Defective arachidonate release and PGE2 production in Gi alpha2-deficient intestinal and colonic subepithelial myofibroblasts.
BACKGROUND
Mice lacking the pertussis toxin-sensitive G-protein subunit Gi alpha2 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 Gi alpha2 would result in decreased PGE2 production and tissue PGE2 levels. PGE2 levels were significantly decreased in the colon of Gi alpha2-/- mice.


RESULTS
Gi alpha2-/- myofibroblasts from the small intestine and colon both released asymptotically equal to 50% less arachidonate and 3- to 7-fold less PGE2 and 6-keto PGF1alpha in response to adenosine triphosphate, thrombin, tumor necrosis factor-alpha, 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 Gi alpha2. Basal myofibroblast COX-1 and COX-2 expression was downregulated in Gi alpha2-/- cells. No differences in proliferation rates were found between serum-starved or serum-activated wild-type (WT) and Gi alpha2-/- myofibroblasts. Finally, treatment of Gi alpha2-/- 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 Gi alpha2 in intestinal and colonic myofibroblast-derived prostanoid production and confirm the importance of mucosal PGE2 in the suppression of colitis.
Edwards
Robert Andrew
RA
Department of Pathology, University of California Irvine, Irvine, California 92697-4800, USA. redwards@uci.edu
Smock
Andrew Zoller
AZ
D000818:Animals; D001092:Arachidonate 12-Lipoxygenase / Q000172:deficiency*; D001483:Base Sequence; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology; D051545:Cyclooxygenase 1 / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D015232:Dinoprostone / Q000096:biosynthesis*; D004195:Disease Models, Animal; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D015212:Inflammatory Bowel Diseases / Q000201:enzymology* / Q000473:pathology; D007413:Intestinal Mucosa / Q000201:enzymology / Q000378:metabolism; D007421:Intestine, Small / Q000166:cytology; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity
D001092:Arachidonate 12-Lipoxygenase; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D015232:Dinoprostone