Disruption Of GGPPS In Chondrocytes Causes Accelerated Progression Of Osteoarthritis Under Mechanical Stress And During Ageing In Mice

Objective:osteoarthritis(OA)is a very common degenerative disease of articular cartilage and intolerable pain is one of the main causes of disability among the elderly patients.An increasing number of researchers found that the intermediate products of protein modification and isoprene mevalonate pathway played an pivotal role in regulating the hypertrophic differentiation and the metabolism of chondrocytes.Our hypothesis is that GGPPS,which is a critical enzyme in the process of protein prenylation,is linked to the development of OA.This study is aimed to explore its regulatory role in the pathogenesis of osteoarthritis.Methods and Results:We performed three studies to determine the role of GGPPS in pathogenesis of osteoarthritis.Firstly,we verified that GGPPS protein expression and OA have a significantly strong correlation.The knee cartilage specimen were obtained from primary OA patients undergoing total knee arthroplasty(TKA)and healthy donors.By performing immunohistochemistry staining,we detected the expression pattern of GGPPS in OA cartilage and normal cartilage.And we found that the expression level of GGPPS in OA patients were significantly lower than normal controls.We also repeated this test on OA mice andWT mice.Quantitative analysis of GGPPS indicated that cartilage of OA mice have a significantly reduced GGPPS expression.Expression of GGPPS in aging mice is also reduced when comparing to young mice.All the evidence suggesting that GGPPS may exert a protective role during long-term activities.Secondly,we used GGPPS conditional knockdown mice to explore the direct effect of GGPPS on OA in an animal model.DDM surgery was performed on 8 week-old mice.GGPPS cKO mice and littermate control mice were killed after 8 weeks and 10 weeks post DMM surgery respectively and joints were stained with Safranin O and toluidine blue.OARSI scores demonstrated that GGPPS cKO group displayed a more sever cartilage damage and joint degeneration at 8 and 10 weeks following surgery.This is the first time that we confirmed that disruption of GGPPS aggravates OA progression under mechanical stress.Since ageing is another important reason for OA,we explored the effects after GGPPS was knockdown during ageing.We stained joint sections with toluidine blue using 4 months and 10 month-old mice and carried out a proteoglycan loss score.We found that cartilage matrix proteoglycan of cKO mice was almost completely lost,and it is in a time dependently manner.To assess the potential roles of GGPPS,GGPPS expression in human chondrosarcoma cells(SW1353)was down-regulated by transfecting small interference RNA(siRNA).Cells were treated with IL-1β and the expressions of several matrix-degrading enzymes were examined by using quantitative PCR.We found MMP-13、ADAMTS5 or other matrix-degrading enzymes were significantly upregulated.TUNEL staining indicated that GGPPS cKO group exhibited more chondrocyte apoptosis following 2 weeks after surgery.And the progress of OA may be associated with increased cell apoptosis.Conclusion:In this study,we found that the reduced expression of GGPPS has a correlationship with the development of OA.Disruption of GGPPS can lead to a more sever joint damage in a DMM OA mice and can develop a spontaneous OA phenotype.The cause of this phenomenon may be related to early chondrocyte apoptosis and the imbalance between anabolic and catabolic metabolism in chondrocytes.Our study indicated that GGPPS may serve as a new potential drug target for the treatment of OA.