Integrated electrophysiological and genomic profiles of single cells reveal spiking tumor cells in human glioma

Prior studies have described the complex interplay that exists between glioma cells and neurons, however, the electrophysiological properties endogenous to tumor cells remain obscure. To address this, we employed Patch-sequencing on human glioma specimens and found that one third of patched cells in IDH mutant (IDH mut ) tumors demonstrate properties of both neurons and glia by firing single, short action potentials. To define these hybrid cells (HCs) and discern if they are tumor in origin, we developed a computational tool, Single Cell Rule Association Mining (SCRAM), to annotate each cell individually. SCRAM revealed that HCs represent tumor and non-tumor cells that feature GABAergic neuron and oligodendrocyte precursor cell signatures. These studies are the first to characterize the combined electrophysiological and molecular properties of human glioma cells and describe a new cell type in human glioma with unique electrophysiological and transcriptomic properties that are likely also present in the non-tumor mammalian brain.

Next Directions in the Neuroscience of Cancers Arising outside the CNS

SUMMARY

The field of cancer neuroscience has begun to define the contributions of nerves to cancer initiation and progression; here, we highlight the future directions of basic and translational cancer neuroscience for malignancies arising outside of the central nervous system.

Comparative Transcriptomic Analysis of Cerebellar Astrocytes across Developmental Stages and Brain Regions

Astrocytes are the most abundant glial cell type in the central nervous system, and they play a crucial role in normal brain function. While gliogenesis and glial differentiation occur during perinatal cerebellar development, the processes that occur during early postnatal development remain obscure. In this study, we conducted transcriptomic profiling of postnatal cerebellar astrocytes at postnatal days 1, 7, 14, and 28 (P1, P7, P14, and P28), identifying temporal-specific gene signatures at each specific time point. Comparing these profiles with region-specific astrocyte differentially expressed genes (DEGs) published for the cortex, hippocampus, and olfactory bulb revealed cerebellar-specific gene signature across these developmental timepoints. Moreover, we conducted a comparative analysis of cerebellar astrocyte gene signatures with gene lists from pediatric brain tumors of cerebellar origin, including ependymoma and medulloblastoma. Notably, genes downregulated at P14, such as Kif11 and HMGB2, exhibited significant enrichment across all pediatric brain tumor groups, suggesting the importance of astrocytic gene repression during cerebellar development to these tumor subtypes. Collectively, our studies describe gene expression patterns during cerebellar astrocyte development, with potential implications for pediatric tumors originating in the cerebellum.

The immune system and metabolic products in epilepsy and glioma-associated epilepsy: emerging therapeutic directions

Epilepsy has a profound impact on quality of life. Despite the development of new antiseizure medications (ASMs), approximately one-third of affected patients have drug-refractory epilepsy and are nonresponsive to medical treatment. Nearly all currently approved ASMs target neuronal activity through ion channel modulation. Recent human and animal model studies have implicated new immunotherapeutic and metabolomic approaches that may benefit patients with epilepsy. In this Review, we detail the proinflammatory immune landscape of epilepsy and contrast this with the immunosuppressive microenvironment in patients with glioma-related epilepsy. In the tumor setting, excessive neuronal activity facilitates immunosuppression, thereby contributing to subsequent glioma progression. Metabolic modulation of the IDH1-mutant pathway provides a dual pathway for reversing immune suppression and dampening seizure activity. Elucidating the relationship between neurons and immunoreactivity is an area for the prioritization and development of the next era of ASMs.

Understanding the microenvironment and how this controls cell fate

The microenvironment influences cell fate. In this collection of voices, researchers from the fields of cancer and regeneration highlight approaches to establish the importance of the microenvironment and discuss future directions to understand the complex interaction between cells and their surrounding environment and how this impacts on disease and regeneration.

Subventricular zone cytogenesis provides trophic support for neural repair in a mouse model of stroke

Stroke enhances proliferation of neural precursor cells within the subventricular zone (SVZ) and induces ectopic migration of newborn cells towards the site of injury. Here, we characterize the identity of cells arising from the SVZ after stroke and uncover a mechanism through which they facilitate neural repair and functional recovery. With genetic lineage tracing, we show that SVZ-derived cells that migrate towards cortical photothrombotic stroke in mice are predominantly undifferentiated precursors. We find that ablation of neural precursor cells or conditional knockout of VEGF impairs neuronal and vascular reparative responses and worsens recovery. Replacement of VEGF is sufficient to induce neural repair and recovery. We also provide evidence that CXCL12 from peri-infarct vasculature signals to CXCR4-expressing cells arising from the SVZ to direct their ectopic migration. These results support a model in which vasculature surrounding the site of injury attracts cells from the SVZ, and these cells subsequently provide trophic support that drives neural repair and recovery.

Prevalence of pathogenic germline variants in adult-type diffuse glioma

Background

No consensus germline testing guidelines currently exist for glioma patients, so the prevalence of germline pathogenic variants remains unknown. This study aims to determine the prevalence and type of pathogenic germline variants in adult glioma.

Methods

A retrospective review at a single institution with paired tumor/normal sequencing from August 2018-April 2022 was performed and corresponding clinical data were collected.

Results

We identified 152 glioma patients of which 15 (9.8%) had pathogenic germline variants. Pathogenic germline variants were seen in 11/84 (13.1%) of Glioblastoma, IDH wild type; 3/42 (7.1%) of Astrocytoma, IDH mutant; and 1/26 (3.8%) of Oligodendroglioma, IDH mutant, and 1p/19q co-deleted patients. Pathogenic variants in BRCA2, MUTYH, and CHEK2 were most common (3/15, 20% each). BRCA1 variants occurred in 2/15 (13%) patients, with variants in NF1, ATM, MSH2, and MSH3 occurring in one patient (7%) each. Prior cancer diagnosis was found in 5/15 patients (33%). Second-hit somatic variants were seen in 3/15 patients (20%) in NF1, MUTYH, and MSH2. Referral to genetics was performed in 6/15 (40%) patients with pathogenic germline variants. 14/15 (93%) of patients discovered their pathogenic variant as a result of their paired glioma sequencing.

Conclusions

These findings suggest a possible overlooked opportunity for determination of hereditary cancer syndromes with impact on surveillance as well as potential broader treatment options. Further studies that can determine the role of variants in gliomagenesis and confirm the occurrence and types of pathogenic germline variants in patients with IDH wild type compared to IDH mutant tumors are necessary.

Remote neuronal activity drives glioma progression through SEMA4F

The tumour microenvironment plays an essential role in malignancy, and neurons have emerged as a key component of the tumour microenvironment that promotes tumourigenesis across a host of cancers1,2. Recent studies on glioblastoma (GBM) highlight bidirectional signalling between tumours and neurons that propagates a vicious cycle of proliferation, synaptic integration and brain hyperactivity3-8; however, the identity of neuronal subtypes and tumour subpopulations driving this phenomenon is incompletely understood. Here we show that callosal projection neurons located in the hemisphere contralateral to primary GBM tumours promote progression and widespread infiltration. Using this platform to examine GBM infiltration, we identified an activity-dependent infiltrating population present at the leading edge of mouse and human tumours that is enriched for axon guidance genes. High-throughput, in vivo screening of these genes identified SEMA4F as a key regulator of tumourigenesis and activity-dependent progression. Furthermore, SEMA4F promotes the activity-dependent infiltrating population and propagates bidirectional signalling with neurons by remodelling tumour-adjacent synapses towards brain network hyperactivity. Collectively our studies demonstrate that subsets of neurons in locations remote to primary GBM promote malignant progression, and also show new mechanisms of glioma progression that are regulated by neuronal activity.

Induction of astrocytic Slc22a3 regulates sensory processing through histone serotonylation

Neuronal activity drives alterations in gene expression within neurons, yet how it directs transcriptional and epigenomic changes in neighboring astrocytes in functioning circuits is unknown. We found that neuronal activity induces widespread transcriptional up-regulation and down-regulation in astrocytes, highlighted by the identification of Slc22a3 as an activity-inducible astrocyte gene that encodes neuromodulator transporter Slc22a3 and regulates sensory processing in the mouse olfactory bulb. Loss of astrocytic Slc22a3 reduced serotonin levels in astrocytes, leading to alterations in histone serotonylation. Inhibition of histone serotonylation in astrocytes reduced the expression of γ-aminobutyric acid (GABA) biosynthetic genes and GABA release, culminating in olfactory deficits. Our study reveals that neuronal activity orchestrates transcriptional and epigenomic responses in astrocytes while illustrating new mechanisms for how astrocytes process neuromodulatory input to gate neurotransmitter release for sensory processing.

5-aminolevulinic acid, fluorescein sodium, and indocyanine green for glioma margin detection: analysis of operating wide-field and confocal microscopy in glioma models of various grades

Introduction

Surgical resection remains the first-line treatment for gliomas. Several fluorescent dyes are currently in use to augment intraoperative tumor visualization, but information on their comparative effectiveness is lacking. We performed systematic assessment of fluorescein sodium (FNa), 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX), and indocyanine green (ICG) fluorescence in various glioma models using advanced fluorescence imaging techniques.

Methods

Four glioma models were used: GL261 (high-grade model), GB3 (low-grade model), and an in utero electroporation model with and without red fluorescence protein (IUE +RFP and IUE -RFP, respectively) (intermediate-to-low-grade model). Animals underwent 5-ALA, FNa, and ICG injections and craniectomy. Brain tissue samples underwent fluorescent imaging using a wide-field operative microscope and a benchtop confocal microscope and were submitted for histologic analysis.

Results

Our systematic analysis showed that wide-field imaging of highly malignant gliomas is equally efficient with 5-ALA, FNa, and ICG, although FNa is associated with more false-positive staining of the normal brain. In low-grade gliomas, wide-field imaging cannot detect ICG staining, can detect FNa in only 50% of specimens, and is not sensitive enough for PpIX detection. With confocal imaging of low-intermediate grade glioma models, PpIX outperformed FNa.

Discussion

Overall, compared to wide-field imaging, confocal microscopy significantly improved diagnostic accuracy and was better at detecting low concentrations of PpIX and FNa, resulting in improved tumor delineation. Neither PpIX, FNa, nor ICG delineated all tumor boundaries in studied tumor models, which emphasizes the need for novel visualization technologies and molecular probes to guide glioma resection. Simultaneous administration of 5-ALA and FNa with use of cellular-resolution imaging modalities may provide additional information for margin detection and may facilitate maximal glioma resection.

Inhibitory input directs astrocyte morphogenesis through glial GABABR

Communication between neurons and glia has an important role in establishing and maintaining higher-order brain function1. Astrocytes are endowed with complex morphologies, placing their peripheral processes in close proximity to neuronal synapses and directly contributing to their regulation of brain circuits2-4. Recent studies have shown that excitatory neuronal activity promotes oligodendrocyte differentiation5-7; whether inhibitory neurotransmission regulates astrocyte morphogenesis during development is unclear. Here we show that inhibitory neuron activity is necessary and sufficient for astrocyte morphogenesis. We found that input from inhibitory neurons functions through astrocytic GABAB receptor (GABABR) and that its deletion in astrocytes results in a loss of morphological complexity across a host of brain regions and disruption of circuit function. Expression of GABABR in developing astrocytes is regulated in a region-specific manner by SOX9 or NFIA and deletion of these transcription factors results in region-specific defects in astrocyte morphogenesis, which is conferred by interactions with transcription factors exhibiting region-restricted patterns of expression. Together, our studies identify input from inhibitory neurons and astrocytic GABABR as universal regulators of morphogenesis, while further revealing a combinatorial code of region-specific transcriptional dependencies for astrocyte development that is intertwined with activity-dependent processes.

The genomic landscape of familial glioma

Glioma is a rare brain tumor with a poor prognosis. Familial glioma is a subset of glioma with a strong genetic predisposition that accounts for approximately 5% of glioma cases. We performed whole-genome sequencing on an exploratory cohort of 203 individuals from 189 families with a history of familial glioma and an additional validation cohort of 122 individuals from 115 families. We found significant enrichment of rare deleterious variants of seven genes in both cohorts, and the most significantly enriched gene was HERC2 (P = 0.0006). Furthermore, we identified rare noncoding variants in both cohorts that were predicted to affect transcription factor binding sites or cause cryptic splicing. Last, we selected a subset of discovered genes for validation by CRISPR knockdown screening and found that DMBT1, HP1BP3, and ZCH7B3 have profound impacts on proliferation. This study performs comprehensive surveillance of the genomic landscape of familial glioma.

Social deprivation induces astrocytic TRPA1-GABA suppression of hippocampal circuits

Social experience is essential for the development and maintenance of higher-order brain function. Social deprivation results in a host of cognitive deficits, and cellular studies have largely focused on associated neuronal dysregulation; how astrocyte function is impacted by social deprivation is unknown. Here, we show that hippocampal astrocytes from juvenile mice subjected to social isolation exhibit increased Ca2+ activity and global changes in gene expression. We found that the Ca2+ channel TRPA1 is upregulated in astrocytes after social deprivation and astrocyte-specific deletion of TRPA1 reverses the physiological and cognitive deficits associated with social deprivation. Mechanistically, TRPA1 inhibition of hippocampal circuits is mediated by a parallel increase of astrocytic production and release of the inhibitory neurotransmitter GABA after social deprivation. Collectively, our studies reveal how astrocyte function is tuned to social experience and identifies a social-context-specific mechanism by which astrocytic TRPA1 and GABA coordinately suppress hippocampal circuit function.

Cancer neuroscience: State of the field, emerging directions

The nervous system governs both ontogeny and oncology. Regulating organogenesis during development, maintaining homeostasis, and promoting plasticity throughout life, the nervous system plays parallel roles in the regulation of cancers. Foundational discoveries have elucidated direct paracrine and electrochemical communication between neurons and cancer cells, as well as indirect interactions through neural effects on the immune system and stromal cells in the tumor microenvironment in a wide range of malignancies. Nervous system-cancer interactions can regulate oncogenesis, growth, invasion and metastatic spread, treatment resistance, stimulation of tumor-promoting inflammation, and impairment of anti-cancer immunity. Progress in cancer neuroscience may create an important new pillar of cancer therapy.

Remote neuronal activity drives glioma infiltration via Sema4f

The tumor microenvironment (TME) plays an essential role in malignancy and neurons have emerged as a key component of the TME that promotes tumorigenesis across a host of cancers. Recent studies on glioblastoma (GBM) highlight bi-directional signaling between tumors and neurons that propagates a vicious cycle of proliferation, synaptic integration, and brain hyperactivity; however, the identity of neuronal subtypes and tumor subpopulations driving this phenomenon are incompletely understood. Here we show that callosal projection neurons located in the hemisphere contralateral to primary GBM tumors promote progression and widespread infiltration. Using this platform to examine GBM infiltration, we identified an activity dependent infiltrating population present at the leading edge of mouse and human tumors that is enriched for axon guidance genes. High-throughput, in vivo screening of these genes identified Sema4F as a key regulator of tumorigenesis and activity-dependent infiltration. Furthermore, Sema4F promotes the activity-dependent infiltrating population and propagates bi-directional signaling with neurons by remodeling tumor adjacent synapses towards brain network hyperactivity. Collectively, our studies demonstrate that subsets of neurons in locations remote to primary GBM promote malignant progression, while revealing new mechanisms of tumor infiltration that are regulated by neuronal activity.

Inhibitory input directs astrocyte morphogenesis through glial GABA B R

Communication between neurons and glia plays an important role in establishing and maintaining higher order brain function. Astrocytes are endowed with complex morphologies which places their peripheral processes in close proximity to neuronal synapses and directly contributes to their regulation of brain circuits. Recent studies have shown that excitatory neuronal activity promotes oligodendrocyte differentiation; whether inhibitory neurotransmission regulates astrocyte morphogenesis during development is unknown. Here we show that inhibitory neuron activity is necessary and sufficient for astrocyte morphogenesis. We found that input from inhibitory neurons functions through astrocytic GABA B R and that its deletion in astrocytes results in a loss of morphological complexity across a host of brain regions and disruption of circuit function. Expression of GABA B R in developing astrocytes is regulated in a region-specific manner by SOX9 or NFIA and deletion of these transcription factors results in region-specific defects in astrocyte morphogenesis, which is conferred by interactions with transcription factors exhibiting region-restricted patterns of expression. Together our studies identify input from inhibitory neurons and astrocytic GABA B R as universal regulators of morphogenesis, while further revealing a combinatorial code of region-specific transcriptional dependencies for astrocyte development that is intertwined with activity-dependent processes.

In vivo functional characterization of EGFR variants identifies novel drivers of glioblastoma

BACKGROUND

Glioblastoma is the most common and aggressive primary brain tumor. Large-scale sequencing initiatives have cataloged its mutational landscape in hopes of elucidating mechanisms driving this deadly disease. However, a major bottleneck in harnessing this data for new therapies is deciphering "driver" and "passenger" events amongst the vast volume of information.

METHODS

We utilized an autochthonous, in vivo screening approach to identify driver, EGFR variants. RNA-Seq identified unique molecular signatures of mouse gliomas across these variants, which only differ by a single amino acid change. In particular, we identified alterations to lipid metabolism, which we further validated through an unbiased lipidomics screen.

RESULTS

Our screen identified A289I as the most potent EGFR variant, which has previously not been characterized. One of the mechanisms through which A289I promotes gliomagenesis is to alter cellular triacylglycerides through MTTP. Knockout of Mttp in mouse gliomas, reduces gliomagenesis in multiple models.

CONCLUSIONS

EGFR variants that differ by a single amino acid residue differentially promote gliomagenesis. Among the identified mechanism that drives glioma growth include lipid metabolism through MTTP. Understanding triacylglyceride accumulation may present a prospective therapeutic pathway for this deadly disease.

Glioma epileptiform activity and progression are driven by IGSF3-mediated potassium dysregulation

Seizures are a frequent pathophysiological feature of malignant glioma. Recent studies implicate peritumoral synaptic dysregulation as a driver of brain hyperactivity and tumor progression; however, the molecular mechanisms that govern these phenomena remain elusive. Using scRNA-seq and intraoperative patient ECoG recordings, we show that tumors from seizure patients are enriched for gene signatures regulating synapse formation. Employing a human-to-mouse in vivo functionalization pipeline to screen these genes, we identify IGSF3 as a mediator of glioma progression and dysregulated neural circuitry that manifests as spreading depolarization (SD). Mechanistically, we discover that IGSF3 interacts with Kir4.1 to suppress potassium buffering and found that seizure patients exhibit reduced expression of potassium handlers in proliferating tumor cells. In vivo imaging reveals that dysregulated synaptic activity emanates from the tumor-neuron interface, which we confirm in patients. Our studies reveal that tumor progression and seizures are enabled by ion dyshomeostasis and identify SD as a driver of disease.

Activity-dependent induction of astrocytic Slc22a3 regulates sensory processing through histone serotonylation

Neuronal activity drives global alterations in gene expression within neurons, yet how it directs transcriptional and epigenomic changes in neighboring astrocytes in functioning circuits is unknown. Here we show that neuronal activity induces widespread transcriptional upregulation and downregulation in astrocytes, highlighted by the identification of a neuromodulator transporter Slc22a3 as an activity-inducible astrocyte gene regulating sensory processing in the olfactory bulb. Loss of astrocytic Slc22a3 reduces serotonin levels in astrocytes, leading to alterations in histone serotonylation. Inhibition of histone serotonylation in astrocytes reduces expression of GABA biosynthetic genes and GABA release, culminating in olfactory deficits. Our study reveals that neuronal activity orchestrates transcriptional and epigenomic responses in astrocytes, while illustrating new mechanisms for how astrocytes process neuromodulatory input to gate neurotransmitter release for sensory processing.

CXCR4 expression is associated with proneural-to-mesenchymal transition in glioblastoma

Glioblastoma (GBM) is the most common primary intracranial malignant tumor and consists of three molecular subtypes: proneural (PN), mesenchymal (MES) and classical (CL). Transition between PN to MES subtypes (PMT) is the glioma analog of the epithelial-mesenchymal transition (EMT) in carcinomas and is associated with resistance to therapy. CXCR4 signaling increases the expression of MES genes in glioma cell lines and promotes EMT in other cancers. RNA sequencing (RNAseq) data of PN GBMs in The Cancer Genome Atlas (TCGA) and secondary high-grade gliomas (HGGs) from an internal cohort were examined for correlation between CXCR4 expression and survival as well as expression of MES markers. Publicly available single-cell RNA sequencing (scRNAseq) data was analyzed for cell type specific CXCR4 expression. These results were validated in a genetic mouse model of PN GBM. Higher CXCR4 expression was associated with significantly reduced survival and increased expression of MES markers in TCGA and internal cohorts. CXCR4 was expressed in immune and tumor cells based on scRNAseq analysis. Higher CXCR4 expression within tumor cells on scRNAseq was associated with increased MES phenotype, suggesting a cell-autonomous effect. In a genetically engineered mouse model, tumors induced with CXCR4 exhibited a mesenchymal phenotype and shortened survival. These results suggest that CXCR4 signaling promotes PMT and shortens survival in GBM and highlights its inhibition as a potential therapeutic strategy.

Abstract 2534: Neural control of glioma infiltration

Adult glioblastoma multiforme (GBM) is the most common and deadly form of malignant brain cancer. A broad relationship between tumor progression and neuronal stimulation in the microenvironment is known in peripheral tumors, but only a few interactions between neuronal cues and GBM cells have been characterized. By combining in utero electroporation (IUE) with CRISPR/Cas9 and piggyBac transposase genetics, we have developed an endogenous, immunocompetent, in vivo model with which to study these interactions in a native tumor context. Combining this model with Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) we interrogated tumor-neuron interactions. We assessed molecular and physiological changes in tumors during neural stimulation through tumor development with single cell sequencing and spatial transcriptomics. We examined expression data in populations present under stimulation that did not appear or appeared later in control tumors. These data showed axon guidance genes, a family of genes associated with directed cell motility, were upregulated in these populations. To functionally test these findings, we performed a barcoded screen of axon guidance genes in the IUE model followed by individual confirmation with gain and loss of function of individual genes. We found Sema4F affects infiltration of tumors as well as overall survival. Currently we wish to study the abrogation of this infiltration with Sema4F knockout in the context of DREADD stimulation. Completion of this study will provide new insights into neuronal interactions driving tumor progression in GBM.

Citation Format: Emmet J. Huang-Hobbs, Yi-Ting Cheng, Yeungjun Ko, Junsung Woo, Akdes Harmanci, Ganesh Rao, Benjamin Deneen. Neural control of glioma infiltration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2534.

Sculpting Astrocyte Diversity through Circuits and Transcription

Astrocytes are the most abundant glial cell in the central nervous system and occupy a wide range of roles that are essential for brain function. Over the past few years, evidence has emerged that astrocytes exhibit cellular and molecular heterogeneity, raising the possibility that subsets of astrocytes are functionally distinct and that transcriptional mechanisms are involved in encoding this prospective diversity. In this review, we focus on three emerging areas of astrocyte biology: region-specific circuit regulation, molecular diversity, and transcriptional regulation. This review highlights our nascent understanding of how molecular diversity is converted to functional diversity of astrocytes through the lens of brain region-specific circuits. We articulate our understanding of how transcriptional mechanisms regulate this diversity and key areas that need further exploration to achieve the overarching goal of a functional taxonomy of astrocytes in the brain.

Assessing Gq-GPCR-induced human astrocyte reactivity using bioengineered neural organoids

Astrocyte reactivity can directly modulate nervous system function and immune responses during disease and injury. However, the consequence of human astrocyte reactivity in response to specific contexts and within neural networks is obscure. Here, we devised a straightforward bioengineered neural organoid culture approach entailing transcription factor-driven direct differentiation of neurons and astrocytes from human pluripotent stem cells combined with genetically encoded tools for dual cell-selective activation. This strategy revealed that Gq-GPCR activation via chemogenetics in astrocytes promotes a rise in intracellular calcium followed by induction of immediate early genes and thrombospondin 1. However, astrocytes also undergo NF-κB nuclear translocation and secretion of inflammatory proteins, correlating with a decreased evoked firing rate of cocultured optogenetic neurons in suboptimal conditions, without overt neurotoxicity. Altogether, this study clarifies the intrinsic reactivity of human astrocytes in response to targeting GPCRs and delivers a bioengineered approach for organoid-based disease modeling and preclinical drug testing.

Astrocyte and Oligodendrocyte Responses From the Subventricular Zone After Injury

Under normal conditions, neural stem cells (NSCs or B cells) in the adult subventricular zone (SVZ) give rise to amplifying neural progenitor cells (NPCs or C cells), which can produce neuroblasts (or A cells) that migrate to the olfactory bulb and differentiate into new neurons. However, following brain injury, these cells migrate toward the injury site where they differentiate into astrocytes and oligodendrocytes. In this review, we will focus on recent findings that chronicle how astrocytes and oligodendrocytes derived from SVZ-NSCs respond to different types of injury. We will also discuss molecular regulators of SVZ-NSC proliferation and their differentiation into astrocytes and oligodendrocytes. Overall, the goal of this review is to highlight how SVZ-NSCs respond to injury and to summarize the regulatory mechanisms that oversee their glial response. These molecular and cellular processes will provide critical insights needed to develop strategies to promote brain repair following injury using SVZ-NSCs.

Rnf43 is "lord of the ring" finger proteins in remyelination

Oligodendrocyte precursor cell differentiation into myelinating oligodendrocytes is critical for remyelination in the central nervous system after injury. In this issue of Neuron, Niu et al. (2021) detail a novel role for ring finger protein Rnf43, which is expressed in response to injury and is essential to promote remyelination in vivo.

ZFTA-RELA Dictates Oncogenic Transcriptional Programs to Drive Aggressive Supratentorial Ependymoma

More than 60% of supratentorial ependymomas harbor a ZFTA-RELA (ZRfus) gene fusion (formerly C11orf95-RELA). To study the biology of ZRfus, we developed an autochthonous mouse tumor model using in utero electroporation (IUE) of the embryonic mouse brain. Integrative epigenomic and transcriptomic mapping was performed on IUE-driven ZRfus tumors by CUT&RUN, chromatin immunoprecipitation sequencing, assay for transposase-accessible chromatin sequencing, and RNA sequencing and compared with human ZRfus-driven ependymoma. In addition to direct canonical NFκB pathway activation, ZRfus dictates a neoplastic transcriptional program and binds to thousands of unique sites across the genome that are enriched with PLAGL family transcription factor (TF) motifs. ZRfus activates gene expression programs through recruitment of transcriptional coactivators (Brd4, Ep300, Cbp, Pol2) that are amenable to pharmacologic inhibition. Downstream ZRfus target genes converge on developmental programs marked by PLAGL TF proteins, and activate neoplastic programs enriched in Mapk, focal adhesion, and gene imprinting networks. SIGNIFICANCE: Ependymomas are aggressive brain tumors. Although drivers of supratentorial ependymoma (ZFTA- and YAP1-associated gene fusions) have been discovered, their functions remain unclear. Our study investigates the biology of ZFTA-RELA-driven ependymoma, specifically mechanisms of transcriptional deregulation and direct downstream gene networks that may be leveraged for potential therapeutic testing.This article is highlighted in the In This Issue feature, p. 2113.

Olfactory bulb astrocytes mediate sensory circuit processing through Sox9 in the mouse brain

The role of transcription factors during astrocyte development and their subsequent effects on neuronal development has been well studied. Less is known about astrocytes contributions towards circuits and behavior in the adult brain. Astrocytes play important roles in synaptic development and modulation, however their contributions towards neuronal sensory function and maintenance of neuronal circuit architecture remain unclear. Here, we show that loss of the transcription factor Sox9 results in both anatomical and functional changes in adult mouse olfactory bulb (OB) astrocytes, affecting sensory processing. Indeed, astrocyte-specific deletion of Sox9 in the OB results in decreased odor detection thresholds and discrimination and it is associated with aberrant neuronal sensory response maps. At functional level, loss of astrocytic Sox9 impairs the electrophysiological properties of mitral and tufted neurons. RNA-sequencing analysis reveals widespread changes in the gene expression profiles of OB astrocytes. In particular, we observe reduced GLT-1 expression and consequential alterations in glutamate transport. Our findings reveal that astrocytes are required for physiological sensory processing and we identify astrocytic Sox9 as an essential transcriptional regulator of mature astrocyte function in the mouse OB.

ZFTA Translocations Constitute Ependymoma Chromatin Remodeling and Transcription Factors

ZFTA (C11orf95)-a gene of unknown function-partners with a variety of transcriptional coactivators in translocations that drive supratentorial ependymoma, a frequently lethal brain tumor. Understanding the function of ZFTA is key to developing therapies that inhibit these fusion proteins. Here, using a combination of transcriptomics, chromatin immunoprecipitation sequencing, and proteomics, we interrogated a series of deletion-mutant genes to identify a tripartite transformation mechanism of ZFTA-containing fusions, including: spontaneous nuclear translocation, extensive chromatin binding, and SWI/SNF, SAGA, and NuA4/Tip60 HAT chromatin modifier complex recruitment. Thereby, ZFTA tethers fusion proteins across the genome, modifying chromatin to an active state and enabling its partner transcriptional coactivators to promote promiscuous expression of a transforming transcriptome. Using mouse models, we validate further those elements of ZFTA-fusion proteins that are critical for transformation-including ZFTA zinc fingers and partner gene transactivation domains-thereby unmasking vulnerabilities for therapeutic targeting. SIGNIFICANCE: Ependymomas are hard-to-treat brain tumors driven by translocations between ZFTA and a variety of transcriptional coactivators. We dissect the transforming mechanism of these fusion proteins and identify protein domains indispensable for tumorigenesis, thereby providing insights into the molecular basis of ependymoma tumorigenesis and vulnerabilities for therapeutic targeting.This article is highlighted in the In This Issue feature, p. 2113.

Glial-Specific Deletion of Med12 Results in Rapid Hearing Loss via Degradation of the Stria Vascularis

Mediator protein complex subunit 12 (Med12) is a core component of the basal transcriptional apparatus and plays a critical role in the development of many tissues. Mutations in Med12 are associated with X-linked intellectual disability syndromes and hearing loss; however, its role in nervous system function remains undefined. Here, we show that temporal conditional deletion of Med12 in astrocytes in the adult CNS results in region-specific alterations in astrocyte morphology. Surprisingly, behavioral studies revealed rapid hearing loss after adult deletion of Med12 that was confirmed by a complete abrogation of auditory brainstem responses. Cellular analysis of the cochlea revealed degeneration of the stria vascularis, in conjunction with disorganization of basal cells adjacent to the spiral ligament and downregulation of key cell adhesion proteins. Physiologic analysis revealed early changes in endocochlear potential, consistent with strial-specific defects. Together, our studies reveal that Med12 regulates auditory function in the adult by preserving the structural integrity of the stria vascularis.SIGNIFICANCE STATEMENT Mutations in Mediator protein complex subunit 12 (Med12) are associated with X-linked intellectual disability syndromes and hearing loss. Using temporal-conditional genetic approaches in CNS glia, we found that loss of Med12 results in severe hearing loss in adult animals through rapid degeneration of the stria vascularis. Our study describes the first animal model that recapitulates hearing loss identified in Med12-related disorders and provides a new system in which to examine the underlying cellular and molecular mechanisms of Med12 function in the adult nervous system.

Identification of diverse tumor endothelial cell populations in malignant glioma

BACKGROUND

Glioblastoma is the most common and aggressive type of primary brain tumor, as most patients succumb to the disease less than two years after diagnosis. Critically, studies demonstrate that glioma recruits surrounding blood vessels, while some work suggests that tumor stem cells themselves directly differentiate into endothelial cells, yet the molecular and cellular dynamics of the endothelium in glioma are poorly characterized. The goal of this study was to establish molecular and morphological benchmarks for tumor associated vessels (TAVs) and tumor derived endothelial cells (TDECs) during glioblastoma progression.

METHODS

Using In-Utero Electroporation and CRISPR/Cas9 genome engineering to generate a native, immunocompetent mouse model of glioma, we characterized vascular-tumor dynamics in three dimensions during tumor progression. We employed bulk and single-cell RNA-Sequencing to elucidate the relationship between TAVs and TDECs. We confirmed our findings in a patient derived orthotopic xenograft (PDOX) model.

RESULTS

Using a mouse model of glioma, we identified progressive alteration of vessel function and morphogenesis over time. We also showed in our mouse model that TDECs are a rare subpopulation that contributes to vessels within the tumor, albeit to a limited degree. Furthermore, transcriptional profiling demonstrates that both TAVs and TDECs are molecularly distinct, and both populations feature extensive molecular heterogeneity. Finally, the distinct molecular signatures of these heterogeneous populations are also present in human glioma.

CONCLUSIONS

Our findings show extensive endothelial heterogeneity within the tumor and tumor microenvironment and provide insights into the diverse cellular and molecular mechanisms that drive glioma vascularization and angiogenesis during tumorigenesis.

EPEN-01. C11ORF95-RELA DICTATES ONCOGENIC TRANSCRIPTIONAL PROGRAMS TO DRIVE AGGRESSIVE SUPRATENTORIAL EPENDYMOMA

Over 60% of supratentorial (ST) ependymomas harbor a gene fusion between C11orf95, an uncharacterized gene, and RELA (also known as p65), a main component of the NF-ĸB family of transcription factors. While its sufficiency to drive tumor has been established, the mechanism of tumorigenesis remains elusive. To tackle this question, we developed a natively forming mouse tumor model using in utero electroporation (IUE) of the embryonic mouse brain and performed integrative epigenomic and transcriptomic mapping. Our findings indicate that in addition to direct canonical NF-ĸB pathway activation, C11orf95-RELA (CRfus) dictates a neoplastic transcriptional program and binds to unique sites across the genome enriched with Plagl family transcription factor motifs. CRfus modulates the transcriptional landscape by recruiting transcription co-activators (Brd4, EP300, Cbp, Pol2) which are amenable to pharmacologic inhibition. Downstream CRfus target genes converge on developmental programs marked by Plagl family of transcription factors and activate neoplastic programs enriched in Mapk, focal adhesion, and gene imprinting networks, many of which contain previously unreported therapeutic leads in C11orf95-RELA ependymoma.

POT1 Regulates Proliferation and Confers Sexual Dimorphism in Glioma

Germline POT1 mutations are found in a spectrum of cancers and confer increased risk. Recently, we identified a series of novel germline POT1 mutations that predispose carrier families to the development of glioma. Despite these strong associations, how these glioma-associated POT1 mutations contribute to glioma tumorigenesis remains undefined. Here we show that POT1-G95C increases proliferation in glioma-initiating cells in vitro and in progenitor populations in the developing brain. In a native mouse model of glioma, loss of Pot1a/b resulted in decreased survival in females compared with males. These findings were corroborated in human glioma, where low POT1 expression correlated with decreased survival in females. Transcriptomic and IHC profiling of Pot1a/b-deficient glioma revealed that tumors in females exhibited decreased expression of immune markers and increased expression of cell-cycle signatures. Similar sex-dependent trends were observed in human gliomas that had low expression of POT1. Together, our studies demonstrate context-dependent functions for POT1 mutation or loss in driving progenitor proliferation in the developing brain and sexual dimorphism in glioma. SIGNIFICANCE: This study shows that manipulation of POT1 expression in glioma has sex-specific effects on tumorigenesis and associated immune signatures.

Reactive astrocyte nomenclature, definitions, and future directions

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.

Systematic analysis of purified astrocytes after SCI unveils Zeb2os function during astrogliosis

Spinal cord injury (SCI) is one of the most devastating neural injuries without effective therapeutic solutions. Astrocytes are the predominant component of the scar. Understanding the complex contributions of reactive astrocytes to SCI pathophysiologies is fundamentally important for developing therapeutic strategies. We have studied the molecular changes in the injury environment and the astrocyte-specific responses by astrocyte purification from injured spinal cords from acute to chronic stages. In addition to protein-coding genes, we have systematically analyzed the expression profiles of long non-coding RNAs (lncRNAs) (>200 bp), which are regulatory RNAs that play important roles in the CNS. We have identified a highly conserved lncRNA, Zeb2os, and demonstrated using functional assays that it plays an important role in reactive astrogliosis through the Zeb2os/Zeb2/Stat3 axis. These studies provide valuable insights into the molecular basis of reactive astrogliosis and fill the knowledge gap regarding the function(s) of lncRNAs in astrogliosis and SCI.

EPEN-30. C11ORF95-RELA FUSION PROTEIN ENGAGES NOVEL GENOMIC LOCI TO DRIVE MURINE EPENDYMOMA GROWTH

RATIONALE

Over 70% of supratentorial (ST) ependymoma are characterized by an oncogenic fusion between C11ORF95 and RELA. C11ORF95-RELA fusion is frequently the sole genetic driver detected in ST ependymoma, thus ranking this genomic event as a lead target for therapeutic investigation. RELA is a transcription factor (TF) central to mediating NF-kB pathway activation in processes such as inflammation, cellular metabolism, and chemotaxis. HYPOTHESIS: We posited that C11ORF95-RELA acts as an oncogenic TF that aberrantly shapes the tumor epigenome to drive aberrant transcription. Approach: To this end we developed an in utero electroporation (IUE) mouse model of ependymoma to express C11ORF95-RELA during embryonic development. Our IUE approach allowed us to develop C11ORF95-RELA driven tumor models and cell lines. We comprehensively characterized the epigenome and transcriptome of C11ORF95-RELA fusion driven mouse cells by H3K27ac ChIP-seq, ATAC-seq, and RNA-seq.

RESULTS

This data revealed that: 1) C11ORF95-RELA directly engages ‘open’ chromatin and is enriched at regions with known RELA TF binding sites as well as novel genomic loci/motifs, 2) C11ORF95-RELA preferentially binds to both H3K27ac (active) enhancers and promoters, and 3) Bound C11ORF95-RELA promoter loci are associated with increased transcription of genes shared with human ependymoma.

CONCLUSION

Our findings shed light on the transcriptional mechanisms of C11ORF95-RELA, and reveal downstream targets that may represent cancer dependency genes and molecular targets.

Parallel astrocyte calcium signaling modulates olfactory bulb responses

Astrocytes are the most abundant glial cell in the central nervous system. They modulate synaptic function through a variety of mechanisms, and yet remain relatively understudied with respect to overall neuronal circuit function. Exploiting the tractability of the mouse olfactory system, we manipulated astrocyte activity and examined how astrocytes modulate olfactory bulb responses. Toward this, we genetically targeted both astrocytes and neurons for in vivo widefield imaging of Ca2+ responses to odor stimuli. We found that astrocytes exhibited odor response maps that overlap with excitatory neuronal activity. By manipulating Ca2+ activity in astrocytes using chemical genetics we found that odor-evoked neuronal activity was reciprocally affected, suggesting that astrocyte activation inhibits neuronal odor responses. Subsequently, behavioral experiments revealed that astrocyte manipulations affect both odor detection threshold and discrimination, suggesting that astrocytes play an active role in olfactory sensory processing circuits. Together, these studies show that astrocyte calcium signaling contributes to olfactory behavior through modulation of sensory circuits.

Region-Specific Transcriptional Control of Astrocyte Function Oversees Local Circuit Activities

Astrocytes play essential roles in brain function by supporting synaptic connectivity and associated circuits. How these roles are regulated by transcription factors is unknown. Moreover, there is emerging evidence that astrocytes exhibit regional heterogeneity, and the mechanisms controlling this diversity remain nascent. Here, we show that conditional deletion of the transcription factor nuclear factor I-A (NFIA) in astrocytes in the adult brain results in region-specific alterations in morphology and physiology that are mediated by selective DNA binding. Disruptions in astrocyte function following loss of NFIA are most pronounced in the hippocampus, manifested by impaired interactions with neurons, coupled with diminution of learning and memory behaviors. These changes in hippocampal astrocytes did not affect basal neuronal properties but specifically inhibited synaptic plasticity, which is regulated by NFIA in astrocytes through calcium-dependent mechanisms. Together, our studies reveal region-specific transcriptional dependencies for astrocytes and identify astrocytic NFIA as a key transcriptional regulator of hippocampal circuits.

The Emerging Nature of Astrocyte Diversity

Astrocytes are morphologically complex, ubiquitous cells that are viewed as a homogeneous population tiling the entire central nervous system (CNS). However, this view has been challenged in the last few years with the availability of RNA sequencing, immunohistochemistry, electron microscopy, morphological reconstruction, and imaging data. These studies suggest that astrocytes represent a diverse population of cells and that they display brain area- and disease-specific properties and functions. In this review, we summarize these observations, emphasize areas where clear conclusions can be made, and discuss potential unifying themes. We also identify knowledge gaps that need to be addressed in order to exploit astrocyte diversity as a biological phenomenon of physiological relevance in the CNS. We thus provide a summary and a perspective on astrocyte diversity in the vertebrate CNS.

Pathogenesis of peritumoral hyperexcitability in an immunocompetent CRISPR-based glioblastoma model

Seizures often herald the clinical appearance of gliomas or appear at later stages. Dissecting their precise evolution and cellular pathogenesis in brain malignancies could inform the development of staged therapies for these highly pharmaco-resistant epilepsies. Studies in immunodeficient xenograft models have identified local interneuron loss and excess glial glutamate release as chief contributors to network disinhibition, but how hyperexcitability in the peritumoral microenvironment evolves in an immunocompetent brain is unclear. We generated gliomas in WT mice via in utero deletion of key tumor suppressor genes and serially monitored cortical epileptogenesis during tumor infiltration with in vivo electrophysiology and GCAMP7 calcium imaging, revealing a reproducible progression from hyperexcitability to convulsive seizures. Long before seizures, coincident with loss of inhibitory cells and their protective scaffolding, gain of glial glutamate antiporter xCT expression, and reactive astrocytosis, we detected local Iba1+ microglial inflammation that intensified and later extended far beyond tumor boundaries. Hitherto unrecognized episodes of cortical spreading depolarization that arose frequently from the peritumoral region may provide a mechanism for transient neurological deficits. Early blockade of glial xCT activity inhibited later seizures, and genomic reduction of host brain excitability by deleting MapT suppressed molecular markers of epileptogenesis and seizures. Our studies confirmed xenograft tumor-driven pathobiology and revealed early and late components of tumor-related epileptogenesis in a genetically tractable, immunocompetent mouse model of glioma, allowing the complex dissection of tumor versus host pathogenic seizure mechanisms.

Roadmap for the Emerging Field of Cancer Neuroscience

Mounting evidence indicates that the nervous system plays a central role in cancer pathogenesis. In turn, cancers and cancer therapies can alter nervous system form and function. This Commentary seeks to describe the burgeoning field of "cancer neuroscience" and encourage multidisciplinary collaboration for the study of cancer-nervous system interactions.

Astrocytogenesis: where, when, and how

Astrocytes are the most abundant cell type in the central nervous system and have diverse functions in blood–brain barrier maintenance, neural circuitry formation and function, and metabolic regulation. To better understand the diverse roles of astrocytes, we will summarize what is known about astrocyte development and the challenges limiting our understanding of this process. We will also discuss new approaches and technologies advancing the field.

Regionally Distinct Astrocytes Display Unique Transcription Factor Profiles in the Adult Brain

Astrocytes are the most abundant type of glial cell in the central nervous system and perform a myriad of vital functions, however, the nature of their diversity remains a longstanding question in neuroscience. Using transcription factor motif discovery analysis on region-specific gene signatures from astrocytes we uncovered universal and region-specific transcription factor expression profiles. This analysis revealed that motifs for Nuclear Factor-I (NFI) are present in genes enriched in astrocytes from all regions, with NFIB and NFIX exhibiting pan-astrocyte expression in the olfactory bulb, hippocampus, cortex, and brainstem. Further analysis into region-specific motif patterns, identified Nkx3-1, Stat4, Pgr, and Nkx6-1 as prospective region-specific transcription factors. Validation studies revealed that Nkx6-1 is exclusively expressed in astrocytes in the brainstem and associates with the promoters of several brainstem specific target genes. These studies illustrate the presence of multiple transcriptional layers in astrocytes across diverse brain regions and provide a new entry point for examining how astrocyte diversity is specified and maintained.

PIK3CA variants selectively initiate brain hyperactivity during gliomagenesis

Glioblastoma is a universally lethal form of brain cancer that exhibits an array of pathophysiological phenotypes, many of which are mediated by interactions with the neuronal microenvironment1,2. Recent studies have shown that increases in neuronal activity have an important role in the proliferation and progression of glioblastoma3,4. Whether there is reciprocal crosstalk between glioblastoma and neurons remains poorly defined, as the mechanisms that underlie how these tumours remodel the neuronal milieu towards increased activity are unknown. Here, using a native mouse model of glioblastoma, we develop a high-throughput in vivo screening platform and discover several driver variants of PIK3CA. We show that tumours driven by these variants have divergent molecular properties that manifest in selective initiation of brain hyperexcitability and remodelling of the synaptic constituency. Furthermore, secreted members of the glypican (GPC) family are selectively expressed in these tumours, and GPC3 drives gliomagenesis and hyperexcitability. Together, our studies illustrate the importance of functionally interrogating diverse tumour phenotypes driven by individual, yet related, variants and reveal how glioblastoma alters the neuronal microenvironment.

GENE-21. ROLE OF POT1 MUTATION IN GLIOMA PROLIFERATION AND SEXUAL DIVERGENCE OF SURVIVAL

Germline POT1 mutations are associated with risk of several cancers including glioma. In The Cancer Genome Atlas, we found that the level of POT1 gene expression in tumors is associated with overall survival in IDH wild-type glioma independent of age and tumor grade (P=0.036). To assess if POT1 expression in a native mouse model of IDH wild-type glioma (referred to as C3 tumors) affects survival, we targeted both mouse POT1 orthologs (Pot1a/Pot1b) in C3 tumors using CRISPR/Cas9, generating C5 tumors. Interestingly, we noted a sexual divergence of survival, with female C5 mice dying faster than males (P=0.0034), whereas C3 mice show no sexual divergence in survival. To assess the genes and pathways underlying this divergence, we performed RNAseq profiling on C3 and C5 tumors and normalized the sex differences in the C5 profile for baseline sex differences in the C3 profile. Compared to males, female C5 tumors had lower enrichment of numerous gene sets related to immune surveillance. To specifically assess the effects of glioma-associated human POT1 variants, we expressed these variants in a mouse tumor sphere culture. We noted that expression of POT1-G95C variant increased the rate of sphere formation in vitro. In vivo expression of this variant in embryonic mouse brain during the gliogenic period increased the proliferative rate as assessed by BrdU uptake (P=0.008). These findings suggest a potential role for human POT1 variants in growth and proliferation of glial progenitor cells as well as glioma tumor cells. Additionally, the sexual divergence of survival in C5 tumors points to a differential interaction between POT1 loss and sex in regulation of immune response to these tumors.

Nuclear factor I-A regulates diverse reactive astrocyte responses after CNS injury

Reactive astrocytes are associated with every form of neurological injury. Despite their ubiquity, the molecular mechanisms controlling their production and diverse functions remain poorly defined. Because many features of astrocyte development are recapitulated in reactive astrocytes, we investigated the role of nuclear factor I-A (NFIA), a key transcriptional regulator of astrocyte development whose contributions to reactive astrocytes remain undefined. Here, we show that NFIA is highly expressed in reactive astrocytes in human neurological injury and identify unique roles across distinct injury states and regions of the CNS. In the spinal cord, after white matter injury (WMI), NFIA-deficient astrocytes exhibit defects in blood-brain barrier remodeling, which are correlated with the suppression of timely remyelination. In the cortex, after ischemic stroke, NFIA is required for the production of reactive astrocytes from the subventricular zone (SVZ). Mechanistically, NFIA directly regulates the expression of thrombospondin 4 (Thbs4) in the SVZ, revealing a key transcriptional node regulating reactive astrogenesis. Together, these studies uncover critical roles for NFIA in reactive astrocytes and illustrate how region- and injury-specific factors dictate the spectrum of reactive astrocyte responses.

BRCA1/BRCA2-containing complex subunit 3 controls oligodendrocyte differentiation by dynamically regulating lysine 63-linked ubiquitination

Oligodendrocytes (OLs) provide the myelin sheath surrounding axons that propagates action potentials in the central nervous system (CNS). The metabolism of myelinated membranes and proteins is strictly regulated in the OLs and is closely associated with OL differentiation and maturation. The ubiquitination-associated proteasome and endosomal system have not yet been well studied during OL differentiation and maturation. Here, we determined the functions of the Lys63-linked ubiquitination (K63Ub) and K63-specific deubiquitination (DUB) systems regulated by BRCA1/BRCA2-containing complex subunit 3 (BRCC3) during OL differentiation. The competitive inhibition of K63Ub by overexpression of mutant ubiquitin (K63R) in oligodendrocyte precursor cells (OPCs) indicated that the two major CNS myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), were upregulated in OLs derived from K63R OPCs. In contrast, the knockdown of BRCC3 (BRCC3-KD) through the application of lentivirus-mediated shRNA delivery system into OPCs suppressed OL differentiation by decreasing MBP expression and PLP production. Further immunoprecipitation assays revealed higher levels of sphingolipid GalC, MBP, and PLP, which were associated with K63Ub-immunoprecipitants and detected in endosome/lysosomal compartments, in BRCC3-KD OLs than those in OLs transfected with the scrambled shRNA (scramble OLs). The differentiation of OLs from BRCC3-KD OPCs was impaired in the demyelinating corpus callosum of rats receiving a cuprizone-containing diet. In the demyelinating tissues from human patients suffering from multiple sclerosis, we detected a decreased number of BRCC3-expressing OLs at the lesion site, accompanied by a greater number of OLs expressing EEA1 and K63Ub at high levels. Altogether, the counterbalance of the K63Ub machinery and BRCC3-triggered DUB machinery are important for the cellular trafficking of myelin proteins and OL differentiation.

Brain Region-Specific Gene Signatures Revealed by Distinct Astrocyte Subpopulations Unveil Links to Glioma and Neurodegenerative Diseases

Currently, there are no effective treatments for glioma or for neurodegenerative diseases because of, in part, our limited understanding of the pathophysiology and cellular heterogeneity of these diseases. Mounting evidence suggests that astrocytes play an active role in the pathogenesis of these diseases by contributing to a diverse range of pathophysiological states. In a previous study, five molecularly distinct astrocyte subpopulations from three different brain regions were identified. To further delineate the underlying diversity of these populations, we obtained mouse brain region-specific gene signatures for both protein-coding and long non-coding RNA and found that these astrocyte subpopulations are endowed with unique molecular signatures across diverse brain regions. Additional gene set and single-sample enrichment analyses revealed that gene signatures of different subpopulations are differentially correlated with glioma tumors that harbor distinct genomic alterations. To the best of our knowledge, this is the first study that links transcriptional profiles of astrocyte subpopulations with glioma genomic mutations. Furthermore, our results demonstrated that subpopulations of astrocytes in select brain regions are associated with specific neurodegenerative diseases. Overall, the present study provides a new perspective for understanding the pathophysiology of glioma and neurodegenerative diseases and highlights the potential contributions of diverse astrocyte populations to normal, malignant, and degenerative brain functions.