Transmural pressure inhibits prorenin processing in juxtaglomerular cell

Contribution of nonproteolytically activated prorenin in glomeruli to hypertensive renal damage

Prorenin is activated without proteolysis by binding of prorenin receptor to the pentameric "handle region" (HR) of prorenin prosegment. It was hypothesized that such activation occurs in the kidneys of hypertensive rats and causes tissue renin-angiotensin system (RAS) activation and end-organ damage. Because the HR's binding to its binding protein made the adjacent tetrameric "gate region" (GR) accessible to its specific antibody, immunohistochemistry of the GR was performed to test the hypothesis. Methods also were devised specifically to inhibit the nonproteolytic activation by the decapeptide corresponding to the HR as a decoy. Immunohistochemistry of the GR demonstrated that the majority of nonproteolytically activated prorenin is present in podocytes of the kidneys from stroke-prone spontaneously hypertensive rats, in which activation of renal tissue RAS, proteinuria, and glomerulosclerosis occurred. Continuous subcutaneous administration of the HR decoy peptide completely inhibited both nonproteolytic activation of tissue prorenin and activation of tissue RAS without affecting circulating RAS or arterial pressure and significantly attenuated the development and progression of proteinuria and glomerulosclerosis. These studies clearly demonstrated that nonproteolytic activation of prorenin in glomeruli is critically involved in renal tissue RAS activation, leading to renal damage in hypertensive animals.

COX-2 inhibition prevents downregulation of key renal water and sodium transport proteins in response to bilateral ureteral obstruction

Bilateral ureteral obstruction (BUO) is associated with marked changes in the expression of renal aquaporins (AQPs) and sodium transport proteins. To examine the role of prostaglandin in this response, we investigated whether 24-h BUO changed the expression of cyclooxygenases (COX-1 and -2) in the kidney and tested the effect of the selective COX-2 inhibitor parecoxib (5 mg·kg−1·day−1via osmotic minipumps) on AQPs and sodium transport. Sham and BUO kidneys were analyzed by semiquantitative immunoblotting, and a subset of kidneys was perfusion fixed for immunocytochemistry. BUO caused a significant 14-fold induction of inner medullary COX-2 (14.40 ± 1.8 vs. 1.0 ± 0.4, n = 6; P < 0.0001) and a reduction in medullary tissue osmolality, whereas COX-1 did not change. Immunohistochemistry confirmed increased COX-2 labeling associated with medullary interstitial cells. COX isoforms did not change in cortex/outer medulla after 24-h BUO. In BUO kidneys, inner medullary AQP2 expression was reduced, and this decrease was prevented by parecoxib. In the inner stripe of outer medulla, the type 3 Na+/H+exchanger (NHE3) and apical Na+-K+-2Cl−cotransporter (BSC-1) were significantly reduced by BUO, and this decrease was significantly attenuated by parecoxib. Immunohistochemistry for AQP2, NHE3, and BSC-1 confirmed the effect of parecoxib. Parecoxib had no significant effect on the Na-K-ATPase α1-subunit, type II Na-Picotransporter, or AQP3. In conclusion, acute BUO leads to marked upregulation of COX-2 in inner medulla and selective COX-2 inhibition prevents dysregulation of AQP2, BSC-1, and NHE3 in response to BUO. These data indicate that COX-2 may be an important factor contributing to the impaired renal water and sodium handling in response to BUO.