Deciphering the proteomic signature of human endometrial receptivity.

Are there any proteomic differences between receptive (R) and non-receptive (NR) endometrial receptivity array (ERA)-diagnosed endometria obtained on the same day of a hormonal replacement therapy (HRT) treatment cycle? There is a different proteomic signature between R and NR ERA-diagnosed endometrium obtained on the same day of HRT cycles. The human endometrial transcriptome has been extensively investigated in the last decade resulting in the development of a new diagnostic test based on the transcriptomic signature of the window of implantation (WOI). Much less is known about the proteomics derived from the transcripts present during the WOI. This study was a basic proteomic analysis of human endometrial biopsies taken from twelve IVF patients. Human endometrial biopsies were collected during HRT cycles after 5 days of progesterone (P) administration, and diagnosed as receptive (R; n = 6) or non-receptive (NR; n = 6) by the ERA test. Endometrial proteins were extracted, labelled and separated using differential in-gel electrophoresis (DIGE). Proteins were identified using mass spectrometry, followed up by in silico analysis. Validation studies using western blots and immunolocalization were performed for the progesterone receptor membrane component 1 (PGRMC1) and annexin A6 (ANXA6) proteins. DIGE analysis followed by protein identification by MALDI-MS and database searches revealed 24 differentially expressed proteins in R versus NR samples. In silico analysis showed two pathways which were significantly different between R and NR samples. Expression of PGRMC1 and ANXA6 was validated and localized by western blots and immunohistochemistry. These results highlight these proteins as key targets likely to be important in the comprehension of human endometrial receptivity. This was mainly a descriptive study with no functional studies on the proteins found. We also used a low number of human endometrial samples for the DIGE analysis. This study identified the proteomic profile associated with receptive or non-receptive human endometria. Our findings suggest that although histological dating indicates a putative 'receptive' status within the WOI, a different transcriptomic and proteomic profile is observed in these samples. We should move towards using more personalized WOIs, where identification of the correct endometrial receptivity status, and consequently the success of IVF, relies on individual molecular signatures rather than traditional endometrial dating. F.D.'s participation in this work was supported by the Spanish Ministry of Economy and Competitiveness, through the Miguel Servet Programme (CP13/00075) co-founded by FEDER. The project was also supported by a grant from the Spanish Ministry of Economy and Competitiveness, through the FIS Programme (PI12/00450). The authors have no financial/commercial conflicts of interest to declare.