Renal Proximal Tubule Angiotensin Type 2 Receptor's Role in Pressure Natriuresis

Background: Acute renal angiotensin type 2 receptor (AT 2 R) activation promotes natriuresis, and chronic renal and systemic AT 2 R stimulation blunts angiotensin II-induced hypertension. AT 2 Rs are expressed in renal proximal and distal tubules as well as the renal vasculature. To test the hypothesis that the renal proximal tubule AT 2 R plays a key role in natriuresis and blood pressure control, we generated renal proximal tubule-specific AT 2 R knockout (PT-AT 2 R-/-) mice. Methods and Results: Mice with the AT 2 R exon 3 flanked by loxP sites were crossed with mice overexpressing cre recombinase under the control of the renal proximal tubule cell (RPTC)-specific sodium and glucose cotransporter 2 (Sglt2) promotor. The resulting male and female PT-AT 2 R-/- mice showed a selective deletion of the AT 2 R in proximal tubules with a 79% and 66% (p<0.0001) decrease, respectively, in AT 2 R protein levels. Initial experiments documented the unique role for the RPTC AT 2 R in promoting natriuresis; in PT-AT 2 R-/- mice the natriuretic response was abolished in response to renal interstitial (RI) infusion of the selective AT 2 R agonist C21. Pressure natriuresis is a key mechanism by which sodium excretion and consequently blood pressure is controlled. It is defective in hypertensive humans and animal models of hypertension. To test whether the PT-AT 2 R plays a role in pressure natriuresis, we determined the natriuretic response to an acute increase in renal perfusion pressure (RPP) in PT-AT 2 R-/- and control mice. We found that urinary sodium excretion (UNaV) was reduced by 67% and 59% (p<0.0001), respectively, in male and female PT-AT 2 R -/- mice, when compared to control. Elevated RPP, consistent with earlier results in rats, increased RI cGMP more than 2-fold (p=0.007) in control mice, but no change in cGMP was found in PT-AT 2 R-/- mice. Using confocal immunofluorescence microscopy, we observed that concomitant with reduced sodium excretion, sodium hydrogen exchanger-3 (NHE3) retrieval from brush border microvilli of RPTC was defective in PT-AT 2 R -/- mice in response to increased RPP. Also, while elevated RPP increased phosphorylation of the kinase src in the renal cortex of control mice, this response was abolished in PT-AT 2 R-/- mice. Conclusion: Our results with PT-AT 2 R-/- mice suggest that the RPTC AT 2 R is a key mediator of pressure natriuresis. Targeting the AT 2 R may thus provide a novel approach to improve pressure natriuresis and better control blood pressure in hypertension.