Reactive oxygen species (ROS) are signaling molecules that mediate stress response, apoptosis, DNA damage, gene expression and differentiation. We report here that differentiation of oligodendrocytes, the myelin forming cells in the CNS, is driven by ROS. To dissect the oligodendrocyte differentiation pathway, we used the cell line MO3-13, which display the molecular and cellular features of oligodendrocyte precursors. These cells exposed 1-4 days to low levels of H2O2 or to the protein kinase C (PKC) activator, phorbol-12-Myristate-13-Acetate (PMA) increased the expression of specific oligodendrocyte differentiation markers: the specific nuclear factor Olig-2, and Myelin Basic Protein (MBP), which was processed and accumulated selectively in membranes. The induction of differentiation genes was associated with the activation of ERK1-2 and phosphorylation of the nuclear cAMP responsive element binding protein 1 (CREB). PKC mediates ROS-induced differentiation because PKC depletion or bis-indolyl-maleimide (BIM), a PKC inhibitor, reversed the induction of differentiation markers by H2O2. H2O2 and PMA increased the expression of membrane-bound NADPH oxidases, NOX3 and NOX5. Selective depletion of these proteins inhibited differentiation induced by PMA. Furthermore, NOX5 silencing down regulated NOX3 mRNA levels, suggesting that ROS produced by NOX5 up-regulate NOX3 expression. These data unravel an elaborate network of ROS-generating enzymes (NOX5 to NOX3) activated by PKC and necessary for differentiation of oligodendrocytes. Furthermore, NOX3 and NOX5, as inducers of oligodendrocyte differentiation, represent novel targets for therapies of demyelinating diseases, including multiple sclerosis, associated with impairment of oligodendrocyte differentiation.

Background: Reconstituted high-density lipoprotein (rHDL) is prepared from apolipoprotein A-I, isolated from human plasma, and soybean-derived phosphatidylcholine and exhibits biochemical and functional characteristics similar to endogenous nascent high-density lipoprotein (HDL). This study tested the hypothesis that pretreatment with rHDL may reduce neuronal damage in 2 experimental rat models of stroke. Methods: In the first model, an excitotoxic lesion was induced by unilateral injection of N-methyl-D-aspartate (NMDA) in the right striatum (excitotoxic lesion model). In the second model, temporary occlusion of the middle cerebral artery (MCA) was attained by inserting a nylon thread through the carotid artery and blood flow was restored 30 min later (MCAo model). In both models, either rHDL (120 mg/kg) or saline (control) were infused over 4 h, starting 2 h before the injection of NMDA or the induction of ischemia, respectively. 24 h after the interventions, the rats were sacrificed and the brains removed for histochemical preparation. The necrotic area was delimited using an image analysis system. In addition, the levels of reactive oxygen species (ROS) in human endothelial (ECV 304) and neuroblastoma (SK-N-BE) cell lines were measured fluorometrically as 2′,7′-dichlorofluorescein fluorescence in the presence and absence of rHDL and under basal and stress-induced conditions. Results: In the excitotoxic lesion and MCAo models, pretreatment with rHDL significantly reduced the brain necrotic area by 61 and 76%, respectively (p < 0.01). Overnight incubation of ECV 304 and SK-N-BE cells with 0.5 mg/ml rHDL decreased basal and stress-induced ROS levels by 73 and 72% (ECV 304) and by 76 and 43% (SK-N-BE), respectively (p < 0.01). Conclusion: These results suggest that rHDL reduces neuronal damage after onset of ischemic stroke, possibly by involving an anti-oxidative mechanism. Thus, rHDL may be a powerful neuroprotective tool for the treatment of cerebrovascular diseases.

Inside the adult CNS, oligodendrocyte progenitor cells (OPC_S) are able to proliferate, migrate and differentiate into mature oligodendrocytes (OLs) which are responsible for the production of myelin sheet and energy supply for neurons. Moreover, in demyelinating diseases, OPCs are recruited to the lesion areas where they undergo differentiation and myelin synthesis. Serotonin (5-hydroxytryptamine, 5-HT) is involved in OLs’ development and myelination, but so far the molecular mechanisms involved or the effects of 5-HT on mitochondria function have not yet been well documented. Our data show that 5-HT inhibits migration and proliferation committing cells toward differentiation in an immortalized human oligodendrocyte precursor cell line, M03-13. Migration blockage is mediated by reactive oxygen species (ROS) generation since antioxidants, such as Vit C and Cu-Zn superoxide dismutase, prevent the inhibitory effects of 5-HT on cell migration. 5-HT inhibits OPC migration and proliferation and increases OL phenotypic markers myelin basic protein (MBP) and Olig-2 via protein kinase C (PKC) activation since the inhibitor of PKC, bis-indolyl-maleimide (BIM), counteracts 5-HT effects. NOX inhibitors as well, reverse the effects of 5-HT, indicating that 5-HT influences the maturation process of OPCs by NOX-dependent ROS production. Finally, 5-HT increases mitochondria function and antioxidant activity. The identification of the molecular mechanisms underlying the effects of 5-HT on maturation and energy metabolism of OPCs could pave the way for the development of new treatments for autoimmune demyelinating diseases such as Multiple Sclerosis where oligodendrocytes are the primary target of immune attack.

Ischemic stroke (IS) and multiple sclerosis (MS) are two pathologies of the central nervous system (CNS). At the first look, this appears to be the only similarity between the two diseases, as they seem quite different. Indeed IS has an acute onset compared to MS which develops chronically; IS is consecutive to blood clot migrating to cerebral blood vessels or decrease in cerebral blood flow following atherosclerosis or decreases in cardiac output, whereas MS is an immune disease associated with neurodegeneration. However, both pathologies share similar pathologic pathways and treatments used in MS have been the object of studies in IS. In this mini-review we will discuss similarities between IS and MS on astrocytes and neuroinflammation hallmarks emphasizing the potential for treatments.