Here, we describe the method of generating an artificial decidualization model using the ovariectomized mouse, a classic endometrial decidualization experiment in the research field of endometrial decidualization.
Endometrial decidualization is a unique differentiation process of the endometrium, closely related to menstruation and pregnancy. Impairment of decidualization leads to various endometrial disorders, such as infertility, recurrent miscarriage, and preterm birth. The development and use of the endometrial decidualization model in reproductive studies have been a highlight for reproductive researchers for a long time. The mouse has been extensively used in studying reproduction and decidualization. There are three well-established mouse models regarding decidualization, namely natural pregnancy decidualization (NPD), artificial decidualization (AD), and in vitro decidualization (IVD). Among them, AD is considered a reliable model for mouse decidualization, which is easy to implement and close to NPD. This paper focuses on a modified method of the generation and application process of the mouse artificial decidualization model with ovariectomy to avoid ovarian effects, which can obtain highly reproducible results with small within group variances. This method provides a good and reliable animal model for the study of endometrial decidualization.
With the development of human-assisted reproductive technology, the current clinical pregnancy rate of in vitro fertilization-embryo transfer (IVF-ET) has reached or even exceeded that of natural pregnancy. Despite this, many patients in assisted reproduction clinical practice still undergo multiple embryo transfers but fail to achieve pregnancy as desired. However, its specific molecular mechanism is still unclear, so clinical intervention is ineffective, which is one of the significant challenges facing reproductive medicine1,2.
Endometrial factors account for about two-thirds of the causes of IVF failure3. Human embryo implantation is divided into three stages: positioning, adhesion, and invasion4,5,6. The maternal endometrium undergoes a series of changes to meet the arrival of the embryo. Forming an implantation "window period" provides favorable conditions for embryo implantation7,8.
In most mammals, after the blastocyst adheres to the luminal epithelium of the uterus, the stromal cells surrounding the blastocyst rapidly begin to proliferate and differentiate, and the rapid remodeling of the mesenchyme changes its shape and function, leading to embryo implantation5,9,10. The rapid increase in site volume and weight allows the blastocyst to become embedded in the uterine stroma, a process known as decidualization11. The endometrial stroma differentiates and remodels in preparation for pregnancy, while the transition of stromal cells provides space and new signaling connections for decidual cells to perform their functions12,13. Stromal cells transform into decidual cells and secrete many iconic factors such as prolactin (PRL), insulin-like growth factor-binding protein 1 (Igfbp1), and so on. Studies have shown that abnormal decidualization is one of the key reasons for embryo implantation failure, but the cause of abnormal decidualization is still unclear and needs to be further elucidated1,14.
The mouse artificial decidualization model is essential for studying the physiological process and molecular mechanisms underlying decidualization. Artificial decidualization (AD) mainly refers to the process of endometrial decidualization established by artificial methods to simulate pregnancy or the menstrual cycle. In terms of morphology, there is little overall difference between pregnancy decidualization and artificial decidualization15,16. The uterine glands exist in the endometrium before decidua form and disappear after decidualization. Regarding the gene expression, only a slight difference is identified between natural pregnancy decidualization (NPD) and AD15. Consequently, the artificial decidualization model in mice can simulate pregnancy decidualization to explore the unknown pathogenesis and new treatment of human reproductive diseases.
NPD, AD, and in vitro decidualization (IVD) are three methods to achieve mouse decidualization. The NPD model depends on natural pregnancy and is closest to the maternal physiological state, including the effects from embryos. Comparing the differences between implantation and non-implantation sites is a more physiological and convenient approach for studying decidualization. The AD model was developed by using an intrauterine injection of sesame oil as a stimulant to induce decidualization in a pseudopregnant female mouse mated with vasectomized males to avoid the impact from embryos. Both NPD and AD models play essential roles in different research purposes, but they cannot avoid mating failure and within-group differences caused by the different activities of maternal hormone metabolism. IVD is a method depending on the treatment of combined estrogen and progesterone at the cellular level, which requires more stringent experimental conditions and operating ability. However, the in vitro model cannot fully simulate the decidual response under physiological conditions15. Therefore, we propose a simple and improved induction method modified from traditional AD to reduce the effect of endogenous hormones on decidualization. Based on ensuring the success of decidualization induction, it is closer to the physiological state and more suitable for experiments that need to exclude embryo factors.
Decidualization in mice is a spontaneous process depending on the presence of embryos, which is different from humans. However, it has been found that artificial stimulation such as uterine injection of glass beads and uterine laceration can induce decidualization of the endometrium instead of embryos. In addition, researchers found that many factors could induce decidual or participate in decidualization, such as the injection of steroid hormones, prostaglandins, and growth inhibitory factors into the uterine cavity<sup…
The authors have nothing to disclose.
The authors wish to acknowledge support from the National Nature Science Foundation of China (82001629, XQS), the Youth Program of Natural Science Foundation of Jiangsu Province (BK20200116, XQS), and Jiangsu Province Postdoctoral Research Funding (2021K277B, XQS).
Estrogen | Sigma | E2758 | Hormone supplement |
Progesterone | Sigma | P0130 | Hormone supplement |
Sesame oil | Sigma | S3547 | Hormone supplement |
Sodium pentobarbital | Dainippon Sumitomo Pharma Co.,Ltd. | Anaesthesia | |
Meloxicam injection | Qilu Animal Health Products Co., Ltd | Analgesia | |
Alkaline phophatase stain kit(kaplow's/azo coupling method) | Solarbio | G1480 | Alkaline phophatase stain |
Eosin | Servicebio | G1005-2 | HE stain |
Hematoxylin | Servicebio | G1005-1 | HE stain |
ChamQ Universal SYBR qPCR Master Mix | Vazyme | Q711-02 | qPCR |
70% ethanol | Lircon | ZH1120090 | Disinfect |
Iodophor | Runzekang | RZK-DF | Disinfect |
Erythromycin Eye Ointment | Guangzhou Baiyunshan | Mice eyeball protect | |
4-0 suture | Ethicon | W329 | Incision suture |
10% formalin | Yulu | L25010118 | Tissue fix |
Optimal cutting temperature compound | Sakura | 4583 | Ssection |
Trizol reagent | Ambion | 15596018 | qPCR |