Background: Endometrial remodeling occurs during each menstrual cycle in women. Reports have shown that, in a variety of cell types, processes such as proliferation, signaling complex formation and extra cellular matrix remodeling require a cytoplasmic tyrosine kinase, focal adhesion kinase (FAK). The present study has focused on the expression pattern of FAK in human endometrium during the menstrual cycle. The purpose of this study was to ascertain the probable function of FAK in menstrual cycle changes and the role of FAK in tissue repair and tissue remodeling in vivo. Methods: Formalin-fixed paraffin-embedded endometrial samples were obtained from 400 pre-menopausal, non-pregnant women, who underwent hysterectomy and biopsy for benign diseases. Forty six samples with no tissue abnormalities were studied and ABC staining method of immuno-histochemistry methods was applied. Positive staining of FAK by different cell types of human endometrium was scaled and compared with each other by using histologic score method. Results: All different cell types of endometrium showed various patterns of FAK expression in different stages of menstruation. FAK in glandular and luminal epithelial cells is up-regulated during the early proliferative (EP) to mid-secretory (MS) phases. FAK in stromal cells is up-regulated during the EP, early and MS phases in comparison to the late secretory (LS) phase. FAK expression in endothelial cells is up-regulated during the EP and MS phases in comparison to LS phase. This study showed that endometrial FAK expression is a phase-dependent manner during the menstrual cycle. Conclusion: It appears that up-regulation of FAK during the proliferative phases is responsible for endometrial regeneration and high expression of FAK in the EP and MS phases may associate with the implantation. Down-regulation of FAK during the LS phase may facilitate apoptosis in human endometrium. It seems that FAK as a key kinase plays a critical role in endometrial remodeling that it may regulate by steroid hormones.

Keywords: FAK, Endometrial Remodeling, Steroid hormones, Menstrual cycle

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