Délara Sabéran-Djoneidi

Prenatal inflammatory insults accompany prematurity and provoke diffuse white matter injury (DWMI), which is associated with increased risk of neurodevelopmental pathologies, including autism spectrum disorders. DWMI results from maturation arrest of oligodendrocyte precursor cells (OPCs), a process that is poorly understood. Here, by using a validated mouse model of OPC maturation blockade, we provide the genome-wide ID card of the effects of neuroinflammation on OPCs that reveals the architecture of global cell fate issues underlining their maturation blockade. First, we find that, in OPCs, neuroinflammation takes advantage of a primed epigenomic landscape and induces abnormal overexpression of genes of the immune/inflammatory pathways: these genes strikingly exhibit accessible chromatin conformation in uninflamed OPCs, which correlates with their developmental, stage-dependent expression, along their normal maturation trajectory, as well as their abnormal upregulation upon neuroinflammation. Consistently, we observe the positioning on DNA of key transcription factors of the immune/inflammatory pathways (IRFs, NFkB), in both unstressed and inflamed OPCs. Second, we show that, in addition to the general perturbation of the myelination program, neuroinflammation counteracts the physiological downregulation of the cell cycle pathway in maturing OPCs. Neuroinflammation therefore perturbs cell identity in maturing OPCs, in a global manner. Moreover, based on our unraveling of the activity of genes of the immune/inflammatory pathways in prenatal uninflamed OPCs, the mere suppression of these proinflammatory mediators, as currently proposed in the field, may not be considered as a valid neurotherapeutic strategy.

Patients carrying autosomal dominant mutations in the histone/lysine acetyl transferases CBP or EP300 develop a neurodevelopmental disorder: Rubinstein-Taybi syndrome (RSTS). The biological pathways underlying these neurodevelopmental defects remain elusive. Here, we unravel the contribution of a stress-responsive pathway to RSTS. We characterize the structural and functional interaction between CBP/EP300 and heat-shock factor 2 (HSF2), a tuner of brain cortical development and major player in prenatal stress responses in the neocortex: CBP/EP300 acetylates HSF2, leading to the stabilization of the HSF2 protein. Consequently, RSTS patient-derived primary cells show decreased levels of HSF2 and HSF2-dependent alteration in their repertoire of molecular chaperones and stress response. Moreover, we unravel a CBP/EP300-HSF2-N-cadherin cascade that is also active in neurodevelopmental contexts, and show that its deregulation disturbs neuroepithelial integrity in 2D and 3D organoid models of cerebral development, generated from RSTS patient-derived iPSC cells, providing a molecular reading key for this complex pathology.

The reshaping of the DNA methylome landscape after prenatal alcohol exposure (PAE) has been well-documented in the adult brain, therefore a long time after the end of the exposure. However, the question of the immediate deposition or loss of DNA methylation marks in the prenatal neocortex, just after the end of PAE has not yet been directly addressed, genome widely. Using a binge-drinking-like model of PAE and capture of the DNA methylome, we have identified differentially methylated regions (DMRs) that are established immediately, within two hours after the end of PAE. Remarkably, these DMRs are prominently and statistically associated with: (i) enhancers that are active in the brain, associated with GO terms of importance for neurogenesis, neurodevelopment, and neuronal differentiation; (ii) genes that, in physiological conditions show dynamic gain in chromatin accessibility and/or upregulation of their expression in the time-window of exposure; (iii) imprinted genes and members of protocadherin genes clusters, two gene families playing key roles in neurodevelopment, whose mono-allelically expression is regulated by DNA methylation and impaired upon PAE. We observed that DMR-containing mono-allelically expressed genes, as well as other genes important for neurodevelopment, are also immediately upregulated upon PAE, suggesting that these early DNA methylation perturbations are thus highly susceptible to rapidly alter gene expression after PAE. DMRs in imprinted and protocadherin genes have been previously identified, both in the adult rodent brain prior-exposed to alcohol prenatally, and in cohorts of children diagnosed with fetal alcohol spectrum disorders (FASD). Our study thus strongly suggests that the DNA methylation profiles of key regulatory regions of these gene families are very quickly disturbed after the PAE and that these immediate altered regions could be persistently affected long after the stress. This strongly reinforces their potential as future biomarkers of PAE. In addition, binge-drinking-like PAE provokes immediate rewiring of the transcriptome with potentially dual consequences: 1) beneficial impacts that could support the recovery of cells from alcohol exposure, through slowing down of protein synthesis and energy-consuming respiratory pathways; 2) detrimental effects, through the inappropriate activation of critical pathways may directly perturb neurodevelopment. Ethical issues: The breeding and treatments of wild type C57BL/6N mice, used for the experimental protocols described in this study have been approved by the Institutional Animal Care and Use Ethical Committee of the Paris Cité University (registration number CEEA-40). The project has been recorded under the following reference by the Ministère de l’Enseignement Supérieur et de la Recherche (#2016040414515579). All efforts were made to reduce stress and pain to animals.

Cellular ability to maintain proper protein homeostasis (proteostasis) is essential for survival upon protein-damaging conditions. Heat shock transcription factor 2 (HSF2) is one of the human HSFs activated in response to proteotoxic stress. HSF2 is dispensable for cell survival during acute heat stress, but its amount and DNA-binding activity increase under prolonged proteotoxic stress conditions, such as proteasome inhibition. Nevertheless, the specific role(s) of HSF2 and the global HSF2-dependent gene expression profile during sustained stress have remained elusive. We found that HSF2 is required for cell survival during prolonged proteotoxicity, as shown by treating wild-type and HSF2-deficient human osteosarcoma U2OS cells with the proteasome inhibitor Bortezomib. Strikingly, our RNA-seq analyses revealed that HSF2 disruption leads to marked downregulation of cadherin superfamily genes and subsequent functional impairment of cadherin-mediated cell-cell adhesion. We propose HSF2 as a key regulator of genes belonging to the cadherin superfamily. We also demonstrate that HSF2-dependent downregulation of cadherin-mediated cell-cell adhesion predisposes U2OS cells to Bortezomib-induced proteotoxic stress. In conclusion, we show that by maintaining cell-cell adhesion HSF2 is essential for cell survival and thereby we describe a novel regime in the HSF-mediated protection against stress-induced protein damage.

Summary: Inflammatory insults accompanying prematurity provokes diffuse white matter injury (DWMI) which is associated with increased risk of neurodevelopmental disorders: pre-term infants have a 10 to 18-fold increased risk of developing autism spectrum disorders, compared to term infants. DWMI is due to maturation arrest in oligodendrocyte precursor cells (OPCs). Using integrated genome-wide approaches in a validated mouse perinatal model of DWMI, induced by systemic- and neuro-inflammation based on repeated interleukin-1B administrations, we show that neuroinflammation induces limited epigenomic disturbances in OPCs. In contrast, we unravel marked transcriptomic alterations of genes of the immune/inflammatory pathways, which are expressed in unstressed OPCs and physiologically downregulated along OPC maturation. Consistently, we observe that transcription factors of the inflammatory pathways occupy DNA both in unstressed and inflamed OPCs. Thus, rather than altering genome-wide chromatin accessibility, neuroinflammation takes advantage of open chromatin regions and deeply counteracts the stage-dependent downregulation of these active transcriptional programs. Therefore, our study opens new avenues for the future development of targeted approaches to protect preterm brains. Highlights: ∘ Limited epigenomic impact of inflammation on OPC maturation blockade ∘ Major transcriptomic disturbances take advantage of a primed epigenetic landscape ∘ Proinflammatory genes are active in OPCs and downregulated upon maturation ∘ Neuroinflammation counteracts both this downregulation and maturation in OPCs

Patients suffering from psychiatric disorders have a life span burden, which represents an enormous human, family, social, and economical cost. Several concepts have revolutionized our way of appraising neuropsychiatric disorders (NPDs). They result from a combination of genetic factors and environmental insults, and their etiology finds roots in the neurodevelopmental period. As epigenetic mechanisms tightly control brain development, exposure to adverse conditions disturbing the epigenetic landscape of the fetal brain increases the risk of developing NPDs, due to the persistence of abnormal epigenetic signatures, at distance from the initial stimulus. Here, we review these concepts and discuss recent results based on next‐generation sequencing (NGS) approaches that have shed light on the mechanisms that underlie the emergence of NPDs, highlighting the importance of epigenetic phenomena. Because epigenetic mechanisms are potentially reversible, unraveling the epigenetic contribution to the etiology of NPDs is key to the design of future therapeutic strategies. Early diagnosis of patients prone to NPDs for early intervention represents a challenge that waits for biomarkers of vulnerability, and could be decisive for improving the outcome and prognosis of “at‐risk” patients.