Microglial Kynurenine Pathway and Selective Neuronal Vulnerability

亨廷顿氏病（HD）和阿尔茨海默氏病（AD）是特征在于 通过错误折叠蛋白质的积累。可悲的是，多年的研究机制， 神经变性未能产生阻止或逆转这些疾病的有效疗法。我们 最近完成了一项对S.酿酒酵母单基因缺失菌株， 犬尿氨酸3-单加氧酶（KMO），色氨酸的犬尿氨酸途径（KP）中的酶 降解，作为突变亨廷顿蛋白（HTT）毒性的有效抑制剂。两种神经毒素 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 在早期HD中的新皮质;在三种小鼠模型中存在QUIN和/或3-HK的类似增加 HD的。我们发现，在小鼠海马和内嗅皮层中，QUIN的脑水平增加， AD模型，但不在纹状体或其他未受影响的大脑区域。QUIN和3-HK长期以来一直是 假设与神经系统疾病（包括HD和AD）的病理生理学相关。的确， 纹状体内注射QUIN和3-HK引起类似于HD中发现的纹状体病变， 可能是由N-甲基-D-天冬氨酸（NMDA）受体过度刺激 （兴奋性毒性）和自由基形成。在大鼠中亚慢性脑室内输注QUIN产生 生化变化和记忆缺陷可能与AD患者中发现的相似。在我们 建议，我们提供数据显示用Ro 61-8048治疗HD小鼠模型，Ro 61-8048是一种高亲和力， 口服生物可利用的KMO小分子抑制剂，改善多项行为结局指标 尽管该化合物表现出边缘渗透穿过血脑屏障（BBB）的事实。我们 最近产生了一系列新的脑穿透KMO抑制剂和小鼠携带条件无效 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是否 KP和兴奋毒性在HD和AD小鼠模型中起重要作用。以下具体目标将 开始检验小胶质细胞源性神经毒性KP代谢物增加的假设， 脑微环境的方式，有助于选择性神经元脆弱性的小鼠模型， HD和AD：AIM 1。为了确定小胶质细胞中KMO的遗传和药理学抑制是否改善 HD和AD小鼠模型中的行为和病理结果测量; AIM 2.识别 调节元件和信号转导通路介导突变亨廷顿蛋白（HTT）/淀粉样蛋白（β-蛋白 （一）|3）在小胶质细胞中诱导的KP活化; AIM 3.为了确定细胞机制， HD小鼠模型中离散脑微环境中毒性小胶质细胞KP代谢物的增加。在 总之，这些实验将确定KMO的药理学抑制是否是真正的 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.