Pos0425 single-cell rna sequencing of synovial tissue-derived myeloid cells in psoriatic arthritis patients across disease phases

Background Single cell technologies (scRNAseq) are increasingly applied in rheumatology to identify key cellular phenotypes that drive disease pathogenesis, enabling to deconvolute cellular heterogeneity within tissues. Objectives To investigate ST heterogeneity in terms of myeloid cells enrichment and distribution across different disease phases on ST samples obtained from US-guided biopsies in a bio-samples dataset of patients with Psoriatic Arthritis (PsA). Methods 17 patients fulfilling the CASPAR criteria [1] for PsA underwent US-guided ST biopsy and were included. At baseline, patients were categorized based on their disease phase: n=4 naïve to DMARDs; n=3 resistant to c-DMARDs; n=5 resistant to b-DMARDs; n=2 Difficult to treat and n=3 in sustained clinical and US remission or in low disease activity (LDA) state. All ST specimens were processed for phenotyping and sorting. Alive cells were sorted and loaded onto a Chromium Controller (10x Genomics) for single-cell partitioning, followed by library preparation according to the Chromium Next GEM Single Cell 3′ Reagent Kits v3.1 (Dual Index) protocol. Single-cell libraries were sequenced on the Illumina HiSeq 4000 system to a minimum depth of 20,000 reads per cell. Results After standard data processing and quality control procedures, we obtained transcriptomic profiles for 16701 synovial tissue-derived cells. For analysis of ST myeloid compartment only, 10194 cells were computationally isolated with the subset function from other cell types based on expression of CD14,MARCO,LYZ,CD11b and CD64. We identified 10 different myeloid subclusters from the scRNA-seq profiles using SCTransform integration: 2 clusters of lining layer and 8 sublining layer macrophage named after main differentially expressed (DE) genes (adjusted P < 0.05 by Bonferroni correction and multiple test correction, multiplied by number of tests) and according to the nomenclature established in Alivernini et al 20202. Each cell type group is present across all disease conditions but differences in relative proportions were detected.Specifically, ST of patients with active PsA resistant to pharmacological treatment was significantly enriched in sublining MerTKnegSPP1pos macrophages. In addition, we observed pro-inflammatory changes in lining layer TREM2pos STMs as compared to patients who achieved Remission/LDA status(p<0.001 for both). Conclusion MerTKnegSPP1pos STM macrophage may contribute to synovial pathology of PsA resistant to pharmacological treatment. References [1]Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P, Mielants H; CASPAR Study Group. Classification criteria for psoriatic arthritis: development of new criteria from a large international study. Arthritis Rheum. 2006 Aug;54(8):2665-73. doi: 10.1002/art.21972. PMID: 16871531. Acknowledgements: NIL. Disclosure of Interests None Declared.