Abstract 1416: IGF-1 Gene Transfer Promotes Connexin-43 Expression and Enhances Integration of Bone Marrow Stem Cells in the Infarcted Heart
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-1MSCs) expressed higher IGF-1 (p<0.001) as compared with GFP gene transduced cells (GFPMSCs). After 8h anoxia, MSCs, H2C9 and endothelial cells treated with IGF-1MSCs conditioned medium (IGF-1CM) showed higher survival (p<0.001 vs GFPMSCs conditioned medium (GFPCM) 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-1MSCs and IGF-1CM treated MSCs whereas GFPMSCs and GFPCM treated MSCs showed Cx-43 expression in regions of intimate cell to cell contact only. IGF-1 overexpression or IGF-1CM treatment of MSCs also induced higher level Akt and p27 activation, and Cx-43 expression as compared with GFPMSCs (p= 0.02) which was abolished by wortmannin. For in vivo studies, 70μl DMEM without cells (group-1) or containing 1x106 GFPMSC (group-2) or IGF-1MSC (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-1MSCs 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.