DYSREGULATED EMBRYONIC PLACENTATION IS MORE SIGNIFICANTLY ASSOCIATED WITH RISK OF EARLY SPONTANEOUS PREGNANCY LOSS THAN MATERNAL UTERINE SIGNALING

Abstract

Biochemical pregnancy loss (BPL) rates have remained persistent at 12-15% despite significant developments in in vitro fertilization including improved embryo culture, aneuploidy screening, and endometrial receptivity testing. In order to elucidate factors important for early pregnancy maintenance that could lead to BPL, we utilized a mouse model to investigate sites of implantation corresponding to viable embryos or spontaneous embryo resorption (miscarriage). Uterine and placental gene expression of implantation sites corresponding to either viable or spontaneously resorbing embryos from early murine pregnancy. Female wild-type, outbred CF-1 pregnant mice were identified on day 10.5 of embryonic development for collection of uterine implantation sites containing either viable embryos (controls) or embryos that were in the early stage of resorption and not yet hemorrhagic. Total RNA was isolated from embryonic placentas (n=6 per group) and maternal uterine tissue (n=5 per group). Quantitative real-time PCR was performed on the QuantStudio 5 (Applied Biosystems) for key implantation and early pregnancy genes including: Cd81, Glrx, Bdnf, Cox2, Ptgs2, Vegfa, and Icos. Gene expression data were analyzed by the REST software (Qiagen) and Student’s t-test, with significance at P<0.05. Embryonic placental expression of Cd81 was significantly increased in embryo resorption sites (P<0.001). Elevated Cd81 inhibits cytotrophoblast invasion, indicating that insufficient placentation may have contributed to early pregnancy loss. Expression of embryonic placental Glrx was decreased in resorption sites (P<0.01), suggesting that heightened oxidative stress hindered placentation and/or maternal-fetal communication resulting in fetal loss. On the maternal side, expression of the paracrine growth factor Bdnf was decreased in uterine tissue from embryo resorption sites (P<0.01). Previous studies have reported increased Bdnf in the pregnant uterus and reduced Bdnf in uterine flushings from repeat implantation failure patients. In contrast, genes involved in tissue remodeling, angiogenesis, and decidualization (Cox2, Ptgs2, Vegfa), immune balance (Icos), trophoblast invasion (Cd81), or pinopode formation (Glrx) were not differentially expressed in maternal uterine tissue between viable and resorbing implantation sites. The etiology of BPL is likely diverse and complex. Our preliminary data suggest that dysregulated embryonic placentation is more significantly associated with risk of early pregnancy loss than maternal uterine signaling. As lipid composition and amino acid metabolism are important for implantation, ongoing studies will utilize liquid chromatography mass spectrometry to identify metabolite changes that correlate with these observed significant embryonic placentation changes.