Melatonin Protects Mouse Oocytes From the Environmental Toxicant 6PPD‐Quinone by Preserving Mitochondrial and Endomembrane Homeostasis

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) is a ubiquitous tire-derived transformation product with emerging reproductive toxicity; however, its impact on mammalian oocytes and the potential protective role of melatonin (MT) remain unclear. Here, we evaluate 6PPD-Q-induced impairment of mouse oocyte competence and assess the protective efficacy of MT. 6PPD-Q exposure significantly decreases polar body extrusion, fertilization, and 2-cell embryo formation, whereas MT co-treatment markedly restores these developmental outcomes. Mechanistically, MT alleviates 6PPD-Q-induced meiotic spindle defects and cortical F-actin disorganization, reduces DNA damage, and suppresses early apoptotic signaling. Smart-seq. 2 transcriptomic profiling further reveals that 6PPD-Q triggers extensive transcriptional reprogramming, with prominent disruption of mitochondrial metabolism, oxidative phosphorylation, and organelle homeostasis, whereas MT mitigates these pathway perturbations. Consistently, functional assays demonstrate that MT reduces excessive cellular and mitochondrial reactive oxygen species, restores mitochondrial membrane potential and adenosine triphosphate levels, and mitigates global organellar disorganization. Collectively, these findings identify MT as a cytoprotective modulator of 6PPD-Q-induced oocyte dysfunction by preserving mitochondrial and endomembrane homeostasis, thereby supporting oocyte maturation and fertilization.