Rat costochondral chondrocytes produce 17β-estradiol and regulate its production by 1α,25(OH)2D3

Abstract

Prior studies have shown that 17β-estradiol (17β-E2) regulates growth plate chondrocyte maturation and differentiation. This study examines the hypothesis that 17β-E2 is a local regulator of rat costochondral growth plate chondrocytes by determining whether these cells express aromatase mRNA and enzyme activity, produce 17β-E2, and regulate 17β-E2 production by vitamin D3 metabolites in a gender-specific and cell-maturation-dependent manner. Aromatase gene expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and northern analysis of total RNA from male and female chondrocytes. Aromatase specific activity was measured in cell layer lysates of confluent male and female rat costochondral resting zone (RC) and growth zone (GC) cartilage cells that had been treated for 24 h with 1α, 25(OH)2D3, 24R,25(OH)2D3, or transforming growth factor (TGF)-β1. 17β-E2 released into the culture media of treated cells was measured by radioimmunoassay (RIA). Female RC cells expressed the highest levels of aromatase mRNA compared with male RC cells and both male and female GC cells. Aromatase activity was present in male and female cells and was 1.6 times greater in female RC cells than female GC cells; male RC and GC cells displayed comparable levels. All cultures produced 17β-E2, with a 2.5-fold greater production by female RC cells than female GC cells or either cell type from male rats. Treatment of cultures with 1α,25(OH)2D3 caused a dose-dependent increase in 17β-E2 production by female RC (1.5-fold greater than control cells) and female GC (threefold greater than control cells) cells. In contrast, 1α,25(OH)2D3 had no effect on male GC cells and increased production in male RC cells by only 10% at the highest concentration of 1α,25(OH)2D3 used. Neither 24R, 25(OH)2D3 nor TGF-β1 had an effect on 17β -E2 production. These results support our hypothesis and indicate that 17β-E2 is most likely a local regulator of rat costochondral growth plate chondrocytes.