NG2 cell dynamics in the normal and injured adult central nervous system

描述(申请人提供)：哺乳动物中枢神经系统包含一组不同的神经胶质细胞，支持神经元，调节神经元活动，并能够在损伤后进行修复。除了星形胶质细胞、少突胶质细胞和小胶质细胞外，目前公认的中枢神经系统还含有第四类神经胶质细胞，具有独特的特性。这些丰富的胶质细胞表达血小板衍生生长因子α受体(PDGF1R)和硫酸软骨素蛋白多糖NG2，被称为NG2+胶质细胞(NG2细胞)。NG2细胞延伸高度分叉的突起，带有细丝足状突起，以高度有序或平铺的方式均匀分布于成年中枢神经系统的灰质和白质区域，类似于星形胶质细胞和小胶质细胞。由于这些细胞是少突胶质细胞的前体细胞，NG2细胞的组织和持续的动态可能对取代因正常衰老或多发性硬化症等疾病的急性脱髓鞘而丢失的少突胶质细胞至关重要。然而，NG2细胞在哺乳动物中枢神经系统中的细胞动力学还没有得到研究，对于调控NG2细胞在成年中枢神经系统中的形态、分布和增殖的因素也知之甚少。为了监测NG2细胞在成人大脑中的动态行为，我们最近开发了能够在体内显示NG2细胞的转基因小鼠(NG2-1ck-EGFP小鼠)。利用这些小鼠，可以在静息状态或损伤后观察到存活小鼠大脑皮质中的NG2细胞，表明该方法可用于研究成年脑中NG2细胞过程动力学、增殖和分化的调控机制。在这里，我建议使用躯体感觉皮质中NG2细胞的双光子成像来研究成年小鼠大脑中NG2细胞的行为。我将在几小时、几天和几周的时间内进行时间推移成像，以确定NG2细胞过程的结构动力学，并确定细胞-细胞接触在调节其形态和增殖中的作用。NG2细胞表达离子型谷氨酸受体，在神经胶质细胞中是独一无二的，因为它们与神经元形成直接突触，为神经元提供了一种调节其行为的手段。为了评估NMDA受体信号是否调节NG2细胞的动态行为及其对局灶性损伤的反应，我将在NMDA受体选择性从NG2细胞中删除的转基因小鼠中进行类似的实验。通过监测正常和受损大脑中NG2细胞的体内动态行为，这些研究将进一步加深我们对指导这些无处不在的祖细胞行为的机制的理解。由于这些细胞具有替代少突胶质细胞的能力，并有助于胶质瘢痕的形成，这些研究可能有助于确定加速少突胶质细胞再生和髓鞘修复的新方法，以及促进各种中枢神经系统损伤恢复的新策略。

DESCRIPTION (provided by applicant): The mammalian CNS contains a diverse group of glial cells that support neurons, modulate neuronal activity, and enable repair following injury. In addition to astrocytes, oligodendrocytes and microglial cells, it is now recognized that the CNS contains a fourth class of glial cell that exhibits unique properties. These abundant glial cells express the alpha receptor for platelet derived growth factor (PDGF1R), and the chondroitin sulfate proteoglycan NG2, and have been termed "NG2+ glial cells (NG2 cells)". NG2 cells extend highly branched processes decorated with small filopodia-like protrusions, and are evenly distributed throughout gray and white matter regions of the adult CNS in a highly ordered or "tiled" manner, similar to astrocytes and microglial cells. As these cells serve as progenitors to oligodendrocytes, the organization and ongoing dynamics of NG2 cells may be crucial for replacing oligodendrocytes lost through normal aging or following acute demyelination in diseases such as multiple sclerosis. However, the cellular dynamics of NG2 cells have not been studied in the mammalian CNS in vivo, and little is known about the factors that regulate their morphology, distribution, and proliferation of these cells in the adult CNS. To monitor the dynamic behavior of NG2 cells in the adult brain, we recently developed transgenic mice (NG2-lck-EGFP mice) that allow the visualization of NG2 cells in vivo. Using these mice, NG2 cells in the cortex of living mice can be observed during resting-states or after injury, indicating that this approach can be used to help investigate the mechanisms regulating NG2 cell process dynamics, proliferation, and differentiation in the adult brain. Here, I propose to use two-photon imaging of NG2 cells in the somatosensory cortex to study the behavior of NG2 cells within the adult mouse brain. I will perform time-lapse imaging over a period of hours, days and weeks to define the structural dynamics of NG2 cell processes, and to determine the role of cell-cell contact in the regulation of their morphology and proliferation. NG2 cells express ionotropic glutamate receptors, and are unique among glial cells in that they form direct synapses with neurons, providing a means by which neurons could regulate their behavior. To evaluate whether NMDA receptor signaling regulates the dynamic behavior of NG2 cells and their response to focal injury, I will perform similar experiments in transgenic mice in which NMDA receptors have been selectively deleted from NG2 cells. By monitoring the dynamic behavior of NG2 cells in vivo in the normal and injured brain, these studies will further our understanding of the mechanisms that guide the behavior of these ubiquitous progenitors. As these cells have the capacity to replace oligodendrocytes and contribute to the formation of glial scars, these studies may help identify new approaches for accelerating oligodendrocyte regeneration and myelin repair, as well as new strategies for enhancing recovery from diverse CNS injuries.