Background Synovial inflammation plays a key role in the pathophysiology process of osteoarthritis (OA). We have previously compared the gene expression pattern of synovial cells isolated from inflammatory (I) or normal/reactive (N/R) areas of a synovial membrane harvested from the same OA patient. We identified a large number of mediators belonging to key pathways involved in OA pathogenesis.
Objectives To validate different potential new targets for the diagnosis and/or the treatment OA.
Methods Synovial cells (SC) were isolated from synovial biopsies from OA patients undergoing knee replacement. SC from N/R and I areas were cultured separately for a period of 7 days. Microarray gene expression profiling between N/R and I areas was performed. The biological relevance of regulated genes was analyzed with Ingenuity Pathways Analysis. Western blot and immunohistochemistry confirmed the most differentially expressed genes in the key pathways.
Results 896 genes differentially expressed in N/R and I areas were identified. The key pathways were related to inflammation, cartilage metabolism, Wnt signaling and angiogenesis. In the inflammatory gene pattern, the triggering receptor expressed on myeloid cells-1 (TREM1) and the alarmin S100 calcium binding protein A9 (S100A9) were strongly upregulated. We validated the production of these proteins in OA synovial biopsies by Western blot. TREM1 and S100A9 were increased in I compared to N/R synovial cells culture. S100A9 was observed in the perivascular area and in sublining cells in I synovial biopsies, but not in N/R biopsies. An increased staining was also observed in the intima lining layer of I when compared to N/R biopsies. The most upregulated anabolism enzyme in I synovial biopsies was the hyaluronan synthase-1 (HAS1). Using immunohistochemistry, we observed in I areas an increase of the HAS1-positive cells mainly in the intima lining. We also studied the protein production of the wingless-type MMTV integration site family, member 5A (Wnt-5A), the most upregulated intermediate of Wnt signaling pathway. The protein level was increased in I compared to N/R areas. Finally, in the angiogenesis pathway, one the most up-regulated gene was the stanniocalcin 1 (STC1). A significant increase of STC1 production was observed in I areas compared to N/R areas by Western blot. This result was also supported by the immunohistochemical analysis. In I area, the staining for STC1 was more intense in perivascular and sublining cells.
Conclusions Synovial membrane inflammation is a key target for OA treatments. In this work, we have identified proteins involved in the synovitis pathways like angiogenesis, cells infiltration and matrix remodeling. These proteins could be targeted by drugs and used as companion biomarkers for evaluating their efficacy. Although qualitative, our results could also yield to the identification of markers of the disease. This investigation has to be further pursued.
Disclosure of Interest C. Lambert: None Declared, J.-E. Dubuc: None Declared, E. Montell Employee of: BIOIBÉRICA, S.A, Barcelona, Spain; Pre-Clinical R&D Manager, J. Vergès Employee of: BIOIBÉRICA, S.A, Barcelona, Spain; Medical Director, C. Munaut: None Declared, A. Noël: None Declared, Y. Henrotin Grant/research support from: This study was supported by a grant from BIOIBÉRICA, S.A, Barcelona, Spain