Abstract 1472: Genetic Deficiency in Caveolin-3 Alters Stress Hormone-activated Membrane Signaling in Mouse Hearts
Caveolin-3 is a primary molecular component that forms caveolae, flask-shaped plasma membrane domains in cardiac and skeletal myocytes. Caveolae provide a critical micro-environment to receptors, ion channels and other membrane-bound molecules. In this study, we established a new caveolin-3 knockout (cav3−/−) mouse line and tested whether disruption of caveolin-3 alters the regulation of cardiac excitation-contraction coupling (ECC) by G-protein coupled receptor (GPCR) agonists, including beta-adrenergic agonists and urocortin 2 (Ucn2), a member of the corticotropin-releasing factor, which we have shown to have strong inotropic and lusitropic actions in normal and failing hearts (Bale TL. PNAS. 2004, 101: 3697–3702). We tested baseline phenotypes of our cav3−/− mice by echocardiography at 8, 20, 35 weeks old, as well as challenged with trans-aortic banding for 1 week and confirmed there is no overt cardiac dysfunction developed in these mice, in which missing of caveolae in cardiomyocytes was confirmed by electron microscopy. Cav3−/− mice (10–16 weeks old) and age-matched control C57BL/6 mice (wild type; WT) were first tested in in vivo hemodynamic studies. No obvious difference was observed at baseline between 2 groups. Ucn2 strongly enhanced cardiac contractility in WT. However, the response to Ucn2 was attenuated in cav3−/− (max dP/dt: 18869+−851 mmHg/sec in WT vs. 16797+−1891 in cav3−/−, p=0.01, min dP/dt: −10023+−1023 in WT vs. −8376+−716 in cav3−/−, p<0.01 (ANOVA), n=3). We also tested single adult cardiomyocytes isolated from both animal groups. Consistently with hemodynamic results, Ucn2-dependent enhancement of cell shortening was significantly suppressed in cav3−/− (% sarcomere length shortening, %SLS: 15.17+−3.35% in WT vs. 9.78+−3.41% in cav3−/−, p<0.01, n=26). In contrast, beta2 stimulant (combination of isoproterenol and CGP20712A) response was augmented in cav3−/− (%SLS: 7.44+−2.66% in WT vs. 9.65+−2.92% in cav3−/−, p=0.011, n=21). Calcium transient analyses with Fura2 supported these data. We conclude that caveolin-3 associated membrane micro-environment is critical for normal GPCR signaling and speculate their disease-related alterations affect ECC regulation by various stress-hormones.