Identification of mesenchymal progenitor cells in normal and osteoarthritic human articular cartilage

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Abstract
Objective To determine the presence of mesenchymal progenitor cells (MPCs) in human articular cartilage. Methods Primary cell cultures established from normal and osteoarthritic (OA) human knee articular cartilage were analyzed for the expression of CD105 and CD166, cell surface markers whose coexpression defines mesenchymal stem cells (MSCs) in bone marrow and perichondrium. The potential of cartilage cells to differentiate to adipogenic, osteogenic, and chondrogenic lineages was analyzed after immunomagnetic selection for CD105+/CD166+ cells and was compared with bone marrow–derived MSCs (BM‐MSCs). Results Up to 95% of isolated cartilage cells were CD105+ and ∼5% were CD166+. The mean ± SEM percentage of CD105+/CD166+ cells in normal cartilage was 3.49 ± 1.93%. Primary cell cultures from OA cartilage contained significantly increased numbers of CD105+/CD166+ cells. Confocal microscopy confirmed the coexpression of both markers in the majority of BM‐MSCs and a subpopulation of cartilage cells. Differentiation to adipocytes occurred in cartilage‐derived cell cultures, as indicated by characteristic cell morphology and oil red O staining of lipid vacuoles. Osteogenesis was observed in isolated CD105+/CD166+ cells as well as in primary chondrocytes cultured in the presence of osteogenic supplements. Purified cartilage‐derived CD105+/CD166+ cells did not express markers of differentiated chondrocytes. However, the cells were capable of chondrocytic differentiation and formed cartilage tissue in micromass pellet cultures. Conclusion These findings indicate that multipotential MPCs are present in adult human articular cartilage and that their frequency is increased in OA cartilage. This observation has implications for understanding the intrinsic repair capacity of articular cartilage and raises the possibility that these progenitor cells might be involved in the pathogenesis of arthritis.