LRP4 signaling in neuromuscular junction formation

LRP4 信号在神经肌肉接头形成中的作用

• 批准号: 9604664
• 负责人: Lin Mei
• 金额: $ 16.22万
• 依托单位: CASE WESTERN RESERVE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-06-01 至 2018-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9604664
• 关键词: LRP4; signaling; neuromuscular; junction; formation

DESCRIPTION (provided by applicant): The multi-PI proposal is to investigate how LRP4 regulates the formation of the neuromuscular junction (NMJ), a synapse that has contributed greatly to understanding of synaptogenesis and of neuromuscular disorders. NMJ formation requires precise interaction between motoneurons (MNs) and muscle fibers. In advance of MN arrival, muscle fibers are prepatterned with small, primitive AChR clusters, which are believed to be critical for NMJ formation although genetic evidence is lacking at the moment. In an established pathway, MNs release agrin to promote postsynaptic development. It binds to LRP4 which acts in cis to stimulate the receptor tyrosine kinase MuSK; and ensuing signaling events lead to AChR clustering. However, little is known of how signals are transduced from agrin to MuSK. In preliminary studies, we solved the first crystal structure of an agrin-LRP4 complex, which provides insight into the initial step of the agrin signaling cascade. Our studies of cell-specific knockout (KO) and double KO mice revealed novel functions of LRP4 in NMJ formation. For example, muscle LRP4 may be critical for presynaptic differentiation during initial steps of NMJ formation. On the other hand, MN LRP4 may serve as agrin's receptor in trans to induce AChR clusters. Many of these findings are unexpected and raise critical questions. How does LRP4 relay the signal from agrin to MuSK? Is MN LRP4 sufficient to induce NMJ formation? Is muscle fiber prepatterning critical for NMJ formation? Is the synaptogenic activity critical for NMJ formation? How does muscle LRP4 regulate motor nerve terminal differentiation? To address these questions, we will 1) understand how signal is transduced from LRP4 to MuSK by solving the structure of the agrin- LRP4-MuSK complex; 2) determine if MN LRP4 is sufficient to induce NMJ formation and if muscle fiber prepatterning is necessary for NMJ formation; and 3) investigate mechanisms by which LRP4 in muscle cells controls presynaptic differentiation. The research represents a synergistic strategy that leverages complementary expertise, strengths and existing resources of the two labs. Results will provide a better understanding of cellular as well as molecular mechanisms of mammalian NMJ formation. Pathogenesis of neuromuscular disorders is known to involve abnormal NMJ structure and function. In fact, mutations of agrin/LRP4/MuSK signaling proteins have been implicated in congenital myasthenic syndrome (CMS). Recent evidence from various laboratories including ours indicates that patients with myasthenia gravis (MG) develop antibodies against MuSK and LRP4. Therefore, our research will contribute to a better understanding of pathogenic mechanisms of these neuromuscular disorders.

描述（由申请人提供）：多PI建议是研究LRP4如何调节神经肌肉结（NMJ）的形成，这是一种突触，这有助于理解突触发生和神经肌肉疾病。 NMJ形成需要运动神经元（MN）和肌肉纤维之间的精确相互作用。在MN到达之前，肌肉纤维是用小的，原始的ACHR簇预先展示的，尽管目前缺乏遗传证据，但据信对于NMJ形成至关重要。在既定的途径中，MNS释放Agrin，以促进突触后发育。它与LRP4结合，该LRP4作用于顺式刺激受体酪氨酸激酶麝香。随后的信号事件导致ACHR聚类。然而，几乎不知道信号如何从阿格林转到麝香。在初步研究中，我们解决了Agrin-LRP4复合物的第一个晶体结构，该晶体结构可深入了解Agrin信号级联的初始步骤。我们对细胞特异性敲除（KO）和双KO小鼠的研究揭示了LRP4在NMJ形成中的新功能。例如，在NMJ形成的初始步骤中，肌肉LRP4对于突触前分化至关重要。另一方面，Mn LRP4可以用作反式诱导ACHR簇的Agrin受体。这些发现中的许多是出乎意料的，并提出了关键问题。 LRP4如何将信号从Agrin转移到Musk？ Mn LRP4是否足以诱导NMJ形成？肌肉纤维对NMJ形成至关重要吗？突触活性对于NMJ形成至关重要吗？肌肉LRP4如何调节运动神经末端分化？为了解决这些问题，我们将通过求解农业LRP4-MUSK复合物的结构来了解信号如何从LRP4传递到麝香； 2）确定MN LRP4是否足以诱导NMJ的形成以及NMJ形成的肌肉纤维前期是否需要； 3）研究肌肉细胞中LRP4控制突触前分化的机制。该研究代表了一种协同战略，该战略利用了两个实验室的补充专业知识，优势和现有资源。结果将更好地了解哺乳动物NMJ形成的细胞和分子机制。已知神经肌肉疾病的发病机理涉及异常的NMJ结构和功能。实际上，Agrin/LRP4/Musk信号传导蛋白的突变与先天性肌关系综合征（CMS）有关。来自包括我们的各种实验室的最新证据表明，肌无力重症肌无力（MG）患者对MUSK和LRP4产生抗体。因此，我们的研究将有助于更好地理解这些神经肌肉疾病的致病机制。