Objective: To determine whether the major ovarian factor estrogen modulates peroxisome proliferator-activated receptor (PPAR) alpha actions on obesity and to investigate the mechanism by which estrogen regulates PPARalpha actions.
Research methods and procedures: Female ovariectomized mice were randomly divided into four groups (n = 8/group). After they were treated with combinations of high fat, fenofibrate (FF), or 17beta-estradiol (E) for 13 weeks, variables and determinants of obesity and lipid metabolism were measured using in vivo and in vitro approaches.
Results: When female ovariectomized mice were given a high-fat diet with either FF or E, body weight gain and white adipose tissue mass were significantly reduced and serum lipid profiles were improved compared with control mice fed a high-fat diet alone. When mice were concomitantly treated with FF and E, however, E reversed the effects of FF on body weight gain, serum lipid profiles, and hepatic PPARalpha target gene expression. Consistent with the in vivo data, E not only decreased basal levels of PPARalpha reporter gene activation but also significantly decreased Wy14,643-induced luciferase reporter activity. In addition, inhibition of PPARalpha functions by E did not seem to occur by interfering with the DNA binding of PPARalpha.
Discussion: Our results demonstrate that in vivo and in vitro treatment of estrogen inhibited the actions of FF-activated PPARalpha on obesity and lipid metabolism through changes in the expression of PPARalpha target genes, providing evidence that FF does not regulate obesity in female mice with functioning ovaries.