Vascular-Targeted Overexpression of G Protein-Coupled Receptor Kinase-2 in Transgenic Mice Attenuates β-Adrenergic Receptor Signaling and Increases Resting Blood Pressure

Abstract

Cardiovascular regulation is tightly controlled by signaling through G protein-coupled receptors (GPCRs). ␤-Adrenergic receptors (ARs) are GPCRs that regulate inotropy and chronotropy in the heart and mediate vasodilation, which critically influences systemic vascular resistance. GPCR kinases (GRKs), including GRK2 (or ␤ARK1), phosphorylate and desensitize agonist-activated ␤ARs. Myocardial GRK2 levels are increased in heart failure and data suggest that vascular levels may also be elevated in hypertension. Therefore, we generated transgenic mice with vascular smooth muscle (VSM) targeted overexpression of GRK2, using a portion of the SM22␣ promoter, to determine its impact on vascular ␤AR regulation. VSM ␤AR signaling, as determined by adenylyl cyclase and mitogenactivated protein (MAP) kinase activation assays, was attenuated when GRK2 was overexpressed 2-to 3-fold. In vivo vasodilation in response to ␤AR stimulation using isoproterenol was attenuated and conscious resting mean arterial blood pressure was elevated from 96 Ϯ 2 mm Hg in nontransgenic littermate control (NLC) mice (n ϭ 9) to 112 Ϯ 3 mm Hg and 117 Ϯ 2 mm Hg in two different lines of SM22␣-GRK2 transgenic mice (n ϭ 7 and n ϭ 5, respectively; p Ͻ 0.05). Interestingly, medial VSM thickness was increased 30% from 29.8 Ϯ 1.6 m in NLC mice (n ϭ 6) to 39.4 Ϯ 1.6 m in SM22␣-GRK2 mice (n ϭ 7) (p Ͻ 0.05) and vascular GRK2 overexpression was sufficient to cause cardiac hypertrophy. These data indicate that we have developed a unique mouse model of hypertension, providing insight into the contribution that vascular ␤AR signaling makes toward resting blood pressure and overall cardiovascular regulation. Moreover, they suggest that GRK2 plays an important role in vascular control and may represent a novel therapeutic target for hypertension.␤-Adrenergic receptors (ARs) are critical G protein-coupled receptors (GPCRs) in the regulation of the cardiovascular system. ␤ARs (␤ 1 , ␤ 2 and ␤ 3 subtypes) are involved in the regulation of myocardial function as well as taking part in control of vascular tone (Brodde 1991;Chruscinski et al., 1999;Rohrer et al., 1999). ␤ 1 and ␤ 2 ARs primarily couple to the heterotrimeric G protein Gs, which then dissociates and activates adenylyl cyclase via the ␣-subunit and can also trigger signaling events mediated by the ␤␥-subunits (G ␤␥ ), such as the activation of mitogen-activated protein kinases (MAPKs). Studies so far suggest that stimulation of the ␤ 1 AR primarily mediates inotropy and chronotropy in the heart (Brodde and Michel, 1992;Chruscinski et al., 1999;. In contrast, studies from ␤ 1 AR, ␤ 2 AR, and ␤ 1 /␤ 2 knockout mice imply that vascular smooth muscle (VSM) relaxation seems to be controlled by all three ␤AR subtypes Rohrer et al., 1999).Importantly, several studies have shown that ␤AR levels and signaling can be significantly altered by cardiovascular disease. Among the most well characterized ␤AR derangements are those that take place in chronic heart failure, where ␤ 1 ARs are selectively down-regulated...

Exercise restores β-adrenergic vasorelaxation in aged rat carotid arteries

“…At the vascular level, increased ␤-ARK protein expression was demonstrated in spontaneously hypertensive rats, suggesting that increased ␤-ARK activity might account for the impairment of ␤-AR-mediated vasodilation observed in hypertension (13,14). Consistent with this, a recent report showed impaired ␤-AR vasorelaxation and hypertension in transgenic mice with selective overexpression of ␤-ARK in vascular smooth muscle cells (10). Our results indicate that vascular ␤-ARK is increased and participates in the deterioration of vasodilation to ␤-AR stimulation also in aging.…”

“…In the failing human heart the uncoupling of cardiac ␤ 1 -and ␤ 2 -ARs from G proteins has been attributed to increased levels of myocardial ␤-ARK (38). Abnormalities of ␤-AR signaling due to increase in ␤-ARK activity have been observed in both human (14) and animal (10,13) hypertension.…”

Genetics of arterial hypertension and hypotension

“…Targeted overexpression of GRK2 to the vasculature is accompanied by increases in resting blood pressure and attenuated β-adrenergic signalling (Eckhart et al 2002). Similar results were obtained for the GRK5 isoform (Keys et al 2005).…”

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

“…19 GRK activity and GRK2 expression are increased in human essential hypertension and SHRs, 29 and overexpression of GRK2 in vascular smooth muscles in mice produces hypertension and impairs the vasodilatory action of ␤-adrenergic receptors. 30 However, in SHRs, the increase in GRK activity and GRK2 expression follows rather than precedes the hypertensive process. 29 Moreover, in the current studies, GRK4 As-Odn does not affect GRK2 expression.…”