17β-Estradiol inhibition of PPARγ-induced adipogenesis and adipocyte-specific gene expression

To investigate the molecular interaction of peroxisome proliferator-activated receptor γ (PPARγ) with 17β-estradiol (E) in the regulation of adipogenesis.

Female ovariectomized (OVX) mice and differentiated 3T3-L1 adipocytes were treated with combinations of the PPARγ agonist troglitazone or E, and the variables and determinants of adipogenesis were measured using in vivo and in vitro approaches.

Troglitazone (250 mg·kg(-1)·d(-1) for 13 weeks) decreased the size of adipocytes without the change in white adipose tissue (WAT) mass and increased the expression of adipocyte-specific genes, such as PPARγ, adipocyte fatty acid binding protein, and lipoprotein lipase, compared with OVX control mice. E (0.05 mg/pellet, sc implanted) significantly reduced WAT mass, adipocyte size, and adipose marker gene expression. When mice were concomitantly treated with troglitazone and E, E blunted the effects of troglitazone on WAT mass, adipocyte size, and adipose PPARγ target gene expression. Consistent with the in vivo data, E (10 μmol/L) treatment inhibited lipid accumulation and the expression of adipocyte-specific genes caused by troglitazone (10 μmol/L) in 3T3-L1 cells. E (10 μmol/L) also decreased troglitazone-induced PPARγ reporter activity through both estrogen receptor (ER) α and ERβ. Mechanistic studies indicated that E (0.1 μmol/L) decreased the DNA binding of PPARγ induced by troglitazone (1 μmol/L) and inhibited the recruitment of the PPARγ coactivator CREB-binding protein.

These results suggest that in vivo and in vitro treatment of E interferes with the actions of PPARγ on adipogenesis by down-regulating adipogenesis-related genes, which are mediated through the inhibition of PPARγ coactivator recruitment. In addition, it is likely that the activities of PPARγ activators may be enhanced in estrogen-deficient states.