HLA-G and endometrial receptivity.
Author
Rodríguez Díaz, Rubí NievesDate
2018Abstract
The endometrium is a complex and dynamic tissue, which experiences physiological and cyclical changes each month, in response to
ovarian hormones, cytokines and chemokines [1-3]. The embryo is
capable of attach to the uterine endometrium during a short and selflimited period, in which the endometrial tissue acquires a functional
condition that allows the interaction trophoblast-endometrium and
therefore, it is receptive. The embryo enters the uterine cavity as an
unhatched blastocyst and undergoes its final development through
hatching to attachment to the uterine luminal epithelium within the
environment of uterine fluid. The embryo first enters the uterine cavity as blastocyst and attached to the uterine epithelium [4] (Figure
1). Decidualization of endometrial stromal cells is mainly induced by
ovarian steroids and progesterone-dependent decidualization is mediated in part by the second messenger cAMP [5], decidualization is
taking place with the secretory transformation of the uterine glands,
particularly of specialized uterine natural killer cells and vascular remodelling [6].
Endometrial receptivity (ER) is defined as a temporary unique
factors sequence that make the endometrium receptive to the embryonic implantation [7]. This specific period is regulated by a combination of ovarian steroids hormones and genetic factors and is known
as “window of implantation” (WOI). It takes place between 6 and 10
days after ovulation [8], and it remains receptive during a short period
of time, about the 20-24th of a cycle of 28 days [9]. During this period
the endometrium undergoes morphological, cytoskeletal, biochemical, and genetic changes to become functionally competent [10].
Embryo implantation is a process comprising several cellular,
ultrastructural and molecular mechanisms initiated and mediated by
the endometrium, the embryo and the interaction of both. In order
that the embryonic implantation takes place, there is indispensable
the concurrence of three fundamental elements: embryo quality, endometrial receptivity in WOI and embryo-endometrial interaction
[11-13]. Figure.2 but timing endometrial receptivity is still a challenge. These processes are controlled by different factors, including
ovarian steroids and its receptors, cytokines, growth factors, adhesion
molecules, transcriptional factors and many others [14].
The detection of WOI in every patient, in a personalized way,
would be essential and would allow to increase pregnancy rates in
ART. Failure of the endometrium to achieve receptivity and the timing of the receptive period are now recognised as important issues in
the success of IVF [4].