Objective: To examine monolayer permeability and junctional protein distribution and expression in endothelial cells isolated from women with preeclampsia and from women with normal pregnancies. We hypothesized that increased endothelial monolayer permeability in preeclampsia reflects altered monolayer barrier properties produced by disorganization of endothelial cell junction proteins.
Study design: Endothelial cells were isolated from umbilical veins from women with normal pregnancies (n = 9) and from women with preeclampsia (n = 9) immediately after delivery. In the first passage of endothelial cells, the permeability was determined by measurement of horseradish peroxidase passage through confluent cell monolayers grown on transwell filters, and the distribution and protein expression of vascular endothelial cadherin and occludin were evaluated by use of immunofluorescent staining of the proteins and Western blot analysis. The distribution of vascular endothelial cadherin was also evaluated in the second and third passage endothelial cells. Messenger ribonucleic acid expression of vascular endothelial cadherin and occludin were examined by reverse transcriptase polymerase chain reaction. Data were expressed as mean values (+/- SE) and were analyzed by use of an unpaired t test.
Results: The relative monolayer permeability was significantly increased in the endothelial cells isolated from women with preeclampsia compared with those isolated from women with normal pregnancies (0.271 +/- 0.049 versus 0.086 +/- 0.031 for DeltaOD(470); P <.05). Vascular endothelial cadherin expression for normal endothelial cells showed a continuous staining of the junctional protein that surrounded cell borders. In comparison, vascular endothelial cadherin in endothelial cells from preeclamptic pregnancies exhibited disorganized staining and vascular endothelial cadherin fibrils were retracted, with gaps present at the cell borders. The expression of occludin showed a pattern similar to that of vascular endothelial cadherin in both normal and preeclamptic conditions. Western blot results for expression of vascular endothelial cadherin and occludin also showed decreased expression of junctional proteins. The altered endothelial cell junctional protein distribution and expression of vascular endothelial cadherin and occludin observed in the first passage of endothelial cells from preeclamptic pregnancies was restored to normal by the time cells reached the third passage in vitro. There was no statistical difference in mRNA expression for the vascular endothelial cadherin and occludin between normal endothelial cells and those from preeclamptic pregnancies.
Conclusion: In preeclampsia, increased endothelial cell monolayer permeability appears to reflect disorganized and diminished expression of endothelial cell junctional proteins. The latter response is mediated at the posttranscriptional level. These findings provide new insights about the cellular and molecular basis for altered endothelial cell integrity and barrier dysfunction that are associated with preeclampsia.