Chronic changes in oligodendrocyte sub‐populations after middle cerebral artery occlusion in neonatal mice

Abstract

Neonatal stroke is common and causes life‐long motor and cognitive sequelae. Because neonates with stroke are not diagnosed until days‐months after the injury, chronic targets for repair are needed. We evaluated oligodendrocyte maturity and myelination and assessed oligodendrocyte gene expression changes using single cell RNA sequencing (scRNA seq) at chronic timepoints in a mouse model of neonatal arterial ischemic stroke. Mice underwent 60 min of transient right middle cerebral artery occlusion (MCAO) on postnatal day 10 (p10) and received 5‐ethynyl‐2′‐deoxyuridine (EdU) on post‐MCAO days 3–7 to label dividing cells. Animals were sacrificed 14 and 28–30 days post‐MCAO for immunohistochemistry and electron microscopy. Oligodendrocytes were isolated from striatum 14 days post‐MCAO for scRNA seq and differential gene expression analysis. The density of Olig2+EdU+ cells was significantly increased in ipsilateral striatum 14 days post‐MCAO and the majority of oligodendrocytes were immature. Density of Olig2+EdU+ cells declined significantly between 14 and 28 days post‐MCAO without a concurrent increase in mature Olig2+EdU+ cells. By 28 days post‐MCAO there were significantly fewer myelinated axons in ipsilateral striatum. scRNA seq identified a cluster of “disease associated oligodendrocytes (DOLs)” specific to the ischemic striatum, with increased expression of MHC class I genes. Gene ontology analysis suggested decreased enrichment of pathways involved in myelin production in the reactive cluster. Oligodendrocytes proliferate 3–7 days post‐MCAO and persist at 14 days, but fail to mature by 28 days. MCAO induces a subset of oligodendrocytes with reactive phenotype, which may be a therapeutic target to promote white matter repair.

Perspective from single‐cell sequencing: Is inflammation in acute ischemic stroke beneficial or detrimental?

“…In contrast, adult mice showed a loss of oligodendrocyte progenitors and mature oligodendrocytes during injury, resulting in more severe white matter damage. These data suggest that oligodendrocyte responsiveness to ischemic stroke is age‐dependent 84 . Furthermore, 14 days after MCAO, the number of immature (Olig2+ EdU+ CC1‐) oligodendrocytes significantly increased in the ipsilateral striatum.…”

“…83 Moreover, studies have shown that MCAO can induce a subpopulation of oligodendrocytes with a reactive phenotype and that oligodendrocytes repair white matter damage in response to ischemia. 84 Zheng et al found that oligodendrocytes are enriched in the pathway regulating neuronal apoptosis, 2 which indicates that oligodendrocytes play a role in regulating neuronal homeostasis. Moreover, Frazier et al found that oligodendrocyte responses to stroke depend on age.…”

“…Moreover, Frazier et al found that oligodendrocyte responses to stroke depend on age. 84 In juvenile mice at 25 days, oligodendrocyte progenitor cells (OPCs) were significantly increased in the injured striatum 3-7 days after MCAO, and mature oligodendrocytes were resistant to ischemia in the same time frame, contributing to the relative preservation of the subcortical white matter. 85 In contrast, adult mice showed a loss of oligodendrocyte progenitors and mature oligodendrocytes during injury, resulting in more severe white matter damage.…”

The dynamics of oligodendrocyte populations following permanent ischemia promotes long-term spontaneous remyelination of damaged area

“…Given that NG2 + expression can also be observed in other cellular lineages(He et al ., 2023; Huang et al ., 2020; Kirdajova et al ., 2021), we considered only cells double positive for NG2 and Olig2 (NG2 + /Olig2 + ). The quantification of mature OLGs was calculated using immunofluorescence with the anti-APC (clone CC1) antibody, which specifically recognizes a protein upregulated in myelinating OLGs(Frazier et al ., 2023). Since it has been reported that this antibody can also be detected in a subset of astrocytes(Bin et al ., 2016), we included only CC1 + /Olig2 + cells.…”

“…Mature OLGs provide the rapid saltatory conduction of action potential and ensure protection and nutritional support to axons (Dewar et al ., 2003). Mature OLGs in the adult brain comprise a heterogeneous population, exhibiting morphological and functional differences that are not only dependent on the brain region but also vary throughout the course of diseases (Frazier et al ., 2023; Marques et al ., 2016). The characterization of these OLG subtypes is essential for understanding their role in normal CNS myelination and repair processes.…”