Gene expression pattern of synovial cells from inflammatory and normal areas of osteoarthritis synovial membrane.

Objective: The aim of this study was to compare the gene expression pattern of synovial cells from inflammatory (I) or normal/reactive (N/R) areas of a synovial membrane harvested from the same osteoarthritis (OA) patient. Methods: Synovial tissues were obtained from 12 knee OA patients at the time of total knee replacement. The inflammatory status of the synovial membrane was characterized according to macroscopic criteria and sorted as N/R and I. Biopsies were cultured separately for 7 days. Microarray gene expression profiling between N/R and I areas was performed. Western blot and immunohistochemistry confirmed the identified genes that were differentially expressed. Results: 896 differentially expressed genes between N/R and I zones were identified. The key pathways were related to inflammation, cartilage metabolism, Wnt signaling and angiogenesis. In the inflammatory network, TREM1 and S100A9 were strongly up-regulated. MMP-3 and -9, cathepsin H and S were significantly up-regulated in the cartilage catabolism pathway, whereas the most up-regulated anabolism enzyme was HAS1. Wnt-5A and LRP5 were up-regulated whereas FZD2 and DKK3 were down-regulated in the Wnt signaling. Finally, STC1, a protein involved in angiogenesis was identified as the most up-regulated gene in I zones compared to N/R zones. Conclusion: This study is the first to identify different expression pattern between two areas of the synovial membrane in the same patient. These differences concern several key pathways involved in OA pathogenesis. This analysis also provides information regarding new genes and proteins as potential targets for the future therapeutic. (c) 2013 American College of Rheumatology.