MOLECULAR PHENOTYPING OF THE CYCLING HUMAN ENDOMETRIUM AND HORMONALLY REGULATED GENES IMPORTANT FOR IMPLANTATION

Human endometrium is a dynamic tissue that undergoes proliferation in response to estradiol (E2) in the first half of the menstrual cycle and then differentiation of cellular constituents in the secretory phase, in response to progesterone (P) directly or by paracrine interactions among cell types. Histologic evaluation of endometrium has been the main stay of assessing cycle phase, dating for fertility, and evaluating abnormalities, including endometritis, endometrial hyperplasia, and cancer. However, histologically normal endometrium has been demonstrated to have abnormal expression of specific genes and/or proteins in disorders such as endometriosis, hydrosalpinges, and polycystic ovarian syndrome. We conducted a multi-center clinical study aimed to define the endometrial transcriptome across the menstrual cycle in healthy women and women with endometriosis and compared this to histologic evaluation. Endometrial tissue was obtained from 45 normal subjects undergoing an operative procedure for benign gynecologic conditions and also from some normal volunteers and from 16 subjects with severe endometriosis. RNA was isolated and hybridized to Affymetrix whole genome arrays containing 54,600 genes, and data were subjected to bioinformatic analysis using GeneSpring software and Genontology, and KEGG pathway analysis. Principal Component Analysis revealed clustering of samples into cycle phases, independently of how they were obtained (curetting or biopsy) or indication for surgery. Hierarchical clustering revealed 2 major branches that contained (1) proliferative (PE) and early secretory (ESE) endometrium and (2) mid (MSE) and late (LSE) secretory endometrium. MSE, which corresponds to the window of implantation, revealed numerous genes encoding secretory proteins, cytokines and chemokines, including CXCL14, and members of the innate immune system among others. LSE revealed a transition to a proinflammatory phenotype of the immune response and up-regulation of matrix degrading enzymes and the members of the prostanoid family. In women with moderate-severe endometriosis, there was an abnormal molecular transition from ESE to MSE and a decreased response to P. Others have evaluated the endometrial transcriptome during gonadotropin stimulation cycles that reveals advanced maturation of the endometrium and thus dyssynchrony of gene expression in the implantation window. The data underscore the utility of assessing the endometrial transcriptome in understanding biological processes in the endometrium in the window of implantation and the potential utility of this approach for diagnosing endometrial abnormalities. Supported by NIH U54 HD31398 and the NIH Office of Women's Health Research.