Chen Shuen-Ei, Gerken Eric, Zhang Yingmin, Zhan Mei, Mohan Raja K, Li Andrew S, Reid Michael B, Li Yi-Ping
Department of Medicine, Baylor College of Medicine, One Baylor Plaza 520B, Houston, TX 77030, USA.
Am J Physiol Cell Physiol. 2005 Nov;289(5):C1179-87. doi: 10.1152/ajpcell.00062.2005. Epub 2005 Aug 3.
Recent data suggest a physiological role for the proinflammatory cytokine TNF-alpha in skeletal muscle regeneration. However, the underlying mechanism is not understood. In the present study, we analyzed TNF-alpha-activated signaling pathways involved in myogenesis in soleus muscle injured by cardiotoxin (CTX) in TNF-alpha receptor double-knockout mice (p55(-/-)p75(-/-)). We found that activation of p38MAPK, which is critical for myogenesis, was blocked in CTX-injured p55(-/-)p75(-/-) soleus on day 3 postinjury when myogenic differentiation was being initiated, while activation of ERK1/2 and JNK MAPK, as well as transcription factor NF-kappaB, was not reduced. Consequently, the phosphorylation of transcription factor myocyte enhancer factor-2C, which is catalyzed by p38 and crucial for the expression of muscle-specific genes, was blunted. Meanwhile, expression of p38-dependent differentiation marker myogenin and p21 were suppressed. In addition, expression of cyclin D1 was fivefold that in wild-type (WT) soleus. These results suggest that myogenic differentiation is blocked or delayed in the absence of TNF-alpha signaling. Histological studies revealed abnormalities in regenerating p55(-/-)p75(-/-) soleus. On day 5 postinjury, new myofiber formation was clearly observed in WT soleus but not in p55(-/-)p75(-/-) soleus. To the contrary, p55(-/-)p75(-/-) soleus displayed renewed inflammation and dystrophic calcification. On day 12 postinjury, the muscle architecture of WT soleus was largely restored. Yet, in p55(-/-)p75(-/-) soleus, multifocal areas of inflammation, myofiber death, and myofibers with smaller cross-sectional area were observed. Functional studies demonstrated an attenuated recovery of contractile force in injured p55(-/-)p75(-/-) soleus. These data suggest that TNF-alpha signaling plays a critical regulatory role in muscle regeneration.
近期数据表明促炎细胞因子肿瘤坏死因子-α（TNF-α）在骨骼肌再生中具有生理作用。然而，其潜在机制尚不清楚。在本研究中，我们分析了在肿瘤坏死因子-α受体双敲除小鼠（p55(-/-)p75(-/-)）中，被心脏毒素（CTX）损伤的比目鱼肌中，TNF-α激活的参与肌生成的信号通路。我们发现，对肌生成至关重要的p38丝裂原活化蛋白激酶（p38MAPK）的激活，在损伤后第3天肌源性分化开始时，在CTX损伤的p55(-/-)p75(-/-)比目鱼肌中被阻断，而细胞外信号调节激酶1/2（ERK1/2）和应激活化蛋白激酶（JNK）丝裂原活化蛋白激酶以及转录因子核因子κB（NF-κB）的激活并未降低。因此，由p38催化且对肌肉特异性基因表达至关重要的转录因子肌细胞增强因子-2C（MEF-2C）的磷酸化减弱。同时，p38依赖的分化标志物肌细胞生成素（myogenin）和p21的表达受到抑制。此外，细胞周期蛋白D1（cyclin D1）的表达是野生型（WT）比目鱼肌中的五倍。这些结果表明，在缺乏TNF-α信号的情况下，肌源性分化被阻断或延迟。组织学研究揭示了再生的p55(-/-)p75(-/-)比目鱼肌存在异常。在损伤后第5天，WT比目鱼肌中清楚地观察到新的肌纤维形成，而p55(-/-)p75(-/-)比目鱼肌中则未观察到。相反，p55(-/-)p75(-/-)比目鱼肌出现了再次炎症和营养不良性钙化。在损伤后第12天，WT比目鱼肌的肌肉结构基本恢复。然而，在p55(-/-)p75(-/-)比目鱼肌中，观察到多灶性炎症、肌纤维死亡以及横截面积较小的肌纤维。功能研究表明，损伤的p55(-/-)p75(-/-)比目鱼肌收缩力的恢复减弱。这些数据表明，TNF-α信号在肌肉再生中起关键调节作用。
