Investigating Uterine Natural Killer Cells Through Next Generation Sequencing — A Pilot Gene Expression Study

Abstract

Background: Uterine natural killer (uNK) cells form the major leucocyte population in the stroma in late secretory phase endometrium. Their actual function is unknown with available data suggesting a potential role in angiogenesis regulation, decidualization and placentation. Next generation sequencing (NGS) can be used to accurately define day of menstrual cycle through endometrial gene expression. Genes uniquely expressed by uNK are currently unknown. However, previous studies of first trimester decidua and blood have identified genes that are uniquely expressed by these NK cells. Aim: To identify potential molecular markers of uNK cells. Method: Endometrial samples were collected from 266 reproductive aged women across menstrual cycle. Gene expression profiles in endometrial tissues were generated using Illumina NovaSeq platforms. Gene expression data was normalized for cycle stage. Expression levels of previously known NK cell genes were examined across menstrual cycle. Results: Our analysis has shown that many NK cell genes (95% decidual, 71% peripheral) are expressed by the endometrium. We have identified 12 common genes that are expressed by both decidual and peripheral NK cells, and the endometrium. Expression levels of these common genes (except one) share a similar pattern across menstrual cycle. Their expression levels increase in secretory phase endometrium with peak expression levels at late secretory phase, as predicted by what is known about changing uNK cell numbers in endometrium. One example is the gene NCAM1 which codes for protein CD56 - a specific marker for uNK cells. Conclusion: This study has shown that it is possible to assess uNK cells through molecular approaches. Further molecular study of uNK cells is warranted and will help to provide evidence regarding uNK cells in human reproduction.