OP0094 SPATIAL POSITIONING AND MATRIX PROGRAMS OF SYNOVIAL FIBROBLASTS UNDERPIN IMMUNE CELL ORGANISATION AND SYNOVIAL TISSUE PATHOTYPE

Background Rheumatoid arthritis (RA) is highly heterogenous with distinct cellular and molecular tissue pathotypes that associate disease outcome [1] . The synovial membrane the primary target undergoes significant architectural re-modelling in response to inflammation. While fibroblasts are known shape immune cell compartmentalisation secondary lymphoid organs, by producing sets of chemokines remodelling extracellular matrix (ECM) [2] , mechanisms underlying localisation synovium poorly understood. Objectives To define functional zonation inflamed at single regional level using spatial transcriptomics multiplex imaging. Methods We performed oligonucleotide probe-based spatially resolved on samples obtained minimally invasive, ultrasound guided biopsies patients both rheumatoid osteoarthritis (OA) 10x Visium platform. A total 27 processed sequencing 34170 spot transcriptomes. Each section was composed 1-8 fragments from same donor biopsy sample within each capture area, maximise representation account for sampling variability. Cellular deconvolution transcriptomes reference datasets. Multiplex imaging confirm gene profiles types associated specific patterns. Results identified six niches (or zones) defined expression comprised populations stromal cells. Specific patterns were observed these sub-synovial zones link functions infiltrate recruitment organisation. This pattern maintained across (Fibroid, Lymphocytic) analysis revealed RA formation lymphocytic when compared OA tissue. next areas manually annotating infiltrates (as aggregates) vasculature, based histology. From these, we selected aggregate peri-vascular (Figure 1). have differences between their anatomical location. Peri-vascular related myofibroblast differentiation, ECM deposition modulation (COMP), but also (PLA2G2A), activation (FOS & FOSB), lipid metabolism (APOD), synovium. These display either a TGF-β or NOTCH3 activated [3] program expanded fibroid pauci-Immune) pathotype. Immune interacting (peri-aggregate) contrast, show linked regulation (POSTN), degradation (MMP3) co-ordination recruit cells (SPARC), permit formation. T-cell [4] IFN-γ along IL-1β TNF-α lining layer dominate landscape Conclusion demonstrate cytokine directed fibroblast-immune crosstalk, positional identity, specific, fibroblast programs responsible localising infiltrating defining zonation. data identify novel therapeutically tractable pathways underpin pathogenicity RA. References [1]Lewis et al. Cell Reports 2019;28:2455-2470 [2]Bajénoff M Immunity 2006;25:989–1001 [3]Wei K Nature 2020;582:259-264. [4]Korsunsky I Med (N Y) 2022;3:481-518.e14 Acknowledgements: NIL. Disclosure Interests None Declared.