The brain tumor microenvironment

The transcriptome and miRNome profiling of glioblastoma tissues and peritumoral regions highlights molecular pathways shared by tumors and surrounding areas and reveals differences between short-term and long-term survivors

Glioblastoma multiforme (GBM) is the most common and deadliest primary brain tumor, driving patients to death within 15 months after diagnosis (short term survivors, ST), with the exception of a small fraction of patients (long term survivors, LT) surviving longer than 36 months. Here we present deep sequencing data showing that peritumoral (P) areas differ from healthy white matter, but share with their respective frankly tumoral (C) samples, a number of mRNAs and microRNAs representative of extracellular matrix remodeling, TGFβ and signaling, of the involvement of cell types different from tumor cells but contributing to tumor growth, such as microglia or reactive astrocytes. Moreover, we provide evidence about RNAs differentially expressed in ST vs LT samples, suggesting the contribution of TGF-β signaling in this distinction too. We also show that the edited form of miR-376c-3p is reduced in C vs P samples and in ST tumors compared to LT ones. As a whole, our study provides new insights into the still puzzling distinction between ST and LT tumors, and sheds new light onto that "grey" zone represented by the area surrounding the tumor, which we show to be characterized by the expression of several molecules shared with the proper tumor mass.

Glioma-induced inhibition of caspase-3 in microglia promotes a tumor-supportive phenotype

Glioma cells recruit and exploit microglia (the resident immune cells of the brain) for their proliferation and invasion ability. The underlying molecular mechanism used by glioma cells to transform microglia into a tumor-supporting phenotype has remained elusive. We found that glioma-induced microglia conversion was coupled to a reduction in the basal activity of microglial caspase-3 and increased S-nitrosylation of mitochondria-associated caspase-3 through inhibition of thioredoxin-2 activity, and that inhibition of caspase-3 regulated microglial tumor-supporting function. Furthermore, we identified the activity of nitric oxide synthase 2 (NOS2, also known as iNOS) originating from the glioma cells as a driving stimulus in the control of microglial caspase-3 activity. Repression of glioma NOS2 expression in vivo led to a reduction in both microglia recruitment and tumor expansion, whereas depletion of microglial caspase-3 gene promoted tumor growth. Our results provide evidence that inhibition of the denitrosylation of S-nitrosylated procaspase-3 mediated by the redox protein Trx2 is a part of the microglial pro-tumoral activation pathway initiated by glioma cancer cells.

Adhering towards tumorigenicity: altered adhesion mechanisms in glioblastoma cancer stem cells

Glioblastoma (GBM) is the most aggressive malignant primary brain tumor in adults with a high recurrence and mortality rate. GBM tumors contain a high degree of cellular heterogeneity, with cells exhibiting stem-like properties (cancer stem cells; CSCs) that are highly efficient at tumor initiation and are resistant to conventional therapies. CSCs interact with their tumor microenvironment by a large group of diverse cell adhesion molecules (CAMs) that participate in intercellular, intracellular and cell-extracellular matrix interactions. Despite the initial description of CAMs as tumor suppressors, recent work has highlighted specific CAMs that are essential for CSC maintenance and tumor progression. This review will highlight recent findings that provide support for a context-specific role of CAMs in CSC function and GBM progression.

Magnetic Resonance Imaging-Based Radiomic Profiles Predict Patient Prognosis in Newly Diagnosed Glioblastoma Before Therapy

Magnetic resonance imaging (MRI) is used to diagnose and monitor brain tumors. Extracting additional information from medical imaging and relating it to a clinical variable of interest is broadly defined as radiomics. Here, multiparametric MRI radiomic profiles (RPs) of de novo glioblastoma (GBM) brain tumors is related with patient prognosis. Clinical imaging from 81 patients with GBM before surgery was analyzed. Four MRI contrasts were aligned, masked by margins defined by gadolinium contrast enhancement and T2/fluid attenuated inversion recovery hyperintensity, and contoured based on image intensity. These segmentations were combined for visualization and quantification by assigning a 4-digit numerical code to each voxel to indicate the segmented RP. Each RP volume was then compared with overall survival. A combined classifier was then generated on the basis of significant RPs and optimized volume thresholds. Five RPs were predictive of overall survival before therapy. Combining the RP classifiers into a single prognostic score predicted patient survival better than each alone (P < .005). Voxels coded with 1 RP associated with poor prognosis were pathologically confirmed to contain hypercellular tumor. This study applies radiomic profiling to de novo patients with GBM to determine imaging signatures associated with poor prognosis at tumor diagnosis. This tool may be useful for planning surgical resection or radiation treatment margins.

Progenitor/Stem Cell Markers in Brain Adjacent to Glioblastoma: GD3 Ganglioside and NG2 Proteoglycan Expression

Characterization of tissue surrounding glioblastoma (GBM) is a focus for translational research because tumor recurrence invariably occurs in this area. We investigated the expression of the progenitor/stem cell markers GD3 ganglioside and NG2 proteoglycan in GBM, peritumor tissue (brain adjacent to tumor, BAT) and cancer stem-like cells (CSCs) isolated from GBM (GCSCs) and BAT (PCSCs). GD3 and NG2 immunohistochemistry was performed in paired GBM and BAT specimens from 40 patients. Double-immunofluorescence was carried out to characterize NG2-positive cells of vessel walls. GD3 and NG2 expression was investigated in GCSCs and PCSCs whose tumorigenicity was also evaluated in Scid/bg mice. GD3 and NG2 expression was higher in tumor tissue than in BAT. NG2 decreased as the distance from tumor margin increased, regardless of the tumor cell presence, whereas GD3 correlated with neoplastic infiltration. In BAT, NG2 was coexpressed with a-smooth muscle actin (a-SMA) in pericytes and with nestin in the endothelium. Higher levels of NG2 mRNA and protein were found in GCSCs while GD3 synthase was expressed at similar levels in the 2 CSC populations. PCSCs had lower tumorigenicity than GCSCs. These data suggest the possible involvement of GD3 and NG2 in pre/pro-tumorigenic events occurring in the complex microenvironment of the tissue surrounding GBM.

Increased expression of platelet-derived growth factor associated protein-1 is associated with PDGF-B mediated glioma progression

The current treatment therapies available for malignant gliomas are inadequate. There is an urgent need to develop more effective therapies by characterizing the molecular pathogenesis of the disease. Over expression of platelet-derived growth factor (PDGF) ligands and receptors have been reported in malignant gliomas. Platelet-derived growth factor associated protein-1 (PDAP-1) is reported to modulate the mitogenic activity of PDGF ligands, but to date, there is no information concerning its role in PDGF-mediated glioma cell proliferation. This study aimed to characterize the role of PDAP-1 in PDGF-mediated glioma proliferation. The expression of PDAP-1 was observed to be significantly increased (p<0.05) in grade IV glioma tissue and cell lines compared to grade III. siRNA-mediated knockdown of PDAP-1 reduced the expression of PDGF-B and its downstream genes (Akt1/Protein kinase B (PKB) and phosphoinositide-dependent kinase-1 (PDK1) by up to 50%. In PDAP-1 knockdown glioma cells, more than a twofold reduction was also observed in the level of phosphorylated Akt. Interestingly, knockdown of PDAP-1 in combination with PDGF-B antibody inhibited glioma cell proliferation through activation of Caspase 3/7 and 9. We also demonstrate that PDAP-1 co-localizes with PDGF-B in the cytoplasm of glioma cells, and an interaction between both of the proteins was established. Collectively, these findings suggest that the expression of PDAP-1 is associated with disease malignancy, and its inhibition reduced the proliferation of malignant glioma cells through down-regulation of PDGF-B/Akt/PDK1 signaling. Thus, this study establishes PDAP-1 as an effecter of PDGF signaling in glioma cells and suggests that it could also be a promising therapeutic target.

Antitumor activity of combined endostatin and thymidine kinase gene therapy in C6 glioma models

The combination of Endostatin (ES) and Herpes Simplex Virus thymidine kinase (HSV‐TK) gene therapy is known to have antitumor activity in bladder cancer. The potential effect of ES and TK therapy in glioma has not yet been investigated. In this study, pTK‐internal ribosome entry site (IRES), pIRES‐ES, and pTK‐IRES‐ES plasmids were constructed; pIRES empty vector served as the negative control. The recombinant constructs were transfected into human umbilical vein endothelial cells (HUVECs) ECV304 and C6 rat glioma cell line. Ganciclovir (GCV) was used to induce cell death in transfected C6 cells. We found that ECV304 cells expressing either ES or TK‐ES showed reduced proliferation, decreased migration capacity, and increased apoptosis, as compared to untransfected cells or controls. pTK‐IRES‐ES/GCV or pTK‐IRES/GCV significantly suppressed cell proliferation and induced cell apoptosis in C6 cells, as compared to the control. In addition, the administration of pIRES‐ES, pTK‐IRES/GCV, or pTK‐IRES‐ES/GCV therapy improved animal activity and behavior; was associated with prolonged animal survival, and a lower microvessel density (MVD) value in tumor tissues of C6 glioma rats. In comparison to others, dual gene therapy in form of pTK‐IRES‐ES/GCV had a significant antitumor activity against C6 glioma. These findings indicate combined TK and ES gene therapy was associated with a superior antitumor efficacy as compared to single gene therapy in C6 glioma.

Differential propagation of stroma and cancer stem cells dictates tumorigenesis and multipotency

Glioblastoma Multiforme (GBM) is characterized by high cancer cell heterogeneity and the presence of a complex tumor microenvironment. Those factors are a key obstacle for the treatment of this tumor type. To model the disease in mice, the current strategy is to grow GBM cells in serum-free non-adherent condition, which maintains their tumor-initiating potential. However, the so-generated tumors are histologically different from the one of origin. In this work, we performed high-throughput marker expression analysis and investigated the tumorigenicity of GBM cells enriched under different culture conditions. We identified a marker panel that distinguished tumorigenic sphere cultures from non-tumorigenic serum cultures (high CD56, SOX2, SOX9, and low CD105, CD248, αSMA). Contrary to previous work, we found that 'mixed cell cultures' grown in serum conditions are tumorigenic and express cancer stem cell (CSC) markers. As well, 1% serum plus bFGF and TGF-α preserved the tumorigenicity of sphere cultures and induced epithelial-to-mesenchymal transition gene expression. Furthermore, we identified 12 genes that could replace the 840 genes of The Cancer Genome Atlas (TCGA) used for GBM-subtyping. Our data suggest that the tumorigenicity of GBM cultures depend on cell culture strategies that retain CSCs in culture rather than the presence of serum in the cell culture medium.

Phenotypic dynamics of microglial and monocyte-derived cells in glioblastoma-bearing mice

Inflammatory cells, an integral component of tumor evolution, are present in Glioblastomas multiforme (GBM). To address the cellular basis and dynamics of the inflammatory microenvironment in GBM, we established an orthotopic syngenic model by grafting GL261-DsRed cells in immunocompetent transgenic LysM-EGFP//CD11c-EYFP reporter mice. We combined dynamic spectral two-photon imaging with multiparametric cytometry and multicolor immunostaining to characterize spatio-temporal distribution, morphology and activity of microglia and blood-derived infiltrating myeloid cells in live mice. Early stages of tumor development were dominated by microglial EYFP⁺ cells invading the tumor, followed by massive recruitment of circulating LysM-EGFP⁺ cells. Fluorescent invading cells were conventional XCR1⁺ and monocyte-derived dendritic cells distributed in subpopulations of different maturation stages, located in different areas relative to the tumor core. The lethal stage of the disease was characterized by the progressive accumulation of EGFP⁺/EYFP⁺ monocyte-derived dendritic cells. This local phenotypic regulation of monocyte subtypes marked a transition in the immune response.

Immunological Evasion in Glioblastoma

Glioblastoma is the most aggressive tumor in Central Nervous System in adults. Among its features, modulation of immune system stands out. Although immune system is capable of detecting and eliminating tumor cells mainly by cytotoxic T and NK cells, tumor microenvironment suppresses an effective response through recruitment of modulator cells such as regulatory T cells, monocyte-derived suppressor cells, M2 macrophages, and microglia as well as secretion of immunomodulators including IL-6, IL-10, CSF-1, TGF-β, and CCL2. Other mechanisms that induce immunosuppression include enzymes as indolamine 2,3-dioxygenase. For this reason it is important to develop new therapies that avoid this immune evasion to promote an effective response against glioblastoma.

NLR-regulated pathways in cancer: opportunities and obstacles for therapeutic interventions

NLRs (nucleotide-binding domain, leucine-rich repeat containing receptors) are pattern recognition receptors associated with immunity and inflammation in response to endogenous and exogenous pathogen and damage associated molecular patterns (PAMPs and DAMPs respectively). Dysregulated NLR function is associated with several diseases including cancers, metabolic diseases, autoimmune disorders and autoinflammatory syndromes. In the last decade, distinct cell and organ specific roles for NLRs have been identified however; their roles in cancer initiation, development and progression remain controversial. This review summarizes the emerging role of NLRs in cancer and their possible future as targets for cancer therapeutics.

Gap junctions modulate glioma invasion by direct transfer of microRNA

The invasiveness of high-grade glioma is the primary reason for poor survival following treatment. Interaction between glioma cells and surrounding astrocytes are crucial to invasion. We investigated the role of gap junction mediated miRNA transfer in this context. By manipulating gap junctions with a gap junction inhibitor, siRNAs, and a dominant negative connexin mutant, we showed that functional glioma-glioma gap junctions suppress glioma invasion while glioma-astrocyte and astrocyte-astrocyte gap junctions promote it in an in vitro transwell invasion assay. After demonstrating that glioma-astrocyte gap junctions are permeable to microRNA, we compared the microRNA profiles of astrocytes before and after co-culture with glioma cells, identifying specific microRNAs as candidates for transfer through gap junctions from glioma cells to astrocytes. Further analysis showed that transfer of miR-5096 from glioma cells to astrocytes is through gap junctions; this transfer is responsible, in part, for the pro-invasive effect. Our results establish a role for glioma-astrocyte gap junction mediated microRNA signaling in modulation of glioma invasive behavior, and that gap junction coupling among astrocytes magnifies the pro-invasive signaling. Our findings reveal the potential for therapeutic interventions based on abolishing alteration of stromal cells by tumor cells via manipulation of microRNA and gap junction channel activity.

Loss of CX3CR1 increases accumulation of inflammatory monocytes and promotes gliomagenesis

The most abundant populations of non-neoplastic cells in the glioblastoma (GBM) microenvironment are resident microglia, macrophages and infiltrating monocytes from the blood circulation. The mechanisms by which monocytes infiltrate into GBM, their fate following infiltration, and their role in GBM growth are not known. Here we tested the hypothesis that loss of the fractalkine receptor CX3CR1 in microglia and monocytes would affect gliomagenesis. Deletion of Cx3cr1 from the microenvironment resulted in increased tumor incidence and shorter survival times in glioma-bearing mice. Loss of Cx3cr1 did not affect accumulation of microglia/macrophages in peri-tumoral areas, but instead indirectly promoted the trafficking of CD11b⁺CD45^hiCX3CR1^lowLy-6C^hiLy-6G⁻F4/80^−/low circulating inflammatory monocytes into the CNS, resulting in their increased accumulation in the perivascular area. Cx3cr1-deficient microglia/macrophages and monocytes demonstrated upregulation of IL1β expression that was inversely proportional to Cx3cr1 gene dosage. The Proneural subgroup of the TCGA GBM patient dataset with high IL1β expression showed shorter survival compared to patients with low IL1β. IL1β promoted tumor growth and increased the cancer stem cell phenotype in murine and human Proneural glioma stem cells (GSCs). IL1β activated the p38 MAPK signaling pathway and expression of monocyte chemoattractant protein (MCP-1/CCL2) by tumor cells. Loss of Cx3cr1 in microglia in a monocyte-free environment had no impact on tumor growth and did not alter microglial migration. These data suggest that enhancing signaling to CX3CR1 or inhibiting IL1β signaling in intra-tumoral macrophages can be considered as potential strategies to decrease the tumor-promoting effects of monocytes in Proneural GBM.

Overexpression of interleukin-33 is associated with poor prognosis of patients with glioma

Interleukin-33 (IL-33) has shown diagnostic and prognostic values in multiple human cancers. However, there is little knowledge on the role of IL-33 in human gliomas and its association with disease prognosis. This study aimed to evaluate the value of IL-33 in the prognosis of glioma patients. The expression of IL-33 was determined and compared in surgical specimens from 86 glioma patients and 16 normal brain tissues. The associations of IL-33 expression with the clinicopathological features and prognosis of glioma patients were assessed. qRT-PCR assay showed higher IL-33 mRNA expression in glioma tissues than in normal brain tissue ( p < 0.001), and significantly higher IL-33 mRNA expression was detected in both low- and high-grade glioma tissues relative to normal brain tissues ( p < 0.001). Western blotting revealed elevated IL-33 protein levels in glioma tissues compared to those in normal brain tissues, and immunohistochemical staining showed higher IL-33 protein expression in glioma tissues than in normal brain tissues. IL-33 expression correlated with the glioma grade ( p < 0.001) and Karnofsky performance status score ( p = 0.024), and the glioma patients with high IL-33 expression had a shorter progression-free survival ( p < 0.001) and overall survival ( p < 0.001) than those with low IL-33 expression. The univariate and multivariate analyses showed that IL-33 overexpression and the glioma grade were independent factors of a poor prognosis in glioma patients. Therefore, IL-33 may be a promising biomarker for the detection of gliomas, and IL-33 expression is useful for predicting the prognosis of the disease.

Cancer Stem Cell Hierarchy in Glioblastoma Multiforme

Glioblastoma multiforme (GBM), an aggressive tumor that typically exhibits treatment failure with high mortality rates, is associated with the presence of cancer stem cells (CSCs) within the tumor. CSCs possess the ability for perpetual self-renewal and proliferation, producing downstream progenitor cells that drive tumor growth. Studies of many cancer types have identified CSCs using specific markers, but it is still unclear as to where in the stem cell hierarchy these markers fall. This is compounded further by the presence of multiple GBM and glioblastoma cancer stem cell subtypes, making investigation and establishment of a universal treatment difficult. This review examines the current knowledge on the CSC markers SALL4, OCT-4, SOX2, STAT3, NANOG, c-Myc, KLF4, CD133, CD44, nestin, and glial fibrillary acidic protein, specifically focusing on their use and validity in GBM research and how they may be utilized for investigations into GBM's cancer biology.

KCa3.1 inhibition switches the phenotype of glioma-infiltrating microglia/macrophages

Among the strategies adopted by glioma to successfully invade the brain parenchyma is turning the infiltrating microglia/macrophages (M/MΦ) into allies, by shifting them toward an anti-inflammatory, pro-tumor phenotype. Both glioma and infiltrating M/MΦ cells express the Ca²⁺-activated K⁺ channel (KCa3.1), and the inhibition of KCa3.1 activity on glioma cells reduces tumor infiltration in the healthy brain parenchyma. We wondered whether KCa3.1 inhibition could prevent the acquisition of a pro-tumor phenotype by M/MΦ cells, thus contributing to reduce glioma development. With this aim, we studied microglia cultured in glioma-conditioned medium or treated with IL-4, as well as M/MΦ cells acutely isolated from glioma-bearing mice and from human glioma biopsies. Under these different conditions, M/MΦ were always polarized toward an anti-inflammatory state, and preventing KCa3.1 activation by 1-[(2-Chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), we observed a switch toward a pro-inflammatory, antitumor phenotype. We identified FAK and PI3K/AKT as the molecular mechanisms involved in this phenotype switch, activated in sequence after KCa3.1. Anti-inflammatory M/MΦ have higher expression levels of KCa3.1 mRNA (kcnn4) that are reduced by KCa3.1 inhibition. In line with these findings, TRAM-34 treatment, in vivo, significantly reduced the size of tumors in glioma-bearing mice. Our data indicate that KCa3.1 channels are involved in the inhibitory effects exerted by the glioma microenvironment on infiltrating M/MΦ, suggesting a possible role as therapeutic targets in glioma.

Glioma Stem Cells but Not Bulk Glioma Cells Upregulate IL-6 Secretion in Microglia/Brain Macrophages via Toll-like Receptor 4 Signaling

Peripheral macrophages and resident microglia constitute the dominant glioma-infiltrating cells. The tumor induces an immunosuppressive and tumor-supportive phenotype in these glioma-associated microglia/brain macrophages (GAMs). A subpopulation of glioma cells acts as glioma stem cells (GSCs). We explored the interaction between GSCs and GAMs. Using CD133 as a marker of stemness, we enriched for or deprived the mouse glioma cell line GL261 of GSCs by fluorescence-activated cell sorting (FACS). Over the same period of time, 100 CD133(+ )GSCs had the capacity to form a tumor of comparable size to the ones formed by 10,000 CD133(-) GL261 cells. In IL-6(-/-) mice, only tumors formed by CD133(+ )cells were smaller compared with wild type. After stimulation of primary cultured microglia with medium from CD133-enriched GL261 glioma cells, we observed an selective upregulation in microglial IL-6 secretion dependent on Toll-like receptor (TLR) 4. Our results show that GSCs, but not the bulk glioma cells, initiate microglial IL-6 secretion via TLR4 signaling and that IL-6 regulates glioma growth by supporting GSCs. Using human glioma tissue, we could confirm the finding that GAMs are the major source of IL-6 in the tumor context.

Regulation of microglial survival and proliferation in health and diseases

Microglia play an important role in the development and maintenance of the central nervous system (CNS) under homeostatic conditions as well as during neurodegenerative diseases. Recent observations in human genomics and advances in genetic mouse models have provided insights into signaling pathways that control development, survival, proliferation and function of microglia. Alteration of these pathways contributes to the pathogenesis of CNS diseases. Here we review the current literature regarding the roles of these microglial pathways in both the normal and diseased brain and discuss areas that require further investigation.

Extracellular Vesicles in Brain Tumor Progression

Brain tumors can be viewed as multicellular 'ecosystems' with increasingly recognized cellular complexity and systemic impact. While the emerging diversity of malignant disease entities affecting brain tissues is often described in reference to their signature alterations within the cellular genome and epigenome, arguably these cell-intrinsic changes can be regarded as hardwired adaptations to a variety of cell-extrinsic microenvironmental circumstances. Conversely, oncogenic events influence the microenvironment through their impact on the cellular secretome, including emission of membranous structures known as extracellular vesicles (EVs). EVs serve as unique carriers of bioactive lipids, secretable and non-secretable proteins, mRNA, non-coding RNA, and DNA and constitute pathway(s) of extracellular exit of molecules into the intercellular space, biofluids, and blood. EVs are also highly heterogeneous as reflected in their nomenclature (exosomes, microvesicles, microparticles) attempting to capture their diverse origin, as well as structural, molecular, and functional properties. While EVs may act as a mechanism of molecular expulsion, their non-random uptake by heterologous cellular recipients defines their unique roles in the intercellular communication, horizontal molecular transfer, and biological activity. In the central nervous system, EVs have been implicated as mediators of homeostasis and repair, while in cancer they may act as regulators of cell growth, clonogenicity, angiogenesis, thrombosis, and reciprocal tumor-stromal interactions. EVs produced by specific brain tumor cell types may contain the corresponding oncogenic drivers, such as epidermal growth factor receptor variant III (EGFRvIII) in glioblastoma (and hence are often referred to as 'oncosomes'). Through this mechanism, mutant oncoproteins and nucleic acids may be transferred horizontally between cellular populations altering their individual and collective phenotypes. Oncogenic pathways also impact the emission rates, types, cargo, and biogenesis of EVs, as reflected by preliminary analyses pointing to differences in profiles of EV-regulating genes (vesiculome) between molecular subtypes of glioblastoma, and in other brain tumors. Molecular regulators of vesiculation can also act as oncogenes. These intimate connections suggest the context-specific roles of different EV subsets in the progression of specific brain tumors. Advanced efforts are underway to capture these events through the use of EVs circulating in biofluids as biomarker reservoirs and to guide diagnostic and therapeutic decisions.

Extracellular Vesicles and MicroRNAs: Their Role in Tumorigenicity and Therapy for Brain Tumors

MicroRNAs are small non-coding RNAs which mediate post-transcriptional gene regulation. Recently, microRNAs have also been found to be localized to the extracellular space, often encapsulated in secreted extracellular vesicles (EVs). This tandem of EVs and tissue-specific expressed/secreted microRNAs that can be taken up by neighboring or distant recipient cells, leading to changes in gene expression-suggests a cell-specialized role in physiological and pathological conditions. The complexity of solid tumors and their distinct pathophysiology relies on interactive communications between the various cell types in the neoplasm (tumor, endothelial, or macrophages, for instance). Understanding how such EV/microRNA-mediated communication occurs may actually lead to avenues for therapeutic exploitation and/or intervention, particularly for the most formidable cancers, such as those in the brain. In this review, the role of microRNAs/EVs in brain tumors will be discussed with emphasis on how these molecules could be utilized for tumor therapy.

Galunisertib inhibits glioma vasculogenic mimicry formation induced by astrocytes

Gliomas are among the most lethal primary brain tumors found in humans. In high-grade gliomas, vasculogenic mimicry is often detected and has been correlated with prognosis, thus suggesting its potential as a therapeutic target. Vasculogenic mimicry mainly forms vascular-like channels independent of endothelial cells; however, little is known about the relationship between astrocytes and vasculogenic mimicry. In our study, we demonstrated that the presence of astrocytes promoted vasculogenic mimicry. With suspension microarray technology and in vitro tube formation assays, we identified that astrocytes relied on TGF-β1 to enhance vasculogenic mimicry. We also found that vasculogenic mimicry was inhibited by galunisertib, a promising TGF-β1 inhibitor currently being studied in an ongoing trial in glioma patients. The inhibition was partially attributed to a decrease in autophagy after galunisertib treatment. Moreover, we observed a decrease in VE-cadherin and smooth muscle actin-α expression, as well as down-regulation of Akt and Flk phosphorylation in galunisertib-treated glioma cells. By comparing tumor weight and volume in a xenograft model, we acquired promising results to support our theory. This study expands our understanding of the role of astrocytes in gliomas and demonstrates that galunisertib inhibits glioma vasculogenic mimicry induced by astrocytes.

Mechanical confinement triggers glioma linear migration dependent on formin FHOD3

Glioblastomas are extremely aggressive brain tumors with highly invasive properties. Brain linear tracks such as blood vessel walls constitute their main invasive routes. Here we analyze rat C6 and patient-derived glioma cell motility in vitro using micropatterned linear tracks to mimic blood vessels. On laminin-coated tracks (3-10 μm), these cells used an efficient saltatory mode of migration similar to their in vivo migration. This saltatory migration was also observed on larger tracks (50-400 μm in width) at high cell densities. In these cases, the mechanical constraints imposed by neighboring cells triggered this efficient mode of migration, resulting in the formation of remarkable antiparallel streams of cells along the tracks. This motility involved microtubule-dependent polarization, contractile actin bundles and dynamic paxillin-containing adhesions in the leading process and in the tail. Glioma linear migration was dramatically reduced by inhibiting formins but, surprisingly, accelerated by inhibiting Arp2/3. Protein expression and phenotypic analysis indicated that the formin FHOD3 played a role in this motility but not mDia1 or mDia2. We propose that glioma migration under confinement on laminin relies on formins, including FHOD3, but not Arp2/3 and that the low level of adhesion allows rapid antiparallel migration.

Mir-21-Sox2 Axis Delineates Glioblastoma Subtypes with Prognostic Impact

Glioblastoma (GBM) is the most aggressive human brain tumor. Although several molecular subtypes of GBM are recognized, a robust molecular prognostic marker has yet to be identified. Here, we report that the stemness regulator Sox2 is a new, clinically important target of microRNA-21 (miR-21) in GBM, with implications for prognosis. Using the MiR-21-Sox2 regulatory axis, approximately half of all GBM tumors present in the Cancer Genome Atlas (TCGA) and in-house patient databases can be mathematically classified into high miR-21/low Sox2 (Class A) or low miR-21/high Sox2 (Class B) subtypes. This classification reflects phenotypically and molecularly distinct characteristics and is not captured by existing classifications. Supporting the distinct nature of the subtypes, gene set enrichment analysis of the TCGA dataset predicted that Class A and Class B tumors were significantly involved in immune/inflammatory response and in chromosome organization and nervous system development, respectively. Patients with Class B tumors had longer overall survival than those with Class A tumors. Analysis of both databases indicated that the Class A/Class B classification is a better predictor of patient survival than currently used parameters. Further, manipulation of MiR-21-Sox2 levels in orthotopic mouse models supported the longer survival of the Class B subtype. The MiR-21-Sox2 association was also found in mouse neural stem cells and in the mouse brain at different developmental stages, suggesting a role in normal development. Therefore, this mechanism-based classification suggests the presence of two distinct populations of GBM patients with distinguishable phenotypic characteristics and clinical outcomes.

SIGNIFICANCE STATEMENT

Molecular profiling-based classification of glioblastoma (GBM) into four subtypes has substantially increased our understanding of the biology of the disease and has pointed to the heterogeneous nature of GBM. However, this classification is not mechanism based and its prognostic value is limited. Here, we identify a new mechanism in GBM (the miR-21-Sox2 axis) that can classify ∼50% of patients into two subtypes with distinct molecular, radiological, and pathological characteristics. Importantly, this classification can predict patient survival better than the currently used parameters. Further, analysis of the miR-21-Sox2 relationship in mouse neural stem cells and in the mouse brain at different developmental stages indicates that miR-21 and Sox2 are predominantly expressed in mutually exclusive patterns, suggesting a role in normal neural development.

Calcium signaling orchestrates glioblastoma development: Facts and conjunctures

While it is a relatively rare disease, glioblastoma multiform (GBM) is one of the more deadly adult cancers. Following current interventions, the tumor is never eliminated whatever the treatment performed; whether it is radiotherapy, chemotherapy, or surgery. One hypothesis to explain this poor outcome is the "cancer stem cell" hypothesis. This concept proposes that a minority of cells within the tumor mass share many of the properties of adult neural stem cells and it is these that are responsible for the growth of the tumor and its resistance to existing therapies. Accumulating evidence suggests that Ca(2+) might also be an important positive regulator of tumorigenesis in GBM, in processes involving quiescence, maintenance, proliferation, or migration. Glioblastoma tumors are generally thought to develop by co-opting pathways that are involved in the formation of an organ. We propose that the cells initiating the tumor, and subsequently the cells of the tumor mass, must hijack the different checkpoints that evolution has selected in order to prevent the pathological development of an organ. In this article, two main points are discussed. (i) The first is the establishment of a so-called "cellular society," which is required to create a favorable microenvironment. (ii) The second is that GBM can be considered to be an organism, which fights to survive and develop. Since GBM evolves in a limited space, its only chance of development is to overcome the evolutionary checkpoints. For example, the deregulation of the normal Ca(2+) signaling elements contributes to the progression of the disease. Thus, by manipulating the Ca(2+) signaling, the GBM cells might not be killed, but might be reprogrammed toward a new fate that is either easy to cure or that has no aberrant functioning. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen.

Macrophage Ablation Reduces M2-Like Populations and Jeopardizes Tumor Growth in a MAFIA-Based Glioma Model

Monocytes/macrophages are an influential component of the glioma microenvironment. However, understanding their diversity and plasticity constitute one of the most challenging areas of research due to the paucity of models to study these cells' inherent complexity. Herein, we analyzed the role of monocytes/macrophages in glioma growth by using a transgenic model that allows for conditional ablation of this cell population. We modeled glioma using intracranial GL261-bearing CSF-1R–GFP⁺ macrophage Fas-induced apoptosis (MAFIA) transgenic mice. Conditional macrophage ablation was achieved by exposure to the dimerizer AP20187. Double immunofluorescence was used to characterize M1- and M2-like monocytes/macrophages during tumor growth and after conditional ablation. During glioma growth, the monocyte/macrophage population consisted predominantly of M2 macrophages. Conditional temporal depletion of macrophages reduced the number of GFP⁺ cells, targeting mainly the repopulation of M2-polarized cells, and altered the appearance of M1-like monocytes/macrophages, which suggested a shift in the M1/M2 macrophage balance. Of interest, compared with control-treated mice, macrophage-depleted mice had a lower tumor mitotic index, microvascular density, and reduced tumor growth. These results demonstrated the possibility of studying in vivo the role and phenotype of macrophages in gliomas and suggested that transitory depletion of CSF-1R⁺ population influences the reconstitutive phenotypic pool of these cells, ultimately suppressing tumor growth. The MAFIA model provides a much needed advance in defining the role of macrophages in gliomas.

Glioblastoma: Defining Tumor Niches

Glioblastomas (GBM) are one of the most recalcitrant brain tumors because of their aggressive invasive growth and resistance to therapy. They are highly heterogeneous malignancies at both the molecular and histological levels. Specific histological hallmarks including pseudopalisading necrosis and microvascular proliferation distinguish GBM from lower-grade gliomas, and make GBM one of the most hypoxic as well as angiogenic tumors. These microanatomical compartments present specific niches within the tumor microenvironment that regulate metabolic needs, immune surveillance, survival, invasion as well as cancer stem cell maintenance. Here we review features and functions of the distinct GBM niches, detail the different cell constituents and the functional status of the vasculature, and discuss prospects of therapeutically targeting GBM niche constituents.

Advantages of a dual-color fluorescence-tracing glioma orthotopic implantation model: Detecting tumor location, angiogenesis, cellular fusion and the tumor microenvironment

Various organs of the body have distinct microenvironments with diverse biological characteristics that can influence the growth of tumors within them. However, the mechanisms underlying the interactions between tumor and host cells are currently not well understood. In the present study, a dual-color fluorescence-tracing glioma orthotopic implantation model was developed, in which C6 rat glioma cells labeled with the red fluorescent dye CM-Dil, and SU3 human glioma cells stably expressing red fluorescence protein, were inoculated into the right caudate nucleus of transgenic female C57BL/6 nude mice expressing enhanced green fluorescent protein. The dual-color tracing with whole-body in vivo fluorescence imaging of xenografts was performed using a live imaging system. Frozen sections of the transplanted tumor were prepared for histological analyses, in order to detect the presence of invading tumor cells, blood vessels and cellular fusion. Dual-color images were able to distinguish between red tumor cells and green host cells. The results of the present study suggested that a dual-color fluorescence-tracing glioma orthotopic implantation model may be convenient for detecting tumor location, angiogenesis, cellular fusion, and the tumor microenvironment.

Immune Cell Infiltrates in Pituitary Adenomas: More Macrophages in Larger Adenomas and More T Cells in Growth Hormone Adenomas

Tumor immune microenvironment has been gradually recognized as a key contributor to tumor development, progression, and control. Immune cell infiltrates in brain tumors have been increasingly studied, but few have published on immune cell infiltrates in pituitary adenomas. We quantitatively assessed the infiltration of macrophages and lymphocytes in 35 pituitary adenomas, including 9 densely granulated growth hormone (DG-GH), 9 sparsely granulated growth hormone (SG-GH), 9 null cell (NC), and 8 adrenocorticotropic hormone (ACTH) adenomas. All the adenomas showed varying degrees of CD68+ macrophage infiltration. While SG-GH adenomas were significantly larger in size than DG-GH and ACTH adenomas, the infiltration of CD68+ macrophages was significantly greater in SG-GH than in DG-GH and ACTH adenomas. Similarly, NC adenomas that were significantly larger than DG-GH and ACTH adenomas had significantly greater infiltration of CD68+ macrophages than DG-GH and ACTH adenomas. The numbers of CD68+ macrophages were positively correlated with the tumor sizes and Knosp classification grades for tumor invasiveness. The infiltration of CD4+ and CD8+ T cells was relatively scant in these adenomas, but GH adenomas exhibited significantly more CD4+ and CD8+ T cells than non-GH adenomas. Both DG-GH and SG-GH adenomas had significantly more CD4+ cells than ACTH adenomas and significantly more CD8+ cells than NC adenomas. These results suggest an association of CD68+ macrophage infiltration with an increase in the pituitary adenoma size and invasiveness. Our observation contributes to understanding the growth environment of pituitary adenomas, for which adjuvant immunotherapy may help to constrain the tumor enlargement and invasiveness.

The 18-kDa mitochondrial translocator protein in gliomas: from the bench to bedside

The 18-kDa mitochondrial translocator protein (TSPO) is known to be highly expressed in several types of cancer, including gliomas, whereas expression in normal brain is low. TSPO functions in glioma are still incompletely understood. The TSPO can be quantified pre-operatively with molecular imaging making it an ideal candidate for personalized treatment of patient with glioma. Studies have proposed to exploit the TSPO as a transporter of chemotherapics to selectively target tumour cells in the brain. Our studies proved that positron emission tomography (PET)-imaging can contribute to predict progression of patients with glioma and that molecular imaging with TSPO-specific ligands is suitable to stratify patients in view of TSPO-targeted treatment. Finally, we proved that TSPO in gliomas is predominantly expressed by tumour cells.

Intratumoral heterogeneity in glioblastoma: don't forget the peritumoral brain zone

Glioblastoma (GB) is the most frequent and aggressive primary tumor of the central nervous system. Prognosis remains poor despite ongoing progress. In cases where the gadolinium-enhanced portion of the GB is completely resected, 90% of recurrences occur at the margin of surgical resection in the macroscopically normal peritumoral brain zone (PBZ). Intratumoral heterogeneity in GB is currently a hot topic in neuro-oncology, and the GB PBZ may be involved in this phenomenon. Indeed, this region, which possesses specific properties, has been less studied than the core of the GB tumor. The high rate of local recurrence in the PBZ and the limited success of targeted therapies against GB demonstrate the need for a better understanding of the PBZ. We present here a review of the literature on the GB PBZ, focusing on its radiological, cellular, and molecular characteristics. We discuss how intraoperative analysis of the PBZ is important for the optimization of surgical resection and the development of targeted therapies against GB.

Resident microglia, and not peripheral macrophages, are the main source of brain tumor mononuclear cells

Gliomas consist of multiple cell types, including an abundant number of microglia and macrophages, whereby their impact on tumor progression is controversially discussed. To understand their unique functions and consequently manipulate either microglia or macrophages in therapeutic approaches, it is essential to discriminate between both cell populations. Because of the lack of specific markers, generally total body irradiated chimeras with labeled bone marrow cells were used to identify infiltrated cells within the brain. However, total body irradiation (TBI) affects the blood-brain barrier integrity, which in turn potentially facilitates immune cell infiltration. In this study, changes on the blood-brain barrier were avoided using head-protected irradiation (HPI). Head protection and total body irradiated chimeras exhibited similar reconstitution levels of the myeloid cell lineage in the blood, enabling the comparable analyses of brain infiltrates. We demonstrate that the HPI model impeded a massive unspecific influx of donor-derived myeloid cells into naive as well as tumor-bearing brains. Moreover, experimental artifacts such as an enlarged distribution of infiltrated cells and fourfold increased tumor volumes are prevented in head-protected chimeras. In addition, our data evidenced for the first time that microglia are able to up-regulate CD45 and represent an inherent part of the CD45(high) population in the tumor context. All in all, HPI allowed for the unequivocal distinction between microglia and macrophages without alterations of tumor biology and consequently permits a detailed and realistic description of the myeloid cell composition in gliomas.

Expression of tumor-associated macrophage in progression of human glioma

The aim of this study is to investigate the expression of tumor-associated macrophages (TAMs) M1, M2 phenotypic in human glioma tissues, and to explore the clinical significance and prognostic value of TAMs in glioma patients. A total of 50 glioma samples were obtained from patients diagnosed in our hospital from 2007 to 2010. Clinical follow-up was conducted via return visits and telephone interviews after discharge. Progression free survival (PFS) was calculated based on tumor progression by MRI and CT examination from the primary operation. Overall survival (OS) time was calculated from the initial surgical operation date to end date of follow-up or death. Kaplan-Meier methodology was used to evaluate the survival of patients and log-rank test for comparing differences between groups. The expression levels of CD16 and CD206 were investigated in the 4 μm serial paraffin sections by immunohistochemistry. M1-type macrophages filtrated in all the grades of glioma samples, and the lower expression level was associated with high grade glioma. A negative correlation was found between WHO pathological grades and the expression of M1-type macrophages by Spearman correlation analysis. M2-type macrophages filtrated in all the grades of glioma samples with the higher expression level associated with high grade glioma. A positive correlation was found between WHO pathological grades and the expression of M2-type macrophages by Spearman correlation analysis. The PFS and OS among patients with high levels of M1-type macrophages (CD16+++) were significantly higher than those with less expression. The PFS and OS among patients with high levels of M2-type macrophages (CD206+++) were significantly lower than those with low expression. M1-type macrophages may inhibit the tumor growth and improve the therapeutic outcome of glioma patients. M2 ratios are associated with tumor proliferation and poor prognosis. TAMs phenotypes of glioma samples are the potential biomarkers in assessing the degree of malignancy, tumor invasion, and patient prognosis in clinic.

Hormones and immunity in cancer: are thyroid hormones endocrine players in the microglia/glioma cross-talk?

Accumulating evidence indicates that the endocrine and immune systems engage in complex cross-talks in which a prominent role is played by thyroid hormones (THs). The increase of resident vs. monocyte recruited macrophages was shown to be an important effector of the TH 3,3′,5′-Triiodo-L-thyronine (T3)-induced protection against inflammation and a key role of T3 in inhibiting the differentiation of peripheral monocytes into macrophages was observed. Herein, we report on the role of T3 as a modulator of microglia, the specialized macrophages of the central nervous system (CNS). Mounting evidence supports a role of microglia and macrophages in the growth and invasion of malignant glioma. In this respect, we unveil the putative involvement of T3 in the microglia/glioma cell communication. Since THs are known to cross the blood-brain barrier, we suggest that T3 not only exerts a direct modulation of brain cancer cell itself but also indirectly promotes glioma growth through a modulation of microglia. Our observations expand available information on the role of TH system in glioma and its microenvironment and highlight the endocrine modulation of microglia as an important target for future therapeutic development of glioma treatments.

EGF as a New Therapeutic Target for Medulloblastoma Metastasis

Medulloblastoma (MB) is a malignant pediatric brain tumor known for its aggressive metastatic potential. Despite the well-documented migration of MB cells to other parts of the brain and spinal column, MB chemotaxis is poorly understood. Herein, we examined the in vitro migratory and cellular responses of MB-derived cells to external signaling of Epidermal Growth Factor (EGF), hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF-BB), and the stromal cell-derived factors 1-alpha (SDF-1). Experiments utilized transwell assays and immunocytochemistry to identify receptor activation in MB migration, and used a microfluidic platform to examine directionality, trajectory, and gradient-dependence of motile cells. Data illustrates that MB-derived cells respond strongly to EGF in a dosage and gradient-dependent manner with increased EGF-R activation, and show that high EGF gradient fields cause an increased number of cells to migrate longer directed distances. Our results provide evidence that EGF and its receptor play an important role than previously documented in MB chemotactic migration than previously documented and should be considered for developing migration-target therapies against MB metastasis.

CSF-1-activated macrophages are target-directed and essential mediators of Schwann cell dedifferentiation and dysfunction in Cx32-deficient mice

We investigated connexin 32 (Cx32)-deficient mice, a model for the X-linked form of Charcot-Marie-Tooth neuropathy (CMT1X), regarding the impact of low-grade inflammation on Schwann cell phenotype. Whereas we previously identified macrophages as amplifiers of the neuropathy, we now explicitly focus on the impact of the phagocytes on Schwann cell dedifferentiation, a so far not-yet addressed disease-related mechanism for CMT1X. Using mice heterozygously deficient for Cx32 and displaying both Cx32-positive and -negative Schwann cells in one and the same nerve, we could demonstrate that macrophage clusters rather than single macrophages precisely associate with mutant but not with Cx32-positive Schwann cells. Similarly, in an advanced stage of Schwann cell perturbation, macrophage clusters were strongly associated with NCAM- and L1-positive, dedifferentiated Schwann cells. To clarify the role of macrophages regarding Schwann cell dedifferentiation, we generated Cx32-deficient mice additionally deficient for the macrophage-directed cytokine colony-stimulating factor (CSF)-1. In the absence of CSF-1, Cx32-deficient Schwann cells not only showed the expected amelioration in myelin preservation but also failed to upregulate the Schwann cell dedifferentiation markers NCAM and L1. Another novel and unexpected finding in the double mutants was the retained activation of ERK signaling, a pathway which is detrimental for Schwann cell homeostasis in myelin mutant models. Our findings demonstrate that increased ERK signaling can be compatible with the maintenance of Schwann cell differentiation and homeostasis in vivo and identifies CSF-1-activated macrophages as crucial mediators of detrimental Schwann cell dedifferentiation in Cx32-deficient mice.

Distinctive responses of brain tumor cells to TLR2 ligands

Malignant brain tumor mass contains significant numbers of infiltrating glial cells that may intimately interact with tumor cells and influence cancer treatments. Understanding of characteristic discrepancies between normal GLIA and tumor cells would, therefore, be valuable for improving anticancer therapeutics. Here, we report distinct differences in toll-like receptors (TLR)-2-mediated responses between normal glia and primary brain tumor cell lines. We found that tyrosine phosphorylation of STAT1 by TLR2 ligands and its downstream events did not occur in mouse, rat, or human brain tumor cell lines, but were markedly induced in normal primary microglia and astrocytes. Using TLR2-deficient, interferon (IFN)-γ-deficient, and IFNγ-receptor-1-deficient mice, we revealed that the impaired phosphorylation of STAT1 might be linked with defective TLR2 system in tumor cells, and that a TLR2-dependent pathway, not IFNγ-receptor machinery, might be critical for tyrosine STAT1 phosphorylation by TLR2 ligands. We also found that TLR2 and its heterodimeric partners, TLR1 and 6, on brain tumor cells failed to properly respond to TLR2 ligands, and representative TLR2-dependent cellular events, such as inflammatory responses and cell death, were not detected in brain tumor cells. Similar results were obtained in in vitro and in vivo experiments using orthotopic mouse and rat brain tumor models. Collectively, these results suggest that primary brain tumor cells may exhibit a distinctive dysfunction of TLR2-associated responses, resulting in abnormal signaling and cellular events. Careful targeting of this distinctive property could serve as the basis for effective therapeutic approaches against primary brain tumors.

Tunneling nanotubes between rat primary astrocytes and C6 glioma cells alter proliferation potential of glioma cells

The tunneling nanotube (TNT) is a newly discovered, long and thin tubular structure between cells. In this study, we established a co-culture system for rat primary astrocytes and C6 glioma cells and found that TNTs formed between them. Most of the TNTs initiated from astrocytes towards C6 glioma cells. The formation of TNTs depended on p53. In addition, hydrogen peroxide increased the number of TNTs in the co-culture system. Established TNTs reduced the proliferation of C6 glioma cells. Our data suggest that TNTs between astrocytes and glioma cells facilitate substance transfer and therefore alter the properties, including the proliferation potential, of glioma cells.

γ-H2AX as a marker for dose deposition in the brain of wistar rats after synchrotron microbeam radiation

Objective

Synchrotron radiation has shown high therapeutic potential in small animal models of malignant brain tumours. However, more studies are needed to understand the radiobiological effects caused by the delivery of high doses of spatially fractionated x-rays in tissue. The purpose of this study was to explore the use of the γ-H2AX antibody as a marker for dose deposition in the brain of rats after synchrotron microbeam radiation therapy (MRT).

Methods

Normal and tumour-bearing Wistar rats were exposed to 35, 70 or 350 Gy of MRT to their right cerebral hemisphere. The brains were extracted either at 4 or 8 hours after irradiation and immediately placed in formalin. Sections of paraffin-embedded tissue were incubated with anti γ-H2AX primary antibody.

Results

While the presence of the C6 glioma does not seem to modulate the formation of γ-H2AX in normal tissue, the irradiation dose and the recovery versus time are the most important factors affecting the development of γ-H2AX foci. Our results also suggest that doses of 350 Gy can trigger the release of bystander signals that significantly amplify the DNA damage caused by radiation and that the γ-H2AX biomarker does not only represent DNA damage produced by radiation, but also damage caused by bystander effects.

Conclusion

In conclusion, we suggest that the γ-H2AX foci should be used as biomarker for targeted and non-targeted DNA damage after synchrotron radiation rather than a tool to measure the actual physical doses.

Involvement of ROS-alpha v beta 3 integrin-FAK/Pyk2 in the inhibitory effect of melatonin on U251 glioma cell migration and invasion under hypoxia

BACKGROUND

Melatonin, a well-known antioxidant, has been shown to possess anti-invasive properties for glioma. However, little is known about the effect of melatonin on glioma cell migration and invasion under hypoxia, which is a crucial microenvironment for tumor progress. In addition, focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are closely associated with cell migration and invasion. Therefore, we investigated the possible role of these kinases and its related signaling in the regulation of human U251 glioma cells behavior by melatonin under hypoxia.

METHODS

The abilities of migration and invasion of U251 glioma cells were determined by wound healing and transwell assay in vitro. The intracellular production of reactive oxygen species (ROS) was measured by using the fluorescent probe 6-carboxy-2', 7'-dichorodihydrofluorescein diacetate (DCFH-DA). Immunofluorescence experiments and western blotting analysis were used to detect the expression level of protein. Small interfering RNAs (siRNA) was used to silence specific gene expression.

RESULTS

The pharmacologic concentration (1 mM) of melatonin significantly inhibited the migration and invasion of human U251 glioma cells under hypoxia. The inhibitory effect of melatonin was accompanied with the reduced phosphorylation of FAK and Pyk2, and decreased expression of alpha v beta 3 (αvβ3) integrin. Additionally, inhibition of αvβ3 integrin by siRNA reduced the phosphorylation of FAK/Pyk2 and demonstrated the similar anti-tumor effects as melatonin, suggesting the involvement of αvβ3 integrin- FAK/Pyk2 pathway in the anti-migratory and anti-invasive effect of melatonin. It was also found that melatonin treatment decreased the ROS levels in U251 glioma cells cultured under hypoxia. ROS inhibitor apocynin not only inhibited αvβ3 integrin expression and the phosphorylation levels of FAK and Pyk2, but also suppressed the migratory and invasive capacity of U251 glioma cells under hypoxia.

CONCLUSIONS

These results suggest that melatonin exerts anti-migratory and anti-invasive effects on glioma cells in response to hypoxia via ROS-αvβ3 integrin-FAK/Pyk2 signaling pathways. This provides evidence that melatonin may be a potential therapeutic molecule targeting the hypoxic microenvironment of glioma.

Astroblastoma: beside being a tumor entity, an occasional phenotype of astrocytic gliomas?

The diagnosis of astroblastoma is based on a typical histological aspect with perivascular distribution of cells sending cytoplasmic extensions to the vessels and vascular hyalinization. These criteria are useful for standardizing the identification of the tumor, but, in spite of this, there are discrepancies in the literature concerning the age distribution and the benign or malignant nature of the tumor. Three cases are discussed in this study: Case 1 was a typical high-grade astroblastoma; Case 2 was an oligodendroglioma at the first intervention and an oligoastrocytoma at the second intervention with typical perivascular arrangements in the astrocytic component; Case 3 was a gemistocytic glioma with malignant features and typical perivascular arrangements. Genetic analysis showed genetic alterations that are typical of gliomas of all malignancy grades. Using the neurosphere assay, neurospheres and adherent cells were found to have developed in Case 1, while adherent cells only developed in Case 2, in line with the stemness potential of the tumors. The cases are discussed in relation to their diagnostic assessment as astroblastoma, and it is hypothesized that the typical perivascular distribution of cells may not indicate a separate and unique tumor entity, but may be a peculiarity that can be acquired by astrocytic gliomas when an unknown cause from the tumor microenvironment influences the relationship between vessels and tumor cells.

Cancer stem cell-specific scavenger receptor CD36 drives glioblastoma progression

Glioblastoma (GBM) contains a self-renewing, tumorigenic cancer stem cell (CSC) population which contributes to tumor propagation and therapeutic resistance. While the tumor microenvironment is essential to CSC self-renewal, the mechanisms by which CSCs sense and respond to microenvironmental conditions are poorly understood. Scavenger receptors are a broad class of membrane receptors well characterized on immune cells and instrumental in sensing apoptotic cellular debris and modified lipids. Here, we provide evidence that CSCs selectively use the scavenger receptor CD36 to promote their maintenance using patient-derived CSCs and in vivo xenograft models. CD36 expression was observed in GBM cells in addition to previously described cell types including endothelial cells, macrophages, and microglia. CD36 was enriched in CSCs and was able to functionally distinguish self-renewing cells. CD36 was coexpressed with integrin alpha 6 and CD133, previously described CSC markers, and CD36 reduction resulted in concomitant loss of integrin alpha 6 expression, self-renewal, and tumor initiation capacity. We confirmed oxidized phospholipids, ligands of CD36, were present in GBM and found that the proliferation of CSCs, but not non-CSCs, increased with exposure to oxidized low-density lipoprotein. CD36 was an informative biomarker of malignancy and negatively correlated to patient prognosis. These results provide a paradigm for CSCs to thrive by the selective enhanced expression of scavenger receptors, providing survival, and metabolic advantages.

Glioma cells escaped from cytotoxicity of temozolomide and vincristine by communicating with human astrocytes

Resistance to chemotherapeutic drugs remains a great obstacle to successful treatment of gliomas. Understanding the mechanism of glioma chemoresistance is conducive to develop effective strategies to overcome resistance. Astrocytes are the major stromal cells in the brain and have been demonstrated to play a key role in the malignant phenotype of gliomas. However, little is known regarding its role in glioma chemoresistance. In our study, we established a co-culture system of human astrocytes and glioma in vitro to simulate tumor microenvironment. Our results showed that astrocytes significantly reduced glioma cell apoptosis induced by the chemotherapeutic drugs temozolomide and vincristine. This protective effect was dependent on direct contact between astrocytes and glioma cells through Cx43-GJC. Moreover, in human glioma specimens, we found astrocytes infiltrating around the tumor, with a reactive appearance, suggesting that these astrocytes would play the same chemoprotective effect on gliomas in vivo. Our results expand the understanding of the interaction between astrocytes and glioma cells and provide a possible explanation for unsatisfactory clinical outcomes of chemotherapeutic drugs. Cx43-GJC between astrocytes and glioma cells may be a potential target for overcoming chemoresistance in gliomas clinically.

Extracellular acidosis impairs P2Y receptor-mediated Ca(2+) signalling and migration of microglia

Microglia are the resident macrophage and immune cell of the brain and are critically involved in combating disease and assaults on the brain. Virtually all brain pathologies are accompanied by acidosis of the interstitial fluid, meaning that microglia are exposed to an acidic environment. However, little is known about how extracellular acidosis impacts on microglial function. The activity of microglia is tightly controlled by 'on' and 'off' signals, the presence or absence of which results in generation of distinct phenotypes in microglia. Activation of G protein coupled purinergic (P2Y) receptors triggers a number of distinct behaviours in microglia, including activation, migration, and phagocytosis. Using pharmacological tools and fluorescence imaging of the murine cerebellar microglia cell line C8B4, we show that extracellular acidosis interferes with P2Y receptor-mediated Ca(2+) signalling in these cells. Distinct P2Y receptors give rise to signature intracellular Ca(2+) signals, and Ca(2+) release from stores and Ca(2+) influx are differentially affected by acidotic conditions: Ca(2+) release is virtually unaffected, whereas Ca(2+) influx, mediated at least in part by store-operated Ca(2+) channels, is profoundly inhibited. Furthermore, P2Y1 and P2Y6-mediated stimulation of migration is inhibited under conditions of extracellular acidosis, whereas basal migration independent of P2Y receptor activation is not. Taken together, our results demonstrate that an acidic microenvironment impacts on P2Y receptor-mediated Ca(2+) signalling, thereby influencing microglial responses and responsiveness to extracellular signals. This may result in altered behaviour of microglia under pathological conditions compared with microglial responses in healthy tissue.

Identification of differentially expressed genes regulated by transcription factors in glioblastomas by bioinformatics analysis

The present study aimed to identify differentially expressed genes (DEGs) regulated by transcription factors (TFs) in glioblastoma, by conducting a bioinformatics analysis. The results of the present study may provide potential therapeutic targets that are involved in the development of glioblastoma. The GSE4290 raw data set was downloaded from the Gene Expression Omnibus database, and consisted of 23 non‑tumor samples and 77 glioblastoma (grade 4) tumor samples. Robust Multichip Averaging was used to identify DEGs between the glioblastoma and non‑tumor samples. Functional enrichment analysis of the DEGs was also performed. Based on the TRANSFAC® database, TFs associated with the glioblastoma gene expression profile were used to construct a regulatory network. Furthermore, trimmed subnets were identified according to calculated Z‑scores. A total of 676 DEGs were identified, of which 190 were upregulated and 496 were downregulated. Gene Ontology analysis demonstrated that the majority of these DEGs were functionally enriched in synaptic transmission, regulation of vesicle‑mediated transport and ion‑gated channel activity. In addition, the enriched Kyoto Encyclopedia of Genes and Genomes pathway included neuroactive ligand‑receptor interaction, calcium signaling pathway, p53 signaling pathway and cell cycle. Based on the TRANSFAC® database, transcriptional regulatory networks with 2,246 nodes and 4,515 regulatory pairs were constructed. According to the Z‑scores, the following candidate TFs were identified: TP53, SP1, JUN, STAT3 and SPI1; alongside their downstream DEGs. TP53 was the only differentially expressed TF. These candidate TFs and their downstream DEGs may have important roles in the progression of glioblastoma, and could be potential biomarkers for clinical treatment.

Sevoflurane promotes the expansion of glioma stem cells through activation of hypoxia-inducible factors in vitro

BACKGROUND

Growing evidences indicate that inhalational anaesthetics can enhance the growth and malignant potential of tumour cells and may affect tumour recurrence after surgery. Tumour stem cells play a vital role in tumour recurrence. This study investigates the effect of sevoflurane on glioma stem cells (GSCs) in vitro and the underlying molecular mechanisms in this process.

METHODS

Cultured GSCs were exposed to clinically relevant concentrations and durations of sevoflurane exposure. Cell proliferation and self-renewal capacity were determined. Expression of the stem cell marker CD133, vascular endothelial growth factor (VEGF), hypoxia-inducible factors (HIFs), and phosphorylated Akt, which is a protein kinase invoved in multiple cellular processes, were measured using western blotting. Small interfering RNAs and an Akt inhibitor were used to investigate specific pathways.

RESULTS

Compared with controls, cells exposed to 2% sevoflurane for 6 h induced a larger number of proliferated cells (31.2±7.6% vs 19.0±5.8%; P<0.01). Levels of CD133, VEGF, HIF-1α, HIF-2α, and p-Akt were up-regulated by sevoflurane in a time- and concentration-dependent manner. Small interfering RNA against HIFs decreased the percentage of proliferating GSCs after sevoflurane exposure and pre-treatment of cells with an Akt inhibitor abrogated the expression of HIFs induced by sevoflurane.

CONCLUSIONS

Sevoflurane can promote the expansion of human GSCs through HIFs in vitro. Inhaled anaesthetics may enhance tumour growth through tumour stem cells.