P130 Transcriptomic analysis of synovitis identifies inhibition of CXCL1 as a mechanism contributing to resolution of inflammatory arthritis under IL-27 control
Authors: Burridge Isabel , Eastham Simon , Hill David G , Andrews Robert , Szomolay Barbara , Williams Nigel , Jones Simon A , Jones Gareth W 
Published: April 2023

Abstract

Background/Aims
Interleukin-27 (IL-27) regulates adaptive immune responses and is critical for the timely resolution of inflammation to restore tissue homeostasis. Studies have highlighted roles for IL-27 in limiting immune cell effector function, stromal cell responses and erosive joint pathology in clinical rheumatoid arthritis and experimental models of the disease. In the murine antigen-induced arthritis (AIA) model, IL-27 receptor-deficient (Il27ra-/-) mice develop severe synovitis associated with increased infiltration of synovial CD4+ T cells, development of synovial ectopic lymphoid-like structures and exacerbated cartilage and bone erosion. Similarly, mice with collagen-induced arthritis (CIA) administered IL-27 show improved joint pathology and reduced serum IFN-γ and IL-17 levels. Identifying mechanisms by which IL-27 regulates arthritis progression is key to understanding its therapeutic potential. Using RNA-sequencing of synovial tissue and joint-infiltrating CD4+ T cells we reveal that IL-27 regulates the magnitude of synovitis and genes in CD4+ T cells central to neutrophil recruitment.

Methods
Antigen-induced arthritis (AIA) was established in Il27ra-/- and wild-type control mice. RNA-sequencing was performed on whole synovial tissue and joint-infiltrating CD4+ T cells during the peak of joint inflammation and during the resolution of synovitis. Differentially expressed genes were interrogated by molecular pathway analysis and gene set enrichment analysis. CD4+ T cell culture assays, qPCR and ELISA were used to test and validate genes under IL-27 regulation.

Results
RNA-sequencing of whole synovial tissue revealed that pathways relating to CD4+ T cell and Th17 biology were significantly overrepresented in Il27ra-/- mice with AIA, consistent with a pathogenic role for these cells in inflammatory arthritis. Genes associated with neutrophil effector function (e.g. Elane, Padi4, Prtn3) and recruitment (e.g. Cxcl1, Cxcr2) were also highly expressed in Il27ra-/- synovium and was reflected in the increased number of Ly6G+CD11b+ neutrophils recovered from the joints of Il27ra-/- mice. In contrast to the transcriptomic analysis of inflamed synovial tissue, surprisingly RNA-sequencing of joint-infiltrating CD4+ T cells revealed that the expression of signature Th17 genes (e.g. Il17a, Il17f, Rorc) was comparable between WT and Il27ra-/- T cells. This implies that IL-27 predominantly regulates the magnitude of the joint CD4+ T cell infiltrate more than the effector characteristics of the infiltrating T cells. Differential gene expression analysis revealed heightened Cxcl1 expression in both whole synovial tissue and joint-infiltrating CD4+ T cells recovered from Il27ra-/- mice with AIA. CD4+ T cell differentiation cultures confirmed upregulation of Cxcl1 following T cell receptor activation and under Th1 polarizing conditions. Here, IL-27 suppressed the expression of CXCL1 at the mRNA and protein level.

Conclusion
Together, our data reveals a role for IL-27 in limiting CXCL1 expression in activated and joint-infiltrating CD4+ T cells, highlighting a novel mechanism by which IL-27 may integrate innate and adaptive arms of the immune response to regulate arthritis progression.
Disclosure
I. Burridge: None. S. Eastham: None. D.G. Hill: None. R. Andrews: None. B. Szomolay: None. N. Williams: None. S.A. Jones: None. G.W. Jones: None.