An essential role for a MEK-C/EBP pathway during growth factor-regulated cortical neurogenesis

Neural conditional ablation of the protein tyrosine phosphatase receptor Delta PTPRD impairs gliogenesis in the developing mouse brain cortex

Neurodevelopmental disorders are characterized by alterations in the development of the cerebral cortex, including aberrant changes in the number and function of neural cells. Although neurogenesis is one of the most studied cellular processes in these pathologies, little evidence is known about glial development. Genetic association studies have identified several genes associated with neurodevelopmental disorders. Indeed, variations in the PTPRD gene have been associated with numerous brain disorders, including autism spectrum disorder, restless leg syndrome, and schizophrenia. We previously demonstrated that constitutive loss of PTPRD expression induces significant alterations in cortical neurogenesis, promoting an increase in intermediate progenitors and neurons in mice. However, its role in gliogenesis has not been evaluated. To assess this, we developed a conditional knockout mouse model lacking PTPRD expression in telencephalon cells. Here, we found that the lack of PTPRD in the mouse cortex reduces glial precursors, astrocytes, and oligodendrocytes. According to our results, this decrease in gliogenesis resulted from a reduced number of radial glia cells at gliogenesis onset and a lower gliogenic potential in cortical neural precursors due to less activation of the JAK/STAT pathway and reduced expression of gliogenic genes. Our study shows PTPRD as a regulator of the glial/neuronal balance during cortical neurodevelopment and highlights the importance of studying glial development to understand the etiology of neurodevelopmental diseases.

Gliomas: a reflection of temporal gliogenic principles

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

Associations between polymorphisms in the cannabinoid receptor 1 gene, cognitive impairments and tardive dyskinesia in a Chinese population with schizophrenia

OBJECTIVE

Tardive dyskinesia (TD) is a medically induced movement disorder that occurs as a result of long-term use of antipsychotic medications, commonly seen in patients with schizophrenia (SCZ). The study aimed to investigate the relationship between single nucleotide polymorphisms (SNPs) of the CNR1 gene, TD and cognitive impairments in a Chinese population with SCZ.

METHODS

A total of 216 SCZ patients were recruited. The participants were divided into TD and without TD (WTD) groups using the Schooler-Kane International Diagnostic Criteria. The severity of TD was assessed using the Abnormal Involuntary Movement Scale (AIMS). Cognitive function was assessed using the Repeatable Battery for Assessment of Neuropsychological Status (RBANS) scale. Hardy-Weinberg equilibrium tests, chained disequilibrium analyses and haplotype analyses were performed using SHE-sis software. To explore the main effects of TD diagnosis, genotype and cognitive function, as well as interaction effects, analysis of covariance (ANCOVA) was employed.

RESULTS

The prevalence of TD was approximately 27.3%. Significant differences were observed in the rs806368 CT genotype and rs806370 TC genotype within the hypercongenic pattern between the male TD and WTD groups (OR = 2.508, 95% CI: 1.055-5.961, p = 0.037; OR = 2.552, 95% CI: 1.073-6.069, p = 0.034). Among TD patients, those carrying the rs806368 CC genotype exhibited higher limb trunk scores (p < 0.05). Moreover, there was a statistically significant difference in visuospatial/construction between the TD and WTD groups (p = 0.04), and a borderline significant difference in visuospatial/construction when considering the interaction between TD diagnosis and genotype at the rs806368 locus (p = 0.05).

CONCLUSION

CNR1 rs806368 and rs806370 polymorphisms may play a role in TD susceptibility. Additionally, CNR1 gene polymorphisms were associated with the severity of involuntary movements and cognitive impairments in TD patients.

Unravelling a novel role for cannabidivarin in the modulation of subventricular zone postnatal neurogenesis

Postnatal neurogenesis has been shown to rely on the endocannabinoid system. Here we aimed at unravelling the role of Cannabidivarin (CBDV), a non-psychoactive cannabinoid, with high affinity for the non-classical cannabinoid receptor TRPV1, on subventricular zone (SVZ) postnatal neurogenesis. Using the neurosphere assay, SVZ-derived neural stem/progenitor cells (NSPCs) were incubated with CBDV and/or 5'-Iodoresinferotoxin (TRPV1 antagonist), and their role on cell viability, proliferation, and differentiation were dissected. CBDV was able to promote, through a TRPV1-dependent mechanism, cell survival, cell proliferation and neuronal differentiation. Furthermore, pulse-chase experiments revealed that CBDV-induced neuronal differentiation was a result of cell cycle exit of NSPCs. Regarding oligodendrocyte differentiation, CBDV inhibited oligodendrocyte differentiation and maturation. Since our data suggested that the CBDV-induced modulation of NSPCs acted via TRPV1, a sodium-calcium channel, and that intracellular calcium levels are known regulators of NSPCs fate and neuronal maturation, single cell calcium imaging was performed to evaluate the functional response of SVZ-derived cells. We observed that CBDV-responsive cells displayed a two-phase calcium influx profile, being the initial phase dependent on TRPV1 activation. Taken together, this work unveiled a novel and untapped neurogenic potential of CBDV via TRPV1 modulation. These findings pave the way to future neural stem cell biological studies and repair strategies by repurposing this non-psychoactive cannabinoid as a valuable therapeutic target.

C/EBPβ Regulates TFAM Expression, Mitochondrial Function and Autophagy in Cellular Models of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that results from the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Since there are only symptomatic treatments available, new cellular and molecular targets involved in the onset and progression of this disease are needed to develop effective treatments. CCAAT/Enhancer Binding Protein β (C/EBPβ) transcription factor levels are altered in patients with a variety of neurodegenerative diseases, suggesting that it may be a good therapeutic target for the treatment of PD. A list of genes involved in PD that can be regulated by C/EBPβ was generated by the combination of genetic and in silico data, the mitochondrial transcription factor A (TFAM) being among them. In this paper, we observed that C/EBPβ overexpression increased TFAM promoter activity. However, downregulation of C/EBPβ in different PD/neuroinflammation cellular models produced an increase in TFAM levels, together with other mitochondrial markers. This led us to propose an accumulation of non-functional mitochondria possibly due to the alteration of their autophagic degradation in the absence of C/EBPβ. Then, we concluded that C/EBPβ is not only involved in harmful processes occurring in PD, such as inflammation, but is also implicated in mitochondrial function and autophagy in PD-like conditions.

7-Dehydrocholesterol-derived oxysterols cause neurogenic defects in Smith-Lemli-Opitz syndrome

Defective 3β-hydroxysterol-Δ7 -reductase (DHCR7) in the developmental disorder, Smith-Lemli-Opitz syndrome (SLOS), results in a deficiency in cholesterol and accumulation of its precursor, 7-dehydrocholesterol (7-DHC). Here, we show that loss of DHCR7 causes accumulation of 7-DHC-derived oxysterol metabolites, premature neurogenesis from murine or human cortical neural precursors, and depletion of the cortical precursor pool, both in vitro and in vivo. We found that a major oxysterol, 3β,5α-dihydroxycholest-7-en-6-one (DHCEO), mediates these effects by initiating crosstalk between glucocorticoid receptor (GR) and neurotrophin receptor kinase TrkB. Either loss of DHCR7 or direct exposure to DHCEO causes hyperactivation of GR and TrkB and their downstream MEK-ERK-C/EBP signaling pathway in cortical neural precursors. Moreover, direct inhibition of GR activation with an antagonist or inhibition of DHCEO accumulation with antioxidants rescues the premature neurogenesis phenotype caused by the loss of DHCR7. These results suggest that GR could be a new therapeutic target against the neurological defects observed in SLOS.

Unraveling the Mechanisms of Clinical Drugs-Induced Neural Tube Defects Based on Network Pharmacology and Molecular Docking Analysis

Chemotherapeutic agents such as methotrexate (MTX), raltitrexed (RTX), 5-fluorouracil (5-FU), hydroxyurea (HU), and retinoic acid (RA), and valproic acid (VPA), an antiepileptic drug, all can cause malformations in the developing central nervous system (CNS), such as neural tube defects (NTDs). However, the common pathogenic mechanisms remain unclear. This study aimed to explore the mechanisms of NTDs caused by MTX, RTX, 5-FU, HU, RA, and VPA (MRFHRV), based on network pharmacology and molecular biology experiments. The MRFHRV targets were integrated with disease targets, to find the potential molecules related to MRFHRV-induced NTDs. Protein-protein interaction analysis and molecular docking were performed to analyze these common targets. Utilizing the kyoto encyclopedia of genes and genomes (KEGG) signaling pathways, we analyzed and searched the possible causative pathogenic mechanisms by crucial targets and the signaling pathway. Results showed that MRFHRV induced NTDs through several key targets (including TP53, MAPK1, HSP90AA1, ESR1, GRB2, HDAC1, EGFR, PIK3CA, RXRA, and FYN) and multiple signaling pathways such as PI3K/Akt pathway, suggesting that abnormal proliferation and differentiation could be critical pathogenic contributors in NTDs induced by MRFHRV. These results were further validated by CCK8 assay in mouse embryonic stem cells and GFAP staining in embryonic brain tissue. This study indicated that chemotherapeutic and antiepileptic agents induced NTDs might through predicted targets TP53, MAPK1, GRB2, HDAC1, EGFR, PIK3CA, RXRA, and FYN and multiple signaling pathways. More caution was required for the clinical administration for women with childbearing potential and pregnant.

Short-Term Cortical Electrical Stimulation during the Acute Stage of Traumatic Brain Injury Improves Functional Recovery

Functional restoration is an important issue in the treatment of traumatic brain injury (TBI). Various electrical stimulation devices and protocols have been applied in preclinical studies and have shown therapeutic potential for brain trauma. Short-term invasive cortical electrical stimulation during the acute stage of TBI might be a feasible adjuvant therapy for patients with moderate-to-severe brain injury receiving neurosurgical treatment in the intensive care unit. However, the therapeutic effects of short-term multisession cortical electrical stimulation for brain trauma are not clear. This study explored the therapeutic effects of acute-stage short-term cortical electrical stimulation on TBI. We conducted seven sessions of one-hour cortical electrical stimulation from day 0 to day 6 in rats after brain trauma by controlled cortical impact and then evaluated the functional outcome and histopathological changes. Our data showed that short-term cortical electrical stimulation improved motor coordination, short-term memory, and learning ability and attenuated neurological severity after brain trauma. Lesion volume, apoptosis, and gliosis after brain trauma were reduced, and trauma-induced neurogenesis in the hippocampus for the innate neural reparative response was increased. Our study demonstrated that short-term cortical electrical stimulation applied in the acute stage of traumatic brain injury is a potential adjuvant therapy to improve the recovery of neurological deficits.

Sustained experimental activation of FGF8/ERK in the developing chicken spinal cord models early events in ERK-mediated tumorigenesis

The MAPK/ERK pathway regulates a variety of physiological cellular functions, including cell proliferation and survival. It is abnormally activated in many types of human cancers in response to driver mutations in regulators of this pathway that trigger tumor initiation. The early steps of oncogenic progression downstream of ERK overactivation are poorly understood due to a lack of appropriate models. We show here that ERK1/2 overactivation in the trunk neural tube of the chicken embryo through expression of a constitutively active form of the upstream kinase MEK1 (MEK1ca), rapidly provokes a profound change in the transcriptional signature of developing spinal cord cells. These changes are concordant with a previously established role of the tyrosine kinase receptor ligand FGF8 acting via the ERK1/2 effectors to maintain an undifferentiated state. Furthermore, we show that MEK1ca-transfected spinal cord cells lose neuronal identity, retain caudal markers, and ectopically express potential effector oncogenes, such as AQP1. MEK1ca expression in the developing spinal cord from the chicken embryo is thus a tractable in vivo model to identify the mechanisms fostering neoplasia and malignancy in ERK-induced tumorigenesis of neural origins.

Cannabinoid receptor gene polymorphisms and cognitive performance in patients with schizophrenia and controls

Objective:

To test the hypothesis that genetic variations of cannabinoid receptors contribute to the pathophysiology of cognitive deficits in schizophrenia.

Methods:

In this genetic association case-control study, cannabinoid receptor polymorphisms CNR1 rs12720071 and CNR2 rs2229579 were tested for association with neurocognitive performance in 69 patients with schizophrenia and 45 healthy controls. Neurocognition was assessed by the Brief Assessment of Cognition in Schizophrenia (BACS).

Results:

We found a consistent association between CNR1 rs12720071 polymorphism and the cognitive performance of patients in several cognitive domains. Patients with C/C polymorphism presented significantly worse performance in motor speed, verbal fluency, attention/processing speed and reasoning/problem solving.

Conclusion:

Although limited, our data support the hypothesis that CNR1 variations may be associated with the pathogenesis of cognitive deficits of schizophrenia.

A Novel Methodology Using Dexamethasone to Induce Neuronal Differentiation in the CNS-Derived Catecholaminergic CAD Cells

The Cath.a-differentiated (CAD) cell line is a central nervous system-derived catecholaminergic cell line originating from tyrosine hydroxylase (TH)-producing neurons located around the locus coeruleus area of the mouse brain. CAD cells have been used as an in vitro model for cellular and molecular studies due to their ability to differentiate under serum-free media conditions. However, the lack of serum-derived survival factors, limits the longevity for differentiated CAD cells to be maintained in healthy conditions; thereby, limiting their use in long-term culture studies. Here, we present a novel differentiation method that utilizes dexamethasone (Dex), a synthetic glucocorticoid receptor agonist. Specifically, we discovered that the addition of 100 µM of Dex into the 1% fetal bovine serum (FBS)-supplemented media effectively induced neuronal differentiation of CAD cells, as characterized by neurite formation and elongation. Dex-differentiated CAD cells exited the cell cycle, stopped proliferating, extended the neurites, and expressed neuronal markers. These effects were dependent on the glucocorticoid receptors (GR) as they were abolished by GR knockdown. Importantly, Dex-differentiated CAD cells showed longer survival duration than serum-free differentiated CAD cells. In addition, RNA-sequencing and qPCR data demonstrate that several genes involved in proliferation, neuronal differentiation, and survival pathways were differentially expressed in the Dex-differentiated cells. This is the first study to reveal Dex as a novel differentiation methodology used to generate postmitotic neuronal CAD cells, which may be utilized as an in vitro neuronal model for cellular and molecular neurobiology research.

New Insights Into the Intricacies of Proneural Gene Regulation in the Embryonic and Adult Cerebral Cortex

Historically, the mammalian brain was thought to lack stem cells as no new neurons were found to be made in adulthood. That dogma changed ∼25 years ago with the identification of neural stem cells (NSCs) in the adult rodent forebrain. However, unlike rapidly self-renewing mature tissues (e.g., blood, intestinal crypts, skin), the majority of adult NSCs are quiescent, and those that become 'activated' are restricted to a few neurogenic zones that repopulate specific brain regions. Conversely, embryonic NSCs are actively proliferating and neurogenic. Investigations into the molecular control of the quiescence-to-proliferation-to-differentiation continuum in the embryonic and adult brain have identified proneural genes encoding basic-helix-loop-helix (bHLH) transcription factors (TFs) as critical regulators. These bHLH TFs initiate genetic programs that remove NSCs from quiescence and drive daughter neural progenitor cells (NPCs) to differentiate into specific neural cell subtypes, thereby contributing to the enormous cellular diversity of the adult brain. However, new insights have revealed that proneural gene activities are context-dependent and tightly regulated. Here we review how proneural bHLH TFs are regulated, with a focus on the murine cerebral cortex, drawing parallels where appropriate to other organisms and neural tissues. We discuss upstream regulatory events, post-translational modifications (phosphorylation, ubiquitinylation), protein-protein interactions, epigenetic and metabolic mechanisms that govern bHLH TF expression, stability, localization, and consequent transactivation of downstream target genes. These tight regulatory controls help to explain paradoxical findings of changes to bHLH activity in different cellular contexts.

The Protein Tyrosine Phosphatase Receptor Delta Regulates Developmental Neurogenesis

PTPRD is a receptor protein tyrosine phosphatase that is genetically associated with neurodevelopmental disorders. Here, we asked whether Ptprd mutations cause aberrant neural development by perturbing neurogenesis in the murine cortex. We show that loss of Ptprd causes increases in neurogenic transit-amplifying intermediate progenitor cells and cortical neurons and perturbations in neuronal localization. These effects are intrinsic to neural precursor cells since acute Ptprd knockdown causes similar perturbations. PTPRD mediates these effects by dephosphorylating receptor tyrosine kinases, including TrkB and PDGFRβ, and loss of Ptprd causes the hyperactivation of TrkB and PDGFRβ and their downstream MEK-ERK signaling pathway in neural precursor cells. Moreover, inhibition of aberrant TrkB or MEK activation rescues the increased neurogenesis caused by knockdown or homozygous loss of Ptprd. These results suggest that PTPRD regulates receptor tyrosine kinases to ensure appropriate numbers of intermediate progenitor cells and neurons, suggesting a mechanism for its genetic association with neurodevelopmental disorders.

Emerging Roles of PRDM Factors in Stem Cells and Neuronal System: Cofactor Dependent Regulation of PRDM3/16 and FOG1/2 (Novel PRDM Factors)

PRDI-BF1 (positive regulatory domain I-binding factor 1) and RIZ1 (retinoblastoma protein-interacting zinc finger gene 1) (PR) homologous domain containing (PRDM) transcription factors are expressed in neuronal and stem cell systems, and they exert multiple functions in a spatiotemporal manner. Therefore, it is believed that PRDM factors cooperate with a number of protein partners to regulate a critical set of genes required for maintenance of stem cell self-renewal and differentiation through genetic and epigenetic mechanisms. In this review, we summarize recent findings about the expression of PRDM factors and function in stem cell and neuronal systems with a focus on cofactor-dependent regulation of PRDM3/16 and FOG1/2. We put special attention on summarizing the effects of the PRDM proteins interaction with chromatin modulators (NuRD complex and CtBPs) on the stem cell characteristic and neuronal differentiation. Although PRDM factors are known to possess intrinsic enzyme activity, our literature analysis suggests that cofactor-dependent regulation of PRDM3/16 and FOG1/2 is also one of the important mechanisms to orchestrate bidirectional target gene regulation. Therefore, determining stem cell and neuronal-specific cofactors will help better understanding of PRDM3/16 and FOG1/2-controlled stem cell maintenance and neuronal differentiation. Finally, we discuss the clinical aspect of these PRDM factors in different diseases including cancer. Overall, this review will help further sharpen our knowledge of the function of the PRDM3/16 and FOG1/2 with hopes to open new research fields related to these factors in stem cell biology and neuroscience.

Serotonin Receptor 2A Activation Promotes Evolutionarily Relevant Basal Progenitor Proliferation in the Developing Neocortex

Evolutionary expansion of the mammalian neocortex (Ncx) has been linked to increased abundance and proliferative capacity of basal progenitors (BPs) in the subventricular zone during development. BP proliferation is governed by both intrinsic and extrinsic signals, several of which have been identified. However, a role of neurotransmitters, a canonical class of extrinsic signaling molecules, in BP proliferation remains to be established. Here, we show that serotonin (5-HT), via its receptor HTR2A, promotes BP proliferation in an evolutionarily relevant manner. HTR2A is not expressed in embryonic mouse Ncx; accordingly, 5-HT does not increase mouse BP proliferation. However, ectopic HTR2A expression can increase mouse BP proliferation. Conversely, CRISPR/Cas9-mediated knockout of endogenous HTR2A in embryonic ferret Ncx reduces BP proliferation. Pharmacological activation of endogenous HTR2A in fetal human Ncx ex vivo increases BP proliferation via HER2/ERK signaling. Hence, 5-HT emerges as an important extrinsic pro-proliferative signal for BPs, which may have contributed to evolutionary Ncx expansion.

ETV5 is Essential for Neuronal Differentiation of Human Neural Progenitor Cells by Repressing NEUROG2 Expression

Neural progenitor cells (NPCs) are multipotent cells that have the potential to produce neurons and glial cells in the neural system. NPCs undergo identity maintenance or differentiation regulated by different kinds of transcription factors. Here we present evidence that ETV5, which is an ETS transcription factor, promotes the generation of glial cells and drives the neuronal subtype-specific genes in newly differentiated neurons from the human embryonic stem cells-derived NPCs. Next, we find a new role for ETV5 in the repression of NEUROG2 expression in NPCs. ETV5 represses NEUROG2 transcription via NEUROG2 promoter and requires the ETS domain. We identify ETV5 has the binding sites and is implicated in silent chromatin in NEUROG2 promoter by chromatin immunoprecipitation (ChIP) assays. Further, NEUROG2 transcription repression by ETV5 was shown to be dependent on a transcriptional corepressor (CoREST). During NPC differentiation toward neurons, ETV5 represses NEUROG2 expression and blocks the appearance of glutamatergic neurons. This finding suggests that ETV5 negatively regulates NEUROG2 expression and increases the number of GABAergic subtype neurons derived from NPCs. Thus, ETV5 represents a potent new candidate protein with benefits for the generation of GABAergic neurons.

Early But Not Delayed Optogenetic RAF Activation Promotes Astrocytogenesis in Mouse Neural Progenitors

The RAS/RAF/MEK/ERK pathway promotes gliogenesis but the kinetic role of RAF1, a key RAF kinase, in the induction of astrocytogenesis remains to be elucidated. To address this challenge, we determine the temporal functional outcome of RAF1 during mouse neural progenitor cell differentiation using an optogenetic RAF1 system (OptoRAF1). OptoRAF1 allows for reversible activation of the RAF/MEK/ERK pathway via plasma membrane recruitment of RAF1 based on blue light-sensitive protein dimerizer CRY2/CIB1. We found that early light-induced OptoRAF1 activation in neural progenitor cells promotes cell proliferation and increased expression of glial markers and glia-enriched genes. However, delayed OptoRAF1 activation in differentiated neural progenitor had little effect on glia marker expression, suggesting that RAF1 is required to promote astrocytogenesis only within a short time window. In addition, activation of OptoRAF1 did not have a significant effect on neurogenesis, but was able to promote neuronal neurite growth.

Ternary complex factor regulates pancreatic islet size and blood glucose homeostasis in transgenic mice

A hallmark of diabetes mellitus is the inability of pancreatic β-cells to secrete sufficient amounts of insulin for maintaining normoglycemia. The formation of smaller islets may underlie the development of a diabetic phenotype, as a decreased β-cell mass will produce an insufficient amount of insulin. For a pharmacological intervention it is crucial to identify the proteins determining β-cell mass. Here, we identified the ternary complex factor (TCF) Elk-1 as a regulator of the size of pancreatic islets. Elk-1 mediates, together with a dimer of the serum-response factor (SRF), serum response element-regulated gene transcription. Elk-1 is activated in glucose-treated pancreatic β-cells but the biological functions of this protein in β-cells are so far unknown. Elk-1 and homologous TCF proteins are expressed in islets and insulinoma cells. Gene targeting experiments revealed that the TCF proteins show redundant activities. To solve the problem of functional redundancy of these homologous proteins, we generated conditional transgenic mice expressing a dominant-negative mutant of Elk-1 in pancreatic β-cells. The mutant competes with the wild-type TCFs for DNA and SRF-binding. Expression of the Elk-1 mutant in pancreatic β-cells resulted in the generation of significantly smaller islets and increased caspase-3 activity, indicating that apoptosis was responsible for the reduction of the pancreatic islet size. Glucose tolerance tests revealed that transgenic mice expressing the dominant-negative mutant of Elk-1 in pancreatic β-cells displayed impaired glucose tolerance. Thus, we show here for the first time that TCF controls important functions of pancreatic β-cells in vivo. Elk-1 may be considered as a new therapeutic target for the treatment of diabetes.

Transcriptomic analysis of brain tissues identifies a role for CCAAT enhancer binding protein β in HIV-associated neurocognitive disorder

BACKGROUND

HIV-associated neurocognitive disorders (HAND) persist in the era of combined antiretroviral therapy (ART) despite reductions in viral load (VL) and overall disease severity. The mechanisms underlying HAND in the ART era are not well understood but are likely multifactorial, involving alterations in common pathways such as inflammation, autophagy, neurogenesis, and mitochondrial function. Newly developed omics approaches hold potential to identify mechanisms driving neuropathogenesis of HIV in the ART era.

METHODS

In this study, using 33 postmortem frontal cortex (FC) tissues, neuropathological, molecular, and biochemical analyses were used to determine cellular localization and validate expression levels of the prolific transcription factor (TF), CCAAT enhancer binding protein (C/EBP) β, in brain tissues from HIV+ cognitively normal and HAND cases. RNA sequencing (seq) and transcriptomic analyses were performed on FC tissues including 24 specimens from well-characterized people with HIV that had undergone neurocognitive assessments. In vitro models for brain cells were used to investigate the role of C/EBPβ in mediating gene expression.

RESULTS

The most robust signal for TF dysregulation was observed in cases diagnosed with minor neurocognitive disorder (MND) compared to cognitive normal (CN) cases. Of particular interest, due to its role in inflammation, autophagy and neurogenesis, C/EBPβ was significantly upregulated in MND compared to CN brains. C/EBPβ was increased at the protein level in HAND brains. C/EBPβ levels were significantly reduced in neurons and increased in astroglia in HAND brains compared to CN. Transfection of human astroglial cells with a plasmid expressing C/EBPβ induced expression of multiple targets identified in the transcriptomic analysis of HAND brains, including dynamin-1-like protein (DNM1L) and interleukin-1 receptor-associated kinase 1. Recombinant HIV-Tat reduced and increased C/EBPβ levels in neuronal and astroglial cells, respectively.

CONCLUSIONS

These findings are the first to present RNAseq-based transcriptomic analyses of HIV+ brain tissues, providing further evidence of altered neuroinflammation, neurogenesis, mitochondrial function, and autophagy in HAND. Interestingly, these studies confirm a role for CEBPβ in regulating inflammation, metabolism, and autophagy in astroglia. Therapeutic strategies aimed at transcriptional regulation of astroglia or downstream pathways may provide relief to HIV+ patients at risk for HAND and other neurological disorders.

The impact of RASopathy-associated mutations on CNS development in mice and humans

The RAS signaling pathway is involved in the regulation of developmental processes, including cell growth, proliferation, and differentiation, in the central nervous system (CNS). Germline mutations in the RAS signaling pathway genes are associated with a group of neurodevelopmental disorders, collectively called RASopathy, which includes neurofibromatosis type 1, Noonan syndrome, cardio-facio-cutaneous syndrome, and Costello syndrome. Most mutations associated with RASopathies increase the activity of the RAS-ERK signaling pathway, and therefore, most individuals with RASopathies share common phenotypes, such as a short stature, heart defects, facial abnormalities, and cognitive impairments, which are often accompanied by abnormal CNS development. Recent studies using mouse models of RASopathies demonstrated that particular mutations associated with each disorder disrupt CNS development in a mutation-specific manner. Here, we reviewed the recent literatures that investigated the developmental role of RASopathy-associated mutations using mutant mice, which provided insights into the specific contribution of RAS-ERK signaling molecules to CNS development and the subsequent impact on cognitive function in adult mice.

The Role of Neuronal Factors in the Epigenetic Reprogramming of Microglia in the Normal and Diseased Central Nervous System

Twenty years ago, the scientific community exhibited relatively little interest in the study of microglial cells. However, recent technical and conceptual advances in this field have greatly increased interest in the basic biology of these cells within various neurodegenerative diseases, including multiple sclerosis, Alzheimer’s disease, and traumatic brain/spinal cord injuries. The main functions of these cells in the normal central nervous system (CNS) remain poorly understood, despite considerable elucidation of their roles in pathological conditions. Microglia populate the brain before birth and remain in close lifelong contact with CNS-resident cells under the influence of the local microenvironment. Within the CNS parenchyma, microglia actively interact with two main cell types, astrocytes and neurons, which produce many factors that affect microglia phenotypes in the normal CNS and during neuroinflammation. These factors include interleukin (IL)-34, macrophage colony-stimulating factor, transforming growth factor-β, and IL-4, which promote microglial expansion, survival, and differentiation to an anti-inflammatory phenotype in the normal CNS. Under inflammatory conditions, however, astrocytes produce several pro-inflammatory factors that contribute to microglial activation. The interactions of microglia with neurons in the normal and diseased CNS are especially intriguing. Microglia are known to interact actively with neurons by facilitating axonal pruning during development, while neurons provide specific factors that alter microglial phenotypes and functions. This review focuses mainly on the roles of soluble neuronal factors that affect microglial phenotypes and functions and the possible involvement of these factors in the pathology of neurodegenerative diseases.

Adult Goat Retinal Neuronal Culture: Applications in Modeling Hyperglycemia

Culture of adult neurons of the central nervous system (CNS) can provide a unique model system to explore neurodegenerative diseases. The CNS includes neurons and glia of the brain, spinal cord and retina. Neurons in the retina have the advantage of being the most accessible cells of the CNS, and can serve as a reliable mirror to the brain. Typically, primary cultures utilize fetal rodent neurons, but very rarely adult neurons from larger mammals. Here, we cultured primary retinal neurons isolated from adult goat up to 10 days, and established an in vitro model of hyperglycemia for performing morphological and molecular characterization studies. Immunofluorescence staining revealed that approximately 30–40% of cultured cells expressed neuronal markers. Next, we examined the relative expression of cell adhesion molecules (CAMs) in adult goat brain and retina. We also studied the effect of different glucose concentrations and media composition on the growth and expression of CAMs in cultured retinal neurons. Hyperglycemia significantly enhances neurite outgrowth in adult retinal neurons in culture. Expression of CAMs such as Caspr1, Contactin1 and Prion is downregulated in the presence of high glucose. Hyperglycemia downregulates the expression of the transcription factor CCAAT/enhancer binding protein (C/EBP α), predicted to bind CAM gene promoters. Collectively, our study demonstrates that metabolic environment markedly affects transcriptional regulation of CAMs in adult retinal neurons in culture. The effect of hyperglycemia on CAM interactions, as well as related changes in intracellular signaling pathways in adult retinal neurons warrants further investigation.

Macrocephaly: Solving the Diagnostic Dilemma

Macrocephaly is a relatively common clinical condition affecting up to 5% of the pediatric population. It is defined as an abnormally large head with an occipitofrontal circumference greater than 2 standard deviations above the mean for a given age and sex. Megalencephaly refers exclusively to brain overgrowth exceeding twice the standard deviation. Macrocephaly can be isolated and benign or may be the first indication of an underlying congenital, genetic, or acquired disorder, whereas megalencephaly is more often syndromic. Megalencephaly can be divided into 2 subtypes: metabolic and developmental, caused by genetic defects in cellular metabolism and alterations in signaling pathways, respectively. Neuroimaging plays an important role in the evaluation of macrocephaly, especially in the metabolic subtype which may not be overtly apparent clinically. This article outlines the diverse etiologies of macrocephaly, delineates their clinical and radiographic features, and suggests a clinicoradiological algorithm for evaluation.

Lin28a regulates neurogliogenesis in mammalian retina through the Igf signaling

In the developing central nervous system (CNS) the majority of neurons are born before the generation of glia. Emerging evidence implicates heterochronic gene, Lin28 in the temporal switch between two distinct lineages. However, the respective contributions of Lin28a and Lin28b in neurogliogenesis remain poorly understood. Here, we have examined the relative involvement of Lin28a and Lin28b in mammalian retina, a simple and accessible CNS model where neurogliogenic decision largely occurs postnatally. Examination of Lin28a/b involvement during late histogenesis by the perturbation of function approaches revealed that while Lin28b did not influence differentiation in general Lin28a facilitated and antagonized the generation of neurons and glia, respectively. Silencing of Lin28a expression in vitro and its conditional deletion in vivo during early histogenesis led to premature generation of glia. The instructive role of Lin28a on neuronal differentiation was revealed by its influence to suppress glial-specific genes and directly differentiate glia along the neuronal lineage. This function of Lin28a is likely mediated through the Igf signaling, as inhibition of the pathway abrogated Lin28a-mediated neurogliogenesis. Thus, our observations suggest that Lin28a is an important intrinsic factor that acts in concert with cell-extrinsic factors like Igfs, coordinating the developmental bias of the progenitors and niche, respectively, for the successive generation of neurons and glia.

Transfection of neurotrophin-3 into neural stem cells using ultrasound with microbubbles to treat denervated muscle atrophy

Neurotrophin-3 (NT-3) has potential as a therapeutic agent for the treatment of patients with denervated muscle atrophy. However, the endogenous secretion of NT-3 is low and exogenous NT-3 lacks sufficient time to accumulate due to its short half-life. The transfection of NT-3 has been demonstrated to have a beneficial effect on denervated muscle and motor endplates. Neural stem cells (NSCs) differentiate into neurons and form motor endplate nerve-muscle connections. It has been previously demonstrated that local and noninvasive transfection can be performed using ultrasound with microbubbles (MBs). In the current study, hematoxylin and eosin, acetylcholinesterase and gold chloride staining, as well as transmission electron microscopy, were performed to verify the effects of this treatment strategy. The results demonstrated that using ultrasound with MBs for the transfection of NT-3 into NSCs, and their subsequent transplantation in vivo, attenuated the atrophy of denervated muscle and reduced motor endplate degeneration. This noninvasive, efficient and targeted treatment strategy may therefore be a potential treatment for patients with denervated muscle atrophy.

CCAAT/Enhancer binding protein β silencing mitigates glial activation and neurodegeneration in a rat model of Parkinson's disease

The CCAAT/Enhancer binding protein β (C/EBPβ) is a transcription factor involved in numerous physiological as well as pathological conditions in the brain. However, little is known regarding its possible role in neurodegenerative disorders. We have previously shown that C/EBPβ regulates the expression of genes involved in inflammatory processes and brain injury. Here, we have analyzed the effects of C/EBPβ interference in dopaminergic cell death and glial activation in the 6-hydroxydopamine model of Parkinson's disease. Our results showed that lentivirus-mediated C/EBPβ deprivation conferred marked in vitro and in vivo neuroprotection of dopaminergic cells concomitant with a significant attenuation of the level of the inflammatory response and glial activation. Additionally, C/EBPβ interference diminished the induction of α-synuclein in the substantia nigra pars compacta of animals injected with 6-hydroxydopamine. Taking together, these results reveal an essential function for C/EBPβ in the pathways leading to inflammatory-mediated brain damage and suggest novel roles for C/EBPβ in neurodegenerative diseases, specifically in Parkinson's disease, opening the door for new therapeutic interventions.

The α-Tubulin gene TUBA1A in Brain Development: A Key Ingredient in the Neuronal Isotype Blend

Microtubules are dynamic cytoskeletal polymers that mediate numerous, essential functions such as axon and dendrite growth and neuron migration throughout brain development. In recent years, sequencing has revealed dominant mutations that disrupt the tubulin protein building blocks of microtubules. These tubulin mutations lead to a spectrum of devastating brain malformations, complex neurological and physical phenotypes, and even fatality. The most common tubulin gene mutated is the α-tubulin gene TUBA1A, which is the most prevalent α-tubulin gene expressed in post-mitotic neurons. The normal role of TUBA1A during neuronal maturation, and how mutations alter its function to produce the phenotypes observed in patients, remains unclear. This review synthesizes current knowledge of TUBA1A function and expression during brain development, and the brain malformations caused by mutations in TUBA1A.

Functional non-coding polymorphism in an EPHA2 promoter PAX2 binding site modifies expression and alters the MAPK and AKT pathways

To identify possible genetic variants influencing expression of EPHA2 (Ephrin-receptor Type-A2), a tyrosine kinase receptor that has been shown to be important for lens development and to contribute to both congenital and age related cataract when mutated, the extended promoter region of EPHA2 was screened for variants. SNP rs6603883 lies in a PAX2 binding site in the EPHA2 promoter region. The C (minor) allele decreased EPHA2 transcriptional activity relative to the T allele by reducing the binding affinity of PAX2. Knockdown of PAX2 in human lens epithelial (HLE) cells decreased endogenous expression of EPHA2. Whole RNA sequencing showed that extracellular matrix (ECM), MAPK-AKT signaling pathways and cytoskeleton related genes were dysregulated in EPHA2 knockdown HLE cells. Taken together, these results indicate a functional non-coding SNP in EPHA2 promoter affects PAX2 binding and reduces EPHA2 expression. They further suggest that decreasing EPHA2 levels alters MAPK, AKT signaling pathways and ECM and cytoskeletal genes in lens cells that could contribute to cataract. These results demonstrate a direct role for PAX2 in EPHA2 expression and help delineate the role of EPHA2 in development and homeostasis required for lens transparency.

Stress Increases Peripheral Axon Growth and Regeneration through Glucocorticoid Receptor-Dependent Transcriptional Programs

Stress and glucocorticoid (GC) release are common behavioral and hormonal responses to injury or disease. In the brain, stress/GCs can alter neuron structure and function leading to cognitive impairment. Stress and GCs also exacerbate pain, but whether a corresponding change occurs in structural plasticity of sensory neurons is unknown. Here, we show that in female mice (Mus musculus) basal GC receptor (Nr3c1, also known as GR) expression in dorsal root ganglion (DRG) sensory neurons is 15-fold higher than in neurons in canonical stress-responsive brain regions (M. musculus). In response to stress or GCs, adult DRG neurite growth increases through mechanisms involving GR-dependent gene transcription. In vivo, prior exposure to an acute systemic stress increases peripheral nerve regeneration. These data have broad clinical implications and highlight the importance of stress and GCs as novel behavioral and circulating modifiers of neuronal plasticity.

Mechanisms underlying cognitive deficits in a mouse model for Costello Syndrome are distinct from other RASopathy mouse models

RASopathies, characterized by germline mutations in genes encoding proteins of the RAS-ERK signaling pathway, show overlapping phenotypes, which manifest themselves with a varying severity of intellectual disability. However, it is unclear to what extent they share the same downstream pathophysiology that underlies the cognitive deficits. Costello syndrome (CS) is a rare RASopathy caused by activating mutations in the HRAS gene. Here we investigated the mechanisms underlying the cognitive deficits of HRas^G12V/G12V mice. HRas^G12V/G12V mice showed robust upregulation of ERK signaling, neuronal hypertrophy, increased brain volume, spatial learning deficits, and impaired mGluR-dependent long-term depression (LTD). In contrast, long-term potentiation (LTP), which is affected in other RASopathy mouse models was unaffected. Treatment with lovastatin, a HMG-CoA-Reductase inhibitor which has been shown to rescue the behavioral phenotypes of mouse models of NF1 and Noonan syndrome, was unable to restore ERK signaling and the cognitive deficits of HRas^G12V/G12V mice. Administration of a potent mitogen-activated protein kinase (MEK) inhibitor rescued the ERK upregulation and the mGluR-LTD deficit of HRas^G12V/G12V mice, but failed to rescue the cognitive deficits. Taken together, this study indicates that the fundamental molecular and cellular mechanisms underlying the cognitive aspects of different RASopathies are remarkably distinct, and may require disease specific treatments.

Homozygous ARHGEF2 mutation causes intellectual disability and midbrain-hindbrain malformation

Mid-hindbrain malformations can occur during embryogenesis through a disturbance of transient and localized gene expression patterns within these distinct brain structures. Rho guanine nucleotide exchange factor (ARHGEF) family members are key for controlling the spatiotemporal activation of Rho GTPase, to modulate cytoskeleton dynamics, cell division, and cell migration. We identified, by means of whole exome sequencing, a homozygous frameshift mutation in the ARHGEF2 as a cause of intellectual disability, a midbrain-hindbrain malformation, and mild microcephaly in a consanguineous pedigree of Kurdish-Turkish descent. We show that loss of ARHGEF2 perturbs progenitor cell differentiation and that this is associated with a shift of mitotic spindle plane orientation, putatively favoring more symmetric divisions. The ARHGEF2 mutation leads to reduction in the activation of the RhoA/ROCK/MLC pathway crucial for cell migration. We demonstrate that the human brain malformation is recapitulated in Arhgef2 mutant mice and identify an aberrant migration of distinct components of the precerebellar system as a pathomechanism underlying the midbrain-hindbrain phenotype. Our results highlight the crucial function of ARHGEF2 in human brain development and identify a mutation in ARHGEF2 as novel cause of a neurodevelopmental disorder.

Foxd4 is essential for establishing neural cell fate and for neuronal differentiation

Many molecular factors required for later stages of neuronal differentiation have been identified; however, much less is known about the early events that regulate the initial establishment of the neuroectoderm. We have used an in vitro embryonic stem cell (ESC) differentiation model to investigate early events of neuronal differentiation and to define the role of mouse Foxd4, an ortholog of a forkhead-family transcription factor central to Xenopus neural plate/neuroectodermal precursor development. We found that Foxd4 is a necessary regulator of the transition from pluripotent ESC to neuroectodermal stem cell, and its expression is necessary for neuronal differentiation. Mouse Foxd4 expression is not only limited to the neural plate but it is also expressed and apparently functions to regulate neurogenesis in the olfactory placode. These in vitro results suggest that mouse Foxd4 has a similar function to its Xenopus ortholog; this was confirmed by successfully substituting murine Foxd4 for its amphibian counterpart in overexpression experiments. Thus, Foxd4 appears to regulate the initial steps in establishing neuroectodermal precursors during initial development of the nervous system.

Adenosine A2A receptor and ERK-driven impulsivity potentiates hippocampal neuroblast proliferation

Dampened adenosine A_2A receptor (A_2AR) function has been implicated in addiction through enhancement of goal-directed behaviors. However, the contribution of the A_2AR to the control of impulsive reward seeking remains unknown. Using mice that were exposed to differential reward of low rate (DRL) schedules during Pavlovian-conditioning, second-order schedule discrimination, and the 5-choice serial reaction time task (5-CSRTT), we demonstrate that deficits of A_2AR function promote impulsive responses. Antagonism of the A_2AR lowered ERK1 and ERK2 phosphorylation in the dorsal hippocampus (dHip) and potentiated impulsivity during Pavlovian-conditioning and the 5-CSRTT. Remarkably, inhibition of ERK1 and ERK2 phosphorylation by U0126 in the dHip prior to Pavlovian-conditioning exacerbated impulsive reward seeking. Moreover, we found decreased A_2AR expression, and reduced ERK1 and ERK2 phosphorylation in the dHip of equilibrative nucleoside transporter type 1 (ENT1^-/-) null mice, which displayed exacerbated impulsivity. To determine whether impulsive response behavior is associated with hippocampal neuroblast development, we investigated expression of BrdU⁺ and doublecortin (DCX⁺) following 5-CSRTT testing. These studies revealed that impulsive behavior driven by inhibition of the A_2AR is accompanied by increased neuroblast proliferation in the hippocampus.

Inflammation-induced miRNA-155 inhibits self-renewal of neural stem cells via suppression of CCAAT/enhancer binding protein β (C/EBPβ) expression

Intracerebral inflammation resulting from injury or disease is implicated in disruption of neural regeneration and may lead to irreversible neuronal dysfunction. Analysis of inflammation-related microRNA profiles in various tissues, including the brain, has identified miR-155 among the most prominent miRNAs linked to inflammation. Here, we hypothesize that miR-155 mediates inflammation-induced suppression of neural stem cell (NSC) self-renewal. Using primary mouse NSCs and human NSCs derived from induced pluripotent stem (iPS) cells, we demonstrate that three important genes involved in NSC self-renewal (Msi1, Hes1 and Bmi1) are suppressed by miR-155. We also demonstrate that suppression of self-renewal genes is mediated by the common transcription factor C/EBPβ, which is a direct target of miR-155. Our study describes an axis linking inflammation and miR-155 to expression of genes related to NSC self-renewal, suggesting that regulation of miR-155 may hold potential as a novel therapeutic strategy for treating neuroinflammatory diseases.

Hippocalcin Is Required for Astrocytic Differentiation through Activation of Stat3 in Hippocampal Neural Precursor Cells

Hippocalcin (Hpca) is a neuronal calcium sensor protein expressed in the mammalian brain. However, its function in neural stem/precursor cells has not yet been studied. Here, we clarify the function of Hpca in astrocytic differentiation in hippocampal neural precursor cells (HNPCs). When we overexpressed Hpca in HNPCs in the presence or absence of bFGF, expression levels of nerve-growth factors such as neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5), and brain-derived neurotrophic factor (BDNF), together with the proneural basic helix loop helix (bHLH) transcription factors NeuroD and neurogenin 1 (Ngn1), increased significantly. In addition, there was an increase in the number of cells expressing glial fibrillary acidic protein (GFAP), an astrocyte marker, and in branch outgrowth, indicating astrocytic differentiation of the HNPCs. Downregulation of Hpca by transfection with Hpca siRNA reduced expression of NT-3, NT-4/5, BDNF, NeuroD, and Ngn1 as well as levels of GFAP protein. Furthermore, overexpression of Hpca increased the phosphorylation of STAT3 (Ser727), and this effect was abolished by treatment with a STAT3 inhibitor (S3I-201), suggesting that STAT3 (Ser727) activation is involved in Hpca-mediated astrocytic differentiation. As expected, treatment with Stat3 siRNA or STAT3 inhibitor caused a complete inhibition of astrogliogenesis induced by Hpca overexpression. Taken together, this is the first report to show that Hpca, acting through Stat3, has an important role in the expression of neurotrophins and proneural bHLH transcription factors, and that it is an essential regulator of astrocytic differentiation and branch outgrowth in HNPCs.

Complement component 3 (C3) expression in the hippocampus after excitotoxic injury: role of C/EBPβ

Background

The CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor implicated in the control of proliferation, differentiation, and inflammatory processes mainly in adipose tissue and liver; although more recent results have revealed an important role for this transcription factor in the brain. Previous studies from our laboratory indicated that CCAAT/enhancer-binding protein β is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury. More recently, we have shown that the complement component 3 gene (C3) is a downstream target of CCAAT/enhancer-binding protein β and it could be a mediator of the proinflammatory effects of this transcription factor in neural cells.

Methods

Adult male Wistar rats (8–12 weeks old) were used throughout the study. C/EBPβ^+/+ and C/EBPβ^–/– mice were generated from heterozygous breeding pairs. Animals were injected or not with kainic acid, brains removed, and brain slices containing the hippocampus analyzed for the expression of both CCAAT/enhancer-binding protein β and C3.

Results

In the present work, we have further extended these studies and show that CCAAT/enhancer-binding protein β and C3 co-express in the CA1 and CA3 regions of the hippocampus after an excitotoxic injury. Studies using CCAAT/enhancer-binding protein β knockout mice demonstrate a marked reduction in C3 expression after kainic acid injection in these animals, suggesting that indeed this protein is regulated by C/EBPβ in the hippocampus in vivo.

Conclusions

Altogether these results suggest that CCAAT/enhancer-binding protein β could regulate brain disorders, in which excitotoxic and inflammatory processes are involved, at least in part through the direct regulation of C3.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0742-0) contains supplementary material, which is available to authorized users.

A PBX1 transcriptional network controls dopaminergic neuron development and is impaired in Parkinson's disease

Pre-B-cell leukemia homeobox (PBX) transcription factors are known to regulate organogenesis, but their molecular targets and function in midbrain dopaminergic neurons (mDAn) as well as their role in neurodegenerative diseases are unknown. Here, we show that PBX1 controls a novel transcriptional network required for mDAn specification and survival, which is sufficient to generate mDAn from human stem cells. Mechanistically, PBX1 plays a dual role in transcription by directly repressing or activating genes, such as Onecut2 to inhibit lateral fates during embryogenesis, Pitx3 to promote mDAn development, and Nfe2l1 to protect from oxidative stress. Notably, PBX1 and NFE2L1 levels are severely reduced in dopaminergic neurons of the substantia nigra of Parkinson's disease (PD) patients and decreased NFE2L1 levels increases damage by oxidative stress in human midbrain cells. Thus, our results reveal novel roles for PBX1 and its transcriptional network in mDAn development and PD, opening the door for new therapeutic interventions.

Neural stem cells secrete factors facilitating brain regeneration upon constitutive Raf-Erk activation

The intracellular Raf-Erk signaling pathway is activated during neural stem cell (NSC) proliferation, and neuronal and astrocytic differentiation. A key question is how this signal can evoke multiple and even opposing NSC behaviors. We show here, using a constitutively active Raf (ca-Raf), that Raf-Erk activation in NSCs induces neuronal differentiation in a cell-autonomous manner. By contrast, it causes NSC proliferation and the formation of astrocytes in an extrinsic autocrine/paracrine manner. Thus, treatment of NSCs with medium (CM) conditioned in ca-Raf-transduced NSCs (Raf-CM; RCM) became activated to form proliferating astrocytes resembling radial glial cells (RGCs) or adult-type NSCs. Infusion of Raf-CM into injured mouse brains caused expansion of the NSC population in the subventricular zone, followed by the formation of new neurons that migrated to the damaged site. Our study shows an example how molecular mechanisms dissecting NSC behaviors can be utilized to develop regenerative therapies in brain disorders.

Proneurogenic Ligands Defined by Modeling Developing Cortex Growth Factor Communication Networks

The neural stem cell decision to self-renew or differentiate is tightly regulated by its microenvironment. Here, we have asked about this microenvironment, focusing on growth factors in the embryonic cortex at a time when it is largely comprised of neural precursor cells (NPCs) and newborn neurons. We show that cortical NPCs secrete factors that promote their maintenance, while cortical neurons secrete factors that promote differentiation. To define factors important for these activities, we used transcriptome profiling to identify ligands produced by NPCs and neurons, cell-surface mass spectrometry to identify receptors on these cells, and computational modeling to integrate these data. The resultant model predicts a complex growth factor environment with multiple autocrine and paracrine interactions. We tested this communication model, focusing on neurogenesis, and identified IFNγ, Neurturin (Nrtn), and glial-derived neurotrophic factor (GDNF) as ligands with unexpected roles in promoting neurogenic differentiation of NPCs in vivo.

RTVP-1 promotes mesenchymal transformation of glioma via a STAT-3/IL-6-dependent positive feedback loop

Glioblastomas (GBMs), the most aggressive primary brain tumors, exhibit increased invasiveness and resistance to anti-tumor treatments. We explored the role of RTVP-1, a glioma-associated protein that promotes glioma cell migration, in the mesenchymal transformation of GBM. Analysis of The Cancer Genome Atlas (TCGA) demonstrated that RTVP-1 expression was higher in mesenchymal GBM and predicted tumor recurrence and poor clinical outcome. ChiP analysis revealed that the RTVP-1 promoter binds STAT3 and C/EBPβ, two master transcription factors that regulate mesenchymal transformation of GBM. In addition, IL-6 induced RTVP-1 expression in a STAT3-dependent manner. RTVP-1 increased the migration and mesenchymal transformation of glioma cells. Similarly, overexpression of RTVP-1 in human neural stem cells induced mesenchymal differentiation, whereas silencing of RTVP-1 in glioma stem cells (GSCs) decreased the mesenchymal transformation and stemness of these cells. Silencing of RTVP-1 also increased the survival of mice bearing GSC-derived xenografts. Using gene array analysis of RTVP-1 silenced glioma cells we identified IL-6 as a mediator of RTVP-1 effects on the mesenchymal transformation and migration of GSCs, therefore acting in a positive feedback loop by upregulating RTVP-1 expression via the STAT3 pathway. Collectively, these results implicate RTVP-1 as a novel prognostic marker and therapeutic target in GBM.

Cell type-specific roles of RAS-MAPK signaling in learning and memory: Implications in neurodevelopmental disorders

The RAS-mitogen-activated protein kinase (MAPK) signaling pathway plays critical roles in brain function, including learning and memory. Mutations of molecules in the RAS-MAPK pathway are associated with a group of disorders called RASopathies, which include Noonan syndrome, neurofibromatosis type 1, Costello syndrome, Noonan syndrome with multiple lentigines, Legius syndrome, and cardio-facio-cutaneous syndrome. RASopathies share certain clinical symptoms, including craniofacial abnormalities, heart defects, delayed growth, and cognitive deficits such as learning disabilities, while each individual syndrome also displays unique phenotypes. Recent studies using mouse models of RASopathies showed that each disorder may have a distinct molecular and cellular etiology depending on the cellular specificity of the mutated molecules. Here, we review the cell-type specific roles of the regulators of the RAS-MAPK pathway in cognitive function (learning and memory) and their contribution to the development of RASopathies. We also discussed recent technical advances in analyzing cell type-specific transcriptomes and proteomes in the nervous system. Understanding specific mechanisms for these similar but distinct disorders would facilitate the development of mechanism-based individualized treatment for RASopathies.

Cell type-dependent Erk-Akt pathway crosstalk regulates the proliferation of fetal neural progenitor cells

Neural progenitor (NP) cells are the multipotent cells that produce neurons and glia in the central nervous system. Compounds regulating their proliferation are key to both understanding brain development and unlocking their potential in regenerative repair. We discuss a chemical screen that unexpectedly identified inhibitors of Erk signaling potently promoting the self-renewing divisions of fetal NP cells. This occurred through crosstalk between Erk and Akt signaling cascades. The crosstalk mechanism is cell type-specific, and is not detected in adult NP cells as well as brain tumor cells. The mechanism was also shown to be independent from the GSK-3 signaling pathway, which has been reported to be a major regulator of NP cell homeostasis and inhibitors to which were also identified in the screen. In vitro Erk inhibition led to the prolonged rapid expansion of fetal NP cells while retaining their multipotency. In vivo inhibitor administration significantly inhibited the neuronal differentiation, and resulted in increased proliferative progenitor cells in the ventricular/subventricular zone (VZ/SVZ) of the embryonic cortex. Our results uncovered a novel regulating pathway for NP cell proliferation in the developing brain. The discovery provides a pharmacological basis for in vitro expansion and in vivo manipulation of NP cells.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Glial progenitors as targets for transformation in glioma

Glioma is the most common primary malignant brain tumor and arises throughout the central nervous system. Recent focus on stem-like glioma cells has implicated neural stem cells (NSCs), a minor precursor population restricted to germinal zones, as a potential source of gliomas. In this review, we focus on the relationship between oligodendrocyte progenitor cells (OPCs), the largest population of cycling glial progenitors in the postnatal brain, and gliomagenesis. OPCs can give rise to gliomas, with signaling pathways associated with NSCs also playing key roles during OPC lineage development. Gliomas can also undergo a switch from progenitor- to stem-like phenotype after therapy, consistent with an OPC-origin even for stem-like gliomas. Future in-depth studies of OPC biology may shed light on the etiology of OPC-derived gliomas and reveal new therapeutic avenues.

Gene networks underlying convergent and pleiotropic phenotypes in a large and systematically-phenotyped cohort with heterogeneous developmental disorders

Readily-accessible and standardised capture of genotypic variation has revolutionised our understanding of the genetic contribution to disease. Unfortunately, the corresponding systematic capture of patient phenotypic variation needed to fully interpret the impact of genetic variation has lagged far behind. Exploiting deep and systematic phenotyping of a cohort of 197 patients presenting with heterogeneous developmental disorders and whose genomes harbour de novo CNVs, we systematically applied a range of commonly-used functional genomics approaches to identify the underlying molecular perturbations and their phenotypic impact. Grouping patients into 408 non-exclusive patient-phenotype groups, we identified a functional association amongst the genes disrupted in 209 (51%) groups. We find evidence for a significant number of molecular interactions amongst the association-contributing genes, including a single highly-interconnected network disrupted in 20% of patients with intellectual disability, and show using microcephaly how these molecular networks can be used as baits to identify additional members whose genes are variant in other patients with the same phenotype. Exploiting the systematic phenotyping of this cohort, we observe phenotypic concordance amongst patients whose variant genes contribute to the same functional association but note that (i) this relationship shows significant variation across the different approaches used to infer a commonly perturbed molecular pathway, and (ii) that the phenotypic similarities detected amongst patients who share the same inferred pathway perturbation result from these patients sharing many distinct phenotypes, rather than sharing a more specific phenotype, inferring that these pathways are best characterized by their pleiotropic effects.

Developmental disorders occur in ∼3% of live births, and exhibit a broad range of abnormalities including: intellectual disability, autism, heart defects, and other neurological and morphological problems. Often, patients are grouped into genetic syndromes which are defined by a specific set of mutations and a common set of abnormalities. However, many mutations are unique to a single patient and many patients present a range of abnormalities which do not fit one of the recognized genetic syndromes, making diagnosis difficult. Using a dataset of 197 patients with systematically described abnormalities, we identified molecular pathways whose disruption was associated with specific abnormalities among many patients. Importantly, patients with mutations in the same pathway often exhibited similar co-morbid symptoms and thus the commonly disrupted pathway appeared responsible for the broad range of shared abnormalities amongst these patients. These findings support the general concept that patients with mutations in distinct genes could be etiologically grouped together through the common pathway that these mutated genes participate in, with a view to improving diagnoses, prognoses and therapeutic outcomes.

Integrin-associated protein promotes neuronal differentiation of neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) proliferate and differentiate depending on their intrinsic properties and local environment. During the development of the mammalian nervous system, NSPCs generate neurons and glia sequentially. However, little is known about the mechanism that determines the timing of switch from neurogenesis to gliogenesis. In this study, we established a culture system in which the neurogenic potential of NSPCs is decreased in a time-dependent manner, so that short-term-cultured NSPCs differentiate into more neurons compared with long-term-cultured NSPCs. We found that short-term-cultured NSPCs express high levels of integrin-associated protein form 2 (IAP2; so-called CD47) mRNA using differential display analysis. Moreover, IAP2 overexpression in NSPCs induced neuronal differentiation of NSPCs. These findings reveal a novel mechanism by which IAP2 induces neuronal differentiation of NSPCs.

Effects of neurotrophin-3 on the differentiation of neural stem cells into neurons and oligodendrocytes

In this study, cells from the cerebral cortex of fetal rats at pregnant 16 days were harvested and cultured with 20 μg/L neurotrophin-3. After 7 days of culture, immunocytochemical staining showed that, 22.4% of cells were positive for nestin, 10.5% were positive for β-III tubulin (neuronal marker), and 60.6% were positive for glial fibrillary acidic protein, but no cells were positive for O₄ (oligodendrocytic marker). At 14 days, there were 5.6% nestin-, 9.6% β-III tubulin-, 81.1% glial fibrillary acidic protein-, and 2.2% O₄-positive cells. In cells not treated with neurotrophin-3, some were nestin-positive, while the majority showed positive staining for glial fibrillary acidic protein. Our experimental findings indicate that neurotrophin-3 is a crucial factor for inducing neural stem cells differentiation into neurons and oligodendrocytes.

CCAAT/enhancer binding protein β directly regulates the expression of the complement component 3 gene in neural cells: implications for the pro-inflammatory effects of this transcription factor

Background

The CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor, which was first identified as a regulator of differentiation and inflammatory processes mainly in adipose tissue and liver; however, its function in the brain was largely unknown for many years. Previous studies from our laboratory indicated that C/EBPβ is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury.

Methods

We first performed cDNA microarrays analysis using hippocampal RNA isolated from C/EBPβ^+/+ and C/EBPβ^−/− mice. Immunocytochemical and immunohistochemical studies were done to evaluate C/EBPβ and C3 levels. Transient transfection experiments were made to analyze transcriptional regulation of C3 by C/EBPβ. To knockdown C/EBPβ and C3 expression, mouse astrocytes were infected with lentiviral particles expressing an shRNA specific for C/EBPβ or an siRNA specific for C3.

Results

Among the genes displaying significant changes in expression was complement component 3 (C3), which showed a dramatic decrease in mRNA content in the hippocampus of C/EBPβ^−/− mice. C3 is the central component of the complement and is implicated in different brain disorders. In this work we have found that C/EBPβ regulates C3 levels in rodents glial in vitro and in the rat Substantia nigra pars compacta (SNpc) in vivo following an inflammatory insult. Analysis of the mouse C3 promoter showed that it is directly regulated by C/EBPβ through a C/EBPβ consensus site located at position −616/-599 of the gene. In addition, we show that depletion of C/EBPβ by a specific shRNA results in a significant decrease in the levels of C3 together with a reduction in the increased levels of pro-inflammatory agents elicited by lipopolysaccharide treatment.

Conclusions

Altogether, these results indicate that C3 is a downstream target of C/EBPβ, and it could be a mediator of the pro-inflammatory effects of this transcription factor in neural cells.