MK increased the protective effects of MSCs on H9C2 cells. A: Flow cytometry analysis of the proportion of GFP + cells in the bottom hypoxic H9C2 wells. B: Protective effects of MSCs, MSCs-GFP and MSCs-MK on hypoxic H9C2 cells, measured by Annexin V-PE/7AAD staining. The graph shows the percentages of Annexin V-PE + and 7AAD + (apoptotic) cells as the means ± SEM for three independent experiments. C: Caspase-3 activity of H9C2 was analyzed by Western blot. MSCs-GFP, Mesenchymal stem cells-green fluorescent protein; MSCs-MK, Mesenchymal stem cells-midkine.