Co-culture of cardiac fibroblasts and myocytes enhances functional assembly of engineered myocardium

Introduction: Native myocardium consists of several cell types of which 1/3 are myocytes and most of the non-myocytes are fibroblasts [1]. Cardiac myocytes are the largest cells in the myocardium, they occupy ~90% of the volume and are responsible for synchronous contractions of the ventricles. The main roles of cardiac fibroblasts are to secrete the components of the extra-cellular matrix (ECM) mainly collagen (Burlew 2002) and to transmit mechanical force by the receptor mediated connections to the ECM [2]. The exact composition of the ECM is regulated by a cross-talk between myocytes and fibroblasts [2]. Recent studies demonstrated that cardiac fibroblasts can propagate electrical stimuli over the distances on the order of 100μm via gap junctional communications [3]. By analogy with monolayer culture in which fibroblasts are removed to prevent overgrowth, early attempts to engineer myocardium utilized cell suspensions enriched for cardiac myocytes (~80-90% cardiac myocytes) by preplating [4, 5]. The engineered cardiac constructs exhibited markers of cardiac differentiation and were able to propagate electrical signals over several millimeters. However, cells in these constructs did not align in parallel as in the native myocardium and neither the force of contraction nor the macroscopic contractile response were investigated. We hypothesized that the co-culture of cardiac fibroblasts and cardiac myocytes will enhance functional assembly of the engineered cardiac constructs by enabling scaffold remodeling and active cross-talk between cells.