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Ethylene glycol butyl ether (EGBE), a type of glycol ethers, is a common chemical used in both industrial and household products. Increasing animal studies have indicated that it produces reproductive problems, such as testicular damage, reduced female fertility, death of embryos, and birth defects. However, how it influences the female germ cells has not yet determined. Here, we found that EGBE exposure resulted in the defective porcine oocyte maturation via disruption of cytoskeleton dynamics, showing the abnormal spindle assembly, chromosome alignment, and actin organization. Meanwhile, EGBE exposure perturbed the mitochondrial distribution and function, leading to the accumulation of reactive oxygen species (ROS) and generation of DNA damage and apoptosis. Of note, nicotinamide mononucleotide (NMN) supplementation rescued the meiotic defects caused by EGBE exposure via restoring NAD+ level and mitochondrial function and thus eliminating the excessive ROS. Taken together, our observations illustrate that NMN supplementation is an effective strategy to protect oocyte quality against environmental pollutant-induced deterioration, contributing to improve the animal and human fertility.

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SIRT6, the sixth member of the sirtuin family proteins, has been characterized as a crucial regulator in multiple molecular pathways related to aging, including genome stability, DNA damage repair, telomere maintenance, and inflammation. However, the exact roles of SIRT6 during female germ cell development have not yet been fully determined. Here, we assessed the acquisition of meiotic competency of porcine oocytes by inhibition of SIRT6 activity. We observed that SIRT6 inhibition led to the oocyte meiotic defects by showing the impairment of polar body extrusion and cumulus cell expansion. Meanwhile, the compromised spindle/chromosome structure and actin dynamics were also present in SIRT6-inhibited oocytes. Moreover, SIRT6 inhibition resulted in the defective cytoplasmic maturation by displaying the disturbed distribution dynamics of cortical granules and their content ovastacin. Notably, we identified that transcript levels of genes related to oocyte meiosis, oxidative phosphorylation, and cellular senescence were remarkably altered in SIRT6-inhibited oocytes by transcriptome analysis and validated that the meiotic defects caused by SIRT6 inhibition might result from the excessive reactive oxygen species (ROS)-induced early apoptosis in oocytes. Taken together, our findings demonstrate that SIRT6 promotes the porcine oocyte meiotic maturation through maintaining the redox homeostasis.

Copper (Cu) is an essential trace element for animals, and also an important nutritional component for the normal physiology and metabolism of animal reproductive systems. An excess or lack of Cu will directly or indirectly affect animal reproductive activities. However, the effect of Cu, in particular excessive Cu, on the reproductive performance of sows has not been studied. Here, we report that excessive Cu had negative effects on oocyte maturation and organelle functions. We showed that Cu exposure perturbed porcine oocyte meiotic maturation and impaired spindle/chromosome structure, resulting in a defective spindle assembly, as well as the abnormal distribution of actin dynamics and cortical granules. In addition, single-cell transcriptome analysis identified the target effectors of Cu actions in porcine oocytes, further demonstrating that Cu exposure affects the mitochondrial distribution and function, leading to the high levels of reactive oxygen species, DNA damage, and early apoptosis of porcine oocytes. These findings demonstrate that Cu exposure causes abnormalities in the mitochondrial distribution and function, resulting in the increased oxidative stress and levels of reactive oxygen species, DNA damage, and apoptosis, ultimately leading to a decreased porcine oocyte quality.