Roles of reticulon proteins in neurodegenerative disorders

 描述(申请人提供)：随着人类寿命的延长，保持老年人的生活质量变得越来越重要。衰老是一种危险因素 阿尔茨海默病(AD)，其特点是脑内有两个典型的病理特征：细胞外神经炎斑块和神经元内神经原纤维缠结。神经性斑块是聚集的β-淀粉样多肽的沉积，在AD脑中通常被营养不良的神经突起和反应性神经胶质细胞包围。在这一应用中，我们旨在研究网状蛋白3(RTN3)在调节这些病理特征的形成中的作用。RTN3是一种神经细胞蛋白，属于网状蛋白家族，在进化过程中高度保守。利用酿酒酵母模型进行的遗传学研究表明，RTN的原型功能是塑造管状内质网(ER)结构。缺乏RTN3的小鼠表现出以下特征：1)对Aü生成至关重要的BACE1的蛋白水平显著升高；2)tau的磷酸化显著增加，过度磷酸化的tau与形成螺旋缠绕的细丝和神经元内缠结联系在一起。另一方面，RTN3的过度表达导致RTN3的聚集，特别是在海马区，这与RTN3免疫反应性营养不良神经元(RIDN)的形成有关。RIDN通常存在于AD或老化大脑中淀粉样蛋白沉积的周围。RIDN的存在，我们已经证明是不容易可逆的，损害学习和记忆，如各种测试，包括电生理记录，行为测试和形态确认。在寻找RTN3相互作用蛋白的过程中，我们发现内质网小管蛋白REEP2与RTN3特异地相互作用，并与RTN3共存于RIDNS中，提示小管ER在衰老和AD脑中可能存在功能障碍。因此，从RTN3单体蛋白到RTN3聚集蛋白的转变会导致与RTN3低表达和高表达相关的负面影响。有鉴于此，我们建议进一步扩展我们的研究，在这一新的应用中检验我们的新假设，即衰老通过改变RTN3单体和聚集形式之间的平衡，导致BACE1表达的变化，tau的过度磷酸化，以及RIDN的积累，导致肾小管内质网功能障碍。将使用生化和小鼠遗传学方法来测试以下三个具体目标。我们的前两个目标集中在RTN3基因缺失小鼠身上看到的新结果。目的1研究RTN3缺陷对BACE1基因表达的影响。目的2旨在确定RTN3缺乏如何增加tau的磷酸化。由于我们假设衰老诱导RTN3表达和肾小管内质网功能障碍，目标3旨在探讨肾小管内质网功能障碍的潜在贡献如何导致RTN3聚集和RIDN的形成。从这一应用中获得的知识将有助于开发治疗药物，这些药物将抑制营养不良轴突的形成和认知能力下降，和/或预防AD患者的小管内质网功能障碍。

 DESCRIPTION (provided by applicant): With the lifespan of humans increasing, preserving the quality of life among elderly people becomes increasingly important. Aging is a risk factor for Alzheimer's disease (AD), which is characterized by two typical pathological features in the brain: extracellular neuritic plaques and intraneuronal neurofibrillary tangles. Neuritic plaques are deposits of aggregated ß-amyloid peptides (Aß), which are often surrounded by dystrophic neurites and reactive glial cells in AD brains. In this application, we aim to investigate the roleof reticulon 3 (RTN3) in regulating the formation of these pathological features. RTN3 is a neuronal protein belonging to the reticulon family, which is highly conserved through evolution. Genetic studies using a S. cerevisiae model suggest that the prototypical function of RTN is to shape tubular endoplasmic reticulum (ER) structure. Mice deficient in RTN3 show the following features: 1) protein levels of BACE1, an enzyme critical for Aß generation, are significantly elevated; and 2) phosphorylation of tau is significantly increased, and the hyper- phosphorylated tau is linked to form helically wound filaments and intraneuronal tangles. On the other hand, overexpression of RTN3 results in RTN3 aggregation, particularly in the hippocampus, which correlates with the formation of RTN3-immunoreactive dystrophic neurites (RIDNs). RIDNs are commonly present surrounding amyloid deposits in AD or aging brains. The presence of RIDNs, which we have demonstrated is not readily reversible, impairs learning and memory as shown by various assays, including electrophysiological recordings, behavioral tests and morphological confirmations. In searching for RTN3-interacting proteins, we discovered that the ER tubular protein REEP2 specifically interacted with RTN3 and co-existed with RTN3 in RIDNs, suggesting a potential dysfunction of tubular ER in aging and AD brains. Thus, a shift from RTN3 monomeric protein to RTN3 aggregation results in negative effects associated with both under- and overexpression of RTN3. In light of this knowledge, we propose to further extend our study by testing our novel hypothesis in this renewal application that aging induces tubular ER dysfunction via shifting the balance between RTN3 monomer and aggregated forms, leading to changes in BACE1 expression, tau hyper- phosphorylation, and the accumulation of RIDNs. Biochemical and mouse genetic approaches will be employed to test the following three Specific Aims. Our first two aims focus on the novel results seen in RTN3-null mice. Aim 1 is designed to investigate the effects of RTN3 deficiency on BACE1 expression. Aim 2 is designed to determine how RTN3 deficiency increases tau phosphorylation. Since we postulate that aging induces RTN3 expression and tubular ER dysfunction, Aim 3 is designed to explore how the potential contribution of the dysfunctional tubular ER structure leads to the formation of RTN3 aggregation and RIDNs. The knowledge gained from this application will be useful for the development of therapeutic agents that will inhibit dystrophic neurite formation and cognitive decline and/or prevent tubular ER dysfunction in AD.