Unravelling inclusion body myositis using a patient‐derived fibroblast model

Abstract

Background 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. Methods 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. Results 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. Conclusions 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.

Mitochondrial defects in sporadic inclusion body myositis—causes and consequences

“…Second, a high level of deglycase DJ-1, an important mitochondrial protective protein against oxidative stress ( Taira et al, 2004 ), has been found in the mitochondria of sIBM muscle ( Terracciano et al, 2008 ), indicating the mitochondria are under high oxidative stress and require stronger protection. In support of this notion, fibroblasts cultured from sIBM patients displayed higher oxidative stress, concomitant with increased antioxidant defense ( Cantó-Santos et al, 2023 ). Furthermore, the protein amount and gene expression of ROS scavengers, Cu, Zn- superoxide dismutase (Cu, Zn-SOD) and manganese superoxide dismutase (Mn-SOD), are augmented in vacuolated myofibers in sIBM ( Askanas and Engel, 1998 ; Tsuruta et al, 2002 ).…”

“…Nevertheless, a substantial number of sIBM patients displayed no elevated anti-cN-1A antibody in their circulation, suggesting that the presence of antibody should not be considered a necessary criterion in the disease diagnosis ( Mavroudis et al, 2021 ; Diederichsen et al, 2023 ). While histological analysis of muscle biopsy remains an essential procedure for sIBM diagnosis ( Papadimas et al, 2019 ; Winkler et al, 2021 ), other methods such as multi-osmics profiling are being developed to screen for novel biomarkers with 100% sensitivity and specificity ( Cantó Santos et al, 2023 ).…”

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

“…Considering the lack of appropriate pre-clinical models, alternative technologies need to be exploited. Omics approaches have been recently contributing to improving our understanding of the disease [ 67 , 258 , 259 , 260 , 261 , 262 , 263 , 264 ]. Proteomics analysis performed on skeletal muscle biopsies of patients with sIBM has revealed alterations of pathways related to oxidative stress and regulation of apoptosis [ 261 ].…”

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

“…So far, most of the pathophysiology of IBM has been revealed through the analysis of biological samples from the target tissue (muscle histopathology studies, RNA-seq, etc.) or peripheral tissues (mainly lymphocyte RNA-seq and metabolome phenotyping) [ 5 , 7 , 13 , 14 ]. A mouse xenograft containing IBM muscle biopsies [ 15 ] served as a breakthrough in the field, facilitating the in vivo evaluation of disease pathophysiology.…”

“…The major contribution of this model was the finding that rimmed vacuoles resisted after the murine xenografts were treated with anti-CD3+, which reduced CD8+ T cell levels and impaired MHC-I upregulation, thus supporting the idea that new treatments should target degeneration to treat muscle weakness. Another relevant model of IBM was developed and validated by our group [ 13 ] using patient-derived fibroblasts. This model recapitulated the main hallmarks of the target tissue of the disease (inflammatory, degenerative, and metabolic muscle imbalances).…”