ANGIOTENSIN-II INDUCES SUPEROXIDE ANION PRODUCTION BY MESANGIAL CELLS

Background. The recognized role of angiotensin II (Ang II) in the path ogenesis of the progression of renal disease cannot be solely attribut ed to Ang II's hemodynamic effects. Indeed, growth stimulating signals driven by Ang II promote mesangial cell (MC) hypertrophy and extracel lular matrix production, prominent features of progressive glomerular injury. Superoxide anion (O-2(-)) avidly interacts with nitric oxide, an endogenous vasodilator that inhibits growth factor stimulated MC gr owth and matrix production. In addition. O-2(-) acting as an intracell ular signal is linked to growth related responses such as activation o f mitogen activated protein (MAP) kinases. The studies reported herein were designed to investigate: (a) whether Ang II induces MC O-2(-) pr oduction and (b) if increased O-2(-) production elicits growth respons es in MC. Methods. MC were exposed to Ang II for 24 or 48 hours. In so me experiments, in addition to Ang II, MC were exposed to: diphenyleni eodonium (DPI), an inhibitor of the flavin containing NADH/NADPH oxida se; losartan (LOS), an Ang II type 1 (AT1) receptor blocker; PD 98059, a MAP kinases inhibitor; the protein kinase C inhibitors Calphostin C or H-7; and the tyrosine kinase inhibitors, herbymycin A or genistein . Results. Ang II (10(-5) M to 10(-8) M) dose dependently increased MC O-2(-) production up to 125% above control (ED 50 5 x 10(-7) M). LOS as well as DPI, and the PKC inhibitors blocked Ang II stimulated MC O- 2(-) production. Ang II dose dependently increased MC H-3-leucine inco rporation, and MC protein content, two markers of MC hypertrophy, as w ell as H-3-thymidine incorporation, a marker of MC hyperplasia. PD9805 9, a specific inhibitor of MAP kinases prevented Ang II induced MC hyp ertrophy. Moreover, LOS, DPI, and the PKC inhibitors each independentl y inhibited MC H-3-leucine incorporation, thereby establishing the spe cificity of Ang II induced O-2(-) in driving MC hypertrophy. Conclusio ns. The current studies demonstrate a previously unrecognized link bet ween Ang II and MC O-2(-) production that may participate in the patho physiology of progressive renal disease by concomitantly affecting the hemodynamics of the glomerular microcirculation as well as growth rel ated responses of MC to injury.