Molecular Mechanisms of Axon Degeneration

描述(申请人提供)：轴突变性发生在神经系统损伤后和神经退行性疾病中。轴突和突触的丢失会导致神经回路的崩溃，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。轴突切断后轴突变性的研究(即沃勒变性)已被证明是阐明驱动轴突自身破坏的基本细胞事件的一种非常有用的方法。例如，先前对小鼠沃勒变性慢分子(WldS)的研究发现--令人惊讶的是--在某些条件下，远端切断的轴突纤维可以在没有细胞体的情况下存活很长一段时间并保持功能完整(即轴突切断后数周)。在表达轴突的WldS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活跃过程，类似于细胞凋亡。在我们的第一个资金周期中，我们开发了第一个果蝇沃勒变性模型，并证明了切断的苍蝇轴突经历沃勒变性，这可以被小鼠WldS分子有效地抑制。这些数据表明沃勒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WldS的启发，我们对抑制沃勒变性的果蝇突变进行了第一次正向基因筛查。令人惊讶的是，我们发现，失去激酶适配器分子DSARM(不育的阿尔法/Armadillo/Toll-IL受体同源结构域蛋白)可以在果蝇的寿命(&gt；3周)内抑制沃勒变性。我们还发现，在哺乳动物中，这一途径在功能上是保守的：Sarm1-/-小鼠在体内和体外都表现出对沃勒变性的强烈抑制。该数据表明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断后的轴突变性。在这项提案的目标1和2中，我们将使用果蝇来研究DSARM促进轴突退化的细胞和分子机制。在目标3中，我们将描述我们最近分离的一系列新的果蝇突变体，这些突变体也可以有效地抑制轴突死亡，如DSARM。这些研究是我们长期、全面的努力的核心，目的是了解轴突在受伤后如何自我摧毁。我们预计我们的发现将对我们对损伤后或人类疾病中轴突变性的理解产生重大影响，我们识别的新分子将是治疗涉及轴突和突触丢失的人类神经疾病的极佳候选分子。

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.