G protein-coupled kinase type 4 (GRK4) gene variants (R65L, A142V, and A486V) selectively desensitizes the dopamine-1 receptor (DIR) and not the D5R, which upregulates the angiotensin type 1 receptor (ATIR). The net result of a desensitized DIR (natriuretic) and upregulated ATIR (antinatriuretic) is a net sodium reabsorption by the kidney. However, the molecular mechanisms responsible for DIR desensitization, ATIR upregulation, and the integration of these two pathways on net sodium metabolism are not well understood. We hypothesize that the membrane localization and ultimate activity of the DIR, D5R, and ATIR are regulated by oligomerization and spatial orientation via scaffolding proteins (e.g. caveolin-l (CAV1)), which ultimately regulate their interaction with intracellular second messengers. Specifically, GRK4 binds to caveolin-l (CAV1) which is interrupted by the presence of gene variants. We further hypothesize that a molecular trimeric D1R/CAV1/GRK4 association may be necessary for dopaminergic inhibition of NaKATPase activity via intracellular internalization in conjunction with adapter protein-2 (AP-2).
Specific Aim 1 will examine the spatiotemporal transregulation of the DIR, D5R, ATIR, and CAV1 and their link to intracellular second messengers. In order to increase the relevance of our studies to human physiology and pathophysiology, we will study these phenomenon in 60 human renal proximal tubular cells (RPTCs) lines that have been genotyped for GRK4 variants.
Specific Aim 2 will study spatiotemporal transregulation of the DIR, D5R, ATIR, and CAVIand their effect on the activity of the principal sodium transporters in human RPTCs NaKATPase and NHE3. The study of the effect of gene variants of GKR4 on the single RPTC physiology representing wide genetic diversity will improve our understanding of how the renal proximal tubule controls renal sodium excretion, and lead to potential novel therapeutic targets for the development of targeted and personalized antihypertensive therapeutics.
Understanding the dynamic relationships between two key sodium regulatory pathways in the kidney is essential to deciphering the basic etiology of hypertension and salt sensitivity, major causes of common serious diseases. Since these diseases disproportionatly effect low income populations, effective targeted treatments are needed to reduce the burden on medicaid and medicare reciptients.
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