Oligodendrocyte Maturation Alters the Cell Death Mechanisms That Cause Demyelination.

Myelinating oligodendrocytes die in human disease and early in aging. Despite this, the mechanisms that underly oligodendrocyte death are not resolved and it is also not clear whether these mechanisms change as oligodendrocyte lineage cells are undergoing differentiation and maturation. Here, we used a combination of intravital imaging, single-cell ablation, and cuprizone-mediated demyelination, in both female and male mice, to discover that oligodendrocyte maturation dictates the dynamics and mechanisms of cell death. After single-cell phototoxic damage, oligodendrocyte precursor cells underwent programmed cell death within hours, differentiating oligodendrocytes died over several days, while mature oligodendrocytes took weeks to die. Importantly cells at each maturation stage all eventually died but did so with drastically different temporal dynamics and morphological features. Consistent with this, cuprizone treatment initiated a caspase-3-dependent form of rapid cell death in differentiating oligodendrocytes, while mature oligodendrocytes never activated this executioner caspase. Instead, mature oligodendrocytes exhibited delayed cell death which was marked by DNA damage and disruption in poly-ADP-ribose subcellular localization. Thus, oligodendrocyte maturation plays a key role in determining the mechanism of death a cell undergoes in response to the same insult. This means that oligodendrocyte maturation is important to consider when designing strategies for preventing cell death and preserving myelin while also enhancing the survival of new oligodendrocytes in demyelinating conditions.

Clemastine and metformin extend the window of NMDA receptor surface expression in ageing oligodendrocyte precursor cells.

In the central nervous system, oligodendrocyte precursor cells (OPCs) proliferate and differentiate into myelinating oligodendrocytes throughout life, allowing for ongoing myelination and myelin repair. With age, differentiation efficacy decreases and myelin repair fails; therefore, recent therapeutic efforts have focused on enhancing differentiation. Many cues are thought to regulate OPC differentiation, including neuronal activity, which OPCs can sense and respond to via their voltage-gated ion channels and glutamate receptors. However, OPCs' density of voltage-gated ion channels and glutamate receptors differs with age and brain region, and correlates with their proliferation and differentiation potential, suggesting that OPCs exist in different functional cell states, and that age-associated states might underlie remyelination failure. Here, we use whole-cell patch-clamp to investigate whether clemastine and metformin, two pro-remyelination compounds, alter OPC membrane properties and promote a specific OPC state. We find that clemastine and metformin extend the window of NMDAR surface expression, promoting an NMDAR-rich OPC state. Our findings highlight a possible mechanism for the pro-remyelinating action of clemastine and metformin, and suggest that OPC states can be modulated as a strategy to promote myelin repair.

A Matter of State: Diversity in Oligodendrocyte Lineage Cells.

Oligodendrocyte precursor cells (OPCs) give rise to oligodendrocytes which myelinate axons in the central nervous system. Although classically thought to be a homogeneous population, OPCs are reported to have different developmental origins and display regional and temporal diversity in their transcriptome, response to growth factors, and physiological properties. Similarly, evidence is accumulating that myelinating oligodendrocytes display transcriptional heterogeneity. Analyzing this reported heterogeneity suggests that OPCs, and perhaps also myelinating oligodendrocytes, may exist in different functional cell states. Here, we review the evidence indicating that OPCs and oligodendrocytes are diverse, and we discuss the implications of functional OPC states for myelination in the adult brain and for myelin repair.

Combining whole-cell patch clamp and dye loading in acute brain slices with bulk RNA sequencing in embryonic to aged mice.

Single-cell electrophysiological recordings combined with dye loading and immunohistochemistry provide unparalleled single-cell resolution of cell physiology, morphology, location, and protein expression. When correlated with bulk RNA sequencing, these data can define cell identity and function. Here, we describe a protocol to prepare acute brain slices from embryonic and postnatal mice for whole-cell patch clamp, dye loading and post-hoc immunohistochemistry, and cell isolation for bulk RNA sequencing. While we focus on oligodendrocyte precursor cells, this protocol is applicable to other brain cells. For complete details on the use and execution of this protocol, please refer to Spitzer et al. (2019).

Unraveling Myelin Plasticity.

Plasticity in the central nervous system (CNS) allows for responses to changing environmental signals. While the majority of studies on brain plasticity focus on neuronal synapses, myelin plasticity has now begun to emerge as a potential modulator of neuronal networks. Oligodendrocytes (OLs) produce myelin, which provides fast signal transmission, allows for synchronization of neuronal inputs, and helps to maintain neuronal function. Thus, myelination is also thought to be involved in learning. OLs differentiate from oligodendrocyte precursor cells (OPCs), which are distributed throughout the adult brain, and myelination continues into late adulthood. This process is orchestrated by numerous cellular and molecular signals, such as axonal diameter, growth factors, extracellular signaling molecules, and neuronal activity. However, the relative importance of, and cooperation between, these signaling pathways is currently unknown. In this review, we focus on the current knowledge about myelin plasticity in the CNS. We discuss new insights into the link between this type of plasticity, learning and behavior, as well as mechanistic aspects of myelin formation that may underlie myelin plasticity, highlighting OPC diversity in the CNS.

TMEM10 Promotes Oligodendrocyte Differentiation and is Expressed by Oligodendrocytes in Human Remyelinating Multiple Sclerosis Plaques.

Oligodendrocyte precursor cells (OPCs) differentiate during postnatal development into myelin-forming oligodendrocytes, in a process distinguished by substantial changes in morphology and the onset of myelin gene expression. A mammalian-specific CNS myelin gene, tmem10, also called Opalin, encodes a type 1 transmembrane protein that is highly upregulated during early stages of OPC differentiation; however, a function for TMEM10 has not yet been identified. Here, consistent with previous studies, we detect TMEM10 protein in mouse brain beginning at ~P10 and show that protein levels continue to increase as oligodendrocytes differentiate and myelinate axons in vivo. We show that constitutive TMEM10 overexpression in the Oli-neu oligodendroglial cell line promotes the expression of the myelin-associated genes MAG, CNP and CGT, whereas TMEM10 knock down in primary OPCs reduces CNP mRNA expression and decreases the percentage of MBP-positive oligodendrocytes that differentiate in vitro. Ectopic TMEM10 expression evokes an increase in process extension and branching, and blocking endogenous TMEM10 expression results in oligodendrocytes with abnormal cell morphology. These findings may have implications for human demyelinating disorders, as oligodendrocytes expressing TMEM10 are detected in human remyelinating multiple sclerosis lesions. Together, our findings provide evidence that TMEM10 promotes oligodendrocyte terminal differentiation and may represent a novel target to promote remyelination in demyelinating disorders.

Neuronal activity-dependent myelin repair after stroke.

Brain tissue undergoes substantial activity-dependent reorganisation after stroke due to neuronal plasticity, leading to partial functional recovery in patients. Concurrent myelin repair is crucial for proper neuronal network function and reorganisation. Myelin repair after stroke might occur as myelin plasticity or as remyelination through the recruitment and differentiation of oligodendrocyte precursor cells (OPCs), which become myelin-forming oligodendrocytes (OLs). These two processes might share a similar guiding mechanism, which is postulated to depend on neuronal activity and glutamate signaling to OPCs. However, with ageing, the ability of OPCs to differentiate into myelinating OLs decreases due to changes in their ion channel and neurotransmitter receptor expression profile, rendering them less sensitive to neuronal activity. Because of their unique ability to replace damaged OLs, OPCs represent a potential therapeutic target for myelin repair in the context of stroke.

Oligodendrocyte Progenitor Cells Become Regionally Diverse and Heterogeneous with Age.

Oligodendrocyte progenitor cells (OPCs), which differentiate into myelinating oligodendrocytes during CNS development, are the main proliferative cells in the adult brain. OPCs are conventionally considered a homogeneous population, particularly with respect to their electrophysiological properties, but this has been debated. We show, by using single-cell electrophysiological recordings, that OPCs start out as a homogeneous population but become functionally heterogeneous, varying both within and between brain regions and with age. These electrophysiological changes in OPCs correlate with the differentiation potential of OPCs; thus, they may underlie the differentiational differences in OPCs between regions and, likewise, differentiation failure with age.