LPS mediated injury to oligodendrocytes is mediated by the activation of nNOS: relevance to human demyelinating disease

The NG2-glia is a potential target to maintain the integrity of neurovascular unit after acute ischemic stroke

The neurovascular unit (NVU) plays a critical role in health and disease. In the current review, we discuss the critical role of a class of neural/glial antigen 2 (NG2)-expressing glial cells (NG2-glia) in regulating NVU after acute ischemic stroke (AIS). We first introduce the role of NG2-glia in the formation of NVU during development as well as aging-induced damage to NVU and accompanying NG2-glia change. We then discuss the reciprocal interactions between NG2-glia and the other component cells of NVU, emphasizing the factors that could influence NG2-glia. Damage to the NVU integrity is the pathological basis of edema and hemorrhagic transformation, the most dreaded complication after AIS. The role of NG2-glia in AIS-induced NVU damage and the effect of NG2-glia transplantation on AIS-induced NVU damage are summarized. We next discuss the role of NG2-glia and the effect of NG2-glia transplantation in oligodendrogenesis and white matter repair as well as angiogenesis which is associated with the outcome of the patients after AIS. Finally, we review the current strategies to promote NG2-glia proliferation and differentiation and propose to use the dental pulp stem cells (DPSC)-derived exosome as a promising strategy to reduce AIS-induced injury and promote repair through maintaining the integrity of NVU by regulating endogenous NG2-glia proliferation and differentiation.

Sarsasapogenin and fluticasone combination improves DNFB induced atopic dermatitis lesions in BALB/c mice

OBJECTIVE

Atopic dermatitis (AD) is a pruritic, chronic, relapsing inflammatory skin disease. The research aims to study the effects of Sarsasapogenin and its combination with Fluticasone in 2, 4-Dinitrofluorobenzene (DNFB) induced atopic dermatitis in BALB/c mice.

MATERIAL AND METHODS

Thirty male Balb/c mice were divided into 5 groups: (i) Normal control (NC), (ii) Disease control (DNFB), (iii) Sarsasapogenin (SG) (50 µg/mice), (iv) Fluticasone (FC) (50 µg/mice), (v) Sarsasapogenin + Fluticasone (SG + FC) combination (25 µg/mice). Dermatitis was induced by repeated application of DNFB in Balb/c mice. On topical application of SG, FC, and SG + FC combination on the ear and skin lesions, body weight, ear weight, ear thickness, erythema score, spleen weight, cytokines, immunoglobulin E (IgE) levels, nitric oxide (NO) level, hematological parameters, and oxidative stress markers were evaluated. Histological analysis of the ear tissue was also done.

RESULTS

The results stated that SG and SG + FC treatment to mice considerably decrease the ear weight, ear thickness, spleen weight, serum IgE, cytokines, NO levels, and restoration of antioxidant stress markers with elevation in the hematological parameters. The observations were further confirmed by histopathological analysis of ear tissue.

CONCLUSION

These data specify that SG has been demonstrated as a probable therapy for the treatment of allergic skin diseases in combination with FC by decreasing its dose from 50 to 25 µg/mice to avoid the chronic side effects of FC. Hence, it can be concluded that SG and SG + FC combination significantly improved the AD-like symptoms in the DNFB sensitized mice through mitigating the production of proinflammatory mediators and restoration of oxidative stress markers.

Transient receptor potential ankyrin 1 contributes to the lysophosphatidylcholine-induced oxidative stress and cytotoxicity in OLN-93 oligodendrocyte

Transient receptor potential ankyrin 1 (TRPA1), the non-selective cation channel, was found that can mediate the generation of multiple sclerosis, while the mechanism is still controversial. Lysophosphatidylcholine (LPC) is a critical trigger of multiple sclerosis which results from the syndrome of neuronal inflammation and demyelination. In this work, we suggested that TRPA1 can mediate the LPC-induced oxidative stress and cytotoxicity in OLN-93 oligodendrocyte. The expression of TRPA1 in OLN-93 was detected by using quantitative real-time PCR (qRT-PCR) and immunofluorescence. The calcium overload induced by LPC via TRPA1 was detected by calcium imaging. The mechanism of LPC-induced mitochondrial reactive oxygen species (mtROS) generation, mitochondria membrane depolarization, nitric oxide (NO) increase, and development of superoxide production via TRPA1 was verified by using confocal imaging. The cell injury elicited by LPC via TRPA1 was confirmed by both CCK-8 and LDH cytotoxicity detection. These results indicate that TRPA1 plays an important role of the LPC-induced oxidative stress and cell damage in OLN-93 oligodendrocyte. Therefore, inhibition of TRPA1 may protect the LPC-induced demyelination.

TNF-α antagonist attenuates systemic lipopolysaccharide-induced brain white matter injury in neonatal rats

Background

Systemic inflammation is an important risk factor for neurodevelopmental impairments in preterm infants. Premyelinating oligodendrocytes are main building blocks of white matter in preterm infants and vulnerable to oxidative stress and excitotoxic stress. Tumour necrosis factor-α (TNF-α) plays important roles in systemic inflammation and local inflammation leading to apoptosis of premyelinating oligodendrocytes and white matter injury (WMI) in brain tissue. This study was conducted to investigate whether etanercept, a TNF-α antagonist, could attenuate systemic lipopolysaccharide (LPS)-induced WMI in the immature brain.

Results

We found that intraperitoneal LPS administration caused systemic and local inflammation in brain tissue. Subsequent etanercept treatment significantly attenuated LPS-induced inflammation in brain tissue as well as in systemic circulation. Intraperitoneal LPS also induced microgliosis and astrocytosis in the cingulum and etanercept treatment reduced LPS-induced microgliosis and astrocytosis. Additionally, systemic LPS-induced apoptosis of oligodendrocyte precursor cells was observed, which was lessened by etanercept treatment. The concentration of etanercept in the CSF was higher when it was administrated with LPS than when administrated with a vehicle.

Conclusions

It appears that etanercept reduce WMI in the neonatal rat brain via attenuation of systemic and local inflammation. This study provides preclinical data suggesting etanercept-mediated modulation of inflammation as a promising approach to reduce WMI caused by sepsis or necrotizing enterocolitis in preterm infants.

Therapeutic Effect of the Mitochondria-Targeted Antioxidant SkQ1 on the Culture Model of Multiple Sclerosis

Multiple sclerosis (MS) is a heterogeneous autoimmune disease of unknown etiology characterized by inflammation, demyelination, and axonal degeneration that affects both the white and gray matter of CNS. Recent large-scale epidemiological and genomic studies identified several genetic and environmental risk factors for the disease. Among them are environmental factors of infectious origin, possibly causing MS, which include Epstein-Barr virus infection, reactivation of some endogenous retrovirus groups, and infection by pathogenic bacteria (mycobacteria, Chlamydia pneumoniae, and Helicobacter pylori). However, the nature of the events leading to the activation of immune cells in MS is mostly unknown and there is no effective therapy against the disease. Amazingly, whatever the cause of the disease, signs of damage to the nerve tissue with MS lesions were the same as with infectious leprosy, while in the latter case nitrozooxidative stress was suggested as the main cause of the nerve damage. With this in mind and following the hypothesis that excessive production of mitochondrial reactive oxygen species critically contributes to MS pathogenesis, we studied the effect of mitochondria-targeted antioxidant SkQ1 in an in vitro MS model of the primary oligodendrocyte culture of the cerebellum, challenged with lipopolysaccharide (LPS). SkQ1 was found to accumulate in the mitochondria of oligodendrocytes and microglial cells, and it was also found to prevent LPS-induced inhibition of myelin production in oligodendrocytes. The results implicate that mitochondria-targeted antioxidants could be promising candidates as components of a combined therapy for MS and related neurological disorders.

The solid-state fermentation of Artemisia capillaris leaves with Ganoderma lucidum enhances the anti-inflammatory effects in a model of atopic dermatitis

Artemisia capillaris, which belongs to the Asteraceae family and the genus Artemisia, has been reported to exert inhibitory effects on diabetes, cancer and inflammation. In this study, in order to enhance the bioactivity potential of the leaves of Artemisia by Ganoderma lucidum mycelium, we prepared aqueous samples of Artemisia capillaris (Ac) leaves, Ganoderma lucidum (Gl) and aqueous fractions produced by the solid fermentation of Ganoderma lucidum on Artemisia capillaris leaves (afAc/Gl). Thereafter, we evaluated whether these samples have potential to attenuate inflammation-related symptoms in an amimal model of 2,4-dinitrofluorobenzene (DNFB)-induced atopic dermatitis. We found that afAc/Gl exhibited enhanced anti-inflamamatory activity following the solid fermentation process when compared with Ac or Gl on ear thickness, ear epidermal thickness and eosinophil infiltration in the skin tissues. The expression of nitric oxide (NO) synthases (NOSs) was measured by immunohistochemical staining. The results revealed that afAc/Gl decreased endothelial NOS and inducible NOS expression compared with the DNFB group, while neuronal NOS expression was not altered. By comparing NO production, we found that as opposed to Ac, afAc/Gl has potential to inhibit atopic dermatitis-related symptoms during the inflammatory event. As regards matrix metalloproteinase (MMP) expression patterns, afAc/Gl exerted potent inhibitory activity on the mRNA expression of MMP-2, -7, -9, -12, -14 and -19. Taken together, these results suggest that the solid state fermentation of Ac by Gl is an effective strategy to obtaining useful ingredients which are converted into valuable compounds during an atopic inflammatory insult.

Neuroglia and their roles in central respiratory control; an overview

While once viewed as mere housekeepers, providing structural and metabolic support for neurons, it is now clear that neuroglia do much more. Phylogenetically, they have undergone enormous proliferation and diversification as central nervous systems grew in their complexity. In addition, they: i) are morphologically and functionally diverse; ii) play numerous, vital roles in maintaining CNS homeostasis; iii) are key players in brain development and responses to injury; and, iv) via gliotransmission, are likely participants in information processing. In this review, we discuss the diverse roles of neuroglia in maintaining homeostasis in the CNS, their evolutionary origins, the different types of neuroglia and their functional significance for respiratory control, and finally consider evidence that they contribute to the processing of chemosensory information in the respiratory network and the homeostatic control of blood gases.

Effect of berberine on nitric oxide production during oxygen-glucose deprivation/reperfusion in OLN-93 oligodendrocytes

In this study, the effect of berberine, an isoquinoline alkaloid isolated from Coptidis rhizoma, on Nitric Oxide (NO) production, as a possible involved factor, during excitotoxic injury in oligodendroglial cells were evaluated. The overactivation of ionotropic glutamate receptors which is known as the excitotoxicity, is an important phenomenon because of the contribution in acute injury to the central nervous system, chronic neurodegenerative disorders, oligodendrocyte loss and demyelinating diseases as Multiple Sclerosis (MS). Intracellular Ca2+ overload, have a key role during excitotoxic injury and such increase in cytoplasmic Ca2+ triggers a series of events such as production of NO that end to cell death. Previous report showed the protective effects of berberine on ischemic-induced excitotoxic insult in oligodendrocytes. Hereby, we intended to know if the NO production could be associated with oxygen-glucose deprivation/reperfusion-induced excitotoxic damage in oligodendrocyte; moreover, the alteration of NO production could be considered as an involved mechanism for protective effect of berberine in such condition. Therefore, the effect of berberine (2 μM) on NO production during oxygen-glucose deprivation/24 h reperfusion in oligodendrocytes were examined. The OLN-93 cell line (a permanent immature rat oligodendrocyte) was used as a model of oligodendrocyte. Thirty minutes-oxygen-glucose deprivation/24 h reperfusion was used to induce excitotoxicity. NO production was evaluated by Griess method. Our results demonstrated that berberine (2 μM) significantly decreased NO production during 30 min oxygen-glucose deprivation/reperfusion. It seems that blockade of NO production by berberine may also participate in oligodendroglial cell protection against oxygen-glucose deprivation/reperfusion-induced insult.

Biological role of Toll-like receptor-4 in the brain

The Toll-like receptors (TLRs) are a family of microbe-sensing receptors that play a central role in the regulation of the host immune system. TLR4 has been described in the brain and seems to regulate some physiological processes, such as neurogenesis. TLR4 has also been reported to play a role during neurodegenerative disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis and Parkinson's disease. This review is focused on reports concerning recent insights into the role and activation mechanisms of TLR4 in the brain, in pathological and physiological conditions, as well as the therapeutic benefit that could derive from TLR4 modulation.

Activation of NOD2/RIPK2 pathway induces mitochondrial injury to oligodendrocyte precursor cells in vitro and CNS demyelination in vivo

We examined the activation of innate immune pathway mediated by nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in oligodendrocyte precursor cells (OPCs). We show that activation of NOD2 by ligand peptidoglycan (PGN) leads to the recruitment and phosphorylation of receptor-interacting serine/threonine kinase 2 (RIPK2). Phosphorylation of RIPK2 is followed by phosphorylation of neuronal nitric oxide synthase (nNOS), increase in NOS activity and subsequent accumulation of nitric oxide (NO) mediated N-tyrosinylated compounds in OPCs. The reversal of NOS activity by the nNOS inhibitor 7-nitroindazole (7-NI), but not by the iNOS inhibitor L-canavanine, supported the conclusion that the increased NOS activity was due to the selective activation of nNOS in OPCs. In addition, NO mediated injury to OPC was reflected in reduction in activity of respiratory enzymes such as complex I and IV, decrease in mitochondrial membrane potential and release of cytochrome-C from mitochondria. Furthermore, intracerebral injection of PGN into corpus callosum (CC) of rats led to the development of demyelination, which appeared as early as by day 3 post-injection, and involved the trunk of the CC by day 14. Accumulation of N-tyrosinylated proteins was seen in oligodendrocytes in regions of the CC which were in close proximity to the injection site. Taken together, these results suggest that PGN induced formation of NO, mitochondrial dysfunction and accumulation of N-tyrosinylated proteins in oligodendrocytes are likely mediators of central nervous system demyelination.

Astrogliopathy and oligodendrogliopathy are early events in CNS demyelination

We examined the phenotypic composition of cells and the underlying mechanisms of demyelination following injection of lipopolysaccharide (LPS) into the corpus callosum of rats. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed fragmented DNA, which co-localized with oligodendrocytes in areas of demyelination following intracerebral injection with LPS. Immunostaining showed the presence of caspase 3 in cells which expressed the oligodendrocyte markers, suggesting activation of the apoptotic pathway. Commensurate reduction in glial fibrillary acid protein (GFAP)+/ gap junction protein connexin43+ (Cx43) cells, was also seen in the corpus callosum prior to histochemical evidence of demyelination. Expression of mRNA for proinflammatory cytokines was maximal 3 day postinjection, at a time when the numbers of TUNEL positive cells in the corpus callosum were declining and the total number of CD68+ cells peaked at day 14 postinjection. Our studies suggest that death of oligodendrocytes is an early event in LPS model of demyelination. We believe that the innate immune model of oligodendrocyte death will be useful in the development of neuroprotective agents capable of rescuing oligodendrocytes from apoptosis.

Interaction of inflammation and hyperoxia in a rat model of neonatal white matter damage

Intrauterine infection and inflammation are major reasons for preterm birth. The switch from placenta-mediated to lung-mediated oxygen supply during birth is associated with a sudden rise of tissue oxygen tension that amounts to relative hyperoxia in preterm infants. Both infection/inflammation and hyperoxia have been shown to be involved in brain injury of preterm infants. Hypothesizing that they might be additive or synergistic, we investigated the influence of a systemic lipopolysaccharide (LPS) application on hyperoxia-induced white matter damage (WMD) in newborn rats. Three-day-old Wistar rat pups received 0.25 mg/kg LPS i.p. and were subjected to 80% oxygen on P6 for 24 h. The extent of WMD was assessed by immunohistochemistry, western blots, and diffusion tensor (DT) magnetic resonance imaging (MRI). In addition, the effects of LPS and hyperoxia were studied in an in vitro co-culture system of primary rat oligodendrocytes and microglia cells. Both noxious stimuli, hyperoxia, and LPS caused hypomyelination as revealed by western blot, immunohistochemistry, and altered WM microstructure on DT-MRI. Even so, cellular changes resulting in hypomyelination seem to be different. While hyperoxia induces cell death, LPS induces oligodendrocyte maturity arrest without cell death as revealed by TUNEL-staining and immunohistological maturation analysis. In the two-hit scenario cell death is reduced compared with hyperoxia treated animals, nevertheless white matter alterations persist. Concordantly with these in vivo findings we demonstrate that LPS pre-incubation reduced premyelinating-oligodendrocyte susceptibility towards hyperoxia in vitro. This protective effect might be caused by upregulation of interleukin-10 and superoxide dismutase expression after LPS stimulation. Reduced expression of transcription factors controlling oligodendrocyte development and maturation further indicates oligodendrocyte maturity arrest. The knowledge about mechanisms that triggered hypomyelination contributes to a better understanding of WMD in premature born infants.

Effects of an aqueous extract of North American ginseng on MOG(35-55)-induced EAE in mice

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system, in which the release of reactive oxygen species by infiltrating immune cells contributes to demyelination. American ginseng ( Panax quinquefolius ) is a natural health product with numerous beneficial properties, including anti-inflammatory and anti-oxidant effects. The purpose of this study was to determine whether ginseng could influence the course of the disease experimental autoimmune encephalomyelitis (EAE), an animal model of MS. C57BL/6J mice were immunized with MOG((35-55)) peptide to induce EAE. After clinical disease appeared, mice received either oral doses of an aqueous extract of ginseng (150 mg/kg body mass), or the vehicle. Clinical symptoms were recorded, and spinal cord tissue samples were analyzed for pathological signs of disease. The aqueous extract of ginseng significantly decreased (i) clinical signs of EAE, (ii) levels of circulating TNF-α, and (iii) central nervous system immunoreactive iNOS and demyelination scores, without a change in other neuropathological measures. This study shows that an aqueous extract of ginseng may be able to attenuate certain signs of EAE, suggesting that it may be a useful adjuvant therapy for MS.

Role of glial cells in innate immunity and their role in CNS demyelination

The adaptive and innate arms of the immune system are the two pillars of host defense against environmental pathogens. Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS which is considered to be autoimmune and is thought to result from breakdown in the usual checks and balances of the adaptive immune response. The major pathological outcome of the disease is "the MS plaque" a unique feature of CNS demyelination characterized by the destruction of oligodendrocytes with loss of myelin and underlying axons. The MS plaque is not seen in other inflammatory disorders of the CNS. The prevailing opinion suggests that MS is mediated by the activation of an adaptive immune response which targets neural antigens. Currently, the role of an innate immune in the development of the lesions in MS has remained unclear. We explore the potential cellular elements of the innate immune system and in particular glial cells, which are likely candidates in inducing the specific pathological picture that is evident in MS. Activated microglia and the release of molecules which are detrimental to oligodendrocyte have been suggested as mechanisms by which innate immunity causes demyelination in MS. However a microglia/macrophage centric model does not explain the specificity of lesion development in MS. We propose that activation pathways of receptors of the innate immune system present on oligodendrocytes and astrocytes rather than microglia are central to the pathogenesis of demyelination seen in MS.

Distinct role of nitric oxide and peroxynitrite in mediating oligodendrocyte toxicity in culture and in experimental autoimmune encephalomyelitis

Nitric oxide has been implicated in the pathogenesis of multiple sclerosis. However, it is still unclear whether nitric oxide plays a protective role or is deleterious. We have previously shown that peroxynitrite, a reaction product of nitric oxide and superoxide, is toxic to mature oligodendrocytes (OLs). The toxicity is mediated by intracellular zinc release, phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), activation of 12-lipoxygenase (12-LOX) and the formation of reactive oxygen species (ROS). In this study, we found that the donors of nitric oxide, dipropylenetriamine NONOate (DPT NONOate) and diethylenetriamine NONOate (DETA NONOate), protected OLs from peroxynitrite or zinc-induced toxicity. The protective mechanisms appear to be attributable to their inhibition of peroxynitrite- or zinc-induced ERK1/2 phosphorylation and 12-LOX activation. In cultures of mature OLs exposed to lipopolysaccharide (LPS), induction of inducible nitric oxide synthase (iNOS) generated nitric oxide and rendered OLs resistant to peroxynitrite-induced toxicity. The protection was eliminated when 1400W, a specific inhibitor of iNOS, was co-applied with LPS. Using MOG35-55-induced experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, we found that nitrotyrosine immunoreactivity, an indicator of peroxynitrite formation, was increased in the spinal cord white matter, which correlated with the loss of mature OLs. Targeted gene deletion of the NADPH oxidase component gp91phox reduced clinical scores, the formation of nitrotyrosine and the loss of mature OLs. These results suggest that blocking the formation specifically of peroxynitrite, rather than nitric oxide, may be a protective strategy against oxidative stress induced toxicity to OLs.

In vitro and in vivo induction and activation of nNOS by LPS in oligodendrocytes

There are currently four known isoforms of nitric oxide synthase (NOS). Of these, neuronal NOS (nNOS) is known to be present exclusively in neurons, endothelial NOS (eNOS) in vascular endothelium, while the inducible form of NOS (iNOS) is known to be activated in oligodendrocytes, astrocytes and microglia. The fourth isoform, mitochondrial NOS (mtNOS), represents a post-translational modification of nNOS. Using western blotting and real time-PCR, we show induction and activation of nNOS following culture of oligodendrocyte progenitor cells (OPC) with lipopolysaccharide (LPS). Activation of nNOS results in accumulation of peroxynitrite and tyrosine nitration of proteins in oligodendrocytes resulting in reduced cell viability. Injection of LPS in vivo into the corpus callosum of rats leads to the development of extensive demyelination of the white matter tracts. Immunostaining of regions close to the injection site shows the presence of nNOS, but not iNOS, in oligodendrocytes. Neither iNOS nor nNOS was seen in astrocytes in areas of demyelination. These studies suggest that activation of nNOS in oligodendrocytes leads to oligodendrocyte injury resulting in demyelination.