Pathological autoantibody internalisation in myositis.

OBJECTIVES: Autoantibodies targeting intracellular proteins are common in various autoimmune diseases. In the context of myositis, the pathologic significance of these autoantibodies has been questioned due to the assumption that autoantibodies cannot enter living muscle cells. This study aims to investigate the validity of this assumption. METHODS: Confocal immunofluorescence microscopy was employed to localise antibodies and other proteins of interest in myositis muscle biopsies. Bulk RNA sequencing was used to examine the transcriptomic profiles of 669 samples, including those from patients with myositis, disease controls and healthy controls. Additionally, antibodies from myositis patients were introduced into cultured myoblasts through electroporation, and their transcriptomic profiles were analysed using RNA sequencing. RESULTS: In patients with myositis autoantibodies, antibodies accumulated inside myofibres in the same subcellular compartment as the autoantigen. Bulk RNA sequencing revealed that muscle biopsies from patients with autoantibodies targeting transcriptional regulators exhibited transcriptomic patterns consistent with dysfunction of the autoantigen. For instance, in muscle biopsies from patients with anti-PM/Scl autoantibodies recognising components of the nuclear RNA exosome complex, an accumulation of divergent transcripts and long non-coding RNAs was observed; these RNA forms are typically degraded by the nuclear RNA exosome complex. Introducing patient antibodies into cultured muscle cells recapitulated the transcriptomic effects observed in human disease. Further supporting evidence suggested that myositis autoantibodies recognising other autoantigens may also disrupt the function of their targets. CONCLUSIONS: This study demonstrates that, in myositis, autoantibodies are internalised into living cells, causing biological effects consistent with the disrupted function of their autoantigen.

Phenotypic spectrum of inclusion body myositis.

Inclusion body myositis (IBM) is a progressive, debilitating muscle disease commonly encountered in patients over the age of 50. IBM typically presents with asymmetric, painless, progressive weakness and atrophy of deep finger flexors and/or quadriceps muscle. Many patients with IBM develop dysphagia. However, atypical presentations of IBM with isolated dysphagia, asymptomatic hyper-CKemia, foot drop, proximal weakness, axial weakness, and facial diplegia have been reported. Other acquired and some inherited disorders may present similar to IBM, and this list gets more expansive when considering atypical presentations. In general, disease progression of IBM leads to loss of hand function and impaired ambulation, and most IBM patients become wheelchair dependent within 13-15 years of disease onset. Hence, IBM impacts negatively patients' quality of life and reduces longevity compared to the general population. Acknowledging the complete clinical spectrum of IBM presentation and excluding mimics would shorten the time to diagnosis, lead to prompt initiation of supportive management and avoid unproven therapy. Ongoing advanced phase studies in IBM provide hope that a therapy may soon be available. Therefore, an added potential benefit of early diagnosis would be prompt initiation of disease-modifying therapy once available.

Mitochondrial transfer and implications for muscle function in idiopathic inflammatory myopathies.

Impairment in cellular bioenergetics as either the cause, consequence, or major contributor of tissue damage has drawn increasing scientific curiosity across aging and chronic health conditions, with mitochondrial dysfunction emerging as a central mechanism in the pathogenesis of a variety of inflammatory and degenerative disorders. Beyond bioenergetics, mitochondria play critical regulatory roles in programmed cell death of dysfunctional/defective cells as well as in metabolite synthesis and metabolic signalling. Further, extra-cellular exposure to fragmentation of injured mitochondria is associated with incitement of systemic and organ-based inflammation. Thus, mitochondrial function has recently drawn intense, spectral scientific interest as an integral component across maladies.In muscle, mitochondrial dysfunction is clinically associated with atrophy and diminished endurance. Direct myo-histopathological evidence characterising loss of mitochondrial integrity as a hallmark of muscle compromise was first noticed in inclusion body myositis (IBM). This was followed by the discovery of multiple deletions in mitochondrial DNA in sarcopenia, IBM, and other inflammatory myopathies, like dermatomyositis. Though fraught with bioethical considerations, the transplant technology of mitochondrial transfer is swiftly gaining prominence in cellular biology and muscle physiology to remediate mitochondrial diminution and dysfunction. Assembling seminal works and recent developments, this review ventures into the rapidly evolving landscape of mitochondrial transfer, focusing on its implications on muscle function, and offers an integrated perspective on the potential roles of mitochondrial transfer and its implications for preserving and restoring muscle health. Presented here is a consolidated viewpoint on mitochondrial transfer in idiopathic inflammatory myopathies.

Collaborative research in myositis-related disorders: MIHRA, a global shared community model.

Myositis International Health and Research Collaborative Alliance (MIHRA) is a newly formed purpose-built non-profit charitable research organization dedicated to accelerating international clinical trial readiness, global professional and lay education, career development and rare disease advocacy in IIM-related disorders. In its long form, the name expresses the community's scope of engagement and intent. In its abbreviation, MIHRA, conveys linguistic roots across many languages, that reflects the IIM community's spirit with meanings such as kindness, community, goodness, and peace. MIHRA unites the global multi-disciplinary community of adult and pediatric healthcare professionals, researchers, patient advisors and networks focused on conducting research in and providing care for pediatric and adult IIM-related disorders to ultimately find a cure. MIHRA serves as a resourced platform for collaborative efforts in investigator-initiated projects, consensus guidelines for IIM assessment and treatment, and IIM-specific career development through connecting research networks.MIHRA's infrastructure, mission, programming and operations are designed to address challenges unique to rare disease communities and aspires to contribute toward transformative models of rare disease research such as global expansion and inclusivity, utilization of community resources, streamlining ethics and data-sharing policies to facilitate collaborative research. Herein, summarises MIHRA operational cores, missions, vision, programming and provision of community resources to sustain, accelerate and grow global collaborative research in myositis-related disorders.

A protocol for scoping reviews on the role of whole-body and dedicated body-part magnetic resonance imaging for assessment of adult and juvenile idiopathic inflammatory myopathies.

Currently, standardized magnetic resonance imaging (MRI) scoring systems and protocols for assessment of idiopathic inflammatory myopathies (IIMs) in children and adults are lacking. Therefore, we will perform a scoping review of the literature to collate and evaluate the existing semi-quantitative and quantitative MRI scoring systems and protocols for the assessment and monitoring of skeletal muscle involvement in patients with IIMs. The aim is to compile evidence-based information that will facilitate the future development of a universal standardized MRI scoring system for both research and clinical applications in IIM. A systematic search of electronic databases (PubMed, EMBASE, and Cochrane) will be undertaken to identify relevant articles published between January 2000 and October 2023. Data will be synthesized narratively. This scoping review seeks to comprehensively summarize and evaluate the evidence on the scanning protocols and scoring systems used in the assessment of diagnosis, disease activity, and damage using skeletal muscle MRI in IIMs. The results will allow the development of consensus recommendations for clinical practice and enable the standardization of research methods for the MRI assessment of skeletal muscle changes in patients with IIMs.

Mitochondrial myopathies diagnosed in adulthood: clinico-genetic spectrum and long-term outcomes.

Mitochondrial myopathies are frequently recognized in childhood as part of a broader multisystem disorder and often overlooked in adulthood. Herein, we describe the phenotypic and genotypic spectrum and long-term outcomes of mitochondrial myopathies diagnosed in adulthood, focusing on neuromuscular features, electrodiagnostic and myopathological findings and survival. We performed a retrospective chart review of adult patients diagnosed with mitochondrial myopathy at Mayo Clinic (2005-21). We identified 94 patients. Median time from symptom onset to diagnosis was 11 years (interquartile range 4-21 years). Median age at diagnosis was 48 years (32-63 years). Primary genetic defects were identified in mitochondrial DNA in 48 patients (10 with single large deletion, 38 with point mutations) and nuclear DNA in 29. Five patients had multiple mitochondrial DNA deletions or depletion without nuclear DNA variants. Twelve patients had histopathological features of mitochondrial myopathy without molecular diagnosis. The most common phenotypes included multisystem disorder (n = 30); mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (14); limb myopathy (13); chronic progressive external ophthalmoplegia (12); and chronic progressive external ophthalmoplegia-plus (12). Isolated skeletal muscle manifestations occurred in 27%. Sixty-nine per cent had CNS and 21% had cardiac involvement. Mutations most frequently involved MT-TL1 (27) and POLG (17); however, a wide spectrum of established and novel molecular defects, with overlapping phenotypes, was identified. Electrodiagnostic studies identified myopathy (77%), fibrillation potentials (27%) and axonal peripheral neuropathy (42%, most common with nuclear DNA variants). Among 42 muscle biopsies available, median percentage counts were highest for cytochrome C oxidase negative fibres (5.1%) then ragged blue (1.4%) and ragged red fibres (0.5%). Skeletal muscle weakness was mild and slowly progressive (decline in strength summated score of 0.01/year). Median time to gait assistance was 5.5 years from diagnosis and 17 years from symptom onset. Thirty patients died, with median survival of 33.4 years from symptom onset and 10.9 years from diagnosis. Median age at death was 55 years. Cardiac involvement was associated with increased mortality [hazard ratio 2.36 (1.05, 5.29)]. There was no difference in survival based on genotype or phenotype. Despite the wide phenotypic and genotypic spectrum, mitochondrial myopathies in adults share similar features with slowly progressive limb weakness, contrasting with common multiorgan involvement and high mortality.

Diagnosing Peripheral Neuropathy in Patients With Alcohol Use Disorder.

With the lack of distinctive features or diagnostic biomarkers, peripheral neuropathy in patients with excessive alcohol consumption is often misdiagnosed as alcohol-related neuropathy, influenced by underlying implicit and explicit bias against patients with an alcohol use disorder (AUD). Alcohol-related nerve toxicity has been attributed to various underlying mechanisms including altered trophic factor signaling, disrupted protein synthesis, free radical injury from oxidative stress, and nutritional deficiencies. Alcohol-related neuropathy has been most described as mild but painful, predominantly affecting small sensory fibers, without major functional limitations. This phenotype may be indistinguishable from a chronic idiopathic axonal neuropathy; hence, a causal relationship with AUD cannot be established with certainty. Searching for alternative causes is warranted, especially in patients with a more severe or rapidly progressive peripheral neuropathy. At the same time, there is underlying implicit and explicit bias in the medical field against patients with AUDs. Patients often experience devaluation and stigma, which can affect their adherence to medical advice and may lead to social reclusion. Addressing biases in health care workers is crucial to ensure that individuals receive proper care and are not subjected to stigmatization. In this article, we present a comprehensive narrative review of the literature on the clinical presentation and underlying pathomechanisms of alcohol-related peripheral neuropathy, raising awareness of the bias in the medical field against patients with AUD.

272nd ENMC international workshop: 10 Years of progress - revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness. 16-18 June 2023, Hoofddorp, The Netherlands.

Since the publication of the 2013 European Neuromuscular Center (ENMC) diagnostic criteria for Inclusion Body Myositis (IBM), several advances have been made regarding IBM epidemiology, pathogenesis, diagnostic tools, and clinical trial readiness. Novel diagnostic tools include muscle imaging techniques such as MRI and ultrasound, and serological testing for cytosolic 5'-nucleotidase-1A antibodies. The 272nd ENMC workshop aimed to develop new diagnostic criteria, discuss clinical outcome measures and clinical trial readiness. The workshop started with patient representatives highlighting several understudied symptoms and the urge for a timely diagnosis. This was followed by presentations from IBM experts highlighting the new developments in the field. This report is composed of two parts, the first part providing new diagnostic criteria on which consensus was achieved. The second part focuses on the use of outcome measures in clinical practice and clinical trials, highlighting current limitations and outlining the goals for future studies.

NLRP3 inflammasome activation and altered mitophagy are key pathways in inclusion body myositis.

Background: Inclusion body myositis (IBM) is the most prevalent muscle disease in adults for which no current treatment exists. The pathogenesis of IBM remains poorly defined. Inflammation and mitochondrial dysfunction are the most common histopathological findings. In this study, we aimed to explore the interplay between inflammation and mitochondrial dysfunction in IBM patients, highlighting sex differences. Methods: We included 38 IBM patients and 22 age- and sex-matched controls without myopathy. Bulk RNA sequencing, Meso Scale Discovery ELISA, western blotting, histochemistry and immunohistochemistry were performed on frozen muscle samples from the study participants. Results: We demonstrated activation of the NLRP3 inflammasome in IBM muscle samples, with the NLRP3 inflammasome pathway being the most upregulated. On muscle histopathology, there is increased NRLP3 immunoreactivity in both inflammatory cells and muscle fibers. Mitophagy is critical for removing damaged mitochondria and preventing the formation of a vicious cycle of mitochondrial dysfunction-NLRP3 activation. In the IBM muscle samples, we showed altered mitophagy, most significantly in males, with elevated levels of p-S65-Ubiquitin, a mitophagy marker. Furthermore, p-S65-Ubiquitin aggregates accumulated in muscle fibers that were mostly type 2 and devoid of cytochrome-c-oxidase reactivity. Type 2 muscle fibers are known to be more prone to mitochondrial dysfunction. NLRP3 RNA levels correlated with p-S65-Ubiquitin levels in both sexes but with loss of in muscle strength only in males. Finally, we identified sex-specific molecular pathways in IBM, with females having activation of pathways that could offset some of the pathomechanisms of IBM. Conclusions: NLRP3 inflammasome is activated in IBM, along with altered mitophagy particularly in males, which is of potential therapeutic significance. These findings suggest sex-specific mechanisms in IBM that warrant further investigation.

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.