Effects of HIF-1α on MSC engraftment in the border zone. A) Engrafted mesenchymal stem cells (MSCs) stained with DiR (red) were detected one week, two weeks and three weeks after cell injection. The samples were stained with anti-α-SA antibody (green) and 4, 6-diamino-2-phenylindole (DAPI) (blue). B, C) Three weeks after cell injection, five hearts from three groups were harvested and imaged for detection of red fluorescence. The optical density (photon/s/mm2) from a fixed region of interest (ROI) was measured. D) Donor male cells persistent in the female hearts were detected by quantitative PCR for the SRY gene one week and three weeks after cell injection. ▲P <0.05 vs. MSCs group, △P <0.01 vs. MSCs group. HIF-1α, hypoxia-inducible factor-1α.