A knock-in/knock-out mouse model of HSPB8-associated distal hereditary motor neuropathy and myopathy reveals toxic gain-of-function of mutant Hspb8
A knock-in/knock-out mouse model of HSPB8-associated distal hereditary motor neuropathy and myopathy reveals toxic gain-of-function of mutant Hspb8
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DOI：
10.1007/s00401-017-1756-0
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发表时间：
2018-01-01
影响因子：
12.7
通讯作者：
Timmerman, Vincent
中科院分区：
文献类型：
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作者：
Bouhy, Delphine;Juneja, Manisha;Timmerman, Vincent
小热休克蛋白B8基因（HSPB 8/HSP 22）的突变与远端遗传性运动神经病、腓骨肌萎缩症和最近的远端肌病有关。目前尚不清楚突变型HSPB 8如何诱导神经和肌肉表型，以及这些疾病背后是否存在共同的发病机制。越来越多的证据指向HSPB 8在分子伴侣相关的自噬中的作用，这已被证明是神经退行性疾病中多聚谷氨酰胺聚集体清除的决定因素，而且也是骨骼肌肌原纤维维持的决定因素。为了检验这一假设，并更好地剖析突变型HSPB 8的病理机制，我们产生了一种新的转基因小鼠模型，导致内源性蛋白HSPB 8的突变蛋白（敲入系）或功能丧失（功能敲除系）的表达。虽然纯合基因敲入小鼠出现与周围神经变性和严重肌肉萎缩相关的运动缺陷，证实了患者数据，但纯合基因敲除小鼠的运动表现与野生型动物相当。症状后纯合子敲入的远端骨骼肌显示Z盘紊乱，颗粒丝状物质积累沿着Hspb 8、α B-晶体蛋白（HSPB 5/HSPAB）和结蛋白聚集体。聚集体的存在与有效自噬的标记物减少相关。纯合敲入小鼠的坐骨神经的特征在于在症状前的低自噬潜力和在症状后的动物中的Hspb 8聚集体。另一方面，纯合子敲除小鼠的坐骨神经呈现正常形态，其远端肌肉显示异常线粒体的积累，但完整的肌纤维和Z线组织。因此，我们的数据表明，毒性功能获得性突变Hspb 8聚集体是周围神经病变和肌病的主要贡献者。此外，突变型Hspb 8诱导自噬损伤，这可能加重表型。
Mutations in the small heat shock protein B8 gene (HSPB8/HSP22) have been associated with distal hereditary motor neuropathy, Charcot-Marie-Tooth disease, and recently distal myopathy. It is so far not clear how mutant HSPB8 induces the neuronal and muscular phenotypes and if a common pathogenesis lies behind these diseases. Growing evidence points towards a role of HSPB8 in chaperone-associated autophagy, which has been shown to be a determinant for the clearance of poly-glutamine aggregates in neurodegenerative diseases but also for the maintenance of skeletal muscle myofibrils. To test this hypothesis and better dissect the pathomechanism of mutant HSPB8, we generated a new transgenic mouse model leading to the expression of the mutant protein (knock-in lines) or the loss-of-function (functional knock-out lines) of the endogenous protein Hspb8. While the homozygous knock-in mice developed motor deficits associated with degeneration of peripheral nerves and severe muscle atrophy corroborating patient data, homozygous knock-out mice had locomotor performances equivalent to those of wild-type animals. The distal skeletal muscles of the post-symptomatic homozygous knock-in displayed Z-disk disorganisation, granulofilamentous material accumulation along with Hspb8, alpha B-crystallin (HSPB5/CRYAB), and desmin aggregates. The presence of the aggregates correlated with reduced markers of effective autophagy. The sciatic nerve of the homozygous knock-in mice was characterized by low autophagy potential in pre-symptomatic and Hspb8 aggregates in post-symptomatic animals. On the other hand, the sciatic nerve of the homozygous knock-out mice presented a normal morphology and their distal muscle displayed accumulation of abnormal mitochondria but intact myofiber and Z-line organisation. Our data, therefore, suggest that toxic gain-of-function of mutant Hspb8 aggregates is a major contributor to the peripheral neuropathy and the myopathy. In addition, mutant Hspb8 induces impairments in autophagy that may aggravate the phenotype.