Transplantation of c kit RCSC

Transplantation of c-kit+ RCSC shifted the balance between pro- and anti-angiogenic proteins in the pressure-overloaded LV myocardium towards pro-angiogenic mediators and the myocardium of transplanted mice showed an increased density of endothelial (CD31+) cells. In contrast, GFP+ cardiomyocytes were only identified in a small minority of the animals despite very meticulous examination. Transplanted cells transdifferentiated partly into smooth muscle cells and CD31+ endothelial cells and pressure overload further increased their percentage. The histological characterization of endothelial-transdifferentiating cells can be difficult because non-endothelial GFP+ cells lay in the vicinity of endothelial cells. To overcome this issue, we used Tie-2-GFP mice as donor animals for additional transplantation studies. In these animals, cells are expressing GFP by the endothelial Tie-2-promoter and c-kit+ RCSC in this model only express GFP after differentiating towards endothelial phenotype (Müller et al. 2009). The data therefore strongly suggest that differentiation took place. Reduction of endothelial cell number and number of rxr receptor during sustained pressure overload caused by decrease in myocardial content of Hif1α leads to progression of heart failure. (Kazakov et al. 2012; Müller et al. 2009; Müller et al. 2008; Sano et al. 2007). Hence, the increase of the numbers of CD31-positive endothelial cells and enhanced myocardial expression of Hif1α after transplantation of the adult stem cells represent additional protecting effects (Gyongyosi et al. 2010; Tillmanns et al. 2008). Circulating stem cells demonstrate increased intracellular expression of Hif1α under normoxic conditions induced by ligand of c-kit stem cell factor (Piccoli et al. 2007). Moreover, inhibition of c-kit abrogates Hif1α-mediated angiogenic activity of hematopoietic stem cells and cancer cells (Litz and Krystal 2006; Pedersen et al. 2008). These findings suggest that paracrine effects and differentiation into non-cardiomyocytes represent the primary underlying mechanisms of the cell therapy (Beltrami et al. 2003; Ellison et al. 2013; Elnakish et al. 2013; Li et al. 2011; Ramkisoensing et al. 2014; van Berlo et al. 2014). Cardiac fibrosis is an important part of ventricular remodeling and an independent and predictive risk factor for heart failure (Burchfield et al. 2013; Segura et al. 2014). Pathological stress elicited by pressure overload induces fibroblast proliferation, migration of fibrocytes to the heart increasing production of extracellular matrix proteins such as collagen I, collagen III and fibronectin (Kazakov et al. 2013; Kazakov et al. 2012; Müller et al. 2009; Müller et al. 2008). In our study transplantation of cardiac stem cells decreased the number of fibronectin-positive fibroblasts in LV and the production of the main component of extracellular matrix, collagen I. Furthermore, cardiac fibroblasts respond to pressure overload by increase in production of specific cytokines and growth factors (Segura et al. 2014). Connective tissue growth factor plays a pivotal role in development of cardiac fibrosis and hypertrophy (Daniels et al. 2009; Szabo et al. 2014; Yoon et al. 2010). Our findings are consistent with previous investigations demonstrating reduction of cardiac fibrosis and cardiomyocyte hypertrophy after diminishing CTGF-level in pressure-overloaded LV myocardium (Szabo et al. 2014; Yoon et al. 2010). Increased oxidative stress during pressure overload has been shown to elevate fibroblast numbers and the production of extracellular matrix in the left ventricular myocardium (Segura et al. 2014). Immunostaining for oxidative stress marker 8-hydroxy-guanosine revealed significant amelioration of oxidative stress both in cardiomyocytes and in non-cardiomyocytes after stem cell transplantation. Transplantation of c-kit+ RCSC but not of c-kit− cardiac cells reduces cardiac fibrosis in pressure-overloaded myocardium demonstrating specificity of fibrosis reduction after c-kit+ stem cell transplantation. Therefore, intravenous transplantation of c-kit+ RCSC reduces cardiac fibrosis acting on several of the main pathogenetic mechanisms of fibrogenesis.