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Amici DR, Pinal-Fernandez I, Mázala DAG, Lloyd TE, Corse AM, Christopher-Stine L, Mammen AL, Chin ER. Calcium dysregulation, functional calpainopathy, and endoplasmic reticulum stress in sporadic inclusion body myositis. Acta Neuropathol Commun 2017; 5:24. [PMID: 28330496 PMCID: PMC5363023 DOI: 10.1186/s40478-017-0427-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 03/12/2017] [Indexed: 01/08/2023] Open
Abstract
Sporadic inclusion body myositis (IBM) is the most common primary myopathy in the elderly, but its pathoetiology is still unclear. Perturbed myocellular calcium (Ca2+) homeostasis can exacerbate many of the factors proposed to mediate muscle degeneration in IBM, such as mitochondrial dysfunction, protein aggregation, and endoplasmic reticulum stress. Ca2+ dysregulation may plausibly be initiated in IBM by immune-mediated membrane damage and/or abnormally accumulating proteins, but no studies to date have investigated Ca2+ regulation in IBM patients. We first investigated protein expression via immunoblot in muscle biopsies from IBM, dermatomyositis, and non-myositis control patients, identifying several differentially expressed Ca2+-regulatory proteins in IBM. Next, we investigated the Ca2+-signaling transcriptome by RNA-seq, finding 54 of 183 (29.5%) genes from an unbiased list differentially expressed in IBM vs. controls. Using an established statistical approach to relate genes with causal transcription networks, Ca2+ abundance was considered a significant upstream regulator of observed whole-transcriptome changes. Post-hoc analyses of Ca2+-regulatory mRNA and protein data indicated a lower protein to transcript ratio in IBM vs. controls, which we hypothesized may relate to increased Ca2+-dependent proteolysis and decreased protein translation. Supporting this hypothesis, we observed robust (4-fold) elevation in the autolytic activation of a Ca2+-activated protease, calpain-1, as well as increased signaling for translational attenuation (eIF2α phosphorylation) downstream of the unfolded protein response. Finally, in IBM samples we observed mRNA and protein under-expression of calpain-3, the skeletal muscle-specific calpain, which broadly supports proper Ca2+ homeostasis. Together, these data provide novel insight into mechanisms by which intracellular Ca2+ regulation is perturbed in IBM and offer evidence of pathological downstream effects.
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Lloyd TE, Pinal-Fernandez I, Michelle EH, Christopher-Stine L, Pak K, Sacktor N, Mammen AL. Overlapping features of polymyositis and inclusion body myositis in HIV-infected patients. Neurology 2017; 88:1454-1460. [PMID: 28283597 DOI: 10.1212/wnl.0000000000003821] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 01/18/2017] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To characterize patients with myositis with HIV infection. METHODS All HIV-positive patients with myositis seen at the Johns Hopkins Myositis Center from 2003 to 2013 were included in this case series. Muscle biopsy features, weakness pattern, serum creatine kinase (CK) level, and anti-nucleotidase 1A (NT5C1A) status of HIV-positive patients with myositis were assessed. RESULTS Eleven of 1,562 (0.7%) patients with myositis were HIV-positive. Myositis was the presenting feature of HIV infection in 3 patients. Eight of 11 patients had weakness onset at age 45 years or less. The mean time from the onset of weakness to the diagnosis of myositis was 3.6 years (SD 3.2 years). The mean of the highest measured CK levels was 2,796 IU/L (SD 1,592 IU/L). On muscle biopsy, 9 of 10 (90%) had endomysial inflammation, 7 of 10 (70%) had rimmed vacuoles, and none had perifascicular atrophy. Seven of 11 (64%) patients were anti-NT5C1A-positive. Upon presentation, all had proximal and distal weakness. Five of 6 (83%) patients followed 1 year or longer on immunosuppressive therapy had improved proximal muscle strength. However, each eventually developed weakness primarily affecting wrist flexors, finger flexors, knee extensors, or ankle dorsiflexors. CONCLUSIONS HIV-positive patients with myositis may present with some characteristic polymyositis features including young age at onset, very high CK levels, or proximal weakness that improves with treatment. However, all HIV-positive patients with myositis eventually develop features most consistent with inclusion body myositis, including finger and wrist flexor weakness, rimmed vacuoles on biopsy, or anti-NT5C1A autoantibodies.
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Tiniakou E, Mammen AL. Idiopathic Inflammatory Myopathies and Malignancy: a Comprehensive Review. Clin Rev Allergy Immunol 2017; 52:20-33. [PMID: 26429706 DOI: 10.1007/s12016-015-8511-x] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of autoimmune diseases (collectively known as myositis) affecting the skeletal muscles as well as other organ systems such as skin, lungs, and joints. The primary forms of myositis include polymyositis (PM), dermatomyositis (PM), and immune-mediated necrotizing myopathy (IMNM). Patients with these diseases experience progressive proximal muscle weakness, have characteristic muscle biopsy findings, and produce autoantibodies that are associated with unique clinical features. One distinguishing feature of these patients is that they are also known to have an increased risk of cancer. Since the first description of the association in 1916, it has been extensively reported in the medical literature. However, there have been significant variations between the different studies with regard to the degree of cancer risk in patients with IIM. These discrepancies can, in part, be attributed to differences in the definition of malignancy-associated myositis used in different studies. In recent years, significant advances have been made in defining specific features of IIM that are associated with the development of malignancy. One of these has been myositis-specific antibodies (MSAs), which are linked to distinct clinical phenotypes and categorize patients into groups with more homogeneous features. Indeed, patients with certain MSAs seem to be at particularly increased risk of malignancy. This review attempts a systematic evaluation of research regarding the association between malignancy and myositis.
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Pinal-Fernandez I, Parks C, Werner JL, Albayda J, Paik J, Danoff SK, Casciola-Rosen L, Christopher-Stine L, Mammen AL. Longitudinal Course of Disease in a Large Cohort of Myositis Patients With Autoantibodies Recognizing the Signal Recognition Particle. Arthritis Care Res (Hoboken) 2016; 69:263-270. [PMID: 27111848 DOI: 10.1002/acr.22920] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Revised: 03/07/2016] [Accepted: 04/19/2016] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Patients with immune-mediated necrotizing myopathy (IMNM) often have autoantibodies recognizing the signal recognition particle (SRP) or HMG-CoA reductase (HMGCR). Here, we studied a cohort of anti-SRP patients to identify factors associated with disease severity and clinical improvement; we also compared the severity of weakness in those with anti-SRP versus anti-HMGCR autoantibodies. METHODS All anti-SRP patients in the Johns Hopkins Myositis Cohort from 2002 to 2015 were included. Longitudinal information regarding proximal muscle strength, creatine kinase (CK) levels, and immunosuppressive therapy was recorded at each visit. Univariate and multivariate multilevel regression models were used to assess prognostic factors influencing recovery. Strength in the anti-SRP patients was compared to strength in 49 previously described anti-HMGCR subjects. RESULTS Data from 37 anti-SRP patients and 380 total clinic visits were analyzed. Younger age at onset was associated with more severe weakness at the first visit (P = 0.02) and all subsequent visits (P = 0.002). Only 50% of patients reached near-full or full strength after 4 years of treatment, and most of these continued to have elevated CK levels. Rituximab appeared to be effective in 13 of 17 anti-SRP patients. Anti-SRP patients were significantly weaker than those with anti-HMGCR autoantibodies (-1.3 strength points; P = 0.001). CONCLUSION Younger age at onset is associated with more severe weakness in anti-SRP myositis. Furthermore, even among anti-SRP patients whose strength improved with immunosuppression, most had ongoing disease activity as demonstrated by elevated CK levels. Finally, anti-SRP patients were significantly weaker than anti-HMGCR patients, providing evidence that these autoantibodies are associated with distinct forms of IMNM.
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Pinal-Fernandez I, Casal-Dominguez M, Carrino JA, Lahouti AH, Basharat P, Albayda J, Paik JJ, Ahlawat S, Danoff SK, Lloyd TE, Mammen AL, Christopher-Stine L. Thigh muscle MRI in immune-mediated necrotising myopathy: extensive oedema, early muscle damage and role of anti-SRP autoantibodies as a marker of severity. Ann Rheum Dis 2016; 76:681-687. [PMID: 27651398 DOI: 10.1136/annrheumdis-2016-210198] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 08/12/2016] [Accepted: 08/27/2016] [Indexed: 11/04/2022]
Abstract
OBJECTIVES The aims of this study were to define the pattern of muscle involvement in patients with immune-mediated necrotising myopathy (IMNM) relative to those with other inflammatory myopathies and to compare patients with IMNM with different autoantibodies. METHODS All Johns Hopkins Myositis Longitudinal Cohort subjects with a thigh MRI (tMRI) who fulfilled criteria for IMNM, dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM) or clinically amyopathic DM (CADM) were included in the study. Muscles were assessed for intramuscular and fascial oedema, atrophy and fatty replacement. Disease subgroups were compared using univariate and multivariate analyses. Patients with IMNM with anti-signal recognition particle (SRP) autoantibodies were compared with those with IMNM with anti-HMG-CoA reductase (HMGCR) autoantibodies. RESULTS The study included 666 subjects (101 IMNM, 176 PM, 219 DM, 17 CADM and 153 IBM). Compared with DM or PM, IMNM was characterised by a higher proportion of thigh muscles with oedema, atrophy and fatty replacement (p<0.01). Patients with IMNM with anti-SRP had more atrophy (19%, p=0.003) and fatty replacement (18%, p=0.04) than those with anti-HMGCR. In IMNM, muscle abnormalities were especially common in the lateral rotator and gluteal groups. Fascial involvement was most widespread in DM. Fatty replacement of muscle tissue began early during the course of disease in IMNM and the other groups. An optimal combination of tMRI features had only a 55% positive predictive value for diagnosing IMNM. CONCLUSIONS Compared with patients with DM or PM, IMNM is characterised by more widespread muscle involvement. Anti-SRP-positive patients have more severe muscle involvement than anti-HMGCR-positive patients.
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Fiorentino DF, Presby M, Baer AN, Petri M, Rieger KE, Soloski M, Rosen A, Mammen AL, Christopher-Stine L, Casciola-Rosen L. PUF60: a prominent new target of the autoimmune response in dermatomyositis and Sjögren's syndrome. Ann Rheum Dis 2016; 75:1145-51. [PMID: 26253095 PMCID: PMC4828328 DOI: 10.1136/annrheumdis-2015-207509] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 07/13/2015] [Indexed: 01/28/2023]
Abstract
OBJECTIVES Autoantibodies are used clinically to phenotype and subset patients with autoimmune rheumatic diseases. We detected a novel 60 kDa autoantibody specificity by immunoblotting using a dermatomyositis (DM) patient's serum. Our objective was to identify the targeted autoantigen and to evaluate disease specificity and clinical significance of this new autoantibody. METHODS A new 60 kDa specificity was detected by immunoblotting HeLa cell lysates. The targeted autoantigen was identified as poly(U)-binding-splicing factor 60 kDa (PUF60) using (i) a human protein array and (ii) two-dimensional gel electrophoresis and liquid chromatography tandem mass spectrometry peptide sequencing. Anti-PUF60 antibodies were assayed by ELISA using sera from patients with primary Sjögren's syndrome (SS; n=84), systemic lupus erythematosus (SLE; n=71), DM (n=267), polymyositis (n=45), inclusion body myositis (n=45) and healthy controls (n=38). RESULTS PUF60 was identified as a new autoantigen. Anti-PUF60 antibodies were present in 25/84 (30%) patients with SS, 6/71 (8.5%) patients with SLE and 2/38 (5.0%) control subjects (SS vs controls, p=0.002; SLE vs controls, p=0.711). Anti-PUF60 antibodies were present in 48/267 (18.0%) patients with DM versus 4/45 (8.9%) and 5/45 (11.1%) patients with inclusion body myositis and polymyositis, respectively. The antibody was significantly associated with anti-Ro52 antibodies, rheumatoid factor and hyperglobulinemia in the patients with primary SS. In patients with DM, the antibody was associated with anti-transcription intermediary factor 1 gamma seropositivity and Caucasian race. CONCLUSIONS PUF60 represents a novel autoantigen in patients with SS and DM. PUF60 antibodies are associated with distinct clinical features and different immune responses in different diseases.
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Rajan A, Heery CR, Perry S, Keen C, Mammen AL, Berman AW, Pittaluga S, Lepone LM, Donahue RN, Grenga I, Schlom J, Hassan R, Gulley JL. Safety and clinical activity of anti-programmed death-ligand 1 (PD-L1) antibody (ab) avelumab (MSB0010718C) in advanced thymic epithelial tumors (TETs). J Clin Oncol 2016. [DOI: 10.1200/jco.2016.34.15_suppl.e20106] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Lloyd TE, Christopher-Stine L, Pinal-Fernandez I, Tiniakou E, Petri M, Baer A, Danoff SK, Pak K, Casciola-Rosen LA, Mammen AL. Cytosolic 5'-Nucleotidase 1A As a Target of Circulating Autoantibodies in Autoimmune Diseases. Arthritis Care Res (Hoboken) 2016; 68:66-71. [PMID: 25892010 DOI: 10.1002/acr.22600] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2015] [Revised: 03/04/2015] [Accepted: 04/07/2015] [Indexed: 01/02/2023]
Abstract
OBJECTIVE Prior investigations demonstrated that autoantibodies recognizing cytosolic 5'-nucleotidase 1A (NT5C1A) are found in 33-76% of patients with inclusion body myositis (IBM) but are observed only rarely in patients with polymyositis (PM). Thus, anti-NT5C1A may help distinguish IBM from PM. Although 4-21% of patients with dermatomyositis (DM) were shown to be anti-NT5C1A antibody positive, the clinical features of anti-NT5C1A-positive patients with DM have not been described. Furthermore, the prevalence of anti-NT5C1A antibodies in other rheumatic conditions has not been reported. This study was undertaken to define the prevalence and clinical features of anti-NT5C1A-positive patients with DM, PM, IBM, or other systemic autoimmune diseases. METHODS We screened for anti-NT5C1A autoantibodies in patients with IBM, DM, PM, Sjögren's syndrome (SS), or systemic lupus erythematosus (SLE) and in healthy volunteers. Clinical characteristics were compared between patients who were anti-NT5C1A positive and those who were anti-NT5C1A negative. RESULTS Anti-NT5C1A autoantibodies were detected in 71 (61%) of 117 patients with IBM, 2 (5%) of 42 patients with PM, 2 (5%) of 42 healthy volunteers, 24 (15%) of 159 patients with DM, 10 (23%) of 44 patients with SS, and 13 (14%) of 96 patients with SLE. No anti-NT5C1A antibody-positive patients with SS or SLE had muscle involvement. Anti-NT5C1A-positive patients with IBM had a lower prevalence of rimmed vacuoles (62% versus 83% of antibody-negative patients; P = 0.02). No differences in the clinical characteristics of antibody-positive and antibody-negative patients with DM, SS, or SLE were observed. CONCLUSION Anti-NT5C1A is a common target of circulating autoantibodies, especially in IBM but also in several different autoimmune diseases. In SLE and SS, anti-NT5C1A autoreactivity is not associated with muscle disease.
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Paik JJ, Wigley FM, Lloyd TE, Corse AM, Casciola-Rosen L, Shah AA, Boin F, Hummers LK, Mammen AL. Spectrum of Muscle Histopathologic Findings in Forty-Two Scleroderma Patients With Weakness. Arthritis Care Res (Hoboken) 2015; 67:1416-25. [PMID: 25989455 DOI: 10.1002/acr.22620] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Revised: 03/30/2015] [Accepted: 05/05/2015] [Indexed: 11/08/2022]
Abstract
OBJECTIVE To determine if distinct muscle pathologic features exist in scleroderma subjects with weakness. METHODS This retrospective study included weak scleroderma subjects with muscle biopsies available for review. Biopsies were systematically assessed for individual pathologic features, including inflammation, necrosis, fibrosis, and acute neurogenic atrophy. Based on the aggregate individual features, biopsies were assigned a histopathologic category of polymyositis, dermatomyositis, necrotizing myopathy, nonspecific myositis, "acute denervation," "fibrosis only," or "other." Clinical data analyzed included autoantibody profiles, scleroderma subtype and disease duration, Medsger muscle severity scores, creatine kinase, electromyography, and muscle magnetic resonance imaging. RESULTS A total of 42 subjects (79% female and 64% diffuse scleroderma) were included in this study. Necrosis (67%), inflammation (48%), acute neurogenic atrophy (48%), and fibrosis (33%) were the most prevalent pathologic features. The presence of fibrosis was strongly associated with anti-PM-Scl antibodies. Histopathologic categories included nonspecific myositis (36%), necrotizing myopathy (21%), dermatomyositis (7%), "acute denervation" (7%), "fibrosis only" (7%), and polymyositis (5%). Disease duration of scleroderma at the time of muscle biopsy was shorter in polymyositis than other histopathologic categories. Patients with anti-PM-Scl and Scl-70 antibodies also had a shorter disease duration than those with other autoantibody profiles. CONCLUSION Nonspecific myositis and necrotizing myopathy were the most common histopathologic categories in weak scleroderma subjects. Surprisingly, nearly half of the subjects studied had histologic evidence of acute motor denervation (acute neurogenic atrophy); this has not been previously reported. Taken together, these observations suggest that a variety of pathologic mechanisms may underlie the development of myopathy in scleroderma.
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Nichols L, Pfeifer K, Mammen AL, Shahnoor N, Konersman CG. An Unusual Case of Statin-Induced Myopathy: Anti-HMGCoA Necrotizing Autoimmune Myopathy. J Gen Intern Med 2015; 30:1879-83. [PMID: 25855481 PMCID: PMC4636568 DOI: 10.1007/s11606-015-3303-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 10/27/2014] [Accepted: 03/16/2015] [Indexed: 12/15/2022]
Abstract
Statins are some of the most widely prescribed medications, and though generally well tolerated, can lead to a self-limited myopathy in a minority of patients. Recently, these medications have been associated with a necrotizing autoimmune myopathy (NAM). Statin-associated NAM is characterized by irritable myopathy on electromyography (EMG) and muscle necrosis with minimal inflammation on muscle biopsy. The case presented is a 63-year-old woman who has continued elevation of creatine kinase (CK) after discontinuation of statin therapy. She has irritable myopathy on EMG and NAM is confirmed by muscle biopsy. She subsequently tests positive for an experimental anti-3-hydroxy-3-methylglutaryl-coenzyme A (anti-HMGCoA) antibody that is found to be present in patients with statin-associated NAM. Though statin-associated NAM is a relatively rare entity, it is an important consideration for the general internist in patients who continue to have CK elevation and weakness after discontinuation of statin therapy. Continued research is necessary to better define statin-specific and dose-dependent risk, as well as optimal treatment for this condition.
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Mammen AL, Casciola-Rosen L, Christopher-Stine L, Lloyd TE, Wagner KR. Myositis-specific autoantibodies are specific for myositis compared to genetic muscle disease. NEUROLOGY-NEUROIMMUNOLOGY & NEUROINFLAMMATION 2015; 2:e172. [PMID: 26668818 PMCID: PMC4676353 DOI: 10.1212/nxi.0000000000000172] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 09/16/2015] [Indexed: 11/22/2022]
Abstract
Objective: To determine the specificity of myositis-specific autoantibodies (MSAs) for autoimmune myopathy compared with inherited muscle diseases. Methods: Serum samples from 47 patients with genetically confirmed inherited muscle diseases were screened for the most common MSAs, including those recognizing TIF1γ, NXP2, Mi2, MDA5, Jo1, SRP, and HMGCR. We compared these results with the findings in a cohort of patients with dermatomyositis (DM) previously screened for anti-TIF1γ, -NXP2, -Mi2, -MDA5, and -Jo1. Results: Overall, the presence of anti-TIF1γ, -NXP2, -Mi2, -MDA5, or -Jo1 was 96% specific and 67% sensitive for DM compared to patients with genetic muscle diseases. No patients with inherited muscle disease had anti-SRP or anti-HMGCR autoantibodies. Only 2 patients with genetic muscle disease had a MSA. One patient with anti-Mi2 autoantibodies had both genetically confirmed facioscapulohumeral dystrophy and dermatomyositis based on a typical skin rash and partial response to immunosuppressive medications. A second patient with anti-Jo-1 autoantibodies had both genetically defined limb-girdle muscular dystrophy type 2A (i.e., calpainopathy) and a systemic autoimmune process based on biopsy-confirmed lupus nephritis, sicca symptoms, and anti-Ro52 autoantibodies. Conclusions: The MSAs tested for in this study are highly specific for autoimmune muscle disease and are rarely, if ever, found in patients who only have genetic muscle disease. In patients with genetic muscle disease, the presence of a MSA should suggest the possibility of a coexisting autoimmune process.
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Pinal-Fernandez I, Casciola-Rosen LA, Christopher-Stine L, Corse AM, Mammen AL. The Prevalence of Individual Histopathologic Features Varies according to Autoantibody Status in Muscle Biopsies from Patients with Dermatomyositis. J Rheumatol 2015; 42:1448-1454. [PMID: 26443871 PMCID: PMC6544046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
OBJECTIVE Individual dermatomyositis (DM)-associated autoantibodies are associated with distinct clinical phenotypes. This study was undertaken to explore the association of these autoantibodies with specific muscle biopsy features. METHODS DM subjects with a muscle biopsy reviewed at Johns Hopkins had sera screened for autoantibodies recognizing Mi-2, transcriptional intermediary factor 1-γ (TIF1-γ), NXP2, MDA5, Ro52, PM-Scl, and Jo1. We also included anti-Jo1–positive patients with polymyositis (PM) who had a biopsy read at Johns Hopkins. Analyzed histological features included perifascicular atrophy, perivascular inflammation, mitochondrial dysfunction, primary inflammation, and myofiber necrosis. Duration of disease, biopsy location, and treatment at biopsy were also analyzed. RESULTS We studied 91 DM and 7 anti-Jo1–positive patients with PM. In univariate analyses, TIF1-γ+ patients had more mitochondrial dysfunction (47% vs 18%; p = 0.05), NXP2+ patients had less primary inflammation (0% vs 28%; p = 0.01), Mi-2+ patients had more primary inflammation (50% vs 19%; p = 0.03), and PM-Scl+ patients had more primary inflammation (67% vs 18%; p = 0.004) than those who were negative for each autoantibody. Although reliability was limited because of small sample numbers, multivariate analysis confirmed that TIF1-γ+ patients had more mitochondrial dysfunction [prevalence ratio (PR) 2.6, 95% CI 1.0–6.5, p = 0.05] and PM-Scl+ patients had more primary inflammation (PR 5.2, 95% CI 2.0–13.4; p = 0.001) independent of disease duration at biopsy, biopsy site, and treatment at biopsy. No differences in muscle biopsy features were noted between anti-Jo1–positive patients diagnosed with DM and PM. CONCLUSION The prevalence of different histological features varies according to autoantibody status in DM. Muscle biopsy features are similar in anti-Jo1 patients with and without a rash.
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Pinal-Fernandez I, Casciola-Rosen LA, Christopher-Stine L, Corse AM, Mammen AL. The Prevalence of Individual Histopathologic Features Varies according to Autoantibody Status in Muscle Biopsies from Patients with Dermatomyositis. J Rheumatol 2015; 41:2347-51. [DOI: 10.3899/jrheum.141443] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Objective.Individual dermatomyositis (DM)-associated autoantibodies are associated with distinct clinical phenotypes. This study was undertaken to explore the association of these autoantibodies with specific muscle biopsy features.Methods.DM subjects with a muscle biopsy reviewed at Johns Hopkins had sera screened for autoantibodies recognizing Mi-2, transcriptional intermediary factor 1-γ (TIF1-γ), NXP2, MDA5, Ro52, PM-Scl, and Jo1. We also included anti-Jo1–positive patients with polymyositis (PM) who had a biopsy read at Johns Hopkins. Analyzed histological features included perifascicular atrophy, perivascular inflammation, mitochondrial dysfunction, primary inflammation, and myofiber necrosis. Duration of disease, biopsy location, and treatment at biopsy were also analyzed.Results.We studied 91 DM and 7 anti-Jo1–positive patients with PM. In univariate analyses, TIF1-γ+ patients had more mitochondrial dysfunction (47% vs 18%; p = 0.05), NXP2+ patients had less primary inflammation (0% vs 28%; p = 0.01), Mi-2+ patients had more primary inflammation (50% vs 19%; p = 0.03), and PM-Scl+ patients had more primary inflammation (67% vs 18%; p = 0.004) than those who were negative for each autoantibody. Although reliability was limited because of small sample numbers, multivariate analysis confirmed that TIF1-γ+ patients had more mitochondrial dysfunction [prevalence ratio (PR) 2.6, 95% CI 1.0–6.5, p = 0.05] and PM-Scl+ patients had more primary inflammation (PR 5.2, 95% CI 2.0–13.4; p = 0.001) independent of disease duration at biopsy, biopsy site, and treatment at biopsy. No differences in muscle biopsy features were noted between anti-Jo1–positive patients diagnosed with DM and PM.Conclusion.The prevalence of different histological features varies according to autoantibody status in DM. Muscle biopsy features are similar in anti-Jo1 patients with and without a rash.
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Tiniakou E, Mammen AL. Necrotizing myopathy caused by central hypothyroidism. Muscle Nerve 2015; 52:152-3. [PMID: 25808401 DOI: 10.1002/mus.24637] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Chung T, Christopher-Stine L, Paik JJ, Corse A, Mammen AL. The composition of cellular infiltrates in anti-HMG-CoA reductase-associated myopathy. Muscle Nerve 2015; 52:189-95. [PMID: 25737145 DOI: 10.1002/mus.24642] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 02/23/2015] [Accepted: 02/28/2015] [Indexed: 11/05/2022]
Abstract
INTRODUCTION To characterize cellular infiltrates in muscle biopsies from patients with anti-3-hydroxy-3-methyl-gulatryl-CoA reductase (HMGCR)-associated myopathy. METHODS Biopsies from 18 anti-HMGCR myopathy and 7 control dermatomyositis patients were analyzed. RESULTS CD4+ and CD8+ T-cells were scattered within the endomysium in 50% of anti-HMGCR biopsies. All anti-HMGCR biopsies included increased endomysial and/or perivascular CD163+ M2 macrophages; CD11c+ M1 macrophages were present in 18.8%. CD123+ plasmacytoid dendritic (PD) cells were observed within the endomysium and perivascular spaces in 62.5% of anti-HMGCR biopsies. Membrane attack complex was deposited on endothelial cells in 50% and on the sarcolemma of nonnecrotic muscle fibers in 85.7% of anti-HMGCR cases. Major histocompatibility complex class I antigen was up-regulated in 87.5% of the anti-HMGCR cases. CONCLUSIONS In addition to necrosis, scattered CD4+, CD8+, and PD cells are characteristic of anti-HMGCR myopathy. Predominant M2 polarization suggests infiltrating macrophages are more likely to be involved with tissue repair than destruction.
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Ramanathan S, Langguth D, Hardy TA, Garg N, Bundell C, Rojana-Udomsart A, Dale RC, Robertson T, Mammen AL, Reddel SW. Clinical course and treatment of anti-HMGCR antibody-associated necrotizing autoimmune myopathy. NEUROLOGY-NEUROIMMUNOLOGY & NEUROINFLAMMATION 2015; 2:e96. [PMID: 25866831 PMCID: PMC4386794 DOI: 10.1212/nxi.0000000000000096] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/24/2014] [Accepted: 01/20/2015] [Indexed: 01/19/2023]
Abstract
OBJECTIVE We examined a cohort of Australian patients with statin exposure who developed a necrotizing autoimmune myopathy (NAM) associated with a novel autoantibody against 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) and describe the clinical and therapeutic challenges of managing these patients and an optimal therapeutic strategy. METHODS Clinical, laboratory, EMG, and histopathologic results and response to immunomodulation are reported in 6 Australian patients with previous statin exposure and antibodies targeting HMGCR. RESULTS All patients presented with painless proximal weakness following statin therapy, which persisted after statin cessation. Serum creatine kinase (CK) levels ranged from 2,700 to 16,200 IU/L. EMG was consistent with a myopathic picture. Muscle biopsies revealed a pauci-immune necrotizing myopathy. Detailed graphical representation of the clinical course of these patients showed a close association with rising CK and an increase in clinical weakness signifying relapses, particularly upon weaning or ceasing steroids. All 6 patients were responsive to initial steroid therapy, with 5 relapsing upon attempts to wean steroids. Both CK and clinical strength improved with the reinstitution of immunotherapy, in particular steroids and IV immunoglobulin (IVIg). All patients required treatment with varying multiagent immunosuppressive regimens to achieve clinical remission, including prednisone (n = 6), IVIg (n = 5), plasmapheresis (n = 2), and additional therapy including methotrexate (n = 6), cyclophosphamide (n = 2), rituximab (n = 2), azathioprine (n = 1), and cyclosporine (n = 1). CONCLUSIONS Recognition of HMGCR antibody-associated NAM is important because these patients are responsive to immunosuppression, and early multiagent therapy and a slow and cautious approach to withdrawing steroids may improve outcomes.
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Mohassel P, Rosen P, Casciola-Rosen L, Pak K, Mammen AL. Expression of the dermatomyositis autoantigen transcription intermediary factor 1γ in regenerating muscle. Arthritis Rheumatol 2015; 67:266-72. [PMID: 25186009 DOI: 10.1002/art.38863] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Accepted: 08/26/2014] [Indexed: 02/01/2023]
Abstract
OBJECTIVE Autoantibodies against transcription intermediary factor 1γ (TIF1γ) are found in many patients with dermatomyositis (DM). Although TIF1γ is known to play a role in the differentiation of other tissues, its functional role in muscle regeneration has not been elucidated. This study was undertaken to explore the regulation and functional role of this protein during muscle differentiation and regeneration. METHODS TIF1γ expression was analyzed in human muscle biopsy specimens using immunofluorescence microscopy. Immunofluorescence microscopy and immunoblotting analyses were used to study TIF1γ expression in a mouse model of muscle injury and repair. The effect of premature TIF1γ silencing on muscle differentiation was studied in cultured mouse myoblasts. RESULTS In muscle biopsy specimens from DM patients, TIF1γ was expressed at low levels in the nuclei of histologically normal muscle cells but at high levels in the centralized nuclei of atrophic, perifascicular myofibers expressing markers of regeneration. TIF1γ levels were also increased in regenerating myonuclei following muscle injury in mice. Premature silencing of TIF1γ in vitro using small interfering RNA did not accelerate the expression of myogenin, a transcription factor that plays a central role in regulating relatively early stages of muscle differentiation. However, premature silencing of TIF1γ did accelerate myotube fusion and the expression of myosin heavy chain (MyHC), a later marker of muscle differentiation. CONCLUSION The DM autoantigen TIF1γ is markedly up-regulated during muscle regeneration in human and mouse muscle cells. Premature silencing of this protein in cultured myoblasts accelerates MyHC expression and myoblast fusion. However, TIF1γ may function independently of, or downstream from, myogenin.
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Mammen AL, Sartorelli V. IL-6 Blockade as a Therapeutic Approach for Duchenne Muscular Dystrophy. EBioMedicine 2015; 2:274-5. [PMID: 26137566 PMCID: PMC4486189 DOI: 10.1016/j.ebiom.2015.03.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Abstract
Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.
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Roda RH, Schindler AB, Blackstone C, Mammen AL, Corse AM, Lloyd TE. Laing distal myopathy pathologically resembling inclusion body myositis. Ann Clin Transl Neurol 2014; 1:1053-8. [PMID: 25574480 PMCID: PMC4284131 DOI: 10.1002/acn3.140] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 10/13/2014] [Accepted: 10/14/2014] [Indexed: 11/18/2022] Open
Abstract
Mutations in MYH7 cause autosomal dominant Laing distal myopathy. We present a family with a previously reported deletion (c.5186_5188delAGA, p.K1729del). Muscle pathology in one family member was characterized by an inflammatory myopathy with rimmed vacuoles, increased MHC Class I expression, and perivascular and endomysial muscle inflammation comprising CD3+, CD4+, CD8+, and CD68+ inflammatory cells. Interestingly, this biopsy specimen contained TDP-43, p62, and SMI-31-positive protein aggregates typical of inclusion body myositis. These findings should alert physicians to the possibility that patients with MYH7 mutations may have muscle biopsies showing pathologic findings similar to inclusion body myositis.
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Johnson C, Connors GR, Oaks J, Han S, Truong A, Richardson B, Lechtzin N, Mammen AL, Casciola-Rosen L, Christopher-Stine L, Danoff SK. Clinical and pathologic differences in interstitial lung disease based on antisynthetase antibody type. Respir Med 2014; 108:1542-8. [PMID: 25269710 DOI: 10.1016/j.rmed.2014.09.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 09/04/2014] [Accepted: 09/08/2014] [Indexed: 01/22/2023]
Abstract
BACKGROUND Interstitial lung disease (ILD) is a common extramuscular manifestation of the idiopathic inflammatory myopathies (IIMs), dermatomyositis (DM) and polymyositis (PM). Patients with antisynthetase antibodies (ASA) demonstrate some or all of the features of the antisynthetase syndrome including IIM and ILD. It has been hypothesized that the clinical expression of antisynthetase syndrome varies between specific ASAs. OBJECTIVE We sought to determine whether the myositis-associated ILD (MA-ILD) phenotype differs based on the presence of ASAs and by ASA subtype. METHODS A cross-sectional and longitudinal analysis of consecutive patients enrolled at the Johns Hopkins Myositis Center with ILD in the setting of clinically diagnosed autoimmune myositis was conducted. RESULTS Seventy-seven subjects were included; 36 were ASA negative, 28 were anti-Jo1 positive, and 13 were non-Jo1 ASA positive (5 anti-PL-12, 4 anti-PL-7, 2 anti-EJ, and 2 anti-OJ). Non-Jo1 ASA positive participants were more likely to be African-American than Caucasian as compared to both the anti-Jo1 positive (p = 0.01) and ASA negative groups (p < 0.01). ASA negative participants had better mean forced vital capacity percent predicted (FVC%) and total computed tomography scores over time compared to those with anti-Jo1 after controlling for potential confounders. CONCLUSIONS ASA status was significantly different by race. Those with anti-Jo1 antibodies had worse lung function and CT scores over time compared to those without detectable antisynthetase antibodies. Further prospective study in a larger cohort is needed to determine whether these apparent antibody-specific differences in demographics and manifestations of disease translate into meaningful disparities in clinical outcomes.
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Sharma K, Orbai AM, Desai D, Cingolani OH, Halushka MK, Christopher-Stine L, Mammen AL, Wu KC, Zakaria S. Brief report: antisynthetase syndrome-associated myocarditis. J Card Fail 2014; 20:939-45. [PMID: 25084215 DOI: 10.1016/j.cardfail.2014.07.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Revised: 05/23/2014] [Accepted: 07/23/2014] [Indexed: 01/16/2023]
Abstract
BACKGROUND The antisynthetase (AS) syndrome is characterized by autoimmune myopathy, interstitial lung disease, cutaneous involvement, arthritis, fever, and antibody specificity. We describe 2 patients with AS syndrome who also developed myocarditis, depressed biventricular function, and congestive heart failure. METHODS AND RESULTS Both patients were diagnosed with AS syndrome based on clinical manifestations, detection of serum AS antibodies, and myositis confirmation with the use of skeletal muscle magnetic resonance imaging and skeletal muscle biopsy. In addition, myocarditis resulting in heart failure was confirmed with the use of cardiac magnetic resonance imaging and from endomyocardial biopsy findings. After treatment for presumed AS syndrome-associated myocarditis, one patient recovered and the other patient died. CONCLUSIONS AS syndrome is a rare entity with morbidity and mortality typically attributed to myositis and lung involvement. This is the first report of AS syndrome-associated myocarditis leading to congestive heart failure in 2 patients. Given the potentially fatal consequences, myocarditis should be considered in patients with AS syndrome presenting with heart failure.
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Albayda J, Mammen AL. Is Statin-Induced Myositis Part of the Polymyositis Disease Spectrum? Curr Rheumatol Rep 2014; 16:433. [DOI: 10.1007/s11926-014-0433-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Lloyd TE, Mammen AL, Amato AA, Weiss MD, Needham M, Greenberg SA. Evaluation and construction of diagnostic criteria for inclusion body myositis. Neurology 2014; 83:426-33. [PMID: 24975859 DOI: 10.1212/wnl.0000000000000642] [Citation(s) in RCA: 161] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To use patient data to evaluate and construct diagnostic criteria for inclusion body myositis (IBM), a progressive disease of skeletal muscle. METHODS The literature was reviewed to identify all previously proposed IBM diagnostic criteria. These criteria were applied through medical records review to 200 patients diagnosed as having IBM and 171 patients diagnosed as having a muscle disease other than IBM by neuromuscular specialists at 2 institutions, and to a validating set of 66 additional patients with IBM from 2 other institutions. Machine learning techniques were used for unbiased construction of diagnostic criteria. RESULTS Twenty-four previously proposed IBM diagnostic categories were identified. Twelve categories all performed with high (≥97%) specificity but varied substantially in their sensitivities (11%-84%). The best performing category was European Neuromuscular Centre 2013 probable (sensitivity of 84%). Specialized pathologic features and newly introduced strength criteria (comparative knee extension/hip flexion strength) performed poorly. Unbiased data-directed analysis of 20 features in 371 patients resulted in construction of higher-performing data-derived diagnostic criteria (90% sensitivity and 96% specificity). CONCLUSIONS Published expert consensus-derived IBM diagnostic categories have uniformly high specificity but wide-ranging sensitivities. High-performing IBM diagnostic category criteria can be developed directly from principled unbiased analysis of patient data. CLASSIFICATION OF EVIDENCE This study provides Class II evidence that published expert consensus-derived IBM diagnostic categories accurately distinguish IBM from other muscle disease with high specificity but wide-ranging sensitivities.
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Leung DG, Taylor HA, Lindy AS, Basehore MJ, Mammen AL. A case of progressive quadriceps weakness and elevated creatine kinase level mimicking inclusion body myositis. Arthritis Care Res (Hoboken) 2014; 66:328-33. [PMID: 24022920 DOI: 10.1002/acr.22156] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 09/03/2013] [Indexed: 11/11/2022]
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Fiorentino DF, Chung LS, Christopher-Stine L, Zaba L, Li S, Mammen AL, Rosen A, Casciola-Rosen L. Most patients with cancer-associated dermatomyositis have antibodies to nuclear matrix protein NXP-2 or transcription intermediary factor 1γ. ACTA ACUST UNITED AC 2014; 65:2954-62. [PMID: 24037894 DOI: 10.1002/art.38093] [Citation(s) in RCA: 263] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Accepted: 07/11/2013] [Indexed: 12/14/2022]
Abstract
OBJECTIVE Since dermatomyositis (DM) is associated with an increased risk of malignancy, accurate identification of patients likely to harbor cancers is important. Using immunoprecipitations from radiolabeled cell lysates, several groups recently showed that anti-transcription intermediary factor 1γ (anti-TIF-1γ) antibodies are associated with malignancy in DM. We undertook this study to develop sensitive, specific assays to detect antibodies against TIF-1γ and nuclear matrix protein NXP-2 and to evaluate their association with malignancy in DM. METHODS To detect anti-TIF-1γ antibodies, immunoprecipitations were performed using lysates made from HeLa cells overexpressing TIF-1γ, with detection by immunoblotting. Anti-NXP-2 antibodies were assayed by immunoprecipitation using (35) S-methionine-labeled NXP-2 generated by in vitro transcription/translation. We analyzed patient sera from DM cohorts seen at the Stanford University Dermatology Clinic (n = 111) and the Johns Hopkins Myositis Center (n = 102). RESULTS A total of 17% and 38% of patients had antibodies against NXP-2 and TIF-1γ, respectively. Reactivity against either NXP-2 or TIF-1γ identified 83% of patients with cancer-associated DM. In addition to older age and male sex, cancer was associated with antibodies to NXP-2 or TIF-1γ on multivariate analysis (odds ratio 3.78 [95% confidence interval 1.33-10.8]). Stratification by sex revealed that anti-NXP-2 was specifically associated with cancer in males (odds ratio 5.78 [95% confidence interval 1.35-24.7]). CONCLUSION These studies demonstrate that anti-NXP-2 and anti-TIF-1γ antibodies are frequent DM specificities (found in 55% of patients) and are present in most patients with cancer-associated DM.
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Paik JJ, Corse AM, Mammen AL. The co-existence of myasthenia gravis in patients with myositis: a case series. Semin Arthritis Rheum 2013; 43:792-6. [PMID: 24412588 DOI: 10.1016/j.semarthrit.2013.12.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 12/12/2013] [Accepted: 12/13/2013] [Indexed: 10/25/2022]
Abstract
OBJECTIVE Myositis and myasthenia gravis (MG) are both autoimmune disorders presenting with muscle weakness. Rarely, they occur simultaneously in the same patient. Since the management of myasthenia gravis differs from that of myositis, it is important to recognize when patients have both diseases. We reviewed the cases of 6 patients with both myositis and MG to identify clinical features that suggest the possibility of co-existing MG in myositis patients. METHODS We identified 6 patients with dermatomyositis or polymyositis and MG. We reviewed their medical records to assess their clinical presentations, laboratory findings, and electrophysiological features. RESULTS All 6 patients had definite dermatomyositis or polymyositis by the criteria of Bohan and Peter as well as electrophysiologic and/or serologic confirmation of MG. Among overlap patients, 5/6 (83%) had bulbar weakness, 2/6 (33%) had ptosis, and 1/6 (17%) had diplopia. Fatigable weakness was noted by 5/6 (83%) patients. Treatment with pyridostigmine improved symptoms in 5/6 (83%) patients. High-dose steroids were associated with worsening weakness in 2/6 (33%) patients. CONCLUSIONS Prominent bulbar symptoms, ptosis, diplopia, and fatigable weakness should suggest the possibility of MG in patients with myositis. A suspicion of MG may be confirmed through appropriate electrophysiologic and laboratory testing. In those with myositis-MG overlap, high-dose steroids may exacerbate symptoms and pyridostigmine may play an important therapeutic role.
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Abstract
PURPOSE This article reviews the most important muscle toxins, many of which are widely prescribed medications. Particular emphasis is placed on statins, which cause muscle symptoms in a relatively large proportion of the patients who take them. RECENT FINDINGS As with other toxic myopathies, most cases of statin-associated myotoxicity are self-limited and subside with discontinuation of the offending agent. Importantly, about 2% of the population is homozygous for a single nucleotide polymorphism, and these individuals have a dramatically increased risk of self-limited statin myopathy. Much more rarely, statins trigger a progressive autoimmune myopathy characterized by a necrotizing muscle biopsy and autoantibodies recognizing hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase, the pharmacologic target of statins. SUMMARY In most cases, toxic myopathies resolve after the toxic agent is stopped. Recognizing that statins can cause an autoimmune necrotizing myopathy is important because patients with this form of statin-triggered muscle disease usually require immunosuppressive therapy.
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Mohassel P, Mammen AL. Statin-associated autoimmune myopathy and anti-HMGCR autoantibodies. Muscle Nerve 2013; 48:477-83. [DOI: 10.1002/mus.23854] [Citation(s) in RCA: 100] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/15/2013] [Indexed: 11/11/2022]
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Werner JL, Christopher-Stine L, Ghazarian SR, Pak KS, Kus JE, Daya NR, Lloyd TE, Mammen AL. Antibody levels correlate with creatine kinase levels and strength in anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase-associated autoimmune myopathy. ACTA ACUST UNITED AC 2013; 64:4087-93. [PMID: 22933019 DOI: 10.1002/art.34673] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 08/09/2012] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Autoantibodies recognizing 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) are found in patients with statin-associated immune-mediated necrotizing myopathy and, less commonly, in statin-unexposed patients with autoimmune myopathy. The main objective of this study was to define the association of anti-HMGCR antibody levels with disease activity. METHODS Anti-HMGCR levels, creatine kinase (CK) levels, and strength were assessed in anti-HMGCR-positive patients. Associations of antibody level with CK level and strength at visit 1 were analyzed in 55 patients, 40 of whom were exposed to statins. In 12 statin-exposed and 5 statin-unexposed patients with serum from 5 serial visits, the evolution of antibody levels, CK levels, and strength was investigated. RESULTS Antibody levels were associated with CK levels (P < 0.001), arm strength (P < 0.05), and leg strength (P < 0.05) at visit 1, but these associations were only significant among statin-exposed patients in stratified analyses. With immunosuppressive treatment over 26.2 ± 12.6 months (mean ± SD), antibody levels declined (P < 0.05) and arm abduction strength improved (P < 0.05) in the 17 patients followed up longitudinally. The separate analysis showed that statin-exposed patients developed decreased antibody levels (P < 0.01), decreased CK levels (P < 0.001), improved arm strength (P < 0.05), and improved hip flexion strength (P < 0.05) with treatment. Anti-HMGCR antibody levels did not normalize in any patient. CONCLUSION In the entire cohort, initial anti-HMGCR levels correlated with indicators of disease activity; with immunosuppressive treatment, antibody levels declined and arm strength improved. Statin-exposed patients had significant improvements in CK levels and strength whereas statin-unexposed patients did not, suggesting a phenotypic difference between statin-exposed and statin-unexposed anti-HMGCR-positive patients.
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Mammen AL, Gaudet D, Brisson D, Christopher-Stine L, Lloyd TE, Leffell MS, Zachary AA. Increased frequency of DRB1*11:01 in anti-hydroxymethylglutaryl-coenzyme A reductase-associated autoimmune myopathy. Arthritis Care Res (Hoboken) 2012; 64:1233-7. [PMID: 22422616 PMCID: PMC3400716 DOI: 10.1002/acr.21671] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
OBJECTIVE To investigate the association of anti-hydroxymethylglutaryl-coenzyme A reductase (anti-HMGCR) myopathy with HLA class I and II antigens. METHODS HLA antigens were determined in 1) 20 white and 8 African American anti-HMGCR patients, 2) 487 white and 167 African American controls, and 3) 51 white subjects with mild self-limited statin intolerance. RESULTS White anti-HMGCR patients had a higher frequency of the combination HLA-DR11, DQA5, and DQB7 than controls or statin-intolerant subjects (70% versus 17%; odds ratio [OR] 11.7 [95% confidence interval (95% CI) 4.0-35.3], P = 4.1 × 10(-7) and 70% versus 21%; OR 8.3 [95% CI 2.2-33.9], P = 5.4 × 10(-4) , respectively). This combination was not increased in African American anti-HMGCR subjects compared to controls (13% versus 3%; OR 4.6 [95% CI 0.2-53.3], P = 0.2). However, DR11 was increased in African American anti-HMGCR patients compared to controls (88% versus 21%; OR 26.4 [95% CI 3.1-590.3], P = 0.0002). High-resolution mapping showed that 95% with DR11 had DRB1*11:01. DQA1 and DQB6 were less frequent in white anti-HMGCR-positive patients compared to controls (25% versus 65%; OR 0.2 [95% CI 0.1-0.5], P = 5.5 × 10(-4) and 0% versus 45%; OR 0.0 [95% CI 0.0-0.3], P = 2.1 × 10(-5) , respectively). DRB11 was not associated with particular disease features. CONCLUSION DRB1*11:01 is associated with an increased risk of anti-HMGCR myopathy in whites and African Americans. These findings suggest a mechanistic link between statin exposure, increased HMGCR expression, and the possible presentation of HMGCR-derived peptide(s) by DRB1*11:01.
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Casciola-Rosen L, Hall JC, Mammen AL, Christopher-Stine L, Rosen A. Isolated elevation of aldolase in the serum of myositis patients: a potential biomarker of damaged early regenerating muscle cells. Clin Exp Rheumatol 2012; 30:548-553. [PMID: 22703875 PMCID: PMC3786178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Accepted: 12/13/2011] [Indexed: 06/01/2023]
Abstract
OBJECTIVES Elevated serum aldolase A levels occur in the absence of elevated creatine kinase M (CK) levels in a subset of myositis patients. This study was undertaken to investigate the cell biology of this unexplained clinical observation. METHODS Cultured human myoblasts were differentiated in vitro. RNA and protein lysates were prepared and used to determine aldolase and CK gene and protein expression by QPCR and immunoblotting. Cardiotoxin was used to induce muscle injury and repair in an experimental mouse model, and aldolase A and CK were immunoblotted in the muscle lysates. Immunohistochemical staining was performed on myositis patient muscle paraffin sections to assess aldolase A and CK staining in vivo. RESULTS Aldolase A mRNA and protein expression is highest in differentiating myoblasts, and remains robust throughout differentiation. In contrast, CK mRNA and protein levels are low in undifferentiated myoblasts and become strikingly upregulated as differentiation progresses. Aldolase A protein expression is high in regenerating muscle in the mouse model of injury/repair, while CK expression was low. Immunohistochemical staining of human myositis biopsies showed that muscle cells with the highest levels of aldolase and no CK staining have features of regeneration. CONCLUSIONS In undifferentiated muscle cells, and those early in the differentiation process, aldolase A is expressed in the absence of CK. Thereafter, both are expressed. We propose that isolated serum aldolase A elevation in myositis patients (i) reflects preferential immune-mediated damage of early regenerative cells, and (ii) is a biomarker of damaged early regenerating muscle cells.
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Ostrow LW, Corse AM, Morrison BM, Huff CA, Carrino JA, Hoke A, Mammen AL. Expanding the spectrum of monoclonal light chain deposition disease in muscle. Muscle Nerve 2012; 45:755-61. [PMID: 22499107 DOI: 10.1002/mus.23287] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
INTRODUCTION The diagnosis of amyloid myopathy is delayed when monoclonal gammopathies are not detected on initial testing and muscle biopsies are nondiagnostic, and the EMG and symptoms can mimic an inflammatory myopathy. METHODS Case report of a patient presenting with severe progressive muscle weakness of unclear etiology despite an extensive workup including two nondiagnostic muscle biopsies. RESULTS Directed by MRI, a third biopsy revealed amyloid angiopathy and noncongophilic kappa light chain deposition in scattered subsarcolemmal rings and perimysial regions. A serum free light chain (FLC) assay revealed a kappa monoclonal gammopathy, which was not detected by multiple immunofixations. CONCLUSIONS The spectrum of immunoglobulin deposition in muscle is similar to other organs. It comprises a continuum that includes parenchymal amyloid deposition, amyloid angiopathy, and noncongophilic Light Chain Deposition Disease (LCDD). We recommend including the FLC assay in the routine investigation for monoclonal gammopathies. This case also highlights the value of MRI-guided muscle biopsy.
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Mammen AL, Pak K, Williams EK, Brisson D, Coresh J, Selvin E, Gaudet D. Rarity of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibodies in statin users, including those with self-limited musculoskeletal side effects. Arthritis Care Res (Hoboken) 2012; 64:269-72. [PMID: 21972203 DOI: 10.1002/acr.20662] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
OBJECTIVE Statins, among the most commonly prescribed medications, are associated with a wide range of musculoskeletal side effects. These include a progressive autoimmune myopathy with anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) antibodies that requires immunosuppression. However, it remains unknown whether these antibodies are found in statin users with and without self-limited musculoskeletal side effects; this limits their diagnostic utility. The current work assessed the prevalence of anti-HMGCR antibodies in these groups of statin users. METHODS We determined the prevalence of anti-HMGCR antibodies in 1,966 participants (including 763 current statin users) in a substudy of the community-based Atherosclerosis Risk in Communities (ARIC) Study and 98 French Canadian subjects with familial hypercholesterolemia, including 51 with documented statin intolerance. RESULTS No participant in the ARIC substudy, including those with past or current statin exposure at the time of sample collection, had anti-HMGCR antibodies. Similarly, none of 51 patients with self-limited statin intolerance or 47 statin-tolerant patients receiving maximal statin therapy were anti-HMGCR positive. CONCLUSION The majority of patients with and without statin exposure, including those with self-limited statin intolerance, do not develop anti-HMGCR antibodies. Therefore, anti-HMGCR antibodies are highly specific for those with an autoimmune myopathy.
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Mammen AL, Mahoney JA, St. Germain A, Badders N, Taylor JP, Rosen A, Spinette S. A novel conserved isoform of the ubiquitin ligase UFD2a/UBE4B is expressed exclusively in mature striated muscle cells. PLoS One 2011; 6:e28861. [PMID: 22174917 PMCID: PMC3235170 DOI: 10.1371/journal.pone.0028861] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 11/16/2011] [Indexed: 12/29/2022] Open
Abstract
Yeast Ufd2p was the first identified E4 multiubiquitin chain assembly factor. Its vertebrate homologues later referred to as UFD2a, UBE4B or E4B were also shown to have E3 ubiquitin ligase activity. UFD2a function in the brain has been well established in vivo, and in vitro studies have shown that its activity is essential for proper condensation and segregation of chromosomes during mitosis. Here we show that 2 alternative splice forms of UFD2a, UFD2a-7 and -7/7a, are expressed sequentially during myoblast differentiation of C2C12 cell cultures and during cardiotoxin-induced regeneration of skeletal muscle in mice. UFD2a-7 contains an alternate exon 7, and UFD2a-7/7a, the larger of the 2 isoforms, contains an additional novel exon 7a. Analysis of protein or mRNA expression in mice and zebrafish revealed that a similar pattern of isoform switching occurs during developmental myogenesis of cardiac and skeletal muscle. In vertebrates (humans, rodents, zebrafish), UFD2a-7/7a is expressed only in mature striated muscle. This unique tissue specificity is further validated by the conserved presence of 2 muscle-specific splicing regulatory motifs located in the 3' introns of exons 7 and 7a. UFD2a interacts with VCP/p97, an AAA-type ATPase implicated in processes whose functions appear to be regulated, in part, through their interaction with one or more of 15 previously identified cofactors. UFD2a-7/7a did not interact with VCP/p97 in yeast 2-hybrid experiments, which may allow the ATPase to bind cofactors that facilitate its muscle-specific functions. We conclude that the regulated expression of these UFD2a isoforms most likely imparts divergent functions that are important for myogenisis.
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Del Grande F, Carrino JA, Del Grande M, Mammen AL, Christopher Stine L. Magnetic resonance imaging of inflammatory myopathies. Top Magn Reson Imaging 2011; 22:39-43. [PMID: 22648079 DOI: 10.1097/rmr.0b013e31825b2c35] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The following article reviews the role of magnetic resonance imaging (MRI) in patients with idiopathic inflammatory myopathies (IIMs), focusing on the 3 major types of IIM: polymyositis, dermatomyositis, and inclusion-body myositis. After a brief introduction with general information about IIM, we will discuss the reasons why MRI plays an important role in the diagnosis and management of patients with polymyositis, dermatomyositis, and inclusion-body myositis. Magnetic resonance imaging can confirm the diagnosis and can help to phenotype the disease. Moreover, the support of MRI is important in addressing the muscle biopsy site and in reducing the high false-negative rate of biopsy when performed in a blind fashion. In monitoring therapy, MRI can add important information about the activity of the muscle disease and can identify cases where continued immunosuppressive therapy is no longer warranted owing to complete fatty replacement of the muscles. Lastly, we provide an overview about some advanced MRI techniques that focus more on function than on morphology of muscle.
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Mammen AL, Chung T, Christopher-Stine L, Rosen P, Rosen A, Doering KR, Casciola-Rosen LA. Autoantibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase in patients with statin-associated autoimmune myopathy. ARTHRITIS AND RHEUMATISM 2011; 63:713-21. [PMID: 21360500 PMCID: PMC3335400 DOI: 10.1002/art.30156] [Citation(s) in RCA: 451] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE In addition to inducing a self-limited myopathy, statin use is associated with an immune-mediated necrotizing myopathy (IMNM), with autoantibodies that recognize ∼200-kd and ∼100-kd autoantigens. The purpose of this study was to identify these molecules to help clarify the disease mechanism and facilitate diagnosis. METHODS The effect of statin treatment on autoantigen expression was addressed by immunoprecipitation using sera from patients. The identity of the ∼100-kd autoantigen was confirmed by immunoprecipitation of in vitro-translated 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) protein. HMGCR expression in muscle was analyzed by immunofluorescence. A cohort of myopathy patients was screened for anti-HMGCR autoantibodies by enzyme-linked immunosorbent assay and genotyped for the rs4149056 C allele, a predictor of self-limited statin myopathy. RESULTS Statin exposure induced expression of the ∼200-kd/∼100-kd autoantigens in cultured cells. HMGCR was identified as the ∼100-kd autoantigen. Competition experiments demonstrated no distinct autoantibodies recognizing the ∼200-kd protein. In muscle biopsy tissues from anti-HMGCR-positive patients, HMGCR expression was up-regulated in cells expressing neural cell adhesion molecule, a marker of muscle regeneration. Anti-HMGCR autoantibodies were found in 45 of 750 patients presenting to the Johns Hopkins Myositis Center (6%). Among patients ages 50 years and older, 92.3% had taken statins. The prevalence of the rs4149056 C allele was not increased in patients with anti-HMGCR. CONCLUSION Statins up-regulate the expression of HMGCR, the major target of autoantibodies in statin-associated IMNM. Regenerating muscle cells express high levels of HMGCR, which may sustain the immune response even after statins are discontinued. These studies demonstrate a mechanistic link between an environmental trigger and the development of sustained autoimmunity. Detection of anti-HMGCR autoantibodies may facilitate diagnosis and direct therapy.
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Christopher-Stine L, Casciola-Rosen LA, Hong G, Chung T, Corse AM, Mammen AL. A novel autoantibody recognizing 200-kd and 100-kd proteins is associated with an immune-mediated necrotizing myopathy. ACTA ACUST UNITED AC 2010; 62:2757-66. [PMID: 20496415 DOI: 10.1002/art.27572] [Citation(s) in RCA: 332] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
OBJECTIVE Myofiber necrosis without prominent inflammation is a nonspecific finding in patients with dystrophies and toxic or immune-mediated myopathies. However, the etiology of a necrotizing myopathy is often obscure, and the question of which patients would benefit from immunosuppression remains unanswered. The aim of this study was to identify novel autoantibodies in patients with necrotizing myopathy. METHODS Muscle biopsy specimens and serum samples were available for 225 patients with myopathy. Antibody specificities were determined by performing immunoprecipitations from (35)S-methionine-labeled HeLa cell lysates. Selected biopsy specimens were stained for membrane attack complex, class I major histocompatibility complex (MHC), and endothelial cell marker CD31. RESULTS Muscle biopsy specimens from 38 of 225 patients showed predominantly myofiber necrosis. Twelve of these patients had a known autoantibody association with or other etiology for their myopathy. Sixteen of the remaining 26 sera immunoprecipitated 200-kd and 100-kd proteins; this specificity was observed in only 1 of 187 patients without necrotizing myopathy. Patients with the anti-200/100 autoantibody specificity had proximal weakness (100%), high creatine kinase levels (mean maximum 10,333 IU/liter), and an irritable myopathy on electromyography (88%). Sixty-three percent of these patients had been exposed to statins prior to the onset of weakness. All patients responded to immunosuppressive therapy, and many experienced a relapse of weakness when the medication was tapered. Immunohistochemical studies showed membrane attack complex on small blood vessels in 6 of 8 patients and on the surface of non-necrotic myofibers in 4 of 8 patients. Five of 8 patients had abnormal capillary morphology, and 4 of 8 patients expressed class I MHC on the surface of non-necrotic myofibers. CONCLUSION An anti-200/100-kd specificity defines a subgroup of patients with necrotizing myopathy who previously were considered to be autoantibody negative. We propose that these patients have an immune-mediated myopathy that is frequently associated with prior statin use and should be treated with immunosuppressive therapy.
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Mammen AL. Dermatomyositis and polymyositis: Clinical presentation, autoantibodies, and pathogenesis. Ann N Y Acad Sci 2010; 1184:134-53. [PMID: 20146695 DOI: 10.1111/j.1749-6632.2009.05119.x] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Dermatomyositis (DM) and polymyositis (PM) are autoimmune myopathies characterized clinically by proximal muscle weakness, muscle inflammation, extramuscular manifestations, and frequently, the presence of autoantibodies. Although there is some overlap, DM and PM are separate diseases with different pathophysiological mechanisms. Furthermore, unique clinical phenotypes are associated with each of the myositis-specific autoantibodies (MSAs) associated with these disorders. This review will focus on the clinical features, pathology, and immunogenetics of PM and DM with an emphasis on the importance of autoantibodies in defining unique phenotypes and, perhaps, as clues to help elucidate the mechanisms of disease.
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Mammen AL, Casciola-Rosen LA, Hall JC, Christopher-Stine L, Corse AM, Rosen A. Expression of the dermatomyositis autoantigen Mi-2 in regenerating muscle. ACTA ACUST UNITED AC 2010; 60:3784-93. [PMID: 19950298 DOI: 10.1002/art.24977] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Autoantibodies against the chromatin remodeler Mi-2 are found in a distinct subset of patients with dermatomyositis (DM). Previous quantitative immunoblotting experiments demonstrated that Mi-2 protein levels are up-regulated in DM muscle. This study was undertaken to define the population of cells expressing high levels of Mi-2 in DM muscle and to explore the regulation and functional role of Mi-2 during muscle regeneration. METHODS The expression of Mi-2 was analyzed by immunofluorescence microscopy in human muscle biopsy specimens. In an experimental mouse model, cardiotoxin was used to induce muscle injury and repair, and expression of Mi-2 during muscle regeneration was studied in this model by immunofluorescence and immunoblotting analyses. In addition, a cell culture system of muscle differentiation was utilized to artificially modulate Mi-2 levels during proliferation and differentiation of myoblasts. RESULTS In human DM muscle tissue, increased Mi-2 expression was found preferentially in the myofibers within fascicles affected by perifascicular atrophy, particularly in the centralized nuclei of small perifascicular muscle fibers expressing markers of regeneration. In injured mouse muscle tissue, Mi-2 levels were dramatically and persistently up-regulated during muscle regeneration in vivo. Premature silencing of Mi-2 with RNA interference in vitro resulted in accelerated myoblast differentiation. CONCLUSION Expression of Mi-2 is markedly up-regulated during muscle regeneration in a mouse model of muscle injury and repair. It is also up-regulated in human DM myofibers expressing markers of regeneration. Results of the in vitro studies indicate that this protein may play a role in modulating the kinetics of myoblast differentiation. Our findings thus suggest that high levels of Mi-2 expression in muscle biopsy tissue from patients with DM reflect the presence of incompletely differentiated muscle cells.
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Ritu RV, Casciola-Rosen L, Hong G, Mammen AL, Christopher-Stine L. Rituximab therapy for myopathy associated with anti-srp antibodies: A case series: Authors reply. Arthritis Care Res (Hoboken) 2010. [DOI: 10.1002/acr.20387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Mammen AL, Chaudhry V. The difficulties of diagnosing neuromuscular complications. THE JOURNAL OF SUPPORTIVE ONCOLOGY 2005; 3:285-6. [PMID: 16092598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
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Mammen AL, Kameyama K, Roche KW, Huganir RL. Phosphorylation of the alpha-amino-3-hydroxy-5-methylisoxazole4-propionic acid receptor GluR1 subunit by calcium/calmodulin-dependent kinase II. J Biol Chem 1997; 272:32528-33. [PMID: 9405465 DOI: 10.1074/jbc.272.51.32528] [Citation(s) in RCA: 343] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Modulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic Acid (AMPA) receptors in the brain by protein phosphorylation may play a crucial role in the regulation of synaptic plasticity. Previous studies have demonstrated that calmodulin (CaM) kinase II can phosphorylate and modulate AMPA receptors. However, the sites of CaM kinase phosphorylation have not been unequivocally identified. In the current study, we have generated two phosphorylation site-specific antibodies to analyze the phosphorylation of the glutamate receptor GluR1 subunit. These antibodies recognize GluR1 only when it is phosphorylated on serine residues 831 or 845. We have used these antibodies to demonstrate that serine 831 is specifically phosphorylated by CaM kinase II in transfected cells expressing GluR1 as well as in hippocampal slice preparations. Two-dimensional phosphopeptide mapping experiments indicate that Ser-831 is the major site of CaM kinase II phosphorylation on GluR1. In addition, treatment of hippocampal slice preparations with phorbol esters and forskolin increase the phosphorylation of serine 831 and 845, respectively, indicating that protein kinase C and protein kinase A phosphorylate these residues in hippocampal slices. These results identify the site of CaM kinase phosphorylation of the GluR1 subunit and demonstrate that GluR1 is multiply phosphorylated by protein kinase A, protein kinase C, and CaM kinase II in situ.
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O'Brien RJ, Mammen AL, Blackshaw S, Ehlers MD, Rothstein JD, Huganir RL. The development of excitatory synapses in cultured spinal neurons. J Neurosci 1997; 17:7339-50. [PMID: 9295380 PMCID: PMC6573451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Immunohistochemical studies of synapses in the CNS have demonstrated that glutamate receptors (GluRs) are concentrated at postsynaptic sites in vivo and in vitro (Baude et al., 1995). The mechanisms leading to receptor clustering at excitatory synapses are far less understood than those governing acetylcholine receptor accumulation at the neuromuscular junction () or glycine receptor aggregation at central inhibitory synapses (). Using cultured rat spinal cord neurons, we demonstrate that clustering of the AMPA receptor subunit GluR1 is among the earliest events in excitatory synapse formation in vitro, coincident with the onset of miniature EPSCs and in many cases preceding presynaptic vesicle accumulation. Postsynaptic receptor clustering is induced in a highly specific and reiterative pattern, independent of receptor activation, by contact with a subset of axons capable of inducing receptor clusters. The subunit composition of AMPA receptor clusters varied significantly between neurons but was invariant within a given neuron. The presence of either GluR2 or GluR3 was common to all receptor clusters. Neither high-affinity glutamate transporters nor NMDA receptors appeared to be concentrated with AMPA receptor subunits at these excitatory synapses.
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Mammen AL, Huganir RL, O'Brien RJ. Redistribution and stabilization of cell surface glutamate receptors during synapse formation. J Neurosci 1997; 17:7351-8. [PMID: 9295381 PMCID: PMC6573457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Although the regulation of neurotransmitter receptors during synaptogenesis has been studied extensively at the neuromuscular junction, little is known about the control of excitatory neurotransmitter receptors during synapse formation in central neurons. Using antibodies against extracellular N-terminal (N-GluR1) and intracellular C-terminal (C-GluR1) domains of the AMPA receptor subunit GluR1, combined with surface biotinylation and metabolic labeling studies, we have characterized the redistribution and metabolic stabilization of the AMPA receptor subunit GluR1 during synapse formation in culture. Before synapse formation, GluR1 is distributed widely, both on the surface and within the dendritic cytoplasm of these neurons. The diffuse cell surface pool of receptor appears to be mobile within the membrane and can be induced to cluster by the addition of N-GluR1 to live neurons. As cultures mature and synapses form, there is a redistribution of surface GluR1 into clusters at excitatory synapses where it appears to be immobilized. The change in the distribution of GluR1 is accompanied by an increase in both the half-life of the receptor and the percentage of the total pool of GluR1 that is present on the cell surface. Blockade of postsynaptic AMPA and NMDA receptors had no effect on the redistribution of GluR1. These results begin to characterize the events regulating the distribution of AMPA receptors and demonstrate similarities between synapse formation at the neuromuscular junction and at excitatory synapses in cultured neurons.
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Abstract
The proper targeting and clustering of neurotransmitter receptors at appropriate postsynaptic sites are principal requirements for the formation of functional synapses. Recently, new studies have begun to elucidate the mechanisms underlying the targeting and clustering of glutamate receptors at excitatory synapses in the brain. Members of the SAP90/PSD-95 family of proteins have emerged as potential regulators of glutamate-receptor membrane distribution. Further, targeting motifs within glutamate receptor subunits have been identified. These findings provide important clues in the effort to understand the molecular features of synaptic organization.
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