Effects of chondroitin sulfate on the gene expression profile in IL-1β stimulated synovial fibroblast cells cultures

Purpose: Chondroitin sulfate (CS) is one the most used molecules in the management of OA. In this study, we performed a microarray analysis and identified a differential expression profile between control and IL-1β stimulated synovial fibroblast cells cultures. In a second step, we investigated the effects of CS on this gene expression profile.
Methods: OA synovial specimens were obtained from 12 patients undergoing knee replacement. At the surgery time, the synovial membrane was dissected. Synovial fibroblast cells (SFC) were enzymatically isolated and used after four passages (P4). SFC were pre-treated 1 hour with highly purified bovine CS (200 µg/ml, Bioibérica S.A., Barcelona, Spain) before treatment with IL-1β (1 ng/ml) for 24 hours. Total RNA was extracted using the RNeasy Mini Kit. RNA purity and quality were evaluated using the Experion RNA StdSens Analysis kit (Bio-rad Laboratories). Gene expression profiling was performed using Illumina’s multi-sample format Human HT-12 BeadChip (Illumina Inc.). Differential analysis was performed with the BRB array tools software. Class comparison test between control (Ctl) and interleukin (IL)-1β conditions, Ctl and Ctl/CS and IL-1β and IL-1β/CS conditions was based on paired t-test where Ctl and IL-1β, Ctl and Ctl/CS and IL-1β and IL-1β/CS were paired for each patient. The biological relevance of up- and down-regulated genes was analyses with Ingenuity Pathways Analysis (Ingenuity® Systems). Probes with a p-value below 0.001 were chosen and classified as up- or down-regulated ones.
Results: 3308 genes were identified as differentially expressed genes between Ctl and IL-1β conditions. We observed a differential profile of expression of major pathways involved in OA pathogenesis. The key identified pathways were related to inflammation, complement cascade, angiogenesis, cartilage catabolism and anabolism and Wnt signaling. In the inflammatory network, the most upregulated cytokines were IL-8 and IL-6 with a fold change of 156.25 and 58.8 respectively. We also identified several chemokines, enzymes and metallothioneins (MTs). Complement factor B (CFB) and complement component 3 (C3) are two factors upregulated in the inflammatory complement cascade. We also identified some genes implicated in the angiogenesis pathway. The most upregulated was Stanniocalcin 1 (STC1) with a fold change of 9.09. The differential expression of intermediates involved in both cartilage anabolism and catabolism was revealed by the IL-1β stimulation, showing an imbalance in favour of catabolism. MMP-3 was largely upregulated (fold change of 62.5). Wnt 5A and low density lipoprotein receptor-related protein (LRP8) were significantly upregulated while frizzled homolog 2 (FZD2) and dickkopf homolog 3 (DKK3) were downregulated in the Wnt signaling pathway. We next performed a class comparison test between Ctl and Ctl/CS in one hand and IL-1β and IL-1β/CS on the other hand. 660 genes were identified as differentially expressed between Ctl and Ctl/CS conditions while 241 genes were identified between IL-1β and IL-1β/CS. Among them, our attention was focused on two genes upregulated in the presence of CS: lysyl oxidase-like 4 (LOXL4) and claudin 11 (CDLN11), two genes that negatively regulate cell invasion.
Conclusions: We here evidenced in synovial fibroblast cells the modulation of gene expression following IL-1β stimulation. We also demonstrated the modulatory effects of CS on gene expression and isolated several CS-modulated genes of interest such as LOXL4 and CDLN11, which could constitute new mechanisms of action of the molecule and contribute to explain the symptomatic efficacy of CS in the treatment of OA.