Cell-Induced Alignment Augments Twitch Force in Fibrin Gel–Based Engineered Myocardium via Gap Junction Modification

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Abstract
A high-potential therapy for repairing the heart post-myocardial infarction is the implantation of tissue-engineered myocardium. While several groups have developed constructs that mimic the aligned structure of the native myocardium, to date no one has investigated the particular functional benefits conferred by alignment. In this study we created myocardial constructs in both aligned and isotropic configurations by entrapping neonatal rat cardiac cells in fibrin gel. Constructs were cultured statically for 2 weeks, and then characterized. Histological staining showed spread cells that express typical cardiac cell markers in both configurations. Isotropic constructs had higher final cell and collagen densities, but lower passive mechanical properties than aligned constructs. Twitch force associated with electrical pacing, however, was 181% higher in aligned constructs, and this improvement was greater than what would be expected from merely aligning the cells in the isotropic constructs in the force measurement direction. Our hypothesis was that this was due to improved gap junction formation/function facilitated by cell alignment, and further analyses of the twitch force data, as well as Western blot results of connexin 43 expression and phosphorylation state, support this hypothesis. Regardless of the specific mechanism, the results presented in this study underscore the importance of recapitulating the anisotropy of the native tissue in engineered myocardium.