There are 3 layers in the human uterus called the perimetrium, the myometrium, and the endometrium. The outer layer is known as the perimetrium that is made of serous cells while the middle layer is the thick myometrium made of smooth muscle cells. The inner layer is the endometrium that is made of epithelial cells and stromal cells.
The endometrium is composed of the functionalis layer which responds to the hormones secreted from the pituitary gland and the ovaries via changes in morphology and biochemistry. These hormones as known are released in a coordinated fashion to cause what is called “the menstrual cycle” or the reproductive cycle. This cycle produces changes in the endometrium so that it can receive the embryo in the event of fertilization. The 3 phases of the menstrual cycle are the proliferative phase where the functionalis layer undergoes proliferation followed by the secretory phase that involves the maturation of these cells. In the event fertilization does not occur, shedding of this functionalis layer occurs leading to the menstrual phase. The events involved to cause this shedding are yet to be ascertained. Another layer of cells in the endometrium is called the basalis layer containing stem cells thought to replenish the shed cells.
The use of in vitro cell culture systems allows for the development of models; endometrial cultures can allow studies in understanding the synchronous biology of the shedding of these cells as well as diseases such as reproductive diseases, infections and cancers.
A team led by Jividen published in the Journal of visualized experiments in 2014 two approaches to establish primary endometrium cultures from hysterectomy samples. One uses blades to mechanically scrape out tissue with 1x1x1 cm of tissue seeded in medium. The other approach is the use of trypsin (0.25%) to digest a sample size of 0.5×0.5×0.5 cm. While both yielded primary cultures, the scraping approach could be completed in 30 minutes while the trypsin approach allowed for faster observation of viable cells.
A clear marker to confirm the presence of endometrial cells is yet to be reported. The cells can be confirmed to be endometrial cells due to the presence of vimentin and the absence of cytokeratin and E cadherin. (In the case of samples during pregnancy, HLA-A, -B, -C are additional markers).
Research published in 2011 in Bioessays proposed that menstruation is due to the differentiation of endometrium cells during the secretory phase-called “spontaneous decidualization”. Hence, primary endometrium cultures were exposed to Medroxyprogesterone acetate (MPA) and 8- bromoadenosine 3’,5’-cyclic monophosphate (cAMP) due to which the expression of Prolactin (PRL) and Insulin-like Growth Factor Binding Protein 1 (IGFBP1) was observed showing that primary endometrium cultures can be established.
Primary endometrium cultures can allow studies to explore the processes of menstruation and disease. This becomes relevant given that 10% of women suffer from infertility across the world according to WHO. Access to treatment was sought by 7.4 million women and their partners between 2006 and 2010 (American Society for Reproductive Medicine). The involvement of the lack of decidualization has been connected to infertility. Hence, the search for mechanisms and biomarkers of the disease can be obtained from valuable primary cultures.
Jividen, K., Movassagh, M. J., Jazaeri, A., & Li, H. (2014). Two methods for establishing primary human endometrial stromal cells from hysterectomy specimens. Journal of visualized experiments: JoVE, (87), 51513. https://doi.org/10.3791/51513
Emera D, Romero R, Wagner G. The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness. Bioessays. 2011;34:26–35.
American Society for Reproductive Medicine: Quick facts about infertility. 2013. Available from: http://www.asrm.org/detail.aspx?id=2322.