Suppressor of cytokine signaling 1 expression protects oligodendrocytes from the deleterious effects of interferon-gamma

hsa-MiR-19a-3p and hsa-MiR-19b-3p Are Associated with Spinal Cord Injury-Induced Neuropathic Pain: Findings from a Genome-Wide MicroRNA Expression Profiling Screen

Neuropathic pain in spinal cord injury (SCI) is associated with inflammation in both the peripheral and central nervous system (CNS), which may contribute to the initiation and maintenance of persistent pain. An understanding of factors contributing to neuroinflammation may lead to new therapeutic targets for neuropathic pain. Moreover, novel circulating biomarkers of neuropathic pain may facilitate earlier and more effective treatment. MicroRNAs (miRNAs) are short, non-coding single-stranded RNA that have emerged as important biomarkers and molecular mediators in physiological and pathological conditions. Using a genome-wide miRNA screening approach, we studied differential miRNA expression in plasma from 68 healthy, community-dwelling adults with and without SCI enrolled in ongoing clinical studies. We detected 2367 distinct miRNAs. Of these, 383 miRNAs were differentially expressed in acute SCI or chronic SCI versus no SCI and 71 were differentially expressed in chronic neuropathic pain versus no neuropathic pain. We selected homo sapiens (hsa)-miR-19a-3p and hsa-miR-19b-3p for additional analysis based on p-value, fold change, and their known role as regulators of neuropathic pain and neuroinflammation. Both hsa-miR-19a-3p and hsa-miR-19b-3p levels were significantly higher in those with chronic SCI and severe neuropathic pain versus those with chronic SCI and no neuropathic pain. In confirmatory studies, both hsa-miR-19a-3p and hsa-miR-19b-3p have moderate to strong discriminative ability to distinguish between those with and without pain. After adjusting for opioid use, hsa-miR-19b-3p levels were positively associated with pain interference with mood. Because hsa-miR-19 levels have been shown to change in response to exercise, folic acid, and resveratrol, these studies suggest that miRNAs are potential targets of therapeutic interventions.

Evaluation of the Effect of Mannuronic Acid as a Novel NSAID With Immunosuppressive Properties on Expression of SOCS1, SOCS3, SHIP1, and TRAF6 Genes and Serum Levels of IL-6 and TNF-α in Patients With Multiple Sclerosis

Multiple sclerosis (MS) is described as a chronic inflammatory, demyelinating disease of the central nervous system on an autoimmune basis, which is the most frequent reason for nontraumatic disability in youth. The efficacy and safety of β-D-nannuronic acid (M2000) as a novel immunosuppressive drug (patented PCT/EP2017/067920) has been shown in an experimental model of MS and also in a phase 2 clinical trial. The effects of M2000 on SOCS1, SOCS3, TRAF6, and SHIP1 gene expression and also serum levels of IL-6 and TNF-α in secondary progressive multiple sclerosis patients have been assessed in this study. In this study, 14 secondary progressive multiple sclerosis patients and 14 healthy subjects (as the control group) were recruited from the phase 2 clinical trial (Clinical Trial identifier, IRCT2016111313739N6). Gene expression of SOCS1, SOCS3, TRAF6, and SHIP1 was measured at baseline and after 6 months of therapy with M2000 using a quantitative real-time polymerase chain reaction method. Furthermore, the serum levels of IL-6 and TNF-α were assessed by the enzyme-linked immunosorbent assay method. Our results showed that the gene expression of SOCS1, SOCS3, and SHIP1 was increased after 6 months of therapy with M2000 in MS patients. Moreover, the serum levels of IL-6 and TNF-α of patients declined compared with baseline, but this was not statistically significant. The results of this study demonstrated that M2000, with immunosuppressive properties, could upregulate SOCS1, SOCS3, and SHIP1 genes in patients with secondary progressive multiple sclerosis.

Heparanome-Mediated Rescue of Oligodendrocyte Progenitor Quiescence following Inflammatory Demyelination

The proinflammatory cytokine IFN-γ, which is chronically elevated in multiple sclerosis, induces pathologic quiescence in human oligodendrocyte progenitor cells (OPCs) via upregulation of the transcription factor PRRX1. In this study using animals of both sexes, we investigated the role of heparan sulfate proteoglycans in the modulation of IFN-γ signaling following demyelination. We found that IFN-γ profoundly impaired OPC proliferation and recruitment following adult spinal cord demyelination. IFN-γ-induced quiescence was mediated by direct signaling in OPCs as conditional genetic ablation of IFNγR1 (Ifngr1) in adult NG2⁺ OPCs completely abrogated these inhibitory effects. Intriguingly, OPC-specific IFN-γ signaling contributed to failed oligodendrocyte differentiation, which was associated with hyperactive Wnt/Bmp target gene expression in OPCs. We found that PI-88, a heparan sulfate mimetic, directly antagonized IFN-γ to rescue human OPC proliferation and differentiation in vitro and blocked the IFN-γ-mediated inhibitory effects on OPC recruitment in vivo Importantly, heparanase modulation by PI-88 or OGT2155 in demyelinated lesions rescued IFN-γ-mediated axonal damage and demyelination. In addition to OPC-specific effects, IFN-γ-augmented lesions were characterized by increased size, reactive astrogliosis, and proinflammatory microglial/macrophage activation along with exacerbated axonal injury and cell death. Heparanase inhibitor treatment rescued many of the negative IFN-γ-induced sequelae suggesting a profound modulation of the lesion environment. Together, these results suggest that the modulation of the heparanome represents a rational approach to mitigate the negative effects of proinflammatory signaling and rescuing pathologic quiescence in the inflamed and demyelinated human brain.SIGNIFICANCE STATEMENT The failure of remyelination in multiple sclerosis contributes to neurologic dysfunction and neurodegeneration. The activation and proliferation of oligodendrocyte progenitor cells (OPCs) is a necessary step in the recruitment phase of remyelination. Here, we show that the proinflammatory cytokine interferon-γ directly acts on OPCs to induce pathologic quiescence and thereby limit recruitment following demyelination. Heparan sulfate is a highly structured sulfated carbohydrate polymer that is present on the cell surface and regulates several aspects of the signaling microenvironment. We find that pathologic interferon-γ can be blocked by modulation of the heparanome following demyelination using either a heparan mimetic or by treatment with heparanase inhibitor. These studies establish the potential for modulation of heparanome as a regenerative approach in demyelinating disease.

Chemokine CXCL10 and Coronavirus-Induced Neurologic Disease

Chemokines (chemotactic cytokines) are involved in a wide variety of biological processes. Following microbial infection, there is often robust chemokine signaling elicited from infected cells, which contributes to both innate and adaptive immune responses that control growth of the invading pathogen. Infection of the central nervous system (CNS) by the neuroadapted John Howard Mueller (JHM) strain of mouse hepatitis virus (JHMV) provides an excellent example of how chemokines aid in host defense as well as contribute to disease. Intracranial inoculation of the CNS of susceptible mice with JHMV results in an acute encephalomyelitis characterized by widespread dissemination of virus throughout the parenchyma. Virus-specific T cells are recruited to the CNS, and control viral replication through release of antiviral cytokines and cytolytic activity. Sterile immunity is not acquired, and virus will persist primarily in white matter tracts leading to chronic neuroinflammation and demyelination. Chemokines are expressed and contribute to defense as well as chronic disease by attracting targeted populations of leukocytes to the CNS. The T cell chemoattractant chemokine CXCL10 (interferon-inducible protein 10 kDa, IP-10) is prominently expressed in both stages of disease, and serves to attract activated T and B lymphocytes expressing CXC chemokine receptor 3 (CXCR3), the receptor for CXCL10. Functional studies that have blocked expression of either CXCL10 or CXCR3 illuminate the important role of this signaling pathway in host defense and neurodegeneration in a model of viral-induced neurologic disease.

Increase in chemokine CXCL1 by ERβ ligand treatment is a key mediator in promoting axon myelination

Estrogen receptor β (ERβ) ligands promote remyelination in mouse models of multiple sclerosis. Recent work using experimental autoimmune encephalomyelitis (EAE) has shown that ERβ ligands induce axon remyelination, but impact peripheral inflammation to varying degrees. To identify if ERβ ligands initiate a common immune mechanism in remyelination, central and peripheral immunity and pathology in mice given ERβ ligands at peak EAE were assessed. All ERβ ligands induced differential expression of cytokines and chemokines, but increased levels of CXCL1 in the periphery and in astrocytes. Oligodendrocyte CXCR2 binds CXCL1 and has been implicated in normal myelination. In addition, despite extensive immune cell accumulation in the CNS, all ERβ ligands promoted extensive remyelination in mice at peak EAE. This finding highlights a component of the mechanism by which ERβ ligands mediate remyelination. Hence, interplay between the immune system and central nervous system may be responsible for the remyelinating effects of ERβ ligands. Our findings of potential neuroprotective benefits arising from the presence of CXCL1 could have implications for improved therapies for multiple sclerosis.

Opportunities for Translation from the Bench: Therapeutic Intervention of the JAK/STAT Pathway in Neuroinflammatory Diseases

Pathogenic CD4+ T cells and myeloid cells play critical roles in the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS. These immune cells secrete aberrantly high levels of pro-inflammatory cytokines that pathogenically bridge the innate and adaptive immune systems and damage neurons and oligodendrocytes. These cytokines include interleukin-2 (IL-2), IL-6, IL-12, IL-21, IL-23, granulocyte macrophage-colony stimulating factor (GM-CSF), and interferon-γ (IFN-γ). It is, therefore, not surprising that both the dysregulated expression of these cytokines and the subsequent activation of their downstream signaling cascades is a common feature in MS/EAE. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is utilized by numerous cytokines for signal transduction and is essential for the development and regulation of immune responses. Unbridled activation of the JAK/STAT pathway by pro-inflammatory cytokines has been demonstrated to be critically involved in the pathogenesis of MS/EAE. In this review, we discuss recent advancements in our understanding of the involvement of the JAK/STAT signaling pathway in the pathogenesis of MS/EAE, with a particular focus on therapeutic approaches to target the JAK/STAT pathway.

Structure-activity studies of peptidomimetics based on kinase-inhibitory region of suppressors of cytokine signaling 1

Suppressors of Cytokine Signaling (SOCS) proteins are negative regulators of JAK proteins that are receptor-associated tyrosine kinases, which play key roles in the phosphorylation and subsequent activation of several transcription factors named STATs. Unlike the other SOCS proteins, SOCS1 and 3 show, in the N-terminal portion, a small kinase inhibitory region (KIR) involved in the inhibition of JAK kinases. Drug discovery processes of compounds based on KIR sequence demonstrated promising in functional in vitro and in inflammatory animal models and we recently developed a peptidomimetic called PS5, as lead compound. Here, we investigated the cellular ability of PS5 to mimic SOCS1 biological functions in vascular smooth muscle cells and simultaneously we set up a new binding assay for the screening and identification of JAK2 binders based on a SPR experiment that revealed more robust with respect to previous ELISAs. On this basis, we designed several peptidomimetics bearing new structural constraints that were analyzed in both affinities toward JAK2 and conformational features through Circular Dichroism and NMR spectroscopies. Introduced chemical modifications provided an enhancement of serum stabilities of new sequences that could aid the design of future mimetic molecules of SOCS1 as novel anti-inflammatory compounds.

The control of oligodendrocyte bioenergetics by interferon-gamma (IFN-γ) and Src homology region 2 domain-containing phosphatase-1 (SHP-1)

Glycolysis and mitochondrial respiration are essential for oligodendrocyte metabolism in both the developing and adult CNS. Based on recent reports on the effects of the proinflammatory cytokine IFN-γ on metabolism and on oligodendrocytes, we addressed whether IFN-γ may affect oligodendrocyte bioenergetics in ways relevant to CNS disease. Oligodendrocytes of mice treated with IFN-γ showed significant reductions in aerobic glycolysis and mitochondrial respiration. As expected, IFN-γ treatment led to the induction of STAT1 in oligodendrocytes indicating active signaling into these cells. To determine the direct effects of IFN-γ on oligodendrocyte metabolism, cultured oligodendrocytes were treated with IFN-γ in vitro, which resulted in suppression of glycolysis similar to oligodendrocytes of animals treated with IFN-γ in vivo. Mice lacking SHP-1, a key regulator of IFN-γ and STAT1 signaling in CNS glia, had high constitutive levels of STAT1 and decreased aerobic glycolysis and mitochondrial respiration rates relative to wild type mouse oligodendrocytes. Together, these data show that IFN-γ and SHP-1 control oligodendrocyte bioenergetics in ways that may relate to the role of this cytokine in CNS disease.

Loss of Gas6 and Axl signaling results in extensive axonal damage, motor deficits, prolonged neuroinflammation, and less remyelination following cuprizone exposure

The TAM (Tyro3, Axl, and MerTK) family of receptor tyrosine kinases (RTKs) and their ligands, Gas6 and ProS1, are important for innate immune responses and central nervous system (CNS) homeostasis. While only Gas6 directly activates Axl, ProS1 activation of Tyro3/MerTK can indirectly activate Axl through receptor heterodimerization. Therefore, we generated Gas6^-/- Axl^-/- double knockout (DKO) mice to specifically examine the contribution of this signaling axis while retaining ProS1 signaling through Tyro3 and MerTK. We found that naïve young adult DKO and WT mice have comparable myelination and equal numbers of axons and oligodendrocytes in the corpus callosum. Using the cuprizone model of demyelination/remyelination, transmission electron microscopy revealed extensive axonal swellings containing autophagolysosomes and multivesicular bodies, and fewer myelinated axons in brains of DKO mice at 3-weeks recovery from a 6-week cuprizone diet. Analysis of immunofluorescent staining demonstrated more SMI32+ and APP+ axons and less myelin in the DKO mice. There were no significant differences in the number of GFAP+ astrocytes or Iba1+ microglia/macrophages between the groups of mice. However, at 6-weeks cuprizone and recovery, DKO mice had increased proinflammatory cytokine and altered suppressor of cytokine signaling (SOCS) mRNA expression supporting a role for Gas6-Axl signaling in proinflammatory cytokine suppression. Significant motor deficits in DKO mice relative to WT mice on cuprizone were also observed. These data suggest that Gas6-Axl signaling plays an important role in maintaining axonal integrity and regulating and reducing CNS inflammation that cannot be compensated for by ProS1/Tyro3/MerTK signaling.

Regulation of Macrophage, Dendritic Cell, and Microglial Phenotype and Function by the SOCS Proteins

Macrophages are innate immune cells of dynamic phenotype that rapidly respond to external stimuli in the microenvironment by altering their phenotype to respond to and to direct the immune response. The ability to dynamically change phenotype must be carefully regulated to prevent uncontrolled inflammatory responses and subsequently to promote resolution of inflammation. The suppressor of cytokine signaling (SOCS) proteins play a key role in regulating macrophage phenotype. In this review, we summarize research to date from mouse and human studies on the role of the SOCS proteins in determining the phenotype and function of macrophages. We will also touch on the influence of the SOCS on dendritic cell (DC) and microglial phenotype and function. The molecular mechanisms of SOCS function in macrophages and DCs are discussed, along with how dysregulation of SOCS expression or function can lead to alterations in macrophage/DC/microglial phenotype and function and to disease. Regulation of SOCS expression by microRNA is discussed. Novel therapies and unanswered questions with regard to SOCS regulation of monocyte-macrophage phenotype and function are highlighted.

Promoting remyelination: utilizing a viral model of demyelination to assess cell-based therapies

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS. While a broad range of therapeutics effectively reduce the incidence of focal white matter inflammation and plaque formation for patients with relapse-remitting forms of MS, a challenge within the field is to develop therapies that allow for axonal protection and remyelination. In the last decade, growing interest has focused on utilizing neural precursor cells (NPCs) to promote remyelination. To understand how NPCs function in chronic demyelinating environments, several excellent pre-clinical mouse models have been developed. One well accepted model is infection of susceptible mice with neurotropic variants of mouse hepatitis virus (MHV) that undergo chronic demyelination exhibiting clinical and histopathologic similarities to MS patients. Combined with the possibility that an environmental agent such as a virus could trigger MS, the MHV model of demyelination presents a relevant mouse model to assess the therapeutic potential of NPCs transplanted into an environment in which inflammatory-mediated demyelination is established.

Quantitative analysis of the suppressors of cytokine signaling 1 and 3 in peripheral blood leukocytes of patients with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease characterized by a triad of inflammation, demyelination and gliosis. Because the suppressors of cytokine signaling (Socs) regulate the immune response, we quantified SOCS1 and SOCS3 transcription in peripheral blood leukocytes of patients with MS. SOCS1 transcription decreased significantly in MS patients compared with neurologically healthy persons (0.08±0.02 vs. 1.02±0.23; p=0.0001); while SOCS3 transcription increased in MS patients compared with controls (2.76±0.66 vs. 1.03±0.27; p=0.0008). Our results showed an imbalance of SOCS1 and SOCS3 transcription in MS patients, and a moderated negative correlation between them (Spearman's r=-0.57; p=0.0003).

SOCS1 prevents graft arteriosclerosis by preserving endothelial cell function

OBJECTIVES

The aim of this study was to determine the role of suppressor of cytokine signaling 1 (SOCS1) in graft arteriosclerosis (GA).

BACKGROUND

GA, the major cause of late cardiac allograft failure, is initiated by immune-mediated endothelial activation resulting in vascular inflammation and consequent neointima formation. SOCS1, a negative regulator of cytokine signaling, is highly expressed in endothelial cells (ECs) and may prevent endothelial inflammatory responses and phenotypic activation.

METHODS

Clinical specimens of coronary arteries with GA, with atherosclerosis, or without disease were collected for histological analysis. SOCS1 knockout or vascular endothelial SOCS1 (VESOCS1) transgenic mice were used in an aorta transplant model of GA. Mouse aortic ECs were isolated for in vitro assays.

RESULTS

Dramatic but specific reduction of endothelial SOCS1 was observed in human GA and atherosclerosis specimens, which suggested the importance of SOCS1 in maintaining normal endothelial function. SOCS1 deletion in mice resulted in basal EC dysfunction. After transplantation, SOCS1-deficient aortic grafts augmented leukocyte recruitment and neointima formation, whereas endothelial overexpression of SOCS1 diminished arterial rejection. Induction of endothelial adhesion molecules in early stages of GA was suppressed by the VESOCS1 transgene, and this effect was confirmed in cultured aortic ECs. Moreover, VESOCS1 maintained better vascular function during GA progression. Mechanistically, endothelial SOCS1, by modulating both basal and cytokine-induced expression of the adhesion molecules platelet/endothelial cell adhesion molecule-1, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, restrained leukocyte adhesion and transendothelial migration during inflammatory cell infiltration.

CONCLUSIONS

SOCS1 prevents GA progression by preserving endothelial function and attenuating cytokine-induced adhesion molecule expression in vascular endothelium.

AMP-activated protein kinase signaling protects oligodendrocytes that restore central nervous system functions in an experimental autoimmune encephalomyelitis model

AMP-activated protein kinase (AMPK) signaling is reported to protect neurons under pathologic conditions; however, its effect on oligodendrocytes (OLs) remains to be elucidated. We investigated whether AMPK signaling protects OLs to restore central nervous system (CNS) functions in an experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis. Increased inflammation and demyelination in the CNS and peripheral immune responses were consistent with the observed clinical impairments in EAE animals, which were attenuated by treatment with metformin compared with vehicle. In addition, expressions of neurotrophic factors and of signatory genes of OL lineages were increased in the CNS of metformin-treated EAE animals. Likewise, metformin attenuated inflammatory response and enhanced expressions of neurotrophic factors, thereby protecting OLs via AMPK activation in mixed glial cultures stimulated with lipopolysaccharide/interferon γ in vitro, as evidenced by analysis of the expression of signatory genes of O1(+)/MBP(+) OLs and their cellular populations. Metformin also attenuated oxidative stress and malondialdehyde-containing protein levels, with corresponding induction of antioxidative defenses in OLs exposed to cytokines via AMPK activation. These effects of metformin were evident in the CNS of EAE animals. These data provide evidence that AMPK signaling is crucial to protect OLs and, thus, CNS functions in EAE animals. We conclude that AMPK activators, including metformin, have the potential to limit neurologic deficits in multiple sclerosis and related neurodegenerative disorders.

Oligodendrocyte-specific activation of PERK signaling protects mice against experimental autoimmune encephalomyelitis

There is compelling evidence that oligodendrocyte apoptosis, in response to CNS inflammation, contributes significantly to the development of the demyelinating disorder multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Therefore, approaches designed to protect oligodendrocytes would likely have therapeutic value. Activation of pancreatic endoplasmic reticulum kinase (PERK) signaling in response to endoplasmic reticulum (ER) stress increases cell survival under various cytotoxic conditions. Moreover, there is evidence that PERK signaling is activated in oligodendrocytes within demyelinating lesions in multiple sclerosis and EAE. Our previous study demonstrated that CNS delivery of the inflammatory cytokine interferon-γ before EAE onset protected mice against EAE, and this protection was dependent on PERK signaling. In our current study, we sought to elucidate the role of PERK signaling in oligodendrocytes during EAE. We generated transgenic mice that allow for temporally controlled activation of PERK signaling, in the absence of ER stress, specifically in oligodendrocytes. We demonstrated that persistent activation of PERK signaling was not deleterious to oligodendrocyte viability or the myelin of adult animals. Importantly, we found that enhanced activation of PERK signaling specifically in oligodendrocytes significantly attenuated EAE disease severity, which was associated with reduced oligodendrocyte apoptosis, demyelination, and axonal degeneration. This effect was not the result of an altered degree of the inflammatory response in EAE mice. Our results provide direct evidence that activation of PERK signaling in oligodendrocytes is cytoprotective, protecting mice against EAE.

Molecular mechanisms of oligodendrocyte injury in multiple sclerosis and experimental autoimmune encephalomyelitis

New evidence has emerged over the last decade indicating that oligodendrocyte injury in multiple sclerosis (MS) is not a single unified phenomenon but rather a spectrum of processes ranging from massive immune destruction to a subtle cell death in the absence of significant inflammation. Experimentally, protection of oligodendrocytes against inflammatory injury results in protection against experimental autoimmune encephalitis, the animal model of multiple sclerosis. In this review, we will discuss the molecular mechanisms regulating oligodendrocyte injury and inflammatory demyelination. We draw attention to the injurious role of IFN-γ signaling in oligodendrocytes and the pro-inflammatory effect of their death. In conclusion, studying the molecular mechanisms of oligodendrocyte injury is likely to provide new perspective on the pathogenesis of MS and a rationale for cell protective therapies.

IFN-γ-induced apoptosis of human embryonic stem cell derived oligodendrocyte progenitor cells is restricted by CXCR2 signaling

Engraftment of human embryonic stem cell (hESC)-derived OPCs in animal models of demyelination results in remyelination and clinical recovery, supporting the feasibility of cell replacement therapies in promoting repair of damaged neural tissue. A critical gap in our understanding of the mechanisms associated with repair revolves around the effects of the local microenvironment on transplanted cell survival. We have determined that treatment of human ESC-derived OPCs with the pleiotropic cytokine IFN-γ promotes apoptosis that is associated with mitochondrial cytochrome c released into the cytosol with subsequent caspase 3 activation. IFN-γ-induced apoptosis is mediated, in part, by secretion of the CXC chemokine ligand 10 (CXCL10) from IFN-γ-treated cells. Signaling through the chemokine receptor CXCR2 by the ligand CXCL1 functions in a tonic manner by muting apoptosis and this is associated with reduced levels of cytosolic cytochrome c and impaired cleavage of caspase 3. These findings support a role for both IFN-γ and CXCL10 in contributing to neuropathology by promoting OPC apoptosis. In addition, these data suggest that hOPCs used for therapeutic treatment for human neurologic disease/damage are susceptible to death through exposure to local inflammatory cytokines present within the inflammatory milieu.

CXCR2 signaling and host defense following coronavirus-induced encephalomyelitis

Inoculation of the neurotropic JHM strain of mouse hepatitis virus (JHMV) into the central nervous system (CNS) of susceptible strains of mice results in wide-spread replication within glial cells accompanied by infiltration of virus-specific T lymphocytes that control virus through cytokine secretion and cytolytic activity. Virus persists within white matter tracts of surviving mice resulting in demyelination that is amplified by inflammatory T cells and macrophages. In response to infection, numerous cytokines/chemokines are secreted by resident cells of the CNS and inflammatory leukocytes that participate in both host defense and disease. Among these are the ELR-positive chemokines that are able to signal through CXC chemokine receptors including CXCR2. Early following JHMV infection, ELR-positive chemokines contribute to host defense by attracting CXCR2-expressing cells including polymorphonuclear cells to the CNS that aid in host defense through increasing the permeability the blood-brain-barrier (BBB). During chronic disease, CXCR2 signaling on oligodendroglia protects these cells from apoptosis and restricts the severity of demyelination. This review covers aspects related to host defense and disease in response to JHMV infection and highlights the different roles of CXCR2 signaling in these processes.

Overexpression of the dominant-negative form of interferon regulatory factor 1 in oligodendrocytes protects against experimental autoimmune encephalomyelitis

Interferon regulatory factor 1 (IRF-1) is a transcription factor that has been implicated in the pathogenesis of the human autoimmune demyelinating disease multiple sclerosis (MS) and in its animal model, experimental autoimmune encephalomyelitis (EAE). The goal of the present study was to directly examine the role of IRF-1 in oligodendrocyte injury and inflammatory demyelination. For the purpose of this study, we generated a transgenic mouse line (CNP/dnIRF-1) that overexpresses the dominant-negative form of IRF-1 (dnIRF1) specifically in oligodendrocytes. CNP/dnIRF-1 mice exhibited no phenotypic abnormalities but displayed suppressed IRF-1 signaling in oligodendrocytes. The major finding of our study was that the CNP/dnIRF-1 mice, compared with the wild-type mice, were protected against EAE, a phenomenon associated with significant reduction of inflammatory demyelination and with oligodendrocyte and axonal preservation. The observed protection was related to suppressed IRF-1 signaling and impaired expression of immune and proapoptotic genes in oligodendrocytes. No significant differences in the peripheral immune responses between the wild-type and the CNP/dnIRF-1 mice were identified throughout the experiments. This study indicates that IRF-1 plays a critical role in the pathogenesis of EAE by mediating oligodendrocyte response to inflammation and injury. It also suggests that oligodendrocytes are actively involved in the neuroimmune network, and that exploring oligodendrocyte-related pathogenic mechanisms, in addition to the conventional immune-based ones, may have important therapeutic implications in MS.

CXCR2 signaling protects oligodendrocyte progenitor cells from IFN-γ/CXCL10-mediated apoptosis

Infiltration of activated lymphocytes into the central nervous system (CNS) is potentially harmful by damaging resident cells through release of cytokines. Among these is IFN-γ that is secreted by activated natural killer (NK) cells and T lymphocytes and can exert a cytotoxic effect on resident glial populations including oligodendrocytes. Here we show that treatment of mouse oligodendrocyte progenitor cell (OPC)-enriched cultures with IFN-γ resulted in a dose-dependent increase in apoptosis. IFN-γ-induced apoptosis is mediated, in part, through induction of the CXC chemokine ligand 10 (CXCL10; IP-10) from cultured OPCs. Treatment of OPCs with CXCL10 resulted in cell death in a concentration-dependent manner and IFN-γ-treatment of CXCL10-/- OPCs resulted in >50% reduction in cell death. Further, treatment of CXCR3-/- OPC cultures with either IFN-γ or CXCL10 resulted in reduced cell death supporting an important role for CXCL10 signaling in IFN-γ-mediated OPC apoptosis. Data is also provided demonstrating that signaling through CXCR2 protects either IFN-γ or CXCL10-treated OPC cultures from apoptosis and this effect is abolished in CXCR2-/- OPCs. CXCR2-mediated protection from apoptosis is associated with impaired cleavage of caspase 3 and elevated expression of the anti-apoptotic protein Bcl-2. These findings demonstrate a previously unappreciated role for CXCL10 in contributing to neuropathology by promoting oligodendrocyte apoptosis and emphasize the potential relevance in targeting CXCL10 in treating human demyelinating diseases including multiple sclerosis (MS).

Cooperative contributions of interferon regulatory factor 1 (IRF1) and IRF8 to interferon-γ-mediated cytotoxic effects on oligodendroglial progenitor cells

Background

Administration of exogenous interferon-γ (IFNγ) aggravates the symptoms of multiple sclerosis (MS), whereas interferon-β (IFNβ) is used for treatment of MS patients. We previously demonstrated that IFNγ induces apoptosis of oligodendroglial progenitor cells (OPCs), suggesting that IFNγ is more toxic to OPCs than IFNβ. Thus we hypothesized that a difference in expression profiles between IFNγ-inducible and IFNβ-inducible genes in OPCs would predict the genes responsible for IFNγ-mediated cytotoxic effects on OPCs. We have tested this hypothesis particularly focusing on the interferon regulatory factors (IRFs) well-known transcription factors up-regulated by IFNs.

Methods

Highly pure primary rat OPC cultures were treated with IFNγ and IFNβ. Cell death and proliferation were assessed by MTT reduction, caspse-3-like proteinase activity, Annexin-V binding, mitochondrial membrane potential, and BrdU-incorporation. Induction of all nine IRFs was comprehensively compared by quantitative PCR between IFNγ-treated and IFNβ-treated OPCs. IRFs more strongly induced by IFNγ than by IFNβ were selected, and tested for their ability to induce OPC apoptosis by overexpression and by inhibition by dominant-negative proteins or small interference RNA either in the presence or absence of IFNγ.

Results

Unlike IFNγ, IFNβ did not induce apoptosis of OPCs. Among nine IRFs, IRF1 and IRF8 were preferentially up-regulated by IFNγ. In contrast, IRF7 was more robustly induced by IFNβ than by IFNγ. Overexpressed IRF1 elicited apoptosis of OPCs, and a dominant negative IRF1 protein partially protected OPCs from IFNγ-induced apoptosis, indicating a substantial contribution of IRF1 to IFNγ-induced OPC apoptosis. On the other hand, overexpression of IRF8 itself had only marginal proapoptotic effects. However, overexpressed IRF8 enhanced the IFNγ-induced cytotoxicity and the proapoptotic effect of overexpressed IRF1, and down-regulation of IRF8 by siRNA partially but significantly reduced preapoptotic cells after treatment with IFNγ, suggesting that IRF8 cooperatively enhances IFNγ-induced OPC apoptosis.

Conclusions

This study has identified that IRF1 and IRF8 mediate IFNγ-signaling leading to OPC apoptosis. Therapies targeting at these transcription factors and their target genes could reduce IFNγ-induced OPC loss and thereby enhance remyelination in MS patients.

The pathogenesis of murine coronavirus infection of the central nervous system

Mouse hepatitis virus (MHV) is a positive-strand RNA virus that causes an acute encephalomyelitis that later resolves into a chronic fulminating demyelinating disease. Cytokine production, chemokine secretion, and immune cell infiltration into the central nervous system are critical to control viral replication during acute infection. Despite potent antiviral T-lymphocyte activity, sterile immunity is not achieved, and MHV chronically persists within oligodendrocytes. Continued infiltration and activation of the immune system, a result of the lingering viral antigen and RNA within oligodendrocytes, lead directly to the development of an immune-mediated demyelination that bears remarkable similarities, both clinically and histologically, to the human demyelinating disease multiple sclerosis. MHV offers a unique model system for studying host defense during acute viral infection and immune-mediated demyelination during chronic infection.

CXCR2 signaling protects oligodendrocytes and restricts demyelination in a mouse model of viral-induced demyelination

BACKGROUND

The functional role of ELR-positive CXC chemokines during viral-induced demyelination was assessed. Inoculation of the neuroattenuated JHM strain of mouse hepatitis virus (JHMV) into the CNS of susceptible mice results in an acute encephalomyelitis that evolves into a chronic demyelinating disease, modeling white matter pathology observed in the human demyelinating disease Multiple Sclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

JHMV infection induced the rapid and sustained expression of transcripts specific for the ELR+ chemokine ligands CXCL1 and CXCL2, as well as their binding receptor CXCR2, which was enriched within the spinal cord during chronic infection. Inhibiting CXCR2 signaling with neutralizing antiserum significantly (p<0.03) delayed clinical recovery. Moreover, CXCR2 neutralization was associated with an increase in the severity of demyelination that was independent of viral recrudescence or modulation of neuroinflammation. Rather, blocking CXCR2 was associated with increased numbers of apoptotic cells primarily within white matter tracts, suggesting that oligodendrocytes were affected. JHMV infection of enriched oligodendrocyte progenitor cell (OPC) cultures revealed that apoptosis was associated with elevated expression of cleaved caspase 3 and muted Bcl-2 expression. Inclusion of CXCL1 within JHMV infected cultures restricted caspase 3 cleavage and increased Bcl-2 expression that was associated with a significant (p<0.001) decrease in apoptosis. CXCR2 deficient oligodendrocytes were refractory to CXCL1 mediated protection from JHMV-induced apoptosis, readily activating caspase 3 and down regulating Bcl-2.

CONCLUSION/SIGNIFICANCE

These findings highlight a previously unappreciated role for CXCR2 signaling in protecting oligodendrocyte lineage cells from apoptosis during inflammatory demyelination initiated by viral infection of the CNS.

Effect of thalidomide and pentoxifylline on experimental autoimmune encephalomyelitis (EAE)

BACKGROUND

Autoimmune encephalomyelitis (EAE) in Lewis rats is a classical experimental model of demyelinating inflammatory disease of the central nervous system. EAE is widely accepted for study of immune-inflammatory mechanisms in the CNS related to multiple sclerosis (MS) due to similar clinical evolution.

OBJECTIVES

In the present study we investigated the effects of Thalidomide and pentoxifylline during EAE development in Lewis rats.

METHODS

EAE was induced in Lewis rats and treatment with Thalidomide or pentoxifylline was performed. Clinical evaluation was carried out daily. Histopathological analysis of the brain tissue and spinal cord was performed. Griess method was used for determination of NO serum levels. TNF-alpha and IFN-gamma serum levels were investigated using ELISA method.

RESULTS

Thalidomide and pentoxifylline treatment is associated with significant reduction of neuroinflammation in CNS. Serum levels of NO, IFN-gamma and TNF-alpha showed a marked reduction. Such findings were correlated with improvement of clinical symptoms, particularly in thalidomide treated rats.

CONCLUSIONS

Taken together the data suggested that thalidomide and pentoxifylline may be therapeutic options for the treatment of MS, however further experiments must be performed to investigate this hypothesis.

STAT1/IRF-1 signaling pathway mediates the injurious effect of interferon-gamma on oligodendrocyte progenitor cells

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that is critically involved in the pathogenesis of inflammatory demyelinating diseases. There is strong evidence that IFN-gamma can function as a distinct and independent injurious factor to oligodendrocyte progenitor cells (OPCs). The intracellular signaling pathways leading to OPC death, however, remain poorly understood. In this study, we examined IFN-gamma signaling in OPCs in relation to cell death in vitro. Using expression knock-down and forced overexpression methods, we directly demonstrated the role of signal transducer and transcription activator 1 (STAT1) and interferon-regulated factor 1 (IRF-1) in IFN-gamma- induced OPC death. In addition, our study identified two proapoptotic genes, caspase 1 and double-stranded RNA-dependent protein kinase (PKR), whose expression was upregulated by IFN-gamma and transcriptionally controlled by IRF-1. The conclusion of this study is that STAT1 and IRF-1 function as components of the signaling pathway that mediates IFN-gamma-induced OPC death.

Nature killer cells in the central nervous system

Natural killer (NK) cells, a prominent component of the innate immune system, are large granular lymphocytes that respond rapidly to a variety of insults via cytokine secretion and cytolytic activity. Recently, there has been growing insight into the biological functions of NK cells, in particular into their roles in infection, tumorurveillance and autoimmunity. Under these pathophysiological circumstances, NK cells readily home to the central nervous system (CNS) tissues to combat infection and presumably to curb progression of tumor. Bystander neuronal and/or glial cell damage can occur in this setting. Paradoxically, NK cells appear to have an inhibitory role for autoimmune responses within the CNS. As in the periphery, NK cells act in concert with T cells and other lymphocytes responsible for CNS pathology and immune regulation. Insights into the molecular signals and pathways governing the diverse biological effects of NK cells are keys for designing NK cell-based therapy for CNS infections, tumor and autoimmune diseases.NK cells readily accumulate in homing to CNS tissues under the pathophysiological situations. This process is tightly controlled by a number of chemokines and chemokine receptors. There is ample of evidence that NK cells within the CNS contribute to the control of infections and might limit progression of certain tumor. Bystander neuronal and/or glial cell damage can occur. In certain autoimmune conditions of the CNS, NK cells appear to have an inhibitory role. Disassociation of disease-inhibiting versus disease-promoting effects of NK cells is a key to harnessing NK cells for therapeutic purposes. To achieve this goal, a generation of genetic models with selective NK cell deficiency, and development of reagents (antibodies) for visualizing subsets of NK cells in situ will be necessary.

What is the optimal value of the g-ratio for myelinated fibers in the rat CNS? A theoretical approach

BACKGROUND

The biological process underlying axonal myelination is complex and often prone to injury and disease. The ratio of the inner axonal diameter to the total outer diameter or g-ratio is widely utilized as a functional and structural index of optimal axonal myelination. Based on the speed of fiber conduction, Rushton was the first to derive a theoretical estimate of the optimal g-ratio of 0.6 [1]. This theoretical limit nicely explains the experimental data for myelinated axons obtained for some peripheral fibers but appears significantly lower than that found for CNS fibers. This is, however, hardly surprising given that in the CNS, axonal myelination must achieve multiple goals including reducing conduction delays, promoting conduction fidelity, lowering energy costs, and saving space.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we explore the notion that a balanced set-point can be achieved at a functional level as the micro-structure of individual axons becomes optimized, particularly for the central system where axons tend to be smaller and their myelin sheath thinner. We used an intuitive yet novel theoretical approach based on the fundamental biophysical properties describing axonal structure and function to show that an optimal g-ratio can be defined for the central nervous system (approximately 0.77). Furthermore, by reducing the influence of volume constraints on structural design by about 40%, this approach can also predict the g-ratio observed in some peripheral fibers (approximately 0.6).

CONCLUSIONS/SIGNIFICANCE

These results support the notion of optimization theory in nervous system design and construction and may also help explain why the central and peripheral systems have evolved different g-ratios as a result of volume constraints.

Transgenic models for cytokine-induced neurological disease

Considerable evidence supports the idea that cytokines are important mediators of pathophysiologic processes within the central nervous system (CNS). Numerous studies have documented the increased production of various cytokines in the human CNS in a variety of neurological and neuropsychiatric disorders. Deciphering cytokine actions in the intact CNS has important implications for our understanding of the pathogenesis and treatment of these disorders. One approach to address this problem that has been used widely employs transgenic mice with CNS-targeted production of different cytokines. Transgenic production of cytokines in the CNS of mice allows not only for the investigation of complex cellular responses at a localized level in the intact brain but also more closely recapitulates the expression of these mediators as found in disease states. As discussed in this review, the findings show that these transgenic animals exhibit wide-ranging structural and functional deficits that are linked to the development of distinct neuroinflammatory responses which are relatively specific for each cytokine. These cytokine-induced alterations often recapitulate those found in various human neurological disorders not only underscoring the relevance of these models but also reinforcing the clinicopathogenetic significance of cytokines in diseases of the CNS.

SOCS1 and SOCS3 in the control of CNS immunity

In the decade following their initial discovery, the suppressor of cytokine signaling (SOCS) proteins have been studied for their potential use as immunomodulators in disease. SOCS proteins, especially SOCS1 and SOCS3, are expressed by immune cells and cells of the central nervous system (CNS) and have the potential to impact immune processes within the CNS, including inflammatory cytokine and chemokine production, activation of microglia, macrophages and astrocytes, immune cell infiltration and autoimmunity. We describe CNS-relevant in vitro and in vivo studies that have examined the function of SOCS1 or SOCS3 under various neuroinflammatory or neuropathological conditions, including exposure of CNS cells to inflammatory cytokines or bacterial infection, demyelinating insults, stroke, spinal cord injury, multiple sclerosis and glioblastoma multiforme.

Enhanced integrated stress response promotes myelinating oligodendrocyte survival in response to interferon-gamma

The T-cell-derived, pleiotropic cytokine interferon (IFN)-gamma is believed to play a key regulatory role in immune-mediated demyelinating disorders of the central nervous system, including multiple sclerosis and experimental autoimmune encephalomyelitis. Our previous work has demonstrated that the endoplasmic reticulum (ER) stress response modulates the response of oligodendrocytes to this cytokine. The ER stress response activates the pancreatic ER kinase, which coordinates an adaptive program known as the integrated stress response by phosphorylating translation initiation factor 2alpha (eIF2alpha). In this study, we found that growth arrest and DNA damage 34 (GADD34), a stress-inducible regulatory subunit of a phosphatase complex that dephosphorylates eIF2alpha, was selectively up-regulated in myelinating oligodendrocytes in mice that ectopically expressed IFN-gamma in the central nervous system. We also found that a GADD34 mutant strain of mice displayed increased levels of phosphorylated eIF2alpha (p-eIF2alpha) in myelinating oligodendrocytes when exposure to IFN-gamma, as well as diminished oligodendrocyte loss and hypomyelination. Furthermore, treatment with salubrinal, a small chemical compound that specifically inhibits protein phosphatase 1(PP1)-GADD34 phosphatase activity, increased the levels of p-eIF2alpha and ameliorated hypomyelination and oligodendrocyte loss in cultured hippocampal slices exposed to IFN-gamma. Thus, our data provide evidence that an enhanced integrated stress response could promote oligodendrocyte survival in immune-mediated demyelination diseases.

Expression and functional significance of SOCS-1 and SOCS-3 in astrocytes

Astrocytes play a number of important physiological roles in CNS homeostasis. Inflammation stimulates astrocytes to secrete cytokines and chemokines that guide macrophages/microglia and T cells to sites of injury/inflammation. Herein, we describe how these processes are controlled by the suppressor of cytokine signaling (SOCS) proteins, a family of proteins that negatively regulate adaptive and innate immune responses. In this study, we describe that the immunomodulatory cytokine IFN-beta induces SOCS-1 and SOCS-3 expression in primary astrocytes at the transcriptional level. SOCS-1 and SOCS-3 transcriptional activity is induced by IFN-beta through IFN-gamma activation site (GAS) elements within their promoters. Studies in STAT-1alpha-deficient astrocytes indicate that STAT-1alpha is required for IFN-beta-induced SOCS-1 expression, while STAT-3 small interfering RNA studies demonstrate that IFN-beta-induced SOCS-3 expression relies on STAT-3 activation. Specific small interfering RNA inhibition of IFN-beta-inducible SOCS-1 and SOCS-3 in astrocytes enhances their proinflammatory responses to IFN-beta stimulation, such as heightened expression of the chemokines CCL2 (MCP-1), CCL3 (MIP-1alpha), CCL4 (MIP-1beta), CCL5 (RANTES), and CXCL10 (IP-10), and promoting chemotaxis of macrophages and CD4(+) T cells. These results indicate that IFN-beta induces SOCS-1 and SOCS-3 in primary astrocytes to attenuate its own chemokine-related inflammation in the CNS.

From fish to man: understanding endogenous remyelination in central nervous system demyelinating diseases

In the central nervous system (CNS) of man, evolutionary pressure has preserved some capability for remyelination while axonal regeneration is very limited. In contrast, two efficient programmes of regeneration exist in the adult fish CNS, neurite regrowth and remyelination. The rapidity of CNS remyelination is critical since it not only restores fast conduction of nerve impulses but also maintains axon integrity. If myelin repair fails, axons degenerate, leading to increased disability. In the human CNS demyelinating disease multiple sclerosis (MS), remyelination often takes place in the midst of inflammation. Here, we discuss recent studies that address the innate repair capabilities of the axon-glia unit from fish to man. We propose that expansion of this research field will help find ways to maintain or enhance spontaneous remyelination in man.

Genetic analysis of CNS remyelination

Myelin repair (remyelination) following the demyelination of central nervous system (CNS) axons in diseases such as multiple sclerosis plays a critical role in determining the level of accompanying neurologic disability. While remyelination can be quite robust, in multiple sclerosis it often fails. Understanding and stimulating the remyelination process are therefore important goals in MS research. Remyelination is a complex cellular process that involves an intimate interplay between the myelin-producing cells of the CNS (oligodendrocytes), the axons to be myelinated, as well as CNS-infiltrating immune cells. Genetic analysis can be a powerful tool for the functional analysis of complex cellular processes and has recently been applied to the problem of remyelination failure during disease. This chapter reviews the recent use of genetic approaches for the study of CNS remyelination in mouse models of demyelinating disease.

Expression of SOCS-1 in the liver tissues of chronic hepatitis B and its clinical significance

AIM: To study the expression of suppressor of cytokine signaling-1 (SOCS-1) in the liver tissues of chronic hepatitis B (CHB) and the clinical significance of this expression.

METHODS: The expression of SOCS-1 in liver tissues of 45 cases of CHB was investigated by immunohistochemical staining, and its correlations with inflammation grades and fibrosis stage were analyzed by SPSS statistics software.

RESULTS: The result showed SOCS-1 expressing could be observed in the liver tissue of CHB. The expression of SOCS-1 was mainly distributed near the portal area in the liver tissue of mild inflammation CHB group, and was diffusely distributed in the liver tissue of moderate and severe inflammation groups. SOCS-1 positive stains mainly appear in the hepatocytes, only a few of liver interstitial cells were involved. Inside the hepatocyte, SOCS-1 positive stains are mainly distributed in the plasma. Some of the staining was observed on the membrane. The inclusion bodies in the plasma of hepatocytes were observed occasionally. There were both obvious correlations between the expression of SOCS-1 and the inflammatory grade, and that between the expression of SOCS-1 and the fibrosis stage.

CONCLUSION: The distribution of SOCS-1 in the liver tissue of CHB is variable. This expression was correlated with the inflammation grade and fibrosis stage.

HIV-1 TAT inhibits microglial phagocytosis of Abeta peptide

Human immunodeficiency virus (HIV)-associated dementia (HAD) is a subcortical neuropsychiatric syndrome that has increased in prevalence in the era of highly active antiretroviral therapy (HAART). Several studies demonstrated increased amyloidosis in brains of HIV patients and suggested that there may be a significant number of long-term HIV survivors with co-morbid Alzheimer's disease (AD) in the future. We show HIV-1 Tat protein inhibits microglial uptake of Abeta1-42 peptide, a process that is enhanced by interferon-gamma (IFN-gamma) and rescued by the STAT1 inhibitor (-)-epigallocatechin-3-gallate (EGCG). It is hypothesized that reduced Abeta uptake occurs through IFN-gamma mediated STAT1 activation. This process promotes a switch from a phagocytic to an antigen presenting phenotype in microglia through activation of class II transactivator (CIITA). Additionally, we show that HIV-1 Tat significantly disrupts apolipoprotein-3 (Apo-E3) promoted microglial Abeta uptake. As Tat has been shown to directly interact with the low density lipoprotein (LRP) receptor and thus inhibit the uptake of its ligands including apolipoprotein E4 (Apo-E4) and Abeta peptide in neurons, we further hypothesize that a similar inhibition of LRP may occur in microglia. Future studies will be required to fully characterize the mechanisms underlying IFN-gamma enhancement of HIV-1 Tats disruption of microglial phagocytosis of Abeta and Apo-E3.

The involvement of mitochondria in the pathogenesis of multiple sclerosis

Multiple sclerosis is an immune-mediated disorder of the central nervous system. Major pathological characteristics include the loss of oligodendrocytes, demyelination and neuroaxonal depletion in association with inflammation. The complex pathophysiology of tissue loss is only partially understood. Here we discuss a variety of mitochondrion-driven mechanisms involved in immune regulation, oligodendrocyte depletion and neurodegeneration. The recognition of a mitochondrial link between inflammation and neurodegeneration underscores the importance of an early aggressive intervention for halting inflammation and preventing neurodegeneration, and identifies the mitochondrion as a potential target in neuroprotection.

The integrated stress response prevents demyelination by protecting oligodendrocytes against immune-mediated damage

In response to ER stress, the pancreatic endoplasmic reticulum kinase (PERK) coordinates an adaptive program known as the integrated stress response (ISR) by phosphorylating the alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha). IFN-gamma, which activates the ER stress response in oligodendrocytes, is believed to play a critical role in the immune-mediated CNS disorder multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE). Here we report that CNS delivery of IFN-gamma before EAE onset ameliorated the disease course and prevented demyelination, axonal damage, and oligodendrocyte loss. The beneficial effects of IFN-gamma were accompanied by PERK activation in oligodendrocytes and were abrogated in PERK-deficient animals. Our results indicate that IFN-gamma activation of PERK in mature oligodendrocytes attenuates EAE severity and suggest that therapeutic approaches to activate the ISR could prove beneficial in MS.

Diminished degradation of myelin basic protein by anti-sulfatide antibody and interferon-gamma in myelin from glia maturation factor-deficient mice

In this study we show the effect of anti-sulfatide (RmAb) antibodies and inflammatory cytokines, TNF-alpha and IFN-gamma in inducing myelin basic protein (MBP) degradation in myelin isolated from control wild type (WT) and glia maturation factor (GMF)-deficient (GMF-KO) mice. GMF was not detected in isolated myelin from WT and GMF-KO mice although it is present in brains of WT mice. Our results show that calcium-dependent neutral protease activity caused significantly elevated degradation of 18.5 and/or 17.5kDa isoforms of MBP in WT myelin treated with RmAb or IFN-gamma. In contrast, MBP degradation in isolated myelin from GMF-KO mice remained unaffected following treatment with RmAb, IFN-gamma, or GM-CSF. Neither the 14kDa isoform of MBP nor proteolipid protein (PLP) showed an elevated degradation compared to controls. A virtual absence of GM-CSF, TNF-alpha and IFN-gamma in GMF-KO brain compared to WT was also evident when the animals were challenged with MOG 35-55. Additionally, the myelin from GMF-KO mice showed difference in distribution of myelin oligodendrocyte glycoprotein (MOG) and beta-tubulin in a sucrose density gradient myelin-axolemmal fractions compared to WT. Taken together, our data suggests a role for GMF in the biochemical organization of myelin and thereby its effect on MBP degradation induced by RmAb and IFN-gamma.

Interferon-gamma-oligodendrocyte interactions in the regulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of the human demyelinating disorder multiple sclerosis (MS). The immune cytokine interferon-gamma (IFN-gamma) is believed to participate in disease pathogenesis in both EAE and MS. In the present study, we examined the significance of IFN-gamma-oligodendrocyte interactions in the course of EAE. For the purpose of our study, we used the previously described [proteolipid protein/suppressor of cytokine signaling 1 (PLP/SOCS1)] transgenic mouse line that displays suppressed oligodendrocyte responsiveness to IFN-gamma. PLP/SOCS1 mice developed EAE with an accelerated onset associated with enhanced early inflammation and markedly increased oligodendrocyte apoptosis. Moreover, we found that IFN-gamma pretreatment of mature oligodendrocytes in vitro had a protective effect against oxidative stress and the inhibition of proteasome activity and resulted in upregulation in expression of a number of chemokines, including CXCL10 (IP10), CCL2 (MCP-1), CCL3 (MCP-1alpha), and CCL5 (RANTES). These results suggest that IFN-gamma-oligodendrocyte interactions are of significance to the clinical and pathological aspects of EAE. In addition, the present study suggests that oligodendrocytes are not simply targets of inflammatory injury but active participants of the neuroimmune network operating during the course of EAE.

IL-10 Inhibits Lipopolysaccharide-Induced CD40 Gene Expression through Induction of Suppressor of Cytokine Signaling-3

Costimulation between T cells and APCs is required for adaptive immune responses. CD40, an important costimulatory molecule, is expressed on a variety of cell types, including macrophages and microglia. The aberrant expression of CD40 is implicated in diseases including multiple sclerosis, rheumatoid arthritis, and Alzheimer's disease, and inhibition of CD40 signaling has beneficial effects in a number of animal models of autoimmune diseases. In this study, we discovered that IL-10, a cytokine with anti-inflammatory properties, inhibits LPS-induced CD40 gene expression. We previously demonstrated that LPS induction of CD40 in macrophages/microglia involves both NF-kappaB activation and LPS-induced production of IFN-beta, which subsequently activates STAT-1alpha. IL-10 inhibits LPS-induced IFN-beta gene expression and subsequent STAT-1alpha activation, but does not affect NF-kappaB activation. Our results also demonstrate that IL-10 inhibits LPS-induced recruitment of STAT-1alpha, RNA polymerase II, and the coactivators CREB binding protein and p300 to the CD40 promoter, as well as inhibiting permissive histone H3 acetylation (AcH3). IL-10 and LPS synergize to induce suppressor of cytokine signaling (SOCS)-3 gene expression in macrophages and microglia. Ectopic expression of SOCS-3 attenuates LPS-induced STAT activation, and inhibits LPS-induced CD40 gene expression, comparable to that seen by IL-10. These results indicate that SOCS-3 plays an important role in the negative regulation of LPS-induced CD40 gene expression by IL-10.