Abstract 2961: CCN2/CTGF - Connective Tissue Growth Factor - Reduces β-Adrenergic Receptor Responsiveness and Catecholamine-Induced Cardiotoxicity by Upregulation of Cardiac Myocyte G Protein-Coupled Receptor Kinase-5
Background: Myocardial CTGF is dramatically induced in CHF, a condition associated with diminution of β-adrenergic receptor (βAR) responsiveness. Accordingly, we aimed to investigate if CTGF is mechanistically involved in desensitization of βARs in this condition.
Methods and results: Transgenic mice with cardiac-restricted overexpression of CTGF (Tg-CTGF) were generated and compared with nontransgenic control mice (NLC). Stimulation of ventricular muscle strips with increasing concentrations of βAR agonist isoproterenol (ISO) revealed substantial attenuation of maximal inotropic response of muscle fibers from Tg-CTGF vs. NLC mice (increase of force [(dF/dt)max] 123±14% vs. 427±27%, p<0.01). Concentration-effect curves of ISO-stimulated cAMP generation in adult cardiac myocytes from Tg-CTGF hearts revealed reduced efficacy of ISO compared with cardiac myocytes from NLC hearts. Indeed, similar reduction of efficacy of ISO was observed in ventricular muscle strips of Tg-CTGF hearts. Furthermore, no differences in maximal contractile responses upon stimulation with cAMP analogue dibutyryl-cAMP were detected; excluding affection of downstream signalling pathways or contractile proteins. Analysis of [125I]-iodocyanopindolol binding did not disclose alterations in βAR densities on cardiac myocytes from Tg-CTGF versus NLC mice. Real time qPCR analysis revealed a three fold upregulation of cardiac myocyte G-protein receptor kinase 5 (GRK5) in Tg-CTGF hearts, while levels of other cardiac GRKs (2, 3 and 6) were unaltered among the groups. ISO-stimulated cardiac myocytes from Tg-CTGF mice also displayed enhanced ERK-phosphorylation (Thr202/Tyr204), indicating activation of GRK5 dependent β-arrestin-mediated cytoprotective pathways. Chronic exposure to ISO for 14 days delivered through mini-osmotic pumps, revealed attenuated myocardial hypertrophy in Tg-CTGF versus NLC mice, and preserved cardiac function as evaluated by echocardiography.
Conclusion: CTGF desensitizes βAR signaling in the heart through induction of myocardial GRK5. Desensitization of βAR on cardiac myocytes may contribute to cytoprotection and maintenance of cardiac function. CTGF might be an important mediator of reduced βAR responsiveness in CHF.