Objective: To investigate the anti-apoptotic effects of mesenchymal stem cells (MSCs) on hypoxia-injured cardiac myocytes.
Methods: MSCs were isolated from the bone marrow of 6 - 8 week-old Sprague-Dawley rats. Cardiac myocytes from neonatal rat were cultured under hypoxia, then the hypoxia-injured cardiac myocytes were divided into 3 groups: cultured alone (control group), co-cultured with the MSCs, or co-cultured in MSC-conditioned media in conditions of anoxia (95% N(2) + 5% CO(2), continuous hypoxia group) or normoxia [hypoxia/reoxygen (H/R) group] for 72 hours. The cell apoptosis was measured by Hoechst staining, and Western blotting was used to test the protein expression of Bcl-2 and Bax in the cardiac myocytes.
Results: The apoptotic rate of the cardiac myocytes cultured under hypoxia was 51.6% +/- 2.4%, significantly higher than those of the cardiac myocytes co-cultured with MSCs and MSC-conditioned media respectively (15.1% +/- 5.4% and 24.0% +/- 4.2% respectively, both P < 0.001). The apoptotic rate of the H/R group was 20.9% +/- 2.7%, significant higher than that of the MSC group (11.5% +/- 3.7%, P < 0.05), however, not significantly different from that of the MSC-conditioned media group (20.1% +/- 4.2%, P > 0.05). The protein expression of Bcl-2 was not significantly different among different groups. The Bax protein expression of the MSC group and MSC-conditioned media group were 2.28 +/- 0.46 and 3.01 +/- 0.26 respectively, both significantly lower than that of the control group (7.62 +/- 1.28, both P < 0.05). The decreased expression of Bax in the cardiac myocytes was greatly related to the decreasing of apoptosis.
Conclusion: Co-cultured MSCs show significant anti-apoptotic effects on cardiac myocytes both in continuous hypoxia and in H/R conditions with the possible mechanism of direct cell to cell interaction and paracrine of cytokines which effect the expression of Bax in the myocytes.