Abstract 096: Renal-Specific Deletion of (Pro)Renin Receptor in Mice Induces Hyperkalemia During High Potassium Intake

We have previously shown that systemic administration of (pro)renin receptor (PRR) decoy inhibitor PRO20 impaired kaliuretic response to high K + (HK) intake (5% KCl in diet). The present study extends this observation by examining the phenotype of inducible renal tubule-specific PRR knockout (RT PRR KO) mice fed a HK diet. The null mice were generated by breeding Floxed PRR mice with mice transgenic for Pax8-rtTA and LC-1 transgene. To induce RT PRR KO, mice with homozygous for Floxed PRR gene and hemizygous for the Pax8-rtTA and the LC-1 transgene were given 2 mg/ml doxycycline in 5% sucrose drinking water for 14 days followed by 4-wk off doxycycline. Following 1-wk HK intake, RT PRR KO mice had decreased urinary K + (by 33.6%) excretion and elevated plasma K + level (KO+HK: 5.38 ± 0.21 vs. Floxed+HK: 3.98 ± 0.03 mM, P <0.001), accompanied with a reduction of urinary prorenin/renin content (by 56.5%), urinary renin activity (by 69.6%), urinary free and total Aldo excretion (by 41.2% and 25.3%, respectively), and kidney cortical and medullary Aldo levels (by 62.0% and 64.2%, respectively), without affecting plasma Aldo or renin levels. HK upregulated renal protein expression of fPRR (cortical: 170.4%, medullary: 195.0%), sPRR (cortical: 138.0%, medullary: 180.1%), prorenin (cortical: 217.5%, medullary: 164.0%), renin (cortical: 183.2%, medullary: 153.1%), Aldo synthase CYP11B2 (cortical: 321.6%, medullary: 243.8%), ROMK (165.4%), α-BK (161.4%), α-Na + -K + -ATPase (160.3%), β-ENaC (130.2%), and cleaved-γ-ENaC (542.0%), and downregulated phosphorylated NCC-T53 (pNCC-T53) protein expression, all of which were significantly blunted in RT PRR KO mice (by 25-80%). In Flp-In T-REX 293 NCC cell line (stably expressing NCC), PRR siRNA significantly increased pNCC-T53 (by 72.3%) and partially reversed prorenin (100 nM)-induced inhibition of pNCC-T53 (by 38.2%). sPRR-His (10 nM) inhibited pNCC-T53 (by 48.9%), which were significantly reversed by losartan or angiotensin II receptor type 1 (AT1R) siRNA, without affecting total NCC expression. Together, these results suggest that PRR/sPRR contributes to the kaliuretic response through an impact on the intrarenal RAAS and the K + secretory machinery in the distal nephron.