Abstract P227: Prostaglandin EP 4 Receptor Mediate Angiotensin II-induced Hypertension via Activation of PRR/ENaC Pathway

Abstract

Activation of COX-2/EP 4 pathway is shown to upregulate renal (pro) renin receptor (PRR) contributing angiotensin II (Ang II)-induced hypertension but the underlying mechanism remains unclear. Here, we tested the hypothesis that activation of EP 4 receptors increases ENaC expression/activity through PRR in the setting of Ang II treatment. Sprague-Dawley rats were infused for 2 weeks with vehicle, Ang II alone (100 ng/kg/min), or in combination with an EP 4 antagonist ONO-AE3-208 (ONO) (0.2 mg/kg/d). Following 14-d AngII treatment, 24-h urine volume and 24-h urinary Na + excretion both exhibited a significant increase which was completely blocked by ONO. Ang II infusion selectively elevated α-ENaC protein abundance (1.9-fold) in the renal medulla but not in the renal cortex, which was completely blocked by ONO, as assessed by immunoblotting. Interestingly, Ang II infusion elevated the cleaved γ-ENaC protein in both medulla and cortex, which was similarly abolished by ONO. In response to Ang II infusion, the increases in renal medullary mRNA were 1.7-fold for α-ENaC, 1.3-fold for β-ENaC, 2.4-fold for γ-ENaC as assessed by qRT-PCR; in contrast, none of the ENaC subunits showed obvious changes in the renal cortex. Ang II-induced increases in α-ENaC mRNA were reduced 41% by ONO with a modest effect on the response of β-ENaC and γ-ENaC. In cultured mpkCCD cells, Ang II treatment at 500 nM for 24 h induced a 2.5-fold increase of ENaC activity as assessed by epithelial volt-ohmmeter, which was completely blocked by ONO (10 μM) or a specific PRR inhibitor PRO20 (1.0 μM). To further determine the role of the EP4 receptor in the regulation of ENaC activity, the mpkCCD cells were treated with vehicle, CAY10580 alone (agonist of the EP 4 receptor, 10 μM), or in combination with PRO20 for 24 h. The ENaC activity showed a 2.0-fold increase in response to CAY10580, which was nearly completely abolished by PRO20 (n = 6-8, p<0.05). CAY10580 induced a 2.1-fold increase in PRR protein abundance. Overall, these results suggest that activation of EP 4 induces PRR, leading enhancement of ENaC expression/activity, eventually contributing to increased blood pressure in response to Ang II treatment.