Role of GluA2-containing AMPARs in Oligodendrocyte Lineage Cells

Abstract

Oligodendrocytes precursor cells (OPC), also called NG2 cells, proliferate or differentiate into myelin-producing oligodendrocytes throughout life. Myelination depends on neuronal activity. Although NG2 cells receive neuronal glutamatergic synaptic input throughout the CNS, factors mediating activity-dependent control of the oligodendrocyte lineage cell fate have not been resolved yet. Glutamatergic signalling in NG2 cells is mainly mediated by AMPARs. During the postnatal period, AMPARs are calcium impermeable due to the expression of the GluA2 subunit. Later in the adult period, NG2 cells downregulate the GluA2 subunit, therefore they express GluA2-lacking AMPARs, permeable to calcium. Thus, the decline of the proliferation rate of NG2 cells observed during the transition from the postnatal to the adult period is mirrored by an increase in the calcium-permeability of synaptic AMPA receptors. We hypothesized that the postnatally expressed GluA2 subunit enables the proliferation of NG2 cells by suppressing calcium entry during synaptic activity. Here, we assessed the impact of postnatal GluA2 subunit deletion on the oligodendrocyte lineage cell fate. In order to induce a conditional deletion of the GluA2 subunit in NG2 cells, we crossed the three following mouse lines. NG2CreER mouse line conditionally express Cre under the NG2 promotor. R26REYFP mouse line express the yellow fluorescent protein reporter after Cre expression. GluA2lox mouse line undergoes a deletion of Gria2 allele responsible for GluA2 expression. First, we followed the oligodendrocyte lineage cell fate with the BrdU and PCNA markers to examine NG2 cell proliferation, the cleaved caspase-3 marker to probe for cell death, and the CC1 marker to analyse differentiation of NG2 cells into oligodendrocytes. We found that GluA2 deletion in early postnatal NG2 cells increased BrdU uptake in NG2 cells without increasing cell density or cell death in the oligodendrocyte lineage cell population. Secondly, we investigated the role of GluA2 subunit on myelination establishment by measuring the internodes length during myelination onset and at a later timepoint during the postnatal phase. GluA2 deletion in NG2 cells shortened immature internodes during myelination onset. Thirdly, the role of the GluA2 subunit in NG2 cells was investigated in a motor learning task requiring newly formed oligodendrocytes. GluA2 deletion altered the motor learning performance in mice. Although it did not affect the myelination properties investigated or NG2 cells proliferation. Overall, the GluA2 subunit in postnatal NG2 cells regulates DNA synthesis in NG2 cells and myelination onset through the regulation of internode elongation. Our study highlights the prominence of glutamatergic synaptic input integration in postnatal NG2 cells to regulate oligodendrocyte lineage cell fate.