Expression Patterns of VEGF and Flk-1 in Human Endometrium during the Menstrual Cycle

BACKGROUND The VEGF is essential in the process of tissue remodeling and angiogenesis. Limited data is available on the expression and regulation of VEGF and its receptors in the human endometrium. The aim of this study was evaluation of expression patterns of VEGF and Flk-1 in human endometrium during the menstrual cycle. METHODS Sixty paraffin-embedded blocks of endometrial tissues from the patients with normal menstrual cycles were obtained. Tissue samples were assembled into tissue microarray slides and classified by histological dating into five phases: the proliferative (n = 14), peri-ovulatory (n = 9), early-secretory (n = 12), mid-secretory (n = 11) and late-secretory (n = 14) phases. Immunohistochemical staining was performed using VEGF or Flk-1 monoclonal antibodies. The intensity of immunostaining was evaluated by the semi-quantitative scoring method (HSCORE). Kruskal-Wallis one-way analysis of variance and Scheff's post-hoc test were used for statistical analysis. A p-value of <0.05 was considered statistically significant. RESULTS VEGF and Flk-1 were expressed in the three components of the endometrium at various phases of the menstrual cycle. In the stroma, the expression of VEGF varied among the phases (p < 0.05). The expression of Flk-1 in the luminal and glandular epithelium revealed stronger intensity of immunostaining as compared with the stroma at the different phases (p < 0.05). The level of Flk-1 expression also showed significant differences among the phases in the glandular epithelium with greatest expression at late-secretory phase (p < 0.05). CONCLUSION Temporal and spatial distribution of VEGF and Flk-1 expression in the three components of human endometrium during menstrual cycle suggests the functional role of angiogenesis in the remodeling process of endometrial tissue.