Abstract
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.
Highlights
A variety of small mammals use torpor to reduce energy expenditures and enhance survival during inactive parts of the day especially when faced with stressful conditions
Data collected from free-ranging gray mouse lemurs show that daily torpor bouts are several hours in duration with a minimum Tb of $27 °C whereas hibernation bouts in this species can last up to 4 weeks with a minimum Tb of 11.5 °C [16]
Studies on little brown bats have demonstrated the susceptibility of this species to white nose disease during hibernation, suggesting a depressed or unresponsive systemic immune response [17,18,19,20,21,22,23]
Summary
A variety of small mammals use torpor to reduce energy expenditures and enhance survival during inactive parts of the day especially when faced with stressful conditions (e.g., nutrient or water limitation, or low ambient temperatures). The gray mouse lemur (Microcebus murinus) uses daily torpor cycles during the dry season as an energy conservation mechanism, which is thought to be related to the extreme fluctuations of the resource availability in the seasonally-arid regions of Madagascar where this species inhabits [1,2]. Lemurs exhibit low resting metabolic rates and can further reduce their basal metabolic rate to 20%–30% of their euthermic counterparts by entering torpor, thereby conserving significant amounts of fuel and energy [2,3,4,5]. The reallocation of energy resources toward essential metabolic processes may create energy deficits in other ‘‘non-essential’’ physiological processes, such as the activity of immune system
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