Mechanisms of neuromuscular junction formation

神经肌肉接头形成机制

• 批准号: 10267688
• 负责人: WEN-CHENG XIONG
• 金额: $ 56.87万
• 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: 2013-07-01 至 2023-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10267688
• 关键词: Adaptor Signaling Protein; Address; Agrin; Amino Acids; Axon; Behavior; Binding; Cells; Complex; Congenital Myasthenic Syndromes; Development; Diagnostic; Down Syndrome Cell Adhesion Molecule; Family; Knock-in; Knock-in Mouse; Life; Low Density Lipoprotein Receptor; MUSK gene; Mediating; Molecular; Motor Neurons; Mus; Muscle; Muscle Cells; Muscle Fibers; Mutant Strains Mice; Mutation; Myasthenia Gravis; Neuromuscular Diseases; Neuromuscular Junction; Neurons; Pathogenesis; Pathogenicity; Presynaptic Terminals; Proteins; Regulation; Research; Role; Signal Transduction; Signaling Protein; Skeletal Muscle; Structure; Synapses; Synapsins; Testing; Therapeutic; Ubiquitin Like Proteins; agrin receptor; base; enzyme activity; experimental study; in vitro activity; insight; member; neural circuit; novel; peripheral membrane protein 43K; presynaptic; synaptogenesis; ubiquitin-protein ligase

The neuromuscular junction (NMJ), a synapse formed between motoneurons and muscle fibers, has contributed greatly to understanding of the general principles of synaptogenesis, as well as of neuromuscular disorders. NMJ formation requires intimate interaction between motoneurons and muscle fibers. For example, in antegrade signaling, motoneurons release agrin that binds LRP4, a member of the LDL receptor family, in muscle cells to activate the receptor tyrosine kinase MuSK, both of which are required for NMJ formation. Downstream of MuSK was not well understood, except that AChR concentration absolutely requires the adapter protein rapsyn. However, exactly how signals are transduced from MuSK activation to AChR concentration is not well understood. On the other hand, skeletal muscles are known to be critical to the development of axon terminals of motoneurons. In contrast to antegrade regulation, much less is understood about molecular mechanisms of retrograde regulation of presynaptic differentiation by muscle fibers. In preliminary studies, we discovered that the classic adaptor protein rapsyn is an E3 ligase. Knockin mice carrying the mutation of a single residue necessary for the enzymatic activity are unable to form the NMJ. Our results suggest that rapsyn contributes to AChR clustering by promoting neddylation. These observations identify a previously unappreciated enzymatic activity of rapsyn and a role of neddylation in synapse formation. Our studies of LRP4 suggest that it could regulate developing axons by mechanisms independent of MuSK. The proposal will test two hypotheses. First, MuSK increases rapsyn enzyme activity to promote neddylation for AChR clustering and NMJ formation. Second, muscle regulates presynaptic differentiation via LRP4. Results of this proposal will provide a better understanding of cellular as well as molecular mechanisms of mammalian NMJ formation and contribute to a better understanding of pathogenic mechanisms of neuromuscular disorders.

神经肌肉连接（NMJ），一种在运动神经元和肌肉纤维之间形成的突触， 已经为理解突触发生的一般原理做出了巨大贡献， 神经肌肉疾病。 NMJ形成需要运动神经元之间的紧密相互作用 和肌肉纤维。例如，在流步信号传导中，运动神经元释放了结合的agrin LRP4是LDL受体家族的成员，在肌肉细胞中激活受体酪氨酸 激酶麝香，两者都需要NMJ形成。麝香的下游不好 理解，除了ACHR浓度绝对需要衔接蛋白RAPSYN。 但是，确切的信号是如何从麝香激活转换为ACHR浓度的，不是 理解。另一方面，已知骨骼肌肉对于发育至关重要 运动神经元的轴突末端。与步立监管相反，更不用说了解 关于肌肉突触前分化的逆行调节的分子机制 纤维。在初步研究中，我们发现经典的适配器蛋白Rapsyn是E3 连接酶。敲打蛋白的小鼠携带酶促的单个残留物的突变 活动无法形成NMJ。我们的结果表明Rapsyn有助于ACHR 通过促进Neddylation进行聚类。这些观察结果确定了先前未欣赏的 Rapsyn的酶活性和Neddylation在突触形成中的作用。我们对LRP4的研究 表明它可以通过独立于麝香的机制来调节发育的轴突。这 提案将检验两个假设。首先，麝香增加RAPSYN酶的活性以促进 neddylation用于ACHR聚类和NMJ形成。其次，肌肉调节突触前 通过LRP4分化。该提案的结果将更好地理解细胞 以及哺乳动物NMJ形成的分子机制，并有助于更好 了解神经肌肉疾病的致病机制。