Objectives Systemic juvenile idiopathic arthritis (SJIA) confers high risk for macrophage activation syndrome (MAS), a life-threatening cytokine storm driven by interferon (IFN)-γ. SJIA monocytes display IFN-γ hyper-responsiveness, but the molecular basis of this remains unclear. The objective of this study is to identify circulating monocyte and bone marrow macrophage (BMM) polarisation phenotypes in SJIA including molecular features contributing to IFN response.
Methods Bulk RNA-seq was performed on peripheral blood monocytes (n=26 SJIA patients) and single cell (sc) RNA-seq was performed on BMM (n=1). Cultured macrophages were used to define consequences of tripartite motif containing 8 (TRIM8) knockdown on IFN-γ signalling.
Results Bulk RNA-seq of SJIA monocytes revealed marked transcriptional changes in patients with elevated ferritin levels. We identified substantial overlap with multiple polarisation states but little evidence of IFN-induced signature. Interestingly, among the most highly upregulated genes was TRIM8, a positive regulator of IFN-γ signalling. In contrast to PBMC from SJIA patients without MAS, scRNA-seq of BMM from a patient with SJIA and MAS identified distinct subpopulations of BMM with altered transcriptomes, including upregulated IFN-γ response pathways. These BMM also showed significantly increased expression of TRIM8. In vitro knockdown of TRIM8 in macrophages significantly reduced IFN-γ responsiveness.
Conclusions Macrophages with an ‘IFN-γ response’ phenotype and TRIM8 overexpression were expanded in the bone marrow from an MAS patient. TRIM8 is also upregulated in SJIA monocytes, and augments macrophage IFN-γ response in vitro, providing both a candidate molecular mechanism and potential therapeutic target for monocyte hyper-responsiveness to IFNγ in cytokine storms including MAS.
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Handling editor Josef S Smolen
Contributors GS and AAG designed the study. GS, TD, SD, NF and ST performed the experiments. GS, AP, DS, MM, NS and AAG performed gene expression analysis. GS and AAG wrote the first draft of the manuscript. All authors contributed to the final manuscript and approved its submission.
Funding This work was supported by the Systemic Juvenile Idiopathic Arthritis Foundation; National Institutes of Health K08-AR072075 (GS), R01-AR059049 (AAG) and P30-AR070549; Cincinnati Children’s Research Foundation ARC Grant (GS&AAG); and an unrestricted gift from the Jellen Family Foundation.
Competing interests GS has served as a consultant for Novartis and Sobi. AAG has served as a consultant for Juno and Novartis, and has received research support from Sobi and AB2Bio. All other authors declare no conflicts of interest.
Patient consent for publication Not required.
Ethics approval This study was approved by the institutional review board of CCHMC (IRB# 2012–0160).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available in a public, open access repository. All data relevant to the study are included in the article or uploaded as online supplemental information. Bulk and single-cell RNA-seq datasets have been deposited in gene expression omnibus (GSE147608 and GSE147795, respectively).
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