Abstract/Project Summary Microbes interact with the intestinal epithelium in ways that modulate susceptibility to infection, malnutrition, and predisposition to chronic metabolic diseases such as obesity and diabetes. However, the host signaling pathways utilized by microbes to promote health and disease are poorly understood. The powerful genetic tools provided by the model arthropod Drosophila melanogaster have enabled many discoveries that form the basis of our modern understanding of innate immunity. Here we propose to exploit the Drosophila melanogaster model to define the host signaling pathways that detect intestinal microbes and orchestrate the innate immune response of the intestinal epithelium. Drosophila intestinal stem cells, enterocytes and enteroendocrine cells (EECs) carry out functions similar to those of the mammalian intestine. EECs, which constitute 5-10% of cells in the intestinal epithelium, secrete enteroendocrine peptides (EEPs) that modulate host metabolic functions such as insulin signaling, satiety, and intestinal contractions. We have identified a subset of EECs that responds uniquely to the microbial fermentation product acetate by activating innate immune signaling through the TNF-like Immunodeficiency (IMD) pathway. In these EECs, IMD signaling increases transcription of the genes encoding EEPs. These EEPs, in turn, coordinate the response of the diverse cell types in the intestine to microbes. Here we investigate the mechanism by which microbes activate the intestinal innate immune response and the ultimate impact of this regulatory pathway on susceptibility to infection. In this proposal, we will investigate the role of chromatin remodeling in acetate-mediated IMD signaling, the contribution of peptidoglycan to intestinal IMD signaling, the role of EEPs as cytokines, and finally the cell- specific roles of EEPs in modulating susceptibility to intestinal infection. The overarching objective of this research is to uncover novel paradigms of the intestinal innate immune response to microbes with the goal of informing therapies that modify nutrient utilization in malnutrition, chronic metabolic diseases and susceptibility to intestinal infection.

Relevance Recent work has demonstrated that a healthy intestinal microbiota protects against intestinal infection, while a dysbiotic microbiota may accelerate malnutrition and the development of chronic metabolic diseases such as obesity and diabetes. This work seeks to harness the power of the model organism Drosophila with its extensive and accessible genetic tools to dissect the pathways through which microbes communicate with the host intestine, to establish the bacterial signals that contribute to activation of a robust intestinal innate immune response, and to understand how the diverse cell types in the intestine coordinate their response to intestinal invasion. These studies may identify host proteins and signaling pathways that can be targeted with prebiotics, probiotics, or small molecules to promote metabolic homeostasis and a protective response to intestinal infection.