Cumulus cell-enclosed oocytes acquire a capacity to synthesize GSH by FSH stimulation during in vitro maturation in pigs.

We investigated (i) follicle stimulating hormone (FSH)-modulated changes in the expression of glutathione (GSH) and its rate-limiting enzyme, glutamate cysteine ligase (GCL), in porcine oocytes and cumulus cells, and (ii) the contribution of gap-junctional communications (GJCs) in cumulus-oocyte complexes (COCs) to intraoocyte GSH accumulation. In experiment (i), COCs were cultured for 48 h with (+FSH group) or without FSH (-FSH group). The GSH content of oocytes increased with cultivation time in the +FSH group, but decreased in the -FSH group. The GSH content of cumulus cells at 48 h was also higher in the +FSH group than that in the -FSH group. Expression of GCL subunit mRNAs in oocytes and cumulus cells was increased by FSH stimulation until 12 h, and then fell to the baseline level. On the other hand, the amount of GCL subunit proteins in oocytes and cumulus cells increased gradually throughout the period of culture with FSH. In experiment (ii), blocking of GJCs in COCs during 0-24 h of culture led to a decrease in the GSH content of oocytes at 24 h of culture, whereas the GSH content at 48 h of culture did not differ even after blocking of the GJCs during 24-48 h of culture. These findings indicate that FSH initiates GSH synthesis in cumulus cells and oocytes by modulating the expression of GCL, and that porcine oocytes are able to synthesize GSH without GJC-mediated support from cumulus cells, at least in the later half of maturation culture.