Contribution of epithelial innate immunity to systemic protection afforded by prolyl hydroxylase inhibition in murine colitis

Pharmacological stabilization of hypoxia-inducible factor (HIF) through prolyl hydroxylase (PHD) inhibition limits mucosal damage associated with models of murine colitis. However, little is known about how PHD inhibitors (PHDi) influence systemic immune function during mucosal inflammation or the relative importance of immunological changes to mucosal protection. We hypothesized that PHDi enhances systemic innate immune responses to colitis-associated bacteremia. Mice with colitis induced by TNBS were treated with AKB-4924, a new HIF-1 isoform-predominant PHDi and clinical, immunological and biochemical endpoints were assessed. Administration of AKB-4924 led to significantly reduced weight loss and disease activity compared to vehicle controls. Treated groups were pyrexic, but did not become subsequently hypothermic. PHDi treatment augmented epithelial barrier function and led to an approximately 50-fold reduction in serum endotoxin during colitis. AKB-4924 also decreased cytokines involved in pyrogenesis and hypothermia, significantly reducing serum levels of IL-1β, IL-6 and TNF-α, while increasing IL-10. Treatment offered no protection against colitis in epithelial-specific HIF-1α deficient mice, strongly implicating epithelial HIF-1α as the tissue target for AKB-4924-mediated protection. Taken together, these results indicate that inhibition of prolyl hydroxylase with AKB-4924 enhances innate immunity and identifies the epithelium is a central site of inflammatory protection afforded by PHDi in murine colitis.