Improved contractile force generation of tissue-engineered skeletal muscle constructs by IGF-I and Bcl-2 gene transfer with electrical pulse stimulation

Introduction: Tissue-engineered skeletal muscle constructs should be designed to generate contractile force with directional movement. Because electrical impulses from a somatic nervous system are crucial for in vivo skeletal muscle development, electrical pulse stimulation (EPS) culture as an artificial exercise is essential to fabricate functional skeletal muscle tissues in vitro. To further improve muscle functions, the activation of cell-signaling pathways from myogenic growth factors, such as insulin-like growth factor (IGF)-I, is also important. Because tissue-engineered skeletal muscle constructs should maintain a high cell-dense structure, the expression of an anti-apoptotic factor, such as B-cell lymphoma 2 (Bcl-2), could be effective in preventing cell death. Methods: In the present study, myoblasts were genetically modified with inducible expression units of IGF-I and Bcl-2 genes, and the tissue-engineered skeletal muscle constructs fabricated from the myoblasts were cultured under continuous EPS. Results: Overexpression of IGF-I gene induced muscular hypertrophy in the muscle tissue constructs, and Bcl-2-overexpressing myoblasts formed significantly cell-dense and viable muscle tissue constructs. Furthermore, the combination of IGF-I and Bcl-2 gene transfer with EPS culture highly improved the force generation of the tissue-engineered skeletal muscle constructs. Conclusions: This approach has the potential to yield functional skeletal muscle substitutes with high force generation ability.