GRK4γ R65L Causes Salt-Sensitive Hypertension by Increasing Renal SLC4A5 Expression Through the HDAC1 Pathway

Background: Variants of human G protein-coupled receptor kinase 4γ (hGRK4γ) are associated with hypertension. hGRK4γ A142V causes hypertension, in part, by increasing the expression of the angiotensin II type 1 receptor (AT1R) and impairing the function of renal dopamine receptors, D1R and D3R. hGRK4γ A486V impairs renal D1R function and causes oxidative stress. The role of hGRK4γ R65L in the pathogenesis of hypertension has not been reported. Methods: hGRK4γ wild-type (WT) and hGRK4γ R65L knock-in mice were generated through CRISP/Cas9-mediated homology-directed repair in C57Bl/6J mice. Mice were fed either a normal (0.8% NaCl), or high salt diet (6% NaCl) for 3 weeks. Blood pressure (BP) was measured from the carotid artery by telemetry. The kidneys were obtained for RT-PCR, immunohistochemistry, and immunoblotting. Sodium transport was measured in human renal proximal tubule cells (hRPTCs) with WT or GRK4γ variants Results: Global expression of hGRK4γR65L in mice causes salt-sensitive hypertension, due in part to an increase in endogenous renal GRK4 and AT1R expression. Grk4 knockout (Grk4-/-) mice have decreased BP and are salt-resistant. The expression of hGRK4γ R65L only in the kidney of Grk4-/- mice increases BP in response to a high salt diet. The renal expression of SLC4A5 is increased in hGRK4γ R65L transgenic mice, relative to GRK4γ WT transgenic mice, without the endogenous mGrk4. hRPTCs endogenously expressing hGRK4γ WT and SLC4A5 WT, SLC4A5 variants, hGRK4γ R65L, and both hGRK4γ R65L and SLC4A5 variants were studied. SLC4A5 expression is increased in hRPTCs expressing hGRK4γ R65L and in cells expressing both GRK4γ R65L and SLC4A5 variants compared with hGRK4γ WT and SLC4A5 WT. Luminal and basolateral sodium transports in hRPTCs are increased in the presence of both hGRK4γ R65L and SLC4A5 variants. Mice expressing hGRK4γ R65L only in the kidney have decreased expression but increased phosphorylation of histone deacetylase 1 (HDAC1). HDAC1 expression is decreased and HDAC1 but not HDAC2 phosphorylation is increased in hRPTCs expressing both hGRK4γ R65L and SLC4A5 variants. The presence of hGRK4γ R65L decreases HDAC1 expression but increases AT1R expression in the kidneys of mice fed a high salt diet. Conclusion: hGRK4γ R65L causes salt-sensitive hypertension by increasing renal SLC4A5 and AT1R expressions by inhibiting the HDAC1 pathway. Funding: NIDDK Support