Data from: Serum Amyloid A Induces Toll-Like Receptor 2-Dependent Inflammatory Cytokine Expression and Atrophy in C2C12 Skeletal Muscle Myotubes

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Skeletal muscle wasting is an important comorbidity of Chronic Obstructive Pulmonary Disease (COPD) and is strongly correlated with morbidity and mortality. Patients who experience frequent acute exacerbations of COPD (AECOPD) have more severe muscle wasting and reduced recovery of muscle mass and function after each exacerbation. Serum levels of the pro-inflammatory acute phase protein Serum Amyloid A (SAA) can rise more than 1000-fold in AECOPD and are predictively correlated with exacerbation severity. The direct effects of SAA on skeletal muscle are poorly understood. Here we have examined SAA effects on pro-inflammatory cachectic cytokine expression (IL-6 and TNFα) and atrophy in C2C12 myotubes.

SAA increased IL-6 (31-fold) and TNFα (6.5-fold) mRNA levels compared to control untreated cells after 3h of SAA treatment, and increased secreted IL-6 protein at 24h. OxPAPC, a dual TLR2 and TLR4 inhibitor, reduced the response to SAA by approximately 84% compared to SAA alone, and the TLR2 neutralising antibody T2.5 abolished SAA-induced expression of IL-6, indicating that SAA signalling in C2C12 myotubes is primarily via TLR2. SAA also reduced myotube width by 10–13% and induced a 2.5-fold increase in the expression of the muscle atrophy gene Atrogin-1, suggesting direct effects of SAA on muscle wasting. Blocking of TLR2 inhibited the SAA-induced decrease in myotube width and Atrogin-1 gene expression, indicating that SAA induces atrophy through TLR2.

These data demonstrate that SAA stimulates a robust pro-inflammatory response in skeletal muscle myotubes via the TLR2-dependent release of IL-6 and TNFα. Furthermore, the observed atrophy effects indicate that SAA could also be directly contributing to the wasting and poor recovery of muscle mass. Therapeutic strategies targeting this SAA-TLR2 axis may therefore ameliorate muscle wasting in AECOPD and a range of other inflammatory conditions associated with loss of muscle mass.

随附文件为本关联文章提供补充数据集。
骨骼肌消耗（Skeletal muscle wasting）是慢性阻塞性肺疾病（COPD）的重要合并症，且与发病率及死亡率密切相关。慢性阻塞性肺疾病急性加重（AECOPD）频发患者的骨骼肌消耗更为严重，且每次加重后肌肉质量与功能的恢复能力均有所下降。在AECOPD患者体内，促炎性急性期蛋白血清淀粉样蛋白A（SAA）的血清水平可升高1000倍以上，且与加重严重程度具有预测相关性。目前对于SAA对骨骼肌的直接作用机制尚不清楚，本研究针对C2C12肌管中SAA对促炎性恶病质细胞因子（IL-6与TNFα）表达及肌肉萎缩的影响展开了检测。
经SAA处理3小时后，与未处理的对照组细胞相比，SAA可使IL-6 mRNA水平升高31倍、TNFα mRNA水平升高6.5倍，并在24小时时升高分泌型IL-6蛋白水平。双重Toll样受体2（TLR2）与Toll样受体4（TLR4）抑制剂OxPAPC可使SAA诱导的应答较单独SAA处理组降低约84%；而TLR2中和性抗体T2.5可完全阻断SAA诱导的IL-6表达，这表明C2C12肌管中的SAA信号转导主要通过TLR2介导。SAA还可使肌管宽度降低10%~13%，并使肌肉萎缩基因Atrogin-1的表达升高2.5倍，这提示SAA对骨骼肌消耗具有直接作用。阻断TLR2可抑制SAA诱导的肌管宽度降低及Atrogin-1基因表达上调，表明SAA通过TLR2介导肌肉萎缩。
上述实验数据表明，SAA可通过依赖TLR2的IL-6与TNFα释放途径，在骨骼肌肌管中触发强烈的促炎性应答。此外，本次研究观察到的萎缩效应提示，SAA还可直接导致肌肉质量消耗及恢复不良。因此，以SAA-TLR2信号轴为靶点的治疗策略，或可改善AECOPD患者的骨骼肌消耗，以及其他一系列伴随肌肉质量丢失的炎性疾病中的肌肉消耗症状。