Nephron-Specific Disruption of Polycystin-1 Induces Cyclooxygenase-2-Mediated Blood Pressure Reduction Independent of Cystogenesis.

Abstract

Hypertension often occurs before renal function deteriorates in autosomal dominant polycystic kidney disease (ADPKD). It is unknown whether the <i>Pkd1</i> gene product polycystin-1-the predominant causal factor in ADPKD-itself contributes to ADPKD hypertension independent of cystogenesis. We induced nephron-specific disruption of the <i>Pkd1</i> gene in 3-month-old mice and examined them at 4-5 months of age. Kidneys from the Pkd1 knockout mice showed no apparent renal cysts, tubule dilation, or increased cell proliferation. Compared with control mice, Pkd1 knockout mice exhibited reduced arterial pressure during high salt intake; this associated with an increased natriuretic, diuretic, and kaliuretic response during the first 2-3 days of salt loading. The lower arterial pressure and enhanced natriuresis during high salt loading in Pkd1 knockout mice were associated with lower urinary nitrite/nitrate excretion and markedly increased urinary PGE₂ excretion, whereas GFR, plasma renin concentration, and urinary endothelin-1 excretion were similar between knockout and control mice. Kidney cyclooxygenase-2 protein levels were increased in Pkd1 knockout mice during high salt intake; administration of NS-398, a selective cyclooxygenase-2 inhibitor, abolished the arterial pressure difference between the knockout and control mice during high salt intake. Total kidney Na⁺/K⁺/2Cl^- cotransporter isoform 2 (NKCC2) levels were greatly reduced in Pkd1 knockout mice fed a high salt diet compared with controls. These studies suggest that nephron polycystin-1 deficiency does not itself contribute to ADPKD hypertension and that it may, in fact, exert a relative salt-wasting effect. The work seems to comprise the first <i>in vivo</i> studies to describe a potential physiologic role for nephron polycystin-1 in the absence of cysts, tubule dilation, or enhanced cell proliferation.