Role of cytosolic phospholipase A(2) in prostaglandin E(2) production by lung fibroblasts

Abstract

Prostaglandin (PG)E2 acts in an autocrine fashion to suppress proliferation of lung fibroblasts and production of collagen, and may negatively regulate pulmonary fibrosis. The role of Group IVA cytosolic phospholipase A2 alpha (cPLA2 alpha) in PGE2 production was investigated by comparing lung fibroblasts from wild-type and cPLA2 alpha-deficient mice. Arachidonic acid release from wild-type mouse lung fibroblasts (MLF+/+) was stimulated by serum, A23187 plus phorbol-myristate acetate (PMA), and lysophosphatidic acid (LPA) plus platelet-derived growth factor, but was > or = 80% lower from cPLA2 alpha-deficient MLF (MLF-/-). Transforming growth factor-beta increased cyclooxygenase-2 (COX2) expression to similar levels in MLF+/+ and MLF-/-, but MLF+/+ produced an order of magnitude more PGE2 than MLF-/- in response to A23187/PMA or platelet-derived growth factor/LPA. MLF+/+ synthesized less collagen than MLF-/-, supporting a role for PGE2 in suppressing collagen production. An SV40 immortalized line developed from MLF+/+ released arachidonic acid and expressed COX2 to levels similar to those of primary fibroblasts but produced 30-fold lower amounts of PGE2. Unlike primary fibroblasts, immortalized cells were deficient in microsomal PGE synthase (mPGES) but expressed slightly higher levels of cytosolic PGES. The results demonstrate a primary role for cPLA2 alpha in providing arachidonic acid for PGE2 production in mouse lung fibroblasts and support a role for this pathway in regulating collagen production.