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