Nitric Oxide Inhibits Stretch-Induced MAPK Activation in Mesangial Cells Through RhoA Inactivation

Glomerular capillary hypertension is an important determinant of glomerulosclerosis in rats with subtotal renal ablation. Dietary supplementation with L-arginine increases renal nitric oxide (NO) production and limits glomerular injury in this model, and early benefits are seen without altered glomerular capillary pressure. In an in vitro model of hemodynamically mediated signaling, the authors have reported that subjecting MC to cyclic stretch/relaxation activates the mitogen-activated protein kinase p42/44 (Erk) cascade and that NO and cyclic GMP abrogate stretch-induced Erk activation by inducing actin cytoskeletal disassembly. The actin cytoskeleton is regulated by the Rho family of GTPases, including RhoA; therefore, the authors examined the role of RhoA in stretch-induced Erk activation and as an NO target. In primary rat MC subjected to cyclic mechanical strain, RhoA activity was maximally increased (2.4-fold) after 1 min of stretch, and Erk activation temporally followed. The Rho-kinase inhibitor Y-27632 attenuated Erk activation in a dose-dependent manner and prevented stretch-induced actin stress fiber formation. The NO donors S-nitroso-N-acetylpenicillamine and cGMP both inhibited stretch-induced RhoA and Erk activation and stress fiber formation. Infection of MC with the RhoA mutant RhoA-Ala188, which is resistant to NO-dependent phosphorylation, abrogated the effects of NO and cGMP on stretch-induced Erk activation and stress fiber formation. The authors conclude that the early activation of RhoA is essential for stretch-induced actin stress fiber formation and Erk activation in MC, events which are prevented by NO and cGMP through their action on RhoA. Inhibition of RhoA may thus be a new approach to the prevention of hemodynamically mediated glomerular injury.