RRAD-reduction reveals efficacy of targeting L-type calcium channel regulation for treatment of heart failure

Heart failure with reduced ejection fraction (HFrEF) is a major health problem. Increasing L-type calcium channel (LTCC) activity deteriorates heart function; however, myocardial RRAD knockout (cRAD^Δ/Δ) instills tonic modulated LTCC current (I_Ca,L) that preserves healthy myocardium. Thus, we chose to challenge the dogma that enhanced trigger Ca²⁺ is maladaptive. The study objective was to test the hypothesis that modulated I_Ca,L in cRAD^Δ/Δ mice rescues dilated cardiomyopathy by providing tonic modulated trigger Ca²⁺.

Mouse and human models were tested. The muscle lim protein knockout mouse (MLPKO) is a murine model of dilated cardiomyopathy (DCM) and HFrEF. The experimental timeline was to induce cRAD^Δ/Δ after onset of DCM (2.5 months of age) and follow subjects for up to 1-year. Longitudinal echocardiography and cardiac magnetic resonance imaging (CMR) showed that cRAD^Δ/Δ intervention rescued systolic function. Patch clamp recordings of isolated cardiomyocytes of MLPKO with cRAD^Δ/Δ demonstrated augmented LTCC activity, along with rescue of dysfunctional Ca²⁺ handling and sarcomere function. Bulk RNAseq of hearts demonstrated down-regulated pathological signalling cascades and pro-hypertrophic gene expression which comported with the reduction in eccentric hypertrophy observed with gravimetrics, CMR, and echocardiography. RRAD knockdown effects translate from mouse to human heart. Ventricle slices from HFrEF patients were treated with lentiviral shRNA targeting RRAD and recapitulated the inotropic and lusitropic effects observed in the mouse model of DCM.

Induction of cardiomyocyte-restricted RAD knockout in MLPKO mice after onset of DCM rescued cardiac dysfunction and attenuated pathological remodelling. cRAD^Δ/Δ intervention provided positive inotropy and lusitropy and reverted transcriptional signatures towards healthy myocardium. This study introduces targeting myocardial RAD regulation of the LTCC as a novel therapeutic strategy for systolic heart failure.