PROJECTS

GliomaSignals - Oncometabolitic control of tumor growth and epileptogenesis in IDH mutated gliomas: D2HG signaling mechanism.

Funding: ERC consolidator grant

Dysregulated growth processes of gliomas interact with pro-epileptic plasticity of brain circuits in such a way that the excitatory transmitter glutamate promotes autocrine tumor invasion as well as epileptic synchrony in surrounding cortical regions. Most low-grade gliomas are associated with mutations of Isocitrate DesHydrogenase (IDH) genes which lead to an excess of the oncometabolite D-2Hydroxyglutarate (D2HG). With a structure mimicking glutamate, D2HG is thought to participate in both epileptogenic and oncologic processes. Importantly, while epileptic activity is accentuated, tumor prognosis is improved in affected people. My preliminary data now suggest a dual function for D2HG, acting as a glutamatergic agonist at high levels, but as an antagonist in the presence of glutamate. Solving this paradox will be a step forward in glioma science.

The GliomaSignals project will examine the role of D2HG in the neurobiology of gliomas bringing electrophysiology concepts and tools to neuro-oncology, seeking to transform our understanding. It seeks to better understand how D2HG modulates glutamatergic signaling, affects neuronal excitability and tumor growth, and to detect the extent to which tumor infiltration colocalizes with epileptic remodeling. In vivo and in vitro work mostly on human tissue will aim at:

1- Map biomarkers of epileptic activity / tumor infiltration by cortical recordings during surgery using unique next generation Neurogrid electrodes

2- Correlate D2HG levels, glutamate concentrations and tumor infiltration with recordings in peritumoral cortex at an unprecedented resolution

3- Identify D2HG effects on glutamate signaling in human tissue slices producing epileptic activities and in a rodent model

4- Explore D2HG long-term effects on epileptic activity and tumor growth / infiltration in co-cultures of tumors with surrounding peritumoral cortex by exploiting our unique capabilities for long-term human cortex organotypic cultures

Long-term in vitro effects of D2HG on epileptogenic and tumor growth / infiltration processes.

Since epileptogenesis and tumor growth processes take time, they are hardly questionable in acute slices, only recorded during up to 12 hours. This WP aims at validating, via a more integrated and weeks lasting study, the hypothesis that in IDH mutated (producing high intra- and peri-tumoral D2HG concentrations) LGGs (probably characterized by a limited and essentially intra-tumoral glutamate increase), D2HG exhibits pro-epileptic peritumoral effects on neuronal glutamatergic excitatory activity whereas in the tumor, D2HG antagonizes the glutamate-promoting effects on tumor cell division / migration. This would result in better prognosis and increased epileptogenicity. In contrast, in high-grade, non-mutated IDH gliomas producing very high levels of glutamate not antagonized by D2HG (not produced by these tumors), glutamate promotes tumor growth. Independently of the pro-epileptic effects of glutamate, rapid tumor growth and high excitotoxicity probably do not allow peritumoral neurons to establish epileptogenic networks.

MICRODYSCOG: Micro-electrocorticography-based mapping of Dysfunctionning Cognitive networks using evoked high frequency oscillations

Starting from the hypotheses that a) microelectrodes arrays are able to disentangle multiple microdomains of HGR/HFO sources, b) HFOs transiently disrupt the local functioning of the area directly involved in the generation of the pathological activity, and c) that spared regions still maintain the capability to produce HFG in response to ongoing tasks and processing, our project aims at 1) exploring the presence or absence of stimulus-locked HFG and HFO responses in pathological regions; 2) determining the relationship of HGR with ongoing pathological HFOs; 3) measuring the transient impact of HFO on the performance of cognitive tasks, with the idea that such impairment could serve as a new biomarker of dysfunctional tissue. The whole study will be performed on patients during glioma surgery in awake conditions. MICRODYSCOG project will take advantage of a clinical trial exploring the safety, ease of use and signal quality of Panaxium microelectrodes, sponsored by INSERM.

Funding: ANR

Collaboration: Michel le Van Quyen, LIB, Paris

Dynamics of glioma cells interactions during tumor progression: a multidimensional characterization.

Cells grow in an environment that influences them. This is especially true for tumor cells, as part of an ecosystem are influenced by interactions with other tumor cell types and with the tumor microenvironment. Detailed molecular characterization of cell types composing glioma brain tumors has been performed but a lot less is known regarding the influence of the cell types on each other and how this contributes to tumor progression.

We aim to decipher how the tumor cell types influence each other, how they interact with neurons, and how these interactions contribute to tumor progression through specific transcriptional programs.  We will especially focus on the interactions between different tumor cell types, and tumor cells and neurons, for which important key aspects still need to be discovered. This project focuses on high-grade diffuse gliomas, the most common adult brain tumor which are incurable to date. 

Performing cortex-glioma co-cultures, we study the effect of normal tissue interaction on glioma transcriptome. Then, we will generate a new Patch-seq data type allowing a morphological and electrophysiological characterization as well as single-cell transcriptional profiling of a given cell. We will therefore characterize the feature of tumor cells receiving a neuronal synapse and decipher tumor cell-neuron interactions following neuronal activation and their effect on the transcriptional program driving tumor growth. Overall, this project will provide novel biological insights into functional glioma tumor heterogeneity, a new mechanistic understanding of tumor cell interactions, and their effect on tumor progression. Ultimately, our findings could lead to further development of pre-clinical models and novel rationales for therapeutic targeting.

Funding: INCa - PLBIO

Collaboration: Florence Cavalli, Institut Curie, Paris

                      François Ducray HCL, Lyon

Synaptic signaling and neuronal interactions during seizure initiation in postoperative human epileptic tissue: dynamic interactions between pyramidal cells and interneurons, intracellular Cl^- and extracellular K⁺.  

Cellular and synaptic mechanisms of seizure initiation have not yet been resolved in human tissue or in animal models. Most work on animals has used normal tissue in a hyperexcited state which effectively excludes any role for synaptic remodeling. Postoperative tissue from focal brain regions of epileptic patients generates spontaneous interictal-like discharges. The use of this model opens unique opportunities to study basic mechanism of epilepsy. Using this model, we showed that increasing neuronal excitability results in a progressive build-up of distinct pre-ictal discharges. Non-epileptic tissue does not generate pre-ictal discharges or seizure-like events. The transition from pre-ictal discharges to seizure seems to occur when clusters of these events trigger tonic interneuron firing. High-frequency inhibitory cell firing intensifies Cl^--dependent depolarizing effects of GABA and increases external K⁺. The effects of GABAergic activity on neuronal Cl^- and increased external K⁺ to enhance neuronal firing are both regulated by K-Cl cotransporters. We study how these processes combine during ictogenesis? 

INSERM protocol C20-75 NeuroTissus

Ultrasound signals. Focused Ultrasound stimulation of nervous tissue: mechanisms of action and new method for synaptic plasticity induction. 

Ultrasound stimulation is known to be able to induce firing of peripheral nerves and neurons in central nervous tissue. Optimal stimulus parameters, activated surfaces and mechanisms are however not clear. In this project we attempt to remedy this lack of clarity using focused, low energy ultrasound for brain stimulation.  Small, surface probes have been developed to deliver ultrasonic stimulation and have been used to perform repeated stimulations on rodent hippocampal slices. There are many possibilities for this novel technology ranging from brain stimulation during neurosurgery to brain training during functional rehabilitation. We aim to define the spatial and temporal effects of different stimulus parameters and to ask which elements of brain tissue are stimulated (neurons, astrocytes, microglia; axons, somata, synapses, ionic channels) Finally, we should compare sites and mechanisms of plasticity induced by ultra-sound versus electrical stimulation and assess its mechanism. 

Funding : ANR NeuraActive 2022