Two-dimensional liquid chromatography with tandem mass spectrometry-based proteomic characterization of endometrial luminal epithelial surface proteins responsible for embryo implantation.

OBJECTIVE:To identify endometrial epithelial cell surface proteins essential for blastocysts implantation. DESIGN:Isolation of cell-surface labeled prereceptive (pregnancy day 1) and receptive (pregnancy day 4) mouse endometrial proteins coupled to two-dimensional liquid chromatography with tandem mass spectrometry. SETTING:University research laboratory. ANIMAL(S):Sexually mature female imprinting control region (ICR) mice. INTERVENTION(S):Labeling, purification, and identification of endometrial luminal surface proteins with differentially expressing proteins determined by significant analysis of a microarray algorithm and selected differentially expressed proteins verified by immunohistochemistry and functional assay. MAIN OUTCOME MEASURE(S):Investigation in endometrial luminal surface proteome of prereceptive and receptive endometria of the expression of four of the differentially expressed proteins and functional analysis of aminopeptidase N in a three-dimensional blastocyst-endometrial coculture model. RESULT(S):We identified 104 cell surface proteins from prereceptive and receptive pregnant mouse endometria and found that 27 were statistically significantly up-regulated and 18 were statistically significantly down-regulated in the receptive endometrium. Immunohistochemical analysis of four of the differentially expressed proteins in the endometrium showed concordant results. Functional assay showed that blastocyst attachment was statistically significantly reduced upon inhibition of aminopeptidase N. CONCLUSION(S):The luminal cell surface proteome of the prereceptive and receptive endometria differs, and aminopeptidase N is potentially involved in embryo attachment.