also assessed. RESULTS: The main effect of age was observed in blood markers of renal functions such as creatinine, which was higher among females. Additionally, blood urea nitrogen significantly increased with age and is potentially linked to chronic renal insufficiency, which has been described in captive mouse lemurs. The results demonstrated significant effects related to season, especially in blood protein levels and glucose rates; these effects were observed regardless of gender or age and were likely due to seasonal variations in food intake, which is very marked in this species. CONCLUSION: These results were highly similar with those obtained in other primate species and can serve as references for future research of the Grey Mouse Lemur.

Fatty acid composition of the brain, retina, liver and adipose tissue of the grey mouse lemur (Microcebus murinus, primate).

The particular interest in supplementing human foods with n-3 fatty acids has arisen from the findings that this series of polyunsaturated fatty acids (PUFA) have an impact on neuronal functions. Indeed vertebrates, including humans, preferentially use docosahexaenoic acid (DHA, 22:6n-3) over other long-chain n-3 PUFA for the genesis of their neuronal and retinal membranes. The grey mouse lemur is a nocturnal prosimian primate originating from Madagascar. The increased use of this omnivorous primate in nutritional studies (chronic caloric restriction, n-3 fatty acids supplementation), justifies the interest of determining their fatty acids body composition. In the present study, we report the fatty acid composition in lipid classes from the main target tissues (brain, retina, liver and adipose tissue) of six adult mouse lemurs raised under laboratory nutritional conditions. Among the main findings, n-6-docosapentaenoic acid (n-6-DPA; 22:5n-6) is very low in the brain cortex and retina, whereas there is a very high accumulation of docosahexaenoic acid (DHA, 22:6n-3) in the neural tissues compared to liver and plasma. In particular, DHA accounts for about one half of the total fatty acids in the retina ethanolamine glycerophospholipids. This high concentration clearly indicates that DHA is efficiently transferred from blood lipids to the outer segment of the mouse lemur retina. We conclude that the mouse lemur n-3 PUFA metabolism efficiently drives DHA to neural tissues, through the blood-brain barrier and the blood-retina barrier.

Distribution of lithostathine in the mouse lemur brain with aging and Alzheimer's-like pathology.

We analyzed the cellular distribution of the pancreatic inflammatory protein lithostathine and its receptor EXTL3 in the brain of the lemurian primate Microcebus murinus which develops amyloid deposits along with aging. In adult animals (2-4.5 years old), lithostathine and EXTL3 immunoreactivities were largely distributed in the whole brain, and more intensively in almost all cortical layers and hippocampal formation. Lithostathine was observed in the perikarya and neurites of cortical neurons but also in glial cells in the border of the ventricle and the corpus callosum. In healthy aged animals (8-13 years old), highest densities of lithostathine-containing cells were observed, mainly in occipital and parietal cortex. In aged animals with Aß deposits, the increase in lithostathine immunoreactivity was lower as compared with aged animals. Noteworthy, lithostathine-immunopositive cells did almost never colocalize with Aß plaques. In conclusion, lithostathine immunoreactivity in adult Microcebus murinus appeared ubiquitous and particularly in visual, sensorial, and cognitive brain areas. Immunoreactivity increased with aging and appeared markedly affected in neuropathological conditions. Its possible neuroprotection or neurodegeneration role in Alzheimer pathology deserves therefore to be investigated.

Torpor use during gestation and lactation in a primate.

Torpor is an energy-saving mechanism that allows endotherms to overcome energetic challenges. Torpor should be avoided during reproduction because of potential incompatibility with offspring growth. To test if torpor can be used during gestation and lactation to compensate for food shortage, we exposed reproductive female grey mouse lemurs (Microcebus murinus), a heterothermic primate, to different levels of food availability. Torpor use was characterised by daily skin temperature profiles, and its energetic outcome was assessed from changes in body mass. Food shortage triggered torpor during the end of the gestation period (n = 1), ranging from shallow in response to 40% food restriction to deep daily torpor in response to 80% restriction. During the early period of lactation, females fed ad libitum (n = 2) or exposed to a 40% restriction (n = 4) remained normothermic; but 80% food restricted females (n = 5) gave priority to energy saving, increasing the frequency and depth of torpor bouts. The use of torpor was insufficient to compensate for 80% energetic shortage during lactation resulting in loss of mass from the mother and delayed growth in the pups. This study provides the first evidence that a heterothermic primate can use torpor to compensate for food shortages even during reproduction. This physiological flexibility likely evolved as a response to climate-driven fluctuations in food availability in Madagascar.

The development of small primate models for aging research.

Nonhuman primate (NHP) aging research has traditionally relied mainly on the rhesus macaque. But the long lifespan, low reproductive rate, and relatively large body size of macaques and related Old World monkeys make them less than ideal models for aging research. Manifold advantages would attend the use of smaller, more rapidly developing, shorter-lived NHP species in aging studies, not the least of which are lower cost and the ability to do shorter research projects. Arbitrarily defining "small" primates as those weighing less than 500 g, we assess small, relatively short-lived species among the prosimians and callitrichids for suitability as models for human aging research. Using the criteria of availability, knowledge about (and ease of) maintenance, the possibility of genetic manipulation (a hallmark of 21st century biology), and similarities to humans in the physiology of age-related changes, we suggest three species--two prosimians (Microcebus murinus and Galago senegalensis) and one New World monkey (Callithrix jacchus)--that deserve scrutiny for development as major NHP models for aging studies. We discuss one other New World monkey group, Cebus spp., that might also be an effective NHP model of aging as these species are longer-lived for their body size than any primate except humans.

Distinct transcriptome expression of the temporal cortex of the primate Microcebus murinus during brain aging versus Alzheimer's disease-like pathology.

Aging is the primary risk factor of neurodegenerative disorders such as Alzheimer's disease (AD). However, the molecular events occurring during brain aging are extremely complex and still largely unknown. For a better understanding of these age-associated modifications, animal models as close as possible to humans are needed. We thus analyzed the transcriptome of the temporal cortex of the primate Microcebus murinus using human oligonucleotide microarrays (Affymetrix). Gene expression profiles were assessed in the temporal cortex of 6 young adults, 10 healthy old animals and 2 old, "AD-like" animals that presented ß-amyloid plaques and cortical atrophy, which are pathognomonic signs of AD in humans. Gene expression data of the 14,911 genes that were detected in at least 3 samples were analyzed. By SAM (significance analysis of microarrays), we identified 47 genes that discriminated young from healthy old and "AD-like" animals. These findings were confirmed by principal component analysis (PCA). ANOVA of the expression data from the three groups identified 695 genes (including the 47 genes previously identified by SAM and PCA) with significant changes of expression in old and "AD-like" in comparison to young animals. About one third of these genes showed similar changes of expression in healthy aging and in "AD-like" animals, whereas more than two thirds showed opposite changes in these two groups in comparison to young animals. Hierarchical clustering analysis of the 695 markers indicated that each group had distinct expression profiles which characterized each group, especially the "AD-like" group. Functional categorization showed that most of the genes that were up-regulated in healthy old animals and down-regulated in "AD-like" animals belonged to metabolic pathways, particularly protein synthesis. These data suggest the existence of compensatory mechanisms during physiological brain aging that disappear in "AD-like" animals. These results open the way to new exploration of physiological and "AD-like" aging in primates.

Non-shivering thermogenesis activation and maintenance in the aging gray mouse lemur (Microcebus murinus).

The cold-induced enhancement of non-shivering thermogenesis (NST), involving brown-adipose tissue (BAT) metabolism, could participate to impair energy balance in the aged gray mouse lemur (Microcebus murinus). We first investigated the age-related modulations of cold-stimulated BAT cell morphology and contents. Then, NST was pharmacologically stimulated to assess whether aging impaired NST activation in the mouse lemur. In reference conditions, the ability to activate NST was preserved during aging in the mouse lemur as BAT morphology and UCP-1 presence did not differ between adult and aged mouse lemurs. Also, the pharmacological activation of NST revealed similar increased levels of O(2) consumption in adult and aged animals, confirming that no age effect could be evidenced on NST activation at 25 degrees C. However, preliminary histological data revealed a lack of lipid resources in one aged individual during cold exposure. Surprisingly, the pharmacological activation of NST revealed an impaired evacuation of the excess body heat in aged animals, associated with increased energy expenditure. Thus, aging seems to be related to decreased capacities in the maintenance of NST rather than in its activation. Energy mobilization could be impaired in the aging mouse lemur but remains to be demonstrated.

The grey mouse lemur uses season-dependent fat or protein sparing strategies to face chronic food restriction.

During moderate calorie restriction (CR) the heterotherm Microcebus murinus is able to maintain a stable energy balance whatever the season, even if only wintering animals enter into torpor. To understand its energy saving strategies to respond to food shortages, we assessed protein and energy metabolisms associated with wintering torpor expression or summering torpor avoidance. We investigated body composition, whole body protein turnover, and daily energy expenditure (DEE), during a graded (40 and 80%) 35-day CR in short-days (winter; SD40 and SD80, respectively) and long-days (summer; LD40 and LD80, respectively) acclimated animals. LD40 animals showed no change in fat mass (FM) but a 12% fat free mass (FFM) reduction. Protein balance being positive after CR, the FFM loss was early and rapid. The 25% DEE reduction, in LD40 group was mainly explained by FFM changes. LD80 animals showed a steady body mass loss and were excluded from the CR trial at day 22, reaching a survival-threatened body mass. No data were available for this group. SD40 animals significantly decreased their FM level by 21%, but maintained FFM. Protein sparing was achieved through a 35 and 39% decrease in protein synthesis and catabolism (protein turnover), respectively, overall maintaining nitrogen balance. The 21% reduction in energy requirement was explained by the 30% nitrogen flux drop but also by torpor as DEE FFM-adjusted remained 13% lower compared to ad-libitum. SD80 animals were unable to maintain energy and nitrogen balances, losing both FM and FFM. Thus summering mouse lemurs equilibrate energy balance by a rapid loss of active metabolic mass without using torpor, whereas wintering animals spare protein and energy through increased torpor expression. Both strategies have direct fitness implication: 1) to maintain activities at a lower body size during the mating season and 2) to preserve an optimal wintering muscle mass and function.

Plasma levels of interferon-gamma correlate with age-related disturbances of circadian rhythms and survival in a non-human primate.

Aging can be associated with changes in circadian rhythms and reduction in adaptive immune responses accompanied by expansion of memory T cells and elevated levels of pro-inflammatory cytokines. Recent findings suggest the cytokine interferon-gamma (IFN-gamma) can affect the function of the hypothalamic suprachiasmatic nucleus (SCN), the master mammalian circadian pacemaker, both in vitro and in vivo. We studied the correlation of plasma levels of IFN-gamma and changes in circadian rhythms in a non-human primate species, the nocturnal mouse lemur (Microcebus murinus). Plasma IFN-gamma and dehydroepiandrosterone sulfate (DHEA-S), a known biomarker of aging, were determined in middle- to old-age animals by immunoenzymoassay. Daily rhythms of locomotor activity and body temperature as well as survival time of the lemurs were recorded. With aging, mean levels of DHEA-S decreased whereas IFN-gamma increased. Aged animals showed biological rhythm alterations characterized by a high percentage of diurnal activity, anticipation of the activity onset relative to lights-off, short free-running period, and delayed occurrence of minimal body temperature. The magnitude of these disturbances was correlated with the plasma level of IFN-gamma but not DHEA-S. Most remarkably, in contrast to DHEA-S, increased levels of IFN-gamma correlated with duration of the lifetime of the lemurs. These results show the degree of circadian rhythm alterations in an individual is correlated with plasma IFN-gamma level during aging, and that plasma IFN-gamma level may predict survival, at least in this non-human primate.