A few years ago, we discovered that HLH-30/TFEB, which belongs to the MiT transcription factor family, is essential for C. elegans defense against bacterial infections in the intestine. We also discovered that TFEB is important for pro-inflammatory polarization of mouse macrophages, and thus its function in innate immunity is evolutionarily conserved. The long-term goal of this project is to understand the sequence of events linking pathogen detection, organismal signal transduction, and host defense induction via HLH-30/TFEB. In the previous funding period, we discovered that the nervous system is required for HLH-30 activation in peripheral tissues. We also uncovered two opposing mechanisms of gene regulation downstream of HLH-30, mediated by uncharacterized orphan nuclear receptors (NRs). Currently there is little information on the mechanisms by which the nervous system regulates MiT factor-mediated mechanisms of innate immunity and inflammation in any organism. Moreover, such MiT-mediated defense mechanisms are largely unknown. These are important knowledge gaps that impede fundamental understanding of homeostasis and host defense, and that conceal therapeutic opportunities to treat infections or inflammatory diseases. The overall objectives of this project are to elucidate the roles of sensory neurons in sensing bacterial pathogens and microbiota to activate HLH-30/TFEB, and of HLH-30-regulated NRs. The central hypothesis is that specific bacteria, through their action on sensory neural circuits, induce the cholinergic nervous system to activate HLH-30/TFEB in target tissues, thus eliciting a specific host defense response that is modulated by conserved orphan nuclear receptors. To test this hypothesis, we will define regulation of HLH-30/TFEB by the nervous system and define mechanisms of action for two NRs downstream of TFEB. The proposed research is technically innovative because of innovations in the application of single-neuron and “whole brain” imaging to live infected animals in real time, and in the use of knockdown strategies in primary mouse macrophages to translate the C. elegans findings on the transcriptional mediators of TFEB functions in innate immunity. Additionally, the proposed work is conceptually innovative for its implication of specific neurons as part of a novel mechanism of microbiota/infection sensing and inter-tissue communication with the intestine, and for identifying mechanistic links among intestinal infection and neuronal degeneration within a TFEB-mediated mechanism of the microbiota-gut-brain axis. This proposal is highly relevant to human health because it focuses on genes and pathways that are conserved, and directly linked to disease in humans. This proposal is highly significant in the context of fundamental knowledge of the brain-gut-microbiota axis because it directly addresses important knowledge gaps and successful completion of the work will greatly advance our knowledge about the interplay among mi...