Chemical induced conversion of mouse fibroblasts and human adipose-derived stem cells into skeletal muscle-like cells

Use of stem cells in regenerative medicine holds great promise in treating people suffering from various otherwise incurable ailments. Direct conversion of somatic cells to other lineages thereby bypassing the intermediate pluripotent state has enormous applicability with respect to time requirement for conversion as well as safety issues. Among various approaches, chemical induced cell conversion is safe yet effective, and the use of small molecules has thus increased greatly in recent years in regenerative fields due to easy applicability, efficient scalability, and consistent reproducibility. Here we report a combination of small molecules capable of converting mouse fibroblasts into skeletal muscle-like cells (SMLCs) without requiring ectopic transcription factor expression. We observed that a combination of chemicals is necessary and sufficient to convert mouse fibroblast to SMLCs that have functional similarity to skeletal muscles. In addition, we also found that cytokines responsible for modulating several key signaling pathways enhance the maturation of converted SMLCs into multinucleated myocytes. Epigenetic analysis revealed that this conversion is accomplished by an epigenetic overhaul, followed by activation of key signal pathways responsible for activating skeletal specific loci. We further observed that human adipocyte-derived stem cells can be converted into SMLCs under conditions similar to that of fibroblasts. This study not only provides an example of chemical induced direct conversion, but also underlines the key signaling pathways that are needed to induce mesodermal lineages and muscles from pleotropic type cells.