The D1 dopamine receptor (D1R) is important in the regulation of blood pressure (BP). Drd1 germline deletion in mice causes hypertension. G protein-coupled receptor kinase type 4 (GRK4) is important in the normal cellular recycling and function of D1R. However, some of the recycled D1R has to be targeted to lipid rafts to be functional. Thus, mutant D1Rs 347C>A and 351C>A still target to the plasma membrane but fail to localize in lipid rafts; these mutations prevent the increase in D1R-mediated stimulation of cAMP production in renal proximal tubule cells (RPTCs) and impair (e.g., 347C>A) normal BP regulation in mice. C347 and C351 in D1R are palmitoylation sites; SNX19 functions as a scaffold protein for the palmitoylation of D1R at the Golgi, via Golgi-specific zinc finger protein. Lipid rafts are also needed for the proper membrane distribution and maintenance of adenylyl cyclases 5 and 6 and regulation by D1R. Inhibition or molecular biological disruption of palmitoylation prevents D1R targeting to lipid rafts, impairs D1R function, and causes hypertension. Silencing SNX19 impairs D1R-mediated increase in cAMP and decrease in Na+ transport in RPTCs but not distal convoluted tubule cells. Renal SNX19 is important in the regulation of BP; renal-restricted silencing of Snx19 increases BP in C57Bl/6 mice on normal but not low salt diet. Germline deletion of SNX19 in mice also increases BP on normal salt diet. SNX19 is upstream of D1R. SNX19 rs2298566 is associated with decreased ability to excrete Na+ and high BP in humans and impairs D1R function in human (h)RPTCs. SNX19 protein is decreased in hRPTCs from hypertensive humans. We will test the overall hypothesis that SNX19 is important in the trafficking of D1R to lipid rafts in the RPT plasma membrane for normal D1R function. Impaired functioning of D1R in the kidney, caused by its impaired trafficking to lipid rafts in RPT plasma membranes, causes salt-sensitive hypertension.
Specific Aim 1 will test the hypothesis that SNX19 targeting of D1R into the lipid rafts of RPTC plasma membrane is crucial for normal D1R function. SNX19 and GRK4 interact in lipid rafts to regulate D1R function, including D1R-mediated inhibition of Na+ transport in RPTCs.
Specific aim 2 will test the hypothesis that mutations of the palmitoylation sites in the D1R gene prevent the ability of SNX19 to target the D1R to lipid rafts in the RPTC plasma membrane. Germline deletion or renal-restricted deletion of SNX19 in C57Bl/6 mice causes salt- sensitive hypertension. Mutating DRD1 to prevent D1R targeting to lipid rafts of RPTC plasma membrane also causes salt-sensitive hypertension. These genes and their proteins could be targets in the treatment of human essential hypertension.
Knowledge of the details of the interactions of D1R, GRK4, and SNX19 in the kidney is important because these genes and their protein products could be targets in the treatment of human essential hypertension. One can take advantage of the low minor allele frequencies of SNX19 polymorphisms to develop pharmacological agents to increase D1R expression and function; DRD1 and GRK4 minor allele frequencies are common (15-40%) that are variant and ethnicity specific.