PATHOGENESIS AND TREATMENT OF NEURODEGENERATIVE DISEASE

该项目旨在发现改善影响运动和认知功能的神经退行性疾病的医学治疗方法。目前正在探索开发姑息疗法和保护疗法的新方法。关于帕金森病的对症治疗，我们已经大大提高了我们对为什么标准治疗药物左旋多巴会随着疾病的进展而产生越来越多的并发症的理解。早期的实验室结果表明，由纹状体中棘神经元树突上表达的多巴胺能受体的慢性非生理刺激诱导的运动功能障碍与附近的多巴胺能受体敏感性的改变有关，包括N-甲基-D-天冬氨酸（NMDA）和α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）亚型。这些离子通道复合物的功能特性由其磷酸化状态调节。损伤大鼠黑质纹状体多巴胺系统可诱导帕金森病症状，并增加纹状体NMDA受体亚单位的酪氨酸和丝氨酸/苏氨酸磷酸化。纹状体内给予能够磷酸化这些亚基的激酶的某些抑制剂产生拟多巴胺运动反应。每天两次用左旋多巴治疗这些帕金森病大鼠诱导了人类运动并发症综合征的许多特征性特征，并进一步增加了NMDAR 2A和NMDAR 2B亚基上特定丝氨酸/苏氨酸和酪氨酸残基的磷酸化。同样，纹状体内施用某些丝氨酸和酪氨酸激酶的选择性抑制剂逆转了磷酸化变化，并减轻了与左旋多巴治疗相关的运动并发症。各种NMDA受体拮抗剂，包括一些非竞争性通道阻滞剂，在啮齿动物和灵长类动物模型中既有缓解作用，又有抑制作用，以逆转左旋多巴诱导的反应改变。类似地，我们的临床研究现已证明，包括金刚烷胺在内的几种NMDA拮抗剂在改善运动并发症以及帕金森症状方面具有实质性和显著有效性。最近在动物模型中的观察进一步表明，一些AMPA拮抗剂减轻而一些AMPA激动剂加重这些左旋多巴诱导的并发症。总之，这些结果为我们的观点提供了越来越多的支持，即某些多巴胺能受体的超敏性有助于人类左旋多巴相关运动并发症的发病机制以及帕金森症状的最初出现，并且抑制这些受体或其异常磷酸化可以大大减少运动残疾。目前正在启动对照的原理验证临床试验，以进一步探索AMPA和NMDAR 2B选择性拮抗剂的这一假设。针对人类神经退行性疾病的神经保护性治疗的研究越来越多地表明，NF-κ B信号转导级联的激活可能有助于纹状体GABA能、黑质多巴胺能和内侧前脑胆碱能神经元的凋亡性死亡。例如，在大鼠纹状体棘状神经元中，兴奋毒素诱导的程序性细胞死亡现在似乎涉及以下顺序：半胱天冬酶-3激活、IkB-alpha降解、NF κ B核翻译，随后增加c-Myc和p53表达。通过几种方法中的任何一种阻断NF-κ B的核转位都会减弱这些兴奋性毒性反应。在SY 5 Y神经元细胞系中，细胞质蛋白α-突触核蛋白的降解被发现主要是泛素-蛋白酶体介导的;此外，突触核蛋白的A53 T突变体（发生在帕金森病的家族形式中）的catalysis明显受损，从而有利于这种潜在的促凋亡蛋白的神经元内积累。在大鼠基底前脑神经元中，已经观察到p75（神经生长因子的低亲和力受体）的激活选择性地增强这些胆碱能神经元对兴奋性毒素以及淀粉样蛋白通过NFkB信号传导途径诱导的凋亡的脆弱性。这些趋同的研究结果对人类神经退行性疾病的保护性干预措施的发展的影响，目前正在积极说服。

This project seeks to discover improved medical treatments for neurodegenerative disorders affecting motor and cognitive function. Novel approaches to the development of both palliative and protective therapies are currently being explored. In relation to the symptomatic treatment of Parkinsons disease, we have significantly improved our understanding of why the standard therapeutic agent, levodopa, generates increasing complications as the disease advances. Earlier laboratory results indicated that motor dysfunction induced by the chronic nonphysiologic stimulation of dopaminergic receptors expressed on the dendrites of striatal medium spiny neurons is associated with alterations in the sensitivity of nearby glutamatergic receptors, including those of the N-methyl-D-aspartate (NMDA) and the a-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) subtypes. Functional characteristics of these ionotropic channel complexes are regulated by their phosphorylation state. Lesioning the nigrostriatal dopamine system of rats induces parkinsonian signs and increases the tyrosine as well as serine/threonine phosphorylation of striatal NMDA receptor subunits. The intrastriatal administration of certain inhibitors of kinases capable of phosphorylating these subunits produces adopaminomimetic motor response. Treating these parkinsonian rats twice daily with levodopa induces many of the characteristic features of the human motor complication syndrome and further increases the phosphorylation of specific serine/threonine and tyrosine residues on NMDAR2A and NMDAR2B subunits. Again, the intrastriatal administration of selective inhibitors of certain serine and tyrosine kinases reverses the phosphorylation changes and alleviates the motor complications associated with levodopa therapy. Various NMDA receptor antagonists, including some non-competitive channel blockers, act both palliatively and prophylactically in rodent and primate models to reverse the levodopa-induced response alterations. Similarly, our clinical studies have now demonstrated that several NMDA antagonists including amantadine are substantially and enduringly effective in ameliorating motor complications as well as parkinsonian symptoms. Recent observations in animal models further indicated that some AMPA antagonists alleviate while some AMPA agonists exacerbate these levodopa induced complications. Taken together, these results provide increasing support for our view that supersensitivity of certain glutamatergic receptors contributes to the pathogenesis of human levodopa-associated motor complications as well as to the initial appearance of parkinsonian symptoms and that inhibition of these receptors or of their aberrant phosphorylation can substantially reduce motor disability. Controlled proof-of-principle clinical trials to further explore this hypothesis with AMPA and NMDAR2B selective antagonists are now being initiated. Studies addressing the development of neuroprotective treatments for human neurodegenerative disease increasingly suggest that activation of the NF-kB signal transduction cascade may contribute to the apoptotic death striatal GABAergic, nigral dopaminergic, and medial forebrain cholinergic neurons. For example, in rat striatal spiny neurons, excitotoxin induced programmed cell death now appears to involve the following sequence: caspase-3 activation, IkB-alpha degradation, NFKB nuclear translation, followed by increased c-Myc and p53 expression. Blocking the nuclear translocation of NF-kB by any of several means attenuates these excitotoxic responses. In a SY5Y neuronal cell line, degradation of the cytoplasmic protein alpha-synuclein was found to be primarily ubiquitin-proteasome mediated; furthermore, catabolism of the A53T mutant of synuclein, which occurs in a familial form of Parkinsons disease, was markedly impaired, thus favoring the intraneuronal accumulation of this potentially proapoptotic protein. In rat basal forebrain neurons, activation of p75, the low affinity receptor for nerve growth factor, has been observed to selectively enhance the vulnerability of these cholinergic neurons to excitotoxin- as well as amyloid-induced apoptosis via the NFkB signaling pathway. The implications of these convergent findings for the development of protective interventions for human neurodegenerative disease are currently being actively persued.