Axon Degeneration and Apoptosis: Molecular Intersection of Two Distinct Pathways

描述（由申请人提供）：神经元能够激活通过细胞凋亡引起整个细胞或仅轴突变性的途径。轴突特异性变性在生理学上是重要的，因为它允许神经元去除过多或误导的轴突分支，并允许神经元连接的可塑性。然而，神经元究竟如何激活和划分这种退化途径以破坏其轴突而不使细胞的其他部分处于危险之中尚不清楚。这是特别有趣的，因为最近的研究证实Bax，在细胞凋亡途径中的关键蛋白，也调节轴突特异性变性。 我们的目标是专注于细胞凋亡和轴突特异性变性途径之间的分子交叉。首先，我们建立了一个基于微流控室的交感神经元模型，其中从轴突隔室中剥夺神经生长因子（NGF）仅诱导轴突特异性变性，而从轴突和索马隔室中剥夺NGF诱导细胞凋亡。第二，我们发现细胞凋亡和轴突特异性变性之间存在大量重叠，但也发现了明显和意想不到的差异。例如，虽然细胞凋亡需要Apaf-1和Caspase-9（Casp 9），但我们发现轴突变性需要Casp 9，但令人惊讶的是，不需要Apaf-1。我们的研究结果还表明，神经元能够选择性地参与细胞凋亡或轴突特异性变性，因为成熟神经元完全限制细胞凋亡，但仍然允许轴突变性。 在这个提议中，我们将研究神经元调节轴突特异性变性的几种新机制。我们将特别关注Bax在这一通路中是如何被激活的（目标1），研究Casp 9独立于Apaf-1被激活的机制（目标2），并探索成熟神经元选择性限制凋亡但仍然允许轴突变性的机制（目标3）。这些研究无疑将揭示神经元如何利用许多相同的成分进行细胞凋亡和轴突选择性变性的关键方面，但涉及不同的机制，以允许对这些通路的激活进行精确的空间和时间控制。

DESCRIPTION (provided by applicant): Neurons have the capability to activate pathways that cause degeneration of either the entire cell by apoptosis or only the axons. Axon-specific degeneration is physiologically important as it allows neurons to remove excessive or misguided axon branches and permit plasticity in neuronal connections. However, exactly how a neuron can activate and compartmentalize this degenerative pathway to destroy its axon without putting the rest of the cell at risk is unclear. This is particularly interesting since recent studies idenified Bax, a key protein in the apoptosis pathway, to also regulate axon-specific degeneration. Our goal is to focus on the molecular intersection between apoptosis and axon-specific degeneration pathways. First, we established a microfluidic chamber-based model of sympathetic neurons where deprivation of nerve growth factor (NGF) from the axon compartment only induces axon-specific degeneration whereas NGF deprivation from the axon and soma compartments induces apoptosis. Second, we found substantial overlap between apoptosis and axon-specific degeneration but also identified distinct and unexpected differences. For example, while apoptosis required both Apaf-1 and Caspase-9 (Casp9), we found axon degeneration to require Casp9 but, surprisingly, not Apaf-1. Our results also show that neurons are exquisitely capable of selectively engaging apoptosis or axon-specific degeneration as mature neurons completely restrict apoptosis but remain permissive for axon degeneration. In this proposal, we will investigate several novel mechanisms by which neurons regulate axon-specific degeneration. We will focus specifically on determining how Bax is activated in this pathway (Aim 1), examining the mechanism by which Casp9 is activated independently of Apaf-1 (Aim 2), and probing the mechanism by which mature neurons selectively restrict apoptosis but remain permissive for axon degeneration (Aim 3). These studies will undoubtedly uncover critical aspects of how neurons utilize many of the same components for apoptosis and axon-selective degeneration but engage distinct mechanisms to allow precise spatial and temporal control over the activation of these pathways.