| Objective: To explore the effect of extracellular signal regulated kinase (ERK) inhibitor U0126 on autophagy at the early stage of osteoarthritis in rabbits. Methods: We randomly and equally assigned 24 male rabbits into control group, OA group and OA+U0126 group. In control group rabbits were not given any treatments; in OA group and OA+U0126 group, rabbits were treated with intra articular injection of papain into the knees for 3 days. Then we conducted intra articular injection of U0126 into the rabbits in OA+U0126 group after 7 days. Fifteen days later, all rabbits were sacrificed for general observation of the knees. Medial condyle cartilages were excised for histological observation and Western blotting. Semiquantitative analysis of glycosaminoglycan (GAG) was performed according to toluidine blue staining. The OARSI scoring system was introduced to assess the severity and extent of OA by HE staining and Safranin O and Fast green staining. We also analyzed the levels of phosphorylated ERK (P-ERK), matrix metalloproteinase 3 (MMP3), UNC-51 like kinase 1 (ULK1), autophagy related protein Beclin1 and LC3II/I by Western blotting. Results: The average weights of rabbits in each group before the study and at the execution had no significant difference. Compared to the control group whose cartilages showed a thin, light, hardened and smooth surface without fissures, proliferation and edema in synovium or exudation of joint fluid, OA+ U0126 group exhibited a slight dark and thicken surface with an increase of joint fluid. Representative OA changes could be seen in OA group, which was characterized by thick and tough cartilage surface, cell disorientation and clustering tendency, as well as a loss of dying of matrix and proliferation of chondrocytes. However, these changes were attenuated in OA+U0126 group compared to OA group. Contents of GAG in OA group and OA+U0126 group were significantly lower than in the control group (P＜0.05), and GAG content in OA+U0126 group was significantly higher than in OA group (P<0.01). OARSI scores in OA group and OA+U0126 group were significantly higher than in the control group (P<0.05), and those in OA+U0126 group were significantly lower than in OA group (P<0.01). Compared to the control group, levels of MMP3 and P-ERK were increased, while LC3II/I, ULK1 and Beclin1 were decreased in OA group and OA+U0126 group (P<0.05). In contrast to OA group, OA+U0126 group had a lower level of MMP3 and P-ERK and a higher level of LC3II/I, ULK1 and Beclin1 (P<0.05). Conclusions: Our study demonstrated that U0126, an ERK inhibitor, could relieve the OA process by reducing MMP3 and promoting autophagy. |
