Int J Biol Sci 2020; 16(6):970-980. doi:10.7150/ijbs.39015 This issue
1. Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, Department of Implant Dentistry, Xi'an Jiaotong University College of Stomatology, Xi'an, Shaanxi, China
2. Department of Orthopedic Surgery, Rush University Medical Center, Chicago, Illinois, USA
3. Department of Orthopaedic Surgery, The First Affiliated Hospital of Zhejiang Chinese Medical University, Hangzhou, Zhejiang, China
4. School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania, USA
* These authors have contributed equally to this work.
Osteoarthritis (OA) is a whole-joint disease characterized by cartilage destruction, subchondral bone sclerosis, osteophyte formation, and synovitis. However, it remains unclear which part of the joint undergoes initial pathological changes that drives OA onset and progression. In the present study, we investigated the longitudinal alterations of the entire knee joint using a surgically-induced OA mouse model. Histology analysis showed that synovitis occurred as early as 1 week after destabilization of the medial meniscus (DMM), which preceded the events of cartilage degradation, subchondral sclerosis and osteophyte formation. Importantly, key pro-inflammatory cytokines such as IL-1β, IL-6, TNFα, and Ccl2, major matrix degrading enzymes including Adamts4, Mmp3 and Mmp13, as well as nerve growth factor (NGF), all increased significantly in both synovium and articular cartilage. It is notable that the inductions of these factors in synovium are far more extensive than those in articular cartilage. Results from behavioral tests demonstrated that sensitization of knee joint pain developed after 8 weeks, later than histological and molecular changes. In addition, the nanoindentation modulus of the medial tibiae decreased 4 weeks after DMM surgery, simultaneous with histological OA signs, which is also later than appearance of synovitis. Collectively, our data suggested that synovitis precedes and is associated with OA, and thus synovium may be an important target to intervene in OA treatment.
Keywords: osteoarthritis, cartilage, synovitis, subchondral bone