Expression of membrane protein disulphide isomerase A1 (PDIA1) disrupt a reducing microenvironment in endometrial epithelium for embryo implantation.

Various proteins in the endometrial epithelium are differentially expressed in the receptive phase and play a pivotal role in embryo implantation. The Protein Disulphide Isomerase (PDI) family contains 21 members that function as chaperone proteins through their redox activities. Although total PDIA1 protein expression was high in four common receptive (Ishikawa and RL95-2) and non-receptive (HEC1-B and AN3CA) endometrial epithelial cell lines, significantly higher membrane PDIA1 expression was found in non-receptive AN3CA cells. In Ishikawa cells, oestrogen up-regulated while progesterone down-regulated membrane PDIA1 expression. Moreover, mid-luteal phase hormone treatment down-regulated membrane PDIA1 expression. Furthermore, oestrogen at 10 nM reduced spheroid attachment on Ishikawa cells. Interestingly, inhibition of PDIA1 function by bacitracin or 16F16 increased the spheroid attachment rate onto non-receptive AN3CA cells. Over-expression of PDIA1 in receptive Ishikawa cells reduced the spheroid attachment rate and significantly down-regulated integrin ß3 levels, but not integrin αV and E-cadherin. Addition of reducing agent TCEP induced a sulphydryl-rich microenvironment and increased spheroid attachment onto AN3CA cells and human primary endometrial epithelial cells collected at LH+7/8 days. The luminal epithelial cells from human endometrial biopsies had higher PDIA1 protein expression in the proliferative phase than in the secretory phase. Our findings suggest oestrogen and progesterone regulate PDIA1 expression, resulting in the differential expressions of membrane PDIA1 protein to modulate endometrial receptivity. This suggests that membrane PDIA1 expression prior to embryo transfer could be used to predict endometrial receptivity and embryo implantation in women undergoing assisted reproduction treatment.

ACE inhibitors on ACE1, ACE2, and TMPRSS2 expression and spheroid attachment on human endometrial Ishikawa cells.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters cells via receptor angiotensin-converting enzyme 2 (ACE2) and co-receptor transmembrane serine protease 2 (TMPRSS2). However, patients with SARS-CoV-2 infection receiving ACE1 inhibitors had higher ACE2 expression and were prone to poorer prognostic outcomes. Until now, information on the expression of ACE1, ACE2, and TMPRSS2 in human endometrial tissues, and the effects of ACE inhibitors on embryo implantation are limited. We found human endometria expressed ACE1, ACE2, and TMPRSS2 transcripts and proteins. Lower ACE1, but higher ACE2 transcripts were found at the secretory than in the proliferative endometria. ACE1 proteins were weakly expressed in endometrial epithelial and stromal cells, whereas ACE2 and TMPRSS2 proteins were highly expressed in luminal and glandular epithelial cells. However, ACE1 and TMPRSS4 were highly expressed in receptive human endometrial epithelial (Ishikawa and RL95-2) cells, but not in non-receptive AN3CA and HEC1-B cells. Treatment of human endometrial epithelial cells with ACE1 (Captopril, Enalaprilat, and Zofenopril) or ACE2 (DX600) inhibitors did not significantly alter the expression of ACE1, ACE2 and TMPRSS2 transcripts and spheroid (blastocyst surrogate) attachment onto Ishikawa cells in vitro. Taken together, our data suggest that higher ACE2 expression was found in mid-secretory endometrium and the use of ACE inhibitors did not alter endometrial receptivity for embryo implantation.