Translation of dipeptide repeat proteins in C9ORF72 ALS/FTD through unique and redundant AUG initiation codons

A hexanucleotide repeat expansion in C9ORF72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). A hallmark of ALS/FTD pathology is the presence of dipeptide repeat (DPR) proteins, produced from both sense GGGGCC (poly-GA, poly-GP, poly-GR) and antisense CCCCGG (poly-PR, poly-PG, poly-PA) transcripts. Translation of sense DPRs, such as poly-GA and poly-GR, depends on non-canonical (non-AUG) initiation codons. Here, we provide evidence for canonical AUG-dependent translation of two antisense DPRs, poly-PR and poly-PG. A single AUG is required for synthesis of poly-PR, one of the most toxic DPRs. Unexpectedly, we found redundancy between three AUG codons necessary for poly-PG translation. Further, the eukaryotic translation initiation factor 2D (EIF2D), which was previously implicated in sense DPR synthesis, is not required for AUG-dependent poly-PR or poly-PG translation, suggesting that distinct translation initiation factors control DPR synthesis from sense and antisense transcripts. Our findings on DPR synthesis from the C9ORF72 locus may be broadly applicable to many other nucleotide repeat expansion disorders.

Kozak Similarity Score Algorithm Identifies Alternative Translation Initiation Codons Implicated in Cancers

Ribosome profiling and mass spectroscopy have identified canonical and noncanonical translation initiation codons (TICs) that are upstream of the main translation initiation site and used to translate oncogenic proteins. There have previously been conflicting reports about the patterns of nucleotides that surround noncanonical TICs. Here, we use a Kozak Similarity Score algorithm to find that nearly all of these TICs have flanking nucleotides closely matching the Kozak sequence. Remarkably, the nucleotides flanking alternative noncanonical TICs are frequently closer to the Kozak sequence than the nucleotides flanking TICs used to translate the gene’s main protein. Of note, the 5′ untranslated region (5‘UTR) of cancer-associated genes with an upstream TIC tend to be significantly longer than the same region in genes not associated with cancer. The presence of a longer-than-typical 5′UTR increases the likelihood of ribosome binding to upstream noncanonical TICs, and may be a distinguishing feature of a number of genes overexpressed in cancer. Noncanonical TICs that are located in the 5′UTR, although thought by some to be disadvantageous and suppressed by evolution, may translate oncogenic proteins because of their flanking nucleotides.

A C. elegans model of C9orf72-associated ALS/FTD uncovers a conserved role for eIF2D in RAN translation

A hexanucleotide repeat expansion GGGGCC in the non-coding region of C9orf72 is the most common cause of inherited amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Toxic dipeptide repeats (DPRs) are synthesized from GGGGCC via repeat-associated non-AUG (RAN) translation. Here, we develop C. elegans models that express, either ubiquitously or exclusively in neurons, 75 GGGGCC repeats flanked by intronic C9orf72 sequence. The worms generate DPRs (poly-glycine-alanine [poly-GA], poly-glycine-proline [poly-GP]) and poly-glycine-arginine [poly-GR]), display neurodegeneration, and exhibit locomotor and lifespan defects. Mutation of a non-canonical translation-initiating codon (CUG) upstream of the repeats selectively reduces poly-GA steady-state levels and ameliorates disease, suggesting poly-GA is pathogenic. Importantly, loss-of-function mutations in the eukaryotic translation initiation factor 2D (eif-2D/eIF2D) reduce poly-GA and poly-GP levels, and increase lifespan in both C. elegans models. Our in vitro studies in mammalian cells yield similar results. Here, we show a conserved role for eif-2D/eIF2D in DPR expression.

RNA-binding protein altered expression and mislocalization in MS

Objective

To determine whether there are nuclear depletion and cellular mislocalization of RNA-binding proteins (RBPs) transactivation response DNA-binding protein of 43 kDa (TDP-43), fused in sarcoma (FUS), and polypyrimidine tract–binding protein (PTB) in MS, as is the case in amyotrophic lateral sclerosis (ALS) and oligodendrocytes infected with Theiler murine encephalomyelitis virus (TMEV), we examined MS lesions and in vitro cultured primary human brain–derived oligodendrocytes.

Methods

Nuclear depletion and mislocalization of TDP-43, FUS, and PTB are thought to contribute to the pathogenesis of ALS and TMEV demyelination. The latter findings prompted us to investigate these RBPs in the demyelinated lesions of MS and in in vitro cultured human brain–derived oligodendrocytes under metabolic stress conditions.

Results

We found (1) mislocalized TDP-43 in oligodendrocytes in active lesions in some patients with MS; (2) decreased PTB1 expression in oligodendrocytes in mixed active/inactive demyelinating lesions; (3) decreased nuclear expression of PTB2 in neurons in cortical demyelinating lesions; and (4) nuclear depletion of TDP-43 in oligodendrocytes under metabolic stress induced by low glucose/low nutrient conditions compared with optimal culture conditions.

Conclusion

TDP-43 has been found to have a key role in oligodendrocyte function and viability, whereas PTB is important in neuronal differentiation, suggesting that altered expression and mislocalization of these RBPs in MS lesions may contribute to the pathogenesis of demyelination and neurodegeneration. Our findings also identify nucleocytoplasmic transport as a target for treatment.

Knockdown of GADD34 in neonatal mutant SOD1 mice ameliorates ALS

Mutations in Cu/Zn superoxide dismutase (SOD1) cause ~20% of familial ALS (FALS), which comprises 10% of total ALS cases. In mutant SOD1- (mtSOD1-) induced ALS, misfolded aggregates of SOD1 lead to activation of the unfolded protein response/integrated stress response (UPR/ISR). Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), a kinase that phosphorylates eukaryotic translation initiator factor 2α (p-eIF2α), coordinates the response by causing a global suppression of protein synthesis. Growth arrest and DNA damage 34 (GADD34) dephosphorylates p-eIF2α, allowing protein synthesis to return to normal. If the UPR/ISR is overwhelmed by the amount of misfolded protein, CCAAT/enhancer-binding homologous protein (CHOP) is activated leading to apoptosis. In the current study we investigated the effect of knocking down CHOP and GADD34 on disease of G93A and G85R mtSOD1 mice. Although a CHOP antisense oligonucleotide had no effect on survival, an intravenous injection of GADD34 shRNA encoded in adeno-associated virus 9 (AAV9) into neonatal G93A as well as neonatal G85R mtSOD1 mice led to a significantly increased survival. G85R mtSOD1 mice had a reduction in SOD1 aggregates/load, astrocytosis, and microgliosis. In contrast, there was no change in disease phenotype when GADD34 shRNA was delivered to older G93A mtSOD1 mice. Our current study shows that GADD34 shRNA is effective in ameliorating disease when administered to neonatal mtSOD1 mice. Targeting the UPR/ISR may be beneficial in mtSOD1-induced ALS as well as other neurodegenerative diseases in which misfolded proteins and ER stress have been implicated.

TDP-43 proteinopathy in Theiler's murine encephalomyelitis virus infection

TDP-43, an RNA-binding protein that is primarily nuclear and important in splicing and RNA metabolism, is mislocalized from the nucleus to the cytoplasm of neural cells in amyotrophic lateral sclerosis (ALS), and contributes to disease. We sought to investigate whether TDP-43 is mislocalized in infections with the acute neuronal GDVII strain and the persistent demyelinating DA strain of Theiler's virus murine encephalomyelitis virus (TMEV), a member of the Cardiovirus genus of Picornaviridae because: i) L protein of both strains is known to disrupt nucleocytoplasmic transport, including transport of polypyrimidine tract binding protein, an RNA-binding protein, ii) motor neurons and oligodendrocytes are targeted in both TMEV infection and ALS. TDP-43 phosphorylation, cleavage, and cytoplasmic mislocalization to an aggresome were observed in wild type TMEV-infected cultured cells, with predicted splicing abnormalities. In contrast, cells infected with DA and GDVII strains that have L deletion had rare TDP-43 mislocalization and no aggresome formation. TDP-43 mislocalization was also present in neural cells of TMEV acutely-infected mice. Of note, TDP-43 was mislocalized six weeks after DA infection to the cytoplasm of oligodendrocytes and other glial cells in demyelinating lesions of spinal white matter. A recent study showed that TDP-43 knock down in oligodendrocytes in mice led to demyelination and death of this neural cell [1], suggesting that TMEV infection mislocalization of TDP-43 and other RNA-binding proteins is predicted to disrupt key cellular processes and contribute to the pathogenesis of TMEV-induced diseases. Drugs that inhibit nuclear export may have a role in antiviral therapy.

Translation of dipeptide repeat proteins from the C9ORF72 expanded repeat is associated with cellular stress

Expansion of a hexanucleotide repeat (HRE), GGGGCC, in the C9ORF72 gene is recognized as the most common cause of familial amyotrophic lateral sclerosis (FALS), frontotemporal dementia (FTD) and ALS-FTD, as well as 5-10% of sporadic ALS. Despite the location of the HRE in the non-coding region (with respect to the main C9ORF72 gene product), dipeptide repeat proteins (DPRs) that are thought to be toxic are translated from the HRE in all three reading frames from both the sense and antisense transcript. Here, we identified a CUG that has a good Kozak consensus sequence as the translation initiation codon. Mutation of this CTG significantly suppressed polyglycine-alanine (GA) translation. GA was translated when the G₄C₂ construct was placed as the second cistron in a bicistronic construct. CRISPR/Cas9-induced knockout of a non-canonical translation initiation factor, eIF2A, impaired GA translation. Transfection of G₄C₂ constructs induced an integrated stress response (ISR), while triggering the ISR led to a continuation of translation of GA with a decline in conventional cap-dependent translation. These in vitro observations were confirmed in chick embryo neural cells. The findings suggest that DPRs translated from an HRE in C9ORF72 aggregate and lead to an ISR that then leads to continuing DPR production and aggregation, thereby creating a continuing pathogenic cycle.

Interleukin-34 restores blood-brain barrier integrity by upregulating tight junction proteins in endothelial cells

Interleukin-34 (IL-34) is a newly discovered cytokine as an additional ligand for colony stimulating factor-1 receptor (CSF1R), and its functions are expected to overlap with colony stimulating factor-1/macrophage-colony stimulating factor. We have previously shown that the IL-34 is primarily produced by neurons in the central nervous system (CNS) and induces proliferation and neuroprotective properties of microglia which express CSF1R. However, the functions of IL-34 in the CNS are still elucidative. Here we show that CNS capillary endothelial cells also express CSF1R. IL-34 protected blood–brain barrier integrity by restored expression levels of tight junction proteins, which were downregulated by pro-inflammatory cytokines. The novel function of IL-34 on the blood–brain barrier may give us a clue for new therapeutic strategies in neuroinflammatory and neurodegenerative diseases such as multiple sclerosis and Alzheimer's disease.

Interleukin-1β induces blood-brain barrier disruption by downregulating Sonic hedgehog in astrocytes

The blood–brain barrier (BBB) is composed of capillary endothelial cells, pericytes, and perivascular astrocytes, which regulate central nervous system homeostasis. Sonic hedgehog (SHH) released from astrocytes plays an important role in the maintenance of BBB integrity. BBB disruption and microglial activation are common pathological features of various neurologic diseases such as multiple sclerosis, Parkinson’s disease, amyotrophic lateral sclerosis, and Alzheimer’s disease. Interleukin-1β (IL-1β), a major pro-inflammatory cytokine released from activated microglia, increases BBB permeability. Here we show that IL-1β abolishes the protective effect of astrocytes on BBB integrity by suppressing astrocytic SHH production. Astrocyte conditioned media, SHH, or SHH signal agonist strengthened BBB integrity by upregulating tight junction proteins, whereas SHH signal inhibitor abrogated these effects. Moreover, IL-1β increased astrocytic production of pro-inflammatory chemokines such as CCL2, CCL20, and CXCL2, which induce immune cell migration and exacerbate BBB disruption and neuroinflammation. Our findings suggest that astrocytic SHH is a potential therapeutic target that could be used to restore disrupted BBB in patients with neurologic diseases.

Granulocyte-colony stimulating factor attenuates oligomeric amyloid β neurotoxicity by activation of neprilysin

Soluble oligomeric amyloid β (oAβ) causes synaptic dysfunction and neuronal cell death, which are involved in the pathogenesis of Alzheimer's disease (AD). The hematopoietic growth factor granulocyte-colony stimulating factor (G-CSF) is expressed in the central nervous system (CNS) and drives neurogenesis. Here we show that G-CSF attenuated oAβ neurotoxicity through the enhancement of the enzymatic activity of Aβ-degrading enzyme neprilysin (NEP) in neurons, while the NEP inhibitor thiorphan abolished the neuroprotection. Inhibition of MEK5/ERK5, a major downstream effector of G-CSF signaling, also ablated neuroprotective effect of G-CSF. Furthermore, intracerebroventricular administration of G-CSF enhanced NEP enzymatic activity and clearance of Aβ in APP/PS1 transgenic mice. Thus, we propose that G-CSF may be a possible therapeutic strategy against AD.

FGF-2 released from degenerating neurons exerts microglial-induced neuroprotection via FGFR3-ERK signaling pathway

Background

The accumulation of activated microglia is a hallmark of various neurodegenerative diseases. Microglia may have both protective and toxic effects on neurons through the production of various soluble factors, such as chemokines. Indeed, various chemokines mediate the rapid and accurate migration of microglia to lesions. In the zebra fish, another well-known cellular migrating factor is fibroblast growth factor-2 (FGF-2). Although FGF-2 does exist in the mammalian central nervous system (CNS), it is unclear whether FGF-2 influences microglial function.

Methods

The extent of FGF-2 release was determined by ELISA, and the expression of its receptors was examined by immunocytochemistry. The effect of several drug treatments on a neuron and microglia co-culture system was estimated by immunocytochemistry, and the neuronal survival rate was quantified. Microglial phagocytosis was evaluated by immunocytochemistry and quantification, and microglial migration was estimated by fluorescence-activated cell sorting (FACS). Molecular biological analyses, such as Western blotting and promoter assay, were performed to clarify the FGF-2 downstream signaling pathway in microglia.

Results

Fibroblast growth factor-2 is secreted by neurons when damaged by glutamate or oligomeric amyloid β 1-42. FGF-2 enhances microglial migration and phagocytosis of neuronal debris, and is neuroprotective against glutamate toxicity through FGFR3-extracellular signal-regulated kinase (ERK) signaling pathway, which is directly controlled by Wnt signaling in microglia.

Conclusions

FGF-2 secreted from degenerating neurons may act as a ‘help-me’ signal toward microglia by inducing migration and phagocytosis of unwanted debris.

GM-CSF increases LPS-induced production of proinflammatory mediators via upregulation of TLR4 and CD14 in murine microglia

BACKGROUND

Microglia are resident macrophage-like cells in the central nervous system (CNS) and cause innate immune responses via the LPS receptors, Toll-like receptor (TLR) 4 and CD14, in a variety of neuroinflammatory disorders including bacterial infection, Alzheimer's disease, and amyotrophic lateral sclerosis. Granulocyte macrophage-colony stimulating factor (GM-CSF) activates microglia and induces inflammatory responses via binding to GM-CSF receptor complex composed of two different subunit GM-CSF receptor α (GM-CSFRα) and common β chain (βc). GM-CSF has been shown to be associated with neuroinflammatory responses in multiple sclerosis and Alzheimer's disease. However, the mechanisms how GM-CSF promotes neuroinflammation still remain unclear.

METHODS

Microglia were stimulated with 20 ng/ml GM-CSF and the levels of TLR4 and CD14 expression were evaluated by RT-PCR and flowcytometry. LPS binding was analyzed by flowcytometry. GM-CSF receptor complex was analyzed by immunocytochemistry. The levels of IL-1β, IL-6 and TNF-α in culture supernatant of GM-CSF-stimulated microglia and NF-κB nuclear translocation were determined by ELISA. Production of nitric oxide (NO) was measured by the Griess method. The levels of p-ERK1/2, ERK1/2, p-p38 and p38 were assessed by Western blotting. Statistically significant differences between experimental groups were determined by one-way ANOVA followed by Tukey test for multiple comparisons.

RESULTS

GM-CSF receptor complex was expressed in microglia. GM-CSF enhanced TLR4 and CD14 expressions in microglia and subsequent LPS-binding to the cell surface. In addition, GM-CSF priming increased LPS-induced NF-κB nuclear translocation and production of IL-1β, IL-6, TNF-α and NO by microglia. GM-CSF upregulated the levels of p-ERK1/2 and p-p38, suggesting that induction of TLR4 and CD14 expression by GM-CSF was mediated through ERK1/2 and p38, respectively.

CONCLUSIONS

These results suggest that GM-CSF upregulates TLR4 and CD14 expression in microglia through ERK1/2 and p38, respectively, and thus promotes the LPS receptor-mediated inflammation in the CNS.

TGF-β induced by interleukin-34-stimulated microglia regulates microglial proliferation and attenuates oligomeric amyloid β neurotoxicity

Microglia play critical roles in the pathogenesis of Alzheimer's disease (AD). We have previously shown that interleukin-34 (IL-34) enhances microglial proliferation and induces microglial neuroprotective properties against oligomeric amyloid β (oAβ) toxicity by producing insulin degrading enzyme, an Aβ degrading enzyme, and anti-oxidant enzyme heme oxygenase-1. In this study, we found that IL-34 dose-dependently induces TGF-β in microglia, and that TGF-β attenuates oAβ neurotoxicity in neuron microglial co-cultures. The TGF-β 1 receptor kinase inhibitor SD208 enhances microglial proliferation by IL-34 and suppresses the neuroprotective effect of IL-34-treated microglia. These findings suggest that TGF-β produced by IL-34-treated microglia is a negative regulator of microglial proliferation and enhances the neuroprotective property of microglia.

Midkine inhibits inducible regulatory T cell differentiation by suppressing the development of tolerogenic dendritic cells

Midkine (MK), a heparin-binding growth factor, reportedly contributes to inflammatory diseases, including Crohn's disease and rheumatoid arthritis. We previously showed that MK aggravates experimental autoimmune encephalomyelitis (EAE) by decreasing regulatory CD4(+)CD25(+)Foxp3(+) T cells (Tregs), a population that regulates the development of autoimmune responses, although the precise mechanism remains uncertain. In this article, we show that MK produced in inflammatory conditions suppresses the development of tolerogenic dendritic cells (DCregs), which drive the development of inducible Treg. MK suppressed DCreg-mediated expansion of the CD4(+)CD25(+)Foxp3(+) Treg population. DCregs expressed significantly higher levels of CD45RB and produced significantly less IL-12 compared with conventional dendritic cells. However, MK downregulated CD45RB expression and induced IL-12 production by reducing phosphorylated STAT3 levels via src homology region 2 domain-containing phosphatase-2 in DCreg. Inhibiting MK activity with anti-MK RNA aptamers, which bind to the targeted protein to suppress the function of the protein, increased the numbers of CD11c(low)CD45RB(+) dendritic cells and Tregs in the draining lymph nodes and suppressed the severity of EAE, an animal model of multiple sclerosis. Our results also demonstrated that MK was produced by inflammatory cells, in particular, CD4(+) T cells under inflammatory conditions. Taken together, these results suggest that MK aggravates EAE by suppressing DCreg development, thereby impairing the Treg population. Thus, MK is a promising therapeutic target for various autoimmune diseases.

Immunoglobulin G(1) immune complex upregulates interferon-γ-induced nitric oxide production via ERK1/2 activation in murine microglia

Intrathecal Immunoglobulin G (IgG) is elevated in some central nervous system (CNS) diseases and microglia upregulate Fcγ receptors in various neurological disorders. However, the interaction between IgG or IgG immune complexes and microglial Fcγ receptors is not fully understood. In this study, the effect of IgG(1) immune complexes on microglia was investigated. IgG(1) immune complexes increased nitric oxide production in murine microglia in the presence of interferon (IFN)-γ. These effects were dependent upon IgG(1) immune complex-induced activation of spleen tyrosine kinase with subsequent activation of extracellular signal regulated kinase1/2. Collectively, these results indicate that IgG(1) immune complexes can exert immunomodulatory effects in various central nervous system disorders.

The gap-junction inhibitor carbenoxolone suppresses the differentiation of Th17 cells through inhibition of IL-23 expression in antigen presenting cells

Carbenoxolone (CBX) is a widely used gap-junction inhibitor. We have previously shown that treatment with CBX significantly delayed the onset of experimental autoimmune encephalomyelitis (EAE). However, the mechanism by which CBX delays the onset of EAE remains to be elucidated. Here, we show that CBX specifically inhibits the production of IL-23 by dendritic cells (DCs) and microglia in vitro. CBX treatment significantly reduced the population of Th17 cells in EAE mice. Furthermore, CBX downregulated the expression of IL-23 p19 via increased production of protein phosphatase 2A (PP2A). Thus, CBX may be an effective therapeutic strategy against Th17-mediated autoimmune diseases, such as multiple sclerosis.

Interleukin-34 selectively enhances the neuroprotective effects of microglia to attenuate oligomeric amyloid-β neurotoxicity

Microglia, macrophage-like resident immune cells in the brain, possess both neurotoxic and neuroprotective properties and have a critical role in the development of Alzheimer's disease (AD). We examined the function of Interleukin-34 (IL-34), a newly discovered cytokine, on microglia because it reportedly induces proliferation of monocytes and macrophages. We observed that the neuronal cells primarily produce IL-34 and that microglia express its receptor, colony-stimulating factor 1 receptor. IL-34 promoted microglial proliferation and clearance of soluble oligomeric amyloid-β (oAβ), which mediates synaptic dysfunction and neuronal damage in AD. IL-34 increased the expression of insulin-degrading enzyme, aiding the clearance of oAβ, and induced the antioxidant enzyme heme oxygenase-1 in microglia to reduce oxidative stress, without producing neurotoxic molecules. Consequently, microglia treated with IL-34 attenuated oAβ neurotoxicity in primary neuron-microglia co-cultures. In vivo, intracerebroventricular administration of IL-34 ameliorated impairment of associative learning and reduced oAβ levels through up-regulation of insulin-degrading enzyme and heme oxygenase-1 in an APP/PS1 transgenic mouse model of AD. These findings support the idea that enhancement of the neuroprotective property of microglia by IL-34 may be an effective approach against oAβ neurotoxicity in AD.

Blockade of gap junction hemichannel suppresses disease progression in mouse models of amyotrophic lateral sclerosis and Alzheimer's disease

Background

Glutamate released by activated microglia induces excitotoxic neuronal death, which likely contributes to non-cell autonomous neuronal death in neurodegenerative diseases, including amyotrophic lateral sclerosis and Alzheimer's disease. Although both blockade of glutamate receptors and inhibition of microglial activation are the therapeutic candidates for these neurodegenerative diseases, glutamate receptor blockers also perturbed physiological and essential glutamate signals, and inhibitors of microglial activation suppressed both neurotoxic/neuroprotective roles of microglia and hardly affected disease progression. We previously demonstrated that activated microglia release a large amount of glutamate specifically through gap junction hemichannel. Hence, blockade of gap junction hemichannel may be potentially beneficial in treatment of neurodegenerative diseases.

Methods and Findings

In this study, we generated a novel blood-brain barrier permeable gap junction hemichannel blocker based on glycyrrhetinic acid. We found that pharmacologic blockade of gap junction hemichannel inhibited excessive glutamate release from activated microglia in vitro and in vivo without producing notable toxicity. Blocking gap junction hemichannel significantly suppressed neuronal loss of the spinal cord and extended survival in transgenic mice carrying human superoxide dismutase 1 with G93A or G37R mutation as an amyotrophic lateral sclerosis mouse model. Moreover, blockade of gap junction hemichannel also significantly improved memory impairments without altering amyloid β deposition in double transgenic mice expressing human amyloid precursor protein with K595N and M596L mutations and presenilin 1 with A264E mutation as an Alzheimer's disease mouse model.

Conclusions

Our results suggest that gap junction hemichannel blockers may represent a new therapeutic strategy to target neurotoxic microglia specifically and prevent microglia-mediated neuronal death in various neurodegenerative diseases.

IL-9 promotes Th17 cell migration into the central nervous system via CC chemokine ligand-20 produced by astrocytes

Newly discovered IL-9-producing helper T cells (Th9) reportedly exert both aggravating and suppressive roles on experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. However, it is still unclear whether Th9 is a distinct Th cell subset and how IL-9 functions in the CNS. In this study, we show that IL-9 is produced by naive CD4(+) T cells that were stimulated with anti-CD3 and anti-CD28 Abs under the conditions of Th2-, inducible regulatory T cell-, Th17-, and Th9-polarizing conditions and that IL-9 production is significantly suppressed in the absence of IL-4, suggesting that IL-4 is critical for the induction of IL-9 by each producing cell. The IL-9 receptor complex, IL-9R and IL-2Rγ, is constitutively expressed on astrocytes. IL-9 induces astrocytes to produce CCL-20 but not other chemokines, including CCL-2, CCL-3, and CXCL-2 by astrocytes. The conditioned medium of IL-9-stimulated astrocytes induces Th17 cell migration in vitro, which is cancelled by adding anti-CCL-20 neutralizing Abs. Treating with anti-IL-9 neutralizing Abs attenuates experimental autoimmune encephalomyelitis, decreases the number of infiltrating Th17 cells, and reduces CCL-20 expression in astrocytes. These results suggest that IL-9 is produced by several Th cell subsets in the presence of IL-4 and induces CCL-20 production by astrocytes to induce the migration of Th17 cells into the CNS.

Production and functions of IL-33 in the central nervous system

Interleukin-33 (IL-33) is a novel multifunctional IL-1 family cytokine. IL-33 signals via a heterodimer composed of IL-1 receptor-related protein ST2 and IL-1 receptor accessory protein (IL-1RAcP). IL-33 has been shown to activate T helper 2 cells (Th2), mast cells and basophils to produce a variety of Th2 cytokines and mediate allergic-type immune responses. Recent studies have revealed that glial cells are induced to express IL-33 mRNA and protein. However, the functions of IL-33 and its producing cells in the central nervous system (CNS) are still uncertain. In this study, we investigated the expression and function of IL-33 in the CNS. IL-33 is produced by endothelial cells and astrocytes but not by microglia or neurons. The IL-33 receptors are expressed mainly in microglia and astrocytes. IL-33 dose-dependently induces the proliferation of microglia and enhances the production of pro-inflammatory cytokines, such as IL-1β and TNFα, as well as the anti-inflammatory cytokine IL-10. It also enhances chemokines and nitric oxide production and phagocytosis by microglia. Thus, IL-33 produced in the CNS activates microglia and may function as a pro-inflammatory mediator in the pathophysiology of the CNS.

Fractalkine attenuates excito-neurotoxicity via microglial clearance of damaged neurons and antioxidant enzyme heme oxygenase-1 expression

Glutamate-induced excito-neurotoxicity likely contributes to non-cell autonomous neuronal death in neurodegenerative diseases. Microglial clearance of dying neurons and associated debris is essential to maintain healthy neural networks in the central nervous system. In fact, the functions of microglia are regulated by various signaling molecules that are produced as neurons degenerate. Here, we show that the soluble CX3C chemokine fractalkine (sFKN), which is secreted from neurons that have been damaged by glutamate, promotes microglial phagocytosis of neuronal debris through release of milk fat globule-EGF factor 8, a mediator of apoptotic cell clearance. In addition, sFKN induces the expression of the antioxidant enzyme heme oxygenase-1 (HO-1) in microglia in the absence of neurotoxic molecule production, including NO, TNF, and glutamate. sFKN treatment of primary neuron-microglia co-cultures significantly attenuated glutamate-induced neuronal cell death. Using several specific MAPK inhibitors, we found that sFKN-induced heme oxygenase-1 expression was primarily mediated by activation of JNK and nuclear factor erythroid 2-related factor 2. These results suggest that sFKN secreted from glutamate-damaged neurons provides both phagocytotic and neuroprotective signals.

Phenytoin at optimum doses ameliorates experimental autoimmune encephalomyelitis via modulation of immunoregulatory cells

We investigated the optimum doses of phenytoin for treatment of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE). Oral and intraperitoneal administrations of 0.25 to 1.0mg per mouse (12.5-50mg/kg) 3 times a week improved the clinical course. Intraperitoneal injections of 1.0mg phenytoin were the most effective, as a significant reduction in EAE severity was seen after only 2 administrations with that protocol. Treatment efficacy was associated with amelioration of cellular infiltrates in the CNS, and an increase in CD4(+)Foxp3(+) and CD4(+)CD25(+)CD127(-) regulatory T cells as well as CD8(+) suppressor/cytotoxic T cells in blood.

Glutamate induces neurotrophic factor production from microglia via protein kinase C pathway

Microglia are intrinsic immune cells in the central nervous system and play key roles in the pathogenesis of various central nervous system disorders. Microglia have been shown to attack damaged neurons by secreting a variety of neurotoxic factors including inflammatory cytokines, reactive oxygen species and glutamate. On the other hand, they can produce neurotrophic factors (NTFs) which support neuronal survival and growth. However, the precise mechanism that regulates microglial NTF production is not fully understood, and the relation between glutamate and NTFs remains unclear. In the present study, we show that glutamate significantly induces microglial NTF production by the activation of N-methyl-d-aspartate (NMDA) receptors, group III metabotropic glutamate receptors, and glutamate transporters. Activation of NMDA receptors and group III metabotropic glutamate receptors induces intracellular Ca(2+) release from the endoplasmic reticulum. Further, stimulation of glutamate transporters leads to influx of extracellular Ca(2+) in a Na(+)-dependent manner. This intracellular Ca(2+) elevation activates the protein kinase C pathway which induces microglial NTF expression and production. These results suggest that microglia play a neuroprotective role during the excitotoxic state in neurodegenerative diseases.

Interleukin-25 expressed by brain capillary endothelial cells maintains blood-brain barrier function in a protein kinase Cepsilon-dependent manner

Interleukin (IL)-25, a member of the IL-17 family of cytokines, is expressed in the brains of normal mice. However, the cellular source of IL-25 and its function in the brain remain to be elucidated. Here, we show that IL-25 plays an important role in preventing infiltration of the inflammatory cells into the central nervous system. Brain capillary endothelial cells (BCECs) express IL-25. However, it is down-regulated by inflammatory cytokines, including tumor necrosis factor (TNF)-alpha, IL-17, interferon-gamma, IL-1beta, and IL-6 in vitro, and is also reduced in active multiple sclerosis (MS) lesions and in the inflamed spinal cord of experimental autoimmune encephalomyelitis, an animal model of MS. Furthermore, IL-25 restores the reduced expression of tight junction proteins, occludin, junction adhesion molecule, and claudin-5, induced by TNF-alpha in BCECs and consequently repairs TNF-alpha-induced blood-brain barrier (BBB) permeability. IL-25 induces protein kinase Cepsilon (PKCepsilon) phosphorylation, and up-regulation of claudin-5 is suppressed by PKCepsilon inhibitor peptide in the IL-25-stimulated BCECs. These results suggest that IL-25 is produced by BCECs and protects against inflammatory cytokine-induced excessive BBB collapse through a PKCepsilon-dependent pathway. These novel functions of IL-25 in maintaining BBB integrity may help us understand the pathophysiology of inflammatory brain diseases such as MS.

Blockade of glutamate release from microglia attenuates experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system. Despite a variety of anti-inflammatory or immunomodulation drugs including interferon-beta are effective to reduce relapse risk, most patients have progressive neurological deterioration due to axonal degeneration. Accumulation of activated microglia is a pathological hallmark of active MS lesion. Microglia can act as not only antigen-presenting cells but also effector cells to damage other cells in the central nervous system. Especially, glutamate released by activated microglia induces excito-neurotoxicity and may contribute to neurodegeneration in MS. Gap junction is a major cell-to-cell channel and is composed of paired hemichannels on coupled cells. Recent studies showed that cells release various small molecules (including ions, ATP, and amino acids) from unpaired hemichannel of gap junction that is openly exposed to the extracellular space. We have previously revealed that activated microglia produce glutamate via glutaminase and release it through hemichannels of gap junctions. Thus, in this study, we examined whether the glutaminase inhibitor and the gap junction blocker relieved experimental autoimmune encephalomyelitis (EAE) that is an animal model of MS. Here we show that the gap junction blocker carbenoxolone (CBX) and the glutaminase inhibitor 6-diazo-5-oxo-L-norleucine (DON) decreased glutamate release from activated microglia and rescued neuronal death in a dose-dependent manner in vitro. In EAE mice, treatment with CBX or DON also attenuated EAE clinical symptoms. Thus, blockade of glutamate release from activated microglia with CBX or DON may be an effective therapeutic strategy against neurodegeneration in MS.

Interferon-gamma directly induces neurotoxicity through a neuron specific, calcium-permeable complex of IFN-gamma receptor and AMPA GluR1 receptor

Interferon-gamma (IFN-gamma) is a proinflammatory cytokine that plays a pivotal role in pathology of diseases in the central nervous system (CNS), such as multiple sclerosis. However, the direct effect of IFN-gamma on neuronal cells has yet to be elucidated. We show here that IFN-gamma directly induces neuronal dysfunction, which appears as dendritic bead formation in mouse cortical neurons and enhances glutamate neurotoxicity mediated via alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) receptors but not N-methyl-D-aspartate receptors. In the CNS, IFN-gamma receptor forms a unique, neuron-specific, calcium-permeable receptor complex with AMPA receptor subunit GluR1. Through this receptor complex, IFN-gamma phosphorylates GluR1 at serine 845 position by JAK1.2/STAT1 pathway, increases Ca(2+) influx and following nitric oxide production, and subsequently decreases ATP production, leading to the dendritic bead formation. These findings provide novel mechanisms of neuronal excitotoxicity, which may occur in both inflammatory and neurodegenerative diseases in the CNS.

Chronological changes of CD4(+) and CD8(+) T cell subsets in the experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS). The etiology of MS remains unclear, but T cells specific for myelin components, such as myelin oligodendrocyte glycoprotein (MOG), are thought to play a critical role in the onset of MS. Experimental autoimmune encephalomyelitis (EAE) has been used as an animal model of MS, and T helper type 1 (Th1) cells play an essential role for the pathogenesis of EAE through the production of Th1 cytokines, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). We examined CD4(+) and CD8(+) T cell responses in the spleen and CNS of EAE mice, generated by immunization with a peptide (35-55 amino acid residues) of MOG. The number of both CD4(+) and CD8(+) T cells and their MOG-reactivity in the CNS were associated with increasing disease severity but not those in the spleen, suggesting that the MOG-specific CD4(+) and CD8(+) T cells in the CNS are involved in the development of EAE. Polymerase chain reaction analysis suggested that both CD4(+) and CD8(+) T cells produced IFN-gamma and TNF-alpha, while CD4(+) T cells also produced interleukin-17 (IL-17), an important factor in the development of EAE. Thus, CD4(+) T cells may contribute to the induction of EAE by producing IL-17. Furthermore, CD8(+) T cells express higher levels of a suppressive cytokine, IL-10. Taking together, our data suggest that CD4(+) T cells are involved in the early phase of EAE, whereas CD8(+) T cells have a regulatory role in the later stage of EAE.

Microglia express a functional receptor for interleukin-23

Interleukin (IL)-23 plays a predominant role in the development of autoimmune diseases by inducing IL-17-producing helper T (Th17) cells. The receptor for IL-23 consists of a heterodimer composed of the IL-12 receptor beta1 (IL-12Rbeta1) and the IL-23 receptor (IL-23R), which is mainly expressed on Th17 cells. A recent study showed that macrophages express IL-23R mRNA and can be distinguished from microglia by IL-23R expression. However, in this study, we show by RT-PCR and immunocytochemistry that microglia express IL-23R and IL-12Rbeta1 mRNA and protein, respectively. Additionally, microglia expressed a functional receptor for IL-23, as IL-23 enhanced the Interferon (IFN)-gamma-induced signal transducer and activator of transcription (STAT)1 phosphorylation and chemokine production. Thus, IL-23R expression does not discriminate peripheral macrophages from microglia. Moreover, since microglia produce IL-23, it may function in an autocrine manner to recruit inflammatory cells by inducing chemokine production.

Interferon-β is neuroprotective against the toxicity induced by activated microglia

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system characterized by demyelination, T lymphocyte infiltration, and neuronal degeneration. Interferon-beta (IFN)-beta reduces symptoms of the relapsing-remitting form of MS. In this study, we investigated whether IFN-beta is neuroprotective against the toxicity induced by activated microglia in cortical neurons and microglia co-cultures. IFN-beta suppressed the production of glutamate and superoxide by activated microglia to 70% and 75% of lipopolysaccharide stimulation, respectively, and prevented microglial-induced neuronal cell death. Although IFN-beta enhanced the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and nitric oxide (NO) by activated microglia, these molecules did not directly induce neurotoxicity in cultured cortical neurons. IFN-beta did not prevent neuronal cell death induced by the peroxynitrite donor 3-morpholinosydnonimine (SIN-1) or ionotropic glutamate receptor agonists such as N-methyl-D-aspartic acid (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). These results suggest that IFN-beta may be a useful agent counteracting neurotoxicity associated with activated microglia.

The role of TNF-alpha and its receptors in the production of NGF and GDNF by astrocytes

The neurotrophic factors, nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF), are produced by astrocytes, and are induced by inflammatory stimuli including bacterial lipopolysaccharide and pro-inflammatory cytokines. In this study, we examined the regulatory mechanisms of tumor necrosis factor-alpha (TNF-alpha)-induced production of neurotrophic factors. We show here that cultured astrocytes express both TNF-alpha receptor 1 (TNFR1) and TNFR2, and that activation of these receptors by TNF-alpha promotes expression of both NGF and GDNF. In addition, we observe that not only exogenous TNF-alpha but also TNF-alpha produced by astrocytes induce NGF and GDNF production in astrocytes. These results suggest that an autocrine loop involving TNF-alpha contributes to the production of neurotrophic factors in response to inflammation.

Tumor necrosis factor-alpha induces neurotoxicity via glutamate release from hemichannels of activated microglia in an autocrine manner

Glutamate released by activated microglia induces excitoneurotoxicity and may contribute to neuronal damage in neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and multiple sclerosis. In addition, tumor necrosis factor-alpha (TNF-alpha) secreted from activated microglia may elicit neurodegeneration through caspase-dependent cascades and silencing cell survival signals. However, direct neurotoxicity of TNF-alpha is relatively weak, because TNF-alpha also increases production of neuroprotective factors. Accordingly, it is still controversial how TNF-alpha exerts neurotoxicity in neurodegenerative diseases. Here we have shown that TNF-alpha is the key cytokine that stimulates extensive microglial glutamate release in an autocrine manner by up-regulating glutaminase to cause excitoneurotoxicity. Further, we have demonstrated that the connexin 32 hemichannel of the gap junction is another main source of glutamate release from microglia besides glutamate transporters. Although pharmacological blockade of glutamate receptors is a promising therapeutic candidate for neurodegenerative diseases, the associated perturbation of physiological glutamate signals has severe adverse side effects. The unique mechanism of microglial glutamate release that we describe here is another potential therapeutic target. We rescued neuronal cell death in vitro by using a glutaminase inhibitor or hemichannel blockers to diminish microglial glutamate release without perturbing the physiological glutamate level. These drugs may give us a new therapeutic strategy against neurodegenerative diseases with minimum adverse side effects.

Production of IL-27 and other IL-12 family cytokines by microglia and their subpopulations

Production of IL-27 and other IL-12 family cytokines by murine microglia were examined using RT-PCR, real-time RT-PCR and Western blot analysis. We show for the first time that murine microglia produce IL-27 in response to lipopolysaccharide (LPS) and/or interferon-gamma. Primary microglia, but not their cell lines, also induce IL-12 and IL-23 upon above stimulation. Therefore, microglia may play a critical role initiating Th1 responses via producing IL-12 family cytokines in the brain.

Histamine: its novel role as an endogenous regulator of Con A-dependent T cell proliferation

OBJECTIVE AND DESIGN

The roles of histamine formed by the macrophage - T lymphocyte system were evaluated in the regulation of lymphocyte proliferation using mice lacking histamine receptors.

METHODS

Mice deficient in histamine type 1 (H1R), type 2 (H2R) or both receptors were employed to estimate possible intervention of the receptors in the histamine-dependent lymphocyte proliferation.

RESULTS

Histamine was produced de novo by spleen cells. Con A-dependent T cell proliferation decreased when histamine produced in the culture was degraded by the addition of histaminase. The H2R-deficient mice also showed a significant decrease in the Con A-dependent T cell proliferation, whereas it was not modulated in the H1R-deleted mice. Consistent with the reduction in T cell proliferation, there was a significant down-regulation of the production of IL-2, a T cell growth factor, in the H2R-deficient mice. Con A-dependent IL-2 synthesis was abrogated by the addition of histaminase.

CONCLUSION

Con A-dependent T cell proliferation is (up)regulated by histamine produced de novo through the H2R, suggesting that histamine is a newly found regulator of T cell proliferation.

Regulation of Con A ? dependent cytokine production from CD4+ and CD8+ T lymphocytes by autosecretion of histamine

OBJECTIVES

Previously we have shown that both CD4+ T cells and CD8+ T cells produce histamine when activated with Con A. The aim of this study was to examine whether cytokine production by these cells is regulated by autosecretion of histamine.

MATERIALS

CD4+ and CD8+ T cells were separated from spleen cells of C57BL/6 mice and mice lacking the H1 receptor (H1R) or H2R, using anti-CD4+- and anti-CD8+-coupled magnetic beads, respectively.

RESULTS

Depletion of the H1R resulted in decreases in the release of IL-2 and IL-10 from both CD4+ and CD8+ cells and increases in the release of IL-4 from CD4+ T cells and IFN-gamma from CD8+ cells. Mice lacking the H2R showed up-regulation of IFN-gamma secretion from CD8+ cells and of IL-4 from CD4+ and CD8+ T cells. Release of IL-2 and IL-10 from CD4+ as well as CD8+ cells was down-regulated in these mice. Both CD4+ and CD8+ T cell fractions synthesized histamine, which was enhanced in the H1R-deficient CD8+ T cells. Treatment of the cells with alpha-fluoromethyl-histidine, a specific inhibitor of HDC, or histaminase increased IFN-gamma from CD8+ cells, whereas it had no appreciable effect on IL-4 secretion from CD4+ cells.

CONCLUSION

These results suggest that cytokine production by CD4+ and CD8+ T lymphocytes is regulated by autosecretion of histamine.

Expression of three cell proliferation-associated antigens, DNA polymerase alpha, Ki-67 antigen and transferrin receptor in nodal and cutaneous T-cell lymphomas

We studied the expression of three cell proliferation-associated antigens: DNA polymerase alpha, Ki-67 antigen, and transferrin receptor, in 35 T-cell lymphomas of nodal origin (T-NL) and 40 cutaneous T-cell lymphomas (CTCL). Immunohistochemical staining was carried out on frozen tissue sections of these specimens using three monoclonal antibodies, DAKO-PC, CL22-2-42B (DNA polymerase alpha), and OKT9. The proportion of cells positive for CL22-2-42B, DAKO-PC, or OKT9 among all tumor cells was correlated with four histologic subtypes: malignant lymphoma (ML), diffuse, small; mixed; large; and large cell immunoblastic in both T-NL and CTCL. A strong correlation was noted between positivity for CL22-2-42B and that for DAKO-PC or OKT9. On the other hand, no difference in the expression of these three antigens was noted between T-NL and CTCL in the high, intermediate or low grade-malignancy group. In CTCL as well as in T-NL, cells positive for CL22-2-42B, DAKO-PC or OKT9 were significantly more numerous in the high-grade group than the intermediate-grade group, and in the intermediate-grade group than the low-grade group. Furthermore, a significant correlation between survival period and the number of CL22-2-42B-positive cells was noted when the T cell malignancies, CTCL and T-NL were considered (t value = 2.015, p less than 0.05). Thus, the expression of DNA-polymerase alpha, Ki-67 antigen or OKT9 seems to well reflect the biological behavior and/or clinical prognosis of T-cell lymphoma.

In vitro and in vivo release of soluble erbB-2 protein from human carcinoma cells

An enzyme-linked immunosorbent assay (ELISA) was developed to measure soluble erbB-2 protein in culture supernatants of various human cell lines and sera of patients suffering from recurrent breast carcinoma. Soluble erbB-2 protein was demonstrated in culture supernatants of cell lines that expressed high levels of erbB-2 protein as shown by western blot analysis of cell lysates. Increased levels of the protein, 40- to 190-fold higher than in healthy controls, were demonstrated in sera of 3 out of 12 patients with breast carcinomas. On immunohistological study of tumor tissues from 9 patients, high immune reaction with the anti-erbB-2 protein antibody was observed in 2 cases. These were two of the three patients who had elevated levels of erbB-2 protein in serum (a sample was not available from the third patient). These results raise the possibility that soluble erbB-2 protein level in serum can be used as an indicator for spread of carcinomas that overexpress erbB-2 protein.