Regeneration of Infarcted Myocardium by Intramyocardial Implantation of Ex Vivo Transforming Growth Factor-β–Preprogrammed Bone Marrow Stem Cells

Abstract

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)-β–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-β. 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-β₁) CD117⁺ cells intramyocardially. TGF-β 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-β–preprogrammed or untreated CD117⁺ cells. Moreover, many of the TGF-β–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-β–preprogrammed cells but not untreated cells. Furthermore, the left ventricular percent fraction shortening was significantly higher after the implantation of TGF-β–preprogrammed cells than after the implantation of untreated CD117⁺ cells. Conclusions— TGF-β conducted the myogenic differentiation of CD117⁺ stem cells by upregulating GATA-4 and NKx-2.5 expression. Therefore, the intramyocardial implantation of TGF-β–preprogrammed CD117⁺ cells effectively assisted the myocardial regeneration and induced therapeutic angiogenesis, contributing to functional cardiac regeneration.