Vulnerability of Aging White Matter to Ischemia

摘要 中风是导致死亡和残疾的主要原因，中风的风险随着年龄的增长而增加。其作用机制 导致卒中后缺血后损伤的机制尚不完全清楚，因此大多数临床上 到目前为止，进行的中风疗法试验都失败了。没有考虑到白质(WM)损伤是一种 成功的中风治疗发展的关键差距。由于WM损伤的机制不同于 灰质和随着年龄的变化，理想的中风治疗必须不仅针对神经元和 跨年龄的轴突保护，也必须在损伤后应用时恢复功能。我们的一个重要的 上一个供资周期的研究成果表明，第一类人类发展援助中心的激活有助于 缺血时的兴奋性毒性，并通过损害 线粒体的结构和功能。应用I类HDAC抑制促进轴突功能恢复 青年和老年西医缺血前后的作用机制不明。我们目前的提案重点是 抑制I类HDAC对青年和老年西医脑缺血后保护作用机制的研究 虽然人们对这种保护现象背后的基因调控机制知之甚少，但一种 影响细胞存活的HDACs和miRNAs水平之间出现了有趣的相互关系 中风后。在缺血调节的miRNAs中，miR-331被预测为靶向I类HDAC。缺血 上调年轻和老年西医的第I类HDAC水平。我们的初步发现显示，脑缺血导致 MiR-331水平降低伴随着HDAC表达的增加和HDAC抑制的上调 MIR-331高于控制水平。因此，miR-331模拟会抑制HDAC水平，这表明 第I类HDAC和MIR-331之间的相互调节。此外，WM缺血可激活一氧化氮 合酶(NOS)，通过线粒体功能障碍导致氧化损伤，以及I类HDAC抑制 减弱一氧化氮合酶活性。鉴于这些信息，我们建议进一步扩大这些研究，通过测试我们的 一种新的假说：I类HDAC激活通过增加 氧化应激，线粒体功能受损，下调miR-331的神经胶质表达。 我们的总体目标是确定I类HDAC是直接行动还是招募NOS或与miR-331交互以 对青年和老年西医造成缺血后损伤。电生理、生化和小鼠遗传学研究 将使用体外和体内方法来测试以下特定目标：AIM 1旨在 调查I类HDAC激活是否以特定于年龄、特定细胞和特定异构体的方式招募一氧化氮合酶；目标2 旨在确定I类HDAC激活是否直接介导线粒体损伤 Aim 3的设计目的是确定I类HDAC是否与miR-331相互作用以调节 缺血性西医损伤。总体而言，本项目将揭示I类HDAC活动在WM缺血中的作用 以帮助设计新的治疗方法，将患者的缺血后损伤降至最低。

Abstract Stroke is a leading cause of death and disability and the risk for stroke increases with age. The mechanisms that contribute to post-ischemic injury after stroke are not completely understood, and as a result most clinical trials conducted to date for stroke therapeutics have failed. Failure to consider white matter (WM) injury is a critical gap in the development of successful stroke therapy. As mechanisms of WM injury differ from those in gray matter and change with age, an ideal stroke therapeutic must not only be directed towards neuronal and axonal protection across age, but also must restore function when applied after injury. One of our significant research achievements during the previous funding cycle established that Class I HDAC activation contributes to excitotoxicity during ischemia and contributes to oxidative injury during the post-ischemic period by impairing mitochondrial structure and function. Class I HDAC inhibition promotes axon function recovery when applied before or after ischemia in young and aging WM through unknown mechanisms. Our current proposal focuses on the mechanisms of post-ischemic protection conferred by Class I HDAC inhibition in young and aging WM. While little is known about the gene regulatory mechanisms underlying this protective phenomenon, an intriguing reciprocal relationship has emerged between levels of HDACs and miRNAs affecting cellular survival following stroke. Among ischemia-regulated miRNAs, miR-331 is predicted to target Class I HDACs. Ischemia up-regulates Class I HDAC levels in young and aging WM. Our preliminary findings show that ischemia led to decreased levels of miR-331 concomitant with increased HDAC expression and HDAC inhibition upregulated miR-331 above control levels. Consequently, an miR-331 mimic suppresses HDAC levels, indicating a reciprocal regulation between Class I HDACs and miR-331. Furthermore, WM ischemia activates nitric oxide synthase (NOS), leading to oxidative injury via mitochondrial dysfunction, and Class I HDAC inhibition attenuates NOS activity. In light of this information, we propose to further extend these studies by testing our novel hypothesis that Class I HDAC activation mediates WM ischemic injury by contributing to increased oxidative stress, impairing mitochondrial function, and down-regulating glial expression of miR-331. Our overall goal is to determine whether Class I HDACs act directly or recruit NOS or interact with miR-331 to exert post-ischemic injury in young and aging WM. Electrophysiological, biochemical, and mouse genetic in vitro and in vivo approaches will be employed to test the following Specific Aims: Aim 1 is designed to investigate whether Class I HDAC activation recruits NOS in an age-, cell-, and isoform-specific manner; Aim 2 is designed to determine whether Class I HDAC activation directly mediates mitochondrial injury during ischemia; and Aim 3 is designed to establish whether Class I HDACs interact with miR-331 to mediate ischemic WM injury. Overall, the present project will unravel the role of Class I HDAC activity in WM ischemic injury in order to help in the design of novel therapies to minimize post-ischemic injury in patients.