The Necessity of Vesicle-Associated Membrane Protein Expression by NG2 Glia for Maintenance of Glial and Neuronal Health

NG2 glia are vital for the myelination of axons in the brain and spinal cord. Many NG2 cells receive synaptic inputs from neurons through neurotransmitters such as glutamate and GABA, but the consequences of this input have remained unclear. Interestingly, NG2 cells express voltage-dependent Ca2+ channels and transcripts encoding SNARE proteins that are necessary for vesicle docking in neurons. We therefore hypothesized that NG2 cells respond to neuronal synaptic inputs by releasing bioactive molecules in a Ca2+-dependent manner. To test this, we generated double transgenic mice in which a cre-inducible botulinum toxin (BoNT/B) is constitutively expressed by NG2 cells (IBOT:NG2cre mice). In the IBOT:NG2cre line, BoNT/B cleaves vesicle-associated membrane proteins (VAMPs) in NG2 cells and their progeny. IBOT:NG2cre mice exhibited a robust phenotype, with severe motor defects and translucent spinal cords suggestive of severe hypomyelination. Immunostaining for MBP supported these findings, as IBOT:NG2cre spinal cord sections displayed pronounced hypomyelination throughout dorsal and anterolateral funiculi, particularly in the ventral region of the dorsal column, which notably contains the corticospinal tract. Staining for the oligodendrocyte antigen CC1 and with NG2 also showed a significant decrease in oligodendrocyte population density, but not in NG2 cell density, suggesting an additional defect in NG2 cell differentiation and/or oligodendrocyte survival. Lastly, through transmission electron microscopy, we observed large, misshapen myelinated axons around the corticospinal tract of the spinal cord. Our findings suggest that vesicle-associated membrane proteins in NG2 cells play a key role in myelination, NG2 cell differentiation, and/or oligodendrocyte survival, possibly mediated by exocytotic events observable in cultured primary NG2 cells