Abstract 707: Genetically Modified Mesenchymal stem cells (MSCs) Overexpressing Chemokine Receptor CCR1 Improves Cellular Engraftment and Tissue Repair of Ischemic myocardium
Bone marrow-derived mesenchymal stem cells (BM-MSCs) may promote structural and functional repair in the myocardium following acute myocardial infarction (MI). However, the cytotactic factors/receptors responsible for MSC engraftment to the injured myocardial tissue have not been fully elucidated. Chemokines, important agents controlling cell locomotion and trafficking, are upregulated in the heart following MI and have been implicated in regulating engraftment and homing of MSCs to infarcted tissue. We hypothesized that over expression of certain chemokine receptors in MSCs will augment cell engraftment of injected MSCs in infarcted tissue. Our previous experiments indicated that CCL7(/MCP3) and SDF-1 expression was upregulated in infarcted myocardium. However, the level of expression of receptors corresponding to these chemokines in MSCs is low. In this study, we retrovirally transduced murine BM-MSCs with CCR1 or CXCR4 (receptors for CCL7 and SDF-1, respectively) genes under the control of the constitutively expressed promoter, a LTR from the murine stem cell PCMV virus. We found that overexpression of CCR1 or CXCR4 increased chemokine-induced MSC chemokinesis in vitro as measured by transwell assays (1.4-fold, P<0.05, n=3). Interestingly, overexpression of CCR1 but not CXCR4 protected MSC in cell culture from serum deprivation-induced cell apoptosis (the caspase 3 activity was reduced 0.33-fold, P<0.05, n=3–6). After 24 hours serum deprivation, the condition medium (CM) of CCR1 overexpressing MSCs showed a higher angiogenetic potency compared with CM of control MSCs (2-fold, P<0.05, n=3) by HUVEC tube formation assay. To examine the in vivo effects of chemokine receptor overexpression, MSCs (0.3x106) were injected intramyocardially 1 hour after the permanent ligation of the LAD. Three days post-MI, hearts injected with MSCs overexpressing CCR1, but not CXCR4 exhibited a reduced infarct size compared to hearts injected with control MSCs (35.2±3.5% vs 48.1±3.6%, n=6 – 8, P<0.05). Furthermore, enhanced angiogenesis was observed in CCR1 group. In summary, our results revealed that CCR1 expressed on MSCs improves engraftment of MSCs and subsequent repair of ischemic myocardium through increasing cell migration/viability.