Objectives: We previously reported that combined transplantation of skeletal myoblasts and AC-133+ cells leads to improved left ventricular function, reduced infarct size and myocardial apoptosis in a model of chronic ischemia. The aim of this study is to elucidate on the possible mechanisms and to assess new implications in increasing cell therapy efficacy in chronic ischemia.
Methods: Heart failure was induced by LAD-ligation in nude rats. (a) Homologous skeletal myoblasts (SM), (b) human derived AC-133+ cells (SC), (c) combination of both cells (Comb) and (d) culture medium (CM) were injected in the infarct and peri-infarct area, respectively, four weeks after infarction. Cell engraftment was detected by fluorescence microscopy and confirmed by immunohistochemical techniques. Cardiac gene expression levels of VEFG-A, cardiac troponin, ACTA2, SDF-1, TGF-beta-1, were assessed by RT-PCR.
Results: Both cell types were detected in the injection areas four weeks after cell transplantation. Double cell therapy led to increased cell engraftment (SM: 52+/-13/mm(2), SC: 45+/-8 in the combination group vs. SM: 31+/-9 and 23+/-7 in the monotherapy groups, P=0.007). This effect was confirmed using PCR. Apoptotic index among engrafted cells was significantly lower in the Comb group (Comb: 0.53+/-0.12 for myoblasts and 0.34+/-0.09 for SC, vs. SM: 0.76+/-0.19 and SC: 0.63+/-0.16, P=0.013). Expression of cardiac troponin was higher in the combination group in the peri-infarct area. Evaluation of capillary density revealed increased angiogenesis in the combination group (Comb: 12.3+/-2.3, SM: 5.2+/-1.2, SC: 8.3+/-1.8, P=0.002). Neoangiogenesis was associated with higher levels of VEGF-A and TGF-beta in the injection areas as detected by RT-PCR. The higher SDF-1 expression in the injected areas implies an increased secretion of chemoattractants by the injected cells, which suggests that the effect of combined cell transplantation is mainly associated with paracrine mechanisms.
Conclusions: The mechanism of functional improvement after combined transplantation of skeletal myoblasts and AC-133+ progenitors in ischemic heart failure is mainly associated with increased angiogenesis based on paracrine factors, which leads to improved survival and lower apoptosis rates of the injected cells.