Progenitor cells from cartilage--no osteoarthritis-grade-specific differences in stem cell marker expression.

Tissue engineering efforts for the fabrication of cartilage substitutes head toward applicability in osteoarthritis (OA). Progenitor cells can be harvested from the osteoarthritic joint itself, resembling multipotent mesenchymal stromal cells (MSC). Our objective was to analyze MSC characteristics of those cells in respect to the OA-related damage of their harvest site. OA cartilage was obtained from six patients during alloarthroplastic knee surgery, sample grading was done according to Outerbridge's classification. Upon enzymatic dissociation, primary chondrocytes were expanded in two-dimensional monolayer culture. At distinct cell passages, the process of dedifferentiation was phenotypically monitored; cell surface expression of classical MSC markers was analyzed by flow cytometry. Cells were subjected to chondrogenesis and osteogenesis after their fourth passage. At third passage, 95% of cells became positive for cluster of differentiation (CD)105 and further subclassification revealed that the majority of them were positive for both CD73 and CD90. CD105(+) CD73(+) CD90(+) phenotype meets thus the minimal surface antigen criteria for MSC definition. More than one-third of dedifferentiated chondrocytes displayed a coexpression of CD9(+) CD166(+) CD90(+) and to a lesser extent CD105(+) CD73(+) CD44(+) , irrespective of the stage of the original cartilage degradation. Finally, we could successfully demonstrate a redifferentiation of these progenitors into sulfated glycosaminoglycan producing cells. The basic level of alkaline phosphatase activity could not be enhanced upon osteogenic differentiation. In conclusion, chondrogenic progenitors derived from OA cartilages with low or high Outerbridge's grade can be seen as a potential cellular source for cartilage replacement.