Amyloid deposits and inflammatory infiltrates in sporadic inclusion body myositis: the inflammatory egg comes before the degenerative chicken

Late-onset myopathies

PURPOSE OF REVIEW

Late-onset myopathies are defined as muscle diseases that begin after the age of 50 years. Some myopathies present classically in the elderly, whereas others may have a variable age of onset, including late-onset presentation. The purpose of this review is to summarize and comment on the most recent evidence regarding the main diagnosis of late-onset myopathies focusing on genetic causes.

RECENT FINDINGS

Although late-onset myopathies (LOM) are expected to be predominantly acquired myopathies, some common genetic myopathies, such as facioscapulohumeral muscular dystrophy (FSHD), can present late in life, usually with an atypical presentation. In addition, metabolic myopathies, which are classically early-onset diseases, are also diagnoses to be considered, particularly as they may be treatable. Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) has recently been identified as a cause of subacute LOM with a dramatic response to riboflavin supplementation.

SUMMARY

Inclusion body myositis is the most frequent of all LOM. Myotonic dystrophy type 2, FSHD and oculopharyngeal muscular dystrophy are the most frequent causes of genetic LOM. We summarize the major differential diagnoses and the clinical features on clinical examination that are suggestive of a genetic diagnosis to provide a diagnostic approach.

SKN-1 is indispensable for protection against Aβ-induced proteotoxicity by a selenopeptide derived from Cordyceps militaris

Oxidative stress (OS) and disruption of proteostasis caused by aggregated proteins are the primary causes of cell death in various diseases. Selenopeptides have shown the potential to control OS and alleviate inflammatory damage, suggesting promising therapeutic applications. However, their potential function in inhibiting proteotoxicity is not yet fully understood. To address this gap in knowledge, this study aimed to investigate the effects and underlying mechanisms of the selenopeptide VPRKL(Se)M on amyloid β protein (Aβ) toxicity in transgenic Caenorhabditis elegans. The results revealed that supplementation with VPRKL(Se)M can alleviate Aβ-induced toxic effects in the transgenic C. elegans model. Moreover, the addition of VPRKL(Se)M inhibited the Aβ aggregates formation, reduced the reactive oxygen species (ROS) levels, and ameliorated the overall proteostasis. Importantly, we found that the inhibitory effects of VPRKL(Se)M on Aβ toxicity and activation of the unfolded protein are dependent on skinhead-1 (SKN-1). These findings suggested that VPRKL(Se)M is a potential bioactive agent for modulating SKN-1, which subsequently improves proteostasis and reduces OS. Collectively, the findings from the current study suggests VPRKL(Se)M may play a critical role in preventing protein disorder and related diseases.

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.

Evaluation of Neuromuscular Diseases and Complaints by Quantitative Muscle MRI

Background: Quantitative muscle MRI (qMRI) is a promising tool for evaluating and monitoring neuromuscular disorders (NMD). However, the application of different imaging protocols and processing pipelines restricts comparison between patient cohorts and disorders. In this qMRI study, we aim to compare dystrophic (limb-girdle muscular dystrophy), inflammatory (inclusion body myositis), and metabolic myopathy (Pompe disease) as well as patients with post-COVID-19 conditions suffering from myalgia to healthy controls. Methods: Ten subjects of each group underwent a 3T lower extremity muscle MRI, including a multi-echo, gradient-echo, Dixon-based sequence, a multi-echo, spin-echo (MESE) T2 mapping sequence, and a spin-echo EPI diffusion-weighted sequence. Furthermore, the following clinical assessments were performed: Quick Motor Function Measure, patient questionnaires for daily life activities, and 6-min walking distance. Results: Different involvement patterns of conspicuous qMRI parameters for different NMDs were observed. qMRI metrics correlated significantly with clinical assessments. Conclusions: qMRI metrics are suitable for evaluating patients with NMD since they show differences in muscular involvement in different NMDs and correlate with clinical assessments. Still, standardisation of acquisition and processing is needed for broad clinical use.

Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging

Sporadic inclusion body myositis (sIBM) is the most common muscle disease of older people and is clinically characterized by slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors. At present, there are no enduring treatments for this relentless disease that eventually leads to severe disability and wheelchair dependency. Although sIBM is considered a rare muscle disorder, its prevalence is certainly higher as the disease is often undiagnosed or misdiagnosed. The histopathological phenotype of sIBM muscle biopsy includes muscle fiber degeneration and endomysial lymphocytic infiltrates that mainly consist of cytotoxic CD8+ T cells surrounding nonnecrotic muscle fibers expressing MHCI. Muscle fiber degeneration is characterized by vacuolization and the accumulation of congophilic misfolded multi-protein aggregates, mainly in their non-vacuolated cytoplasm. Many players have been identified in sIBM pathogenesis, including environmental factors, autoimmunity, abnormalities of protein transcription and processing, the accumulation of several toxic proteins, the impairment of autophagy and the ubiquitin-proteasome system, oxidative and nitrative stress, endoplasmic reticulum stress, myonuclear degeneration, and mitochondrial dysfunction. Aging has also been proposed as a contributor to the disease. However, the interplay between these processes and the primary event that leads to the coexistence of autoimmune and degenerative changes is still under debate. Here, we outline our current understanding of disease pathogenesis, focusing on degenerative mechanisms, and discuss the possible involvement of aging.

Complement and MHC patterns can provide the diagnostic framework for inflammatory neuromuscular diseases

Histopathological analysis stands as the gold standard for the identification and differentiation of inflammatory neuromuscular diseases. These disorders continue to constitute a diagnostic challenge due to their clinical heterogeneity, rarity and overlapping features. To establish standardized protocols for the diagnosis of inflammatory neuromuscular diseases, the development of cost-effective and widely applicable tools is crucial, especially in settings constrained by limited resources. The focus of this review is to emphasize the diagnostic value of major histocompatibility complex (MHC) and complement patterns in the immunohistochemical analysis of these diseases. We explore the immunological background of MHC and complement signatures that characterize inflammatory features, with a specific focus on idiopathic inflammatory myopathies. With this approach, we aim to provide a diagnostic algorithm that may improve and simplify the diagnostic workup based on a limited panel of stainings. Our approach acknowledges the current limitations in the field of inflammatory neuromuscular diseases, particularly the scarcity of large-scale, prospective studies that validate the diagnostic potential of these markers. Further efforts are needed to establish a consensus on the diagnostic protocol to effectively distinguish these diseases.

High-resolution HLA genotyping in inclusion body myositis refines 8.1 ancestral haplotype association to DRB1*03:01:01 and highlights pathogenic role of arginine-74 of DRβ1 chain

OBJECTIVES

Inclusion body myositis (IBM) is a progressive inflammatory-degenerative muscle disease of older individuals, with some patients producing anti-cytosolic 5'-nucleotidase 1A (NT5C1A, aka cN1A) antibodies. Human Leukocyte Antigens (HLA) is the highest genetic risk factor for developing IBM. In this study, we aimed to further define the contribution of HLA alleles to IBM and the production of anti-cN1A antibodies.

METHODS

We HLA haplotyped a Western Australian cohort of 113 Caucasian IBM patients and 112 ethnically matched controls using Illumina next-generation sequencing. Allele frequency analysis and amino acid alignments were performed using the Genentech/MiDAS bioinformatics package. Allele frequencies were compared using Fisher's exact test. Age at onset analysis was performed using the ggstatsplot package. All analysis was carried out in RStudio version 1.4.1717.

RESULTS

Our findings validated the independent association of HLA-DRB1*03:01:01 with IBM and attributed the risk to an arginine residue in position 74 within the DRβ1 protein. Conversely, DRB4*01:01:01 and DQA1*01:02:01 were found to have protective effects; the carriers of DRB1*03:01:01 that did not possess these alleles had a fourteenfold increased risk of developing IBM over the general Caucasian population. Furthermore, patients with the abovementioned genotype developed symptoms on average five years earlier than patients without. We did not find any HLA associations with anti-cN1A antibody production.

CONCLUSIONS

High-resolution HLA sequencing more precisely characterised the alleles associated with IBM and defined a haplotype linked to earlier disease onset. Identification of the critical amino acid residue by advanced biostatistical analysis of immunogenetics data offers mechanistic insights and future directions into uncovering IBM aetiopathogenesis.

Face to Face: deciphering facial involvement in inclusion body myositis

OBJECTIVE

The objective of this study is to evaluate the frequency and characteristics of facial involvement in inclusion body myositis (IBM) patients and to compare it to the one previously described in facioscapulohumeral dystrophy (FSHD) patients.

METHODS

Thirty-two IBM patients were included and compared to 29 controls and 39 FSHD patients. All participants were recorded in a video as they performed a series of seven facial tasks. Five raters independently assessed facial weakness using both a qualitative evaluation and a semi-quantitative facial weakness score (FWS).

RESULTS

IBM patients had higher FWS than controls (7.89 ± 7.56 vs 1.06 ± 0.88, p < 0.001). Twenty IBM patients (63%) had a facial weakness with a FWS above the maximum value for controls. All facial tasks were significantly more impaired in IBM patients compared to controls (p < 0.001), task 2 evaluating orbiculari oculi muscle weakness being the most affected. IBM patients with facial weakness reported more swallowing troubles than IBM patients without facial weakness (p = 0.03). FSHD patients displayed higher FWS than IBM patients (12.16 ± 8.37 vs 7.89 ± 7.56, p = 0.01) with more pronounced facial asymmetry (p = 0.01). FWS inter-rater ICC was 0.775.

CONCLUSION

This study enabled us to estimate the frequency of facial impairment in IBM in more than half of patients, to detail its characteristics and to compare them with those of FSHD patients. The standardized, semi-quantitative FWS is an interesting diagnostic help in IBM as it appeared more sensitive than qualitative evaluation to detect mild facial weakness.

Stromal vascular fraction in the treatment of myositis

Muscle regeneration is a physiological process that converts satellite cells into mature myotubes under the influence of an inflammatory environment progressively replaced by an anti-inflammatory environment, with precise crosstalk between immune and muscular cells. If the succession of these phases is disturbed, the immune system can sometimes become auto-reactive, leading to chronic muscular inflammatory diseases, such as myositis. The triggers of these autoimmune myopathies remain mostly unknown, but the main mechanisms of pathogenesis are partially understood. They involve chronic inflammation, which could be associated with an auto-reactive immune response, and gradually with a decrease in the regenerative capacities of the muscle, leading to its degeneration, fibrosis and vascular architecture deterioration. Immunosuppressive treatments can block the first part of the process, but sometimes muscle remains weakened, or even still deteriorates, due to the exhaustion of its capacities. For patients refractory to immunosuppressive therapies, mesenchymal stem cells have shown interesting effects but their use is limited by their availability. Stromal vascular fraction, which can easily be extracted from adipose tissue, has shown good tolerance and possible therapeutic benefits in several degenerative and autoimmune diseases. However, despite the increasing use of stromal vascular fraction, the therapeutically active components within this heterogeneous cellular product are ill-defined and the mechanisms by which this therapy might be active remain insufficiently understood. We review herein the current knowledge on the mechanisms of action of stromal vascular fraction and hypothesise on how it could potentially respond to some of the unmet treatment needs of refractory myositis.

Integrated Multi-Omics Analysis for Inferring Molecular Players in Inclusion Body Myositis

Inclusion body myositis (IBM) is an acquired inflammatory myopathy affecting proximal and distal muscles that leads to weakness in patients over 50. It is diagnosed based on clinical and histological findings in muscle related to inflammation, degeneration, and mitochondria. In relation to IBM, a shortage of validated disease models and a lack of biomarkers and effective treatments constitute an unmet medical need. To overcome these hurdles, we performed an omics analysis of multiple samples from IBM patients (saliva, fibroblasts, urine, plasma, and muscle) to gain insight into the pathophysiology of IBM. Degeneration was evident due to the presence of amyloid β peptide 1-42 (Aβ1-42) in the saliva of the analyzed IBM patients. The presence of metabolic disarrangements in IBM was indicated by an imbalanced organic acid profile in fibroblasts and urine. Specifically, abnormal levels of L-pyroglutamic and orotic acid were supported by the abnormal expression of related metabolites in plasma and urine (glutathione and pyrimidines) and the aberrant expression of upstream gene regulators (L2HGDH, IDH2, OPLAH, and ASL) in muscle. Combined levels of L-pyroglutamic and orotic acid displayed an outstanding biomarker signature in urine with 100% sensitivity and specificity. The confirmation of systemic metabolic disarrangements in IBM and the identification of novel biomarkers reported herein unveil novel insights that require validation in larger cohorts.

Inflammasome in Skeletal Muscle: NLRP3 Is an Inflammatory Cell Stress Component in Inclusion Body Myositis

Inclusion body myositis (IBM) is a chronic, mostly treatment-resistant, inflammatory myopathy with a pathology that centers around specific interactions between inflammation and protein accumulation. The study aimed to identify the inflammasome as a key event in the complex network of pathomechanisms. Regulation of the inflammasome was assessed in a well-established pro-inflammatory cell culture model using human myoblasts and primary human myotubes. By quantitative PCR, western blot and immunocytochemistry, inflammasome markers including NLRP3 were assessed in muscle cells exposed to the cytokines IL-1β and IFN-γ. The data were corroborated by analysis of muscle biopsies from patients with IBM compared to other myositis subtypes. In the cell culture model of IBM, the NLRP3 inflammasome was significantly overexpressed, as evidenced by western blot (p = 0.03) and quantitative PCR (p < 0.01). Target genes that play a role in inflammasome assembly, T-cell migration, and MHC-I expression (p = 0.009) were highly co-upregulated. NLRP3 was significantly overexpressed in muscle biopsies from IBM samples compared to disease controls (p = 0.049), including other inflammatory myopathies. Due to the extraordinary features of the pathogenesis and the pronounced upregulation of NLRP3 in IBM, the inflammasome could serve as a key molecule that drives the inflammatory cascade as well as protein accumulation in the muscle. These data can be useful for future therapeutic developments.

Characterizing Ventilatory Muscle Dysfunction in Inclusion Body Myositis

OBJECTIVE

Investigation of the frequency and progression of ventilatory muscle dysfunction in patients with inclusion body myositis, the most common myopathy after age of 50 yrs. Prior research is limited to case series and cross-section studies.

DESIGN

This is a retrospective review of pulmonary function tests, respiratory symptoms, and muscle strength testing.

RESULTS

Of the 54 patients reviewed (mean age: 65 ± 9 yrs and disease duration: 7 ± 7 yrs), the majority ( n = 32, 59%) had restrictive forced vital capacity deficits at initial visit. Patients with reduced forced vital capacity showed higher prevalence of respiratory symptoms; but age, body mass index, and limb strength were similar when compared with patients without restrictive forced vital capacity. Mean rate of forced vital capacity decline of 0.108 l/yr in inclusion body myositis patients. Lower baseline limb strength correlated with longer disease duration and future forced vital capacity decline (eg, weaker patients experienced faster decline).

CONCLUSIONS

Based on forced vital capacity, there is a high frequency of ventilatory pump muscle weakness in inclusion body myositis, which is associated with a higher burden of respiratory symptoms. Baseline strength may indicate risk of respiratory decline and need for vigilant screening. Importantly, ventilatory and limb muscle decline may not progress in a corresponding manner, highlighting the importance of pulmonary function surveillance.

Clinical Subgroups and Factors Associated With Progression in Patients With Inclusion Body Myositis

BACKGROUND AND OBJECTIVES

Sporadic inclusion body myositis (IBM) is the most common acquired myopathy in individuals older than 50 years. The disorder is slowly progressive, and although many therapies have been investigated, response has generally been poor. Clinical heterogeneity may influence treatment responsiveness; however, data regarding heterogeneity in IBM are limited and often conflicting. We aim to identify clinically distinct subgroups within a large IBM cohort and prognostic factors for disease progression.

METHODS

Clinical, histologic, radiologic, and electrophysiologic data were analyzed for all patients with IBM and other forms of myositis enrolled in a longitudinal cohort from The Johns Hopkins Myositis Center from 2003 to 2018. Patients with IBM were included if they met at least one of the following criteria: Griggs possible, European Neuromuscular Centre 2011 probable, or Lloyd-Greenberg data-derived criteria for IBM. Univariate, multivariate, and graphical analyses were used to identify prognostic factors in patients with IBM. Thus, linear and logistic regressions were used to adjust for potential confounding variables. The evolution of creatine kinase and muscle strength was studied using multilevel linear regression models. Nonmodifiable risk factors (sex, race, disease duration, and age at the onset of first symptoms) were used as adjusting covariates for the regression analyses.

RESULTS

Among the 335 patients meeting the inclusion criteria for IBM, 64% were male with an average age of disease onset of 58.7 years and delay to diagnosis of 5.2 years. Initial misdiagnosis (52%) and immunosuppressant treatment (42%) were common. Less than half (43%) of muscle biopsies demonstrated all 3 pathologic hallmarks: endomysial inflammation, mononuclear cell invasion, and rimmed vacuoles. Black patients had significantly weaker arm abductors, hip flexors, and knee flexors compared with non-Black patients. Female patients had stronger finger flexors and knee extensors compared with their male counterparts. Younger age (<50 years) at onset was not associated with increased weakness.

DISCUSSION

Our study demonstrates that female and Black patients have distinct clinical phenotypes and trajectories within the overarching IBM clinical phenotype. These subgroups may have different responses to therapies, which may influence the design of future clinical trials in IBM.

Inclusion body myositis: from genetics to clinical trials

Inclusion body myositis (IBM) belongs to the group of idiopathic inflammatory myopathies and is characterized by a slowly progressive disease course with asymmetric muscle weakness of predominantly the finger flexors and knee extensors. The disease leads to severe disability and most patients lose ambulation due to lack of curative or disease-modifying treatment options. Despite some genes reported to be associated with hereditary IBM (a distinct group of conditions), data on the genetic susceptibility of sporadic IBM are very limited. This review gives an overview of the disease and focuses on the current genetic knowledge and potential therapeutic implications.

Combination of sporadic inclusion body myositis and primary Sjцgren’s syndrome: clinical case and review of literature

The article presents a review of the literature and a clinical observation of a patient with long-term anamnesis of primary Sjцgren's syndrome (SS) in combination with sporadic inclusion body myositis (sIBM). The diagnosis of SS was confirmed in accordance with the Russian diagnostic criteria for SS 2001, as well as with the ACR 2012 and ACR/EULAR 2016 criteria. The diagnosis of sIBM was established on the basis of a characteristic clinical picture: the development of the disease in a woman after 50 years of age with slowly progressive asymmetric muscle weakness and a typical distribution, a moderate increase in the level of creatine phosphokinase (<10 norms for the entire observation period), the presence of a generalized primary muscle process according to needle electromyography, a typical picture of muscle involvement according to magnetic resonance imaging, and the ineffectiveness of high doses of glucocorticoids. The absence of histological confirmation does not contradict the diagnosis, since morphological examination of muscles in patients with a typical course of the disease fails to detect characteristic signs of sIBM in 20% of cases.Currently, there is no effective pathogenetic therapy for sIBM. Understanding the mechanisms of sIBM development will allow to develop effective methods of its treatment.

Immunosuppressive and immunomodulatory therapies for idiopathic inflammatory myopathies

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

This protocol is for two separate reviews to assess the effects (benefits and harms) of immunosuppressant and immunomodulatory treatments for the idiopathic inflammatory myopathies.  

Preservation of shortening velocity and power output in single muscle fibres from patients with idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are autoimmune disorders of skeletal muscle causing weakness and disability. Utilizing single fibre contractility studies, we have previously shown that contractility is affected in muscle fibres from individuals with IIMs. For the current study, we hypothesized that a compensatory increase in shortening velocity occurs in muscle fibres from individuals with IIMs in an effort to maintain power output. We performed in vitro single fibre contractility studies to assess force-velocity relationships and maximum shortening velocity (V_max) of muscle fibres from individuals with IIMs (25 type I and 58 type IIA) and healthy controls (66 type I and 27 type IIA) and calculated maximum power output (W_max) for each fibre. We found significantly higher V_max (mean ± SEM) of fibres from individuals with IIMs, for both type I (1.40 ± 0.31 fibre lengths/s, n = vs. 0.63 ± 0.13 fibre lengths/s; p = 0.0019) and type IIA fibres (2.00 ± 0.17 fibre lengths/s vs 0.77 ± 0.10 fibre lengths/s; p < 0.0001). Furthermore, W_max (mean ± SEM) was maintained compared to fibres from healthy controls, again for both type I and type IIA fibres (4.10 ± 1.00 kN/m²·fibre lengths/s vs. 2.00 ± 0.16 kN/m²·fibre lengths/s; p = ns and 9.00 ± 0.64 kN/m²·fibre lengths/s vs. 6.00 ± 0.67 kN/m²·fibre lengths/s; p = ns respectively). In addition, type I muscle fibres from individuals with IIMs was able to develop maximum power output at lower relative force. The findings of this study suggest that compensatory responses to maintain power output, including increased maximum shortening velocity and improved efficiency, may occur in muscle of individuals with IIMs. The mechanism underlying this response is unclear, and different hypotheses are discussed.

Longitudinal Changes in MRI Muscle Morphometry and Composition in People With Inclusion Body Myositis

BACKGROUND AND OBJECTIVES

Limited data suggest that quantitative MRI (qMRI) measures have potential to be used as trial outcome measures in sporadic inclusion body myositis (sIBM) and as a noninvasive assessment tool to study sIBM muscle pathologic processes. Our aim was to evaluate changes in muscle structure and composition using a comprehensive multiparameter set of qMRI measures and to assess construct validity and responsiveness of qMRI measures in people with sIBM.

METHODS

This was a prospective observational cohort study with assessments at baseline (n = 30) and 1 year (n = 26). qMRI assessments include thigh muscle volume (TMV), inter/intramuscular adipose tissue (IMAT), muscle fat fraction (FF), muscle inflammation (T2 relaxation time), IMAT from T2* relaxation (T2*-IMAT), intermuscular connective tissue from T2* relaxation (T2*-IMCT), and muscle macromolecular structure from the magnetization transfer ratio (MTR). Physical performance assessments include sIBM Physical Functioning Assessment (sIFA), 6-minute walk distance, and quantitative muscle testing of the quadriceps. Correlations were assessed using the Spearman correlation coefficient. Responsiveness was assessed using the standardized response mean (SRM).

RESULTS

After 1 year, we observed a reduction in TMV (6.8%, p < 0.001) and muscle T2 (6.7%, p = 0.035), an increase in IMAT (9.7%, p < 0.001), FF (11.2%, p = 0.030), connective tissue (22%, p = 0.995), and T2*-IMAT (24%, p < 0.001), and alteration in muscle macromolecular structure (ΔMTR = -26%, p = 0.002). A decrease in muscle T2 correlated with an increase in T2*-IMAT (r = -0.47, p = 0.008). Deposition of connective tissue and IMAT correlated with deterioration in sIFA (r = 0.38, p = 0.032; r = 0.34, p = 0.048; respectively), whereas a decrease in TMV correlated with a decrease in quantitative muscle testing (r = 0.36, p = 0.035). The most responsive qMRI measures were T2*-IMAT (SRM = 1.50), TMV (SRM = -1.23), IMAT (SRM = 1.20), MTR (SRM = -0.83), and T2 relaxation time (SRM = -0.65).

DISCUSSION

Progressive deterioration in muscle quality measured by qMRI is associated with a decline in physical performance. Inflammation may play a role in triggering fat infiltration into muscle. qMRI provides valid and responsive measures that might prove valuable in sIBM experimental trials and assessment of muscle pathologic processes.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that qMRI outcome measures are associated with physical performance measures in patients with sIBM.

Inclusion body myositis: The interplay between ageing, muscle degeneration and autoimmunity

Inclusion body myositis (IBM) is a slowly progressive muscle disease affecting ageing individuals. IBM presents with a distinctive pattern of weakness involving the quadriceps and finger flexor muscles, although other muscles including pharyngeal muscles become affected over time. Pathological hallmarks of IBM include autoimmune features, including endomysial infiltration by highly differentiated T cells, as well as degenerative features marked by intramyofibre protein aggregates organised into inclusion bodies. Despite some progress in understanding the cellular pathways involved in IBM, it remains untreatable, and the progression of the disease leads to progressive weakness, disability, wheelchair dependency and loss of independence. Therefore, there is an urgent need to improve our understanding of the underlying mechanisms and pathways involved in this disease to identify new treatment targets. Here, we discuss the current understanding of aetiopathogenesis, the interrelationship between autoimmunity and degeneration, and how ageing is a major influencer of both these features.

Clinical implication of denervation in sporadic inclusion body myositis

INTRODUCTION

Sporadic inclusion body myositis (sIBM) is often accompanied by signs suggestive of denervation on electromyography (EMG), which mimics neurogenic disorders. Hence, the current study aimed to assess reinnervation after denervation in sIBM and its clinical impllcation.

METHODS

We retrospectively examined consecutive muscle biopsy specimens collected from 109 sIBM patients who were referred to our institution for diagnostic muscle biopsy from 2001 to 2018. Reinnervation after denervation in sIBM patients was assessed via muscle biopsy and EMG. The levels of acetylcholine receptor subunit γ (Chrng) and muscle-specific kinase (MuSK) mRNA, which are markers of denervation, were examined using real-time polymerase chain reaction. Response to treatment was defined as an increase of grade 1 or higher in two or more muscle groups as assessed using the Medical Research Council scale.

RESULTS

In total, 93 (85.3%) of 109 sIBM patients had reinnervation after denervation on histological examination and/or EMG. The mean disease duration before biopsy was significantly longer in patients with reinnervation after denervation than in those without (p < 0.00001). Patients with denervation had significantly higher levels of Chrng and MuSK mRNA than those without. The proportion of patients who responded to immunosuppressive therapies was smaller in the patients with denervation than those without (p < 0.05). However, there was no significant difference regarding time from onset to using a walking aid between the two groups.

DISCUSSION

Reinnervation after denervation is associated with disease duration and short-term response to therapy in individuals with sIBM.

Inclusion body myositis and associated diseases: an argument for shared immune pathologies

Inclusion body myositis (IBM) is the most prevalent idiopathic inflammatory myopathy (IIM) affecting older adults. The pathogenic hallmark of IBM is chronic inflammation of skeletal muscle. At present, we do not classify IBM into different sub-entities, with the exception perhaps being the presence or absence of the anti-cN-1A-antibody. In contrast to other IIM, IBM is characterized by a chronic and progressive disease course. Here, we discuss the pathophysiological framework of IBM and highlight the seemingly prototypical situations where IBM occurs in the context of other diseases. In this context, understanding common immune pathways might provide insight into the pathogenesis of IBM. Indeed, IBM is associated with a distinct set of conditions, such as human immunodeficiency virus (HIV) or hepatitis C-two conditions associated with premature immune cell exhaustion. Further, the pathomorphology of IBM is reminiscent of other muscle diseases, notably HIV-associated myositis or granulomatous myositis. Distinct immune pathways are likely to drive these commonalities and senescence of the CD8+ T cell compartment is discussed as a possible mechanism of pathogenesis. Future effort directed at understanding the co-occurrence of IBM and associated diseases could prove valuable to better understand the enigmatic IBM pathophysiology.

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

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

Sirolimus leads to rapid and sustained clinical improvement of motor deficits in a patient with inclusion body myositis

BACKGROUND AND PURPOSE

To provide further evidence for sirolimus, a mammalian target of rapamycin inhibitor, as a treatment strategy for patients with inclusion body myositis (IBM).

METHODS

We acquired longitudinal clinical data and immunological assessments of CD8⁺ T-cell subsets in peripheral blood for evaluation of potential anti-inflammatory treatment effects of sirolimus.

RESULTS

Therapy with sirolimus 2 mg/day by mouth led to rapid and sustained clinical improvement of motor symptoms for an observation period of more than 1 year. Treatment was well tolerated, with no occurrence of adverse effects. We did not observe a meaningful alteration of CD8⁺ T-cell subsets in our patient after 9 and 12 months compared to baseline.

CONCLUSIONS

The significant and persistent clinical improvement highlights the use of sirolimus as a potential treatment option in patients with IBM. In light of the lack of immunological treatment effects observed for cytotoxic CD8⁺ T cells, further studies should investigate the potential myoprotective effects of sirolimus.

Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis

Sporadic inclusion body myositis (IBM) is the most common acquired muscle disease in adults over age 50, yet it remains unclear whether the disease is primarily driven by T cell–mediated autoimmunity. IBM muscle biopsies display nuclear clearance and cytoplasmic aggregation of TDP-43 in muscle cells, a pathologic finding observed initially in neurodegenerative diseases, where nuclear loss of TDP-43 in neurons causes aberrant RNA splicing. Here, we show that loss of TDP-43–mediated splicing repression, as determined by inclusion of cryptic exons, occurs in skeletal muscle of subjects with IBM. Of 119 muscle biopsies tested, RT-PCR–mediated detection of cryptic exon inclusion was able to diagnose IBM with 84% sensitivity and 99% specificity. To determine the role of T cells in pathogenesis, we generated a xenograft model by transplanting human IBM muscle into the hindlimb of immunodeficient mice. Xenografts from subjects with IBM displayed robust regeneration of human myofibers and recapitulated both inflammatory and degenerative features of the disease. Myofibers in IBM xenografts showed invasion by human, oligoclonal CD8+ T cells and exhibited MHC-I up-regulation, rimmed vacuoles, mitochondrial pathology, p62-positive inclusions, and nuclear clearance and cytoplasmic aggregation of TDP-43, associated with cryptic exon inclusion. Reduction of human T cells within IBM xenografts by treating mice intraperitoneally with anti-CD3 (OKT3) suppressed MHC-I up-regulation. However, rimmed vacuoles and loss of TDP-43 function persisted. These data suggest that T cell depletion does not alter muscle degenerative pathology in IBM.

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.

Diagnosis and Clinical Development of Sporadic Inclusion Body Myositis and Polymyositis With Mitochondrial Pathology: A Single-Center Retrospective Analysis

To review our diagnostic and treatment approaches concerning sporadic inclusion body myositis (sIBM) and polymyositis with mitochondrial pathology (PM-Mito), we conducted a retrospective analysis of clinical and histological data of 32 patients diagnosed as sIBM and 7 patients diagnosed as PM-Mito by muscle biopsy. Of 32 patients identified histologically as sIBM, 19 fulfilled the 2011 European Neuromuscular Center (ENMC) diagnostic criteria for "clinico-pathologically defined sIBM" at the time of biopsy. Among these, 2 patients developed sIBM after years of immunosuppressive treatment for organ transplantation. Of 11 patients fulfilling the histological but not the clinical criteria, including 3 cases with duration <12 months, 8 later fulfilled the criteria for clinico-pathologically defined sIBM. Of 7 PM-Mito patients, 4 received immunosuppression with clinical improvement in 3. One of these later developed clinico-pathologically defined sIBM; 1 untreated patient progressed to clinically defined sIBM. Thus, muscle histology remains important for this differential diagnosis to identify sIBM patients not matching the ENMC criteria and the PM-Mito group. In the latter, we report at least 50% positive, if occasionally transient, response to immunosuppressive treatments and progression to sIBM in a minority. The mitochondrial abnormalities defining PM-Mito do not seem to define the threshold to immunosuppression unresponsiveness.

Computational Design and Analysis of a Multi-epitope Against Influenza A virus

Influenza A viruses are among the most studied viruses, however no effective prevention against influenza infection has been developed. So, designing an effective vaccine against Influenza A virus is a critical issue in the field of medical biotechnology. For this reason, to combat this disease, we have designed a novel multi-epitope vaccine candidate based on the several conserved and potential linear B-cell and T-cell binding epitopes by using the in silico approach. This vaccine consists of an ER signal conserved sequence, the PADRE conserved epitope and two conserved epitopes of Influenza matrix protein 2. T-cell binding epitopes from Matrix protein 2 were predicted by in silico tools of epitope prediction. The selected epitopes were joined by flexible linkers and physicochemical properties, toxicity, and allergenecity were investigated. The designed vaccine was antigenic, immunogenic, and non-allergenic with suitable physicochemical properties and has higher solubility. The final multi-epitope construct was modeled, confirmed by different programs and the molecular interactions with immune receptors were considered. The molecular docking assay indicated the interactions with immune-stimulatory toll-like receptor 3 (TLR3) and major histocompatibility complex class I (MHCI). The HADDOCK and H DOCK servers were used to make docking analysis, respectively. The docking analysis indicated a strong and stable binding interaction between the vaccine construct with major histocompatibility complex (MHC) class I and toll-like receptor 3. Overall, the findings suggest that the current vaccine may be a promising vaccine to prevent Influenza infection.

Biomarker und Histologie bei idiopathischen inflammatorischen Myopathien

Die idiopathischen inflammatorischen Myopathien (IIM) sind eine Gruppe entzündlicher Muskelerkrankungen für deren Diagnosestellung, Verlaufsbeurteilung, Prognoseabschätzung und Risikostratifizierung Biomarker eine jeweils essentielle Rolle spielen. Biomarker in diesem Kontext können sowohl „herkömmliche“ serologische Marker wie Muskelenzyme oder Autoantikörper, histologische Marker wie entitätsspezifische inflammatorische Muster, aber auch genomische und genetische Marker sein. Der vorliegende Artikel gibt einen Überblick über bewährte und innovative Marker.

Updates on the Immunopathology in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

To review recent advances in immunopathology for idiopathic inflammatory myopathies, focusing on widely available immunohistochemical analyses.

RECENT FINDINGS

Sarcoplasmic expression of myxovirus resistance protein A (MxA) is specifically observed in all types of dermatomyositis and informs that type I interferons are crucially involved in its pathogenesis. It is a more sensitive diagnostic marker than perifascicular atrophy. Diffuse tiny dots in the sarcoplasm highlighted by p62 immunostaining are characteristically seen in immune-mediated necrotizing myopathy. This feature is linked to a chaperone-assisted selective autophagy pathway. Myofiber invasion by highly differentiated T cells, a marker of which is KLRG1, is specific to inclusion body myositis and has a crucial role in its pathogenesis. The recent advances in immunopathology contribute to increased diagnostic accuracy and a better understanding of the underlying pathophysiology in different types of idiopathic inflammatory myopathies.

The role of interferons type I, II and III in myositis: A review

The classification of idiopathic inflammatory myopathies (IIM) is based on clinical, serological and histological criteria. The identification of myositis‐specific antibodies has helped to define more homogeneous groups of myositis into four dominant subsets: dermatomyositis (DM), antisynthetase syndrome (ASyS), sporadic inclusion body myositis (sIBM) and immune‐mediated necrotising myopathy (IMNM). sIBM and IMNM patients present predominantly with muscle involvement, whereas DM and ASyS patients present additionally with other extramuscular features, such as skin, lung and joints manifestations. Moreover, the pathophysiological mechanisms are distinct between each myositis subsets. Recently, interferon (IFN) pathways have been identified as key players implicated in the pathophysiology of myositis. In DM, the key role of IFN, especially type I IFN, has been supported by the identification of an IFN signature in muscle, blood and skin of DM patients. In addition, DM‐specific antibodies are targeting antigens involved in the IFN signalling pathways. The pathogenicity of type I IFN has been demonstrated by the identification of mutations in the IFN pathways leading to genetic diseases, the monogenic interferonopathies. This constitutive activation of IFN signalling pathways induces systemic manifestations such as interstitial lung disease, myositis and skin rashes. Since DM patients share similar features in the context of an acquired activation of the IFN signalling pathways, we may extend underlying concepts of monogenic diseases to acquired interferonopathy such as DM. Conversely, in ASyS, available data suggest a role of type II IFN in blood, muscle and lung. Indeed, transcriptomic analyses highlighted a type II IFN gene expression in ASyS muscle tissue. In sIBM, type II IFN appears to be an important cytokine involved in muscle inflammation mechanisms and potentially linked to myodegenerative features. For IMNM, currently published data are scarce, suggesting a minor implication of type II IFN. This review highlights the involvement of different IFN subtypes and their specific molecular mechanisms in each myositis subset.

Pathogenesis of inclusion body myositis

PURPOSE OF REVIEW

To review the pathogenesis of inclusion body myositis (IBM).

RECENT FINDINGS

IBM is an autoimmune disease. Multiple arms of the immune system are activated, but a direct attack on muscle fibers by highly differentiated T cells drives muscle destruction.

SUMMARY

Further understanding of the pathogenesis of IBM guides rational approaches to developing therapeutic strategies.

Longitudinal observational study investigating outcome measures for clinical trials in inclusion body myositis

OBJECTIVE

To describe decline in muscle strength and physical function in patients with sporadic inclusion body myositis (IBM).

METHODS

Manual muscle testing (MMT), quantitative muscle testing (QMT) and disability scoring using the IBM Functional Rating Scale (IBMFRS) were undertaken for 181 patients for up to 7.3 years. The relationship between MMT, QMT and IBMFRS composite scores and time from onset were examined using linear mixed effects models adjusted for gender and age of disease onset. Adaptive LASSO regression analysis was used to identify muscle groups that best predicted the time elapsed from onset. Cox proportional hazards regression was used to evaluate time to use of a mobility aid.

RESULTS

Multilevel modelling of change in percentage MMT, QMT and IBMFRS score over time yielded an average decline of 3.7% (95% CI 3.1% to 4.3%), 3.8% (95% CI 2.7% to 4.9%) and 6.3% (95% CI 5.5% to 7.2%) per year, respectively. The decline, however, was not linear, with steeper decline in the initial years. Older age of onset was associated with a more rapid IBMFRS decline (p=0.007), but did not influence the rate of MMT/QMT decline. Combination of selected muscle groups allowed for generation of single measures of patient progress (MMT and QMT factors). Median (IQR) time to using a mobility aid was 5.4 (3.6-9.2) years, significantly affected by greater age of onset (HR 1.06, 95% CI 1.04 to 1.09, p<0.001).

CONCLUSION

This prospective observational study represents the largest IBM cohort to date. Measures of patient progress evaluated in this study accurately predict disease progression in a reliable and useful way to be used in trial design.

In Pursuit of an Effective Treatment: the Past, Present and Future of Clinical Trials in Inclusion Body Myositis

Purpose of review

No clinical trial in sporadic inclusion body myositis (IBM) thus far has shown a clear and sustained therapeutic effect. We review previous trial methodology, explore why results have not translated into clinical practice, and suggest improvements for future IBM trials.

Recent findings

Early trials primarily assessed immunosuppressive medications, with no significant clinical responses observed. Many of these studies had methodological issues, including small participant numbers, nonspecific diagnostic criteria, short treatment and/or assessment periods and insensitive outcome measures. Most recent IBM trials have instead focused on nonimmunosuppressive therapies, but there is mounting evidence supporting a primary autoimmune aetiology, including the discovery of immunosuppression-resistant clones of cytotoxic T cells and anti-CN-1A autoantibodies which could potentially be used to stratify patients into different cohorts. The latest trials have had mixed results. For example, bimagrumab, a myostatin blocker, did not affect the 6-min timed walk distance, whereas sirolimus, a promotor of autophagy, did. Larger studies are planned to evaluate the efficacy of sirolimus and arimoclomol.

Summary

Thus far, no treatment for IBM has demonstrated a definite therapeutic effect, and effective treatment options in clinical practice are lacking. Trial design and ineffective therapies are likely to have contributed to these failures. Identification of potential therapeutic targets should be followed by future studies using a stratified approach and sensitive and relevant outcome measures.

The Role of Immune Cells in the Pathogenesis of Idiopathic Inflammatory Myopathies

Idiopathic inflammatory myopathies (IIMs) are chronic autoimmune disorders involving multiple organs, such as the muscle, skin, lungs and joints. Although the detailed pathogenesis of IIMs remains unclear, immune mechanisms have long been recognised as of key importance. Immune cells contribute to many inflammatory processes via intercellular interactions and secretion of inflammatory factors, and many studies have demonstrated the participation of a variety of immune cells, such as T cells and B cells, in the development of IIMs. Here, we summarise the current knowledge regarding immune cells in IIM patients and discuss their potential roles in IIM pathogenesis.

NAD+ boosting reduces age-associated amyloidosis and restores mitochondrial homeostasis in muscle

Aging is characterized by loss of proteostasis and mitochondrial homeostasis. Here, we provide bioinformatic evidence of dysregulation of mitochondrial and proteostasis pathways in muscle aging and diseases. Moreover, we show accumulation of amyloid-like deposits and mitochondrial dysfunction during natural aging in the body wall muscle of C. elegans, in human primary myotubes, and in mouse skeletal muscle, partially phenocopying inclusion body myositis (IBM). Importantly, NAD⁺ homeostasis is critical to control age-associated muscle amyloidosis. Treatment of either aged N2 worms, a nematode model of amyloid-beta muscle proteotoxicity, human aged myotubes, or old mice with the NAD⁺ boosters nicotinamide riboside (NR) and olaparib (AZD) increases mitochondrial function and muscle homeostasis while attenuating amyloid accumulation. Hence, our data reveal that age-related amyloidosis is a contributing factor to mitochondrial dysfunction and that both are features of the aging muscle that can be ameliorated by NAD⁺ metabolism-enhancing approaches, warranting further clinical studies.

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Amyloidosis and mitochondrial dysfunction typify muscle aging and disease across species

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NAD⁺ homeostasis is required to maintain proteostasis in nematodes and mammalian cells

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Reducing age-associated amyloidosis improves healthspan and mitochondrial function

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Late-life NAD⁺ boosting reduces amyloidosis and mitochondrial dysfunction during aging

Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial

BACKGROUND

Inclusion body myositis is the most frequent myositis in patients older than 50 years. Classical immunosuppressants are ineffective in treating inclusion body myositis, and to date there are no recommendations for pharmacological approaches to treatment. When used after organ transplantation, sirolimus can block the proliferation of effector T cells, while preserving T regulatory cells, and induce autophagy, all of which are processes that are impaired in inclusion body myositis. In this pilot study, we aimed to test the efficacy of sirolimus in patients with inclusion body myositis.

METHODS

This randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial was done at a single hospital in Paris, France. The study included men and women (aged 45-80 years) who had a defined diagnosis of inclusion body myositis according to established criteria. Eligible participants were randomly assigned (1:1) to receive once-daily oral sirolimus 2 mg or placebo. Centralised balanced block randomisation (blocks of four) was computer generated without stratification. The study comprised a 15-day screening period (days -15 to 0) and a 52-week treatment period (day 0 to month 12). The primary endpoint was the relative percentage change from baseline to month 12 in maximal voluntary isometric knee extension strength. Secondary endpoints included the following assessments at months 6 and 12: 6-min walking distance, isometric muscle strength for hand grip (finger flexors), knee flexion and elbow flexion and extension, forced vital capacity, muscle replacement with fat measured by quantitative nuclear MRI, Inclusion Body Myositis Weakness Composite Index (IBMWCI), Inclusion Body Myositis Functional Rating Scale (IBMFRS), Health Assessment Questionnaire without Disability Index (HAQ-DI), and analyses of T-cell subpopulations by mass cytometry. The primary analysis was done on the intention-to-treat population. The trial is registered at ClinicalTrials.gov, NCT02481453.

FINDINGS

Between July 15, 2015, and May 13, 2016, we screened 285 patients, 44 of whom were randomly allocated to sirolimus (22 patients) or placebo (22 patients). We observed no difference in the primary outcome of relative percentage change from baseline to month 12 of the maximal voluntary isometric knee extension strength (median difference 3·78, 95% CI -10·61 to 17·31; p=0·85). For secondary outcomes, differences between the groups were not significant for changes in strength of other muscle groups (grip, elbow flexion and extension, or knee flexion), IBMWCI, IBMFRS, and lower limb muscle fat fraction. However, we observed significant differences in favour of sirolimus between the study groups for HAQ-DI, forced vital capacity, thigh fat fraction, and 6-min walking distance. Ten (45%) of 22 patients in the sirolimus group had a serious adverse event compared with six (27%) of 22 patients in the placebo group. Four (18%) patients in the sirolimus group stopped their treatment because of adverse events (severe mouth ulcers, aseptic pneumonia, renal insufficiency, and peripheral lower limb oedema), which resolved after treatment discontinuation. Canker sores were the most frequent side-effect and were mainly mild or moderate in ten patients.

INTERPRETATION

We found no evidence for efficacy of sirolimus for treating inclusion body myositis based on maximal voluntary isometric knee extension strength and other muscle strength measures, and the side-effects of treatment were substantial for some patients. However, we believe there was enough evidence of benefit in certain secondary outcomes to pursue a multicentre phase 3 trial to further assess the safety and efficacy of sirolimus.

FUNDING

Institut national de la santé et de la recherche médicale, Direction générale de l'offre de soins, and Association Française contre les Myopathies.

Beta-amyloid deposition around hepatic bile ducts is a novel pathobiological and diagnostic feature of biliary atresia

BACKGROUND AND AIMS

Biliary atresia (BA) is a poorly understood and devastating obstructive bile duct disease of newborns. It is often diagnosed late, is incurable and frequently requires liver transplantation. In this study, we aimed to investigate the underlying pathogenesis and molecular signatures associated with BA.

METHODS

We combined organoid and transcriptomic analysis to gain new insights into BA pathobiology using patient samples and a mouse model of BA.

RESULTS

Liver organoids derived from patients with BA and a rhesus rotavirus A-infected mouse model of BA, exhibited aberrant morphology and disturbed apical-basal organization. Transcriptomic analysis of BA organoids revealed a shift from cholangiocyte to hepatocyte transcriptional signatures and altered beta-amyloid-related gene expression. Beta-amyloid accumulation was observed around the bile ducts in BA livers and exposure to beta-amyloid induced the aberrant morphology in control organoids.

CONCLUSION

The novel observation that beta-amyloid accumulates around bile ducts in the livers of patients with BA has important pathobiological implications, as well as diagnostic potential.

LAY SUMMARY

Biliary atresia is a poorly understood and devastating obstructive bile duct disease of newborns. It is often diagnosed late, is incurable and frequently requires liver transplantation. Using human and mouse 'liver mini-organs in the dish', we unexpectedly identified beta-amyloid deposition - the main pathological feature of Alzheimer's disease and cerebral amyloid angiopathy - around bile ducts in livers from patients with biliary atresia. This finding reveals a novel pathogenic mechanism that could have important diagnostic and therapeutic implications.

Refining myositis associated with primary Sjögren’s syndrome: data from the prospective cohort ASSESS

Objectives

To refine the prevalence, characteristics and response to treatment of myositis in primary SS (pSS).

Methods

The multicentre prospective Assessment of Systemic Signs and Evolution in Sjögren’s Syndrome (ASSESS) cohort of 395 pSS patients with ≥60 months’ follow-up was screened by the 2017 EULAR/ACR criteria for myositis. Extra-muscular complications, disease activity and patient-reported scores were analysed.

Results

Before enrolment and during the 5-year follow-up, myositis was suspected in 38 pSS patients and confirmed in 4 [1.0% (95% CI: 0.40, 2.6)]. Patients with suspected but not confirmed myositis had higher patient-reported scores and more frequent articular and peripheral nervous involvement than others. By contrast, disease duration in patients with confirmed myositis was 3-fold longer than without myositis. Two of the four myositis patients fulfilled criteria for sporadic IBM. Despite receiving three or more lines of treatment, they showed no muscle improvement, which further supported the sporadic IBM diagnosis. The two other patients did not feature characteristics of a myositis subtype, which suggested ‘pure’ pSS myositis. Steroids plus MTX was then efficient in achieving remission.

Conclusions

Myositis, frequently suspected, occurs in 1% of pSS patients. Especially when there is resistance to treatment, sporadic IBM should be considered and might be regarded as a late complication of this disease.

Inclusion body myositis in patients with spinocerebellar ataxia types 3 and 6

OBJECTIVES

To describe the combination of spinocerebellar ataxia (SCA) types 3 and 6 and sporadic inclusion body myositis (IBM).

METHODS

A description of five patients with SCA type 3 and 6 who were diagnosed with IBM. We explore possible mechanisms explaining the coexistence of both diseases.

RESULTS

The patients with SCA-3 (n=4) and SCA-6 (n=1) developed asymmetric muscle weakness in a pattern suggestive of IBM in the course of their disease. Based on findings of neurological examination and additional investigations (muscle ultrasound, muscle biopsy), the diagnosis of IBM was made in all patients.

CONCLUSION

We report on five patients with concomitant SCA and IBM. Our cases may merely illustrate coincidental co-occurrence of IBM and SCA-3/SCA-6. However, the presence of SCA mutations could predispose to the development of IBM in some SCA patients, or, the presence of toxic aggregates and malfunctioning of cellular quality control processes in both diseases could indicate a convergence of disease mechanisms.

An exploratory study of contractile force production in muscle fibers from patients with inflammatory myopathies

INTRODUCTION

The mechanism by which weakness develops in idiopathic inflammatory myopathies (IIMs) is still unclear. In this study we investigated the maximum force of single muscle fibers from patients with IIMs.

METHODS

Permeabilized single muscle fibers from patients with IIMs and healthy controls were subjected to contractility measurements. Maximum force and specific force production (maximum force normalized to fiber size) and fiber type were determined for each isolated fiber.

RESULTS

A total of 178 fibers were studied from five patients with IIMs and 95 fibers from four controls. Specific force production was significantly lower in the IIM group for all fiber types.

DISCUSSION

The findings from this exploratory study suggest that weakness in IIMs may, in part, be caused by dysfunction of the contractile apparatus. These findings provide a basis for further studies into the mechanisms underlying weakness in IIMs.

Inclusion body myositis: clinical features and pathogenesis

Inclusion body myositis (IBM) is often viewed as an enigmatic disease with uncertain pathogenic mechanisms and confusion around diagnosis, classification and prospects for treatment. Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases. Although IBM T cell autoimmunity has long been recognized, enormous attention has been focused for decades on several biomarkers of myofibre protein aggregates, which are present in <1% of myofibres in patients with IBM. This focus has given rise, together with the relative treatment refractoriness of IBM, to a competing view that IBM is not an autoimmune disease. Findings from the past decade that implicate autoimmunity in IBM include the identification of a circulating autoantibody (anti-cN1A); the absence of any statistically significant genetic risk factor other than the common autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies; the presence of a marked cytotoxic T cell signature in gene expression studies; and the identification in muscle and blood of large populations of clonal highly differentiated cytotoxic CD8⁺ T cells that are resistant to many immunotherapies. Mounting evidence that IBM is an autoimmune T cell-mediated disease provides hope that future therapies directed towards depleting these cells could be effective.

Autophagy Defects in Skeletal Myopathies

Autophagy is an evolutionarily conserved catabolic process that targets different types of cytoplasmic cargo (such as bulk cytoplasm, damaged cellular organelles, and misfolded protein aggregates) for lysosomal degradation. Autophagy is activated in response to biological stress and also plays a critical role in the maintenance of normal cellular homeostasis; the latter function is particularly important for the integrity of postmitotic, metabolically active tissues, such as skeletal muscle. Through impairment of muscle homeostasis, autophagy dysfunction contributes to the pathogenesis of many different skeletal myopathies; the observed autophagy defects differ from disease to disease but have been shown to involve all steps of the autophagic cascade (from induction to lysosomal cargo degradation) and to impair both bulk and selective autophagy. To highlight the molecular and cellular mechanisms that are shared among different myopathies with deficient autophagy, these disorders are discussed based on the nature of the underlying autophagic defect rather than etiology or clinical presentation.

Up-regulation of Toll-like receptors 7 and 9 and its potential implications in the pathogenic mechanisms of LMNA-related myopathies

Laminopathies are a heterogeneous group of diseases, caused by mutations in lamin A/C proteins. The most common laminopathy (LMNA-related myopathies, LMNA-RM) affects skeletal and cardiac muscles; muscle histopathology is variable, ranging from mild unspecific changes to dystrophic features, sometimes with inflammatory evidence. Whether the genetic defect might activate innate immune components, leading to chronic inflammation, myofiber necrosis and fibrosis, is still unknown. By qPCR, a significant up-regulation of Toll-like receptor (TLR) 7 and 9 transcripts was found in LMNA-RM compared to other myopathic and non-myopathic muscles. A marked TLR7/9 staining was observed on LMNA-RM blood vessels and muscle fibers and, when present, on infiltrating cells, mainly macrophages, scattered in the tissue or localized close to degenerated muscle fibers and connective tissue. Our results recognize innate immunity as a player in LMNA-RM pathogenesis. Modulation of TLR7/9 signaling pathways and decrease of macrophage-mediated inflammation might be potential therapeutic strategies in LMNA-RM management.

Abbreviations: DMD, Duchenne muscular dystrophy; EDMD2, Emery-Dreifuss muscular dystrophy type 2; FSHD, facio-scapulo-humeral muscular dystrophy; LGMD1B, limb-girdle muscular dystrophy type 1B; LMNA-CMD, LMNA-related congenital muscular dystrophy; LMNA-RM, LMNA-related myopathies; sIBM, sporadic inclusion body myositis; TLR, Toll-like receptor

Cardiac Phenotypes in Hereditary Muscle Disorders: JACC State-of-the-Art Review

Hereditary muscular diseases commonly involve the heart. Cardiac manifestations encompass a spectrum of phenotypes, including both cardiomyopathies and rhythm disorders. Common biomarkers suggesting cardiomuscular diseases include increased circulating creatine kinase and/or lactic acid levels or disease-specific metabolic indicators. Cardiac and extra-cardiac traits, imaging tests, family studies, and genetic testing provide precise diagnoses. Cardiac phenotypes are mainly dilated and hypokinetic in dystrophinopathies, Emery-Dreifuss muscular dystrophies, and limb girdle muscular dystrophies; hypertrophic in Friedreich ataxia, mitochondrial diseases, glycogen storage diseases, and fatty acid oxidation disorders; and restrictive in myofibrillar myopathies. Left ventricular noncompaction is variably associated with the different myopathies. Conduction defects and arrhythmias constitute a major phenotype in myotonic dystrophies and skeletal muscle channelopathies. Although the actual cardiac management is rarely based on the cause, the cardiac phenotypes need precise characterization because they are often the only or the predominant manifestations and the prognostic determinants of many hereditary muscle disorders.

Sequestosome-1 (p62) expression reveals chaperone-assisted selective autophagy in immune-mediated necrotizing myopathies

Diffuse myofiber necrosis in the context of inflammatory myopathy is the hallmark of immune‐mediated necrotizing myopathy (IMNM). We have previously shown that skeletal muscle fibers of IMNM patients may display nonrimmed vacuoles and sarcoplasmic irregularities. The dysfunctional chaperone activity has been linked to the defective assembly of skeletal muscle proteins and their degradation via lysosomes, autophagy and the proteasomal machinery. This study was undertaken to highlight a chaperone‐assisted selective autophagy (CASA) pathway, functionally involved in protein homeostasis, cell stress and the immune response in skeletal muscle of IMNM patients. Skeletal muscle biopsies from 54 IMNM patients were analyzed by immunostaining, as well as by qPCR. Eight biopsies of sIBM patients served as pathological controls, and eight biopsies of nondisease control subjects were included. Alteration of autophagy was detectable in all IMNM biopsy samples highlighted via a diffuse sarcoplasmic staining pattern by p62 and LC3 independent of vacuoles. This pattern was at variance with the coarse focal staining pattern mostly confined to rimmed vacuoles in sIBM. Colocalization of p62 with the chaperone proteins HSP70 and αB‐crystalline points to the specific targeting of misfolded proteins to the CASA machinery. Bcl2‐associated athanogene 3 (BAG3) positivity of these fibers emphasizes the selectivity of autophagy processes and these fibers also express MHC class I sarcolemma. Expression of genes involved in autophagy and endoplasmic reticulum (ER) stress pathways studied here is significantly upregulated in IMNM. We highlight that vacuoles without sarcolemmal features may arise in IMNM muscle biopsies, and they must not be confounded with sIBM‐specific vacuoles. Further, we show the activation of selective autophagy and emphasize the role of chaperones in this context. CASA occurs in IMNM muscle, and specific molecular pathways of autophagy differ from the ones in sIBM, with p62 as a unique identifier of this process.

CYLD dysregulation in pathogenesis of sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is the most commonly acquired myopathy in middle-aged and elderly people. The muscle histology is characterized by both inflammation and degeneration, including sarcoplasmic aggregation of TDP-43. Cylindromatosis (CYLD) is a deubiquitinating enzyme that targets Lys63-linked ubiquitin chains and negatively regulates signal transduction pathways, such as NF-κB signalling pathways. We examined localization of CYLD as well as phosphorylated TDP-43, phosphorylated p62, and Lys63-linked ubiquitin in muscle tissues of sIBM patients and muscle-specific wild-type TDP-43 transgenic (TDP-43 TG) mice. We investigated whether overexpression of CYLD can affect muscle toxicity in the cell models treated by endoplasmic reticulum (ER) stress inducers tunicamycin and thapsigargin. CYLD expressed with phosphorylated TDP-43, phosphorylated p62, and Lys63-linked ubiquitin in the nuclear and perinuclear regions of muscle fibres of wild-type TDP-43 TG mice and the degenerative myofibres of sIBM patients with rimmed vacuoles and endomysial cellular infiltration. Although expression levels of CYLD decreased and cell viability was reduced in cells treated with ER stress inducers, wild-type CYLD, but not the catalytic mutant, substantially improved cell viability based on the deubiquitinase activity. Dysregulation of CYLD may reinforce myodegeneration in the pathophysiology of sIBM by attenuating autophagic clearance of protein aggregates. Regulating CYLD in muscle fibres might serve as a novel therapeutic strategy for sIBM treatment.

A Patient with Sjogren's Syndrome and Subsequent Diagnosis of Inclusion Body Myositis and Light-Chain Amyloidosis

We discuss a challenging case of a 58-year-old Vietnamese-American woman who presented to her new primary care provider with an 8-year history of slowly progressive dysphagia, hoarseness, muscle weakness with associated frequent falls, and weight loss. She eventually reported dry eyes and dry mouth, and she was diagnosed with Sjogren's syndrome. Subsequently, she was additionally diagnosed with inclusion body myositis and gastric light-chain (AL) amyloidosis. Although inclusion body myositis has been previously associated with Sjogren's syndrome, inclusion body myositis is rare in non-Caucasians, and the trio of Sjogren's syndrome, inclusion body myositis, and AL amyloidosis has not been previously reported. Sjogren's syndrome is a systemic autoimmune condition characterized by ocular and oral dryness. It is one of the most common rheumatologic disorders in the USA and worldwide. Early diagnosis of Sjogren's is particularly important given the frequency and variety of associated autoimmune diseases and extraglandular manifestations. Furthermore, although inclusion body myositis has a low prevalence, it is the most common inflammatory myopathy in older adults and is unfortunately associated with long delays in diagnosis, so knowledge of this disorder is also crucial for practicing internists.