Intratubular Angiotensin II and AT1a Receptors in The Proximal Tubules: Roles in Hypertension and Kidney Injury

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Hypertension is the most important risk factor for cardiovascular diseases, stroke, and end-stage kidney failure. In the United States, nearly 46% of adults develop hypertension and will be treated with antihypertensive drugs in their lifetime. Only 50% of hypertensive patients are responsive to current antihypertensive drugs, whereas 1/3 of remaining hypertensive patients will develop cardiovascular, stroke and renal complications. The mechanisms responsible for the development of cardiovascular and kidney injury and the reasons for poor responses to current antihypertensive therapies remain incompletely understood. Thus, further studies are necessary in order to uncover new mechanisms, pathways, and therapeutic targets of uncontrolled hypertension and target organ injury. In preliminary studies, we used the state of the art SGLT2-Cre/LoxP approach to delete angiotensin II (ANG II) AT1a receptors, the Na+/H+ exchanger 3 (NHE3), or a key mitochondrial protein sirtuin 3 (SIRT3) selectively in the S1 and S2 segments of the proximal tubules in the kidney. We have evidence that proximal tubule-specific deletion of AT1a or NHE3 decreases basal blood pressure, augments the pressure natriuresis response, and attenuates ANG II-induced hypertension, and that proximal tubule-specific deletion of AT1a receptors significantly attenuated, whereas proximal tubule-specific deletion of SIRT3 significantly worsened renal ischemia and reperfusion (I/R) injury. These preliminary studies strongly suggest that intratubular ANG II and its AT1a receptors and SIRT3 in the proximal tubules play an important role in the development of hypertension and renal I/R injury. In this proposal, we will test the hypotheses that intratubular ANG II and AT1a receptors in the proximal tubules of the kidney are required for the development of ANG II-induced hypertension and renal I/R injury, and that deletion of AT1a receptors or angiotensinogen (AGT) selectively in the proximal tubules will attenuate ANG II-induced hypertension and renal I/R injury in two specific aims. Specific Aim 1 will test the hypothesis that intratubular ANG II and AT1a receptors in the proximal tubules play a key role in maintaining basal blood pressure homeostasis and the development of ANG II-induced hypertension, via the activation of the Na+/H+ antiporter (NHE3), Na+ and glucose cotransporter 2 (sglt2), and the regulation of the pressure natriuresis response. Specific Aim 2 will test the hypothesis that AT1a receptors in the proximal tubules play a key role in the pathogenesis of renal I/R injury, activated by intratubular and intracellular ANG II to upregulate Toll-Like receptor 4 (TLR-4), downregulate mitochondrial SIRT3 expression, and impair mitochondrial function in the proximal tubules. These hypotheses will be tested using highly innovative mouse models with global and proximal tubule-specific knockout of a) AT1a receptors; b) angiotensinogen; c) NHE3; d) SGLT2; e) TLR4; or f) SIRT3. ANG II-dependent hypertension and renal I/R injury will be induced by a) infusing a native ANG II; b) 2-kidney, 1-clip renal hypertension; c) a genetically encoded circulating Elastin-Like Polypeptide-ANG II (ELP-ANG II); or d) overexpressing a proximal tubule- specific, mitochondria-targeting intracellular ECFP/ANG II. Telemetry blood pressure, the pressure natriuresis response, noninvasive glomerular filtration rate, intravital two-photon imaging and XFe24 Extracellular Flux Analyzer to measure mitochondrial function, electron microscopic and immunohistochemical imaging, and Western blot analyses of proinflammatory, profibrotic and signaling proteins will be studied. The proposed studies are highly significant and clinically relevant, and the new knowledge will lead to a paradigm shift on understanding the pathogenesis of hypertension and renal I/R injury, and help develop proximal tubule-targeting drugs to treat poorly controlled hypertension and renal I/R injury.