Sasarman Florin, Nishimura Tamiko, Antonicka Hana, Weraarpachai Woranontee, Shoubridge Eric A
Montreal Neurological Institute and Department of Human Genetics, McGill University, Montreal, QC H3A 2B4, Canada.
Montreal Neurological Institute and Department of Human Genetics, McGill University, Montreal, QC H3A 2B4, Canada
Hum Mol Genet. 2015 Jan 15;24(2):480-91. doi: 10.1093/hmg/ddu468. Epub 2014 Sep 11.
French Canadian Leigh Syndrome (LSFC) is an early-onset, progressive neurodegenerative disorder with a distinct pattern of tissue involvement. Most cases are caused by a founder missense mutation in LRPPRC. LRPPRC forms a ribonucleoprotein complex with SLIRP, another RNA-binding protein, and this stabilizes polyadenylated mitochondrial mRNAs. LSFC fibroblasts have reduced levels of LRPPRC and a specific complex IV assembly defect; however, further depletion of mutant LRPPRC results in a complete failure to assemble a functional oxidative phosphorylation system, suggesting that LRPPRC levels determine the nature of the biochemical phenotype. We tested this hypothesis in cultured muscle cells and tissues from LSFC patients. LRPPRC levels were reduced in LSFC muscle cells, resulting in combined complex I and IV deficiencies. A similar combined deficiency was observed in skeletal muscle. Complex IV was only moderately reduced in LSFC heart, but was almost undetectable in liver. Both of these tissues showed elevated levels of complexes I and III. Despite the marked biochemical differences, the steady-state levels of LRPPRC and mitochondrial mRNAs were extremely low, LRPPRC was largely detergent-insoluble, and SLIRP was undetectable in all LSFC tissues. The level of the LRPPRC/SLIRP complex appeared much reduced in control tissues by the first dimension blue-native polyacrylamide gel electrophoresis (BN-PAGE) analysis compared with fibroblasts, and even by second dimension analysis it was virtually undetectable in control heart. These results point to tissue-specific pathways for the post-transcriptional handling of mitochondrial mRNAs and suggest that the biochemical defects in LSFC reflect the differential ability of tissues to adapt to the mutation.
法裔加拿大人 Leigh 综合征（LSFC）是一种早发性、进行性神经退行性疾病，具有独特的组织受累模式。大多数病例由 LRPPRC 中的奠基者错义突变引起。LRPPRC 与另一种 RNA 结合蛋白 SLIRP 形成核糖核蛋白复合物，这可稳定多聚腺苷酸化的线粒体 mRNA。LSFC 成纤维细胞中 LRPPRC 水平降低且存在特定的复合体 IV 组装缺陷；然而，进一步消耗突变型 LRPPRC 会导致功能性氧化磷酸化系统完全无法组装，这表明 LRPPRC 水平决定了生化表型的性质。我们在 LSFC 患者的培养肌肉细胞和组织中验证了这一假设。LSFC 肌肉细胞中 LRPPRC 水平降低，导致复合体 I 和复合体 IV 联合缺陷。在骨骼肌中也观察到类似的联合缺陷。在 LSFC 心脏中，复合体 IV 仅适度降低，但在肝脏中几乎检测不到。这两种组织中复合体 I 和复合体 III 的水平均升高。尽管存在明显的生化差异，但 LRPPRC 和线粒体 mRNA 的稳态水平极低，LRPPRC 在很大程度上不溶于去污剂，并且在所有 LSFC 组织中均检测不到 SLIRP。通过一维蓝色天然聚丙烯酰胺凝胶电泳（BN-PAGE）分析，与成纤维细胞相比，对照组织中 LRPPRC/SLIRP 复合物的水平似乎大幅降低，甚至通过二维分析，在对照心脏中也几乎检测不到。这些结果表明线粒体 mRNA 转录后处理存在组织特异性途径，并提示 LSFC 中的生化缺陷反映了组织适应突变的不同能力。
