Bisphenol TMC Impaired Mouse Oocyte Maturation by Disrupting Spindle Assembly via NEK3-Mediated Microtubule Acetylation

Bisphenol TMC (BPTMC) is a novel substitute for bisphenol A (BPA) and is increasingly detected in the environment and in human tissues. Despite its potent estrogenic activity, BPTMC's impact on mammalian oocyte quality remains poorly understood. In this study, we examined whether BPTMC exposure affected oocyte maturation in vitro by screening the first polar body and spindle morphology. The results showed that BPTMC significantly reduced the rate of polar body extrusion (MII oocytes) in a dose-dependent manner. Furthermore, BPTMC exposure disrupted cytoplasmic maturation, evidenced by abnormal mitochondrial distribution, elevated reactive oxygen species (ROS) accumulation, and increased apoptosis. These cytoplasmic defects correlated with lower fertilization ability and impaired embryonic development, indicated by reduced percentages of pronuclei and 2-cell embryo formation. Mechanistic analysis showed that BPTMC caused abnormal spindle assembly due to reduced microtubule acetylation, which was mediated by downregulation of the NEK3 protein. Collectively, our findings first demonstrated that BPTMC impaired oocyte maturation through oxidative stress and NEK3-dependent disruption of the cytoskeleton, providing important evidence for risk assessment of emerging bisphenol substitutes.