Endothermic mammals have a high energy cost to maintain a stable and high body temperature (Tb , around 37°C).
Thyroid hormones are a major regulator for energy metabolism and Tb . The gut microbiota is involved in modulating host energy metabolism. However, whether the interaction between the gut microbiota and
thyroid hormones is involved in metabolic and thermal regulations is unclear. We hypothesized that
thyroid hormones via an interaction with gut microbiota orchestrate host thermogenesis and Tb .
l-thyroxine-induced
hyperthyroid Mongolian gerbils (Meriones unguiculatus) increased resting metabolic rate (RMR) and Tb , whereas
Methimazole-induced hypothyroid animals decreased RMR. Both hypothyroid and
hyperthyroid animals differed significantly in faecal bacterial community.
Hyperthyroidism increased the relative abundance of pathogenic bacteria, such as Helicobacter and Rikenella, and decreased abundance of beneficial bacteria Butyricimonas and Parabacteroides, accompanied by reduced total
bile acids and
short-chain fatty acids. Furthermore, the
hyperthyroid gerbils transplanted with the microbiota from control donors increased type 2
deiodinase (DIO2) expression in the liver and showed a greater rate of decline of both serum T3 and T4 levels and, consequently, a more rapid recovery of normal RMR and Tb . These findings indicate that
thyroid hormones regulate thermogenesis depending on gut microbiota and colonization with normal microbiota by caecal microbial
transplantation attenuates hyperthyroid-induced thermogenesis. This work reveals the functional consequences of the gut microbiota-thyroid axis in controlling host metabolic physiology and Tb in endotherms.