Oligodendroglial Lineage Research Articles

NF-Y-dependent regulation of glutamate receptor 4 expression and cell survival in cells of the oligodendrocyte lineage.

Glutamate receptor subunit 4 (GluA4) is highly expressed by neural cells sensitive to excitotoxicity, and is the predominant subunit expressed by oligodendrocyte precursor cells (OPC) during a key period of vulnerability to hypoxic‐ischemic injury. Therefore, transcriptional networks downstream of excitotoxic GluA4 activation represent a promising area for therapeutic intervention. In this work, we identify the CCAAT binding transcription factor NF‐Yb as a novel transcriptional regulator of Gria4 (GluA4 gene), and a controller of excitotoxic death in the oligodendroglial lineage. We describe a novel regulatory region within Gria4 containing CCAAT sequences whose binding by NF‐Yb is regulated by excitotoxicity. Excitotoxicity‐induced alterations in NF‐Yb binding are associated with changes in Gria4 transcription, while knockdown of NF‐Yb alters the transcription of reporter constructs containing this regulatory region. Data from immortalized and primary OPC reveal that RNAi and pharmacological disruption of NF‐Yb alter Gria4 transcription, with the latter inducing apoptosis and influencing a set of apoptotic genes similarly regulated during excitotoxicity. These data provide the first definition of a trans‐acting mechanism regulating Gria4, and identify the NF‐Y network as a potential source of pharmacological targets for promoting OPC survival.

The Stem Cell Factor Sox2 Is a Positive Timer of Oligodendrocyte Development in the Postnatal Murine Spinal Cord

Myelination in the central nervous system takes place predominantly during the postnatal development of humans and rodents by myelinating oligodendrocytes (OLs), which are differentiated from oligodendrocyte progenitor cells (OPCs). We recently reported that Sox2 is essential for developmental myelination in the murine brain and spinal cord. It is still controversial regarding the role of Sox2 in oligodendroglial lineage progression in the postnatal murine spinal cord. Analyses of a series of cell- and stage-specific Sox2 mutants reveal that Sox2 plays a biphasic role in regulating oligodendroglial lineage progression in the postnatal murine spinal cord. Sox2 controls the number of OPCs for subsequent differentiation through regulating their proliferation. In addition, Sox2 regulates the timing of OL differentiation and modulates the rate of oligodendrogenesis. Our experimental data prove that Sox2 is an intrinsic positive timer of oligodendroglial lineage progression and suggest that interventions affecting oligodendroglial Sox2 expression may be therapeutic for overcoming OPC differentiation arrest in dysmyelinating and demyelinating disorders.

A single‐cell analysis reveals multiple roles of oligodendroglial lineage cells during post‐ischemic regeneration

NG2 cells represent precursors of oligodendrocytes under physiological conditions; however, following cerebral ischemia they play an important role in glial scar formation. Here, we compared the expression profiles of oligodendroglial lineage cells, after focal cerebral ischemia (FCI) and in Alzheimer's-like pathology using transgenic mice, which enables genetic fate-mapping of Cspg4-positive NG2 cells and their progeny, based on the expression of red fluorescent protein tdTomato. tdTomato-positive cells possessed the expression profile of NG2 cells and oligodendrocytes; however, based on the expression of cell type-specific genes, we were able to distinguish between them. To shed light on the changes in the expression patterns caused by FCI, we employed self-organizing Kohonen maps, enabling the division of NG2 cells and oligodendrocytes into subpopulations based on similarities in the expression profiles of individual cells. We identified three subpopulations of NG2 cells emerging after FCI: proliferative; astrocyte-like and oligodendrocyte-like NG2 cells; such phenotypes were further confirmed by immunohistochemistry. Oligodendrocytes themselves formed four subpopulations, which reflected the process of oligodendrocytes maturation. Finally, we used 5-ethynyl-2' deoxyuridine (EdU) labeling to reveal that NG2 cells can differentiate directly into reactive astrocytes without preceding proliferation. In contrast, in Alzheimer's-like pathology we failed to identify these subpopulations. Collectively, here we identified several yet unknown differences between the expression profiles of NG2 cells and oligodendrocytes, and characterized specific genes contributing to oligodendrocyte maturation and phenotypical changes of NG2 cells after FCI. Moreover, our results suggest that, unlike in Alzheimer's-like pathology, NG2 cells acquire a multipotent phenotype following FCI.

Sox2 Is Essential for Oligodendroglial Proliferation and Differentiation during Postnatal Brain Myelination and CNS Remyelination.

In the CNS, myelination and remyelination depend on the successful progression and maturation of oligodendroglial lineage cells, including proliferation and differentiation of oligodendroglial progenitor cells (OPCs). Previous studies have reported that Sox2 transiently regulates oligodendrocyte (OL) differentiation in the embryonic and perinatal spinal cord and appears dispensable for myelination in the postnatal spinal cord. However, the role of Sox2 in OL development in the brain has yet to be defined. We now report that Sox2 is an essential positive regulator of developmental myelination in the postnatal murine brain of both sexes. Stage-specific paradigms of genetic disruption demonstrated that Sox2 regulated brain myelination by coordinating upstream OPC population supply and downstream OL differentiation. Transcriptomic analyses further supported a crucial role of Sox2 in brain developmental myelination. Consistently, oligodendroglial Sox2-deficient mice developed severe tremors and ataxia, typical phenotypes indicative of hypomyelination, and displayed severe impairment of motor function and prominent deficits of brain OL differentiation and myelination persisting into the later CNS developmental stages. We also found that Sox2 was required for efficient OPC proliferation and expansion and OL regeneration during remyelination in the adult brain and spinal cord. Together, our genetic evidence reveals an essential role of Sox2 in brain myelination and CNS remyelination, and suggests that manipulation of Sox2 and/or Sox2-mediated downstream pathways may be therapeutic in promoting CNS myelin repair.SIGNIFICANCE STATEMENT Promoting myelin formation and repair has translational significance in treating myelin-related neurological disorders, such as periventricular leukomalacia and multiple sclerosis in which brain developmental myelin formation and myelin repair are severely affected, respectively. In this report, analyses of a series of genetic conditional knock-out systems targeting different oligodendrocyte stages reveal a previously unappreciated role of Sox2 in coordinating upstream proliferation and downstream differentiation of oligodendroglial lineage cells in the mouse brain during developmental myelination and CNS remyelination. Our study points to the potential of manipulating Sox2 and its downstream pathways to promote oligodendrocyte regeneration and CNS myelin repair.

Abstract PL05-03: Histone-3K27M mutant diffuse midline gliomas of childhood: Epigenetic pathogenesis and therapeutic opportunities

Abstract High-grade gliomas of childhood occur in a striking spatiotemporal pattern, with tumors of the midline occurring chiefly in the first decade of life and tumors of the cerebral lobes occurring later in adolescence and young adulthood. This pattern of gliomagenesis bespeaks dysregulation of a developmental process, and maps well onto discrete waves of developmental myelination of the nervous system, a process that spans over 3 decades in humans. Increasing data from our group and from others implicate myelin-forming precursor cells as putative cells of origin for the most common and best-studied diffuse midline glioma, diffuse intrinsic pontine glioma (DIPG). DIPG is a fatal pediatric cancer peaking in incidence at age 6-7 years with a median survival of only 9 months and 5-year survival of less than 1%. DIPG affects 300-400 children each year in the US and represents the leading cause of brain tumor-related death in children. Therapeutic options are limited, and effective treatment is direly needed. During the early part of this decade, next-generation sequencing technologies enabled a comprehensive view of the DIPG genome. DIPG and other diffuse gliomas of the midline structures of the central nervous system, in particular the thalamus and spinal cord, exhibit a specific and highly recurrent mutation in histone-3 (H3K27M). The H3K27M mutation, occurring in genes encoding histone H3.3 and H3.1, affect ~80% of DIPG cases and the majority of thalamic and spinal cord gliomas as well. The H3K27M mutation causes perturbation of Polycomb repressive complex 2 (PRC2) function, resulting in global hypomethylation of K27 in all H3 variants. The broad epigenetic dysregulation and characteristic gene expression changes that ensue are believed to be central to DIPG oncogenesis. We have generated a panel of patient-derived DIPG cultures and correlate orthotopic xenograft models and have used these new resources for drug screening efforts. DIPG cells are vulnerable to HDAC inhibition, which we found restores H3 trimethyl mark and normalizes gene expression, an unexpected finding that may be explained by actetyl groups on nearby residues sterically interfering with the interaction between PRC2 and the aberrant methionine. We have also found that DIPG is vulnerable to transcriptional disruption using bromodomain inhibition or CDK7 blockade. Targeting oncogenic transcription through either of these methods synergizes with HDAC inhibition, and DIPG cells resistant to HDAC inhibitor therapy retain sensitivity to CDK7 blockade. A clinical trial of panobinostat for DIPG is ongoing, and follow-on trials of combination therapy hold promise. Other forms of diffuse midline gliomas, including H3K27M-mutant gliomas of the spinal cord and thalamus, may respond similarly to therapeutic strategies targeting the regulation of gene expression. Identification of super-enhancers in DIPG highlights oligodendroglial lineage genes, supporting the hypothesis that precursor cells in the oligodendroglial lineage are the cell of origin, and reveals unexpected mechanisms mediating tumor viability and invasion, including potassium channel function and EPH receptor signaling. Also highlighted by super-enhancer analysis are genes traditionally involved in neuronal communication. Normal oligodendroglial lineage precursor cell function is critically regulated by interactions with active neurons during development and as part of ongoing neural plasticity. We have recently shown that neuronal activity robustly promotes the proliferation of both normal and neoplastic glial cells. A key mechanism mediating neuronal influences on glioma growth is the activity-regulated secretion of the synaptic protein neuroligin-3 into the glioma microenvironment. Blocking neuroligin-3 secretion by inhibiting the enzyme responsible for its cleavage and release from normal synapses has proven robustly effective in slowing the growth of DIPG and other gliomas in preclinical models. Targeting neuron-glioma interactions represents a promising and largely unexplored avenue for glioma therapy. A therapeutic strategy is thus emerging that involves a multipronged approach, targeting the cell-intrinsic vulnerabilities of histone-3 mutant gliomas together with key microenvironmental targets central to glioma growth and progression. Increasingly effective therapy for these deadly brain cancers of childhood will be enabled by answers to outstanding basic questions, such as why H3K27M-mutant gliomas occur only in midline structures, how the tumors hijack mechanisms of normal neural development and plasticity, and what mechanisms the tumor utilizes to evolve resistance to therapy. Citation Format: Michelle Monje. Histone-3K27M mutant diffuse midline gliomas of childhood: Epigenetic pathogenesis and therapeutic opportunities [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr PL05-03.

Oligodendroglia Are Particularly Vulnerable to Oxidative Damage After Neurotrauma In Vivo

In the paper “Oligodendroglia are particularly vulnerable to oxidative damage after neurotrauma in vivo,” we determined the extent of oxidative damage to specific cellular subpopulations and structures within regions vulnerable to secondary degeneration and assessed the effect this had on oligodendroglial function. Comparative assessment of oxidative damage demonstrated selective vulnerability of oligodendroglia, specifically oligodendrocyte progenitor cells (OPCs) to DNA oxidation in vivo. Immunohistochemical fate mapping along the oligodendroglial lineage showed a transient susceptibility of these cells to DNA oxidation, protein nitration, and lipid peroxidation, with mature oligodendrocytes derived immediately after injury more vulnerable to DNA oxidation than their counterparts existing at the time of injury or later derived. In situ hybridization demonstrated a reduction in myelin regulatory factor (MyRF) messenger RNA (mRNA) fluorescence in newly derived mature oligodendrocytes, suggesting a compromise in the production and maintenance of the myelin sheath in these cells. The data imply a deficit in the normal differentiation of OPCs to myelinating oligodendrocytes, associated with a transient increase in oxidative damage, which may contribute to the dysmyelinating phenotype seen at chronic time points after injury. Identifying and understanding the sources of this oxidative damage is integral for the development of therapeutic interventions for neurotrauma.

PATH-38. COMPREHENSIVE GENOMIC PROFILING OF OLIGODENDROGLIOMAS REFINES TUMOR DIAGNOSES AND IDENTIFIES PATIENTS FOR TARGETED THERAPIES AND IMMUNE CHECKPOINT INHIBITORS

Oligodendrogliomas (ODG) are diffusely infiltrating gliomas characterized by IDH mutations and 1p/19q co-deletion. Distinguishing between diffuse gliomas can be challenging based solely on microscopic features and lead to misclassification of glioma lineage. Genomic profiling of oligodendrogliomas is critical to ensuring diagnostic accuracy and identifying therapeutic options for patients with progressive and/or malignant tumors. DESIGN: Comprehensive genomic profiling (CGP) was performed on FFPE material acquired from 200 consecutive submitted cases of locally diagnosed ODG. CGP identifies tumor mutational burden, microsatellite instability status (MSI) and all classes of genomic alterations in 315 cancer-associated genes including a validated novel algorithm that accurately determines 1p/19q co-deletion status. Among the 202 ODG samples, 1p/19q co-deletion was identified in 152 (75.2%) of cases and in these tumors, the most frequently altered genes were TERT, IDH1/2, CIC, FUBP1, PIK3CA/PIK3R1 and NOTCH1/2. Notably in these tumors activating alterations were frequently detected in PI3K pathway genes including PIK3CA (19.5%), PIK3R1 (7.5%) and PTEN (1.3%). Of the 50 (24.8%) ODG negative for 1p/19q co-deletion (24.8%), the genomic profiles supported astrocytic lineage gliomas (IDH1, TP53, ATRX, TERT, CDKN2A/B and PTEN mutations) warranting tumor reclassification. Among the 1p/19q co-deleted ODG, the median TMB was 2.7 mutations/Mb (range <1 to 818 mutations/Mb) with 8.6% (n=13) of tumors demonstrating hypermutation (≥20 mutations/Mb). MSI-High status was not detected in any ODG. By characterizing 1p/19q co-deletion and genomic profiles of diffuse gliomas, CGP ensures diagnostic accuracy by distinguishing between oligodendroglial and astrocytic lineage tumors. CGP identified pathways for therapeutic intervention in 1p/19q positive ODG including IDH, PI3K pathway and NOTCH1/2 inhibitors. We also report that a subpopulation of oligodendrogliomas with high TMB may benefit from immune checkpoint inhibitors.

Sox8 and Sox10 jointly maintain myelin gene expression in oligodendrocytes.

In Schwann cells of the vertebrate peripheral nervous system, induction of myelination and myelin maintenance both depend on the HMG-domain-containing transcription factor Sox10. In oligodendrocytes of the central nervous system, Sox10 is also essential for the induction of myelination. Its role in late phases of myelination and myelin maintenance has not been studied so far. Here, we show that these processes are largely unaffected in mice that lack Sox10 in mature oligodendrocytes. As Sox10 is co-expressed with the related Sox8, we also analyzed oligodendrocytes and myelination in Sox8-deficient mice. Again, we could not detect any major abnormalities. Expression of many myelin genes was only modestly reduced in both mouse mutants. Dramatic reductions in expression levels and phenotypic disturbances became only apparent once Sox8 and Sox10 were both absent. This argues that Sox8 and Sox10 are jointly required for myelin maintenance and impact myelin gene expression. One direct target gene of both Sox proteins is the late myelin gene Mog. Our results point to at least partial functional redundancy between both related Sox proteins in mature oligodendrocytes and are the first report of a substantial function of Sox8 in the oligodendroglial lineage.

Multinodular and vacuolating neuronal tumors in epilepsy: dysplasia or neoplasia?

Multinodular and vacuolating neuronal tumor (MVNT) is a new pattern of neuronal tumour included in the recently revised WHO 2016 classification of tumors of the CNS. There are 15 reports in the literature to date. They are typically associated with late onset epilepsy and a neoplastic vs. malformative biology has been questioned. We present a series of ten cases and compare their pathological and genetic features to better characterized epilepsy‐associated malformations including focal cortical dysplasia type II (FCDII) and low‐grade epilepsy‐associated tumors (LEAT). Clinical and neuroradiology data were reviewed and a broad immunohistochemistry panel was applied to explore neuronal and glial differentiation, interneuronal populations, mTOR pathway activation and neurodegenerative changes. Next generation sequencing was performed for targeted multi‐gene analysis to identify mutations common to epilepsy lesions including FCDII and LEAT. All of the surgical cases in this series presented with seizures, and were located in the temporal lobe. There was a lack of any progressive changes on serial pre‐operative MRI and a mean age at surgery of 45 years. The vacuolated cells of the lesion expressed mature neuronal markers (neurofilament/SMI32, MAP2, synaptophysin). Prominent labelling of the lesional cells for developmentally regulated proteins (OTX1, TBR1, SOX2, MAP1b, CD34, GFAPδ) and oligodendroglial lineage markers (OLIG2, SMI94) was observed. No mutations were detected in the mTOR pathway genes, BRAF, FGFR1 or MYB. Clinical, pathological and genetic data could indicate that MVNT aligns more with a malformative lesion than a true neoplasm with origin from a progenitor neuro‐glial cell type showing aberrant maturation.

Melanocortin receptor subtypes are expressed on cells in the oligodendroglial lineage and signal ACTH protection.

ACTH, a melanocortin peptide used to treat multiple sclerosis (MS) relapses, acts by stimulating adrenal corticosteroid (CS) production via melanocortin receptor 2 (MC2R), but it may also exert a therapeutic effect independent of CS by stimulating other melanocortin receptors (MCR) distributed in many tissues, including the brain. We reported that oligodendroglia (OL) and oligodendroglial precursor cells (OPC) express MC4R, and that ACTH 1-39 protects OL and OPC in vitro from cell death induced by mechanisms likely involved in white matter damage in MS. This study investigates expression of MC1R, MC2R, MC3R and MC5R in OL and MC4R in OPC using immunocytochemistry with MCR subtype specific antibodies. OL express surface MC1R, MC3R and MC5R, in addition to MC4R. To investigate whether these receptors are functional, we asked if signaling through MCR is involved in ACTH protection of cultured rat OL from apoptosis (staurosporine), or cell death induced by excitotoxicity (glutamate), reactive oxygen species (ROS), or an inflammatory mediator (quinolinic acid). Like ACTH 1-39, MCR subtype specific agonists for MC1R, MC3R, MC4R and MC5R all protected OL from these insults. Conversely, antagonists for MC3R and MC4R blocked ACTH protection of OL. We then investigated the role of MC4R, as a prototype MCR, in protection and proliferation of OPC; MC4R agonists protected OPC and increased their proliferation, while antagonists blocked these effects. Our results demonstrate that MCR on OL and OPC are functional and activate signaling pathways that protect against mechanisms involved in OL damage in MS, suggesting potential beneficial effects in neurologic diseases.

Exercise in Adulthood after Irradiation of the Juvenile Brain Ameliorates Long-Term Depletion of Oligodendroglial Cells.

Cranial radiation severely affects brain health and function, including glial cell production and myelination. Recent studies indicate that voluntary exercise has beneficial effects on oligodendrogenesis and myelination. Here, we hypothesized that voluntary running would increase oligodendrocyte numbers in the corpus callosum after irradiation of the juvenile mouse brain. The brains of C57Bl/6J male mice were 6 Gy irradiated on postnatal day 9 during the main gliogenic developmental phase, resulting in a loss of oligodendrocyte precursor cells. Upon adulthood, the mice were injected with bromodeoxyuridine and allowed to exercise on a running wheel for four weeks. Cell proliferation and survival, Ascl1+ oligodendrocyte precursor and Olig2+ oligodendrocyte cell numbers as well as CC1+ mature oligodendrocytes were quantified using immunohistology. Radiation induced a reduction in the number of Olig2+ oligodendrocytes by nearly 50% without affecting production or survival of new Olig2+ cells. Ascl1+ cells earlier in the oligodendroglial cell lineage were also profoundly affected, with numbers reduced by half. By three weeks of age, Olig2+ cell numbers had not recovered, and this was paralleled by a volumetric loss in the corpus callosum. The deficiency of Olig2+ oligodendrocytes persisted into adulthood. Additionally, the depletion of Ascl1+ progenitor cells was irreversible, and was even more pronounced at 12 weeks postirradiation compared to day 2 postirradiation. Furthermore, the overall number of CC1+ mature oligodendrocytes decreased by 28%. The depletion of Olig2+ cells in irradiated animals was reversed by 4 weeks of voluntary exercise. Moreover, voluntary exercise also increased the number of Ascl1+ progenitor cells in irradiated animals. Taken together, these results demonstrate that exercise in adulthood significantly ameliorates the profound and long-lasting effects of moderate exposure to immature oligodendrocytes during postnatal development.

Issue Cover (August 2017)

Front cover: Rat spinal cord oligodendrocytes differentiating in vitro. A pure oligodendroglial lineage cell (OLC) culture from the rat neonatal spinal cord is stained for oligodendrocyte markers, O4 antigen (red) and galactocerebroside (green) by immunocytochemistry. Nuclei are stained with DAPI (Blue). By comparing pure oligodendrocyte cultures from rat spinal cords and forebrains, we demonstrated differing intrinsic biological properties between these two OLC groups originated from distinct CNS regions. Further understanding the regional differences of oligodendrocytes will help to improve treatments for demyelination in different CNS regions and to facilitate the development of stem cell-derived OLCs for cell transplantation therapies for demyelination. Read the full article ‘Differing intrinsic biological properties between forebrain and spinal oligodendroglial lineage cells’ by M. Horiuchi, Y. Suzuki-Horiuchi, T. Akiyama, A. Itoh, D. Pleasure, E. Carstens and T. Itoh (J. Neurochem. 2017, vol. 142 (3), pp. 378–391) on doi: 10.1111/jnc.14074

The Role of the Oligodendrocyte Lineage in Acute Brain Trauma.

An acute brain injury is commonly characterized by an extended cellular damage. The post-injury process of scar formation is largely determined by responses of various local glial cells and blood-derived immune cells. The role of astrocytes and microglia have been frequently reviewed in the traumatic sequelae. Here, we summarize the diverse contributions of oligodendrocytes (OLs) and their precursor cells (OPCs) in acute injuries. OLs at the lesion site are highly sensitive to a damaging insult, provoked by Ca2+ overload after hyperexcitation originating from increased levels of transmitters. At the lesion site, differentiating OPCs can replace injured oligodendrocytes to guarantee proper myelination that is instrumental for healthy brain function. In contrast to finally differentiated and non-dividing OLs, OPCs are the most proliferative cells of the brain and their proliferation rate even increases after injury. There exist even evidence that OPCs might also generate some type of astrocyte beside OLs. Thereby, OPCs can contribute to the generation and maintenance of the glial scar. In the future, detailed knowledge of the molecular cues that help to prevent injury-evoked glial cell death and that control differentiation and myelination of the oligodendroglial lineage will be pivotal in developing novel therapeutic approaches.

Differing intrinsic biological properties between forebrain and spinal oligodendroglial lineage cells.

Differentiation of oligodendroglial progenitor cells (OPCs) into myelinating oligodendrocytes is known to be regulated by the microenvironment where they differentiate. However, current research has not verified whether or not oligodendroglial lineage cells (OLCs) derived from different anatomical regions of the central nervous system (CNS) respond to microenvironmental cues in the same manner. Here, we isolated pure OPCs from rat neonatal forebrain (FB) and spinal cord (SC) and compared their phenotypes in the same invitro conditions. We found that although FB and SC OLCs responded differently to the same external factors; they were distinct in proliferation response to mitogens, oligodendrocyte phenotype after differentiation, and cytotoxic responses to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-type glutamate receptor-mediated excitotoxicity at immature stages of differentiation in a cell-intrinsic manner. Moreover, transcriptome analysis identified genes differentially expressed between these OPC populations, including those encoding transcription factors (TFs), cell surface molecules, and signaling molecules. Particularly, FB and SC OPCs retained the expression of FB- or SC-specific TFs, such as Foxg1 and Hoxc8, respectively, even after serial passaging invitro. Given the essential role of these TFs in the regional identities of CNS cells along the rostrocaudal axis, our results suggest that CNS region-specific gene regulation by these TFs may cause cell-intrinsic differences in cellular responses between FB and SC OLCs to extracellular molecules. Further understanding of the regional differences among OPC populations will help to improve treatments for demyelination in different CNS regions and to facilitate the development of stem cell-derived OPCs for cell transplantation therapies for demyelination. Cover Image for this issue: doi. 10.1111/jnc.13809.

Increasing Human Neural Stem Cell Transplantation Dose Alters Oligodendroglial and Neuronal Differentiation after Spinal Cord Injury.

SummaryMultipotent human central nervous system-derived neural stem cells transplanted at doses ranging from 10,000 (low) to 500,000 (very high) cells differentiated predominantly into the oligodendroglial lineage. However, while the number of engrafted cells increased linearly in relationship to increasing dose, the proportion of oligodendrocytic cells declined. Increasing dose resulted in a plateau of engraftment, enhanced neuronal differentiation, and increased distal migration caudal to the transplantation sites. Dose had no effect on terminal sensory recovery or open-field locomotor scores. However, total human cell number and decreased oligodendroglial proportion were correlated with hindlimb girdle coupling errors. Conversely, greater oligodendroglial proportion was correlated with increased Ab step pattern, decreased swing speed, and increased paw intensity, consistent with improved recovery. These data suggest that transplant dose, and/or target niche parameters can regulate donor cell engraftment, differentiation/maturation, and lineage-specific migration profiles.

Transcriptional Dependencies in Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is a fatal pediatric cancer with limited therapeutic options. The majority of cases of DIPG exhibit a mutation in histone-3 (H3K27M) that results in oncogenic transcriptional aberrancies. We show here that DIPG is vulnerable to transcriptional disruption using bromodomain inhibition or CDK7 blockade. Targeting oncogenic transcription through either of these methods synergizes with HDAC inhibition, and DIPG cells resistant to HDAC inhibitor therapy retain sensitivity to CDK7 blockade. Identification of super-enhancers in DIPG provides insights toward the cell of origin, highlighting oligodendroglial lineage genes, and reveals unexpected mechanisms mediating tumor viability and invasion, including potassium channel function and EPH receptor signaling. The findings presented demonstrate transcriptional vulnerabilities and elucidate previously unknown mechanisms of DIPG pathobiology.

BDE-99 impairs differentiation of human and mouse NPCs into the oligodendroglial lineage by species-specific modes of action

Polybrominated diphenyl ethers (PBDEs) are bioaccumulating flame retardants causing developmental neurotoxicity (DNT) in humans and rodents. Their DNT effects are suspected to involve thyroid hormone (TH) signaling disruption. Here, we tested the hypothesis whether disturbance of neural progenitor cell (NPC) differentiation into the oligodendrocyte lineage (O4+ cells) by BDE-99 involves disruption of TH action in human and mouse (h,m)NPCs. Therefore, we quantified differentiation of NPCs into O4+ cells and measured their maturation via expression of myelin-associated genes (hMBP, mMog) in presence and absence of TH and/or BDE-99. T3 promoted O4+ cell differentiation in mouse, but not hNPCs, and induced hMBP/mMog gene expression in both species. BDE-99 reduced generation of human and mouse O4+ cells, but there is no indication for BDE-99 interfering with cellular TH signaling during O4+ cell formation. BDE-99 reduced hMBP expression due to oligodendrocyte reduction, but concentrations that did not affect the number of mouse O4+ cells inhibited TH-induced mMog transcription by a yet unknown mechanism. In addition, ascorbic acid antagonized only the BDE-99-dependent loss of human, not mouse, O4+ cells by a mechanism probably independent of reactive oxygen species. These data point to species-specific modes of action of BDE-99 on h/mNPC development into the oligodendrocyte lineage.

Impaired oligodendroglial turnover is associated with myelin pathology in focal cortical dysplasia and tuberous sclerosis complex

Conventional antiepileptic drugs suppress the excessive firing of neurons during seizures. In drug‐resistant patients, treatment failure indicates an alternative important epileptogenic trigger. Two epilepsy‐associated pathologies show myelin deficiencies in seizure‐related brain regions: Focal Cortical Dysplasia IIB (FCD) and cortical tubers in Tuberous Sclerosis Complex (TSC). Studies uncovering white matter‐pathology mechanisms are therefore urgently needed to gain more insight into epileptogenesis, the propensity to maintain seizures, and their associated comorbidities such as cognitive defects. We analyzed epilepsy surgery specimens of FCD IIB (n = 22), TSC (n = 8), and other malformations of cortical development MCD (n = 12), and compared them to autopsy and biopsy cases (n = 15). The entire lesional pathology was assessed using digital immunohistochemistry, immunofluorescence and western blotting for oligodendroglial lineage, myelin and mTOR markers, and findings were correlated to clinical parameters. White matter pathology with depleted myelin and oligodendroglia were found in 50% of FCD IIB and 62% of TSC cases. Other MCDs had either a normal content or even showed reactive oligodendrolial hyperplasia. Furthermore, myelin deficiency was associated with increased mTOR expression and the lower amount of oligodendroglia was linked with their precursor cells (PDGFRa). The relative duration of epilepsy (normalized to age) also correlated positively to mTOR activation and negatively to myelination. Decreased content of oligodendroglia and missing precursor cells indicated insufficient oligodendroglial development, probably mediated by mTOR, which may ultimately lead to severe myelin loss. In terms of disease management, an early and targeted treatment could restore normal myelin development and, therefore, alter seizure threshold and improve cognitive outcome.

Transcription factor 7 like 2 promotes oligodendrocyte differentiation and remyelination.

Transcription factor 7 like 2 (TCF7L2, also termed TCF4), is a Wnt effector induced transiently in the oligodendroglial lineage. The current well accepted hypothesis is that TCF7L2 inhibits oligodendrocyte differentiation and remyelination through canonical Wnt/β-catenin signaling. However, recent studies indicated that TCF7L2 activity is required during oligodendrocyte differentiation and remyelination. In order to clarify this, in situ hybridization, immunofluorescence and western blot analysis using in vivo TCF7L2 conditional knockout mice, were performed and it was found that TCF7L2 promotes oligodendrocyte differentiation during myelin formation and remyelination. Furthermore, it was established that TCF7L2 does not affect oligodendrocyte precursor cells during remyelination. These data are of important clinical significance to develop novel therapeutic targets to overcome multiple sclerosis and other demyelinating diseases.

Regulation of Asymmetric Cell Division in Mammalian Neural Stem and Cancer Precursor Cells.

Stem and progenitor cells are characterized by their abilities to self-renew and produce differentiated progeny. The balance between self-renewal and differentiation is achieved through control of cell division mode, which can be either asymmetric or symmetric. Failure to properly control cell division mode may result in premature depletion of the stem/progenitor cell pool or abnormal growth and impaired differentiation. In many tissues, including the brain, stem cells and progenitor cells undergo asymmetric cell division through the establishment of cell polarity. Cell polarity proteins are therefore potentially critical regulators of asymmetric cell division. Decrease or loss of asymmetric cell division can be associated with reduced differentiation common during aging or impaired remyelination as seen in demyelinating diseases. Progenitor-like glioma precursor cells show decreased asymmetric cell division rates and increased symmetric divisions, which suggests that asymmetric cell division suppresses brain tumor formation. Cancer stem cells, on the other hand,still undergo low rates of asymmetric cell division, which may provide them with a survival advantage during therapy.These findings led to the hypotheses that asymmetric cell divisions are not always tumor suppressive but can also be utilized to maintain a cancer stem cell population. Proper control of cell division mode is therefore not only deemed necessary to generate cellular diversity during development and to maintain adult tissue homeostasis but may also prevent disease and determine disease progression. Since brain cancer is most common in the adult and aging population, we review here the current knowledge on molecular mechanisms that regulate asymmetric cell divisions in the neural and oligodendroglial lineage during development and in the adult brain.