Changes in chromatin state reveal ARNT2 at a node of a tumorigenic transcription factor signature driving glioblastoma cell aggressiveness.

Although a growing body of evidence indicates that phenotypic plasticity exhibited by glioblastoma cells plays a central role in tumor development and post-therapy recurrence, the master drivers of their aggressiveness remain elusive. Here we mapped the changes in active (H3K4me3) and repressive (H3K27me3) histone modifications accompanying the repression of glioblastoma stem-like cells tumorigenicity. Genes with changing histone marks delineated a network of transcription factors related to cancerous behavior, stem state, and neural development, highlighting a previously unsuspected association between repression of ARNT2 and loss of cell tumorigenicity. Immunohistochemistry confirmed ARNT2 expression in cell sub-populations within proliferative zones of patients' glioblastoma. Decreased ARNT2 expression was consistently observed in non-tumorigenic glioblastoma cells, compared to tumorigenic cells. Moreover, ARNT2 expression correlated with a tumorigenic molecular signature at both the tissue level within the tumor core and at the single cell level in the patients' tumors. We found that ARNT2 knockdown decreased the expression of SOX9, POU3F2 and OLIG2, transcription factors implicated in glioblastoma cell tumorigenicity, and repressed glioblastoma stem-like cell tumorigenic properties in vivo. Our results reveal ARNT2 as a pivotal component of the glioblastoma cell tumorigenic signature, located at a node of a transcription factor network controlling glioblastoma cell aggressiveness.

Time-dependent impact of glutamatergic modulators on the promnesiant effect of 5-HT6R blockade on mice recognition memory.

Selective antagonists at serotonin 5-HT6 receptors (5-HT6R) improve memory performance in rodents and are currently under clinical investigations. If blockade of 5-HT6R is known to increase glutamate release, only two studies have so far demonstrated an interaction between 5-HT6R and glutamate transmission, but both, using the non-competitive NMDA antagonist MK-801, insensitive to variations of glutamate concentrations. In a place recognition task, we investigated here in mice the role of glutamate transmission in the beneficial effects of 5-HT6R blockade (SB-271046). Through the use of increasing intervals (2, 4 and 6h) between acquisition and retrieval, we investigated the time-dependent impact of two different glutamatergic modulators. NMDAR-dependant glutamate transmission (NMDA Receptors) was either blocked by the competitive antagonist at NMDAR, CGS 19755, or potentiated by the glycine transporter type 1 (GlyT1) inhibitor, NFPS. Results showed that neither SB-271046, nor CGS 19755, nor NFPS, alter behavioural performances after short intervals, i.e. when control mice displayed significant memory performances (2h and 4h) (respectively 10, 3, and 0.625mg.kg-1). Conversely, with the 6h-interval, a situation in which spontaneous forgetting is observed in control mice, SB-271046 improved recognition memory performances. This beneficial effect was prevented when co-administered with either CGS 19755 or NFPS, which themselves had no effect. Interestingly, a dose-dependent effect was observed with NFPS, with promnesic effect observed at lower dose (0.156mg.kg-1) when administrated alone, whereas it did no modify promnesic effect of SB-271046. These results demonstrate that promnesiant effect induced by 5-HT6R blockade is sensitive to the competitive blockade of NMDAR and underline the need of a fine adjustment of the inhibition of GlyT1. Overall, our findings support the idea of a complex crosstalk between serotonergic and glutamatergic systems in the promnesic properties of 5-HT6R antagonists.

Glioblastoma cell motility depends on enhanced oxidative stress coupled with mobilization of a sulfurtransferase.

Cell motility is critical for tumor malignancy. Metabolism being an obligatory step in shaping cell behavior, we looked for metabolic weaknesses shared by motile cells across the diverse genetic contexts of patients' glioblastoma. Computational analyses of single-cell transcriptomes from thirty patients' tumors isolated cells with high motile potential and highlighted their metabolic specificities. These cells were characterized by enhanced mitochondrial load and oxidative stress coupled with mobilization of the cysteine metabolism enzyme 3-Mercaptopyruvate sulfurtransferase (MPST). Functional assays with patients' tumor-derived cells and -tissue organoids, and genetic and pharmacological manipulations confirmed that the cells depend on enhanced ROS production and MPST activity for their motility. MPST action involved protection of protein cysteine residues from damaging hyperoxidation. Its knockdown translated in reduced tumor burden, and a robust increase in mice survival. Starting from cell-by-cell analyses of the patients' tumors, our work unravels metabolic dependencies of cell malignancy maintained across heterogeneous genomic landscapes.

Capture at the single cell level of metabolic modules distinguishing aggressive and indolent glioblastoma cells.

Glioblastoma cell ability to adapt their functioning to microenvironment changes is a source of the extensive intra-tumor heterogeneity characteristic of this devastating malignant brain tumor. A systemic view of the metabolic pathways underlying glioblastoma cell functioning states is lacking. We analyzed public single cell RNA-sequencing data from glioblastoma surgical resections, which offer the closest available view of tumor cell heterogeneity as encountered at the time of patients' diagnosis. Unsupervised analyses revealed that information dispersed throughout the cell transcript repertoires encoded the identity of each tumor and masked information related to cell functioning states. Data reduction based on an experimentally-defined signature of transcription factors overcame this hurdle. It allowed cell grouping according to their tumorigenic potential, regardless of their tumor of origin. The approach relevance was validated using independent datasets of glioblastoma cell and tissue transcriptomes, patient-derived cell lines and orthotopic xenografts. Overexpression of genes coding for amino acid and lipid metabolism enzymes involved in anti-oxidative, energetic and cell membrane processes characterized cells with high tumorigenic potential. Modeling of their expression network highlighted the very long chain polyunsaturated fatty acid synthesis pathway at the core of the network. Expression of its most downstream enzymatic component, ELOVL2, was associated with worsened patient survival, and required for cell tumorigenic properties in vivo. Our results demonstrate the power of signature-driven analyses of single cell transcriptomes to obtain an integrated view of metabolic pathways at play within the heterogeneous cell landscape of patient tumors.