NG2+ glial cells: a novel glial cell population in the adult brain.

We describe a major glial cell population in the central nervous system (CNS) that can be identified by the expression of 2 cell surface molecules, the NG2 proteoglycan and the alpha receptor for platelet-derived growth factor (PDGF alphaR). In vitro and in the developing brain in vivo, NG2 and PDGF alphaR are expressed on oligodendrocyte progenitor cells but are down-regulated as the progenitor cells differentiate into mature oligodendrocytes. In the mature CNS, numerous NG2+/PDGF alphaR+ cells with extensive arborization of their cell processes are found ubiquitously long after oligodendrocytes are generated. NG2+ cells in the mature CNS do not express antigens specific to mature oligodendrocytes, astrocytes, microglia, or neurons, suggesting that they are a novel population of glial cells. Recently NG2+ cells in the adult CNS have been shown to undergo proliferation and morphological changes in response to a variety of stimuli, such as demyelination and inflammation, suggesting that they are dynamic cells capable of responding to changes in the environment. Furthermore, high levels of NG2+ and PDGF alphaR are expressed on oligodendroglioma cells, raising the possibility that the NG2+/PDGF alphaR+ cells in the mature CNS contribute to glial neoplasm.