Emerging evidence has linked the gut microbiome to human obesity. We performed a metagenome-wide association study and serum metabolomics profiling in a cohort of lean and obese, young, Chinese individuals. We identified obesity-associated gut microbial species linked to changes in circulating metabolites. The abundance of Bacteroides thetaiotaomicron, a glutamate-fermenting commensal, was markedly decreased in obese individuals and was inversely correlated with serum glutamate concentration. Consistently, gavage with B. thetaiotaomicron reduced plasma glutamate concentration and alleviated diet-induced body-weight gain and adiposity in mice. Furthermore, weight-loss intervention by bariatric surgery partially reversed obesity-associated microbial and metabolic alterations in obese individuals, including the decreased abundance of B. thetaiotaomicron and the elevated serum glutamate concentration. Our findings identify previously unknown links between intestinal microbiota alterations, circulating amino acids and obesity, suggesting that it may be possible to intervene in obesity by targeting the gut microbiota.
Obesity occurs when excess energy accumulates in white adipose tissue (WAT), whereas brown adipose tissue (BAT), specialized for energy expenditure through thermogenesis, potently counteracts obesity. Factors that induce brown adipocyte commitment and energy expenditure would be a promising defence against adiposity. Here, we show that Lgr4 homozygous mutant (Lgr4(m/m)) mice show reduced adiposity and resist dietary and leptin mutant-induced obesity with improved glucose metabolism. Lgr4(m/m) mice show a striking increase in energy expenditure, and exhibit brown-like adipocytes in WAT depots with higher expression of BAT and beige cell markers. Furthermore, Lgr4 ablation potentiates brown adipocyte differentiation from the stromal vascular fraction of epididymal WAT, partially through retinoblastoma 1 gene (Rb1) reduction. A functional low-frequency human LGR4 variant (A750T) has been associated with body mass index in a Chinese obese-versus-control study. Our results identify an important role for LGR4 in energy balance and body weight control through regulating the white-to-brown fat transition.
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