Screening of anti-atrophic peptides by using photo-cleavable peptide array and 96-well scale contractile human skeletal muscle atrophy models.

Skeletal muscle atrophy is characterized by decreases in protein content, myofiber diameter, and contractile force generation. As muscle atrophy worsens the quality of life, the development of anti-atrophic substances is desirable. In this study, we aimed to demonstrate a screening process for anti-atrophic peptides using photo-cleavable peptide array technology and human contractile atrophic muscle models. We developed a 96-well system and established a screening process with less variability. Dexamethasone-induced human atrophic tissue was constructed in the system. Eight peptides were selected from the literature and used for the screening of peptides for preventing the decrease of the contractile forces of tissues. The peptide QIGFIW, which showed preventive activity, was selected as the seed sequence. As a result of amino acid substitution, we obtained QIGFIQ as a peptide with higher anti-atrophic activity. These results indicate that the combinatorial use of the photo-cleavable peptide array technology and 96-well screening system could comprise a powerful approach to obtaining anti-atrophic peptides, and suggest that the 96-well screening system and atrophic model represent a practical and powerful tool for the development of drugs/functional food ingredients.

In Vitro Model of Human Skeletal Muscle Tissues with Contractility Fabricated by Immortalized Human Myogenic Cells.

In the development process for drugs used to treat skeletal muscle, cell-based contractile force assays have been considered as a useful in vitro test. Immortalized human myogenic cells are promising as cell sources for reproducible and well-characterized in vitro models. In this study, it is investigated whether immortalized human myogenic cells, Hu5/KD3, have suitable contractile ability and the potential to be used as cell sources for contractile force assays. Muscle tissues are fabricated using Hu5/KD3 cells on the microfabricated devices used to measure contractile force. The tissues generate a tetanic force of ≈30 µN in response to the electrical pulse stimulation (EPS). Gene expression analysis of the myosin heavy chain (MYH) isoform indicates that the tissues mostly consisted of muscle fibers expressing MYH7 or/and MYH8. The addition of dexamethasone or lovastatin decreases the contractile force of the tissues, indicating that the tissues have the potential to evaluate drug candidates designed to treat muscle atrophy or statin-induced myopathy. It is also demonstrated that the contractile force of tissues increased when EPS is applied as an artificial exercise. These results indicate that the Hu5/KD3 tissues can be employed for contractile force assays and would be useful for in vitro human skeletal muscle models.

Effect of cell-extracellular matrix interaction on myogenic characteristics and artificial skeletal muscle tissue.

Although various types of artificial skeletal muscle tissue have been reported, the contractile forces generated by tissue-engineered artificial skeletal muscles remain to be improved for biological model and clinical applications. In this study, we investigated the effects of extracellular matrix (ECM) and supplementation of a small molecule, which has been reported to enhance α7ß1 integrin expression (SU9516), on cell migration speed, cell fusion rate, myoblast (mouse C2C12 cells) differentiation and contractile force generation of tissue-engineered artificial skeletal muscles. When cells were cultured on varying ECM coated-surfaces, we observed significant enhancement in the migration speed, while the myotube formation (differentiation ratio) decreased in all except for cells cultured on Matrigel coated-surfaces. In contrast, SU9516 supplementation resulted in an increase in both the myotube width and differentiation ratio. Following combined culture with a Matrigel-coated surface and SU9516 supplementation, myotube width was further increased. Additionally, contractile forces produced by the tissue-engineered artificial skeletal muscles was augmented following combined culture. These findings indicate that regulation of the cell-ECM interaction is a promising approach to improve the function of tissue-engineered artificial skeletal muscles.

Fabrication of contractile skeletal muscle tissues using directly converted myoblasts from human fibroblasts.

Transplantation of stem cell-derived myoblasts is a promising approach for the treatment of skeletal muscle function loss. Myoblasts directly converted from somatic cells that bypass any stem cell intermediary stages can avoid the problem of tumor formation after transplantation. Previously, we reported that co-transduction with the myogenic differentiation 1 (MYOD1) gene and the v-myc avian myelocytomatosis viral oncogene lung carcinoma derived homolog (MYCL) gene efficiently converted human fibroblasts into myoblasts. Although the directly converted myoblasts efficiently fused into multinucleated myotubes in vitro and in vivo, it is not clear whether they have the contractile ability, which is the most significant phenotype of the muscle. In the present study, we aimed to examine the in vitro contractile ability of the myotubes differentiated from the directly converted myoblasts by the overexpression of MYOD1 and MYCL. We fabricated three-dimensional (3D) tissues on a microdevice for force measurement. The 3D culture enhanced the differentiation of the myoblasts into myotubes, which were confirmed by gene expression analysis of skeletal muscle-related genes. The tissues started to generate contractile force in response to electrical stimulation after 4 days of culture, which reached approximately 12 µN after 10 days. The addition of IGF-I decreased the contractile force of the 3D tissues, while the use of cryopreserved cells increased it. We confirmed that the tissues fabricated from the cells derived from three different donors generated forces of similar magnitude. Thus, directly converted myoblasts by the overexpression of MYOD1 and MYCL could be a promising cell source for cell therapy.