Vulnerability of Aging White Matter to Ischemia

描述（由申请人提供）：缺血性中风的风险随着年龄的增长而急剧增加。虽然这归因于血管因素，但衰老可能导致中枢神经系统（CNS）本身对缺血性损伤的易感性增加。脑白质（WM）在大多数中风中受损，轴突损伤和功能障碍是导致许多与临床缺陷相关的残疾的原因。我们认为，未能保护WM是导致卒中治疗缺乏成功的主要原因之一。长期目标是确定在缺血性损伤模型中，衰老WM功能是否可以通过减弱氧化损伤和通过阻断年龄特异性兴奋毒性通路来保持线粒体完整性来改善。最近，我们报道了老年动物的中枢神经系统WM本质上更容易受到缺血性损伤。在年轻WM中，缺血性损伤涉及能量消耗（离子途径）、谷氨酸过度释放（兴奋毒性）、活性氧的产生和氧化应激（氧化途径）的顺序。视神经中AMPA或kainate受体的过度激活而胼胝体中Ca2+可渗透AMPA受体的激活介导了损伤，提示年轻WM缺血性损伤的区域特异性机制。在老年WM中，损伤是由Ca2+非依赖性兴奋性毒性和谷氨酸转运体GLT1上调相关的更早和更强的谷氨酸释放介导的。我们的初步研究表明，兴奋性毒性导致与轴突线粒体动力学改变相关的衰老WM氧化应激。目前尚不清楚以年龄特异性方式操纵兴奋性毒性是否可以挽救轴突功能，减少氧化应激和维持线粒体动力学。本研究结合电生理学、免疫组织化学、共聚焦成像、生化测量和转基因小鼠来验证兴奋性毒性的增加是由于谷氨酸的多个释放位点和释放机制，以细胞特异性的方式激活年龄特异性谷氨酸受体，这是通过破坏线粒体动力学和加重氧化损伤来增加衰老WM对缺血的易感性的原因。这一提议的三个具体目的是为了更好地了解衰老WM缺血期间兴奋毒性与氧化损伤和线粒体功能障碍之间的细胞位点和机制。急性分离的视神经和胼胝体切片将用于确定WM功能和结构的定量测量。我们的重点是为中风和其他涉及WM的神经退行性疾病确定合适的年龄特异性治疗靶点。

DESCRIPTION (provided by applicant): The risk for ischemic stroke increases drastically with age. Although this has been attributed to vascular factors, aging could result in changes such that the central nervous system (CNS) itself has an increased vulnerability to ischemic injury. White matter (WM) is injured in most strokes and axonal injury and dysfunction are responsible for much of the disability associated with clinical deficits. We suggest that failure to protect WM is one of the primary reasons contributing to the lack of successful stroke therapy. The long term goal is to determine if aging WM function can be improved in a model of ischemic injury by attenuating oxidative injury and by preserving mitochondrial integrity through blockade of age-specific excitotoxic pathways. Recently, we reported that CNS WM is intrinsically more vulnerable to ischemic injury in older animals. In young WM, the damage from ischemic injury involves the sequence of energy depletion (ionic pathway), excessive glutamate release (excitotoxicity), generation of reactive oxygen species and oxidative stress (oxidative pathway). Overactivation of either AMPA or kainate receptors in optic nerve but activation of Ca2+permeable AMPA receptors in corpus callosum mediate injury, suggesting a region specific mechanism of ischemic injury in young WM. In older WM, the injury is mediated by Ca2+independent excitotoxicity and an earlier and more robust glutamate release associated with upregulation of glutamate transporter GLT1. Our preliminary studies suggest that excitotoxicity leads to oxidative stress in aging WM associated with alterations in axonal mitochondrial dynamics. It is not known whether manipulating excitotoxicity in an age-specific manner can rescue axon function, reducing oxidative stress and maintaining mitochondrial dynamics. This proposal combines electrophysiology, immunohistochemistry, confocal imaging, biochemical measurements, and genetically modified mice to test the hypothesis that increased excitotoxicity is due to multiple release sites and release mechanisms of glutamate, activating age-specific glutamate receptors in a cell-specific manner, and that, this is responsible for increased vulnerability of aging WM to ischemia by disrupting mitochondrial dynamics and aggravating oxidative injury. The three specific aims of this proposal are designed to better understand the cellular sites and mechanisms that link excitotoxicity to oxidative injury and mitochondrial dysfunction during ischemia in aging WM. Acutely isolated optic nerve and corpus callosum slices will be used to ascertain quantitative measurements of WM function and structure. Our focus is to define appropriate age-specific therapeutic targets for stroke and other neurodegenerative diseases involving WM.