Anti-aminoacyl-tRNA synthetase-related myositis and dermatomyositis: clues for differential diagnosis on muscle biopsy

Autoantigenic properties of the aminoacyl tRNA synthetase family in idiopathic inflammatory myopathies

OBJECTIVES

Autoantibodies are thought to play a key role in the pathogenesis of idiopathic inflammatory myopathies (IIM). However, up to 40% of IIM patients, even those with clinical manifestations of anti-synthetase syndrome (ASSD), test seronegative to known myositis-specific autoantibodies. We hypothesized the existence of new potential autoantigens among human cytoplasmic aminoacyl tRNA synthetases (aaRS) in patients with IIM.

METHODS

Plasma samples from 217 patients with IIM according to 2017 EULAR/ACR criteria, including 50 patients with ASSD, 165 without, and two with unknown ASSD status were identified retrospectively, as well as age and gender-matched sera from 156 population controls, and 219 disease controls. Patients with previously documented ASSD had to test positive for at least one of the five most common anti-aaRS autoantibodies (anti-Jo1, -PL7, -PL12, -EJ, and -OJ) and present with one or more of the following clinical manifestations: interstitial lung disease, myositis, arthritis, Raynaud's phenomenon, fever, or mechanic's hands. Demographics, laboratory, and clinical data of the IIM cohort (ASSD and non-ASSD) were compared. Samples were screened using a multiplex bead array assay for presence of autoantibodies against a panel of 117 recombinant protein variants, representing 33 myositis-related proteins, including all nineteen cytoplasmic aaRS. Prospectively collected clinical data for the IIM cohort were retrieved and compared between groups within the IIM cohort and correlated with the results of the autoantibody screening. Principal component analysis was used to analyze clinical manifestations between ASSD, non-ASSD groups, and individuals with novel anti-aaRS autoantibodies.

RESULTS

We identified reactivity towards 16 aaRS in 72 of the 217 IIM patients. Twelve patients displayed reactivity against nine novel aaRS. The novel autoantibody specificities were detected in four previously seronegative patients for myositis-specific autoantibodies and eight with previously detected myositis-specific autoantibodies. IIM individuals with novel anti-aaRS autoantibodies (n = 12) all had signs of myositis, and they had either muscle weakness and/or muscle enzyme elevation, 2/12 had mechanic's hands, 3/12 had interstitial lung disease, and 2/12 had arthritis. The individuals with novel anti-aaRS and a pathological muscle biopsy all presented widespread up-regulation of major histocompatibility complex class I. The reactivities against novel aaRS could be confirmed in ELISA and western blot. Using the multiplex bead array assay, we could confirm previously known reactivities to four of the most common aaRS (Jo1, PL12, PL7, and EJ (n = 45)) and identified patients positive for anti-Zo, -KS, and -HA (n = 10) that were not previously tested. A low frequency of anti-aaRS autoantibodies was also detected in controls.

CONCLUSION

Our results suggest that most, if not all, cytoplasmic aaRS may become autoantigenic. Autoantibodies against new aaRS may be found in plasma of patients previously classified as seronegative with potential high clinical relevance.

Comparison of cytokine/chemokine profiles between dermatomyositis and anti-synthetase syndrome

Objectives

Dermatomyositis (DM) and anti-synthetase syndrome (ASS) are autoimmune diseases with multisystem involvement. Despite sharing some clinical and myopathological features, these are two diseases with different pathogeneses and prognoses. We aimed to clarify and compare cytokine/chemokine profiles in both disorders, which may help in the differential diagnosis.

Materials and methods

We collected clinical data and serum samples of consecutive patients with DM and ASS. Quantibody^® Human Inflammation Array 3 for cytokines/chemokines was performed in the serum of all participants. Receiver operating characteristic analysis with the area under the curve and Youden's index were performed.

Results

Eight newly diagnosed and treatment-naïve patients with DM, nine newly diagnosed and treatment-naïve patients with ASS, and 14 healthy controls were enrolled. Serum C-C motif chemokine ligand (CCL) 2, CCL4, C-X-C motif chemokine ligand (CXCL) 13, and tumor necrosis factor receptor 2 (TNFR2) were increased in patients with both DM and ASS. Serum interleukin (IL)-1 receptor type 1 (IL-1ra), IL-1b, CCL1, CXCL11, and CCL3 were modulated in patients with DM only, and IL-8, CXCL9, and tissue inhibitors of metalloproteinases-1 (TIMP-1) in patients with ASS only. Serum CCL2, CXCL13, and TNFR2 accurately distinguished patients with DM and ASS from healthy controls, as shown by the area under the curve >0.80. Moreover, receiver operating characteristic analysis showed that, as biomarkers for discrimination between DM and ASS, the combination of IL-1ra and TIMP-1, had an area under the curve of 0.944, a sensitivity of 87.5%, and a specificity of 88.9%.

Conclusion

Our study demonstrated that serum levels of cytokines/chemokines showed a different pattern in newly diagnosed patients with DM and ASS, in which serum IL-1ra and TIMP-1 could be used to distinguish between the two diseases.

Aminoacyl-tRNA Synthetases: On Anti-Synthetase Syndrome and Beyond

Anti-synthetase syndrome (ASSD) is an autoimmune disease characterized by the presence of autoantibodies targeting one of several aminoacyl t-RNA synthetases (aaRSs) along with clinical features including interstitial lung disease, myositis, Raynaud’s phenomenon, arthritis, mechanic’s hands, and fever. The family of aaRSs consists of highly conserved cytoplasmic and mitochondrial enzymes, one for each amino acid, which are essential for the RNA translation machinery and protein synthesis. Along with their main functions, aaRSs are involved in the development of immune responses, regulation of transcription, and gene-specific silencing of translation. During the last decade, these proteins have been associated with cancer, neurological disorders, infectious responses, and autoimmune diseases including ASSD. To date, several aaRSs have been described to be possible autoantigens in different diseases. The most commonly described are histidyl (HisRS), threonyl (ThrRS), alanyl (AlaRS), glycyl (GlyRS), isoleucyl (IleRS), asparaginyl (AsnRS), phenylalanyl (PheRS), tyrosyl (TyrRS), lysyl (LysRS), glutaminyl (GlnRS), tryptophanyl (TrpRS), and seryl (SerRS) tRNA synthetases. Autoantibodies against the first eight autoantigens listed above have been associated with ASSD while the rest have been associated with other diseases. This review will address what is known about the function of the aaRSs with a focus on their autoantigenic properties. We will also describe the anti-aaRSs autoantibodies and their association to specific clinical manifestations, and discuss their potential contribution to the pathogenesis of ASSD.

Immune-mediated necrotizing myopathy (IMNM): A myopathological challenge

This review is focused on the myopathological spectrum of immune mediated necrotizing myopathies (IMNMs) and its differentiation with other, potentially mimicking, inflammatory and non-inflammatory myopathies. IMNMs are a subgroup of idiopathic inflammatory myopathies (IIMs) characterized by severe clinical presentation with rapidly progressive muscular weakness and creatine kinase elevation, often requiring early aggressive immunotherapy, associated to the presence of muscle specific autoantibodies (MSA) against signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Muscle biopsy usually shows unspecific features consisting in prominent necrosis and regeneration of muscle fibres with mild or absent inflammatory infiltrates, inconstant and faint expression of major histocompatibility complex (MHC) class I and variable deposition of C5b-9 on sarcolemma. Several conditions could present similar histopathological findings leading to possible misdiagnosis of IMNM with other IIMs or non-inflammatory myopathies (nIMs) and viceversa. This review analyses the muscle biopsy data in IMNMs through a systematic revision of the literature from the last five decades. Several histopathological variables have been considered in both SRP- and HMGCR-IMNM, and compared to other IIMs - as dermatomyositis (DM) and anti-synthethase syndrome (ASS) - or other nIMs -as toxic myopathies (TM), critical illness myopathy (CIM) and muscular dystrophy (MD) - to elucidate similarities and differences among these potentially mimicking conditions. The major histopathological findings of IMNMs were: very frequent necrosis and regeneration of muscle fibres (93%), mild inflammatory component mainly constituted by scattered isolated (65%) CD68-prevalent (68%) cells, without CD8 invading/surrounding non-necrotic fibres, variable expression of MHC-I in non-necrotic fibres (56%) and constant expression of sarcoplasmic p62, confirming those that are widely considered the major histological characteristics of IMNMs. Conversely, only 42% of biopsies showed a sarcolemmal deposition of C5b-9 component. Few differences between SRP and HMGCR IMNMs consisted in more severe necrosis and regeneration in SRP than in HMGCR (p = 0.01); more frequent inflammatory infiltrates (p = 0.007) with perivascular localization (p = 0.01) and clustered expression of MHC-I (p = 0.007) in HMGCR; very low expression of sarcolemmal C5b-9 in SRP (18%) compared to HMGCR (56%) (p = 0.0001). Milder necrosis and regeneration, detection of perifascicular pathology, presence of lymphocytic inflammatory infiltrates and myofibre expression of MxA help to distinguish DM or ASS from IMNM. nIMs can present signs of inflammation at muscle biopsy. Low fibre size variability with overexpression of both MHC-I and II, associated with C5b-9 deposition, could could be observed in CIM, while increased connective tissue should lead to consider MD, or TM in absence of C5b-9 deposition. Nevertheless, these features are not constantly detected and muscle biopsy could not be diriment. For this reason, muscle biopsy should always be critically considered in light of the clinical context before concluding for a definite diagnosis of IMNM, only based on histopathological findings. More rigorous collection and analysis of muscle biopsy is warranted to obtain a higher quality and more homogeneous histopathological data in inflammatory myopathies.

Mitochondrial morphology and MAVS-IFN1 signaling pathway in muscles of anti-MDA5 dermatomyositis

Objective

This study aimed to investigate mitochondrial changes and the mitochondrial antiviral‐signaling protein (MAVS)‐type I interferon (IFN1) signaling pathway in the muscles of anti‐melanoma differentiation gene 5(MDA5) dermatomyositis (DM) patients.

Methods

Eleven anti‐MDA5 DM and ten antibody‐negative DM patients were included. Muscle biopsies were performed in all patients. Muscle pathology and mitochondrial morphology in particular were compared between two groups. The expression of MDA5, MAVS, interferon (IFN) regulatory factor 7, and IFN‐stimulated gene 15, which are components of the MAVS‐IFN1 signaling pathway, was measured in muscle specimen. The correlation between MAVS expression in muscles and disease phenotypes and muscle pathology were analyzed.

Results

Anti‐MDA5 DM showed a significantly lower incidence of the characteristic DM pathology (P < 0.05) than antibody‐negative DM, including perifascicular fiber atrophy, inflammation, and vasculopathy. Mitochondrial abnormalities in anti‐MDA5 patients revealed a high incidence of (8/11,72.7%) and different pattern from that in antibody‐negative DM. MDA5, MAVS, IFN regulatory factor 7, and IFN stimulated gene 15 expression levels in the muscles of anti‐MDA5 DM patients were higher than those of the controls (P < 0.05) but lower than those of antibody‐negative DM patients (P < 0.05). The MAVS levels negatively correlated with manual muscle test 8 scores (r = 0.701, P = 0.016).

Conclusions

Compared to antibody‐negative DM, we presented a different distribution of the mitochondrial pathology and less severe morphology in anti‐MDA5 DM. We also revealed the enhanced but less intensive MAVS‐IFN1 signaling pathway activity in muscles of anti‐MDA5 DM. Such disparity suggested the potentially different mechanism of muscle injury in two DM groups.

Gasdermine E-Dependent Mitochondrial Pyroptotic Pathway in Dermatomyositis: A Possible Mechanism of Perifascicular Atrophy

Different mechanisms have been proposed to explain the pathological basis of perifascicular atrophy (PFA), a pathognomonic histologic feature of dermatomyositis (DM); however, the detailed mechanisms remain to be elucidated. There is mitochondrial dysfunction in PFA and expression of mitochondrial apoptosis molecules has been reported in DM. Overexpression of gasdermin E (GSDME) can turn mitochondrial apoptosis to mitochondrial pyroptosis, a newly characterized form of programmed cell death. We determined the expression of proteins involved in the caspase-3- and GSDME-dependent mitochondrial pyroptotic pathway, including BAX, BAK, cytochrome C, caspase-9, caspase-3, GSDME, and IL-1α, in biopsied muscles from DM and control patients. Immunohistochemical analysis showed that those markers were expressed in most fibers in PFA in DM. GSDME-positive and IL-1α-positive staining was mainly localized around punched-out vacuoles or sarcolemma. These markers were significantly upregulated at the protein and mRNA levels in DM versus controls. Our results suggest that caspase-3- and GSDME-dependent mitochondrial pyroptosis are involved in the pathogenetic mechanisms of PFA in DM and that targeting GSDME-dependent mitochondrial pyroptosis may be an effective therapeutic approach for this condition.