CYTOKINE-STIMULATED SECRETION OF GROUP-II PHOSPHOLIPASE-A(2) BY RAT MESANGIAL CELLS - ITS CONTRIBUTION TO ARACHIDONIC-ACID RELEASE AND PROSTAGLANDIN SYNTHESIS BY CULTURED RAT GLOMERULAR CELLS

Potent pro-inflammatory cytokines, such as interleukin 1 (IL-1) or tum or necrosis factor (TNF) alpha have been found to increase group II ph ospholipase A2 (PLA2) synthesis and secretion by mesangial cells. In a ll cases 85-90% of the enzyme is secreted from the cells and a paralle l increase in prostaglandin (PG)E2 synthesis is observed. We report he re that co-incubation with a monoclonal antibody that specifically bin ds and neutralizes rat group II PLA2 attenuates IL-1beta and TNFalpha- stimulated PGE2 production by 45% and 52%, respectively.CGP43182, a sp ecific inhibitor of group II PLA2, potently blocks mesangial cell grou p II PLA2 in vitro with a half-maximal inhibitory concentration (IC50) of 1.5 muM, while only slightly affecting mesangial cell high molecul ar weight PLA2 . CGP 43182 markedly attenuates IL-1beta- and TNFalpha- stimulated PGE2 synthesis in intact mesangial cells with IC50's of 1.3 and 1.0 muM, respectively. PLA2 secreted from cytokine-stimulated mes angial cells was purified to homogeneity. Addition of the purified enz yme to unstimulated mesangial cells causes a marked release of arachid onic acid and a subsequent increased synthesis of PGE2. Moreover, addi tion of purified PLA2 to a cloned rat glomerular epithelial cell line and cultured bovine glomerular endothelial cells augmented both arachi donic acid release and PGE, synthesis, with the endothelial cells bein g especially sensitive. Thus, cytokine-triggered synthesis and secreti on of group II PLA2 by mesangial cells contributes, at least in part, to the observed synthesis of PGE2 that occurs in parallel to the enzym e secretion. Furthermore, extracellular PLA2 secreted by mesangial cel ls is able to stimulate arachidonic acid release and PGE2 synthesis by the adjacent endothelial and epithelial cells. These data suggest tha t expression and secretion of group II PLA2 triggered by pro-inflammat ory cytokines may crucially participate in the pathogenesis of inflamm atory processes within the glomerulus.