miRNAs associated with endoplasmic reticulum stress and unfolded protein response during decidualization

Research question: Do microRNAs (miRNAs) play a role in regulating endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) in decidualized cells and endometrium associated with reproductive failures?Design: Endometrial stromal cell line St-T1b was decidualized in vitro with 8-Br-cAMP over 5 days, or treated with the ERS inducer thapsigargin. Expression of ERS sensors, UPR markers and potential miRNA regulators was analysed by quantitative PCR. Endometrial biopsies from patients with recurrent pregnancy loss (RPL) and recurrent implantation failure (RIF) were investigated for the location of miRNA expression.Results: Decidualization of St-T1b cells resulted in increased expression of ERS sensors including ATF6a, PERK and IRE1a, and the UPR marker, CHOP. TXNIP, which serves as a link between the ERS pathway and inflammation, as well as inflammasome NLRP3 and interleukin 1b expression increased in decidualized cells. An in-silico analysis identified miR-17-5p, miR-21-5p and miR-193b-3p as miRNAs potentially involved in regulation of the ERS/UPR pathways and inflammation associated with embryo implantation. Their expression decreased significantly (P <= 0.0391) in non-decidualized cells in the presence of thapsigargin. Finally, expression of the selected miRNAs was localized by in-situ hybridization in stromal and glandular epithelial cells in endometrial samples from patients with RPL and RIF. Expression in stroma cells from patients with RPL was lower in comparison with stroma cells from patients with RIF.Conclusions: Decidualization in St-T1b cells is accompanied by ERS/UPR processes, associated with an inflammatory response that is potentially influenced by miR-17-5p, miR-21-5p and miR-193b-3p. These miRNAs are expressed differentially in stromal cells from patients with RPL and RIF, indicating an alteration in regulation of the ERS/UPR pathways.