Toll-like receptors promote inflammation in idiopathic inflammatory myopathies

High-mobility group box-1 impedes skeletal muscle regeneration via downregulation of Pax-7 synthesis by increasing miR-342-5p expression

High mobility group box-1 (HMGB1) is a driver of inflammation in various muscular diseases. In a previous study, we determined that HMGB1 induced the atrophy of skeletal muscle by impairing myogenesis. Skeletal muscle regeneration after injury is dependent on pair box 7 (Pax-7)-mediated myogenic differentiation. In the current study, we determined that the HMGB1-induced downregulation of Pax-7 expression in myoblasts inhibited the regeneration of skeletal muscle. We also determined that HMGB1 inhibits Pax-7 and muscle differentiation by increasing miR-342-5p synthesis via receptors for advanced glycation end-products (RAGE), toll-like receptor (TLR) 2, TLR4, and c-Src signaling pathways. In a mouse model involving glycerol-induced muscle injury, the therapeutic inhibition of HMGB1 was shown to rescue Pax-7 expression and muscle regeneration. The HMGB1/Pax-7 axis is a promising therapeutic target to promote muscular regeneration.

Toll-like receptors and IL-7 as potential biomarkers for immune-mediated necrotizing myopathies

We aimed to verify whether the immune system may represent a source of potential biomarkers for the stratification of immune-mediated necrotizing myopathies (IMNMs) subtypes. A group of 22 patients diagnosed with IMNM [7 with autoantibodies against signal recognition particle (SRP) and 15 against 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR)] and 12 controls were included. A significant preponderance of M1 macrophages was observed in both SRP+ and HMGCR+ muscle samples (p < 0.0001 in SRP+ and p = 0.0316 for HMGCR+ ), with higher values for SRP+ (p = 0.01). Despite the significant increase observed in the expression of TLR4 and all endosomal Toll-like receptors (TLRs) at protein level in IMNM muscle tissue, only TLR7 has been shown considerably upregulated compared to controls at transcript level (p = 0.0026), whereas TLR9 was even decreased (p = 0.0223). Within IMNM subgroups, TLR4 (p = 0.0116) mRNA was significantly increased in SRP+ compared to HMGCR+ patients. Within IMNM group, only IL-7 was differentially expressed between SRP+ and HMGCR+ patients, with higher values in SRP+ patients (p = 0.0468). Overall, innate immunity represents a key player in pathological mechanisms of IMNM. TLR4 and the inflammatory cytokine IL-7 represent potential immune biomarkers able to differentiate between SRP+ and HMGCR+ patients.

Antigen-driven T cell-macrophage interactions mediate the interface between innate and adaptive immunity in histidyl-tRNA synthetase-induced myositis

Introduction

Previous work in humans has demonstrated that both innate and adaptive immune signaling pathways contribute to the pathogenesis of idiopathic inflammatory myopathy (IIM), a systemic autoimmune disease targeting muscle as well as extra-muscular organs. To better define interactive signaling networks in IIM, we characterized the cellular phenotype and transcriptomic profiles of muscle-infiltrating cells in our established murine model of histidyl-tRNA synthetase (HRS)-induced myositis.

Methods

Myositis was induced in wild type (WT) and various congenic/mutant strains of C57BL/6 mice through intramuscular immunization with recombinant HRS. Histopathological, immunohistochemical, flow cytometric, and transcriptomic assessments were used to characterize the functional relationship between muscle-infiltrating cell populations in these strains lacking different components of innate and/or adaptive immune signaling.

Results

RAG1 KO mice developed markedly reduced muscle inflammation relative to WT mice, demonstrating a key requirement for T cells in driving HRS-induced myositis. While the reduction of mononuclear cell infiltrates in CD4-Cre.MyD88fl/fl conditional knockout mice and OT-II TCR transgenic mice highlighted roles for both innate and TCR-mediated/adaptive immune signaling in T cells, diminished inflammation in Lyz2-Cre.MyD88fl/fl conditional knockout mice underscored the importance of macrophage/myeloid cell populations in supporting T cell infiltration. Single cell RNA sequencing-based clustering of muscle-infiltrating subpopulations and associated pathway analyses showed that perturbations of T cell signaling/function alter the distribution and phenotype of macrophages, fibroblasts, and other non-lymphoid cell populations contributing to HRS-induced myositis.

Discussion

Overall, HRS-induced myositis reflects the complex interplay between multiple cell types that collectively drive a TH1-predominant, pro-inflammatory tissue phenotype requiring antigen-mediated activation of both MyD88- and TCR-dependent T cell signaling pathways.

Five genes as diagnostic biomarkers of dermatomyositis and their correlation with immune cell infiltration

Background

Dermatomyositis (DM) is a rare autoimmune disease characterized by severe muscle dysfunction, and the immune response of the muscles plays an important role in the development of DM. Currently, the diagnosis of DM relies on symptoms, physical examination, and biopsy techniques. Therefore, we used machine learning algorithm to screen key genes, and constructed and verified a diagnostic model composed of 5 key genes. In terms of immunity, The relationship between 5 genes and immune cell infiltration in muscle samples was analyzed. These diagnostic and immune-cell-related genes may contribute to the diagnosis and treatment of DM.

Methods

GSE5370 and GSE128470 datasets were utilised from the Gene Expression Omnibus database as DM test sets. And we also used R software to merge two datasets and to analyze the results of differentially expressed genes (DEGs) and functional correlation analysis. Then, we could detect diagnostic genes adopting least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine recursive feature elimination (SVM-RFE) analyses. The validity of putative biomarkers was assessed using the GSE1551 dataset, and we confirmed the area under the receiver operating characteristic curve (AUC) values. Finally, CIBERSORT was used to evaluate immune cell infiltration in DM muscles and the correlations between disease-related biomarkers and immune cells.

Results

In this study, a total of 414 DEGs were screened. ISG15, TNFRSF1A, GUSBP11, SERPINB1 and PTMA were identified as potential DM diagnostic biomarkers(AUC > 0.85),and the expressions of 5 genes in DM group were higher than that in healthy group (p < 0.05). Immune cell infiltration analyses indicated that identified DM diagnostic biomarkers may be associated with M1 macrophages, activated NK cells, Tfh cells, resting NK cells and Treg cells.

Conclusion

The study identified that ISG15, TNFRSF1A, GUSBP11, SERPINB1 and PTMA as potential diagnostic biomarkers of DM and these genes were closely correlated with immune cell infiltration.This will contribute to future studies in diagnosis and treatment of DM.

Update on Myositis Therapy: from Today's Standards to Tomorrow's Possibilities

Inflammatory myopathies, in short, myositis, are heterogeneous disorders that are characterized by inflammation of skeletal muscle and weakness of arms and legs. Research over the past few years has led to a new understanding regarding the pathogenesis of myositis. The new insights include different pathways of the innate and adaptive immune response during the pathogenesis of myositis. The importance of non-inflammatory mechanisms such as cell stress and impaired autophagy has been recently described. New target-specific drugs for myositis have been developed and are currently being tested in clinical trials. In this review, we discuss the mechanisms of action of pharmacological standards in myositis and provide an outlook of future treatment approaches.

The pathophysiological effects of exercise in the management of idiopathic inflammatory myopathies: A scoping review

Idiopathic inflammatory myopathy (IIM) is a term used for a heterogeneous group of diseases characterized by severe muscle weakness. In addition to pharmacological treatment options, non-pharmacological methods such as exercising are essential for proper management of myositis. The present article aimed to provide an insight into the potential pathophysiological mechanisms underlying exercise-related benefits in myositis. A systematic search was performed on PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar using the following keywords and their combinations: "idiopathic inflammatory myopathy", "inflammatory myopathy", "myositis", "polymyositis", "dermatomyositis", "inclusion body myositis", and "exercise". Current literature indicates that exercising has impact on both immune and non-immune pathways in patients with IIM. Exercise-related benefits include (a) increased mitochondrial biogenesis/enzyme activity, (b) reconditioning of immune/inflammatory pathways, (c) decreased endoplasmic reticulum stress, (d) modulation of gene expression, (e) increased protein synthesis and cytoskeletal remodeling, and (f) decreased muscle fibrosis and non-muscle area infiltrates. With its certain benefits, exercise stands as a precious non-pharmacological treatment option for patients with IIM.

TLR expression in peripheral monocyte subsets of patients with idiopathic inflammatory myopathies: association with clinical and immunological features

BACKGROUND

Monocytes and toll-like receptors (TLR) have been found in the inflammatory infiltrate of muscle biopsies in patients with idiopathic inflammatory myopathies (IIM), suggesting an important role of these cells in the pathogenesis of myositis. The monocyte subsets, their TLR expression in peripheral blood and their relationship with the clinical characteristics of patients with IIM has not been addressed.

METHODS

We recruited 45 patients with IIM diagnosis and 15 age and sex-adjusted healthy controls. We assessed the disease activity and damage, performed a nailfold capillaroscopy and registered the cardio-pulmonary parameters from the medical charts. Monocyte subsets, their expression of TLR2 and TLR4 and the serum Th1/Th2/Th17 cytokines levels were evaluated by flow cytometry. We expressed quantitative variables as medians and interquartile ranges (IQR) or minimum and maximum (min-max). Differences between groups were assessed with Mann-Whitney U and the Kruskal-Wallis tests. Correlation between quantitative variables was assessed with Spearman Rho.

RESULTS

Twenty-nine patients were women (64.4%) and 32 (71.1%) had dermatomyositis. In comparison to healthy controls, patients with active IIM had a higher percentage of intermediate monocytes and lower amounts of classical monocytes. Patients with IIM had a higher expression of TLR4 in all their monocyte subsets, regardless of disease activity and prednisone treatment. Serum IL-6 correlated with the TLR2 expression in every monocyte subset and the expression of TLR2 in intermediate monocytes was higher among patients with dysphagia. Subjects with nailfold capillaroscopy abnormalities had a higher amount of TLR2+ classical and non-classical monocytes and those with interstitial lung disease (ILD) had a higher percentage of TLR4+ non-classical monocytes. The classical and intermediate monocytes from patients with anti Mi2 antibodies had a higher expression of TLR4. The percentage of intermediate monocytes and the expression of TLR4 in all monocyte subsets showed a good diagnostic capacity in patients with IIM.

CONCLUSION

Patients with IIM have a differential pool of monocyte subsets with an enhanced expression of TLR2 and TLR4, which correlates with disease activity and distinctive clinical features including dysphagia, ILD, vasculopathy, and pro-inflammatory cytokines. These immunological features might be useful as a potential diagnostic tool as well as novel disease activity biomarkers in IIM.

Polymyositis and dermatomyositis - challenges in diagnosis and management

Polymyositis (PM) and dermatomyositis (DM) are different disease subtypes of idiopathic inflammatory myopathies (IIMs). The main clinical features of PM and DM include progressive symmetric, predominantly proximal muscle weakness. Laboratory findings include elevated creatine kinase (CK), autoantibodies in serum, and inflammatory infiltrates in muscle biopsy. Dermatomyositis can also involve a characteristic skin rash. Both polymyositis and dermatomyositis can present with extramuscular involvement. The causative factor is agnogenic activation of immune system, leading to immunologic attacks on muscle fibers and endomysial capillaries. The treatment of choice is immunosuppression. PM and DM can be distinguished from other IIMs and myopathies by thorough history, physical examinations and laboratory evaluation and adherence to specific and up-to-date diagnosis criteria and classification standards. Treatment is based on correct diagnosis of these conditions.

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Challenges of diagnosis and management influences the clinical research and practice of Polymyositis and dermatomyositis.

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Diagnostic criteria have been updated and novel therapies have been developed in PM/DM.

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Pathogenesis investigation and diagnosis precision improvement may help to guide future treatment strategies.

Myalgia with the presence of pathologic EMG correlates with perimysial inflammatory infiltrates

Objective

We aimed to define normal numbers of inflammatory cells in muscle biopsies and to identify the predictive value of isolated muscle pain and increased creatine kinase regarding the diagnosis of myositis.

Methods

We analyzed muscle biopsies of 71 patients using immunostains for CD3+, CD4+, CD8+, CD68+, major histocompatibility complex class I, perforin, and myeloid-related protein (MRP) 8. Patients were categorized as follows—group 1: myalgia without further clinical or laboratory abnormalities (n = 24); group 2: asymptomatic elevation of creatine kinase (hyperCKemia, n = 26); group 3: myalgia and pathologic EMG findings (n = 9); and group 4: otherwise healthy controls who had malignant hyperthermia susceptibility testing (n = 12).

Results

In the normal muscle biopsy specimens from group 4, mean endomysial macrophage (CD68+) density was 21.7 ± 5.6/mm2, and perimysial density was 13.0 ± 5.6/mm2. Numbers of T-lymphocytes (CD3+) were 5 ± 3.5 endomysially and 2.2 ± 3.9/mm2 perimysially. This was not different from groups 1 and 2. Only group 3 patients had increased mean numbers of perimysial macrophages (24.1 ± 6.3/mm2; p = 0.0005), CD3+ (7.6 ± 4.9/mm2; p = 0.0056), and CD8+ T-lymphocytes (5.4 ± 3.1/mm2; p = 0.0008) and displayed the activation marker MRP8 in all cases. Although inflammatory cells were increased in the perimysium in group 3, histology did not fulfill the criteria for dermatomyositis, polymyositis, or inclusion body myositis.

Conclusions

Normal muscle contains a considerable number of macrophages and T-lymphocytes. Muscle biopsy is likely to detect inflammatory changes in patients with myalgia or hyperCKemia only if pathologic EMG findings are present.

Exacerbation of Murine Experimental Autoimmune Myositis by Toll-Like Receptor 7/8

OBJECTIVE

Toll-like receptor 7 (TLR-7), TLR-8, and interferon (IFN)-induced genes are expressed in patients with idiopathic inflammatory myositis. This study was undertaken to investigate whether their activation influences the natural history of the disease.

METHODS

Experimental autoimmune myositis was induced in mice by injection of the amino-terminal portion of the murine histidyl-transfer RNA synthetase (HisRS). Disease was compared in the presence or the absence of the TLR-7/8 agonist R-848 in wild-type mice and in mice that fail to express the IFNα/β receptor (IFNα/βR-null mice).

RESULTS

Experimental autoimmune myositis induced by a single intramuscular immunization with HisRS spontaneously abated after 7-8 weeks. In contrast, levels of anti-HisRS autoantibodies, endomysial/perimysial leukocyte infiltration, and myofiber regeneration persisted at the end of the follow-up period (22 weeks after immunization) in mice immunized with HisRS in the presence of R-848. Myofiber major histocompatibility complex (MHC) class I molecules were detectable only in mice immunized with both HisRS and R-848. MHC up-regulation occurred early and in muscles that were not directly injected with HisRS. Muscle MHC expression paralleled with leukocyte infiltration. MHC class I molecules were selectively up-regulated in myotubes challenged with R-848 in vitro. Type I IFN was necessary for the prolonged autoantibody response and for the spreading of the autoimmune response, as demonstrated using IFNα/βR-null mice. Muscle infiltration was maintained in the injected muscle up to the end of the follow-up period.

CONCLUSION

TLR-7/8 activation is necessary to induce and maintain a systemic autoimmune response targeting the skeletal muscle. This experimental autoimmune myositis model reproduces many characteristics of human idiopathic inflammatory myopathies and may represent a tool for preclinical studies.

Immune checkpoint failures in inflammatory myopathies: An overview

Dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), immune mediated necrotizing myopathy (IMNM) and overlap myositis (OM) are classified as inflammatory myopathies (IM) with involvement of autoimmune features such as autoreactive lymphocytes and autoantibodies. Autoimmunity can be defined as a loss in self-tolerance and attack of autoantigens by the immune system. Self-tolerance is achieved by a group of immune mechanisms occurring in central and periphal lymphoid organs and tissues, called immune checkpoints, that work in synergy to protect the body from harmful immune reactions. Autoimmune disorders appear when immune checkpoints fail. In this review, the different immune checkpoint failures are discussed in DM, PM, IBM and IMNM. Exploring research contribution in each of these immune checkpoints might help to highlight research perspectives in the field and obtain a more complete picture of IM disease pathology.

Splicing variant of WDFY4 augments MDA5 signalling and the risk of clinically amyopathic dermatomyositis

OBJECTIVES

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of rare autoimmune diseases in which both genetic and environmental factors play important roles. To identify genetic factors of IIM including polymyositis, dermatomyositis (DM) and clinically amyopathic DM (CADM), we performed the first genome-wide association study for IIM in an Asian population.

METHODS

We genotyped and tested 496 819 single nucleotide polymorphism for association using 576 patients with IIM and 6270 control subjects. We also examined the causal mechanism of disease-associated variants by in silico analyses using publicly available data sets as well as by in in vitro analyses using reporter assays and apoptosis assays.

RESULTS

We identified a variant in WDFY4 that was significantly associated with CADM (rs7919656; OR=3.87; P=1.5×10-8). This variant had a cis-splicing quantitative trait locus (QTL) effect for a truncated WDFY4isoform (tr-WDFY4), with higher expression in the risk allele. Transexpression QTL analysis of this variant showed a positive correlation with the expression of NF-κB associated genes. Furthermore, we demonstrated that both WDFY4 and tr-WDFY4 interacted with pattern recognition receptors such as TLR3, TLR4, TLR9 and MDA5 and augmented the NF-κB activation by these receptors. WDFY4 isoforms also enhanced MDA5-induced apoptosis to a greater extent in the tr-WDFY4-transfected cells.

CONCLUSIONS

As CADM is characterised by the appearance of anti-MDA5 autoantibodies and severe lung inflammation, the WDFY4 variant may play a critical role in the pathogenesis of CADM.

Toll-Like Receptor 4-Myeloid Differentiation Primary Response Gene 88 Pathway Is Involved in the Inflammatory Development of Polymyositis by Mediating Interferon-γ and Interleukin-17A in Humans and Experimental Autoimmune Myositis Mouse Model

OBJECTIVE

Toll-like receptor 4 (TLR4) is one of the key players in the development of many autoimmune diseases. To determine the possible role of TLR4 in polymyositis (PM) development, we collected muscle samples from PM patients and mice subjected to an experimental autoimmune myositis (EAM) model.

METHODS

We measured TLR4-MyD88 pathway-related factors, interferon-γ (IFN-γ), and interleukin-17A (IL-17A) in EAM mice and PM patients. Then, we observed the changes of above factors and the inflammatory development of EAM mice with TLR4 antagonist TAK-242, IFN-γ, or IL-17A antibody treatment.

RESULTS

The expression of TLR4, MyD88, and NF-κB was significantly upregulated in the muscle tissues both in 22 patients with PM and in the EAM model. As expected, increased levels of various cytokines, such as IL-1β, IL-6, IL-10, IL-12, tumor necrosis factor-α, TGF-β, IFN-γ, and IL-17A, were evident in the serum of EAM mice. Moreover, mRNA expression levels of IFN-γ and IL-17A were significantly increased in both PM patients and EAM mice. Consistently, the levels of these factors were positively correlated with the degree of muscle inflammation in EAM mice. However, when EAM mice were treated with TLR4 antagonist TAK-242, the expression of IFN-γ and IL-17A was decreased. When the cytokines were neutralized by anti-IFN-γ or anti-IL-17A antibody, the inflammatory development of EAM exacerbated or mitigated.

CONCLUSION

The present study provided the important evidence that the TLR4-MyD88 pathway may be involved in the immune mechanisms of PM by mediating IFN-γ and IL-17A.

p53 amplifies Toll-like receptor 5 response in human primary and cancer cells through interaction with multiple signal transduction pathways

The p53 tumor suppressor regulates transcription of genes associated with diverse cellular functions including apoptosis, growth arrest, DNA repair and differentiation. Recently, we established that p53 can modulate expression of Toll-like receptor (TLR) innate immunity genes but the degree of cross-talk between p53 and TLR pathways remained unclear. Here, using gene expression profiling we characterize the global effect of p53 on the TLR5-mediated transcription in MCF7 cells. We found that combined activation of p53 and TLR5 pathways synergistically increases expression of over 200 genes, mostly associated with immunity and inflammation. The synergy was observed in several human cancer cells and primary lymphocytes. The p53-dependent amplification of transcriptional response to TLR5 activation required expression of NFκB subunit p65 and was mediated by several molecular mechanisms including increased phosphorylation of p38 MAP kinase, PI3K and STAT3 signaling. Additionally, p53 induction increased cytokine expression in response to TNFα, another activator of NFκB and MAP kinase pathways, suggesting a broad interaction between p53 and these signaling pathways. The expression of many synergistically induced genes is elevated in breast cancer patients responsive to chemotherapy. We suggest that p53's capacity to enhance immune response could be exploited to increase antitumor immunity and to improve cancer treatment.

Role of Jo-1 in the Immunopathogenesis of the Anti-synthetase Syndrome

Histidyl-tRNA synthetase (HRS = Jo-1) represents a key autoantibody target in the anti-synthetase syndrome that is marked by myositis as well as extra-muscular organ complications including interstitial lung disease (ILD). Over the last 25 years, a wealth of clinical, epidemiological, genetic, and experimental data have collectively supported a role for Jo-1 in mediating deleterious cell-mediated, adaptive immune responses contributing to the disease phenotype of the anti-synthetase syndrome. Complementing these studies, more recent work suggests that unique, non-enzymatic functional properties of Jo-1 also endow this antigen with the capacity to activate components of the innate immune system, particularly cell surface as well as endosomal Toll-like receptors and their downstream signaling pathways. Combining these facets of Jo-1-mediated immunity now supports a more integrated model of disease pathogenesis that should lead to improved therapeutic targeting in the anti-synthetase syndrome and related subsets of idiopathic inflammatory myopathy.

The role of toll like receptors in giant cell arteritis

GCA is a common primary systemic vasculitis that results in granulomatous inflammation of medium to large arteries. Both innate and adaptive immune mechanisms combine to drive intimal hyperplasia, luminal stenosis and ultimately occlusion. While the pathogenesis of GCA is incompletely understood, the activation of resident adventitial dendritic cells via toll like receptors (TLRs) appears to be a crucial inciting event. Here we explore the role of TLRs in the pathogenesis of GCA, including their effects on dendritic cell and T cell activation and recruitment, putative infectious triggers for GCA and the potential of TLR inhibition as a novel therapeutic strategy in GCA.

Calprotectin in rheumatic diseases

Calprotectin is a heterodimer formed by two proteins, S100A8 and S100A9, which are mainly produced by activated monocytes and neutrophils in the circulation and in inflamed tissues. The implication of calprotectin in the inflammatory process has already been demonstrated, but its role in the pathogenesis, diagnosis, and monitoring of rheumatic diseases has gained great attention in recent years. Calprotectin, being stable at room temperature, is a candidate biomarker for the follow-up of disease activity in many autoimmune disorders, where it can predict response to treatment or disease relapse. There is evidence that a number of immunomodulators, including TNF-α inhibitors, may reduce calprotectin expression. S100A8 and S100A9 have a potential role as a target of treatment in murine models of autoimmune disorders, since the direct or indirect blockade of these proteins results in amelioration of the disease process. In this review, we will go over the biologic functions of calprotectin which might be involved in the etiology of rheumatic disorders. We will also report evidence of its potential use as a disease biomarker. Impact statement Calprotectin is an acute-phase protein produced by monocytes and neutrophils in the circulation and inflamed tissues. Calprotectin seems to be more sensitive than CRP, being able to detect minimal residual inflammation and is a candidate biomarker in inflammatory diseases. High serum levels are associated with some severe manifestations of rheumatic diseases, such as glomerulonephritis and lung fibrosis. Calprotectin levels in other fluids, such as saliva and synovial fluid, might be helpful in the diagnosis of rheumatic diseases. Of interest is also the potential role of calprotectin as a target of treatment.

Role of Toll-like receptors and retinoic acid inducible gene I in endogenous production of type I interferon in dermatomyositis

To explore the possible mechanisms implicated in the endogenous production of type I interferons within the muscle tissue of dermatomyositis (DM) patients. We detected the co-localization of plasmacytoid dendritic cells (pDCs) with Toll-like receptors (TLRs) and retinoic acid inducible gene (RIG)-I by immunohistochemistry and immunofluorescence. Western blotting confirmed the expression of TLRs and RIG-I. TLR-3 and RIG-I was preferentially expressed in the perifascicular atrophy fibers of DM. TLR-7 was only in inflammatory infiltrates of a few DM patients. TLR-4 and TLR-9 was expressed mainly in inflammatory infiltrates. Immunofluorescence showed extensive co-localization of BDCA-2 with TLR-9 and little co-localization with TLR-7. Western blotting showed upregulation of expression of TLRs and RIG-I in DM compared with the controls. Our findings indicate that endogenous production of type I IFN in DM is generated by pDCs, mainly through the TLR-9 pathway and in part by TLR-7. TLR-3 and RIG-I are implicated in the formation of perifascicular atrophy in DM.

Serum progranulin levels are elevated in dermatomyositis patients with acute interstitial lung disease, predicting prognosis

Introduction

Progranulin (PGRN), a pleiotropic growth factor, has emerged as an immunoregulatory molecule. Because the roles of PGRN in dermatomyositis (DM) are still unknown, we investigated whether serum PGRN levels are associated with disease activity and prognosis in DM patients, particularly in those with DM complicated with interstitial lung disease (ILD).

Methods

The serum levels of PGRN were measured by enzyme-linked immunosorbent assay in patients with DM (n =57; acute/subacute interstitial pneumonia (A/SIP): n =17, chronic interstitial pneumonia (CIP): n =24, without ILD: n =16), polymyositis (PM, n =21; including 6 with ILD) and normal healthy controls (NHCs, n =60). We assessed the correlation between the serum PGRN levels and the activity indexes of ILD or prognosis in DM patients with ILD.

Results

Serum PGRN levels were significantly higher in DM patients than in PM patients (P =0.0025) and in NHCs (P <0.0001). In DM patients, the levels were significantly higher in patients with A/SIP than in those with CIP (P <0.0001) or without ILD (P =0.0003). The serum PGRN levels in DM patients with ILD significantly correlated with serum ferritin (r_S =0.77, P <0.0001), lactate dehydrogenase (r_S =0.54, P =0.0003) and C-reactive protein (r_S =0.48, P =0.0015) levels. Moreover, in DM patients with ILD, the cumulative survival rate for 6 months was significantly lower in the group with serum PGRN levels ≥200 ng/ml (67%) than in the group with serum PGRN levels <200 ng/ml (100%) (P =0.0009).

Conclusions

Serum PGRN is associated with disease activity and prognosis of DM with ILD. PGRN may play a role in the pathogenesis of DM and could be a useful biomarker.

Autophagy, inflammation and innate immunity in inflammatory myopathies

Autophagy has a large range of physiological functions and its dysregulation contributes to several human disorders, including autoinflammatory/autoimmune diseases such as inflammatory myopathies (IIMs). In order to better understand the pathogenetic mechanisms of these muscular disorders, we sought to define the role of autophagic processes and their relation with the innate immune system in the three main subtypes of IIM, specifically sporadic inclusion body myositis (sIBM), polymyositis (PM), dermatomyositis (DM) and juvenile dermatomyositis (JDM). We found that although the mRNA transcript levels of the autophagy-related genes BECN1, ATG5 and FBXO32 were similar in IIM and controls, autophagy activation in all IIM subgroups was suggested by immunoblotting results and confirmed by immunofluorescence. TLR4 and TLR3, two potent inducers of autophagy, were highly increased in IIM, with TLR4 transcripts significantly more expressed in PM and DM than in JDM, sIBM and controls, and TLR3 transcripts highly up-regulated in all IIM subgroups compared to controls. Co-localization between autophagic marker, LC3, and TLR4 and TLR3 was observed not only in sIBM but also in PM, DM and JDM muscle tissues. Furthermore, a highly association with the autophagic processes was observed in all IIM subgroups also for some TLR4 ligands, endogenous and bacterial HSP60, other than the high-mobility group box 1 (HMGB1). These findings indicate that autophagic processes are active not only in sIBM but also in PM, DM and JDM, probably in response to an exogenous or endogenous 'danger signal'. However, autophagic activation and regulation, and also interaction with the innate immune system, differ in each type of IIM. Better understanding of these differences may lead to new therapies for the different IIM types.

Toll-like receptor 4-mediated signaling participates in apoptosis of hippocampal neurons

The phosphatidylinositol 3 kinase (PI3K)/protein kinase B (AKT) signaling pathway is considered important for cell survival and has been shown to mediate various anti-apoptotic biological effects. This study explored the role of the Toll-like receptor 4 (TLR4)-mediated PI3K/AKT-glycogen syn-thase kinase 3β (GSK-3β) signaling pathways in lipopolysaccharide-induced apoptosis in a primary culture of hippocampal neurons. Results demonstrated that the apoptotic ratio of hippocampal neurons stimulated by lipopolysaccharide was significantly higher compared with the control group. Both the expression of P-AKT^Ser473 and P-GSK-3β^Ser9 in hippocampal neurons stimulated by lipopo-polysaccharide decreased compared with the control, while the level of active Caspase-3 and the ratio of Bax/Bcl-2 were significantly increased. The level of active Caspase-3 and the ratio of Bax/Bcl-2 in hippocampal neurons treated with TLR4 antibody or the GSK-3β inhibitor, LiCl, creased before intervention with lipopolysaccharide, but increased after treatment with the AKT hibitor, LY294002. These findings suggest that the TLR4-PI3K/AKT-GSK3β signaling pathway may be involved in lipopolysaccharide-induced apoptosis of hippocampal neurons.

The role of interleukin-17 in immune-mediated inflammatory myopathies and possible therapeutic implications

The idiopathic inflammatory myopathies are a heterogeneous group of autoimmune muscle disorders with distinct clinical and pathological features and underlying immunopathogenic mechanisms. Traditionally, CD4(+) Th1 cells or CD8(+) cytotoxic effector T cells and type I/II interferons have been primarily implicated in the pathogenesis of the inflammatory myopathies. The presence of IL-17A producing cells in the inflamed muscle tissue of myositis patients and the results of in vitro studies suggest that IL-17A and the Th17 pathway may also have a key role in these diseases. The contribution of IL-17A to other chronic inflammatory and autoimmune diseases has been well established and clinical trials of IL-17A inhibitors are now at an advanced stage. However the precise role of IL-17A in the various forms of myositis and the potential for therapeutic targeting is currently unknown and warrants further investigation.

Vitamin D receptor agonists: suitable candidates as novel therapeutic options in autoimmune inflammatory myopathy

The primary aim in the treatment of autoimmune inflammatory myopathies (IMs) is to recover muscle function. The presence of immune/inflammatory cell infiltrates within muscle tissues represents the common feature of different IM subtypes, albeit a correlation between muscular damage extent and inflammation degree is often lacking. Treatments for IMs are based on life-long immunosuppressive therapy, with the well known adverse effects; recovery is incomplete for many patients. More effective therapies, with reduced side-effects, are highly desirable. Vitamin D receptor (VDR) agonists emerge to retain pleiotropic anti-inflammatory properties, since they regulate innate and adaptive immunity by switching the immune response from proinflammatory T helper 1 (Th1) type to tolerogenic T helper 2 (Th2) type dominance. In skeletal muscle cells less hypercalcemic VDR ligands target powerful mediators of inflammation, such as TNFα and TNFα driven paths, without affecting immune or muscle cells viability, retaining the potentiality to counteract Th1 driven overreactivity established by the self-enhancing inflammatory loop between immune and skeletal muscle cells. This review summarizes those features of VDR agonists as candidates in future treatment of IM.

Functional redundancy of MyD88-dependent signaling pathways in a murine model of histidyl-transfer RNA synthetase-induced myositis

We have previously shown that i.m. administration of bacterially expressed murine histidyl-tRNA synthetase (HRS) triggers florid muscle inflammation (relative to appropriate control proteins) in various congenic strains of mice. Because severe disease develops even in the absence of adaptive immune responses to HRS, we sought to identify innate immune signaling components contributing to our model of HRS-induced myositis. In vitro stimulation assays demonstrated HRS-mediated activation of HEK293 cells transfected with either TLR2 or TLR4, revealing an excitatory capacity exceeding that of other bacterially expressed fusion proteins. Corresponding to this apparent functional redundancy of TLR signaling pathways, HRS immunization of B6.TLR2(-/-) and B6.TLR4(-/-) single-knockout mice yielded significant lymphocytic infiltration of muscle tissue comparable to that produced in C57BL/6 wild-type mice. In contrast, concomitant elimination of TLR2 and TLR4 signaling in B6.TLR2(-/-).TLR4(-/-) double-knockout mice markedly reduced the severity of HRS-induced muscle inflammation. Complementary subfragment analysis demonstrated that aa 60-90 of HRS were absolutely required for in vitro as well as in vivo signaling via these MyD88-dependent TLR pathways--effects mediated, in part, through preferential binding of exogenous ligands capable of activating specific TLRs. Collectively, these experiments indicate that multiple MyD88-dependent signaling cascades contribute to this model of HRS-induced myositis, underscoring the antigenic versatility of HRS and confirming the importance of innate immunity in this system.

Idiopathic inflammatory myopathies: pathogenic mechanisms of muscle weakness

Idiopathic inflammatory myopathies (IIMs) are a heterogenous group of complex muscle diseases of unknown etiology. These diseases are characterized by progressive muscle weakness and damage, together with involvement of other organ systems. It is generally believed that the autoimmune response (autoreactive lymphocytes and autoantibodies) to skeletal muscle-derived antigens is responsible for the muscle fiber damage and muscle weakness in this group of disorders. Therefore, most of the current therapeutic strategies are directed at either suppressing or modifying immune cell activity. Recent studies have indicated that the underlying mechanisms that mediate muscle damage and dysfunction are multiple and complex. Emerging evidence indicates that not only autoimmune responses but also innate immune and non-immune metabolic pathways contribute to disease pathogenesis. However, the relative contributions of each of these mechanisms to disease pathogenesis are currently unknown. Here we discuss some of these complex pathways, their inter-relationships and their relation to muscle damage in myositis. Understanding the relative contributions of each of these pathways to disease pathogenesis would help us to identify suitable drug targets to alleviate muscle damage and also improve muscle weakness and quality of life for patients suffering from these debilitating muscle diseases.

Human β-defensin-3 correlates with muscle fibre degeneration in idiopathic inflammatory myopathies

Sporadic inclusion body myositis (sIBM) and polymyositis (PM) are characterized by muscle inflammation, with sIBM showing additional degenerative alterations. In this study we investigated human beta defensins and associated TLRs to elucidate the role of the innate immune system in idiopathic inflammatory myopathies (IIM), and its association with inflammatory and degenerative alterations. Expression levels of human beta-defensin (HBD)-1, HBD-2, HBD-3 and TLR2, 3, 4, 7 and 9 were analysed by quantitative real-time PCR in skeletal muscle tissue. Localization of HBD-3, collagen 6, dystrophin, CD8-positive T-cells, CD-68-positive macrophages, β-amyloid, the autophagy marker LC3, and TLR3 were detected by immunofluorescence and co-localization was quantified. HBD-3 and all TLRs except for TLR9 were overexpressed in both IIM with significant overexpression of TLR3 in sIBM. HBD-3 showed characteristic intracellular accumulations near deposits of β-amyloid, LC3 and TLR3 in sIBM, and was detected in inflammatory infiltrations and macrophages invading necrotic muscle fibres in both IIM. The characteristic intracellular localization of HBD-3 near markers of degeneration and autophagy, and overexpression of endosomal TLR3 in sIBM hint at different pathogenetic mechanisms in sIBM compared with PM. This descriptive study serves as a first approach to the role of the innate immune system in sIBM and PM.

Dysferlin-deficient muscular dystrophy and innate immune activation

Cells encounter many physical, chemical and biological stresses that perturb plasma membrane integrity, warranting an immediate membrane repair response to regain cell homeostasis. Failure to respond properly to such perturbation leads to individual cell death, which may also produce systemic influence by triggering sterile immunological responses. In this review, we discuss recent progress on understanding the mechanisms underlying muscle cell membrane repair and the potential mediators of innate immune activation when the membrane repair system is defective, specifically focusing on pathology associated with dysferlin deficiency.