Alpha-melanocyte stimulating hormone protects against H2O2-induced inhibition of wound restitution in IEC-6 cells via a Syk kinase- and NF-kappabeta-dependent mechanism.

Epithelial injury and repair are central consequences of ischemia and reperfusion of the gut. Intestinal mucosal wounds are repaired in part by epithelial restitution. However, the signaling mechanisms regulating restitution remain poorly understood, and few therapies to enhance restitution have been described. Previously we demonstrated that alpha-melanocyte-stimulating hormone (alpha-MSH) protected against postischemic gut injury in the rat. In this report, we tested the effects and mechanisms of alpha-MSH on wound restitution of rat small intestine (IEC-6) cells subjected to H2O2 stress with or without scrape wounding. H2O2 treatment resulted in tyrosine phosphorylation of Syk kinase and its downstream target IkappaBalpha, with subsequent NF-kappaB activation. Alpha-MSH and the Syk kinase inhibitor piceatannol blocked these processes. In scrape-wounded cells, H2O2 inhibited wound restitution, and this was partially restored by cotreatment with alpha-MSH or piceatannol. In contrast, overexpression of NF-kappaB p65 or Syk kinase, but not a dominant-negative mutant of Syk kinase, aggravated H2O2 inhibition of wound restitution, and inhibitors of c-Src tyrosine kinase or phosphatidylinositol-3 kinase were without effect. The results indicate an important role for Syk tyrosine kinase and the NF-kappaB pathway in the response to oxidant stress and the impairment of epithelial restitution in IEC-6 cells. The data also disclose that the beneficial effects of alpha-MSH on gut ischemia/reperfusion injury may relate to its acceleration of epithelial restitution.