Clonal chondroprogenitors maintain telomerase activity and Sox9 expression during extended monolayer culture and retain chondrogenic potential

SummaryObjectiveArticular cartilage contains mesenchymally derived chondroprogenitor cells that have the potential to be used for stem cell therapy. The aim of this study was to characterise the growth kinetics and properties of in vitro expanded cloned chondroprogenitors and determine if critical determinants of the progenitor phenotype were maintained or lost in culture.MethodsChondroprogenitors were isolated from immature bovine metacarpalphalangeal joints by differential adhesion to fibronectin. Cloned colonies were expanded in vitro up to 50 population doublings (PD). Growth characteristics were assessed by cell counts, analysis of telomere length, telomerase activity, expression of senescence-associated β-galactosidase activity and real-time quantitative polymerase chain reaction to analyse the gene expression patterns of sox9 and Notch-1 in chondroprogenitors.ResultsCloned chondroprogenitors exhibited exponential growth for the first 20PD, 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