Light pollution impairs ovarian function via m6A-dependent miR-421-5p processing-mediated clock disruption

Light pollution disrupts circadian rhythms and impairs ovarian function, but the underlying molecular mechanisms remain unclear. This study investigates whether the METTL14-miR-421-5p-CLOCK axis mediates these effects. Female rats were exposed to normal or continuous light. Estrous cycles, ovarian morphology, and hormone levels were assessed, alongside analysis of METTL14, miR-421-5p, and CLOCK expression. In human KGN granulosa cells, METTL14 was knocked down or overexpressed to examine its role in miR-421-5p maturation, and CLOCK regulation. Cell viability, migration, and apoptosis were measured. Light-exposed rats exhibited disrupted estrous cycles, irregular follicular development, and hormonal imbalance, with a 40% decrease in E₂ and a 1.5-fold increase in testosterone. Ovarian m6A levels increased, with upregulated Mettl14 and a 50% reduction in Clock expression. Altered miRNA processing was observed, leading to elevated mature miR-421-5p. Similar phenomena were also observed in rat ovarian granulosa cells. In KGN cells, METTL14 knockdown suppressed m6A methylation and miR-421-5p maturation, thereby increasing CLOCK expression and restoring granulosa cell function. Conversely, METTL14 overexpression exacerbated miR-421-5p-mediated CLOCK suppression and cellular dysfunction. Light pollution upregulates METTL14, enhancing m6A-dependent maturation of miR-421-5p, which post-transcriptionally represses CLOCK. This novel epi-transcriptomic mechanism disrupts steroidogenesis and ovulation, offering new insights for preventing pollution-related reproductive diseases.