| Osteoarthritis (OA) is the most common joint disorder affecting the elderly throughout the world. It is a leading cause of disability and has a formidable societal and public health impact. Osteoarthritis is characterized by the degeneration of the articular cartilage, the formation of osteophytosis and the narrowness of joint space. A great deal of study has focused on osteoarthritis recent years, however, the mechanism of OA developing still not clear. It is generally accepted that osteoarthritis is the result of imbalance of increased cartilage synthesis and degeneration, favoring degeneration, which leads to cartilage softening, fibrillation, ulceration, and finally to cartilage loss. The present study aims at manifesting that there is apparent increased cartilage synthesis responding to cartilage over degeneration, but the responsive repair is disorder. The hypothesis is as follow. (1) the responsive proliferation of chondrocytes might be the reason for abnormal cartilage fibrosis and osteophytosis; (2) the effect of over degeneration of cartilage and non-effective cartilage self-repair will finally lead to osteoarthritis.The results show that: (1) compared with healthy control group, percentage of G2/M phase chondrocytes increased in osteoarthritis model group, meanwhile the growth rate was higher in this group, suggesting that responsive proliferation is obvious in osteoarthritis cartilage chondrocytes. (2) collagen type II reduced and type I mRNA increased obviously, suggesting that proliferated cells tend to be to fibro-cartilage cell; at the same time collagen type X mRNA increased , suggesting that cartilage ossification appeared in osteoarthritis chondrocoytes. (3) Matrix metalloproteinases (MMP), such as MMP-1, MMP-3 and MMP-13 expression increased. Although there was increase in TIMP-1 mRNA, the change was less than MMPs. The imbalance of MMPs and TIMPs suggests that the cartilage catabolism enhanced (4) early phase apoptotic cells increased, and inflammatory cytokines IL-1βand TNF-αcontent increased, suggesting that the cell death may increase. Based on the results, osteoarthritis chondrocytes were treated with different concentration of velvet polypeptide (VAP; 6.25, 12.5, 25ug/mL)c the results were as follows: (1) cell cycle and growth rate changed little, suggesting that VAP has little effect on the proliferation of OA chondrocytes; (2) collagen type I , X mRNA decreased, type II increased, suggesting that VAP may control chondrocyte phenotype and inhibit cartilage cell differentiation or anti-differentiation; (3) MMP-1 and MMP-13 mRNA decreased , MMP-3 and TIMP-1 mRNA did not change significantly, suggesting that VAP may inhibit the over degradation of extracellular matrix by regulating MMP activity; (4) the content of IL-1βand TNF-αdecreased, and the early phase apoptotic cells decreased, suggesting that VAP can protect cartilage chondrocytes against inflammatory cytokines. The results above suggest that VAP may protect articular cartilage by way of keeping chondrocyte phonotype, inhibiting extracellular matrix over degeneration and chondrocyte apoptosis. Finally, we did some elementary studies on the mechanism of VAP protection effect from anti-oxidative stress aspect. The results showed that VAP can inhibit the elevation of intracellular ROS, reduce NO content, and improve SOD and GSH-Px activity. Besides, in Comet assay experiment. VAP can decrease the percentage of smearing cells. The result of Western Blotting experiment shows that VAP can inhibit the activation of NF-kB. These results suggest that the VAP may protect cartilage by its antioxidant effect. In a word, this study discusses the mechanism of OA from disorder proliferation of OA chondrocyte. This study can be useful for the new drug development and the cure of OA in the future.
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