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.

干细胞来源的成肌细胞的移植是一种治疗骨骼肌功能丧失的有前途的方法。从体细胞直接转化的成肌细胞绕过任何干细胞的中间阶段，可以避免移植后肿瘤形成的问题。以前，我们报道了与肌原性分化1（MYOD1）基因和v-myc禽骨髓瘤病病毒癌基因肺癌同源基因（MYCL）基因的共转导有效地将人类成纤维细胞转化为成肌细胞。尽管直接转化的成肌细胞在体外和体内都能有效融合到多核肌管中尚不清楚它们是否具有收缩能力，这是肌肉最显着的表型。在本研究中，我们旨在检查通过MYOD1和MYCL的过表达而与直接转化的成肌细胞相区别的肌管的体外收缩能力。。我们在微型设备上制作了三维（3D）组织以进行力测量。3D培养增强了成肌细胞向肌管的分化，这通过骨骼肌相关基因的基因表达分析得以证实。培养4天后，组织开始响应电刺激产生收缩力，在10天后达到约12μN。加入IGF-I会降低3D组织的收缩力，而使用冷冻保存的细胞会增加3D组织的收缩力。我们证实，由来自三个不同供体的细胞制成的组织产生了相似大小的力。因此，通过过度表达MYOD1和MYCL直接转化的成肌细胞可能是细胞治疗的有希望的细胞来源。