Homeostatic PPARα Signaling Limits Inflammatory Responses to Commensal Microbiota in the Intestine.

Dietary lipids and their metabolites activate members of the peroxisome proliferative-activated receptor (PPAR) family of transcription factors and are critical for colonic health. The PPARα isoform plays a vital role in regulating inflammation in various disease settings, but its role in intestinal inflammation, commensal homeostasis, and mucosal immunity in the gut are unclear. In this study, we demonstrate that the PPARα pathway in innate immune cells orchestrates gut mucosal immunity and commensal homeostasis by regulating the expression of IL-22 and the antimicrobial peptides RegIIIβ, RegIIIγ, and calprotectin. Additionally, the PPARα pathway is critical for imparting regulatory phenotype in intestinal macrophages. PPARα deficiency in mice led to commensal dysbiosis in the gut, resulting in a microbiota-dependent increase in the expression of inflammatory cytokines and enhanced susceptibility to intestinal inflammation. Pharmacological activation of this pathway decreased the expression of inflammatory cytokines and ameliorated colonic inflammation. Taken together, these findings identify a new important innate immune function for the PPARα signaling pathway in regulating intestinal inflammation, mucosal immunity, and commensal homeostasis. Thus, the manipulation of the PPARα pathway could provide novel opportunities for enhancing mucosal immunity and treating intestinal inflammation.