High mobility group box 1 (HMGB1)-RAGE interaction mediates ectopic Intestinal inflammation in NAFLD.

Recent clinical studies found a strong association of colonic inflammation with NAFLD yet the mechanisms remain largely unknown. The present study identifies HMGB1 as a key mediator of intestinal inflammation in NAFLD and outlines a detailed redox signaling mechanism for such a pathway. NAFLD mice showed liver damage and release of higher HMGB1 in systemic circulation, increased intestinal tyrosine nitration that was dependent on NADPH oxidase. Intestines from NAFLD mice showed higher TLR4 activation and proinflammatory cytokine release, an outcome strongly dependent on the existence of NAFLD pathology and NADPH oxidase. In vitro experimentation using IE6 cells showed the HMGB1 activation of Toll like receptor (TLR-4) was both NADPH oxidase and peroxynitrite dependent with the latter being formed from the activation of NADPH oxidase. Proinflammatory cytokine production was significantly blocked by the specific peroxynitrite scavenger Phenyl Boronic Acid (FBA), AKT inhibitor (LY294002) and NADPH oxidase inhibitor Apocynin suggesting NADPH oxidase-dependent peroxynitrite as a key mediator in TLR-4 activation and cytokine release via an AKT dependent pathway. Studies to ascertain the mechanism of HMGB1-mediatied NADPH oxidase activation showed a distinct role of RAGE as the use of inhibitors targeted against RAGE prevented NADPH oxidase activation, peroxynitrite formation, TLR4 activation and finally cytokine release. Thus in conclusion, the present study identifies a novel HMGB1 mediated inflammatory pathway that is RAGE and redox signaling dependent and helps promote ectopic intestinal inflammation in NAFLD.