Anabolic resistance of skeletal muscle in cancer cachexia is caused by impaired IGF1 expression to mechanical loading. Anabolic resistance of skeletal muscle in cancer cachexia is caused by impaired IGF1 expression to mechanical loading

Cachexia is a systemic metabolic syndrome characterized by loss of fat and skeletal muscle mass in chronic wasting diseases such as cancer. The regulation of cellular protein synthesis in response to workload in skeletal muscle is generally blunted in cancer cachexia; however, the precise molecular regulation is largely unknown. In this study, to examine the molecular mechanism of skeletal muscle protein metabolism in cancer cachexia, we analyzed comprehensive gene expression in skeletal muscle using microarrays. CD2F1 mice (male, 7 weeks old) were subcutaneously transplanted (1*10^6 cells per mouse) with a mouse colon cancer-derived cell line (C26) as a model of cancer cachexia. Functional overload of the plantaris muscle by synergist ablation was performed at the 2nd week, and the plantaris muscle was sampled at the 4th week of cancer transplantation. The hypertrophy of skeletal muscle (increased skeletal muscle weight/protein synthesis efficiency and activation of mTOR signaling) associated with compensatory overload was significantly suppressed with the cancer cachexia. Gene expression profiling and pathway analysis by microarray showed that resistance to muscle protein synthesis associated with cancer cachexia was induced by downregulation of insulin-like growth factor-1. These observations show that cancer cachexia induces resistance to muscle protein synthesis, which could be a potential factor inhibiting the adaptation of skeletal muscle growth to physical exercise. Overall design: Colon 26 (C26) carcinoma tumor-bearing CD2F1 mice were employed as the model for the study of cancer cachexia. The C26 carcinoma (RCB2657) was provided by RIKEN BRC through the National Bio-Resource Project of MEXT, Japan. All cell culture experiments were performed in a humidified environment at 37 °C in a 5% CO2 atmosphere. The C26 cells were grown in RPMI-1640 medium (FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan) supplemented with 10% FBS and penicillin–streptomycin. After trypsinization and neutralization, 1 × 10^6 C26 cells per individual were suspended with 100 μL of PBS and subcutaneously implanted into the flank region of the abdominal wall unilaterally using a 26G syringe as previously described. The control group was injected with an equal amount of PBS.

恶病质（Cachexia）是一种系统性代谢综合征，以癌症等慢性消耗性疾病中的脂肪与骨骼肌质量丢失为核心特征。骨骼肌在应对负荷时的细胞蛋白质合成调控，在癌症恶病质状态下普遍受损，但精确的分子调控机制在很大程度上尚未明确。本研究为探究癌症恶病质中骨骼肌蛋白质代谢的分子机制，采用微阵列（microarray）技术分析骨骼肌的全基因表达谱。选用CD2F1雄性小鼠（7周龄），每只小鼠皮下移植1×10^6个小鼠结肠癌细胞系C26，以构建癌症恶病质模型。于癌症移植后第2周，通过协同肌切除法对跖肌实施功能性超负荷刺激，并于移植后第4周采集跖肌样本。结果显示，与代偿性超负荷相关的骨骼肌肥大（骨骼肌重量提升/蛋白质合成效率增强及mTOR信号通路激活）在癌症恶病质状态下被显著抑制。通过微阵列进行的基因表达谱分析与通路分析表明，癌症恶病质诱导的骨骼肌蛋白质合成抵抗，源于胰岛素样生长因子-1（insulin-like growth factor-1）的下调。上述结果证实，癌症恶病质可诱导骨骼肌蛋白质合成抵抗，这或为抑制骨骼肌生长适应体育锻炼的潜在因素。总体实验设计：本研究以结肠26（C26）癌荷瘤CD2F1小鼠作为癌症恶病质的研究模型。C26癌细胞（RCB2657）由日本文部科学省（MEXT）国家生物资源项目通过理化学研究所生物资源中心（RIKEN BRC）提供。所有细胞培养实验均在37℃、5%CO2的湿润环境中开展。C26细胞培养于添加10%胎牛血清（FBS）与青霉素-链霉素的RPMI-1640培养基（日本大阪富士胶片和光纯药株式会社，FUJIFILM Wako Pure Chemical Corporation）中。经胰酶消化并中和后，将每只小鼠所需的1×10^6个C26细胞重悬于100μL磷酸盐缓冲液（PBS）中，使用26G注射器于单侧腹壁皮下腹侧区域进行皮下接种，操作参照既往研究方法。对照组注射等量PBS。