Amelioration of Genetic Hypertension by Suppression of Renal G Protein–Coupled Receptor Kinase Type 4 Expression

Abstract

Abstract-Abnormalities in D 1 dopamine receptor function in the kidney are present in some types of human essential and rodent genetic hypertension. We hypothesize that increased activity of G protein-coupled receptor kinase type 4 (GRK4) causes the impaired renal D 1 receptor function in hypertension. We measured renal GRK4 and D 1 and serine-phosphorylated D 1 receptors and determined the effect of decreasing renal GRK4 protein by the chronic renal cortical interstitial infusion (4 weeks) of GRK4 antisense oligodeoxynucleotides (As-Odns) in conscious-uninephrectomized spontaneously hypertensive rats (SHRs) and their normotensive controls, Wistar-Kyoto (WKY) rats. Basal GRK4 expression and serine-phosphorylated D 1 receptors were Ϸ90% higher in SHRs than in WKY rats and were decreased to a greater extent in SHRs than in WKY rats with GRK4 As-Odns treatment. Basal renal D 1 receptor protein was similar in both rat strains. GRK4 As-Odns, but not scrambled oligodeoxynucleotides, increased sodium excretion and urine volume, attenuated the increase in arterial blood pressure with age, and decreased protein excretion in SHRs, effects that were not observed in WKY rats. These studies provide direct evidence of a crucial role of renal GRK4 in the D 1 receptor control of sodium excretion and blood pressure in genetic hypertension. The uncoupling of the D 1 -like receptor from its effector proteins in the kidney in hypertension is associated with increased phosphorylation of the D 1 receptor. 4,5 In human essential hypertension, single nucleotide polymorphisms of the G protein-coupled receptor (GPCR) kinase 4 (GRK4) are associated with constitutive phosphorylation and desensitization of the D 1 receptor in renal proximal tubules. 4 -6 These lead to sodium retention and hypertension. Indeed, transgenic mice expressing the GRK4 variant, GRK4␥A142V, develop hypertension that is associated with an impaired D 1 receptormediated natriuresis. 5 To determine whether aberrant GRK4 function contributes to the impaired renal D 1 receptor function in SHRs, we studied the renal expression of GRK4 and the effects of decreasing its expression in the kidney by a chronic renal cortical interstitial infusion of GRK4 antisense (As) oligodeoxynucleotides (Odns) in conscious SHRs and their normotensive controls, Wistar-Kyoto (WKY) rats. If an increased GRK4 activity in the kidney is responsible for the increased blood pressure in SHRs, this maneuver should improve D 1 receptor-mediated renal tubular handling of sodium and ameliorate the high blood pressure in SHRs without affecting these variables in WKY rats.

G Protein-coupled Receptor Kinase 4 (GRK4) Regulates the Phosphorylation and Function of the Dopamine D3 Receptor

“…Of the four GRK4 splice variants described in humans (11), only GRK4-␣, the full-length version, and GRK4-␥, which lacks the sequence encoded by exon 15 resulting in a 46-residue deletion near the C terminus, are able to phosphorylate D 3 R upon agonist activation. GRK4-␥ results in a 3-fold increase in D 3 R phosphorylation, whereas GRK4-␣ leads to a 2-fold increase, indicating that both variants are important in D 3 R signaling in hPTCs where all four GRK4 splice variants are expressed (44). The extent of GRK4-mediated D 3 R phosphorylation is similar to that observed in agonistactivated D 1 R by GRK4-␣ in HEK-293 cells (47).…”

“…in proximal and distal tubules and the glomeruli, and hence co-localization is mostly observed in these structures. Although GRK4 expression was first thought to be confined mainly to the testis and the brain (11,43), later reports showed that GRK4 isoforms, especially GRK4␥, are expressed in the human kidney (12,44), especially in the proximal tubules (13), and in other tissues, such as the human myometrium (45).…”

G Protein–Coupled Receptor Kinase 4

“…33 Renal GRK4 plays a role in the high blood pressure of SHRs. 21 Both GRK4 and GRK2 have been implicated in the D 1 R dysfunction in obese rats. 34 GRK2 activity is increased in SHRs and is responsible for the impaired renal D 1 R function with aging and hyperglycemia.…”

“…A fifth Grk4 isoform, Grk4E, which lacks exons 6 and 14, may be the functional isoform expressed in rat kidney cortex. 21 The differential tissue distribution of Grk4A, Grk4B, and Grk4E suggests that individual GRK4 splice variants may serve distinct physiological functions. …”

Regulation of renalase expression by D5 dopamine receptors in rat renal proximal tubule cells

“…Our present study found that stimulation of D 1 -like receptor with fenoldopam increases renalase expression in WKY cells but not in SHR cells. We have reported that the renal D 1 -like receptor function is impaired in SHRs due to the hyperphosphorylation of the D 1 receptor (17,31), which has been ascribed to increased constitutive activity of G protein-coupled receptor kinase 4 (GRK4) (17, 31). Whether or not this strategy is helpful in increasing renalase expression and activity in kidney of SHRs needs to be confirmed in the future.…”