MicroRNAs Expression in Endometriosis and Their Relation to Angiogenic Factors

Abstract

Despite the high prevalence of endometriosis and its incapacitating symptoms, pathogenic mechanisms of this multifactorial disease are unclear. A number of studies have reported that angiogenesis may play an important role in the growth of endometrium outside the uterus. In recent years, microRNAs (miRNAs) have emerged as regulators of gene expression implicated in fundamental biological processes and the pathology of many diseases. Recent studies have suggested that these small (21–22 nucleotide) noncoding RNAs may be important regulators of angiogenesis. Several studies have evaluated possible differential expression of miRNAs in eutopic compared with ectopic endometrium and reported conflicting results. Other angiogenic factors have been implicated in the pathogenesis of endometriosis. Increased levels of vascular endothelial growth factor (VEGF), a potent angiogenic factor, have been reported in endometriosis. Moreover, increased levels of an inhibitor of angiogenesis, thrombospondin-1 (TSP-1) in ovarian endometrioma have been reported. This study investigated several miRNAs implicated in regulation of angiogenesis and their relationship with the angiogenic factors, VEGF-A and TSP-1, comparing their angiogenic activity in endometriotic lesions (ovarian endometrioma, peritoneal lesion, and rectovaginal nodule) and eutopic endometrium from women with endometriosis. The expression of 8 miRNAs (miRNAs-15b, -16, -17-5p, -20a, -21, -125a, -221, and -222).was assessed using TaqMan real-time polymerase chain reaction. Expression of VEGF-A and TSP-1 mRNA were assessed by real-time polymerase chain reaction; protein levels of these 2 angiogenic factors were quantified by ELISA (enzyme-linked immunoadsorbent assay). Study subjects were 58 women with endometriosis; the control group was composed of 38 women without endometriosis. Paired biopsy samples from the eutopic endometrium and ovarian endometriomas of 41 patients with endometriosis were obtained. Compared with eutopic endometrium, paired extracts of ovarian endometriomata showed significantly lower expression of VEGF-A mRNA (P = 0.02) and protein (P = 0.002) and increased expression of antiangiogenic miRNAs (miR-125a [P = 0.003] and miR-222 [P < 0.001]). However, there was an increase in expression of the antiangiogenic factor, TSP-1 and a decrease in the expression of a proangiogenic miRNA (miR-17-5p) in ovarian endometrioma compared with eutopic endometrium (P < 0.001). Significant inverse correlations were observed between miR-222 and VEGF-A protein levels (−0.267, P = 0.018) and between miR-17-5p and TSP-1 protein levels (−0.260, P = 0.022). There were significantly higher VEGF-A protein levels in peritoneal lesions compared with ovarian endometriomata (P < 0.01). These findings suggest that expression of miRNAs regulating angiogenesis may modulate the expression of angiogenic factors and have an important role in the pathogenesis of endometriosis.