Collagen scaffold enhances the regenerative properties of mesenchymal stromal cells.

MSCs are widely applied to regenerate heart tissue in myocardial diseases but when grown in standard two-dimensional (2D) cultures exhibit limited potential for cardiac repair and develop fibrogenic features with increasing culture time. MSCs can undergo partial cardiomyogenic differentiation, which improves their cardiac repair capacity. When applied to collagen patches they may improve cardiac tissue regeneration but the mechanisms remain elusive. Here, we investigated the regenerative properties of MSCs grown in a collagen scaffold as a three-dimensional (3D) culture system, and performed functional analysis using an engineered heart tissue (EHT) model. We showed that the expression of cardiomyocyte-specific proteins by MSCs co-cultured with rat neonatal cardiomyocytes was increased in collagen patches versus conventional cultures. MSCs in 3D collagen patches were less fibrogenic, secreted more cardiotrophic factors, retained anti-apoptotic and immunomodulatory function, and responded less to TLR4 ligand lipopolysaccharide (LPS) stimulation. EHT analysis showed no effects by MSCs on cardiomyocyte function, whereas control dermal fibroblasts abrogated the beating of cardiac tissue constructs. We conclude that 3D collagen scaffold improves the cardioprotective effects of MSCs by enhancing the production of trophic factors and modifying their immune modulatory and fibrogenic phenotype. The improvement in myocardial function by MSCs after acquisition of a partial cardiac cell-like phenotype is not due to enhanced MSC contractility. A better understanding of the mechanisms of MSC-mediated tissue repair will help to further enhance the therapeutic potency of MSCs