CD34+ synovial fibroblasts exhibit high osteogenic potential in synovial chondromatosis

Abstract

Abstract Backgroud Synovial chondromatosis (SC) is a disorder of the synovium characterized by the formation of cartilaginous nodules within the synovium. The aim of this study was to identify the abnormally differentiated progenitor cells and possible pathogenic signaling pathways. Methods Loose bodies and synovium were obtained from patients with SC during knee arthroplasty. Single cell RNA sequencing was used to identify cell subsets and their gene signatures in SC synovium. Cells derived from osteoarthritis (OA) synovium were used as control. Multi-differentiation and colony-forming assays were used to identify progenitor cells. Roles of transcription factors and signaling pathways were investigated through computational analysis and experimental verification. Results We identified changes in the proportions of CD34 + sublining fibroblasts in SC synovium. CD34 + CD31- cells and CD34-CD31- cells were sorted from SC synovium. Compared with CD34- cells, CD34 + cells had larger alkaline phosphatase (ALP)-stained area and calcified area after osteogenic induction. In addition, CD34 + cells exhibited a stronger tube formation ability than CD34-cells. Our bioinformatic analysis suggested the expression of TWIST1 suppressed the osteogenic potential of CD34- sublining fibroblasts and was regulated by TGF-β signaling pathway. Experiment showed that the combination of TGF-β1 and harmine, an inhibitor of TWIST1, could further stimulate the osteogenesis of CD34 + cells. Conclusions Overall, CD34 + stromal cells in SC synovium have multiple differentiation potentials, especially osteogenic differentiation potential, which may be responsible for the pathogenesis of SC.