Problems and Pitfalls of Identifying Remyelination in Multiple Sclerosis.

Regenerative medicines that promote remyelination in multiple sclerosis (MS) are making the transition from laboratory to clinical trials. While animal models provide the experimental flexibility to analyze mechanisms of remyelination, here we discuss the challenges in understanding where and how remyelination occurs in MS.The authors acknowledge the following support: The UK Multiple Sclerosis Society (RTK, CZ, RJMF), The Adelson Medical Research Foundation (DSR, DEB, RJMF), Intramural Research Program of NINDS/NIH (DSR), European Research Council (ERC) under the European Union Horizon 2020 Re- search and Innovation Program (RTK), The Lister Institute (RTK), and a core support grant from the Wellcome and MRC to the Wellcome-Medical Research Council Cambridge Stem Cell Institute (RTK, RJMF)

Opposing roles for Hoxa2 and Hoxb2 in hindbrain oligodendrocyte patterning

Oligodendrocytes are the myelin-forming cells of the vertebrate CNS. Little is known about the molecular control of region-specific oligodendrocyte development. Here, we show that oligodendrogenesis in the mouse rostral hindbrain, which is organized in a metameric series of rhombomere-derived (rd) territories, follows a rhombomere-specific pattern, with extensive production of oligodendrocytes in the pontine territory (r4d) and delayed and reduced oligodendrocyte production in the prepontine region (r2d, r3d). We demonstrate that segmental organization of oligodendrocytes is controlled by Hoxgenes, namely Hoxa2 and Hoxb2. Specifically, Hoxa2 loss of function induced a dorsoventral enlargement of the Olig2/Nkx2.2-expressing oligodendrocyte progenitor domain, whereas conditional Hoxa2 overexpression in the Olig2(+) domain inhibited oligodendrogenesis throughout the brain. In contrast, Hoxb2 deletion resulted in a reduction of the pontine oligodendrogenic domain. Compound Hoxa2(-/-)/Hoxb2(-/-) mutant mice displayed the phenotype of Hoxb2(-/-) mutants in territories coexpressing Hoxa2 and Hoxb2 (rd3, rd4), indicating that Hoxb2 antagonizes Hoxa2 during rostral hindbrain oligodendrogenesis. This study provides the first in vivo evidence that Hox genes determine oligodendrocyte regional identity in the mammalian brain

Live imaging of targeted cell ablation in Xenopus:a new model to study demyelination and repair

Live imaging studies of the processes of demyelination and remyelination have so far been technically limited in mammals. We have thus generated a Xenopus laevis transgenic line allowing live imaging and conditional ablation of myelinating oligodendrocytes throughout the central nervous system (CNS). In these transgenic pMBP-eGFP-NTR tadpoles the myelin basic protein (MBP) regulatory sequences, specific to mature oligodendrocytes, are used to drive expression of an eGFP (enhanced green fluorescent protein) reporter fused to the E. coli nitroreductase (NTR) selection enzyme. This enzyme converts the innocuous pro-drug metronidazole (MTZ) to a cytotoxin. Using two-photon imaging in vivo, we show that pMBP-eGFP-NTR tadpoles display a graded oligodendrocyte ablation in response to MTZ, which depends on the exposure time to MTZ. MTZ-induced cell death was restricted to oligodendrocytes, without detectable axonal damage. After cessation of MTZ treatment, remyelination proceeded spontaneously, but was strongly accelerated by retinoic acid. Altogether, these features establish the Xenopus pMBP-eGFP-NTR line as a novel in vivo model for the study of demyelination/remyelination processes and for large-scale screens of therapeutic agents promoting myelin repair

FAS-dependent cell death in α-synuclein transgenic oligodendrocyte models of multiple system atrophy

Multiple system atrophy is a parkinsonian neurodegenerative disorder. It is cytopathologically characterized by accumulation of the protein p25α in cell bodies of oligodendrocytes followed by accumulation of aggregated α-synuclein in so-called glial cytoplasmic inclusions. p25α is a stimulator of α-synuclein aggregation, and coexpression of α-synuclein and p25α in the oligodendroglial OLN-t40-AS cell line causes α-synuclein aggregate-dependent toxicity. In this study, we investigated whether the FAS system is involved in α-synuclein aggregate dependent degeneration in oligodendrocytes and may play a role in multiple system atrophy. Using rat oligodendroglial OLN-t40-AS cells we demonstrate that the cytotoxicity caused by coexpressing α-synuclein and p25α relies on stimulation of the death domain receptor FAS and caspase-8 activation. Using primary oligodendrocytes derived from PLP-α-synuclein transgenic mice we demonstrate that they exist in a sensitized state expressing pro-apoptotic FAS receptor, which makes them sensitive to FAS ligand-mediated apoptosis. Immunoblot analysis shows an increase in FAS in brain extracts from multiple system atrophy cases. Immunohistochemical analysis demonstrated enhanced FAS expression in multiple system atrophy brains notably in oligodendrocytes harboring the earliest stages of glial cytoplasmic inclusion formation. Oligodendroglial FAS expression is an early hallmark of oligodendroglial pathology in multiple system atrophy that mechanistically may be coupled to α-synuclein dependent degeneration and thus represent a potential target for protective intervention

Problems and Pitfalls of Identifying Remyelination in Multiple Sclerosis

The authors acknowledge the following support: The UK Multiple Sclerosis Society (MS50 to R.T.K., C.Z., and R.J.M.F.), The Adelson Medical Research Foundation (D.S.R., D.E.B., and R.J.M.F.), Intramural Research Program of NINDS/NIH (D.S.R.), European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (771411 to R.T.K.), The Lister Institute (R.T.K.), and a core support grant from the Wellcome and MRC to the Wellcome-Medical Research Council Cambridge Stem Cell Institute (203151/Z/16/Z to R.T.K. and R.J.M.F.). Publisher Copyright: © 2020 Elsevier Inc.Regenerative medicines that promote remyelination in multiple sclerosis (MS) are making the transition from laboratory to clinical trials. While animal models provide the experimental flexibility to analyze mechanisms of remyelination, here we discuss the challenges in understanding where and how remyelination occurs in MS.Peer reviewe

Live-Imaging of Myelin in Animal Models and in Human

International audienceThe pioneer work of Paul Broca (1824-1880) was the first demonstration that brain is functionally not homogeneous, but on the contrary constituted by the assembly of different areas each responsible for specific function. Investigating aphasic patients Broca described a small area in the left frontal lobe, which he described as responsible for articulate language [1, 2]. This region is now known as Broca’s area. Since then the localizationism theory has extended and in association to the long-life concept that only neurons were true functional cells, it has generally been assumed that each brain function is driven by some groups or subpopulation of neurons. As a consequence, any neurological dysfunction had to be attributed to the lesion of a subgroup of neuronal cell. One of the most puzzling situation had been reached by Gerstmann’s syndrome, a condition where a small lesion localized in the dominant inferior parietal lobe results in the association of four apparently completely unrelated symptoms: dysgraphia/agraphia dyscalculia/acalculia, finger agnosia, and left-right disorientation. First described in 1924 by Joseph Gerstmann [3, 4] this syndrome has stirred a controversy for over 80 years among neurologists questioning which population of cortical neurons localized in the angular and supramarginal gyrus could be responsible for such a diversity of cognitive functions. It is only very recently with the development ofdiffusion tensor technique associated with functional MRI that Rusconi and colleagues have succeeded to solve this enigma showing that a pure form ofGerstmann’s syndrome might arise from disconnection, via a lesion, to separate but co-localized myelinated fiber tracts in the parietal lobe [5]. This has been an exemplary demonstration on how structural and functional connectivity studies contribute to improve the understanding of cognitive deficits. It is of interest to note that recent reinvestigation by magnetic resonance of the brain of Louis Victor Leborgne, Broca’s first patient, (also known as « Tan-Tan » since this was the only syllable the patient could articulate), has shown disruption extended to connections projecting to areas distant from the lesion, illustrating that the damaged tract were linking areas functionally engaged for tasks related to language production [6]. Altogether these examples demonstrate the crucial importance of visualization of myelinated tracts. The aim of this special issue of “Brain Plasticity” is to collect contributions both in animal models as well as in human on how to investigate in vivo white matter tracts. Je Bin and David Lyons illustrate the immense advantage of combining fluorescent reporter genetically introduced into transparent vertebrates, zebra fish and xenopus tadpoles. Geneviève Rougon, Sophie Brasselet and Franck Debarbieux address the recent development of intravital imaging techniques in rodent, with a special focus on observation of inflammatory response and demyelinating lesions accompanied by axonal degeneration during Experimental Autoimmune Encephalomyelitis. In human, myelination begins during fetal development. Jessica Dubois and colleagues illustrate how the recent use of non-invasive techniques such as magnetic resonance imaging (MRI) and magneto- and electroencephalography (M/EEG) has opened the possibility to link the progressive acquisition of sensorimotor and cognitive functions with myelination of fiber tracts transferring and processing information between different brain regions. In contrast to any other membrane the lipid/protein ratio of myelin is 70/30, i.e., an inverted ratio in comparison with other biological membranes. As a consequence it is estimated that 40% of the mass of myelin is compartmentalized water. Conventional MRI is based on the resonance of proton, and the majority of the signal measured by magnetic resonance (MR) emanates from hydrogen in water molecules. Although white matter tracts may therefore appear not ideal structures to be visualized by conventional MRI, Cornelia Laule and Alex MacKay show how more sophisticated treatment of MR signal allows measuring the water content of myelin. In their review, they illustrate how myelin content imaging can be used to study animal models and different human neurological conditions. To have access to direct measurement of myelin Benedetta Bodini and Bruno Stankoff have developed different ligands, which bind to myelin components. After labeling with a positron emitter, such myelin ligands allow direct visualization of myelinated tracts and quantification of myelin content using PositronEmission Tomography (PET). Finally, Hughes Duffau reviews original data obtained during neurosurgical intervention on human by direct axonal electrostimulation of myelinated tracts in adults, with regard to the functional connectivity mediating the sensorimotor, visuo-spatial, language, cognitive and emotional functions, as well as the interactions between these different sub-networks, leading ultimately to explore consciousness

Etude de la neurogénèse et de la gliogénèse dans le diencephale de souris

Depuis de nombreuses années, il existe un débat sur le mode de formation des neurones et des cellules gliales, précocement, à partir de la zone ventriculaire. Ces deux types cellulaires sont-ils issus d une même cellule ventriculaire où bien existe-t-il deux progeniteurs chacun dédié à la mise en place d un seul lignage ? Pour répondre à cette question, nous avons cherché un marqueur exprimé dans un domaine restreint de la zone ventriculaire au cours des périodes de neurogénèse et de gliogénèse et notre choix s est porté sur le transcrit plp. L étude des cellules plp+ ventriculaires à deux stades de développement, E9,5 et E13,5 nous a permis de démontrer par des cultures clonales in vitro et grâce a un marquage génétique permanent, in vivo, l existence de deux progeniteurs plp+ indépendants : un progeniteur neuronal précoce et un progeniteur glial plus tardif. Ces résultats sont donc en faveur de l existence de deux progeniteurs distincts, chacun dédié a un lignage neural, dans la zone ventriculaire. Par la suite, l analyse du lignage plp par utilisation d une souris transgénique plp-Cre a confirmé que ces cellules étaient capables de donner naissance à des cellules gliales et à des neurones et nous a permis d établir un cartographie diencéphalique des dérivés neuronaux. Ceux-ci se repartissent dans différents noyaux prethalamiques et hypothalamiques, à l intérieur desquels ils représentent une sous-population. Nous avons également cherché à mettre en évidence des facteurs impliqués dans la transition neurone/glie. Pour cela, nous avons comparé, par la technique des puces à ADN, le transcriptome des progeniteurs neuronaux plp+ avec celui des progeniteurs gliaux. Cette technique nous a permis de sélectionner trois gènes candidats potentiellement impliqués dans la gliogenèse.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

DEVELOPPEMENT DU LIGNAGE OLIGODENDROCYTAIRE ; MISE EN EVIDENCE DES SITES D'EMERGENCE AU COURS DU DEVELOPPEMENT EMBRYONNAIRE

LE BUT DE CE TRAVAIL A ETE D'ETUDIER LE DEVELOPPEMENT DU LIGNAGE OLIGODENDROCYTAIRE. LES QUESTIONS AUXQUELLES NOUS AVONS TENTE D'APPORTER UNE REPONSE ETAIENT : OU ET QUAND SONT GENERES LES OLIGODENDROCYTES ? JUSQU'A RECEMMENT, ON PENSAIT QUE CES CELLULES ETAIENT GENEREES TARDIVEMENT AU COURS DU DEVELOPPEMENT, A PARTIR DE CELLULES PROGENITRICES DES ZONES SUBVENTRICULAIRES. LES TRAVAUX DU GROUPE DE B. ZALC ONT PERMIS D'IDENTIFIER UNE POPULATION CELLULAIRE VENTRICULAIRE, CARACTERISEE PAR L'EXPRESSION DU GENE PLP/DM-20, CODANT POUR LA PROTEINE MAJORITAIRE DE LA MYELINE : LA PROTEOLIPIDE PROTEINE PLP/DM-20. CES RESULTATS ONT CONDUIT A EMETTRE L'HYPOTHESE D'UNE EMERGENCE TRES PRECOCE DES OLIGODENDROCYTES, CONCOMITTENTE A CELLE DES PREMIERS NEURONES. MON TRAVAIL DE THESE A CONSISTE A TESTER CETTE HYPOTHESE. POUR CELA, DEUX APPROCHES EXPERIMENTALES ONT ETE COMBINEES : LA TRANSGENESE MURINE ET LA MICROCHIRURGIE EMBRYONNAIRE AVIAIRE. L'UTILISATION DE LA SOURIS TRANSGENIQUE PLP-SH BLE-LACZ NOUS A PERMIS DE DEMONTRER QUE LES CELLULES DE LA ZONE VENTRICULAIRE EXPRIMANT LE TRANSCRIT PLP/DM-20 SONT EFFECTIVEMENT DES PRECURSEURS D'OLIGODENDROCYTES. CES CELLULES APPARAISSENT DANS DES TERRITOIRES RESTREINTS DU TUBE NEURAL ET SEMBLENT INDEPENDANTES DU PDGF-AA POUR LEUR SURVIE ET LEUR PROLIFERATION. CES OBSERVATIONS NOUS ONT DONC CONDUIT A PROPOSER L'EXISTENCE D'AU MOINS DEUX POPULATIONS DE PRECURSEURS D'OLIGODENDROCYTES : L'UNE CARACTERISEE PAR L'EXPRESSION DE PLP/DM-20, ET L'AUTRE PAR L'EXPRESSION DU RECEPTEUR AU PDGF-AA. PAR AILLEURS, NOUS AVONS ETUDIE CHEZ LA SOURIS, L'INDUCTION PAR SONIC HEDGEHOG DE L'EMERGENCE DES OLIGODENDROCYTES DANS LE TELENCEPHALE, ET IDENTIFIE UN SITE ROSTRAL D'OLIGODENDROGENESE, LOCALISE DANS LE BULBE OLFACTIF. L'ANALYSE DES CHIMERES AVIAIRES NOUS A D'AUTRE PART PERMIS DE DECRIRE LES VOIES DE MIGRATION DES PROGENITEURS OLIGODENDROCYTAIRES DEPUIS LEURS FOYERS D'ORIGINE, ET NOUS A CONDUIT A PROPOSER UNE COMPARTIMENTATION DES OLIGODENDROCYTES CEREBRAUX EN UNE POPULATION CAUDALE AUX MIGRATIONS TANGENTIELLES LIMITEES ET AU DEVELOPPEMENT SEGMENTAIRE, ET UNE POPULATION ROSTRALE, PROSENCEPHALIQUE, AUX MIGRATIONS TANGENTIELLES EXTENSIVES.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Rôle des fractones, structure de la matrice extracellulaire, dans la niche neurogénique adulte

Chez l adulte, les cellules souches neurales (CSN) prolifèrent et se différencient dans des niches restreintes telles que la zone sous ventriculaire (ZSV). Au cœur de ces niches, facteurs de croissance et molécules de la matrice extracellulaire (MEC) sont impliqués dans le devenir de ces CSN. J ai eu pour objectif de caractériser une structure atypique de MEC, appelée fractone et d étudier son rôle dans la ZSE. J ai montré que les fractones étaient composées de molécules ubiquitaires de la MEC, que la formation de nouvelles cellules se faisait à proximité des fractones et que les fractones capturaient le facteur de croissance FGF-2 par un mécanisme de liaison aux chaines heparan sulfate. Par la suite, je me suis intéressé au rôle du Perlecan (HSPG présent dans les fractones) dans la niche neurogénique adulte. J ai mis en évidence que le Perlecan était nécessaire à la maintenance des CSN et à l action du FGF-2 sur les CSN pour leur passage d un stade quiescent vers un stade prolifératif. L ensemble de ces travaux suggère que les protéoglycanes constitutifs des fractones sont des molécules clés régulant la neurogenèse chez l adultePARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Développement du lignage oligodendrocytaire dans le cerveau embryonnaire de poulet

This work examines the spatio-temporal development of the oligodendrocyte lineage in the bird embryo. The first part deals with the specification ofthe oligodendrocyte progenitors and the second part provides a study oftheir migration patterns. In the mouse the oligodendrocytes emerge from restricted and isolated territories along the neural tube which are characterised by the expression ofthe gene transcript plp/dm2O (Spassky et al 1998). My work consisted in the first instance in establishing if in the avian model the expression of the gene plp/dm2O also defines an oligodendrocyte lineage, as is the case in mammals. A comparative study has been carried out concerning the expression ofthe gene pip /dm2O as well as ofestablished markers ofthe oligodendrocyte lineage during the course ofthe embryonic development ofthe chick. This has allowed us to propose a map of ventricular foci of oligodendrogenesis and to show that oligodendrocyte emergence is very precocious and concomitant with the appearance of the first neurons. My studies have subsequently been directed towards the migration pathways of the oligodendrocyte precursors from their original focus. Using the system of embryonic chimerism between quail and chick and with the collaboration of I. Cobos and S. Martinez we have shown a subdivision of cerebral oligodendrocytes into a caudal population with radial and limited migration displaying a segmentary development, and a rostral population which is prosencephalic and shows extensive tangential migration.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF