Glutathione synthesis during in vitro maturation of bovine oocytes: Role of cumulus cells

Glutathione (GSH) synthesis during in vitro maturation (IVM) has been shown to play an important role in embryo development. The present study was carried out to evaluate the role of cumulus cells in GSH synthesis during IVM of bovine oocytes in the presence of cystine, cysteine, the cysteine analogue N-acetylcysteine, and cysteamine. For this purpose, cumulus-oocyte complexes (COCs), denuded oocytes (DOs), and DOs in coculture with a cumulus cell monolayer were used. An increase in GSH level stimulated by cystine was observed only in the presence of cumulus cells, either with COCs or in DOs matured on a coculture monolayer. Addition of cysteine and cysteamine to IVM medium increased GSH levels in COCs and DOs. N-Acetylcysteine increased GSH levels only in DOs. Moreover, cumulus cells contributed to the stimulatory effect exerted by cysteine and cysteamine on GSH synthesis in COCs. These results indicate that cumulus cells during IVM play an important role in oocyte GSH synthesis, allowing the oocytes to use cystine and contributing to the stimulatory effect exerted by cysteine and cysteamine. In addition, these results demonstrate that IVM medium supplemented with cysteine or cysteamine increased GSH content in oocytes without cumulus mass (DO) and in the absence of a cumulus cell monolayer. This may be useful to increase the efficacy of IVM of those oocytes having few cumulus cell layers, in a system without coculture.