Evidence of chondrocyte repopulation in adult ovine articular cartilage following cryoinjury and long-term transplantation

Objective: To characterize the response of articular chondrocytes to a spec ific cryoinjury that leads to cluster formation following long-term transpl antation. Design: Osteochondral dowels from 20 adult sheep were cryopreserved to opti mize the recovery of chondrocytes immediately after thawing. The dowels wer e transplanted as allografts and observed at 3 and 12 months. Chondrocyte d istribution and viability was assessed using paravital dyes after transplan tation. Chondrocyte phenotype was assessed by in situ hybridization and Imm unohistochemistry to detect type II collagen. An anticentrosome antibody wa s used to identify cells undergoing cell cycle progression towards mitosis. Results: All cryopreserved grafts showed the presence of spheroidal cluster s of chondrocytes I year after transplantation while the host cartilage adj acent to the graft appeared morphologically normal. The average size of the clusters increased from four cells at 3 months to 12 cells at I year. The chondrocytes in the clusters displayed newly formed type II collagen protei n and mRNA. Some cells within clusters were observed with two centrosomes, indicative of cells progressing through the S phase of the cell cycle. Conclusion: Adult articular chondrocytes retain the ability to repopulate t he matrix, an ability which is demonstrated with this specific cryoinjury. This may be an initial stage of cartilage regeneration. (C) 2001 OsteoArthr itis Research Society International.