Microglial Kynurenine Pathway and Selective Neuronal Vulnerability

亨廷顿病(HD)和阿尔茨海默病(AD)是以神经退行性疾病为特征的疾病 通过错误折叠的蛋白质的积累。可悲的是，多年来对这一机制的研究 神经退行性变未能产生有效的治疗方法来阻止或逆转这些疾病。我们 最近完成了对酿酒酵母的基因组筛选，发现了单基因缺失菌株 犬尿氨酸3-单加氧酶(KMO)，色氨酸犬尿氨酸途径(KP)中的一种酶 降解，作为突变亨廷顿蛋白(HTT)毒性的有效抑制者。脑内两种神经毒性物质的水平 KP中的代谢物喹啉酸(Quin)和3-羟基犬尿氨酸(3-HK)在纹状体中增加 和新皮质在早期HD；Quin和/或3-HK在三个小鼠模型中出现类似的增加 高清。我们发现，在小鼠的海马体和内嗅觉皮质，大脑中Quin的水平增加。 阿尔茨海默病模型，但不在纹状体或其他未受影响的脑区。奎恩和3-HK长期以来一直 假设与包括HD和AD在内的神经系统疾病的病理生理学有关。的确， Quin和3-HK联合纹状体内注射可引起与HD相似的纹状体损害 可能是通过A/-甲基D-天冬氨酸(NMDA)受体过度刺激的组合而介导的 (兴奋性毒性)和自由基的形成。奎宁在大鼠脑室内亚慢性注入产生 生化变化和记忆缺陷可能与AD患者的相似之处。在我们的 建议，我们提供数据显示用高亲和力、高亲和力、 口服生物利用度小分子KMO抑制剂，改善多项行为结果指标 尽管这种化合物显示出对血脑屏障(BBB)的边际穿透。我们 最近产生了一系列新的脑穿透KMO抑制剂和携带条件无效的小鼠 KMO等位基因。有了这些工具，我们第一次能够严格测试小胶质细胞 KP和兴奋性毒性在HD和AD小鼠模型中起重要作用。以下具体目标将 开始测试小胶质细胞衍生的神经毒性KP代谢物增加在不同的 在小鼠模型中，脑微环境导致选择性神经元脆弱性 HD和AD：目的1.确定KMO对小胶质细胞的遗传和药物抑制是否改善 HD和AD小鼠模型的行为学和病理学结果指标；目的2.确定 亨廷顿蛋白(HTT)/淀粉样蛋白(3-蛋白)突变的调控元件和信号转导途径 (A|3)诱导小胶质细胞的KP激活；目的3.确定介导的细胞机制 HD小鼠模型离散脑微环境中有毒小胶质细胞KP代谢物的增加。在……里面 总之，这些实验将确定KMO的药理抑制是否是真正的 治疗HD和AD的治疗方法。

Huntington's Disease (HD) and Alzheimer's disease (AD) are neurodegenerative disorders characterized by the accumulation of misfolded proteins. Sadly, many years of research into the mechanisms of neurodegeneration have failed to produce effective therapies that halt or reverse these diseases. We recently completed a genomic screen in S. cerevisiae with single gene deletion strains that identified kynurenine 3-monooxygenase (KMO), an enzyme in the kynurenine pathway (KP) of tryptophan degradation, as a potent suppressor of mutant huntingtin (htt) toxicity. The brain levels of two neurotoxic metabolites in the KP, quinolinic acid (QUIN) and 3-hydroxykynurenine (3-HK), are increased in the striatum and neocortex in early grade HD; similar increases in QUIN and/or 3-HK are present in three mouse models of HD. We show that brain levels of QUIN are increased in the hippocampus and entorhinal cortex of mouse models of AD, but not in the striatum or other unaffected brain regions. QUIN and 3-HK have long been hypothetically linked to the pathophysiology of neurological diseases including HD and AD. Indeed, intrastriatal injection of QUIN together with 3-HK causes striatal lesions resembling those found in HD that may be mediated by the combination of A/-methyl D-aspartate (NMDA) receptor over-stimulation (excitotoxicity) and free radical formation. Subchronic intraventricular infusion of QUIN in rats produces biochemical changes and memory deficits that may share similarities with those found in AD patients. In our proposal, we present data showing that treatment of a mouse model of HD with Ro 61-8048, a high-affinity, orally bioavailable, small-molecule inhibitor of KMO, improved multiple behavioral outcome measures despite the fact that this compound displayed marginal penetration across the blood brain barrier (BBB). We recently generated a novel series of brain penetrating KMO inhibitors and mice that carry a conditional null allele of Kmo. With these tools in hand, we are for the first time in a position to test rigorously if the microglial KP and excitotoxicity play important roles in mouse models of HD and AD. The following specific aims will begin to test the hypothesis that microglial derived increases in neurotoxic KP metabolites occur in distinct brain microenvironments in a manner that contributes to selective neuronal vulnerability in mouse models of HD and AD: AIM 1. To determine if genetic and pharmacological inhibition of KMO in microglia improves behavioral and pathological outcome measures in mouse models of HD and AD; AIM 2. To identify the regulatory elements and signal transduction pathways that mediate mutant huntingtin (htt)/amyloid (3-protein (A|3)-induced KP activation in microglia; AIM 3. To determine the cellular mechanisms that mediate increases in toxic microglial KP metabolites in discrete brain microenvironments in a mouse model of HD. In summary, these experiments will determine if pharmacological inhibition of KMO may be a bona fide therapeutic approach to treating HD and AD.