Hypertension and salt sensitivity are major contributors to human morbidity and mortality. However, there has been slow progress in the understanding of the etiology or the link between personal genetics, biochemical regulation, and environmental influences. Our work has shown that two renal regulatory pathways that counter-regulate sodium reabsorption in the renal tubule, namely, dopamine (inhibitory) and angiotensin (stimulatory), are central in the etiology of hypertension and salt sensitivity. We have reported that increased activity of G protein-coupled receptor kinase type 4 (GRK4), because of activating variants, directly causes the dysregulation of dopamine receptors, as well as the angiotensin receptors, in renal proximal tubule cells (RPTCs) from humans with essential hypertension. In animal models, transgenic mice over expressing GRK4y wild-type gene are normotensive, while GRK4Y 142V transgenic mice are hypertensive and salt-sensitive, while GRK4y486V transgenic mice are salt-sensitive. The overall objective of this program project is the study of novel mechanisms of trans-regulation, including protein degradation, between the dopamine and angiotensin receptors in renal tubule cells. These novel mechanisms will be examined in novel mouse models, and in humans in whom in vivo renal functional studies will be correlated with studies in freshly voided renal tubule cells obtained from the same individual. Supported by administrative, analytical, and animal core laboratories, Project 1 will test the hypothesis that novel spatiotemporal interactions between and among dopaminergic and angiotensin receptors and several key regulatory proteins (DiR, D5R, ATiR, and GRK4) occur in lipid rafts and are regulated by the interaction between caveolin-1 and GRK4 in human RPTCs. We also hypothesize that the facilitatory effect of caveolin-1 on DiR function is impaired by GRK4 gene variants. Project 2 will test the hypothesis that ATiR-mediated antinatriuresis is opposed by DiRs and D3RS, acting in concert in normal human subjects, and that this protective mechanism is deficient in patients with essential hypertension. The physiologic responses to selective dopaminergic and angiotensin system stimulation from a specific subject will be correlated with single renal cell physiological responses from the urine-derived cells obtained from the same subject. This will enable us to correlate renal functional responses with renal cellular studies in the same subject. Project 3 will test the hypothesis that the hypertension that occurs with decreased D3R expression or function (caused by GRK4 gene variants) is due to increased activity and expression of NHE3, NCC, and ENaC;their increased expression is caused by decreased degradation due to their deubiquitination (a.k.a. deubiquitinylation) by USP48. This basic and translational grant application will delineate new insights into the interactions between the dopaminergic and renin-angiotensin systems and provide new insight that will lead to new therapeutic approaches.
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