Mir-125a-3p negatively regulates oligodendrocyte precursor cells maturation and is altered in human multiple sclerosis

In the central nervous system, oligodendrocytes provide support to axons thanks to the production of a myelin sheath. During their maturation oligodendroglial precursors (OPCs) follow a very precise differentiation program, finely orchestrated by transcription factors, epigenetic factors and microRNAs, a class of small non-coding RNAs involved in post-transcriptional regulation. Any alterations in this program can potentially contribute to dysregulated myelination, impaired remyelination and neurodegenerative conditions, as it happens in multiple sclerosis. Recently, we identified miR-125a-3p as a new actor of oligodendroglial maturation, that could also be involved in the pathological consequences of multiple sclerosis, showing that its over-expression impairs, whereas its silencing promotes, oligodendrocyte maturation (Lecca et al., Sci Rep, 2016). To shed light on the mechanism underlying this effect, we performed a microarray analysis on OPCs after miR-125a-3p over-expression. This analysis suggested that miR-125a-3p is indeed involved in the regulation of biological processes important for OPC maturation, such as cell-cell interaction and morphological differentiation. To evaluate whether miR-125a-3p modulation may influence the progression of remyelination in vivo, we overexpressed the miR-125a-3p by lentiviral approach in a focal lysolecithin-mediated demyelinating lesion in the subcortical white matter of adult mice. Interestingly, also in this case, we found that miRNA-overexpressing OPCs persisted in an immature (i.e. PDGR\u3b1+/NG2+) state. Moreover, we found that miR-125a-3p levels are altered in both brain active lesions and cerebrospinal fluid of multiple sclerosis patients, suggesting that it could be a potential biomarker of disease. The identification of a new miRNA modulating oligodendrocyte differentiation provides new findings about the complex regulation of myelination processes and we postulate that an antago-miRNA for miR-125a-3p may help promoting oligodendrocyte maturation in diseases characterized by impaired myelin repair. Sponsored by Fondazione Italiana Sclerosi Multipla 2013/R-1 project to MPA and by Fondazione Cariplo, grant n\ub0 2014-1207 to DL

Elovl5 is required for proper action potential conduction along peripheral myelinated fibers

Elovl5 elongates fatty acids with 18 carbon atoms and in cooperation with other enzymes guarantees the normal levels of very long‐chain fatty acids, which are necessary for a proper membrane structure. Action potential conduction along myelinated axons depends on structural integrity of myelin, which is maintained by a correct amount of fatty acids and a proper interaction between fatty acids and myelin proteins. We hypothesized that in Elovl5 (−/−) mice, the lack of elongation of Elovl5 substrates might cause alterations of myelin structure. The analysis of myelin ultrastructure showed an enlarged periodicity with reduced G‐ratio across all axonal diameters. We hypothesized that the structural alteration of myelin might affect the conduction of action potentials. The sciatic nerve conduction velocity was significantly reduced without change in the amplitude of the nerve compound potential, suggesting a myelin defect without a concomitant axonal degeneration. Since Elovl5 is important in attaining normal amounts of polyunsaturated fatty acids, which are the principal component of myelin, we performed a lipidomic analysis of peripheral nerves of Elovl5‐deficient mice. The results revealed an unbalance, with reduction of fatty acids longer than 18 carbon atoms relative to shorter ones. In addition, the ratio of saturated to unsaturated fatty acids was strongly increased. These findings point out the essential role of Elovl5 in the peripheral nervous system in supporting the normal structure of myelin, which is the key element for a proper conduction of electrical signals along myelinated nerves

Detrimental and protective action of microglial extracellular vesicles on myelin lesions: astrocyte involvement in remyelination failure

Microglia are highly plastic immune cells which exist in a continuum of activation states. By shaping the function of oligodendrocyte precursor cells (OPCs), the brain cells which differentiate to myelin-forming cells, microglia participate in both myelin injury and remyelination during multiple sclerosis. However, the mode(s) of action of microglia in supporting or inhibiting myelin repair is still largely unclear. Here, we analysed the effects of extracellular vesicles (EVs) produced in vitro by either pro-inflammatory or pro-regenerative microglia on OPCs at demyelinated lesions caused by lysolecithin injection in the mouse corpus callosum. Immunolabelling for myelin proteins and electron microscopy showed that EVs released by pro-inflammatory microglia blocked remyelination, whereas EVs produced by microglia co-cultured with immunosuppressive mesenchymal stem cells promoted OPC recruitment and myelin repair. The molecular mechanisms responsible for the harmful and beneficial EV actions were dissected in primary OPC cultures. By exposing OPCs, cultured either alone or with astrocytes, to inflammatory EVs, we observed a blockade of OPC maturation only in the presence of astrocytes, implicating these cells in remyelination failure. Biochemical fractionation revealed that astrocytes may be converted into harmful cells by the inflammatory EV cargo, as indicated by immunohistochemical and qPCR analyses, whereas surface lipid components of EVs promote OPC migration and/or differentiation, linking EV lipids to myelin repair. Although the mechanisms through which the lipid species enhance OPC maturation still remain to be fully defined, we provide the first demonstration that vesicular sphingosine 1 phosphate stimulates OPC migration, the first fundamental step in myelin repair. From this study, microglial EVs emerge as multimodal and multitarget signalling mediators able to influence both OPCs and astrocytes around myelin lesions, which may be exploited to develop novel approaches for myelin repair not only in multiple sclerosis, but also in neurological and neuropsychiatric diseases characterized by demyelination

Modelling of Short-Term Interactions Between Concrete Support and the Excavated Damage Zone Around Galleries Drilled in Callovo–Oxfordian Claystone

peer reviewedProduction of energy from nuclear power plants generates high-level radioactive nuclear waste, harmful during dozens of thousand years. Deep geological disposal of nuclear waste represents the most reliable solutions for its safe isolation. Confinement of radioactive wastes relies on the multi-barrier concept in which isolation is provided by a series of engineered (canister, backfill) and natural (host rock) barriers. Few underground research laboratories have been built all over the world to test and validate storage solutions. The underground drilling process of disposal drifts may generate cracks, fractures/strain localisation in shear bands within the rock surrounding the gallery especially in argillaceous rocks. These degradations affect the hydro-mechanical properties of the material, such as permeability, e.g. creating a preferential flow path for radionuclide migration. Hydraulic conductivity increase within this zone must remain limited to preserve the natural barrier. In addition galleries are currently reinforced by different types of concrete supports such as shotcrete and/or prefab elements. Their purpose is twofold: avoiding partial collapse of the tunnel during drilling operations and limiting convergence of the surrounding rock. Properties of both concrete and rock mass are time dependent, due to shotcrete hydration and hydromechanical couplings within the host rock. By the use of a hydro-mechanical coupled Finite Element Code with a Second Gradient regularization, this paper aims at investigating and predicting support and rock interactions (convergence, stress field). The effect of shotcrete hydration evolution, spraying time and use of compressible wedges is studied in order to determine their relative influence

Functional roles of extracellular vesicles derived from microglia with diverse activation states

Microglia respond to all types of CNS injury and acquire different activated phenotypes, participating not only in mechanisms of injury but also in tissue repair (1). However, the mode(s) of action of these cells in fostering or inhibiting CNS repair is still largely unclear. Here, we investigated the action of extracellular vesicles (EVs) released by microglia with diverse activation states (2) on Oligodendrocyte Precursor Cells (OPCs) and hippocampal neurons. Fluorescence analysis of OPCs exposed to EVs together with the proliferative marker EdU showed that EVs produced by pro-inflammatory cells limit OPC proliferation, while EVs released by pro-regenerative microglia tend to increase it. Stronger proliferative action was observed in vivo upon delivery of EVs derived from pro-regenerative microglia to mice with focal myelin lesions, with a significant increase in the density of proliferating NG2+ cells at the lesion site. Immunocytochemistry and western-blot analysis of markers of mature oligodendrocytes revealed that EVs derived from both inflammatory and pro- regenerative microglia, but not from unstimulated cells, promote OPC maturation in vitro, with EVs released by pro-regenerative microglia displaying higher differentiation activity and significantly fostering myelin deposition in an in vitro system of OPCs co-cultured with DRG neurons. Globally these results show that through EVs, pro-regenerative microglia and, at lesser extent, pro-inflammatory and resting cells may exert a beneficial action on OPCs, promoting their differentiation and myelin formation. Conversely, a clear detrimental action of EVs derived from inflammatory microglia was observed in cultured hippocampal neurons, highlighting a previously unrecognized role of microglia-derived EVs in inflammation-induced synaptic alteration. Indeed, immunofluorescence and western blotting analysis for synaptic markers showed that EVs secreted from inflammatory but not pro-regenerative microglia decrease the density of dendritic spines and cause destabilization of excitatory synapses. Molecular mechanisms underlying such synaptic alterations will be discussed

The Recently Identified P2Y-Like Receptor GPR17 Is a Sensor of Brain Damage and a New Target for Brain Repair

Deciphering the mechanisms regulating the generation of new neurons and new oligodendrocytes, the myelinating cells of the central nervous system, is of paramount importance to address new strategies to replace endogenous damaged cells in the adult brain and foster repair in neurodegenerative diseases. Upon brain injury, the extracellular concentrations of nucleotides and cysteinyl-leukotrienes (cysLTs), two families of endogenous signaling molecules, are markedly increased at the site of damage, suggesting that they may act as “danger signals” to alert responses to tissue damage and start repair. Here we show that, in brain telencephalon, GPR17, a recently deorphanized receptor for both uracil nucleotides and cysLTs (e.g., UDP-glucose and LTD4), is normally present on neurons and on a subset of parenchymal quiescent oligodendrocyte precursor cells. We also show that induction of brain injury using an established focal ischemia model in the rodent induces profound spatiotemporal-dependent changes of GPR17. In the lesioned area, we observed an early and transient up-regulation of GPR17 in neurons expressing the cellular stress marker heat shock protein 70. Magnetic Resonance Imaging in living mice showed that the in vivo pharmacological or biotechnological knock down of GPR17 markedly prevents brain infarct evolution, suggesting GPR17 as a mediator of neuronal death at this early ischemic stage. At later times after ischemia, GPR17 immuno-labeling appeared on microglia/macrophages infiltrating the lesioned area to indicate that GPR17 may also acts as a player in the remodeling of brain circuitries by microglia. At this later stage, parenchymal GPR17+ oligodendrocyte progenitors started proliferating in the peri-injured area, suggesting initiation of remyelination. To confirm a specific role for GPR17 in oligodendrocyte differentiation, the in vitro exposure of cortical pre-oligodendrocytes to the GPR17 endogenous ligands UDP-glucose and LTD4 promoted the expression of myelin basic protein, confirming progression toward mature oligodendrocytes. Thus, GPR17 may act as a “sensor” that is activated upon brain injury on several embryonically distinct cell types, and may play a key role in both inducing neuronal death inside the ischemic core and in orchestrating the local remodeling/repair response. Specifically, we suggest GPR17 as a novel target for therapeutic manipulation to foster repair of demyelinating wounds, the types of lesions that also occur in patients with multiple sclerosis

The neurogenic potential of astrocytes is regulated by inflammatory signals

Although the adult brain contains neural stem cells (NSCs) that generate new neurons throughout life, these astrocyte-like populations are restricted to two discrete niches. Despite their terminally differentiated phenotype, adult parenchymal astrocytes can re-acquire NSC-like characteristics following injury, and as such, these 'reactive' astrocytes offer an alternative source of cells for central nervous system (CNS) repair following injury or disease. At present, the mechanisms that regulate the potential of different types of astrocytes are poorly understood. We used in vitro and ex vivo astrocytes to identify candidate pathways important for regulation of astrocyte potential. Using in vitro neural progenitor cell (NPC)-derived astrocytes, we found that exposure of more lineage-restricted astrocytes to either tumor necrosis factor alpha (TNF-α) (via nuclear factor-κB (NFκB)) or the bone morphogenetic protein (BMP) inhibitor, noggin, led to re-acquisition of NPC properties accompanied by transcriptomic and epigenetic changes consistent with a more neurogenic, NPC-like state. Comparative analyses of microarray data from in vitro-derived and ex vivo postnatal parenchymal astrocytes identified several common pathways and upstream regulators associated with inflammation (including transforming growth factor (TGF)-β1 and peroxisome proliferator-activated receptor gamma (PPARγ)) and cell cycle control (including TP53) as candidate regulators of astrocyte phenotype and potential. We propose that inflammatory signalling may control the normal, progressive restriction in potential of differentiating astrocytes as well as under reactive conditions and represent future targets for therapies to harness the latent neurogenic capacity of parenchymal astrocytes

Detection of Methoxymethanol as a Photochemistry Product of Condensed Methanol

We report the identification of methoxymethanol (CH3OCH2OH) as a photochemistry product of condensed methanol (CH3OH) based on temperature-programmed desorption studies conducted following photon irradiation at energies below the ionization threshold (9.8 eV) of condensed methanol. The first detection of methoxymethanol in the interstellar medium was reported in 2017 based on data from Bands 6 and 7 from the Atacama Large Millimeter/submillimeter Array (ALMA). The cosmic synthesis of “complex” organic molecules such as methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), acetic acid (CH3COOH), ethylene glycol (HOCH2CH2OH), and glycolaldehyde (HOCH2CHO) has been attributed to UV photolysis of condensed methanol found in interstellar ices. Experiments conducted in 1995 demonstrated that electron-induced radiolysis of methanol cosmic ice analogues yields methoxymethanol. In three recent publications (2016, 2017, and 2018), methoxymethanol was considered as a potential tracer for reactions induced by secondary electrons resulting from the interaction of cosmic rays with interstellar ices. However, the results presented in this study suggest that methoxymethanol can be formed from both radiation chemistry and photochemistry of condensed methanol

Electron-Induced Radiolysis of Astrochemically Relevant Ammonia Ices

We elucidate mechanisms of electron-induced radiolysis in cosmic (interstellar, planetary, and cometary) ice analogs of ammonia (NH3), likely the most abundant nitrogen-containing compound in the interstellar medium (ISM). Astrochemical processes were simulated under ultrahigh vacuum conditions by high-energy (1 keV) and low-energy (7 eV) electron-irradiation of nanoscale thin films of ammonia deposited on cryogenically cooled metal substrates. Irradiated films were analyzed by temperature-programmed desorption (TPD). Experiments with ammonia isotopologues provide convincing evidence for the electron-induced formation of hydrazine (N2H4) and diazene (N2H2) from condensed NH3. To understand the dynamics of ammonia radiolysis, the dependence of hydrazine and diazene yields on incident electron energy, electron flux, electron fluence, film thickness, and ice temperature were investigated. Radiolysis yield measurements versus (1) irradiation time and (2) film thickness are semiquantitatively consistent with a reaction mechanism that involves a bimolecular step for the formation of hydrazine and diazene from the dimerization of amidogen (NH2) and imine (NH) radicals, respectively. The apparent decrease in radiolysis yield of hydrazine and diazene with decreasing electron flux at constant fluence may be due to the competing desorption of these radicals at 90 K under low incident electron flux conditions. The production of hydrazine at electron energies as low as 7 eV and an ice temperature of 22 K is consistent with condensed phase radiolysis being mediated by low-energy secondary electrons produced by the interaction of high-energy radiation with matter. These results provide a basis from which we can begin to understand the mechanisms by which ammonia can form more complex species in cosmic ices