Placental inflammation and oxidative stress in the mouse model of assisted reproduction
Introduction
Despite being viewed as a relatively safe and effective way to conceive for infertility, pregnancies achieved by in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are associated with higher incidence of induced labor, Caesarean section, premature birth, small-for-gestational age babies, pediatric cancer, imprinting disorders and congenital abnormalities [1], [2], [3], [4].
Although the mechanism for higher rates of negative outcomes occurring in pregnancies where assisted reproduction technologies (ART) are used is unknown, several studies implicate placental dysfunction as a critical factor. Higher placental weight, delayed placental development (without structural abnormalities), decreased steroid levels in the fetal compartment, increased placental steroid glucuronidation and altered placental metabolism have been documented in mice [5], [6], [7], [8], [9]. In humans, higher rates of placenta previa, abruption, premature rupture of the membranes, pre-eclampsia, unusual shape and umbilical cord insertion have also been reported [3], [10], [11]. Therefore, elucidating the effects of assisted reproduction on placental function is a promising avenue for unraveling the mechanisms behind unsatisfactory pregnancy outcomes associated with ART.
In terms of placental research, mouse and human structures are similar in form and function, but structurally different. According to Grosser’s classification, murine placentas are hemotrichorial. The maternal decidua and spongiotrophoblast are partially embedded in the endometrium and maternal-fetal exchange occurring in the labyrinth, consisting of syncitiotrophoblasts, chorionic trophoblasts, stroma, and blood vessels [12]. In humans, the classification is hemomonochorial since the placenta is not embedded and the chorionic villi are bathed directly in maternal blood [12]. In spite of these differences placental function is similar and it remains vital for fetal well-being in both species, due to its critical role in transport of substances (including steroids and other hormones, nutrients and essential minerals) to the fetus, as well as removing wastes.
A previous key finding in this same cohort of ART animals was that progesterone levels were decreased in the placenta, but not systemically in the mother or fetus [8]. In pregnancy, progesterone suppresses inflammatory responses [13], [14] and prevents premature parturition and fetal growth restriction [15], [16], [17], [18], [19]. We hypothesized that negative outcomes from ART may be mediated by placental inflammation and oxidative stress. Herein, using a mouse model of ART, we demonstrate that placental antioxidant defense enzymes are severely compromised with concurrently greater placental inflammation, lower placental lipid, increased apoptosis and degraded intracellular nucleotides. These data confirm inflammation and oxidative stress as contributors to placental dysfunction in ART, which may provide a mechanism for the higher incidence of negative reproductive outcomes.
Section snippets
Reagents
Mineral oil was purchased from Squibb and Sons (Princeton, NJ); pregnant mares’ serum gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) were from Calbiochem (Spring Valley, CA); assay kits for antioxidant enzymes were from Cayman Chemical Company (Ann Arbor, MI). All other chemicals were obtained from Sigma Chemical Co. (St Louis, MO) unless otherwise stated.
Animals, in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI)
The animals used and IVF/ICSI methods were previously described. However, the current results are novel and do not in any way
Production of fetuses after mating, IVF and ICSI
As previously described [8], three females were mated with all becoming pregnant, providing 26 fetuses. When embryos produced by IVF and ICSI were transferred into the oviducts of pseudopregnant females, all females (3 per group) became pregnant with 37 (IVF) and 25 (ICSI) fetuses produced. Placenta weights averaged 89.5 ± 12.5 mg in normally conceived fetuses (n = 26) and were significantly higher in IVF (104.9 ± 19.7, P < 0.001, n = 37) and ICSI (108.6 ± 19.1 mg, P < 0.001, n = 25). There
Discussion
This study suggests that placental inflammation and oxidative stress are significantly raised in the mouse model of ART. Although no structural abnormalities in placentas from ART pregnancies have been noted here, or by others [5], [8], further testing revealed significantly lower placental lipid loading, increased placental cell death (apoptosis) and compromised intracellular nucleotides (lower RNA levels and integrity, higher DNA damage). Furthermore, ART manipulation resulted in increasing
Authorship contributions
Research design: Collier, Ward.
Conducted experiments: Raunig, Collier, Yamauchi.
Performed data analysis: Raunig, Collier.
Wrote or contributed to the writing of the manuscript:
Raunig,Ward and Collier.
Other: Collier and Ward acquired funding for this research.
Disclosure statement
The authors have nothing to declare.
Financial support
The study was supported by NIH HD058059 and P20RR024206 (project 2) grants to M.A.W. and NIH RR024206 (Project 4) to A.C.C.
Acknowledgements
We thank Dr. Diane Wallace-Taylor for allowing us to use her bright-field microscope and image capture system. We also acknowledge Miyoko Bellinger from the JABSOM Histology core for outstanding sectioning of tissues.
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