Abstract：
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the TYMP gene, which encodes thymidine phosphorylase (TP). As a cytosolic metabolic enzyme, TP defects affect biological processes that are thought to not be limited to the abnormal replication of mitochondrial DNA. This study aimed to elucidate the characteristic metabolic alterations and associated homeostatic regulation caused by TYMP deficiency. The pathogenicity of novel TYMP variants was evaluated in terms of clinical features, genetic analysis, and structural instability. We analyzed plasma samples from three patients with MNGIE; three patients with m.3243A > G mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); and four healthy controls (HC) using both targeted and untargeted metabolomics techniques. Transcriptomics analysis and bioenergetic studies were performed on skin fibroblasts from participants in these three groups. A TYMP overexpression experiment was conducted to rescue the observed changes. Compared with controls, specific alterations in nucleosides, bile acids, and steroid metabolites were identified in the plasma of MNGIE patients. Comparable mitochondrial dysfunction was present in fibroblasts from patients with TYMP deficiency and in those from patients with the m.3243A > G mutation. Distinctively decreased sterol regulatory element binding protein (SREBP) regulated cholesterol metabolism and fatty acid (FA) biosynthesis as well as reduced FA degradation were revealed in fibroblasts with TYMP deficiency. The restoration of thymidine phosphorylase activity rescued the observed changes in MNGIE fibroblasts. Our findings indicated that more widespread metabolic disturbance may be caused by TYMP deficiency in addition to mitochondrial dysfunction, which expands our knowledge of the biochemical outcome of TYMP deficiency. KEY MESSAGES: Distinct metabolic profiles in patients with TYMP deficiency compared to those with m.3243A > G mutation. TYMP deficiency leads to a global disruption of nucleoside metabolism. Cholesterol and fatty acid metabolism are inhibited in individuals with MNGIE. TYMP is functionally related to SREBP-regulated pathways. Potential metabolite biomarkers that could be valuable clinical tools to improve the diagnosis of MNGIE.
摘要：
线粒体神经胃肠脑肌病（MNGIE）是由TYMP基因突变引起的，编码胸苷磷酸化酶(TP)。作为一种胞质代谢酶，TP缺陷影响被认为不限于线粒体DNA的异常复制的生物过程。本研究旨在阐明TYMP缺乏引起的特征性代谢改变和相关的稳态调节。根据临床特征评估新型TYMP变异体的致病性，遗传分析,结构不稳定。我们分析了3名MNGIE患者的血浆样本；3名m.3243A>G线粒体脑病患者，乳酸性酸中毒,和中风样发作（MELAS）；以及使用靶向和非靶向代谢组学技术的四个健康对照（HC）。对来自这三组参与者的皮肤成纤维细胞进行转录组学分析和生物能量研究。进行TYMP过表达实验以挽救观察到的变化。与对照组相比，核苷的特异性改变，胆汁酸，在MNGIE患者的血浆中鉴定出类固醇代谢产物。来自TYMP缺乏症患者的成纤维细胞和来自m.3243A>G突变患者的成纤维细胞中存在相当的线粒体功能障碍。在TYMP缺乏症的成纤维细胞中显示出明显减少的固醇调节元件结合蛋白（SREBP）调节的胆固醇代谢和脂肪酸（FA）生物合成以及减少的FA降解。胸苷磷酸化酶活性的恢复挽救了MNGIE成纤维细胞中观察到的变化。我们的发现表明，更广泛的代谢紊乱可能是由TYMP缺乏以及线粒体功能障碍引起的。这扩大了我们对TYMP缺乏症生化结果的认识。关键信息：TYMP缺乏症患者与m.3243A>G突变患者的代谢谱不同。TYMP缺乏导致核苷代谢的整体破坏。在患有MNGIE的个体中,胆固醇和脂肪酸代谢被抑制。TYMP在功能上与SREBP调节途径相关。潜在的代谢物生物标志物可能是提高MNGIE诊断的有价值的临床工具。
