NO DAMAGE TO FOLATE CYCLE IN THE CENTRAL NERVOUS SYSTEM

描述（由申请人提供）：流行病学数据表明，单碳代谢的叶酸途径的成分在老年人中受到损害，在痴呆症（如阿尔茨海默病，AD）或运动神经元疾病（如肌萎缩侧索硬化症，ALS）的情况下更是如此。此外，叶酸途径酶的罕见先天性缺陷不可避免地导致神经系统疾病。目前还没有找到解释为什么老年人或神经系统疾病患者的叶酸周期受损的解释。我们的实验室已经记录了AD大脑和ALS动物模型中蛋白质氧化的模式，这表明叶酸周期损伤的机制。我们假设在衰老的中枢神经系统中内源性产生的活性氮物种（RNS）损伤叶酸通路的关键酶，特别是维生素b12依赖的蛋氨酸合成酶（MS），导致神经系统疾病。这一假设的推论是，旨在增强叶酸循环功能的营养补充策略，特别是在MS酶水平上，应该减轻某些类型的中枢神经系统退化。我们试图在五个具体目标中开始批判性地测试这些想法，其目标如下：(1)确定阿尔茨海默病大脑中已知不同RNS应激区域的叶酸循环酶水平和活性。(2)确定在公认的家族性ALS动物模型（即G93A-SOD1转基因小鼠，其经历与蛋白质氧化和氮化反应相应的运动神经元退化）中叶酸循环酶水平和活性是否降低，以及在该动物中营养补充叶酸加维生素B12（钴胺素）类似物是否减轻疾病。(3)确定叶酸单独或联合钴胺素类似物是否能保护星形胶质细胞或神经元在一氧化氮直接刺激下的叶酸循环完整性（NO）。(4)确定NO是否仅通过形成亚硝基钴胺素复合物或通过产生次级碳中心自由基和氧自由基使MS失活，以及该过程是否直接导致MS全酶功能丧失。

DESCRIPTION (provided by applicant): Epidemiological data indicates that components of the folic acid pathway of one-carbon metabolism are compromised in aged humans, and more so in cases of dementia (such as Alzheimer's disease, AD) or motor neuron disease (such as amyotrophic lateral sclerosis, ALS). Moreover, rare congenital defects in folate pathway enzymes inevitably precipitate neurological disease. No explanations have been found to explain why the folate cycle is impaired in the aged individuals or those with neurological disease. Our laboratory has documented a pattern of protein oxidation in AD brain and in an animal model for ALS that suggests a mechanism for folate cycle impairment. We hypothesize that reactive nitrogen species (RNS) generated endogenously within the aging CNS damage key enzymes of the folate pathway, particularly the vitamin B12-dependent methionine synthase (MS), contributing to neurological disease. The corollary to this hypothesis is that nutritional supplementation strategies aimed at bolstering function of the folate cycle, particularly at the level of the MS enzyme, should mitigate some types of CNS degenerating. We seek to begin critically testing these ideas in five specific aims whose goals are as follows: (1) Determine folate cycle enzyme levels and activities in regions of the AD brain known to differentially experience RNS stress. (2) Determine whether folate cycle enzyme levels and activities are reduced in an accepted animal model for familial ALS (namely the G93A-SOD1 transgenic mouse, which experiences motor neuron degeneration commensurate with protein oxidation and nitration) and whether disease in this animal is mitigated by nutritional supplementation with folic acid plus vitamin B12 (cobalamin) analogs. (3) Determine whether folic acid, alone or in combination with cobalamin analogs, protects the folate cycle integrity in astrocytes or neurons challenged directly with nitric oxide (NO). (4) Determine whether NO inactivates MS solely by formation of a nitrosyl-cobalamin complex or through generation of secondary carbon-centered and oxyradicals and whether this process directly precipitates loss of function in the MS holoenzyme.