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Balanced immune responses are essential for the maintenance of successful pregnancy. Aberrant responses of immune system during pregnancy increase the risk of preeclampsia. Toll-like receptor 4 (TLR4) plays a crucial role in the activation of immune system at the maternal-fetal interface. This study aimed to generate a rat model of preeclampsia by lipopolysaccharide (LPS, a TLR4 agonist) administration on gestational day (GD) 5 as rats are subjected to placentation immediately after implantation between GDs 4 and 5, and to assess the contribution of TLR4 signaling to the development of preeclampsia. Single administration of 0.5 μg/kg LPS significantly increased blood pressure of pregnant rats since GD 6 (systolic blood pressure, 124.89 ± 1.79 mmHg versus 119.02 ± 1.80 mmHg, P < 0.05) and urinary protein level since GD 9 (2.02 ± 0.29 mg versus 1.11 ± 0.18 mg, P < 0.01), but barely affected blood pressure or proteinuria of virgin rats compared with those of saline-treated pregnant rats. This was accompanied with adverse pregnancy outcomes including fetal growth restriction. The expression of TLR4 and NF-κB p65 were both increased in the placenta but not the kidney from LPS-treated pregnant rats, with deficient trophoblast invasion and spiral artery remodeling. Furthermore, the levels of inflammatory cytokines were elevated systemically and locally in the placenta from pregnant rats treated with LPS. TLR4 signaling in the placenta was activated, to which that in the placenta of humans with preeclampsia changed similarly. In conclusion, LPS administration to pregnant rats in early pregnancy could elicit TLR4-mediated immune response at the maternal-fetal interface contributing to poor early placentation that may culminate in the preeclampsia-like syndrome.

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Preeclampsia (PE) is considered to be initiated by abnormal placentation in early pregnancy and results in systemic endothelial cell dysfunction in the second or third trimester. MicroRNAs (miRs) expressed in the human placenta can be secreted into maternal circulation via exosomes, which are secreted extracellular vesicles that serve important roles in intercellular communication. The present study hypothesized that upregulation of placenta‑associated serum exosomal miR‑155 from patients with PE may suppress endothelial nitric oxide synthase (eNOS) expression in endothelial cells. The results demonstrated that placenta‑associated serum exosomes from patients with PE decreased nitric oxide (NO) production and eNOS expression in primary human umbilical vein endothelial cells (HUVECs). Subsequently, an upregulation of placenta‑associated serum exosomal miR‑155 was detected in patients with PE compared with in gestational age‑matched normal pregnant women. In addition, the results demonstrated that overexpression of exosomal miR‑155 from BeWo cells was internalized into HUVECs, and was able to suppress eNOS expression by targeting its 3'‑untranslated region. The results of the present study indicated that placenta‑associated serum exosomes may inhibit eNOS expression in endothelial cell during PE development in humans, and this phenomenon may be partly due to increased miR‑155 expression in placenta‑associated serum exosomes.