FTO-mediated NR1D1 m6A demethylation contributes to hyperandrogenemia during continuous light–induced circadian disruption

N6-methyladenosine (m 6 A) is a key epigenetic modification closely associated with reproductive physiology; however, its involvement in circadian-related ovarian dysfunction remains unclear. Female Sprague Dawley rats were exposed continuously to light for 10 weeks (LL group) to induce circadian desynchrony, with controls maintained under standard cycles (DL group). Transcriptomic analysis was performed to identify markedly dysregulated pathways, which were validated via qRT‒PCR, immunoblotting, and KGN cell models. Continuous light exposure induced PCOS-like phenotypes in female rats, including disrupted estrous cycles, polycystic ovarian morphology, and hyperandrogenemia. At the molecular level, constant light disrupted circadian regulation of steroidogenic enzymes, increasing and phase-shifting steroidogenic acute regulatory protein ( StAR ) and Cytochrome P450 Family 11 Subfamily A Member 1 ( Cyp11a1 ), and elevating but arrhythmically expressing 3β-hydroxysteroid dehydrogenase type 2 ( Hsd3β2 ). Mechanistically, continuous light upregulated the m 6 A demethylase fat mass and obesity-associated protein (FTO), which promoted m 6 A erasure on Nuclear receptor subfamily 1 group D member 1 (NR1D1) mRNA, reducing NR1D1 expression and relieving NR1D1-mediated repression of StAR, thereby promoting androgen biosynthesis and potentially contributing to hyperandrogenemia. Our study demonstrated that FTO-mediated regulation of NR1D1 is associated with alterations in StAR expression and androgen synthesis, providing a mechanistic link between environmental circadian disruption and ovarian steroidogenic imbalance and suggesting a potential molecular target for circadian rhythm-associated ovarian dysfunction.