Transduction Mechanisms Mediating Nerve Growth Cone Guidance

描述（由申请人提供）：发育轴突的生长锥通过感测启动吸引或排斥转向的环境引导线索的梯度来引导轴突延伸穿过细胞外基质（ECM）。趋化性生长锥引导在神经系统损伤的情况下也是重要的，因为从髓磷脂分解释放的因子可以充当化学排斥剂并抑制轴突伸长，从而阻止功能恢复。了解介导生长锥引导的分子机制可以为开发增强损伤或神经退行性疾病后再生的策略提供重要的见解。细胞质Ca 2+信号介导许多引导信号的作用，但表面受体活化和Ca 2+信号传导之间的联系在很大程度上是未知的。同样，对生长锥趋化性的细胞过程的理解仍然不完整。目前的模型在很大程度上依赖于细胞骨架重排，但体内研究表明，调节粘附到ECM也是至关重要的适当的指导。拟议的研究的目标是确定轴突生长锥的趋化导向的转导机制。具体来说，我们的目标是定义细胞内信号，介导细胞外的指导线索，早期信号转导通路之间的相互作用，和下游效应器的过程，控制轴突延伸的方向的调节生长锥检测。我们的初步研究结果使我们建立了一个中枢假说，即生长锥对引导信号的检测是由表面膜上的极化磷酸肌醇3-激酶（PI 3 K）和Akt信号介导的，其触发局部Ca 2+信号并刺激内吞和外吞机制，以在生长锥表面不对称地重新分配ECM和引导信号的受体，并启动趋化引导。本论文的主要研究内容包括：第一，PI 3 K/Akt信号在生长锥趋化性调控中的作用;第二，PI 3 K/Akt信号如何激活生长锥中的Ca ~（2+）导向信号;第三，PI 3 K/Akt和Ca ~（2+）信号如何调控生长锥转向过程中的囊泡动力学;第四，PI 3 K/Akt和Ca 2+信号传导如何调节生长锥转动过程中整合素和导向受体的运输。这项研究将提供新的见解，早期信号介导的检测指导线索，放大的指导信号，并调节细胞机械，控制膜动力学和表面受体的再分布在趋化生长锥的指导。 公共卫生相关性：在发育中的神经系统中，神经细胞的生长尖端通过感知引导线索的梯度而延伸穿过复杂的环境基质到达适当的靶细胞，所述引导线索启动吸引或排斥转向。这种指导在神经系统损伤的情况下也很重要，因为髓鞘分解释放的因子可能起到排斥剂的作用并抑制延伸，从而阻止功能恢复。本研究的目标是定义介导引导线索检测的信号，并确定这些信号如何调节细胞过程以控制延伸方向。这些发现将有助于我们了解神经系统的发育，并为促进神经退行性疾病或损伤后再生的潜在治疗方法提供见解。

DESCRIPTION (provided by applicant): The growth cone of developing axons guides axon extension through the extracellular matrix (ECM) by sensing gradients of environmental guidance cues that initiate attractive or repulsive steering. Chemotactic growth cone guidance is also important in the context of nervous system injury, as factors released from the breakdown of myelin may act as chemorepellents and inhibit axon elongation, thereby preventing functional recovery. Understanding the molecular mechanisms that mediate growth cone guidance could provide important insights for developing strategies to enhance regeneration after injury or neurodegenerative disease. Cytoplasmic Ca2+ signals mediate the action of many guidance cues, but the link between surface receptor activation and Ca2+ signaling is largely unknown. Likewise, an understanding of the cellular processes underlying growth cone chemotaxis remains incomplete. Current models rely heavily on cytoskeletal rearrangements, but in vivo studies have demonstrated that regulated adhesion to the ECM is also critical for proper guidance. The goal of the proposed research is to define the transduction mechanisms underlying the chemotactic guidance of axonal growth cones. Specifically, we aim to define the intracellular signals that mediate growth cone detection of extracellular guidance cues, the interactions between early signal transduction pathways, and the regulation of downstream effector processes that control the direction of axon extension. Our preliminary findings have led us to establish a CENTRAL HYPOTHESIS that growth cone detection of guidance cues is mediated by polarized phosphoinositide 3-kinase (PI3K) and Akt signaling at the surface membrane, which triggers local Ca2+ signals and stimulates endocytic and exocytic machinery to redistribute receptors for ECM and guidance cues asymmetrically at the growth cone surface and initiate chemotactic guidance. The proposal is organized into four interrelated specific aims that will define the following: first, the role of PI3K/Akt signaling in mediating growth cone chemotaxis; second, how PI3K/Akt signaling activates Ca2+ guidance signals in the growth cone; third, how PI3K/Akt and Ca2+ signaling regulate vesicle dynamics during growth cone turning; and fourth, how PI3K/Akt and Ca2+ signaling regulate trafficking of integrin and guidance receptors during growth cone turning. This study will provide novel insights into the early signals that mediate the detection of guidance cues, the amplification of guidance signals, and the regulation of cellular machinery that controls membrane dynamics and the redistribution of surface receptors during chemotactic growth cone guidance. PUBLIC HEALTH RELEVANCE: In the developing nervous system the growing tip of nerve cells extends through a complex environmental matrix to the appropriate target cells by sensing gradients of guidance cues that initiate attractive or repulsive steering. This guidance is also important in the context of nervous system injury, as factors released from the breakdown of myelin may act as repellents and inhibit elongation, thereby preventing functional recovery. The goal of this research is to define signals that mediate the detection of guidance cues and determine how these signals regulate cellular processes to control the direction of extension. The findings will contribute to our understanding of the development of the nervous system and provide insights into potential therapeutic approaches for promoting regeneration after neurodegenerative disease or injury.