Abstract 1416: IGF-1 Gene Transfer Promotes Connexin-43 Expression and Enhances Integration of Bone Marrow Stem Cells in the Infarcted Heart

Abstract

For functional benefits, bone marrow stem cells should engraft and develop functional syncitium with the host myocytes in the infarcted heart. We report that IGF-1 overexpression significantly enhances connexin-43 (Cx-43) in mesenchymal stem cells (MSCs) which promotes their survival and functional integration with host myocardium post-engraftment. IGF-1 gene transduced MSCs ( IGF-1 MSCs) expressed higher IGF-1 ( p < 0.001 ) as compared with GFP gene transduced cells ( GFP MSCs). After 8h anoxia, MSCs, H2C9 and endothelial cells treated with IGF-1 MSCs conditioned medium ( IGF-1 CM) showed higher survival ( p < 0.001 vs GFP MSCs conditioned medium ( GFP CM) supported by higher Akt activation which was abolished by wortmannin. Immunodetection showed Cx-43 plaques in the peripheral areas besides punctate distribution in the cytoplasm around the nucleus in IGF-1 MSCs and IGF-1 CM treated MSCs whereas GFP MSCs and GFP CM treated MSCs showed Cx-43 expression in regions of intimate cell to cell contact only. IGF-1 overexpression or IGF-1 CM treatment of MSCs also induced higher level Akt and p27 activation, and Cx-43 expression as compared with GFP MSCs ( p = 0.02 ) which was abolished by wortmannin. For in vivo studies, 70 μ l DMEM without cells (group-1) or containing 1x10 6 GFP MSC (group-2) or IGF-1 MSC (group-3) were injected intramyocardially in female rat model of coronary artery ligation (n=16/group). The animals were harvested on 7 days and 6 weeks after cell engraftment. FISH and sry -gene analysis on 7 day showed extensive survival of the male donor cells in the heart. Real-time PCR and Western blot on the heart tissue showed higher level of Cx-43 and activation of p27 in group-3 ( p < 0.05 vs group-2). The number of TUNEL + cells was lower in group-3 ( p = 0.01 vs group-2). Immunostaining for α -sarcomeric actin and Cx-43 showed extensive myogenic differentiation of IGF-1 MSCs and gap junction formation between adjacent neofibers. Indices of heart function including ejection fraction (63.05±1.37%) and fractional shortening (28.54±0.92%) were improved in group-3 ( p < 0.001 vs group-2 ) . IGF-1 enhances Cx-43 expression in MSCs and promotes their engraftment and functional integration in the heart and improves heart function.