Nervous System Control of Intestinal Host Defense in<i>C. elegans</i>

The physiological mechanisms that connect pathogen detection to the induction of host defense in the whole organism are incompletely understood. We use C. elegans as a powerful discovery platform to uncover novel mechanisms of pathogen detection and signal transduction in the whole animal. We discovered that transcription factor HLH-30 (homologous to mammalian TFEB) acutely activates during intestinal infections, and is required for about 80% of the transcriptional host response to infection. In subsequent work, we uncovered an upstream pathway that activates HLH-30, composed of Gαq, PLC, and protein kinase D (PRKD). However, the mechanism of Gαq activation remained unknown. Based on our discovery of the neurotransmitter acetylcholine as a trigger for a parallel pathway, we investigated the role of acetylcholine in the Gαq-HLH-30 pathway. Objective: To uncover the physiological mechanisms regulating host defense responses in the intestinal epithelium of C. elegans during bacterial infection, focusing on upstream signals and pathways driving protective transcriptional programs through HLH-30/TFEB. Hypothesis: Acetylcholine, released during infection, activates intestinal muscarinic receptors, triggering a signaling cascade that drives the activation of transcription factor HLH-30/TFEB to induce intestinal host defense. Methods: We investigated HLH-30 activation by infection in C. elegans mutants defective in acetylcholine release. Pharmacological stimulation with acetylcholine analogs was used to study HLH-30/TFEB activation independently of infection. Using fluorescence microscopy of transgenic animals expressing HLH-30::GFP, we tracked nuclear localization, while genetic and pharmacological approaches dissected the roles of the Gαq-PLC-PRKD pathway. In murine macrophages, we examined cholinergic regulation of TFEB activation and transcriptional responses through fluorescence imaging and transcriptomics. Results: Acetylcholine release was required for HLH-30 activation during infection in C. elegans. Acetylcholine analogs induced HLH-30 nuclear localization and transcriptional activation independently of infection via the Gαq-PLC-PRKD pathway. In murine macrophages, cholinergic agonists activated TFEB and drove a pro-inflammatory transcriptional program through nicotinic receptors, revealing species-specific receptor utilization in the cholinergic regulation of immune physiology. These findings suggest that acetylcholine is a conserved regulator of mucosal immunity. Conclusion: Acetylcholine coordinates the physiological response to infection by driving both molecular host defense mechanisms in the intestinal epithelium and behavioral strategies. In C. elegans, acetylcholine drives HLH-30 activation in the intestinal epithelium, while in mammals, it induces TFEB activity in macrophages. This study highlights how neural and immune physiology converge through the brain-gut axis to synchronize behavioral and molecular responses to infection, offering insights into cholinergic regulation of innate immunity and potential therapeutic targets for modulating neuro-immune interactions. This research was supported in part by grant R35GM149284 from the National Institute of General Medical Sciences of the National Institutes of Health of the USA. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.