Role of calcium-independent phospholipase A2 in complement-mediated glomerular epithelial cell injury

Abstract

In experimental membranous nephropathy, complement C5b-9-induced glomerular epithelial cell (GEC) injury leads to morphological changes in GEC and proteinuria, in association with phospholipase A(2) (PLA(2)) activation. The present study addresses the role of calcium-independent PLA(2) (iPLA(2)) in GEC injury. iPLA(2)beta short and iPLA(2)gamma were expressed in cultured rat GEC and normal rat glomeruli. To determine whether iPLA(2) is involved in complement-mediated arachidonic acid (AA) release, GEC were stably transfected with iPLA(2)gamma or iPLA(2)beta cDNAs (GEC-iPLA(2)gamma; GEC-iPLA(2)beta). Compared with control cells (GEC-Neo), GEC-iPLA(2)gamma and GEC-iPLA(2)beta demonstrated greater expression of iPLA(2) proteins and activities. Complement-mediated release of [(3)H]AA was augmented significantly in GEC-iPLA(2)gamma compared with GEC-Neo, and the augmented [(3)H]AA release was inhibited by the iPLA(2)-directed inhibitor bromoenol lactone (BEL). For comparison, overexpression of iPLA(2)gamma also amplified [(3)H]AA release after incubation of GEC with H(2)O(2), or chemical anoxia followed by reexposure to glucose (in vitro ischemia-reperfusion injury). In parallel with release of [(3)H]AA, complement-mediated production of prostaglandin E(2) was amplified in GEC-iPLA(2)gamma. Complement-mediated cytotoxicity was attenuated significantly in GEC-iPLA(2)gamma compared with GEC-Neo, and the cytoprotective effect of iPLA(2)gamma was reversed by BEL, and in part by indomethacin. Overexpression of iPLA(2)beta did not amplify complement-dependent [(3)H]AA release, but nonetheless attenuated complement-mediated cytotoxicity. Thus iPLA(2)gamma may be involved in complement-mediated release of AA. Expression of iPLA(2)gamma or iPLA(2)beta induces cytoprotection against complement-dependent GEC injury. Modulation of iPLA(2) activity may prove to be a novel approach to reducing GEC injury.