Peroxisome proliferator-activated receptor-γ coactivator 1α-mediated pathway as a possible therapeutic target in endometriosis

Abstract

Study question: Is a peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α)-mediated pathway involved in the development of endometriosis?

Summary answer: PGC-1α plays critical roles in inflammation and cell proliferation of endometriotic tissues and may be involved in the development of endometriosis.

What is known already: Expression levels of PGC-1α are higher in ovarian endometrioma (OE) than normal endometrium (NE). PGC-1α also stimulates aromatase activity and promotes local estrogen biosynthesis in OE.

Study design, size, duration: This is a case-controlled biological study using endometrial cells and tissues derived from 23 women with, and 10 women without, OE.

Participants/materials, setting, methods: Ectopic endometriotic and eutopic endometrial stromal cells (SCs) were isolated and maintained in culture. PGC-1α was either overexpressed in the cells or knocked down using siRNA. The expression of PGC-1α and other factors during endometriosis was examined using real-time PCR and western blotting, cell proliferation was measured using Cell Counting Kit-8 (WST-8) assays and transcriptional activity was assessed using luciferase reporter assays.

Main results and the role of chance: PGC-1α overexpression promoted the proliferation of OESCs in a time-dependent manner (P < 0.01 versus control) but not NESCs. PGC-1α stimulated aromatase (P < 0.01 versus control) and interleukin (IL)-6/IL-8 mRNA expression levels (P < 0.05 versus control for each) and led to inhibitor kappa B phosphorylation protein expression and upregulation of the apoptosis inhibitors X-linked inhibitor of apoptosis protein and survivin at mRNA level (P < 0.05 versus control for each). HX531, a selective retinoid-X receptor-α (RXRα) antagonist, suppressed the PGC-1α-induced cell proliferation (P < 0.05 versus control), aromatase/IL-6/IL-8/survivin mRNA expression (P < 0.05 versus control for each) and transcription reporter activity of PGC-1α in a dose-dependent manner (P < 0.01 versus control). Moreover, HX531 downregulated PGC-1α-induced aromatase-promoter PI.3-II transcripts in OESCs, and PGC-1α knockdown reduced aromatase, IL-6/IL-8 and antiapoptotic factors mRNA expression (P < 0.05 versus control for each). Notably, the Histogram score, which was used for quantifying RXRα status, was markedly higher in OE than in NE tissue (P < 0.01).

Large scale data: N/A.

Limitations, reasons for caution: Only OE tissues were included in this study, while peritoneal and deep infiltrating endometriotic tissues were not. Therefore, these findings might not be generalized to other types of endometriosis.

Wider implications of the findings: In OESC, PGC-1α stimulated cell proliferation and was involved in local estrogen biosynthesis, inflammation and apoptosis, and these effects of PGC-1α were inhibited by HX531. The suppression of PGC-1α-induced proliferation by HX531 in OESCs but not NESCs suggests that the PGC-1α-RXRα axis could play critical roles in promoting endometriosis. This is the first report of a relationship between PGC-1α and inhibitor of apoptosis proteins in endometriosis. Based on these findings, the PGC-1α-mediated pathway could represent a potential target in molecular therapy of endometriosis.

Study funding/competing interest(s): The study is supported in part by Grants-in-Aid for Scientific Research (15 K10681 and 15 K10726) from the Ministry of Education, Culture, Sports, Science, and Technology (Japan). The authors have no conflicts of interest to disclose.

Keywords: PGC-1α; apoptosis; endometriosis; estrogen dependence; inflammation.