Induction of oligodendrocyte differentiation by Olig2 and Sox10: evidence for reciprocal interactions and dosage-dependent mechanisms

The myelination-associated G protein-coupled receptor 37 is regulated by Zfp488, Nkx2.2, and Sox10 during oligodendrocyte differentiation

Oligodendrocyte differentiation and myelination in the central nervous system are controlled and coordinated by a complex gene regulatory network that contains several transcription factors, including Zfp488 and Nkx2.2. Despite the proven role in oligodendrocyte differentiation little is known about the exact mode of Zfp488 and Nkx2.2 action, including their target genes. Here, we used overexpression of Zfp488 and Nkx2.2 in differentiating CG4 cells to identify aspects of the oligodendroglial expression profile that depend on these transcription factors. Although both transcription factors are primarily described as repressors, the detected changes argue for an additional function as activators. Among the genes activated by both Zfp488 and Nkx2.2 was the G protein-coupled receptor Gpr37 that is important during myelination. In agreement with a positive effect on Gpr37 expression, downregulation of the G protein-coupled receptor was observed in Zfp488- and in Nkx2.2-deficient oligodendrocytes in the mouse. We also identified several potential regulatory regions of the Gpr37 gene. Although Zfp488 and Nkx2.2 both bind to one of the regulatory regions downstream of the Gpr37 gene in vivo, none of the regulatory regions was activated by either transcription factor alone. Increased activation by Zfp488 or Nkx2.2 was only observed in the presence of Sox10, a transcription factor continuously present in oligodendroglial cells. Our results argue that both Zfp488 and Nkx2.2 also act as transcriptional activators during oligodendrocyte differentiation and cooperate with Sox10 to allow the expression of Gpr37 as a modulator of the myelination process.

Evolution of glial cells: a non-bilaterian perspective

Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.

Regulators of Oligodendrocyte Differentiation

Myelination has evolved as a mechanism to ensure fast and efficient propagation of nerve impulses along axons. Within the central nervous system (CNS), myelination is carried out by highly specialized glial cells, oligodendrocytes. The formation of myelin is a prolonged aspect of CNS development that occurs well into adulthood in humans, continuing throughout life in response to injury or as a component of neuroplasticity. The timing of myelination is tightly tied to the generation of oligodendrocytes through the differentiation of their committed progenitors, oligodendrocyte precursor cells (OPCs), which reside throughout the developing and adult CNS. In this article, we summarize our current understanding of some of the signals and pathways that regulate the differentiation of OPCs, and thus the myelination of CNS axons.

Transcription Factors Sox2 and Sox3 Directly Regulate the Expression of Genes Involved in the Onset of Oligodendrocyte Differentiation

Rapid information processing in the central nervous system requires the myelination of axons by oligodendrocytes. The transcription factor Sox2 and its close relative Sox3 redundantly regulate the development of myelin-forming oligodendrocytes, but little is known about the underlying molecular mechanisms. Here, we characterized the expression profile of cultured oligodendroglial cells during early differentiation and identified Bcas1, Enpp6, Zfp488 and Nkx2.2 as major downregulated genes upon Sox2 and Sox3 deletion. An analysis of mice with oligodendrocyte-specific deletion of Sox2 and Sox3 validated all four genes as downstream targets in vivo. Additional functional assays identified regulatory regions in the vicinity of each gene that are responsive to and bind both Sox proteins. Bcas1, Enpp6, Zfp488 and Nkx2.2 therefore likely represent direct target genes and major effectors of Sox2 and Sox3. Considering the preferential expression and role of these genes in premyelinating oligodendrocytes, our findings suggest that Sox2 and Sox3 impact oligodendroglial development at the premyelinating stage with Bcas1, Enpp6, Zfp488 and Nkx2.2 as their major effectors.

Impaired oligodendrogenesis in the white matter of aged mice following diffuse traumatic brain injury

Senescence is a negative prognostic factor for outcome and recovery following traumatic brain injury (TBI). TBI-induced white matter injury may be partially due to oligodendrocyte demise. We hypothesized that the regenerative capacity of oligodendrocyte precursor cells (OPCs) declines with age. To test this hypothesis, the regenerative capability of OPCs in young [(10 weeks ±2 (SD)] and aged [(62 weeks ±10 (SD)] mice was studied in mice subjected to central fluid percussion injury (cFPI), a TBI model causing widespread white matter injury. Proliferating OPCs were assessed by immunohistochemistry for the proliferating cell nuclear antigen (PCNA) marker and labeled by 5-ethynyl-2'-deoxyuridine (EdU) administered daily through intraperitoneal injections (50 mg/kg) from day 2 to day 6 after cFPI. Proliferating OPCs were quantified in the corpus callosum and external capsule on day 2 and 7 post-injury (dpi). The number of PCNA/Olig2-positive and EdU/Olig2-positive cells were increased at 2dpi (p < .01) and 7dpi (p < .01), respectively, in young mice subjected to cFPI, changes not observed in aged mice. Proliferating Olig2+/Nestin+ cells were less common (p < .05) in the white matter of brain-injured aged mice, without difference in proliferating Olig2+/PDGFRα+ cells, indicating a diminished proliferation of progenitors with different spatial origin. Following TBI, co-staining for EdU/CC1/Olig2 revealed a reduced number of newly generated mature oligodendrocytes in the white matter of aged mice when compared to the young, brain-injured mice (p < .05). We observed an age-related decline of oligodendrogenesis following experimental TBI that may contribute to the worse outcome of elderly patients following TBI.

MicroRNAs dysregulated in multiple sclerosis affect the differentiation of CG-4 cells, an oligodendrocyte progenitor cell line

Introduction

Demyelination is one of the hallmarks of multiple sclerosis (MS). While remyelination occurs during the disease, it is incomplete from the start and strongly decreases with its progression, mainly due to the harm to oligodendrocyte progenitor cells (OPCs), causing irreversible neurological deficits and contributing to neurodegeneration. Therapeutic strategies promoting remyelination are still very preliminary and lacking within the current treatment panel for MS.

Methods

In a previous study, we identified 21 microRNAs dysregulated mostly in the CSF of relapsing and/or remitting MS patients. In this study we transfected the mimics/inhibitors of several of these microRNAs separately in an OPC cell line, called CG-4. We aimed (1) to phenotypically characterize their effect on OPC differentiation and (2) to identify corroborating potential mRNA targets via immunocytochemistry, RT-qPCR analysis, RNA sequencing, and Gene Ontology enrichment analysis.

Results

We observed that the majority of 13 transfected microRNA mimics decreased the differentiation of CG-4 cells. We demonstrate, by RNA sequencing and independent RT-qPCR analyses, that miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage as evidenced by the downregulation of premyelinating oligodendrocyte (OL) [Tcf7l2, Cnp (except for miR-145-5p)] and mature OL (Plp1, Mbp, and Mobp) markers, whereas only miR-214-3p promotes OPC differentiation. We further propose a comprehensive exploration of their change in cell fate through Gene Ontology enrichment analysis. We finally confirm by RT-qPCR analyses the downregulation of several predicted mRNA targets for each microRNA that possibly support their effect on OPC differentiation by very distinctive mechanisms, of which some are still unexplored in OPC/OL physiology.

Conclusion

miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage, whereas miR-214-3p promotes the differentiation of CG-4 cells. We propose several potential mRNA targets and hypothetical mechanisms by which each microRNA exerts its effect. We hereby open new perspectives in the research on OPC differentiation and the pathophysiology of demyelination/remyelination, and possibly even in the search for new remyelinating therapeutic strategies in the scope of MS.

Gliomas: a reflection of temporal gliogenic principles

The hijacking of early developmental programs is a canonical feature of gliomas where neoplastic cells resemble neurodevelopmental lineages and possess mechanisms of stem cell resilience. Given these parallels, uncovering how and when in developmental time gliomagenesis intersects with normal trajectories can greatly inform our understanding of tumor biology. Here, we review how elapsing time impacts the developmental principles of astrocyte (AS) and oligodendrocyte (OL) lineages, and how these same temporal programs are replicated, distorted, or circumvented in pathological settings such as gliomas. Additionally, we discuss how normal gliogenic processes can inform our understanding of the temporal progression of gliomagenesis, including when in developmental time gliomas originate, thrive, and can be pushed towards upon therapeutic coercion.

Exosome-specific loading Sox10 for the treatment of Cuprizone-induced demyelinating model

Demyelination is a pathological feature commonly observed in various central nervous system diseases. It is characterized by the aggregation of oligodendrocyte progenitor cells (OPCs) in the lesion area, which face difficulties in differentiating into mature oligodendrocytes (OLGs). The differentiation of OPCs requires the presence of Sox10, but its expression decreases under pathological conditions. Therefore, we propose a therapeutic strategy to regulate OPCs differentiation and achieve myelin repair by endogenously loading Sox10 into exosomes. To accomplish this, we generated a lentivirus-armed Sox10 that could anchor to the inner surface of the exosome membrane. We then infected HEK293 cells to obtain exosomes with high expression of Sox10 (exosomes-Sox10, ExoSs). In vitro, experiments confirmed that both Exos and ExoSs can be uptaken by OPCs, but only ExoSs exhibit a pro-differentiation effect on OPCs. In vivo, we administered PBS, Exos, and ExoSs to cuprizone-induced demyelinating mice. The results demonstrated that ExoSs can regulate the differentiation of PDGFRα+ OPCs into APC+ OLGs and reduce myelin damage in the corpus callosum region of the mouse brain compared to other groups. Further testing suggests that Sox10 may have a reparative effect on the myelin sheath by enhancing the expression of MBP, possibly facilitated by the exosome delivery of the protein into the lesion. This endogenously loaded technology holds promise as a strategy for protein-based drugs in the treatment of demyelinating diseases.

Context-dependent regulation of Notch signaling in glial development and tumorigenesis

In the mammalian brain, Notch signaling maintains the cortical stem cell pool and regulates the glial cell fate choice and differentiation. However, the function of Notch in regulating glial development and its involvement in tumorigenesis have not been well understood. Here, we show that Notch inactivation by genetic deletion of Rbpj in stem cells decreases astrocytes but increases oligodendrocytes with altered internal states. Inhibiting Notch in glial progenitors does not affect cell generation but instead accelerates the growth of Notch-deprived oligodendrocyte progenitor cells (OPCs) and OPC-related glioma. We also identified a cross-talk between oligodendrocytes and astrocytes, with premyelinating oligodendrocytes secreting BMP4, which is repressed by Notch, to up-regulate GFAP expression in adjacent astrocytes. Moreover, Notch inactivation in stem cells causes a glioma subtype shift from astroglia-associated to OPC-correlated patterns and vice versa. Our study reveals Notch's context-dependent function, promoting astrocytes and astroglia-associated glioma in stem cells and repressing OPCs and related glioma in glial progenitors.

Consequences of oxygen deprivation on myelination and sex-dependent alterations

Oxygen deprivation is one of the main causes of morbidity and mortality in newborns, occurring with a higher prevalence in preterm infants, reaching 20 % to 50 % mortality in newborns in the perinatal period. When they survive, 25 % exhibit neuropsychological pathologies, such as learning difficulties, epilepsy, and cerebral palsy. White matter injury is one of the main features found in oxygen deprivation injury, which can lead to long-term functional impairments, including cognitive delay and motor deficits. The myelin sheath accounts for much of the white matter in the brain by surrounding axons and enabling the efficient conduction of action potentials. Mature oligodendrocytes, which synthesize and maintain myelination, also comprise a significant proportion of the brain's white matter. In recent years, oligodendrocytes and the myelination process have become potential therapeutic targets to minimize the effects of oxygen deprivation on the central nervous system. Moreover, evidence indicate that neuroinflammation and apoptotic pathways activated during oxygen deprivation may be influenced by sexual dimorphism. To summarize the most recent research about the impact of sexual dimorphism on the neuroinflammatory state and white matter injury after oxygen deprivation, this review presents an overview of the oligodendrocyte lineage development and myelination, the impact of oxygen deprivation and neuroinflammation on oligodendrocytes in neurodevelopmental disorders, and recent reports about sexual dimorphism regarding the neuroinflammation and white matter injury after neonatal oxygen deprivation.

A subset of OPCs do not express Olig2 during development which can be increased in the adult by brain injuries and complex motor learning

Oligodendrocyte precursor cells (OPCs) are uniformly distributed in the mammalian brain; however, their function is rather heterogeneous in respect to their origin, location, receptor/channel expression and age. The basic helix-loop-helix transcription factor Olig2 is expressed in all OPCs as a pivotal determinant of their differentiation. Here, we identified a subset (2%-26%) of OPCs lacking Olig2 in various brain regions including cortex, corpus callosum, CA1 and dentate gyrus. These Olig2 negative (Olig2^neg ) OPCs were enriched in the juvenile brain and decreased subsequently with age, being rarely detectable in the adult brain. However, the loss of this population was not due to apoptosis or microglia-dependent phagocytosis. Unlike Olig2^pos OPCs, these subset cells were rarely labeled for the mitotic marker Ki67. And, accordingly, BrdU was incorporated only by a three-day long-term labeling but not by a 2-hour short pulse, suggesting these cells do not proliferate any more but were derived from proliferating OPCs. The Olig2^neg OPCs exhibited a less complex morphology than Olig2^pos ones. Olig2^neg OPCs preferentially remain in a precursor stage rather than differentiating into highly branched oligodendrocytes. Changing the adjacent brain environment, for example, by acute injuries or by complex motor learning tasks, stimulated the transition of Olig2^pos OPCs to Olig2^neg cells in the adult. Taken together, our results demonstrate that OPCs transiently suppress Olig2 upon changes of the brain activity.

Myelinated axon as a plastic cable regulating brain functions

Each oligodendrocyte (OC) forms myelin approximately in around 10 different axons to coordinate information transfer by regulating conduction velocity in the central nervous system (CNS). In the classical view, myelin has been considered a static structure that rarely turns over under healthy conditions because myelin tightly holds axons by their laminar complex structure. However, in recent decades, the classical views of static myelin have been renewed with pioneering studies that showed plastic changes in myelin throughout life with new experiences, such as the acquisition of new motor skills and the formation of memory. These changes in myelin regulate conduction velocity to optimize the temporal pattern of neuronal circuit activity among distinct brain regions associated with skill learning and memory. Here, we introduce pioneering studies and discuss the implications of plastic myelin on neural circuits and brain function.

Pregnenolone enhances the proliferation of mouse neural stem cells and promotes oligodendrogenesis, together with Sox10, and neurogenesis, along with Notch1 and Pax6

BACKGROUND

Pregnenolone is a precursor of various steroid hormones involved in osteoblast proliferation, microtubules polymerization and cell survival protection. Previous reports focused on the effects of pregnenolone metabolites on stem cell proliferation and differentiation; however, the effects of pregnenolone itself has not been well explored. The present study aimed to investigate the role of pregnenolone on NSC proliferation and to determine the doses required for NSC differentiation as well as the various genes involved in its mechanism of action.

METHODS

NSCs were isolated from the embryonic cortex of E14 mice, incubated for 5 days, and then treated with pregnenolone doses of 2, 5, 10, 15 and 20 μM for another 5 days. The number of neurospheres and neurosphere derived cells were then counted. Flow cytometry was used to evaluate the differentiation of NSCs into oligodendrocytes, astrocytes, and neurons. The expression level of Notch1, Pax6 and Sox10 genes were also measured by Real Time PCR after 5 days of treatment.

RESULTS

Our data suggest that treatment with 10 μM pregnenolone is optimal for NSC proliferation. In fact, this concentration caused the highest increase in the number of neurospheres and neurosphere derived cells, compared to the control group. In addition, treatment with low doses of pregnenolone (5 and 10 μM) caused a significant increase in NSC differentiation towards immature (Olig2⁺) and mature (MBP⁺) oligodendrocyte cell populations, compared to controls. However, NSC differentiation into neurons (beta III tubulin ⁺ cells) increased in all treatment groups, with the highest and most significant increase obtained at 15 μM concentration. It is worth noting that pregnenolone at the highest concentration of 15 μM decreased the number of astrocytes (GFAP+). Furthermore, there was an increase of Sox10 expression with low pregnenolone doses, leading to oligodendrogenesis, whereas Notch1 and Pax6 gene expression increased in pregnenolone groups with more neurogenesis.

CONCLUSION

Pregnenolone regulates NSCs proliferation in vitro. Treatment with low doses of pregnenolone caused an increase in the differentiation of NSCs into mature oligodendrocytes while higher doses increased the differentiation of NSCs into neurons. Oligodendrogenesis was accompanied by Sox10 while neurogenesis occurred together with Notch1 and Pax6 expression.

OLIG2 is an in vivo bookmarking transcription factor in the developing neural tube in mouse

Cells possess intrinsic features that are inheritable via epigenetic regulation, such as DNA methylation and histone modification. These inheritable features maintain a unique gene expression pattern, underlying cellular memory. Because of the degradation or displacement of mitotic chromosomes, most transcription factors do not contribute to cellular memory. However, accumulating in vitro evidence indicates that some transcription factors can be retained in mitotic chromosomes called as bookmarking. Such transcription factors may contribute to a novel third mechanism of cellular memory. Since most findings of transcription factor bookmarking have been reported in vitro, little is currently known in vivo. In the neural tube of mouse embryos, we discovered that OLIG2, a basic helix loop helix (bHLH) transcription factor that regulates proliferation of neural progenitors and the cell fate of motoneurons and oligodendrocytes, binds to chromatin through every cell cycle including M-phase. OLIG2 chromosomal localization coincides with mitotic cell features such as the phosphorylation of histone H3, KI67, and nuclear membrane breakdown. Chromosomal localization of OLIG2 is regulated by an N-terminus triple serine motif. Photobleaching analysis revealed slow OLIG2 mobility, suggesting a high affinity of OLIG2 to DNA. In Olig2 N-terminal deletion mutant mice, motoneurons and oligodendrocyte progenitor numbers are reduced in the neural tube, suggesting that the bookmarking regulatory domain is important for OLIG2 function. We conclude that OLIG2 is a de novo in vivo bookmarking transcription factor. Our results demonstrate the presence of in vivo bookmarking in a living organism and illustrate a novel function of transcription factors.

Development of myelinating glia: An overview

Myelin is essential to nervous system function, playing roles in saltatory conduction and trophic support. Oligodendrocytes (OLs) and Schwann cells (SCs) form myelin in the central and peripheral nervous systems respectively and follow different developmental paths. OLs are neural stem-cell derived and follow an intrinsic developmental program resulting in a largely irreversible differentiation state. During embryonic development, OL precursor cells (OPCs) are produced in distinct waves originating from different locations in the central nervous system, with a subset developing into myelinating OLs. OPCs remain evenly distributed throughout life, providing a population of responsive, multifunctional cells with the capacity to remyelinate after injury. SCs derive from the neural crest, are highly dependent on extrinsic signals, and have plastic differentiation states. SC precursors (SCPs) are produced in early embryonic nerve structures and differentiate into multipotent immature SCs (iSCs), which initiate radial sorting and differentiate into myelinating and non-myelinating SCs. Differentiated SCs retain the capacity to radically change phenotypes in response to external signals, including becoming repair SCs, which drive peripheral regeneration. While several transcription factors and myelin components are common between OLs and SCs, their differentiation mechanisms are highly distinct, owing to their unique lineages and their respective environments. In addition, both OLs and SCs respond to neuronal activity and regulate nervous system output in reciprocal manners, possibly through different pathways. Here, we outline their basic developmental programs, mechanisms regulating their differentiation, and recent advances in the field.

Rapid differentiation of hiPSCs into functional oligodendrocytes using an OLIG2 synthetic modified messenger RNA

Transcription factors (TFs) have been introduced to drive the highly efficient differentiation of human-induced pluripotent stem cells (hiPSCs) into lineage-specific oligodendrocytes (OLs). However, effective strategies currently rely mainly on genome-integrating viruses. Here we show that a synthetic modified messenger RNA (smRNA)-based reprogramming method that leads to the generation of transgene-free OLs has been developed. An smRNA encoding a modified form of OLIG2, in which the serine 147 phosphorylation site is replaced with alanine, OLIG2^S147A, is designed to reprogram hiPSCs into OLs. We demonstrate that repeated administration of the smRNA encoding OLIG2^S147A lead to higher and more stable protein expression. Using the single-mutant OLIG2 smRNA morphogen, we establish a 6-day smRNA transfection protocol, and glial induction lead to rapid NG2⁺ OL progenitor cell (OPC) generation (>70% purity) from hiPSC. The smRNA-induced NG2⁺ OPCs can mature into functional OLs in vitro and promote remyelination in vivo. Taken together, we present a safe and efficient smRNA-driven strategy for hiPSC differentiation into OLs, which may be utilized for therapeutic OPC/OL transplantation in patients with neurodegenerative disease.

The use of synthetic modified messenger RNA (smRNA) allows for the differentiation of human-induced pluripotent stem cells (hiPSCs) into lineage-specific oligodendrocytes.

The effect of Zingiber Officinale Extract on Preventing Demyelination of Corpus Callosum in a Rat Model of Multiple Sclerosis

Background

Multiple sclerosis (MS) is the most prevalent neurological disability of young adults. Anti-inflammatory drugs have relative effects on MS. The anti-inflammatory and antioxidative effects of Zingiber officinale (ginger) have been proven in some experimental and clinical investigations. The aim of this study was to evaluate the effects of ginger extract on preventing myelin degradation in a rat model of MS.

Methods

Forty nine male Wistar rats were used in this study and divided into four control groups: the normal group, cuprizone-induced group, sham group (cuprizone [CPZ] + sodium carboxymethyl cellulose [NaCMC]), standard control group (fingolimod + cuprizone), including three experimental groups of CPZ, each receiving three different doses of ginger extract: 150, 300, and 600mg/kg /kg/day.

Results

Ginger extract of 600 mg/kg prevented corpus callosum from demyelination; however, a significant difference was observed in the fingolimod group (p < 0.05). Difference in the CPZ group was quite significant (p < 0.05).

Conclusion

Treatment with ginger inhibited demyelination and alleviated remyelination of corpus callosum in rats. Therefore, it could serve as a therapeutic agent in the MS.

MicroRNAs in oligodendrocyte development and remyelination

Oligodendrocytes are the glial cells responsible for the formation of myelin around axons of the central nervous system (CNS). Myelin is an insulating layer that allows electrical impulses to transmit quickly and efficiently along neurons. If myelin is damaged, as in chronic demyelinating disorders such as multiple sclerosis (MS), these impulses slow down. Remyelination by oligodendrocytes is often ineffective in MS, in part because of the failure of oligodendrocyte precursor cells (OPCs) to differentiate into mature, myelinating oligodendrocytes. The process of oligodendrocyte differentiation is tightly controlled by several regulatory networks involving transcription factors, intracellular signaling pathways, and extrinsic cues. Understanding the factors that regulate oligodendrocyte development is essential for the discovery of new therapeutic strategies capable of enhancing remyelination. Over the past decade, microRNAs (miRNAs) have emerged as key regulators of oligodendrocyte development, exerting effects on cell specification, proliferation, differentiation, and myelination. This article will review the role of miRNAs on oligodendrocyte biology and discuss their potential as promising therapeutic tools for remyelination.

EGF signaling promotes the lineage conversion of astrocytes into oligodendrocytes

Background

The conversion of astrocytes activated by nerve injuries to oligodendrocytes is not only beneficial to axonal remyelination, but also helpful for reversal of glial scar. Recent studies have shown that pathological niche promoted the Sox10-mediated astrocytic transdifferentiation to oligodendrocytes. The extracellular factors underlying the cell fate switching are not known.

Methods

Astrocytes were obtained from mouse spinal cord dissociation culture and purified by differential adherent properties. The lineage conversion of astrocytes into oligodendrocyte lineage cells was carried out by Sox10-expressing virus infection both in vitro and in vivo, meanwhile, epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR) inhibitor Gefitinib were adopted to investigate the function of EGF signaling in this fate transition process. Pharmacological inhibition analyses were performed to examine the pathway connecting the EGF with the expression of oligodendrogenic genes and cell fate transdifferentiation.

Results

EGF treatment facilitated the Sox10-induced transformation of astrocytes to O4⁺ induced oligodendrocyte precursor cells (iOPCs) in vitro. The transdifferentiation of astrocytes to iOPCs went through two distinct but interconnected processes: (1) dedifferentiation of astrocytes to astrocyte precursor cells (APCs); (2) transformation of APCs to iOPCs, EGF signaling was involved in both processes. And EGF triggered astrocytes to express oligodendrogenic genes Olig1 and Olig2 by activating extracellular signal-regulated kinase 1 and 2 (Erk1/2) pathway. In addition, we discovered that EGF can enhance astrocyte transdifferentiation in injured spinal cord tissues.

Conclusions

These findings provide strong evidence that EGF facilitates the transdifferentiation of astrocytes to oligodendrocytes, and suggest that targeting the EGF-EGFR-Erk1/2 signaling axis may represent a novel therapeutic strategy for myelin repair in injured central nervous system (CNS) tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00478-5.

Human iPSC-Derived Neural Models for Studying Alzheimer's Disease: from Neural Stem Cells to Cerebral Organoids

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study mechanisms of human neural development, disease modeling, and drug discovery in vitro. Especially in the field of Alzheimer’s disease (AD), where this treatment is lacking, tremendous effort has been put into the investigation of molecular mechanisms behind this disease using induced pluripotent stem cell-based models. Numerous of these studies have found either novel regulatory mechanisms that could be exploited to develop relevant drugs for AD treatment or have already tested small molecules on in vitro cultures, directly demonstrating their effect on amelioration of AD-associated pathology. This review thus summarizes currently used differentiation strategies of induced pluripotent stem cells towards neuronal and glial cell types and cerebral organoids and their utilization in modeling AD and potential drug discovery.

Ethanol effects on cerebellar myelination in a postnatal mouse model of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) are alarmingly common, result in significant personal and societal loss, and there are no effective treatments for these disorders. Cerebellar neuropathology is common in FASD and can cause impaired cognitive and motor function. The current study evaluates the effects of ethanol on oligodendrocyte-lineage cells, as well as molecules that modulate oligodendrocyte differentiation and function in the cerebellum in a postnatal mouse model of FASD. Neonatal mice were treated with ethanol from P4-P9 (postnatal day), the cerebellum was isolated at P10, and mRNAs encoding oligodendrocyte-associated molecules were quantitated by qRT-PCR. Our studies demonstrated that ethanol significantly reduced the expression of markers for multiple stages of oligodendrocyte maturation, including oligodendrocyte precursor cells, pre-myelinating oligodendrocytes, and mature myelinating oligodendrocytes. Additionally, we determined that ethanol significantly decreased the expression of molecules that play critical roles in oligodendrocyte differentiation. Interestingly, we also observed that ethanol significantly reduced the expression of myelin-associated inhibitors, which may act as a compensatory mechanism to ethanol toxicity. Furthermore, we demonstrate that ethanol alters the expression of a variety of molecules important in oligodendrocyte function and myelination. Collectively, our studies increase our understanding of specific mechanisms by which ethanol modulates myelination in the developing cerebellum, and potentially identify novel targets for FASD therapy.

Using the lineage determinants Olig2 and Sox10 to explore transcriptional regulation of oligodendrocyte development

The transcription factors Olig2 and Sox10 jointly define oligodendroglial identity. Because of their continuous presence during development and in the differentiated state they shape the oligodendroglial regulatory network at all times. In this review, we exploit their eminent role and omnipresence to elaborate the central principles that organize the gene regulatory network in oligodendrocytes in such a way that it preserves its identity, but at the same time allows defined and stimulus-dependent changes that result in an ordered lineage progression, differentiation, and myelination. For this purpose, we outline the multiple functional and physical interactions and intricate cross-regulatory relationships with other transcription factors, such as Hes5, Id, and SoxD proteins, in oligodendrocyte precursors and Tcf7l2, Sip1, Nkx2.2, Zfp24, and Myrf during differentiation and myelination, and interpret them in the context of the regulatory network.

Transcription Factor-Based Strategies to Generate Neural Cell Types from Human Pluripotent Stem Cells

In the last years, the use of pluripotent stem cells in studies of human biology has grown exponentially. These cells represent an infinite source for differentiation into several human cell types facilitating the investigation on biological processes, functionality of cells, or diseases mechanisms in relevant human models. In the neurobiology field, pluripotent stem cells have been extensively used to generate the main neuronal and glial cells of the brain. Traditionally, protocols following developmental cues have been applied to pluripotent stem cells to drive differentiation toward different cell lineages; however, these protocols give rise to populations with mixed identities. Interestingly, new protocols applying overexpression of lineage-specific transcription factors (TFs) have emerged and facilitated the generation of highly pure populations of specific subtypes of neurons and glial cells in an easy, reproducible, and rapid manner. In this study, we review protocols based on this strategy to generate excitatory, inhibitory, dopaminergic, and motor neurons as well as astrocytes, oligodendrocytes, and microglia. In addition, we will discuss the main applications for cells generated with these protocols, including disease modeling, drug screening, and mechanistic studies. Finally, we will discuss the advantages and disadvantages of TF-based protocols and present our view of the future in this field.

OLIG2 regulates lncRNAs and its own expression during oligodendrocyte lineage formation

BACKGROUND

Oligodendrocytes, responsible for axon ensheathment, are critical for central nervous system (CNS) development, function, and diseases. OLIG2 is an important transcription factor (TF) that acts during oligodendrocyte development and performs distinct functions at different stages. Previous studies have shown that lncRNAs (long non-coding RNAs; > 200 bp) have important functions during oligodendrocyte development, but their roles have not been systematically characterized and their regulation is not yet clear.

RESULTS

We performed an integrated study of genome-wide OLIG2 binding and the epigenetic modification status of both coding and non-coding genes during three stages of oligodendrocyte differentiation in vivo: neural stem cells (NSCs), oligodendrocyte progenitor cells (OPCs), and newly formed oligodendrocytes (NFOs). We found that 613 lncRNAs have OLIG2 binding sites and are expressed in at least one cell type, which can potentially be activated or repressed by OLIG2. Forty-eight of them have increased expression in oligodendrocyte lineage cells. Predicting lncRNA functions by using a "guilt-by-association" approach revealed that the functions of these 48 lncRNAs were enriched in "oligodendrocyte development and differentiation." Additionally, bivalent genes are known to play essential roles during embryonic stem cell differentiation. We identified bivalent genes in NSCs, OPCs, and NFOs and found that some bivalent genes bound by OLIG2 are dynamically regulated during oligodendrocyte development. Importantly, we unveiled a previously unknown mechanism that, in addition to transcriptional regulation via DNA binding, OLIG2 could self-regulate through the 3' UTR of its own mRNA.

CONCLUSIONS

Our studies have revealed the missing links in the mechanisms regulating oligodendrocyte development at the transcriptional level and after transcription. The results of our research have improved the understanding of fundamental cell fate decisions during oligodendrocyte lineage formation, which can enable insights into demyelination diseases and regenerative medicine.

Emerging Role of m6 A Methylome in Brain Development: Implications for Neurological Disorders and Potential Treatment

Dynamic modification of RNA affords proximal regulation of gene expression triggered by non-genomic or environmental changes. One such epitranscriptomic alteration in RNA metabolism is the installation of a methyl group on adenosine [N⁶-methyladenosine (m⁶A)] known to be the most prevalent modified state of messenger RNA (mRNA) in the mammalian cell. The methylation machinery responsible for the dynamic deposition and recognition of m⁶A on mRNA is composed of subunits that play specific roles, including reading, writing, and erasing of m⁶A marks on mRNA to influence gene expression. As a result, peculiar cellular perturbations have been linked to dysregulation of components of the mRNA methylation machinery or its cofactors. It is increasingly clear that neural tissues/cells, especially in the brain, make the most of m⁶A modification in maintaining normal morphology and function. Neurons in particular display dynamic distribution of m⁶A marks during development and in adulthood. Interestingly, such dynamic m⁶A patterns are responsive to external cues and experience. Specific disturbances in the neural m⁶A landscape lead to anomalous phenotypes, including aberrant stem/progenitor cell proliferation and differentiation, defective cell fate choices, and abnormal synaptogenesis. Such m⁶A-linked neural perturbations may singularly or together have implications for syndromic or non-syndromic neurological diseases, given that most RNAs in the brain are enriched with m⁶A tags. Here, we review the current perspectives on the m⁶A machinery and function, its role in brain development and possible association with brain disorders, and the prospects of applying the clustered regularly interspaced short palindromic repeats (CRISPR)–dCas13b system to obviate m⁶A-related neurological anomalies.

Oxidative stress and impaired oligodendrocyte precursor cell differentiation in neurological disorders

Oligodendrocyte precursor cells (OPCs) account for 5% of the resident parenchymal central nervous system glial cells. OPCs are not only a back-up for the loss of oligodendrocytes that occurs due to brain injury or inflammation-induced demyelination (remyelination) but are also pivotal in plastic processes such as learning and memory (adaptive myelination). OPC differentiation into mature myelinating oligodendrocytes is controlled by a complex transcriptional network and depends on high metabolic and mitochondrial demand. Mounting evidence shows that OPC dysfunction, culminating in the lack of OPC differentiation, mediates the progression of neurodegenerative disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. Importantly, neurodegeneration is characterised by oxidative and carbonyl stress, which may primarily affect OPC plasticity due to the high metabolic demand and a limited antioxidant capacity associated with this cell type. The underlying mechanisms of how oxidative/carbonyl stress disrupt OPC differentiation remain enigmatic and a focus of current research efforts. This review proposes a role for oxidative/carbonyl stress in interfering with the transcriptional and metabolic changes required for OPC differentiation. In particular, oligodendrocyte (epi)genetics, cellular defence and repair responses, mitochondrial signalling and respiration, and lipid metabolism represent key mechanisms how oxidative/carbonyl stress may hamper OPC differentiation in neurodegenerative disorders. Understanding how oxidative/carbonyl stress impacts OPC function may pave the way for future OPC-targeted treatment strategies in neurodegenerative disorders.

Oligodendrocyte Development and Regenerative Therapeutics in Multiple Sclerosis

Myelination by oligodendrocytes (OLs) is an important biological process essential for central nervous system (CNS) development and functions. Oligodendroglial lineage cells undergo several morphological and molecular changes at different stages of their lineage progression into myelinating OLs. The transition steps of the oligodendrocyte progenitor cells (OPCs) to myelinating oligodendrocytes are defined by a specific pattern of regulated gene expression, which is under the control of coordinated signaling pathways. Any abnormal development, loss or failure of oligodendrocytes to myelinate axons can lead to several neurodegenerative diseases like multiple sclerosis (MS). MS is characterized by inflammation and demyelination, and current treatments target only the immune component of the disease, but have little impact on remyelination. Recently, several pharmacological compounds enhancing remyelination have been identified and some of them are in clinical trials. Here, we will review the current knowledge on oligodendrocyte differentiation, myelination and remyelination. We will focus on MS as a pathological condition, the most common chronic inflammatory demyelinating disease of the CNS in young adults.

Impact of the Olig Family on Neurodevelopmental Disorders

The Olig genes encode members of the basic helix-loop-helix (bHLH) family of transcription factors. Olig1, Olig2, and Olig3 are expressed in both the developing and mature central nervous system (CNS) and strictly regulate cellular specification and differentiation. Extensive studies have established functional roles of Olig1 and Olig2 in directing neuronal and glial formation during different stages in development. Recently, Olig2 overexpression was implicated in neurodevelopmental disorders down syndrome (DS) and autism spectrum disorder (ASD) but its influence on cognitive and intellectual defects remains unknown. In this review, we summarize the biological functions of the Olig family and how it uniquely promotes cellular diversity in the CNS. This is followed up with a discussion on how abnormal Olig2 expression impacts brain development and function in DS and ASD. Collectively, the studies described here emphasize vital features of the Olig members and their distinctive potential roles in neurodevelopmental disease states.

Region-specific distribution of Olig2-expressing astrocytes in adult mouse brain and spinal cord

Olig2 is an important transcription factor essential for the specification and differentiation of oligodendrocytes as well as astrocytes and neurons during developmental stages. However, Olig2 distribution pattern and its relationship among different types of glial cells in the adult central nervous system (CNS) are not well characterized. Here, we systematically examined Olig2 expression pattern in combination with major markers of neurons and glial cells throughout the brain and spinal cord in the adult mice. As expected, Olig2 is universally expressed in oligodendrocytes and oligodendrocyte precursor cells (OPCs), but not in neurons or microglia. Interestingly, we discover a subpopulation of Olig2+ astrocytes that are highly enriched in some specific regions including the olfactory bulb, thalamus, midbrain, medulla, and spinal cord in the adult mice. Moreover, OPCs have high expression level of Olig2, whereas oligodendrocytes and astrocytes have similar level of Olig2 expression. Our results suggest that a distinct population of Olig2+ astrocytes are highly concentrated in discrete regions in the adult CNS. Investigating the functional significance of these Olig2+ astrocytes in both resting state and pathological state of the brain and spinal cord may broaden our understanding on astrocytic heterogeneity and functions.

yippee like 3 (ypel3) is a novel gene required for myelinating and perineurial glia development

Hypomyelination, a neurological condition characterized by decreased production of myelin sheets by glial cells, often has no known etiology. Elucidating the genetic causes of hypomyelination provides a better understanding of myelination, as well as means to diagnose, council, and treat patients. Here, we present evidence that YIPPEE LIKE 3 (YPEL3), a gene whose developmental role was previously unknown, is required for central and peripheral glial cell development. We identified a child with a constellation of clinical features including cerebral hypomyelination, abnormal peripheral nerve conduction, hypotonia, areflexia, and hypertrophic peripheral nerves. Exome and genome sequencing revealed a de novo mutation that creates a frameshift in the open reading frame of YPEL3, leading to an early stop codon. We used zebrafish as a model system to validate that YPEL3 mutations are causative of neuropathy. We found that ypel3 is expressed in the zebrafish central and peripheral nervous system. Using CRISPR/Cas9 technology, we created zebrafish mutants carrying a genomic lesion similar to that of the patient. Our analysis revealed that Ypel3 is required for development of oligodendrocyte precursor cells, timely exit of the perineurial glial precursors from the central nervous system (CNS), formation of the perineurium, and Schwann cell maturation. Consistent with these observations, zebrafish ypel3 mutants have metabolomic signatures characteristic of oligodendrocyte and Schwann cell differentiation defects, show decreased levels of Myelin basic protein in the central and peripheral nervous system, and develop defasciculated peripheral nerves. Locomotion defects were observed in adult zebrafish ypel3 mutants. These studies demonstrate that Ypel3 is a novel gene required for perineurial cell development and glial myelination.

Chromatin remodelers in oligodendroglia

Oligodendrocytes, the myelinating cells in the vertebrate central nervous system, produce myelin sheaths to enable saltatory propagation of action potentials. The process of oligodendrocyte myelination entails a stepwise progression from precursor specification to differentiation, which is coordinated by a series of transcriptional and chromatin remodeling events. ATP-dependent chromatin remodeling enzymes, which utilize ATP as an energy source to control chromatin dynamics and regulate the accessibility of chromatin to transcriptional regulators, are critical for oligodendrocyte lineage development and regeneration. In this review, we focus on the latest insights into the spatial and temporal specificity of chromatin remodelers during oligodendrocyte development, myelinogenesis, and regeneration. We will also bring together various plausible mechanisms by which lineage specific transcriptional regulators coordinate with chromatin remodeling factors for programming genomic landscapes to specifically modulate these different processes during developmental myelination and remyelination upon injury.

White matter alterations in Alzheimer's disease without concomitant pathologies

Aims

Most individuals with AD neuropathological changes have co‐morbidities which have an impact on the integrity of the WM. This study analyses oligodendrocyte and myelin markers in the frontal WM in a series of AD cases without clinical or pathological co‐morbidities.

Methods

From a consecutive autopsy series, 206 cases had neuropathological changes of AD; among them, only 33 were AD without co‐morbidities. WM alterations were first evaluated in coronal sections of the frontal lobe in every case. Then, RT‐qPCR and immunohistochemistry were carried out in the frontal WM of AD cases without co‐morbidities to analyse the expression of selected oligodendrocyte and myelin markers.

Results

WM demyelination was more marked in AD with co‐morbidities when compared with AD cases without co‐morbidities. Regarding the later, mRNA expression levels of MBP, PLP1, CNP, MAG, MAL, MOG and MOBP were preserved at stages I–II/0–A when compared with middle‐aged (MA) individuals, but significantly decreased at stages III–IV/0–C. This was accompanied by reduced expression of NG2 and PDGFRA mRNA, reduced numbers of NG2‐, Olig2‐ and HDAC2‐immunoreactive cells and reduced glucose transporter immunoreactivity. Partial recovery of some of these markers occurred at stages V–VI/B–C.

Conclusions

The present observations demonstrate that co‐morbidities have an impact on WM integrity in the elderly and in AD, and that early alterations in oligodendrocytes and transcription of genes linked to myelin proteins in WM occur in AD cases without co‐morbidities. These are followed by partial recovery attempts at advanced stages. These observations suggest that oligodendrocytopathy is part of AD.

Advances in Transcription Factors Related to Neuroglial Cell Reprogramming

Neuroglial cells have a high level of plasticity, and many types of these cells are present in the nervous system. Neuroglial cells provide diverse therapeutic targets for neurological diseases and injury repair. Cell reprogramming technology provides an efficient pathway for cell transformation during neural regeneration, while transcription factor-mediated reprogramming can facilitate the understanding of how neuroglial cells mature into functional neurons and promote neurological function recovery.

Differential Inhibition of Sox10 Functions by Notch-Hes Pathway

In the developing central nervous system, the terminal differentiation of oligodendrocytes (OLs) is regulated by both extrinsic and intrinsic factors. Recent studies have suggested that the Notch-Hes signaling pathway influences the maturation of oligodendrocytes in culture and during development. However, the specific Notch receptors and their downstream effectors Hes genes that are involved in oligodendrocyte maturation have not been investigated systematically. In this study, we showed that Notch1 and Notch3 are expressed in oligodendrocyte precursor cells (OPCs) during gliogenesis, and Hes5 is the major Notch downstream transcription factor that is transiently expressed in OPCs. Overexpression of Notch intracellular domain (NICD) and Hes5 proteins in embryonic chicken spinal cord suppressed both the endogenous and Sox10-induced Mbp gene expression. Unexpectedly, overexpression of NICD/Hes5 did not inhibit Sox10 induction of Olig2 expression and Myrf induced Mbp expression, suggesting the differential inhibitory effects of NICD/Hes5 signaling on Sox10 activation of myelin-related genes and early progenitor genes.

Olig2 regulates terminal differentiation and maturation of peripheral olfactory sensory neurons

The bHLH transcription factor Olig2 is required for sequential cell fate determination of both motor neurons and oligodendrocytes and for progenitor proliferation in the central nervous system. However, the role of Olig2 in peripheral sensory neurogenesis remains unknown. We report that Olig2 is transiently expressed in the newly differentiated olfactory sensory neurons (OSNs) and is down-regulated in the mature OSNs in mice from early gestation to adulthood. Genetic fate mapping demonstrates that Olig2-expressing cells solely give rise to OSNs in the peripheral olfactory system. Olig2 depletion does not affect the proliferation of peripheral olfactory progenitors and the fate determination of OSNs, sustentacular cells, and the olfactory ensheathing cells. However, the terminal differentiation and maturation of OSNs are compromised in either Olig2 single or Olig1/Olig2 double knockout mice, associated with significantly diminished expression of multiple OSN maturation and odorant signaling genes, including Omp, Gnal, Adcy3, and Olfr15. We further demonstrate that Olig2 binds to the E-box in the Omp promoter region to regulate its expression. Taken together, our results reveal a distinctly novel function of Olig2 in the periphery nervous system to regulate the terminal differentiation and maturation of olfactory sensory neurons.

Sox9 overexpression exerts multiple stage-dependent effects on mouse spinal cord development

The high-mobility-group (HMG)-domain protein Sox9 is one of few transcription factors implicated in gliogenesis in the vertebrate central nervous system. To further study the role of Sox9 in early spinal cord development, we generated a mouse that allows expression of Sox9 in a temporally and spatially controlled manner. Using this mouse, we show that premature Sox9 expression in neural precursor cells disrupted the neuroepithelium of the ventricular zone. Sox9 also compromised development and survival of neuronal precursors and neurons. Additionally, we observed in these mice substantial increases in oligodendroglial and astroglial cells. Reversing the normal order of appearance of essential transcriptional regulators during oligodendrogenesis, Sox10 preceded Olig2. Our study reinforces the notion that Sox9 has a strong gliogenic activity. It also argues that Sox9 expression has to be tightly controlled to prevent negative effects on early spinal cord structure and neuronal development.

Transcriptional control of myelination and remyelination

Myelination is an evolutionary recent differentiation program that has been independently acquired in vertebrates by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. Therefore, it is not surprising that regulating transcription factors differ substantially between both cell types. However, overall principles are similar as transcriptional control in Schwann cells and oligodendrocytes combines lineage determining and stage-specific factors in complex regulatory networks. Myelination does not only occur during development, but also as remyelination in the adult. In line with the different conditions during developmental myelination and remyelination and the distinctive properties of Schwann cells and oligodendrocytes, transcriptional regulation of remyelination exhibits unique features and differs between the two cell types. This review gives an overview of the current state in the field.

Transient Improvement of Cerebellar Oligodendroglial Development in a Neonatal Hyperoxia Model by PDGFA Treatment

In preterm infants, the changes from fetal life to ex-utero conditions often coincide with reduced growth and white matter damage of the cerebellum. The premature increase in arterial oxygen tension caused by preterm birth may dysregulate cerebellar development. In a hyperoxia rat model of white matter damage to mimic a steep increase in oxygen levels by 24 h exposure to 80% O2 from postnatal day 6 (P6) to day 7, we analyzed growth factor (GF) synthesis of cerebellar astrocytes. Determination of GF production was performed in astrocytes after Magnetic-activated cell sorting (MACS) isolation from cerebelli after hyperoxia exposure ex vivo, and also in astroglial cultures. Oligodendrocyte progenitor cell (OPC) function was analyzed in cerebellar OPCs isolated by MACS after hyperoxia. Administration of PDGFA from P6 to P11, during hyperoxia and during 4 days recovery, was finally tested for protection of oligodendroglia and myelination. As a result, expression of the GFs Pdgfa, Fgf2, and Bdnf was diminished in cerebellar astrocytes in vitro and in vivo. Gene expression of Olig1, Olig2, Sox9, Sox10, and Cnp was reduced in OPCs in vivo. Nasal PDGFA application improved oligodendroglial proliferation after hyperoxia at P7. However, this treatment effect vanished until P9. Impaired MBP expression after hyperoxia was attenuated by PDGFA treatment until P11, but not beyond when PDGFA supply was stopped. In this study on neonatal cerebellar injury, it is documented for the first time that improvement of oligodendroglial proliferation and of myelination can be achieved by PDGFA treatment. However, the treatment benefit is not maintained long term.

Molecular Control of Oligodendrocyte Development

Myelin is a multilayer lipid membrane structure that wraps and insulates axons, allowing for the efficient propagation of action potentials. During developmental myelination of the central nervous system (CNS), oligodendrocyte progenitor cells (OPCs) proliferate and migrate to their final destination, where they terminally differentiate into mature oligodendrocytes and myelinate axons. Lineage progression and terminal differentiation of oligodendrocyte lineage cells are under tight transcriptional and post-transcriptional control. The characterization of several recently identified regulatory factors that govern these processes, which are the focus of this review, has greatly increased our understanding of oligodendrocyte development and function. These insights are critical to facilitate efforts to enhance OPC differentiation in neurological disorders that disrupt CNS myelin.

Attenuating Spinal Cord Injury by Conditioned Medium from Bone Marrow Mesenchymal Stem Cells

Spinal cord injury (SCI) is a devastating neurological condition and might even result in death. However, current treatments are not sufficient to repair such damage. Bone marrow mesenchymal stem cells (BM-MSC) are ideal transplantable cells which have been shown to modulate the injury cascade of SCI mostly through paracrine effects. The present study investigates whether systemic administration of conditioned medium from MSCs (MSCcm) has the potential to be efficacious as an alternative to cell-based therapy for SCI. In neuron-glial cultures, MSC coculture effectively promoted neuronal connection and reduced oxygen glucose deprivation-induced cell damage. The protection was elicited even if neuron-glial culture was used to expose MSCcm, suggesting the effects possibly from released fractions of MSC. In vivo, intravenous administration of MSCcm to SCI rats significantly improved behavioral recovery from spinal cord injury, and there were increased densities of axons in the lesion site of MSCcm-treated rats compared to SCI rats. At early days postinjury, MSCcm treatment upregulated the protein levels of Olig 2 and HSP70 and also increased autophage-related proteins in the injured spinal cords. Together, these findings suggest that MSCcm treatment promotes spinal cord repair and functional recovery, possibly via activation of autophagy and enhancement of survival-related proteins.

Interactive Repression of MYRF Self-Cleavage and Activity in Oligodendrocyte Differentiation by TMEM98 Protein

Myelin sheath formed by oligodendrocytes (OLs) is essential for the rapid propagation of action potentials in the vertebrate CNS. Myelin regulatory factor (MYRF) is one of the critical factors that control OL differentiation and myelin maintenance. Previous studies showed that MYRF is a membrane-bound transcription factor associated with the endoplasmic reticulum (ER). After self-cleavage, the N-fragment of MYRF is released from the ER and translocated into the nucleus where it functions as a transcription factor to activate myelin gene expression. At present, it remains unknown whether MYRF self-cleavage and functional activation can be regulated during OL differentiation. Here, we report that TMEM98, an ER-associated transmembrane protein, is capable of binding to the C-terminal of MYRF and inhibiting its self-cleavage and N-fragment nuclear translocation. In the developing CNS, TMEM98 is selectively expressed in early maturing OLs in mouse pups of either sex. Forced expression of TMEM98 in embryonic chicken spinal cord of either sex suppresses endogenous OL differentiation and MYRF-induced ectopic expression of myelin genes. These results suggest that TMEM98, through inhibiting the self-cleavage of MYRF, functions as a negative feedback regulator of MYRF in oligodendrocyte differentiation and myelination.SIGNIFICANCE STATEMENT MYRF protein is initially synthesized as an ER-associated membrane protein that undergoes autoproteolytic cleavage to release the N-fragment, which is then transported into the nucleus and activates the transcription of myelin genes. To date, the molecular mechanisms that regulate the self-cleavage and function of MYRF in regulating oligodendrocyte differentiation have remained unknown. In this study, we present the molecular and functional evidence that TMEM98 membrane protein physically interacts with MYRF in the ER and subsequently blocks its self-cleavage, N-terminal nuclear translocation, and functional activation of myelin gene expression. To our knowledge, this is the first report on the regulation of MYRF self-proteolytic activity and function by an interacting protein, providing new insights into the molecular regulation of OL differentiation and myelinogenesis.

In vivo conversion of astrocytes into oligodendrocyte lineage cells with transcription factor Sox10; Promise for myelin repair in multiple sclerosis

Recent studies demonstrate that astroglial cells can be directly converted into functional neurons or oligodendrocytes. Here, we report that a single transcription factor Sox10 could reprogram astrocytes into oligodendrocyte-like cells, in vivo. For transdifferentiation, Sox10-GFP expressing viral particles were injected into cuprizone-induced demyelinated mice brains after which we assessed for the presence of specific oligodendrocyte lineage cell markers by immunohistofluorescence (IHF). As control, another group of demyelinated mice received GFP expressing viral particles. After 3 weeks, the majority of transduced (GFP+) cells in animals which received control vector were astrocytes, while in animals which received Sox10-GFP vector, the main population of GFP+ cells were positive for oligodendrocyte lineage markers. We also extracted primary astrocytes from mouse pups and purified them. Primary astrocytes were transduced in vitro and then transplanted into demyelinated brains for later fate mapping. After three weeks, in vitro transduced and then transplanted astrocytes showed oligodendrocyte progenitor and mature oligodendrocyte markers. Further confirmation was done by transduction of astrocytes with lentiviral particles that expressed Sox10 and GFP and their culture in the oligodendrocyte progenitor medium. The induced cells expressed oligodendrocyte progenitor cells (iOPCs) markers. Our findings showed the feasibility of reprogramming of astrocytes into oligodendrocyte-like cells in vivo, by using a single transcription factor, Sox10. This finding suggested a master regulatory role for Sox10 which enabled astrocytes to change their fate to OPC-like cells and establish an oligodendroglial phenotype. We hope this approach lead to effective myelin repair in patients suffering from myelination deficit.

Improvement by Human Oligodendrocyte Progenitor Cells of Neurobehavioral Disorders in an Experimental Model of Neonatal Periventricular Leukomalacia

The effects of human oligodendrocyte progenitor (F3.olig2) cells on improving neurobehavioral deficits were investigated in an experimental model of periventricular leukomalacia (PVL). Seven-day-old male rats were subjected to hypoxia-ischemia-lipopolysaccharide injection (HIL), and intracerebroventricularly transplanted with F3.olig2 (4 × 10⁵ cells/rat) once at post-natal day (PND) 10 or repeatedly at PND10, 17, 27, and 37. Neurobehavioral disorders were evaluated at PND14, 20, 30, and 40 via cylinder test, locomotor activity, and rotarod performance, and cognitive function was evaluated at PND41-45 through passive avoidance and Morris water-maze performances. F3.olig2 cells recovered the rate of use of the forelimb contralateral to the injured brain, improved locomotor activity, and restored rotarod performance of PVL animals; in addition, marked improvement of learning and memory function was seen. It was confirmed that transplanted F3·olig2 cells migrated to injured areas, matured to oligodendrocytes expressing myelin basic protein (MBP), and markedly attenuated the loss of host MBP in the corpus callosum. The results indicate that the transplanted F3.olig2 cells restored neurobehavioral functions by preventing axonal demyelination, and that human oligodendrocyte progenitor cells could be a candidate for cell therapy of perinatal hypoxic-ischemic and infectious brain injuries including PVL and cerebral palsy.

Oligodendroglia Are Particularly Vulnerable to Oxidative Damage after Neurotrauma In Vivo

Loss of function following injury to the CNS is worsened by secondary degeneration of neurons and glia surrounding the injury and is initiated by oxidative damage. However, it is not yet known which cellular populations and structures are most vulnerable to oxidative damage in vivo Using Nanoscale secondary ion mass spectrometry (NanoSIMS), oxidative damage was semiquantified within cellular subpopulations and structures of optic nerve vulnerable to secondary degeneration, following a partial transection of the optic nerve in adult female PVG rats. Simultaneous assessment of cellular subpopulations and structures revealed oligodendroglia as the most vulnerable to DNA oxidation following injury. 5-Ethynyl-2'-deoxyuridine (EdU) was used to label cells that proliferated in the first 3 d after injury. Injury led to increases in DNA, protein, and lipid damage in oligodendrocyte progenitor cells and mature oligodendrocytes at 3 d, regardless of proliferative state, associated with a decline in the numbers of oligodendrocyte progenitor cells at 7 d. O4⁺ preoligodendrocytes also exhibited increased lipid peroxidation. Interestingly, EdU⁺ mature oligodendrocytes derived after injury demonstrated increased early susceptibility to DNA damage and lipid peroxidation. However, EdU^- mature oligodendrocytes with high 8-hydroxyguanosine immunoreactivity were more likely to be caspase3⁺ By day 28, newly derived mature oligodendrocytes had significantly reduced myelin regulatory factor gene mRNA, indicating that the myelination potential of these cells may be reduced. The proportion of caspase3⁺ oligodendrocytes remained higher in EdU^- cells. Innovative use of NanoSIMS together with traditional immunohistochemistry and in situ hybridization have enabled the first demonstration of subpopulation specific oligodendroglial vulnerability to oxidative damage, due to secondary degeneration in vivoSIGNIFICANCE STATEMENT Injury to the CNS is characterized by oxidative damage in areas adjacent to the injury. However, the cellular subpopulations and structures most vulnerable to this damage remain to be elucidated. Here we use powerful NanoSIMS techniques to show increased oxidative damage in oligodendroglia and axons and to demonstrate that cells early in the oligodendroglial lineage are the most vulnerable to DNA oxidation. Further immunohistochemical and in situ hybridization investigation reveals that mature oligodendrocytes derived after injury are more vulnerable to oxidative damage than their counterparts existing at the time of injury and have reduced myelin regulatory factor gene mRNA, yet preexisting oligodendrocytes are more likely to die.