NMDARs Regulate The Differentiation Of Oligodendrocyte Precursor Cells And Remyelination In The Cuprizone Model

In the CNS, oligodendrocytes are responsible for myelin production. Oligodendrocytes develop from proliferating oligodendrocyte progenitor cells (OPCs) that arise at mid-late gestation from the germinal ventricular zones of the embryonic brain. OPCs go through proliferation and migration in the effect of local signal then arrive at the white matter with rich axons then differentiate into mature oligodendrocytes. Oligodendrocytes extend their processes to wrap the axon and begin myelination. During remyelination, the recruitment and activation of resident OPCs play a critical role in the repair process because these cells have the capacity to differentiate into functional myelinating cells. But the presence of precursor and immature oligodendrocytes in some non-repairing lesions of MS patients suggests a mechanism in which impaired remyelination may result from the inhibition of the differentiation of OPCs. In order to more effectively treat these devastating conditions, it is essential to expand our knowledge of how the differentiation of OPCs is regulated.During the central neural system development, neuron/axon and the myelinating glias keep constant bidirectional communication. The process of myelin formation is precise controlled and dependent on a reciprocal and intimate relationship between neurons and the myelin-forming oligodendrocyte in brain. A lot of research work showed that the electrical activity of neuron could regulate the development of OPCs and myelination. How such local regulation is achieved by the axon-glial interaction is unknown. The neuronal electrical activity, astrocytes and unmyelinated axon in the white matter all can release glutamate neurotransmitter. But the function of these glutamates is completely not known. Interestingly, it is reported that the functional ionotropic glutamate NMDARs exist on oligodendrocyte lineage cells (OLs) and contribute to the pathophysiology of myelin damage in a variety of diseases. However, the role of NMDAR in the development of OPCs and myelination is obscure. The preferential location of NMDA receptors in processes on OLs especially in the myelin sheath and AMPA/Kainate receptors mainly on the cell soma suggests NMDAR may be involved in the interaction between axon and oligodendrocyte and regulate the development of oligodendrocyte lineage cells and myelination induced by glutamate.In this study, using immunochemistry we tested the expression of NMDAR subunits GluN1,GluN2A,GluN2B on OLs in vivo and in vitro. It is showed that NMDAR subunits GluN1,GluN2A,GluN2B were expressed in A2B5+or NG2+OPCs,01+ immature oligodendrocyte and MBP+mature oligodendrocyte. In vitro purified rat OPC culture system, NMDA stimulation could enhance OPC differentiation by increasing myelin basic protein (MBP) expression in a concentration-dependent manner. While specific knockdown of GluN1 by RNA interference in OPCs or NMDAR antagonists prohibited the role of NMDA. NMDA stimulation also can promote the 04+ oligodendrocyte processes branching. For further research, it demonstrated NMDA regulated differentiation of oligodendrocyte at the immature oligodendrocyte to mature oligodendrocyte transition as assessed by the expression of stage specific antigens and myelin proteins including NG2,04, 01, MBP and MOG. In DRG/OPC coculture system, NMDA treatment can increase the numbers of myelin segments. It suggested that activation of NMDAR could enhance the myelination of OPCs in DRG/OPC coculture system. Finally, NMDAR specific antagonist MK801 delayed remyelination in the cuprizone model examined by LFB/PAS, immunofluorescence and electron microscopy. This effect appeared to result from inhibiting the differentiation of OPCs as more NG2+OPCs but less GST-Ï€+mature oligodendrocytes were observed in the mice injected with MK801 which did not affect the numbers of positive microglia and GFAP positive astrocytes.Together, our results provide evidence that NMDAR activation played a critical role in regulation of OPC differentiation and remyelination that may provide reference for the treatment of demyelination disease.