| Objective To explore the dynamic expression of synovium in pathological Characters and the role of hypoxia-inducible factor-1α(HIF-1α) and vascular endothelial growth factor(VEGF) in the pathogenesis of rheumatoid arthritis(RA).Methods To establish the bovine collagenⅡ(CⅡ)-induced arthritis (CIA) rat model, and observe the histopathological features of the synovial membrane. To selecte 50 SD rats, 8-weeks old, randomly divided into five groups with random allocation: one control group (10 SD rats) and four model groups (40 SD rats). The model groups were intradermally sensitized under anesthesia with 0.5ml bovine type II collagen, emulsified in cold Freund's incomplete adjuvant. The normal groups were intradermally with 0.9% NaCl in the same way. Seven days later, the rats received an intradermal booster injection of half the volume used for sensitization. Through these CIA rats, we made a further study on the joint inflammation and pathological change. The arthritis activity, pathological changes and expression of HIF-1αand VEGF on synovium on days 21, 28, 35, 42 of ankle joints were observed through HE and immunohistochemistry staining. The correlations of HIF-1αand VEGF expression with the CIA arthritis activity indexes and pathological scores were analyzed.Results In the control group, there was no joint swelling in the ankles of the rats, with the paw swelling induced in the CIA groups were manifest higher comparing with normal rats from 12th day and reached peak value on day 21 to 28. The paw swelling was monitored up to the time that the animals were killed (42 days after immunization). The radiographic findings of ankle joint shows that:①The control group hasn't soft-tissue swelling, articular bone erosions in the tarsal and metatarsal. The structures were integrated, and the toe joint space was clear.②On day 21 after immunization, the soft-tissue swelling, articular bone erosions in the tarsal and metatarsal in the CIA groups.③On the day 42, skeletal structure was disordered, joint space blured, bone resorption and new bone formation, chronicity rodent arthritis, which suggested that chronic erosive arthritis occurred. In the control groups, the synovial lining cells were one to three layers without infiltration, vascular proliferation, and the articular cartilage layer was much thicker, the surface was smooth and the joint space was normal. While in the CIA groups, the proliferation of synovial lining cells resulted in more than ten layers, the dropsy of joints and infiltrate of lymphocytes manifest higher than normal rats at the 21 day after injection. From day 42 after immunization, there is diffuse infiltration of macrophages in the sublining regions, synovitis, pannus formation, cartilage and bone erosions and new bone formation. HIF-1αand VEGF protein were expessed in both the lining and sublining area of synovium in CIA, both of them were positive correlation obviously, the correlation coefficient was 0.75(P<0.01). The results of immunohischemistry staining showed that the expression of HIF-1αand VEGF in synovial membrane was strongest on the 21th day, and then declined gradually with the prolonged disease course. The expression of HIF-1αprotein correlated significantly with total pathological score, synovial hyperplasia score and angiogenesis scorer, and the correlation coefficient was 0.4, 0.48 and 0.5(P<0.05), but not with inflammation score which the correlation coefficient was 0.3(P<0.05).Conclusion CollagenⅡ-induced arthritis (CIA) animal model has been successfully established with typeⅡcollagne. The expressions of HIF-1αand VEGF in RA synovial tissues are positively correlated to the inflammation severity. This suggests that HIF-1αand VEGF play a very important role in the hyperplasia of RA synovial tissue and angiogenesis. This research contributes to the further understanding the roles of HIF-1αand VEGF in the pathogenesis of RA, which will provide new ideas for the clinical treatment of RA.
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