Upregulation of the long non-coding RNA TUG1 inhibits granulosa cell apoptosis and autophagy in polycystic ovary syndrome by regulating ERK/MAPK pathway

Polycystic ovary syndrome ( PCOS) is the most common cause of anovulatory infertility in women of reproductive age, and its etiology remains poorly understood. Evidence has indicated that the increase in granulosa cell (GC) proliferation is associated with PCOS. Altered activities of long non-coding RNAs (lncRNAs) have been associated with human diseases and development. Taurine upregulated gene 1 (TUG1), an evolutionarily conserved lncRNA, has been shown to play an oncogenic role in various cancers. However, little is known about the role of TUG1 in PCOS. Therefore, the aim of this study is to explore the potential role of TUG1 in the pathogenesis of PCOS. We measured TUG1 lncRNA expression levels in GCs from 58 PCOS patients and 58 controls. Also, TUG1 was knocked down in a human GC tumor-derived cell line, KGN, to investigate the role of TUG1 and its molecular mechanism in cell apoptosis and autophagy. GCs were collected from women with or without PCOS undergoing IVF or ICSI treatment. The PCOS diagnosis was based on the Rotterdam revised criteria, and control patients were limited to male factor or tubal disease and had a normal ovarian reserve. Quantitative real-time PCR was used to measure the differential expression levels of TUG1 between PCOS patients and controls. The receiver operating characteristic (ROC) curve was drawn to evaluate the diagnostic values of TUG1 in PCOS. In the KGN cell line, TUG1 was knocked down with locked nucleic acid GapmeRs. Cell counting kit-8 assays, ethynyl-2-deoxyuridine assays and flow cytometry were used to study the role of TUG1 in cell proliferation and apoptosis, and western blotting was performed to detect the potential underlying mechanism. We first found that TUG1 lncRNA was significantly upregulated in PCOS GCs and was associated with the antral follicle count (R = 0.264, P < 0.01 versus control). The ROC curves illustrated strong separation between all the PCOS patients and the control group (AUC: 0.627; 95% CI: 0.526–0.728; P =0.017). TUG1 was primarily localized in the nuclei of GCs. TUG1 knockdown in KGN cells inhibited cell proliferation and promoted cell apoptosis. In addition, TUG1 knockdown induced an increase in the protein levels of bax, bak, cleaved caspase-3, caspase-9, cleaved caspase-9, LC3B and phosphorylated ERK (p-ERK), and a decrease in the protein levels of bcl-2 and p62. Furthermore, inhibition of the ERK/MAPK pathway with U0126, the upregulation of p-ERK, bax, bak, cleaved caspase-3, caspase-9, cleaved caspase-9, LC3B, and the downregulation of bcl-2 and p62 by the knockdown of TUG1 were all attenuated. Therefore, downregulation of TUG1 may promote cell apoptosis and autophagy by activation of the ERK/MAPK pathway. Our study first reported that the expression of TUG1 was significantly higher in the PCOS group than that in the control group, TUG1 may inhibit cell apoptosis and autophagy in GCs through inhibition of the ERK/MAPK pathway and contribute to excess antral follicles. TUG1 has potential diagnostic value in PCOS. Therefore, analysis of TUG1 and its molecular mechanisms of action provide new insights into the pathogenesis of PCOS.