A Role for the orphan nuclear receptor estrogen-related receptor alpha in endometrial stromal cell decidualization and expression of genes implicated in energy metabolism

Abstract

Context: Differentiation (decidualization) of endometrial stromal cells (ESC) is an essential prerequisite for successful implantation and establishment of pregnancy.

Objective: The aim was to determine whether the orphan nuclear receptor estrogen-related receptor α (ERRα, NR3B1), and its target genes, medium chain specific acyl-CoA dehydrogenase (MCAD, ACADM), pyruvate dehydrogenase kinase 4 (PDK4), and phosphoenolpyruvate carboxykinase 2 (PEPCK, PCK2), play a role in the decidualization process.

Setting: We conducted the study at a University Research Institute.

Patients and methods: Endometrial tissues were collected from women with regular menstrual cycles; tissues were used for recovery of primary ESC or RNA extraction or were fixed for immunohistochemistry. Primary ESC were decidualized in vitro; some cells were treated with XCT790 (ERRα inverse agonist).

Results: Decidualization of ESC in vitro was associated with a significant increase in expression of transcripts encoding ERRα and its coactivator peroxisome proliferator-activated receptor γ coactivator-1 α. Expression of ERRα target genes was altered with increased expression of MCAD and PDK4 and reduced expression of PEPCK. Incubation of decidualized ESC with XCT790 reduced expression of ERRα and markers of decidualization such as IGFBP-1.

Conclusion: Increased expression of ERRα may play a role in altering the bioenergetics of decidualized ESC in preparation for implantation of the embryo and successful establishment of early pregnancy.

Figure 1

ERRα is expressed in human endometrium during the menstrual cycle and up-regulated upon in vitro stromal cell decidualization. Expression of mRNAs encoding ERα (A) and ERRα (B) were quantified in staged human endometrial biopsies using qRTPCR with 18S as a comparator. Data are expressed as mean ± sem (M, menstrual; P, proliferative; ES, early secretory; MS, midsecretory; LS, late secretory). The number of samples analyzed from each stage (n) is indicated on the x-axis. *, P = 0.03 between P and LS. C, ERRα protein was immunolocalized to epithelial cells lining glands (g), stromal fibroblasts (s), and endothelial cells (arrowhead) in human endometrium at all stages of the cycle. Illustrated is a section of endometrium from the MS phase; inset, negative control of same tissue sample. The scale bar represents 50 μm. D–I, Results of qRTPCR analysis of primary ESC incubated in the presence or absence of decidualization medium for 4 d. Decidualization was confirmed by a significant increase in expression of IGFBP-1 (D, P < 0.001). In the same cells, there was a significant increase in mRNAs encoding ERRα (E) and the coactivator PGC1α (F), and changes in expression of mRNAs for three known ERRα target genes: PDK4 (G), MCAD (H), and PEPCK (I). *, P < 0.001 decidualized ESC compared with control (E to I). Data are expressed as fold changes from the control; data represent the average of four fibroblast cultures (±sem), and the experiments were done in duplicate.

Figure 2

Pharmacological inhibition of ERRα with the inverse agonist XCT790 impairs the induction and maintenance of a decidualized phenotype. A, Experimental protocol. ESC were either decidualized for 4 d in the presence of XCT790 (protocol A) or decidualized for 4 d, then incubated with DM containing XCT790 (1, 5, or 10 μm; protocol B). B and C, IGFBP-1 protein detected in medium by ELISA after protocols A or B. D–I, mRNA concentrations of IGFBP-1 (D and E), prolactin (F and G), or ERRα (H and I) for protocols A and B, respectively, in each case. Note that incubation of cells with XCT790 had a significant impact on gene expression (*, P < 0.05; **, P < 0.01; ***, P < 0.001) compared with DMSO controls (n = 4).