Dipartimento di Endocrinologia, Fisiopatologia e Biologia Applicata (Center of Excellence on Neurodegenerative Diseases, CEND), Università degli Studi di Milano, Milano, Italy.
Hum Mol Genet. 2010 Sep 1;19(17):3440-56. doi: 10.1093/hmg/ddq257. Epub 2010 Jun 22.
Several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), are characterized by the presence of misfolded proteins, thought to trigger neurotoxicity. Some familial forms of ALS (fALS), clinically indistinguishable from sporadic ALS (sALS), are linked to superoxide dismutase 1 (SOD1) gene mutations. It has been shown that the mutant SOD1 misfolds, forms insoluble aggregates and impairs the proteasome. Using transgenic G93A-SOD1 mice, we found that spinal cord motor neurons, accumulating mutant SOD1 also over-express the small heat shock protein HspB8. Using motor neuronal fALS models, we demonstrated that HspB8 decreases aggregation and increases mutant SOD1 solubility and clearance, without affecting wild-type SOD1 turnover. Notably, HspB8 acts on mutant SOD1 even when the proteasome activity is specifically blocked. The pharmacological blockage of autophagy resulted in a dramatic increase of mutant SOD1 aggregates. Immunoprecipitation studies, performed during autophagic flux blockage, demonstrated that mutant SOD1 interacts with the HspB8/Bag3/Hsc70/CHIP multiheteromeric complex, known to selectively activate autophagic removal of misfolded proteins. Thus, HspB8 increases mutant SOD1 clearance via autophagy. Autophagy activation was also observed in lumbar spinal cord of transgenic G93A-SOD1 mice since several autophago-lysosomal structures were present in affected surviving motor neurons. Finally, we extended our observation to a different ALS model and demonstrated that HspB8 exerts similar effects on a truncated version of TDP-43, another protein involved both in fALS and in sALS. Overall, these results indicate that the pharmacological modulation of HspB8 expression in motor neurons may have important implications to unravel the molecular mechanisms involved both in fALS and in sALS.
几种神经退行性疾病，包括肌萎缩侧索硬化症（ALS），其特征是存在错误折叠的蛋白质，被认为引发神经毒性。一些家族性肌萎缩侧索硬化症（fALS）与超氧化物歧化酶 1（SOD1）基因突变有关，与散发性肌萎缩侧索硬化症（sALS）在临床上无法区分。已经表明，突变的 SOD1错误折叠，形成不溶性聚集体并损害蛋白酶体。使用转基因 G93A-SOD1 小鼠，我们发现脊髓运动神经元中积累突变 SOD1 的细胞也过度表达小热休克蛋白 HspB8。使用运动神经元 fALS 模型，我们证明 HspB8 减少了聚集并增加了突变 SOD1 的溶解度和清除率，而不影响野生型 SOD1 的周转率。值得注意的是，即使蛋白酶体活性被特异性阻断，HspB8 也可以作用于突变 SOD1。自噬的药理学阻断导致突变 SOD1 聚集体的急剧增加。在自噬流阻断期间进行的免疫沉淀研究表明，突变 SOD1 与 HspB8/Bag3/Hsc70/CHIP 多异源复合物相互作用，该复合物已知选择性激活错误折叠蛋白的自噬清除。因此，HspB8 通过自噬增加突变 SOD1 的清除率。在转基因 G93A-SOD1 小鼠的腰椎脊髓中也观察到自噬激活，因为受影响的存活运动神经元中存在几种自噬溶酶体结构。最后，我们将我们的观察结果扩展到另一个 ALS 模型，并证明 HspB8 对 TDP-43 的截断版本也具有相似的作用，TDP-43 是另一种涉及 fALS 和 sALS 的蛋白质。总之，这些结果表明，在运动神经元中对 HspB8 表达进行药理学调节可能对揭示涉及 fALS 和 sALS 的分子机制具有重要意义。
