member

Research work

The current projects of his group include:

• 1. Transcription regulation of gliogenesis: a play between transcription factors and chromatin remodelers

Oligodendrocytes (OLs) are myelin-forming cells of the central nervous system wrapping axons and allowing the saltatory conduction of action potentials. These cells arise from the differentiation of oligodendrocyte precursor cells (OPCs), which requires significant genetic reprogramming implicating transcription factors but also chromatin remodelers. We have previously demonstrated the role of two of those, Chd7 and Chd8, in some aspects of OPC biology, like differentiation, proliferation and survival. Both of them are involved in diseases affecting brain development as mutations in Chd7 and Chd8 gene cause CHARGE syndrome and Autism Spectrum Disorder (ASD), respectively. In this study, we used OPCs as a model to understand the specificity of Chd7 and Chd8, as well as their compensatory effect on each other. To that purpose, we are looking at OPC processes and transcription deregulation (RNA-seq) caused by the loss of each factor or both. With the help of binding profiles (ChIP-seq) of these factors, we aim to understand their direct regulation in OPC biology. This study will allow a better understanding of the molecular mechanisms controlled by two chromatin remodelers involved in brain development and diseases.  

• 2. Characterization of the molecular mechanisms of Tns3 function in oligodendroglia

Multiple sclerosis (MS) is a neurological disease characterized by a loss of oligodendrocytes, the myelinating cell of the Central Nervous System. Despite recent advances leading to stop the immune system from attacking oligodendrocytes, efficient remyelinating therapies are still lacking. In MS, the spontaneous remyelination from the oligodendrocyte precursor cells (OPCs) present all over the brain is inefficient and diminishes with age. The observation that OPCs are present within demyelinating MS lesions, but fail to differentiate into myelinating cells, suggests that induction of OPC differentiation is a critical event for successful remyelination. We have recently identified Tns3 (Tensin 3) as a gene target of Ascl1 and Olig2, two key oligodendrogenic transcription factors, and showed that Tns3 is strongly induced at the timing of oligodendrocyte differentiation while downregulated in mature oligodendrocytes, constituting a good marker for immature oligodendrocytes. Using Tns3Tns3-V5 knock-in mice, we found that Tns3 protein tagged at C-terminal end with the small V5 epitope was detected specifically in oligodendroglia, where it is mainly restricted to immature OL stage, being localized to the perinuclear cytoplasm and cell processes. This expression pattern is the also found during adult brain remyelination after LPC injection, where Tns3 is found in newly formed OLs. Therefore, Tns3 constitutes a novel marker for immature OLs. In vivo Tns3 loss-of-function (LOF) by CRISPR/Cas9 technology in neonatal neural stem cells (NSCs) of the subventricular zone blocks oligodendrocyte differentiation without affecting OPC survival or proliferation. We reproduced this differentiation defect in OPC differentiating cultures using an AAV9 vectors to induce CRISPR-mediated Tns3 LOF. We generated a Tns3Flox mouse allele, and are currently inducing an OPC-specific Tns3 LOF in vivo and in vitro to confirm these results and explore cellular phenotypes of mutant OPCs. Using the V5-tagged Tns3 mouse line, we will perform proteomics to identify Tns3 partner proteins and understand its molecular mechanisms of Tns3 function in oligodendrocyte differentiation.  

• 3. Pharmacogenomics identification of small bioactive molecules for promoting oligodendrogenesis in a model of neonatal brain injury (project funded by the ANR 2017-2022)

In the context of our NeoRepair project, we proposed and successfully achieved the following objectives: We generated gene sets with enriched-expression in oligodendroglia, see figure 1 (step 3), by their expression in dorsal NSC/NPCs that actively promote oligodendrogenesis at neonatal stages (1), and by their enriched expression in oligodendroglial cells, compared to other brain cell-types (2). These oligodendroglial gene sets were then subjected to bioinformatics tools to identify their transcriptional networks and hubs (4), and to pharmacogenomics analysis to identify small bioactive molecules (drugs) promoting their expression (5). Given the large number of hits obtained by these approaches and in order to evaluate their impact in oligodendrogenesis, we introduced a knowledge-driven scoring procedure (6) based on functional studies demonstrating the requirement of a given gene in different aspects of oligodendrogenesis (OPC specification, proliferation, migration, survival, differentiation, myelination, and remyelination), by curating more than 2000 publications implicating around 400 genes. Pharmacogenomics analysis of this curated gene set allowed us to identify 393 small molecules promoting different aspects of oligodendrogenesis (7), with 221 of them regulating also our larger oligodendroglial-enriched gene sets. Levering our scoring procedure, we could rank the small molecules by the impact of their curated target-genes in different processes of oligodendrogenesis (8), and select 40 novel small molecules with putative pro-oligodendrogenic activity. Pharmacological analyses (drug pharmacokinetics and dynamics) led us to select from them 12 small molecules (9). Finally, we validated the pro-oligodendrogenic activity of these small molecules in differentiating cultures using either neural progenitors (10) or primary OPCs (11), with most small molecules showing stronger activity compared to positives controls currently under clinical trials, such as thyroid hormone (T3) normally used to foster OPC differentiation in culture, or clemastine, an antihistaminic drug.  

• 4. Molecular mechanisms of Ascl1 function in oligodendrogenesis versus neurogenesis

 

• 5. Assessing novel FDA-approved drugs with validated in vitro oligodendrogenic activity in preclinical mouse models of multiple sclerosis (proposed for funding to the ARSEP in 2021)

 

• 6. The dose requirement CHD8 & Chd7 chromatin remodelers in the diverse genetic programs of both oligodendrocyte progenitors and neuronal progenitors