Yaacobi-Artzi Shira, Shimoni Chen, Kalo Dorit, Hansen Peter J, Roth Zvi
Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, 76100, Israel.
Department of Animal Sciences, University of Florida, Gainesville, FL, USA.
Theriogenology. 2020 Dec;158:477-489. doi: 10.1016/j.theriogenology.2020.09.039. Epub 2020 Oct 1.
Heat stress is associated with increased production of reactive oxygen species (ROS) and disruption of bovine oocyte function. Here, we examined whether the antioxidant melatonin can alleviate the deleterious effects of heat stress on oocyte developmental competence. Cumulus-oocyte complexes were matured for 22 h at 38.5 °C (control) or for 22 h at 41.5 °C (heat shock) with or without 1.0 × 10 M melatonin. At the end of maturation, a subgroup of oocytes was examined for nuclear and cytoplasmic maturation, ROS level and mitochondrial membrane potential. A second subgroup of oocytes underwent fertilization (18 h), and putative zygotes were cultured in an incubator equipped with a time-lapse system for ∼190 h. Cleavage rate and the proportion of blastocysts, as well as embryo kinetics were recorded. Expanded blastocysts were collected and their transcript abundance was evaluated. Heat shock increased ROS and reduced the proportion of oocytes that resumed meiosis and reached the metaphase-II stage. Exposing oocytes to heat shock with melatonin alleviated these effects to some extent, expressed by a marginal reduction in ROS level and increased proportion of metaphase-II stage oocytes. Neither the distribution of oocyte cortical granules nor polarization of the mitochondrial membrane differed between control and heat-shocked oocytes cultured with or without melatonin. Heat shock reduced the proportion of embryos that cleaved and developed to blastocysts, characterized by alterations in kinetics of the developed embryos expressed by a delay in the first cleavage, second cleavage and blastocyst formation for heat-shock vs. control groups. Melatonin did not restore the competence or kinetics of embryos developed from heat-shocked oocytes. However, expanded blastocysts developed from heat-shocked oocytes treated with melatonin expressed a higher transcript abundance of genes associated with mitochondrial function, relative to the control and heat-shock group. In summary, melatonin improved the oxidative status of heat-shocked oocytes to some extent and had a beneficial effect on maternal mitochondrial transcripts in the developed blastocysts.
热应激与活性氧（ROS）生成增加以及牛卵母细胞功能紊乱有关。在此，我们研究了抗氧化剂褪黑素是否能减轻热应激对卵母细胞发育能力的有害影响。卵丘 - 卵母细胞复合体在38.5°C下成熟22小时（对照组），或在41.5°C下成熟22小时（热休克组），添加或不添加1.0×10⁻⁶ M褪黑素。成熟结束时，检查一部分卵母细胞的核成熟和细胞质成熟、ROS水平及线粒体膜电位。另一部分卵母细胞进行受精（18小时），假定的受精卵在配备延时系统的培养箱中培养约190小时。记录分裂率、囊胚比例以及胚胎发育动力学。收集扩张的囊胚并评估其转录本丰度。热休克增加了ROS水平，降低了恢复减数分裂并达到中期II期的卵母细胞比例。用褪黑素处理热休克卵母细胞在一定程度上减轻了这些影响，表现为ROS水平略有降低以及中期II期卵母细胞比例增加。无论是否添加褪黑素培养，对照组和热休克组卵母细胞的皮质颗粒分布和线粒体膜极化均无差异。热休克降低了分裂并发育成囊胚的胚胎比例，其特征是发育胚胎的动力学改变，表现为热休克组与对照组相比，第一次分裂、第二次分裂和囊胚形成延迟。褪黑素未能恢复热休克卵母细胞发育的胚胎的能力或动力学。然而，与对照组和热休克组相比，用褪黑素处理的热休克卵母细胞发育的扩张囊胚表达了更高的与线粒体功能相关基因的转录本丰度。总之，褪黑素在一定程度上改善了热休克卵母细胞的氧化状态，并对发育囊胚中的母源线粒体转录本有有益影响。
