Cytoplasmic glutathione regulated by cumulus cells during porcine oocyte maturation affects fertilization and embryonic development in vitro

It is generally accepted that cumulus cells support the nuclear maturation of mammalian oocytes. In the present study, we examined relationships between the cytoplasmic glutathione (GSH) content of porcine oocytes, and oocyte nuclear maturation, fertilization or subsequent embryonic development. Cumulus-oocyte complexes (COCs; control group) and oocytes denuded of cumulus cells after collection (DO 0 h group) were cultured for 24 h with dibutyryl cAMP, eCG and hCG (first culture step) and then for a further 20 h without supplements (second culture step; 44 h total culture). After the first culture step, some of the COCs were denuded, either completely (DO 24 h group) or partly (H-DO 24 h group), and then matured by the second culture step. Also, in the second culture step, some DOs were co-cultured with cumulus cells that had been pre-cultured for 24 h (DO 24 h + CC group). The maturation rates of all the cumulus-removed groups (DO 0 h, DO 24 h, H-DO 24 h and DO 24 h + CC groups) were lower (34.3–45.0%) than that of the control group (64.5%; P < 0.05). The GSH contents of matured oocytes in the completely denuded groups (DO 0 h, DO 24 h and DO 24 h + CC groups) were lower (4.03–5.26 pmol/oocyte) than that of the control group (9.60 pmol/oocyte; P < 0.05); however, the H-DO 24 h group had an intermediate value (7.0 pmol/oocyte). The male pronuclear formation rates of completely denuded oocytes were lower (41.4–59.3%) than that of the control group (89.4%; P < 0.05), whereas the H-DO 24 h group had an intermediate rate (80.0%). The blastocyst formation rates of the completely denuded oocytes were lower (3.0–4.5%) than that of the control group (19.9%; P < 0.05), and the H-DO 24 h group again had an intermediate rate (11.6%). The GSH content was correlated with the rates of male pronuclear formation (P < 0.01) and blastocyst formation (P < 0.01), and also with the number of cells per blastocyst (P < 0.01). In conclusion, we inferred that GSH synthesized by intact cumulus cells during maturation culture improved oocyte maturation and played an important role in fertilization and embryonic development.