Uterine focal adhesions are retained at implantation after rat ovarian hyperstimulation

Abstract

Controlled ovarian hyperstimulation is an essential component of IVF techniques to ensure proliferation and development of multiple ovarian follicles, but the effects of these hormones on the endometrium are largely unknown. During normal pregnancy in rats, there are significant changes in the basal plasma membrane of uterine epithelial cells (UECs) at the time of receptivity, including loss of focal adhesions. This enables the UECs to be removed from the implantation chamber surrounding the blastocyst, thus allowing invasion into the underlying stroma. This study investigated the influence of ovarian hyperstimulation (OH) on the basal plasma membrane of UECs during early pregnancy in the rat. Immunofluorescence results demonstrate the presence of paxillin, talin, integrin β1 and phosphorylated FAK (Y397FAK) in the basal portion of UECs at the time of implantation in OH pregnancy. TEM analysis demonstrated a flattened basal lamina and the presence of focal adhesions on the basal surface at this time in OH pregnancy. Significantly low full-length paxillin, high paxillin δ and integrin β1 were seen at the time of implantation in OH compared with those in normal pregnancy. The increase in paxillin δ suggests that these cells are less mobile, whereas the increase in integrin β1 and Y397FAK suggests the retention of a stable FA complex. Taken together with the increase in morphological focal adhesions, this represents a cell type that is stable and less easily removed for blastocyst implantation. This may be one mechanism explaining lower implantation rates after fresh embryo transfers compared with frozen cycles.

Prominin-2 Prevents the Formation of Caveolae in Normal and Ovarian Hyperstimulated Pregnancy

“…While prominin-2 is lost from the basal plasma membrane at the time of implantation during normal pregnancy, prominin-2 remains in both the lateral and basal plasma membranes throughout OH pregnancy. The basal plasma membrane at both the time of fertilization and the time of implantation in OH pregnancy is very flattened 59 ; therefore prominin-2 is again unlikely to be located in plasma membrane protrusions in this domain. The basolateral localization of prominin-2 during OH pregnancy is similar to the distribution of prominin-2 seen in ovariectomized rats treated with estrogen and therefore may be caused by the supraphysiological level of estrogen that results from OH treatment.…”

“…37 Curiously, this basal localization is seen at a time when the basal plasma membrane of UECs is flattened. 14,59 Therefore, it is unlikely that prominin-2 is localized within protrusions of this plasma membrane. At the time of implantation during normal pregnancy, the basal plasma membrane becomes highly tortuous 14 and prominin-2 is lost from this membrane and becomes restricted to the apical portion of the lateral plasma membrane of UECs.…”

“…Randomly selected regions of remaining uterine horns were routinely examined to validate removal of epithelial cells only. 59 The cell suspension was agitated through a 23-gauge needle and centrifuged at 10 000 g for 30 seconds. The supernatant was collected and protein concentration was determined using a BCA protein assay (MicroBCA Protein Assay Kit; Thermo Fisher Scientific, Waltham, Massachusetts) and POLARstar Galaxy microplate reader (BMG Lab Technologies, Ortenberg, Germany).…”

“…The present study demonstrates a low abundance of morphological caveolae in the basal plasma membrane of UECs throughout OH pregnancy, when morphological focal adhesions are retained. 59 These caveolae are required for the removal of focal adhesions from the basal plasma membrane at the time of implantation during normal pregnancy. [14][15][16]18,22,23 This loss of focal adhesions allows the UECs to become less adherent to the underlying basal lamina, such that they may be removed to allow the blastocyst to invade the underlying stroma.…”

Fifty years of reproductive biology in Australia: highlights from the 50th Annual Meeting of the Society for Reproductive Biology (SRB)

“…The endometrium produces many signalling molecules that drive its cyclical remodelling, enabling the embryo to implant and a placenta to develop. Although oestrogen and progesterone, along with the pituitary hormones, are important regulators of a woman's reproductive cyclicity, the exogenous hormones used in infertility clinics during ovarian stimulation are detrimental to uterine function and establishing pregnancy (Lindsay et al 2016). Lessons learnt about the endometrial contribution to optimal blastocyst development within the uterine cavity could lead to further improvement of embryo culture techniques (Xiao et al 2017).…”