Under endoplasmic reticulum (ER)-stress conditions, the unfolded protein response (UPR) generates a defense mechanism in mammalian cells. The regulation of UPR signaling is important in oocyte maturation, embryo development, and female reproduction of pigs. Recent studies have shown that melatonin plays an important role as an antioxidant to improve pig oocyte maturation. However, there is no report on the role of melatonin in the regulation of UPR signaling and ER-stress during in vitro maturation (IVM) of porcine oocytes. Therefore, the objective of this study was to investigate the antioxidative effects of melatonin on porcine oocyte maturation through the regulation of ER-stress and UPR signaling. We investigated the changes in the mRNA/protein expression levels of three UPR signal genes (Bip/Grp78, ATF4, P90/50ATF6, sXbp1, and CHOP) on oocytes, cumulus cells, and cumulus-oocyte complexes (COCs) during IVM (metaphase I; 22 hours and metaphase II; 44 hours) by Western blot and reverse transcription-polymerase chain reaction analysis. Treatment with the ER-stress inducer, tunicamycin (Tm), significantly increased expression of UPR markers. Additionally, cumulus cell expansion and meiotic maturation of oocytes were reduced in COCs of Tm-treated groups (1, 5, and 10 μg/mL). We confirmed the reducing effects of melatonin (0.1 μmol/L) on ER-stress after pretreatment with Tm (5 μg/mL; 22 hours) in maturing COCs. Addition of melatonin (0.1 μmol/L) to Tm-pretreated COCs recovered meiotic maturation rates and expression of most UPR markers. In conclusion, we confirmed a role for melatonin in the modulation of UPR signal pathways and reducing ER-stress during IVM of porcine oocytes.

中文翻译：

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褪黑素可通过减少体外成熟过程中的内质网应激来改善猪卵母细胞的减数分裂成熟。

在内质网（ER）应激条件下，未折叠的蛋白质反应（UPR）在哺乳动物细胞中产生防御机制。UPR信号的调节在猪的卵母细胞成熟，胚胎发育和雌性繁殖中很重要。最近的研究表明，褪黑激素作为一种抗氧化剂，可以改善猪卵母细胞的成熟。但是，尚无关于褪黑素在猪卵母细胞体外成熟（IVM）过程中对UPR信号和ER应激的调节中的作用的报道。因此，本研究的目的是通过调节ER应激和UPR信号传导来研究褪黑激素对猪卵母细胞成熟的抗氧化作用。我们调查了三个UPR信号基因（Bip / Grp78，ATF4，P90 / 50ATF6，sXbp1，通过Western blot和逆转录聚合酶链反应分析在IVM（中期I； 22小时和中期II； 44小时）中卵母细胞，卵丘细胞和卵丘-卵母细胞复合物（COC）上的表达。ER应激诱导剂衣霉素（Tm）的治疗显着增加了UPR标记的表达。此外，在Tm处理组的COC中（1、5和10μg/ mL），卵母细胞的积丘细胞扩增和减数分裂成熟减少。我们证实了在成熟的COC中用Tm（5μg/ mL; 22小时）预处理后，褪黑激素（0.1μmol/ L）对内质网应激的减少作用。在经Tm预处理的COC中添加褪黑激素（0.1μmol/ L）可恢复减数分裂成熟率和大多数UPR标记物的表达。综上所述，