Etude du rôle de l'AMPK dans la régulation du potentiel de différenciation et de survie des cellules souches en vue de leur utilisation en thérapie cellulaire cardiaque

Myocardial ischemia induces cardiomyocyte destruction and decreased left ventricular function thereby causing heart failure. In recent decades, stem cells transplantation was assessed by various clinical studies. These have shown promising but modest results. New strategies for improving beneficial effect of cell therapy aim to promote stem cells differentiation before transplantation and to help these cells survive after transplantation. The AMP-activated protein kinase (AMPK) regulates cellular events involved in the adaptation to ischemia that could improve such cell therapy. Besides its metabolic-linked protective role during myocardial ischemia, it is recognized that AMPK is closely involved in other biological cellular functions such as cell proliferation, mitochondrial biogenesis and cell structure organization known to be interrelated and involved in cell differentiation process. Through its multiple functions, AMPK would be a prime target in order to improve the therapeutic potential of stem cells in cell therapy treatment of myocardial infarction. The aim of our study was to assess the impact of modulating AMPK activity on (i) stem cells differentiation, and (ii) on mature cells survival in hypoxic conditions. We have shown that chronic AMPK activation inhibits mesenchymal stem cell (MSC) proliferation without causing any cell death. Inasmuch as stem cell proliferation rate is known to be inversely correlated to their capacity to differentiate, such AMPK action was worthwhile. Among AMPK downstream targets proposed to regulate cell proliferation, we showed that neither the p70S6K/ eEF2-dependent protein synthesis pathway nor p21cip1 are involved. However, we have demonstrated a critical role of p27kip1 in the antiproliferative effect of AMPK. Furthermore, we also showed that AMPK activation stimulates mitochondrial biogenesis, a crucial process in stem cells differentiation. We therefore examined two differentiation processes, osteocyte differentiation of MSCs and cardiac differentiation of embryonic stem cells (ESCs) in the presence of specific differentiation cocktails. We observed that osteocyte differentiation of MSCs is delayed in the absence of AMPK. Conversely, A-769662-dependent AMPK activation induces a more intense osteocyte differentiation. Similarly, preliminary data confirm a positive role of AMPK in ESC cardiac differentiation. Concerning the aspect of survival of undifferentiated and differentiated stem cells, we demonstrated that MSCs are glycolytic cells very resistant to hypoxia in an AMPK-independent manner. However, pharmacological AMPK activation should theoretically ensure survival of predifferentiated stem cells, characterized by a mitochondrial oxidative metabolism, under hypoxic condition. We established this concept by using adult cardiomyocytes. We showed that, when combined to hypoxia or other AMP-dependent AMPK activators, A-769662 promotes an overstimulation of AMPK pathway and glucose metabolism. This synergistic effect of A-769662 under such ischemia-mimetic conditions protected cardiomyocytes against reactive oxygen species production and cell death. In conclusion, our study leads us to believe that AMPK regulation may be beneficial to ultimately improve the efficacy of cardiac cell therapy after myocardial infarction.