Depressed β‐adrenergic inotropic responsiveness and intracellular calcium handling abnormalities in Duchenne Muscular Dystrophy patients’ induced pluripotent stem cell–derived cardiomyocytes

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is an X‐linked disease affecting male and rarely adult heterozygous females, resulting in death by the late 20s to early 30s. Previous studies reported depressed left ventricular function in DMD patients which may result from deranged intracellular Ca(2+)‐handling. To decipher the mechanism(s) underlying the depressed LV function, we tested the hypothesis that iPSC‐CMs generated from DMD patients feature blunted positive inotropic response to β‐adrenergic stimulation. To test the hypothesis, [Ca(2+)](i) transients and contractions were recorded from healthy and DMD‐CMs. While in healthy CMs (HC) isoproterenol caused a prominent positive inotropic effect, DMD‐CMs displayed a blunted inotropic response. Next, we tested the functionality of the sarcoplasmic reticulum (SR) by measuring caffeine‐induced Ca(2+) release. In contrast to HC, DMD‐CMs exhibited reduced caffeine‐induced Ca(2+) signal amplitude and recovery time. In support of the depleted SR Ca(2+) stores hypothesis, in DMD‐CMs the negative inotropic effects of ryanodine and cyclopiazonic acid were smaller than in HC. RNA‐seq analyses demonstrated that in DMD CMs the RNA‐expression levels of specific subunits of the L‐type calcium channel, the β1‐adrenergic receptor (ADRβ1) and adenylate cyclase were down‐regulated by 3.5‐, 2.8‐ and 3‐fold, respectively, which collectively contribute to the depressed β‐adrenergic responsiveness.