Integrative metabolism of oocyte development and its modulation by maternal diet

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Project Summary AAccumulating evidence indicates that an inability of oocyte mitochondria to meet the energy demands of maturation, fertilization, and embryo development contributes to infertility, chromosomal abnormalities and poor assisted reproduction outcomes. This is particularly relevant in the context of maternal aging, where a loss of oocyte mitochondrial content is thought to limit oxidative phosphorylation (OXPHOS) capacity secondary to reductions in mtDNA content or replication. However, our understanding of oocyte and embryo energy metabolism has been limited by inherent technical challenges, and so is currently based largely on indirect estimates of mitochondrial capacity/content, marker enzyme activities and metabolite analyses. To overcome this limitation, our team has developed the first miniaturized metabolic multi-sensor capable of real-time monitoring of mitochondrial respiration, glycolytic flux and extracellular acidification in single oocytes and embryos. Using this new technology in an equine model, we have found that oocyte OXPHOS rate indeed declines with maternal age, but its mitochondrial respiratory capacity actually increases, arguing against the hypothesis that a loss of mitochondrial content/capacity impairs oocyte metabolic potential with age. In parallel studies of granulosa cell metabolism using high-resolution respirometry and fluorometry, we found that maternal aging does not impair OXPHOS capacity, but dramatically increases release of mitochondria-derived reactive oxygen species. This could be reversed by modulating maternal dietary composition for 8 weeks, consistent with potential links between maternal lifestyle, the follicular environment, and oocyte metabolic competence. The aim of this proposal is to apply state-of-the-art methods toward characterizing the integrative metabolic phenotype of mammalian oocytes and embryos during development, and evaluate the impact of nutritional interventions applied both in vivo (maternal) and in vitro (media composition) on these parameters. In Aim 1, we will establish the developmental time-course of metabolic changes that occur from oocyte maturation to the blastocyst stage, and evaluate the influence of incubation media composition, maternal aging and obesity/hyperglycemia on these processes. Studies are proposed in bovine, equine and human oocyte samples for feasibility testing and to establish the value of animal modeling for future applications. In Aim 2, we will test the hypothesis that maternal dietary omega-3 fatty acid supplementation alters oocyte metabolism and improves embryo development, based on preliminary studies in an equine model. Our long-term goal is to establish methods, instrumentation and reference values for integrative metabolic monitoring of oocyte and embryo development to facilitate scientific and therapeutic advances that optimize human reproductive fitness and assisted reproduction outcomes. Our investigative team combines expertise in oocyte biology and assisted reproduction technology, mitochondrial metabolism and respirometry, and biomedical engineering that are uniquely suited to achieving the aims and long-term goals of this project.