Abstract
Low vitamin D status potentiates experimental colitis, but the vitamin D-responsive cell in colitis has not been defined. We hypothesized that vitamin D has distinct roles in colonic epithelial cells and in nonepithelial cells during colitis. We tested this hypothesis by using mice with vitamin D receptor (VDR) deletion from colon epithelial cells (CEC-VDRKO) or nonintestinal epithelial cells (NEC-VDRKO). Eight-week-old mice were treated with 1.35% dextran sulfate sodium (DSS) for 5 days and then euthanized 2 or 10 days after removal of DSS. DSS induced body weight loss and increased disease activity index and spleen size. This response was increased in NEC-VDRKO mice but not CEC-VDRKO mice. DSS-induced colon epithelial damage and immune cell infiltration scores were increased in both mouse models. Although the epithelium healed between 2 and 10 days after DSS administration in control and CEC-VDRKO mice, epithelial damage remained high in NEC-VDRKO mice 10 days after removal of DSS, indicating delayed epithelial healing. Gene expression levels for the proinflammatory, M1 macrophage (Mɸ) cytokines tumor necrosis factor-α, nitric oxide synthase 2, and interleukin-1β were significantly elevated in the colon of NEC-VDRKO mice at day 10. In vitro experiments in murine peritoneal Mɸs demonstrated that 1,25 dihydroxyvitamin D directly inhibited M1 polarization, facilitated M2 polarization, and regulated Mɸ phenotype switching toward the M2 and away from the M1 phenotype. Our data revealed unique protective roles for vitamin D signaling during colitis in the colon epithelium as well as nonepithelial cells in the colon microenvironment (i.e., modulation of Mɸ biology).