PATHOGENESIS AND TREATMENT OF NEURODEGENERATIVE DISEASE

该项目旨在发现影响运动和认知功能的神经退行性疾病的改进医学治疗方法。目前正在探索开发姑息治疗和保护性治疗的新方法。关于帕金森病的对症治疗，我们已经大大提高了对为什么标准治疗剂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。早期的实验结果表明，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生性刺激引起的运动功能障碍与附近谷氨酸能受体的敏感性改变有关，包括n -甲基- d -天冬氨酸（NMDA）和a-氨基-3-羟基-5-甲基-4-异氧唑固有酸（AMPA）亚型。这些离子型通道复合物的功能特性受其磷酸化状态的调控。损伤大鼠黑质纹状体多巴胺系统可诱发帕金森症状，增加纹状体NMDA受体亚基的酪氨酸和丝氨酸/苏氨酸磷酸化。某些能够磷酸化这些亚基的激酶抑制剂的胃内给药可产生过继拟胺运动反应。每天两次左旋多巴治疗这些帕金森大鼠可诱导许多人类运动并发症综合征的特征，并进一步增加NMDAR2A和NMDAR2B亚基上特定丝氨酸/苏氨酸和酪氨酸残基的磷酸化。同样，某些丝氨酸和酪氨酸激酶的选择性抑制剂的肠腔内给药逆转了磷酸化的变化，减轻了左旋多巴治疗相关的运动并发症。在啮齿动物和灵长类动物模型中，各种NMDA受体拮抗剂，包括一些非竞争性通道阻滞剂，可以缓解和预防左旋多巴诱导的反应改变。同样，我们的临床研究现在已经证明，包括金刚烷胺在内的几种NMDA拮抗剂在改善运动并发症和帕金森症状方面具有实质性和持久的效果。最近在动物模型中的观察进一步表明，一些AMPA拮抗剂减轻了这些左旋多巴引起的并发症，而一些AMPA激动剂加重了这些并发症。综上所述，这些结果为我们的观点提供了越来越多的支持，即某些谷氨酸能受体的超敏感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初始出现，抑制这些受体或其异常磷酸化可以大大减少运动障碍。目前正在启动AMPA和NMDAR2B选择性拮抗剂的对照原理验证临床试验，以进一步探索这一假设。针对人类神经退行性疾病的神经保护治疗发展的研究越来越多地表明，NF-kB信号转导级联的激活可能有助于纹状体gaba能神经元、黑质多巴胺能神经元和内侧前脑胆碱能神经元的凋亡死亡。例如，在大鼠纹状体棘神经元中，兴奋毒素诱导的程序性细胞死亡现在似乎涉及以下顺序：caspase-3激活，ikb - α降解，NFKB核翻译，然后是c-Myc和p53表达增加。通过多种方式阻断NF-kB的核易位可减弱这些兴奋性毒性反应。在SY5Y神经元细胞系中，发现细胞质蛋白α -突触核蛋白的降解主要是泛素蛋白酶体介导的；此外，突触核蛋白的A53T突变体的分解代谢（发生在家族性帕金森病中）明显受损，从而有利于这种潜在的促凋亡蛋白在神经元内的积累。在大鼠基底前脑神经元中，已观察到p75（神经生长因子的低亲和力受体）的激活选择性地增强了这些胆碱能神经元对兴奋毒素的易感性，以及通过NFkB信号通路介导淀粉样蛋白诱导的凋亡。目前正在积极研究这些趋同的发现对人类神经退行性疾病保护性干预发展的影响。

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.