The Mechanism Of SDF-1α/CXCR4 Signal Axis In Regulation Of Subchondral Bone Remodeling And Cartilage Degeneration

Objective1.To investigate the effect of exogenous SDF-1α on differentiation and maturation of bone marrow mesenchymal stem cells(MSCs)and chondrocytes in vitro and explore their mechanism.2.To obeserve the effect of SDF-1α blocker AMD3100 on the pathological changes of osteoarthritis in post-traumatic osteoarthritis(PTOA)model mice and to explore the mechanism of SDF-1α/CXCR4 signal axis in subchondral bone changes and cartilage degeneration.Methods1.In vitro,MSCs were induced to differentiate into chondrocytes under cartilage induction medium and the expression of CXCR4 in MSCs was verified.In addition,MSCs were treated with SDF-la(concentration of 50ng/mL and 100ng/mL),detected by Alkaline phosphatase(ALP)staining,Alcian blue staining and detection of cartilage differentiation related proteins in the differentiation and maturation of chondrocytes,and use primary chondrocytes for further validation.2.In the current study,we used a destabilisation OA animal model to investigate the effects of SDF-1α/CXCR4 signalling in the tibial subchondral bone and the OA pathological process.Post-traumatic osteoarthritis(PTOA)mice models were prepared by transecting the anterior cruciate ligament(ACLT),or a sham surgery was performed,in a total of 30 mice.Mice were treated with PBS or AMD3100(an inhibitor of CXCR4)and sacrificed at 30 days post ACLT or sham surgery.Tibial subchondral bone status was quantified by micro-computed tomography(μCT).Knee-joint histology was analysed to examine the articular cartilage and joint degeneration.The levels of SDF-1α and collagen typeⅠ c-telopeptide fragments(CTX-I)were quantified by ELISA.Bone marrow mononuclear cells(BMMC)were used to clarify the effects of SDF-1α on osteoclast formation and activity in vivo.Results1.In vitro,we found that SDF-1α promoted the expression of CollagenX and MMP13 in MSCs cartilage differentiation under the condition of cartilage differentiation induced culture,but it had no effect on the expression of CollagenⅡ and Aggrecan and the formation of cartilage matrix in early cartilage differentiation.it shown similar effect on primary chondrocytes.At the same time,we detected that SDF-1α promoted the activation of Wnt/β-catenin pathway in MSCs.After inhibiting Wnt/β-catenin,we found that SDF-1α disappeared to MSCs cartilage differentiation.2.μCT analysis revealed significant loss of trabecular bone from tibial subchondral bone post-ACLT,which was effectively prevented by AMD3100.AMD3100 could partially prevent bone loss and articular cartilage degeneration.Serum biomarkers revealed an increase in SDF-1α and bone resorption,which were also reduced by AMD3100.SDF-1α can promote osteoclast formation and the expression of tartrate resistant acid phosphatase(TRAP),cathepsin K(CK),and matrix metalloproteinase(MMP)-9 in osteoclasts by activating the MAPK pathway,including ERK and p38,but not JNK.Conclusion1.Our results demonstrate that SDF-la promotes cartilage maturation and transformation into hypertrophic cartilage,and the effect is mediated by activation of the Wnt/P-catenin pathway.2.Our study also shows that SDF-la promotes osteoclast differentiation by activating the MAPK pathway,blocking that SDF-1α inhibits osteoclast formation in vitro and in vivo.AMD3100 is able to prevent loss of trabecular bone in PTOA mice and thus attenuates cartilage degeneration.These results suggest that AMD3100 may be a potential treatment for PTOA.