Understanding NLRP6 function in intestinal homeostasis

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PROJECT SUMMARY Nod-like receptors (NLRs) are intracellular pattern-recognition receptors that are involved in host defense, but have emerged as critical players in the maintenance of tissue homeostasis, especially within the intestine. Capable of sensing microbial products as well as endogenous ligands related to tissue injury, NLRs activate multiple downstream inflammatory signaling pathways, including the inflammasome, to promote the production of cytokines and chemokines important for pathogen clearance and the timely repair of intestinal epithelial damage. There is also increasing evidence that NLRs participate in the regulation of the gut microbiome. Consequently, mice that are deficient in certain NLRs have altered microbiomes associated with increased susceptibility to colitis and colon tumorigenesis. In particular, mice deficient in NLRP6 develop more severe inflammation and tumors compared to wildtype mice in mouse models of inflammatory bowel disease and inflammation-associated colon cancer. This phenotype is associated with impaired IL-18 production and an altered microbiome. However, the cellular mechanisms by which NLRP6 mediate its protective effects within the colon is unclear. NLRP6 is highly expressed in the epithelium and consistently, there have been multiple reports that demonstrate epithelial-specific roles for NLRP6, including the production of IL-18, antimicrobial peptides, and mucus. However, NLRP6 expression can also be induced in hematopoietic cells, and our published data suggests important roles for NLRP6 in the regulation of IL-18 and intestinal inflammatory responses in hematopoietic cells. Thus, the mechanism by which NLRP6 protects against colitis is likely to be complex. The goal of the current proposal is to further delineate NLRP6 function in myeloid cells and the inflammatory signaling pathways NLRP6 engages in to affect resistance to intestinal pathology.