Fibroblast sheets co-cultured with endothelial progenitor cells improve cardiac function of infarcted hearts

We have already confirmed that cell sheet transplantation can improve damaged heart function via continuous cytokine secretion. In this study, we hypothesized that cytokine-secreting cell sheets co-cultured with an endothelial cell source may be more effective for repairing ischemic myocardium. Confluent rat fibroblasts cultured on temperature-responsive culture dishes were harvested as contiguous cell sheets by temperature reduction. Green fluorescent protein (GFP)-positive endothelial progenitor cells (EPCs) were seeded on fibroblast sheets to create co-cultured cell sheets, and sandwich-like constructs were engineered by stacking of the co-cultured cell sheets. These constructs were transplanted into rat myocardial infarction models. Cardiac function and histology were assessed in four groups: the sham operation (C) group, the isolated EPC injection (E) group, the transplantation of triple-layer fibroblast sheets (F) group, and the transplantation of triple-layer sandwich-like constructs (E + F) group. Echocardiography showed significant improvement of the fractional shortening in the E + F group in comparison with the C group (0.25 +/- 0.05 vs. 0.16 +/- 0.02). On histological examination, significantly less connective tissue formation was observed in the E, F, and E + F groups when compared to the C group (C, E, F, and E + F groups: 53 +/- 2%, 41 +/- 4%, 40 +/- 4%, and 32 +/- 7%, respectively). Additionally, increased blood vessel formation was detected in the E, F, and E + F groups compared with the C group (C, E, F, and E + F groups: 1.9% +/- 0.6%, 6.7% +/- 0.6%, 7.8% +/- 0.9%, and 10.2% +/- 2.4%, respectively). Furthermore, GFP-staining demonstrated that the newly formed blood vessels were composed of the co-cultured EPCs. Transplantation of cell sheets co-cultured with an endothelial cell source may be a new therapeutic strategy for myocardial tissue regeneration.