Stage specific effect of leptin on the expressions of estrogen receptor and extracellular matrix in a model of chondrocyte differentiation

Endochondral ossification is a dynamic process. The interaction between leptin and estrogen in this process is complicated. Whether there is a stage specific crosstalk between leptin and estrogen in the differentiation process of the chondrocytes in the growth plate remains unknown. The aim of our study was to investigate the effect of leptin on the expression of estrogen receptors and extracellular matrix in ATDC5 cells, an in vitro model of endochondral ossification. First, we quantified the physiological expressions of estrogen receptors alpha, beta (ER alpha, ER beta), leptin receptor (Ob-Rb), type II and type X collagens in definite stages of endochondral ossification in ATDC5 cells using real-time PCR. Dynamic and stage specific expression characteristics of these target genes were observed. Simultaneous expressions of Ob-Rb with ER alpha or ER beta in ATDC5 cells were also found with dual-label confocal immunofluorescency. Then using Western blotting analysis and/or real-time PCR, we detected that, leptin treatment up-regulated the expressions of ER alpha, ER beta and type II collagen, but down-regulated type X collagen expression and the ER alpha/ER beta ratio in the chondrogenic differentiation stage. Meanwhile, leptin down-regulated the expressions of ER alpha, type II and type X collagens, and the ER alpha/ER beta ratio, but up-regulated the expression of ER beta in the hypertrophic differentiation stage. Significant positive correlation existed between ER alpha and type II collagen expression, and between the ratio of ER alpha/ER beta and type X collagen production. In summary, the crosstalk between leptin and estrogen receptor might be differentiation stage specific in ATDC5 cells. (C) 2013 Elsevier Ltd. All rights reserved.