In this study, we hypothesized that bone marrow stem cells (BMSCs) protect ischemic myocardium through paracrine effects that can be further augmented with preconditioning. In in vitro experiments, cell survival factors such as Akt and eNOS were significantly increased in BMSCs following anoxia. In the second series of experiments following coronary ligation in mice, left ventricles were randomly injected with the following: DMEM (G-1), BMSCs (G-2), and preconditioned BMSCs (G-3). Four days after myocardial infarction, BMSCs were observed within injured myocardium in G-2 and G-3. Apoptotic cardiomyocytes within periinfarct area were significantly reduced in G-3. Four weeks after myocardial infarction, smaller left ventricular (LV) dimension and increased LV ejection fraction were observed in G-3. Infarct area was significantly reduced in G-3. However, GFP+ cardiomyocytes were observed in low numbers within periinfarct area in G-2 and G-3. In conclusion, BMSCs secreted cell survival factors under ischemia, and they prevented apoptosis in cardiomyocytes adjacent to the infarcted area. Preconditioning of BMSCs enhanced their survival and ability to attenuate LV remodeling, which was attributable, in part, to paracrine effects.
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