Sezione di Biomedicina e Endocrinologia, Dipartimento di Scienze Farmacologiche e Biomolecolari, Centro di Eccellenza sulle Malattie Neurodegenerative, Università degli Studi di Milano Milano, Italy ; Centro InterUniversitario sulle Malattie Neurodegenerative, Università degli Studi di Firenze Milano, Genova e Roma Tor Vergata, Italy.
Front Cell Neurosci. 2013 Nov 26;7:234. doi: 10.3389/fncel.2013.00234. eCollection 2013.
Amyotrophic lateral sclerosis (ALS) is a motoneuron disease characterized by misfolded proteins aggregation in affected motoneurons. In mutant SOD1 (mutSOD1) ALS models, aggregation correlates to impaired functions of proteasome and/or autophagy, both essential for the intracellular chaperone-mediated protein quality control (PQC), and to a reduced mutSOD1 clearance from motoneurons. Skeletal muscle cells are also sensitive to mutSOD1 toxicity, but no mutSOD1 aggregates are formed in these cells, that might better manage mutSOD1 than motoneurons. Thus, we analyzed in spinal cord and in muscle of transgenic (tg) G93A-SOD1 mice at presymptomatic (PS, 8 weeks) and symptomatic (S, 16 weeks) stages, and in age-matched control mice, whether mutSOD1 differentially modulates relevant PQC players, such as HSPB8, BAG3, and BAG1. Possible sex differences were also considered. No changes of HSPB8, BAG3, and BAG1 at PS stage (8 weeks) were seen in all tissues examined in tg G93A-SOD1 and control mice. At S stage (16 weeks), HSPB8 dramatically increased in skeletal muscle of tg G93A-SOD1 mice, while a minor increase occurred in spinal cord of male, but not female tg G93A-SOD1 mice. BAG3 expression increased both in muscle and spinal cord of tg G93A-SOD1 mice at S stage, BAG1 expression increased only in muscle of the same mice. Since, HSPB8-BAG3 complex assists mutSOD1 autophagic removal, we analyzed two well-known autophagic markers, LC3 and p62. Both LC3 and p62 mRNAs were significantly up-regulated in skeletal muscle of tg G93A-SOD1 mice at S stage (16 weeks). This suggests that mutSOD1 expression induces a robust autophagic response specifically in muscle. Together these results demonstrate that, in muscle mutSOD1-induced autophagic response is much higher than in spinal cord. In addition, if mutSOD1 exerts toxicity in muscle, this may not be mediated by misfolded proteins accumulation. It remains unclear whether in muscle mutSOD1 toxicity is related to aberrant autophagy activation.
肌萎缩侧索硬化症（ALS）是一种运动神经元疾病，其特征是受影响的运动神经元中错误折叠的蛋白质聚集。在突变 SOD1（mutSOD1）ALS 模型中，聚集与蛋白酶体和/或自噬功能受损相关，这两者对于细胞内伴侣介导的蛋白质质量控制（PQC）都是必不可少的，并且与运动神经元中 mutSOD1 的清除减少有关。骨骼肌细胞对 mutSOD1 也很敏感，但这些细胞中没有形成 mutSOD1 聚集体，这可能比运动神经元更好地管理 mutSOD1。因此，我们在转基因（tg）G93A-SOD1 小鼠的脊髓和肌肉中分析了在无症状（PS，8 周）和有症状（S，16 周）阶段以及年龄匹配的对照小鼠中，mutSOD1 是否差异调节相关的 PQC 蛋白，如 HSPB8、BAG3 和 BAG1。还考虑了可能的性别差异。在所有检查的组织中，在 PS 阶段（8 周）均未观察到 HSPB8、BAG3 和 BAG1 的变化 tg G93A-SOD1 和对照小鼠。在 S 阶段（16 周），HSPB8 在 tg G93A-SOD1 小鼠的骨骼肌中急剧增加，而在雄性但不是雌性 tg G93A-SOD1 小鼠的脊髓中仅发生轻微增加。BAG3 表达在 S 阶段 tg G93A-SOD1 小鼠的肌肉和脊髓中均增加，BAG1 表达仅在同一小鼠的肌肉中增加。由于 HSPB8-BAG3 复合物有助于 mutSOD1 自噬清除，因此我们分析了两种众所周知的自噬标记物，LC3 和 p62。在 S 阶段（16 周），tg G93A-SOD1 小鼠的骨骼肌中 LC3 和 p62 mRNA 均显著上调。这表明 mutSOD1 表达在肌肉中诱导了强烈的自噬反应。这些结果表明，在肌肉中，mutSOD1 诱导的自噬反应远高于脊髓。此外，如果 mutSOD1 在肌肉中产生毒性，这可能不是由错误折叠的蛋白质积累介导的。尚不清楚在肌肉中 mutSOD1 毒性是否与异常自噬激活有关。
