Genetic Evidence for A Critical Role of Intratubular Angiotensin II AT1aReceptors in The Proximal Tubules of The Kidney in Two‐Kidney, One‐Clip Goldblatt Hypertension in PT‐Agtr1a‐/‐Mice

Abstract

It was previously reported the activation of the renin‐angiotensin system (RAS) in the clipped kidney plays a critical role in the development of two‐kidney, one‐clip Goldblatt hypertension (2K1C). However, most of previous studies used the global angiotensin II (Ang II) type 1a (AT1a) receptor (Agtr1a‐/‐) knockout model or used systemic AT1receptor blockers (ARB) to determine renal mechanisms of 2K1C hypertension. The roles of intratubular AT1 (AT1a) receptors or its downstream target Na+/H+ exchanger 3 (NHE3) in the proximal tubules in the development of 2K1C hypertension has not been determined previously. In the present study, we tested the hypothesis that genetic deletion of AT1 (AT1a) receptors selectively in the proximal tubules attenuates the development of 2K1C hypertension via AT1 (AT1a) receptor‐mediated, Na+/H+ exchanger 3 (NHE3)‐dependent mechanisms. To test the hypothesis, 2K1C Goldblatt hypertension was induced by placing a silver clip, 0.12 mm internal diameter, on the left renal artery for 4 weeks in adult male wild‐type (WT), global Agtr1a‐/‐, proximal tubule (PT)‐specific PT‐Agtr1a‐/‐, or PT‐Nhe3‐/‐ (Na+/H+ exchanger 3) mice, respectively. As expected, systolic blood pressure increased in a time‐dependent manner in wild‐type mice, reaching a maximal response by Week 3 (Basal: 112 ± 2 vs. 2K1C: 149 ± 4 mmHg, n=12, P<0.01). 2K1C hypertension in WT mice was associated with increases in renin mRNA expression in the clipped kidney (Control: 2066 ± 255 vs. Clipped: 3144 ± 569 copies/ng RNA, P<0.01), and decreases in renin mRNA expression in the nonclipped right kidney (1738 ± 341 copies/ng RNA, P<0.05). Plasma Ang II levels were significantly increased in WT mice with 2K1C hypertension (Control: 50.2 ± 7.2 vs. 2K1C: 109.7 ± 17.2 pg/ml, P<0.05). Glomerular and tubulointerstitial fibrotic responses were also significantly increased in the clipped kidney (P<0.01). By comparisons, the development of 2K1C hypertension was entirely prevented in Agtr1a‐/‐ (Basal: 88 ± 4 vs. 2K1C: 92 ± 2 mmHg, n=9, n.s.), or significantly attenuated in PT‐Agtr1a‐/‐ mice (Basal: 101 ± 2 vs. 2K1C: 104 ± 4 mmHg, n=12, n.s.) or in PT‐Nhe3‐/‐ mice (Basal: 103 ± 3 vs. 109 ± 5 mmHg, n.s.). Renin mRNA expression was not different in clipped and nonclipped kidney of Agtr1a‐/‐ mice, but it was decreased in the nonclipped kidney of PT‐Agtr1a‐/‐ mice (P<0.05). Furthermore, glomerular and tubulointerstitial fibrotic responses were also markedly attenuated in the clipped kidney in PT‐Agtr1a‐/‐ mice (P<0.05). We conclude that the results of the present study provide strong evidence for a critical role of AT1a receptors and NHE3 in the proximal tubules of the kidney in the development of 2K1C Goldblatt hypertension in mice.