Coordinated local RNA overexpression of complement induced by interferon gamma in myositis

Abstract

Complement proteins are deposited in the muscles of patients with myositis. However, the local expression and regulation of complement genes within myositis muscle have not been well characterized. In this study, bulk RNA sequencing (RNAseq) analyses of muscle biopsy specimens revealed that complement genes are locally overexpressed and correlate with markers of myositis disease activity, including the expression of interferon-gamma (IFNγ)-induced genes. Single cell and single nuclei RNAseq analyses showed that most local expression of complement genes occurs in macrophages, fibroblasts, and satellite cells, with each cell type expressing different sets of complement genes. Biopsies from immune-mediated necrotizing myopathy patients, who have the lowest levels of IFNγ-induced genes, also had the lowest complement gene expression levels. Furthermore, data from cultured human cells showed that IFNγ upregulates complement expression in macrophages, fibroblasts, and muscle cells. Taken together, our results suggest that in myositis muscle, IFNγ coordinates the local overexpression of complement genes that occurs in several cell types.

IFNγ causes mitochondrial dysfunction and oxidative stress in myositis

“…All muscle biopsies analyzed in this study belonged to participants in institutional review board (IRB)-approved longitudinal cohorts from the National Institutes of Health in Bethesda, MD the Johns Hopkins Myositis Center in Baltimore, MD, the Vall d’Hebron Hospital, and the Clinic Hospital in Barcelona 70 . All participants signed a written informed consent form, and all methods were performed in accordance with the relevant guidelines and regulations.…”

“…Bulk RNAseq of frozen muscle biopsy samples was carried out as previously described 70 , 72 . TRIzol (Thermo Fisher Scientific) was used for RNA extraction.…”

“…Normal human skeletal muscle myoblasts (Lonza) were cultured as previously described 70 . When reaching 80% confluence, myotube differentiation was induced by replacement of the growth medium by differentiation medium (Dulbecco’s modified Eagle’s medium with 2% horse serum and L-glutamine).…”