Insights into the Regulation of the Glycine Transporter 1 (GlyT1)

描述(申请人提供)：甘氨酸是脑干和脊髓中的主要抑制性神经递质，在那里它作用于特定的士的宁敏感的甘氨酸受体。此外，甘氨酸作为谷氨酸在含有突触的N-甲基-D-天冬氨酸(NMDA)受体上必不可少的共同激动剂参与兴奋性神经传递；因此，NMDA受体的激活受到突触前神经元和邻近神经胶质细胞中存在的质膜甘氨酸转运体1(GlyT1)活性的严格调控。功能性NMDA受体数量的改变被认为是精神分裂症一些症状的基础，主要是在认知功能方面。GlyT1一直是精神分裂症药物开发的主要靶点；然而，转运蛋白是如何被调控的仍然知之甚少。单胺转运体家族中的几个成员都知道，转运蛋白的活性与蛋白激酶C(PKC)的激活有关；然而，大脑中的调节机制存在争议或未知。鉴于临床和药理学数据表明精神分裂症患者谷氨酸受体功能障碍以及甘氨酸转运体作为潜在药物靶点的作用，在本研究中，我们的目标是使用两种表达系统来表征GlyT1的调节机制：(A)小鼠GlyTIa在模型细胞系(HeLa和猪主动脉内皮细胞，PAE)中表达；(B)在大鼠海马区原代培养的内源性GlyT1。根据我们实验室的初步数据，表明在HeLa细胞中表达GlyT1可以增强PKC依赖的泛素化和内吞作用，我们假设PKC激活导致GlyT1泛素化和脑内下调，有助于调节甘氨酸转运蛋白。这项研究将为治疗精神分裂症等神经疾病提供新的潜在药理靶点。

DESCRIPTION (provided by applicant): Glycine is the major inhibitory neurotransmitter in the brainstem and spinal cord, where it functions at specific strychnine-sensitive glycine receptors. In addition, glycine participates in excitatory neurotransmission as an essential co-agonist of glutamate at N-methyl-D-aspartate (NMDA) receptor containing synapses; therefore, NMDA receptor activation is tightly modulated by the activity of the plasma membrane glycine transporter 1 (GlyT1) present in presynaptic neurons and neighboring glial cells. Altered numbers of functional NMDA receptors have been suggested to underlie some of the symptoms in schizophrenia, primarily in cognitive functions. The GlyT1 has been the main target for drug development in schizophrenia; however, how the transporter is regulated remains poorly understood. It is known for several members of the monoamine transporter family that transport activity is linked to activation of Protein Kinase C (PKC); however, the mechanism of regulation is controversial or unknown in the brain. Given the strength of clinical and pharmacological data suggesting glutamate receptor dysfunction in schizophrenia and the role of the glycine transporter as a potential drug target, in this study our goal is to characterize the regulatory mechanism of the GlyT1 using two expression systems: (a) mouse GlyTIa expressed in model cell lines (HeLa and Porcine Aortic Endothelial cells, PAE) and (b) endogenous GlyT1 in primary cultures from rat hippocampus. Based on preliminary data from our laboratory that suggest enhanced PKC-dependent ubiquitination and endocytosis obtained by expressing GlyT1 in HeLa cells, we hypothesize that PKC activation results in GlyT1 ubiquitination and down-regulation in the brain, contributing to the regulation of the glycine transporter. This research will offer new potential pharmacological targets to treat neurological disorders, such as schizophrenia.