Engraftment of MSCs into the infarcted murine heart; lack of transdifferentiation of MSCs. (A) Massive engraftment of EGFP+ MSCs (green) in a cryoinfarcted heart 29 days after injection of 2 × 106 cells (passage 3); inset shows a transmission light picture of the heart; the infarcted area is marked by a white dotted line. (B) Cryosection of border zone of the infarction demonstrating prominent engraftment of EGFP+ MSCs (green) 7 days after injecting 1 × 105 cells (passage 4). (C) Engrafted EGFP+ MSCs (green) in the infarcted area 24 days after transplantation of 1 × 105 cells (passage 3); these displayed round or elongated shape but were negative for alpha-actinin (red) and desmin (white). (D) Cardiomyocytes in the intact heart (same section as shown in panel C) displayed typical shape and distinct cross-striation. (E) PECAM (red, endothelial marker)– and alpha-smooth muscle-actin (magenta)–positive small vessels were identified in vicinity to engrafted MSCs (green) within and around the lesioned area. None of the vessels showed EGFP+ endothelial or smooth muscle cells. Some of the vessels were missing the smooth muscle layer, indicating vessel neoformation. Nuclei were stained with Hoechst dye (blue). Bar represents 1000 μm (panel A), 2500 μm (panel A inset), 470 μm (panel B), 18 μm (panels C,E), and 8 μm (panel D). See “Materials and Methods; Image acquisition and preparation” for microscopy details.
