Viral expression of a SERCA2a-activating PLB mutant improves calcium cycling and synchronicity in dilated cardiomyopathic hiPSC-CMs

There is increasing momentum toward the development of gene therapy for heart failure (HF), cardiomyopathy, and other progressive cardiac diseases that correlate with impaired calcium (Ca 2+ ) transport and reduced contractility. We have used FRET between fluorescently-tagged SERCA2a (the cardiac Ca 2+ pump) and PLB (its ventricular peptide inhibitor) to test directly the effectiveness of loss-of-inhibition/gain-of-binding (LOI/GOB) PLB mutants (PLB M ) that were engineered to compete with the binding of inhibitory wild type PLB (PLB WT ). Our therapeutic strategy is to relieve PLB WT inhibition of SERCA2a by utilizing the reserve adrenergic capacity of PLB to enhance baseline cardiac contractility. Using a FRET assay, we determined that the combination of a LOI PLB mutation (L31A) and a GOB PLB mutation (I40A) results in a novel engineered LOI/GOB PLB M (L31A/I40A) that effectively competes with PLB WT binding to cardiac SERCA2a in HEK293-6E cells. We demonstrated that co-expression of L31A/I40A-PLB M enhances SERCA Ca-ATPase activity by increasing enzyme Ca 2+ affinity (1/K Ca ) in PLB WT -inhibited HEK cell homogenates. For an initial assessment of PLB M physiological effectiveness, we used human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) from a healthy individual. In this system, we observed that adeno-associated virus 2 (rAAV2)-driven expression of L31A/I40A-PLB M enhances the amplitude of SR Ca 2+ release and the rate of SR Ca 2+ re-uptake. To assess therapeutic potential, we used an hiPSC-CM model of dilated cardiomyopathy (DCM) containing PLB mutation R14del, where we observed that rAAV2-driven expression of L31A/I40A-PLB M rescues arrhythmic Ca 2+ transients and alleviates decreased Ca 2+ transport. Based on these results, PLB M transgene expression is a promising gene therapy strategy for cardiomyopathies associated with impaired Ca 2+ transport and decreased contractility.