The Role of Bile Salt Hydrolase in Glucose Metabolism

PROJECT SUMMARY/ABSTRACT Currently, 34.2 million US adults, or approximately 10.3% of the total population, have diabetes. The prevalence of diabetes is two-fold higher among Veterans (20.5%) and it is the leading cause of kidney failure, lower-limb amputations, and adult-onset blindness both in Veterans and the general population. Over the last two decades, multiple metabolic studies have demonstrated that bile acids play an unexpected but important role in glucose homeostasis and metabolic syndrome. Correlational 16S and metagenomic studies suggest that gut microflora can affect host glucose homeostasis through modification of bile acids. The overall goal of this proposal is to determine the mechanisms by which the gut microflora affect host glucose homeostasis. To have a better functional understanding of this relationship, investigators need to assess the role of specific bacterial bile acid biotransformations and investigate their effects on the gut luminal ecology, the flux of metabolites and nutrients, and ultimately, physiology in conventionally-raised (as opposed to microbiome-depleted) hosts. Thus, there is a critical need for a tool that will facilitate knocking-in of specific bacterial functions into the gut microbiome and investigate their effects on the host glucose metabolism and insulin sensitivity. The investigators demonstrate an innovative strategy that addresses this need using engineered native bacteria. This novel approach allows quick and effective knocking-in of a beneficial function into the gut microbiome. The function is sustained, potentially for perpetuity, in conventionally-raised hosts with a single treatment and without the need for microbiome depletion. To date, the investigators have demonstrated that tractable native bacteria can be engineered to modify bile acids ex vivo, reintroduced to the host, engraft the entire gut, deliver an intended beneficial function, alter luminal and serum metabolites as intended, affect host metabolism, and even reverse disease. These functions affect host physiology and potentially alleviate disease. Using this new approach, the investigators will pursue the overall goal by addressing the central hypothesis that gut microbiome affects host insulin sensitivity through bile acid deconjugation and that these functions can be used to treat type 2 diabetes. In the next four years, the investigators will pursue the proposal's central hypothesis with three specific aims. The first aim will determine if bacterial bile acid deconjugation affects ileal and hepatic glucoregulatory transcripts in conventionally-raised C57Bl6 mice. Ultimately this aim will determine the relationship between bacterial bile acid modification and host bile acid signaling, gluconeogenesis, and incretin production. The second aim will determine if the glucoregulatory effects of microbial bile acid deconjugation are mediated by the farnesoid X receptor (FXR), a major bile acid receptor. This will be done using engineered native bacteria with and without BSH in FXR knockout mice. In the end, this aim will determine the importance of the role of FXR in mediating the metabolic effects of gut microbiome. The third aim will determine how diet affects the bacterial bile acid deconjugation influence on the host metabolic homeostasis, using both the diet-induced obesity model (which uses a high-fat diet) and ob/ob mice (which uses normal chow diet). Because bile acid signaling is heavily influenced by diet, this aim will further elucidate the relationship between bacterial bile acid modifications, nutrient intake, and host glucoregulatory response. The expected outcome of these studies is a better understanding of a) how the gut microbiome affects host glucose regulation and b) whether the gut microbiome can be manipulated to improve insulin sensitivity. The outcome will have a positive translational impact because it will lead to novel therapeutic targets to T2D using the signaling pathways and functions employed by the gut microbiome.