Fig. 1

Schematic representation of glial cells in the CNS, along with their classification and representative marker genes. Oligodendrocytes, astrocytes, and microglia are the major population of glial cells in CNS. Oligodendrocytes (OLs) are myelinating cells derived from oligodendrocyte progenitor cells (OPCs). OLs and OPCs are important cellular components for remyelination, which is an important regenerative process to restore lost neurological function. OPCs express PDGFRα (platelet-derived growth factor receptor α), the transcription factor SOX10, NG2, Olig2, and A2B5. After OPCs generate OLs, the cells start to express O4, galactocerebroside. Finally, mature myelinating OLs express myelin-associated glycoprotein (MAG), myelin basic protein (MBP), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG). Astrocytes are the most abundant cells in the mammalian CNS with the function of forming and maintaining blood-brain barrier (BBB), regulating regional blood flow, proving trophic, antioxidant and metabolic support to neurons, neurotransmitter recycling, immune signaling, and regulating neuronal synaptogenesis and synaptic transmission. Reactive astrocytes can be classified into two subtypes, termed as “A1” (neurotoxic)/ “A2” (neuroprotective) astrocytes, with the specific marker genes identified from the previous transcriptome analysis [49]. Microglia can be classified into two states: M1 (classic) or M2 (alternative), which are responsible for tissue injury and repair, respectively