Effects of fibroblast growth factor 4 on the proliferation of fibroblast-like synoviocytes in rheumatoid arthritis

Objective To investigate the expression of fibroblast growth factor 4 (FGF4) in serum of active rheumatoid arthritis (RA) and its role in RA synoviocyte proliferation. Methods The serum level of FGF4 were detected by protein arrays in 20 patients with RA, and 20 age and gender matched healthy controls. FLSs were isolated from RA synovium, and were co-cultured with recombinant human FGF4 (rhFGF4). Cell proliferation was quantified by Cell Counting Kit-8 assay and cell cycle distribution was evaluated by flow-cytometry. The protein levels of cyclin D1, phospho-Akt (p-Akt) and phospho-p38 (p-p38) were measured by western blot. Results The serum expression of FGF4 in RA group was higher than that in control group (P=0.041). After being treated with different concentrations of rhFGF4 (12.5, 25, 50, and 100 ng/ml), RA-FLS showed significant increase in cell proliferation, with different rates of [(121±8)%], [(126±12)%], [(129±12)%], and [(134±14)%] respectively, comparing with that of the controls [(100±0)%, (P12.5=0.049, P25=0.009, P50=0.004, P100=0.001).]. Among them, the percentage of G2/M+S phase cells were [(12.6±3.6)%], [(15.3±4.5)%], [(17.1±5.1)%], [(19.6±4.1)%] respectively, and except the lowest rhFGF4 concentration treatment group of 12.5 ng/ml, G2/M+S phase cells in other groups was significantly increased compared with the controls [(5.4±2.4)%] (P12.5=0.159, P25=0.042, P50=0.018, P100=0.005). And the protein expression of cyclin D1 was up-regulated after being treated with 50 ng/ml and 100 ng/ml rhFGF4 (P50=0.035, P100=0.027). FGF4 transiently increased the expression of p-Akt and p-p38 protein at the concentration of 50 ng/ml. Comparisons of data between groups were performed by independent sample Student's t-test. Statistical significant differences among groups were tested by one-way analysis of variance (ANOVA) or the Kruskal-Wallis test. The Dunnett's t-test was used for multiple comparisons. A P-value of <0.05 was considered statistically significant. Conclusion Our results suggest that FGF4 is highly expressed in the serum of active RA patients. FGF4 may promote the proliferation of RA-FLS via modulating PI3K/Akt and p38-MAPK signaling pathways, which subsequently contributs to synovial hyperplasia. Key words: Arthritis, rheumatoid; Fibroblast growth factor 4; Fibroblast-like synoviocytes; Cell proliferation