Experimental chondrocyte hypertrophy is promoted by the activation of discoidin domain receptor 2.

The aim of the present study was to assess the association between chondrocytes and the extracellular matrix (ECM), and determine whether this contributes to osteoarthritis (OA). Chondrocyte hypertrophy was measured in articular cartilage samples from early-stage OA patients. In addition, rat chondrocytes were cultured and divided into four groups (A to D): Group A was an untreated control group, group B was incubated with chicken collagen II, group C was transfected with the discoidin domain of discoidin domain receptor-2 (DDR2) and group D was transfected with full­length DDR2. The expression levels of DDR2 and hypertrophic markers in each group were then measured by quantitative polymerase chain reaction (qPCR) and western blot analyses. Chondrocyte hypertrophy was identified in samples of early­stage OA patients. In rat chondrocyte cultures, the relative mRNA and protein expression levels of hypertrophic markers were determined as: Group D > B > C > A. In conclusion, transfection with DDR2 induced the expression of hypertrophic markers, as assessed by qPCR and western blot analyses. DDR2 therefore promoted chondrocyte hypertrophy and terminal differentiation.