Abstract 115: Renal-Specific Expression of Human Grk4 R65L in Mice Lacking Grk4 Increases Blood Pressure

Abstract

The genetic causes of salt (NaCl) sensitivity in humans are not well understood. The kidney is critical to the overall fluid and electrolyte balance and long-term regulation of blood pressure (BP). Therefore, the pathogenesis of salt sensitivity must involve a deficient renal NaCl handling. The renal paracrine inhibition of Na + transport by dopamine is impaired in salt-sensitive rats, mice, and humans due to decreased dopamine D1 receptor (D1R) function and not related to a primary defect of the D1R gene but rather due to its uncoupling from second messengers caused by activating variants of the human G protein-coupled receptor kinase type 4 (h GRK4 ) (R65L, A142V, and A486V). We have shown that global transgenic mice expressing hGRK4 R65L variant have salt-sensitive hypertension. To determine the role of the kidney in the salt-sensitivity of these mice, we developed a mouse model of kidney-specific expression of the R65L variant (KS hGRK4 R65L) by bilateral ureteral infusion of AAV vectors carrying the variant in GRK4 knockout mice. Mice infused with hGRK4 wild-type served as controls (KS hGRK4 WT). Systolic BP (SBP) was measured under anesthesia in the mice before and after infusion of the AAV vectors. SBP before AAV was similar in both groups. SBP post AAV increased in KS hGRK4 R65L (93±1 vs 117±4 mmHg, P<0.05, n=4) but not in KS hGRK4 WT (96±2 vs 105±6, n=5). Renal mRNA expressions of dopamine 1 (D1R, 0.81±0.01 vs 1.28±0.04, P<0.01), D3R (0.44±0.02 vs 1.27±0.07, P<0.01) and angiotensin AT1A (AT1A, 0.78±0.02 vs 1.02±0.02, P<0.01) receptors were decreased in renal cortex of KS hGRK4 R65L relative to KS hGRK4 WT. In addition, the expressions of Na + /K + ATPase (1.12±0.03 vs 1.0 ±0.007, P<0.05) and ENaC (1.4±0.14 vs 1.0±0.11, P<0.05) were increased while those of the proximal tubule Na + transporters NaPi2 (0.81±0.02 vs 1.04±0.02), SGLT2 (0.89±0.03 vs 1.07±0.05), and NBCe2 (0.50±0.07 vs 1.15±0.03) were decreased. Our results show that kidney specific expression of hGRK4 R65L increased SBP and produced changes in the expression of receptors and Na + transporters, pump, and channel but their roles in the increased SBP remain to be determined.