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Hoch, D.
Maternal Obesity in Early Human Pregnancy: Placental DNA Integrity and Stress Response
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2021. pp.

Authors Med Uni Graz:
Advisor:: Desoye Gernot; Gauster Martin
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Abstract:: In the first trimester (FT) of human pregnancy, the intrauterine environment directly affects development of the rapidly growing placenta. Maternal obesity - a frequent manifestation of metabolic derangements - is associated with metabolic complications, systemic low-grade inflammation and genotoxicity. Considering that the developing placenta is exposed to obesity-associated changes in the early intrauterine environment, we hypothesize that maternal obesity affects DNA integrity that triggers DNA damage responses (ATM/ATR signaling) and affects placental stress response with consequences for trophoblast turnover in early human pregnancy, respectively. The present study aimed to determine FT placental DNA damage, telomere shortening and subsequent effects on DNA damage repair and cell cycle regulation. Furthermore, we aimed to characterize FT placental stress status and final effects on trophoblast proliferation and apoptosis. For this purpose, placental tissue (week 4-12 p.m.) was obtained from non-smoking (self-report and serum cotinine measurement) women terminating pregnancy for psycho-social reasons. DNA damage and oxygen-induced modification in total tissue were determined by COMET assay. We quantified DNA damage (γH2AX) and oxidative DNA modification (8-OHdG), proliferation (Ki67) and apoptosis (TUNEL, caspase cleaved cytokeratin 18) in villous cytotrophoblasts (CTB) using a semi-quantitative in situ analysis based on immunofluorescence triple-staining. Telomere length in total placental tissue and laser-capture microdissected trophoblast was quantified by RT-qPCR and confirmed by quantitative fluorescence in situ hybridization (Q-FISH). Pre-selected placental stress markers, cytokines, DNA damage repair and cell cycle related genes were assessed using a PCR-gene panel and Nanostring assay, while proteins were quantified by a cell cycle-specific protein array or immunoblotting. Data was analyzed using a multivariate linear regression model with adjustments for gestational age and tissue processing time. The key findings of this study were: i. Maternal obesity in early pregnancy was not associated with oxidative DNA modifications (8-OHdG) in total tissue and CTB. Other indicators of oxidative stress such as products of lipid peroxidation and protein nitration as well as the classical stress marker HSP70 were unaltered by maternal obesity in early pregnancy. Furthermore, gene expression of placental antioxidants (MGST3, SOD3, GSTP1, GLRX, TXNRD1) and heme oxygenase 1 (HO-1) was lower in obese pregnant women, while placental Nrf2 expression and HO-1 protein levels were not altered in samples from obese pregnant women. ii. ii.Maternal obesity affected placental inflammatory cytokine expression (IL1A, IL6) and stress signaling genes (ASK2, MAPK11, MAPK12, MAPK13, JNK1) in FT placentas. iii. iii.Maternal obesity induced placental DNA damage specifically in CTBs. CTB telomeres in situ were shorter in maternal obesity. Shortening was associated with high C-peptide levels, low insulin sensitivity or high BMI. Despite higher ATM/ATR protein levels and increased substrate phosphorylation in FT placentas of obese pregnant women, selected downstream proteins remained unaffected, while central DNA damage repair transducers (HDAC1, HDAC8, PARP1, FEN1, ku70, BLM) were downregulated in FT placentas from obese pregnant women. This dysregulated damage repair was also accompanied by an induction of cell cycle arrest. iv. iv.Finally, we found decreased CTB proliferation and an increase in apoptosis in FT placentas from obese pregnant women, while senescence was unaltered. Altogether, these results argue for absence of oxidative stress in first trimester placentas of obese women. They also suggest that maternal obesity in the first trimester affects CTB turnover and therefore alter placental development, potentially ensuing adverse consequences for maternal and fetal health.