Abstract 1279: Combined Stem Cell Mobilization via CXCR4 Antagonist Augments Recruitment of EPCs Following Sonic Hedgehog Gene Therapy via Increased Local Expression of VEGF and SDF-1
Background EPC recruitment into the myocardium can be viewed as a 2-step process that begins by mobilization of EPC from the bone marrow, followed by homing into the myocardium. Recent data have demonstrated that the embryonic sonic hedgehog (Shh) pathway can be reactivated in adults in the setting of ischemia and its activation induces recruitment of EPCs to sites of myocardial neovascularization. We hypothesized that combining a mobilization agent with a strategy to improve EPC incorporation could exert synergistic therapeutic effects compared to monotherapy. In the present study, we performed experiments to evaluate a strategy of mobilization by the CXCR4 antagonist AMD3100 combined with expression of Shh to enhance EPC incorporation and functional recover in ischemic myocardium.
Methods and results MI was induced in C57 mice by ligation of the LAD. Mice were then randomized to one of four treatment groups in a 2×2 study design: placebo, Shh gene therapy (local delivery of naked DNA into the peri-infarct region) alone; AMD (single subcutaneous injection) or combined Shh gene therapy plus AMD. AMD alone induced EPC mobilization as expected, however the level of local cytokine expression (SDF-1 α, VEGF) in the heart remained unchanged. In contrast, Shh gene therapy increased expression of both SDF-1 and VEGF compared to control and AMD treated mice (p<.01). NIH 3T3 fibroblasts were treated either with Shh protein or transfected with Shh plasmid. Cytokine expression by the fibroblasts was analyzed by QRT-PCR and ELISA immunoassay, both of which showed significantly increased VEGF and SDF-1 α in Shh treated vs. controls. Conditioned media from treated vs. control fibroblasts were used in EPC functional assays, revealing that treated Shh fibroblasts release factors that induce migration and proliferative activity of EPCs.
Conclusions Shh augments expression chemo-attractive cytokines implicated in the incorporation of EPCs into the ischemic tissue. These data suggest that combining AMD treatment with local Shh administration into the myocardium may have synergistic therapeutic potential in individuals with MI via increasing incorporation of EPCs into the threatened myocardium. Ongoing studies are evaluating the physiologic effects of this strategy.