Regulation of host weight gain and lipid metabolism by bacterial bile acid modification in the gut

Alterations in the gastrointestinal microbiota have been implicated in obesity in mice and humans, but the conserved microbial functions that influence host energy metabolism and adiposity have not been determined. Here we show that bacterial bile salt hydrolase (BSH) controls a microbe-host dialogue which functionally regulates host lipid metabolism and weight gain. Expression of cloned BSH enzymes in the GI tract of gnotobiotic or conventional mice significantly altered plasma bile acid signatures and regulated transcription of key genes involved in lipid metabolism (PPARgamma angptl4), cholesterol metabolism (abcg5/8), gastrointestinal homeostasis (regIIIgamma) and circadian rhythm (dbp, per1/2) in the liver or small intestine. High-level expression of BSH in conventionally raised mice resulted in significant reduction of host weight-gain, plasma cholesterol and liver triglycerides. We demonstrate that bacterial BSH activity significantly impacts systemic metabolic processes and adiposity in the host, and represents a key mechanistic target for the control of obesity and hypercholesterolaemia.