A key process enabling the correct functioning of neural circuits involves the formation of multi‐layered membranous myelin sheaths around axons. Myelin sheaths, made by specialised glial cells called oligodendrocytes in the central nervous system (CNS), metabolically support underlying axons and speed up electrical impulse conduction, aiding efficient communication between neurons. As only a subset of axons in the CNS are myelinated, with unique patterns developed therein, it raises the questions: how does an oligodendrocyte choose which axon to myelinate and what regulates the amount of myelin made? The production of myelin sheaths by the oligodendrocyte, is under strong influence from of a range of signals including those mediated by G protein‐coupled receptor (GPR) superfamily members. One GPR, Endothelin receptor B (EDNRB), best known for regulating blood flow, had previously been demonstrated to both positively and negatively influence myelination. I have investigated how EDNRB regulates myelination using an in vitro myelination assay, alongside in vivo analysis in zebrafish and mice. These systems identified a direct signalling role for EDNRB in the promotion of myelin sheath number. Furthermore, profiling the protein signalling cascade downstream of this receptor identified a range of known and novel factors involved in the regulation of myelin sheath number including the MAPK pathway, Src family kinases, ErbB receptors, protein kinase C ε, NMDAR and AMPAR. Functional analyses of a subset of these factors elucidate how EDNRB signalling, potentially connecting signals from a range of cell types, ensures correct adequate myelination in the CNS.

Les oligodendrocytes (OLs) sont les cellules myélinisantes du système nerveux central, s’enroulant autour des axones et permettant la conduction saltatoire du potentiel d’action. Dans la Sclérose en Plaques, des gaines de myélines sont détruites et l’efficacité de la remyélinisation par les précurseurs d’oligodendrocytes (OPCs) diminue avec la progression de la maladie. Une meilleure compréhension du mécanisme qui contrôle la génération des OPCs et leur différentiation est donc essentielle pour développer des thérapies efficaces de remyélinisation. L’oligodendrogenèse, qui comprend les étapes de génération des OPCs, de différenciation et de maturation des OLs, est un processus contrôlé par des facteurs de transcription spécifiques incluant Ascl1, Olig2 and Sox10 mais le mécanisme impliqué est encore peu connu. Sachant que les facteurs du remodelage de la chromatine sont des régulateurs nécessaires à la formation de la boucle promoter-enhancer permettant l’initiation de la transcription, nous nous sommes focalisé sur Chd7 (Chromodomain-Helicase-DNA-Binding 7), un membre de la famille de protéine CHD. Dans une première étude, nous avons montré que Chd7 est hautement enrichi dans le lignage oligodendroglial avec un pic d’expression pendant la différenciation des OLs. Nous avons également montré que la délétion conditionnelle de Chd7 diminuait la différentiation des OLs pendant la (re)myélinisation. Dans un seconde étude, nous avons utilisé des techniques de génomique sur les OPCs purifiés pour étudier la régulation par Chd7 de gènes impliqués dans la différenciation, la survie et la prolifération des OPCs. Dans ce but, nous avons générer des délétions inductible de Chd7 spécifiquement dans les OPCs (Chd7iKO) et nous avons analysé le transcriptome (RNA-seq) d’OPCs purifiés à partir de cerveaux de souris P7 comparé à des contrôles. Nous avons trouvé que Chd7 activait l’expression des gènes impliqué dans la différenciation des OPCs et la myélinisation et inhibait l’apoptose, sans montré de défaut de prolifération. Pour aller plus loin, nous avons étudié Chd8, un paralogue de Chd7, et nous avons montré qu’il est exprimé dans le lignage oligodendrocytaire avec un pic d’expression dans les OL en différenciation, similairement à Chd7. Les données de fixation (ChIP-seq) de Chd7 et Chd8 indiquent que ces deux facteurs du remodelage de la chromatine se fixent sur des gènes communs reliés au processus de différenciation, de survie et de prolifération des OPCs. Intégrant ces données avec celles de facteurs transcriptionnels clés dans l’oligodendrogenèse (Olig2, Ascl1 et Sox10), nous avons construit un modèle de la régulation de l’expression de gènes contrôlés dans le temps et impliqué dans chacune des étapes de la différenciation des oligodendrocytes. / Oligodendrocytes (OLs) are myelin-forming cells of the central nervous system wrapping axons and allowing the saltatory conduction of action potentials. In Multiple sclerosis (MS), myelin sheath is destroyed and effective remyelination by oligodendrocyte precursor cells (OPCs) diminishes with disease progression. Therefore, a better understanding of the mechanisms controlling OPC generation and differentiation is essential to develop efficient remyelinating therapies. Oligodendrogenesis, involving the steps of OPC generation, OPC differentiation and maturation of OLs, is a process controlled by specific transcription factors including Ascl1, Olig2 and Sox10 but the mechanisms involved are poorly understood. As it is known that chromatin remodelers are regulatory factors necessary in the formation of the promoter-enhancer loop prior to transcription, we focused our study on Chd7 (Chromodomain-Helicase-DNA-Binding 7), a member of the CHD protein family. In a first study, we showed that Chd7 is highly enriched in the oligodendroglial lineage cells with a peak of expression during OL differentiation and that Chd7 OPC-conditional deletion impairs OL differentiation during (re)myelination. In a second study, we used unbiased genome wide technics in purified OPCs to study Chd7 regulation of genes involved in OPC differentiation, proliferation and survival. To this aim, we have generated OPC-specific inducible Chd7 knock-out (Chd7-iKO) and analyse the transcriptome (RNA-seq) of purified OPCs from P7 mouse cortices compared to control littermates. We found that Chd7 promote the expression genes involved in OPC differentiation and myelination and inhibits apoptosis, without affecting OPC proliferation. Furthermore, we investigated Chd8, a paralog of Chd7, showing that it is expressed in the oligodendroglial lineage with a peak of expression in differentiating oligodendrocytes, similar to Chd7. Genome wide binding (ChIP-seq) profiling for Chd7 and Chd8 indicate that these two chromatin remodelers bind to common genes related to OPC differentiation, survival and proliferation. Integrating these datasets with other key transcriptional regulators of oligodendrogenesis (Olig2, Ascl1 & Sox10), we have built a model accounting for the time-controlled regulate expression of genes involved in each step of OL differentiation.

No description available.

Correct myelin formation and maintenance is essential for normal functioning and is affected in the demyelinating disease, Multiple Sclerosis (MS). To better understand this disease and identify important targets in promoting remyelination, the study of developmental myelination is important. Galanin, a 29 amino acid neuropeptide has been identified as a potentially important modulator in early myelin development. In our Galanin transgenic mouse model, myelin basic protein (MBP) levels are highly elevated at postnatal day 10 compared to the wild type. A preliminary investigation of Galanin’s behavior at various doses in vitro, yielded results that agreed with Galanin’s effect in vivo. Proteolipid protein (PLP) was highly elevated in the 10nM dose in vitro indicating Galanin exerts its effects in a time and dose dependent manner. Overall, this study identifies Galanin as a potentially important modulator of developmental myelination that may become a therapeutic target in future studies of demyelinating diseases.

No description available.

In neurodegenerative diseases, the CNS becomes inflamed through activation of pathways, including the NF-B pathway. Some of the therapies for those diseases target neuroinflammatory pathways. Here, we explore the mechanisms for the upregulation of a subset of genes following a restimulation of the NF-B pathway. We discover that this upregulation occurs independent of IRF1 expression and type 1 interferon signaling. A knockdown of IRF1 using siRNA and an inhibition of JAK proteins using inhibitor AG490 both had no effect on priming. A secreted factor was found to upregulate the expression of both this subset of genes and genes encoding pro-inflammatory cytokines induced by NF-B activation. We also explored the role of IRF1 in a mouse model of multiple sclerosis. We found that the deletion of IRF1 from oligodendrocytes diminished EAE severity. A deletion of IRF1 from myeloid cells within mice did not diminish EAE severity, however showed a promising decrease in the expression of certain inflammatory genes. Thus, IRF1 plays a critical role in fine-tuning inflammatory responses in the brain.

Apoptosis is essential not only to the normal development of a multicellular organism but also for the maintenance of tissue homeostasis. This proposal seeks to investigate, in part, the role of oligodendrocyte (OL) apoptosis in myelination. We used an OL-specific conditional knockout animal to study caspase-8 function in OL development; analyzing histological differences in myelination at postnatal day 10 and alterations to OL proliferation, differentiation, and cell death in culture. Our preliminary data suggests that deletion of caspase-8 did not alter OL proliferation or differentiation in culture, but reduced the percentage of apoptotic cells following nutrient deprivation. In vivo, we found an increase in myelinated axons in the spinal cord of caspase-8 deficient mice, indicating a role for caspase-8 in the myelination process. This study also seeks to investigate mechanisms of cell death in OLs, astrocytes, and neurons following oxidative injury. Exposure of primary OLs, astrocytes, and neurons to arachidonic acid (AA) resulted in oxidative stress and cell death. Necrostation-1, the specific inhibitor of receptor interacting protein kinase 1 (RIP-1), markedly prevented AA-induced oxidative death in OLs and astrocytes, but not in neurons. Similarly, we found that blockade of 12-lipoxygenase (LOX) and c-Jun N-terminal kinase (JNK) protected OLs and astrocytes but not neurons against AA toxicity. Consistent with the inability of necrostatin-1 to rescue neurons, we found very low expression of RIP-1 as well as RIP-3 in neurons. Finally, the zinc chelator TPEN effectively abolished AA-induced oxidative death in all three cell types, suggesting zinc release as a common mechanism. Taken together, our findings indicate differences in cell death mechanisms following oxidative injury in astrocytes, OLs, and neurons.

Tuberous Sclerosis Complex (TSC) is an autosomal dominant syndrome characterized by epilepsy, intellectual disability, and autism. Recent studies have suggested that white matter abnormalities, including hypomyelination, contribute to the cognitive deficits in TSC patients, but the mechanism has remained elusive. I used the neuron-specific Tsc1 knockout mice that display a marked decrease in myelin and show that oligodendrocytes are arrested at immature stages of development in vivo resulting in a reduction in the number of myelinating cells. I established an oligodendrocyte culture system and examined the effect of neuron-conditioned media and found that the Tsc1 mutant phenotype was replicable in vitro using medium collected from Tsc1 knockdown (TSC-KD) neurons, confirming that a secreted signal is responsible for inhibiting differentiation of the oligodendrocytes. I took an unbiased genome-wide approach and identified Connective Tissue Growth Factor (CTGF) as a putative candidate for the secreted signal. I confirmed that CTGF was upregulated in Tsc1 mutant neurons and characterized its spatial and developmental expression pattern in our mouse model. In vitro, CTGF was sufficient to inhibit differentiation of oligodendrocytes. The addition of CTGF neutralizing antibody to the TSC-KD neuronal media was able to reverse the suppression of oligodendrocyte maturation, strongly suggesting that CTGF is a major component of the oligodendrocyte inhibitory signal derived from Tsc mutant neurons. Since TSC mutation affects all cells, I investigated the role of TSC in oligodendrocytes. In response to TSC knockdown, oligodendrocytes demonstrate an upregulation of cellular stress marker. I also found a decrease in myelin protein genes, a finding that offers interesting implications for the role of TSC in hypomyelination. Furthermore, I expanded my research into Zellweger disease, a syndrome that involves TSC in its neuropathological manifestations including white matter deficits, and found that localization of TSC to the peroxisome is a critical factor in neuron development. Together, this body of work developed new approaches in Tuberous Sclerosis research in the brain to investigate a previously under-appreciated aspect of TSC pathology - myelination. I have demonstrated that the TSC pathway has important roles in neuron-oligodendrocyte communication and emphasize the critical importance of neuron-derived signals in the establishment of myelination.

Multiple sclerosis is a demyelinating disease affecting the central nervous system. It is the most prevalent disabling neurological condition among young adults, with onset typically between 20 and 40 years of age. Infiltrating immune cells and microglia activations are associated with inflammatory and neurodegenerative mechanisms. Current available disease modifying therapies suppress or modulate the immune system. These pharmaceuticals differ with respect to administration route and frequency, adverse effects, and efficacy. This paper provides a thorough manuscript illustrating the major prescribing factors, efficacy profiles, adverse events, and contraindications that patients and clinicians should consider while choosing a treatment. Despite the advancements made over the past 20 years, patients with progressive multiple sclerosis have few therapeutic options. Additionally, this paper assesses emerging therapies and disease targets on the pharmaceutical horizon, which have shown promise for all disease phenotypes.

No description available.