C-28/I2 and T/C-28a2 chondrocytes as well as human primary articular chondrocytes express sex hormone and insulin receptors--Useful cells in study of cartilage metabolism

Sex hormones and insulin have been implicated in articular cartilage metabolism. To supplement previous findings on the regulation of matrix synthesis with 17β-estradiol and insulin and to find a possible model to study cartilage metabolism in vitro, we evaluated the expression of estrogen receptors α and β (ERα, ERβ), androgen receptor (AR) and insulin receptor (IR), in immortalized C-28/I2 and T/C-28a2 chondrocytes and in human primary articular cartilage cells. Chondrocytes were treated with increasing concentrations of 17β-estradiol, dihydrotestosterone or insulin and analyzed by means of RT-PCR and Western blotting. Both cell lines as well as human articular chondrocytes expressed ER α and β, AR and IR at mRNA and protein levels. In immortalized C-28/I2 chondrocytes, we showed that increasing concentrations of 17β-estradiol diminished the 95kDa band of IR. Since 17β-estradiol suppresses insulin-induced proline incorporation and type II collagen synthesis, as we have previously demonstrated, our findings give the first clue that 17β-estradiol may have negative effects on cartilage anabolism triggered by insulin during hormonal imbalance. Compared to chondrocytes cultured without hormones, immunostaining for ERα/β, AR and IR was decreased in both cell lines after incubation of cells with the receptor-specific hormones. It can be assumed that C-28/I2 and T/C-28a2 chondrocytes interact with the respective hormones. Our findings provide a reproducible model for investigating sex hormone and insulin receptors, which are present in low concentrations in articular chondrocytes, in the tissue-specific context of cartilage metabolism.