| BackgroundOsteoarthritis is the most prevalent disorder of the musculoskela system。Osteoarthritis leads eventually to the complete destruction and loss of articular cartilage.The disease process leads to limitation of joint movement,joint deformity, tenderness,inflammation,and severe pain.Currently,most people of the age of 65 years have some osteoarthritis.Currently there is no treatment available to stop or slow down the progression of the disease.The only treatment is pain medication to relieve the pain and,eventually,total joint replacement surgery.Even though total joint replacement surgery is relatively successful,the lifespan of artificial joints is limited,and here are still significant problems with implant loosening and failure.Therefore,a better understanding of the cellular and molecular mechanisms involved in the progression of osteoarthritis is of great importance,changes of cellular phenotype in osteoarthritis could be the possible reason for tissue failureo So maintaining the articular chondrocyte phenotype and preventing these cells from undergoing hypertrophic and terminal differentiation might provide novel therapeutic targets to prevent onset or progression of osteoarthritis。ObjectivesThe objective of this study is to investigate whether c-maf is expressed in OA cartilage,and study the c-maf transcriptional role for mmp-13。Further studies were undertaken to validate the differential expression status and to understand the impacts of the upregulation of c-maf on chondrocyte phenotype modulation.MethodNormal articular cartilage(NC)was obtained from the femoral condyle or head of 10 patients that was diagnosis with uncurable severe leg trauma or femoral neck fracture that had performed amputation or half/total hip replacement.Osteoarthritic cartilage was obtained from10 patients that was diagnosis with OA in the knee and had undergo a total knee replacement.Outbridge classification system was used to categorize cartilage samples from OA condyles into Outbridge classification l(OA1)and normal cartilage into Outbridge classification 0 control(NC)。RNA in situ hybridization was subsequentially carried out to observe the distribution difference of c-maf gene expression in normal and OA cartilage.The differentially expression profile of c-maf between normal and OA chondrocytes,was confirmed with real-time RT-PCR technique.SiRNA interference was subsequentially performed to knock-down the mRNA expression level of c-maf to mimic c-maf downregulation in osteoarthritic chondrocytes.After c-maf knock-down,the expression level of mmp-13 ALP,Collagen X m RNA and protein were compared with that before c-maf knock-down.chromatin immunoprecipitation(ChIP)analysis using an anti-c-Maf antibody was performed to examine whether the induction of mmp-13 expression by c-Maf is a direct interaction with mmp-13 gene in vivo。Resutlsc-maf was upregulated in osteoarthritic cartilage,The distribution of a specific c-maf mRNA signal was limited to the superficial,particularly in proliferating"chondrocyte cluster".But in normal cartilage,almost no positive-c-maf cells were found.By gene suppression with RNAi technology,we could show that c-maf downregulation leads to a reduced expression of MMP13,ALP,Collagen X.Chromatin immunoprecipitation assays reveal that c-maf binds to the MMP-13 gene promoter to a region of the MMP-13 promoter containing the AP-1 site.Conclusionsoverexpression of c-maf is a common feature in OA,which may provide novel insight into the pathogenesis of this disease as well as new diagnosis tool.C-maf may be potential therapeutic target gene to Prevent chondrocyte from undergoing hypertrophic and terminal differentiation,c-maf bound mmp-13 promotor region, transcriptionally regulated mmp-13 expression via AP-1.This may indicate that c-maf is physiologically involved in hypertrophy and differentiation of chondrocytes and may be responsible,at least in part,for the progression of OA.
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