LAUSR

Background Rheumatoid Arthritis (RA) is a chronic and heterogenous condition characterized by inflammatory involvement of the synovial membrane in multiple joints. Synovial biopsies are used in research setting in order to identify diagnostic and theranostic markers. Many studies have shown a high degree of heterogeneity in histological and transcriptomic profiles between patients. Objectives We wanted to explore histological and transcriptomic profile of synovial biopsies across pairs of joints in the same patients to assess heterogeneity at the individual level. Methods Synovial biopsies were performed simultaneously in one small and one large joint per patient using needle-arthroscopy for the knee and US-guided needle biopsy for the hand or foot. Synovium from individuals with osteoarthritis (OA) were used as control. Paraffine-embedded samples were stained for CD3, CD 20, CD 68 and CD138. Whole-tissue RNA was extracted and hybridized on GeneChip Human Genome U133 Plus 2.0 Array (Affymetrix). The samples were tested for RNA integrity by Bioanalyzer (Agilent). Normalization and statistical analyzes were performed on Genespring. Pathway analysis were performed using DAVID. Results 10 RA patients were included (females: 10/10, ACPA/RF positivity: 8/10, mean age (± SEM): 54.4 (± 4.4) years, mean disease duration (± SEM): 13.3 (± 3.7) years, mean DAS28CRP (± SEM): 5.01 (± 0,34), mean HAQ (± SEM): 1.7 (± 0.28)). Quantification of histological markers did not show differences in population of macrophages, plasmocytes, T and B Cells, across pairs of joints. After correction for multiple comparisons, no transcripts were differentially expressed between large and small joints. Similarly, we did not find any significant difference in the expression of transcripts involved in pathways (TCR-activation and cell-division) specifically overexpressed in RA compared to OA synovial tissue. In order to increase our ability to observe pair-wise differences in gene expression profiles, we studied correlations between transcripts significantly overexpressed in RA compared to OA joints with a fold change > 2 (n = 581) and clinical or biological markers of disease activity (DAS28-CRP, CRP, Physician Global Assessment of disease activity). Similar patterns of correlations indicated that disease activity was not driven by different pathways in small versus large joints. Conclusion This study is an important methodological milestone in the field of synovial biopsies, as it indicates that cellular and molecular alterations occurring in RA synovitis are similar across small and large joints from the same patient. Hence, biopsy of a single joint is representative and can be used to explore pathogenic processes or potential biomarkers in RA. Acknowledgement This work was funded in part by grants from Cap48 (RTBF), Fonds National de la Recherche Scientifique (FNRS, Communauté française de Belgique) and Fondation Saint-Luc. Disclosure of Interests Clément Triaille: None declared, Louise Vansteenkiste: None declared, Laurent Meric de Bellefon: None declared, Adrien Nzeusseu: None declared, Christine Galant: None declared, Patrick Durez Speakers bureau: Bristol-Myers Squibb, Eli Lilly, Sanofi, Celltrion, Bernard Lauwerys: None declared