Lysosomal degradation of GMPPB is associated with limb-girdle muscular dystrophy type 2T
Lysosomal degradation of GMPPB is associated with limb-girdle muscular dystrophy type 2T
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GMPPB 的溶酶体降解与 2T 型肢带型肌营养不良症相关
DOI：
10.1002/acn3.787
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发表时间：
2019
影响因子：
5.3
通讯作者：
Li Cao
中科院分区：
文献类型：
--
作者：
Wotu Tian;Haiyan Zhou;Feixia Zhan;Zeyu Zhu;Jie Yang;Shengdi Chen;Xinghua luan;Li Cao
GMPPB-甘露糖焦磷酸化酶B（GMPPB）相关表型谱范围广泛，从先天性肌无力综合征（CMS）、肢带型肌营养不良2 T型（LGMD 2 T）到严重的先天性肌眼脑综合征。我们的研究调查了novelGMPPB突变患者的临床病理特征，并探讨了发病mechanism.MethodsThe患者是一名22岁的女性，患有慢性近端肢体无力9年，没有认知功能恶化。疲劳之后，虚弱变得更厉害了。记录血清肌酸激酶升高和重复神经刺激试验下降。MRI T1序列显示下肢肌肉及肩胛带脂肪浸润。开放肌肉活检和遗传学分析performed.ResultsMuscle活检显示肌源性改变。在该患者中发现两个错义突变（c.803T>C和c.1060G>A）。蛋白质印迹和免疫染色显示患者肌肉中存在GMPPB和α-肌营养不良聚糖缺陷。在体外，形成细胞质聚集体的突变体GMPPB与微管相关蛋白1轻链3-II（LC 3-II）完全共定位，LC 3-II是自噬体的经典标志物。GMPPB的降解伴随着LC 3-II的上调，这可以通过溶酶体抑制剂亮抑酶肽（leupeptin）来恢复。我们提供了初步的证据，突变体GMPPB与自噬体共定位在亚细胞水平。通过自噬-溶酶体途径降解的GMPPB突变体与LGMD 2 T相关。本研究为酶替代疗法的研究提供了新的思路，酶替代疗法有可能成为今后研究的治疗靶点之一。
ObjectiveGDP‐mannose pyrophosphorylase B (GMPPB) related phenotype spectrum ranges widely from congenital myasthenic syndrome (CMS), limb‐girdle muscular dystrophy type 2T (LGMD 2T) to severe congenital muscle‐eye‐brain syndrome. Our study investigates the clinicopathologic features of a patient with novelGMPPBmutations and explores the pathogenetic mechanism.MethodsThe patient was a 22‐year‐old woman with chronic proximal limb weakness for 9 years without cognitive deterioration. Weakness became worse after fatigue. Elevated serum creatine kinase and decrements on repetitive nerve stimulation test were recorded. MRI showed fatty infiltration in muscles of lower limbs and shoulder girdle on T1 sequence. Open muscle biopsy and genetic analysis were performed.ResultsMuscle biopsy showed myogenic changes. Two missense mutations inGMPPBgene (c.803T>C and c.1060G>A) were identified in the patient. Western blotting and immunostaining showed GMPPB andα‐dystroglycan deficiency in the patient's muscle. In vitro, mutant GMPPB forming cytoplasmic aggregates completely colocalized with microtubule‐associated protein 1 light chain 3‐II (LC3‐II), a classical marker of autophagosome. Degradation of GMPPB was accompanied by an upregulation of LC3‐II, which could be restored by lysosomal inhibitor leupeptin.InterpretationWe identified two novelGMPPBmutations causing overlap phenotype between LGMD 2T and CMS. We provided the initial evidence that mutant GMPPB colocalizes with autophagosome at subcellular level. GMPPB mutants degraded by autophagy‐lysosome pathway is associated with LGMD 2T. This study shed the light into the enzyme replacement which could become one of the therapeutic targets in the future study.