Maternal-Restraint Stress Increases Oocyte Aneuploidy by Impairing Metaphase I Spindle Assembly and Reducing Spindle Assembly Checkpoint Proteins in Mice1

Abstract

Studies in both humans and animals suggest detrimental effects of psychological stress on reproduction. Although our recent study shows that maternal-restraint stress diminishes oocyte developmental potential, the mechanism behind this effect is unknown. This prompted us to study the potential role of maternal-restraint stress in the genesis of aneuploidy during meiosis I. At 24 h after equine chorionic gonadotropin injection, mice were subjected to restraint stress for 24 h. After the restraint, some mice were killed to recover immature oocytes for in vitro maturation, while others were injected with human chorionic gonadotropin to recover in vivo matured oocytes. Analysis on chromosome complements of both mature oocytes and parthenotes confirmed that maternal restraint increased aneuploidy in both in vivo and in vitro matured oocytes and that the percentage of aneuploid oocytes were three times higher in the earlier matured oocytes than in the later matured ones. Further observations indicated that maternal restraint 1) impaired metaphase I (MI) spindle assembly while inhibiting MAPK activities, 2) accelerated progression of anaphase I while down-regulating the expression of spindle assembly checkpoint (SAC) proteins, and 3) induced intraoocyte oxidative stress. The following possible model was proposed to explain the results. Maternal-restraint stress increased oocyte aneuploidy by impairing MI spindle assembly and decreasing the SAC. Whereas abnormal spindles would affect centromere attachments, a reduction in SAC would accelerate the anaphase I progression. Failure of centromere attachment, together with the hastened anaphase, would result in nondisjunction of the unattached chromosomes. Furthermore, maternal-restraint stress might also impair spindle assembly and SAC function by inducing intraoocyte oxidative stress, which would then reduce MAPK activity, a critical regulator of microtubule assembly and the establishment and maintenance of the SAC during oocyte maturation.

Antioxidant supplementation overcomes the deleterious effects of maternal restraint stress-induced oxidative stress on mouse oocytes

“…Notably, oxidative stress index is considered to be a more accurate index of oxidative stress, because it represents a comprehensive measurement of total antioxidant status and total oxidant status. Oxidative stress in an oocyte is usually determined by measuring the levels of ROS (Nasr-Esfahani et al 1990, Zhou et al 2012) and glutathione (Boerjan & de Boer 1990, Zhou et al 2012, because it is known that GSH/GSSG is the main redox buffer and the GSH:GSSG ratio is a very important indicator of the redox status (Wu et al 2004, Ojha & Srivastava 2012. By measuring total oxidant status, total antioxidant status, and oxidative stress index, the present study showed that oxidative stress increased in both blood and ovaries after restraint stress exposure.…”

“…It has been reported that stresses including restraint stress cause the disruption of homeostasis and an imbalanced antioxidant status in blood and several organs (Sahin et al 2004, Derin et al 2006, Sahin & Gü mü şlü 2007. However, stress-induced oxidative stress has not been observed in ovaries, although our previous study has indicated that restraint stress causes oxidative stress in oocytes (Zhou et al 2012). Furthermore, measurement of total oxidant status, total antioxidant status, and oxidative stress index in ovaries has not been reported.…”

“…Figure 3A and B shows MII oocytes with a normal haploid (nZ20) and a hyperhaploid (nZ21) complement of chromosomes. According to our reported criteria (Zhou et al 2012), whereas the barrel-shaped spindles and the chromosomes that were well congressed on the metaphase plate were considered normal, the asymmetric spindles with one pole wider than the other and the chromosomes that were not well congressed on the metaphase plate (often with displaced chromosomes) were considered abnormal. Thus, in this study, the MI oocytes were classified into those with both normal chromosomes and normal spindles (Fig.…”

“…Furthermore, studies using rat models have demonstrated that restraint stress induces oxidative stress in different organs (Zaidi et al 2003, Derin et al 2006, Sahin et al 2006, Akpinar et al 2008. However, although our recent study has provided preliminary evidence that maternal restraint stress increases oxidative stress in the oocyte (Zhou et al 2012), reports on whether restraint stress causes oxidative stress in the ovary are limited. Thus, further trials are necessary to confirm the causal link between maternal restraint stress and oocyte oxidative stress and to elucidate the precise mechanisms through which oxidative stress affects the oocyte.…”

“…According to Hobel & Culhane (2003), stressors present early in pregnancy are most probably present before pregnancy, and, hence, to improve pregnancy outcome, interventions will have to begin before conception. However, evidence for the direct effect of psychological stress on the oocyte is limited (Zhang et al 2011, Zhou et al 2012.…”