Characterization of auricular chondrocytes and auricular/articular chondrocyte co-cultures in terms of an application in articular cartilage repair

Cartilage injury remains a challenge in orthopedic surgery as articular cartilage only has a limited capacity for intrinsic healing. Autologous chondrocyte transplantation (ACT) is a suitable technique for cartilage repair, but requires articular cartilage biopsies for autologous chondrocyte expansion. The use of heterotopic chondrocytes derived from non-articular cartilage sources such as auricular chondrocytes may be a novel approach for ACT. The aim of the study is to evaluate whether co-cultured articular/auricular chondrocytes exhibit characteristics comparable to articular chondrocytes. Analysis of the proliferation rate, extracellular cartilage matrix (ECM) gene and protein expression (type II and I collagen, elastin, lubricin), β1-integrins and the chondrogenic transcription factor sox9 in articular/auricular chondrocytes was performed using RTD-PCR, flow cytometry, immunofluorescence microscopy and Western blot analysis. Additionally, three-dimensional (3D) chondrocyte mono- and co-cultures were established. The proliferative activity and elastin gene expression were lower and that of type II collagen and lubricin was higher in articular compared with auricular chondrocytes. The species generally did not influence the chondrocyte characteristics, with the exception of type I collagen and sox9 expression, which was higher in porcine but not in human articular chondrocytes compared with both types of auricular chondrocytes. β1-integrin gene expression did not differ significantly between the chondrocyte types. The type II collagen gene and protein expression was higher in articular chondrocyte monocultures and was slightly higher in co-cultures compared with monocultured auricular chondrocytes. Both chondrocyte types survived in co-culture. Despite their differing expression profiles, co-cultures revealed some adjustment in the ECM expression of both chondrocyte types.