Who drives the progress of osteoarthritis? -The crosstalk between synoviumand meniscus plays an important role

Background The incidence of osteoarthritis (OA) increases with each passing year. The degeneration of the meniscus and synovium is considered the initial factor of knee osteoarthritis (KOA), but their synergistic mechanism has not been clarified. Methods In this study, single-cell RNA sequencing (scRNA-seq) was employed to establish 16 normal or degenerated meniscus samples and 6 synovium samples based on the meniscus and synovium tissues of 16 patients. A cell atlas comprising 124,026 single cells in total was established (including 8 patients from the public database The Genome Sequence Archive for Human [GSA-Human] PRJCA008120). Based on that, the meniscus/synovium microenvironment homeostasis and the crosstalk between both during their degeneration were explored. Results In this study, the cell types in the meniscus and synovium were analyzed. Besides, new fibroblast subtypes related to the degeneration of the meniscus and synovium were identified. Additionally, the interaction between meniscus and synovium and different cell subtypes was analyzed. Moreover, the mechanism involving vascular growth, immune cell infiltration, and common or different genes during the degeneration of synovium and meniscus tissues was investigated. Conclusions This study may provide the atlas of synovium and meniscus with the largest number of cells in osteoarthritis (OA) to date, reflecting the comprehensive cellchat of synovium and meniscus during degeneration. These findings suggested that the synovium was involved in the crosstalk of intra-articular tissues (synovium/meniscus), thus participating in the degeneration in OA.