16.05.2019: Some people would love to rest (stay inactive) straight through the winter – something that hibernators can do every year. The role of body lipid composition on winter hibernation was now examined for the first time in wild brown bears by an international team led by researchers from the University of Strasbourg and the Vetmeduni Vienna. The two most important findings: unsaturated fatty acids play an important role during hibernation and the composition of the fat stores of large hibernating animals is very similar to that of small hibernators.

Hibernating bears lower their body temperature only slightly (2–5°C) to a value between 30°C and 36°C. This is significantly different compared to small hibernators such as alpine marmots or dormice. The lipid composition, however, is very similar in both. In general, hibernators retain polyunsaturated fatty acids (“PUFAs”) in their body fat stores prior to entering torpor, resulting in improved energy savings during hibernation. Although the role of fatty acids has been extensively studied in small hibernating mammals, there has been no systematic study to date of the seasonal changes in lipid composition in large species such as the brown bear.

First scientific study on seasonal lipid shifts in wild brown bears

A recently published study in the leading journal Frontiers in Physiology provides a first detailed examination of the changes in lipid composition of fat stores, muscle and blood plasma of brown bears during winter hibernation. As study author Sylvain Giroud of the Research Institute of Wildlife Ecology at Vetmeduni Vienna’s Department of Integrative Biology and Evolution explains: “The results from our study on wild Scandinavian brown bears (Ursus arctos) strongly suggest that, despite a few differences with regard to other hibernating species, the shift in lipid composition is an evolutionarily conserved phenomenon of hibernation that seems to be independent of body mass and body temperature of the animals.” The analysis of individual lipid moieties, showing the largest changes during hibernation, revealed that membrane fluidity, lipoprotein metabolism, protein conformation (the three-dimensional structure of proteins), and kinase activations were the main pathways targeted by the lipid composition of hibernating bears in winter.

Effect on body functions as a starting point for further studies

According to Giroud, further studies are needed to link lipid composition to specific functions during hibernation in bears. These include, for example, the regulation of the cardiovascular system (such as stabilisation of the heart rate), the induction and maintenance of active metabolic suppression, and the preservation of muscle mass despite inactivity during winter.

First study of its kind of brown bears in their natural environment

The findings represent a unique dataset that assesses, for the first time, the seasonal changes of lipid composition of brown bears in their natural environment. The study was made possible by the participation of the research team from the Scandinavian Brown Bear Research Project (SBBRP). This is the only team in the world that has the experience to capture free-living hibernating brown bears and to study them scientifically in their natural habitat. “This expertise allowed us to study the lipid retention and utilisation of bears during their hibernation period from February to April,” Giroud says.

The article “Lipidomics Reveals Seasonal Shifts in a Large-Bodied Hibernator, the Brown Bear” by Sylvain Giroud, Isabelle Chery, Fabrice Bertile, Justine Bertrand-Michel, Georg Tascher, Guillemette Gauquelin-Koch, Jon M. Arnemo, Jon E. Swenson, Navinder J. Singh, Etienne Lefai, Alina L. Evans, Chantal Simon and Stéphane Blanc was published in Frontiers in Physiology.