Reactive oxygen species mediate angiotensin II induced PGE2 and PGI2 production in rat mesangial cells via transcriptional upregulation of cyclooxygenase-2

Abstract

Prostaglandins (PG) and Angiotensin II (AII) are important modulators of the renal microcirculation. PGE2 (via activation of the type 4 PGE2 receptor) and PGI2 have vasodilatory effects in the glomerular microcirculation that counteract the vasoconstrictory effects of AII. We have shown that in mesangial cells (MC) AII upregulates NADH/NADPH oxidase (Kidney Int ’98) which results in reactive oxygen species (ROS) production and MC hypertrophy. Here we investigated: 1) whether ROS originated from AII mediate the upregulation of cyclooxygenase-2 (COX-2) and 2) whether AII induces PGE2 and PGI2 production in MC via COX-2. MC were incubated with AII (10−5 M) for 24 hours with and without the NADH/NADPH oxidase inhibitor diphenylene iodinium (DPI, 10−5 M), the superoxide anion (O2-) scavenger tiron (5 X 10−3 M), catalase (CAT, 800 U/ml), the AT1 receptor blocker irbesartan (IRB, 10−6 M) and the COX-2 inhibitor NS-398 (10−7 M). PGE2 and PGI2 were measured by EIA and factored by protein content and COX-2 mRNA expression was assessed by RT-PCR. AII significantly increased MC PGE2 (300%, P < 0.05) and PGI2 (200%, P < 0.05) production that was blocked by the AT1 receptor blocker irbesartan as well as the selective COX-2 inhibitor NS-398. Furthermore DPI, catalase and tiron inhibited AII induced PGE2 and PGI2 production suggesting that AII induced ROS (O2- and H2O2) mediate COX-2 upregulation. These changes in PGE2 and PGI2 production correlated with similar directional changes in COX-2 mRNA expression which was significantly increased. Further, the MAPK inhibitor PD98059 (10−6 M) inhibited AII induced MC PGE2 and PGI2 production indicating that COX-2 upregulation is dependent on ROS mediated MAPK activation. These studies provide an insight into the mechanisms involved in AII driven renal PGE2 and PGI2 production and suggest that COX-2 inhibition may have a potential deleterious effect on the renal microcirculation when the renin angiotensin system is activated. (See Table) P < 0.05 vs other conditions, n = 3 to 6. P < 0.05 vs other conditions, n = 3 to 6.