Gene expression in the prefrontal cortex during adolescence: implications for the onset of schizophrenia

Standardization of a silver stain to reveal mesoscale myelin in histological preparations of the mammalian brain

BACKGROUND

The brain is built of neurons supported by myelin, a fatty substance that improves cellular communication. Noninvasive magnetic resonance imaging (MRI) is now able to measure brain structure like myelin and requires histological validation.

NEW METHOD

Here we present work in small and large biomedical model mammals to standardize a silver impregnation method as a high-throughput histological myelin visualization procedure. Specifically, we built a new staining well plate to increase batch size, and then systematically varied the staining and clearing cycles to describe the staining response curve across taxa and conditions. We compared tissues fixed by immersion or perfusion, mounted versus free-floating, and cut as thicker or thinner slices, with two-weeks of post-fixation.

RESULTS

The staining response curves show optimal staining with a single exposure across taxa when incubation and clearing epochs are held to within 3-9 min. We show that clearing was slower in mounted vs free-floating tissue, and that staining was faster and caused fracturing earlier in thinner sliced and smaller volumes of tissue.

COMPARISON WITH EXISTING METHODS

We developed a batch processing approach to increase throughput while ensuring reproducibility and demonstrate the optimal conditions for fine myelinated fiber morphology visualization with short cycles (<9 minutes).

CONCLUSIONS

We present our optimized protocol to reveal mesoscale neuroanatomical myelin content in histology across mammals. This standard staining procedure will facilitate multiscale analyses of myelin content across development as well as in the presence of injury or disease.

Sex-specific interactions between stress axis and redox balance are associated with internalizing symptoms and brain white matter microstructure in adolescents

Adolescence is marked by the maturation of systems involved in emotional regulation and by an increased risk for internalizing disorders (anxiety/depression), especially in females. Hypothalamic-pituitary-adrenal (HPA)-axis function and redox homeostasis (balance between reactive oxygen species and antioxidants) have both been associated with internalizing disorders and may represent critical factors for the development of brain networks of emotional regulation. However, sex-specific interactions between these factors and internalizing symptoms and their link with brain maturation remain unexplored. We investigated in a cohort of adolescents aged 13-15 from the general population (n = 69) whether sex-differences in internalizing symptoms were associated with the glutathione (GSH)-redox cycle homeostasis and HPA-axis function and if these parameters were associated with brain white matter microstructure development. Female adolescents displayed higher levels of internalizing symptoms, GSH-peroxidase (GPx) activity and cortisol/11-deoxycortisol ratio than males. There was a strong correlation between GPx and GSH-reductase (Gred) activities in females only. The cortisol/11-deoxycortisol ratio, related to the HPA-axis activity, was associated with internalizing symptoms in both sexes, whereas GPx activity was associated with internalizing symptoms in females specifically. The cortisol/11-deoxycortisol ratio mediated sex-differences in internalizing symptoms and the association between anxiety and GPx activity in females specifically. In females, GPx activity was positively associated with generalized fractional anisotropy in widespread white matter brain regions. We found that higher levels of internalizing symptoms in female adolescents than in males relate to sex-differences in HPA-axis function. In females, our results suggest an important interplay between HPA-axis function and GSH-homeostasis, a parameter strongly associated with brain white matter microstructure.

Striatal correlates of Bayesian beliefs in self-efficacy in adolescents and their relation to mood and autonomy: a pilot study

Major depressive disorder often originates in adolescence and is associated with long-term functional impairment. Mechanistically characterizing this heterogeneous illness could provide important leads for optimizing treatment. Importantly, reward learning is known to be disrupted in depression. In this pilot fMRI study of 21 adolescents (16-20 years), we assessed how reward network disruption impacts specifically on Bayesian belief representations of self-efficacy (SE-B) and their associated uncertainty (SE-U), using a modified instrumental learning task probing activation induced by the opportunity to choose, and an optimal Hierarchical Gaussian Filter computational model. SE-U engaged caudate, nucleus accumbens (NAcc), precuneus, posterior parietal and dorsolateral prefrontal cortex (PFWE < 0.005). Sparse partial least squares analysis identified SE-U striatal activation as associating with one's sense of perceived choice and depressive symptoms, particularly anhedonia and negative feelings about oneself. As Bayesian uncertainty modulates belief flexibility and their capacity to steer future actions, this suggests that these striatal signals may be informative developmentally, longitudinally and in assessing response to treatment.

Neurodevelopmental trajectories, polygenic risk, and lipometabolism in vulnerability and resilience to schizophrenia

BACKGROUND

Schizophrenia (SZ) arises from a complex interplay involving genetic and molecular factors. Early intervention of SZ hinges upon understanding its vulnerability and resiliency factors in study of SZ and genetic high risk for SZ (GHR).

METHODS

Herein, using integrative and multimodal strategies, we first performed a longitudinal study of neural function as measured by amplitude of low frequency function (ALFF) in 21 SZ, 26 GHR, and 39 healthy controls to characterize neurodevelopmental trajectories of SZ and GHR. Then, we examined the relationship between polygenic risk score for SZ (SZ-PRS), lipid metabolism, and ALFF in 78 SZ, and 75 GHR in cross-sectional design to understand its genetic and molecular substrates.

RESULTS

Across time, SZ and GHR diverge in ALFF alterations of the left medial orbital frontal cortex (MOF). At baseline, both SZ and GHR had increased left MOF ALFF compared to HC (P < 0.05). At follow-up, increased ALFF persisted in SZ, yet normalized in GHR. Further, membrane genes and lipid species for cell membranes predicted left MOF ALFF in SZ; whereas in GHR, fatty acids best predicted and were negatively correlated (r = -0.302, P < 0.05) with left MOF.

CONCLUSIONS

Our findings implicate divergence in ALFF alteration in left MOF between SZ and GHR with disease progression, reflecting vulnerability and resiliency to SZ. They also indicate different influences of membrane genes and lipid metabolism on left MOF ALFF in SZ and GHR, which have important implications for understanding mechanisms underlying vulnerability and resiliency in SZ and contribute to translational efforts for early intervention.

LIN28 expression and function in medulloblastoma

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Current treatment modalities are not completely effective and can lead to severe neurological and cognitive adverse effects. In addition to urgently needing better treatment approaches, new diagnostic and prognostic biomarkers are required to improve the therapy outcomes of MB patients. The RNA-binding proteins, LIN28A and LIN28B, are known to regulate invasive phenotypes in many different cancer types. However, the expression and function of these proteins in MB had not been studied to date. This study identified the expression of LIN28A and LIN28B in MB patient samples and cell lines and assessed the effect of LIN28 inhibition on MB cell growth, metabolism and stemness. LIN28B expression was significantly upregulated in MB tissues compared to normal brain tissues. This upregulation, which was not observed in other brain tumors, was specific for the aggressive MB subgroups and correlated with patient survival and metastasis rates. Functionally, pharmacological inhibition of LIN28 activity concentration-dependently reduced LIN28B expression, as well as the growth of D283 MB cells. While LIN28 inhibition did not affect the levels of intracellular ATP, it reduced the expression of the stemness marker CD133 in D283 cells and the sphere formation of CHLA-01R cells. LIN28B, which is highly expressed in the human cerebellum during the first few months after birth, subsequently decreased with age. The results of this study highlight the potential of LIN28B as a diagnostic and prognostic marker for MB and open the possibility to utilize LIN28 as a pharmacological target to suppress MB cell growth and stemness.

Transcriptomic analyses of patient peripheral blood with hemoglobin depletion reveal glioblastoma biomarkers

Peripheral blood is gaining prominence as a noninvasive alternative to tissue biopsy to develop biomarkers for glioblastoma (GBM); however, widely utilized blood-based biomarkers in clinical settings have not yet been identified due to the lack of a robust detection approach. Here, we describe the application of globin reduction in RNA sequencing of whole blood (i.e., WBGR) and perform transcriptomic analysis to identify GBM-associated transcriptomic changes. By using WBGR, we improved the detection sensitivity of informatic reads and identified differential gene expression in GBM blood. By analyzing tumor tissues, we identified transcriptomic traits of GBM blood. Further functional enrichment analyses retained the most changed genes in GBM. Subsequent validation elicited a 10-gene panel covering mRNA, long noncoding RNA, and microRNA (i.e., GBM-Dx panel) that has translational potential to aid in the early detection or clinical management of GBM. Here, we report an integrated approach, WBGR, with comprehensive analytic capacity for blood-based marker identification.

Dendritic Spines: Synaptogenesis and Synaptic Pruning for the Developmental Organization of Brain Circuits

Synaptic overproduction and elimination is a regular developmental event in the mammalian brain. In the cerebral cortex, synaptic overproduction is almost exclusively correlated with glutamatergic synapses located on dendritic spines. Therefore, analysis of changes in spine density on different parts of the dendritic tree in identified classes of principal neurons could provide insight into developmental reorganization of specific microcircuits.The activity-dependent stabilization and selective elimination of the initially overproduced synapses is a major mechanism for generating diversity of neural connections beyond their genetic determination. The largest number of overproduced synapses was found in the monkey and human cerebral cortex. The highest (exceeding adult values by two- to threefold) and most protracted overproduction (up to third decade of life) was described for associative layer IIIC pyramidal neurons in the human dorsolateral prefrontal cortex.Therefore, the highest proportion and extraordinarily extended phase of synaptic spine overproduction is a hallmark of neural circuitry in human higher-order associative areas. This indicates that microcircuits processing the most complex human cognitive functions have the highest level of developmental plasticity. This finding is the backbone for understanding the effect of environmental impact on the development of the most complex, human-specific cognitive and emotional capacities, and on the late onset of human-specific neuropsychiatric disorders, such as autism and schizophrenia.

STAT3 is a biologically relevant therapeutic target in H3K27M-mutant diffuse midline glioma

Background

H3K27M-mutant diffuse midline glioma (DMG) is a lethal brain tumor that usually occurs in children. Despite advances in our understanding of its underlying biology, efficacious therapies are severely lacking.

Methods

We screened a library of drugs either FDA-approved or in clinical trial using a library of patient-derived H3K27M-mutant DMG cell lines with cell viability as the outcome. Results were validated for clinical relevance and mechanistic importance using patient specimens from biopsy and autopsy, patient-derived cell lines, inhibition by gene knockdown and small molecule inhibitors, and patient-derived xenografts.

Results

Kinase inhibitors were highly toxic to H3K27M-mutant DMG cells. Within this class, STAT3 inhibitors demonstrated robust cytotoxic activity in vitro. Mechanistic analyses revealed one form of activated STAT3, phospho-tyrosine- 705 STAT3 (pSTAT3), was selectively upregulated in H3K27M-mutant cell lines and clinical specimens. STAT3 inhibition by CRISPR/Cas9 knockout, shRNA or small molecule inhibition reduced cell viability in vitro, and partially restored expression of the polycomb repressive mark H3K27me3, which is classically lost in H3K27M-mutant DMG. Putative STAT3-regulated genes were enriched in an H3K27M-knockout DMG cell line, indicating relative gain of STAT3 signaling in K27M-mutant cells. Treatment of patient-derived intracranial xenografts with WP1066, a STAT3 pathway inhibitor currently in clinical use for pediatric brain tumors, resulted in stasis of tumor growth, and increased overall survival. Finally, pSTAT3(Y705) was detected in circulating plasma extracellular vesicles of patients with H3K27M-mutant DMG.

Conclusions

STAT3 is a biologically relevant therapeutic target in H3K27M-mutant DMG. STAT3 inhibition should be considered in future clinical trials.

MicroRNAs in the Onset of Schizophrenia

Mounting evidence implicates microRNAs (miRNAs) in the pathology of schizophrenia. These small noncoding RNAs bind to mRNAs containing complementary sequences and promote their degradation and/or inhibit protein synthesis. A single miRNA may have hundreds of targets, and miRNA targets are overrepresented among schizophrenia-risk genes. Although schizophrenia is a neurodevelopmental disorder, symptoms usually do not appear until adolescence, and most patients do not receive a schizophrenia diagnosis until late adolescence or early adulthood. However, few studies have examined miRNAs during this critical period. First, we examine evidence that the miRNA pathway is dynamic throughout adolescence and adulthood and that miRNAs regulate processes critical to late neurodevelopment that are aberrant in patients with schizophrenia. Next, we examine evidence implicating miRNAs in the conversion to psychosis, including a schizophrenia-associated single nucleotide polymorphism in MIR137HG that is among the strongest known predictors of age of onset in patients with schizophrenia. Finally, we examine how hemizygosity for DGCR8, which encodes an obligate component of the complex that synthesizes miRNA precursors, may contribute to the onset of psychosis in patients with 22q11.2 microdeletions and how animal models of this disorder can help us understand the many roles of miRNAs in the onset of schizophrenia.

Oxidative Stress in the Early Stage of Psychosis

BACKGROUND

In the past few decades, increasing evidence in the literature has appeared describing the role of the antioxidant defense system and redox signaling in the multifactorial pathophysiology of psychosis. It is of interest to clinicians and researchers alike that abnormalities of the antioxidant defense system are associated with alterations of cellular membranes, immune functions and neurotransmission, all of which have some clinical implications.

METHODS

This narrative review summarizes the evidence regarding oxidative stress in the early stages of psychosis. We included 136 peer-reviewed articles published from 2007 to 2020 on PubMed EMBASE, The Cochrane Library and Google Scholar.

RESULTS

Patients affected by psychotic disorders show a decreased level of non-enzymatic antioxidants, an increased level of lipid peroxides, nitric oxides, and a homeostatic imbalance of purine catabolism. In particular, a significantly reduced antioxidant defense has been described in the early onset first episode of psychosis, including reduced levels of glutathione. Also, it has been shown that a decreased basal low -antioxidant capacity correlates with cognitive deficits and negative symptoms, mostly related to glutamate-receptor hypofunction. In addition, atypical antipsychotic drugs seem to show significant antioxidant activity. These factors are critical in order to treat cases of first-onset psychosis effectively.

CONCLUSION

This systematic review indicates the importance that must be given to anti-oxidant defense systems.

High fat diet consumption restricted to adolescence has minimal effects on adult executive function that vary by sex

Early life environment can have a lasting effect on brain development and behavior. Diet is a potent environmental factor that can positively or negatively affect neurodevelopment, and unfortunately, the likelihood of a poor diet is high during adolescence. Adverse effects of adolescent high fat diet have been observed on reward-related behaviors, reversal learning, and hippocampal-dependent learning tasks in rodents when tested in adulthood. The prefrontal cortex (PFC) continues to develop throughout adolescence and is thus vulnerable to environmental insults such as poor diet. Therefore, we sought to examine the effects of a high fat diet (HFD) consumed only during adolescence on later life adult PFC-dependent executive function. Male and female mice were fed a HFD (60% energy from fat) during either early or late adolescence then switched to standard chow and tested in a battery of touchscreen-based operant tests of executive function in adulthood. Contrary to our prediction of an adverse effect of HFD, there was no effect of adolescent HFD in males, and females showed faster learning and decreased inattention in adulthood. We conclude that the effects of adolescent-limited HFD on adult executive function are mild, positive, and vary by sex.

Neuronal signatures in cancer

Despite advances in the treatment of solid tumors, the prognosis of patients with many cancers remains poor, particularly of those with primary and metastatic brain tumors. In the last years, "Cancer Neuroscience" emerged as novel field of research at the crossroads of oncology and classical neuroscience. In primary brain tumors, including glioblastoma (GB), communicating networks that render tumor cells resistant against cytotoxic therapies were identified. To build these networks, GB cells extend neurite-like protrusions called tumor microtubes (TMs). Synapses on TMs allow tumor cells to retrieve neuronal input that fosters growth. Single cell sequencing further revealed that primary brain tumors recapitulate many steps of neurodevelopment. Interestingly, neuronal characteristics, including the ability to extend neurite-like protrusions, neuronal gene expression signatures and interactions with neurons, have now been found not only in brain and neuroendocrine tumors but also in some cancers of epithelial origin. In this review, we will provide an overview about neurite-like protrusions as well as neurodevelopmental origins, hierarchies and gene expression signatures in cancer. We will also discuss how "Cancer Neuroscience" might provide a framework for the development of novel therapies.

Targeting NAD+ Biosynthesis Overcomes Panobinostat and Bortezomib-Induced Malignant Glioma Resistance

To improve therapeutic responses in patients with glioma, new combination therapies that exploit a mechanistic understanding of the inevitable emergence of drug resistance are needed. Intratumoral heterogeneity enables a low barrier to resistance in individual patients with glioma. We reasoned that targeting two or more fundamental processes that gliomas are particularly dependent upon could result in pleiotropic effects that would reduce the diversity of resistant subpopulations allowing convergence to a more robust therapeutic strategy. In contrast to the cytostatic responses observed with each drug alone, the combination of the histone deacetylase inhibitor panobinostat and the proteasome inhibitor bortezomib synergistically induced apoptosis of adult and pediatric glioma cell lines at clinically achievable doses. Resistance that developed was examined using RNA-sequencing and pharmacologic screening of resistant versus drug-naïve cells. Quinolinic acid phosphoribosyltransferase (QPRT), the rate-determining enzyme for de novo synthesis of NAD⁺ from tryptophan, exhibited particularly high differential gene expression in resistant U87 cells and protein expression in all resistant lines tested. Reducing QPRT expression reversed resistance, suggesting that QPRT is a selective and targetable dependency for the panobinostat-bortezomib resistance phenotype. Pharmacologic inhibition of either NAD⁺ biosynthesis or processes such as DNA repair that consume NAD⁺ or their simultaneous inhibition with drug combinations, specifically enhanced apoptosis in treatment-resistant cells. Concomitantly, de novo vulnerabilities to known drugs were observed. IMPLICATIONS: These data provide new insights into mechanisms of treatment resistance in gliomas, hold promise for targeting recurrent disease, and provide a potential strategy for further exploration of next-generation inhibitors.

Combined Therapy of AXL and HDAC Inhibition Reverses Mesenchymal Transition in Diffuse Intrinsic Pontine Glioma

PURPOSE

Diffuse intrinsic pontine glioma (DIPG) is an incurable type of pediatric brain cancer, which in the majority of cases is driven by mutations in genes encoding histone 3 (H3K27M). We here determined the preclinical therapeutic potential of combined AXL and HDAC inhibition in these tumors to reverse their mesenchymal, therapy-resistant, phenotype.

EXPERIMENTAL DESIGN

We used public databases and patient-derived DIPG cells to identify putative drivers of the mesenchymal transition in these tumors. Patient-derived neurospheres, xenografts, and allografts were used to determine the therapeutic potential of combined AXL/HDAC inhibition for the treatment of DIPG.

RESULTS

We identified AXL as a therapeutic target and regulator of the mesenchymal transition in DIPG. Combined AXL and HDAC inhibition had a synergistic and selective antitumor effect on H3K27M DIPG cells. Treatment of DIPG cells with the AXL inhibitor BGB324 and the HDAC inhibitor panobinostat resulted in a decreased expression of mesenchymal and stem cell genes. Moreover, this combination treatment decreased expression of DNA damage repair genes in DIPG cells, strongly sensitizing them to radiation. Pharmacokinetic studies showed that BGB324, like panobinostat, crosses the blood-brain barrier. Consequently, treatment of patient-derived DIPG xenograft and murine DIPG allograft-bearing mice with BGB324 and panobinostat resulted in a synergistic antitumor effect and prolonged survival.

CONCLUSIONS

Combined inhibition of AXL and HDACs in DIPG cells results in a synergistic antitumor effect by reversing their mesenchymal, stem cell-like, therapy-resistant phenotype. As such, this treatment combination may serve as part of a future multimodal therapeutic strategy for DIPG.

Celastrol-induced degradation of FANCD2 sensitizes pediatric high-grade gliomas to the DNA-crosslinking agent carboplatin

Background

Pediatric high-grade gliomas (pHGG) are the leading cause of cancer-related death during childhood. Due to their diffuse growth characteristics, chemoresistance and location behind the blood-brain barrier (BBB), the prognosis of pHGG has barely improved in the past decades. As such, there is a dire need for new therapies that circumvent those difficulties. Since aberrant expression of DNA damage-response associated Fanconi anemia proteins play a central role in the onset and therapy resistance of many cancers, we here investigated if FANCD2 depletion could sensitize pHGG to additional DNA damage.

Methods

We determined the capacity of celastrol, a BBB-penetrable compound that degrades FANCD2, to sensitize glioma cells to the archetypical DNA-crosslinking agent carboplatin in vitro in seven patient-derived pHGG models. In addition, we tested this drug combination in vivo in a patient-derived orthotopic pHGG xenograft model. Underlying mechanisms to drug response were investigated using mRNA expression profiling, western blotting, immunofluorescence, FANCD2 knockdown and DNA fiber assays.

Findings

FANCD2 is overexpressed in HGGs and depletion of FANCD2 by celastrol synergises with carboplatin to induce cytotoxicity. Combination therapy prolongs survival of pHGG-bearing mice over monotherapy and control groups in vivo (P<0.05). In addition, our results suggest that celastrol treatment stalls ongoing replication forks, causing sensitivity to DNA-crosslinking in FANCD2-dependent glioma cells.

Interpretation

Our results show that depletion of FANCD2 acts as a chemo-sensitizing strategy in pHGG. Combination therapy using celastrol and carboplatin might serve as a clinically relevant strategy for the treatment of pHGG.

Funding

This study was funded by a grant from the Children Cancer-Free Foundation (KIKA, project 210). The disclosed funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The Protracted Maturation of Associative Layer IIIC Pyramidal Neurons in the Human Prefrontal Cortex During Childhood: A Major Role in Cognitive Development and Selective Alteration in Autism

The human specific cognitive shift starts around the age of 2 years with the onset of self-awareness, and continues with extraordinary increase in cognitive capacities during early childhood. Diffuse changes in functional connectivity in children aged 2-6 years indicate an increase in the capacity of cortical network. Interestingly, structural network complexity does not increase during this time and, thus, it is likely to be induced by selective maturation of a specific neuronal subclass. Here, we provide an overview of a subclass of cortico-cortical neurons, the associative layer IIIC pyramids of the human prefrontal cortex. Their local axonal collaterals are in control of the prefrontal cortico-cortical output, while their long projections modulate inter-areal processing. In this way, layer IIIC pyramids are the major integrative element of cortical processing, and changes in their connectivity patterns will affect global cortical functioning. Layer IIIC neurons have a unique pattern of dendritic maturation. In contrast to other classes of principal neurons, they undergo an additional phase of extensive dendritic growth during early childhood, and show characteristic molecular changes. Taken together, circuits associated with layer IIIC neurons have the most protracted period of developmental plasticity. This unique feature is advanced but also provides a window of opportunity for pathological events to disrupt normal formation of cognitive circuits involving layer IIIC neurons. In this manuscript, we discuss how disrupted dendritic and axonal maturation of layer IIIC neurons may lead into global cortical disconnectivity, affecting development of complex communication and social abilities. We also propose a model that developmentally dictated incorporation of layer IIIC neurons into maturing cortico-cortical circuits between 2 to 6 years will reveal a previous (perinatal) lesion affecting other classes of principal neurons. This "disclosure" of pre-existing functionally silent lesions of other neuronal classes induced by development of layer IIIC associative neurons, or their direct alteration, could be found in different forms of autism spectrum disorders. Understanding the gene-environment interaction in shaping cognitive microcircuitries may be fundamental for developing rehabilitation and prevention strategies in autism spectrum and other cognitive disorders.

Novel Complex Interactions between Mitochondrial and Nuclear DNA in Schizophrenia and Bipolar Disorder

Mitochondrial dysfunction has been associated with schizophrenia (SZ) and bipolar disorder (BD). This review examines recent publications and novel associations between mitochondrial genes and SZ and BD. Associations of nuclear-encoded mitochondrial variants with SZ were found using gene- and pathway-based approaches. Two control region mitochondrial DNA (mtDNA) SNPs, T16519C and T195C, both showed an association with SZ and BD. A review of 4 studies of A15218G located in the cytochrome B oxidase gene (CYTB, SZ = 11,311, control = 35,735) shows a moderate association with SZ (p = 2.15E-03). Another mtDNA allele A12308G was nominally associated with psychosis in BD type I subjects and SZ. The first published study testing the epistatic interaction between nuclear-encoded and mitochondria-encoded genes demonstrated evidence for potential interactions between mtDNA and the nuclear genome for BD. A similar analysis for the risk of SZ revealed significant joint effects (34 nuclear-mitochondria SNP pairs with joint effect p ≤ 5E-07) and significant enrichment of projection neurons. The mitochondria-encoded gene CYTB was found in both the epistatic interactions for SZ and BD and the single SNP association of SZ. Future efforts considering population stratification and polygenic risk scores will test the role of mitochondrial variants in psychiatric disorders.

Identification of CD24 as a marker of Patched1 deleted medulloblastoma-initiating neural progenitor cells

High morbidity and mortality are common traits of malignant tumours and identification of the cells responsible is a focus of on-going research. Many studies are now reporting the use of antibodies specific to Clusters of Differentiation (CD) cell surface antigens to identify tumour-initiating cell (TIC) populations in neural tumours. Medulloblastoma is one of the most common malignant brain tumours in children and despite a considerable amount of research investigating this tumour, the identity of the TICs, and the means by which such cells can be targeted remain largely unknown. Current prognostication and stratification of medulloblastoma using clinical factors, histology and genetic profiling have classified this tumour into four main subgroups: WNT, Sonic hedgehog (SHH), Group 3 and Group 4. Of these subgroups, SHH remains one of the most studied tumour groups due to the ability to model medulloblastoma formation through targeted deletion of the Shh pathway inhibitor Patched1 (Ptch1). Here we sought to utilise CD antibody expression to identify and isolate TIC populations in Ptch1 deleted medulloblastoma, and determine if these antibodies can help classify the identity of human medulloblastoma subgroups. Using a fluorescence-activated cell sorted (FACS) CD antibody panel, we identified CD24 as a marker of TICs in Ptch1 deleted medulloblastoma. CD24 expression was not correlated with markers of astrocytes or oligodendrocytes, but co-labelled with markers of neural progenitor cells. In conjunction with CD15, proliferating CD24+/CD15+ granule cell precursors (GCPs) were identified as a TIC population in Ptch1 deleted medulloblastoma. On human medulloblastoma, CD24 was found to be highly expressed on Group 3, Group 4 and SHH subgroups compared with the WNT subgroup, which was predominantly positive for CD15, suggesting CD24 is an important marker of non-WNT medulloblastoma initiating cells and a potential therapeutic target in human medulloblastoma. This study reports the use of CD24 and CD15 to isolate a GCP-like TIC population in Ptch1 deleted medulloblastoma, and suggests CD24 expression as a marker to help stratify human WNT tumours from other medulloblastoma subgroups.

Temporal proteomic profiling of postnatal human cortical development

Healthy cortical development depends on precise regulation of transcription and translation. However, the dynamics of how proteins are expressed, function and interact across postnatal human cortical development remain poorly understood. We surveyed the proteomic landscape of 69 dorsolateral prefrontal cortex samples across seven stages of postnatal life and integrated these data with paired transcriptome data. We detected 911 proteins by liquid chromatography-mass spectrometry, and 83 were significantly associated with postnatal age (FDR < 5%). Network analysis identified three modules of co-regulated proteins correlated with age, including two modules with increasing expression involved in gliogenesis and NADH metabolism and one neurogenesis-related module with decreasing expression throughout development. Integration with paired transcriptome data revealed that these age-related protein modules overlapped with RNA modules and displayed collinear developmental trajectories. Importantly, RNA expression profiles that are dynamically regulated throughout cortical development display tighter correlations with their respective translated protein expression compared to those RNA profiles that are not. Moreover, the correspondence between RNA and protein expression significantly decreases as a function of cortical aging, especially for genes involved in myelination and cytoskeleton organization. Finally, we used this data resource to elucidate the functional impact of genetic risk loci for intellectual disability, converging on gliogenesis, myelination and ATP-metabolism modules in the proteome and transcriptome. We share all data in an interactive, searchable companion website. Collectively, our findings reveal dynamic aspects of protein regulation and provide new insights into brain development, maturation, and disease.

Prefrontal cortical trkB, glucocorticoids, and their interactions in stress and developmental contexts

The tropomyosin/tyrosine receptor kinase B (trkB) and glucocorticoid receptor (GR) regulate neuron structure and function and the hormonal stress response. Meanwhile, disruption of trkB and GR activity (e.g., by chronic stress) can perturb neuronal morphology in cortico-limbic regions implicated in stressor-related illnesses like depression. Further, several of the short- and long-term neurobehavioral consequences of stress depend on the developmental timing and context of stressor exposure. We review how the levels and activities of trkB and GR in the prefrontal cortex (PFC) change during development, interact, are modulated by stress, and are implicated in depression. We review evidence that trkB- and GR-mediated signaling events impact the density and morphology of dendritic spines, the primary sites of excitatory synapses in the brain, highlighting effects in adolescents when possible. Finally, we review the role of neurotrophin and glucocorticoid systems in stress-related metaplasticity. We argue that better understanding the long-term effects of developmental stressors on PFC trkB, GR, and related factors may yield insights into risk for chronic, remitting depression and related neuropsychiatric illnesses.

Transcriptomic Evidence for Alterations in Astrocytes and Parvalbumin Interneurons in Subjects With Bipolar Disorder and Schizophrenia

BACKGROUND

High-throughput expression analyses of postmortem brain tissue have been widely used to study bipolar disorder and schizophrenia. However, despite the extensive efforts, no consensus has emerged as to the functional interpretation of the findings. We hypothesized that incorporating information on cell type-specific expression would provide new insights.

METHODS

We reanalyzed 15 publicly available bulk tissue expression datasets on schizophrenia and bipolar disorder, representing various brain regions from eight different cohorts of subjects (unique subjects: 332 control, 129 bipolar disorder, 341 schizophrenia). We studied changes in the expression profiles of cell type marker genes and evaluated whether these expression profiles could serve as surrogates for relative abundance of their corresponding cells.

RESULTS

In both bipolar disorder and schizophrenia, we consistently observed an increase in the expression profiles of cortical astrocytes and a decrease in the expression profiles of fast-spiking parvalbumin interneurons. No changes in astrocyte expression profiles were observed in subcortical regions. Furthermore, we found that many of the genes previously identified as differentially expressed in schizophrenia are highly correlated with the expression profiles of astrocytes or fast-spiking parvalbumin interneurons.

CONCLUSIONS

Our results indicate convergence of transcriptome studies of schizophrenia and bipolar disorder on changes in cortical astrocytes and fast-spiking parvalbumin interneurons, providing a unified interpretation of numerous studies. We suggest that these changes can be attributed to alterations in the relative abundance of the cells and are important for understanding the pathophysiology of the disorders.

Transcriptional co-expression regulatory network analysis for Snail and Slug identifies IL1R1, an inflammatory cytokine receptor, to be preferentially expressed in ST-EPN-RELA and PF-EPN-A molecular subgroups of intracranial ependymomas

Recent molecular subgrouping of ependymomas (EPN) by DNA methylation profiling has identified ST-EPN-RELA and PF-EPN-A subgroups to be associated with poor outcome. Snail/Slug are cardinal epithelial-to-mesenchymal transcription factors (EMT-TFs) and are overexpressed in several CNS tumors, including EPNs. A systematic analysis of gene-sets/modules co-expressed with Snail and Slug genes using published expression microarray dataset (GSE27279)identified 634 genes for Snail with enriched TGF-β, PPAR and PI3K signaling pathways, and 757 genes for Slug with enriched focal adhesion, ECM-receptor interaction and regulation of actin cytoskeleton related pathways. Of 37 genes commonly expressed with both Snail and Slug, IL1R1, a cytokine receptor of interleukin-1 receptor family, was positively correlated with Snail (r=0.43) and Slug (r=0.51), preferentially expressed in ST-EPN-RELA and PF-EPN-A molecular groups, and enriched for pathways related to inflammation, angiogenesis and glycolysis. IL1R1 expression was fairly specific to EPNs among various CNS tumors analyzed. It also showed significant positive correlation with EMT, stemness and MDSC (myeloid derived suppressor cell) markers. Our study reports IL1R1 as a poor prognostic marker associated with EMT-like phenotype and stemness in EPNs. Our findings emphasize the need to further examine and validate IL1R1 as a novel therapeutic target in aggressive subsets of intracranial EPNs.

Transcriptomic analysis reveals oxidative phosphorylation activation in an adolescent social isolation rat model

Complex interactions between genetic and environmental factors exert a sustained influence on the pathogenesis of schizophrenia (SCZ). Adolescent social isolation is regarded as a typical paradigm for SCZ. However, the underlying pathological mechanisms are not fully understood. In this study, adolescent Sprague-Dawley (SD) rats were placed in isolation rearing (IR) or social rearing (SR) conditions from postnatal day (PND) 21 to 34 to establish a SCZ disease model and a control model, respectively. Prepulse inhibition (PPI) assays and elevated plus maze tests were performed on PND 56. Next, prefrontal cortex (PFC) tissues were isolated for transcriptomic sequencing and RT-qPCR analyses. The results indicated that adolescent social isolation induced anxious behaviors and disrupted PPIs as well as specific PFC gene expression patterns in adult SD rats. A total of 196 genes were identified as upregulated, and 748 genes were identified as down-regulated in the IR group compared with those in the SR group. Differentially expressed genes (DEGs) were highly enriched in the KEGG pathways associated with the comorbidity of neurological disorder and oxidative phosphorylation (OXPHOS); 26 out of 27 comorbid neurological disorder-associated DEGs overlapped with 31 OXPHOS-associated DEGs. Those 26 overlapping DEGs were all upregulated in the IR group and could easily distinguish the IR group from the SR group; 6 of these DEGs (COX7C, NDUFB11, NDUFA2, NDUFC2, ATP5C1, and COX6A1) were verified by RT-qPCR. Here, we provide a systematic overview of gene expression alterations in adolescent-social-isolation-induced SCZ (ASI-SCZ), which suggests that genes that are associated with the comorbidity of neurological disorders, especially OXPHOS-related genes, contribute to the pathogenesis of ASI-SCZ.

A Novel Ultrasensitive In Situ Hybridization Approach to Detect Short Sequences and Splice Variants with Cellular Resolution

Investigating the expression of RNAs that differ by short or single nucleotide sequences at a single-cell level in tissue has been limited by the sensitivity and specificity of in situ hybridization (ISH) techniques. Detection of short isoform-specific sequences requires RNA isolation for PCR analysis-an approach that loses the regional and cell-type-specific distribution of isoforms. Having the capability to distinguish the differential expression of RNA variants in tissue is critical because alterations in mRNA splicing and editing, as well as coding single nucleotide polymorphisms, have been associated with numerous cancers, neurological and psychiatric disorders. Here we introduce a novel highly sensitive single-probe colorimetric/fluorescent ISH approach that targets short exon/exon RNA splice junctions using single-pair oligonucleotide probes (~ 50 bp). We use this approach to investigate, with single-cell resolution, the expression of four transcripts encoding the neuregulin (NRG) receptor ErbB4 that differ by alternative splicing of exons encoding two juxtamembrane (JMa/JMb) and two cytoplasmic (CYT-1/CYT-2) domains that alter receptor stability and signaling modes, respectively. By comparing ErbB4 hybridization on sections from wild-type and ErbB4 knockout mice (missing exon 2), we initially demonstrate that single-pair probes provide the sensitivity and specificity to visualize and quantify the differential expression of ErbB4 isoforms. Using cell-type-specific GFP reporter mice, we go on to demonstrate that expression of ErbB4 isoforms differs between neurons and oligodendrocytes, and that this differential expression of ErbB4 isoforms is evolutionarily conserved to humans. This single-pair probe ISH approach, known as BaseScope, could serve as an invaluable diagnostic tool to detect alternative spliced isoforms, and potentially single base polymorphisms, associated with disease.

Signaling pathways and mesenchymal transition in pediatric high-grade glioma

Pediatric high-grade gliomas (pHGG), including diffuse intrinsic pontine gliomas (DIPG), are the most lethal types of cancer in children. In recent years, it has become evident that these tumors are driven by epigenetic events, mainly mutations involving genes encoding Histone 3, setting them apart from their adult counterparts. These tumors are exceptionally resistant to chemotherapy and respond only temporarily to radiotherapy. Moreover, their delicate location and diffuse growth pattern make complete surgical resection impossible. In many other forms of cancer, chemo- and radioresistance, in combination with a diffuse, invasive phenotype, are associated with a transcriptional program termed the epithelial-to-mesenchymal transition (EMT). Activation of this program allows cancer cells to survive individually, invade surrounding tissues and metastasize. It also enables them to survive exposure to cytotoxic therapy, including chemotherapeutic drugs and radiation. We here suggest that EMT plays an important, yet poorly understood role in the biology and therapy resistance of pHGG and DIPG. This review summarizes the current knowledge on the major signal transduction pathways and transcription factors involved in the epithelial-to-mesenchymal transition in cancer in general and in pediatric HGG and DIPG in particular. Despite the fact that the mesenchymal transition has not yet been specifically studied in pHGG and DIPG, activation of pathways and high levels of transcription factors involved in EMT have been described. We conclude that the mesenchymal transition is likely to be an important element of the biology of pHGG and DIPG and warrants further investigation for the development of novel therapeutics.

From Shortage to Surge: A Developmental Switch in Hippocampal-Prefrontal Coupling in a Gene-Environment Model of Neuropsychiatric Disorders

Cognitive deficits represent a major burden of neuropsychiatric disorders and result in part from abnormal communication within hippocampal–prefrontal circuits. While it has been hypothesized that this network dysfunction arises during development, long before the first clinical symptoms, experimental evidence is still missing. Here, we show that pre-juvenile mice mimicking genetic and environmental risk factors of disease (dual-hit GE mice) have poorer recognition memory that correlates with augmented coupling by synchrony and stronger directed interactions between prefrontal cortex and hippocampus. The network dysfunction emerges already during neonatal development, yet it initially consists in a diminished hippocampal theta drive and consequently, a weaker and disorganized entrainment of local prefrontal circuits in discontinuous oscillatory activity in dual-hit GE mice when compared with controls. Thus, impaired maturation of functional communication within hippocampal–prefrontal networks switching from hypo- to hyper-coupling may represent a mechanism underlying the pathophysiology of cognitive deficits in neuropsychiatric disorders.

Divergent prefrontal dopaminergic mechanisms mediate drug- and fear-associated cue extinction during adolescence versus adulthood

Cue-associated learning is vital to guiding behaviour for survival. Adolescence represents a key developmental stage for perturbations in cue-related learning, including a characteristic deficit in cue extinction learning. The present review summarizes evidence from animal and human literature that cue extinction is critically mediated by prefrontal dopamine, a system that undergoes dramatic reorganization during adolescence. We propose that extinction learning and memory is governed by a developmentally dynamic balance of dopamine receptors in the prefrontal cortex, which changes across adolescence into adulthood. This is contrary to the previous idea that extinction deficits during adolescence reflect inefficiency in the same neural circuitry as adults. This leads to proposal of the novel theory that cue extinction involves divergent prefrontal dopaminergic mechanisms depending on the age of extinction.

Basal Dendritic Morphology of Cortical Pyramidal Neurons in Williams Syndrome: Prefrontal Cortex and Beyond

Williams syndrome (WS) is a unique neurodevelopmental disorder with a specific behavioral and cognitive profile, which includes hyperaffiliative behavior, poor social judgment, and lack of social inhibition. Here we examined the morphology of basal dendrites on pyramidal neurons in the cortex of two rare adult subjects with WS. Specifically, we examined two areas in the prefrontal cortex (PFC)-the frontal pole (Brodmann area 10) and the orbitofrontal cortex (Brodmann area 11)-and three areas in the motor, sensory, and visual cortex (BA 4, BA 3-1-2, BA 18). The findings suggest that the morphology of basal dendrites on the pyramidal neurons is altered in the cortex of WS, with differences that were layer-specific, more prominent in PFC areas, and displayed an overall pattern of dendritic organization that differentiates WS from other disorders. In particular, and unlike what was expected based on typically developing brains, basal dendrites in the two PFC areas did not display longer and more branched dendrites compared to motor, sensory and visual areas. Moreover, dendritic branching, dendritic length, and the number of dendritic spines differed little within PFC and between the central executive region (BA 10) and BA 11 that is part of the orbitofrontal region involved into emotional processing. In contrast, the relationship between the degree of neuronal branching in supra- versus infra-granular layers was spared in WS. Although this study utilized tissue held in formalin for a prolonged period of time and the number of neurons available for analysis was limited, our findings indicate that WS cortex, similar to that in other neurodevelopmental disorders such as Down syndrome, Rett syndrome, Fragile X, and idiopathic autism, has altered morphology of basal dendrites on pyramidal neurons, which appears more prominent in selected areas of the PFC. Results were examined from developmental perspectives and discussed in the context of other neurodevelopmental disorders. We have proposed hypotheses for further investigations of morphological changes on basal dendrites in WS, a syndrome of particular interest given its unique social and cognitive phenotype.

Oxidative stress, prefrontal cortex hypomyelination and cognitive symptoms in schizophrenia

Schizophrenia (SZ) is a neurodevelopmental disorder with a broad symptomatology, including cognitive symptoms that are thought to arise from the prefrontal cortex (PFC). The neurobiological aetiology of these symptoms remains elusive, yet both impaired redox control and PFC dysconnectivity have been recently implicated. PFC dysconnectivity has been linked to white matter, oligodendrocyte (OL) and myelin abnormalities in SZ patients. Myelin is produced by mature OLs, and OL precursor cells (OPCs) are exceptionally susceptible to oxidative stress. Here we propose a hypothesis for the aetiology of cognitive symptomatology in SZ: the redox-induced prefrontal OPC-dysfunctioning hypothesis. We pose that the combination of genetic and environmental factors causes oxidative stress marked by a build-up of reactive oxygen species that, during late adolescence, impair OPC signal transduction processes that are necessary for OPC proliferation and differentiation, and involve AMP-activated protein kinase, Akt-mTOR-P70S6K and peroxisome proliferator receptor alpha signalling. OPC dysfunctioning coincides with the relatively late onset of PFC myelination, causing hypomyelination and disruption of connectivity in this brain area. The resulting cognitive deficits arise in parallel with SZ onset. Hence, our hypothesis provides a novel neurobiological framework for the aetiology of SZ cognitive symptoms. Future research addressing our hypothesis could have important implications for the development of new (combined) antioxidant- and promyelination-based strategies to treat the cognitive symptoms in SZ.

Comparison of the adolescent and adult mouse prefrontal cortex proteome

Adolescence is a developmental period characterized by unique behavioral phenotypes (increased novelty seeking, risk taking, sociability and impulsivity) and increased risk for destructive behaviors, impaired decision making and psychiatric illness. Adaptive and maladaptive adolescent traits have been associated with development of the medial prefrontal cortex (mPFC), a brain region that mediates regulatory control of behavior. However, the molecular changes that underlie brain development and behavioral vulnerability have not been fully characterized. Using high-throughput 2D DIGE spot profiling with identification by MALDI-TOF mass spectrometry, we identified 62 spots in the PFC that exhibited age-dependent differences in expression. Identified proteins were associated with diverse cellular functions, including intracellular signaling, synaptic plasticity, cellular organization and metabolism. Separate Western blot analyses confirmed age-related changes in DPYSL2, DNM1, STXBP1 and CFL1 in the mPFC and expanded these findings to the dorsal striatum, nucleus accumbens, motor cortex, amygdala and ventral tegmental area. Ingenuity Pathway Analysis (IPA) identified functional interaction networks enriched with proteins identified in the proteomics screen, linking age-related alterations in protein expression to cellular assembly and development, cell signaling and behavior, and psychiatric illness. These results provide insight into potential molecular components of adolescent cortical development, implicating structural processes that begin during embryonic development as well as plastic adaptations in signaling that may work in concert to bring the cortex, and other brain regions, into maturity.

Preclinical evaluation of convection-enhanced delivery of liposomal doxorubicin to treat pediatric diffuse intrinsic pontine glioma and thalamic high-grade glioma

OBJECTIVE Pediatric high-grade gliomas (pHGGs) including diffuse intrinsic pontine gliomas (DIPGs) are primary brain tumors with high mortality and morbidity. Because of their poor brain penetrance, systemic chemotherapy regimens have failed to deliver satisfactory results; however, convection-enhanced delivery (CED) may be an alternative mode of drug delivery. Anthracyclines are potent chemotherapeutics that have been successfully delivered via CED in preclinical supratentorial glioma models. This study aims to assess the potency of anthracyclines against DIPG and pHGG cell lines in vitro and to evaluate the efficacy of CED with anthracyclines in orthotopic pontine and thalamic tumor models. METHODS The sensitivity of primary pHGG cell lines to a range of anthracyclines was tested in vitro. Preclinical CED of free doxorubicin and pegylated liposomal doxorubicin (PLD) to the brainstem and thalamus of naïve nude mice was performed. The maximum tolerated dose (MTD) was determined based on the observation of clinical symptoms, and brains were analyzed after H & E staining. Efficacy of the MTD was tested in adult glioma E98-FM-DIPG and E98-FM-thalamus models and in the HSJD-DIPG-007-Fluc primary DIPG model. RESULTS Both pHGG and DIPG cells were sensitive to anthracyclines in vitro. Doxorubicin was selected for further preclinical evaluation. Convection-enhanced delivery of the MTD of free doxorubicin and PLD in the pons was 0.02 mg/ml, and the dose tolerated in the thalamus was 10 times higher (0.2 mg/ml). Free doxorubicin or PLD via CED was ineffective against E98-FM-DIPG or HSJD-DIPG-007-Fluc in the brainstem; however, when applied in the thalamus, 0.2 mg/ml of PLD slowed down tumor growth and increased survival in a subset of animals with small tumors. CONCLUSIONS Local delivery of doxorubicin to the brainstem causes severe toxicity, even at doxorubicin concentrations that are safe in the thalamus. As a consequence, the authors could not establish a therapeutic window for treating orthotopic brainstem tumors in mice. For tumors in the thalamus, therapeutic concentrations to slow down tumor growth could be reached. These data suggest that anatomical location determines the severity of toxicity after local delivery of therapeutic agents and that caution should be used when translating data from supratentorial CED studies to treat infratentorial tumors.

Prefrontal Dopaminergic Mechanisms of Extinction in Adolescence Compared to Adulthood in Rats

Adolescents with anxiety disorders attain poorer outcomes following extinction-based treatment compared to adults. Extinction deficit during adolescence has been identified to involve immaturity in the medial prefrontal cortex (mPFC). Findings from adult rodents suggest extinction involves dopamine signaling in the mPFC. This system changes dramatically during adolescence, but its role in adolescent extinction is unknown. Therefore, we investigated the role of prefrontal dopamine in extinction using Pavlovian fear conditioning in adolescent and adult rats. Using quantitative PCR (qPCR) analyses, we measured changes in dopamine receptor gene expression in the mPFC before and after extinction. We then enhanced dopamine 1 receptor (D1R) or dopamine 2 receptor (D2R) signaling in the infralimbic cortex (IL) of the mPFC using agonists at the time of extinction. Adolescent rats displayed a deficit in extinction retention compared to adults. Extinction induced a reduction in D1R compared to D2R gene expression in adolescent rats, whereas an increase of D1R compared to D2R gene expression was observed in adult rats. Acutely enhancing IL D1R signaling using SKF-81297 had no effect on extinction at either age. In contrast, acutely enhancing IL D2R signaling with quinpirole significantly enhanced long-term extinction in adolescents, and impaired within-session extinction in adults. Our results suggest a dissociated role for prefrontal dopamine in fear extinction during adolescence compared to adulthood. Findings highlight the dopamine system as a potential pharmacological target to improve extinction-based treatments for adolescents.

Inflammation and the neural diathesis-stress hypothesis of schizophrenia: a reconceptualization

An interaction between external stressors and intrinsic vulnerability is one of the longest standing pathoaetiological explanations for schizophrenia. However, novel lines of evidence from genetics, preclinical studies, epidemiology and imaging have shed new light on the mechanisms that may underlie this, implicating microglia as a key potential mediator. Microglia are the primary immune cells of the central nervous system. They have a central role in the inflammatory response, and are also involved in synaptic pruning and neuronal remodeling. In addition to immune and traumatic stimuli, microglial activation occurs in response to psychosocial stress. Activation of microglia perinatally may make them vulnerable to subsequent overactivation by stressors experienced in later life. Recent advances in genetics have shown that variations in the complement system are associated with schizophrenia, and this system has been shown to regulate microglial synaptic pruning. This suggests a mechanism via which genetic and environmental influences may act synergistically and lead to pathological microglial activation. Microglial overactivation may lead to excessive synaptic pruning and loss of cortical gray matter. Microglial mediated damage to stress-sensitive regions such as the prefrontal cortex and hippocampus may lead directly to cognitive and negative symptoms, and account for a number of the structural brain changes associated with the disorder. Loss of cortical control may also lead to disinhibition of subcortical dopamine-thereby leading to positive psychotic symptoms. We review the preclinical and in vivo evidence for this model and consider the implications this has for treatment, and future directions.

Myelination of parvalbumin interneurons: a parsimonious locus of pathophysiological convergence in schizophrenia

Schizophrenia is a debilitating psychiatric disorder characterized by positive, negative and cognitive symptoms. Despite more than a century of research, the neurobiological mechanism underlying schizophrenia remains elusive. White matter abnormalities and interneuron dysfunction are the most widely replicated cellular neuropathological alterations in patients with schizophrenia. However, a unifying model incorporating these findings has not yet been established. Here, we propose that myelination of fast-spiking parvalbumin (PV) interneurons could be an important locus of pathophysiological convergence in schizophrenia. Myelination of interneurons has been demonstrated across a wide diversity of brain regions and appears highly specific for the PV interneuron subclass. Given the critical influence of fast-spiking PV interneurons for mediating oscillations in the gamma frequency range (~30-120 Hz), PV myelination is well positioned to optimize action potential fidelity and metabolic homeostasis. We discuss this hypothesis with consideration of data from human postmortem studies, in vivo brain imaging and electrophysiology, and molecular genetics, as well as fundamental and translational studies in rodent models. Together, the parvalbumin interneuron myelination hypothesis provides a falsifiable model for guiding future studies of schizophrenia pathophysiology.

Parvalbumin neurons and perineuronal nets in the mouse prefrontal cortex

The prefrontal cortex (PFC) plays a key role in cognitive functions, memory, and attention. Alterations in parvalbumin interneurons (PV neurons) and perineuronal nets (PNNs) within the PFC have been implicated in schizophrenia and autism spectrum disorder pathology. However, it remains unclear why PV neurons and PNNs in the PFC are selectively impaired. Here we aimed to clarify if PV neurons and PNNs in the PFC have region-specific features. We found that PV neurons and PNNs were increased in a region-specific manner in the PFC during postnatal development. In the mature PFC, the expression of PV protein is lower than in other parts of the cortex. Furthermore, PNNs in the mature PFC are not typical lattice-like structures and do not have the major components of PNNs and tenascin-R. The present study indicates that PV neurons and PNNs have region-specific features, and our results suggest that PV neurons and PNNs have structural vulnerability within the PFC.

microRNAs and the adolescent brain: Filling the knowledge gap

Over two decades ago the discovery of microRNAs (miRNA) broadened our understanding of the diverse molecular pathways mediating post-transcriptional control over gene expression. These small non-coding RNAs dynamically fluctuate, temporally and spatially, throughout the lifespan of all organisms. The fundamental role that miRNAs have in shaping embryonic neurodevelopment provides strong evidence that adolescent brain remodeling could be rooted in the changing miRNA landscape of the cell. Few studies have directly measured miRNA gene expression changes in the brain across pubertal development, and even less is known about the functional impact of those miRNAs on the maturational processes that occur in the developing adolescent brain. This review summarizes miRNA biogenesis and function in the brain in the context of normal (i.e. not diseased) physiology. These landmark studies can guide predictions about the role of miRNAs in facilitating maturation of the adolescent brain. However, there are clear indicators that adolescence/puberty is a unique life stage, suggesting miRNA function during adolescence is distinct from those in any other previously described system.

Redox dysregulation, neuroinflammation, and NMDA receptor hypofunction: A "central hub" in schizophrenia pathophysiology?

Accumulating evidence points to altered GABAergic parvalbumin-expressing interneurons and impaired myelin/axonal integrity in schizophrenia. Both findings could be due to abnormal neurodevelopmental trajectories, affecting local neuronal networks and long-range synchrony and leading to cognitive deficits. In this review, we present data from animal models demonstrating that redox dysregulation, neuroinflammation and/or NMDAR hypofunction (as observed in patients) impairs the normal development of both parvalbumin interneurons and oligodendrocytes. These observations suggest that a dysregulation of the redox, neuroimmune, and glutamatergic systems due to genetic and early-life environmental risk factors could contribute to the anomalies of parvalbumin interneurons and white matter in schizophrenia, ultimately impacting cognition, social competence, and affective behavior via abnormal function of micro- and macrocircuits. Moreover, we propose that the redox, neuroimmune, and glutamatergic systems form a "central hub" where an imbalance within any of these "hub" systems leads to similar anomalies of parvalbumin interneurons and oligodendrocytes due to the tight and reciprocal interactions that exist among these systems. A combination of vulnerabilities for a dysregulation within more than one of these systems may be particularly deleterious. For these reasons, molecules, such as N-acetylcysteine, that possess antioxidant and anti-inflammatory properties and can also regulate glutamatergic transmission are promising tools for prevention in ultra-high risk patients or for early intervention therapy during the first stages of the disease.

Nonlinear transcriptomic response to dietary fat intake in the small intestine of C57BL/6J mice

BACKGROUND

A high caloric diet, in conjunction with low levels of physical activity, promotes obesity. Many studies are available regarding the relation between dietary saturated fats and the etiology of obesity, but most focus on liver, muscle and white adipose tissue. Furthermore, the majority of transcriptomic studies seek to identify linear effects of an external stimulus on gene expression, although such an assumption does not necessarily hold. Our work assesses the dose-dependent effects of dietary fat intake on differential gene expression in the proximal, middle and distal sections of the small intestine in C57BL/6J mice. Gene expression is analyzed in terms of either linear or nonlinear responses to fat intake.

RESULTS

The highest number of differentially expressed genes was observed in the middle section. In all intestine sections, most of the identified processes exhibited a linear response to increasing fat intake. The relative importance of logarithmic and exponential responses was higher in the proximal and distal sections, respectively. Functional enrichment analysis highlighted a constantly linear regulation of acute-phase response along the whole small intestine, with up-regulation of Serpina1b. The study of gene expression showed that exponential down-regulation of cholesterol transport in the middle section is coupled with logarithmic up-regulation of cholesterol homeostasis. A shift from linear to exponential response was observed in genes involved in the negative regulation of caspase activity, from middle to distal section (e.g., Birc5, up-regulated).

CONCLUSIONS

The transcriptomic signature associated with inflammatory processes preserved a linear response in the whole small intestine (e.g., up-regulation of Serpina1b). Processes related to cholesterol homeostasis were particularly active in the middle small intestine and only the highest fat intake down-regulated cholesterol transport and efflux (with a key role played by the down-regulation of ATP binding cassette transporters). Characterization of nonlinear patterns of gene expression triggered by different levels of dietary fat is an absolute novelty in intestinal studies. This approach helps identifying which processes are overloaded (i.e., positive, logarithmic regulation) or arrested (i.e., negative, exponential regulation) in response to excessive fat intake, and can shed light on the relationships linking lipid intake to obesity and its associated molecular disturbances.

Evidence of Mitochondrial Dysfunction within the Complex Genetic Etiology of Schizophrenia

Genetic evidence has supported the hypothesis that schizophrenia (SZ) is a polygenic disorder caused by the disruption in function of several or many genes. The most common and reproducible cellular phenotype associated with SZ is a reduction in dendritic spines within the neocortex, suggesting alterations in dendritic architecture may cause aberrant cortical circuitry and SZ symptoms. Here, we review evidence supporting a multifactorial model of mitochondrial dysfunction in SZ etiology and discuss how these multiple paths to mitochondrial dysfunction may contribute to dendritic spine loss and/or underdevelopment in some SZ subjects. The pathophysiological role of mitochondrial dysfunction in SZ is based upon genomic analyses of both the mitochondrial genome and nuclear genes involved in mitochondrial function. Previous studies and preliminary data suggest SZ is associated with specific alleles and haplogroups of the mitochondrial genome, and also correlates with a reduction in mitochondrial copy number and an increase in synonymous and nonsynonymous substitutions of mitochondrial DNA. Mitochondrial dysfunction has also been widely implicated in SZ by genome-wide association, exome sequencing, altered gene expression, proteomics, microscopy analyses, and induced pluripotent stem cell studies. Together, these data support the hypothesis that SZ is a polygenic disorder with an enrichment of mitochondrial targets.

GDH-Dependent Glutamate Oxidation in the Brain Dictates Peripheral Energy Substrate Distribution

Glucose, the main energy substrate used in the CNS, is continuously supplied by the periphery. Glutamate, the major excitatory neurotransmitter, is foreseen as a complementary energy contributor in the brain. In particular, astrocytes actively take up glutamate and may use it through oxidative glutamate dehydrogenase (GDH) activity. Here, we investigated the significance of glutamate as energy substrate for the brain. Upon glutamate exposure, astrocytes generated ATP in a GDH-dependent way. The observed lack of glutamate oxidation in brain-specific GDH null CnsGlud1(-/-) mice resulted in a central energy-deprivation state with increased ADP/ATP ratios and phospho-AMPK in the hypothalamus. This induced changes in the autonomous nervous system balance, with increased sympathetic activity promoting hepatic glucose production and mobilization of substrates reshaping peripheral energy stores. Our data reveal the importance of glutamate as necessary energy substrate for the brain and the role of central GDH in the regulation of whole-body energy homeostasis.

Pre-B-cell leukemia homeobox interacting protein 1 is overexpressed in astrocytoma and promotes tumor cell growth and migration

BACKGROUND

Glial brain tumors cause considerable mortality and morbidity in children and adults. Innovative targets for therapy are needed to improve survival and reduce long-term sequelae. The aim of this study was to find a candidate tumor-promoting protein, abundantly expressed in tumor cells but not in normal brain tissues, as a potential target for therapy.

METHODS

In silico proteomics and genomics, immunohistochemistry, and immunofluorescence microscopy validation were performed. RNA interference was used to ascertain the functional role of the overexpressed candidate target protein.

RESULTS

In silico proteomics and genomics revealed pre-B-cell leukemia homeobox (PBX) interacting protein 1 (PBXIP1) overexpression in adult and childhood high-grade glioma and ependymoma compared with normal brain. PBXIP1 is a PBX-family interacting microtubule-binding protein with a putative role in migration and proliferation of cancer cells. Immunohistochemical studies in glial tumors validated PBXIP1 expression in astrocytoma and ependymoma but not in oligodendroglioma. RNAi-mediated PBXIP1-knockdown in glioblastoma cell lines strongly reduced proliferation and migration and induced morphological changes, indicating that PBXIP1 knockdown decreases glioma cell viability and motility through rearrangements of the actin cytoskeleton. Furthermore, expression of PBXIP1 was observed in radial glia and astrocytic progenitor cells in human fetal tissues, suggesting that PBXIP1 is an astroglial progenitor cell marker during human embryonic development.

CONCLUSION

PBXIP1 is a novel protein overexpressed in astrocytoma and ependymoma, involved in tumor cell proliferation and migration, that warrants further exploration as a novel therapeutic target in these tumors.

Glutathione deficit impairs myelin maturation: relevance for white matter integrity in schizophrenia patients

Schizophrenia pathophysiology implies both abnormal redox control and dysconnectivity of the prefrontal cortex, partly related to oligodendrocyte and myelin impairments. As oligodendrocytes are highly vulnerable to altered redox state, we investigated the interplay between glutathione and myelin. In control subjects, multimodal brain imaging revealed a positive association between medial prefrontal glutathione levels and both white matter integrity and resting-state functional connectivity along the cingulum bundle. In early psychosis patients, only white matter integrity was correlated with glutathione levels. On the other side, in the prefrontal cortex of peripubertal mice with genetically impaired glutathione synthesis, mature oligodendrocyte numbers, as well as myelin markers, were decreased. At the molecular levels, under glutathione-deficit conditions induced by short hairpin RNA targeting the key glutathione synthesis enzyme, oligodendrocyte progenitors showed a decreased proliferation mediated by an upregulation of Fyn kinase activity, reversed by either the antioxidant N-acetylcysteine or Fyn kinase inhibitors. In addition, oligodendrocyte maturation was impaired. Interestingly, the regulation of Fyn mRNA and protein expression was also impaired in fibroblasts of patients deficient in glutathione synthesis. Thus, glutathione and redox regulation have a critical role in myelination processes and white matter maturation in the prefrontal cortex of rodent and human, a mechanism potentially disrupted in schizophrenia.

Modular organization of the white spruce (Picea glauca) transcriptome reveals functional organization and evolutionary signatures

Transcript profiling has shown the molecular bases of several biological processes in plants but few studies have developed an understanding of overall transcriptome variation. We investigated transcriptome structure in white spruce (Picea glauca), aiming to delineate its modular organization and associated functional and evolutionary attributes. Microarray analyses were used to: identify and functionally characterize groups of co-expressed genes; investigate expressional and functional diversity of vascular tissue preferential genes which were conserved among Picea species, and identify expression networks underlying wood formation. We classified 22 857 genes as variable (79%; 22 coexpression groups) or invariant (21%) by profiling across several vegetative tissues. Modular organization and complex transcriptome restructuring among vascular tissue preferential genes was revealed by their assignment to coexpression groups with partially overlapping profiles and partially distinct functions. Integrated analyses of tissue-based and temporally variable profiles identified secondary xylem gene networks, showed their remodelling over a growing season and identified PgNAC-7 (no apical meristerm (NAM), Arabidopsis transcription activation factor (ATAF) and cup-shaped cotyledon (CUC) transcription factor 007 in Picea glauca) as a major hub gene specific to earlywood formation. Reference profiling identified comprehensive, statistically robust coexpressed groups, revealing that modular organization underpins the evolutionary conservation of the transcriptome structure.

Sensory Deprivation during Early Postnatal Period Alters the Density of Interneurons in the Mouse Prefrontal Cortex

Early loss of one sensory system can cause improved function of other sensory systems. However, both the time course and neuronal mechanism of cross-modal plasticity remain elusive. Recent study using functional MRI in humans suggests a role of the prefrontal cortex (PFC) in cross-modal plasticity. Since this phenomenon is assumed to be associated with altered GABAergic inhibition in the PFC, we have tested the hypothesis that early postnatal sensory deprivation causes the changes of inhibitory neuronal circuit in different regions of the PFC of the mice. We determined the effects of sensory deprivation from birth to postnatal day 28 (P28) or P58 on the density of parvalbumin (PV), calbindin (CB), and calretinin (CR) neurons in the prelimbic, infralimbic, and dorsal anterior cingulate cortices. The density of PV and CB neurons was significantly increased in layer 5/6 (L5/6). Moreover, the density of CR neurons was higher in L2/3 in sensory deprived mice compared to intact mice. These changes were more prominent at P56 than at P28. These results suggest that long-term sensory deprivation causes the changes of intracortical inhibitory networks in the PFC and the changes of inhibitory networks in the PFC may contribute to cross-modal plasticity.

Associations between DNA methylation and schizophrenia-related intermediate phenotypes - a gene set enrichment analysis

Multiple genetic approaches have identified microRNAs as key effectors in psychiatric disorders as they post-transcriptionally regulate expression of thousands of target genes. However, their role in specific psychiatric diseases remains poorly understood. In addition, epigenetic mechanisms such as DNA methylation, which affect the expression of both microRNAs and coding genes, are critical for our understanding of molecular mechanisms in schizophrenia. Using clinical, imaging, genetic, and epigenetic data of 103 patients with schizophrenia and 111 healthy controls of the Mind Clinical Imaging Consortium (MCIC) study of schizophrenia, we conducted gene set enrichment analysis to identify markers for schizophrenia-associated intermediate phenotypes. Genes were ranked based on the correlation between DNA methylation patterns and each phenotype, and then searched for enrichment in 221 predicted microRNA target gene sets. We found the predicted hsa-miR-219a-5p target gene set to be significantly enriched for genes (EPHA4, PKNOX1, ESR1, among others) whose methylation status is correlated with hippocampal volume independent of disease status. Our results were strengthened by significant associations between hsa-miR-219a-5p target gene methylation patterns and hippocampus-related neuropsychological variables. IPA pathway analysis of the respective predicted hsa-miR-219a-5p target genes revealed associated network functions in behavior and developmental disorders. Altered methylation patterns of predicted hsa-miR-219a-5p target genes are associated with a structural aberration of the brain that has been proposed as a possible biomarker for schizophrenia. The (dys)regulation of microRNA target genes by epigenetic mechanisms may confer additional risk for developing psychiatric symptoms. Further study is needed to understand possible interactions between microRNAs and epigenetic changes and their impact on risk for brain-based disorders such as schizophrenia.

Neuregulin 1 expression and electrophysiological abnormalities in the Neuregulin 1 transmembrane domain heterozygous mutant mouse

Background

The Neuregulin 1 transmembrane domain heterozygous mutant (Nrg1 TM HET) mouse is used to investigate the role of Nrg1 in brain function and schizophrenia-like behavioural phenotypes. However, the molecular alterations in brain Nrg1 expression that underpin the behavioural observations have been assumed, but not directly determined. Here we comprehensively characterise mRNA Nrg1 transcripts throughout development of the Nrg1 TM HET mouse. In addition, we investigate the regulation of high-frequency (gamma) electrophysiological oscillations in this mutant mouse to associate molecular changes in Nrg1 with a schizophrenia-relevant neurophysiological profile.

Methods

Using exonic probes spanning the cysteine-rich, epidermal growth factor (EGF)-like, transmembrane and intracellular domain encoding regions of Nrg1, mRNA levels were measured using qPCR in hippocampus and frontal cortex from male and female Nrg1 TM HET and wild type-like (WT) mice throughout development. We also performed electrophysiological recordings in adult mice and analysed gamma oscillatory at baseline, in responses to auditory stimuli and to ketamine.

Results

In both hippocampus and cortex, Nrg1 TM HET mice show significantly reduced expression of the exon encoding the transmembrane domain of Nrg1 compared with WT, but unaltered mRNA expression encoding the extracellular bioactive EGF-like and the cysteine-rich (type III) domains, and development-specific and region-specific reductions in the mRNA encoding the intracellular domain. Hippocampal Nrg1 protein expression was not altered, but NMDA receptor NR2B subunit phosphorylation was lower in Nrg1 TM HET mice. We identified elevated ongoing and reduced sensory-evoked gamma power in Nrg1 TM HET mice.

Interpretation

We found no evidence to support the claim that the Nrg1 TM HET mouse represents a simple haploinsufficient model. Further research is required to explore the possibility that mutation results in a gain of Nrg1 function.

EFEMP1 induces γ-secretase/Notch-mediated temozolomide resistance in glioblastoma

Glioblastoma is the most common malignant primary brain tumor. Temozolomide (TMZ) is the standard chemotherapeutic agent for this disease. However, intrinsic and acquired TMZ-resistance represents a major obstacle for this therapy. In order to identify factors involved in TMZ-resistance, we engineered different TMZ-resistant glioblastoma cell lines. Gene expression analysis demonstrated that EFEMP1, an extracellular matrix protein, is associated with TMZ-resistant phenotype. Silencing of EFEMP1 in glioblastoma cells resulted in decreased cell survival following TMZ treatment, whereas overexpression caused TMZ-resistance. EFEMP1 acts via multiple signaling pathways, including γ-secretase-mediated activation of the Notch pathway. We show that inhibition of γ-secretase by RO4929097 causes at least partial sensitization of glioblastoma cells to temozolomide in vitro and in vivo. In addition, we show that EFEMP1 expression levels correlate with survival in TMZ-treated glioblastoma patients. Altogether our results suggest EFEMP1 as a potential therapeutic target to overcome TMZ-resistance in glioblastoma.