Mobilizing of haematopoietic stem cells to ischemic myocardium by plasmid-mediated stromal-cell-derived factor-1α treatment

A concentration gradient of stromal-cell-derived factor-1α (SDF-1α) is the major mechanism for homing of haematopoietic stem cells (HSCs) in bone marrow. We tested the hypothesis that a gene therapy using SDF-1α can enhance HSCs recruiting to the heart upon myocardial infarction (MI). Adult mice with surgically induced myocardial ischemia were injected intramyocardially with either saline (n=12) or SDF-1α plasmid (n=12) in 50 μl volume in the ischemic border zone of the infarcted heart 2 weeks after myocardial infarction. Donor Lin-c-kit+ HSCs from isogenic BalB/c mice were harvested, sorted through magnetic cell sorting (MACS) and labeled with PKH26 Red. Three days after plasmid or saline injection, 1×10⁵ labeled cells were injected intravenously (i.v.) into saline mice (n=4) and SDF-1α plasmid mice (n=4). The hearts and other tissue were removed for Western blot assay 2 weeks after plasmid or saline treatment. The labeled Lin-c-kit+ cells were identified with immunofluoresent staining and endogenous c-kit+ cells were identified by immunohistochemical staining. In mice killed at 1 month postinfarct, Western blot showed higher levels of SDF-1α expression in SDF-1α-treated mouse ischemic hearts compared to saline-treated hearts and other tissues. In the SDF-1α plasmid-treated hearts, SDF-1α is overexpressed in the periinfarct zone. The labeled stem cells engrafted to the SDF-1α positive site in the myocardium. There was also evidence for endogenous stem cell recruiting. The density of c-kit+ cells in border zone, an index of endogenous stem cell mobilization, was significantly higher in the SDF-1α-treated group than in the saline group (14.63±1.068 cells/hpf vs. 11.31±0.65 cells/hpf, P=0.013) at 2 weeks after SDF-1α or saline treatment. Following myocardial infarction, treatment with SDF-1α recruits stem cells to damaged heart where they may have a role in repairing and regeneration. The gene therapy with an SDF-1α vector offers a promising therapeutic strategy for mobilizing stem cells to the ischemic myocardium.