Single-Cell Atlas Of Human Infrapatellar Fat Pad And Synovium Unravels Mechanisms Of Osteoarthritis-Induced Joint Pathology

Purpose: Osteoarthritis (OA) is the most common degenerative musculoskeletal disorder, affecting hundreds of millions of patients around the world. The pathogenesis of knee OA involves the whole joint, including cartilage, synovium, meniscus, fat pad, subchondral bone and other structures. The infrapatellar fat pad (IPFP) is a unique type of white adipose tissuebecause of its direct, constant contact with synovium located between the patellar ligament, femoral condyle and tibial condyle in the keen joint. Its described functions are to maintain mechanical stability of the joint in response to sport injury, regulate the distribution of synovial fluid, and participate in cartilage homeostasis. Under pathological conditions in the setting of OA, IPFP secretes inflammatory cytokines and develops fibrosis, whereas low-grade synovial inflammation occurs in most OA patients. While the pathological changes of IPFP and synovium in OA progression are widely recognized, both tissues have not been systematically and unbiasedly investigated at a cellular level under healthy and OA conditions.