Progesterone regulates the secretion of GnRH in bovine endometrial cells via the Erk1/2-ARRB1 pathway

In ruminants, progesterone promotes uterine development to create a favourable environment for an embryo. However, the mechanisms by which progesterone regulates the function of the endometrial epithelial cells that line the uterus remain unclear. To investigate likely mechanisms, this study used different concentrations of progesterone to treat cells from a bovine endometrial epithelial cell (BEEC) line. The effect of the treatments was assessed by constructing mRNA expression profiles of the cells using RNA sequencing (RNA-Seq). Compared to the control cells (0 ng/mL progesterone), it was revealed that expression of the cytokine interleukin 6 (IL6) was upregulated (P < 0.05) with both the 10 ng/mL and 15 ng/mL progesterone treatment of the BEECs. There was decreased expression of the matrix metallopeptidase 9 (MMP9) enzyme (P < 0.05) and increased expression of the vascular endothelial growth factor (VEGF) gene (P < 0.05) in the 5, 10, and 15 ng/mL progesterone treated BEECs. In total, 138, 132 and 385 differentially expressed genes (DEGs) were identified in the BEECs treated with 5, 10 and 15 ng/mL of progesterone respectively, with these genes mainly associated with leukotriene and oxytocin signalling pathways, cell surface receptor signalling and GnRH secretion, multicellular organism process regulation, and TNF-related signalling pathways. The study revealed that BEECs treated with 10 ng/mL progesterone had increased β-arrestin 1 gene (ARRB1) expression, which would inhibit the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway, and reduce gonadotropin-releasing hormone (GnRH) secretion, thus potentially affecting follicle stimulating hormone (FSH) and luteinising hormone (LH) activity. A small interfering RNA (siRNA) approach was then employed to disrupt ARRB1 expression. The siRNA suppressed ARRB1 expression, promoted Erk1/2 expression, and increased GnRH secretion. In conclusion, progesterone induces concentration-dependent gene expression changes in BEECs, and inhibits GnRH secretion in BEECs through the ARRB1-Erk1/2 signalling pathway. These findings provide in-vitro mechanistic insights into the direct actions of progesterone on endometrial epithelial cells.