Division of Clinical and Metabolic Genetics, Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
Department of Microbiology, Biochemistry, and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, USA.
Hum Mol Genet. 2019 Jan 15;28(2):290-306. doi: 10.1093/hmg/ddy351.
LonP1 is crucial for maintaining mitochondrial proteostasis and mitigating cell stress. We identified a novel homozygous missense LONP1 variant, c.2282 C > T, (p.Pro761Leu), by whole-exome and Sanger sequencing in two siblings born to healthy consanguineous parents. Both siblings presented with stepwise regression during infancy, profound hypotonia and muscle weakness, severe intellectual disability and progressive cerebellar atrophy on brain imaging. Muscle biopsy revealed the absence of ragged-red fibers, however, scattered cytochrome c oxidase-negative staining and electron dense mitochondrial inclusions were observed. Primary cultured fibroblasts from the siblings showed normal levels of mtDNA and mitochondrial transcripts, and normal activities of oxidative phosphorylation complexes I through V. Interestingly, fibroblasts of both siblings showed glucose-repressed oxygen consumption compared to their mother, whereas galactose and palmitic acid utilization were similar. Notably, the siblings' fibroblasts had reduced pyruvate dehydrogenase (PDH) activity and elevated intracellular lactate:pyruvate ratios, whereas plasma ratios were normal. We demonstrated that in the siblings' fibroblasts, PDH dysfunction was caused by increased levels of the phosphorylated E1α subunit of PDH, which inhibits enzyme activity. Blocking E1α phosphorylation activated PDH and reduced intracellular lactate concentrations. In addition, overexpressing wild-type LonP1 in the siblings' fibroblasts down-regulated phosphoE1α. Furthermore, in vitro studies demonstrated that purified LonP1-P761L failed to degrade phosphorylated E1α, in contrast to wild-type LonP1. We propose a novel mechanism whereby homozygous expression of the LonP1-P761L variant leads to PDH deficiency and energy metabolism dysfunction, which promotes severe neurologic impairment and neurodegeneration.
LonP1 对于维持线粒体蛋白稳态和减轻细胞应激至关重要。我们通过全外显子组和 Sanger 测序在两名出生于健康近亲父母的兄弟姐妹中鉴定出一种新的纯合错义 LONP1 变体，c.2282 C>T，（p.Pro761Leu）。这对兄弟姐妹在婴儿期出现进行性衰退，表现为严重的智力障碍和进行性小脑萎缩。肌肉活检显示无红纤维肌病，但可见散在的细胞色素 c 氧化酶阴性染色和电子致密的线粒体包涵体。来自兄弟姐妹的原代培养成纤维细胞显示 mtDNA 和线粒体转录物水平正常，氧化磷酸化复合物 I 至 V 的活性正常。有趣的是，与他们的母亲相比，两兄弟的成纤维细胞表现出葡萄糖抑制的耗氧量，而半乳糖和棕榈酸的利用则相似。值得注意的是，与他们的母亲相比，这对兄弟姐妹的成纤维细胞丙酮酸脱氢酶（PDH）活性降低，细胞内乳酸：丙酮酸比率升高，而血浆比率正常。我们证明，在这对兄弟姐妹的成纤维细胞中，PDH 功能障碍是由 PDH 磷酸化 E1α 亚基水平升高引起的，该亚基抑制酶活性。阻断 E1α 磷酸化可激活 PDH 并降低细胞内乳酸浓度。此外，在兄弟姐妹的成纤维细胞中过表达野生型 LonP1 可下调磷酸化 E1α。此外，体外研究表明，与野生型 LonP1 相比，纯化的 LonP1-P761L 无法降解磷酸化的 E1α。我们提出了一种新的机制，即 LonP1-P761L 变体的纯合表达导致 PDH 缺乏和能量代谢功能障碍，从而促进严重的神经损伤和神经退行性变。
