Objective: It is well documented that anti-angiogenic factors are likely to play essential roles in the etiology of pre-eclampsia. Apelin is a small peptide that may potentially act as an angiogenic factor. The expression of apelin was examined at the RNA and protein levels in this study.
Methods: We compared the expression of apelin, examined using quantitative reverse-transcription polymerase chain reaction, western blotting, enzyme-linked immunosorbent assay and immunostaining, between pre-eclamptic patients and normotensive controls.
Results: Apelin messenger RNA is significantly decreased in pre-eclamptic placentas compared with normotensive pregnancies (p<0.05). Apelin protein levels are also lower in pre-eclamptic placentas than the controls but higher in the maternal circulation in pre-eclampsia patients. Immunohistochemical signals for apelin and its receptor APJ were detected mainly in the cytoplasm of syncytiotrophoblasts in chorionic villi and trophoblast-lineage cells in the decidua of term placentas. In early gestation, stronger APJ signals were observed at the cellular membrane.
Conclusions: A functional role of the apelin--APJ system is likely in early gestation, and this raises the possibility that a dysfunctional apelin--APJ system contributes to the onset of pre-eclampsia via decreased angiogenic activity in placental implantation.