Abnormalities of beta2-adrenergic receptor (beta2-AR) function have been found in human essential hypertension and animal models of genetic hypertension. Mice with disrupted beta2- AR genes and their regulators are in loci associated with hypertension and genetic variations of beta2-AR are associated with hypertension. Beta2-ARs increase cAMP production, Na+/K+ATPase activity, and sodium transport; a decrease in these actions can cause the increased vascular reactivity in hypertension, However, a decrease in beta2-AR function in renal tubules should lead to sodium loss, which potentially could lead to a decrease in blood pressure, offsetting the effect on vascular reactivity. The overall hypothesis is that in the kidney beta2-AR single nucleotide polymorphisms (SNPs) do not lead to sodium loss because sodium/hydrogen exchanger (NHE)-3 activity is increased in the kidney. We hypothesize that renal NHE3 activity is increased in subjects with beta2-AR SNPs because of an increased binding affinity of variant beta2-ARs to the NHE regulatory factor (NHERF). This leads to a decrease in NHERF available to inhibit NHE3 activity.
Specific aim 1 will determine whether the interaction between beta2-AR in a heterologous expression system. We will determine whether genetically hypertensive rats have beta2-ARs SNPs. Even if there are no beta2-AR SNPs in genetically hypertensive rats, the reported increase in beta2-ARs in the kidney in genetically hypertensive rats may still result in increased binding of NHERF with the same consequences as variant beta2-ARs. Therefore, we will also quantify beta2-ARs, NHERF, and NHE3 protein in renal tubules and determine whether the binding of beta2-ARs to NHERF is increased in genetically hypertensive rats. Preliminary data indicate that the activity of a G protein-coupled receptor kinase, GRK6, is increased in renal proximal tubule cells of spontaneously hypertensive rats (SHR) compared with their normotensive controls, Wistar-Kyoto (WKY) rats. Because GRK6 can phosphorylate both beta2-AR and NHERF, specific aim 2 will determine if GRK6 activity in renal proximal tubules is, indeed, increased in SHR. We will also determine if the phosphorylation of beta2-ARs and NHERF is increased in SHR and whether such an increase is caused by increased GRK6 activity. Finally, the mechanism of the increased GRK6 activity in SHRs will be determined. These studies should allow us to determine the role of aberrant beta2-AR regulation of NHERF in genetic hypertension.
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