Attenuation of endoplasmic reticulum stress improves in vitro growth and subsequent maturation of bovine oocytes

Endoplasmic reticulum (ER) stress interferes with developmental processes in oocyte maturation and embryo development. In vitro growth (IVG) is associated with low developmental competence, and ER stress during IVG culture may play a role. Therefore, this study aimed to examine the effect of tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, on the IVG of bovine oocytes to understand the role of ER stress. Oocyte-granulosa cell complexes (OGCs) were collected from early antral follicles (1.5-1.8 mm) and allowed to grow in vitro for 5 days at 38.5 degrees C in a humidified atmosphere containing 5% CO2. Basic growth culture medium was supplemented with TUDCA at various concentrations (0, 50, 100, 250, and 500 mu M). After IVG, oocyte diameters were similar among groups, but the antrum formation rate tended to be higher in the TUDCA 100 mu M group. The mRNA expression levels of ER stress-associated genes (PERK, ATF6, ATF4, CHOP, BAX, IRE1, and XBP1) in OGCs were downregulated in the TUDCA 100 mu M group than those in the control group. Moreover, the TUDCA 100 mu M group exhibited reduced ROS production with higher GSH levels and improved in vitro-grown oocyte maturation compared with those in the control group. In contrast, no difference in the developmental competence of embryos following in vitro fertilization was observed between the control and TUDCA 100 mu M groups. These results indicate that ER stress could impair IVG and subsequent maturation rate of bovine oocytes, and TUDCA could alleviate these detrimental effects. These outcomes might improve the quality of oocytes in IVG culture in assisted reproductive technology.