Expressions of vitamin D metabolic components VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR in placentas from normal and preeclamptic pregnancies

Abstract

Vitamin D insufficiency/deficiency during pregnancy has been linked to increased risk of preeclampsia. Placenta dysfunction plays an important role in the pathogenesis of this pregnancy disorder. In this study, we tested the hypothesis that disturbed vitamin D metabolism takes place in preeclamptic placentas. Protein expressions of vitamin D binding protein (VDBP), 25-hydroxylase (CYP2R1), 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), and vitamin D receptor (VDR) were examined in placentas from normotensive and preeclamptic pregnancies. By immunostaining we found that in normal placenta VDBP, CYP24A1, and VDR expressions are localized mainly in trophoblasts, whereas CYP2R1 and CYP27B1 expressions are localized mainly in villous core fetal vessel endothelium. Protein expressions of CYP2R1 and VDR are reduced, but CYP27B1 and CYP24A1 expressions are elevated, in preeclamptic compared with normotensive placentas. Because increased oxidative stress is an underlying pathophysiology in placental trophoblasts in preeclampsia, we further determined whether oxidative stress contributes to altered vitamin D metabolic system in placental trophoblasts. Trophoblasts isolated from normal-term placentas were treated with hypoxic-inducing agent CoCl(2), and protein expressions of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR were determined. We found that hypoxia-induced downregulation of VDBP, CYP2R1, and VDR and upregulation of CYP27B1 and CYP24A1 expressions were consistent with that seen in preeclamptic placentas. CuZnSOD expression was also downregulated in trophoblasts treated with CoCl(2). These results provide direct evidence of disrupted vitamin D metabolic homeostasis in the preeclamptic placenta and suggest that increased oxidative stress could be a causative factor of altered vitamin D metabolism in preeclamptic placentas.

Fig. 1.

Expressions of vitamin D binding protein (VDBP), 25-hydroxylase (CYP2R1), 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), and vitamin D receptor (VDR) in normal and preeclamptic placentas. Top: representative immunostaining images of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR expressions in tissue sections from normal and preeclamptic placentas. A–E: normal placentas. F–J: preeclamptic (PE) placentas. Bar, 50 μm. Bottom: protein expressions of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR in snap-frozen tissues from normal and preeclamptic placentas by Western blot. The bar graphs show the relative density of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR protein expressions after normalization with β-actin expression. *P < 0.05 and **P < 0.01; PE vs. normal. ST, syncytiotrophoblasts; V, villous fetal vessels.

Fig. 2.

Expression and distribution of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR in placentas from 1st-trimester, 2nd-trimester, and term pregnancies. A1–A5: 1st trimester. B1–B5: 2nd trimester. C1–C5: term placentas. Arrowhead, cytotrophoblasts (CT); arrow, ST; V, villous fetal vessels. Bar, 50 μm.

Fig. 3.

Effects of hypoxia-mediated expressions of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR in placental trophoblasts. Primary isolated trophoblasts from normal-term placentas were treated with the hypoxic mimetic agent CoCl₂ at 0, 100, 250, and 500 μmol for 48 h. Left: protein expressions of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR in placental trophoblasts treated with or without CoCl₂. Right: bar graphs showing the relative density of VDBP, CYP2R1, CYP27B1, CYP24A1, and VDR expressions after normalization by β-actin expression in each sample in 3 independent trophoblast culture experiments, *P < 0.05 and **P < 0.01; CoCl₂-treated vs. untreated controls, respectively.

Fig. 4.

Expressions of CuZn superoxide dismutase (CuZnSOD) and catalase in placental trophoblasts treated with different concentrations of CoCl₂. The bar graphs show relative CuZnSOD and catalase expressions after normalization with β-actin expression in 3 independent trophoblast culture experiments. *P < 0.05 and **P < 0.01; CoCl₂-treated vs. untreated controls, respectively.