Glutamate transporters as regulators of CNS myelination

 描述（由申请人提供）：少突胶质细胞（OLG）是中枢神经系统（CNS）的髓鞘形成细胞，当它们首先从双极OLG祖细胞成熟为延伸复杂和扩展的突起网络的髓鞘形成前OLG，然后成熟为产生髓鞘的成熟OLG时，其形态发生广泛变化。与这种谱系进展相关的形态学变化在很大程度上是由肌动蛋白细胞骨架组织的变化驱动的，这需要肌动蛋白丝的良好协调的动态周转，并且被认为是由细胞外信号调节的，所述细胞外信号可以至少部分是轴突衍生的。然而，尽管进行了深入的研究，但参与调节肌动蛋白细胞因子驱动的OLG形态（即OLG形态发生和CNS髓鞘形成）中的这种细胞外信号调节变化的信号传导途径目前仅具有很差的特征。值得注意的是，细胞外环境的变化和肌动蛋白细胞骨架机制的失调都被认为有助于OLG形态发生和髓鞘再生的限制，如在人类主要脱髓鞘疾病多发性硬化症（MS）的CNS内所见。因此，在试图确定新的治疗MS的治疗靶点，我们的长期目标是确定和表征信号轴，促进发育OLG形态发生和CNS髓鞘形成通过细胞外信号肌动蛋白细胞骨架途径，但在MS病变中被错误调节。在这方面，我们的初步数据表明，涉及钠依赖性谷氨酸转运蛋白的活性和随后的钙/钙调蛋白依赖性蛋白激酶II β（CaMK II β）的肌动蛋白结合活性的变化的信号传导轴对于有效的OLG形态发生和适当厚度（g-比率）的髓鞘的产生是至关重要的。值得注意的是，我们的初步数据与先前发表的研究结果一起指向MS病变内该信号传导轴的失调。基于我们的初步数据，我们因此制定了中央的假设，即有效的髓鞘形成，即建立一个适当的g-比例的髓鞘，是由谷氨酸转运蛋白-CaMKIII-肌动蛋白细胞骨架轴，是在分化OLG操作。为了解决上述中心假设，我们提出完成以下两个具体目标：1）在体内表征在分化OLG中明显功能上占优势的钠依赖性谷氨酸转运蛋白GLT-1在调节发育髓鞘形成中的作用，和2）在体外表征谷氨酸转运蛋白-CaMK Ⅱ-肌动蛋白细胞骨架轴在调节OLG形态发生中的作用。我们预期这些实验将为继续研究奠定基础，在这些研究中，确定特异性靶向CaMK Ⅱ独特的肌动蛋白结合特性和/或GLT-1信号传导的策略，以尝试开发新的髓鞘再生促进治疗策略，并改善与CNS脱髓鞘相关的神经系统疾病的治疗。

 DESCRIPTION (provided by applicant): Oligodendrocytes (OLGs), the myelinating cells of the central nervous system (CNS), undergo extensive changes in morphology when they mature first from bipolar OLG progenitors into premyelinating OLGs extending a complex and expanded process network and then into mature OLGs generating the myelin sheath. The morphological changes associated with this lineage progression are to a large extent driven by changes in the organization of the actin cytoskeleton, which require a well-coordinated dynamic turnover of actin filaments and are thought to be regulated by extracellular signals, which may, at least in part, be axon-derived. Despite intensive research, however, the signaling pathways involved in regulating such extracellular signal-regulated changes in actin cytoskeleton-driven OLG morphology, i.e. OLG morphogenesis, and CNS myelination are currently only poorly characterized. Notably, both changes in the extracellular milieu and a misregulation of actin cytoskeletal mechanisms have been proposed to contribute to the limitations in OLG morphogenesis and remyelination as seen within the CNS of the major demyelinating disease in human, Multiple Sclerosis (MS). Thus and in an attempt to identify novel therapeutic targets for the treatment of MS, our long-term goal is to identify and characterize signaling axes that promote developmental OLG morphogenesis and CNS myelination via an extracellular signal to actin cytoskeleton pathway but are misregulated within MS lesions. In this regard, our preliminary data suggest that a signaling axis involving the activity of sodium- dependent glutamate transporters and subsequent changes in the actin-binding activity of calcium/calmodulin- dependent protein kinase IIß (CaMKIIß) is critical for efficient OLG morphogenesis and the generation of a myelin sheath of proper thickness (g-ratio). Notably, our preliminary data together with previously published findings point toward a misregulation of this signaling axis within MS lesions. Based on our preliminary data, we thus formulate the central hypothesis that efficient myelination, i.e. the establishment of myelin with a proper g-ratio, is regulated by a glutamate transporter-CaMKIIß-actin cytoskeleton axis that is operative within differentiating OLGs. To address the above stated central hypothesis we propose the completion of the following two specific aims: 1) to characterize in vivo the role of the apparentl functionally predominant sodium-dependent glutamate transporter in differentiating OLGs, GLT-1, in regulating developmental myelination and 2) to characterize in vitro the role of the glutamate transporter-CaMKIIß-actin cytoskeleton axis in regulating OLG morphogenesis. We anticipate that these experiments will build the basis for continuing studies in which to define strategies to specifically target CaMKIIß's unique actin binding properties and/or GLT-1 signaling as an attempt toward the development of novel remyelination promoting therapeutic strategies and toward improving the treatment of neurologic diseases associated with CNS demyelination.