Decreased glutathione synthesis in granulosa cells, but not oocytes, of growing follicles decreases fertility in mice

Prior studies showed that mice deficient in the modifier subunit of glutamate cysteine ligase (Gclm), the rate-limiting enzyme in synthesis of the thiol antioxidant glutathione, have decreased ovarian glutathione concentrations, chronic ovarian oxidative stress, poor oocyte quality resulting in early preimplantation embryonic mortality and decreased litter size, and accelerated age-related decline in ovarian follicle numbers. Global deficiency of the catalytic subunit of this enzyme, Gclc, is embryonic lethal. We tested the hypothesis that granulosa cell- or oocyte-specific deletion of Gclc recapitulates the female reproductive phenotype of global Gclm deficiency. We deleted Gclc in granulosa cells or oocytes of growing follicles using Gclc floxed transgenic mice paired with Amhr2-Cre or Zp3-Cre alleles, respectively. We discovered that granulosa cell-specific deletion of Gclc in Amhr2Cre;Gclc(f/-) mice recapitulates the decreased litter size observed in Gclm-/- mice but does not recapitulate the accelerated age-related decline in ovarian follicles observed in Gclm-/- mice. In addition to having lower glutathione concentrations in granulosa cells, Amhr2Cre;Gclc(f/-) mice also had decreased glutathione concentrations in oocytes. By contrast, oocyte-specific deletion of Gclc in Zp3Cre;Gclc(f/-) mice did not affect litter size or accelerate the age-related decline in follicle numbers, and these mice did not have decreased oocyte glutathione concentrations, consistent with transport of glutathione between cells via gap junctions. The results suggest that glutathione deficiency at earlier stages of follicle development may be required to generate the accelerated follicle depletion phenotype observed in global Gclm null mice.