Abstract 042: A Novel (pro)renin Receptor Variant Prr24 As A Specific Renin Receptor And Key Regulator Of Nkcc2 And Urine Concentrating Capability

Abstract

(Pro)renin receptor (PRR) has emerged as a key regulator of renal handling of Na + and water, and blood pressure (BP). Renal action of PRR is at least in part mediated through its ability to activate tissue prorenin and renin. In preliminary studies, investigation of a “non-specific” protein band recognized by an anti-PRR antibody against the extracellular domain led to identification of a novel 24-kDa isoform of PRR, termed as PRR24. PRR24 was encoded by a novel cDNA with part of 5’UTR arising from retention of intron 3 and an ATG in exon 5 as an alternative start codon so that this isoform overlaps completely with PRR except that N-terminal 136 amino acids are missing. PRR24 selectively bound and activated renin but not prorenin whereas PRR non-selectively interacted both prorenin and renin. PRR24 protein and mRNA expression was exclusively detected in the renal medulla but not renal cortex or extrarenal organs. Within the kidney, PRR24 mRNA was restricted to medullary thick ascending limb (mTAL) as assessed by RT-PCR on microdissected nephron segments. Using CRISP/Cas9 strategy, we generated a mouse model with mutagenesis of the start codon in exon 5 (termed PRR24 mut ) by replacing methionine with glutamine in PRR. Renal medullary protein expression of PRR24 was barely detectable contrasting unchanged PRR abundance in the null mice. PRR24 mut mice was born at Mendelian ratio and didn’t exhibit developmental abnormalities or mortality as seen in systemic PRR KO mice. PRR24 mut mice developed polyuria, hypoosmotic urine, polydipsia, hypotension (radiotelemetry MAP: WT 120 + 0.8 vs. Mutant 112 + 1.4 mmHg; p<0.05). Plasma volume assessed indirectly by hematocrit and directly assessed by using a fluorescent tracer was consistently reduced by 5-10%. Renal expression of NKCC2 was downregulated by 70% in parallel with reduced diuretic response to furosemide. Following 24-h water deprivation, the upregulation of NKCC2 expression was blunted in PRR24 mut mice associated with impaired urine concentrating capability as assessed by urine volume and osmolality. Overall, PRR24 is a novel PRR variant and serves as a specific renin receptor to regulate renal NKCC2 expression to ultimately determine urine concentrating capability.