Mitochondrial pore and synaptic stress in Alzheimer's disease

描述(申请人提供)：线粒体功能障碍和突触丢失是阿尔茨海默病的早期病理特征。最近的研究表明，AD中线粒体的改变是Abeta介导的突触病理的基础，观察表明：1)AD患者线粒体功能障碍与突触丢失显著相关；2)线粒体的保护减弱了Abeta诱导的突触变化。然而，Abeta诱导的线粒体功能障碍以及由此导致的突触损伤的机制尚未完全阐明。值得注意的是，神经元中的线粒体在性质上是不同的。位于突触的神经元线粒体的一个亚群，即突触线粒体，由于其物理上与突触的接近，在维持突触活动/功能方面发挥着关键作用。因此，阐明Abeta增强突触线粒体功能障碍的机制对于加深对AD发病机制中突触病理的认识具有重要意义。在初步研究中，我们已经证明在Abeta环境中，过度表达Abeta的转基因AD小鼠突触线粒体对亲环素D(CypD)介导的线粒体通透性转换孔(MPTP)的倾向增加。伴随着这些变化，Abeta诱导的突触线粒体出现了呼吸缺陷。此外，Abeta处理导致培养的海马神经元轴突线粒体密度降低和突触丢失。相比之下，这些对突触线粒体和突触改变的不利影响可以通过阻断cypD的基因缺失而显著减弱。因此，我提出了一个假设，即cypD介导的MPTP是Abeta诱导的突触线粒体功能障碍和突触改变的潜在机制。为了解决这一概念，我将利用AD小鼠模型(APP小鼠)和一种新的基因操纵的转基因小鼠模型(遗传cypD缺陷的APP小鼠)以及cypD缺乏的海马神经元培养来进行本申请中提出的研究。本项目包含三个目标：1)。目的：研究cypD介导的MPTP对APP小鼠突触线粒体功能的影响；2)研究cypD介导的MPTP对Aβ环境下突触(轴突)线粒体动力学和运动性的影响；3)确定cypD介导的突触线粒体功能障碍是否参与Aβ诱导的APP小鼠突触改变。本项目完成后，我将确定cypD介导的MPTP在Abeta诱导的突触线粒体功能障碍中的作用，以及cypD介导的MPTP对APP/Abeta高表达小鼠突触线粒体动力学和运动性、突触功能以及动物学习记忆能力的影响。这项研究的发现将对AD治疗新的治疗方法的发展产生积极的影响。这个项目也将作为我科学生涯的坚实基础，通过结合AD的突触线粒体功能障碍和突触改变来建立一个有别于我导师的研究方向。

DESCRIPTION (provided by applicant): Mitochondrial dysfunction and synaptic loss are early pathological features of Alzheimer's disease. Recent studies indicate that mitochondrial alterations in AD underlie Abeta-mediated synaptic pathology as evidenced by the observations: 1) significant correlation of mitochondrial dysfunction with synaptic loss in AD; and 2) the protection of mitochondria attenuates Abeta -induced synaptic changes. However, the mechanisms of Abeta -induced mitochondrial dysfunction and the consequent synaptic damages have not fully delineated. Notably, mitochondria in neurons are heterogeneous in their properties. A sub-group of neuronal mitochondria locating at synapses or namely synaptic mitochondria play a pivotal role in maintaining synaptic activity/function due to their physical proximity to synapses. Thus, to elucidate the mechanisms underlying Abeta -potentiated synaptic mitochondrial dysfunction is of great significance to deepen our understanding of the synaptic pathology in the pathogenesis of the AD. In the preliminary studies, we have demonstrated that synaptic mitochondria undergo increased propensity towards cyclophilin D (cypD)-mediated mitochondrial permeability transition pore (mPTP) in the Abeta milieu, transgenic AD mice overexpressing Abeta. Along with these changes, Abeta -insulted synaptic mitochondria underwent respiration defects. In addition, Abeta treatment resulted in decreased axonal mitochondrial density and the loss of synapses in cultured hippocampal neurons. As a contrast, these detrimental effects on synaptic mitochondrial and synaptic alterations were significantly attenuated by the blockade of cypD through genetic depletion of cypD. Thus, I have formulated a hypothesis that cypD-mediated mPTP is a potential mechanism underlying Abeta-induced synaptic mitochondrial dysfunction and synaptic alterations. To address this concept, I will utilize an AD mouse model (APP mice) and a novel genetically manipulated transgenic mouse model (genetic cypD-deficient APP mice) as well as cypD-deficiency hippocampal neuron cultures for the studies proposed in this application. This project contains three aims: 1). to determine the impact of cypD-mediated mPTP on synaptic mitochondrial function in APP mice; 2) to determine the impact of cypD-mediated mPTP on synaptic (axonal) mitochondrial dynamics and motility in Abeta milieus; and 3) to determine whether cypD-mediated synaptic mitochondrial dysfunction contributes to Abeta -induced synaptic alterations in APP mice. Upon the completion of this project, I will determine the involvement of cypD mediated mPTP in Abeta induced synaptic mitochondrial dysfunction, and the impact of cypD mediated mPTP on synaptic mitochondrial dynamics and motility, and synaptic function as well as animal learning/memory ability in APP/ Abeta overexpressing mice. Finding derived from this study will have positive impact on the development of new therapeutic approaches for AD treatment. This project will also serve as a firm foundation of my scientific career to establish a research direction distinct from my mentors' by the combination of synaptic mitochondrial dysfunction and synaptic alterations in AD.