LRP4 Is Critical for Neuromuscular Junction Maintenance
LRP4 Is Critical for Neuromuscular Junction Maintenance
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DOI：
10.1523/jneurosci.1733-14.2014
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发表时间：
2014-10-15
影响因子：
5.3
通讯作者：
Mei, Lin
中科院分区：
文献类型：
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作者：
Barik, Arnab;Lu, Yisheng;Mei, Lin
神经肌肉连接（NMJ）是运动神经元和骨骼肌纤维之间的突触，对肌肉收缩的控制至关重要。它的形成需要神经元蛋白结合LRP4来刺激麝香。在先天性重症肌无力综合征患者中发现了agrin、MuSK和LRP4的突变，重症肌无力患者会产生针对agrin、LRP4和MuSK的抗体。然而，目前尚不清楚agrin信号通路是否对NMJ维持至关重要，因为这三种基因中的任何一种的零突变都是围产期致命的。在这项研究中，我们产生了imKO小鼠，这是一种突变株，其LRP4基因可以通过多西环素（Dox）处理在肌肉中删除。成人肌肉中LRP4基因的消融使其在NMJ维持中的作用得以研究。我们证明，P30小鼠的Dox治疗降低了肌肉力量和复合肌肉动作电位。AChR簇分裂，连接褶皱和突触囊泡减少。微型终板电位的振幅和频率降低，表明神经肌肉传递受损，并提供成人LRP4缺乏的细胞机制。我们发现LRP4消融导致突触agrin和90kda片段的丢失，其发生在其他突触前和突触后成分之前，这表明LRP4可能调节突触agrin的稳定性。这些观察结果表明，LRP4对于维持NMJ的结构和功能完整性至关重要，成年期肌肉LRP4的丧失足以引起肌无力症状。
The neuromuscular junction (NMJ) is a synapse between motor neurons and skeletal muscle fibers, and is critical for control of muscle contraction. Its formation requires neuronal agrin that acts by binding to LRP4 to stimulate MuSK. Mutations have been identified in agrin, MuSK, and LRP4 in patients with congenital myasthenic syndrome, and patients with myasthenia gravis develop antibodies against agrin, LRP4, and MuSK. However, it remains unclear whether the agrin signaling pathway is critical for NMJ maintenance because null mutation of any of the three genes is perinatal lethal. In this study, we generated imKO mice, a mutant strain whose LRP4 gene can be deleted in muscles by doxycycline (Dox) treatment. Ablation of the LRP4 gene in adult muscle enabled studies of its role in NMJ maintenance. We demonstrate that Dox treatment of P30 mice reduced muscle strength and compound muscle action potentials. AChR clusters became fragmented with diminished junctional folds and synaptic vesicles. The amplitude and frequency of miniature endplate potentials were reduced, indicating impaired neuromuscular transmission and providing cellular mechanisms of adult LRP4 deficiency. We showed that LRP4 ablation led to the loss of synaptic agrin and the 90 kDa fragments, which occurred ahead of other prejunctional and postjunctional components, suggesting that LRP4 may regulate the stability of synaptic agrin. These observations demonstrate that LRP4 is essential for maintaining the structural and functional integrity of the NMJ and that loss of muscle LRP4 in adulthood alone is sufficient to cause myasthenic symptoms.