Introduction PCOS is the most common disorder encompassing reproductive, metabolic, and endocrine abnormalities, and has an increased risk of adverse pregnancy and neonatal complications, such as miscarriage, gestational diabetes mellitus, and preterm birth. Many studies suggested that oocyte quality is compromised in patients with PCOS compared to those without PCOS. To systematically characterize the follicular fluid (FF) proteomic landscape and identify potential biomarkers for oocyte quality assessment, we conducted a label-free proteomics analysis between patients with and without PCOS. Methods Gonadotropin-releasing hormone antagonist was used for ovarian stimulation. FF was collected by transvaginal ultrasound-guided aspiration 36 h after human chorionic gonadotropin administration, followed by centrifugation at 800 x g for 10 min at 4°C, and then the supernatants were collected for proteomic analysis. Embryo outcome was compared using a Cox model analysis adjusted for age, BMI and duration years of infertility. The fundamental procedure of proteomics included depletion of highly abundant proteins, extraction of proteins, filter aided proteome preparation, desalination of peptides, LC-MS/MS analysis, and bioinformatics analysis. ELISA assay was employed to validate the expression levels of proteins in FF. Results Our study has demonstrated that the normal fertilization rate among PCOS patients was markedly lower compared to controls when adjusted for age, body mass index (BMI), and duration of infertility. The proteomics analysis has identified 11 upregulated and 17 downregulated DEPs in the PCOS group, notably, VNN1 expression was upregulated, while PLTP and HYOU1 were downregulated. The proteomic sequencing results categorized according to the quality rate of D3 embryos revealed that DEPs in FF were significantly enriched in cholesterol metabolism. Oocyte quality declines in association with abnormal PLTP and cholesterol metabolism, and activated endoplasmic stress in FF of PCOS. Discussion PCOS patients exhibit significantly lower fertilization rate compared to the controls. Our findings delineate a distinct proteomic signature in PCOS FF featuring downregulated PLTP and HYOU1 concomitant with VNN1 overexpression, implicating their pivotal involvement in the pathophysiological mechanisms underlying oocyte competence impairment. Furthermore, the observed correlation between dysregulated lipid homeostasis and compromised oocyte developmental potential suggests a mechanistic link between follicular microenvironment alterations and reproductive outcomes in PCOS.
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