OP0100 IL-17A BLOCKADE MODULATES DISEASE SPECIFIC IMMUNE AND STROMAL PATHWAYS IN PERIPHERAL SPONDYLOARTHRITIS SYNOVITIS

Abstract

BackgroundThe cellular and molecular mechanisms driving inflammation and structural remodelling in spondyloarthritis (SpA) remain largely unknown, though the IL-23/IL-17 pathway can contribute to synovial inflammation and radiographic progression.ObjectivesTo investigate the molecular pathways affected by IL-17A blockade (IL-17Ai) with secukinumab in SpA synovitis, and assess if this response is tissue- and/or treatment-specific.MethodsSynovial biopsies were obtained from peripheral SpA patients by needle arthroscopy before and after 12 weeks of IL-17Ai with secukinumab (n=12), and analyzed by RNA-sequencing and qPCR. We performed pathway enrichment analysis of the differentially expressed genes (DEGs) to identify pathways modulated after treatment. We compared the synovial tissue response in patients with psoriatic arthritis (PsA) in our cohort (n=7) with open source gene expression data of skin biopsies of psoriasis patients receiving secukinumab (n=22)[1] and of synovial biopsies of PsA patients receiving IL-12p40/IL-23p40 blockade (n=7)[2].ResultsIL-17Ai significantly modulated the expression of 1255 genes (549 up- and 706 down-regulated, FDR 0.1) in the synovium at week 12 compared to baseline (Figure 1). Genes downregulated upon IL-17Ai were significantly enriched in GO terms and KEGG pathways related to immune and inflammatory responses, including neutrophil and monocyte chemotaxis, TNF-mediated, NF-κB-, Wnt-, and JAK-STAT signalling pathways, and, importantly, bone-remodelling responses, such as osteoblast and osteoclast differentiation. Upregulated genes are enriched in JNK-, MAPK-, Wnt-, and PI3K-Akt signalling and negative regulation of osteoblast differentiation. We validated differential expression of selected genes from several pathways by qPCR, including: IL1B, p=0.027; CXCL6, p=0.020; ADAMTS4, p=0.002; MMP3, p=0.020; and CHRDL2, p= 0.039.Figure 1.Heatmap of differentially expressed genes (DEGs) and pathway enrichment analyses of changes in peripheral SpA synovium 12 weeks after anti-IL-17A treatment (IL-17Ai). A. Hierarchical cluster analysis of the top 100 most significant DEGs (FDR < 0.1) modulated by IL-17Ai separates pre- and post-treated groups. Normalized and scaled log2 gene expression levels are shown. B. Pathway enrichment analysis through DAVID. Enriched (p < 0.05) gene ontology terms from IL-17Ai-induced up- and down-regulated DEGs in peripheral SpA synovium are shown.To assess if this response is tissue- and/or treatment-specific, we compared changes in gene expression by IL-17Ai in PsA synovium versus psoriatic skin, and in the PsA synovium after IL-17Ai versus IL-12p40/IL-23p40 blockade. While many inflammation-related GO terms and KEGG pathways were over-represented in both tissues and treatments, NF-κB-, JAK-STAT-, and PI3K-Akt-signaling were enriched in DEGs in both skin and synovium after IL-17Ai, whereas JNK cascade, IL-17 signalling pathway and Th17 cell differentiation were overrepresented in DEGs after IL-17Ai in the synovium specifically. Remarkably, IL-17Ai, but not IL-12p40/IL-23p40 blockade, modulated multiple bone-remodelling related pathways. Also, IL-17Ai modulated ossification and collagen catabolic process terms in PsA synovium and psoriatic skin in the opposite direction: these terms were over-represented in downregulated genes in synovium, but in upregulated genes in skin. Accordingly, genes upregulated after IL-17Ai were enriched in negative regulation of osteoblast differentiation in the synovium, but in positive regulation of osteoblast differentiation in the skin.ConclusionThese first in vivo human data provide molecular confirmation of previously reported animal data[3] that demonstrated down-modulation of disease-relevant immune and stromal pathways in the synovium in response to IL-17Ai.