Molecular basis of vitamin D action in inflammatory bowel disease

There is growing evidence of vitamin D involvement in immune regulation and gut barrier function, suggesting that vitamin D may play a critical role in the development of inflammatory bowel disease (IBD). This review presents advances in the molecular mechanisms of vitamin D and vitamin D receptor (VDR) signaling with respect to barrier integrity and innate/adaptive immunity in the gut, as well as recent findings in uncovering the biological link between vitamin D-associated genetic variants and IBD. Experimental data have revealed a mechanistic basis for the contribution of vitamin D to the pathogenesis of IBD. The vitamin D/VDR complex is involved in the regulation of innate and adaptive immune responses to pathogenic threats by acting as an immunomodulator and alleviating inflammation in experimental IBD models and IBD patients, contributing to intestinal homeostasis. Vitamin D has been associated with the promotion of antimicrobial peptide secretion, down-regulation of dendritic cell activity, induction of tolerogenic rather than pro-inflammatory T-cell differentiation and function, and increased production of anti-inflammatory cytokines, highlighting its potential therapeutic value for IBD. Elucidating the complex interplay between vitamin D/VDR and the pathogenesis of IBD is critical for the development of novel therapeutic interventions and for the potential use of this molecule as a prognostic and diagnostic tool in clinical practice.