Gap Junction Remodeling in a Novel Engineered Heart Tissue System Cultured under Point Stimulation

Abstract

Recent advances have shown the importance of electrical stimulation in enhancing maturation and differentiation of engineered heart tissues (EHTs). Conventional electrical maturation protocols pace their EHTs with field stimulation - the tissues are paced simultaneously in a uniform electrical field. This method has been shown to improve cellular alignment, increase contractility, and increase gap junction (Cx43) production. While Cx43 production is increased, the anisotropic ratio is not fully preserved in these culture systems [Trantidou et al, PMID 4459200]. Native cardiac tissue demonstrates an anisotropic propagation of action potHential; in adult rat ventricles the conduction velocity (CV) is 3x faster in the longitudinal direction than the transverse direction [Zimmermann et al, PMID 16582915]. We hypothesize that the loss of anisotropy is due to field stimulation not accurately recapitulating the conditions caused by a depolarizing wave traveling through the tissue. In order to better reproduce native myocardium, we designed a bioreactor which applies a point stimulation at one end of our EHT and allows the wave to propagate down the tissue. We hypothesize that this propagating wave will provide the necessary signals to enhance Cx43 production as well as improve localization of gap junction proteins. Maturity was assessed by the measurement of twitch kinetics, peak force, and conduction velocity. We anticipate that establishing a more realistic expression and subcellular localization of gap junction proteins will improve the utility of future studies involving cell lines from patients with arrhythmogenic cardiomyopathies.