Molecular Mechanisms of Axon Degeneration

描述（由申请人提供）：轴突变性发生在神经系统损伤和神经退行性疾病中。轴突和突触的丧失导致神经回路的破坏，被认为是导致神经系统疾病患者功能丧失的主要因素。尽管它在疾病中具有广泛的重要性，但在任何情况下，人们对驱动轴突退化的分子机制知之甚少。研究轴突切除后的轴突退化（即沃勒氏变性）已被证明是一种非常有用的方法来阐明驱动轴突自我破坏的基本细胞事件。例如，先前对小鼠沃勒氏变性慢分子（wld）的研究令人惊讶地显示，在某些条件下，在没有细胞体的情况下，远端切断的轴突纤维可以存活并保持功能完整相当长一段时间（即在轴突切除后数周）。在表达轴突的wds中观察到的长期存活提出了一种有趣的可能性，即轴突退化可能是轴突自我破坏的一个活跃过程，类似于凋亡细胞死亡。在我们的第一个资助周期中，我们开发了第一个果蝇沃勒氏变性模型，并证明了被切断的果蝇轴突经历了沃勒氏变性，这种变性可以被小鼠wld分子有效地抑制。这些数据表明，沃勒氏变性的分子机制是神经细胞类型的一个古老而保守的特征。受wld的启发，我们对抑制沃勒氏变性的果蝇突变进行了首次前向基因筛选。引人注目的是，我们发现激酶接头分子dSarm（不育α /犰狳/ toll -白细胞介素受体同源结构域蛋白）的缺失抑制了果蝇的沃勒氏变性（50 - 3周）。我们还令人兴奋地发现，这一途径在哺乳动物中是功能保守的：在体内和体外，Sarm1-/-小鼠都表现出对沃勒氏变性的强大抑制。这些数据表明，dSarm/Sarm1是一个保守的“轴突死亡”基因，其内源性功能是促进轴突切除后的轴突变性。在本提案的目的1和目的2中，我们将利用果蝇研究dSarm促进轴突变性的细胞和分子机制。在Aim 3中，我们将描述我们最近分离的一组新的果蝇突变体，它们也能像dsarm一样有效地抑制轴突死亡。这些研究是我们了解轴突在受伤后如何自我破坏的长期、全面努力的核心。我们期望我们的发现对我们理解损伤后或人类疾病中的轴突退化有重大影响，我们鉴定的新分子将成为治疗涉及轴突和突触丧失的人类神经系统疾病的极好候选者。

DESCRIPTION (provided by applicant): Axon degeneration occurs after nervous system injury and in neurodegenerative disease. Loss of axons and synapses results in neural circuit breakdown and is thought to be a primary factor driving functional loss in patients with neurological disorders. Despite its widespread importance in disease, remarkably little is known about the molecular mechanisms driving axon degeneration in any context. Studies of axon degeneration after axotomy (i.e. Wallerian degeneration) have proven an extremely useful approach to elucidate fundamental cellular events driving axon auto-destruction. For example, previous work on the mouse Wallerian degeneration slow molecule (WldS) revealed- surprisingly-that under certain conditions distal severed axon fibers can survive and remain functionally intact for remarkably long periods of time (i.e. weeks after axotomy) in the absence of a cell body. The long-term survival observed in WldS expressing axons raised the intriguing possibility that axon degeneration might be an active process of axon auto-destruction, akin to apoptotic cell death. In our first funding cycle we developed the first Drosophila models for Wallerian degeneration and demonstrated that severed fly axons undergo Wallerian degeneration that can be potently suppressed by the mouse WldS molecule. These data indicated the molecular mechanisms of Wallerian degeneration are an ancient, and conserved feature of neuronal cell types. Inspired by WldS we performed the first forward genetic screen for Drosophila mutations that suppressed Wallerian degeneration. Strikingly, we found that loss of the kinase adaptor molecule dSarm (sterile alpha/Armadillo/Toll-Interleukin receptor homology domain protein) suppressed Wallerian degeneration for the lifespan of the fly (>3 weeks). We also made the exciting discovery that this pathway was functionally conserved in mammals: Sarm1-/- mice exhibited robust suppression of Wallerian degeneration both in vivo and in vitro. This data identifies dSarm/Sarm1 as a conserved "axon death" gene, whose endogenous function is to promote axon degeneration after axotomy. In Aims 1 and 2 of this proposal we will use Drosophila to study the cellular and molecular mechanisms by which dSarm promotes axonal degeneration. In Aim 3 we will characterize a collection of novel Drosophila mutants that we have recently isolated that also potently suppress axon death like dsarm. These studies are at the heart of our long-term, comprehensive effort to understand how axons destroy themselves after injury. We expect our findings to have a major impact on our understanding of axon degeneration after injury or in human disease, and the novel molecules we identify will be excellent candidates for therapeutic intervention in human neurological disorders involving axonal and synaptic loss.