Neuronal activity and AMPA‐type glutamate receptor activation regulates the morphological development of oligodendrocyte precursor cells

Abstract

Myelination is initiated when oligodendrocyte precursor cells (OPC) contact target axons. Neuronal activity promotes myelination through actions that may involve OPC AMPA and NMDA glutamate receptors (AMPAR, NMDAR). Therefore, activity and AMPAR/NMDAR activation are predicted to promote the morphological development of OPC. AMPAR can regulate OPC development, but this analysis was not performed in situ and the role of action potentials was not examined. Hence, the influence of activity and AMPAR on OPC morphology and development remain untested in the CNS where axon-glial interactions are preserved. Data on NMDAR are mixed with conflicting results from in vitro and in vivo work. To gain a fuller understanding of activity-dependent OPC development in situ, we explored the role of AMPAR and NMDAR in cerebellar slice cultures that permit the study of endogenous OPC development and myelination. The structure of individual OPC was resolved from cells labeled with membrane targeted GFP. Morphological data were then validated against assays of OPC development. Blocking either activity or AMPAR impaired the morphological development of OPC and promoted proliferation and differentiation. Increasing the pool of oligodendrocytes by blocking activity or AMPAR failed to promote myelination. Instead both myelination and the expression of myelin basic protein were reduced by these treatments suggesting that full differentiation to a myelinating phenotype did not occur. Blocking NMDAR left OPC proliferation, differentiation and morphology unchanged. These data indicate an important role for AMPAR but not NMDAR in mediating the activity-dependent signals that regulate OPC morphology, development and myelination.

Myelination and mTOR

“…The molecular players underlying such activity‐dependent myelination are not univocally defined. Both ATP and glutamate are released by synaptic vesicles and regulate OL myelination (Stevens, Porta, Haak, Gallo, & Fields, 2002; Wake et al, 2011), and the relative contribution of each of the three classes of glutamate receptors—NMDA, AMPA, and metabotropic receptors (mGluRs)—is somewhat controversial (De Biase et al, 2011; Fannon, Tarmier, & Fulton, 2015; Guo et al, 2012; Kougioumtzidou et al, 2017; Lundgaard et al, 2013). …”

NF‐Y‐dependent regulation of glutamate receptor 4 expression and cell survival in cells of the oligodendrocyte lineage

“…This concentration was selected based on pilot studies examining treatment with log concentrations of Garcinol (1–1,000 µM), in which concentrations >10 µM caused catastrophic cell detachment and death (data not shown). BrdU (Sigma‐Aldrich Company Ltd) stocks were prepared as described by Fannon et al (2015). …”

“…Immunofluorescent staining was performed using a protocol previously used in our lab to label brain slices (Fannon et al, 2015). The protocol was adapted for use on Oli‐neu cells as follows.…”

“…For AMPA 24h experiments BrdU treatments were introduced during the last 7 hr of treatment. BrdU was detected as previously described (Fannon et al, 2015) and proliferation quantified as the % DAPI + /BrdU + cells from five randomly selected fields/well from seven to eight independent well replicates. Apoptosis was examined by immunofluorescent labelling for cleaved Caspase3 24 hr after treatment of cells with Garcinol (5 hr, 10 µM), or the vehicle control (DMSO, 0.001%).…”

“…Oligodendrocyte precursor cells (OPC) express AMPA‐type glutamate receptors (AMPAR) whose activation in the healthy CNS has been shown to influence various functions including migration, proliferation, differentiation and survival (Fannon, Tarmier, & Fulton, 2015; Gallo et al, 1996; Gudz, Komuro, & Macklin, 2006; Kougioumtzidou et al, 2017; Yuan, Eisen, McBain, & Gallo, 1998). AMPAR also mediate injury to these cells under pathological conditions.…”