Thermoregulatory Adaptations
Credit: Wiki
Thermogenesis in endotherms does not only occur via shivering or activity, but also via non-shivering thermogenesis (NST). Mammalian NST is mediated by the uncoupling protein 1 in the brown adipose tissue (BAT) and possibly involves an additional mechanism of NST in skeletal muscle.
This alternative mechanism is based on Ca2+-slippage by a sarcoplasmatic reticulum Ca2+-ATPase (SERCA) and is controlled by the protein sarcolipin. The existence of muscle based NST has been discussed for a long time and is likely present in all mammals.
In this series of projects, we aim at investigating the role and implication of muscle NST in enabling endothermic species to maintain relatively high core body temperature independently of environmental contraints.
The main collaborations for the development of this research projects include Prof Walter Arnold (Vetmeduni Vienna), Prof Lars Folkow (Arctic University of Norway), Prof Thomas Ruf (Vetmeduni Vienna), and Dr Julia Nowack (Liverpool John Moores University). This research is conducted on species on contrasted body size and individuals of different life stages.
Role of Muscle Non-Shivering Thermogenesis During Development
Credit: Wiki
Mechanisms for muscle non-shivering thermogenesis in the Hooded seal
In Collaboration with the Department of Arctic and Marine Biology at the Arctic University of Norway
Hooded seals (Cystophora cristata) are marine mammals and are characterised as an “Arctic seal” species due to their close association to the pack ice. Their relationship with the ice and water creates challenges in maintaining an internal body temperature of ~37°C. In homeothermic animals, such as the hooded seal, shivering is used for thermogenesis, however this can rapidly fatigue skeletal muscle. Other mechanisms of thermogenesis have been found which do not employ the use of shivering thermogenesis and are termed non-shivering thermogenesis (NST) mechanisms.
A common area of NST study is the thermogenic mechanism found in brown adipose tissue (BAT). The presence of BAT in mammals is common, particularly in the neonatal life stages where surface area to volume ratio is high and is noticeably present in other seal species e.g. harp seals, which share the same distribution and environmental hardships as hooded seals. However, the presence of BAT has not been reported in hooded seals.
Interestingly, studies in other species have shown that in the absence of BAT, skeletal muscle tissue can be utilised in a non-shivering mechanism using an interaction between Sarcolipin (SLN) and Ca2+ ATPase (SERCA) transport protein that produces futile cycling of Ca2+, as well as through a decreased efficiency in mitochondrial processes known as mitochondrial proton LEAK.
This project aims at determining whether hooded seals utilise these skeletal muscle based, non-shivering thermogenesis mechanisms and whether those mechanisms are most likely to be found during early life stages compared to adult stages.
Implication of Muscle Non-Shivering Thermogenesis During Torpor
Credit: S. Giroud
Credit: B. Mahlert
Regional body temperatures and fatty acid compositions in hibernating garden dormice: a focus on cardiac adaptations
Master thesis of Sandra Stickler at the Research Institute of Wildlife Ecology, Vetmeduni Vienna [2020-2022]
Torpor is known to entail a controlled reduction of body temperature, metabolic rate, heart rate, and other physiological functions, while omega fatty acids play a major role in adaptation of tissues to changes in temperatures.
This study investigated differences in body temperatures across different regions, e.g., mouth, heart, white adipose tissue and leg in relation to the fatty acid profile of the corresponding tissues or organelles in the garden dormouse, Eliomys quercinus, during torpor and interbout euthermia (IBE). We further determined the effects of specific fatty acids on the cardiac function by relating the fatty acid composition of the sarcoplasmic reticulum (SR) phospholipid membrane to the activity of SR Ca2+ ATPase 2a (SERCA2a) and determined SERCA2a quantity during torpor and IBE.
We found significant differences among regional body temperatures within the states. In comparison to the other organs, the heart showed the warmest temperature with 10°C vs. 2°C of core body (abdominal) temperature during torpor, emphasizing the importance of a maintained cardiac function during hibernation.
These findings strongly suggest a potential role of muscle non-shivering thermogenesis for local heat generation in the cardiac muscle during the torpid state of reduced body temperatures.