Remodeling of the interstitial extracellular matrix in white matter multiple sclerosis lesions:Implications for remyelination (failure)

The extracellular matrix (ECM) provides protection, rigidity, and structure toward cells. It consists, among others, of a wide variety of glycoproteins and proteoglycans, which act together to produce a complex and dynamic environment, most relevant in transmembrane events. In the brain, the ECM occupies a notable proportion of its volume and maintains the homeostasis of central nervous system (CNS). In addition, remodeling of the ECM, that is transient changes in ECM proteins regulated by matrix metalloproteinases (MMPs), is an important process that modulates cell behavior upon injury, thereby facilitating recovery. Failure of ECM remodeling plays an important role in the pathogenesis of multiple sclerosis (MS), a neurodegenerative demyelinating disease of the CNS with an inflammatory response against protective myelin sheaths that surround axons. Remyelination of denuded axons improves the neuropathological conditions of MS, but this regeneration process fails over time, leading to chronic disease progression. In this review, we uncover abnormal ECM remodeling in MS lesions by discussing ECM remodeling in experimental demyelination models, that is when remyelination is successful, and compare alterations in ECM components to the ECM composition and MMP expression in the parenchyma of demyelinated MS lesions, that is when remyelination fails. Inter- and intralesional differences in ECM remodeling in the distinct white matter MS lesions are discussed in terms of consequences for oligodendrocyte behavior and remyelination (failure). Hence, the review will aid to understand how abnormal ECM remodeling contributes to remyelination failure in MS lesions and assists in developing therapeutic strategies to promote remyelination

The Glial Regenerative Response to Central Nervous System Injury Is Enabled by Pros-Notch and Pros-NFκB Feedback

Organisms are structurally robust, as cells accommodate changes preserving structural integrity and function. The molecular mechanisms underlying structural robustness and plasticity are poorly understood, but can be investigated by probing how cells respond to injury. Injury to the CNS induces proliferation of enwrapping glia, leading to axonal re-enwrapment and partial functional recovery. This glial regenerative response is found across species, and may reflect a common underlying genetic mechanism. Here, we show that injury to the Drosophila larval CNS induces glial proliferation, and we uncover a gene network controlling this response. It consists of the mutual maintenance between the cell cycle inhibitor Prospero (Pros) and the cell cycle activators Notch and NFκB. Together they maintain glia in the brink of dividing, they enable glial proliferation following injury, and subsequently they exert negative feedback on cell division restoring cell cycle arrest. Pros also promotes glial differentiation, resolving vacuolization, enabling debris clearance and axonal enwrapment. Disruption of this gene network prevents repair and induces tumourigenesis. Using wound area measurements across genotypes and time-lapse recordings we show that when glial proliferation and glial differentiation are abolished, both the size of the glial wound and neuropile vacuolization increase. When glial proliferation and differentiation are enabled, glial wound size decreases and injury-induced apoptosis and vacuolization are prevented. The uncovered gene network promotes regeneration of the glial lesion and neuropile repair. In the unharmed animal, it is most likely a homeostatic mechanism for structural robustness. This gene network may be of relevance to mammalian glia to promote repair upon CNS injury or disease

Ultrastructural Characterization of SARS Coronavirus

Severe acute respiratory syndrome (SARS) was first described during a 2002–2003 global outbreak of severe pneumonia associated with human deaths and person-to-person disease transmission. The etiologic agent was initially identified as a coronavirus by thin-section electron microscopic examination of a virus isolate. Virions were spherical, 78 nm in mean diameter, and composed of a helical nucleocapsid within an envelope with surface projections. Herein, we show that infection with the SARS-associated coronavirus resulted in distinct ultrastructural features: double-membrane vesicles, nucleocapsid inclusions, and large granular areas of cytoplasm. These three structures and the coronavirus particles were shown to be positive for viral proteins and RNA by using ultrastructural immunogold and in situ hybridization assays. In addition, ultrastructural examination of a bronchiolar lavage specimen from a SARS patient showed numerous coronavirus-infected cells with features similar to those in infected culture cells. Electron microscopic studies were critical in identifying the etiologic agent of the SARS outbreak and in guiding subsequent laboratory and epidemiologic investigations

Interaction of PLP with GFP-MAL2 in the Human Oligodendroglial Cell Line HOG

The velocity of the nerve impulse conduction of vertebrates relies on the myelin sheath, an electrically insulating layer that surrounds axons in both the central and peripheral nervous systems, enabling saltatory conduction of the action potential. Oligodendrocytes are the myelin-producing glial cells in the central nervous system. A deeper understanding of the molecular basis of myelination and, specifically, of the transport of myelin proteins, will contribute to the search of the aetiology of many dysmyelinating and demyelinating diseases, including multiple sclerosis. Recent investigations suggest that proteolipid protein (PLP), the major myelin protein, could reach myelin sheath by an indirect transport pathway, that is, a transcytotic route via the plasma membrane of the cell body. If PLP transport relies on a transcytotic process, it is reasonable to consider that this myelin protein could be associated with MAL2, a raft protein essential for transcytosis. In this study, carried out with the human oligodendrocytic cell line HOG, we show that PLP colocalized with green fluorescent protein (GFP)-MAL2 after internalization from the plasma membrane. In addition, both immunoprecipitation and immunofluorescence assays, indicated the existence of an interaction between GFP-MAL2 and PLP. Finally, ultrastructural studies demonstrated colocalization of GFP-MAL2 and PLP in vesicles and tubulovesicular structures. Taken together, these results prove for the first time the interaction of PLP and MAL2 in oligodendrocytic cells, supporting the transcytotic model of PLP transport previously suggested

Myelin-mediated inhibition of oligodendrocyte precursor differentiation can be overcome by pharmacological modulation of Fyn-RhoA and protein kinase C signalling

Failure of oligodendrocyte precursor cell (OPC) differentiation contributes significantly to failed myelin sheath regeneration (remyelination) in chronic demyelinating diseases. Although the reasons for this failure are not completely understood, several lines of evidence point to factors present following demyelination that specifically inhibit differentiation of cells capable of generating remyelinating oligodendrocytes. We have previously demonstrated that myelin debris generated by demyelination inhibits remyelination by inhibiting OPC differentiation and that the inhibitory effects are associated with myelin proteins. In the present study, we narrow down the spectrum of potential protein candidates by proteomic analysis of inhibitory protein fractions prepared by CM and HighQ column chromatography followed by BN/SDS/SDS–PAGE gel separation using Nano-HPLC-ESI-Q-TOF mass spectrometry. We show that the inhibitory effects on OPC differentiation mediated by myelin are regulated by Fyn-RhoA-ROCK signalling as well as by modulation of protein kinase C (PKC) signalling. We demonstrate that pharmacological or siRNA-mediated inhibition of RhoA-ROCK-II and/or PKC signalling can induce OPC differentiation in the presence of myelin. Our results, which provide a mechanistic link between myelin, a mediator of OPC differentiation inhibition associated with demyelinating pathologies and specific signalling pathways amenable to pharmacological manipulation, are therefore of significant potential value for future strategies aimed at enhancing CNS remyelination

KV7/KCNQ Channels Are Functionally Expressed in Oligodendrocyte Progenitor Cells

Background: KV7/KCNQ channels are widely expressed in neurons and they have multiple important functions, including control of excitability, spike afterpotentials, adaptation, and theta resonance. Mutations in KCNQ genes have been demonstrated to associate with human neurological pathologies. However, little is known about whether K V7/KCNQ channels are expressed in oligodendrocyte lineage cells (OLCs) and what their functions in OLCs. Methods and Findings: In this study, we characterized KV7/KCNQ channels expression in rat primary cultured OLCs by RT-PCR, immunostaining and electrophysiology. KCNQ2-5 mRNAs existed in all three developmental stages of rat primary cultured OLCs. K V7/KCNQ proteins were also detected in oligodendrocyte progenitor cells (OPCs, early developmental stages of OLCs) of rat primary cultures and cortex slices. Voltage-clamp recording revealed that the IM antagonist XE991 significantly reduced KV7/KCNQ channel current (IK(Q)) in OPCs but not in differentiated oligodendrocytes. In addition, inhibition of K V7/KCNQ channels promoted OPCs motility in vitro. Conclusions: These findings showed that K V7/KCNQ channels were functionally expressed in rat primary cultured OLCs an

Oligodendrocytes: biology and pathology

Oligodendrocytes are the myelinating cells of the central nervous system (CNS). They are the end product of a cell lineage which has to undergo a complex and precisely timed program of proliferation, migration, differentiation, and myelination to finally produce the insulating sheath of axons. Due to this complex differentiation program, and due to their unique metabolism/physiology, oligodendrocytes count among the most vulnerable cells of the CNS. In this review, we first describe the different steps eventually culminating in the formation of mature oligodendrocytes and myelin sheaths, as they were revealed by studies in rodents. We will then show differences and similarities of human oligodendrocyte development. Finally, we will lay out the different pathways leading to oligodendrocyte and myelin loss in human CNS diseases, and we will reveal the different principles leading to the restoration of myelin sheaths or to a failure to do so