Abstract 17124: Myoscape Controls Cardiomyocyte Calcium Cycling and Contractile Function in vivo via Regulation of L-type Calcium Channel Surface Expression
Alterations in cardiomyocyte calcium cycling have been shown to play a major role in the pathophysiology of contractile dysfunction, hypertrophy and the progression of heart failure. The L-type Ca2+channel controls calcium entry and subsequent calcium-induced calcium release. Here we report a novel muscle enriched protein termed Myoscape which directly interacts with the distal C-terminus of the L-type Ca2+channel (LTCC) and cardiac Alpha-Actinin 2. Knockdown of Myoscape in adult rat ventricular cardiomyocytes (ARVCMs) leads to a decrease in global calcium transients, with smaller Ca2+ amplitudes (n=4, p<0.001), lower diastolic Ca2+content and a prolonged time to peak. Consistently, analysis of single LTCC currents in ARVCM confirmed a significant reduction upon Myoscape ablation. Conversely, overexpression of Myoscape significantly increases global Ca2+transients and enhances LTCC currents. Moreover, overexpression of Myoscape almost completely restores decreased LTCC currents in failing ARVCMs. As a functional consequence, knockdown of Myoscape significantly reduced contractility of ARVCM, as assessed by fractional shortening measurements (n=3, p<0.001). Myoscape knockout mice develop reduced fractional shortening after 8 weeks which progresses to advanced cardiomyopathy after one year follow up (FS 51.7% ±4.2. vs. 33.3%±3.7, n=10). After 4 weeks of aortic constriction Myoscape null mice showed deteriorated contractile function with ventricular dilatation, enhanced fibrosis and increased pulmonary blood congestion as compared to wildtype mice. Myoscape KO’s showed increased heart weight to tibia length ratios and developed significantly exaggerated cardiomyocyte hypertrophy. Mechanistically, myoscape KO mice showed significantly reduced L-Type Ca2+currents, cell capacity and current densities (pA/pF 3.72±0.4 vs. 2.48±0.2) without affection of CDI and CDF. Instead, loss of Myoscape leads to reduced plasma membrane content of LTCC and its stabilizing agent Alpha Actinin 2 in vitro and in vivo, as assessed by surface membrane biotinylation assays and confocal immunofluorescence microscopy. Taken together, we have identified a novel modulator of cardiomyocyte L-type calcium channels and contractile function.
Author Disclosures: M. Eden: None. B. Meder: None. M. Voelkers: None. R. Will: None. M. Poomvanicha: None. K. Domes: None. A. Bernt: None. C. Heymes: None. W. Rottbauer: None. H. Franz: None. N. Frey: None.
- © 2014 by American Heart Association, Inc.