White matter damage in Alzheimer?s disease: New cellular targets and mechanisms

描述(申请人提供)：这项“探索性”申请的目标是提供对淀粉样蛋白(A？)易感性的新的机械理解，以及A？通过何种途径破坏在维持正常髓鞘形成中至关重要的那些细胞的功能。我们最近发现了一种新的调控途径，它提供了氧化变化和细胞信号控制之间的顺序联系。在这一途径中，细胞暴露于具有促氧化剂活性的各种化学物质所引起的氧化状态的增加会导致Fyn激酶的激活。这导致了c-Cbl的激活，c-Cbl是Fyn的靶标，是一种E3泛素连接酶。C-Cb1的激活导致其靶蛋白的泛素化，其中包括受体酪氨酸激酶(RTK)的一个子集。由于它们与c-Cbl的相互作用，这些RKT的降解被增强，导致下游信号的抑制。这种降解的结果是，ERK1/2和Akt等信号介质的下游激活受到抑制。正如人们可以从这种效应中预测的那样，细胞分裂受到抑制，细胞生存也可能受到损害。我们建议现在验证Fyn/c-Cbl通路的激活在淀粉样蛋白(A？)毒性中起重要作用的假设。由于髓鞘损伤在AD病理中的重要性，实验建议重点关注A？肽对少突胶质细胞及其前体细胞的影响。此外，由于Fyn/c-Cbl假说还预测，暴露在亚致死浓度的促氧化剂刺激下将抑制细胞分裂，我们将进一步检验Aβ肽对少突胶质细胞具有细胞毒性的假说，但也抑制产生它们的祖细胞的分裂。如果这一预测是正确的，这将表明A既破坏髓鞘形成细胞，又抑制修复所需的细胞分裂。因此，这项研究提出了一种新的分子途径，Aβ通过这种途径影响细胞功能。已有多项研究表明Fyn在AD的发病机制中起重要作用。我们的研究将为Fyn激活可能扰乱AD细胞功能的机制提供新的见解。目的1验证一种假说，即少突胶质细胞及其前体细胞暴露于A？可导致氧化还原/Fyn/c-Cbl途径激活，c-Cbl靶向RTK降解，并选择性抑制这些RTK下游信号事件。这与抑制祖细胞分裂(亚致死剂量)和诱导较高浓度的祖细胞和/或少突胶质细胞死亡有关，具体取决于A的类型和浓度以及所检测的细胞类型。目的2验证Fyn/c-Cbl通路激活在A？介导的抑制少突胶质细胞系细胞分裂和/或诱导细胞死亡中起重要作用的假说。目的3验证抗氧化剂和营养因子抑制A介导的氧化还原/Fyn/c-Cbl途径激活的假说，从而为抗氧化剂在AD中的保护作用提供新的潜在作用部位。 公共卫生相关性：这项研究为淀粉样蛋白在阿尔茨海默病中导致中枢神经系统损伤的方式提供了新的见解。我们的研究确定了一种新的淀粉样蛋白扰乱细胞功能的分子途径，对这种疾病中有髓神经束的广泛损害的发病机制有了新的见解，并对抗氧化治疗保护其免受淀粉样蛋白影响的方法有了新的理解。这项研究将有助于确定防止淀粉样蛋白毒性的新方法。

DESCRIPTION (provided by applicant): The goal of this "exploratory" application is to provide a novel mechanistic understanding of vulnerability to amyloid (A ¿) protein, and of the pathways through which A¿ disrupts function of those cells critical in maintenance of normal myelination. We have recently discovered a novel regulatory pathway that provides a sequential linkage between oxidative changes and control of cell signaling. In this pathway, increases in oxidative status caused by exposure of cells to chemically diverse substances with pro-oxidant activity cause activation of Fyn kinase. This leads to activation of c-Cbl, an E3 ubiquitin ligase that is a target of Fyn. Activation of c-Cbl leads to ubiquitylation of its target proteins, which include among them a subset of receptor tyrosine kinases (RTKs). As a result of their interaction with c-Cbl, degradation of these RKTs is enhanced, leading to a suppression of downstream signaling. As a consequence of this degradation, downstream activation of such signaling mediators as Erk1/2 and Akt are suppressed. As one would predict from such an effect, cell division is suppressed and cell survival may also be impaired. We propose to now test the hypothesis that activation of the Fyn/c-Cbl pathway plays an important role in amyloid (A¿) toxicity. The experiments proposed focus on the effects of A¿ peptides on oligodendrocytes and their progenitor cells, due to the importance of myelin damage in AD pathology. Moreover, as the Fyn/c- Cbl hypothesis also predicts that exposure to sublethal concentrations of pro-oxidant stimuli will suppress cell division, we will further test the hypothesis that A¿ peptides are cytotoxic for oligodendrocytes but also suppress division of the progenitors from which they are generated. If this prediction is correct, this would indicate that A¿ both damages myelin-forming cells and suppresses the cell division required for repair. This research thus proposes a new molecular pathway by which A¿ affects cell function. Several studies have previously suggested an important role of Fyn in the pathogenesis of AD. Our studies will provide novel insights into the mechanism by which Fyn activation may disrupt cellular function in AD. Aim 1 tests the hypothesis that exposure of oligodendrocytes and their progenitors to A¿ causes activation of the redox/Fyn/c-Cbl pathway, degradation of RTKs that are c-Cbl targets, and selective suppression of downstream signaling events from these RTKs. This is associated with, depending on the type and concentration of A¿ and the cell type examined, suppression of progenitor cell division (at sublethal doses) and induction of progenitor cell and/or oligodendrocyte death at higher concentrations. Aim 2 tests the hypothesis that activation of the Fyn/c-Cbl pathway is functionally important in A¿ -mediated suppression of cell division and/or induction of cell death in the oligodendrocyte lineage. Aim 3 tests the hypothesis that anti-oxidants and trophic factors that protect against toxic effects of A¿ suppress A¿ -mediated activation of the redox/Fyn/c-Cbl pathway, thus providing a novel potential site of action for the protective effects of anti-oxidants in AD. PUBLIC HEALTH RELEVANCE: This research provides novel insights into the means by which amyloid ¿ protein causes damage to the central nervous system in Alzheimer's disease. Our studies identify a novel molecular pathway by which amyloid ¿ protein disrupts cell function, new insights into the pathogenesis of the extensive damage to myelinated tracts in this disease, and a new understanding of means by which anti-oxidant therapy protects from the effects of amyloid ¿ protein. This research will help in identifying new means of protecting against amyloid ¿ toxicity.