MSX1-expression during the different phases in healthy human endometrium

Abstract

Purpose: The human endometrium consists of different layers (basalis and functionalis) and undergoes different phases throughout the menstrual cycle. In a former paper our research group was able to describe MSX1 as a positive prognosticator in endometrial carcinomas. The aim of this study was to examine the MSX1 expression in healthy endometrial tissue throughout the different phases to gain more insight on the mechanics of MSX-regulation in the female reproductive system. Materials and Methods: In this retrospective study we investigated a total of 19 normal endometrial tissues (7 during proliferative phase and each 6 during early and late secretory phase). We used immunohistochemical staining and an immunoreactive score (IRS) to evaluate MSX1 expression. We also investigated correlations with other proteins, that have already been examined in our research group using the same patient collective. Results: MSX1 is highly expressed during the proliferative phase and downregulated at early and late secretory phase (p=0.018). Also, a positive correlation between MSX1 and the progesterone-receptor A (PR-A) (correlation coefficient (cc)=0.0671; p=0.024), the progesterone receptor B (PR-B) (cc=0.0691; p=0.018) was found. A trend towards negative correlation was recognized between MSX1 and Inhibin Beta-C-expression in glandular cells (cc=-0.583; p-value=0.060). Conclusion: MSX1 is known as a member of the muscle segment homeobox gene family. MSX1 is a p53-interacting protein and overexpression of homeobox MSX1 induced apoptosis of cancer cells. Here we show that MSX1 is highly expressed especially in the proliferative phase of glandular epithelial tissue of the normal endometrium. Because MSX1 is known to be downregulated by progesterone, the found correlation of MSX1 and both PR-A and -B may represent a direct regulation of the MSX1 gene by a PR-response element.