Osteoblasts Regulate The Expression Of ADAMTs And MMPs In Chondrocytes Through ERK Signaling Pathway

Objective: Degradative enzymes such as matrix metalloproteinase(MMP)and disintegrin metalloproteinase with platelet thrombin-sensitive protein-like motif(ADAMTS)play a key role in the development of osteoarthritis.To investigate the effects of OA subchondral osteoblasts on the expression of ADAMTS4,ADAMTS5,MMP-3,MMP-9 and MMP-13 in chondrocytes and the regulation of mitogen-activated protein kinase(MAPK)signaling pathway.Methods:Rat knee osteoarthritis model was constructed by cutting the anterior cruciate ligament of the knee joints,and normal rat articular cartilage chondrocytes(N-ACC),OA rat articular cartilage chondrocytes(O-ACC),normal subchondral bone osteoblasts(N-SBO)and OA subchondral bone osteoblasts(O-SBO)were isolated and extracted.Chondrocytes were identified by immunofluorescence of collagen II and toluidine blue staining,and osteoblasts were identified by type I collagen immunofluorescence,alkaline phosphatase(ALP)and alizarin red staining.Gene expression of type I collagen,type II collagen and aggrecan in normal chondrocytes and OA chondrocytes,gene expression of osteoblast ALP and osteocalcin(OCN)were detected by RT-PCR to identificate the two chondrocytes and the two osteoblast phenotype.Constructing N-ACC group,O-ACC group,N-ACC+N-SBO group,N-ACC+O-SBO group,O-ACC+N-SBO group,O-ACC+O-SBO group,I+N-ACC+O-SBO group and I+O-ACC+O-SBO group cell culture,the expression of ERK,ADAMTS4,ADAMTS5,MMP-3,MMP-9 and MMP-13 genes in chondrocytes cultured for 0h,24 h,48h and 72 h was detected by RT-PCR.The protein expressions of pERK,ADAMTS4,ADAMTS5,MMP-3,MMP-9 and MMP-13 were detected by Western blot.Results: 1.The osteoarthritis model in rat was constructed successfully,and the knee joint operated was deformed.The X-ray showed that the knee joint space of the affected limb became narrow.2.Toluidine blue staining and type II collagen staining of the extracted chondrocytes were positive.The results of RT-PCR of type II collagen and aggrecan gene in OA and normal chondrocytes suggest that the relative expression of COL2 in OA articular chondrocytes(0.24±0.07)is significantly lower than that in normal cartilage(0.61±0.07)(P<0.05).The relative expression of AGG(0.37±0.16)in OA chondrocytes was significantly lower than that of normal chondrocytes AGG(1.30±0.25)(P<0.05).The expression of COL1 was very low,and there was not statistically significant.3.Type I collagen,ALP and OCN staining were positive in the extracted osteoblasts.The results of RT-PCR of osteoblast ALP and OCN gene indicated that Gene expression of ALP(12.30±1.17)and OCN(20.47±4.19)was up-regulated when compared with the relative expression of ALP(4.66±0.71)(P<0.05)and OCN(12.17±2.76)(P<0.05)in normal osteoblasts,indicating that osteoblasts of OA have greater osteogenic potential than normal osteoblasts.4..The expressions of ADAMTS4,ADAMTS5,MMP-3,MMP-9 and MMP-13 genes and proteins in OA chondrocytes or normal chondrocytes were basically unchanged when they were co-cultured with normal osteoblasts.Indirect co-culture of OA osteoblasts and chondrocytes could promote the expression of ADAMTS4,ADAMTS5,MMP-3,MMP-9 and MMP-13 genes and proteins in chondrocytes.Overexpression of ADAMTS and MMP in co-culture systems can be reversed by MAPK-ERK inhibitors.Conclusion: 1.OA subchondral bone osteoblasts can promote the overexpression of ADAMTS and MMPs in chondrocytes.2.ERK signaling pathway may be involved in the regulation of the effect of subchondral bone osteoblasts on chondrocytes.