LAUSR

The binding of prorenin to the (pro)renin receptor (PRR) stimulates MAPK/ERK1/2, cyclooxygenase-2 (COX-2), NOX-4-dependent production of reactive oxygen species (ROS), transforming growth factor-β (TGF-β), pro-fibrotic factors connecting tissue growth factor (CTGF), and plasminogen activator inhibitor (PAI-I) in collecting duct (CD) cells. However, the specific role of COX-2 and the intracellular signaling pathways involved is not clear. Here, we tested the hypothesis that PRR activation increases profibrotic factors through activation of COX-2-mediated PGE 2 / E prostanoid receptor 4 (EP4), NOX-4/ROS, and Smad pathway. Activation of PRR in M-1cells treated with recombinant prorenin increased ROS production and protein levels of CTGF, PAI-I and TGF-β. Inhibition of MAPK, NOX-4 and COX-2 prevented these effects. Inhibition of MAKP, COX-2 and EP4 also prevented the upregulation of NOX-4. Because TGF-β activates Smad pathway, we further evaluated phosphorylation of Smad 2/3. Either COX-2 inhibition or EP4 antagonism significantly prevented the phosphorylation of Smad 2/3. Importantly, mice chronically infused with recombinant prorenin (100 ng/ml/h) showed increases in CTGF, PAI-I, TGF- β, fibronectin and collagen I expression levels in isolated CD as well as high expression of alpha smooth muscle actin (α-SMA) and interleukin 1 beta mRNA (IL 1β) in renal tissues, which was ameliorated by concomitant COX-2 inhibition. These results indicate that the induction of TGF-β, CTGF, PAI-I and ROS occurs through PRR-dependent activation of MAPK and NOX-4 via a mechanism that depends on COX-2-derived PGE 2 production, activation of EP4, and Smad pathway.