At the time of implantation the basolateral plasma membrane of luminal uterine epithelial cells (UECs) is drastically altered from smooth to highly tortuous, with the loss of integrin based focal adhesions and also an increase in the number of vesicles. These changes are essential for successful implantation of the blastocyst.  Caveolin is a major protein of caveolae, which are known to be involved in endocytosis and membrane curvature and have also been reported to be involved in the internalisation of integrin β1 (Intβ1).

This study investigated the localisation and expression of caveolin-1,-2 and tyrosine phosphorylated caveolin -1 (pcav-1(Y14)) during early pregnancy and in response to ovarian hormones to explore the roles of these proteins  remodelling of UECs during early pregnancy in the rat.

Immunofluorescence microscopy demonstrated a cytoplasmic pool of caveolin-1 and-2 on d1 of pregnancy which becomes basal at the time of implantation. This corresponds to an increase in the number of morphological caveolae present at the time of implantation seen by TEM. Protein analyses have shown a statistically significant increase in caveolin-1 and a decrease in caveolin-2 at the time of implantation. Localisation of pcav-1(Y14) is basal throughout early pregnancy in UECs and in response to cytochalasin D basal localisation was reduced. Ovariectomised rats treated with different hormonal regimes indicated that expression and basal localisation of caveolin-1 and 2 in luminal UECs is dependent on progesterone. Co-immunoprecipitation studies showed an interaction between Intβ1 and caveolin-1.

The localisation and expression of caveolin 1 and 2 in luminal uterine epithelium at the time of implantation suggest caveolin 1 is involved in the internalisation of Intβ1 and facilitates the disassembly of focal adhesions. Caveolin may also contribute to  membrane curvature seen seen at the basolateral membrane on day 6 of pregnancy. These potential functions of caveolin during early pregnancy may be important for successful blastocyst implantation.