Heterogeneous Characteristics of the CD90⁺ Progenitors in the Fibrocartilage of Different Joints

ObjectiveThis study aimed to isolate and compare the mesenchymal stem cell characteristics of CD90⁺ cells from different fibrocartilage tissues in the temporomandibular joint (TMJ), the knee joint, and the intervertebral joint to further understand the similarities and differences of these 4 fibrocartilage tissues.MethodsCD90⁺ cells were isolated from TMJ disc, condylar cartilage, meniscus, and intervertebral disc by using magnetic-activated cell sorting. Cellular assays including 4.5-ethynyl-2'-deoxyuridine labeling, multilineage differentiation, colony formation, and cell migration were conducted to compare their mesenchymal stem cell characteristics. Immunofluorescent staining was performed for observing the expression of actively proliferating CD90⁺ cells within the tissues. H&E staining and Safranine O staining were used to compare the histological features.ResultsThe CD90⁺ cells derived from these 4 fibrocartilage tissues exhibited comparable cell proliferation abilities. However, the cells from the TMJ disc displayed limited multilineage differentiation potential, colony formation, and cell migration abilities in comparison with the cells from the other fibrocartilage tissues. In vivo, there was relatively more abundant expression of CD90⁺ cells in the TMJ disc during the early postnatal stage. The limited EDU⁺ cell numbers signified a low proliferation capacity of CD90⁺ cells in the TMJ disc. In addition, we observed a significant decrease in cell density and a restriction in the synthesis of extracellular proteoglycans in the TMJ disc.ConclusionOur study highlights the spatial heterogeneity of CD90⁺ cells in the fibrocartilages of different joint tissues, which may contribute to the limited cartilage repair capacity in the TMJ disc.