Background: Vitamin D deficiency is common in patients with inflammatory bowel diseases. The vitamin D receptor (VDR) is a nuclear hormone receptor mediating the activity of vitamin D hormone. Our previous studies showed that intestinal epithelial VDR signaling inhibits colitis by protecting the mucosal epithelial barrier, and this activity is independent of non-epithelial immune VDR actions. Interleukin (IL)-10-deficient mouse is a chronic colitis model that develops colitis due to aberrant immune responses. Here we used IL-10 null (IL-10KO) model to assess the anti-colitic activity of epithelial VDR in the setting of an aberrant immune system.
Methods: We crossed IL-10KO mice with villin promoter-driven human (h) VDR transgenic (Tg) mice to generate IL-10KO mice that carry the hVDR transgene in intestinal epithelial cells (IL-10KO/Tg). IL-10KO and IL-10KO/Tg littermates were studied in parallel and followed for up to 25 weeks.
Results: By 25 weeks of age, accumulatively 79 % IL-10KO mice developed prolapse, whereas only 40 % IL-10KO/Tg mice did so (P < 0.001). Compared with IL-10KO mice, IL-10KO/Tg littermates showed markedly reduced mucosal inflammation in both small and large intestines, manifested by attenuation in immune cell infiltration and histological damage and a marked decrease in pro-inflammatory cytokine production. IL-10KO/Tg mice also showed reduced intestinal epithelial cell apoptosis as a result of diminished PUMA induction and caspase 3 activation.
Conclusion: These observations demonstrate that targeting hVDR expression to intestinal epithelial cells is sufficient to attenuate spontaneous colitis caused by an ill-regulated immune system, confirming a critical role of the epithelial VDR signaling in blocking colitis development.