Human chondrocytes isolated from articular cartilage (AC) lesions as an alternative cell source to the standard nonweight-bearing notch biopsy site may hold clinical potential for cell-based therapies. The aim was to characterize human AC lesion site chondrocytes, compare them to notch chondrocytes, and evaluate their redifferentiation potential after monolayer expansion and subsequent three-dimensional (3D) alginate bead culture. Lesion chondrocytes from knee joints of 20 patients with International Cartilage Repair Society (ICRS) grade 3 and 4 cartilage defects were analyzed ex vivo or cultured in primary alginate bead culture, monolayer expansion, or redifferentiated in alginate culture following monolayer expansion. The mRNA expression of the types I, II, and X collagen, and the proteoglycan aggrecan was compared between the four groups. In addition, notch chondrocytes of nine patients were compared to lesion chondrocytes ex vivo. AC lesion chondrocytes displayed ex vivo a nondegenerative phenotype, characterized by a relatively high mRNA expression of aggrecan and type II and X collagen, but a low type I collagen expression and a low ratio of type I to II collagen mRNA expression. Compared to notch chondrocytes, the mRNA expression of aggrecan and type II collagen was comparable and the ratio of type I to II collagen mRNA expression was below 1 in both groups, indicating a functional chondrocyte phenotype. Dedifferentiation led to a significantly altered degenerative mRNA expression profile. Induced redifferentiation in alginate beads after monolayer expansion significantly improved the mRNA expression of aggrecan, the type I and II collagen, and the type I to II collagen ratio, compared to monolayer expansion only. These data suggested that redifferentiating lesion chondrocytes after monolayer expansion in alginate beads resulted in a pool of cells with greater chondrogenic potential, compared to expanded dedifferentiated chondrocytes. Collectively, these data suggest that ex vivo and redifferentiated lesion chondrocytes may hold nonutilized clinical potential for the tissue engineering of AC.
Keywords: aggrecan; alginate bead culture; articular cartilage; chondrocyte; dedifferentiation; mRNA expression; metabolism; monolayer culture; redifferentiation; type I collagen; type II collagen; type X collagen.