The impact of ultra-low oxygen IVF on preimplantation and postnatal development

PROJECT SUMMARY Assisted Reproductive Technologies (ART) are non-coital methods of achieving a pregnancy, and most often involve the manipulation of gametes or embryos. Importantly, the use of ART is increasing as they become more accessible and more couples experience infertility or postpone childbearing. In vitro fertilization (IVF) is one of the most common ART used in clinics today, in which eggs are combined with sperm and cultured until the blastocyst stage before transfer to a recipient female. Although beneficial and safe, IVF procedures have been associated with suboptimal outcomes for mother and baby including pre-eclampsia, fetal and placental growth abnormalities, an increased rate of rare imprinting disorders, and dysregulated postnatal metabolism. Indeed, human IVF children experience elevated body weight, glucose intolerance, and insulin resistance beginning in adolescence. These outcomes may result from IVF procedures, especially embryo culture, which exposes a developing embryo to altered environmental conditions not normally experienced in vivo during a time in which the epigenome must be reprogrammed for proper development. One important environmental factor during embryonic development is oxygen (O2), which can influence gene expression, metabolism, and the activity of important epigenetic enzymes. Today, the lowest O2 tension used during embryo culture is 5%, despite evidence that sections of the mammalian female reproductive tract have O2 levels as low as 2%. Thus, decreased O2 tension during embryo culture may better mimic the in vivo environment, leading to improved pre- and postnatal outcomes in the offspring. Consistently, preliminary studies from my thesis lab have demonstrated that culture at 2% O2 improves blastocyst morphology, molecular signatures in embryonic liver, and placental outcomes compared to culture at 5% O2. Given that culture at 2% O2 improves some offspring outcomes, I hypothesize that the molecular profiles of embryos cultured at 2% O2 will more closely resemble naturally-conceived embryos (Naturals). Additionally, I hypothesize adult IVF offspring after 2% O2 culture (IVF 2%) will display less severe metabolic outcomes compared to 5% O2 culture (IVF 5%) IVF offspring. To test these important hypotheses, I will use our validated IVF mouse model, which recapitulates many of the phenotypes observed after IVF in humans. In Aim 1, I will explore how culture under difference oxygen tensions (2 vs. 5%) impacts gene expression, DNA methylation, and histone posttranslational modifications in blastocysts. In Aim 2 I will determine if metabolic outcomes in adult IVF offspring are improved after culture at 2% O2, and whether this improvement translates to the transcriptome and methylome of the liver. This project will determine how embryo culture at 2% O2 impacts both preimplantation development and adult metabolic health outcomes. Overall, this research will contribute foundational insights to our understanding of the role of O2 in early development, with key implications for clinical IVF practices.