Abstract
In several species, oocyte and embryo competence are improved by the addition of endoplasmic reticulum (ER) stress inhibitors to in vitro maturation (IVM) medium and/or in vitro culture (IVC) medium. This study aimed to evaluate the effects of three concentrations of tauroursodeoxycholic acid (TUDCA; 50, 200, and 1,000 μM), a chemical chaperone for relieving ER stress, during IVM of bovine cumulus–oocyte complexes (COCs) for 24 h. Treated oocytes were analyzed for nuclear maturation, reactive oxygen species (ROS) production, mitochondrial activity, and abundance of target transcripts. In addition, the number of pronuclei in oocytes was evaluated after 18–20 h of insemination, and the rates of blastocyst and hatched blastocyst formation were evaluated after 7 and 8/9 days of culture, respectively. We further evaluated the transcript abundance of embryonic quality markers. Our findings showed that supplementation of IVM medium with 200 μM of TUDCA decreased ROS production and increased abundance of transcripts related to antioxidant activity in oocytes (CAT, GPX1, and HMOX1) and embryos (GPX1 and PRDX3). Interestingly, high concentration of TUDCA (1,000 μM) was toxic to oocytes, reducing the nuclear maturation rate, decreasing mitochondrial activity, and increasing the abundance of ER stress (HSPA5) and cellular apoptosis (CASP3 and CD40) related transcripts. The results of this study suggest that treatment with 200 μM of TUDCA is associated with a greater resistance to oxidative stress and indirectly with ER stress relief in bovine oocytes.
Highlights
In vitro maturation (IVM) is one of the main restrictive steps in the optimization of in vitro production (IVP)
After 24 h of IVM, the proportion of oocytes that reached metaphase II (MII) was similar among the Control, to obtain 50 μM (T50), and T200 groups (Figure 2)
The present study demonstrated that supplementing the IVM medium with tauroursodeoxycholic acid (TUDCA) may relieve endoplasmic reticulum (ER) stress by decreasing reactive oxygen species (ROS) production in the oocyte and increasing the abundance of transcripts related to antioxidant activity in bovine oocytes and embryos developed in vitro
Summary
In vitro maturation (IVM) is one of the main restrictive steps in the optimization of in vitro production (IVP). During IVM, oocytes acquire the intrinsic capacity for gradual development until activation of the embryonic genome after fertilization (Ferreira et al, 2009; Gilchrist, 2011). Previous studies have indicated that in vitro conditions in which oocytes are exposed to a variety of cellular stresses contribute to the greater incidence of loss of competence in in vitro. Response to exogenous stress is a vital part of cellular physiology and it is increasingly becoming apparent that one of the main mechanisms involved in initiating the cellular response to a variety of exogenous stressors is associated with the endoplasmic reticulum (ER; Guzel et al, 2017). ER stress is triggered when misfolded or unfolded proteins accumulate in the lumen of the ER. When ER stress exceeds its threshold, cellular damages such as apoptosis, degeneration, and carcinogenesis ensue (Olzmann et al, 2013; Yoon et al, 2014)
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