The Hibernation Continuum: Physiological and Molecular Aspects of Metabolic Plasticity in Mammals

Abstract

Mammals are often considered to be masters of homeostasis, with the ability to maintain a constant internal milieu, despite marked changes in the environment; however, many species exhibit striking physiological and biochemical plasticity in the face of environmental fluctuations. Here, we review metabolic depression and body temperature fluctuation in mammals, with a focus on the extreme example of hibernation in small-bodied eutherian species. Careful exploitation of the phenotypic plasticity of mammals with metabolic flexibility may provide the key to unlocking the molecular secrets of orchestrating and surviving reversible metabolic depression in less plastic species, including humans.

Modelling mammalian energetics: the heterothermy problem

“…When attempting to model how a species will respond to changes in climate, it is important to have an understanding of how often, and for how long, they will be able to employ torpor. For a species with readily predictable torpor bout lengths and hibernation seasons of a set length, such as the Holarctic ground squirrels (family Sciuridae, tribe Marmotini, [142]), this would often cover the winter months only (eg. [143]), although this may also change based on latitude or local climate conditions [144,145].…”

Nature's fat-burning machine: brown adipose tissue in a hibernating mammal

“…Although global suppression of mRNA transcription occurs during torpor (Morin and Storey, 2009;Storey and Storey, 2004;van Breukelen and Martin, 2002; as reviewed by van Breukelen and Martin, 2015), it was initially suggested that BAT might be an exception to the general observation of arrested translation given that polyribosomes appeared to remain intact and protein synthesis may continue during torpor (Hittel and Storey, 2002). However, there is now evidence for general suppression of transcription in the BAT of hibernating thirteen-lined ground squirrels via low T b during 2-week torpor periods and the action of epigenetic controls .…”

“…Specifically, inhibitory transcriptional controls largely remain in place during the arousal phase of the torpor cycle and general reactivation of gene expression can occur during IBA . Thus, transcription is needed to sustain the thermogenic function of BAT and replenish proteins that are damaged during longer term torpor ; as reviewed by van Breukelen and Martin, 2015). Moreover, BAT microRNAs were assessed during torpor in thirteen-lined ground squirrels and those with altered expression were linked to β-oxidation (Wu et al, 2014).…”

Living in a seasonal world: 15th international hibernation symposium

“…For instance, virtually, all hibernators experience periodic rewarming. More recent work demonstrates some tropical species that avoid use of periodic rewarming (tenrecs and dwarf lemurs in certain situations; reviewed in van Breukelen and Martin 2015). Inclusion of the Austral and tropical hibernators may provide a new mechanistic insight that will challenge our biases regarding the evolution of hibernation, the use of periodic rewarming, and even the role of abiotic factors such as fire in promoting torpor use.…”