Department of Animal and Marine Bioresource Sciences, Graduate School of Agriculture, Kyushu University, Fukuoka, Japan.
Am J Physiol Cell Physiol. 2011 Nov;301(5):C1270-9. doi: 10.1152/ajpcell.00257.2011. Epub 2011 Aug 24.
Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory signals of such coordination remain unclear, although axon-guidance molecules may be involved. Recently, satellite cells, resident myogenic stem cells positioned beneath the basal lamina and at high density at the myoneural junction regions of mature fibers, were shown to upregulate a secreted neural chemorepellent semaphorin 3A (Sema3A) in response to in vivo muscle-crush injury. The initial report on that expression centered on the observation that hepatocyte growth factor (HGF), an essential cue in muscle fiber growth and regeneration, remarkably upregulates Sema3A expression in early differentiated satellite cells in vitro [Tatsumi et al., Am J Physiol Cell Physiol 297: C238-C252, 2009]. Here, we address regulatory effects of basic fibroblast growth factor (FGF2) and transforming growth factor (TGF)-βs on Sema3A expression in satellite cell cultures. When treated with FGF2, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Sema3A upregulation by FGF2 was dose dependent with a maximum (8- to 1-fold relative to the control) at 2.5 ng/ml (150 pM) and occurred exclusively at the early differentiation stage. The response was highly comparable in dose response and timing to effects of HGF treatment, without any additive or synergistic effect from treatment with a combination of both potent upregulators. In contrast, TGF-β2 and -β3 potently decreased basal Sema3A expression; the maximum effect was at very low concentrations (40 and 8 pM, respectively) and completely cancelled the activities of FGF2 and HGF to upregulate Sema3A. These results therefore encourage the prospect that a time-coordinated increase in HGF, FGF2, and TGF-β ligands and their receptors promotes a programmed strategy for Sema3A expression that guarantees successful intramuscular motor reinnervation by delaying sprouting and reattachment of motoneuron terminals onto damaged muscle fibers early in regeneration pending restoration of muscle fiber contractile integrity.
成功地再生和重塑肌内运动神经元网络和神经肌肉连接对于恢复骨骼肌功能和生理特性至关重要。尽管轴突导向分子可能参与其中，但这种协调的调节信号仍不清楚。最近，卫星细胞（位于基底膜下的常驻肌源性干细胞，在成熟纤维的肌神经连接区域高密度分布）被证明在体内肌肉挤压损伤后上调一种分泌的神经化学引诱物 Sema3A（信号素 3A）。最初关于该表达的报告集中在观察到，肝细胞生长因子（HGF）是肌肉纤维生长和再生的重要线索，可显著上调体外早期分化的卫星细胞中的 Sema3A 表达[Tatsumi 等人，Am J Physiol Cell Physiol 297：C238-C252，2009]。在这里，我们研究了碱性成纤维细胞生长因子（FGF2）和转化生长因子（TGF）-β对卫星细胞培养物中 Sema3A 表达的调节作用。通过逆转录-聚合酶链反应和免疫化学研究发现，用 FGF2 处理时，Sema3A 消息和蛋白质均上调。FGF2 诱导的 Sema3A 上调呈剂量依赖性，与对照相比最大（8-至 1 倍）为 2.5ng/ml（150pM），仅发生在早期分化阶段。该反应在剂量反应和时间上与 HGF 处理的效果高度可比，没有来自两种强效上调剂组合处理的任何附加或协同作用。相比之下，TGF-β2 和-β3 强力降低基础 Sema3A 表达；最大作用发生在非常低的浓度（分别为 40 和 8pM），并完全取消了 FGF2 和 HGF 上调 Sema3A 的活性。因此，这些结果鼓励这样一种前景，即 HGF、FGF2 和 TGF-β配体及其受体的时间协调增加促进了 Sema3A 表达的程序化策略，通过延迟运动神经元末梢在再生早期对受损肌纤维的发芽和重新附着，保证了肌内运动神经元的成功再支配，直到肌肉纤维收缩完整性得到恢复。
