Innate Immune System Stimulation During Pregnancy Upregulates Thromboxane Synthesis in Rat Maternal Heart

Abstract

BackgroundInfections during pregnancy are associated with adverse maternal and fetal outcomes. We previously showed that exposure to immunostimulatory CpG oligonucleotides (ODN2395, synthetic Toll‐like receptor 9 agonist) during pregnancy induces maternal vascular inflammation and enhances vascular tone in pregnant rats. These outcomes were mediated in part by activation of the cyclooxygenase/thromboxane A2 (COX/TxA2) pathway. The objective of this study was to investigate the impact of ODN2395‐induced immune system stimulation on maternal hearts during pregnancy.HypothesesExposure to TLR9‐mediated immune system activation during pregnancy upregulates the COX/TxA2signaling pathway in maternal cardiac tissues.MethodsRats were treated with a synthetic CpG DNA (ODN2395, 1 mg/kg, intraperitoneal injection) or vehicle (saline) in late pregnancy (gestational day (GD) 14, 16, and 18) and euthanized on GD 20 (term 22‐23). Fetoplacental biometrics were recorded after euthanasia and maternal hearts were collected to assess COX‐1 and COX‐2 expression via western blotting and 6‐keto PGF1α (PGI2 metabolic byproduct) and TxB2 (TxA2 metabolic byproduct) production use ELISA.ResultsMaternal heart weights did not differ between groups (ODN2395: 0.26 g/100 g BW vs. Vehicle: 0.23 g/100 g BW, n≥7, p=0.11). Left ventricular tissues from dams treated with ODN2395 released higher concentrations of TxB2compared to cardiac tissues from vehicle‐treated dams (ODN2395: 0.56 ± 0.06 ng/mg total protein vs. Vehicle: 0.31 ± 0.04 ng/mg total protein, n≥5, p=0.0041) but there were no differences in cardiac 6‐keto PGF1α release between groups (p=0.16). COX‐2 expression was lower in left ventricles from ODN2395‐treated rats compared to vehicle‐treated rats (p=0.009). There were no differences in cardiac COX‐1 expression between groups (p=0.27). Exposure to ODN2395 during pregnancy did not affect fetal weights (ODN2395: 2.28 ± 0.03 g vs. Vehicle: 2.25 ± 0.06 g, n≥7, p=0.9) or placenta weights (ODN2395: 0.44 ± 0.02 g vs. Vehicle 0.49 ± 0.01 g, n≥7, p=0.06), but increased fetal‐placental weight ratio (ODN2395: 5.3 ± 0.22 vs. Vehicle: 4.7 ± 0.15, p = 0.04). COX‐2 expression was greater in placental tissues from ODN2395‐treated rats (p=0.004) but there were no differences in placental 6‐keto PGF1α(p=0.51) and TxB2 production (p=0.32).ConclusionExposure to immunostimulatory CpG ODN during pregnancy induces upregulation of TxB2 synthesis in maternal cardiac tissues coupled with a reduction in COX‐2 expression. We suggest that cardiac inflammation during pregnancy may increase maternal risk for future cardiovascular events.