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

The present study used a novel mouse model with proximal tubule-specific knockout of AT 1a receptors in the kidney, PT- Agtr1a −/− , to test the hypothesis that intratubular Ang II (angiotensin II) and AT 1a receptors in the proximal tubules are required for maintaining normal blood pressure and the development of Ang II–induced hypertension. Twenty-six groups (n=6–15 per group) of adult male wild-type, global Agtr1a −/− , and PT- Agtr1a −/− mice were infused with Ang II (1.5 mg/kg per day, IP), or overexpressed an intracellular Ang II fusion protein in the proximal tubules for 2 weeks. Basal telemetry blood pressure were ≈15±3 mm Hg lower in PT- Agtr1a −/− than wild-type mice and ≈13±3 mm Hg higher than Agtr1a −/− mice ( P <0.01). Basal glomerular filtration was ≈23.9% higher ( P <0.01), whereas fractional proximal tubule Na + reabsorption was lower in PT- Agtr1a −/− mice ( P <0.01). Deletion of AT 1a receptors in the proximal tubules augmented the pressure-natriuresis response ( P <0.01) and natriuretic responses to salt loading or Ang III infusion ( P <0.01). Ang II induced hypertension in wild-type, PT- Agtr1a −/− and PT- Nhe3 −/− mice, but the pressor response was ≈16±2 mm Hg lower in PT- Agtr1a −/− and PT- Nhe3 −/− mice ( P <0.01). Deletion of AT 1a receptors or NHE3 (Na + /H + exchanger 3) in the proximal tubules attenuated ≈50% of Ang II–induced hypertension in wild-type mice ( P <0.01), but blocked intracellular Ang II fusion protein-induced hypertension in PT- Agtr1a −/− mice ( P <0.01). Taken together, the results of the present study provide new insights into the critical role of intratubular Ang II/AT 1 (AT 1a )/NHE3 pathways in the proximal tubules in normal blood pressure control and the development of Ang II–induced hypertension.

Intratubular, Intracellular, and Mitochondrial Angiotensin II/AT1 (AT1a) Receptor/NHE3 Signaling Plays a Critical Role in Angiotensin II-Induced Hypertension and Kidney Injury

“…We and others have evidence that intracellular administration of Ang II induces the expression of nuclear factor-κB ( Brasier et al, 2000 ; Ruiz-Ortega et al, 2000 ; Zhuo et al, 2006b , 2016 ; Schupp et al, 2007 ; Li and Zhuo, 2008a ), monocyte chemoattractant protein 1 (MCP-1; Zhuo, 2004 ; Li and Zhuo, 2008a ; Takahashi et al, 2008 ), TNF-α ( Takahashi et al, 2008 ), TGF-β1, and NHE3 ( Kagami et al, 1994 ; Wolf et al, 1999 ; Weigert et al, 2002 ), and induces production in the mitochondria and nucleus of the proximal tubule cells ( Gwathmey et al, 2010a , b ; Li et al, 2020 ). Furthermore, global or proximal tubule-specific overexpression of an intracellular ANG II fusion protein selectively in the proximal tubules of the kidney, Ad-sglt2-ECFP/Ang II ( Figure 1 ), or in the mitochondria of the proximal tubules, Ad-sglt2-mito-ECFP/Ang II, developed antinatriuretic responses and elevated blood pressure by altering the mitochondrial functions ( Li et al, 2011b , 2020 , 2021 ; Li and Zhuo, 2013 ). Overall, these proof of concept studies strongly support a new paradigm of a functional proximal tubule intratubular, intracellular, and mitochondrial Ang II system in the development of hypertension and renal injury.…”

“…The pressure-natriuresis response is a central element of the overall feedback mechanism for long-term control of arterial pressure, in which an increase in arterial pressure will lead to a decrease in Na + reabsorption and a natriuresis response in the kidney and restore blood pressure to normal ( Roman, 1986 ; Cowley and Roman, 1996 ; Hall et al, 1996 ; Granger et al, 2002 ; Li et al, 2018 , 2019a , 2021 ). The pressure natriuresis response is reportedly mediated by: (a) inhibition of proximal tubule Na + transport ( Moreno et al, 2001 ; Dos Santos et al, 2004 ), (b) increase in renal interstitial hydrostatic pressure ( Li and Zhuo, 2013 ), (c) increase in renal medullary blood flow ( Roman, 1986 ; Williams et al, 2007 ), (d) increase in 20-HETE production ( Moreno et al, 2001 ; Dos Santos et al, 2004 ; Williams et al, 2007 ), (e) increase in AT 2 -mediated cGMP production ( Siragy and Carey, 1996 ; Jin et al, 2001 , 2004 ), (f) increased dopamine-induced signaling ( Hussain and Lokhandwala, 1998 ; Banday and Lokhandwala, 2008 ; Wang et al, 2009 ), or (g) increased renal nitric oxide ( Majid et al, 1993 , 1998 ).…”

“…We hypothesized that intratubular Ang II via activating AT 1 (AT 1a ) receptors in the proximal tubules plays a key role in the regulation of the pressure natriuresis response and it is resetting in Ang II-dependent hypertension. Indeed, an impaired pressure natriuresis response has been reported in SHR ( Roman and Cowley, 1985 ; Roman, 1987 ) and animal models of L-NAME- ( Majid et al, 1993 ; Granger and Alexander, 2000 ), 2-Kidney, 1-Clip ( Rostand et al, 1982 ), TGR (mRen-2)27- ( Gross et al, 1994 ; Zhuo et al, 1999 ), and Ang II-induced hypertension ( Mattson et al, 1991 ; Wang et al, 2000 ; Zhuo et al, 2002 ; Li et al, 2011a , 2021 ). Most, if not all, of these hypertension models involve the activation of intratubular Ang II and AT 1 (AT 1a ) receptors in the proximal tubules, which stimulates proximal tubule Na + reabsorption and induces Na + retention.…”

“…To overcome the limitation of these technical approaches, we have recently used the Sglt2-Cre / Agtr1a -foxed recombination to delete AT 1 (AT 1a ) receptors selectively in the proximal tubules of the kidney and to determine the specific roles of intratubular Ang II and AT 1 (AT 1a ) receptors in basal blood pressure homeostasis and the development of hypertension induced by circulating or intracellular Ang II ( Rubera et al, 2004 ; Li et al, 2011b , 2021 ; Rateri et al, 2011 ). The hypothesis to be tested was that intratubular Ang II and AT 1a receptors in the proximal tubules are required for maintaining normal blood pressure and the development of Ang II-induced hypertension.…”

“…), a slow pressor dose of Ang II (0.5 mg/kg/day, i.p. ), or with adenovirus-mediated overexpression of an intracellular Ang II fusion protein in the proximal tubules of the kidney for 2 weeks ( Figure 2 ; Li et al, 2021 ). Deletion of AT 1a receptors in the proximal tubules led to a decrease in basal telemetry blood pressure by ~15 ± 3 mmHg in PT- Agtr1a −/− than wild-type mice, which was ~13 ± 3 mmHg higher than the whole-body Agtr1a −/− mice.…”