Alteration in Endometrial Proteins during Early- and Mid-Secretory Phases of the Cycle in Women with Unexplained Infertility

BACKGROUND: Compromised receptivity of the endometrium is a major cause of unexplained infertility, implantation failure and subclinical pregnancy loss. In order to investigate the changes in endometrial protein profile as a cause of unexplained infertility, the current study was undertaken to analyze the differentially expressed proteins of endometrium from early-secretory (LH+2) to mid-secretory phase (LH+7), in women with unexplained infertility. METHODS: 2-D gel electrophoresis was performed to analyze the proteomic changes between early- (n = 8) and mid-secretory (n = 8) phase endometrium of women with unexplained infertility. The differentially expressed protein spots were identified by LC-MS analysis and validated by immunoblotting and immuno-histochemical analysis in early- (n = 4) and mid-secretory (n = 4) phase endometrium of infertile women. Validated proteins were also analyzed in early- (n = 4) and mid-secretory (n = 4) phase endometrium of fertile women. RESULTS: Nine proteins were found to be differentially expressed between early- and mid- secretory phases of endometrium of infertile women. The expression of Ras-related protein Rap-1b, Protein disulfide isomerase A3, Apolipoprotein-A1 (Apo-A1), Cofilin-1 and RAN GTP-binding nuclear protein (Ran) were found to be significantly increased, whereas, Tubulin polymerization promoting protein family member 3, Superoxide dismutase [Cu-Zn], Sorcin, and Proteasome subunit alpha type-5 were significantly decreased in mid- secretory phase endometrium of infertile women as compared to early-secretory phase endometrium of infertile women. Validation of 4 proteins viz. Sorcin, Cofilin-1, Apo-A1 and Ran were performed in separate endometrial biopsy samples from infertile women. The up-regulated expression of Sorcin and down-regulated expression of Cofilin-1 and Apolipoprotein-A1, were observed in mid-secretory phase as compared to early-secretory phase in case of fertile women. CONCLUSIONS: De-regulation of the expression of Sorcin, Cofilin-1, Apo-A1 and Ran, during early- to mid-secretory phase may have physiological significance and it may be one of the causes for altered differentiation and/or maturation of endometrium, in women with unexplained infertility.