Interactions of glutathione, reactive oxygen species, and lipids on oocyte mitochondrial function

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PROJECT SUMMARY/ABSTRACT Mature oocytes have among the highest intracellular concentrations of the potent antioxidant glutathione (GSH). Female mice lacking the modifier subunit of glutamate cysteine ligase (GCLM), the rate-limiting enzyme in GSH synthesis, have low GSH concentrations in oocytes, poor oocyte quality that manifests as increased embryonic mortality prior to the blastocyst stage, chronic ovarian oxidative stress, and accelerated post-pubertal, age-related decline in the primordial follicle pool, which constitutes the irreplaceable ovarian reserve. Therefore, compared to many genetically modified mouse models, which have complete ovarian follicle depletion prior to puberty, these mice more closely model pathological conditions with diminished ovarian reserve in humans. Female Gclm null mice are also resistant to diet- and age-associated gains in body weight and adipose tissue, have decreased hepatic expression of lipogenesis genes, and have increased hepatic mitochondrial oxygen consumption; however, the effects of Gclm deletion on oocyte lipid metabolism and mitochondrial function have not been studied. Gclm null mice thus constitute an excellent model in which to investigate the hypothesis that GSH deficiency causes oocyte mitochondrial dysfunction via increased reactive oxygen species that directly damage mitochondrial macromolecules and/or via decreased lipogenesis resulting in decreased oocyte mitochondrial fatty acid beta oxidation. This hypothesis will be tested via two specific aims: 1) Determine whether oocyte GSH deficiency due to Gclm deletion results in increased oocyte mitochondrial ROS generation, mitochondrial oxidative lipid and DNA damage, and decreased mitochondrial function. 2) Assess the effects of Gclm deficiency on the serum and oocyte lipidomes and on lipogenesis and fatty acid beta oxidation in the oocyte. The proposed studies will address the knowledge gap in understanding the association between decreased ovarian reserve and poor oocyte quality by examining whether oxidative damage to oocyte mitochondria and disruption of oocyte lipid homeostasis are mechanistically involved in decreased oocyte quality in Gclm-/- mice.