When exposed to cold temperatures, you begin shivering to compensate for the sudden temperature decrease. Biologically, exposure to cold environment can induce brown adipose tissue differentiation and catabolism of lipids to produce heat. The gastrointestinal tract is an important site for the regulation of our energy metabolism, and as we know, harbors a diverse population of gut bacteria. A team of researchers sought to investigate what role the microbiome of mice plays in induction of physiological changes to cold exposure.
The researchers exposed different groups of mice to cold temperatures for 31 days, and the initial observation was attenuation of energy expenditure and white fat. Importantly, food intake was consistent throughout the trial, pointing to a temperature-driven effect. Fecal collection and post-mortem intestinal analysis revealed marked shifts in microbiota compositions of cold-exposed mice as compared to those kept at room temperature. Notably, families within Actinobacteria, Verrucomicrobia, and Tenericutes were less abundant in the cold sample mice, and Akkermansia muciniphila species were observed to be significantly decreased in the cold mice. The researchers also transplanted microbiota from cold-group mice to naïve, germ-free mice. Upon cold temperature exposure, germ-free mice demonstrated heightened insulin sensitivity, browning of white fat, increased energy expenditure, and white fat loss, indicative of a tolerance to the cold. Prolonged cold exposure in both cold-exposed and cold-transplanted mice also induced adaptive biological mechanisms in intestinal villi and microvilli to maximize caloric uptake, ultimately attenuating weight loss. This increase in intestinal absorption was observed concomitant to altered intestinal gene expression, as genes that promote tissue remodeling where upregulated while apoptotic genes were suppressed. In a final experiment, the aforementioned effect was reduced when Akkermansia muciniphila (which were originally observed to decrease in cold-induced mice) were transplanted to cold-exposed mice, supporting a microbiota-driven relationship.
This was a very interesting study that sheds lights on organismal adaptive mechanisms during energy scarcity brought on by factors such as cold temperatures. Again we observe heavy involvement of the microbiome in these processes, a finding that calls for more investigation.