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

Abstract

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.