Twenty pregnant C57BL/6 mice, each weighing 16 to 20 g, were randomly divided into 4 groups, including the 12-d control group, 12-d
infection group, 18-d control group and 18-d
infection group. Mice in the 12-d and 18-d
infection groups were injected intraperitoneally with 150 tachyzoites of the T. gondii PRU strain on day 6 of pregnancy, while mice in the 12-d control and 18-d control groups were injected with the same volume of
phosphate buffered saline (PBS). Mice in the control and
infection groups were sacrificed on days 12 and 18 of pregnancy, and the placental and uterine specimens of the pregnant mice in each group were sampled for pathological examinations. The
mRNA expression of HIF-1α, HIF-1β and
vascular endothelial growth factor (
VEGF) was quantified using quantitative fluorescent real-time PCR (qPCR) assay in the placental and uterine specimens, and the correlation between HIF-1α and
VEGF mRNA expression was examined. In addition, and the HIF-1α expression was detected using immunohistochemical staining in the placental and uterine specimens of pregnant mice.
RESULTS: Compared with the 12-d and 18-d control groups, adverse pregnant outcomes were observed in mice in 12-d and 18-d
infection groups, such as teratism and placental dysplasia. HE staining showed swelling and blood stasis of cells, sinusoid reduction and inflammatory cell infiltration in the labyrinth area of the placenta specimens of mice in 12-d and 18-d
infection groups relative to 12-d and 18-d control groups, and columnar epithelial cell injury and inflammatory cell infiltration were seen in the mouse uterine specimens in both
infection groups. qPCR assay detected significantly higher HIF-1α (F = 132.6, P < 0.05) and HIF-1β
mRNA expression (F = 286.9, P < 0.05) in the placental specimens and lower HIF-1α (F = 111.5, P < 0.05) and HIF-1β
mRNA expression (F = 55.2, P < 0.05) in the uterine specimens in the 12-d
infection group than in the 12-day control group, and significantly lower HIF-1α and HIF-1β
mRNA expression was detected in the placental and uterine specimens in the 18-d
infection group than in the 18-day control group (F = 215.8, 418.9, 156.8 and 200.1; all P values < 0.05). Significantly lower
VEGF-A (F = 426.2, P < 0.05),
VEGF-B (F = 104.6, P < 0.05) and
VEGF-C mRNA expression (F = 566.9, P < 0.05) in the placental specimens and higher
VEGF-A (F = 426.2, P < 0.05),
VEGF-B (F = 104.6, P < 0.05) and
VEGF-C mRNA expression (F = 566.9, P < 0.05) in the uterine specimens were detected in the 12-d
infection group than in the 12-d control group, and higher
VEGF-A,
VEGF-B and
VEGF-C mRNA expression was found in the placental and uterine specimens in the 18-d
infection group than in the 18-d control group (F = 521.9, 100.6, 275.9, 224.6, 108.2 and 333.4; all P values < 0.05). Immunohistochemical staining showed strongly and mildly positive HIF-1α expression in the mouse placental labyrinth area in the 12-d and 18-d
infection groups relative to 12-d and 18-d control groups, while no HIF-1α expression was detected in mouse uterine specimens.
CONCLUSIONS: HIF-1α expression appears a tendency towards a rise in the second trimester and a reduction in the third trimester in mice following T. gondii
infection during early pregnancy, which is contrary to the changing tendency of
VEGF-A,
VEGF-B, and
VEGF-C expression. It is hypothesized that HIF-1α inhibits placental angiogenesis in mice during pregnancy through suppressing
VEGF expression, resulting in adverse pregnant outcomes.