Mechanical Stress Regulates Subchondral Bone Remodeling In Early OA Via Activating Mig6-EGFR Pathway In Osteoblasts

ObjectiveOsteoarthritis(OA)is one of the most common degenerative joint disease.The pathogenesis of OA is still unknown,and there is no effective drug to delay the process of the disease.Therefore,it is very urgent to explore the mechanism of osteoarthritis and find the corresponding drug targets.The regulation of subchondral bone remodeling is an important direction for the research of OA drug targets.Combined with the early results of our group,this study focuses on the EGFR signaling pathway,which regulates bone development and metabolism,to clarify the mechanism of EGFR signaling pathway regulating subchondral bone remodeling in osteoarthritis,and to provide a new idea for finding OA drug targets.MethodWestern blot and immunohistochemistry were used to verify the activation of Mig6-EGFR signal in OA subchondral bone in vivo.The growth and development signs of the mice with Mig6 deletion were recorded.Micro-CT,Trap staining and immunohistochemical staining were used to evaluate the effects of EGFR activation by Mig6 deletion on the functions of osteoclasts and osteoblasts in the subchondral bone of the knee.To evaluate the effect of Mig6 knockout EGFR activation on subchondral bone remodeling and cartilage degeneration,a DMM-OA model was constructed in the knee joint of transgenic mice.Multiple fluorescence immunohistochemical staining verified that Mig6-EGFR signaling axis activation in osteoblasts affected osteoclasts by affecting the secretion of Rankl/OPG.A mechanical stress loading model of osteoblasts was constructed in vitro,and Transwell chamber was used to simulate the interaction between osteoblasts and osteoclasts.Through co-culture of osteoblasts and osteoclasts,it was proved that Mig6-EGFR signal axis of osteoblasts could activate osteoclasts under mechanical stress.Alizarin red staining and ALP staining confirmed that Mig6-EGFR signaling axis had the function of regulating osteoblast differentiation.ResultsMig6-EGFR signaling axis is over-activated in osteoblasts of subchondral bone in human and mouse knee OA.Osteoblast-specific deletion of Mig6 affects the growth and development of mice,but does not cause embryonic death or limb deformity.Osteoblast-specific deletion of Mig6 promotes the activation of osteoclasts and differentiation of osteoblasts in the subchondral bone of the fifth lumbar spine and knee.The bone turnover rate of the mice is enhanced,and the degree of mineralization is decreased.Osteoblast-specific deletion of Mig6 accelerates subchondral bone remodeling,osteoarthritis progression and cartilage degeneration by up-regulating the ratio of Rankl/OPG and activating osteoclasts.Mig6-EGFR signaling axis plays a biphasic role in regulating osteoblast differentiation.Mig6-EGFR promotes osteoclast differentiation and enhances osteoclast bone resorption in response to mechanical stress.ConclusionMig6-EGFR signaling axis is a classical receptor tyrosine kinase pathway,and its role in bone metabolism is closely related to mechanical stress.The regulation of Mig6-EGFR can effectively regulate subchondral bone remodeling in OA and affect the progress of OA,which provides an important reference for early OA drug targets.