Abstract 124: Soluble (Pro)Renin Receptor Regulation of ENaC in Angiotensin II Signaling in the Collecting Duct

Abstract

We have shown that activation of (pro)renin receptor (PRR) and local renin response in the collecting duct (CD) contributes to AngII-induced hypertension. Moreover, the 28 kDa soluble (pro)renin receptor (sPRR) derived from cleavage of the extracellular domain of PRR is elevated by AngII and stimulated AQP2 expression via activation of frizzled-8/β-catenin pathway. Here we examined sPRR regulation of ENaC and further explored its implication in AngII signaling. In cultured mpkCCD cells, a recombinant histidine-tagged rat sPRR, sPRR-His, at 10 nM for 24 h induced a 3-fold increase in α-ENaC protein abundance. The native sPRR generated by immunoprecipitation with anti-sPRR antibody from either mouse or human urine exhibited a similar stimulatory effect on α-ENaC expression. The sPRR-His-induced α-ENaC expression was nearly completely abolished by a frizzled-8 inhibitor OMP54F03 (OMP). Similarly, amiloride-sensitive Na + transport as assessed by epithelial volt-ohmmeter was elevated by exposure to sPRR-His within minutes, which was abolished by OMP. In mpkCCD cells expressing a β-catenin-driven luciferase construct, the reporter activity was increased by 2.5-fold which was sensitive to OMP. In these cells, ENaC activity was transiently stimulated by exposure to 100 nM AngII within minutes, which was abolished by a sPRR neutralizing antibody. ELISA demonstrated that 24-h AngII treatment induced a 7-fold increase in medium sPRR concentrations. In floxed mice, urinary sPRR excretion was increased by AngII infusion whereas CD-specific PRR KO mice exhibited a reduced bassline level of urinary sPRR excretion which was not responsive to AngII infusion (300 ng/kg/min). Radiotelemetry demonstrated that the null mice were largely resistant to AngII-induced hypertension (MAP: Floxed/CTR: 105.9±1.6; Floxed/AngII: 136.3±3.1; KO/CTR:106.3±3.6; KO/AngII: 118.7±3.1 mmHg) which was fully restored after sPRR-His infusion via catheterization of jugular vein at 30 μg/kg/d (MAP: KO/AngII+sPRR-His: 135±7.5 mmHg). The MAP returned to normal when sPRR-His was terminated. Together, the present study reveals frizzled-8/β-catenin-dependent activation of α-ENaC in response to sPRR that at least in part contributes to AngII-induced hypertension.