Defective arachidonate release and PGE2 production in Giα2-deficient intestinal and colonic subepithelial myofibroblasts

Abstract

Background: Mice lacking the pertussis toxin-sensitive G-protein subunit Giα2 spontaneously develop colitis and colon cancer. In the gut, arachidonate-derived prostaglandin E2 (PGE2) modulates intestinal immune responses and epithelial restitution and is derived largely from subepithelial myofibroblasts. Methods: We tested whether known decreases in arachidonate release in cells lacking Giα2 would result in decreased PGE2 production and tissue PGE2 levels. PGE2 levels were significantly decreased in the colon of Giα2-/- mice. Results: Giα2-/- myofibroblasts from the small intestine and colon both released 50% less arachidonate and 3- to 7-fold less PGE 2 and 6-keto PGF1α in response to adenosine triphosphate, thrombin, tumor necrosis factor-α, or lipopolysaccharide, in a partially cyclooxygenase (COX)-2-dependent manner. Decreased arachidonate release did not appear to be caused by a defect in cPLA2 translocation in the absence of Giα2. Basal myofibroblast COX-1 and COX-2 expression was downregulated in Giα2-/- cells. No differences in proliferation rates were found between serum-starved or serum-activated wild-type (WT) and Giα2 -/- myofibroblasts. Finally, treatment of Giα2-/- mice with the EP4-specific PGE2 receptor agonist ONO-AE1-329 significantly decreased the severity of established colitis. Conclusions: These findings confirm a requirement for Giα2 in intestinal and colonic myofibroblast-derived prostanoid production and confirm the importance of mucosal PGE2 in the suppression of colitis. Copyright © 2006 by Lippincott Williams & Wilkins.