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疗方法。目前正在探索开发姑息疗法和保护性疗法的新方法。在帕金森氏病的对症治疗方面，我们显著提高了对标准治疗剂左旋多巴随着疾病进展而产生越来越多并发症的理解。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理性刺激引起的运动功能障碍与邻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α-氨基-3-羟基-5-甲基-4-异恶唑(AMPA)亚型。这些离子亲电通道复合体的功能特性受其磷酸化状态的调节。损毁大鼠黑质纹状体多巴胺系统可诱导帕金森症状，并增加纹状体NMDA受体亚单位酪氨酸和丝氨酸/苏氨酸的磷酸化。纹状体内给药某些能够磷酸化这些亚基的酶抑制剂会产生拟多巴胺样的运动反应。用左旋多巴每天两次治疗这些帕金森病大鼠，可诱导人类运动并发症综合征的许多特征，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，纹状体内给予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起姑息作用又起预防作用，以逆转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实质上和持久地有效。最近在动物模型中的观察进一步表明，一些AMPA拮抗剂缓解，而一些AMPA激动剂加剧这些左旋多巴引起的并发症。综上所述，这些结果为我们的观点提供了更多的支持，即某些谷氨酸能受体的超敏反应是人类左旋多巴相关运动并发症以及帕金森症状最初出现的原因，抑制这些受体或其异常磷酸化可以显著减少运动障碍。用AMPA和NMDAR2B选择性拮抗剂进一步探索这一假说的对照原则临床试验现在正在启动。针对人类神经退行性疾病的神经保护治疗的研究越来越多地表明，核因子-kB信号转导通路的激活可能导致纹状体GABA能、黑质多巴胺能和前脑内侧胆碱能神经元的凋亡。例如，在大鼠纹状体棘神经元中，兴奋性毒素诱导的细胞程序性死亡现在似乎涉及以下序列：caspase-3激活，IKB-α降解，NFKB核翻译，随后c-Myc和P53表达增加。用几种方法中的任何一种方法阻断核因子-kB的核转位都可以减弱这些兴奋性毒性反应。在SY5Y神经细胞系中，胞浆蛋白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A53T突变体的分解代谢明显受损，从而有利于这种潜在的促凋亡蛋白在神经元内积累。在大鼠基底前脑神经元中，神经生长因子的低亲和力受体p75的激活被观察到通过NFkB信号通路选择性地增强这些胆碱能神经元对兴奋性毒素和淀粉样蛋白诱导的细胞凋亡的易感性。这些一致的发现对开发人类神经退行性疾病的保护性干预措施的影响目前正在积极寻求。

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.