Impact of expansion and redifferentiation conditions on chondrogenic capacity of cultured chondrocytes.

Cartilage regeneration based on isolated and culture-expanded chondrocytes is studied in a variety of in vitro models, but with varying morphological quality of tissue synthesized. The goal of the present study was to investigate the extent of the influence of expansion and redifferentiation conditions on final tissue morphology by comparing 2 expansion and redifferentiation methods. Chondrocytes from 9 human donors were expanded in medium without growth factor supplementation (basic expansion condition [BEC]) or in medium with basic fibroblast growth factor (bFGF) supplementation (growth factor supplemented expansion condition [GFSEC]). After expansion, cells were either redifferentiated in pellet culture or seeded on collagen type II-coated filters. Post-expansion mRNA levels of collagen type I and II and Sox-5, -6, and 9, measured by semiquantitative real-time polymerase chain reaction (PCR), suggested that expansion in GFSEC results in increased dedifferentiation compared to BEC. However, after 28 days of redifferentiation culture, morphology of tissue synthesized by GFSEC-expanded chondrocytes scored significantly higher on the Bern scale compared to BEC (6.4 +/- 0.3 points vs. 4.5 +/- 0.3 points in pellet culture and 6.0 +/- 0.4 points vs. 4.5 +/- 0.3 points on collagen-coated filters; p < 0.05). Expansion in GFSEC compared to BEC increased proteoglycan (PG) synthesis rate at day 9 (4.0-fold in pellet culture and 1.9-fold on collagen-coated filters; p < 0.01), PG release (6.7-fold in pellet culture and 3.2-fold on collagen-coated filters; p < 0.001), and final PG content at day 28 (1.6-fold in pellet culture and 1.5-fold on collagen-coated filters; p < 0.05). Redifferentiation on collagen-coated filters compared to pellet culture increased PG synthesis rate at day 9 (5.2-fold in BEC-expanded chondrocytes and 2.6-fold in GFSEC-expanded chondrocytes; p < 0.01), PG release (4.2-fold in BEC-expanded chondrocytes and 3.1-fold in GFSECexpanded chondrocytes; p < 0.01), and final PG content (1.3-fold in BEC-expanded chondrocytes and 1.9- fold in GFSEC-expanded chondrocytes; p < 0.01). Moreover, as visualized via electron microscopy, chondrocytes and organization of extracellular matrix cultured on filters was more similar to those found for hyaline cartilage. In conclusion, chondrocyte expansion in GFSEC and redifferentiation on collagen-coated filters resulted in most optimal chondrogenesis.