Supplementary Table S1-S5

The <i>dystrophin</i> (<i>DMD)</i> gene is recognized for its significance in Duchenne muscular dystrophy (DMD), a lethal and progressive skeletal muscle disease. Some DMD patients, as well as model mice with muscular dystrophy (mdx), spontaneously develop various types of tumors, among which rhabdomyosarcoma (RMS) is the most prominent. By contrast, spindle cell sarcoma (SCS) has rarely been reported in patients or mdx mice. In this study, we aimed to use metabolomics to better understand the rarity of SCS development in mdx mice. Gas chromatography-mass spectrometry was employed to compare the metabolic profiles of spontaneously developed SCS and RMS tumors from mdx<i> </i>mice, and metabolite supplementation assays and silencing experiments were used to assess the effects of metabolic differences in SCS tumor-derived cells. The levels of 75 metabolites exhibited differences between RMS and SCS, 25 of which were significantly altered. Further characterization revealed downregulation of non-essential amino acids, including alanine, in SCS tumors. Alanine supplementation enhanced the growth, epithelial-mesenchymal transition, and invasion of SCS cells. Reduction of intracellular alanine via knockdown of the alanine transporter Slc1a5 reduced the growth of SCS cells. Lower metabolite secretion and reduced proliferation of SCS tumors may explain the lower detection rate of SCS in mdx mice. Targeting of alanine depletion pathways may have potential as a novel treatment strategy.肌营养不良蛋白（dystrophin, DMD）基因因其在杜兴氏肌营养不良症（Duchenne muscular dystrophy, DMD）中的重要作用而备受关注，后者是一种致死性且呈进行性发展的骨骼肌疾病。部分DMD患者以及罹患肌营养不良症的模型小鼠（mdx小鼠）可自发形成多种肿瘤，其中横纹肌肉瘤（rhabdomyosarcoma, RMS）最为多见。与之形成鲜明对比的是，梭形细胞肉瘤（spindle cell sarcoma, SCS）在患者或mdx小鼠中鲜有报道。本研究旨在借助代谢组学手段，深入阐明mdx小鼠中SCS发生率极低的内在机制。本研究采用气相色谱-质谱法，对比分析mdx小鼠自发形成的SCS与RMS肿瘤的代谢谱；并通过代谢物补充实验及基因沉默实验，评估代谢差异对SCS肿瘤细胞的影响。研究结果显示，RMS与SCS肿瘤间共有75种代谢物存在表达差异，其中25种代谢物的水平发生了显著改变。进一步的表征分析发现，SCS肿瘤中包括丙氨酸在内的非必需氨基酸表达水平下调。补充丙氨酸可增强SCS细胞的增殖能力、上皮间质转化（epithelial-mesenchymal transition）进程及侵袭活性。通过敲低丙氨酸转运体Slc1a5以降低细胞内丙氨酸水平，可显著抑制SCS细胞的增殖。SCS肿瘤较低的代谢物分泌水平与增殖速率，或可解释其在mdx小鼠中检出率较低的现象。靶向丙氨酸耗竭通路有望成为治疗该类肿瘤的全新策略。