Skeletal muscle is susceptible to injury. Muscle stem cells (satellite cells) are responsible for the remarkable ability of muscle to regenerate. Upon injury, the quiescent muscle satellite cells are activated and undergo proliferation and differentiation for tissue repair. Some satellite cells will undergo self-renew to replenish the stem cell pool. The paired-box transcriptional factor Pax7 is a gene specifically expressed in both quiescent and activated satellite cells. However, the regulation of Pax7 expression is not clear. Previous studies showed that basic fibroblast growth factor (bFGF) is required for proliferation of both fetal myoblasts in chicken hind limb and mouse C2C12 myoblast cell line. SB202190, a specific p38 MAP kinase inhibitor was also known to promote musc...[ Read more ]

Skeletal muscle is susceptible to injury. Muscle stem cells (satellite cells) are responsible for the remarkable ability of muscle to regenerate. Upon injury, the quiescent muscle satellite cells are activated and undergo proliferation and differentiation for tissue repair. Some satellite cells will undergo self-renew to replenish the stem cell pool. The paired-box transcriptional factor Pax7 is a gene specifically expressed in both quiescent and activated satellite cells. However, the regulation of Pax7 expression is not clear. Previous studies showed that basic fibroblast growth factor (bFGF) is required for proliferation of both fetal myoblasts in chicken hind limb and mouse C2C12 myoblast cell line. SB202190, a specific p38 MAP kinase inhibitor was also known to promote muscle satellite cell expansion. Using bFGF together with SB202190, I was able to expand satellite cells in vitro for at least three passages with increased cell proliferation without a significant decrease in the ratio of Pax7+ muscle satellite cells. In addition, I observed upregulated Pax7 expression in satellite cells by immunostaining after bFGF treatment. To reveal the underlying mechanisms, I first checked the mRNA level of Pax7 by RT-qPCR with RNA extracted from satellite cells cultured with or without bFGF. Pax7 mRNA in bFGF-treated cells was largely increased compared with that in non-treated cells. Furthermore, consistent with published reports, I found that FGFR1 and FGFR4 are expressed in muscle satellite cells. Since bFGF could activate multiple intracellular signal transduction pathways including the PI3K/AKT pathway, JAK/Stat pathway, MEK/ERK pathway and PLCϒ/Ca2+ pathway, I also made some initial effort to study which of these pathways is utilized by bFGF to regulate Pax7 expression in muscle satellite cells. My preliminary data are interesting and provide the basis for future in-depth mechanistic study of Pax7 regulation by bFGF.