Bovine articular chondroprogenitors: tools for cartilage tissue engineering [Abstract]

Introduction The use of stem/progenitor cells whose progeny have the capacity to form good quality cartilage matrix has been targeted as a therapeutic goal for the treatment of large defects of articular cartilage. Previously we reported the isolation and characterisation of a progenitor cell population that resides in the surface layer of neonatal bovine articular cartilage. Here we show that chondroprogenitors maintain sox9 expression, telomere length and telomerase activity following clonal expansion. Materials and Methods Telomere length and telomerase activity of samples was assayed using Southern blotting and TRAP assay, respectively. Pellet culture utilised 1 · 106 cells grown in high-density culture in chondrogenic medium for 4 weeks. Results Cloned chondroprogenitors exhibited exponential growth for the first 20 population doublings (PD), then slower linear growth with evidence of replicative senescence at later passages. Mean telomere lengths of exponentially growing chondroprogenitors were significantly longer than dedifferentiated chondrocytes that had undergone a similar number of PD (P < 0.05). Chondroprogenitors also had 2.6-fold greater telomerase activity and had similar sox9 and had reduced Notch-1 gene expression levels when compared to dedifferentiated chondrocytes. Chondroprogenitors were induced to differentiate into cartilage in 3D pellet cultures, immunological investigation of sox9, Notch- 1, aggrecan and PCNA expression showed evidence of coordinated growth and differentiation within the cartilage pellet. Discussion Clonal chondroprogenitors are a useful tool to analyse progenitor cell growth and differentiation chracteristics. Whether chondroprogenitor cells from immature articular cartilage differ from those derived from more mature tissue may shed light on the variable nature of cell-based cartilage repair therapies