Differing intrinsic biological properties between forebrain and spinal oligodendroglial lineage cells

Glial progenitor heterogeneity and key regulators revealed by single-cell RNA sequencing provide insight to regeneration in spinal cord injury

Recent studies have revealed the heterogeneous nature of astrocytes; however, how diverse constituents of astrocyte-lineage cells are regulated in adult spinal cord after injury and contribute to regeneration remains elusive. We perform single-cell RNA sequencing of GFAP-expressing cells from sub-chronic spinal cord injury models and identify and compare with the subpopulations in acute-stage data. We find subpopulations with distinct functional enrichment and their identities defined by subpopulation-specific transcription factors and regulons. Immunohistochemistry, RNAscope experiments, and quantification by stereology verify the molecular signature, location, and morphology of potential resident neural progenitors or neural stem cells in the adult spinal cord before and after injury and uncover the populations of the intermediate cells enriched in neuronal genes that could potentially transition into other subpopulations. This study has expanded the knowledge of the heterogeneity and cell state transition of glial progenitors in adult spinal cord before and after injury.

SKAP2 as a new regulator of oligodendroglial migration and myelin sheath formation

Oligodendroglial progenitor cells (OPCs) are highly proliferative and migratory cells, which differentiate into complex myelin forming and axon ensheathing mature oligodendrocytes during myelination. Recent studies indicate that the oligodendroglial cell population is heterogeneous on transcriptional and functional level depending on the location in the central nervous system. Here, we compared intrinsic properties of OPC from spinal cord and brain on functional and transcriptional level. Spinal cord OPC demonstrated increased migration as well as differentiation capacity. Moreover, transcriptome analysis revealed differential expression of several genes between both OPC populations. In spinal cord OPC, we confirmed upregulation of SKAP2, a cytoplasmatic adaptor protein known for its implication in cytoskeletal remodeling and migration in other cell types. Recent findings suggest that actin dynamics determine not only oligodendroglial migration, but also differentiation: Whereas actin polymerization is important for process extension, actin destabilization and depolymerization is required for myelin sheath formation. Downregulation or complete lack of SKAP2 in OPC resulted in reduced migration and impaired morphological maturation in oligodendrocytes. In contrast, overexpression of SKAP2 as well as constitutively active SKAP2 increased OPC migration suggesting that SKAP2 function is dependent on activation by phosphorylation. Furthermore, lack of SKAP2 enhanced the positive effect on OPC migration after integrin activation suggesting that SKAP2 acts as modulator of integrin dependent migration. In summary, we demonstrate the presence of intrinsic differences between spinal cord and brain OPC and identified SKAP2 as a new regulator of oligodendroglial migration and sheath formation.

Heterogeneity of the Endocannabinoid System Between Cerebral Cortex and Spinal Cord Oligodendrocytes

In the last years, regional differences have been reported between the brain and spinal cord oligodendrocytes, which should be considered when designing therapeutic strategies for myelin repair. Promising targets to achieve myelin restoration are the different components of the endocannabinoid system (ECS) that modulate oligodendrocyte biology, but almost all studies have been focused on brain-derived cells. Therefore, we compared the ECS between the spinal cord and cerebral cortex-derived oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes (OLs). Cells from both regions express synthesizing and degrading enzymes for the endocannabinoid 2-arachidonoylglycerol, and degrading enzymes increase with maturation, more notably in the spinal cord (monoglyceride lipase-MGLL, alpha/beta hydrolase domain-containing 6-ABHD6, and alpha/beta hydrolase domain-containing 12-ABHD12). In addition, spinal cord OPCs express higher levels of the synthesizing enzymes diacylglycerol lipases alpha (DAGLA) and beta (DAGLB) than cortical ones, DAGLA reaching statistical significance. Cells from both the cortex and spinal cord express low levels of NAEs synthesizing enzymes, except for the glycerophosphodiester phosphodiesterase 1 (GDE-1) but high levels of the degrading enzyme fatty acid amidohydrolase (FAAH) that increases with maturation. Finally, cells from both regions show similar levels of CB1 receptor and GPR55, but spinal cord-derived cells show significantly higher levels of transient receptor potential cation channel V1 (TRPV1) and CB2. Overall, our results show that the majority of the ECS components could be targeted in OPCs and OLs from both the spinal cord and brain, but regional heterogeneity has to be considered for DAGLA, MGLL, ABHD6, ABHD12, GDE1, CB2, or TRPV1.

Semaphorins and Plexins in central nervous system patterning: the key to it all?

Semaphorins and Plexins constitute one of the largest family of guidance molecules and receptors involved in setting critical biological steps for central nervous system development. The role of these molecules in axonal development has been extensively characterized but Semaphorins and Plexins are also involved in a variety of other developmental processes, spanning from cell polarization to migration, laminar segregation and neuronal maturation. In this review, we aim to gather discoveries carried in the field of neurodevelopment over the last decade, during which Semaphorin/Plexin complexes have emerged as key regulators of neurogenesis, neural cell migration and adult gliogenesis. As well, we report mechanisms that brought a better understanding of axonal midline crossing.

The effects of developmental and current niches on oligodendrocyte precursor dynamics and fate

Oligodendrocyte precursor cells (OPCs), whose primary function is to generate myelinating oligodendrocytes, are distributed widely throughout the developing and mature central nervous system. They originate from several defined subdomains in the embryonic germinal zones at different developmental stages and in the adult. While many phenotypic differences have been observed among OPCs in different anatomical regions and among those arising from different germinal zones, we know relatively little about the molecular and cellular mechanisms by which the historical and current niches shape the behavior of oligodendrocyte lineage cells. This minireview will discuss how the behavior of oligodendrocyte lineage cells is influenced by the developmental niches from which subpopulations of OPCs emerge, by the current niches surrounding OPCs in different regions, and in pathological states that cause deviations from the normal density of oligodendrocyte lineage cells and myelin.

Endothelin signalling mediates experience-dependent myelination in the CNS

Experience and changes in neuronal activity can alter CNS myelination, but the signalling pathways responsible remain poorly understood. Here we define a pathway in which endothelin, signalling through the G protein-coupled receptor endothelin receptor B and PKC epsilon, regulates the number of myelin sheaths formed by individual oligodendrocytes in mouse and zebrafish. We show that this phenotype is also observed in the prefrontal cortex of mice following social isolation, and is associated with reduced expression of vascular endothelin. Additionally, we show that increasing endothelin signalling rescues this myelination defect caused by social isolation. Together, these results indicate that the vasculature responds to changes in neuronal activity associated with experience by regulating endothelin levels, which in turn affect the myelinating capacity of oligodendrocytes. This pathway may be employed to couple the metabolic support function of myelin to activity-dependent demand and also represents a novel mechanism for adaptive myelination.

Xeno-free culture for generation of forebrain oligodendrocyte precursor cells from human pluripotent stem cells

Oligodendrocytes (OLs) show heterogeneous properties that depend on their location in the central nervous system (CNS). In this regard, the investigation of oligodendrocyte precursor cells (OPCs) derived from human pluripotent stem cells (hPSCs) should be reconsidered, particularly in cases of brain-predominant disorders for which brain-derived OPCs are more appropriate than spinal cord-derived OPCs. Furthermore, animal-derived components are responsible for culture variability in the derivation and complicate clinical translation. In the present study, we established a xeno-free system to induce forebrain OPCs from hPSCs. We induced human forebrain neural stem cells (NSCs) on Laminin 511-E8 and directed the differentiation to the developmental pathway for forebrain OLs with SHH and FGF signaling. OPCs were characterized by the expression of OLIG2, NKX2.2, SOX10, and PDGFRA, and subsequent maturation into O4⁺ cells. In vitro characterization showed that >85% of the forebrain OPCs (O4⁺ ) underwent maturation into OLs (MBP⁺ ) 3 weeks after mitogen removal. Upon intracranial transplantation, the OPCs survived, dispersed in the corpus callosum, and matured into (GSTπ⁺ ) OLs in the host brains 3 months after transplantation. These findings suggest our xeno-free induction of forebrain OPCs from hPSCs could accelerate clinical translation for brain-specific disorders.