The Myostatin Induced The Molecular Mechanisms Of Tumor Cell Apoptosis

Myostatin (MSTN) is a member of the TGF-βsuperfamily. It has a negative effect on skeletal muscles, including inhibition of the proliferation and differentiation of myoblasts in the embryo stages, and also avoidance of hypertrophy in adult skeletal muscles. In cultured myoblasts, administering MSTN to the cell for 24 hours can significantly inhibit the growth of myoblasts, and the cell cannot differentiate to myotubes after this treatment by MSTN in a differentiation medium. Molecular genetics evidence showed that the doubled- muscle cattle generated by genetic selection had a mutation of the Myostatin gene. Also, Myostain knock out mice have 3 times the weight of skeletal muscle compared to wild type mice and less adipose tissue. Myostatin has a similar effect in humans, which was identified a boy with a myostain mutation.The TGF-βsuperfamily has generally inhibited functions of cell proliferation, and the abnormality of this pathway often leads the tissues to form tumors. However, we know that TGF-βhas different functions at different stages for different tissue types. As a member of the TGF-βsuperfamily, what is myostatin's function on tumors? When we added the Myostatin to several tumor cell lines from different tissues, some cells were resistant while others died.Specifically, cell death can be divided into Programmed Cell Death and Necrosis. There are 3 types of Programmed Cell Death: Apoptosis, Autophagy and Programmed Necrosis. We stained the cell treated with Myostatin with either Hoechst or DAPI and observed it by a fluroscence microscope. The pictures showed that the nucleus had a typical apoptosis phenomenon, which was nuclear condensation. These results indicate that the cell death caused by Myostatin is apoptosis. In addition, the results of Annexin V + PI staining detected by Flow Cytometry can tell us that the Myostatin- induced-apoptosis is both time and dosage dependent.There is often caspase activation in the process of apoptosis. We detected aspase activity by Western blot and Caspase activity kits and found that caspases were activated by Myostatin in the process of apoptosis. In order to investigate if the apoptosis is through the intrinsic or mitochondrial pathway, like TGF-β, we tested the Caspase-9 cleavage by Western blot, and the results suggested that Caspase-9 was activated 24 hours after treatment. A common and important event leading to Caspase-9 activation and further apoptosis is Cytochrome-C release. The results of subcelluler isolation coupled with Western blots and immunofluroscence indicated that Cytochrome-C was released from the mitochondrial inner- membrane to the cyotosol in the process of Myostatin-induced-apoptosis. Further molecular study indicated that the proapoptotic factor, Bim (BH3 only protein), is upregulated by Myostatin, suggesting that Bim may be involved in the Myostatin-induced-apoptosis.