Oocyte quality significantly impacts female fertility, influencing sperm-egg interaction, early embryonic development, and pregnancy outcome [1,2]. Oogenesis, a complex and discontinuous meiotic process in female mammals, generates numerous oocytes. Arrested at the germinal vesicle (GV) stage in the initial prophase of meiosis (G2), these oocytes contain a distinct nucleus. Upon sexual maturity, hormonal signals trigger germinal vesicle breakdown (GVBD), initiating the G2-M transition and resuming meiosis I [3]. Spindle formation, dependent on microtubule organization, and homologous chromosome alignment along the equatorial plate are key events in metaphase I (MI). Subsequent homologous chromosome segregation leads to the extrusion of the first polar body, and arrest at metaphase II (MII), producing a mature oocyte primed for fertilization. [4]. Proper spindle assembly is essential for meiotic fidelity, as disruptions in spindle architecture and chromosome alignment contribute to meiotic errors, embryonic abnormalities, miscarriage, and congenital disorders [5,6]. Investigating the molecular mechanisms governing oocyte development and identifying regulatory targets hold substantial theoretical and clinical significance.

Ferroptosis is a regulated form of cell death driven by iron-dependent lipid oxidation, distinct both mechanistically and morphologically from apoptosis and other regulated cell death pathways [7]. Its initiation is primarily influenced by polyunsaturated fatty acids, iron, and reactive oxygen species (ROS) [8]. Within the cell membrane, polyunsaturated fatty acids undergo conversion into polyunsaturated phospholipids through the enzymatic actions of long-chain acyl-CoA synthetase family 4 (ACSL4) and lysophosphatidylcholine acyltransferase 3 (LPCAT3). These phospholipids, in turn, utilize Fe2+ to catalyze the Fenton reaction with O2, facilitating electron transfer to H2O2, generating ROS, and ultimately inducing lipid peroxidation and ferroptosis [9]. Ferroptosis plays a significant role in female reproductive disorders [10]. Conditions such as premature ovarian insufficiency, endometriosis, polycystic ovary syndrome, and trophoblastic dysfunction exhibit varying degrees of ferroptosis, indicating its potential as a therapeutic target. For instance, basonuclin zinc finger protein 1 (BNC1) mutations in both humans and mice drive ferroptosis-mediated oocyte loss and follicular atresia, culminating in premature ovarian insufficiency. In murine models, ferroptosis inhibition mitigates Bnc1 mutation-induced premature ovarian insufficiency [11]. Emerging evidence highlights a strong correlation between ferroptosis and defects in oocyte meiotic maturation [[12], [13], [14], [15]]; however, current understanding of its precise role in this process remains incomplete.

Ferroptosis suppressor protein 1 (FSP1), also known as apoptosis-inducing factor mitochondria-associated 2 (AIFM2), is a highly conserved flavoprotein initially identified as a p53-responsive gene due to its structural resemblance to apoptosis-inducing factor (AIF). Emerging evidence highlights FSP1 as a glutathione-independent ferroptosis inhibitor that mediates ubiquinone (CoQ10) reduction, thereby preventing lipid oxidation [16,17]. N-myristoylated and localized to the plasma membrane, FSP1 facilitates CoQ10 recruitment to the cell membrane, where NADPH catalyzes its reduction to ubiquinol (CoQ10H2). In this reduced form, CoQ10H2 neutralizes free radicals, mitigating lipid peroxidation and suppressing ferroptotic cell death [18,19]. Operating alongside glutathione and glutathione peroxidase 4 (GPX4), the FSP1-CoQ10-NADPH axis constitutes an independent and parallel defense system critical for preserving phospholipid redox equilibrium by restraining both ferroptosis and phospholipid peroxidation. The selective FSP1 inhibitor iFSP1 [20] binds to FSP1 at the plasma membrane, disrupting its NADH oxidase activity [21]. Consequently, iFSP1 serves as a widely utilized tool in FSP1-related research, with well-documented inhibitory effects. Notably, recent findings in pigs reveal that FSP1 inhibition impairs early embryonic development [22], suggesting a fundamental role in gametogenesis and embryogenesis. However, the involvement of FSP1 in oocyte meiosis remains unclear, necessitating further investigation to delineate its mechanistic contributions to oocyte quality.

The study explored FSP1's role in mouse oocyte meiosis through the application of the FSP1 inhibitor. Results indicated cytoplasmic localization of FSP1 during this process. Inhibition of FSP1 disrupted oocyte maturation while inducing ferroptosis and mitochondrial dysfunction. These findings provide initial evidence of FSP1's essential involvement in mouse oocyte meiosis.