Plasticizer Bis(2-ethylhexyl) Phthalate Causes Meiosis Defects and Decreases Fertilization Ability of Mouse Oocytes in Vivo

Bis(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer in polyvinyl chloride (PVC) plastics. Humans and animals are widely and continuously exposed to DEHP, especially with respect to diet, which is associated with reproductive diseases. Nevertheless, the effects and underlying mechanisms of DEHP exposure on oocytes in vivo remain ambiguous. In this study, we found that oral administration of DEHP (40 μg/kg body weight per day for 14 days) markedly reduced the maturation and fertilization of oocytes in vivo. In addition, DEHP caused oxidative stress, increased reactive oxygen species generation, promoted early apoptosis, and resulted in DNA damage in mouse oocytes. Moreover, DEHP exposure caused mitochondrial damage, reduced ATP content, down-regulated actin expression, and disturbed the spindle assembly and chromosome alignment in mouse oocytes. Furthermore, DEHP exposure remarkably impaired the localization and protein level of Juno, the sperm receptor on the membrane of oocytes. The levels of DNA methylation, H3K9me3, and H3K9ac were also altered in the DEHP-exposed mouse oocytes. Thus, our results indicated that DEHP exposure reduced the maturation and fertilization capabilities of mouse oocytes by affecting cytoskeletal dynamics, oxidative stress, early apoptosis, meiotic spindle morphology, mitochondria, ATP content, Juno expression, DNA damage, and epigenetic modifications in mouse oocytes.

Tributyltin oxide exposure impairs mouse oocyte maturation and its possible mechanisms

Tributyltin oxide (TBTO) has been widely used as marine antifouling composition, preservative, biocide, and a stabilizer in plastic industry. Previous studies have indicated that TBTO can cause immunotoxicity as an environmental pollutant. However, little is known about its reproductive toxicity, especially on female oocyte maturation and the underlying mechanisms. In this study, mouse oocytes were cultured with different concentrations of TBTO in vitro, and several crucial events during meiotic maturation were evaluated. We found that the first polar body extrusion rate was significantly reduced, which reflected the disruption of meiotic maturation. The rate of abnormal spindle organization increased significantly, accompanied with a higher rate of chromosome misalignment. In addition, TBTO treatment increased reactive oxygen species generation markedly, which also accelerated the early-stage apoptosis. Moreover, heterogeneous mitochondrial distribution, mitochondrial dysfunction, and higher rate of aneuploidy were detected, which consequently disrupted in vitro fertilization. In conclusion, our results indicated that TBTO exposure could impair mouse oocyte maturation by affecting spindle organization, chromosome alignment, mitochondria functions, oxidative stress, and apoptosis.

Chronic restraint stress disturbs meiotic resumption through APC/C-mediated cyclin B1 excessive degradation in mouse oocytes

Psychological stress, which exerts detrimental effects on human reproduction, may compromise the meiotic competence of oocytes. Meiotic resumption, germinal vesicle breakdown (GVBD), is the first milestone to confer meiotic competence to oocytes. In the practice of assisted reproductive technology (ART), the timing for GVBD is associated with the rates of cleavage and blastocyst formation. However, whether chronic stress compromises oocyte competence by influencing GVBD and the underlying mechanisms are unclear. In the present study, a chronic restraint stress (CRS) mouse model was used to investigate the effects of stress on oocyte meiotic resumption, as well as the mechanisms. Following a 4-week chronic restraint stress in female mice, the percentage of abnormal bipolar spindles increased and indicated compromised oocyte competence in the CRS group. Furthermore, we identified a decreased percentage of GVBD and prolonged time of GVBD in the CRS mouse oocytes compared with the control group. CRS simultaneously reduced the expression of cyclin B1 (CCNB1), which represents a regulatory subunit of M-phase/mature promoting factor (MPF). However, MG132, an inhibitor of anaphase-promoting complex/cyclosome (APC/C), could rescue the prolonged time of GVBD and increase the expression level of CCNB1 of oocytes from the CRS mice. Collectively, our results demonstrated that stress disturbed meiotic resumption through APC/C-mediated CCNB1 degradation, thus providing a novel understanding for stress-related oocyte quality decline; moreover, it may provide a non-invasive approach to select high-quality gametes and novel targets for molecular therapy to treat stress-related female infertility.