Reagents were obtained from the following sources: PHA-665752, Cayman Chemical, MI; Rapamycin, LC Laboratories, MA; SU5402, Merck Millipore, MA; Wortmannin, AdipoGen, CA; PD98059, ALEXIS Biochemicals, CA; Dorsomorphin, FUJIFILM Wako Pure Chemical Corp., Osaka, Japan; and SB216763, Merck Millipore, MA. Statistical Analysis All experimental data are shown as mean SE. Further, immunohistochemistry revealed that pre-treatment with GAPDH remarkably increases the number of PAX7+EdU+ proliferative satellite cells in regenerating muscles (Figures 7G and Mps1-IN-3 7H). These results suggest that GAPDH acts as a DMDF, promoting activation and proliferation of satellite cells during muscle regeneration culture study revealed that growth-factor-enriched media accelerate proliferation of satellite cells post treatment with DMDFs. Treatment with recombinant GAPDH, which is one of the DMDFs, prior to muscle injury also promoted satellite cell proliferation during muscle regeneration knock-in mice were?used for muscle damage experiments em in?vivo /em . The Ethical Committee for Animal Care and Use (no. 1203190970) of Nagasaki University and Kumamoto University (A30-098) approved all experimental procedures. Cell Culture To assay satellite cells associated with myofibers, we used a floating culture method using individual myofibers (Ono et?al., 2015) that allowed determination of satellite cell fate from the quiescent to the activation state. Individual myofibers associated with satellite cells were isolated from EDL muscles using 0.2% type I collagenase (Worthington Biochemical, Lakewood, NJ) in DMEM (Thermo Fisher Scientific, MA) for 90?min at 37C and 5% CO2. Following purification of myofibers, isolated myofibers were further incubated in DMEM for 3?h at 37C under 5% CO2 to eliminate dying contracted myofibers during isolation (Figure?S1). For a co-culture assay, equal numbers of isolated myofibers were cultured with or without damaged myofibers under floating conditions (Figure?2A). DMEM and non-glucose DMEM (Wako, Osaka, Japan) were used. The volume of medium was determined by a ratio of 50 myofibers/mL volume. GM (DMEM supplemented with 30% fetal bovine serum, 1% chicken-embryo extract, 10?ng/mL basic fibroblast growth factor, and 1% penicillin-streptomycin) and plating medium (DMEM supplemented with 10% horse serum, 0.5% chicken-embryo extract, and 1% penicillin-streptomycin) were used for satellite cell activation (Figure?6) and as a positive control (Figures 2 and ?and3),3), respectively. To obtain muscle tissue extracts, TA muscle tissues of adult mice were isolated and crushed in a bead crusher. Tissue homogenates were then filtered with a 0.45?m filter before use as muscle extracts. Isolated myofibers associated with satellite cells were treated with muscle tissue extracts in DMEM under floating culture conditions (Figure?1A). To obtain mechanically damaged myofibers, healthy intact myofibers were directly damaged with a Pasteur pipette in the culture dish. The damaged myofibers were detected by shrunken morphology (Figure?2A). The ratio of intact to damaged myofibers was 1:1 in the co-culture condition and the total numbers of myofibers were equivalent between conditions (Figures 2 and ?and3).3). Cells were labeled with EdU (Thermo Fisher Scientific) in the culture medium for 6?h prior to fixation. Reagents were obtained from the following sources: PHA-665752, Cayman Chemical, MI; Rapamycin, LC Laboratories, MA; SU5402, BTLA Merck Millipore, MA; Wortmannin, AdipoGen, CA; PD98059, ALEXIS Biochemicals, CA; Dorsomorphin, FUJIFILM Wako Pure Chemical Corp., Osaka, Japan; and SB216763, Merck Mps1-IN-3 Millipore, MA. Statistical Analysis All experimental data are shown as mean SE. The comparison between two conditions was done by unpaired t test. A one-way repeated-measures ANOVA was applied to identify significant differences among conditions or groups. When a significant difference was observed, the data were subjected to post hoc analysis. A p? 0.05 was considered significant. Author Contributions Y.T. designed and performed the experiments, interpreted and analyzed the data, and wrote the manuscript. Mps1-IN-3 Y.K. and H.M. performed the experiments and interpreted and analyzed the data. Y.O. designed and performed the experiments, interpreted the data, assembled the input data, and wrote the manuscript. All authors discussed the results and implications and commented on?the manuscript. All authors read and approved the final manuscript. Acknowledgments We thank all the lab members for technical support. This work was?supported by the Japan Agency for Medical Research and Development (AMED, 16bm0704010h0001, 18ek0109383h0001, and 19bm0704036h0001), and the Grant-in-Aid for Scientific Research KAKENHI (17K13138, 18H03193, and 18K19749). This work was also supported, in part, by the Takeda Science.