Defects of subcellular glutamate transporter localization in schizophrenia

描述(申请人提供)：虽然用抗精神病药物治疗精神分裂症彻底改变了这种疾病的临床管理，但尽管进行了多次抗精神病药物试验，大约三分之一的精神分裂症患者仍有持续的阳性症状。最近，治疗精神分裂症的新策略已经出现，包括调节谷氨酸受体，这一方法在一定程度上是基于越来越多的证据，从尸检、成像和临床前研究中发现谷氨酸传递的变化。虽然精神分裂症最初的谷氨酸假说集中在NMDA受体功能障碍上，但这个假说已经扩展到包括其他谷氨酸受体、转运体和参与谷氨酸传递的酶。精神分裂症患者死后谷氨酸能分子表达的变化可能被概念化为重塑谷氨酸突触的功能改变，仅次于慢性严重精神疾病的潜在病理生理学和终生精神药物治疗。我们发现精神分裂症患者神经胶质谷氨酸转运体的表达减少，这表明谷氨酸突触在谷氨酸缓冲和重摄取能力方面有改变。谷氨酸转运体通过限制谷氨酸溢出到相邻突触来促进兴奋性神经传递，我们假设精神分裂症患者皮层丘脑回路中兴奋性氨基酸转运体(EAATs)的定位发生了改变，从而导致了这种疾病的精神病理。具体地说，我们假设EAAT的细胞特异性定位在精神分裂症中发生了改变。我们还假设，在本病中存在EAAT的运输和亚细胞定位缺陷。为了评估这些假说，我们将使用免疫荧光、亚细胞分离和Western印迹分析来评估EAAT亚型在精神分裂症患者和对照组死后组织中的定位。我们的研究将集中在丘脑背内侧核和前扣带回皮质，这两个区域具有密集的相互神经支配，与这种疾病的病理生理有关。我们还计划评估慢性、典型和非典型抗精神病药物治疗对大鼠大脑中谷氨酸转运体定位的影响。这些啮齿动物研究将提供关于慢性抗精神病药物治疗对兴奋性突触组成的影响的新数据，并称赞我们对尸检结果的解释，因为这些受试者中的大多数都接受了抗精神病药物治疗。在这组实验的结论中，我们将检验这一假设，即精神分裂症患者谷氨酸转运体的细胞和亚细胞定位发生改变，表明突触周围缓冲和谷氨酸的重新摄取减少，谷氨酸溢出增加。这些研究将把精神分裂症的谷氨酸假说扩展到NMDA受体之外，并为这种往往具有破坏性的疾病的诊断和治疗提供新的底物。

DESCRIPTION (provided by applicant): While the treatment of schizophrenia with antipsychotic medications revolutionized the clinical management of this illness, approximately one-third of patients with schizophrenia have persistent positive symptoms despite multiple trials of antipsychotic medicines. Recently, new strategies for the treatment of schizophrenia have emerged, including modulation of glutamate receptors, an approach which was developed, in part, based on an accumulating body of evidence of alterations in glutamate transmission from postmortem, imaging, and preclinical studies. While the initial glutamate hypothesis of schizophrenia was focused on NMDA receptor dysfunction, this hypothesis has been extended to include other glutamate receptors, transporters, and enzymes involved in glutamate transmission. Postmortem findings of changes in the expression of glutamatergic molecules in schizophrenia may be conceptualized as functional alterations of remodeled glutamate synapses, secondary to the underlying pathophysiology of chronic severe mental illness and a lifetime of treatment with psychotropic medications. We have found decreased expression of glial glutamate transporters in subjects with schizophrenia, suggesting that glutamate synapses have alterations in glutamate buffering and reuptake capacity. Glutamate transporters facilitate excitatory neurotransmission by limiting glutamate spillover to adjacent synapses, and we postulate that the localization of excitatory amino acid transporters (EAATs) is altered in corticothalamic circuits in schizophrenia, contributing to the psychopathology of this disease. Specifically, we hypothesize that cell-specific localization of EAATs is altered in schizophrenia. We also hypothesize that there are defects of trafficking and subcellular localization of EAATs in this illness. To evaluate these hypotheses, we will assess the localization of EAAT isoforms using immunofluorescence, subcellular fractionization, and Western blot analysis in postmortem tissue from subjects with schizophrenia and a comparison group. Our studies will focus on the dorsomedial nucleus of the thalamus and the anterior cingulate cortex, regions with dense reciprocal innervation that are implicated in the pathophysiology of this illness. We also plan to assess the effects of chronic typical and atypical antipsychotic treatment on localization of glutamate transporters in the rat brain. These rodent studies will provide novel data on the effects of chronic antipsychotic treatment on the composition of excitatory synapses, and compliment the interpretation of our postmortem findings, since most of these subjects were treated with antipsychotics. At the conclusion of this set of experiments, we will have tested the hypothesis that cellular and subcellular localization of glutamate transporters is altered in schizophrenia, suggesting decreased perisynaptic buffering and reuptake of glutamate and increased glutamate spillover. These studies will extend the glutamate hypothesis of schizophrenia beyond the NMDA receptor and provide new substrates for diagnosis and treatment of this often devastating illness.