Vitamin D receptor negatively regulates bacterial-stimulated NF-κB activity in intestine

Vitamin D receptor (VDR) plays an essential role in gastrointestinal inflammation. Most investigations have focused on the immune response; however, how bacteria regulate VDR and how VDR modulates the nuclear factor (NF)-κB pathway in intestinal epithelial cells remain unexplored. This study investigated the effects of VDR ablation on NF-κB activation in intestinal epithelia and the role of enteric bacteria on VDR expression. We found that VDR^-/- mice exhibited a pro-inflammatory bias. After Salmonella infection, VDR^-/- mice had increased bacterial burden and mortality. Serum interleukin-6 in noninfected VDR^+/+ mice was undetectable, but was easily detectable in VDR^-/- mice. NF-κB p65 formed a complex with VDR in noninfected wild-type mouse intestine. In contrast, deletion of VDR abolished VDR/P65 binding. P65 nuclear translocation occurred in colonic epithelial cells of untreated VDR^-/- mice. VDR deletion also elevated NF-κB activity in intestinal epithelia. VDR was localized to the surface epithelia of germ-free mice, but to crypt epithelial cells in conventionalized mice. VDR expression, distribution, transcriptional activity, and target genes were regulated by Salmonella stimulation, independent of 1,25-dihydroxyvitamin D3. Our study demonstrates that commensal and pathogenic bacteria directly regulate colonic epithelial VDR expression and location in vivo. VDR negatively regulates bacterial-induced intestinal NF-κB activation and attenuates response to infection. Therefore, VDR is an important contributor to intestinal homeostasis and host protection from bacterial invasion and infection.