Molecular mechanisms underlying the GRK4 65L‐mediated hypertension in mice

Abstract

The genetic causes of salt sensitivity andhypertension in humans are not completely understood. The kidney plays a preeminent regulatory rolein blood pressure (BP) homeostasis and water and electrolyte balance. The renaldopamine receptors, D1R and D3R, engender natriuresis viathe inhibition of renal Na+ transport, whereas the angiotensin IItype 1 receptor (AT1R) does the opposite. The renal paracrineinhibition of Na+ transport by dopamine is impaired insalt‐sensitive rats, mice, and humans. Agonist activation promotes thephosphorylation of D1R and D3R by the G protein‐coupledreceptor kinase type 4 (GRK4), whose gene variants impair D1R and D3Ractivity. The global expression of GRK4 65R>L in transgenic mice results in salt‐sensitive hypertension, in part, due toincreased endogenous GRK4 and AT1R expression. To demonstrate thespecific renal causal mechanisms in GRK4 65R>L‐mediated hypertension, weheterologously expressed the GRK4 65R>Lvs. GRK4 wild‐type (WT) transgenes in the kidneys of Grk4 knockout mice on normal salt diet. The transgenes were delivered selectively into the renal tubules by thebilateral retrograde ureteral infusion of AAV‐9 vectors. The expression anddistribution along the entire nephron of the GRK4 WT and GRK4 65R>L were similar in both groups. However, the renal tubule‐restricted expression ofGRK4 65R>L increased the BP (117±4vs. 93±1 mm Hg, P<0.05, n=4), while that of the GRK4 WT only tendedto increase the BP (105±6 vs. 96±2 mmHg, n=5), indicating that the presence of the GRK4 variant in the kidney causedthe increase in BP. We next evaluated the renal expression profiles of selectgenes. We found that the pro‐natriuretic D1R (0.81±0.01 vs. 1.28±0.04, P<0.01) and D3R(0.44±0.02 vs. 1.27±0.07, P<0.01)were decreased whereas the anti‐natriuretic Na+/K+‐ ATPase(1.14±0.024 vs. 1.0 ±0.007, P<0.05) and α‐ENaC (1.4±0.14 vs. 1.0±0.11, P<0.05) were increased, demonstrating themechanistic changes that underlie the hypertension in these mice. Interestingly, we also observed that 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), NBCe2(0.50±0.07 vs. 1.15±0.03), and the AT1R(0.82±0.02 vs 1.02±0.02) were decreased, which may represent insufficientcompensatory mechanisms against the increase in BP. Our results highlight theunderlying and compensatory renal mechanisms for the hypertension thatdeveloped in mice with either kidney‐restricted or globally expressed GRK4 65R>L.Support or Funding InformationR01DK039308, R01HL092196, and P01HL074940This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.