Microbial regulation of intestinal lipid metabolism and its physiological consequences

ABSTRACT Intestinal microbiota are known to promote absorption of dietary fat and to confer susceptibility to diet-induced obesity. However, there exist fundamental gaps in our knowledge of the underlying mechanisms. Our long-term goal is to understand the mechanisms underlying host-microbe interactions and lipid metabolism in the intestine and how they contribute to human physiology and disease. Our preliminary studies in gnotobiotic and conventional mice and zebrafish reveal that microbiota specifically suppress mitochondrial fatty acid oxidation (FAO) in intestinal epithelial cells (IECs), and identify potential upstream microbial and transcriptional regulatory mechanisms. Our genetic analysis in conventional mice also establishes that blocking FAO specifically in IECs promotes dietary fat absorption and modulates intestinal and systemic energy metabolism. The overall objectives of this project are to understand how microbiota regulate FAO in IECs, and define the impact of intestinal FAO on intestinal and systemic physiology. The proposed research will test the central hypothesis that specific bacterial products downregulate FAO in IECs by suppressing FAO gene transcription, which in turn modulates IEC fuel selection and differentiation and promotes positive energy balance. Our rationale is that an improved understanding of how microbes influence intestinal FAO, and how FAO contributes to intestinal physiology and systemic energy metabolism could lead to new strategies for controlling fat metabolism and energy balance in humans and other animals. In Specific Aim 1, we will identify the host and microbial mechanisms by which microbiota suppress FAO in the intestinal epithelium. In Specific Aim 2, we will define the roles of intestinal FAO in fuel selection and differentiation of IECs, and in mediating the influence of the gut microbiota on systemic energy balance. The expected outcomes will vertically advance the field in several ways. First, they will establish intestinal FAO as a major determinant of intestinal and systemic energy balance. Second, they will provide definitive new evidence that intestinal epithelial FAO is a major target of microbial regulation. Third, they will show that the striking resistance of germ-free mice to diet-induced obesity is mediated by intestinal FAO. Finally, they will provide a novel bacteria-host signaling pathway governing intestinal FAO. These results are expected to have a significant impact because they are likely to lead to new microbe- and host-targeted strategies to control energy balance in the context of obesity and malnutrition by manipulating FAO and associated gene expression networks and metabolic pathways in the gut.