Dissecting the function of a microbial sensing gut-brain circuit

About This Grant

PROJECT SUMMARY Microorganisms residing in the intestinal lumen have a significant impact on brain function and behavior. Perturbation of microbe-gut-brain communication is thought to underlie the increased visceral sensitivity and anxiety that occur in disorders of gut-brain interaction (DGBI) like irritable bowel syndrome (IBS). Recent studies suggest that enterochromaffin cells (ECs), a group of enteroendocrine cells in the intestinal epithelium that secrete serotonin, sense microbial irritants. EC activation drives visceral pain and anxiety, suggesting a critical role of EC in mediating the pathophysiological development of IBS. However, the cellular signaling and neuronal circuitry by which EC activation drives anxiety remain largely unknown. Whether and how gut microbiota modulates ECs to promote anxiety also remains unclear. Using in vivo real-time measurements of cell activity in zebrafish, our recent research revealed that specific gut bacteria secrete tryptophan metabolites indole and indole-3-aldehyde (I3A) to directly activate ECs through the receptor transient receptor potential ankyrin A1 (Trpa1). Using optogenetics, gut-brain in vivo imaging, and behavioral analysis, new preliminary data from our laboratory demonstrated that the Trpa1-expressing ECs directly connect and communicate with vagal sensory fibers. Stimulating Trpa1-expressing ECs activate a subset of vagal sensory neurons that express Parvalbumin 7 (Pvalb7). Stimulating Trpa1-expressing ECs with microbial irritants promotes anxiety. This proposal will test the central hypothesis that indole and I3A secretion by enteric irritant bacteria activates the Trpa1+EC- Pvalb7+vagal sensory neuron pathway to promote anxiety. Three Aims were proposed. Aim 1 will use zebrafish and bacterial genetic manipulation to determine molecular mechanisms that promote the formation of EC-vagal synaptic connections and test the hypothesis that microbial irritant signals promote Trpa1+ECs to form synaptic connections with Pvalb7+vagal sensory neurons. Aim 2 will use optogenetics, vagal calcium imaging, and novel genetic reporter lines to image real-time EC-vagal sensory neuron communication in vivo to determine the precise molecular and signaling mechanisms that mediate Trpa1+EC-Pvalb7+vagal sensory neuron communication. Aim 3 will use genetics, optogenetics, brain calcium imaging, and behavioral analysis to determine the key brain region that is activated by the Trpa1+EC-Pvalb7+vagal sensory pathway and underlies microbial irritants-induced anxiety. The proposed project is expected to provide a mechanistic understanding of how microbial irritants perturb EC-vagal communication to alter brain activity and promote anxiety in a microbial, molecular, and cellular-specific manner. The results are expected to provide evidence for new therapeutic approaches that target EC-vagal circuitry to treat DGBIs associated with microbial dysbiosis.