John J. Bright

Curcumin Inhibits Experimental Allergic Encephalomyelitis by Blocking IL-12 Signaling Through Janus Kinase-STAT Pathway in T Lymphocytes

Experimental allergic encephalomyelitis (EAE) is a CD4+ Th1 cell-mediated inflammatory demyelinating autoimmune disease of the CNS that serves as an animal model for multiple sclerosis (MS). IL-12 is a proinflammatory cytokine that plays a crucial role in the induction of neural Ag-specific Th1 differentiation and pathogenesis of CNS demyelination in EAE and MS. Curcumin (1,7-Bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is a naturally occurring polyphenolic phytochemical isolated from the rhizome of the medicinal plant Curcuma longa. It has profound anti-inflammatory activity and been traditionally used to treat inflammatory disorders. In this study we have examined the effect and mechanism of action of curcumin on the pathogenesis of CNS demyelination in EAE. In vivo treatment of SJL/J mice with curcumin significantly reduced the duration and clinical severity of active immunization and adoptive transfer EAE. Curcumin inhibited EAE in association with a decrease in IL-12 production from macrophage/microglial cells and differentiation of neural Ag-specific Th1 cells. In vitro treatment of activated T cells with curcumin inhibited IL-12-induced tyrosine phosphorylation of Janus kinase 2, tyrosine kinase 2, and STAT3 and STAT4 transcription factors. The inhibition of Janus kinase-STAT pathway by curcumin resulted in a decrease in IL-12-induced T cell proliferation and Th1 differentiation. These findings highlight the fact that curcumin inhibits EAE by blocking IL-12 signaling in T cells and suggest its use in the treatment of MS and other Th1 cell-mediated inflammatory diseases.

Peroxisome proliferator-activated receptor-gamma agonists inhibit experimental allergic encephalomyelitis by blocking IL-12 production, IL-12 signaling and Th1 differentiation.

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear receptor transcription factor that regulates adipocyte differentiation and glucose homeostasis. PPARγ agonists are potent therapeutic agents for the treatment of type 2 diabetes and obesity. PPARγ agonists also prevent inflammation in animal models, suggesting their use for the treatment of human inflammatory diseases. Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated inflammatory demyelinating disease model of multiple sclerosis (MS) and IL-12 plays a crucial role in the pathogenesis of EAE and MS. In this study we have examined the effect of PPARγ agonists on the pathogenesis of EAE. In vivo treatment of SJL/J mice with PPARγ agonists, 15-deoxyΔ12,14 prostaglandin J2 or Ciglitazone, decreased the duration and clinical severity of active immunization and adoptive transfer models of EAE. PPARγ agonists inhibited EAE in association with a decrease in IL-12 production and differentiation of neural antigen-specific Th1 cells. In vitro treatment of activated T cells with PPARγ agonists inhibited IL-12-induced activation of JAK-STAT signaling pathway and Th1 differentiation. These findings highlight the fact that PPARγ agonists regulate central nervous system inflammation and demyelination by inhibiting IL-12 production, IL-12 signaling and Th1 differentiation in EAE.

1,25 dihydroxyvitamin‐D3 modulates JAK–STAT pathway in IL‐12/IFNγ axis leading to Th1 response in experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a Th1 cell‐mediated autoimmune disease model of multiple sclerosis (MS). Vitamin D deficiency is commonly observed in MS patients and vitamin D supplements reduce the clinical symptoms of EAE and MS. Earlier studies have shown that in vivo treatment with vitamin D analogs ameliorates EAE in association with the inhibition of IL‐12 production and Th1 differentiation. The mechanisms in the regulation of Th1 response by vitamin D in EAE/MS are, however, not known. We show that in vivo treatment of C57BL/6 and SJL/J mice (i.p.) with 100 ng of 1,25 dihydroxyvitamin D3, on every other day from Day 0–30, ameliorates EAE in association with the inhibition of IL‐12 production and neural antigen‐specific Th1 response. In vitro treatment with 1,25(OH)2D3 inhibited IFNγ‐induced tyrosine phosphorylation of STAT1, without affecting JAK2, in EOC‐20 microglial cells. Treatment of activated T cells with 1,25(OH)2D3 also inhibited the IL‐12‐induced tyrosine phosphorylation of JAK2, TYK2, STAT3, and STAT4 in association with a decrease in T cell proliferation in vitro. These findings highlight the fact that vitamin D modulates JAK‐STAT signaling pathway in IL‐12/IFNγ axis leading to Th1 differentiation and further suggest its use in the treatment of MS and other Th1 cell‐mediated autoimmune diseases.

Peroxisome Proliferator-Activated Receptor-γ-Deficient Heterozygous Mice Develop an Exacerbated Neural Antigen-Induced Th1 Response and Experimental Allergic Encephalomyelitis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor transcription factor that regulates cell growth, differentiation, and homeostasis. PPARγ agonists are potent therapeutic agents for type 2 diabetes, obesity, and inflammation. Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated inflammatory demyelinating autoimmune disease model of multiple sclerosis. We have shown recently that PPARγ agonists inhibit EAE by blocking IL-12 production, IL-12 signaling, and neural Ag-induced Th1 differentiation. In this study, we show that the PPARγ-deficient heterozygous mice develop an exacerbated EAE with prolonged clinical symptoms than the wild-type littermates, following immunization with myelin oligodendrocyte glycoprotein (MOG) p35–55 peptide. The exacerbation of EAE in PPARγ+/− mice associates with an increased expansion of CD4+ and CD8+ T cells and expression of CD40 and MHC class II molecules in response to MOGp35–55 Ag. The PPARγ+/− mice also showed an increase in T cell proliferation and Th1 response to MOGp35–55 Ag than the wild-type littermates. These findings suggest that PPARγ be a critical physiological regulator of CNS inflammation and demyelination in EAE and perhaps multiple sclerosis and other Th1 cell-mediated autoimmune diseases.

EXPRESSION OF IL-12 IN CNS AND LYMPHOID ORGANS OF MICE WITH EXPERIMENTAL ALLERGIC ENCEPHALITIS

EAE is a Th1 cell-mediated inflammatory autoimmune demyelinating disease of the central nervous system. IL-12 is a 70 kd heterodimeric cytokine, capable of regulating a wide range of immune functions. In view of its crucial role in the development of Th1 immune responses, we studied the expression of IL-12 p40 in the CNS and lymphoid organs of mice with EAE. RT-PCR analysis showed an increase in the expression of IL-12 p40 in brain and spinal cord during the acute paralytic phase of EAE and that decreased upon clinical recovery. The expression of p40 mRNA was also increased in spleen, lymph node and liver along with an elevated levels of circulating serum IL-12 during the height of disease. In vivo administration of rIL-12 increased the proliferative response and IFN-gamma production of MBP sensitized T cells and that was decreased following treatment with anti-IL-12 antibody. The expression of IL-12 in the target and lymphoid organs of animals with EAE, the induction of a Th1 type immune response following immunization with neuronal antigens and the inhibition of clinical disease upon treatment with anti-IL-12 antibody, suggest the crucial role of IL-12 in the pathogenesis of EAE.

PPAR Regulation of Inflammatory Signaling in CNS Diseases

Central nervous system (CNS) is an immune privileged site, nevertheless inflammation associates with many CNS diseases. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that regulate immune and inflammatory responses. Specific ligands for PPARα, γ, and δ isoforms have proven effective in the animal models of multiple sclerosis (MS), Alzheimers disease, Parkinsons disease, and trauma/stroke, suggesting their use in the treatment of neuroinflammatory diseases. The activation of NF-κB and Jak-Stat signaling pathways and secretion of inflammatory cytokines are critical in the pathogenesis of CNS diseases. Interestingly, PPAR agonists mitigate CNS disease by modulating inflammatory signaling network in immune cells. In this manuscript, we review the current knowledge on how PPARs regulate neuroinflammatory signaling networks in CNS diseases.

COX-2 Inhibitors Modulate IL-12 Signaling Through JAK-STAT Pathway Leading to Th1 Response in Experimental Allergic Encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). IL-12 plays a crucial role in the pathogenesis of EAE/MS and inhibition of IL-12 production or IL-12 signaling was effective in preventing EAE. Cyclooxygenase (COX-2) is a key enzyme promoting inflammation in rheumatoid arthritis and tumor induced angiogenesis. Recent studies have shown that COX-2 inhibitors prevent EAE, however, their mechanism of action is not fully understood. In this study, we show that in vivo treatment (i.p.) with 100 μg COX-2 selective inhibitors (LM01, LM08, LM11, and NS398), on every other day from day 0 to 30, significantly reduced the incidence and severity of EAE in SJL/J and C57BL/6 mice. Further analyses showed that the COX-2 inhibitors reduced neural antigen-induced IL-12 production, T cell proliferation and Th1 differentiation ex vivo and in vitro. The COX-2 inhibitors also decreased IL-12-induced T cell responses through blocking tyrosine phosphorylation of JAK2, TYK2, STAT3, and STAT4 proteins in T cells. These results demonstrate that COX-2 inhibitors ameliorate EAE in association with the modulation of IL-12 signaling through JAK-STAT pathway leading to Th1 differentiation and suggest their use in the treatment of MS and other Th1 cell-mediated autoimmune diseases.

PPARγ antagonists exacerbate neural antigen-specific Th1 response and experimental allergic encephalomyelitis

Abstract Peroxisome proliferator-activated receptor-gamma is a nuclear receptor transcription factor that regulates cell growth, differentiation and homeostasis. PPARγ agonists have been used in the treatment of obesity, diabetes, cancer and inflammation. We and others have shown recently that PPARγ agonists ameliorate experimental allergic encephalomyelitis (EAE), a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). We have further shown that PPARγ agonists inhibit EAE through blocking IL-12 signaling leading to Th1 differentiation and the PPARγ-deficient heterozygous mice (PPARγ+/−) develop an exacerbated EAE. In this study, we show that in vivo treatment (i.p.) with 100 μg PPARγ antagonists, Bisphenol A diglycidyl ether (BADGE) or 2-Chloro-5-nitro-N-(4-pyridyl)benzamide (T0070907), on every other day from day 0 to 30, increased the severity and duration of EAE in C57BL/6 wild-type and PPARγ+/− mice. The exacerbation of EAE by PPARγ antagonists associates with an augmented neural antigen-induced T cell proliferation, IFNγ production or Th1 differentiation. These results further suggest that PPARγ is a critical physiological regulator of CNS inflammation and demyelination in EAE.

Successful treatment of established relapsing experimental autoimmune encephalomyelitis in mice with a monoclonal natural autoantibody.

We postulated that humoral autoimmunity can play a beneficial role in CNS demyelinating diseases such as multiple sclerosis. We previously demonstrated that monoclonal natural autoantibody SCH94.03 suppresses CNS inflammation and promotes remyelination in a virus-induced model of chronic progressive multiple sclerosis. To further investigate the relationship between natural autoimmunity and CNS demyelination, we examined the effect of SCH94.03 treatment on clinical relapses and pathological disease in SJL/J mice with established adoptive-transfer relapsing experimental autoimmune encephalomyelitis. Treatment with SCH94.03 after recovery from the initial episode of clinical disease reduced relapse rates by half, prolonged relapse onset by 6 days and reduced spinal cord demyelination and meningeal inflammation by 40%. These results are consistent with the hypothesized immunomodulatory function of natural autoantibodies, and are the first direct demonstration that natural humoral autoimmunity can be beneficial in an autoimmune T-cell-mediated CNS demyelinating disease.

Stat4 Isoforms Differentially Regulate Inflammation and Demyelination in Experimental Allergic Encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated autoimmune disease model of multiple sclerosis. Signal transducer and activator of transcription 4 (Stat4) is a transcription factor activated by IL-12 and IL-23, two cytokines known to play important roles in the pathogenesis of EAE by inducing T cells to secrete IFN-γ and IL-17, respectively. We and others have previously shown that therapeutic intervention or targeted disruption of Stat4 was effective in ameliorating EAE. Recently, a splice variant of Stat4 termed Stat4β has been characterized that lacks 44 amino acids at the C terminus of the full-length Stat4α. In this study we examined whether T cells expressing either isoform could affect the pathogenesis of EAE. We found that transgenic mice expressing Stat4β on a Stat4-deficient background develop an exacerbated EAE compared with wild-type mice following immunization with myelin oligodendrocyte glycoprotein peptide 35–55, while Stat4α transgenic mice have greatly attenuated disease. The differential development of EAE in transgenic mice correlates with increased IFN-γ and IL-17 in Stat4β-expressing cells in situ, contrasting increased IL-10 production by Stat4α-expressing cells. This study demonstrates that Stat4 isoforms differentially regulate inflammatory cytokines in association with distinct effects on the onset and severity of EAE.