The orphan nuclear receptor, liver receptor homolog-1 (LRH-1, NR5A2) regulates decidualization

The period of endometrial receptivity in humans coincides with the differentiation of endometrial stromal cells into highly specialized decidual cells through a process known as decidualization. This transformation of endometrial cells is abnormal in recurrent pregnancy loss patients. Liver homolog receptor 1 (LHR-1, NR5A2) is an orphan nuclear receptor and a transcription factor that regulates many reproductive events. The activation of this receptor leads to transcriptional activation of its target genes.  We have previously shown that it is essential for decidualization in the mouse uterus.  LRH-1 is expressed in the human uterus in both proliferative and secretory phases of the menstrual cycle and its expression increases during in vitro decidualization.  We hypothesize that LRH-1 is indispensable for proper decidualization of the endometrial stroma, acting through the transcriptional regulation of genes required for transformation of stromal cells into decidual cells.  To explore the molecular mechanism of transcriptional regulation mediated by this receptor, we established an in vitro model of decidualization, using an immortal human endometrial stromal cell line (hESC).  An overexpression model developed by transfecting the cells with a plasmid constitutively expressing Lrh-1, resulted in 5 fold increases in abundance of transcripts for the decidualization marker genes prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1). Furthermore, the downregulation of the receptor using short hairpin RNA (shRNA) abrogates the decidual reaction, from both a morphological point of view and in terms of expression of the two marker genes. Chromatin immunoprecipitation (ChIP)  analysis showed that LRH-1 binds to genomic regions upstream  of genes important for decidualization such as PRL, wingless-type MMTV integration site family, member 4 (WNT4), wingless-type MMTV integration site family, member 5 (WNT5), cyclin-dependent kinase inhibitor 1A (p21, CDKN1A) and interleukin-24(IL-24). For each of these genes, the binding increased  during in vitro decidualization.  Structural studies have identified phospholipids as potential LRH-1 ligands.  We therefore explored the effect of ligand treatment on LRH-1 with an agonist and an inverse agonist for the nuclear receptor. Analysis by quantitative polymerase chain reaction (qPCR) and Western blot demonstrated that the modulation of LRH-1 activity by its ligands also affects the decidual reaction. Recent studies have shown that  decidualized human stromal cells are biosensors of embryo quality and that they have the capacity to migrate towards the embryo. Our time-lapse evaluation of hESC cells co-cultured with mouse embryos indicates directed migration of the cells toward the embryo.  This effect is markedly diminished when LRH-1 is depleted by shRNA in hESC.   Our data provide evidence that LRH-1 regulates not only the transcription of a set of genes involved in decidualization but also the directional motility of these cells in vitro.

Keyphrases: LRH-1, decidualization, chromatin immunoprecipitation, co-culture, ligands