Caveolins redistribute in uterine epithelial cells during early pregnancy in the rat: an epithelial polarisation strategy?

At the time of implantation, uterine luminal epithelial cells undergo a dramatic change in all plasma membrane domains. Changes in the basolateral plasma membrane at the time of implantation include progression from smooth to highly tortuous, as well as a loss of integrin-based focal adhesions. Another aspect of the basolateral plasma membrane that has not been studied in uterine epithelial cells are caveolae, which are omega-shaped invaginations of the plasma membrane known to be involved in endocytosis and contribute to membrane curvature. The current study investigated caveolin, a major protein of caveolae, to explore the possible roles that they play in the remodelling of the basolateral plasma membrane of uterine epithelial cells during early pregnancy in the rat. Morphological caveolae were found at the time of implantation and were significantly increased compared to day 1 of pregnancy. Caveolins 1 and 2 were found to shift to the basolateral plasma membrane of uterine epithelial cells at the time of implantation as well as when treated with progesterone alone, and in combination with oestrogen. A statistically significant increase in the amount of caveolin-1 and a decrease in caveolin-2 protein in uterine epithelial cells was observed at the time of implantation. Caveolin-1 also co-immunoprecipitated with integrin β1 on day 1 of pregnancy, which is a protein that has been reported to be found in integrin-based focal adhesions at the basolateral membrane on day 1 of pregnancy. The localisation and expression of caveolin-1 at the time of implantation is consistent with the presence and increase of morphological caveolae seen at this time. The localisation and expression of caveolins 1 and 2 in luminal uterine epithelium at the time of implantation suggest a role in trafficking proteins and the maintenance of a polarised epithelium.