Human osteoblast-like cells express aromatase immunoreactivity

The main source of estrogen after menopause is the peripheral aromatization of adrenal androgens. Estrogen synthetase (aromatase) has been described in several tissues including placenta, ovary, testis, brain, and adipose tissue. The possibility that bone cells themselves could be a local source of estrogen production has been raised in previous studies that reported the presence of aromatase activity in crushed rat mandible and human bone cells. To determine the presence of aromatase in bone cells, cultured male and female human osteoblast-like cells were immunostained with a specific antiserum generated against human aromatase. Aromatase-immunopositive granules were found throughout the entire cytoplasm in all cultures. The morphological demonstration of immunoreactive aromatase in bone cells indicates that bone may be a site of extragonadal aromatization in both sexes. These findings open new possibilities for understanding the mechanisms of bone metabolism, the development of peak bone mass, sex differences in bone mass, and issues regarding the role of sex steroids in bone maintenance and repair.