Dual Impact of Interleukin-17A Blockade on Inflammatory and Stromal Pathways in Peripheral Spondyloarthritis

Background: IL-17A plays a role in the pathology of spondyloarthritis (SpA), as evidenced by the clinical efficacy of IL-17A inhibitors (IL-17Ai). Nevertheless, the exact role of IL-17A in driving synovial inflammation and pathological remodeling remains unknown. In this study, we investigated the molecular pathways affected by IL-17Ai in SpA synovitis to determine whether this response is tissue- and/or treatment-specific. Methods: Synovial biopsies from 12 peripheral SpA (pSpA) patients before and after 12 weeks of IL-17Ai treatment were analyzed by RNA-sequencing and qPCRs. The synovial tissue response to IL-17Ai in 7 psoriatic arthritis (PsA) patients was compared to: open-source gene expression data of skin biopsies from 15 psoriasis (PsO) patients treated with IL-17Ai; and synovial biopsies from 7 PsA patients receiving IL-12p40/IL-23p40 blockade. Results: Compared to baseline, IL-17Ai significantly modulated the expression of 1255 genes (549 upregulated and 706 downregulated, FDR < 0.1) in the synovium at week 12. The downregulated genes were predominantly associated with inflammatory processes and stromal functions. Comprehensive analysis revealed that IL-17Ai-mediated suppression of bone remodeling is independent of its inhibition of inflammatory pathways. While IL-17Ai consistently attenuated inflammation-related pathways in both psoriatic joints and skin, its effect on bone remodeling pathways was specific to the synovium. This distinguishes IL-17Ai from IL-12p40/IL-23p40 inhibitors, which, while mitigating synovial inflammation, did not affect tissue remodeling. Conclusions: Our findings provide new insights into the molecular mechanisms of IL-17A blockade in pSpA, underscoring its unique role in selectively targeting bone-remodeling processes specific to the joints of individuals with SpA.