Influence of cartilage interstitial fluid on the mRNA levels of matrix proteins, cytokines, metalloproteases and their inhibitors in synovial membrane

Articular cartilage and the synovial membrane both ensure the smooth action of synovial joints; however, the influence of chondrocytes on synovial metabolism remains unclear. The secretory activity of chondrocytes is usually studied in cell cultures and may differ from that in intact cartilage. According to McCutchen's theory of 'weeping' joint lubrication, loading of the articular cartilage during motion squeezes the fluid with lubricating properties from the cartilage. The purpose of the study was to obtain cartilage interstitial fluid (CIF) from intact cartilage and to evaluate its influence on gene expression in the synovial membrane cells. CIF was rinsed out from the cartilage of newborn rats at a pressure of three bar. The chondrocytes survived rinsing and grew in culture. Cytokines in CIF were detected using the enzyme-linked immunosorbent assay (ELISA). The influence of CIF and CIF-like cocktail (all cytokines found in CIF) on gene expression in the synovial membrane cells was studied after a 4 h-incubation, by real-time PCR. Data were analyzed using the Wilcoxon matched-pair test or by the Mann‑Whitney U test. CIF contained basic fibroblast growth factor (bFGF), insulin-like growth factor (IGF)‑1, transforming growth factor β1 (TGFβ1), bone morphogenetic protein 7 (BMP7), macrophage (M)-colony-stimulating factor (CSF), granulocyte (G)-CSF and leukemia inhibitory factor (LIF). CIF stimulated the expression of hyaluronan synthase (HAS)1 and 2, lubricin, collagen I, versican, aggrecan, matrix metalloproteinases (MMPs)2 and 3, tissue inhibitors of metalloproteinases (TIMPs) 1-3, interleukin (IL)-6 and TGFβ1, and decreased the expression of tumor necrosis factor (TNF) and IL-1β. Incubation of the synovial membrane with CIF-like cocktail partially imitated the effects of CIF. Analysis of CIF composition may help to characterize the secretory activity of chondrocytes in their natural environment under various physiological and pathological conditions and to understand the interactions between articular cartilage and the synovial membrane.