Glycine treatment enhances developmental potential of porcine oocytes and early embryos by inhibiting apoptosis.

Glycine, a component of glutathione (GSH), plays an important role in protection from reactive oxygen species (ROS) and inhibition of apoptosis. The aim of this study was to determine the effect of glycine on in vitro maturation (IVM) of porcine oocytes and their developmental competence after parthenogenetic activation (PA). We examined nuclear maturation, ROS levels, apoptosis, mitochondrial membrane potential (ΔΨm), and ATP concentration, as well as the expression of several genes related to oocyte maturation and development. Our studies found that treatment with glycine in IVM culture medium increased nuclear maturation rate, but varying the concentrations of glycine (0.6, 6, or 12 mM) had no significant effect. Furthermore, 6 mM glycine supported greater blastocyst formation rates and lesser apoptosis after PA than the other concentrations (P < 0.05). All the glycine treatment groups had decreased levels of ROS in both matured oocytes and at the 2-cell stage (P < 0.05). At the 2-cell stage, the 6 mM glycine group had ROS levels that were lesser than the other 2 glycine treatment groups (0.6 and 12 mM). From this, we deemed 6 mM to be the optimal condition, and we then investigated the effects of 6 mM glycine on gene expression. The expression of both FGFR2 and Hsf1 were greater than the control group in mature oocytes. The glycine treatment group had greater levels of expression of an antiapoptotic gene (Bcl2) in mature oocytes and cumulus cells and lesser levels of expression of a proapoptotic gene (Bax) in PA blastocysts (P < 0.05). In addition, mitochondrial ΔΨm and ATP concentration were increased in 6 mM glycine group compared with the control group. In conclusion, our results suggest that glycine plays an important role in oocyte maturation and later development by reducing ROS levels and increasing mitochondrial function to reduce apoptosis.