Limited dCTP Availability Accounts for Mitochondrial DNA Depletion in Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE)
Limited dCTP Availability Accounts for Mitochondrial DNA Depletion in Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE)
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DOI：
10.1371/journal.pgen.1002035
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发表时间：
2011-03-01
期刊：
影响因子：
4.5
通讯作者：
Marti, Ramon
中科院分区：
文献类型：
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作者：
Gonzalez-Vioque, Emiliano;Torres-Torronteras, Javier;Marti, Ramon
线粒体神经胃肠脑肌病 (MNGIE) 是一种由 TYMP 突变引起的严重人类疾病，TYMP 是编码胸苷磷酸化酶 (TP) 的基因。它属于一组更广泛的疾病，其特征是一个或多个组织中线粒体 DNA (mtDNA) 拷贝数显着减少。在大多数情况下，这些疾病是由参与脱氧核糖核苷三磷酸 (dNTP) 代谢的基因突变引起的。人们普遍认为，这些突变导致的线粒体 dNTP 库失衡会干扰 mtDNA 复制。尽管如此，这种效应的精确机制细节，特别是给定 dNTP 的过量（例如，在 TP 缺乏时观察到的不平衡 dTTP 过量）如何可能导致 mtDNA 耗竭，目前仍不清楚。使用分离的鼠肝线粒体的细胞器内复制实验模型，我们观察到 dATP、dGTP 或 dCTP 的过载不会降低 mtDNA 复制率。相反，过量的 dTTP 会减少 mtDNA 合成，但这种效应是由于继发性 dCTP 耗竭而不是 dTTP 本身过量所致。这在人类培养细胞中得到证实，表明我们的结论不依赖于实验模型。我们的结果表明，mtDNA 复制率不受任何 4 种单独 dNTP 过量的影响，并且受到最低浓度 dNTP 的可用性的限制。因此，dNTP 的可用性是导致 mtDNA 耗竭的关键因素，而不是 dNTP 失衡。这些结果首次测试了 MNGIE 中 mtDNA 耗竭的机制，并提供了证据，证明 dNTP 可用性有限是合成代谢或分解代谢 dNTP 途径受损导致 mtDNA 耗竭的常见原因。因此，应该探索专注于恢复缺陷基质的治疗方法。
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a severe human disease caused by mutations in TYMP, the gene encoding thymidine phosphorylase (TP). It belongs to a broader group of disorders characterized by a pronounced reduction in mitochondrial DNA (mtDNA) copy number in one or more tissues. In most cases, these disorders are caused by mutations in genes involved in deoxyribonucleoside triphosphate (dNTP) metabolism. It is generally accepted that imbalances in mitochondrial dNTP pools resulting from these mutations interfere with mtDNA replication. Nonetheless, the precise mechanistic details of this effect, in particular, how an excess of a given dNTP (e. g., imbalanced dTTP excess observed in TP deficiency) might lead to mtDNA depletion, remain largely unclear. Using an in organello replication experimental model with isolated murine liver mitochondria, we observed that overloads of dATP, dGTP, or dCTP did not reduce the mtDNA replication rate. In contrast, an excess of dTTP decreased mtDNA synthesis, but this effect was due to secondary dCTP depletion rather than to the dTTP excess in itself. This was confirmed in human cultured cells, demonstrating that our conclusions do not depend on the experimental model. Our results demonstrate that the mtDNA replication rate is unaffected by an excess of any of the 4 separate dNTPs and is limited by the availability of the dNTP present at the lowest concentration. Therefore, the availability of dNTP is the key factor that leads to mtDNA depletion rather than dNTP imbalances. These results provide the first test of the mechanism that accounts for mtDNA depletion in MNGIE and provide evidence that limited dNTP availability is the common cause of mtDNA depletion due to impaired anabolic or catabolic dNTP pathways. Thus, therapy approaches focusing on restoring the deficient substrates should be explored.