Background
Atmospheric fine particulate matter (PM2.5) can induce abnormal early embryo development, resulting in adverse pregnancy outcomes such as embryo damage and spontaneous abortion. The vascular remodeling of maternal-fetal interface regulated by hypoxia inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF) axis is a key link in early embryo development.
Objective
To investigate the effects of pre-pregnancy PM2.5 exposure on the uterine state of mice before conception and the vascular remodeling of maternal-fetal interface after conception, and to further explore the regulatory role of the HIF-1α/VEGF axis.
Methods
Forty eight-week-old C57BL/6J sexually mature female mice and several males (for mating, without any treatment) were adaptive fed for 1 week. The female mice were divided into a PM2.5 exposure group and a control group, 20 mice per group. The PM2.5 exposure group was given 3 mg·kg−1 PM2.5 suspension by nasal instillation, once every other day for four weeks; the control group were treated with the same dose of blank sampling membrane suspension. Body weight of the mice was recorded every week during the experimental period. At the end of the exposure, six mice from each group were sacrificed. Then the uterus was weighted and its organ coefficients were calculated, a histopathological morphology evaluation was conducted by HE staining, and the mRNA expressions of HIF-1α, VEGF and its receptors Flt-1 and Flk-1 in the uterus samples were further examined. The remaining 14 female mice in each group were caged with male mice overnight with a sex ratio of 2:1, then we calculated the pregnancy rate. On gestation day 10 (GD10), the female mice were decapitated and the uterus was dissected, the histopathological morphology of embryo and placenta were observed by HE staining, and the mRNA expressions of HIF-1α, VEGF and its receptors Flt-1 and Flk-1 were detected as well in the uterus samples.
Results
Compared with the control group, the pre-pregnancy PM2.5 exposure had no significant effect on body weight gain of the female mice, but decreased uterine organ coefficient, accompanied by pathological damage such as endometrium thinning as well as decreased mRNA expressions of HIF-1α, VEGF and its receptors Flt-1 and Flk-1 (all Ps<0.05). After mating, the pre-pregnancy PM2.5 exposure induced a decrease of the pregnancy rate (control group: 9/14; exposure group: 5/14) and abnormal embryo arrangement, small placenta, narrowing of spiral arteries (control group: 1.00±0.06; exposure group: 0.86±0.08; P=0.01), as well as significant decreases in HIF-1α, VEGF and its receptor Flk-1 mRNA expressions. (all Ps <0.05).
Conclusion
Pre-pregnancy PM2.5 exposure has adverse effects on the pathological structure and angiogenesis in female mice uterus, leading to abnormal vascular network remodeling at the mother-fetal interface after conception, and the HIF-1α/VEGF axis may play a regulatory role.
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