Steroid metabolism, nitrosative stress and inflammation : mechanisms for placental dysfunction in assisted reproduction

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Sato, Brittany Leilani Mika
assisted reproduction; blastomere removal; placenta; steroid metabolism; nitrosative stress; inflammation
thesis / dissertation description
Assisted reproduction technologies (ART) have led to the births of more than five million children worldwide. Pre-implantation genetic diagnosis (PGD) is used in conjunction with ART procedures for genetic screening of embryos prior to uterine transfer. While many couples conceive healthy infants through ART, studies suggest an association with ART and negative obstetric, neonatal, and postnatal outcomes; mechanistic studies aimed at uncovering how ART might mediate these outcomes are lacking. In this dissertation, the effects of blastomere removal associated with PGD on sex steroid homeostasis, inflammation, and nitrosative stress were investigated. We hypothesized that blastomere removal, in conjunction with in vitro fertilization (IVF), results in 1) altered sex steroid homeostasis within the maternal-placental-fetal unit, and 2) increased inflammation and nitrosative stress within the placenta, ultimately leading to detrimental obstetric and neonatal outcomes associated with assisted reproduction. Characterization of the ex vivo primary placental explant technique for the study of sex steroid endocrine studies in humans and mice was performed (Chapter 2). Blastomere removal was shown to alter sex steroid hormones (progesterone, estrone, and estradiol) in the fetus and placenta in mice and to significantly downregulate glucuronidation and sulfonation metabolism pathways within the placenta (Chapter 3). Embryo biopsy also increased nitrosative stress within the placenta of mice (Chapter 4), as demonstrated by elevated concentrations of nitrate species, lipid peroxidation and expression of several matrix metalloproteinase (MMP) enzymes. Embryo culture associated with blastomere removal also increased placental interleukin-6 (IL-6) levels from biopsied and sham-biopsied mouse embryos, thus activating the Janus kinase (JAK) signal transducer and activator of transcription (STAT) pathways as seen by significant increase in phosphorylated STAT1 and reduction in negative regulators, SOCS2 and 3. Taken together, these results suggest that blastomere removal in conjunction with IVF induces nitrosative stress and inflammation as well as dysregulation of steroid homeostasis, specifically within the placenta. Activation of signaling pathways associated with these findings provide novel insights into potential mechanisms mediating the negative outcomes associated with ART and illuminates the need to refine these procedures to minimize the maternal and fetal risks, in order to ensure healthy pregnancies.