Molecular evidence for differences in endometrium in severe versus mild endometriosis

Women with stage III/IV versus stage I/II endometriosis have lower implantation and pregnancy rates in natural and assisted reproduction cycles. To elucidate potential molecular mechanisms underlying these clinical observations, herein we investigated the transcriptome of eutopic endometrium across the menstrual cycle in the setting of severe versus mild endometriosis. Proliferative (PE), early secretory (ESE), and mid-secretory (MSE) endometrial tissues were obtained from 63 participants with endometriosis (19 mild and 44 severe). Purified RNA was subjected to microarray analysis using the Gene 1.0 ST Affymetrix platform. Data were analyzed with GeneSpring and Ingenuity Pathway Analysis and subsequently validated. Comparison of differentially regulated genes, analyzed by cycle phase, revealed dysregulation of progesterone and/or cyclic adenosine monophosphate (cAMP)-regulated genes and genes related to thyroid hormone action and metabolism. Also, members of the epidermal growth factor receptor (EGFR) signaling pathway were observed, with the greatest upregulation of EGFR in severe versus mild disease during the early secretory phase. The extracellular matrix proteoglycan versican (VCAN), which regulates cell proliferation and apoptosis, was the most highly expressed gene in severe versus mild disease. Upregulation of microRNA 21 (MIR21) and DICER1 transcripts suggests roles for microRNAs (miRNAs) in the pathogenesis of severe versus mild endometriosis, potentially through regulation of gene silencing and epigenetic mechanisms. These observed differences in transcriptomic signatures and signaling pathways may result in poorly programmed endometrium during the cycle, contributing to lower implantation and pregnancy rates in women with severe versus mild endometriosis.