Exploration of androgen action in the human endometrium
Lourenço, Paula Cristina Costa
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The endometrium undergoes recurrent cycles of dynamic remodelling, involving breakdown and scarless repair, proliferation and differentiation, including decidualisation of the stroma, during the menstrual cycle. Extensive studies have characterised how the steroid hormones oestrogen and progesterone acting via their nuclear receptors coordinate these remarkable changes. Although a few previous studies have postulated a role for androgens the impact of androgens on endometrial function remains understudied. The studies described in this thesis aimed to 1) identify cellular processes, pathways and networks regulated by androgens in human androgen receptor-positive endometrial stromal cells (hESCs), 2) investigate the potential for regulation and determine the regulation of putative dihydrotestosterone (DHT)-regulated gene expression by androgen in hESCs, 3) investigate the expression and regulation of putative androgen-regulated genes in the human endometrium across the menstrual cycle and in early pregnancy and 4) explore the role of androgens in modulating metformin-induced gene expression associated with decidualisation of hESCs. Analysis of data from a whole genome array conducted previously in the laboratory using primary hESCs treated with DHT for 2 or 8 hours identified time dependant putative androgen-regulated mRNAs (34 and 268 genes, respectively). Thereafter, all work was completed by the author. Gene ontology and functional based bioinformatic analyses of the putative androgen-regulated gene sets revealed potential androgen regulation of a variety of cell processes, pathways and networks including those associated with gene transcription, signal transduction pathways (such as phosphatidylinositol, oestrogen receptor alpha (ERα) and Wnt signalling), cancer pathways, metabolism, cell cycle, development, apoptosis/survival. In addition, various transcription factors (e.g. AR, c-Myc, SP1, ERα, p53, E2F1, RUNX2, CREB1 and STAT3) were associated with androgen regulation in hESCs. Consensus androgen receptor binding sites were identified in the promoter sequences of 18 genes by transcription factor binding site sequence analysis. Direct DHT regulation of ten of 15 of these genes was validated in endometrial stromal cells using qRTPCR. Of these genes, RGS2, SIK1, and SNCAIP mRNAs were confirmed as DHT-regulated in hESCs by use of an AR inhibitor (flutamide) and in addition, were not found to be regulated by oestradiol. Discovery bioinformatics predicted these genes may interact in a gene network involving AR and the cAMP transduction pathway. Expression of the 15 putative androgen-regulated genes was confirmed by qRTPCR in intact human endometrial tissue (13 novel) and 9 of these genes were regulated in association with decidualisation i.e. either in the secretory phase, the time at which decidualisation begins and/or in first trimester decidua. Protein expression of RGS2, SIK1 and Synphilin-1 (encoded by SNCAIP) was confirmed by immunohistochemistry in endometrial tissues and protein expression also appeared greater in decidua. Regulation of putative androgen-regulated gene expression by decidualisation was confirmed in 4 out of 8 genes by employing a model of reduced in vivo decidualisation i.e. decidua from ectopic pregnancies. Regulation of 5 out of 7 genes was confirmed in decidualised hESCs (RGS2, SIK1, SLC6A6, SNCAIP and AXIN2) but expression of these genes was not altered by DHT inclusion during decidualisation. Finally, only a high metformin concentration enhanced hESC decidualisation and putative androgen-regulated gene expression (4 genes) in decidualised hESCs. In comparison, in the presence of DHT, a lower clinically relevant metformin concentration (100μM) did enhance decidualisation marker expression but did not alter expression of putative androgen-regulated genes. In summary, these studies have revealed new insights into androgen action in the human endometrium. Studies in hESCs 1) predicted the pathways and interacting transcription factor regulatory networks that may be androgen-dependent in this cell type, these were associated with cell differentiation, apoptosis and proliferation, 2) identified novel putative androgen-regulated genes expressed in hESCs and in endometrial tissues, 3) showed putative androgen-regulated genes are regulated by DHT (possibly via AR) in endometrial stromal cells, some of which are also regulated in association with decidualisation and 4) showed that androgens may enhance decidualisation during exposure to the commonly used drug metformin. Collectively, these new findings support a physiological role for androgens in endometrial function and provide a series of new avenues for further studies of the regulation of differentiation and proliferation.