Muscle Weakness in Myositis: MicroRNA‐Mediated Dystrophin Reduction in a Myositis Mouse Model and Human Muscle Biopsies

Abstract

Objective Muscle inflammation is a feature in myositis and Duchenne muscular dystrophy ( DMD ). Autoimmune mechanisms are thought to contribute to muscle weakness in patients with myositis. However, a lack of correlation between the extent of inflammatory cell infiltration and muscle weakness indicates that nonimmune pathologic mechanisms may play a role. The present study focused on 2 micro RNA (mi RNA ) sets previously identified as being elevated in the muscle of patients with DMD —an “inflammatory” mi RNA set that is dampened with glucocorticoids, and a “dystrophin‐targeting” mi RNA set that inhibits dystrophin translation—to test the hypothesis that these mi RNA s are similarly dysregulated in the muscle of patients with myositis, and could contribute to muscle weakness and disease severity. Methods A major histocompatibility complex class I–transgenic mouse model of myositis was utilized to study gene and mi RNA expression and histologic features in the muscle tissue, with the findings validated in human muscle biopsy tissue from 6 patients with myositis. Mice were classified as having mild or severe myositis based on transgene expression, body weight, histologic disease severity, and muscle strength/weakness. Results In mice with severe myositis, muscle tissue showed mononuclear cell infiltration along with elevated expression of type I interferon and NF ‐κB–regulated genes, including Tlr7 (3.8‐fold increase, P < 0.05). Furthermore, mice with severe myositis showed elevated expression of inflammatory mi RNA s (miR‐146a, miR‐142‐3p, miR‐142‐5p, miR‐455‐3p, and miR‐455‐5p; ~3–40‐fold increase, P < 0.05) and dystrophin‐targeting mi RNA s (miR‐146a, miR‐146b, miR‐31, and miR‐223; ~3–38‐fold increase, P < 0.05). Bioinformatics analyses of chromatin immunoprecipitation sequencing (ChIP‐seq) data identified at least one NF ‐κB consensus element within the promoter/enhancer regions of these mi RNA s. Western blotting and immunofluorescence analyses of the muscle tissue from mice with severe myositis demonstrated reduced levels of dystrophin. In addition, elevated levels of NF ‐κB–regulated genes, TLR 7 , and mi RNA s along with reduced dystrophin levels were observed in muscle biopsy tissue from patients with histologically severe myositis. Conclusion These data demonstrate that an acquired dystrophin deficiency may occur through NF ‐κB–r...

Multi-Omics Identifies Circulating miRNA and Protein Biomarkers for Facioscapulohumeral Dystrophy

“…Serum miR-146b is a pharmacodynamic biomarker in inflammatory bowel disease (IBD) [ 34 , 35 ]. Intriguingly, miR-146b is also known to down-regulate dystrophin in multiple muscle diseases, is increased in dystrophinopathies and in myositis, and is also drug-responsive in the mdx mouse model of DMD [ 30 , 31 ]. Urinary miR-141 provides a promising diagnostic biomarker for the identification of both prostate and bladder cancers [ 69 ]; it will be interesting to determine if this or other candidate miRNAs are also dysregulated in urine from dystrophic patients, as this sampling method could provide a completely non-invasive biomarker.…”

“…In Duchenne and Becker muscular dystrophies, myomiRs are up-regulated in serum from both patient populations, while detection of miR-206 up-regulation can be used to differentially diagnose severe Duchenne versus Becker patients [ 26 , 27 , 28 ]. In addition to myomiRs, inflammatory miRNAs such as miR-146a, miR-146b, miR-221 and miR-155 have been found to be dysregulated in multiple forms of muscular dystrophies [ 29 , 30 , 31 ]. These two classes of miRNA show potential as pharmacodynamic biomarkers, with myomiRs proposed for muscle-stabilizing treatments such as gene therapy [ 32 , 33 ], and inflammatory microRNAs proposed for current steroids [ 34 , 35 ] as well as newly emerging dissociative anti-inflammatory drugs such as vamorolone [ 36 , 37 , 38 ] or edasalonexent [ 39 , 40 ].…”

MiR‐455‐5p monitors myotube morphogenesis by targeting mylip

“…In addition, miR‐455‐5p has been shown to play an anti‐inflammatory role in the immune system 26 . Recent studies have shown that miR‐455‐5p is significantly elevated in mice with severe myositis (~4–6‐fold increase; p < .05), 12 suggesting that miR‐455‐5p may be involved in muscle development. In this study, we showed for the first time that miR‐455‐5p is involved in monitoring myotube morphogenesis in addition to its established roles in cancer and the immune system.…”

“…In mice, miR‐455‐5p is located on chromosome 4 and is encoded by Col27a1 (collagen type XXVII alpha 1 chain). Mice with severe myositis show elevated expression of miR‐455‐5p 13 . TTTY15/miR‐455‐5p/JDP2 axis regulates hypoxia‐induced cell injuries in human cardiomyocyte primary cells 9 .…”

High throughput screening to identify inhibitors of the type I interferon – major histocompatibility complex class I pathway in skeletal muscle

“…Patient muscles exhibiting refractory weakness without inflammatory cell infiltration have been observed to have chronic MHC class I over-expression, even after prednisone treatment (Lundberg et al, 2000; Nyberg et al, 2000). Additionally, transgenic over-expression of MHC class I in mouse skeletal muscle recapitulates many features of myositis, including endoplasmic reticulum (ER) stress and up-regulation of ISGs (Kinder et al, 2020; Nagaraju et al, 2000). Taken together, chronic expression of MHC class I, or certain alleles of it, may be pathogenic in skeletal muscle and could be a therapeutic target in myositis ( Figure 1A ).…”