Estrogen modulates Bcl-2 family protein expression in the sexually dimorphic nucleus of the preoptic area of postnatal rats.

In the sexually dimorphic nucleus of the preoptic area (SDN-POA) of postnatal rats, apoptotic cells are detected more frequently in females than males. This sex difference is under the influence of aromatized androgen. We have reported that there are sex differences in the levels of Bcl-2 (female<male) and Bax (female>male) in the central division of the medial preoptic nucleus (MPNc), a significant component of the SDN-POA, followed by a sex difference in induction of apoptosis via caspase-3 activation (female>male). In the present study, we examined effects of estradiol benzoate (EB) on expression of Bcl-2 and Bax in the MPNc. Female rats were subcutaneously injected with EB (25 or 50 microg per head) on postnatal day 5. MPNc and caudate putamen (CP) tissues were obtained from EB-treated female and male rats on postnatal day 6. Protein levels of Bcl-2 and Bax were determined by Western blotting. In the MPNc of female rats, EB at a dose of 50 microg/head but not 25 microg/head significantly increased Bcl-2 protein level and decreased Bax protein level. The levels of Bcl-2 and Bax of female rats treated with 50 microg of EB were comparable to those of male rats. However, the protein levels of Bcl-2 and Bax in the CP did not change with EB treatment. These results suggest that estrogen up-regulates Bcl-2 expression and down-regulates Bax expression in the MPNc of postnatal rats. Effects of estrogen on the Bcl-2 family are presumably responsible for sex difference in postnatal apoptosis of the SDN-POA.