Cyclic Strain Promotes Myogenesis of Bone Marrow Stromal Stem Cells

Loss of tongue tissue from various causes can profoundly affect a person's quality of life. In order to engineer skeletal muscle that better resembles the physiological architecture, we hypothesized that in vitro cellular alignment induced by cyclic strain might contribute to the myogenic induction of bone marrow stromal stem cells (BMSCs). Objectives: To investigate the effects of cyclic strain on the alignment and myogenic differentiation of BMSC. Methods: Clonal cultures of mouse BMSCs plated onto fibronectin-coated silicone sheets were subjected to a cyclic 10% uniaxial strain (0.17 Hz). Cell alignment, motility, and proliferation under the cyclic condition were determined by photomicroscopy and DNA measurement. Total RNA was prepared 5 days after strain for RT-PCR to examine the expression of Myf5, myogenin, MRF4, tension-induced/inhibited protein (TIP)-1, and TIP-3 transcripts. Expression of myogenin and myosin proteins was also observed by immunocytochemistry. Results: Three days of cyclic strain resulted in a BMSC alignment shift from completely random orientation to well-aligned morphology parallel to the strain vector. The cyclic strain did not affect BMSC proliferation, but restricted cellular motility over the course of the culture period. After 5 days of strain, BMSCs aligned in a unidirectional manner and fused to form multinucleated myotube-like cells with nuclei aligned in the direction of tension application. These cells strongly expressed mRNAs for Myf5, myogenin, MRF4, and proteins for myogenin and myosin. Concurrently, the cyclic strain induced TIP-1 expression while inhibited TIP-3 expression. Conclusions: These data indicate that the cyclic strain induces BMSC alignment parallel to the strain direction and contributes to BMSC myogenic differentiation with subsequent cellular fusion and myotube formation. This study demonstrates the possibility of BMSC myogenic differentiation by cyclic strain and highlights the importance of cellular alignment for creating more physiologically relevant environments to study myogenesis and engineer skeletal muscle.