Laboratory of Muscle and Meat Science, Department of Animal and Marine Bioresource Sciences, Faculty of Agriculture, Graduate School of Agriculture, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan.
Laboratory of Cell and Tissue Biology, Research Faculty of Agriculture, Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan.
Int J Mol Sci. 2021 Apr 26;22(9):4499. doi: 10.3390/ijms22094499.
Resident myogenic stem cells (satellite cells) are attracting attention for their novel roles in myofiber type regulation. In the myogenic differentiation phase, satellite cells from soleus muscle (slow fiber-abundant) synthesize and secrete higher levels of semaphorin 3A (Sema3A, a multifunctional modulator) than those derived from extensor digitorum longus (EDL; fast fiber-abundant), suggesting the role of Sema3A in forming slow-twitch myofibers. However, the regulatory mechanisms underlying fast-twitch myotube commitment remain unclear. Herein, we focused on netrin family members (netrin-1, -3, and -4) that compete with Sema3A in neurogenesis and osteogenesis. We examined whether netrins affect fast-twitch myotube generation by evaluating their expression in primary satellite cell cultures. Initially, netrins are upregulated during myogenic differentiation. Next, we compared the expression levels of netrins and their cell membrane receptors between soleus- and EDL-derived satellite cells; only netrin-1 showed higher expression in EDL-derived satellite cells than in soleus-derived satellite cells. We also performed netrin-1 knockdown experiments and additional experiments with recombinant netrin-1 in differentiated satellite cell-derived myoblasts. Netrin-1 knockdown in myoblasts substantially reduced fast-type myosin heavy chain (MyHC) expression; exogenous netrin-1 upregulated fast-type MyHC in satellite cells. Thus, netrin-1 synthesized in EDL-derived satellite cells may promote myofiber type commitment of fast muscles.
肌源性干细胞（卫星细胞）因其在肌纤维类型调节中的新作用而受到关注。在肌生成分化阶段，来自比目鱼肌（慢纤维丰富）的卫星细胞比来自伸趾长肌（快纤维丰富）的卫星细胞合成和分泌更高水平的神经导向因子 3A（Sema3A，多功能调节剂），表明 Sema3A 在形成慢收缩肌纤维中的作用。然而，快速收缩肌管承诺的调节机制尚不清楚。在此，我们专注于轴突导向因子家族成员（轴突导向因子 1、3 和 4），它们在神经发生和骨生成中与 Sema3A 竞争。我们通过评估原代卫星细胞培养物中的表达来研究 netrins 是否影响快速肌管生成。最初，netrins 在肌生成分化过程中上调。接下来，我们比较了 netrins 及其细胞膜受体在比目鱼肌和伸趾长肌来源的卫星细胞中的表达水平；只有 netrin-1 在伸趾长肌来源的卫星细胞中的表达高于比目鱼肌来源的卫星细胞。我们还进行了 netrin-1 敲低实验和在分化的卫星细胞衍生的成肌细胞中添加重组 netrin-1 的实验。MyHC 表达显著降低；外源性 netrin-1 可上调卫星细胞中的快型肌球蛋白重链（MyHC）。因此，伸趾长肌衍生的卫星细胞中合成的 netrin-1 可能促进快肌肌纤维类型的承诺。
