Proximal Tubule-Specific Deletion of Angiotensin II Type 1a Receptors in the Kidney Attenuates Circulating and Intratubular Angiotensin II-Induced Hypertension in PT- Agtr1a-/- Mice

Abstract

[Figure: see text].

Keywords: angiotensin II; electrolytes; homeostasis; hypertension; natriuresis.

Figure 1.

The effects of global or proximal tubule-specific deletion of AT_1a receptors in the kidney on glomerular and proximal tubular ultrastructure in adult male wild-type (WT), global Agtr1a^−/−, and PT-Agtr1a^−/− mice. A & D: high resolution electron microscopic (EM) micrographs showing the ultrastructure of representative glomerulus (9,720 X) and proximal tubules (32,100 X) in adult male WT mice. B & E: EM micrographs showing the ultrastructure of representative glomerulus (6,430 X) and proximal tubules (32,100 X) in adult male Agtr1a^−/− mice. C & F: EM micrographs showing the ultrastructure of representative glomerulus (6,430 X) and proximal tubules (32,100 X) in adult male PT-Agtr1a^−/− mice. In global Agtr1a^−/− mice, glomerular endothelial, epithelial and mesangial cells were largely similar to those of WT mice, but podocytes were thinner, whereas Bowman’s capsule was wider and the basement thickened, compared with WT mice. There were no significant differences in glomerular and proximal tubular ultrastructure between wild-type and PT-Agtr1a^−/− mice. Abbreviations: Ca, capillaries; Me, mesangial cell; Mito, mitochondria; MV, microvilli of the proximal tubule; N=6 per group.

Figure 2.

Basal systolic, diastolic and mean arterial blood pressure, glomerular filtration rate (GFR), and urinary Na⁺ and K⁺ excretory phenotypes in adult male wild-type, global Agtr1a^−/−, and PT-Agtr1a^−/− mice. Global deletion of AT_1a receptors decreases basal blood pressure by ~30 ± 3 mmHg in Agtr1a^−/− mice, whereas proximal tubule-specific deletion of AT_1a receptors lowers basal blood pressure by ~15 ± 3 mmHg in PT-Agtr1a^−/−mice (A-C). Global deletion of AT_1a receptors decreases in Agtr1a^−/− mice, whereas proximal tubule-specific deletion of AT_1a receptors increases GFR in PT-Agtr1a^−/− mice, respectively (D). Both global and proximal tubule-specific deletion of AT_1a receptors induced significant natriuresis (E) without altering K⁺ excretion (F). *P<0.05 or **P<0.01 vs. WT mice; ⁺⁺P<0.01 vs. global Agtr1a^−/− mice.

Figure 3.

Proximal tubule-specific deletion of AT_1a receptors in the kidney augments the pressure-natriuresis response (A) and the natriuretic response to acute saline expansion (B) or chronic high salt diet (C) in adult male PT-Agtr1a^−/− mice. In response to an increase of ~30 mmHg in renal perfusion pressure (RPP), the pressure-natriureiss response increased ~3-fold in wild-type mice, whereas the response increased ~4-fold in PT-Agtr1a^−/− mice (A, **P<0.01). In response to 10% saline expansion, the natriuretic response increased >6-fold in wild-type, but 10-fold in PT-Agtr1a^−/− mice (B, **P<0.01 vs. control; ⁺⁺P<0.0 vs. wild-type). Finally in response to 2% high salt diet for 2 weeks, 24 h urinary Na⁺ excretion increased 1.9-fold in Agtr1a^−/− and 2.5-fold in PT-Agtr1a^−/− mice, respectively (C, **P<0.01 vs. control; ⁺⁺P<0.0 vs. wild-type).

Figure 4.

Proximal tubule-specific deletion of AT_1a receptors in the kidney significantly attenuates hypertension induced by adenovirus-mediated overexpression of an intracellular Ang II fusion protein, Ad-sglt2-ECFP/Ang II, selectively in the proximal tubules of the kidney (A-C), or by systemic infusion of Ang II (D-F). Please note that systemic infusion of a pressor dose of Ang II for 2 weeks (1.5 mg/kg/day, i.p.) increased blood pressure >45 mmHg in wild-type mice, and this response to Ang II was halved in PT-Agtr1a^−/− mice (B). Concurrent treatment of Ang II-infused wild-type or PT-Agtr1a^−/− mice with the AT₁ receptor blocker losartan (20 mg/kg/day, p.o.) normalized blood pressure to the basal level of wild-type mice (C). In response to proximal tubule-specific expression of Ad-sglt2-ECFP/Ang II, blood pressure increased 17 ± 3 mmHg in wild-type mice, and the response was blocked completely in PT-Agtr1a^−/− mice (E), or by losartan (F). Ang II or Ad-sglt2-ECFP/Ang II had no effect on blood pressure in global Agtr1a^−/− mice (B & E). **P<0.01 vs. wild-type; ⁺P<0.05 or ⁺⁺P<0.01 vs. Agtr1a^−/− mice.

Figure 5.

Effects of proximal tubule-specific deletion of AT_1a receptors in the kidney on 24 h urine excretion, urinary Na⁺ and K⁺ excretion in adult male PT-Agtr1a^−/− mice. Note that systemic Ang II infusion moderately increased 24 h urine and urinary Na⁺ excretion in both wild-type and PT-Agtr1a^−/− mice (A & B) without altering urinary K⁺ excretion (C). By contrast, adenovirus-mediated expression of Ad-sglt2-ECFP/Ang II selectively in the proximal tubules induced antidiuretic and antinatriuretic responses in wild-type mice, but not in PT-Agtr1a^−/− mice (D & E). *P<0.05 or **P<0.01 vs. wild-type mice. ⁺P<0.05 or ⁺⁺P<0.01 vs. wild-type control (D & E) or vs. Ang II in PT-Agtr1a^−/− mice (B).

Figure 6.

Roles of the Na⁺/H⁺ exchanger 3 (NHE3), superoxide, and Ang III in the blood pressure and natriuretic responses to Ang II-induced hypertension in PT-Nhe3^−/− and PT-Agtr1a^−/− mice. Note that proximal tubule-specific deletion of either NHE3 or AT_1a receptors in the kidney lowered basal blood pressure and attenuated Ang II-induced hypertension to a similar extent (A), and induced natriuretic responses to a similar degree under basal conditions and during Ang II-induced hypertension (D). Concurrent Tempol treatment had no effect on Ang II-induced hypertension (B) and natriuretic responses in wild-type and PT-Agtr1a^−/− mice (E). At physiological concentration (10 ng/min, i.v.), Ang III had no effect on blood pressure (C), but induced a significant natriuretic response in PT-Agtr1a^−/− mice (F). **P<0.01 vs. control wild-type (A), PT-Nhe3^−/− or PT-Agtr1a^−/− mice. ⁺P<0.05 or ⁺⁺P<0.01 vs. their respective controls or during Ang II infusion.