Study question: Is overexpression of lysyl oxidase (LOX), an enzyme responsible for the cross-linking of collagens, a cause of anovulation in polycystic ovary syndrome (PCOS)?
Summary answer: LOX overexpression was present in PCOS ovaries, due at least in part to interleukin-1β (IL-1β), and inhibition of LOX activity with β-aminopropionitrile (BAPN) ameliorated polycystic ovary morphology and anovulation.
What is known already: Aberrant ovarian extracellular matrix (ECM) remodeling and inflammation may contribute to the development of PCOS. It remains unknown whether proinflammatory IL-1β is a contributing factor for LOX overexpression in PCOS ovaries and whether inhibition of LOX can improve PCOS conditions.
Study design, size, duration: LOX and IL-1β abundance in the granulosa cells and follicular fluid was compared between non-PCOS (n = 30) and PCOS (n = 39) patients. The effect and mechanism of IL-1β on LOX expression was examined in cultured primary human granulosa cells. The improvements in PCOS conditions by LOX inhibition with BAPN was investigated in a dehydroepiandrosterone (DHEA)-induced PCOS rat model.
Participants/materials, setting, methods: The abundance of LOX and IL-1β was measured with quantitative real-time polymerase chain reaction (qRT-PCR), LOX activity assays and enzyme-linked immunosorbent assays (ELISA), respectively. The effect of IL-1β on LOX expression was examined in the presence or absence of inhibitors for signaling molecules and small interfering RNA-mediated knockdown of the putative transcription factor. Chromatin immunoprecipitation assays were conducted to further identify the responsible transcription factor. The role of LOX in ovulation was investigated in a DHEA-induced PCOS rat model with administration of the LOX inhibitor BAPN. The numbers of retrieved total oocytes and MII oocytes were recorded upon ovarian stimulation.
Main results and the role of chance: Increased abundance of LOX (P < 0.05) and IL-1β (P < 0.05) was observed in the granulosa cells and follicular fluid in PCOS patients. IL-1β increased LOX expression via activation of ERK1/2 and JNK and subsequent activation of the transcription factor c-Jun. Inhibition of LOX with BAPN ameliorated irregular estrous cyclicity (P < 0.05), polycystic ovary morphology and anovulation (P < 0.05) in PCOS rats, but appeared to be ineffective in the improvement of oocyte quality.
Large scale data: N/A.
Limitations, reasons for caution: Ovarian tissue-directed specific inhibition of LOX in combination with oocyte quality-improving drugs may be more effective in the treatment of PCOS.
Wider implications of the findings: Inflammation of the ovary is a contributing factor for the aberrant expression of LOX in the PCOS ovary, and inhibition of LOX together with anti-inflammatory therapy may improve the core features of PCOS.
Study funding/competing interest(s): This work was supported by National Key R & D Program of China (2017YFC1001403) and Doctorial Innovation Fund of Shanghai Jiao Tong University School of Medicine (BXJ201718). The authors declare no competing financial interests.