Tissue Factor and Tissue Factor Pathway Inhibitors TFPI and TFPI2 in Human Secretory Endometrium—Possible Link to Female Infertility

The aim of this study was to investigate tissue factor (TF) and its inhibitors TFPI and TFPI2 in secretory endometrium of fertile women and in women with unexplained infertility in relation to endometrial receptivity. In addition, common variation in the regulatory area of TF and TFPI genes was studied. Immunostaining of TF and TFPI, together with the appearance of pinopodes, revealed similar expression pattern in fertile endometrium throughout the secretory phase, being highest at the time of implantation. When compared protein expression levels at the time of implantation, infertile women demonstrated significantly higher TFPI expression in luminal epithelium. Furthermore, polymorphism TF-603 A/G was associated with the endometrial protein level in infertile women, being highest in women with GG genotype, and variation TFPI-287 T/C was associated with unexplained infertility, where infertile women presented more frequently T allele than fertile women. Contrary to TF and TFPI, TFPI2 showed different mRNA and protein expression patterns in fertile endometrium, and no differences between fertile and infertile women were detected. We conclude that the TF pathway is involved in normal endometrial maturation, where TF and TFPI seem to have important roles at the time of embryo implantation. Higher TFPI expression level during the time of embryo implantation and TFPI-287 T allele could be risk factors for unexplained infertility. No distinct involvement of TFPI2 in the regulation of endometrial receptivity and unexplained infertility was found.