Abstract Text: Single-cell synovial-tissue suspensions from Rheumatoid Arthritis(n=41), individuals ‘at risk’ of RA (n=5) and healthy controls(n=11) were obtained through keyhole mini video-arthroscopy. Synovial-tissue macrophage subsets were examined using advanced flow-cytometric analysis, single-cell and bulk RNA-sequencing, metabolic and functional assays.
Multidimensional analysis identifies enrichment of CD206+CD163+ synovial-tissue macrophages co-expressing CD40 in RA compared to healthy synovial-tissue, with CD206+CD163+CD40+ macrophage frequency associated with increased disease activity and treatment response. In contrast, CX3CR1-expressing macrophages enriched in healthy synovium are significantly depleted in RA. Importantly this signature is an early phenomenon, occurring prior to clinical manifestation of disease in individuals ‘at-risk’ of RA. Bulk RNAseq of RA synovial-macrophages identified distinct inflammatory, phagocytic and tissue-resident gene signatures paralleled by bioenergetically stable profiles as indicated by NAD(P)H emission. Functionally CD206+CD163+ RA macrophages are potent producers of pro-inflammatory mediators (reversed by CD40-signalling inhibition) and induce an invasive phenotype in healthy synovial-fibroblasts.
Single-cell transcriptomic profiling of synovial-tissue cells from RA-patients and healthy individuals gave a unique myeloid atlas from health to disease. Nine distinct synovial-tissue macrophage clusters were further classified into four subpopulations: TREM2high, TREM2low, FOLR2high, IL-1Bhigh. IL-1B+CCL20+ and SPP1+MT2A+ which were identified as pro-inflammatory macrophage populations, are enriched in RA compared to healthy synovial-tissue and display heightened CD40 gene expression. Receptor-ligand interactions indicate that these populations interact with stromal/T-cells to induce pro-inflammatory mechanisms.
These findings identify distinct pathogenic populations of synovial-tissue macrophage involved in shaping the immune response in RA. Crucially, inflammatory myeloid signatures are present pre-disease onset representing a unique opportunity for early diagnosis and therapeutic intervention.
