Estrogen stimulates leptin receptor expression in ATDC5 cells via the estrogen receptor and extracellular signal-regulated kinase pathways.

Regulation of the physiological processes of endochondral bone formation during long bone growth is controlled by various factors including the hormones estrogen and leptin. The effects of estrogen are mediated not only through the direct activity of estrogen receptors (ERs) but also through cross talk with other signaling systems implicated in chondrogenesis. The receptors of both estrogen and leptin (OBR (LEPR)) are detectable in growth plate chondrocytes of all zones. In this study, the expression of mRNA and protein of OBR in chondrogenic ATDC5 cells and the effect of 17b-estradiol (E2 )s timulation were assessed using quantitative PCR and western blotting. We have found that the mRNA of Obr was dynamically expressed during the differentiation of ATDC5 cells over 21 days. Application of E2 (10 K7 M) at day 14 for 48 h significantly upregulated OBR mRNA and protein levels (P!0.05). The upregulation ofObr mRNA by E2 was shown to take place in a concentration-dependent manner, with a concentration of 10 K7 ME 2 having the greatest effect. Furthermore, we have confirmed that E2 affected the phosphorylation of ERK1/2 (MAPK1/MAPK3) in a time-dependent manner where a maximal fourfold change was observed at 10 min following application of E2. Finally, pretreatment of the cells with either U0126 (ERK1/2 inhibitor) or ICI 182 780 (ER antagonist) blocked the upregulation of OBR by E2 and prevented the E2induced phosphorylation of ERK. These data demonstrate, for the first time, the existence of cross talk between estrogen and OBR in the regulation of bone growth whereby estrogen regulates the expression ofObr in growth plate chondrocytes via ERs and the activation of ERK1/2 signaling pathways.