The basic helix-loop-helix transcription factor Olig2 is a key determinant for the specification of neural precursor cells into oligodendrocyte progenitor cells. However, the functional role of Olig2 in oligodendrocyte migration and differentiation remains elusive both during developmental myelination and under demyelinating conditions of the adult central nervous system. To decipher Olig2 functions, we generated transgenic mice (TetOlig2:Sox10(rtTA/+)) overexpressing Olig2 in Sox10(+) oligodendroglial cells in a doxycycline inducible manner. We show that Olig2 overexpression increases the generation of differentiated oligodendrocytes, leading to precocious myelination of the central nervous system. Unexpectedly, we found that gain of Olig2 function in oligodendrocyte progenitor cells enhances their migration rate. To determine whether Olig2 overexpression in adult oligodendrocyte progenitor cells promotes oligodendrocyte regeneration for myelin repair, we induced lysophosphatidylcholine demyelination in the corpus callosum of TetOlig2:Sox10(rtTA/+) and control mice. We found that Olig2 overexpression enhanced oligodendrocyte progenitor cell differentiation and remyelination. To assess the relevance of these findings in demyelinating diseases, we also examined OLIG2 expression in multiple sclerosis lesions. We demonstrate that OLIG2 displays a differential expression pattern in multiple sclerosis lesions that correlates with lesion activity. Strikingly, OLIG2 was predominantly detected in NOGO-A(+) (now known as RTN4-A) maturing oligodendrocytes, which prevailed in active lesion borders, rather than chronic silent and shadow plaques. Taken together, our data provide proof of principle indicating that OLIG2 overexpression in oligodendrocyte progenitor cells might be a possible therapeutic mechanism for enhancing myelin repair.

The identification of new pathways governing myelination provides innovative avenues for remyelination. Liver X receptors (LXRs) α and β are nuclear receptors activated by oxysterols that originated from the oxidation of cholesterol. They are crucial for cholesterol homeostasis, a major lipid constituent of myelin sheaths that are formed by oligodendrocytes. However, the role of LXRs in myelin generation and maintenance is poorly understood. Here, we show that LXRs are involved in myelination and remyelination processes. LXRs and their ligands are present in oligodendrocytes. We found that mice invalidated for LXRs exhibit altered motor coordination and spatial learning, thinner myelin sheaths, and reduced myelin gene expression. Conversely, activation of LXRs by either 25-hydroxycholesterol or synthetic TO901317 stimulates myelin gene expression at the promoter, mRNA, and protein levels, directly implicating LXRα/β in the transcriptional control of myelin gene expression. Interestingly, activation of LXRs also promotes oligodendroglial cell maturation and remyelination after lysolecithin-induced demyelination of organotypic cerebellar slice cultures. Together, our findings represent a conceptual advance in the transcriptional control of myelin gene expression and strongly support a new role of LXRs as positive modulators in central (re)myelination processes.LXR alpha and beta | oligodendrocytes | cerebellum | myelination | oxysterols

Improving oligodendroglial differentiation from human foetal neural progenitor cells remains a primordial issue to accomplish successful cell-based therapies in myelin diseases. Here, we combined in situ, in vitro and in vivo approaches to assess the oligodendrogenic potential of different human foetal forebrain regions during the first trimester of gestation. We show for the first time that the initial wave of oligodendrocyte progenitor emergence in the ventral telencephalon onsets as early as 7.5 weeks into gestation. Interestingly, in vitro, isolation of ganglionic eminences yielded oligodendrocyte progenitor-enriched cultures, as compared with cortex and thalamus. Most importantly, single injection of human neural progenitors into rodent models of focal gliotoxic demyelination revealed the great capacity of these cells to survive, extensively migrate and successfully remyelinate the spinal cord, irrespective of their origin. Thus, our study brings novel insights into the biology of early human foetal neural progenitor cells and offers new support for the development of cellular therapeutics for myelin disorders.

Cdk2 is not essential for oligodendrocyte maturation and myelination during development, but in response to demyelination, it is required for oligodendrocyte precursor cell proliferation (OPC), and its loss accelerates OPC differentiation and remyelination.

Systemically injected neural precursor cells (NPCs) were unexpectedly shown to reach the cerebral parenchyma and induce recovery in various diffuse brain pathologies, including animal models of multiple sclerosis. However, the molecular mechanisms supporting NPC migration across brain endothelium remain elusive. Brain endothelium constitutes the blood-brain barrier, which uniquely controls the access of drugs and trafficking of cells, including leukocytes, from the blood to the brain. Taking advantage of the availability of in vitro models of human and rat blood-brain barrier developed in our laboratory and validated by us and others, we show here that soluble hyaluronic acid, the major ligand of the adhesion molecule CD44, as well as anti-CD44 blocking antibodies, largely prevents NPC adhesion to and migration across brain endothelium in inflammatory conditions. We present further evidence that NPCs, surprisingly, induce the formation of apical cups at the surface of brain endothelial cells, enriched in CD44 and other adhesion molecules, thus hijacking the endothelial signaling recently shown to be involved in leukocyte extravasation. These results demonstrate the pivotal role of CD44 in the transendothelial migration of NPCs across brain endothelial cells: we propose that they may help design new strategies for the delivery of therapeutic NPCs to the brain by systemic administration.

Boundary cap cells (BC), which express the transcription factor Krox20, participate in the formation of the boundary between the central nervous system and the peripheral nervous system. To study BC stemness, we developed a method to purify and amplify BC in vitro from Krox20Cre/+ , R26RYFP/+ mouse embryos. We show that BC progeny are EGF/FGF2-responsive, form spheres, and express neural crest markers. Upon growth factor withdrawal, BC progeny gave rise to multiple neural crest and CNS lineages. Transplanted into the developing murine forebrain, they successfully survived, migrated, and integrated within the host environment. Surprisingly, BC progeny generated exclusively CNS cells, including neurons, astrocytes, and myelin-forming oligodendrocytes. In vitro experiments indicated that a sequential combination of ventralizing morphogens and glial growth factors was necessary to reprogram BC into oligodendrocytes. Thus, BC progeny are endowed with differentiation plasticity beyond the peripheral nervous system. The demonstration that CNS developmental cues can reprogram neural crest-derived stem cells into CNS derivatives suggests that BC could serve as a source of cell type-specific lineages, including oligodendrocytes, for cell-based therapies to treat CNS disorders.dysmyelination | reprogramming | transplantation B oundary cap cells (BC) are neural crest (NC) derivatives and were first described as discrete cell clusters localized at the dorsal root entry zone and motor exit point of the embryonic spinal cord (1). Their specific location at the central nervous system (CNS) and peripheral nervous system (PNS) interface and genetic ablation (2) showed that BC are involved in the formation of PNS-CNS boundaries. BC maintain spinal cord integrity by inhibiting motoneuron cell bodies exit to the periphery (3). Fate mapping, based on the exclusive expression of the zinc finger transcription factor Krox20 by BC between embryonic day (E)10.5 and E15.5, showed that migrating BC derivatives differentiate into Schwann cells (SC) in spinal roots, and satellite cells and a subset of nociceptive neurons in dorsal root ganglia (DRG), suggesting their multipotency (2). HjerlingLeffler and collaborators (4) highlighted the presence of a pluripotent population in the E11 mouse DRG capable of selfrenewal and differentiation into multiple NC derivatives. We reported that BC have a defined molecular signature intermediate between NC cells and SC precursors (3). Furthermore, when transplanted remotely from a focal myelin lesion of the spinal cord, BC generated remyelinating SC and few oligodendrocytes. Overall, these results strongly suggest that BC are stem cells of the embryonic PNS. However, the definition of BC stemness has been hampered by the difficulty of purifying and amplifying this restricted population. In this study, we used cellfate mapping, FACS, and microdissection to isolate, expand, and assess BC stemness in vitro and in vivo. Our data show that BC progeny behave as stem cells that can acquire differentiation plasti...

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Multipotential neural stem/precursor cells of the central nervous system were extensively studied for their properties of generating myelinating oligodendrocytes both in vitro and in vivo upon engraftment in animal models of myelin disorders, such as leucodystrophy and multiple sclerosis. These studies provided proof-of-principle that efficient myelination can be achieved by cell transplantation. However, one major drawback of cell-based therapy of myelin diseases is the difficulty in generating oligodendrocytes efficiently from human fetal neural stem/precursor cells (hNPC). Here we explored whether overexpression of the basic helix-loop-helix (bHLH) transcription factor Olig2 in fetal hNPC could enhance the generation of oligodendrocytes both in vitro and in vivo. We report that transduction of hNPC with Olig2-encoding lentiviral vectors enhances their commitment toward an oligodendroglial fate. Moreover, Olig2-transduced hNPC, grafted into the dysmyelinated shiverer mouse brain, survived up to 9 weeks, migrated extensively, and differentiated into MBP(+) myelinating oligodendrocytes. In contrast, control hNPC remained at a less mature stage and generated very few myelinating oligodendrocytes. Our study indicates that bHLH transcription factors, such as Olig2, are interesting targets for directing hNPC into myelinating oligodendrocytes.