Mechanisms of axon-NG2 cell interaction

描述（申请人提供）：最近的研究表明中枢神经系统（CNS）中的胶质细胞积极参与神经网络。以往关于胶质细胞功能的研究大多集中在星形胶质细胞上，通过胶质丝的存在来鉴定。然而，在成熟的中枢神经系统中，存在另一种主要的大胶质细胞类型，即表达NG2的胶质细胞（NG2细胞），其至少占细胞群的10%。形态学、免疫学和电生理研究表明，NG2细胞不同于星形胶质细胞、成熟少突胶质细胞和小胶质细胞。NG2细胞在体外和体内均有分化为成熟少突胶质细胞的潜力，因此被称为少突胶质细胞祖细胞。然而，大量NG2细胞在成人中枢神经系统灰质和白质中的持续存在，提出了它们除了产生髓鞘少突胶质细胞外还具有其他功能的可能性。基于纯化的NG2蛋白多糖抑制轴突生长和导致生长锥塌陷的能力，有人推测NG2细胞在轴突生长中也起负作用。相反，在Pi的实验室中产生的初步结果表明，生长的轴突广泛接触NG2细胞，并且在遇到NG2细胞时不会立即崩溃。本提案的目的是确定NG2细胞（而不是分子本身）是否促进、抑制或引起轴突发育、再生和发芽的分支，以及这些影响是否被NG2表达水平改变。假设NG2细胞促进或抑制轴突生长取决于表面表达的NG2水平，这可能受到金属蛋白酶的调节。NG2细胞促进或抑制轴突生长的能力作为NG2水平的功能将在分离培养（目的1）、体内和活体胼胝体发育（目的2）以及白质和灰质损伤模型（目的3）中进行研究。这些研究将阐明NG2胶质细胞在轴突发育和再生中的作用，并可能为促进损伤后轴突再生的治疗策略提供新的概念和设计。

DESCRIPTION (provided by applicant): Recent studies suggest that glial cells in the central nervous system (CNS) actively participate in the neural network. Most of the previous studies on the functions of glia have focused on astrocytes identified by the presence of glial filaments. However, in the mature CNS, there exists another major macroglial cells type, the NG2-expressing glia (NG2 cells) which comprise at least 10% of the cell population. Morphological, immunological, and electrophysiological studies indicate that NG2 cells are distinct from astrocytes, mature oligodendrocytes, and microglia. NG2 cells have the potential to differentiate into mature oligodendrocytes in vitro and in vivo and are hence referred to as oligodendrocyte progenitor cells. However, the persistence of a large number of NG2 cells throughout the gray and white matter of adult CNS raises the possibility that they carry out functions besides generating myelinating oligodendrocytes. Based on the ability of purified NG2 proteoglycan to inhibit axonal growth and cause growth cones to collapse, it has been speculated that NG2 cells also play a negative role in axonal growth. On the contrary, preliminary results generated in the Pi's laboratory indicate that growing axons extensively contact NG2 cells and do not immediately collapse upon encountering NG2 cells. The goal of this proposal is to determine whether NG2 cells (and not the molecule itself) promote, inhibit, or cause branching of developing, regenerating, and sprouting axons, and whether these effects are altered by the level of NG2 expression. The hypothesis is that NG2 cells promote or inhibit axonal growth depending on the level of NG2 expressed at the surface, which might be regulated by metalloproteinases. The ability of NG2 cells to promote or inhibit axonal growth as a function of NG2 level will be investigated in dissociated culture (aim 1), in developing corpus callosum in vivo and in living slices (aim 2), and in white matter and gray matter lesion models (aim 3). These studies should elucidate the role of NG2 glia in axonal development and regeneration and may lead to novel concepts and design in therapeutic strategies to promote axonal regeneration following injury.