[iPS cell-based therapy for muscular disorders].

Induced pluripotent stem cells (iPSCs) have been used in research for the development of treatments for various intractable diseases due to their unlimited proliferative and multipotent potential. We are aiming to develop novel therapies for intractable muscular diseases using iPS cells by two approaches i.e. cell therapy and drug screening. In this presentation, I focus on the cell therapy research. We have developed a differentiation induction method that mimics the developmental stages and have succeeded in inducing skeletal muscle stem cells that are applicable to cell transplantation therapy. We have found that cell transplantation into Duchenne muscular dystrophy (DMD) model mice is effective in regenerating more than 10% of dystrophin-positive fibers. In addition, some of the cells have been engrafted as satellite cells in vivo, and it is expected that the therapeutic effect will continue for a long period of time. As for the efficacy to the motor function, we have recently revealed that the regeneration of dystrophin positive myofibers in DMD model mice mainly ameliorates muscle fatigue tolerance rather than maximal contraction force in vivo. We have also developed a differentiation method to induce mesenchymal stromal cells (MSCs) from iPSCs. Transplantation of iPSC-derived MSCs (iMSCs) into Ullrich congenital muscular dystrophy (UCMD) model mice enabled the restoration of collagen type VI which resulted in enhancement of muscle regeneration. Interestingly, somatic MSCs such as bone marrow-derived MSC or adipose-derived MSC do not have therapeutic effect even they can also restore collagen type VI by the transplantation. We have recently found one of the candidates which is responsible for the muscle regeneration and is specifically expressed in the iMSCs.