Inclusion Body Myositis Muscle Research Articles

Effect of sirolimus on muscle in inclusion body myositis observed with magnetic resonance imaging and spectroscopy.

Finding sensitive clinical outcome measures has become crucial in natural history studies and therapeutic trials of neuromuscular disorders. Here, we focus on 1-year longitudinal data from quantitative magnetic resonance imaging (MRI) and phosphorus magnetic resonance spectroscopy (31P MRS) in a placebo-controlled study of sirolimus for inclusion body myositis (IBM), also examining their links to functional, strength, and clinical parameters in lower limb muscles. Quantitative MRI and 31P MRS data were collected at 3T from a single site, involving 44 patients (22 on placebo, 22 on sirolimus) at baseline and year-1, and 21 healthy controls. Assessments included fat fraction (FF), contractile cross-sectional area (cCSA), and water T2 in global leg and thigh segments, muscle groups, individual muscles, as well as 31P MRS indices in quadriceps or triceps surae. Analyses covered patient-control comparisons, annual change assessments via standard t-tests and linear mixed models, calculation of standardized response means (SRM), and exploration of correlations between MRI, 31P MRS, functional, strength, and clinical parameters. The quadriceps and gastrocnemius medialis muscles had the highest FF values, displaying notable heterogeneity and asymmetry, particularly in the quadriceps. In the placebo group, the median 1-year FF increase in the quadriceps was 3.2% (P<0.001), whereas in the sirolimus group, it was 0.7% (P=0.033). Both groups experienced a significant decrease in cCSA in the quadriceps after 1year (P<0.001), with median changes of 12.6% for the placebo group and 5.5% for the sirolimus group. Differences in FF and cCSA changes between the two groups were significant (P<0.001). SRM values for FF and cCSA were 1.3 and 1.4 in the placebo group and 0.5 and 0.8 in the sirolimus group, respectively. Water T2 values were highest in the quadriceps muscles of both groups, significantly exceeding control values in both groups (P<0.001) and were higher in the placebo group than in the sirolimus group. After treatment, water T2 increased significantly only in the sirolimus group's quadriceps (P<0.01). Multiple 31P MRS indices were abnormal in patients compared to controls and remained unchanged after treatment. Significant correlations were identified between baseline water T2 and FF at baseline and the change in FF (P<0.001). Additionally, significant correlations were observed between FF, cCSA, water T2, and functional and strength outcome measures. This study has demonstrated that quantitative MRI/31P MRS can discern measurable differences between placebo and sirolimus-treated IBM patients, offering promise for future therapeutic trials in idiopathic inflammatory myopathies such as IBM.

Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis

Inclusion body myositis (IBM) is unique across the spectrum of idiopathic inflammatory myopathies (IIM) due to its distinct clinical presentation and refractoriness to current treatment approaches. One explanation for this resistance may be the engagement of cell-autonomous mechanisms that sustain or promote disease progression of IBM independent of inflammatory activity. In this study, we focused on senescence of tissue-resident cells as potential driver of disease. For this purpose, we compared IBM patients to non-diseased controls and immune-mediated necrotizing myopathy patients. Histopathological analysis suggested that cellular senescence is a prominent feature of IBM, primarily affecting non-myogenic cells. In-depth analysis by single nuclei RNA sequencing allowed for the deconvolution and study of muscle-resident cell populations. Among these, we identified a specific cluster of fibro-adipogenic progenitors (FAPs) that demonstrated key hallmarks of senescence, including a pro-inflammatory secretome, expression of p21, increased β-galactosidase activity, and engagement of senescence pathways. FAP function is required for muscle cell health with changes to their phenotype potentially proving detrimental. In this respect, the transcriptomic landscape of IBM was also characterized by changes to the myogenic compartment demonstrating a pronounced loss of type 2A myofibers and a rarefication of acetylcholine receptor expressing myofibers. IBM muscle cells also engaged a specific pro-inflammatory phenotype defined by intracellular complement activity and the expression of immunogenic surface molecules. Skeletal muscle cell dysfunction may be linked to FAP senescence by a change in the collagen composition of the latter. Senescent FAPs lose collagen type XV expression, which is required to support myofibers’ structural integrity and neuromuscular junction formation in vitro. Taken together, this study demonstrates an altered phenotypical landscape of muscle-resident cells and that FAPs, and not myofibers, are the primary senescent cell type in IBM.

Sporadic Inclusion Body Myositis

Inclusion body myositis (IBM) is an idiopathic inflammatory muscle disease that predominantly affects elderly men over the age of 50 years, and the number of patients is rapidly increasing in Japan. Generally, muscle weakness and atrophy occur asymmetrically in the flexor muscles of the fingers and wrists and the quadriceps muscles. Invasive muscle biopsy is essential for the diagnosis of IBM. Although its pathogenesis is not yet understood, both inflammatory as well as degenerative mechanisms are postulated to be involved. In particular, degeneration of the IBM muscle may be associated with the IFN-II secretion by highly differentiated CD8+ T lymphocytes. Cytoplasmic 5'-nucleotidase 1A (cN1A) antibody has been detected in the blood samples of approximately half of the patients with IBM. While there are positive opinions about the diagnostic significance of the antibody, its usefulness for the diagnosis of IBM is limited. The results of passive immunization support its etiologic significance; however, more detailed verification, including active immunization, is needed in the future.

Unravelling inclusion body myositis using a patient-derived fibroblast model.

Inclusion body myositis (IBM) is an inflammatory myopathy clinically characterized by proximal and distal muscle weakness, with inflammatory infiltrates, rimmed vacuoles and mitochondrial changes in muscle histopathology. There is scarce knowledge on IBM aetiology, and non-established biomarkers or effective treatments are available, partly due to the lack of validated disease models. We have performed transcriptomics and functional validation of IBM muscle pathological hallmarks in fibroblasts from IBM patients (n=14) and healthy controls (n=12), paired by age and sex. The results comprise an mRNA-seq, together with functional inflammatory, autophagy, mitochondrial and metabolic changes between patients and controls. Gene expression profile of IBM vs control fibroblasts revealed 778 differentially expressed genes (P-value adj<0.05) related to inflammation, mitochondria, cell cycle regulation and metabolism. Functionally, an increased inflammatory profile was observed in IBM fibroblasts with higher supernatant cytokine secretion (three-fold increase). Autophagy was reduced considering basal protein mediators (18.4% reduced), time-course autophagosome formation (LC3BII 39% reduced, P-value<0.05), and autophagosome microscopic evaluation. Mitochondria displayed reduced genetic content (by 33.9%, P-value<0.05) and function (30.2%-decrease in respiration, 45.6%-decline in enzymatic activity (P-value<0.001), 14.3%-higher oxidative stress, 135.2%-increased antioxidant defence (P-value<0.05), 11.6%-reduced mitochondrial membrane potential (P-value<0.05) and 42.8%-reduced mitochondrial elongation (P-value<0.05)). In accordance, at the metabolite level, organic acid showed a 1.8-fold change increase, with conserved amino acid profile. Correlating to disease evolution, oxidative stress and inflammation emerge as potential markers of prognosis. These findings confirm the presence of molecular disturbances in peripheral tissues from IBM patients and prompt patients' derived fibroblasts as a promising disease model, which may eventually be exported to other neuromuscular disorders. We additionally identify new molecular players in IBM associated with disease progression, setting the path to deepen in disease aetiology, in the identification of novel biomarkers or in the standardization of biomimetic platforms to assay new therapeutic strategies for preclinical studies.

Anti-Valosin-Containing Protein (VCP/p97) Autoantibodies in Inclusion Body Myositis and Other Inflammatory Myopathies.

The rationale for this study was based on reports that valosin-containing protein (VCP) mutations are found in hereditary inclusion body myositis (IBM) and VCP was detected in rimmed vacuoles of sporadic IBM (sIBM) muscle biopsies. Autoantibodies to VCP have not been reported in sIBM or other inflammatory myopathies (IIMs). The aim of this study was to determine the frequency and clinical significance of anti-VCP antibodies in sIBM and other IIMs. Sera were collected from 73 patients with sIBM and 383 comparators or controls, including patients with IIM (n=69), those with juvenile dermatomyositis (JDM) (n=67), those with juvenile idiopathic arthritis (JIA) (n=47), those with primary biliary cholangitis (PBC) (n=105), controls that were age matched to patients with sIBM (similarly aged controls [SACs]) (n=63), and healthy controls (HCs) (n=32).Immunoglobulin G antibodies to VCP were detected by addressable laser bead immunoassay using a full-length recombinant human protein. Among patients with sIBM, 26.0% (19/73) were positive for anti-VCP. The frequency in disease controls was 15.0% (48/320). Among SACs, the frequency was 1.6% (1/63), and in HCs 0% (0/32). Frequencies were 17.5% (11/63) for IIM, 25.7% (27/105) for PBC, 3.0% (2/67) for JDM, and 17.0% (8/47) for JIA. The sensitivity, specificity, positive predictive value, and negative predictive value of anti-VCP for sIBM were 26.0%, 87.2%, 28.4%, and 85.9%, respectively. Of patients with sIBM, 15.1% (11/73) were positive for both anti-VCP and anti-cytosolic 5'-nucleotidase 1A (NT5c1A). Eleven percent of patients (8/73) were positive for anti-VCP, but negative for anti-NT5c1A. Anti-VCP has low sensitivity and moderate specificity for sIBM but may help fill the seronegative gap in sIBM. Further studies are needed to determine whether anti-VCP is a biomarker for a clinical phenotype that may have clinical value.

Identification of Hub Genes and Biological Pathways in Inclusion Body Myositis Using Bioinformatics Analysis

BackgroundInclusion body myositis (IBM) is a unique idiopathic inflammatory myopathy with unclear pathogenesis and poor prognosis. Although previous publications have identified some molecular biomarkers, the value of these biomarkers is unknown.ObjectiveTo identify hub genes and signaling pathways related to IBM for understanding the IBM-related mechanisms and providing guidance for therapy development.MethodsTwo microarray datasets (GSE3112 and GSE128470) were downloaded from the Gene Expression Omnibus (GEO) database. GEO2R was used to detect differentially expressed genes (DEGs) between IBM and normal muscle tissues. The hub genes were determined using protein–protein interaction (PPI) network in Cytoscape. The specific signaling pathways and biological functions of IBM were identified using GO, KEGG, and GSEA enrichment analyses. Moreover, CIBERSORT was applied to estimate the expression level of 22 immune cell types in IBM and normal muscle tissue. The relationship between the immune cell types and hub genes was then explored.ResultsA total of 219 DEGs and 10 hub genes were identified. Enrichment analyses revealed that the chemokine signaling pathway, cellular response to interferon-gamma, and P53 pathway have crucial roles in IBM. Immune infiltration analyses showed that IBM was associated with high level of CD8 T cells, Tregs, and macrophages. Finally, five potential drugs were predicted for IBM patients through CMap (connectivity map) database.ConclusionIn this study, the underlying molecular mechanisms and immunological landscape of IBM were investigated, and thus may provide new directions for future research on IBM pathogenesis.

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.

An exploratory study of circulating cytokines and chemokines in patients with muscle disorders proposes CD40L and CCL5 represent general disease markers while CXCL10 differentiates between patients with an autoimmune myositis

Discriminating an autoimmune myositis from other disorders and subtyping of patient groups within this heterogeneous group of conditions remain diagnostic challenges. In our study we explored the potential of cytokine and chemokine typing in patient sera as an addition to the expanding set of blood-accessible diagnostic biomarkers available today. We selected sets of ten patients within well-characterized disease groups representing healthy controls, and patients with hereditary muscular dystrophies, immune-mediated necrotizing myopathy (IMNM) and sporadic inclusion body myositis (IBM). Prescreening using proteome arrays singled out three biomarker candidates, being the cytokine CD40L, and chemokines CXCL10 and CCL5. Enzyme-linked immunosorbent assays showed all three markers to be elevated in muscle disease irrespective of patient subgroup. CXCL10 levels on the other hand were higher in autoimmune myositis only, and levels were significantly higher in IBM compared to IMNM. The strong CXCL10 expression observed in the auto-aggressive inflammatory cells within IBM muscle tissues possibly represents a major source of circulating CXCL10. We conclude that CXCL10 levels could represent a convenient marker for autoimmune myositis indicative of patient subgroups.

Mitochondrial DNA variants in inclusion body myositis characterized by deep sequencing.

Muscle pathology in inclusion body myositis (IBM) typically includes inflammatory cell infiltration, muscle fibers with rimmed vacuoles and cytochrome c oxidase (COX)‐deficient fibers. Previous studies have revealed clonal expansion of large mitochondrial DNA (mtDNA) deletions in the COX‐deficient muscle fibers. Technical limitations have prevented complete investigations of the mtDNA deletions and other mtDNA variants. Detailed characterization by deep sequencing of mtDNA in muscle samples from 21 IBM patients and 10 age‐matched controls was performed after whole genome sequencing with a mean depth of mtDNA coverage of 46,000x. Multiple large mtDNA deletions and duplications were identified in all IBM and control muscle samples. In general, the IBM muscles demonstrated a larger number of deletions and duplications with a mean heteroplasmy level of 10% (range 1%‐35%) compared to controls (1%, range 0.2%‐3%). There was also a small increase in the number of somatic single nucleotide variants in IBM muscle. More than 200 rearrangements were recurrent in at least two or more IBM muscles while 26 were found in both IBM and control muscles. The deletions and duplications, with a high recurrence rate, were mainly observed in three mtDNA regions, m.534‐4429, m.6330‐13993, and m.8636‐16072, where some were flanked by repetitive sequences. The mtDNA copy number in IBM muscle was reduced to 42% of controls. Immunohistochemical and western blot analyses of IBM muscle revealed combined complex I and complex IV deficiency affecting the COX‐deficient fibers. In conclusion, deep sequencing and quantitation of mtDNA variants revealed that IBM muscles had markedly increased levels of large deletions and duplications, and there were also indications of increased somatic single nucleotide variants and reduced mtDNA copy numbers compared to age‐matched controls. The distribution and type of variants were similar in IBM muscle and controls indicating an accelerated aging process in IBM muscle, possibly associated with chronic inflammation.

Inflammatory myopathies: update on diagnosis, pathogenesis and therapies, and COVID-19-related implications.

The inflammatory myopathies constitute a heterogeneous group of acquired myopathies that have in common the presence of endomysial inflammation. Based on steadily evolved clinical, histological and immunopathological features and some autoantibody associations, these disorders can now be classified in five characteristic subsets: Dermatomyositis (DM) Polymyositis (PM), Necrotizing Autoimmune Myositis (NAM), Anti-synthetase syndrome-overlap myositis (Anti-SS-OM), and Inclusion-Body-Myositis (IBM). Each inflammatory myopathy subset has distinct immunopathogenesis, prognosis and response to immunotherapies, necessitating the need to correctly identify each subtype from the outset to avoid disease mimics and proceed to early therapy initiation. The review presents the main clinicopathologic characteristics of each subset highlighting the importance of combining expertise in clinical neurological examination with muscle morphology and immunopathology to avoid erroneous diagnoses and therapeutic schemes. The main autoimmune markers related to autoreactive T cells, B cells, autoantibodies and cytokines are presented and the concomitant myodegenerative features seen in IBM muscles are pointed out. Most importantly, unsettled issues related to a role of autoantibodies and controversies with reference to possible triggering factors related to statins are clarified. The emerging effect SARS-CoV-2 as the cause of hyperCKemia and potentially NAM is addressed and practical guidelines on the best therapeutic approaches and concerns regarding immunotherapies during COVID-19 pandemic are summarized.

Myo-Inositol Transporter SLC5A3 Associates with Degenerative Changes and Inflammation in Sporadic Inclusion Body Myositis

Myo-inositol exerts many cellular functions, which include osmo-protection, membrane functioning, and secondary messaging. Its Na+/myo-inositol co-transporter SLC5A3 is expressed in muscle tissue and further accumulates in myositis. In this study we focused on the peculiar subgroup of sporadic inclusion body myositis (IBM), in which auto-inflammatory responses and degenerative changes co-exist. A cohort of nine patients was selected with clinically confirmed IBM, in which SLC5A3 protein was immune-localized to the different tissue constituents using immunofluorescence, and expression levels were evaluated using Western blotting. In normal muscle tissue, SLC5A3 expression was restricted to blood vessels and occasional low levels on muscle fiber membranes. In IBM tissues, SLC5A3 staining was markedly increased, with discontinuous staining of the muscle fiber membranes, and accumulation of SLC5A3 near inclusions and on the rims of vacuoles. A subset of muscle-infiltrating auto-aggressive immune cells was SLC5A3 positive, of which most were T-cells and M1 lineage macrophages. We conclude that SLC5A3 is overexpressed in IBM muscle, where it associates with protein aggregation and inflammatory infiltration. Based on our results, functional studies could be initiated to explore the possibilities of therapeutic osmolyte pathway intervention for preventing protein aggregation in muscle cells.

P.02Phase 2/3 study of Arimoclomol in sporadic inclusion body myositis: study design

Sporadic inclusion body myositis (IBM) is the most common idiopathic inflammatory myopathy occurring in patients over the age of 45 years. IBM muscle displays both inflammatory and degenerative features, yet immune suppression has proven to be ineffective. Modulating the cytoprotective "heat shock response" (HSR) represents a therapeutic strategy targeting both inflammation and degeneration. Arimoclomol is an orally administered pharmacological agent that can up-regulate the HSR by amplifying heat shock protein expression. In a pilot Phase 2a study Arimoclomol was safe and well tolerated and demonstrated a preliminary signal for potential therapeutic benefit in patients with IBM. These data supported further research of Arimoclomol in IBM. To evaluate the efficacy in a phase 2/3 randomized controlled trial of Arimoclomol in IBM and to gather data on safety and tolerability. We present herein the study protocol of NCT02753530. In this double-blind, placebo-controlled, multicenter, international study, 150 subjects are being randomizing 1:1 to receive orally three times a day either Arimoclomol 400 mg or matching placebo capsules for 20 months. The primary outcome measure is the IBM functional rating scale (IBMFRS) at Month 20. Secondary outcome measures include other efficacy measures, namely manual muscle testing (MMT), dynamometry of the quadriceps and grip, Health Assessment Questionnaire (HAQ-DI) and Short-Form 36 (SF-36). Safety and tolerability will also be evaluated. MRI of the lower extremities is an exploratory outcome measure. This is an ongoing study. We anticipate the last subject will be enrolled by April of 2019. We present herein this pivotal study design and anticipate being able to share results in 2021.

Highly differentiated cytotoxic T cells in inclusion body myositis.

Inclusion body myositis is a late onset treatment-refractory autoimmune disease of skeletal muscle associated with a blood autoantibody (anti-cN1A), an HLA autoimmune haplotype, and muscle pathology characterized by cytotoxic CD8+ T cell destruction of myofibres. Here, we report on translational studies of inclusion body myositis patient muscle compared with a diverse set of other muscle disease samples. Using available microarray data on 411 muscle samples from patients with inclusion body myositis (n = 40), other muscle diseases (n = 265), and without neuromuscular disease (normal, n = 106), we identified a signature of T-cell cytotoxicity in inclusion body myositis muscle coupled with a signature of highly differentiated CD8 T-cell effector memory and terminally differentiated effector cells. Further, we examined killer cell lectin-like receptor G1 (KLRG1) as a marker of this population of cells, demonstrated the correlation of KLRG1 gene expression with lymphocyte cytotoxicity across 28 870 human tissue samples, and identified the presence of KLRG1 on pathogenic inclusion body myositis muscle invading T cells and an increase in KLRG1 expressing T cells in inclusion body myositis blood. We examined inclusion body myositis muscle T-cell proliferation by Ki67 immunohistochemistry demonstrating that diseased muscle-invading T cells are minimally or non-proliferative, in accordance with known properties of highly differentiated or terminally differentiated T cells. We found low expression of KLRG1 on infection-protective human lymphoid tissue central memory T cells and autoimmune-protective human blood regulatory T cells. Targeting highly differentiated cytotoxic T cells could be a favourable approach to treatment of inclusion body myositis.

Sporadic Inclusion Body Myositis: An Acquired Mitochondrial Disease with Extras.

The sporadic form of inclusion body myositis (IBM) is the most common late-onset myopathy. Its complex pathogenesis includes degenerative, inflammatory and mitochondrial aspects. However, which of those mechanisms are cause and which effect, as well as their interrelations, remain partly obscured to this day. In this review the nature of the mitochondrial dysregulation in IBM muscle is explored and comparison is made with other muscle disorders. Mitochondrial alterations in IBM are evidenced by histological and serum biomarkers. Muscular mitochondrial dynamics is disturbed, with deregulated organelle fusion leading to subsequent morphological alterations and muscle displays abnormal mitophagy. The tissue increases mitochondrial content in an attempt to compensate dysfunction, yet mitochondrial DNA (mtDNA) alterations and mild mtDNA depletion are also present. Oxidative phosphorylation defects have repeatedly been shown, most notably a reduction in complex IV activities and levels of mitokines and regulatory RNAs are perturbed. Based on the cumulating evidence of mitochondrial abnormality as a disease contributor, it is therefore warranted to regard IBM as a mitochondrial disease, offering a feasible therapeutic target to be developed for this yet untreatable condition.

The effect of interferon-gamma on skeletal muscle cell biology

Dysimmune and inflammatory myopathies (DIMs) affect around 14/100,000 people worldwide. Based on immupour nopathological criteria, DIMs are divided in four groups: (1) polymyositis (PM)/inclusion body myositis (IBM), (2) dermatomyositis (DM), (3) immune-mediated necrotizing myopathies (IMNM) and (iv) overlapping myositis including anti-synthetase syndrome (ASS). ASS and PM/IBM are characterized by the activation of inflammation with lymphocytic infiltrations. Recently, we showed that an expression of the major histocompatibility complex class 2 (MHC2) was present in myofibers from ASS and IBM muscle biopsies. Interestingly, MHC2 expression is known to be stimulated by Interferon-gamma (IFNγ) in myogenic cells. LTCD8 cells, which are well-known producers of IFNγ, are commonly found in close vicinity to MHC2 positive myofibers. This inflammatory cytokine also inhibits myogenic differentiation in vitro by CIITA-myogenin interaction. The mechanisms involved in the lymphocyte-driven muscle toxicity in DIMs are unclear. The objectives of this project are to characterize IFNγ effects on the biology of human myogenic cells by morphological, molecular and cellular approaches. Then, we aim to investigate the role of IFNγ in these myopathies and its impact during muscular regeneration. In vitro preliminary studies have been performed using human and mouse myoblasts treated or not with IFNγ. Our results should lead to a better understanding of the role of IFNγ in the pathophysiology of DIMs, and would hopefully help identify new therapeutic targets.

NEW INSIGHTS INTO CELLULAR FUNCTIONS: O.9Dysfunctional mitophagy: a potential therapeutic target in inclusion body myositis

Inclusion body myositis (IBM) is the commonest acquired myopathy in adults over 50 years of age. There is no established treatment. Aetiology and pathogenesis are unknown. Diagnosis is based on clinical presentation supported by pathological findings. The combination of protein aggregates and mitochondrial changes in the muscle in IBM suggest that autophagy, a process for recycling damaged cellular components, is defective. Autophagy that recycles mitochondria is called mitophagy. To test our hypothesis that dysregulated mitophagy plays a key role in IBM we studied samples from patients with IBM (n=26) and aged-matched controls(n=39). Muscle mitochondrial DNA (mtDNA) copy number and mtDNA deletions were assessed by Q-PCR and long-range PCR. Fibroblasts were studied using high content imaging (INCell 1000). Energetic stress was achieved by using low glucose media. Mitochondrial membrane potential was assessed using tetramethyrhodamine dye. Mitochondria were evaluated by staining with antibodies to the outer mitochondrial membrane protein TOM-20. Mitophagy was determined by the colocalisation of TOM-20 and autophagosome marker LC3-II. We found that mtDNA copy number was lower in patients with IBM than controls. IBM samples with the lowest mtDNA copy number had greater numbers of cytochrome oxidase negative fibres and more variable mtDNA deletions. High content imaging revealed that fibroblasts from patients with IBM grown under energetically stressful conditions had i) reduced mitochondrial membrane potential, ii) increased mitochondrial volume, and iii) increased colocalisation of mitochondria and autophagosomes. Our findings of increased numbers of damaged and dysfunctional mitochondria in fibroblasts from patients with IBM indicate that mitophagy may be dysregulated. More work is needed to confirm these findings. However, if confirmed, it is possible that drug modulators of mitophagy may improve mitochondrial quality and affect disease progression in IBM.

Inclusion body myositis: advancements in diagnosis, pathomechanisms, and treatment

To review new advances in inclusion body myositis (IBM) and discuss them in light of current knowledge on diagnosis, pathomechanisms, and treatment perspectives. IBM is a treatment refractory inflammatory myopathy in middle-aged patients that leads to a slow, relentlessly progressive muscle weakness, and atrophy. Recent data collections suggest that mortality in IBM patients is somewhat elevated compared with the general population. One major risk factor for death is severe dysphagia, which can now be determined by a novel real-time MRI technique. Recently, proposed diagnostic criteria with a combination of clinical and histopathological features have improved sensitivity and specificity. cytosolic 5'-nucleotidase 1A antibodies have been characterized in IBM patients and their pathophysiologic role has recently been studied. New inflammatory pathomechanisms have been identified in IBM muscle and may help to design novel treatment strategies. A broad spectrum of immunosuppressive and immunomodulatory trials have been conducted, but - so far- no effective treatment is available. Current therapeutic attempts aim to block the myostatin pathway or restore the protein homeostasis. The expanding knowledge of the complex disease, the refinement of diagnostic criteria, and developments in diagnostic procedures are expected to foster the much needed design of new treatment approaches for future clinical trials.

P.201 - Differential type I and type II interferon signatures in primary inflammatory/dysimmune myopathies

Primary inflammatory/dysimmune myopathies (PIDM) include (i) polymyositis (PM)/inclusion body myositis (IBM), (ii) dermatomyositis (DM), (iii) necrotizing autoimmune myopathy, and (iv) overlap myositis (OM) . Type I α/β interferon signature was proposed as a characteristic feature of DM . Since OM and IBM differ from other PIDM by the presence of major histocompatibility complex (MHC)-2 expression by myofibers, we hypothesized that they are characterized by interferon (IFN)γ-mediated inflammation. To test this hypothesis, we evaluated by qPCR the expression of IFNγ, six IFNγ–induced genes (HLA-DM, -DO, -DP, -DR, CIITA, GBP2), and IFNα-induced gene ISG15 in muscle biopsy samples from patients with IBM (n = 10), DM (n = 10), NAM (n = 10), antisynthetase myositis (ASM, n = 10), and normal muscle (n = 10). Muscle IFNγ expression was found increased x50 in ASM and x80 in IBM compared to control, that of CIITA x4 and x3 (respectively) as well of HLA-DR (x5 and x8) and HLA-DM (x16 and x15). None of these genes were overexpressed in DM and NAM. ISG15 was increased x300 in DM, but not in other conditions. Our results confirmed that DM differed from other PIDM by its elective interferon α/β signature, while ASM and IBM were found associated with IFNγ signature.

Association of inclusion body myositis with T cell large granular lymphocytic leukaemia.

SEE HOHLFELD AND SCHULZE-KOOPS DOI101093/BRAIN/AWW053 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Inclusion body myositis and T cell large granular lymphocytic leukaemia are rare diseases involving pathogenic cytotoxic CD8+ T cells. After encountering four patients with both disorders, we prospectively screened 38 patients with inclusion body myositis for the presence of expanded large granular lymphocyte populations by standard clinical laboratory methods (flow cytometry, examination of blood smears, and T cell receptor gene rearrangements), and performed muscle immunohistochemistry for CD8, CD57, and TIA1. Most (22/38; 58%) patients with inclusion body myositis had aberrant populations of large granular lymphocytes in their blood meeting standard diagnostic criteria for T cell large granular lymphocytic leukaemia. These T cell populations were clonal in 20/20 patients and stably present on follow-up testing in 15 patients a median of 350 days later. T cell aberrant loss of CD5 or gain of expression of CD16 and CD94 were common (19/42, 45%). In comparison, 2/15 (14%) age-matched patients with dermatomyositis, polymyositis, or necrotizing myopathy, and 0/20 (0%) age-matched healthy subjects had large granular lymphocyte expansions, with none of these patients having T cell aberrant expression of CD5, CD16 or CD94. Reduced blood CD4/CD8 ratio, increased blood CD8 count, and lymphocytosis were additional biomarkers highly correlated with flow cytometry-measured large granular lymphocyte expansions. Cross-sectional data suggested more aggressive disease in patients with such expansions than without. Muscle immunohistochemistry demonstrated invasion of large granular lymphocytes into muscle in 15/15 inclusion body myositis patients but in only 1/28 patients with dermatomyositis or polymyositis. The extent of CD8+ and CD57+ cells in inclusion body myositis muscle correlated with the size of blood large granular lymphocyte populations. Myofibre-invading cells expressed CD57, a marker of persistent T cell exposure to antigen and T cell aggressiveness. In many patients with inclusion body myositis, the autoimmune T cell expansion has evolved into a neoplastic-like or overtly neoplastic disorder, perhaps contributing to its relative refractoriness to immune-directed therapies previously reported.

Chapter 25 - Autoimmune muscle disease

Patients with polymyositis (PM), dermatomyositis (DM), and immune-mediated necrotizing myopathy (IMNM) present with the subacute onset of symmetric proximal muscle weakness, elevated muscle enzymes, myopathic findings on electromyography, and autoantibodies. DM patients are distinguished by their cutaneous manifestations. Characteristic features on muscle biopsy include the invasion of nonnecrotic muscle fibers by T cells in PM, perifascicular atrophy in DM, and myofiber necrosis without prominent inflammation in IMNM. Importantly, these are regarded as autoimmune diseases and most patients respond partially, if not completely, to immunosuppressive therapy. Patients with inclusion body myositis (IBM) usually present with the insidious onset of asymmetric weakness in distal muscles (e.g., wrist flexors, and distal finger flexors), often when more proximal muscle groups are relatively preserved. Although IBM muscle biopsies usually have focal invasion of myofibers by lymphocytes, the majority of IBM biopsies also include rimmed vacuoles. While most IBM patients do have autoantibodies, treatment with immunosuppressive agents does not improve their clinical course. Along with the presence of abnormally aggregated proteins on muscle biopsy, the refractory nature and relentless course of IBM suggest that the underlying pathophysiology may include a dominant myodegenerative component. This chapter will focus on the epidemiology, clinical presentation, and treatment of the autoimmune myopathies and IBM. An emphasis will be placed on recent advances, indicating that these are a diverse family of diseases and that each of more than a dozen myositis autoantibodies is associated with a distinct clinical phenotype.