Lack of FOS/FOSB Gene Rearrangements in Ischemic Fasciitis Indicates Distinct Pathogenesis from Proliferative Fasciitis and Proliferative Myositis

Ischemic fasciitis is a pseudosarcomatous fibroblastic/myofibroblastic proliferation that shares several overlapping morphological features with proliferative fasciitis and proliferative myositis. Prompted by a recent study that demonstrated FOS gene rearrangements in proliferative fasciitis and proliferative myositis, suggesting that these lesions likely represent examples of "transient neoplasia," we examined a cohort of ischemic fasciitis for similar events. Nine cases of ischemic fasciitis were retrieved from our institutional archives for diagnosis verification, immunostaining for FOSB, and fluorescence in situ hybridization using validated FOS and FOSB break-apart probes. Additionally, RNAseq was performed on a subset of cases. In our cohort, eight out of nine cases of ischemic fasciitis were positive for FOSB IHC, but FISH studies were consistently negative for FOSB and FOS gene rearrangements in all cases. Additionally, RNA sequencing did not detect any gene fusions. These findings suggest that the pathogenesis of ischemic fasciitis is distinct from that of proliferative fasciitis and proliferative myositis.

Comprehensive transcriptomic analysis and machine learning reveal unique gene expression profiles in patients with immune-mediated necrotizing myopathy

BACKGROUND

Immune-mediated necrotizing myopathy (IMNM) is an autoimmune myopathy characterized by severe proximal weakness and muscle fiber necrosis, yet its pathogenesis remains unclear. So far, there are few bioinformatics studies on underlying pathogenic genes and infiltrating immune cell profiles of IMNM. Therefore, we aimed to characterize differentially expressed genes (DEGs) and infiltrating cells in IMNM muscle biopsy specimens, which may be useful for elucidating the pathogenesis of IMNM.

METHODS

Three datasets (GSE39454, GSE48280 and GSE128470) of gene expression profiling related to IMNM were obtained from the Gene Expression Omnibus database. Data were normalized, and DEG analysis was performed using the limma package. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of DEGs were performed using clusterProfiler. The CIBERSORT algorithm was performed to identify infiltrating cells. Machine learning algorithm and gene set enrichment analysis (GSEA) were performed to find distinctive gene signatures and the underlying signaling pathways of IMNM.

RESULTS

DEG analysis identified upregulated and downregulated in IMNM muscle compared to the gene expression levels of other groups. GO and KEGG analysis showed that the pathogenesis of IMNM was notable for the under-representation of pathways that were important in dermatomyositis and inclusion body myositis. Three immune cells (M2 macrophages, resting dendritic cells and resting natural killer cells) with differential infiltration and five key genes (NDUFAF7, POLR2J, CD99, ARF5 and SKAP2) in patients with IMNM were identified through the CIBERSORT and machine learning algorithm. The GSEA results revealed that the key genes were remarkably enriched in diverse immunological and muscle metabolism-related pathways.

CONCLUSIONS

We comprehensively explored immunological landscape of IMNM, which is indicative for the research of IMNM pathogenesis.

K2P2.1 is a regulator of inflammatory cell responses in idiopathic inflammatory myopathies

K2P2.1 (TREK1), a two-pore domain potassium channel, has emerged as regulator of leukocyte transmigration into the central nervous system. In the context of skeletal muscle, immune cell infiltration constitutes the pathogenic hallmark of idiopathic inflammatory myopathies (IIMs). However, the underlying mechanisms remain to be elucidated. In this study, we investigated the role of K2P2.1 in the autoimmune response of IIMs. We detected K2P2.1 expression in primary skeletal muscle and endothelial cells of murine and human origin. We observed an increased pro-inflammatory cell response, adhesion and transmigration by pharmacological blockade or genetic deletion of K2P2.1 in vitro and in in vivo myositis mouse models. Of note, our findings were not restricted to endothelial cells as skeletal muscle cells with impaired K2P2.1 function also demonstrated a strong pro-inflammatory response. Conversely, these features were abrogated by activation of K2P2.1 and improved the disease course of a myositis mouse model. In humans, K2P2.1 expression was diminished in IIM patients compared to non-diseased controls arguing for the translatability of our findings. In summary, K2P2.1 may regulate the inflammatory response of skeletal muscle. Further research is required to understand whether K2P2.1 could serve as novel therapeutic target.

Distinct HLA associations with autoantibody-defined subgroups in idiopathic inflammatory myopathies

BACKGROUND

In patients with idiopathic inflammatory myopathies (IIM), autoantibodies are associated with specific clinical phenotypes suggesting a pathogenic role of adaptive immunity. We explored if autoantibody profiles are associated with specific HLA genetic variants and clinical manifestations in IIM.

METHODS

We included 1348 IIM patients and determined the occurrence of 14 myositis-specific or -associated autoantibodies. We used unsupervised cluster analysis to identify autoantibody-defined subgroups and logistic regression to estimate associations with clinical manifestations, HLA-DRB1, HLA-DQA1, HLA-DQB1 alleles, and amino acids imputed from genetic information of HLA class II and I molecules.

FINDINGS

We identified eight subgroups with the following dominant autoantibodies: anti-Ro52, -U1RNP, -PM/Scl, -Mi2, -Jo1, -Jo1/Ro52, -TIF1γ or negative for all analysed autoantibodies. Associations with HLA-DRB1∗11, HLA-DRB1∗15, HLA-DQA1∗03, and HLA-DQB1∗03 were present in the anti-U1RNP-dominated subgroup. HLA-DRB1∗03, HLA-DQA1∗05, and HLA-DQB1∗02 alleles were overrepresented in the anti-PM/Scl and anti-Jo1/Ro52-dominated subgroups. HLA-DRB1∗16, HLA-DRB1∗07 alleles were most frequent in anti-Mi2 and HLA-DRB1∗01 and HLA-DRB1∗07 alleles in the anti-TIF1γ subgroup. The HLA-DRB1∗13, HLA-DQA1∗01 and HLA-DQB1∗06 alleles were overrepresented in the negative subgroup. Significant signals from variations in class I molecules were detected in the subgroups dominated by anti-Mi2, anti-Jo1/Ro52, anti-TIF1γ, and the negative subgroup.

INTERPRETATION

Distinct HLA class II and I associations were observed for almost all autoantibody-defined subgroups. The associations support autoantibody profiles use for classifying IIM which would likely reflect underlying pathogenic mechanisms better than classifications based on clinical symptoms and/or histopathological features.

FUNDING

See a detailed list of funding bodies in the Acknowledgements section at the end of the manuscript.

Idiopathic inflammatory myopathy and non-coding RNA

Idiopathic inflammatory myopathies (IIMs) are common autoimmune diseases that affect skeletal muscle quality and function. The lack of an early diagnosis and treatment can lead to irreversible muscle damage. Non-coding RNAs (ncRNAs) play an important role in inflammatory transfer, muscle regeneration, differentiation, and regulation of specific antibody levels and pain in IIMs. ncRNAs can be detected in blood and hair; therefore, ncRNAs detection has great potential for diagnosing, preventing, and treating IIMs in conjunction with other methods. However, the specific roles and mechanisms underlying the regulation of IIMs and their subtypes remain unclear. Here, we review the mechanisms by which micro RNAs and long non-coding RNA-messenger RNA networks regulate IIMs to provide a basis for ncRNAs use as diagnostic tools and therapeutic targets for IIMs.

Identification of Unique microRNA Profiles in Different Types of Idiopathic Inflammatory Myopathy

Dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM) are four major types of idiopathic inflammatory myopathy (IIM). Muscle biopsies from each type of IIM have unique transcriptomic profiles. MicroRNAs (miRNAs) target messenger RNAs (mRNAs), thereby regulating their expression and modulating transcriptomic profiles. In this study, 18 DM, 12 IMNM, 6 AS, 6 IBM, and 6 histologically normal muscle biopsies underwent miRNA profiling using the NanoString nCounter system. Eleven miRNAs were exclusively differentially expressed in DM compared to controls, seven miRNAs were only differentially expressed in AS, and nine miRNAs were specifically upregulated in IBM. No differentially expressed miRNAs were identified in IMNM. We also analyzed miRNA-mRNA associations to identify putative targets of differentially expressed miRNAs. In DM and AS, these were predominantly related to inflammation and cell cycle progression. Moreover, our analysis showed an association between miR-30a-3p, miR-30e-3p, and miR-199b-5p downregulation in DM and the upregulation of target genes induced by type I interferon. In conclusion, we show that muscle biopsies from DM, AS, and IBM patients have unique miRNA signatures and that these miRNAs might play a role in regulating the expression of genes known to be involved in IIM pathogenesis.

Deciphering the crosstalk of immune dysregulation between COVID-19 and idiopathic inflammatory myopathy

Background

The coronavirus disease (COVID-19) pandemic is a serious threat to public health worldwide. Growing evidence reveals that there are certain links between COVID-19 and autoimmune diseases; in particular, COVID-19 and idiopathic inflammatory myopathies (IIM) have been observed to be clinically comorbid. Hence, this study aimed to elucidate the molecular mechanisms of COVID-19 and IIM from a genomic perspective.

Methods

We obtained transcriptome data of patients with COVID-19 and IIM separately from the GEO database and identified common differentially expressed genes (DEGs) by intersection. We then performed functional enrichment, PPI, machine learning, gene expression regulatory network, and immune infiltration analyses of co-expressed genes.

Results

A total of 91 common genes were identified between COVID-19 and IIM. Functional enrichment analysis revealed that these genes were mainly involved in immune dysregulation, response to external stimuli, and MAPK signaling pathways. The MCODE algorithm recognized two densely linked clusters in the common genes, which were related to inflammatory factors and interferon signaling. Subsequently, three key genes (CDKN1A, IFI27, and STAB1) were screened using machine learning to predict the occurrence of COVID-19 related IIM. These key genes exhibited excellent diagnostic performance in both training and validation cohorts. Moreover, we created TF-gene and miRNA-gene networks to reveal the regulation of key genes. Finally, we estimated the relationship between key genes and immune cell infiltration, of which IFI27 was positively associated with M1 macrophages.

Conclusion

Our work revealed common molecular mechanisms, core genes, potential targets, and therapeutic approaches for COVID-19 and IIM from a genomic perspective. This provides new ideas for the diagnosis and treatment of COVID-19 related IIM in the future.

Transcriptomic profiling reveals distinct subsets of immune checkpoint inhibitor induced myositis

OBJECTIVES

Inflammatory myopathy or myositis is a heterogeneous family of immune-mediated diseases including dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM). Immune checkpoint inhibitors (ICIs) can also cause myositis (ICI-myositis). This study was designed to define gene expression patterns in muscle biopsies from patients with ICI-myositis.

METHODS

Bulk RNA sequencing was performed on 200 muscle biopsies (35 ICI-myositis, 44 DM, 18 AS, 54 IMNM, 16 IBM and 33 normal muscle biopsies) and single nuclei RNA sequencing was performed on 22 muscle biopsies (seven ICI-myositis, four DM, three AS, six IMNM and two IBM).

RESULTS

Unsupervised clustering defined three distinct transcriptomic subsets of ICI-myositis: ICI-DM, ICI-MYO1 and ICI-MYO2. ICI-DM included patients with DM and anti-TIF1γ autoantibodies who, like DM patients, overexpressed type 1 interferon-inducible genes. ICI-MYO1 patients had highly inflammatory muscle biopsies and included all patients that developed coexisting myocarditis. ICI-MYO2 was composed of patients with predominant necrotising pathology and low levels of muscle inflammation. The type 2 interferon pathway was activated both in ICI-DM and ICI-MYO1. Unlike the other types of myositis, all three subsets of ICI-myositis patients overexpressed genes involved in the IL6 pathway.

CONCLUSIONS

We identified three distinct types of ICI-myositis based on transcriptomic analyses. The IL6 pathway was overexpressed in all groups, the type I interferon pathway activation was specific for ICI-DM, the type 2 IFN pathway was overexpressed in both ICI-DM and ICI-MYO1 and only ICI-MYO1 patients developed myocarditis.

Identification of Novel Associations and Localization of Signals in Idiopathic Inflammatory Myopathies Using Genome-Wide Imputation

OBJECTIVE

The idiopathic inflammatory myopathies (IIMs) are heterogeneous diseases thought to be initiated by immune activation in genetically predisposed individuals. We imputed variants from the ImmunoChip array using a large reference panel to fine-map associations and identify novel associations in IIM.

METHODS

We analyzed 2,565 Caucasian IIM patient samples collected through the Myositis Genetics Consortium (MYOGEN) and 10,260 ethnically matched control samples. We imputed 1,648,116 variants from the ImmunoChip array using the Haplotype Reference Consortium panel and conducted association analysis on IIM and clinical and serologic subgroups.

RESULTS

The HLA locus was consistently the most significantly associated region. Four non-HLA regions reached genome-wide significance, SDK2 and LINC00924 (both novel) and STAT4 in the whole IIM cohort, with evidence of independent variants in STAT4, and NAB1 in the polymyositis (PM) subgroup. We also found suggestive evidence of association with loci previously associated with other autoimmune rheumatic diseases (TEC and LTBR). We identified more significant associations than those previously reported in IIM for STAT4 and DGKQ in the total cohort, for NAB1 and FAM167A-BLK loci in PM, and for CCR5 in inclusion body myositis. We found enrichment of variants among DNase I hypersensitivity sites and histone marks associated with active transcription within blood cells.

CONCLUSION

We found novel and strong associations in IIM and PM and localized signals to single genes and immune cell types.

Epidemiological and genetic features of anti-3‑hydroxy-3-methylglutaryl-CoA reductase necrotizing myopathy: Single-center experience and literature review

OBJECTIVE

To characterize the demographic, genetic, clinical, and serological features of patients with anti-3‑hydroxy-3-methylglutaryl-CoA reductase (HMGCR) immune-mediated necrotizing myopathy (IMNM) in a region of northern Spain.

METHODS

Study of all patients diagnosed with anti-HMGCR IMNM during a 5-year period at a reference hospital in northern Spain. Besides clinical and laboratory data, we analyzed the genetic influence of HLA genes and the rs4149056 (c.521T>C) single nucleotide polymorphism (SNP) in the SLCO1B1 gene.

RESULTS

8 patients (5 women, 3 men) with a mean ± SD age of 64.9 ± 7.3 years, fulfilled the criteria for anti-HMGCR IMNM. The incidence rate was 0.6 per 100.000 person-years and the prevalence 3 per 100.000 population. All patients had been exposed to statins. All of them had predominant lower limb proximal and symmetric muscle weakness that was severe in 2 and had elevated serum CK levels with a median [IQR] of 4488 [2538-9194] IU/L. Serum 25‑hydroxy vitamin D levels were decreased in all patients in whom it was determined. The 3 patients with a previous diagnosis of hypothyroidism had abnormal levels of TSH at the time of diagnosis. All patients experienced improvement with different schemes of immunosuppressive therapy. Noteworthy, 7 of 8 patients carried the HLA-DRB1*11 allele. The frequency of the rs4149056 C allele in the SLCO1B1 gene (12.5%) was similar to that of the general population.

CONCLUSION

In northern Spain, anti-HMGCR IMNM preferentially affects people over 50 years of age who are carriers of the HLA-DRB1*11 allele and take statins. Both low vitamin D levels and hypothyroidism may play a potential predisposing role in the development of this disease.

The Genetics of Autoimmune Myositis

The idiopathic inflammatory myopathies (IIM) are rare, heterogeneous systemic autoimmune disorders, characterized by inflammation of skeletal muscle and multi-organ involvement. Studies to identify genetic risk factors and dysregulated gene expression in IIM aim to increase our understanding of disease pathogenesis. Genome-wide association studies have confirmed the HLA region as the most strongly associated region in IIM, with different associations between clinically-defined subgroups. Associated genes are involved in both the innate and adaptive immune response, while identification of variants reported in other autoimmune disorders suggests shared biological pathways. Targeted imputation analysis has identified key associated amino acid residues within HLA molecules that may influence antigen recognition. These amino acids increase risk for specific clinical phenotypes and autoantibody subgroups, and suggest that serology-defined subgroups may be more homogeneous. Recent data support the contribution of rare genetic variation to disease susceptibility in IIM, including mitochondrial DNA variation in sporadic inclusion body myositis and somatic mutations and loss of heterozygosity in cancer-associated myositis. Gene expression studies in skeletal muscle, blood and skin from individuals with IIM has confirmed the role of interferon signalling and other dysregulated pathways, and identified cell-type specific signatures. These dysregulated genes differentiate IIM subgroups and identify potential biomarkers. Here, we review recent genetic studies in IIM, and how these inform our understanding of disease pathogenesis and provide mechanistic insights into biological pathways.

A network of core and subtype-specific gene expression programs in myositis

Myositis comprises a heterogeneous group of skeletal muscle disorders which converge on chronic muscle inflammation and weakness. Our understanding of myositis pathogenesis is limited, and many myositis patients lack effective therapies. Using muscle biopsy transcriptome profiles from 119 myositis patients (spanning major clinical and serological disease subtypes) and 20 normal controls, we generated a co-expression network of 8101 dynamically regulated transcripts. This network organized the myositis transcriptome into a map of gene expression modules representing interrelated biological processes and disease signatures. Universally myositis-upregulated network modules included muscle regeneration, specific cytokine signatures, the acute phase response, and neutrophil degranulation. Universally myositis-suppressed pathways included a specific subset of myofilaments, the mitochondrial envelope, and nuclear isoforms of the anti-apoptotic humanin protein. Myositis subtype-specific modules included type 1 interferon signaling and titin (dermatomyositis), RNA processing (antisynthetase syndrome), and vasculogenesis (inclusion body myositis). Importantly, therapies exist to target influential proteins in many myositis-dysregulated modules, and nearly all modules contained understudied proteins and non-coding RNAs - many of which were extraordinarily dysregulated in myositis and may represent novel therapeutic targets. Finally, we apply our network to patient classification, finding that a deep learning algorithm trained on patient-level network "images" successfully assigned patients to clinical groups and further into molecular subclusters. Altogether, we provide a global resource to probe and contextualize differential gene expression in myositis.

Abnormal Paraoxonase-1 (PON1) enzyme activity in idiopathic inflammatory myopathies

OBJECTIVES

Patients with idiopathic inflammatory myopathies (IIM) have severe vascular involvement, which contributes to disease morbidity and mortality. Paraoxonase-1 (PON1) is a high-density lipoprotein (HDL) associated protein, which protects the vascular endothelium from oxidative injury and damage. The current work assessed the functional and genetic determinants of PON1 activity in IIM patients.

METHODS

184 IIM patients and 112 healthy controls (HC) were included. PON1 enzyme activity was assessed by paraoxonase, arylesterase and lactonase assays, and the Q192R PON1 single nucleotide polymorphism (SNP) was analyzed. Multivariate regression models examined associations of PON1 activity with IIM diagnosis and myositis disease outcomes.

RESULTS

The arylesterase and lactonase activities of PON1 were significantly lower in IIM patients compared with HC. Higher myositis disease activity, the presence of severe IIM associated interstitial lung disease (ILD), and the presence of MDA5 or anti-synthetase antibodies were significantly associated with lower PON1 activity. The PON1 Q192R polymorphism was strongly linked to the paraoxonase activity of PON1 in IIM, and patients with the PON1 QQ genotype had better IIM disease outcomes compared with patients with the QR or RR genotypes.

CONCLUSIONS

The arylesterase and lactonase activities of PON1 are significantly impaired in IIM patients compared with HC, and inversely associate with IIM disease activity and the presence of severe ILD. The PON1 QQ genotype associates with more favorable disease outcomes in IIM patients. Large prospective studies are needed to further evaluate the role of PON1 and PON1 genetic polymorphisms in the development and propagation of IIM and IIM-ILD.

Familial aggregation and heritability: a nationwide family-based study of idiopathic inflammatory myopathies

OBJECTIVES

The magnitude of the genetic contribution to idiopathic inflammatory myopathies (IIMs) is unknown. In this project, we aimed to investigate the familial aggregation and heritability of IIM.

METHODS

This is a family-based study using nationwide healthcare register data in Sweden. We matched each patient with IIM to individuals without IIM, identified their first-degree relatives and determined the IIM status among all first-degree relatives. We estimated the adjusted ORs (aORs) of familial aggregation of IIM using conditional logistic regression. In addition, we used tetrachoric correlation to estimate the heritability of IIM.

RESULTS

We included 7615 first-degree relatives of 1620 patients with IIM diagnosed between 1997 and 2016 and 37 309 first-degree relatives of 7797 individuals without IIM. Compared with individuals without IIM, patients with IIM were more likely to have ≥1 first-degree relative affected by IIM (aOR=4.32, 95% CI 2.00 to 9.34). Furthermore, the aOR of familial aggregation of IIM in full siblings was 2.53 (95% CI 1.62 to 3.96). The heritability of IIM was 22% (95% CI 12% to 31%) among any first-degree relatives and 24% (95% CI 12% to 37%) among full siblings.

CONCLUSIONS

IIM has a familial component with a risk of aggregation among first-degree relatives and a heritability of about 20%. This information is of importance for future aetiological studies and in clinical counselling.

HLA association with the susceptibility to anti-synthetase syndrome

OBJECTIVE

To investigate the human leukocyte antigen (HLA) association with anti-synthetase syndrome (ASSD).

METHODS

We conducted the largest immunogenetic HLA-DRB1 and HLA-B study to date in a homogeneous cohort of 168 Caucasian patients with ASSD and 486 ethnically matched healthy controls by sequencing-based-typing.

RESULTS

A statistically significant increase of HLA-DRB1*03:01 and HLA-B*08:01 alleles in patients with ASSD compared to healthy controls was disclosed (26.2% versus 12.2%, P=1.56E-09, odds ratio-OR [95% confidence interval-CI]=2.54 [1.84-3.50] and 21.4% versus 5.5%, P=18.95E-18, OR [95% CI]=4.73 [3.18-7.05]; respectively). Additionally, HLA-DRB1*07:01 allele was significantly decreased in patients with ASSD compared to controls (9.2% versus 17.5%, P=0.0003, OR [95% CI]=0.48 [0.31-0.72]). Moreover, a statistically significant increase of HLA-DRB1*03:01 allele in anti-Jo-1 positive compared to anti-Jo-1 negative patients with ASSD was observed (31.8% versus 15.5%, P=0.001, OR [95% CI]=2.54 [1.39-4.81]). Similar findings were observed when HLA carrier frequencies were assessed. The HLA-DRB1*03:01 association with anti-Jo-1 was unrelated to smoking history. No HLA differences in patients with ASSD stratified according to the presence/absence of the most representative non-anti-Jo-1 anti-synthetase autoantibodies (anti-PL-12 and anti-PL-7), arthritis, myositis or interstitial lung disease were observed.

CONCLUSIONS

Our results support the association of the HLA complex with the susceptibility to ASSD.

Machine learning algorithms reveal unique gene expression profiles in muscle biopsies from patients with different types of myositis

OBJECTIVES

Myositis is a heterogeneous family of diseases that includes dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotising myopathy (IMNM), inclusion body myositis (IBM), polymyositis and overlap myositis. Additional subtypes of myositis can be defined by the presence of myositis-specific autoantibodies (MSAs). The purpose of this study was to define unique gene expression profiles in muscle biopsies from patients with MSA-positive DM, AS and IMNM as well as IBM.

METHODS

RNA-seq was performed on muscle biopsies from 119 myositis patients with IBM or defined MSAs and 20 controls. Machine learning algorithms were trained on transcriptomic data and recursive feature elimination was used to determine which genes were most useful for classifying muscle biopsies into each type and MSA-defined subtype of myositis.

RESULTS

The support vector machine learning algorithm classified the muscle biopsies with >90% accuracy. Recursive feature elimination identified genes that are most useful to the machine learning algorithm and that are only overexpressed in one type of myositis. For example, CAMK1G (calcium/calmodulin-dependent protein kinase IG), EGR4 (early growth response protein 4) and CXCL8 (interleukin 8) are highly expressed in AS but not in DM or other types of myositis. Using the same computational approach, we also identified genes that are uniquely overexpressed in different MSA-defined subtypes. These included apolipoprotein A4 (APOA4), which is only expressed in anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) myopathy, and MADCAM1 (mucosal vascular addressin cell adhesion molecule 1), which is only expressed in anti-Mi2-positive DM.

CONCLUSIONS

Unique gene expression profiles in muscle biopsies from patients with MSA-defined subtypes of myositis and IBM suggest that different pathological mechanisms underly muscle damage in each of these diseases.

New Pathogenesis Mechanisms and Translational Leads Identified by Multidimensional Analysis of Necrotizing Myositis in Primates

A fundamental goal of contemporary biomedical research is to understand the molecular basis of disease pathogenesis and exploit this information to develop targeted and more-effective therapies. Necrotizing myositis caused by the bacterial pathogen Streptococcus pyogenes is a devastating human infection with a high mortality rate and few successful therapeutic options. We used dual transcriptome sequencing (RNA-seq) to analyze the transcriptomes of S. pyogenes and host skeletal muscle recovered contemporaneously from infected nonhuman primates. The in vivo bacterial transcriptome was strikingly remodeled compared to organisms grown in vitro, with significant upregulation of genes contributing to virulence and altered regulation of metabolic genes. The transcriptome of muscle tissue from infected nonhuman primates (NHPs) differed significantly from that of mock-infected animals, due in part to substantial changes in genes contributing to inflammation and host defense processes. We discovered significant positive correlations between group A streptococcus (GAS) virulence factor transcripts and genes involved in the host immune response and inflammation. We also discovered significant correlations between the magnitude of bacterial virulence gene expression in vivo and pathogen fitness, as assessed by previously conducted genome-wide transposon-directed insertion site sequencing (TraDIS). By integrating the bacterial RNA-seq data with the fitness data generated by TraDIS, we discovered five new pathogen genes, namely, S. pyogenes 0281 (Spy0281 [dahA]), ihk-irr, slr, isp, and ciaH, that contribute to necrotizing myositis and confirmed these findings using isogenic deletion-mutant strains. Taken together, our study results provide rich new information about the molecular events occurring in severe invasive infection of primate skeletal muscle that has extensive translational research implications.IMPORTANCE Necrotizing myositis caused by Streptococcus pyogenes has high morbidity and mortality rates and relatively few successful therapeutic options. In addition, there is no licensed human S. pyogenes vaccine. To gain enhanced understanding of the molecular basis of this infection, we employed a multidimensional analysis strategy that included dual RNA-seq and other data derived from experimental infection of nonhuman primates. The data were used to target five streptococcal genes for pathogenesis research, resulting in the unambiguous demonstration that these genes contribute to pathogen-host molecular interactions in necrotizing infections. We exploited fitness data derived from a recently conducted genome-wide transposon mutagenesis study to discover significant correlation between the magnitude of bacterial virulence gene expression in vivo and pathogen fitness. Collectively, our findings have significant implications for translational research, potentially including vaccine efforts.

Gene fitness landscape of group A streptococcus during necrotizing myositis

Necrotizing fasciitis and myositis are devastating infections characterized by high mortality. Group A streptococcus (GAS) is a common cause of these infections, but the molecular pathogenesis is poorly understood. We report a genome-wide analysis using serotype M1 and M28 strains that identified GAS genes contributing to necrotizing myositis in nonhuman primates (NHP), a clinically relevant model. Using transposon-directed insertion-site sequencing (TraDIS), we identified 126 and 116 GAS genes required for infection by serotype M1 and M28 organisms, respectively. For both M1 and M28 strains, more than 25% of the GAS genes required for necrotizing myositis encode known or putative transporters. Thirteen GAS transporters contributed to both M1 and M28 strain fitness in NHP myositis, including putative importers for amino acids, carbohydrates, and vitamins and exporters for toxins, quorum-sensing peptides, and uncharacterized molecules. Targeted deletion of genes encoding 5 transporters confirmed that each isogenic mutant strain was significantly (P < 0.05) impaired in causing necrotizing myositis in NHPs. Quantitative reverse-transcriptase PCR (qRT-PCR) analysis showed that these 5 genes are expressed in infected NHP and human skeletal muscle. Certain substrate-binding lipoproteins of these transporters, such as Spy0271 and Spy1728, were previously documented to be surface exposed, suggesting that our findings have translational research implications.

A Mutation in the Mitochondrial Aspartate/Glutamate Carrier Leads to a More Oxidizing Intramitochondrial Environment and an Inflammatory Myopathy in Dutch Shepherd Dogs

BACKGROUND

Inflammatory myopathies are characterized by infiltration of inflammatory cells into muscle. Typically, immune-mediated disorders such as polymyositis, dermatomyositis and inclusion body myositis are diagnosed.

OBJECTIVE

A small family of dogs with early onset muscle weakness and inflammatory muscle biopsies were investigated for an underlying genetic cause.

METHODS

Following the histopathological diagnosis of inflammatory myopathy, mutational analysis including whole genome sequencing, functional transport studies of the mutated and wild-type proteins, and metabolomic analysis were performed.

RESULTS

Whole genome resequencing identified a pathological variant in the SLC25A12 gene, resulting in a leucine to proline substitution at amino acid 349 in the mitochondrial aspartate-glutamate transporter known as the neuron and muscle specific aspartate glutamate carrier 1 (AGC1). Functionally reconstituting recombinant wild-type and mutant AGC1 into liposomes demonstrated a dramatic decrease in AGC1 transport activity and inability to transfer reducing equivalents from the cytosol into mitochondria. Targeted, broad-spectrum metabolomic analysis from affected and control muscles demonstrated a proinflammatory milieu and strong support for oxidative stress.

CONCLUSIONS

This study provides the first description of a metabolic mechanism in which ablated mitochondrial glutamate transport markedly reduced the import of reducing equivalents into mitochondria and produced a highly oxidizing and proinflammatory muscle environment and an inflammatory myopathy.

Effect of Genetic and Laboratory Findings on Clinical Course of Antisynthetase Syndrome in a Hungarian Cohort

The aim of this study was to determine the clinical, serological, and genetic features of anti-Jo-1 positive antisynthetase patients followed by a Hungarian single centre to identify prognostic markers, which can predict disease phenotypes and disease progression. It was a retrospective study using clinical database of 49 anti-Jo-1 positive patients. 100% of patients exhibited myositis, 73% interstitial lung disease, 88% arthritis, 65% Raynaud's phenomenon, 43% fever, 33% mechanic's hand, and 12% dysphagia. We could detect significant correlation between anti-Jo-1 titer and the CK and CRP levels at disease onset and during disease course. HLA DRB1⁎03 positivity was present in 68.96% of patients, where the CK level at diagnosis was significantly lower compared to the HLA DRB1⁎03 negative patients. HLA DQA1⁎0501-DQB1⁎0201 haplotype was found in 58.62% of patients, but no significant correlation was found regarding any clinical or laboratory features. Higher CRP, ESR level, RF positivity, and the presence of fever or vasculitic skin lesions at the time of diagnosis indicated a higher steroid demand and the administration of higher number of immunosuppressants during the follow-up within anti-Jo-1 positive patients. The organ involvement of the disease was not different in HLA-DRB1⁎0301 positive or negative patients who were positive to the anti-Jo-1 antibody; however, initial CK level was lower in HLA-DRB1⁎0301 positive patients. Distinct laboratory and clinical parameters at diagnosis could be considered as prognostic markers.

Molecular markers of systemic autoimmune disorders: the expression of MHC-located HSP70 genes is significantly associated with autoimmunity development

OBJECTIVES

To analyse the expression regulation of two inducible HSP70 genes - HSPA1A and HSPA1B - located within the major histocompatibility complex (MHC) in patients with various systemic autoimmune diseases and to prove the reliability of MHC-located HSP70 genes as molecular markers reflecting the autoimmune process.

METHODS

94 adult patients with idiopathic inflammatory myopathy (IIM, n=31), systemic lupus erythematosus (SLE, n=31) or systemic sclerosis (SSc, n=32) and 37 healthy individuals were analysed. The mRNA expression level was determined using quantitative real-time PCR method. The expression of intracellular HSP70 was established by flow cytometry, the extracellular HSP70 protein was measured in plasma samples using a commercially available sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

The expression of HSPA1A gene was significantly up-regulated in patients with autoimmune diseases (SLE: p<0.01; SSc: p<0.01; IIM: p<0.0001) compared to healthy controls. The expression of HSPA1B gene was increased only in patients with myositis (p<0.05). Furthermore, the HSPA1B gene expression is associated with the HLA-DRB1*03 risk allele in patients with IIM. In addition, we have found a relation between HSPA1A gene expression regulation and the presence of disease specific autoantibodies in patients with SLE and myositis. The level of intracellular HSP70 was not increased; however, the level of extracellular HSP70 protein was increased in patients suffering from SSc and IIM as compared to controls.

CONCLUSIONS

The results suggest an involvement of the MHC-linked HSP70 genes in the pathology of studied autoimmune disorders. Therefore, the HSPA1A and HSPA1B genes might serve as an interesting candidate molecule for development of distinct types of autoimmunities.

Gene Expression Profile of Inflammatory Myopathy with Malignancy is Similar to that of Dermatomyositis rather than Polymyositis

Objective An association has been reported between inflammatory myopathies (IMs), which include polymyositis (PM) and dermatomyositis (DM), and malignancy, and the concept of cancer-associated myositis (CAM) was recently proposed. We herein attempted to determine the features and etiologies of these myopathies. Methods We analyzed the gene expression levels via microarray and real-time quantitative reverse transcription polymerase chain reaction analyses to identify genes that were specifically upregulated or downregulated with suspected inflammatory involvement and verified the microarray data via an immunohistochemical (IHC) analysis in additional cases. Patients We selected 14 patients with the following conditions: PM without malignancy (n=3), DM without malignancy (n=3), CAM (n=3), and Controls (no pathological changes or malignancy; n=5). Results PM was distinct from DM and CAM in a clustering analysis and exhibited the highest numbers of overexpressed genes and specific pathologies in a gene ontology analysis. The IHC analysis confirmed the gene expression results. Conclusion PM is associated with severe inflammatory pathological findings, primarily in the cell-mediated immune system. DM and CAM exhibit similarities in the gene expression and IHC results, which suggest that humoral immunity is the main etiology for both myopathies, indicating the importance of cancer screening in patients with IMs, particularly DM.

Genome-wide association study identifies HLA 8.1 ancestral haplotype alleles as major genetic risk factors for myositis phenotypes

Autoimmune muscle diseases (myositis) comprise a group of complex phenotypes influenced by genetic and environmental factors. To identify genetic risk factors in patients of European ancestry, we conducted a genome-wide association study (GWAS) of the major myositis phenotypes in a total of 1710 cases, which included 705 adult dermatomyositis, 473 juvenile dermatomyositis, 532 polymyositis and 202 adult dermatomyositis, juvenile dermatomyositis or polymyositis patients with anti-histidyl-tRNA synthetase (anti-Jo-1) autoantibodies, and compared them with 4724 controls. Single-nucleotide polymorphisms showing strong associations (P<5×10(-8)) in GWAS were identified in the major histocompatibility complex (MHC) region for all myositis phenotypes together, as well as for the four clinical and autoantibody phenotypes studied separately. Imputation and regression analyses found that alleles comprising the human leukocyte antigen (HLA) 8.1 ancestral haplotype (AH8.1) defined essentially all the genetic risk in the phenotypes studied. Although the HLA DRB1*03:01 allele showed slightly stronger associations with adult and juvenile dermatomyositis, and HLA B*08:01 with polymyositis and anti-Jo-1 autoantibody-positive myositis, multiple alleles of AH8.1 were required for the full risk effects. Our findings establish that alleles of the AH8.1 comprise the primary genetic risk factors associated with the major myositis phenotypes in geographically diverse Caucasian populations.

MyD88 regulates physical inactivity-induced skeletal muscle inflammation, ceramide biosynthesis signaling, and glucose intolerance

Physical inactivity in older adults is a risk factor for developing glucose intolerance and impaired skeletal muscle function. Elevated inflammation and ceramide biosynthesis have been implicated in metabolic disruption and are linked to Toll-like receptor (TLR)/myeloid differentiation primary response 88 (MyD88) signaling. We hypothesize that a physical inactivity stimulus, capable of inducing glucose intolerance, would increase skeletal muscle inflammation and ceramide biosynthesis signaling and that this response would be regulated by the TLR/MyD88 pathway. Therefore, we subjected wild-type (WT) and MyD88(-/-) mice to hindlimb unloading (HU) for 14 days or an ambulatory control period. We observed impaired glucose uptake, muscle insulin signaling (p-Akt), and increased markers of NF-κB signaling (p-IκBα), inflammation (p-JNK, IL-6), TLR4, and the rate-limiting enzyme of ceramide biosynthesis, SPT2, with HU WT (P < 0.05), but not in HU MyD88(-/-) mice. Concurrently, we found that 5 days of bed rest in older adults resulted in whole body glucose dysregulation, impaired skeletal muscle insulin signaling, and upregulation of muscle IL-6 and SPT2 (P < 0.05). Post-bed rest TLR4 abundance was tightly correlated with impaired postprandial insulin and glucose levels. In conclusion, MyD88 signaling is necessary for the increased inflammation, ceramide biosynthesis signaling, and compromised metabolic function that accompanies physical inactivity.

Interferons and systemic sclerosis: correlation between interferon gamma and interferon-lambda 1 (IL-29)

BACKGROUND

Interferon (IFN)-λ1 is a newly described cytokine, member of type III interferons family, which is known for its antiviral, anti-proliferative and antitumor activity. Recent studies indicated that this cytokine has also immune-regulatory function, but its role in the pathogenesis of autoimmune diseases is not established yet. We evaluated serum levels of IFN-λ1 in systemic sclerosis (SSc) patients and healthy controls and its association with IFN-γ and clinical manifestations.

METHODS

IFN-λ1 and IFN-γ serum levels were measured by ELISA from 52 patients with SSc and 53 healthy controls. Association of cytokines serum levels was sought with clinical parameters.

RESULTS

IFN-λ1 and IFN-γ levels in SSc patients were significantly higher than those in healthy individuals (24.82 ± 8.78 and 11.04 ± 3.04 pg/ml, p < 0.0001; 34.11 ± 8.11 and 10.73 ± 2.77 pg/ml, p < 0.0001, respectively). We found a positive correlation between IFN-λ1 and IFN-γ levels in SSc patients (p = 0.0103, r = 0.3526). IFN-γ levels were associated with muscle involvement (p = 0.0483).

CONCLUSION

We first showed raised IFN-λ1 levels in SSc patients. Furthermore, we found a correlation between IFN-λ1 and IFN-γ levels and an association between IFN-γ and myositis. Additional in vitro and in vivo studies are needed to understand IFN-λ1 role in SSc.

Antisynthetase syndrome: a review of etiopathogenesis, diagnosis and management

Antisynthetase syndrome is a group of closely related rare diseases which clinically manifest with inflammatory myopathies, interstitial lung disease, inflammatory arthritis, skin hyperkeratosis (mechanic's hands) and Raynaud phenomenon. The pathophysiology of antisynthetase syndrome is not entirely understood, but genetic predisposition, viral infections and medication use may play a role. Certain antisynthetase antibodies are associated with various clinical presentations and a lower burden of inflammatory myopathies. Patients with antisynthetase syndrome have a worse prognosis than patients with pure inflammatory myopathies mainly because of interstitial lung disease. Future research should further investigate the pathogenesis of antisynthetase syndrome which could identify new therapeutic targets. It will be also important to study whether patients with AS are at increased risk of cancer and whether certain antisynthetase antibodies have any association with the risk of malignancy.

The myositis autoantibody phenotypes of the juvenile idiopathic inflammatory myopathies

The juvenile idiopathic inflammatory myopathies (JIIM) are systemic autoimmune diseases characterized by skeletal muscle weakness, characteristic rashes, and other systemic features. In follow-up to our study defining the major clinical subgroup phenotypes of JIIM, we compared demographics, clinical features, laboratory measures, and outcomes among myositis-specific autoantibody (MSA) subgroups, as well as with published data on adult idiopathic inflammatory myopathy patients enrolled in a separate natural history study. In the present study, of 430 patients enrolled in a nationwide registry study who had serum tested for myositis autoantibodies, 374 had either a single specific MSA (n = 253) or no identified MSA (n = 121) and were the subject of the present report. Following univariate analysis, we used random forest classification and exact logistic regression modeling to compare autoantibody subgroups. Anti-p155/140 autoantibodies were the most frequent subgroup, present in 32% of patients with juvenile dermatomyositis (JDM) or overlap myositis with JDM, followed by anti-MJ autoantibodies, which were seen in 20% of JIIM patients, primarily in JDM. Other MSAs, including anti-synthetase, anti-signal recognition particle (SRP), and anti-Mi-2, were present in only 10% of JIIM patients. Features that characterized the anti-p155/140 autoantibody subgroup included Gottron papules, malar rash, "shawl-sign" rash, photosensitivity, cuticular overgrowth, lowest creatine kinase (CK) levels, and a predominantly chronic illness course. The features that differed for patients with anti-MJ antibodies included muscle cramps, dysphonia, intermediate CK levels, a high frequency of hospitalization, and a monocyclic disease course. Patients with anti-synthetase antibodies had higher frequencies of interstitial lung disease, arthralgia, and "mechanic's hands," and had an older age at diagnosis. The anti-SRP group, which had exclusively juvenile polymyositis, was characterized by high frequencies of black race, severe onset, distal weakness, falling episodes, Raynaud phenomenon, cardiac involvement, high CK levels, chronic disease course, frequent hospitalization, and wheelchair use. Characteristic features of the anti-Mi-2 subgroup included Hispanic ethnicity, classic dermatomyositis and malar rashes, high CK levels, and very low mortality. Finally, the most common features of patients without any currently defined MSA or myositis-associated autoantibodies included linear extensor erythema, arthralgia, and a monocyclic disease course. Several demographic and clinical features were shared between juvenile and adult idiopathic inflammatory myopathy subgroups, but with several important differences. We conclude that juvenile myositis is a heterogeneous group of illnesses with distinct autoantibody phenotypes defined by varying clinical and demographic characteristics, laboratory features, and outcomes.

Daily supplementation of D-ribose shows no therapeutic benefits in the MHC-I transgenic mouse model of inflammatory myositis

Background

Current treatments for idiopathic inflammatory myopathies (collectively called myositis) focus on the suppression of an autoimmune inflammatory response within the skeletal muscle. However, it has been observed that there is a poor correlation between the successful suppression of muscle inflammation and an improvement in muscle function. Some evidence in the literature suggests that metabolic abnormalities in the skeletal muscle underlie the weakness that continues despite successful immunosuppression. We have previously shown that decreased expression of a purine nucleotide cycle enzyme, adenosine monophosphate deaminase (AMPD1), leads to muscle weakness in a mouse model of myositis and may provide a mechanistic basis for muscle weakness. One of the downstream metabolites of this pathway, D-ribose, has been reported to alleviate symptoms of myalgia in patients with a congenital loss of AMPD1. Therefore, we hypothesized that supplementing exogenous D-ribose would improve muscle function in the mouse model of myositis. We treated normal and myositis mice with daily doses of D-ribose (4 mg/kg) over a 6-week time period and assessed its effects using a battery of behavioral, functional, histological and molecular measures.

Results

Treatment with D-ribose was found to have no statistically significant effects on body weight, grip strength, open field behavioral activity, maximal and specific forces of EDL, soleus muscles, or histological features. Histological and gene expression analysis indicated that muscle tissues remained inflamed despite treatment. Gene expression analysis also suggested that low levels of the ribokinase enzyme in the skeletal muscle might prevent skeletal muscle tissue from effectively utilizing D-ribose.

Conclusions

Treatment with daily oral doses of D-ribose showed no significant effect on either disease progression or muscle function in the mouse model of myositis.

The incidence and associations of malignancy in a large cohort of patients with biopsy-determined idiopathic inflammatory myositis

The South Australian (SA) myositis database has registered all patients with biopsy-proven inflammatory myositis in SA from 1980 to 2009. We determined the incidence and associations of malignancy in myositis by linking this database with the SA cancer registry. Standardized incidence ratios (SIR) for malignancy were determined using the total SA population over the same time period, stratified by age and gender. The SIR for cancer in the myositis population (n = 373) was 1.39, p = 0.047. There was a trend towards an increased SIR in dermatomyositis but no increased risk of malignancy in polymyositis or inclusion body myositis. Malignancies of the lung and prostate were the commonest and 28 % of malignancies occurred within one year of IIM diagnosis. The odds of developing cancer were significantly raised in the presence of a shawl sign, male gender, and in patients with overlap syndrome or rheumatoid arthritis whilst myalgia was a significant protective factor. HLA-A28 allele was overrepresented in patients with malignancy (11 vs 2 %, p = 0.006). Patients in SA with myositis are at modestly increased risk for malignancy. We report clinical and genetic risk factors allowing the identification of patients at greatest risk for malignancy.

Macrophagic myofaciitis a vaccine (alum) autoimmune-related disease

Macrophagic myofasciitis (MMF) is an immune-mediated condition first reported in 1998. MMF is characterized by post-vaccination systemic manifestations as well as local-stereotyped and immunologically active lesion in the site of inoculation (deltoid muscle). MMF systemic symptoms included myalgias, arthralgias, marked asthenia, muscle weakness, chronic fatigue, and fever. Recently, studies demonstrated that the local lesion is due to persistence for years at site of injection of an aluminum (Al(OH)3) adjuvant commonly used in human vaccines. Time elapsed from last immunization with an Al(OH)3-containing vaccine to muscle biopsy range from 3 months to 8 years; in rare cases, MMF may be diagnosed even 10 years post-vaccination. The discrepancy between the wide applications of aluminum hydroxide-containing vaccines and the very limited number of MMF cases reported may be resolved by observations suggesting that aluminum-containing vaccinations may trigger MMF in genetically susceptible subjects carrying the HLA-DRB1*01. Thus, MMF may be defined as an emerging novel condition that may be triggered by exposure to alum-containing vaccines, in patients with a specific genetic background, and this temporal association may be exhibited from a few months up to 10 years.

Inflammatory changes in infantile-onset LMNA-associated myopathy

Mutations in LMNA cause wide variety of disorders including Emery-Dreifuss muscular dystrophy, limb girdle muscular dystrophy, and congenital muscular dystrophy. We recently found a LMNA mutation in a patient who was previously diagnosed as infantile onset inflammatory myopathy. In this study, we screened for LMNA mutations in 20 patients suspected to have inflammatory myopathy with onset at 2years or younger. The diagnosis of inflammatory myopathy was based on muscle pathology with presence of perivascular cuffing and/or endomysial/perimysial lymphocyte infiltration. We identified heterozygous LMNA mutations in 11 patients (55%), who eventually developed joint contractures and/or cardiac involvement after the infantile period. Our findings suggest that LMNA mutation should be considered in myopathy patients with inflammatory changes during infancy, and that this may help avoid life-threatening events associated with laminopathy.

Recent advances in the immunogenetics of idiopathic inflammatory myopathy

This review summarizes the previous and current literature on the immunogenetics of idiopathic inflammatory myopathy (IIM) and updates the research progress that has been made over the past decade. A substantial part of the genetic risk for developing adult- and juvenile-onset IIM lies within the major histocompatibility complex (MHC), and a tight relationship exists between individual human leukocyte antigen alleles and specific serological subtypes, which in turn dictate clinical disease phenotypes. Multiple genetic regions outside of the MHC are increasingly being identified in conferring IIM disease susceptibility. We are still challenged with the task of studying a serologically and clinically heterogeneous disorder that is rarer by orders of magnitude than the likes of rheumatoid arthritis. An ongoing and internationally coordinated IIM genome-wide association study may provide further insights into IIM immunogenetics.

Carrier woman of Duchenne muscular dystrophy mimicking inflammatory myositis

Carrier woman of Duchenne muscular dystrophy (DMD) can mimic the inflammatory myositis in presenting symptoms. Two diseases should be differentiated by the clinical history, muscle biopsy and genetic study. There are few reports in which both histochemical and genetic study showed the possible link of overlapping inflammatory pathophysiology with dystrophinopathy. We report a 40-yr-old woman who presented with subacute proximal muscle weakness and high serum level of creatine kinase. She had a history of Graves' disease and fluctuation of serum liver aminotransferase without definite cause. MRI, EMG and NCV were compatible with proximal muscle myopathy. Muscle biopsy on vastus lateralis showed suspicious perifascicular atrophy and infiltration of mono-macrophage lineage cells complicating the diagnosis. Dystrophin staining showed heterogeneous diverse findings from normal to interrupted mosaic pattern. Multiple ligation probe amplification and X chromosome inactivation test confirmed DMD gene deletion mutation in exon 44 and highly skewed X inactivation.

Observations on the classification of the inflammatory myopathies

This brief review considers historical approaches to the classification of the inflammatory myopathies. The last 25 years have seen advances in our knowledge of the underlying immune mechanism but the initial trigger for the idiopathic inflammatory myopathies remains unknown. Existing classifications have their limitations, but with the absence of a "gold standard" a definitive classification is not yet possible. Despite these problems, a working classification is possible that is valuable for everyday clinical practice.

Anti-Jo-1 Antibodies

Anti-Jo-1 antibody is a myositis specific autoantibody most commonly found in patients with idiopathic inflammatory myopathies (IIM). This antibody is directed against the histidyl-tRNA synthetase which catalyses the binding of the histidine to its cognate tRNA during protein synthesis. It can be considered a specific marker of IIM, predominantly found in 20-30% of patients with PM and in the 60-70% of those with interstitial pulmonary fibrosis. These antibodies are also found in DM, although less frequently than in PM, and are rare in children with PM or DM and in other connective tissue diseases.ELISA, CIE and immunoblotting are highly specific and sensitive techniques for testing anti-Jo-1 antibodies. The detection of this antibody is particularly useful in diagnosis and classification of IIM. Moreover, anti-Jo-1 serum levels strongly correlate with disease activity representing a good marker for disease monitoring.

Haploinsufficiency of utrophin gene worsens skeletal muscle inflammation and fibrosis in mdx mice

To address whether mdx mice with haploinsufficiency of utrophin (mdx/utrn+/-) develop more severe skeletal muscle inflammation and fibrosis than mdx mice, to represent a better model for Duchenne muscular dystrophy (DMD), we performed qualitative and quantitative analysis of skeletal muscle inflammation and fibrosis in mdx and mdx/utrn+/- littermates. Inflammation was significantly worse in mdx/utrn+/- quadriceps at age 3 and 6 months and in mdx/utrn+/- diaphragm at age 3 but not 6 months. Fibrosis was more severe in mdx/utrn+/- diaphragm at 6 months, and at this age, mild fibrosis was noted in quadriceps of mdx/utrn+/- but not mdx mice. The findings indicate that utrophin compensates, although insufficiently, for the effects of dystrophin loss with regard to inflammation and fibrosis of both quadriceps and diaphragm muscles in mdx mice. With more severe muscle dystrophy than mdx mice and a longer life span than utrophin-dystrophin-deficient (dko) mice, mdx/utrn+/- mice provide a better mouse model for testing potential therapies for muscle inflammation and fibrosis associated with DMD.

Autoantibodies in Canine Masticatory Muscle Myositis Recognize a Novel Myosin Binding Protein-C Family Member

Inflammatory myopathies are a group of autoimmune diseases that affect muscles. In humans, the most common inflammatory myopathies are polymyositis, dermatomyositis, and inclusion body myositis. Autoantibodies may be found in humans with inflammatory myopathies, and these play an important role in diagnosis and disease classification. However, these Abs are typically not muscle specific. Spontaneously occurring canine inflammatory myopathies may be good parallel disorders and provide insights into human myositis. In dogs with inflammatory myopathy, muscle-specific autoantibodies have been found, especially in masticatory muscle myositis. We have identified the major Ag recognized by the autoantibodies in canine masticatory muscle myositis. This Ag is a novel member of the myosin binding protein-C family, which we call masticatory myosin binding protein-C (mMyBP-C). mMyBP-C is localized not only within the masticatory muscle fibers, but also at or near their cell surface, perhaps making it accessible as an immunogen. The gene for mMyBP-C also exists in humans, and mMyBP-C could potentially play a role in certain human inflammatory myopathies. Understanding the role of mMyBP-C in this canine inflammatory myopathy may advance our knowledge of mechanisms of autoimmune inflammatory muscle diseases, not only in dogs, but also in humans.

Tumour necrosis factor-alpha single nucleotide polymorphisms are not independent of HLA class I in UK Caucasians with adult onset idiopathic inflammatory myopathies

OBJECTIVE

To investigate haplotype tagging single nucleotide polymorphisms (SNPs) in the tumour necrosis factor alpha (TNF-alpha) gene, in UK Caucasian idiopathic inflammatory myopathy (IIM) patients.

METHODS

A cross-sectional, case-control study of four TNF-alpha SNPs was undertaken, comparing cases of polymyositis (PM) (n = 121), dermatomyositis (DM) (n = 109) and myositis overlapping with other connective tissue diseases (CTD-overlap) (n = 73) with normal subjects (n = 177). Subgroup analyses were undertaken after stratifying for myositis specific/associated antibodies.

RESULTS

The TNF-308A allele demonstrated a strong association with each myositis disease subgroup vs controls [PM, odds ratio (OR) 2.8, 95% confidence interval 1.9-4.3; DM, OR 2.5, 1.6-3.8; CTD-overlap, OR 3.3, 2.1-5.1]. The TNF-308GA/AA genotype frequency was significantly increased vs controls (PM, OR 3.7, 2.1-6.3; DM, OR 3.2, 1.8-5.5; CTD-overlap, OR 5.0, 2.6-9.6) suggesting a dominant model. The association was strongest in patients possessing anti-aminoacyl transfer RNA synthetase (anti-synthetase) (OR 5.1, 3.3-8.0) or -PM-Scl (OR 5.0, 2.7-8.9) antibodies. The -1031T allele was also a significant risk factor in DM (OR 2.2, 1.4-3.6), anti-synthetase (OR 2.9, 1.6-5.3) and -PM-Scl (OR 5.6, 1.9-6.4) antibody positive patients. The TNF-308A association was lost after adjusting for HLA-B*08, but remained independent of HLA-DQB1*02 (both are alleles forming part of the common ancestral haplotype). The HLA-B*08/TNF-308A/DRB1*03/DQA1*05/DQB1*02 haplotype was a risk factor in all myositis subgroups vs controls (OR 3.0, 1.8-5.3).

CONCLUSIONS

TNF-308A and -1031T alleles are significant risk factors in the IIMs. In the IIMs, the TNF-308A allele is part of the common ancestral haplotype, but is not independent of HLA-B*08.

Downregulation of selective microRNAs in trigeminal ganglion neurons following inflammatory muscle pain

Active regulation of gene expression in the nervous system plays an important role in the development and/or maintenance of inflammatory pain. MicroRNA (miRNA) negatively regulates gene expression via posttranscriptional or transcriptional inhibition of specific genes. To explore the possible involvement of miRNA in gene regulation during inflammatory pain, we injected complete Freund's adjuvant (CFA) unilaterally into the rat masseter muscle and quantified changes in neuron-specific mature miRNAs in the trigeminal ganglion (TG). Real-time reverse-transcription polymerase chain reaction revealed significant, but differential, downregulation of mature miR-10a, -29a, -98, -99a, -124a, -134, and -183 in the ipsilateral mandibular division (V3) of the TG within 4 hr after CFA. In contrast, levels of tested miRNAs did not change significantly in the contralateral V3 or the ipsilateral ophthalmic and maxillary divisions of the TG from inflamed rats, nor in the ipsilateral V3 of saline-injected animals. The downregulated miRNAs recovered differentially to a level equal to or higher than that in naive animals. Full recovery time varied with miRNA species but was at least 4 days. Expression and downregulation of some miRNAs were further confirmed by in situ hybridization of TG neurons that innervate the inflamed muscle. Although neurons of all sizes expressed these miRNAs, their signals varied between neurons. Our results indicate that miRNA species specific to neurons are quickly regulated following inflammatory muscle pain.

Interferon-gamma and interleukin-4 gene polymorphisms in Caucasian idiopathic inflammatory myopathy patients in UK

OBJECTIVE

To determine whether interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) genes confer susceptibility for the idiopathic inflammatory myopathies (IIMs).

METHODS

A large cross-sectional study of UK caucasian adults with polymyositis (PM, n = 101), dermatomyositis (DM, n = 94) and myositis overlapping with a connective tissue disease (myositis/CTD-overlap, n = 70) was completed. 177 ethnically matched controls were available for comparison. Single-nucleotide polymorphisms (SNPs) within intronic regions coding for IL-4, IFN-gamma and a microsatellite marker within intron 1 of the IFN-gamma gene were typed.

RESULTS

Strong linkage disequilibrium was present between SNPs in each gene. In the IFN-gamma gene, a weak allelic association was observed in PM versus controls at rs1861493 (odds ratio (OR) 1.6, 95% confidence interval (CI) 1.03 to 2.4). The microsatellite IFN-gamma CA(14) allele was associated with risk for IIMs overall (OR 3.3, 95% CI 1.4 to 7.8), the strongest association being observed within the anti-U1-ribonucleoprotein (RNP) group (OR 6.0, 95% CI 1.5 to 23.1), and persisting after adjustment for known myositis human leucocyte antigen (HLA) class II associations.

CONCLUSIONS

Genetic markers in the IFN-gamma gene demonstrate significant allelic associations with the IIMs in a UK Caucasian population. The SNPs tested in this study within the region coding for IL-4 fail to show significant associations with susceptibility to IIM disease.

Genetic determinants of statin intolerance

Background

Statin-related skeletal muscle disorders range from benign myalgias – such as non-specific muscle aches or joint pains without elevated serum creatinine kinase (CK) concentration – to true myositis with >10-fold elevation of serum CK, to rhabdomyolysis and myoglobinuria. The genetic basis of statin-related muscle disorders is largely unknown. Because mutations in the COQ2 gene are associated with severe inherited myopathy, we hypothesized that common, mild genetic variation in COQ2 would be associated with inter-individual variation in statin intolerance. We studied 133 subjects who developed myopathy on statin monotherapy and 158 matched controls who tolerated statins without incident or complaint.

Results

COQ2 genotypes, based on two single nucleotide polymorphisms (SNP1 and SNP2) and a 2-SNP haplotype, all showed significant associations with statin intolerance. Specifically, the odds ratios (with 95% confidence intervals) for increased risk of statin intolerance among homozygotes for the rare alleles were 2.42 (0.99 to 5.89), 2.33 (1.13 to 4.81) and 2.58 (1.26 to 5.28) for SNP1 and SNP2 genotypes, and the 2-SNP haplotype, respectively.

Conclusion

These preliminary pharmacogenetic results, if confirmed, are consistent with the idea that statin intolerance which is manifested primarily through muscle symptoms is associated with genomic variation in COQ2 and thus perhaps with the CoQ10 pathway.

Immunolocalization of interleukin-1 receptors in the sarcolemma and nuclei of skeletal muscle in patients with idiopathic inflammatory myopathies

OBJECTIVE

Interleukin-1 (IL-1) acts via its receptors to induce gene expression that mediates protein synthesis involved in inflammation. Increased expression of IL-1alpha and IL-1beta in muscle tissue from patients with polymyositis and dermatomyositis has been demonstrated. It is not known whether the reciprocal IL-1 receptors are expressed in human muscle tissue. The purpose of this study was to investigate the expression of IL-1 receptors and their ligands in muscle tissue from patients with myositis and from healthy controls.

METHODS

Muscle biopsy tissues from 10 patients with polymyositis or dermatomyositis and 7 healthy control subjects were investigated by immunohistochemistry using antibodies against IL-1 receptor type I (IL-1RI), IL-1RII, IL-1alpha, IL-1beta, and IL-1 receptor antagonist (IL-1Ra). Quantification was performed by computerized image analysis, and localization of expression was determined by double staining using immunofluorescence and confocal microscopy.

RESULTS

In tissue samples from the patients, IL-1RI and IL-1RII were expressed in muscle fibers, inflammatory cells, and endothelial cells. Expression in muscle fibers was localized to the sarcolemma and nuclei. IL-1alpha was expressed in endothelial cells and inflammatory cells, whereas IL-1beta and IL-1Ra were expressed only in inflammatory cells. Expression of the two IL-1 receptors and their ligands was significantly higher in patients than in controls. IL-1 receptor expression on muscle fibers was most pronounced in the vicinity of cells expressing IL-1alpha and IL-1beta.

CONCLUSION

The increased expression of IL-1 receptor and the colocalization with reciprocal ligands in patients with myositis but not in healthy controls support the hypothesis of a crucial role of IL-1 in the pathogenesis of polymyositis and dermatomyositis.

HLA polymorphisms in African Americans with idiopathic inflammatory myopathy: allelic profiles distinguish patients with different clinical phenotypes and myositis autoantibodies

OBJECTIVE

To investigate possible associations of HLA polymorphisms with idiopathic inflammatory myopathy (IIM) in African Americans, and to compare this with HLA associations in European American IIM patients with IIM.

METHODS

Molecular genetic analyses of HLA-A, B, Cw, DRB1, and DQA1 polymorphisms were performed in a large population of African American patients with IIM (n = 262) in whom the major clinical and autoantibody subgroups were represented. These data were compared with similar information previously obtained from European American patients with IIM (n = 571).

RESULTS

In contrast to European American patients with IIM, African American patients with IIM, in particular those with polymyositis, had no strong disease associations with HLA alleles of the 8.1 ancestral haplotype; however, African Americans with dermatomyositis or with anti-Jo-1 autoantibodies shared the risk factor HLA-DRB1*0301 with European Americans. We detected novel HLA risk factors in African American patients with myositis overlap (DRB1*08) and in African American patients producing anti-signal recognition particle (DQA1*0102) and anti-Mi-2 autoantibodies (DRB1*0302). DRB1*0302 and the European American-, anti-Mi-2-associated risk factor DRB1*0701 were found to share a 4-amino-acid sequence motif, which was predicted by comparative homology analyses to have identical 3-dimensional orientations within the peptide-binding groove.

CONCLUSION

These data demonstrate that North American IIM patients from different ethnic groups have both shared and distinct immunogenetic susceptibility factors, depending on the clinical phenotype. These findings, obtained from the largest cohort of North American minority patients with IIM studied to date, add additional support to the hypothesis that the myositis syndromes comprise multiple, distinct disease entities, perhaps arising from divergent pathogenic mechanisms and/or different gene-environment interactions.

A Local Antigen-Driven Humoral Response Is Present in the Inflammatory Myopathies

The inflammatory myopathies are putative autoimmune disorders characterized by muscle weakness and the presence of intramuscular inflammatory infiltrates. Although inclusion body myositis and polymyositis have been characterized as cytotoxic CD8(+) T cell-mediated diseases, we recently demonstrated high frequencies of CD138(+) plasma cells in the inflamed muscle tissue of patients with these diseases. To gain a deeper understanding of the role these B cell family members play in the disease pathology, we examined the molecular characteristics of the H chain portion of the Ag receptor. Biopsies of muscle tissue were sectioned and tissue regions and individual cells were isolated through laser capture microdissection. Ig H chain gene transcripts isolated from the sections, regions, and cells were used to determine the variable region gene sequences. Analysis of these sequences revealed clear evidence of affinity maturation in that significant somatic mutation, isotype switching, receptor revision, codon insertion/deletion, and oligoclonal expansion had occurred within the B and plasma cell populations. Moreover, analysis of tissue regions isolated by laser capture microdissection revealed both clonal expansion and variation, suggesting that local B cell maturation occurs within muscle. In contrast, sequences from control muscle tissues and peripheral blood revealed none of these characteristics found in inflammatory myopathy muscle tissue. Collectively, these data demonstrate that Ag drives a B cell Ag-specific response in muscle in patients with dermatomyositis, inclusion body myositis, and polymyositis. These findings highlight the need for a revision of the current paradigm of exclusively T cell-mediated intramuscular Ag-specific autoimmunity in inclusion body myositis and polymyositis.

[Acute myositis associated with influenza]

Benign acute myositis associated with influenza is reported from all over the world. The characteristics of this disorder is calf pain and difficulty walking during a viral illness (3-8 days) and creatine kinase levels are mildly or moderately elevated. Recovery occurred within 1 week. Midchildhood (mean age: 6-8 years) is most commonly affected and boys are more commonly than girls and its ratio is 2.4 : 1 by Shimizu in Japan (1993). Elderly patients are also reported. Viral studies show that influenza B is more commonly than influenza A and the ratio is 6 : 1 by Hu in Taiwan (2004), 2.4 : 1 by Shimizu in Japan (1993). Muscle histology revealed isolated segmental muscle degeneration and necrosis without frank myositis. A direct role of influenza virus in its genesis is not clear. An age-related response and occurrence primarily on boys may reflect a genetic predisposition.