BackgroundCigarette smoking is known to affect muscle function and exercise capacity, including muscle fatigue resistance. Most studies showed diminished cross‐sectional area and fibre type shifting in slow‐twitch muscles such as the soleus, while effects on fast‐twitch muscles were seldom reported and the differential responses between muscle types in response to exposure to cigarette smoke (CS) were largely unknown. This study aimed to elucidate the histomorphological, biochemical and transcriptomic changes induced by CS on both slow‐twitch and fast‐twitch muscles.MethodMale Sprague–Dawley rats were randomly divided into two groups: sham air (SA) and CS. The rats were exposed to CS for 8 weeks using an exposure chamber system to mimic smoking conditions. Histomorphological analyses on muscle fibre type and cross‐sectional area were determined in soleus and extensor digitorum longus (EDL). Transcriptomic profiles were investigated for identifying differentially expressed genes (DEGs) and potential mechanistic pathways involved. Inflammatory responses in terms of the macrophage population and the level of inflammatory cytokines were measured. Markers for muscle‐specific proteolysis were also examined.ResultSoleus muscle, but not in EDL, exhibited a significant increase in Type IIa fibres (SA: 9.0 ± 3.3%; CS: 19.8 ± 2.4%, p = 0.002) and decrease in Type I fibres (SA: 90.1 ± 3.6%; CS: 77.9 ± 3.3%, p = 0.003) after CS exposure. RNA sequencing revealed 165 identified DEGs in soleus including upregulation of ‘Cd68’, ‘Ccl2’ and ‘Ucp2’ as well as downregulation of ‘Ucp3’, etc. Pathways enrichment analysis revealed that the upregulated pathways in soleus were related to immune system and cellular response, while the downregulated pathways were related to oxidative metabolism. Only 10 DEGs were identified in EDL with less enriched pathways. The soleus also showed elevated pro‐inflammatory cytokines, and the total macrophage marker CD68 was significantly higher in soleus of CS compared to the SA group (CD68+/no. of fibre: SA = 60.3 ± 39.3%; CS = 106.5 ± 27.2%, p = 0.0039), while the two groups in EDL muscle showed no significant difference. The expression of E3 ubiquitin ligase atrogin‐1 associated with muscle degradation pathways was 1.63‐fold higher in the soleus after CS, while no significant differences were observed in the EDL.ConclusionThe CS‐induced inflammatory responses on soleus muscle are likely mediated via targeting mitochondrial‐related signalling, resulting in mitochondrial dysfunction and impaired oxidative capacity. The presumably less active mitochondrial‐related signalling in EDL renders it less susceptible to changes towards CS, accounting for differential impacts between muscle types.

中文翻译：

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转录组学分析揭示了香烟烟雾暴露大鼠模型的慢抽搐和快抽搐肌肉的差异


背景已知吸烟会影响肌肉功能和运动能力，包括肌肉疲劳抵抗力。大多数研究表明，比目鱼肌等慢肌的横截面积和纤维类型偏移减少，而对快肌的影响很少报道，并且肌肉类型对暴露于香烟烟雾 （CS） 的反应差异在很大程度上是未知的。本研究旨在阐明 CS 诱导的慢肌和快肌的组织形态学、生化和转录组学变化。方法将雄性 Sprague–Dawley 大鼠随机分为 2 组：假空气 （SA） 和 CS。大鼠使用暴露室系统暴露于 CS 8 周，以模拟吸烟条件。确定了比目鱼肌和趾长伸肌 （EDL） 中肌肉纤维类型和横截面积的组织形态学分析。研究了转录组谱以识别差异表达基因 （DEG） 和所涉及的潜在机制途径。测量巨噬细胞群和炎性细胞因子水平方面的炎症反应。还检查了肌肉特异性蛋白水解的标志物。结果比目鱼肌（但不在 EDL 中）表现出 IIa 型纤维的显着增加 （SA： 9.0 ± 3.3%;CS：19.8 ± 2.4%，p = 0.002）和 I 型纤维减少（SA：90.1 ± 3.6%;CS：CS：CS 暴露后 77.9 ± 3.3%，p = 0.003）。RNA 测序显示比目鱼体中有 165 个鉴定出的 DEGs，包括 'Cd68'、'Ccl2' 和 'Ucp2' 的上调以及 'Ucp3' 的下调等。通路富集分析显示，比目鱼肌中上调的通路与免疫系统和细胞反应有关，而下调的通路与氧化代谢有关。 在 EDL 中仅鉴定出 10 个 DEGs，通路富集较少。比目鱼肌还显示促炎细胞因子升高，与 SA 组相比，CS 比目鱼肌的总巨噬细胞标志物 CD68 显着升高（CD68+/纤维数量：SA = 60.3 ± 39.3%;CS = 106.5 ± 27.2%，p = 0.0039），而 EDL 肌肉两组差异无统计学意义。CS 后比目鱼肌中与肌肉降解途径相关的 E3 泛素连接酶 atrogin-1 的表达高出 1.63 倍，而在 EDL 中未观察到显着差异。结论CS 诱导的比目鱼肌炎症反应可能是通过靶向线粒体相关信号介导的，导致线粒体功能障碍和氧化能力受损。EDL 中可能不太活跃的线粒体相关信号使其不易受到 CS 变化的影响，从而解释了肌肉类型之间的不同影响。