Role of the Neurotransmitter Glutamate in Neural Stem and Progenitor Cells Differentiation into Oligodendrocytes

Abstract

Various regions of the mammalian brain, including the subventricular zones (SVZs) of the hippocampus and the dentate gyrus (DG), contain niches of undifferentiated neural stem and progenitor cells (NSPCs) which persist from development, all throughout adulthood. These cells can differentiate into the three main cell types found within the brain: neurons, oligodendrocytes (OLs), and astrocytes. Adult NSPCs can be driven to specific cells of interest which can be used to replace lost myelin in some cases of neurodegenerative diseases such as multiple sclerosis (MS) or insults such as spinal cord injury. I investigated the requirements to drive immature NSPCs into oligodendrocyte precursor cells (OPCs) using various driving factors (PDGFα and NT-3) and the neurotransmitter (NT) glutamate. Glutamate is one of the main NTs in the central nervous system (CNS) hence, it may have a role in the differentiation of NSPCs into OPCs. My results demonstrated that among all the driving factors tested, glutamate treatment yielded the highest proportion of OPCs after six days. Flow cytometry was used to verify changes in cell lineage and proportions during the driving experiments. Enriched OPC cultures were purified using a magnetic bead sorting technique after which the cell lineage was confirmed using an immunocytochemistry (ICC) staining technique. Results demonstrated that cells differentiated alone with no external stimulation did not produce the myelin basic protein (MBP). In contrast, almost all OPCs stimulated with glutamate expressed MBP. Purified OPCs grown in a co-culture with DRG neurons for nine days also began expressing MBP which was found to be in close association with the neuronal axons. In order to verify the effect of glutamate in co-cultures of OPCs with DRG neurons, AMPA/kainate inhibitors such as CNQX and DNQX, were tested. Although MBP positive cells were still identified in cultures treated with AMPA inhibitors, in the case of CNQX, the myelin sheath organization appeared distorted compared to the nontreated samples, thus suggesting glutamate does play a key role in oligodendroglial development.