Release of arachidonic acid by complement C5b-9 complex in glomerular epithelial cells.
In experimental membranous nephropathy, C5b-9 induces noncytolytic glomerular epithelial cell (GEC) injury and proteinuria, which in some models is partially mediated by metabolites of arachidonic acid. In cultured GEC, sublytic C5b-9 increases cytosolic Ca2+ concentration ([Ca2+]i), activates phospholipase C (PLC), and releases arachidonic acid and eicosanoids. This study examined mechanisms of arachidonic acid production by C5b-9. In GEC labeled with [3H]arachidonate C5b-9 increased free [3H]arachidonic acid and 1,2-[3H]-arachidonoyl-diacylglycerol (DAG), an endogenous activator of protein kinase C (PKC). Elevated [Ca2+]i was not sufficient to account for increased free arachidonic acid. Moreover, in GEC that had been depleted of PKC by preincubation for 18 h with 2 microM phorbol myristate acetate, the C5b-9-induced arachidonate release was inhibited by greater than 75%. Reacylation of phospholipids was not decreased by C5b-9. Homogenates of GEC that had been stimulated with C5b-9 released more [14C]arachidonate from exogenously added 2-[14C]arachidonoyl-phosphatidyl-ethanolamine or 2-[14C]arachidonoyl-phosphatidylcholine than homogenates of unstimulated cells (assayed at a Ca2+ concentration of 2 mM). These experiments demonstrate directly that C5b-9 increased phospholipase A2 (PLA2) activity. PLA2 appeared to be stimulated as a result of PKC activation (probably secondary to increased DAG) in association with elevated [Ca2+]i. The C5b-9-induced activation of PLA2 may lead to release of eicosanoids, which may contribute toward impaired glomerular capillary wall permselectivity in experimental membranous nephropathy.
Cybulsky
A V
AV
Department of Medicine, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D000001:Calcimycin / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D015938:Complement Membrane Attack Complex / Q000494:pharmacology*; D003512:Cyclohexanones / Q000494:pharmacology; D004075:Diglycerides / Q000378:metabolism / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D007678:Kidney Glomerulus / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008049:Lipase / Q000378:metabolism; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D010743:Phospholipids / Q000096:biosynthesis; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001095:Arachidonic Acids; D015938:Complement Membrane Attack Complex; D003512:Cyclohexanones; D004075:Diglycerides; D005230:Fatty Acids, Nonesterified; D010743:Phospholipids; D016718:Arachidonic Acid; D000001:Calcimycin; D004533:Egtazic Acid; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; C038237:1-oleoyl-2-acetylglycerol; D004492:Edetic Acid; D011493:Protein Kinase C; D008049:Lipase; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium