Mitochondrial metabolism in hibernation and daily torpor: a review

Abstract

Hibernation and daily torpor involve substantial decreases in body temperature and metabolic rate, allowing birds and mammals to cope with cold environments and/or limited food. Regulated suppression of mitochondrial metabolism probably contributes to energy savings: state 3 (phosphorylating) respiration is lower in liver mitochondria isolated from mammals in hibernation or daily torpor compared to normothermic controls, although data on state 4 (non-phosphorylating) respiration are equivocal. However, no suppression is seen in skeletal muscle, and there is little reliable data from other tissues. In both daily torpor and hibernation, liver state 3 substrate oxidation is suppressed, especially upstream of electron transport chain complex IV. In hibernation respiratory suppression is reversed quickly in arousal even when body temperature is very low, implying acute regulatory mechanisms, such as oxaloacetate inhibition of succinate dehydrogenase. Respiratory suppression depends on in vitro assay temperature (no suppression is evident below approximately 30 degrees C) and (at least in hibernation) dietary polyunsaturated fats, suggesting effects on inner mitochondrial membrane phospholipids. Proton leakiness of the inner mitochondrial membrane does not change in hibernation, but this also depends on dietary polyunsaturates. In contrast proton leak increases in daily torpor, perhaps limiting reactive oxygen species production.

Are long chain acyl CoAs responsible for suppression of mitochondrial metabolism in hibernating 13-lined ground squirrels?

“…So although the reduction in T b will depress biochemical reaction rates, it is active suppression of metabolism that initiates and maintains very low MR in torpor. In fact it has been estimated that active suppression accounts for as much as 40-70% of the decrease in MR observed in hibernation (reviewed in Staples and Brown, 2008). Although there have been many attempts to elucidate and understand the suppression of MR observed during torpor, the mechanisms driving suppression remains unclear.…”

“…Arousal from a torpor bout occurs spontaneously: MR rapidly increases and T b is returned to euthermic levels (~37°C) via shivering and non-shivering thermogenesis (reviewed in Staples and Brown, 2008). These brief periods of intense metabolic activity consume ~80% of the energy used throughout the hibernation season (Heldmaier et al, 1993;Wang, 1978;Wang, 1979), however the reason they occur remains unknown.…”

“…The suppression of MR as a hibernator concludes a period of IBE and enters a bout of torpor is known as 'entrance', and involves active inhibition of metabolism in addition to passive thermal effects due to decreasing T b (Geiser, 2004;Staples and Brown, 2008).…”

“…Other strategies aim to avoid the stress altogether, such as migrating to warmer, calorie-rich environments (Hill et al, 2008). An alternate approach to seasonal survival is to reduce energy demands by decreasing MR and, consequently T b , in a process known as hibernation (Reviewed in: Staples and Brown, 2008).…”

On a Hibernation Plankton-Nutrient Chemostat Model with Delayed Response in Growth

“…By hibernation, animals can reduce energy requirement and survive a few months in [10]. Some scholars also proposed that hibernation can make animals through hardship on cold environments and limited availability of food in [11]. However, there are many factors of plankton movements in the lakes, such as currents and river diffusion.…”