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

描述（由申请人提供）：甘氨酸是脑干和脊髓中的主要抑制性神经递质，它在特定的士的宁敏感甘氨酸受体中起作用。此外，甘氨酸作为谷氨酸在含n -甲基- d -天冬氨酸（NMDA）受体突触的重要协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胶质细胞中存在的质膜甘氨酸转运蛋白1 （GlyT1）活性的密切调节。功能性NMDA受体数量的改变被认为是精神分裂症的一些症状的基础，主要是认知功能。GlyT1一直是精神分裂症药物开发的主要靶点；然而，人们对这种转运蛋白是如何调控的仍然知之甚少。众所周知，单胺转运蛋白家族的几个成员的转运活性与蛋白激酶C （PKC）的激活有关；然而，大脑的调节机制是有争议的或未知的。鉴于临床和药理学数据表明精神分裂症中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)内源性GlyT1在大鼠海马原代培养物中表达。我们实验室的初步数据表明，通过在HeLa细胞中表达GlyT1可以增强PKC依赖的泛素化和内噬作用，我们假设PKC激活导致大脑中GlyT1泛素化和下调，从而促进甘氨酸转运蛋白的调节。这项研究将为治疗精神分裂症等神经系统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.