Connective Tissue Growth Factor/CCN2 Attenuates β-Adrenergic Receptor Responsiveness and Cardiotoxicity by Induction of G Protein-Coupled Receptor Kinase-5 in Cardiomyocytes

Myocardial connective tissue growth factor (CTGF/CCN2) is induced in heart failure, a condition associated with diminution of beta-adrenergic receptor (beta-AR) responsiveness. Accordingly, we aimed to investigate whether CTGF could play a mechanistic role in regulation of beta-AR responsiveness. Concentration-response curves of isoproterenol-stimulated cAMP generation in cardiomyocytes from transgenic mice with cardiac-restricted overexpression of CTGF (Tg-CTGF) or cardiomyocytes pre-treated with recombinant human CTGF (rec-hCTGF) revealed marked reduction of both beta(1)-AR and beta(2)-AR responsiveness. Consistently, ventricular muscle strips from Tg-CTGF mice stimulated with isoproterenol displayed attenuation of maximal inotropic responses. However, no differences of maximal inotropic responses of myocardial fibers from Tg-CTGF mice and nontransgenic littermate control (NLC) mice were discerned when stimulated with supramaximal concentrations of dibutyryl-cAMP, indicating preserved downstream responsiveness to cAMP. Congruent with a mechanism of desensitization of beta-ARs, mRNA and protein levels of G protein-coupled receptor kinase 5 (GRK5) were found isoform-selective upregulated in both cardiomyocytes from Tg-CTGF mice and cardiomyocytes exposed to rec-hCTGF. Corroborating a mechanism of GRK5 in CTGF-mediated control of beta-AR sensitivity, Chinese hamster ovary cells pretreated with rec-hCTGF displayed increased agonist-and biased ligand-stimulated beta-arrestin binding to beta-ARs. Despite increased sensitivity of cardiomyocytes from GRK5-knockout (KO) mice to beta-adrenergic agonists, pretreatment of GRK5-KO cardiomyocytes with rec-hCTGF, as opposed to cardiomyocytes from wild-type mice, did not alter beta-AR responsiveness. Finally, Tg-CTGF mice subjected to chronic exposure (14 days) to isoproterenol revealed blunted myocardial hypertrophy and preserved cardiac function versus NLC mice. In conclusion, this study uncovers a novel mechanism controlling beta-AR responsiveness in cardiomyocytes involving CTGF-mediated regulation of GRK5.