ABSTRACT
BACKGROUND: Clinical studies have shown that angiotensin II (Ang II) type 1 (AT1) receptor blockers (ARBs) are able to provide renoprotection independent of their blood pressure lowering effects. ARBs also are reported to suppress oxidative stress, inflammation and certain other cellular responses in a receptor-independent manner. We investigated the effects of an ARB, olmesartan, on the cell migration induced by platelet-derived growth factor (PDGF), a major mitogen involved in the pathogenesis of glomerulonephritis in rat mesangial cells (RMCs). METHODS: Cell migration was determined by a modified Boyden chamber assay. The intracellular signalling pathway was examined by western blotting. AT1 receptor expression was knocked down by small interfering RNAs. The intracellular reactive oxygen species (ROS) was measured by using a fluorescent probe. The O(2)(.-) scavenging activities were studied by the electron paramagnetic resonance-spin trapping method. RESULTS: PDGF-induced cell migration was inhibited by olmesartan in AT1 receptor knockdown RMCs. Olmesartan attenuated big mitogen-activated protein (MAP) kinase 1 (BMK1) and Src activation by PDGF in AT1 receptor knockdown RMCs. PDGF-induced BMK1 activation was suppressed by the Src family tyrosine kinase inhibitors, indicating that Src exists upstream of BMK1. The NADPH oxidase inhibitors inhibited not only PDGF-induced BMK1 and Src activation but also RMC migration. The elevation in ROS generation induced by PDGF was decreased by olmesartan. Olmesartan displayed neither directly ROS scavenging activity nor the inhibition of ROS-mediated intracellular signalling in RMCs. CONCLUSIONS: Olmesartan attenuates ROS generation by PDGF, leading to the subsequent inhibition of Src/ BMK1/migration in an AT1 receptor-independent manner in RMCs.
Subject(s)
Angiotensin II Type 1 Receptor Blockers/pharmacology , Cell Movement/drug effects , Imidazoles/pharmacology , Mesangial Cells/drug effects , Mesangial Cells/physiology , Tetrazoles/pharmacology , Animals , Cell Movement/physiology , Cells, Cultured , Male , Platelet-Derived Growth Factor/physiology , Rats , Rats, Sprague-Dawley , Signal Transduction/drug effectsABSTRACT
Adiponectin, an adipocyte-derived hormone, has been involved in metabolic syndrome, a known risk factor for the development of chronic kidney disease (CKD). Recent studies have demonstrated that plasma adiponectin levels are elevated when kidney function declines in patients with CKD. Excessive mesangial cell (MC) turnover is one of the important features of CKD. The aim of the present study is to elucidate the effects of adiponectin on platelet-derived growth factor (PDGF)-induced cell migration and intracellular signaling pathways, in cultured rat MCs (RMCs). PDGF-induced RMC migration was significantly inhibited by the pretreatment of adiponectin. Adiponectin alone had no effect on RMC migration. Big mitogen-activated protein (MAP) kinase 1 (BMK1), p38 MAP kinase, and Akt were activated by PDGF stimulation in a time- and concentration-dependent manner in RMC. Adiponectin alone did not affect BMK1, p38 MAP kinase, and Akt phosphorylations in RMC. PDGF-induced BMK1 and p38 MAP kinase phosphorylations were significantly attenuated by the pretreatment of adiponectin in RMCs. On the other hand, the phosphorylation of Akt by PDGF was not diminished by the pretreatment of adiponectin. Adiponectin had no effects on PDGF-receptor autophosphorylation by PDGF. We also confirmed that PDGF-induced RMC migration was significantly suppressed by siBMK1 transfection or SB203580, a p38 MAP kinase inhibitor. From these findings, it is implied that the elevated plasma adiponectin levels in patients with CKD might play a compensatory role aimed at counteracting renal dysfunction related to MC disorders.
