Soluble Neuregulins in Neuromuscular and Peripheral Nerve Development

描述（由申请人提供）：神经调节蛋白（NRGs）是一类神经元衍生的生长和分化因子，通过可溶性、肝素结合和膜锚定的可选剪接形式“靶向”轴交界面和神经肌肉连接（NMJs）。它们促进外周和中枢胶质细胞的增殖、迁移、存活和髓鞘形成。在NMJ中，它们的作用尚不清楚，但在不同的发育阶段，肝素结合形式在NMJ的基底层积累，并诱导乙酰胆碱受体，这表明它们促进突触强度。由于轴突与肌肉和雪旺细胞靶点都很接近，NRG1对肌肉和神经的直接和间接影响一直难以确定。我们的实验室主要研究NRG1的可溶性肝素结合形式。我们发现可溶性形式的NRG1在雪旺细胞和肌肉来源的神经营养因子（如BDNF和GDNF）的作用下，从感觉和运动神经元轴突迅速释放，并且这一途径受蛋白激酶c的调节。一旦释放，NRG1通过与硫酸肝素蛋白聚糖（HSPGs）的高度特异性相互作用，在神经和NMJs中集中。在这里，我们将探讨NRG1如何通过两个顺序机制促进鸡和小鼠胚胎的周围神经和NMJ发育。(1)雪旺细胞和肌源性神经营养因子调控轴突释放；(2)神经营养因子诱导的PKC信号传导。一旦从轴突释放，NRG1将定位于通过发育表达的硫酸肝素蛋白聚糖（HSPGs）在细胞外基质中积累的位点。在这些研究的一个重要部分，我们还将测试一种新的治疗方法，利用NRG1的肝素结合结构域作为特定的靶向基序，将生物疗法靶向轴胶质和神经肌肉连接。相关性：迄今为止，周围和中枢神经系统疾病的有效治疗方法很少。克服这一问题的一个有希望的方法是开发生物驱动疗法，使用神经系统形成所需的生长因子。这一建议将试图通过对正常发育的更好理解和改进神经系统内靶向新疗法的方法来克服开发此类疗法的一些主要限制。

DESCRIPTION (provided by applicant): The neuregulins (NRGs) are a family of neuronally-derived growth and differentiation factors that 'target" the axoglial interface and neuromuscular junctions (NMJs) through both soluble, heparin-binding and membrane anchored alternatively spliced forms. They promote proliferation, migration, survival, and myelination of both peripheral and central glia. At the NMJ, their role is less clear, but heparin-binding forms accumulate within the basal lamina of NMJs at distinct developmental stages and induce acetylcholine receptors, suggesting that they promote synaptic strength. Given the close proximity of the axon to both muscle and Schwann cell targets, the direct and indirect effects of NRG1 on muscle and nerve have been difficult to establish. Our laboratory focuses on the soluble, heparin-binding forms of NRG1. We found that soluble forms of NRG1 are rapidly released from both sensory and motor neuron axons in response to Schwann cell and muscle-derived neurotrophic factors such as BDNF and GDNF, and that this pathway is regulated by protein kinase C. Once released, NRG1 becomes concentrated within the nerve and at NMJs through highly specific interactions with heparan sulfate proteoglycans (HSPGs). Here, we will explore how NRG1 promotes peripheral nerve and NMJ development in both chick and mouse embryos through two sequential mechanisms. (1) Regulated release from axons by Schwann cell and muscle-derived neurotrophic factors, (2) Neurotrophic factor-induced PKC signaling. Once released from axons, NRG1 will be localized to sites where it accumulates in the extracellular matrix through developmentally-expressed heparan-sulfate proteoglycans (HSPGs). In an important part of these studies, we will also test a novel therapeutic method to target biological therapeutics to axoglial and neuromuscular junctions using NRG1's heparin-binding domain as a specific targeting motif. Relevance: To date there are few effective treatments for diseases of the peripheral and central nervous systems. A promising means to overcome this is to develop biologically-driven therapeutics that use growth factors required for nervous system formation. This proposal will attempt to overcome some off the major limitations in developing such therapeutics through an improved understanding of normal development and improved ways to target novel therapeutics within the nervous system. PUBLIC HEALTH RELEVANCE: Understanding the mechanisms that regulate the release and localization of neuregulin at the peripheral nerve and neuromuscular junction will be critical to design effective therapeutics for diseases of peripheral nerve and neuromuscular disorders, such as neuropathy andALS,aswellasCNSdisorders,suchasmultiplesclerosisandschizophrenia.Treatmentscould consist of promoting neuregulin or neurotrophin signaling, and/or promoting neuregulin release through activation of PKC-4 signaling. Our studies also test a more general 'targeting' system we invented that effectively delivers therapeutics to specific cell types through their unique heparan sulfate composition.