Gene therapy to inhibit the calcium channel β subunit -: Physiological consequences and pathophysiological effects in models of cardiac hypertrophy

Calcium cycling figures prominently in excitation-contraction coupling and in various signaling cascades involved in the development of left ventricular hypertrophy. We hypothesized that genetic suppression of the L-type calcium channel accessory beta-subunit would modulate calcium current and suppress cardiac hypertrophy. A short hairpin RNA template sequence capable of mediating the knockdown of the L-type calcium channel accessory beta-subunit gene was incorporated into a lentiviral vector (PPT.CG.H1.beta 2). Transduction of ventricular myocytes in vivo with the active short hairpin RNA partially inhibited the L-type calcium current. In neonatal rat cardiomyocytes, L-type calcium channel accessory beta-subunit gene knockdown reduced calcium transient amplitude. Similarly, [H-3] leucine incorporation was attenuated in PPT.CG.H1.beta(2)-transduced neonatal rat cardiomyocytes compared with nonsilencing controls in a phenylephrine-induced hypertrophy model. In vivo gene transfer attenuated the hypertrophic response in an aortic-banded rat model of left ventricular hypertrophy, with reduced left ventricular wall thickness and heart weight/body weight ratios in PPT.CG.H1.beta(2)-injected rats at four weeks post transduction. Fractional shortening was preserved in rats treated with PPT. CG. H1.beta 2. These findings indicate that knockdown of L-type calcium channel accessory beta-subunit is capable of attenuating the hypertrophic response both in vitro and in vivo without compromising systolic performance. Suppression of the calcium channel beta subunit may represent a novel and useful therapeutic strategy for left ventricular hypertrophy.