Effect Of Controlled Ovarian Hyperstimulation On Expression Of Aquaporin-2 In Mouse Implantation Endometrium

Background:Aquaporin (AQP) is an important integral membrane protein channel that facilitate transportion of water in organism. So far 13 isoforms (AQP0-AQP12) have been identified in mammals. The members of aquaporins are located in various tissues in the body and make great contribution to the water permeability. In mammals, AQPs are expressed in a wide variety of reproductive system such as testis, sperm, ovary, uterus, placenta and fetal membrane etc. It has proved that many isoforms of AQP was expressed in both ovariectomized mouse uterus treated with ovarian steroid hormones and in the mouse uterus during the peri-implantation period (on d 1-8 of pregnancy). Among these isoforms, AQP2 was the only one constitutively present in the luminal epithelial cell of mouse uterus, and mostly regulated by estrogen. Nevertheless, we haven't known that the quantity and the function of AQP2 in mouse implantation endometrium, let alone the relationship between AQP2 and embryo implantation.Nowadays, with the development of Assisted Reproductive Technology (ART) used in infertility, people can get more oocytes for embryo implantation by controlled ovarian hyperstimulation(COH). However, pregnancy rate per embryo transfer is still at a low rate. One of the critical reasons is the uterine receptivity forembryonic attachment and invasion. It is known that ovulation and fertilization trigger embryonic development and endometrial differentiation by corpus luteum progesterone production. These two synchronous processes couple about one week later, when the blastocyst begins to implant in the receptive endometrium. This bifactorial, transient period when implantation can start, is called the implantation or nidation window. Implantation cannot occur before or after this implantation window. Recently, many scholars think that super-ovulation can play a negative effect in the uterine receptivity compared with the nature ovulation cycle. There are many molecular factors associated with this effect, such as leukemia inhibitory factor (LIF), integrins, pinopode and so on, which are considered as the biomarkers of the uterine receptivity.. A recent survey found that aquaporin may play a role during embryo implantation by controlling the process of the close of lumen of uterus and attachment of the blastocyst to the uterine luminal surface. Thus, AQPs may be another biomarker of the uterine receptivity.Up to date, there's no study manifesting there are relationships between the function of COH on the uterine receptivity and the role of COH on AQPs expressed in implantation endometrium.Objective:To investigate the effect of Controlled Ovarian Hyperstimulation on expression of aquaporin-2 in mouse implantation endometrium.Materials and Methods:Twenty female mice (6-7 weeks) were randomly allocated into 2 groups, one is control group, the other is COH group. Mice in COH group were superovulated by intraperitoneal injection of 10 IU pregnant mare's serum gonadotropin (PMSG) followed by 10 IU human chorionic gonadotropin (HCG) injection after 48 hours. Nothing was given to mice in control group and the estrus cycle was observed at 9 am everyday. 48 hours after HCG injection(COH group) or the estrus( controlgroup) ,mice were killed by cervical dislocation. Uteruses were collected and used for immunohistochemistry and Semi-quantitative Real-time PCR.Results:1. Immunohistochemical staining: AQP2 was constitutively expressed in the membrane and cytoplasm of luminal and glandular epithelia in mouse endometrium.2. Semi-quantitative Real-time PCR: AQP2 mRNA was significantly increased (P < 0.05) in COH group(ACT=l.055±0.443) compared with the control group(A CT=2.665± 0.755).Conclusions:1. Aquaporin2 was expressed in the mature mice's endometrium during their implantation windows.2. AQP2 was mainly located in endometrial luminal epithelial cells and glandular epithelial cells during the implantation windows of the mice.3. COH can induce the over- physiology growth of AQP2 mRNA in mouse implantation endometrium thus COH may play a negative effect on the implantation of embryo .