Mechanical Overloading Induces Articular Subchondral Bone Resorption <i>via</i> the RANTES-CCRs-Akt2 Axis

Abstract

Background: Early-stage osteoarthritis (OA) is characterized by articular subchondral bone resorption and emerging evidence suggests that mechanical overloading is likely involved. Here, we identified whether and why mechanical overloading could trigger subchondral bone resorption in early-stage OA. Methods: A new mechanical overloading monitoring system for real-time pressure measurement in situ in vivo and a numerically controlled loading device for tissue pressurized culture in vitro were developed. Micro-CT was used to analyze the alterations of microarchitecture in subchondral bone and TRAP staining was harnessed to measure osteoclast differentiation of macrophages. Real-time qPCR, Western blot, ELISA, and immunostaining were conducted to clarify the expression, location, and interaction of relative proteins. Findings: Temporomandibular joint disc displacement yielded about 5 times higher pressure on the articular surface than that of the controls, causing subchondral bone resorption in 3-7 days after disc displacement. RANTES was increased in synovial fluid in early-stage OA in human and expressed in condylar cartilage of rat OA model at 1 week after disc displacement. Mechanistically, RANTES could promote osteoclast recruitment and formation through binding to its receptors CCRs and activating Akt2 pathway. Either Blockade of CCRs or Knockdown of Akt2 rescued RANTES-mediated osteoclast differentiation in vitro . Knockdown of Akt2 prevented the early subchondral bone resorption in OA in vivo. Interpretation: This study unravels a novel mechanism that disc displacement-induced mechanical overloading activates the RANTES-CCRs-Akt2 axis, which plays a critical initial role for the early condylar bone resorption in OA. Funding Information: This work was supported by grants from the National Natural Science Foundation of China (82170979, 81970920, 81772873). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: The approval of synovial fluid experimentations was obtained from the Biomedical Institutional Review Board of the Peking University School and Hospital of Stomatology (PKUSSIRB-201947100), and written informed consents were attained from all participants. The approval of animal studies was obtained from the Peking University Animal Ethics Committee (LA2019310).