Type 1 interferons inhibit myotube formation independently of upregulation of interferon-stimulated gene 15

Interferon-β-Induced Injury During Pediatric Muscle Differentiation: Insight Into Juvenile Dermatomyositis Pathogenesis

OBJECTIVE

Juvenile dermatomyositis (JDM) involves up-regulated type I interferons (IFNs), including IFNβ, yet pathologic mechanisms remain poorly understood. We aimed to characterize the functional and structural effects of IFNβ on in vitro human pediatric myoblast growth and differentiation in a three-dimensional skeletal muscle model (myobundles).

METHODS

Myobundles fabricated from myoblasts of a healthy pediatric donor were exposed to IFNβ at 0 to 5,600 IU/mL during growth (days 1-4), differentiation (days 4-11), and/or mature (days 11-18) periods. To assess myobundle structure and function, contractile force, kinetics, and fatigue were measured at day 18 with subsequent immunohistochemistry.

RESULTS

Myobundles were not functionally affected by IFNβ exposure during growth period alone. However, when IFNβ exposure continued through differentiation, myobundles became dysfunctional (P < 0.0001). IFNβ during differentiation or mature periods alone resulted in dose-dependent decreases in contractility, with greater decrease in the differentiation alone group (P < 0.0001). Twitch kinetics and fatigue remained largely unchanged when myobundles were exposed to IFNβ only during growth, yet twitch time slowed (P < 0.005) and fatigue decreased (P < 0.002) when myobundles were exposed during differentiation or mature stages alone. Nuclei density and myofiber size and organization also decreased when IFNβ was added during differentiation period alone.

CONCLUSION

IFNβ decreases pediatric myobundle contractile function most significantly during differentiation of myoblasts to myotubes. Function is not affected when IFNβ exposure is limited to myoblast proliferation alone. These findings implicate a pathologic role for IFNβ in JDM by impairing myoblast differentiation, leading to subsequent loss of function and ongoing need for muscle regeneration and repair.

Genetic changes from type I interferons and JAK inhibitors: clues to drivers of juvenile dermatomyositis

OBJECTIVE

To better understand the pathogenesis of juvenile dermatomyositis (JDM), we examined the effect of the cytokines type I interferons (IFN I) and JAK inhibitor drugs (JAKi) on gene expression in bioengineered pediatric skeletal muscle.

METHODS

Myoblasts from three healthy pediatric donors were used to create three-dimensional skeletal muscle units termed myobundles. Myobundles were treated with IFN I, either IFNα or IFNβ. A subset of IFNβ-exposed myobundles was treated with JAKi tofacitinib or baricitinib. RNA sequencing analysis was performed on all myobundles.

RESULTS

Seventy-six myobundles were analysed. Principal component analysis showed donor-specific clusters of gene expression across IFNα and IFNβ-exposed myobundles in a dose-dependent manner. Both cytokines upregulated interferon response and proinflammatory genes; however, IFNβ led to more significant upregulation. Key downregulated pathways involved oxidative phosphorylation, fatty acid metabolism and myogenesis genes. Addition of tofacitinib or baricitinib moderated the gene expression induced by IFNβ, with partial reversal of upregulated inflammatory and downregulated myogenesis pathways. Baricitinib altered genetic profiles more than tofacitinib.

CONCLUSION

IFNβ leads to more pro-inflammatory gene upregulation than IFNα, correlating to greater decrease in contractile protein gene expression and reduced contractile force. JAK inhibitors, baricitinib more so than tofacitinib, partially reverse IFN I-induced genetic changes. Increased IFN I exposure in healthy bioengineered skeletal muscle leads to IFN-inducible gene expression, inflammatory pathway enrichment, and myogenesis gene downregulation, consistent with what is observed in JDM.

Pathogenic autoantibody internalization in myositis

Objectives

Myositis is a heterogeneous family of autoimmune muscle diseases. As myositis autoantibodies recognize intracellular proteins, their role in disease pathogenesis has been unclear. This study aimed to determine whether myositis autoantibodies reach their autoantigen targets within muscle cells and disrupt the normal function of these proteins.

Methods

Confocal immunofluorescence microscopy was used to localize antibodies and other proteins of interest in myositis muscle biopsies. Bulk RNA sequencing was used to study the transcriptomic profiles of 668 samples from patients with myositis, disease controls, and healthy controls. Antibodies from myositis patients were introduced into cultured myoblasts by electroporation and the transcriptomic profiles of the treated myoblasts were studied by bulk RNA sequencing.

Results

In patients with myositis autoantibodies, antibodies accumulated inside myofibers in the same subcellular compartment as the autoantigen. Each autoantibody was associated with effects consistent with dysfunction of its autoantigen, such as the derepression of genes normally repressed by Mi2/NuRD in patients with anti-Mi2 autoantibodies, the accumulation of RNAs degraded by the nuclear RNA exosome complex in patients with anti-PM/Scl autoantibodies targeting this complex, and the accumulation of lipids within myofibers of anti-HMGCR-positive patients. Internalization of patient immunoglobulin into cultured myoblasts recapitulated the transcriptomic phenotypes observed in human disease, including the derepression of Mi2/NuRD-regulated genes in anti-Mi2-positive dermatomyositis and the increased expression of genes normally degraded by the nuclear RNA exosome complex in anti-PM/Scl-positive myositis.

Conclusions

In myositis, autoantibodies are internalized into muscle fibers, disrupt the biological function of their autoantigen, and mediate the pathophysiology of the disease.

Effect of type I interferon on engineered pediatric skeletal muscle: a promising model for juvenile dermatomyositis

OBJECTIVE

To investigate pathogenic mechanisms underlying JDM, we defined the effect of type I IFN, IFN-α and IFN-β, on pediatric skeletal muscle function and expression of myositis-related proteins using an in vitro engineered human skeletal muscle model (myobundle).

METHODS

Primary myoblasts were isolated from three healthy pediatric donors and used to create myobundles that mimic functioning skeletal muscle in structural architecture and physiologic function. Myobundles were exposed to 0, 5, 10 or 20 ng/ml IFN-α or IFN-β for 7 days and then functionally tested under electrical stimulation and analyzed immunohistochemically for structural and myositis-related proteins. Additionally, IFN-β-exposed myobundles were treated with Janus kinase inhibitors (JAKis) tofacitinib and baricitinib. These myobundles were also analyzed for contractile force and immunohistochemistry.

RESULTS

IFN-β, but not IFN-α, was associated with decreased contractile tetanus force and slowed twitch kinetics. These effects were reversed by tofacitinib and baricitinib. Type I IFN paradoxically reduced myobundle fatigue, which did not reverse after JAKi. Additionally, type I IFN correlated with MHC I upregulation, which normalized after JAKi treatment, but expression of myositis-specific autoantigens Mi-2, melanocyte differentiation-associated protein 5 and the endoplasmic reticulum stress marker GRP78 were variable and donor specific after type I IFN exposure.

CONCLUSION

IFN-α and IFN-β have distinct effects on pediatric skeletal muscle and these effects can partially be reversed by JAKi treatment. This is the first study illustrating effective use of a three-dimensional human skeletal muscle model to investigate JDM pathogenesis and test novel therapeutics.

Transcriptome analysis of skeletal muscle in dermatomyositis, polymyositis, and dysferlinopathy, using a bioinformatics approach

Background

Polymyositis (PM) and dermatomyositis (DM) are two distinct subgroups of idiopathic inflammatory myopathies. Dysferlinopathy, caused by a dysferlin gene mutation, usually presents in late adolescence with muscle weakness, degenerative muscle changes are often accompanied by inflammatory infiltrates, often resulting in a misdiagnosis as polymyositis.

Objective

To identify differential biological pathways and hub genes related to polymyositis, dermatomyositis and dysferlinopathy using bioinformatics analysis for understanding the pathomechanisms and providing guidance for therapy development.

Methods

We analyzed intramuscular ribonucleic acid (RNA) sequencing data from seven dermatomyositis, eight polymyositis, eight dysferlinopathy and five control subjects. Differentially expressed genes (DEGs) were identified by using DESeq2. Enrichment analyses were performed to understand the functions and enriched pathways of DEGs. A protein-protein interaction (PPI) network was constructed, and clarified the gene cluster using the molecular complex detection tool (MCODE) analysis to identify hub genes.

Results

A total of 1,048, 179 and 3,807 DEGs were detected in DM, PM and dysferlinopathy, respectively. Enrichment analyses revealed that upregulated DEGs were involved in type 1 interferon (IFN1) signaling pathway in DM, antigen processing and presentation of peptide antigen in PM, and cellular response to stimuli in dysferlinopathy. The PPI network and MCODE cluster identified 23 genes related to type 1 interferon signaling pathway in DM, 4 genes (PDIA3, HLA-C, B2M, and TAP1) related to MHC class 1 formation and quality control in PM, and 7 genes (HSPA9, RPTOR, MTOR, LAMTOR1, LAMTOR5, ATP6V0D1, and ATP6V0B) related to cellular response to stress in dysferliniopathy.

Conclusion

Overexpression of genes related to the IFN1 signaling pathway and major histocompatibility complex (MHC) class I formation was identified in DM and PM, respectively. In dysferlinopathy, overexpression of HSPA9 and the mTORC1 signaling pathway genes was detected.

USP18 is an essential regulator of muscle cell differentiation and maturation

The ubiquitin proteasomal system is a critical regulator of muscle physiology, and impaired UPS is key in many muscle pathologies. Yet, little is known about the function of deubiquitinating enzymes (DUBs) in the muscle cell context. We performed a genetic screen to identify DUBs as potential regulators of muscle cell differentiation. Surprisingly, we observed that the depletion of ubiquitin-specific protease 18 (USP18) affected the differentiation of muscle cells. USP18 depletion first stimulated differentiation initiation. Later, during differentiation, the absence of USP18 expression abrogated myotube maintenance. USP18 enzymatic function typically attenuates the immune response by removing interferon-stimulated gene 15 (ISG15) from protein substrates. However, in muscle cells, we found that USP18, predominantly nuclear, regulates differentiation independent of ISG15 and the ISG response. Exploring the pattern of RNA expression profiles and protein networks whose levels depend on USP18 expression, we found that differentiation initiation was concomitant with reduced expression of the cell-cycle gene network and altered expression of myogenic transcription (co) factors. We show that USP18 depletion altered the calcium channel gene network, resulting in reduced calcium flux in myotubes. Additionally, we show that reduced expression of sarcomeric proteins in the USP18 proteome was consistent with reduced contractile force in an engineered muscle model. Our results revealed nuclear USP18 as a critical regulator of differentiation initiation and maintenance, independent of ISG15 and its role in the ISG response.

Update on dermatomyositis

PURPOSE OF REVIEW

This review summarizes and comments on current knowledge in dermatomyositis.

RECENT FINDINGS

The 2018 European Neuromuscular Centre classification of dermatomyositis has been challenging by the discovery of clinicopathological features associated with dermatomyositis-specific antibody (DMSA) that were not incorporated in the original criteria. These features include but may not be limited to the presence of perifascicular necrosis in anti-Mi-2 dermatomyositis; presence of diffuse nonperifascicular sarcoplasmic myxovirus resistance protein A expression in anti-MDA5 dermatomyositis; and dermatomyositis sine dermatitis in anti-NXP-2 dermatomyositis. Variations and subclassifications within the same DMSA subtypes are observed: anti-MDA5 dermatomyositis is clinically subcategorized into good, intermediate, and poor prognostic subgroups; concurrent anti-CCAR1 and anti-TIF1-γ positivity identify anti-TIF1-γ-positive patient with a lower risk for cancer-associated myositis. Owing to distinct IFN1-signaling pathway activation in dermatomyositis, JAK-STAT inhibitor - the pathway-targeted therapy, have been studied with promising results in refractory dermatomyositis and some new-onset dermatomyositis. In addition, the potential serum biomarkers for IFN1 pathway activation are being investigated for their performance in monitoring the disease activity and the efficacy of the treatment.

SUMMARY

DMSA, evidence of prominent IFN1 pathway activation, and risk/severity-associated biomarkers would likely play major roles in future dermatomyositis classification, disease monitoring, and treatment decision.

Identification of Biomarkers Associated With CD4+ T-Cell Infiltration With Gene Coexpression Network in Dermatomyositis

Background

Dermatomyositis is an autoimmune disease characterized by damage to the skin and muscles. CD4⁺ T cells are of crucial importance in the occurrence and development of dermatomyositis (DM). However, there are few bioinformatics studies on potential pathogenic genes and immune cell infiltration of DM. Therefore, this study intended to explore CD4⁺ T-cell infiltration–associated key genes in DM and construct a new model to predict the level of CD4⁺ T-cell infiltration in DM.

Methods

GSE46239, GSE142807, GSE1551, and GSE193276 datasets were downloaded. The WGCNA and CIBERSORT algorithms were performed to identify the most correlated gene module with CD4⁺ T cells. Matascape was used for GO enrichment and KEGG pathway analysis of the key gene module. LASSO regression analysis was used to identify the key genes and construct the prediction model. The correlation between the key genes and CD4⁺ T-cell infiltration was investigated. GSEA was performed to research the underlying signaling pathways of the key genes. The key gene-correlated transcription factors were identified through the RcisTarget and Gene-motif rankings databases. The miRcode and DIANA-LncBase databases were used to build the lncRNA-miRNA-mRNA network.

Results

In the brown module, 5 key genes (chromosome 1 open reading frame 106 (C1orf106), component of oligomeric Golgi complex 8 (COG8), envoplakin (EVPL), GTPases of immunity-associated protein family member 6 (GIMAP6), and interferon-alpha inducible protein 6 (IFI6)) highly associated with CD4⁺ T-cell infiltration were identified. The prediction model was constructed and showed better predictive performance in the training set, and this satisfactory model performance was validated in another skin biopsy dataset and a muscle biopsy dataset. The expression levels of the key genes promoted the CD4⁺ T-cell infiltration. GSEA results revealed that the key genes were remarkably enriched in many immunity-associated pathways, such as JAK/STAT signaling pathway. The cisbp_M2205, transcription factor-binding site, was enriched in C1orf106, EVPL, and IF16. Finally, 3,835 lncRNAs and 52 miRNAs significantly correlated with key genes were used to build a ceRNA network.

Conclusion

The C1orf106, COG8, EVPL, GIMAP6, and IFI6 genes are associated with CD4⁺ T-cell infiltration. The prediction model constructed based on the 5 key genes may better predict the level of CD4⁺ T-cell infiltration in damaged muscle and lesional skin of DM. These key genes could be recognized as potential biomarkers and immunotherapeutic targets of DM.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Involvement of Type-I Interferon Signaling in Muscle Stem Cell Proliferation During Dermatomyositis

Background and objective:

The idiopathic inflammatory myopathy Dermatomyositis (DM) is an acquired disease that combines muscle, lung and skin impairments. DM patients show a wide range of severity of proximal skeletal muscle weakness, associated with inflammatory infiltrates, vasculitis, and capillary dropout, perifascicular myofiber atrophy. Moreover, DM muscles show signs of muscle regeneration. Since muscle stem cells (MuSCs) are responsible for myofiber repair, we asked wether the proliferative properties of muscle stem cells (MuSCs) are altered in DM muscle. We investigated the role of type-I interferon (IFN-I) in this process since DM is associated with sustained inflammation with high IFN-I levels.

Methods:

MuSCs isolated from normal, adult and juvenile DM muscles were grown in culture and were analyzed in vitro for their proliferating properties, their myogenic capacities and their senescence. Gain and loss of function experiments were performed to assess the role of IFN-I signaling in the prolfierative capacities of MuSCs.

Results:

MuSCs derived from 8 DM adult patients (DM-MuSCs) (5 severe form and 3 mild form, established from histological evaluation), from 3 juvenile DM patients and from normal muscle were used to analyze their myogenesis in vitro. DM-MuSCs exhibited strongly reduced proliferating capacities as compared with healthy MuSCs (-31 to -43% for severe and mild DM, respectively), leading to poor myotube formation (-36 to -71%). DM-MuSCs were enriched in senescent, beta-galactosidase positive cells, explaining partly the proliferation defect. Gain and loss of function experiments were performed to assess the role of IFN-I on the proliferative capacity of MuSCs. High concentrations of IFN-I decreased the proliferation of healthy MuSCs. Similarly, conditioned-medium from DM-MuSCs decreased the proliferation of healthy MuSC (-15 to -22%), suggesting the delivery of an autocrine effector. Then, pharmacological blockade of the IFN signaling (using ruxolitinib or anti-IFN-receptor antibodies) in DM-MuSCs rescued their proliferation up to the control values.

Discussion:

These results show that autocrine IFN-I signaling prevents MuSC expansion, leading to muscle repair deficit. This process may explain the persistent muscle weakness observed in severe DM patients.

VDR regulates simulated microgravity-induced atrophy in C2C12 myotubes

Muscle wasting is a major problem leading to reduced quality of life and higher risks of mortality and various diseases. Muscle atrophy is caused by multiple conditions in which protein degradation exceeds its synthesis, including disuse, malnutrition, and microgravity. While Vitamin D receptor (VDR) is well known to regulate calcium and phosphate metabolism to maintain bone, recent studies have shown that VDR also plays roles in skeletal muscle development and homeostasis. Moreover, its expression is upregulated in muscle undergoing atrophy as well as after muscle injury. Here we show that VDR regulates simulated microgravity-induced atrophy in C2C12 myotubes in vitro. After 8 h of microgravity simulated using 3D-clinorotation, the VDR-binding motif was associated with chromatin regions closed by the simulated microgravity and enhancer regions inactivated by it, which suggests VDR mediates repression of enhancers. In addition, VDR was induced and translocated into the nuclei in response to simulated microgravity. VDR-deficient C2C12 myotubes showed resistance to simulated microgravity-induced atrophy and reduced induction of FBXO32, an atrophy-associated ubiquitin ligase. These results demonstrate that VDR contributes to the regulation of simulated microgravity-induced atrophy at least in part by controlling expression of atrophy-related genes.

Skeletal Muscle Is an Early Site of Zika Virus Replication and Injury, Which Impairs Myogenesis

Zika virus (ZIKV) infection became a worldwide concern due to its correlation with the development of microcephaly and other neurological disorders. ZIKV neurotropism is well characterized, but the role of peripheral viral amplification to brain infection remains unknown. Here, we found that ZIKV replicates in human primary skeletal muscle myoblasts, impairing its differentiation into myotubes but not interfering with the integrity of the already-formed muscle fibers. Using mouse models, we showed ZIKV tropism to muscle tissue either during embryogenesis after maternal transmission or when infection occurred after birth. Interestingly, ZIKV replication in the mouse skeletal muscle started immediately after ZIKV inoculation, preceding viral RNA detection in the brain and causing no disruption to the integrity of the blood brain barrier, and remained active for more than 2 weeks, whereas replication in the spleen and liver were not sustained over time. In addition, ZIKV infection of the skeletal muscle induces necrotic lesions, inflammation, and fiber atrophy. We also found a reduction in the expression of regulatory myogenic factors that are essential for muscle repair after injury. Taken together, our results indicate that the skeletal muscle is an early site of viral amplification and lesion that may result in late consequences in muscle development after ZIKV infection.

IMPORTANCE Zika Virus (ZIKV) neurotropism and its deleterious effects on central nervous system have been well characterized. However, investigations of the initial replication sites for the establishment of infection and viral spread to neural tissues remain underexplored. A complete description of the range of ZIKV-induced lesions and others factors that can influence the severity of the disease is necessary to prevent ZIKV’s deleterious effects. ZIKV has been shown to access the central nervous system without significantly affecting blood-brain barrier permeability. Here, we demonstrated that skeletal muscle is an earlier site of ZIKV replication, contributing to the increase of peripheral ZIKV load. ZIKV replication in muscle promotes necrotic lesions and inflammation and also impairs myogenesis. Overall, our findings showed that skeletal muscle is involved in pathogenesis and opens new fields in the investigation of the long-term consequences of early infection.

Transcription factor signal transducer and activator of transcription 6 (STAT6) is an inhibitory factor for adult myogenesis

Background

The signal transducer and activator of transcription 6 (STAT6) transcription factor plays a vitally important role in immune cells, where it is activated mainly by interleukin-4 (IL-4). Because IL-4 is an essential cytokine for myotube formation, STAT6 might also be involved in myogenesis as part of IL-4 signaling. This study was conducted to elucidate the role of STAT6 in adult myogenesis in vitro and in vivo.

Methods

Myoblasts were isolated from male mice and were differentiated on a culture dish to evaluate the change in STAT6 during myotube formation. Then, the effects of STAT6 overexpression and inhibition on proliferation, differentiation, and fusion in those cells were studied. Additionally, to elucidate the myogenic role of STAT6 in vivo, muscle regeneration after injury was evaluated in STAT6 knockout mice.

Results

IL-4 can increase STAT6 phosphorylation, but STAT6 phosphorylation decreased during myotube formation in culture. STAT6 overexpression decreased, but STAT6 knockdown increased the differentiation index and the fusion index. Results indicate that STAT6 inhibited myogenin protein expression. Results of in vivo experiments show that STAT6 knockout mice exhibited better regeneration than wild-type mice 5 days after cardiotoxin-induced injury. It is particularly interesting that results obtained using cells from STAT6 knockout mice suggest that this STAT6 inhibitory action for myogenesis was not mediated by IL-4 but might instead be associated with p38 mitogen-activated protein kinase phosphorylation. However, STAT6 was not involved in the proliferation of myogenic cells in vitro and in vivo.

Conclusion

Results suggest that STAT6 functions as an inhibitor of adult myogenesis. Moreover, results suggest that the IL-4-STAT6 signaling axis is unlikely to be responsible for myotube formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-021-00271-8.

Dermatomyositis: immunological landscape, biomarkers, and potential candidate drugs

INTRODUCTION

Dermatomyositis (DM) is a rare inflammatory disease characterized by the invasion of the skin and muscles. Environmental, genetic, and immunological factors contribute to disease pathology. To date, no bioinformatics studies have been conducted on the potential pathogenic genes and immune cell infiltration in DM. Therefore, we aimed to identify differentially expressed genes (DEGs) and immune cells, as well as potential pathogenic genes and immune characteristics, which may be useful for the diagnosis and treatment of DM.

METHOD

GSE1551, GSE5370, GSE39454, and GSE48280 from Gene Expression Omnibus were included in our study. Limma, ClusterProfiler, and Kyoto Encyclopedia of Genes and Genomes were used to identify DEGs, Gene Ontology (GO), and perform pathway analyses, respectively. Cytoscape was used to construct the protein-protein interaction (PPI) network. Small-molecule drugs were identified using a connectivity map (CMap), and the TIMER database was used to identify infiltrating cells.

RESULTS

DEG analysis identified 12 downregulated and 163 upregulated genes. GO analysis showed that DEGs were enriched in immune-related pathways. Ten hub genes were identified from the PPI network. Additionally, CMap analysis showed that caffeic acid, sulfaphenazole, molindone, tiabendazole, and bacitracin were potential small-molecule drugs with therapeutic significance. We identified eight immune cells with differential infiltration in patients with DM and controls. Finally, we constructed a powerful diagnostic model based on memory B cells, M1, and M2 macrophages.

CONCLUSIONS

This study explored the potential molecular mechanism and immunological landscape of DM and may guide future research and treatment of DM.

KEY POINTS

• We explored the molecular mechanism and immunological landscape of dermatomyositis. • GO analysis showed that DEGs were enriched in immune-related pathways. • We predicted small-molecular drugs with potential therapeutic significance based on bioanalytical techniques. • We identified six immune cells with differential infiltration in patients with DM and controls.

IL18-containing 5-gene signature distinguishes histologically identical dermatomyositis and lupus erythematosus skin lesions

Skin lesions in dermatomyositis (DM) are common, are frequently refractory, and have prognostic significance. Histologically, DM lesions appear similar to cutaneous lupus erythematosus (CLE) lesions and frequently cannot be differentiated. We thus compared the transcriptional profile of DM biopsies with CLE lesions to identify unique features. Type I IFN signaling, including IFN-κ upregulation, was a common pathway in both DM and CLE; however, CLE also exhibited other inflammatory pathways. Notably, DM lesions could be distinguished from CLE by a 5-gene biomarker panel that included IL18 upregulation. Using single-cell RNA-sequencing, we further identified keratinocytes as the main source of increased IL-18 in DM skin. This study identifies a potentially novel molecular signature, with significant clinical implications for differentiating DM from CLE lesions, and highlights the potential role for IL-18 in the pathophysiology of DM skin disease.

IL-18 distinguishes dermatomyositis skin inflammation from cutaneous lupus erythematosus lesions.

Biologic therapy in the idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIM) are a group of autoimmune diseases resulting from inflammation of muscle and manifesting as weakness, though a range of extra-muscular manifestations are observed. These are often correlated closely with disease subtype and the presence of myositis-specific/myositis-associated antibodies. IIM are notoriously difficult to treat and often refractory to glucocorticoid therapy and synthetic immunosuppressants. Both the innate and adaptive immune systems are implicated in the pathogenesis of IIM. A growing understanding of the key cytokines as well as the cell-mediated and antibody effectors of disease has identified multiple potential targets for biologic therapy. The most widely used of these is B-cell depletion via rituximab though the tumour necrosis factor inhibitors and other biologic therapies used in diseases such as rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis have also been trialled. This review summarises the literature thus far on biologic therapy in IIM, highlighting both the significant trials that influence current treatment regimens and also the continuing need for further research to inform more effective therapies.

The innate immune response to ischemic injury: a multiscale modeling perspective

Background

Cell death as a result of ischemic injury triggers powerful mechanisms regulated by germline-encoded Pattern Recognition Receptors (PRRs) with shared specificity that recognize invading pathogens and endogenous ligands released from dying cells, and as such are essential to human health. Alternatively, dysregulation of these mechanisms contributes to extreme inflammation, deleterious tissue damage and impaired healing in various diseases. The Toll-like receptors (TLRs) are a prototypical family of PRRs that may be powerful anti-inflammatory targets if agents can be designed that antagonize their harmful effects while preserving host defense functions. This requires an understanding of the complex interactions and consequences of targeting the TLR-mediated pathways as well as technologies to analyze and interpret these, which will then allow the simulation of perturbations targeting specific pathway components, predict potential outcomes and identify safe and effective therapeutic targets.

Results

We constructed a multiscale mathematical model that spans the tissue and intracellular scales, and captures the consequences of targeting various regulatory components of injury-induced TLR4 signal transduction on potential pro-inflammatory or pro-healing outcomes. We applied known interactions to simulate how inactivation of specific regulatory nodes affects dynamics in the context of injury and to predict phenotypes of potential therapeutic interventions. We propose rules to link model behavior to qualitative estimates of pro-inflammatory signal activation, macrophage infiltration, production of reactive oxygen species and resolution. We tested the validity of the model by assessing its ability to reproduce published data not used in its construction.

Conclusions

These studies will enable us to form a conceptual framework focusing on TLR4-mediated ischemic repair to assess potential molecular targets that can be utilized therapeutically to improve efficacy and safety in treating ischemic/inflammatory injury.

Dysregulated innate immune function in the aetiopathogenesis of idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of systemic muscle conditions that are believed to be autoimmune in nature. They have distinct pathological features, but the aetiopathogenesis of each subtype remains largely unknown. Recently, there has been increased interest in the complex role the innate immune system plays in initiating and perpetuating these conditions, and how this may differ between subtypes. This article summarises the traditional paradigms of IIM pathogenesis and reviews the accumulating evidence for disturbances in innate immune processes in these rare, but debilitating chronic conditions.