Aim: Mesenchymal stem cells (MSC) are a promising candidate for cardiac replacement therapies. However, the majority of transplanted MSC are readily lost after transplantation because of poor blood supply, ischemia-reperfusion, and inflammatory factors. We aimed to study the effects of hypoxia preconditioning (HPC) on hypoxia/reoxygenation-induced apoptosis of MSC. Methods:

Aim: The angiopoietin-1 (Ang1)/Tie-2 signaling system not only plays a pivotal role in vessel growth, remodeling, and maturation, but also reduces apoptosis of endothelial cells, neurons, and cardiomyocytes. However, relatively little is known as to whether Ang1 has a protective effect on mesenchymal stem cells (MSC). The aim of the present study was to investigate the protective effect of Ang1/Tie-2 signaling on MSC against serum deprivation and hypoxia-induced apoptosis, and to determine the possible mechanisms. Methods: Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling staining were used to assess the apoptosis of MSC. The expression of Tie-2, Akt, Bcl-2, Bax, and cleaved caspase-9 and -3 was detected by Western blot analysis. Results: This study showed that MSC expressed Tie-2 receptor, and Ang1 induced Tie-2 receptor phosphorylation. The protective effect of Ang1 on MSC was dose-dependent and peaked at 50 µg/L; however, the soluble Tie-2/Fc fusion protein, which acts as an inhibitor by sequestering Ang1, abrogated the anti-apoptotic effect. Ang1 induced Akt phosphorylation, increased the Bcl-2/Bax ratio, and decreased the activation of caspase-9 and -3. All these effects were attenuated by Tie-2/Fc and a phosphatidylinositol 3 kinase (PI3K) inhibitor, wortmannin. Conclusion: These results demonstrate that Ang1 can protect MSC against serum deprivation and hypoxia-induced apoptosis; Ang1/Tie-2 signaling and its downstream PI3K/Akt messenger pathway are crucial in the processes leading to MSC survival.

Abstract:Objective: The aim of this study was to test the protective effect of mesenchymal stem cells (MSCs) on cardiomyocytes in vitro and to investigate the anti-apoptotic signaling pathway. Methods: MSCs from Sprague-Dawley (SD) rats were separated and cultured. MSC medium was collected from MSCs cultured in serum-free Dulbecco's modified eagle medium (DMEM) under hypoxia. Cultured cardiomyocytes from neonatal SD rats were exposed to hypoxia/reoxygenation (H/R) and treated with MSC medium. The apoptotic cardiomyocytes were stained with Annexin-V-fluorescein isothiocyanate (FITC), Hoechst 33342 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). The mitochondrial transmembrane potential of cardiomyocytes was assessed using a fluorescence microscope. The expression of Bcl-2, Bax, cytochrome C, apoptosis-induced factor (AIF), and caspase-3 was tested by Western blot analysis. Results: Our data demonstrated that MSC medium reduced H/R-induced cardiomyocyte apoptosis, increased the Bcl-2/Bax ratio, and reduced the release of cytochrome C and AIF from mitochondria into the cytosol. Conclusion: MSCs protected the cardiomyocytes from H/R-induced apoptosis through a mitochondrial pathway in a paracrine manner.

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