An original methodology to study the synovial tissue in OA patient

Purpose: Synovial membrane plays a key role in osteoarthritis (OA) pathophysiology, contributing to both patient symptoms and disease progression. Using an original methodology comparing normal/reactive (N/R) and inflammatory (I) synovial membrane areas from the same OA patient, we investigated the crosstalk between inflammation and angiogenesis. We also analyzed the gene expression pattern of synovial cells from these different areas and identified differentially regulated pathways.
Methods: Synovial cells (SC) were isolated from OA synovial specimens obtained from patients undergoing knee replacement. The inflammatory status of the synovial membrane was characterized by the surgeon according the macroscopic criteria including the synovial vascularization, the villi formation and the hypertrophic aspect of the tissue. At the surgery time, the synovial membrane was dissected and the biopsies from N/R and I areas cultured separately for a period of 7 days. Inflammatory and angiogenic mediators were evaluated in the culture supernatant by immunoassays (ELISA) or visualized by immunohistochemistry. Gene expression profiling between N/R and I areas was performed using Illumina’s multi-sample format human HT-12 BeadChip (Illumina Inc.).
Results: Immunohistochemistry showed an increase of lymphocyte infiltration, vascular density and VEGF expression in I compared N/R synovial biopsies. Synovial cells from I areas produced more IL-6, IL-8 and VEGF but less TSP-1 than cells isolated from N/R synovial biopsies. By microarray analysis, 896 differentially expressed genes between N/R and I zones were identified. Among them, 576 genes were upregulated (I/NR > 1.5) and 320 downregulated (I/NR  0.75). A significant number of the top ranking differentially expressed genes were identified as inflammatory, cartilage metabolism, Wnt or angiogenic pathways.
Conclusion: In this study, we have demonstrated the pro-inflammatory and pro-angiogeneic status of I area of the OA synovial membrane. Using a unique culture system, this study is the first to identify different expression pattern between two areas of the synovial membrane in the same OA patient. This original methodology could be further used to go deeper into the knowledge of the role of synovial membrane in OA.
Possibilities for valorization:
This analysis provided interesting information regarding new potent intermediates that could be potential new targets for the diagnosis or treatment of OA.