Ishiyama Akihiko, Sakai Chika, Matsushima Yuichi, Noguchi Satoru, Mitsuhashi Satomi, Endo Yukari, Hayashi Yukiko K, Saito Yoshiaki, Nakagawa Eiji, Komaki Hirofumi, Sugai Kenji, Sasaki Masayuki, Sato Noriko, Nonaka Ikuya, Goto Yu-Ichi, Nishino Ichizo
Department of Child Neurology (A.I., Y.S., E.N., H.K, K.S., M.S.), National Center Hospital; Department of Neuromuscular Research (A.I., S.N., S.M., Y.E., Y.K.H., I. Nonaka, I. Nishino.), National Institute of Neuroscience; Department of Mental Retardation and Birth Defect Research (C.S., Y.M., Y.-i.G.), National Institute of Neuroscience; Department of Radiology (N.S.), National Center Hospital, National Center of Neurology and Psychiatry, Tokyo; Department of Pharmacology (A.I.), Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi; and Department of Pathophysiology (Y.K.H), Tokyo Medical University, Japan.
Neurol Genet. 2017 Sep 8;3(5):e184. doi: 10.1212/NXG.0000000000000184. eCollection 2017 Oct.
To determine the molecular factors contributing to progressive cavitating leukoencephalopathy (PCL) to help resolve the underlying genotype-phenotype associations in the mitochondrial iron-sulfur cluster (ISC) assembly system.
The subjects were 3 patients from 2 families who showed no inconsistencies in either clinical or brain MRI findings as PCL. We used exome sequencing, immunoblotting, and enzyme activity assays to establish a molecular diagnosis and determine the roles of ISC-associated factors in PCL.
We performed genetic analyses on these 3 patients and identified compound heterozygosity for the gene, which encodes the mitochondrial iron-sulfur protein assembly factor. Protein expression analysis revealed substantial decreases in IBA57 protein expression in myoblasts and fibroblasts. Immunoblotting revealed substantially reduced expression of SDHB, a subunit of complex II, and lipoic acid synthetase (LIAS). Levels of pyruvate dehydrogenase complex-E2 and α-ketoglutarate dehydrogenase-E2, which use lipoic acid as a cofactor, were also reduced. In activity staining, SDH activity was clearly reduced, but it was ameliorated in mitochondrial fractions from rescued myoblasts. In addition, NFU1 protein expression was also decreased, which is required for the assembly of a subset of iron-sulfur proteins to SDH and LIAS in the mitochondrial ISC assembly system.
Defects in IBA57 essentially regulate NFU1 expression, and aberrant NFU1 ultimately affects SDH activity and LIAS expression in the ISC biogenesis pathway. This study provides new insights into the role of the iron-sulfur protein assembly system in disorders related to mitochondrial energy metabolism associated with leukoencephalopathy with cavities.
确定导致进行性空泡性白质脑病（PCL）的分子因素，以帮助解析线粒体铁硫簇（ISC）组装系统中潜在的基因型-表型关联。
研究对象为来自2个家庭的3例患者，其临床及脑部MRI表现均符合PCL，无矛盾之处。我们采用外显子组测序、免疫印迹和酶活性测定来进行分子诊断，并确定ISC相关因子在PCL中的作用。
我们对这3例患者进行了基因分析，发现编码线粒体铁硫蛋白组装因子的 基因存在复合杂合性。蛋白质表达分析显示，成肌细胞和成纤维细胞中IBA57蛋白表达大幅下降。免疫印迹显示，复合物II的一个亚基SDHB和硫辛酸合成酶（LIAS）的表达大幅降低。以硫辛酸为辅因子的丙酮酸脱氢酶复合物-E2和α-酮戊二酸脱氢酶-E2的水平也降低。在活性染色中，SDH活性明显降低，但在挽救的成肌细胞的线粒体组分中有所改善。此外，线粒体ISC组装系统中，铁硫蛋白亚群组装至SDH和LIAS所需的NFU1蛋白表达也降低。
IBA57缺陷本质上调节NFU1表达，异常的NFU1最终影响ISC生物合成途径中的SDH活性和LIAS表达。本研究为铁硫蛋白组装系统在与有空泡的白质脑病相关的线粒体能量代谢障碍中的作用提供了新见解。
