Abstract：
Synovial chondromatosis (SC) is a disorder of the synovium characterized by the formation of osteochondral nodules within the synovium. This study aimed to identify the abnormally differentiated progenitor cells and possible pathogenic signaling pathways. 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 controls. Multi-differentiation and colony-forming assays were used to identify progenitor cells. The roles of transcription factors and signaling pathways were investigated through computational analysis and experimental verification. We identified an increased proportion 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, a negative regulator of osteogenesis, in CD34- sublining fibroblasts and was regulated by the TGF-β signaling pathway. The experiment showed that CD34+ cells acquired the TWIST1 expression during culture and the combination of TGF-β1 and harmine, an inhibitor of Twist1, could further stimulate the osteogenesis of CD34+ cells. Overall, CD34+ synovial fibroblasts in SC synovium have multiple differentiation potentials, especially osteogenic differentiation potential, and might be responsible for the pathogenesis of SC.
摘要：
滑膜软骨瘤病（SC）是一种滑膜疾病，其特征是滑膜内形成骨软骨结节。本研究旨在鉴定异常分化的祖细胞和可能的致病信号通路。膝关节置换术期间，从SC患者获得了松散的身体和滑膜。单细胞RNA测序用于鉴定SC滑膜中的细胞亚群及其基因特征。来自骨关节炎(OA)滑膜的细胞用作对照。使用多分化和集落形成测定来鉴定祖细胞。通过计算分析和实验验证，研究了转录因子和信号通路的作用。我们鉴定了SC滑膜中CD34+亚衬成纤维细胞的比例增加。从SC滑膜中分选CD34+CD31-细胞和CD34-CD31-细胞。与CD34-细胞相比，成骨诱导后，CD34细胞的碱性磷酸酶（ALP）染色面积和钙化面积较大。此外,CD34+细胞比CD34-细胞具有更强的成管能力。我们的生物信息学分析表明TWIST1的表达，TWIST1是成骨的负调节因子，在CD34-成纤维细胞中，并受TGF-β信号通路的调节。实验表明，CD34+细胞在培养过程中获得了TWIST1的表达以及TGF-β1和harmine的结合，Twist1的抑制剂，可以进一步刺激CD34+细胞的成骨。总的来说,SC滑膜中的CD34+滑膜成纤维细胞具有多向分化潜能，尤其是成骨分化潜能，并可能与SC的发病机制有关。
