Abstract 5369: Mesenchymal Stem Cells Overexpressing CXCR4 (CXCR4+-MSCs) Attenuate Remodeling of Post-Myocardial Infarction by Releasing Anti-Fibrotic Enzymes
We hypothesize that CXCR4+-MSCs penetrate and proliferate in infracted heart by releasing collagen degrading enzymes. We genetically engineered male mouse MSCs using ex vivo adenoviral transduction for over-expression of CXCR4/GFP or GFP alone. MSCs (G-I) or CXCR4+-MSCs (G-II) or CXCR4+-MSCs treated with epigallocarechin gallate (EGCG, 50μg/ml), a MT1-matrix metalloproteinases (MMPs) inhibitor (G-III) or CXCR4+-MSCs with AMD3100 (5 μg/mL), a CXCR4-selective antagonist (G-IV). A Trans-Matrigel Chemoinvasion Assay was used to evaluate the ability of MSCs to cross the basement membrane. MMPs were analyzed by Western blot and MMP antibody staining. Sex mismatched MSCs were infused into female mice via a tail vein injection 3 days after MI. Mice in G-III were treated with EGCG (100 mg/kg, oral gavage, daily for 2 weeks) to inhibit MMPs and G-IV was treated with AMD3100 (1 mg/kg, i.p. given continually for 6 days after MI). LV fibrosis was detected by Picrosirius red staining. Echocardiography was performed at 4 weeks after MI and hearts were harvested for histological analysis. In vitro, cell migration was significantly higher in G-II in the presence of SDF-1α as compared with other groups, (p <0.01). EGCG or AMD3100 markedly prevented this response. MMP-9 and MT1-MMP were upregulated significantly only in G-II (p<0.01) exposed to hypoxia. Infiltration of GFP and Y chromosome positive cells in the peri- or infarct area was increased significantly in G-II. CXCR4+-MSCs penetrated more effectively into the infarcted region and survived in the ischemic environment as compared to control group. These effects were reduced with EGCG or AMD3100. The ventricular remodeling and interstitial fibrosis were also reduced in G-II but not in other groups. G-II also had less LV dilation (diastolic dimension 4.9±0.2 vs. 6.2±0.3 mm, p<0.05), EF (62±3 vs. 44±4%, p<0.05). Infarct size (31±3.8 vs 43±4.7% of LV, p<0.05) and collagen area fraction (16±2 vs. 28±4 %, p<0.05) were significantly reduced in G-2 compared to G-I. Under hypoxic conditions MMPs were upregulated in CXCR4+-MSCs which crossed the basement membrane by releasing enzymes leading to breakdown or reduction of scar formation thus facilitating cell homing and proliferation.