Effects of chronic psychosocial stress on the development of mouse oocytes and preimplantation embryos.

The impact of psychosocial chronic stress on mammalian oocyte maturation, fertilization and early stages of embryonic development remains poorly understood. This study addresses the effects of chronic psychosocial stress on the reproductive outcome in female mice, i. e. the development of in vitro- and in vivo-derived embryos. The model of chronic stress used in the study comprised a 21-day protocol consisting of a period of social isolation followed by the overcrowding. Two experiments were conducted, varying in the type of fertilization. In experiment 1, female mice were stressed at the folliculogenesis stages; then oocyte maturation and in vitro fertilization were performed, and the early development of the in vitro-derived embryos was studied. Experiment 2 differed in that fertilization was performed in vivo, and the resulting in vivo-derived embryos were cultured in vitro since the two-cell stage. To assess preimplantation embryo development, blastocysts were fixed, stained with the TUNEL/DAPI method and analyzed using fluorescence microscopy, i. e. the number of interphase nuclei and the apoptosis index were estimated. The results of Experiment 1 showed that chronic stress did not affect oocyte maturation or their fertilization capacity. However, embryos from the stress group contained fewer interphase nuclei (p < 0.001), which points to a lower cleavage rate. Meanwhile, the apoptosis rate in these blastocysts was comparable to controls. Experiment 2 showed that chronic stress caused a decrease in the proportion of embryos that achieved the blastocyst stage during the culture period and an increase in the proportion of morulae (p < 0.01), as well as a decrease in the number of interphase nuclei in blastocysts (p < 0.001). Experiments demonstrated that the chronic psychosocial stress exerts a moderate but significant effect on early embryonic development, primarily via the reduced proliferative activity of embryonic cells. These results obtained in mice have a translational value for reproductive medicine and highlight the importance of maternal stress when analyzing ART outcomes.