Background/Purpose:

Although accumulating evidence continues to point toward a critical role for IL23 signaling in spondyloarthritis (SpA), the cellular and molecular events involved, as well as the respective contributions of enthesial and synovial inflammation, remain incompletely understood. In this study we have combined ex vivo organ culture of enthesial and synovial explants from SpA patients and controls with in-situ hybridization (ISH) and gene expression analysis of synovial tissue to further delineate the molecular and cellular pathogenesis underlying SpA.

Methods: Under an HSS IRB approved protocol, patients undergoing total hip replacement (THR) were recruited into 3 groups: SpA (either psoriatic arthritis or ankylosing spondylitis, meeting ASAS or CASPAR criteria or were being treated with DMARDS/biologics); HO (OA patients a previous contralateral THR who had history of post-THR heterotopic ossification) and OA (OA patients a previous contralateral THR with no history of HO. For Phase 1 of this study (n=15/group), synovial tissue was collected intra-operatively and immediately aliquoted into RNAlater for RNA isolation and subsequent sequencing, or OCT for ISH analysis. For Phase 2 (n=10/group), entheseal tissue (ligamentum teres) and synovial tissue were cultured +/- RORgT inhibitor (2 hours) followed by +/- cytokine stimulation (hTNF/hIL23) for 24 and 48 hours. These cultures were analyzed via MSD for secreted cytokines and via TaqMan RT-PCR.

Results:

RNA sequencing identified the presence of a macrophage signature with elevation of MMPs and MARCO in SpA tissue. Additionally preliminary ISH analysis has shown a potential enrichment of CD163 positive macrophages in areas of synovial inflammation. Expression analysis of ALI cultured explants also identified a remarkable enrichment of MARCO-positive macrophages in synovium (cf enthesis) and, consistent with the RNA sequencing of whole tissue, induction of MMP production in synovium following cytokine stimulation. In contrast entheseal tissue that had a lower MMP and MARCO signature, responded to cytokine stimulation with induction of IL17A/F and IFNg. Importantly, this latter effect was most pronounced in SpA patients and inhibited by an ROR inhibitor.

Conclusion:

Our results suggest that the synovial and entheseal tissues in SpA patients have distinct cellular phenotypes and differential responses to cytokines and involvement of RORgt signaling. In line with previous observations (refs) a prominent macrophage signature is seen in the synovium, and this is associated with elevation of MMP induction in SpA. Whereas entheseal tissue produced IL17 and IFNg in response to TNF and IL23, consistent with the presence of a resident population of IL23R positive T cells at this site in SpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differential-involvement-of-synovial-and-entheseal-inflammation-in-mediating-pathological-il23-axis-signaling-in-spondyloarthritis/