Increased adipose tissue in male and female estrogen receptor-alpha knockout mice.

Estrogen regulates the amount of white adipose tissue (WAT) in females, but its role in males and whether WAT effects involve estrogen receptor-alpha (ERalpha) or ERbeta were unclear. We analyzed the role of ERalpha in WAT and brown adipose tissue by comparing these tissues in wild-type (WT) and ERalpha-knockout (alphaERKO) male and female mice. Brown adipose tissue weight was similar in alphaERKO and WT males at all ages. Progressive increases in WAT were seen in alphaERKO males with advancing age. Epididymal, perirenal, and inguinal WAT weighed 139-185% more in alphaERKO than in WT males by 270-360 days of age. Epididymal and perirenal adipocyte size was increased 20% in alphaERKO males. Adipocyte number was 82-168% greater in fat pads of alphaERKO vs. WT males. Compared with WT, 90-day-old alphaERKO females had increases in fat pad weights (54-103%), adipocyte size, and number. Both alphaERKO males and females had insulin resistance and impaired glucose tolerance, similar to humans lacking ERalpha or aromatase. Energy intake was equal in WT and alphaERKO males, indicating that obesity was not induced by hyperphagia. In contrast, energy expenditure was reduced by 11% in alphaERKO compared with WT males, indicating that altered energy expenditure may be important for the observed obesity. In summary, ERalpha absence causes adipocyte hyperplasia and hypertrophy, insulin resistance, and glucose intolerance in both sexes. These results are evidence that estrogen/ERalpha signaling is critical in female and male WAT; obesity in alphaERKO males involves a mechanism of reduced energy expenditure rather than increased energy intake.