Microbial activators of host satiety

PROJECT SUMMARY/ABSTRACT Although a cause-and-effect relationship between the microbiome and obesity—and its related metabolic diseases—has been identified for almost 20 years, there are still no obesity therapies targeting or utilizing the microbiome. This is due, in part, to a lack of mechanistic understanding. The long-term goal is to delineate the mechanisms commensal organisms use to benefit host metabolic regulation and to develop new therapeutics targeting those pathways. We and other groups have identified Blautia species as candidate commensals that supports metabolic and mucosal health. Our prior studies of human subjects demonstrated an association between low Blautia levels and obesity, loss of control eating, and greater fat ingestion in a buffet-meal setting. The overall objective of this proposal is to determine how Blautia, and its metabolites activate signaling events within the gut epithelium. Our central hypothesis, based on our prior studies, is that acyl amines synthesized by Blautia species activate enteroendocrine cell (EEC) production of GLP-1 and PYY, which benefit host metabolism, and GLP-2, which benefits the structure and function of the gut mucosa. The rationale for this project is that a fundamental understanding of how Blautia benefits host metabolism and epithelial health will allow us to harness Blautia, its metabolites and other beneficial commensals to treat obesity and related disorders. The central hypothesis will be tested via two specific aims: 1.) Identify the synthetic processes and microbial products that augment EEC activation by Blautia; and 2.) Delineate the mucosal and metabolic effects of Blautia acyl amine production in vivo. Under the first aim, we will use a CRISPRi system to perform genome editing in Blautia wexlerae—suppressing the expression of native genes in this key commensal organism has not yet been done. To define the bacterium’s genetic requirements for synthesizing EEC-activating acyl amines—as measured by LC-MS—we will knock down candidate acyl transferase genes. We will also screen a library of microbial metabolites for molecules that synergize with acyl amines to boost EEC activation. This will be done high- throughput in a cell culture model of EECs and validated in EEC-containing human organoids. The second aim will delineate the physiologic consequences of B. wexlerae acyl amine production in mice. Here, we will utilize our newly established model of B. wexlerae colonization in germ-free mice, which we have shown increases acyl amine production in the gut by 5-10-fold. We will determine the effects of B. wexlerae on glycemic control, insulin sensitivity, food intake, weight and epithelial proliferation. The work is technically innovative in that it will uniquely combine new bacteriological methods, microbial metabolite analyses, and high-throughput screening of host phenotypes to maximize the likelihood of discovering new host-microbe interactions. The proposed studies are scientifically innovative because they will test a series of mechanism-based hypotheses that focus on advancing our understanding of how Blautia influences the host. Ultimately, this more precise understanding will open new horizons for utilizing Blautia and other microbes for clinical applications.