Expression and regulation of androgen receptor in the mouse uterus during early pregnancy and decidualization

The androgen receptor (AR) is a ligand-activated transcription factor that is important for both the male and female reproductive systems. The expression and regulation of AR in the uterine endometrium during early pregnancy and decidualization remain relatively under-investigated, so we sought to immunohistochemically examine the spatiotemporal expression of AR in mouse uteri during the peri-implantation period as well as in response to specific steroid hormones. AR protein was found in the nuclei of uterine stromal cells starting on pregnancy Days 1 and 2, with its abundance increasing on Days 3 and 4. From pregnancy Days 5 to 9, however, the expression of AR markedly declined in stromal zones of uteri. No signal was detected in the decidualized cells surrounding the site of embryo implantation; moreover, no AR immunostaining was observed in decidualized uterine cells in an artificial oil-induced model of decidualization. Progesterone significantly inhibited AR protein expression, whereas estrogen dramatically elevated AR abundance in the stroma of ovariectomized mouse uteri. Taken together, our results are the first to demonstrate that decidualization and progesterone significantly inhibited the AR protein expression in vivo, whereas estrogen increased AR protein levels in the stromal cells of mouse uteri. These responses might be advantageous for the proliferation and differentiation of uterine stroma and for embryo implantation during early pregnancy.