The main function of mitochondrial fusion protein 1 （Mfn1） and mitochondrial fusion protein 2 （Mfn2） was originally thought to be just regulating the fusion of mitochondrial outer membrane. But in recent years，many studies on these two proteins show that they are involved in many important cellular physiological processes including proliferation，apoptosis，necrosis and regulation of respiratory function and oxidative metabolism. There are many aspects of the influenceof Mfn1 and Mfn2 on cardiomyocyte，which have not been thoroughly studied yet，sometimes with even contradictoryconclusions. But these two proteins definitely have significant impact on the growth，development and physiological functionof cardiomyocyte. To investigate the function and mechanism of Mfn1 and Mfn2 in various physiological processes of cardiomyocyte is of great significance for in vitro studies of physiological functions of cardiomyocyte and technological development of myocardial tissue engineering and transplantation in vivo. This article mainly focuses on recent research progress of the influence of Mfn1 and Mfn2 on various physiological functions of cardiomyocyte.
The establishing of myocardial tissue engineering techniques not only solve a series of issues that generate in cell and tissue transplantation after myocardial infarction, but also create a platform for selecting better materials and transplantation techniques. However, both experimental animal studies and recent clinical trials indicate that current transplantation techniques still have many defects, mainly including lack of suitable seed cells, low survival rate and low differentiation rate after transplantation. In this context, extracellular matrix （ECM）, as myocardial tissue engineering scaffold materials, has gained increasing attention and become a frontier and focus of medical research in recent years. ECM is no longer merely regarded as a scaffold or a tissue, but plays an important role in providing essential signals to influence major intracellular pathways such as cell proliferation, differentiation and metabolism. The involved models of ECM can be classified into following types：natural biological scaffold materials, synthetic polymer scaffold materials and composite scaffold materials with more balanced physical and biological properties. This review mainly introduces research progress of ECM in myocardial tissue engineering and ECM materials.
Objective To use direct adherent method to induce human embryonic stem cells （hESCs） to become cardiomyocytes in vitro and examine their differentiation rate. Methods Undifferentiated hESCs were seeded onto Matrigel-coated plates at a density of 1×105 cells/cm2 and cultured in MEF-conditioned medium （MEF-CM） with 8 ng/ml basic fibroblast growth factor （bFGF） for 6 days. Then MEF-CM was replaced with RPMI 1640/B27 medium supplemented with 100 ng/ml human recombinant activin A for 24 hours in hESCs culture，followed by supplementation of 10 ng/ml human recombinant bone morphogenetic protein 4 （BMP4） for 4 days in hESCs culture. The medium was then replaced with RPMI 1640/B27 medium without supplementary cytokines，and hESCs were refed every 2-3 days for 2-3 additional weeks. Self-beating cardiomyocytes and the beating frequency were observed under the microscope，and the percentage of colonies showing beating cardiomyocytes was calculated. Cardiac troponin T （cTnT），a specific marker of cardiomyocytes，was examined by immunofluorescence. Spontaneous action potentials of cardiomyocytes were measured with patch clamp technique.Apoptotic rate of cardiomyocytes was detected with apoptosis-hoechst staining kit after beating cardiomyocytes were culturedunder hypoxia for 24 hours. Results A large number of spontaneous beating cardiomyocytes were observed 13 days after induction. The average time to show beating cardiomyocytes was 13.0±1.1 days after induction，the percentage of colonies showing beating cardiomyocytes was 66.7%，and the beating frequency of cardiomyocytes was 63.0±7.0 times/minutes. Beating cardiomyocytes were cTnT-positive. Spontaneous action potentials were detected in beating cardiomyocytes.Apoptotic rate of cardiomyocytes was 8.0%±0.5% after beating cardiomyocytes were cultured under hypoxia for 24 hours. Conclusion It’s the first time to use direct adherent method to induce hESCs to become cardiomyocytes in vitro in China with the differentiation rate of 66.7% and differentiation time of 13 days.