br Results and discussion br Conclusions

Results and discussion
Conclusions Our results demonstrate that fetal skeletal muscle contains different progenitor gonadotropin releasing hormone receptor already committed to specific lineages. Among fetal muscle CD34+ cells, we identified not only interstitial myogenic progenitors but also a resident angiogenic population and an adipogenic epimysial cell subset (Fig. 8). Comparison of myogenic efficiency of a mixed CD34+ population with that of purified myogenic subset raises the issue of the role of the microenvironment on both spontaneous muscle regeneration and the fate of transplanted cells. Conditions which hamper cell transplantation efficiency, such as ischemia or adiposis, could be by-passed by using defined fetal muscle cell populations.
Materials and methods
Acknowledgments We would particularly like to thank Dr. Denise Paulin and Dr. Zenli Li for providing desmin mutant mice, Dr. Masura Okabe for his gift of GFP mice, Astellas, Japan for providing FK506 and Prof. Romain Gherardi for donating NG2 antibody sample. This study was funded by grants from the Association Française contre les Myopathies (grant no. 9872), the EEU 6th Framework Programme Network of Excellence MYORES, by the CNRS and by the University of Nantes. The authors would like to thank Dr. Christophe Thiriet for his help with RT-qPCR analysis, fruitful discussions and critical reading of the manuscript.
Introduction In industrial nations, ischemic disorders in general are the main cause of death in human beings (Dickstein et al., 2008). After myocardial infarction, damages of cardiac tissue are irreversible and lead to progressive ischemic cardiomyopathy. However, stem cell mobilization and migration into the heart could be a new therapeutic approach to improve myocardial function and survival after ischemic injury since they stimulate neovascularization and prevent apoptosis of cardiomyocytes by paracrine means (Balsam et al., 2004; Fazel et al., 2006; Murry et al., 2004; Zaruba et al., 2008). While experiments using granulocyte-colony stimulating factor (G-CSF) based stem cell mobilization in mice showed great promise (Deindl et al., 2006; Orlic et al., 2001), only few human trials reported an improvement of cardiac function (Ince et al., 2005a; Ince et al., 2005b), whereas most of them could not demonstrate beneficial effects (Engelmann et al., 2006; Engelmann et al., 2010; Zohlnhofer et al., 2008). Recently, we advanced the approach of therapeutic stem cell mobilization by contemporaneous enhancement of cardiac homing capacity (Zaruba et al., 2009). Although homing of circulating stem cells is mediated by several parameters like stem cell factor (SCF) or hepatocyte growth factor (HGF), the interaction of CXCR4 and myocardial stromal cell-derived factor (SDF-1) appeared to be the most relevant axis (Abbott et al., 2004; Aiuti et al., 1997; Askari et al., 2003; Ceradini et al., 2004; Franz et al., 2003; Saxena et al., 2008; Segers et al., 2007). SDF-1 binds to CXCR-4 in its active form (1–68) (Crump et al., 1997) and is cleaved N-terminally at its position-2 proline by CD26/dipeptidylpeptidase IV (DPP-IV), which is a membrane-bound extracellular peptidase (Christopherson et al., 2004) that is ubiquitously expressed (Huhn et al., 2000; Kahne et al., 1999; Ruiz et al., 1998; Vanham et al., 1993). Combining genetic or pharmacological inhibition of CD26/DPP-IV with G-CSF based stem cell mobilization, we could demonstrate stabilization of myocardial SDF-1, enhanced cardiac recruitment of bone marrow-derived stem cells, improved myocardial function and increased survival in the mouse model (Zaruba et al., 2009). Thereupon, we transferred this new approach from bench to bedside and initiated the first study (SITAGRAMI-Trial) analyzing dual stem cell therapy in patients suffering from acute myocardial infarction (Theiss et al., 2010).
Results
Discussion Recently, we established the new therapeutic concept of a dual stem cell therapy after acute myocardial infarction which combines G-CSF induced stem cell mobilization and pharmacological SDF-1 stabilization by DPP-IV inhibition (Zaruba et al., 2009). However, the precise mechanisms of SDF-1/CXCR4 mediated cardiac repair are still barely understood. Therefore, we aimed to elucidate three important questions which remained open: 1. Were the effects of dual stem cell therapy on cardiac function and survival specifically exerted via the SDF1/CXCR4 axis? 2. Which role do neovascularization and myocardial perfusion play in CXCR4 mediated repair? 3. Does dual stem cell therapy affect the pool of resident cardiac stem cells?