The protective role of nitric oxide in a neurotoxicant-induced demyelinating model

Citrullinated isomer of myelin basic protein can induce inflammatory responses in astrocytes

Purpose

During the course of demyelinating inflammatory diseases, myelin-derived proteins, including myelin basic protein(MBP), are secreted into extracellular space. MBP shows extensive post-translational modifications, including deimination/citrullination. Deiminated MBP is structurally less ordered, susceptible to proteolytic attack, and more immunogenic than unmodified MBP. This study investigated the effect of the deiminated/citrullinated isomer of MBP(C8) and the unmodified isomer of MBP(C1) on cultured primary astrocytes.

Methods

MBP charge isomers were isolated/purified from bovine brain. Primary astrocyte cultures were prepared from the 2-day-old Wistar rats. For evaluation of glutamate release/uptake a Fluorimetric glutamate assay was used. Expression of peroxisome proliferator-activated receptor-gamma(PPAR-γ), excitatory amino acid transporter 2(EAAT2), the inhibitor of the nuclear factor kappa-B(ikB) and high mobility group-B1(HMGB1) protein were assayed by Western blot analysis. IL-17A expression was determined in cell medium by ELISA.

Results

We found that MBP(C8) and MBP(C1) acted differently on the uptake/release of glutamate in astrocytes: C1 increased glutamate uptake and did not change its release, whereas C8 decreased glutamate release but did not change its uptake. Both isomers increased the expression of PPAR-γ and EAAT2 to the same degree. Western blots of cell lysates revealed decreased expression of ikB and increased expression of HMGB1 proteins after treatment of astrocytes by C8. Moreover, C8-treated cells released more nitric oxide and proinflammatory IL-17A than C1-treated cells.

Conclusions

These data suggest that the most immunogenic deiminated isomer C8, in parallel to the decreases in glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B(NF-kB).

Summary statement

The most modified-citrullinated myelin basic protein charge isomer decreases glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B in astrocytes.

Inducible nitric oxide synthase deficiency promotes murine-β-coronavirus induced demyelination

BACKGROUND

Multiple sclerosis (MS) is characterized by neuroinflammation and demyelination orchestrated by activated neuroglial cells, CNS infiltrating leukocytes, and their reciprocal interactions through inflammatory signals. An inflammatory stimulus triggers inducible nitric oxide synthase (NOS2), a pro-inflammatory marker of microglia/macrophages (MG/Mφ) to catalyze sustained nitric oxide production. NOS2 during neuroinflammation, has been associated with MS disease pathology; however, studies dissecting its role in demyelination are limited. We studied the role of NOS2 in a recombinant β-coronavirus-MHV-RSA59 induced neuroinflammation, an experimental animal model mimicking the pathological hallmarks of MS: neuroinflammatory demyelination and axonal degeneration.

OBJECTIVE

Understanding the role of NOS2 in murine-β-coronavirus-MHV-RSA59 demyelination.

METHODS

Brain and spinal cords from mock and RSA59 infected 4-5-week-old MHV-free C57BL/6 mice (WT) and NOS2-/- mice were harvested at different disease phases post infection (p.i.) (day 5/6-acute, day 9/10-acute-adaptive and day 30-chronic phase) and compared for pathological outcomes.

RESULTS

NOS2 was upregulated at the acute phase of RSA59-induced disease in WT mice and its deficiency resulted in severe disease and reduced survival at the acute-adaptive transition phase. Low survival in NOS2-/- mice was attributed to (i) high neuroinflammation resulting from increased accumulation of macrophages and neutrophils and (ii) Iba1 + phagocytic MG/Mφ mediated-early demyelination as observed at this phase. The phagocytic phenotype of CNS MG/Mφ was confirmed by significantly higher mRNA transcripts of phagocyte markers-CD206, TREM2, and Arg1 and double immunolabelling of Iba1 with MBP and PLP. Further, NOS2 deficiency led to exacerbated demyelination at the chronic phase as well.

CONCLUSION

Taken together the results imply that the immune system failed to control the disease progression in the absence of NOS2. Thus, our observations highlight a protective role of NOS2 in murine-β-coronavirus induced demyelination.

Activated microglia drive demyelination via CSF1R signaling

Microgliosis is a prominent pathological feature in many neurological diseases including multiple sclerosis (MS), a progressive auto-immune demyelinating disorder. The precise role of microglia, parenchymal central nervous system (CNS) macrophages, during demyelination, and the relative contributions of peripheral macrophages are incompletely understood. Classical markers used to identify microglia do not reliably discriminate between microglia and peripheral macrophages, confounding analyses. Here, we use a genetic fate mapping strategy to identify microglia as predominant responders and key effectors of demyelination in the cuprizone (CUP) model. Colony-stimulating factor 1 (CSF1), also known as macrophage colony-stimulating factor (M-CSF) - a secreted cytokine that regulates microglia development and survival-is upregulated in demyelinated white matter lesions. Depletion of microglia with the CSF1R inhibitor PLX3397 greatly abrogates the demyelination, loss of oligodendrocytes, and reactive astrocytosis that results from CUP treatment. Electron microscopy (EM) and serial block face imaging show myelin sheaths remain intact in CUP treated mice depleted of microglia. However, these CUP-damaged myelin sheaths are lost and robustly phagocytosed upon-repopulation of microglia. Direct injection of CSF1 into CNS white matter induces focal microgliosis and demyelination indicating active CSF1 signaling can promote demyelination. Finally, mice defective in adopting a toxic astrocyte phenotype that is driven by microglia nevertheless demyelinate normally upon CUP treatment implicating microglia rather than astrocytes as the primary drivers of CUP-mediated demyelination. Together, these studies indicate activated microglia are required for and can drive demyelination directly and implicate CSF1 signaling in these events.

Five Decades of Cuprizone, an Updated Model to Replicate Demyelinating Diseases

INTRODUCTION

Demyelinating diseases of the central nervous system (CNS) comprise a group of neurological disorders characterized by progressive (and eventually irreversible) loss of oligodendrocytes and myelin sheaths in the white matter tracts. Some of myelin disorders include: Multiple sclerosis, Guillain-Barré syndrome, peripheral nerve polyneuropathy and others. To date, the etiology of these disorders is not well known and no effective treatments are currently available against them. Therefore, further research is needed to gain a better understand and treat these patients. To accomplish this goal, it is necessary to have appropriate animal models that closely resemble the pathophysiology and clinical signs of these diseases. Herein, we describe the model of toxic demyelination induced by cuprizone (CPZ), a copper chelator that reduces the cytochrome and monoamine oxidase activity into the brain, produces mitochondrial stress and triggers the local immune response. These biochemical and cellular responses ultimately result in selective loss of oligodendrocytes and microglia accumulation, which conveys to extensive areas of demyelination and gliosis in corpus callosum, superior cerebellar peduncles and cerebral cortex. Remarkably, some aspects of the histological pattern induced by CPZ are similar to those found in multiple sclerosis. CPZ exposure provokes behavioral changes, impairs motor skills and affects mood as that observed in several demyelinating diseases. Upon CPZ removal, the pathological and histological changes gradually revert. Therefore, some authors have postulated that the CPZ model allows to partially mimic the disease relapses observed in some demyelinating diseases.

CONCLUSION

for five decades, the model of CPZ-induced demyelination is a good experimental approach to study demyelinating diseases that has maintained its validity, and is a suitable pharmacological model for reproducing some key features of demyelinating diseases, including multiple sclerosis.

NLR members NLRC4 and NLRP3 mediate sterile inflammasome activation in microglia and astrocytes

Lysophosphatidylcholine is associated with neurodegeneration and demyelination. Freeman et al. demonstrate that lysophosphatidylcholine triggers NLRP3- and NLRC4-dependent inflammasome activation, and in a synergistic fashion, NLRP3 and NLRC4 contribute to a cuprizone-induced demyelination model in vivo.

Inflammation in the brain accompanies several high-impact neurological diseases including multiple sclerosis (MS), stroke, and Alzheimer’s disease. Neuroinflammation is sterile, as damage-associated molecular patterns rather than microbial pathogens elicit the response. The inflammasome, which leads to caspase-1 activation, is implicated in neuroinflammation. In this study, we reveal that lysophosphatidylcholine (LPC), a molecule associated with neurodegeneration and demyelination, elicits NLRP3 and NLRC4 inflammasome activation in microglia and astrocytes, which are central players in neuroinflammation. LPC-activated inflammasome also requires ASC (apoptotic speck containing protein with a CARD), caspase-1, cathepsin-mediated degradation, calcium mobilization, and potassium efflux but not caspase-11. To study the physiological relevance, Nlrc4^−/− and Nlrp3^−/− mice are studied in the cuprizone model of neuroinflammation and demyelination. Mice lacking both genes show the most pronounced reduction in astrogliosis and microglial accumulation accompanied by decreased expression of the LPC receptor G2A, whereas MS patient samples show increased G2A. These results reveal that NLRC4 and NLRP3, which normally form distinct inflammasomes, activate an LPC-induced inflammasome and are important in astrogliosis and microgliosis.

Identifying the Long-Term Role of Inducible Nitric Oxide Synthase after Contusive Spinal Cord Injury Using a Transgenic Mouse Model

Inducible nitric oxide synthase (iNOS) is a potent mediator of oxidative stress during neuroinflammation triggered by neurotrauma or neurodegeneration. We previously demonstrated that acute iNOS inhibition attenuated iNOS levels and promoted neuroprotection and functional recovery after spinal cord injury (SCI). The present study investigated the effects of chronic iNOS ablation after SCI using inos-null mice. iNOS^-/- knockout and wild-type (WT) control mice underwent a moderate thoracic (T8) contusive SCI. Locomotor function was assessed weekly, using the Basso Mouse Scale (BMS), and at the endpoint (six weeks), by footprint analysis. At the endpoint, the volume of preserved white and gray matter, as well as the number of dorsal column axons and perilesional blood vessels rostral to the injury, were quantified. At weeks two and three after SCI, iNOS^-/- mice exhibited a significant locomotor improvement compared to WT controls, although a sustained improvement was not observed during later weeks. At the endpoint, iNOS^-/- mice showed significantly less preserved white and gray matter, as well as fewer dorsal column axons and perilesional blood vessels, compared to WT controls. While short-term antagonism of iNOS provides histological and functional benefits, its long-term ablation after SCI may be deleterious, blocking protective or reparative processes important for angiogenesis and tissue preservation.

Compromised axon initial segment integrity in EAE is preceded by microglial reactivity and contact

Axonal pathology is a key contributor to long-term disability in multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS), but the mechanisms that underlie axonal pathology in MS remain elusive. Evidence suggests that axonal pathology is a direct consequence of demyelination, as we and others have shown that the node of Ranvier disassembles following loss of myelin. In contrast to the node of Ranvier, we now show that the axon initial segment (AIS), the axonal domain responsible for action potential initiation, remains intact following cuprizone-induced cortical demyelination. Instead, we find that the AIS is disrupted in the neocortex of mice that develop experimental autoimmune encephalomyelitis (EAE) independent of local demyelination. EAE-induced mice demonstrate profound compromise of AIS integrity with a progressive disruption that corresponds to EAE clinical disease severity and duration, in addition to cortical microglial reactivity. Furthermore, treatment with the drug didox results in attenuation of AIS pathology concomitantly with microglial reversion to a less reactive state. Together, our findings suggest that inflammation, but not demyelination, disrupts AIS integrity and that therapeutic intervention may protect and reverse this pathology. GLIA 2016;64:1190-1209.

Cellular and molecular neuropathology of the cuprizone mouse model: clinical relevance for multiple sclerosis

The cuprizone mouse model allows the investigation of the complex molecular mechanisms behind nonautoimmune-mediated demyelination and spontaneous remyelination. While it is generally accepted that oligodendrocytes are specifically vulnerable to cuprizone intoxication due to their high metabolic demands, a comprehensive overview of the etiology of cuprizone-induced pathology is still missing to date. In this review we extensively describe the physico-chemical mode of action of cuprizone and discuss the molecular and enzymatic mechanisms by which cuprizone induces metabolic stress, oligodendrocyte apoptosis, myelin degeneration and eventually axonal and neuronal pathology. In addition, we describe the dual effector function of the immune system which tightly controls demyelination by effective induction of oligodendrocyte apoptosis, but in contrast also paves the way for fast and efficient remyelination by the secretion of neurotrophic factors and the clearance of cellular and myelinic debris. Finally, we discuss the many clinical symptoms that can be observed following cuprizone treatment, and how these strengthened the cuprizone model as a useful tool to study human multiple sclerosis, schizophrenia and epilepsy.

Role of iNOS-NO-cGMP signaling in modulation of inflammatory and myelination processes

Nitric oxide (NO) is the main activator of the soluble guanylate cyclase (sGC)-guanosine 3'5' cyclic monophosphate (cGMP) pathway. The level of cGMP is regulated by phosphodiesterases (PDEs), which break down cGMP. It has been reported that levels of NO in the central nervous system (CNS) can greatly increase during demyelination and/or neuroinflammation. Controversially, in demyelination models, mice without iNOS may develop more severe cases of disease. Furthermore, cGMP accumulation caused by PDE inhibitors has an anti-inflammatory/neuroprotective effect in MS-models. The role of the NO-cGMP pathway in the nervous tissue is, therefore, complex and not fully understood. The aim of the present study was to contribute to existing knowledge of the role of this pathway in the CNS. Wild type (WT - C57BL/6) and iNOS(-/-) animals were treated with sildenafil (25mg/kg) for 8 weeks. Control animals were not treated. VCAM and ICAM (adhesion proteins), GFAP and Iba-1 (astrocyte and microglia markers, respectively), PKG (cGMP-dependent protein kinase), sGC, eNOS (constitutive endothelial NO sinthase) and GSTpi (a marker of mature oligodendrocytes) were evaluated in the cerebellum using immunohistochemistry or western blotting. Myelin was assessed by luxol fast blue staining and electron transmission microscopy. Treatment with sildenafil reduced ICAM and VCAM levels (anti-inflammatory effect) and increased GFAP and Iba-1 expression (clearance phenotype) in WT animals. The expression of VCAM, ICAM, GFAP, PKG and sGC was lower in iNOS(-/-) mice than in WT control animals. The treatment of iNOS(-/-) animals with sildenafil resulted in an increase of all proteins (pro-inflammatory effect). There was overexpression of eNOS in untreated iNOS(-/-) mice. The myelin structure of iNOS(-/-) animals was damaged in comparison with WT control. Sildenafil increased GSTpi and resulted in an improved myelin structure in iNOS(-/-) mice. In conclusion, NO-cGMP signaling plays a role in the regulation of inflammation and myelination processes. The accumulation of cGMP produced opposite effects in WT and iNOS(-/-) mice. This can be explained by the overexpression of eNOS in iNOS(-/-) mice, unbalancing cGMP signaling, or cGMP has a dual role in inflammation. Drugs that modulate the NO-sGC-cGMP pathway may be clinically beneficial in the treatment of neuroinflammatory/demyelinating disorders, but further studies of the regulation of this pathway are required.

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Beneficial effect of agmatine in the acute phase of experimental autoimmune encephalomyelitis in iNOS-/- knockout mice

The aim of the study was to investigate the hypothesis that agmatine (AGM) provides protection against oxidative stress in experimental autoimmune encephalomyelitis (EAE). Wild-type (WT) and knockout (KO) CBA/H iNOS-/- 3 months old (15 ± 5 g) mice, were used for EAE induction by myelin basic protein (MBP), dissolved in Complete Freund's Adjuvant (CFA). The animals were divided into control, EAE, CFA, EAE+AGM and AGM groups. After the development of full clinical remission, animals were decapitated and oxidative stress parameters were determined in whole encephalitic mass (WEM) and cerebellum homogenates. The EAE clinical expression manifested to greater extent in WT than KO mice, was significantly decreased during AGM treatment. We demonstrated significant elevations of superoxide dismutase activity in WT and KO EAE animals, in WEM and cerebellum tissues, which were decreased during AGM treatment in both groups. Superoxide anion content was increased in WEM of both study groups, with a decrease during AGM treatment. The observed changes were more pronounced in WT than in KO animals. Also, the increased expressions of transferrin receptor and glial fibrillary acidic protein observed in WT and KO EAE mice were significantly decreased during AGM treatment. The results suggest potentially beneficial AGM effects in EAE, which might be used for a modified antioxidative approach in MS therapy.

Sildenafil (Viagra) protective effects on neuroinflammation: the role of iNOS/NO system in an inflammatory demyelination model

We recently demonstrated that sildenafil reduces the expression of cytokines, COX-2, and GFAP in a demyelinating model induced in wild-type (WT) mice. Herein, the understandings of the neuroprotective effect of sildenafil and the mediation of iNOS/NO system on inflammatory demyelination induced by cuprizone were investigated. The cerebella of iNOS(-/-) mice were examined after four weeks of treatment with cuprizone alone or combined with sildenafil. Cuprizone increased GFAP, Iba-1, TNF- α , COX-2, IL-1 β , and IFN- γ expression, decreased expression of glutathione S-transferase pi (GSTpi), and damaged myelin in iNOS(-/-) mice. Sildenafil reduced Iba-1, IFN- γ , and IL-1 β levels but had no effect on the expression of GFAP, TNF- α , and COX-2 compared to the cuprizone group. Sildenafil elevated GSTpi levels and improved the myelin structure/ultrastructure. iNOS(-/-) mice suffered from severe inflammation following treatment with cuprizone, while WT mice had milder inflammation, as found in the previous study. It is possible that inflammatory regulation through iNOS-feedback is absent in iNOS(-/-) mice, making them more susceptible to inflammation. Sildenafil has at least a partial anti-inflammatory effect through iNOS inhibition, as its effect on iNOS(-/-) mice was limited. Further studies are required to explain the underlying mechanism of the sildenafil effects.

The benefits and detriments of macrophages/microglia in models of multiple sclerosis

The central nervous system (CNS) is immune privileged with access to leukocytes being limited. In several neurological diseases, however, infiltration of immune cells from the periphery into the CNS is largely observed and accounts for the increased representation of macrophages within the CNS. In addition to extensive leukocyte infiltration, the activation of microglia is frequently observed. The functions of activated macrophages/microglia within the CNS are complex. In three animal models of multiple sclerosis (MS), namely, experimental autoimmune encephalomyelitis (EAE) and cuprizone- and lysolecithin-induced demyelination, there have been many reported detrimental roles associated with the involvement of macrophages and microglia. Such detriments include toxicity to neurons and oligodendrocyte precursor cells, release of proteases, release of inflammatory cytokines and free radicals, and recruitment and reactivation of T lymphocytes in the CNS. Many studies, however, have also reported beneficial roles of macrophages/microglia, including axon regenerative roles, assistance in promoting remyelination, clearance of inhibitory myelin debris, and the release of neurotrophic factors. This review will discuss the evidence supporting the detrimental and beneficial aspects of macrophages/microglia in models of MS, provide a discussion of the mechanisms underlying the dichotomous roles, and describe a few therapies in clinical use in MS that impinge on the activity of macrophages/microglia.

Pioglitazone, PPARγ agonist, attenuates experimental autoimmune neuritis

Recent advances demonstrate peroxisome proliferator-activated receptors gamma (PPARγ) agonist, pioglitazone, as an anti-inflammatory drug. We investigated the effect of pioglitazone on experimental autoimmune neuritis (EAN) rats. Pioglitazone was given once daily (10 mg/kg) by oral gavage feeding from day 1-24 (suppressive group) and day 11-24 (therapeutic group). Pioglitazone ameliorated the clinical score of EAN, decreased expression of TNF-α, IFN-γ, and the activation of NF-κB, while increasing the expression of PPARγ and IL-4. Furthermore, we observed higher expression of PPARγ and IL-4 and lower expression of TNF-α, IFN-γ and reduced activation of NF-κB in suppressive group than those in the therapeutic group, which corresponds to lower clinical score and earlier disease recovery. Our data effectively demonstrate the anti-inflammatory properties of pioglitazone in EAN by inhibition of NF-κB signaling pathway.

MyD88 provides a protective role in long-term radiation-induced lung injury

PURPOSE

The role of innate immune regulators is investigated in injury sustained from irradiation as in the clinic for cancer treatment or from a nuclear incident. The protective benefits of flagellin signaling through Toll-like receptors (TLR) in an irradiation setting warrant study of a key intracellular adaptor of TLR signaling, namely Myeloid differentiation primary response factor 88 (MyD88). The role of MyD88 in regulating innate immunity and Nuclear factor kappa-B (NF-κB)-activated responses targets this critical factor for influencing injury and recovery as well as maintaining immune homeostasis.

MATERIALS AND METHODS

To examine the role of MyD88, we examined immune cells and factors during acute pneumonitic and fibrotic phases in Myd88-deficient animals receiving thoracic gamma (γ)-irradiation.

RESULTS

We found that MyD88 supports survival from radiation-induced injury through the regulation of inflammatory factors that aid in recovery from irradiation. The absence of MyD88 resulted in unresolved pulmonary infiltrate and enhanced collagen deposition plus elevated type 2 helper T cell (Th2) cytokines in long-term survivors of irradiation.

CONCLUSIONS

These results based only on a gene deletion model suggest that alterations of MyD88-dependent inflammatory processes impact chronic lung injury. Therefore, MyD88 may contribute to attenuating long-term radiation-induced lung injury and protecting against fibrosis.

Aminoguanidine and N-acetyl-cysteine supress oxidative and nitrosative stress in EAE rat brains

Experimental autoimmune encephalomyelitis (EAE) is a well-established animal model of human multiple sclerosis (MS). We have evaluated the role of oxidative and nitrosative stress, as the causal factors in the development of EAE, responsible for the damage of cardinal cellular components, such as lipids, proteins and nucleic acids, resulting in demyelination, axonal damage, and neuronal death. EAE was induced in female Sprague-Dawley rats, 3 months old (300±20 g), by immunization with myelin basic protein in combination with Complete Freund's adjuvant (CFA). The animals were divided into seven groups: control, EAE, CFA, EAE+aminoguanidine (AG), AG, EAE+N-acetyl-L-cysteine (NAC) and NAC. The animals were sacrificed 15 days after EAE induction, and the levels of nitrosative and oxidative stress were determined in 10% homogenate of the whole encephalitic mass. In EAE rats, brain NO production and MDA level were significantly increased (P<0.001) compared to the control values, whereas AG and NAC treatment decreased both parameters in EAE rats compared to EAE group (P<0.001). Glutathione (GSH) was reduced (P<0.001) in EAE rats in comparison with the control and CFA groups, but increased in EAE+AG and EAE+NAC group compared to the EAE group (P<0.01). Superoxide dismutase (SOD) activity was significantly decreased (P<0.001) in the EAE group compared to all other experimental groups. The clinical expression of EAE was significantly decreased (P<0.05) in the EAE groups treated with AG and NAC compared to EAE rats, during disease development. The obtained results prove an important role of oxidative and nitrosative stress in the pathogenesis of EAE, whereas AG and NAC protective effects offer new possibilities for a modified combined approach in MS therapy.

Identification of a microglia phenotype supportive of remyelination

In multiple sclerosis, endogenous oligodendrocyte precursor cells (OPCs) attempt to remyelinate areas of myelin damage. During disease progression, however, these attempts fail. It has been suggested that modulating the inflammatory environment of the lesion might provide a promising therapeutic approach to promote endogenous remyelination. Microglia are known to play a central role in neuroinflammatory processes. To investigate the microglia phenotype that supports remyelination, we performed genome-wide gene expression analysis of microglia from the corpus callosum during demyelination and remyelination in the mouse cuprizone model, in which remyelination spontaneously occurs after an episode of toxin-induced primary demyelination. We provide evidence for the existence of a microglia phenotype that supports remyelination already at the onset of demyelination and persists throughout the remyelination process. Our data show that microglia are involved in the phagocytosis of myelin debris and apoptotic cells during demyelination. Furthermore, they express a cytokine and chemokine repertoire enabling them to activate and recruit endogenous OPCs to the lesion site and deliver trophic support during remyelination. This study not only provides a detailed transcriptomic analysis of the remyelination-supportive microglia phenotype but also reinforces the notion that the primary function of microglia is the maintenance of tissue homeostasis and the support of regeneration already at the earliest stages in the development of demyelinating lesions.

Macrophages counteract demyelination in a mouse model of globoid cell leukodystrophy

Whether microglia and macrophages are beneficial or harmful in many neurological disorders, including demyelinating diseases such as multiple sclerosis and the leukodystrophies, is currently under debate. Answering this question is of special interest in globoid cell leukodystrophy (GLD), a genetic fatal demyelinating disease, because its rapidly progressive demyelination in the nervous system is accompanied by a characteristic accumulation of numerous globoid macrophages. Therefore, we cross-bred the twitcher (twi) mouse, a bona fide model of GLD, with the macrophage-deficient osteopetrotic mutant and studied the resultant macrophage-deficient twitcher (twi+op) mouse. The twi+op mouse had few microglia and macrophages in the white matter and, interestingly, showed a more severe clinical phenotype compared to the twi mouse. The number of nonmyelinated axons in the spinal cord was significantly higher in twi+op mice than in twi mice at 45 d old. The difference appeared to be due to impaired remyelination in twi+op mice rather than accelerated demyelination. Quantitative reverse transcription PCR and immunohistochemical studies revealed that the recruitment of oligodendrocyte progenitor cells in response to demyelination was compromised in twi+op mice. Increased myelin debris in the white matter parenchyma of twi+op mice suggested that phagocytosis by macrophages may play an important role in promoting remyelination. Macrophage markers for both protective and destructive phenotypes were significantly upregulated in the spinal cord of twi mice but were close to normal in twi+op mice due to the reduced macrophage number. The overall effects of macrophages in GLD appear to be beneficial to myelin by promoting myelin repair.

The inflammasome sensor, NLRP3, regulates CNS inflammation and demyelination via caspase-1 and interleukin-18

Inflammation is increasingly recognized as an important contributor to a host of CNS disorders; however, its regulation in the brain is not well delineated. Nucleotide-binding domain, leucine-rich repeat, pyrin domain containing 3 (NLRP3) is a key component of the inflammasome complex, which also includes ASC (apoptotic speck-containing protein with a card) and procaspase-1. Inflammasome formation can be triggered by membrane P2X(7)R engagement leading to cleavage-induced maturation of caspase-1 and interleukin-1β (IL-1β)/IL-18. This work shows that expression of the Nlrp3 gene was increased >100-fold in a cuprizone-induced demyelination and neuroinflammation model. Mice lacking the Nlrp3 gene (Nlrp3(-/-)) exhibited delayed neuroinflammation, demyelination, and oligodendrocyte loss in this model. These mice also showed reduced demyelination in the experimental autoimmune encephalomyelitis model of neuroinflammation. This outcome is also observed for casp1(-/-) and IL-18(-/-) mice, whereas IL-1β(-/-) mice were indistinguishable from wild-type controls, indicating that Nlrp3-mediated function is through caspase-1 and IL-18. Additional analyses revealed that, unlike the IL-1β(-/-) mice, which have been previously shown to show delayed remyelination, Nlrp3(-/-) mice did not exhibit delayed remyelination. Interestingly, IL-18(-/-) mice showed enhanced remyelination, thus providing a possible compensatory mechanism for the lack of a remyelination defect in Nlrp3(-/-) mice. These results suggest that NLRP3 plays an important role in a model of multiple sclerosis by exacerbating CNS inflammation, and this is partly mediated by caspase-1 and IL-18. Additionally, the therapeutic inhibition of IL-18 might decrease demyelination but enhance remyelination, which has broad implications for demyelinating diseases.

Promoter-specific induction of the phosphatase SHP-1 by viral infection and cytokines in CNS glia

We have previously shown that the protein tyrosine phosphatase SHP-1 is highly expressed in CNS glia and is an important modulator of cytokine signaling. As such, mice genetically lacking SHP-1 display constitutive myelin abnormalities, severe virus-induced demyelinating disease, and defects in innate anti-viral responses in the CNS. In this study, we show the differential distribution of the SHP-1 promoter-specific transcripts and demonstrate that several cytokines significantly induce SHP-1 expression in CNS glia. Consistent with these cytokine effects, infection with a neurotropic virus both in vitro and in vivo up-regulates SHP-1 transcripts and protein in CNS cells. Using CNS glial cultures of gene knockout mice, we show that interferons-beta and interferons-gamma act through STAT-1 and interferon regulatory factor-1 to induce the SHP-1 promoter I transcripts. Conversely, interferons-beta and IL-6 act through STAT-3 to induce SHP-1 promoter II transcripts. This study demonstrates that interferons and other cytokines associated with virus infections in the CNS can significantly induce the expression of SHP-1 through STAT-1/3 activity and provides a better understanding of the molecular mechanisms regulating cytokine-induced expression important for multiple homeostatic functions of SHP-1 in the CNS.

17beta-estradiol protects male mice from cuprizone-induced demyelination and oligodendrocyte loss

In addition to regulating reproductive functions in the brain and periphery, estrogen has tropic and neuroprotective functions in the central nervous system (CNS). Estrogen administration has been demonstrated to provide protection in several animal models of CNS disorders, including stroke, brain injury, epilepsy, Parkinson's disease, Alzheimer's disease, age-related cognitive decline and multiple sclerosis. Here, we use a model of toxin-induced oligodendrocyte death which results in demyelination, reactive gliosis, recruitment of oligodendrocyte precursor cells and subsequent remyelination to study the potential benefit of 17beta-estradiol (E2) administration in male mice. The results indicate that E2 partially ameliorates loss of oligodendrocytes and demyelination in the corpus callosum. This protection is accompanied by a delay in microglia accumulation as well as reduced mRNA expression of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFalpha), and insulin-like growth factor-1 (IGF-1). E2 did not significantly alter the accumulation of astrocytes or oligodendrocyte precursor cells, or remyelination. These data obtained from a toxin-induced, T cell-independent model using male mice provide an expanded view of the beneficial effects of estrogen on oligodendrocyte and myelin preservation.

Role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination of the CNS

As the resident innate immune cells of the central nervous system (CNS), microglia fulfil a critical role in maintaining tissue homeostasis and in directing and eliciting molecular responses to CNS damage. The human disease Multiple Sclerosis and animal models of inflammatory demyelination are characterized by a complex interplay between degenerative and regenerative processes, many of which are regulated and mediated by microglia. Cellular communication between microglia and other neural and immune cells is controlled to a large extent by the activity of cytokines. Here we review the role of cytokines as mediators and regulators of microglial activity in inflammatory demyelination, highlighting their importance in potentiating cell damage, promoting neuroprotection and enhancing cellular repair in a context-dependent manner.

Progressive multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system, which starts in the majority of patients with a relapsing/remitting MS (RRMS) course , which after several years of disease duration converts into a progressive disease. Since anti-inflammatory therapies and immune modulation exert a beneficial effect at the relapsing/remitting stage of the disease, but not in the progressive stage, the question was raised whether inflammation drives tissue damage in progressive MS at all. We show here that also in progressive MS, inflammation is the driving force for brain injury and that the discrepancy between inflammation-driven tissue injury and response to immunomodulatory therapies can be explained by different pathomechanisms acting in RRMS and progressive MS.

Selective reduction in microglia density and function in the white matter of colony-stimulating factor-1-deficient mice

It is still debated whether microglia play a beneficial or harmful role in myelin disorders such as multiple sclerosis and leukodystrophies as well as in other pathological conditions of the central nervous system. The osteopetrotic (op/op) mouse has reduced numbers of cells of monocyte lineage as a result of an inactivating mutation in the colony stimulating factor-1 gene. To determine whether this mutant mouse might be used to study the role of microglia in myelin disorders, we quantified the number of microglia in the central nervous system of op/op mice and explored their ability to respond to brain injury created by a stab wound. Microglial density in the 2-month-old op/op mice was significantly decreased in the white matter tracts compared with the -ge matched wild-type controls (by 63.6% in the corpus callosum and 86.4% in the spinal dorsal column), whereas the decrease was less in the gray matter, cerebral cortex (24.0%). A similar decrease was seen at 7 months of age. Morphometric studies of spinal cord myelination showed that development of myelin was not affected in op/op mice. In response to a stab wound, the increase in the number of microglia/macrophages in op/op mice was significantly less pronounced than that in wild-type control. These findings demonstrate that this mutant is a valuable model in which to study roles of microglia/macrophages in the pathophysiology of myelin disorders.

Modeling multiple sclerosis in laboratory animals

Inflammatory demyelinating disease of the central nervous system is one of the most frequent causes of neurological disability in young adults. While in situ analysis and in vitro models do shed some light onto the processes of tissue damage and cellular interactions, the development of neuroinflammation and demyelination is a far too complex process to be adequately modeled by simple test tube systems. Thus, animal models using primarily genetically modified mice have been proven to be of paramount importance. In this chapter, we discuss recent advances in modeling brain diseases focusing on murine models and report on new tools to study the pathogenesis of complex diseases such as multiple sclerosis.

Activation of inflammatory response by a combination of growth factors in cuprizone-induced demyelinated brain leads to myelin repair

In vivo remyelination promoted by a combination of four oligodendrocyte specific growth factors (GFs) in cuprizone-induced demyelinated mice brains was described recently by our group. Here we report activation of inflammatory response in mice brain following cuprizone-induced demyelination and its further enhancement immediately after injection of growth factors in vivo, while no significant inflammatory response was evident in GFs-injected normal brains. Cuprizone-induced demyelination was accompanied by increased expression of inflammatory cytokines, TNFalpha and IL-1beta, anti-inflammatory cytokines TGFbeta, IL-10 and increased levels of chemokines, CCL2, CCL5, and CXCL10, produced by resident microglia and astrocytes. During demyelination, involvement of oxidative stress was evident by disruption of mitochondrial structure and temporal decline in reduced glutathione levels, later returning to normal. Increase in the cytokines and chemokines was further enhanced within 2 days post injection (dpi) of GFs, coinciding with signal for repair via activation of pAkt and NFkappaB transcription factor reported earlier. Upregulation of mRNA and protein level of antioxidant genes, metallothionein (MT) I/II and activity of a cytosolic oxidoreductase enzyme, glycerolphosphate-3 dehydrogenase (cGPDH) occurred, resulting in a metabolic shuttle with an increase in glycerol in mice brains during period of demyelination and early GF-mediated repair.

Gas6 deficiency increases oligodendrocyte loss and microglial activation in response to cuprizone-induced demyelination

The TAM family of receptor protein tyrosine kinases comprises three known members, namely Tyro3, Axl, and Mer. These receptors are widely expressed in the nervous system, including by oligodendrocytes, the cell type responsible for myelinating the CNS. We examined the potential role of the TAM family and of their principle cognate ligand, Gas6 (growth arrest gene 6), in modulating the phenotype of the cuprizone model of demyelination. We found that the expression profiles of Axl, Mer, and Gas6 mRNA were increased in the corpus callosum in a temporal profile correlating with the increased migration and proliferation of microglia/macrophages in this model. In contrast, expression of Tyro3 decreased, correlating with the loss of oligodendrocytes. Gas6 both promoted in vitro survival of oligodendrocytes (39.3 +/- 3.1 vs 11.8 +/- 2.4%) and modulated markers of activation in purified cultures of microglia (tumor necrosis factor alpha mRNA expression was reduced approximately 48%). In Gas6-/- mice subjected to cuprizone-challenge, demyelination was greater than in control mice, within the rostral region of the corpus callosum, as assessed by luxol fast blue staining (myelination reduced by 36%) and by ultrastructural analysis. An increased loss of Gst-pi (glutathione S-transferase-pi)-positive oligodendrocytes was also identified throughout the corpus callosum of Gas6-/- mice. Microglial marker expression (ionized calcium-binding adapter molecule 1) was increased in Gas6-/- mice but was restricted to the rostral corpus callosum. Therefore, TAM receptor activation and regulation can independently influence both oligodendrocyte survival and the microglial response after CNS damage.

Involvement of nitric oxide in the promotion of cell survival by ceramide 1-phosphate

Macrophages play vital roles in inflammatory responses, and their number at sites of inflammation is strictly regulated by cell death and division. Here, we demonstrate that production of nitric oxide (NO) is a major mechanism whereby ceramide-1-phosphate (C1P) blocks apoptosis in macrophages. However, NO failed to stimulate macrophage proliferation. The prosurvival effect of C1P was blocked by inhibitors of inducible NO synthase. The antiapoptotic effect of C1P was also blocked by phosphatidylinositol 3-kinase or nuclear factor-kappa B inhibitors. Moreover, NO reversed the inhibitory effect of C1P on acid sphingomyelinase, but the prosurvival effect of C1P was independent of this action.

Sequential myelin protein expression during remyelination reveals fast and efficient repair after central nervous system demyelination

To understand the mechanisms of remyelination and the reasons for regeneration failure is one of the major challenges in multiple sclerosis research. This requires a good knowledge and reliable analysis of experimental models. This work was undertaken to characterize the pattern of myelin protein expression during experimental remyelination. Acute demyelination of the corpus callosum was induced by feeding of 0.3% cuprizone for 6 weeks, followed by a 10-week remyelination period. We used a combination of Luxol fast blue (LFB) myelin staining, electron microscopy (EM) and immunohistochemistry for the myelin proteins 2',3'-cyclic nucleotide 3' phosphodiesterase (CNPase), myelin basic protein (MBP), proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG). Early remyelination was detected by the re-expression of CNPase, MBP and PLP as early as 4 days. MOG, as a marker for late differentiation of oligodendrocytes, was not detectable until 2 weeks of remyelination. EM data correlated well with the LFB myelin staining and myelin protein expression, with 50% of the axons being rapidly remyelinated within 2 weeks. While particularly MBP but also PLP and CNPase are re-expressed very early before significant remyelination is observed by EM, the late marker MOG shows a lag behind the remyelination detected by EM. The presented data indicate that immunohistochemistry for various myelin proteins expressed early and late during myelin formation is a suitable and reliable method to follow remyelination in the cuprizone model. Furthermore, investigation of early remyelination confirms that the intrinsic repair programme is very fast and switched on within days.

Lymphotoxin beta receptor (Lt betaR): dual roles in demyelination and remyelination and successful therapeutic intervention using Lt betaR-Ig protein

Inflammation mediated by macrophages is increasingly found to play a central role in diseases and disorders that affect a myriad of organs, prominent among these are diseases of the CNS. The neurotoxicant-induced, cuprizone model of demyelination is ideally suited for the analysis of inflammatory events. Demyelination on exposure to cuprizone is accompanied by predictable microglial activation and astrogliosis, and, after cuprizone withdrawal, this activation reproducibly diminishes during remyelination. This study demonstrates enhanced expression of lymphotoxin beta receptor (Lt betaR) during the demyelination phase of this model, and Lt betaR is found in areas enriched with microglial and astroglial cells. Deletion of the Lt betaR gene (Lt betaR-/-) resulted in a significant delay in demyelination but also a slight delay in remyelination. Inhibition of Lt betaR signaling by an Lt betaR-Ig fusion decoy protein successfully delayed demyelination in wild-type mice. Unexpectedly, this Lt betaR-Ig decoy protein dramatically accelerated the rate of remyelination, even after the maximal pathological disease state had been reached. This strongly indicates the beneficial role of Lt betaR-Ig in the delay of demyelination and the acceleration of remyelination. The discrepancy between remyelination rates in these systems could be attributed to developmental abnormalities in the immune systems of Lt betaR-/- mice. These findings bode well for the use of an inhibitory Lt betaR-Ig as a candidate biological therapy in demyelinating disorders, because it is beneficial during both demyelination and remyelination.

Neuronal nitric oxide synthase plays a key role in CNS demyelination

Nitric oxide (NO) is a small, short-lived molecule released from a variety of cells that is implicated in a multitude of biological processes. In pathological conditions, overproduction of NO may lead to the generation of highly reactive species, such as peroxynitrite and stable nitrosothiols, that may cause irreversible cell damage. Accordingly, several studies have suggested that NO may be involved in the pathogenesis of various neuroinflammatory/degenerative diseases. Increased concentrations of NO in the CNS in such cases are usually attributed to an increase in the inducible isoform of NO synthase (iNOS) usually produced by inflammatory cells. However, recent reports have suggested that the constitutive isoforms of NOS, neuronal (nNOS) and endothelial (eNOS), can also play a role. Here we examined the role that the constitutive isoforms of NOS might play in the cuprizone-induced model of demyelination/remyelination. Our results demonstrate that demyelination was greatly prevented in mice lacking nNOS. Protection was associated with a dramatic increase in mature oligodendrocyte survival and a decrease in apoptosis. Moreover, nNOS-/- mice did not respond to cuprizone with the extensive recruitment of microglia/macrophages and astrocytes, which is a typical feature in wild-type mice. Although demyelinating less, nNOS-/- mice exhibited a delay in remyelination. In eNOS-/- mice, demyelination progressed to the same extent as in wild type, but they showed a slight delay in spontaneous remyelination. In conclusion, this study highlights the importance of considering the source of NO when assessing its role in neuroinflammation/degeneration and emphasizes the differing pathological effects driven by the different NOS isoforms.

Glycochenodeoxycholate (GCDC) inhibits cytokine induced iNOS expression in rat hepatocytes

BACKGROUND

Although the accumulation of hydrophobic bile acid (e.g., glycine conjugated chenodeoxycholic acid, GCDC) is considered to be an important factor contributing to cholestatic liver dysfunction, its pathogenesis is poorly understood. The purpose of this study was to examine the effect of the bile salt GCDC on the regulation of iNOS expression, a key immune modulator during liver inflammation.

MATERIALS AND METHODS

GCDC significantly decreased cytokine-stimulated iNOS promoter activity, and both iNOS mRNA and protein expression. GCDC decreased iNOS promoter activity by preventing IkappaB degradation and inhibiting NF-kappaB DNA-binding activity. To explore the role of iNOS in bile salt induced apoptosis, we also examined the effect of NO on caspase-3 activity.

RESULTS

GCDC strongly induced caspase-3 activity, and this increase was abrogated by both exogenous NO exposure and endogenous NO synthesis. Furthermore, adenoviral iNOS (AdiNOS) pre-treatment decreased acute cholestatic-induced liver injury in a rat bile duct ligation model.

CONCLUSIONS

These findings indicate a novel signaling pathway where potentially toxic bile salts down-regulate hepatic iNOS expression. This blockade of the iNOS mediated antiapoptotic phenotype may have important implications in certain liver disorders.

Increased nitric oxide levels and nitric oxide synthase isoform expression in the cerebellum of the taiep rat during its severe demyelination stage

We have previously reported progressive reactive astrocytes in the cerebellum of taiep rats, one of the most regions affected by demyelination, and activation of cerebellar glial cells in vitro. Based on the hypothesis that activated glial cells produce high levels of reactive nitrogen intermediates, we assessed the production of nitric oxide (NO) and the expression of the three NO synthases (NOS) in the cerebellum of 6-month-old taiep rats. A significant 40% increase of NO levels was measured in taiep rats when compared with controls. The protein and mRNA levels of the three NOS isoforms were also significantly increased. In contrast to controls, immunostaining assays against nNOS or iNOS showed an increased number of immunoreactive glial cells in the granular layer (nNOS) and Purkinje layer (iNOS) of cerebellum of taiep rats. Microglia-macrophages and both CD4- and CD8-immunoreactive cells were observed in cerebellar white matter of taiep rats only, thus suggesting other possible cell sources of those NOSs. Differences in the cellular location for eNOS immunoreactivity were not observed. The enhanced levels of NO, NOS proteins, mRNAs, and NOS immunoreactivities in glial cells and microglia strongly suggest glial activation together with the professional immune cells can aggravate the demyelination of aged taiep rats.

Differences in the early inflammatory responses to toxin-induced demyelination are associated with the age-related decline in CNS remyelination

CNS remyelination occurs more rapidly in young adult rats than in old rats. Since the inflammatory response initiated by demyelination is an important trigger for remyelination, we address whether ageing changes in remyelination are associated with changes in the inflammatory response. Using a toxin model of demyelination, where the inflammatory response largely comprises macrophages, we show that there is a delay in both recruitment and activation of OX-42+ and macrophage scavenger receptor B+ macrophages following demyelination in older rats (10-13 months) compared to young rats (8-10 weeks). This difference is associated with a slower onset of increased expression of several chemokine mRNAs. However, many inflammatory cytokines have similar mRNA expression patterns, with the exception of IL-1beta, IL-6 and TNF-alpha, which have prolonged expression in the older animals. Differences in IL-1beta mRNA expression, a cytokine specifically implicated in CNS remyelination, are not reflected in differences in protein expression detected by immunocytochemistry. These data relate the age-associated delay in remyelination efficiency to changes in the macrophage and inflammatory mediator response to demyelination.

Deleterious role of IFNgamma in a toxic model of central nervous system demyelination

Interferon-gamma (IFNgamma) is a pleiotropic cytokine that plays an important role in many inflammatory processes, including autoimmune diseases such as multiple sclerosis (MS). Demyelination is a hallmark of MS and a prominent pathological feature of several other inflammatory diseases of the central nervous system, including experimental autoimmune encephalomyelitis, an animal model of MS. Accordingly, in this study we followed the effect of IFNgamma in the demyelination and remyelination process by using an experimental autoimmune encephalomyelitis model of demyelination/remyelination after exposure of mice to the neurotoxic agent cuprizone. We show that demyelination in response to cuprizone is delayed in mice lacking the binding chain of IFNgamma receptor. In addition, IFNgammaR(-/-) mice exhibited an accelerated remyelination process after cuprizone was removed from the diet. Our results also indicate that the levels of IFNgamma were able to modulate the microglia/macrophage recruitment to the demyelinating areas. Moreover, the accelerated regenerative response showed by the IFNgammaR(-/-) mice was associated with a more efficient recruitment of oligodendrocyte precursor cells in the demyelinated areas. In conclusion, this study suggests that IFNgamma regulates the development and resolution of the demyelinating syndrome and may be associated with toxic effects on both mature oligodendrocytes and oligodendrocyte precursor cells.

Quantifying the early stages of remyelination following cuprizone-induced demyelination

The demyelinating toxin cuprizone is used increasingly in mouse studies of central nervous system remyelination. The value of this model for such studies depends on an accurate description of its quantifiable features. We therefore investigated histology and ultrastructure during the early oligodendrocyte differentiation phase of remyelination in mice given cuprizone and allowed to recover for 2 weeks. Limiting the dose of cuprizone to 0.2% overcame significant mouse morbidity and weight loss seen with a 0.4% dose, but the distribution of cuprizone-induced demyelination was anatomically variable. The caudal corpus callosum and dorsal hippocampal commissure mostly demyelinated at this dose, but the rostral corpus callosum and rostral cerebellar peduncles did not. This variable response, together with small axon diameters and hence thin myelin sheaths, hindered analysis of the progress of early remyelination. The proportion of myelinated and unmyelinated axons in defined regions followed expected trends, but there was pronounced variation between animals. Furthermore, group mean G ratios did not change as expected during the early stages of remyelination, and regression analysis revealed a complex relationship between axon diameter and myelin sheath thickness during this period. We also noted axonal pathology that persisted for at least 2 weeks after cuprizone withdrawal.

Intracellular zinc release and ERK phosphorylation are required upstream of 12-lipoxygenase activation in peroxynitrite toxicity to mature rat oligodendrocytes

Peroxynitrite toxicity has been implicated in the pathogenesis of white matter injury. The mechanisms of peroxynitrite toxicity to oligodendrocytes (OLs), the major cell type of the white matter, are unknown. Using primary cultures of mature OLs that express myelin basic protein, we found that 3-morpholinosydnonimine, a peroxynitrite generator, caused toxicity to OLs. N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine, a zinc chelator, completely blocked peroxynitrite-induced toxicity. Use of FluoZin-3, a specific fluorescence zinc indicator, demonstrated the liberation of zinc from intracellular stores by peroxynitrite. Peroxynitrite caused the sequential activation of extracellular signal-regulated kinase 42/44 (ERK42/44), 12-lipoxygenase, and generation of reactive oxygen species, which were all dependent upon the intracellular release of zinc. The same cell death pathway was also activated when exogenous zinc was used. These results suggest that in addition to preventing the formation of peroxynitrite, useful strategies in preventing disease progression in pathologies in which peroxynitrite toxicity plays a critical role might include maintaining intracellular zinc homeostasis, blocking phosphorylation of ERK42/44, inhibiting activation of 12-lipoxygenase, and eliminating the accumulation of reactive oxygen species.

Oligodendrocytes and progenitors become progressively depleted within chronically demyelinated lesions

To understand mechanisms that may underlie the progression of a demyelinated lesion to a chronic state, we have used the cuprizone model of chronic demyelination. In this study, we investigated the fate of oligodendrocytes during the progression of a demyelinating lesion to a chronic state and determined whether transplanted adult oligodendrocyte progenitors could remyelinate the chronically demyelinated axons. Although there is rapid regeneration of the oligodendrocyte population following an acute lesion, most of these newly regenerated cells undergo apoptosis if mice remain on a cuprizone diet. Furthermore, the oligodendrocyte progenitors also become progressively depleted within the lesion, which appears to contribute to the chronic demyelination. Interestingly, even if the mice are returned to a normal diet following 12 weeks of exposure to cuprizone, remyelination and oligodendrocyte regeneration does not occur. However, if adult O4+ progenitors are transplanted into the chronically demyelinated lesion of mice treated with cuprizone for 12 weeks, mature oligodendrocyte regeneration and remyelination occurs after the mice are returned to a normal diet. Thus, the formation of chronically demyelinated lesions induced by cuprizone appears to be the result of oligodendrocyte depletion within the lesion and not due to the inability of the chronically demyelinated axons to be remyelinated.

Bone marrow-derived versus parenchymal sources of inducible nitric oxide synthase in experimental autoimmune encephalomyelitis

The role of nitric oxide (NO) in central nervous system (CNS) inflammation is uncertain. Whereas experimental autoimmune encephalomyelitis (EAE) is exacerbated in mice deficient in inducible nitric oxide synthase (iNOS), inhibitor studies have suggested a pro-inflammatory role for NO. These discrepancies may reflect balance between immunoregulatory and neurocytopathologic roles for NO. We investigated selective effects of bone marrow-derived versus CNS parenchymal sources of iNOS in EAE in chimeric mice. Chimeras that selectively expressed or ablated iNOS in leukocytes both showed significant delay in disease onset, with no difference in disease severity. We conclude that bone marrow-derived and CNS parenchymal sources of iNOS-derived NO both play a regulatory role in EAE.

Complete Freund's adjuvant promotes the increases of IFN-gamma and nitric oxide in suppressing chronic arthritis induced by pristane

The aim of this study was to determine therapeutic effects of complete Freund's adjuvant (CFA) on the progression and relapsing of pristine-induced arthritis (PIA) and investigate the mechanism involved. Chronic relapsing arthritis was induced by pristine in LEW rats. After onset of arthritis, rats were intradermally injected CFA and rats in control group were injected the same volume of PBS. Arthritis was monitored visually, and joint pathology was examined histologically. Cytokine mRNA expression in inguinal lymph nodes was assessed by RT-PCR. The levels of nitric oxide (NO) in serum were measured by colorimetric assay. The results showed that CFA significantly suppressed the progression and relapsing of PIA. Relapsing rate of PIA in CFA-treated group was 12.5% and it was 85.7% in PBS-control group (P < 0.005). CFA markedly inhibited the infiltration of inflammatory cells and cartilage damage in the joints of CFA-treated rats and promoted the increases of IFN-y mRNA and NO levels. The present study provided an implication that adjuvant therapy may be a new strategy for the treatments of rheumatoid arthritis (RA) and other chronic inflammatory diseases.

Sustained nitric oxide delivery delays nitric oxide-dependent apoptosis in macrophages: contribution to the physiological function of activated macrophages

Treatment of the macrophage cell line RAW 264.7 with the short-lived NO donor S-nitrosoglutathione triggers apoptosis through the release of mitochondrial mediators. However, continuous supply of NO by long-lived NO donors protected cells from apoptosis through mechanisms that involved the maintenance or an increase in the levels of the inhibitor of apoptosis proteins (IAPs) cIAP-1, cIAP-2, and xIAP and decreases in the accumulation of p53 and in the levels and targeting of Bax to the mitochondria. As a result of these changes, the activation of caspases 9 and 3 was notably delayed, expanding the time of viability of the macrophages. Moreover, inhibition of NO synthase 2 activity after 8 h of stimulation of RAW 264.7 cells with LPS and IFN-gamma accelerated apoptosis via an increase in the processing and activation of caspases. These data suggest that NO exerts an important role in the autoregulation of apoptosis in macrophages.

Functional genomic analysis of remyelination reveals importance of inflammation in oligodendrocyte regeneration

Tumor necrosis factor alpha (TNFalpha), a proinflammatory cytokine, was shown previously to promote remyelination and oligodendrocyte precursor proliferation in a murine model for demyelination and remyelination. We used Affymetrix microarrays in this study to identify (1) changes in gene expression that accompany demyelination versus remyelination and (2) changes in gene expression during the successful remyelination of wild-type mice versus the unsuccessful attempts in mice lacking TNFalpha. Alterations in inflammatory genes represented the most prominent changes, with major histocompatibility complex (MHC) genes dramatically enhanced in microglia and astrocytes during demyelination, remyelination, and as a consequence of TNFalpha stimulation. Studies to examine the roles of these genes in remyelination were then performed using mice lacking specific genes identified by the microarray. Analysis of MHC-II-null mice showed delayed remyelination and regeneration of oligodendrocytes, whereas removal of MHC-I had little effect. These data point to the induction of MHC-II by TNFalpha as an important regulatory event in remyelination and emphasize the active inflammatory response in regeneration after pathology in the brain.

Molecular biology of cervical myelopathy and spinal cord injury: role of oligodendrocyte apoptosis

BACKGROUND CONTEXT

Rational design of treatment strategies for cervical myelopathy and spinal cord injury requires a working knowledge of the molecular biology underlying these pathological processes. The cellular process of apoptosis is an important component of tissue and organ development as well as the natural response to disease and injury. Recent studies have convincingly demonstrated that apoptosis also plays a pivotal role in numerous pathological processes, contributing to the adverse effects of various diseases and traumatic conditions. A growing body of evidence has implicated apoptosis as a key determinant of the extent of neurological damage and dysfunction after acute spinal cord injury and in chronic cervical myelopathy.

PURPOSE

To provide clinicians and research investigators interested in spinal cord injury and myelopathy with a practical and up-to-date basic science review of cellular apoptosis in the context of spinal cord pathology.

STUDY DESIGN/SETTING

A review of recently published or presented data from molecular biological, animal model and human clinical studies.

METHODS

A computer-based comprehensive review of the English-language scientific and medical literature was performed in order to identify relevant publications with emphasis given to more recent studies.

RESULTS

Investigation into the role of apoptosis in spinal cord injury and myelopathy has drawn the interest of an increasing number of researchers and has yielded a substantial amount of new information.

CONCLUSIONS

Apoptosis is a fundamental biological process that contributes to preservation of health as well as development of disease. There is now strong evidence to support a significant role for apoptosis in secondary injury mechanisms after acute spinal cord injury as well in the progressive neurological deficits observed in such conditions as spondylotic cervical myelopathy.

Blocking NO synthesis: how, where and why?

Nitric oxide (NO) is a key physiological mediator, and the association of disordered NO generation with many pathological conditions has led to much interest in pharmacologically modulating NO levels. However, the wide range of processes in which NO has been implicated, and the fact that increases or decreases in NO levels might be therapeutically desirable depending on the condition or even at different stages of the same condition, pose considerable challenges for drug development. Here, we focus on the rationale and potential for approaches that reduce NO synthesis, which have led to the development of several compounds that will shortly be entering clinical trials.

Peripheral macrophage recruitment in cuprizone-induced CNS demyelination despite an intact blood-brain barrier

The contribution of peripheral macrophage was assessed in cuprizone intoxication, a model of demyelination and remyelination in which the blood-brain barrier remains intact. Flow cytometry of brain cells isolated from cuprizone-treated mice revealed an increase in the percentage of Mac-1(+)/CD45(hi) peripheral macrophage. To confirm these results in situ, C57BL/6 mice were lethally irradiated, transplanted with bone marrow from GFP-transgenic mice, and exposed to cuprizone. GFP(+) peripheral macrophages were seen in the CNS after 2 weeks of treatment, and infiltration continued through 6 weeks. While the peripheral macrophages were far outnumbered by the resident microglia, their recruitment across the blood-brain barrier alludes to a potentially important role.

The role of nitric oxide in multiple sclerosis

Nitric oxide (NO) is a free radical found at higher than normal concentrations within inflammatory multiple sclerosis (MS) lesions. These high concentrations are due to the appearance of the inducible form of nitric oxide synthase (iNOS) in cells such as macrophages and astrocytes. Indeed, the concentrations of markers of NO production (eg, nitrate and nitrite) are raised in the CSF, blood, and urine of patients with MS. Circumstantial evidence suggests that NO has a role in several features of the disease, including disruption of the blood-brain barrier, oligodendrocyte injury and demyelination, axonal degeneration, and that it contributes to the loss of function by impairment of axonal conduction. However, despite these considerations, the net effect of NO production in MS is not necessarily deleterious because it also has several beneficial immunomodulatory effects. These dual effects may help to explain why iNOS inhibition has not provided reliable and encouraging results in animal models of MS, but alternative approaches based on the inhibition of superoxide production, partial sodium-channel blockade, or the replacement of lost immunomodulatory function, may prove beneficial.

Differences in peripheral nerve degeneration/regeneration between wild-type and neuronal nitric oxide synthase knockout mice

Nitric oxide (NO), a unique biological messenger molecule, is synthesized by three isoforms of the enzyme NO synthase (NOS) and diffuses from the site of production across cellular membranes. A postulated role for NO in degeneration and regeneration of peripheral nerves has been explored in a sciatic nerve model comparing wild-type mice and mice lacking neuronal NOS after transection and microsurgical repair. In NOS knockout mice, regenerative delay was observed, preceded by a decelerated Wallerian degeneration (WD). In the regenerated nerve, pruning of uncontrolled sprouts was disturbed, leading to an enhanced number of axons, whereas remyelination seemed to be less affected. Delayed regeneration was associated with a delayed recovery of sensor and motor function. In such a context, possible NO targets are neurofilaments and myelin sheaths of the interrupted axon, filopodia of the growth cone, newly formed neuromuscular endplates, and Schwann cells in the distal nerve stump. The results presented suggest that 1) local release of NO following peripheral nerve injury is a crucial factor in degeneration/regeneration, 2) success of fiber regeneration in the peripheral nervous system depends on a regular WD, and 3) manipulation of NO supply may offer interesting therapeutic options for treatment of peripheral nerve lesions.