Cecal microbial transplantation attenuates hyperthyroid-induced thermogenesis in Mongolian gerbils

Abstract

Endothermic mammals have a high energy cost to maintain a stable and high body temperature (T_b , around 37°C). Thyroid hormones are a major regulator for energy metabolism and T_b . 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 T_b . l-thyroxine-induced hyperthyroid Mongolian gerbils (Meriones unguiculatus) increased resting metabolic rate (RMR) and T_b , 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 T_b . 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 T_b in endotherms.

Fig. 1

Metabolic phenotypes and metabolites in the hyperthyroid (Hyper), hypothyroid (Hypo) and control gerbils. A. Food intake. B. Resting metabolic rate (RMR), maximum nonshivering thermogenesis (NST_max) and regulatory NST (NST_reg). C, D. Average core body temperature (T_b ) and activity during the experiment (n = 5 per group). E, F. The expression of type 2 deiodinase (DIO2) in the liver, measured by Western blot (WB) and ELISA. G. The levels of total bile acids in serum. H, I. The concentrations of faecal short‐chain fatty acids (SCFAs). Data are presented as means ± SEM (n = 7‐8 per group, except T_b and activity). *P < 0.05, Hyper vs Control. Different letters above columns indicate significant differences among groups (P < 0.05).

Fig. 2

Thyroid hormone treatments shape bacterial composition. A. Principal coordinate analyses (PCoA) plots based on unweighted and weighted UniFrac distances in faecal microbiota of different groups (unweighted, ANOSIM, R = 0.319, P = 0.001; weighted, ANOSIM, R = 0.212, P = 0.011). The ellipses cover 68% of the data for each group. B. Relative abundance of different bacteria at the phylum and genus levels (‘+’indicates the mean of data). C Differential bacterial taxonomy selected by LEfSe analysis with LDA score > 2 in the faecal microbiota community (Differences between groups are represented by the colour of the most abundant class). D. Venn diagram based on OTUs distribution between groups. E. Heatmap of correlation between specific OTUs and physiological parameters. Data are presented as means ± SEM (n = 7‐8 per group). Different letters above columns indicate significant differences among groups (P < 0.05). Hyper, hyperthyroid; Hypo, hypothyroid.

Fig. 3

Gut microbiota buffer hyperthyroidism‐induced hyperphagia and hypermetabolism. A. Schematic overview of experimental design. B. Food intake in different groups during the experiment. C. Resting metabolic rate (RMR) of every group during the experimental period. D. Average core body temperature (T_b ) of gerbils from different groups. E, F. Serum tri‐iodothyronine (T3) and thyroxine (T4) levels. G, H. Type 2 deiodinase (DIO2) by Western blot (WB) and ELISA. Values are means ± SEM (n = 5 per group). *P < 0.05, Hyper versus Con. # P < 0.05, Hyper‐Con versus Con. + P < 0.05, Hyper‐Con versus Hyper. CMT, caecal microbiota transplantation; Hyper‐Con, Hyper gerbils were colonized with control microbiota; Hyper, Hyper gerbils with sterile saline; Con‐Hyper, control gerbils were colonized with Hyper microbiota; Con, control gerbils with sterile saline.

Fig. 4

Caecal microbiota transplantation (CMT) alters faecal microbiota composition in hyperthyroid gerbils. A. Phylogenetic diversity (PD)—whole tree analysis for the samples. B. Principal coordinate analyses (PCoA) plots based on unweighted and weighted UniFrac distances in faecal microbiota of different groups (unweighted, ANOSIM, R = 0.181, P = 0.005; weighted, ANOSIM, R = 0.083, P = 0.817). C. Relative abundance at the phylum levels in faecal microbiota community one week after CMT in each individual animal of the four groups. D. The relative abundance of different bacteria at the phylum and genus levels in different experimental groups at week 1 after CMT. E. The relative abundance of some specific bacteria in different experimental groups before (week 0) and after CMT (weeks 1 and 6). Data are presented as means ± SEM (n = 5 per group). Different letters above columns indicate significant differences among groups (P < 0.05). Hyper‐Con, Hyper gerbils were colonized with control microbiota; Hyper, Hyper gerbils with sterile saline; Con‐hyper, control gerbils were colonized with hyper microbiota; Con, control gerbils with sterile saline.

Fig. 5

Caecal microbiota transplantation (CMT) did not affect metabolic traits in hypothyroid or control gerbils. A. Schematic overview of experimental design. B. Body mass. C. Food intake. D. Resting metabolic rate (RMR). E. Serum tri‐iodothyronine (T3) levels. Values are means ± SEM (n = 5 per group). *P < 0.05, Hypo versus Con. Hypo‐Con, Hypo gerbils were colonized with control microbiota; Hypo, Hypo gerbils with sterile saline; Con‐hypo, control gerbils were colonized with hypo microbiota; Con, control gerbils with sterile saline.