Nonylphenol exposure affects mouse oocyte quality by inducing spindle defects and mitochondria dysfunction

Nonylphenol (NP) is a chemical raw material and intermediate which is mainly used in the production of surfactants, lubricating oil additives and pesticide emulsifiers. NP is reported to be toxic on the immune system, nervous system and reproductive system due to its binding to estrogen receptors. However, the toxicity of NP on mammalian oocyte quality remains unclear. In present study, we explored the effects of NP exposure on mouse oocyte maturation. Our results showed that 4 weeks of NP exposure increased the number of atresia follicles and decreased oocyte developmental competence. Transcriptomic analysis indicated that NP exposure altered the expression of more than 800 genes in oocytes, including multiple biological pathways. Subcellular structure examination indicated that NP exposure disrupted meiotic spindle organization and caused chromosome misalignment. Moreover, aberrant mitochondrial distribution and decreased membrane potential were also observed, indicating that NP exposure caused mitochondria dysfunction. Further analysis showed that NP exposure resulted in the accumulation of reactive oxygen species (ROS), which causes oxidative stress; and the NP-exposed oocytes showed positive Annexin-V signal, indicating the occurrence of early apoptosis. In summary, our results indicated that NP exposure reduced oocyte quality by affecting cytoskeletal dynamics and mitochondrial function, which further induced oxidative stress and apoptosis in mice.