Regeneration of infarcted myocardium by intramyocardial implantation of ex vivo transforming growth factor-β-preprogrammed bone marrow stem cells

Background - Recent studies have shown that bone marrow - derived stem cells differentiate into the phenotype of cardiomyocytes in vivo and in vitro. We tried to regenerate infarcted myocardium by implanting ex vivo transforming growth factor (TGF)-beta-preprogrammed CD117 (c-kit) - positive (CD117(+)) stem cells intramyocardially. Methods and Results - CD117(+) cells were isolated from the bone marrow mononuclear cells of GFP-transgenic or normal C57/BL6 mice. The myogenic differentiation of CD117(+) cells was achieved by cultivation with TGF-beta. Using an acute myocardial infarction model, we also tried to regenerate infarcted myocardium by implanting untreated ( newly isolated) or preprogrammed ( 24 hours of cultivation with 5 ng/mL TGF-beta(1)) CD117(+) cells intramyocardially. TGF-beta increased the cellular expression of myosin, troponins, connexin-43, GATA-4, and NKx-2.5, which suggested that it induced the myogenic differentiation of CD117(+) cells. Compared with the effects of PBS injection only, the microvessel density in the infarcted myocardium was increased significantly 3 months after the implantation of either TGF-beta-preprogrammed or untreated CD117(+) cells. Moreover, many of the TGF-beta-preprogrammed CD117(+) cells were stained positively for myosin, whereas few of the untreated CD117(+) cells were. Histological analysis revealed newly regenerated myocardium in the left ventricular anterior wall after the implantation of TGF-beta-preprogrammed cells but not untreated cells. Furthermore, the left ventricular percent fraction shortening was significantly higher after the implantation of TGF-beta-preprogrammed cells than after the implantation of untreated CD117(+) cells. Conclusions - TGF-beta conducted the myogenic differentiation of CD117(+) stem cells by upregulating GATA-4 and NKx-2.5 expression. Therefore, the intramyocardial implantation of TGF-beta-preprogrammed CD117(+) cells effectively assisted the myocardial regeneration and induced therapeutic angiogenesis, contributing to functional cardiac regeneration.