Abstract
NG2 cells are a population of CNS cells that are distinct from neurons, mature oligodendrocytes, astrocytes, and microglia. These cells can be identified by their NG2 proteoglycan expression. NG2 cells have a highly branched morphology, with abundant processes radiating from the cell body, and express a complex set of voltage-gated channels, AMPA/kainate, and GABA receptors. Neurons notably form classical and nonclassical synapses with NG2 cells, which have varied characteristics and functions. Neuron-NG2 cell synapses could fine-tune NG2 cell activities, including the NG2 cell cycle, differentiation, migration, and myelination, and may be a novel potential therapeutic target for NG2 cell-related diseases, such as hypoxia-ischemia injury and periventricular leukomalacia. Furthermore, neuron-NG2 cell synapses may be correlated with the plasticity of CNS in adulthood with the synaptic contacts passing onto their progenies during proliferation, and synaptic contacts decrease rapidly upon NG2 cell differentiation. In this review, we highlight the characteristics of classical and nonclassical neuron-NG2 cell synapses, the potential functions, and the fate of synaptic contacts during proliferation and differentiation, with the emphasis on the regulation of the NG2 cell cycle by neuron-NG2 cell synapses and their potential underlying mechanisms.
Highlights
Glial cells expressing nerve/glial antigen 2 (NG2 cells) are widespread cell populations identified by their specific expression of NG2 chondroitin sulphate proteoglycan (CSPG), which in the central nervous system (CNS) accounts for approximately 8% to 9% of the total cell population in adult white matter and 2% to 3% of total cells in adult grey matter [1]
These cells mainly differentiate into oligodendrocytes that participate in myelination; their plasticity is manifested by their ability to become astrocytes or neurons under certain conditions [2,3,4]
The white matter region in the corpus callosum is responsible for interhemispheric communication; the glutamate released by vesicular fusion in callosal axons elicits quantal amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated currents in NG2 cells at anatomically distinct axon-NG2 cell synaptic contacts, which is a typical form of ectopic transmission [24, 25]
Summary
Glial cells expressing nerve/glial antigen 2 (NG2 cells) are widespread cell populations identified by their specific expression of NG2 chondroitin sulphate proteoglycan (CSPG), which in the central nervous system (CNS) accounts for approximately 8% to 9% of the total cell population in adult white matter and 2% to 3% of total cells in adult grey matter [1]. These cells mainly differentiate into oligodendrocytes that participate in myelination; their plasticity is manifested by their ability to become astrocytes or neurons under certain conditions [2,3,4]. This review highlights the classical and nonclassical neuron-NG2 cell synapses, the regulatory functions of neuronNG2 cell synapses on the NG2 cell cycle, and the fate of synaptic junctions during NG2 cell proliferation and differentiation, with an emphasis on the potential functions of neuron-NG2 cell synapses for regulating the proliferation and differentiation of NG2 cells
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