The Potential Role of Osteopontin in the Pathogenesis of Graves’ Ophthalmopathy

PURPOSE: The aim of this study is to evaluate the expression of osteopontin (OPN) and its relationship with relative cytokines in patients with Graves’ ophthalmopathy (GO), and to observe the effect of OPN on orbital fibroblasts (OFs) proliferation, migration, and the expression of relative cytokines, as well as the signaling pathways involved in its effect. METHODS: The orbital adipose connective tissue was obtained from 24 patients with GO (12 cases of active GO, and 12 cases of inactive GO) and 12 healthy controls. OFs were isolated from orbital tissues obtained from patients with active GO who were undergoing orbital decompression surgery. Quantitative PCR and Western blot were performed to detect RNA and protein expression. The proliferation and cell migration rates of OFs were measured by methylthiazol tetrazolium (MTT) and the cell scratch test. Signaling pathway inhibitors, such as OPN monoclonal antibody 1A12, ERK1/2 inhibitor PD98059, and PI3K inhibitor LY294002, were applied to determine the involved pathways. RESULTS: The mRNA and protein levels of OPN were increased in orbital adipose connective tissue from patients with active GO than those from patients with inactive GO (2.83-fold increase, P < 0.001; 1.91-fold increase, P < 0.05). The OPN mRNA level was positively correlated with CD40 ligand (CD40L) and hyaluronan synthases 2 (HAS2) mRNA in patients with GO. OPN promoted proliferation and migration rate of OFs and induced vascular endothelial growth factor (VEGF) and collagen I mRNA expression, and the effects were inhibited by 1A12 or LY294002. CONCLUSIONS: OPN in orbital adipose connective tissues were significantly increase in active GO, and there were significant correlations of OPN with CD40L and HAS2 mRNA levels in patients with GO. OPN promoted proliferation and migration of OFs and induced VEGF and collagen I mRNA expression in OFs through PI3K/Akt signaling pathway. This suggested a role for OPN in the pathogenesis of GO through the activation of OFs.