Defects of immunoregulatory mechanisms in myasthenia gravis: role of IL-17

Non-coding RNA and its network in the pathogenesis of Myasthenia Gravis

Myasthenia Gravis (MG) is a chronic autoimmune disease that primarily affects the neuromuscular junction, leading to muscle weakness in patients with this condition. Previous studies have identified several dysfunctions in thymus and peripheral blood mononuclear cells (PBMCs), such as the formation of ectopic germinal centers in the thymus and an imbalance of peripheral T helper cells and regulatory T cells, that contribute to the initiation and development of MG. Recent evidences suggest that noncoding RNA, including miRNA, lncRNA and circRNA may play a significant role in MG progression. Additionally, the network between these noncoding RNAs, such as the competing endogenous RNA regulatory network, has been found to be involved in MG progression. In this review, we summarized the roles of miRNA, lncRNA, and circRNA, highlighted their potential application as biomarkers in diagnosing MG, and discussed their potential regulatory networks in the abnormal thymus and PBMCs during MG development.

Features and roles of T helper 22 cells in immunological diseases and malignancies

T helper 22 (Th22) cell populations are a newly identified subset of CD4+  T cells that primarily mediate biological effects on the epithelial barrier through interleukin (IL)-22. Although, new studies showed that both Th22 and IL-22 are closely associated with the pathogenesis of inflammatory, autoimmune and allergic disease as well as malignancies. In this review, we aim to describe the development and characteristics of Th22 cells as well as their roles in the immunopathogenesis of immune-related disorders and cancer.

Quantitative features and clinical significance of two subpopulations of AChR-specific CD4+ T cells in patients with myasthenia gravis

Acetylcholine receptor (AChR)-specific CD4+ T cells play a driving role in myasthenia gravis (MG) by regulating the production of autoantibodies. However, the quantitative features of AChR-specific T cells and their clinical significance in MG are unclear. In this study, we adopted standard and cultured enzyme-linked immunosorbent spot (ELISPOT) assays to quantify subpopulations of AChR-specific CD4+ T cells in MG patients, and evaluate their correlation with clinical characteristics. The results showed that Th1- and Th17-AChR-specific CD4+ T cells were detectable by standard and cultured ELISPOT assay respectively, with higher levels observed in MG patients comparing with healthy controls. The number of Th17-AChR-specific CD4+ T cells was positively correlated with anti-AChR antibody titer and quantitative MG score and may have latent capacity to reflect responses to immunosuppressants. These results highlight the differences in quantitative features of AChR-specific CD4+ T cells and imply Th17-AChR-specific CD4+ T cells can serve as a biomarker in MG.

Effect of Grilled Nux Vomica on Differential RNA Expression Profile of Gastrocnemius Muscle and Toll‑Like Receptor 4 (TLR-4)/Nuclear Factor kappa B (NF-κB) Signaling in Experimental Autoimmune Myasthenia Gravis Rats

BACKGROUND Myasthenia gravis (MG) is a progressive autoimmune disorder caused by the production of antibodies directed against acetylcholine receptors (AChRs), resulting in muscle weakness and fatigue. This study aimed to explore the effect and mechanism of grilled nux vomica (GNV) in experimental autoimmune myasthenia gravis (EAMG) rats. MATERIAL AND METHODS Rat 97-116 peptides were used to mediate disease in the EAMG model in SPF female Lewis rats. The treatment groups received grilled nux vomica (75 mg/kg, 150 mg/kg, and 225 mg/kg). The autoantibody and inflammatory cytokines levels were measured by enzyme-linked immunosorbent assay (ELISA). RNA profiling was performed on high-dose and model group rats. Profiling results and TLR-4/NF-kappaB signaling were validated by q-PCR and Western blot analysis. RESULTS The results showed that GNV could attenuate the symptoms of EAMG rats. There was a decreased level of AChR-ab, IFN-γ, TNF-alpha, IL-2, IL-4, and IL-17 levels, and an increased level of TGF-ß1. In total, 235 differentially expressed genes (DEGs), consisting of 175 upregulated DEGs and 60 downregulated DEGs, were identified. Functional annotation demonstrated that DEGs were largely associated with leukocyte cell-cell adhesion, NF-kappa B signaling pathway, muscle contraction, and cardiac muscle contraction pathway. Rac2, Itgb2, Lcp2, Myl3, and Tnni1 were considered as hub genes with a higher degree value in the protein-protein interaction (PPI) network. The q-PCR and Western blot results of hub genes were consistent with RNA profiles. GNV treatment also significantly reduced the TLR-4 and NF-kappaB p65 protein expression in EAMG rats. CONCLUSIONS These results indicate that grilled nux vomica ameliorates EAMG by depressing the TLR-4/NF-kappaB signaling pathway, and hub genes may serve as potential targets for MG treatment.

Inhibition of the transcription factor ROR-γ reduces pathogenic Th17 cells in acetylcholine receptor antibody positive myasthenia gravis

IL-17 producing CD4 T cells (Th17) cells increase significantly with disease severity in myasthenia gravis (MG) patients. To suppress the generation of Th17 cells, we examined the effect of inhibiting retinoic acid receptor-related-orphan-receptor-C (RORγ), a Th17-specific transcription factor critical for differentiation. RORγ inhibition profoundly reduced Th17 cell frequencies, including IFN-γ and IL-17 co-producing pathogenic Th17 cells. Other T helper subsets were not affected. In parallel, CD8 T cell subsets producing IL-17 and IL-17/IFN-γ were increased in MG patients and inhibited by the RORγ inhibitor. These findings provide rationale for exploration of targeted Th17 therapies, including ROR-γ inhibitors, to treat MG patients.

Inhibition of ROCK activity regulates the balance of Th1, Th17 and Treg cells in myasthenia gravis

Aberrant ROCK activation has been found in patients with several autoimmune diseases, but the role of ROCK in myasthenia gravis (MG) has not yet been clearly investigated. Here, we demonstrated that ROCK activity was significantly higher in peripheral blood mononuclear cells (PBMCs) from MG patients. ROCK inhibitor Fasudil down-regulated the proportions of Th1 and Th17 cells in PBMCs of MG patients in vitro. Intraperitoneal injection of Fasudil ameliorated the severity of experimental autoimmune myasthenia gravis (EAMG) rats and restored the balance of Th1/Th2/Th17/Treg subsets. Furthermore, Fasudil inhibited the proliferation of antigen-specific Th1 and Th17 cells, and inhibited CD4 + T cells differentiated into Th1 and Th17 through decreasing phosphorylated Stat1 and Stat3, but promoted Treg cell differentiation through increasing phosphorylated Stat5. We conclude that dysregulated ROCK activity may be involved in the pathogenic immune response of MG and inhibition of ROCK activity might serve as a novel treatment strategy for MG.

An imbalance between regulatory T cells and T helper 17 cells in acetylcholine receptor-positive myasthenia gravis patients

A chronic autoimmune disease, myasthenia gravis (MG) is characterized in 85% of patients by antibodies directed against the acetylcholine receptor (AChR) located at the neuromuscular junction. The functional and effective balance between regulatory T cells (T_reg cells) and effector T cells (T_eff cells) is lost in the hyperplastic thymus of MG patients with antibodies specific for the AChR (AChR⁺ MG patients). The objective of this review is to describe how T_reg cells and inflammatory T cells participate in this imbalance and contribute to induce a chronic inflammatory state in the MG thymus. We discuss the origins and characteristics of T_reg cells and their reported dysfunctions in AChR⁺ MG patients. We also review the inflammatory condition observed in MG thymus, including overexpression of interleukin (IL)-1β, IL-6, and IL-23, cytokines that promote the differentiation of T helper 17 (T_H 17) cells and the expression of IL-17. We summarize the preclinical models used to determine the implication of expression of cytokines, such as IL-6, IL-12 (IL-23 subunit), IL-17, and interferon γ to the development of experimental autoimmune MG. Finally, we suggest that biological agents, such as humanized monoclonal antibodies that target the IL-23/T_H 17 pathway, should be investigated in the context of MG, as they have proven efficiency in other autoimmune diseases.

Balance between Estrogens and Proinflammatory Cytokines Regulates Chemokine Production Involved in Thymic Germinal Center Formation

The early-onset form of Myasthenia Gravis (MG) is prevalent in women and associates with ectopic germinal centers (GCs) development and inflammation in the thymus. we aimed to investigate the contribution of estrogens in the molecular processes involved in thymic GCs formation. We examined expression of genes involved in anti-acetylcholine receptor (AChR) response in MG, MHC class II and α-AChR subunit as well as chemokines involved in GC development (CXCL13, CCL21and CXCL12). In resting conditions, estrogens have strong regulatory effects on thymic epithelial cells (TECs), inducing a decreased protein expression of the above molecules. In knockout mouse models for estrogen receptor or aromatase, we observed that perturbation in estrogen transduction pathway altered MHC Class II, α-AChR, and CXCL13 expression. However, in inflammatory conditions, estrogen effects were partially overwhelmed by pro-inflammatory cytokines. Interestingly, estrogens were able to control production of type I interferon and therefore play dual roles during inflammatory events. In conclusion, we showed that estrogens inhibited expression of α-AChR and HLA-DR in TECs, suggesting that estrogens may alter the tolerization process and favor environment for an autoimmune response. By contrast, under inflammatory conditions, estrogen effects depend upon strength of the partner molecules with which it is confronted to.

Expression of receptor for advanced glycation end-products (RAGE) in thymus from myasthenia patients

OBJECTIVES

The receptor for advanced glycation end-products (RAGE) is a membranous immunoglobulin involved in the pathogenesis of numerous autoimmune diseases and tumors. The aim of this study was to investigate the possible involvement of RAGE in the pathogenesis of myasthenia gravis.

MATERIAL AND METHODS

This prospective study included 41 cases of myasthenia gravis treated at our institution between 2010 and 2015. There were 18 men and 23 women, with an average age of 36.44±14.47 years. The majority of patients (24.4%) were classified as IIb, according to MGFA scoring, and 21 of them required corticosteroid and/or immunosuppressive treatment. Assessment of RAGE in thymus specimens was done by immunohistochemistry using RAGE antibody (C-term). RAGE expression was assessed according to various clinical, paraclinical and pathological parameters.

RESULTS

Histopathological studies found 18 thymomas, 17 hyperplasias and six other types of pathology. Expression of RAGE was negative/weak in 19 cases and moderate/strong in 22 cases. It was more important in thymoma type B2 (P<0.001) and when the duration of myasthenia was short (P=0.04), and was not significantly related to either myasthenia clinical severity or preoperative treatment.

CONCLUSION

Our results suggest that the RAGE pathway is involved in myasthenia gravis pathophysiology, especially at disease onset, and in forms with thymomas. Further studies would be indispensable to explore other aspects of this signaling pathway, especially the potential role of different ligands and soluble forms of RAGE.

Profile of upregulated inflammatory proteins in sera of Myasthenia Gravis patients

This study describes specific patterns of elevated inflammatory proteins in clinical subtypes of myasthenia gravis (MG) patients. MG is a chronic, autoimmune neuromuscular disease with antibodies most commonly targeting the acetylcholine receptors (AChRab), which causes fluctuating skeletal muscle fatigue. MG pathophysiology includes a strong component of inflammation, and a large proportion of patients with early onset MG additionally present thymus hyperplasia. Due to the fluctuating nature and heterogeneity of the disease, there is a great need for objective biomarkers as well as novel potential inflammatory targets. We examined the sera of 45 MG patients (40 AChRab seropositive and 5 AChRab seronegative), investigating 92 proteins associated with inflammation. Eleven of the analysed proteins were significantly elevated compared to healthy controls, out of which the three most significant were: matrix metalloproteinase 10 (MMP-10; p = 0.0004), transforming growth factor alpha (TGF-α; p = 0.0017) and extracellular newly identified receptor for advanced glycation end-products binding protein (EN-RAGE) (also known as protein S100-A12; p = 0.0054). Further, levels of MMP-10, C-X-C motif ligand 1 (CXCL1) and brain derived neurotrophic factor (BDNF) differed between early and late onset MG. These novel targets provide valuable additional insight into the systemic inflammatory response in MG.

Astilbin ameliorates experimental autoimmune myasthenia gravis by decreased Th17 cytokines and up-regulated T regulatory cells

Astilbin, a major bioactive compound extracted from Rhizoma smilacis glabrae (RSG), has been reported to possess immunosuppressive properties. Our study first evaluated the effect of astilbin on experimental autoimmune myasthenia gravis (EAMG) in Lewis rats. The results showed that astilbin could attenuate the severity of EAMG by decreasing antigen-specific autoantibodies with up-regulation of regulatory T cells and down-regulation of Th17 cells. In addition to, astilbin also reduced the efficiency of the antigen presenting cells on which the expression of MHC class II decreased. These results suggest that astilbin might be a candidate drug for immunoregulation of EAMG, and provide us new treatment ideas for human myasthenia gravis (MG).

Elevated plasma interleukin-17A in a subgroup of Myasthenia Gravis patients

To better define the role of IL-17A in myasthenia gravis (MG), we assessed plasma concentrations in 69 adult patients with MG prior to initiation of immunosuppression and monitored their clinical course for the subsequent 2years with quantitative MG scores (QMGS) and Osserman classification. IL-17A was higher among patients than healthy control subjects. Early-onset women without thymoma had greater elevations of IL-17A. Logistic regression analysis indicated that the absence of thymoma rather than women gender or early-onset was the significant determinant associated with IL-17A elevation. Elevated IL-17A levels were associated with more severe MG. In summary, IL-17A has role in the pathogenesis of a subgroup of patients with early-onset women with MG with greater disease severity who are most likely to have thymic hyperplasia. This subgroup may be a target for IL-17 treatments, which are under development.

Low and high doses of ursolic acid ameliorate experimental autoimmune myasthenia gravis through different pathways

Myasthenia gravis (MG) is an autoimmune disease characterized by fatigable muscle weakness. Ursolic acid (UA) is a pentacyclic triterpenoid with anti-inflammatory and immunomodulatory properties, especially inhibiting IL-17. We found that UA ameliorated the symptoms of experimental autoimmune myasthenia gravis (EAMG), a rat model of MG. Although both the low and high doses of UA shifted Th17 to Th2 cytokines, other mechanisms were dose dependent. The low dose enhanced Fas-mediated apoptosis, whereas the high dose up-regulated Treg cells and reduced the concentrations of IgG2b antibodies. These findings suggest a new strategy to treat EAMG and even human MG.

VAV1 and BAFF, via NFκB pathway, are genetic risk factors for myasthenia gravis

Objective

To identify novel genetic loci that predispose to early-onset myasthenia gravis (EOMG) applying a two-stage association study, exploration, and replication strategy.

Methods

Thirty-four loci and one confirmation loci, human leukocyte antigen (HLA)-DRA, were selected as candidate genes by team members of groups involved in different research aspects of MG. In the exploration step, these candidate genes were genotyped in 384 EOMG and 384 matched controls and significant difference in allele frequency were found in eight genes. In the replication step, eight candidate genes and one confirmation loci were genotyped in 1177 EOMG patients and 814 controls, from nine European centres.

Results

Allele frequency differences were found in four novel loci: CD86, AKAP12, VAV1, B-cell activating factor (BAFF), and tumor necrosis factor-alpha (TNF-α), and these differences were consistent in all nine cohorts. Haplotype trend test supported the differences in allele frequencies between cases and controls. In addition, allele frequency difference in female versus male patients at HLA-DRA and TNF-α loci were observed.

Interpretation

The genetic associations to EOMG outside the HLA complex are novel and of interest as VAV1 is a key signal transducer essential for T- and B-cell activation, and BAFF is a cytokine that plays important roles in the proliferation and differentiation of B-cells. Moreover, we noted striking epistasis between the predisposing VAV1 and BAFF haplotypes; they conferred a greater risk in combination than alone. These, and CD86, share the same signaling pathway, namely nuclear factor-kappaB (NFκB), thus implicating dysregulation of proinflammatory signaling in predisposition to EOMG.

Innate immunity in myasthenia gravis thymus: pathogenic effects of Toll-like receptor 4 signaling on autoimmunity

The thymus is the main site of immune sensitization to AChR in myasthenia gravis (MG). In our previous studies we demonstrated that Toll-like receptor (TLR) 4 is over-expressed in MG thymuses, suggesting its involvement in altering the thymic microenvironment and favoring autosensitization and autoimmunity maintenance processes, via an effect on local chemokine/cytokine network. Here, we investigated whether TLR4 signaling may favor abnormal cell recruitment in MG thymus via CCL17 and CCL22, two chemokines known to dictate immune cell trafficking in inflamed organs by binding CCR4. We also investigated whether TLR4 activation may contribute to immunodysregulation, via the production of Th17-related cytokines, known to alter effector T cell (Teff)/regulatory T cell (Treg) balance. We found that CCL17, CCL22 and CCR4 were expressed at higher levels in MG compared to normal thymuses. The two chemokines were mainly detected around medullary Hassall's corpuscles (HCs), co-localizing with TLR4(+) thymic epithelial cells (TECs) and CCR4(+) dendritic cells (DCs), that were present in higher number in MG thymuses compared to controls. TLR4 stimulation in MG TECs increased CCL17 and CCL22 expression and induced the production of Th17-related cytokines. Then, to study the effect of TLR4-stimulated TECs on immune cell interactions and Teff activation, we generated an in-vitro imaging model by co-culturing CD4(+) Th1/Th17 AChR-specific T cells, naïve CD4(+)CD25(+) Tregs, DCs and TECs from Lewis rats. We observed that TLR4 stimulation led to a more pronounced Teff activatory status, suggesting that TLR4 signaling in MG thymic milieu may affect cell-to-cell interactions, favoring autoreactive T-cell activation. Altogether our findings suggest a role for TLR4 signaling in driving DC recruitment in MG thymus via CCL17 and CCL22, and in generating an inflammatory response that might compromise Treg function, favoring autoreactive T-cell pathogenic responses.

Myasthenia gravis: a comprehensive review of immune dysregulation and etiological mechanisms

Autoimmune myasthenia gravis (MG) is characterized by muscle weakness caused by antibodies directed against proteins of the neuromuscular junction. The main antigenic target is the acetylcholine receptor (AChR), but the muscle Specific Kinase (MuSK) and the low-density lipoprotein receptor-related protein (LRP4) are also targets. This review summarizes the clinical and biological data available for different subgroups of patients, who are classified according to antigenic target, age of onset, and observed thymic abnormalities, such as follicular hyperplasia or thymoma. Here, we analyze in detail the role of the thymus in the physiopathology of MG and propose an explanation for the development of the thymic follicular hyperplasia that is commonly observed in young female patients with anti-AChR antibodies. The influence of the pro-inflammatory environment is discussed, particularly the role of TNF-α and Th17-related cytokines, which could explain the escape of thymic T cells from regulation and the chronic inflammation in the MG thymus. Together with this immune dysregulation, active angiogenic processes and the upregulation of chemokines could promote thymic follicular hyperplasia. MG is a multifactorial disease, and we review the etiological mechanisms that could lead to its onset. Recent global genetic analyses have highlighted potential susceptibility genes. In addition, miRNAs, which play a crucial role in immune function, have been implicated in MG by recent studies. We also discuss the role of sex hormones and the influence of environmental factors, such as the viral hypothesis. This hypothesis is supported by reports that type I interferon and molecules mimicking viral infection can induce thymic changes similar to those observed in MG patients with anti-AChR antibodies.

Circulating miRNAs in myasthenia gravis: miR-150-5p as a new potential biomarker

Objective

Myasthenia gravis (MG) is a chronic autoimmune disorder where autoantibodies target the nicotinic acetylcholine receptors (AChR+) in about 85% of cases, in which the thymus is considered to play a pathogenic role. As there are no reliable biomarkers to monitor disease status in MG, we analyzed circulating miRNAs in sera of MG patients to find disease-specific miRNAs.

Methods

Overall, 168 miRNAs were analyzed in serum samples from four AChR+ MG patients and four healthy controls using Exiqon Focus miRNA polymerase chain reaction (PCR) Panel I + II. Specific accumulation pattern of 13 miRNAs from the discovery set was subsequently investigated in the sera of 16 AChR+ MG patients and 16 healthy controls. All patients were without immunosuppressive treatment. Selected specific miRNAs were further analyzed in the serum of nine MG patients before and after thymectomy to assess the effect of thymus removal on the accumulation of the candidate miRNAs in patient sera.

Results

Three miRNAs were specifically dysregulated in AChR+ MG patient sera samples. Hsa-miR150-5p, which induces T-cell differentiation, as well as hsa-miR21-5p, a regulator of Th1 versus Th2 cell responses, were specifically elevated in MG sera. Additionally, hsa-miR27a-3p, involved in natural killer (NK) cell cytotoxicity, was decreased in MG. Hsa-miR150-5p levels had the highest association with MG and were significantly reduced after thymus removal in correlation with disease improvement.

Interpretation

We propose that the validated miRNAs: hsa-miR150-5p, hsa-miR21-5p, and hsa-miR27a-3p can serve as novel serum biomarkers in AChR+ MG. Hsa-miR-150-5p could be a helpful marker to monitor disease severity.

Therapeutic potential of interleukin-17 in inflammation and autoimmune diseases

INTRODUCTION

Interleukin-17 (IL-17) is a proinflammatory cytokine that mainly produced by T helper 17 (Th17) cells. In this article, we discussed the role of IL-17 in inflammation and autoimmune diseases, and the therapeutic strategies targeting IL-17.

AREAS COVERED

In this article, we discussed the proinflammatory cytokine IL-17 and IL-17 receptors signals, and their regulation. IL-17 expression was abnormal in the bacterium, virus and fungus infection, and its higher level caused the tissue inflammation. IL-17 was involved in the pathological process of autoimmune diseases, such as systemic sclerosis, rheumatoid arthritis, ankylosing spondylitis and systemic lupus erythematosus, and IL-17 has been put as a therapeutic target in the clinic.

EXPERT OPINION

IL-17/IL-17R signals and their application in inflammation process still need to be explored. Therapeutic strategies targeting IL-17 in autoimmune diseases ameliorated the inadequate response to anti-TNF-α therapy.

[Myasthenia gravis and autoantibodies: Pathophysiology of the different subtypes]

Myasthenia gravis is characterized by muscle weakness and abnormal fatigability. It is an autoimmune disease caused by the presence of antibodies against components of the muscle membrane localized at the neuromuscular junction. In most cases, the autoantibodies are directed against the acetylcholine receptor (AChR). Recently, other targets have been described, such as muscle-specific kinase protein (MuSK) or lipoprotein related protein 4 (LRP4). The origin of the autoimmune response is not known, but thymic abnormalities and defects in immune regulation certainly play a major role in patients with anti-AChR antibodies. Genetic predisposition probably influences the occurrence of the disease. Sex hormones seem to play a role in the early form of the disease. Muscle weakness is fluctuating and worsens with exercise. Myasthenia gravis could be classified according to the location of the affected muscles (ocular versus generalized), the age of onset of symptoms, thymic abnormalities and profile of autoantibodies. These criteria are used to optimize the management and treatment of patients. In this review, we analyze the latest concepts of the pathophysiology of myasthenia gravis according to the different subgroups of the disease, including a description of the role of immunological, genetic and environmental factors. The potential viral hypothesis of this disease is discussed. Finally, we also discuss the biological assays available to validate the diagnosis.