Genetically Engineered Excitable Cardiac Myofibroblasts Coupled to Cardiomyocytes Rescue Normal Propagation and Reduce Arrhythmia Complexity in Heterocellular Monolayers

RATIONALE AND OBJECTIVE: The use of genetic engineering of unexcitable cells to enable expression of gap junctions and inward rectifier potassium channels has suggested that cell therapies aimed at establishing electrical coupling of unexcitable donor cells to host cardiomyocytes may be arrhythmogenic. Whether similar considerations apply when the donor cells are electrically excitable has not been investigated. Here we tested the hypothesis that adenoviral transfer of genes coding Kir2.1 (I(K1)), Na(V)1.5 (I(Na)) and connexin-43 (Cx43) proteins into neonatal rat ventricular myofibroblasts (NRVF) will convert them into fully excitable cells, rescue rapid conduction velocity (CV) and reduce the incidence of complex reentry arrhythmias in an in vitro model. METHODS AND RESULTS: We used adenoviral (Ad-) constructs encoding Kir2.1, Na(V)1.5 and Cx43 in NRVF. In single NRVF, Ad-Kir2.1 or Ad-Na(V)1.5 infection enabled us to regulate the densities of I(K1) and I(Na), respectively. At varying MOI ratios of 10/10, 5/10 and 5/20, NRVF co-infected with Ad-Kir2.1+ Na(V)1.5 were hyperpolarized and generated action potentials (APs) with upstroke velocities >100 V/s. However, when forming monolayers only the addition of Ad-Cx43 made the excitable NRVF capable of conducting electrical impulses (CV = 20.71±0.79 cm/s). When genetically engineered excitable NRVF overexpressing Kir2.1, Na(V)1.5 and Cx43 were used to replace normal NRVF in heterocellular monolayers that included neonatal rat ventricular myocytes (NRVM), CV was significantly increased (27.59±0.76 cm/s vs. 21.18±0.65 cm/s, p<0.05), reaching values similar to those of pure myocytes monolayers (27.27±0.72 cm/s). Moreover, during reentry, propagation was faster and more organized, with a significantly lower number of wavebreaks in heterocellular monolayers formed by excitable compared with unexcitable NRVF. CONCLUSION: Viral transfer of genes coding Kir2.1, Na(V)1.5 and Cx43 to cardiac myofibroblasts endows them with the ability to generate and propagate APs. The results provide proof of concept that cell therapies with excitable donor cells increase safety and reduce arrhythmogenic potential.