Cellular Localization of Placenta-Specific Human Endogenous Retrovirus (HERV) Transcripts and their Possible Implication in Pregnancy-Induced Hypertension

Abstract We previously investigated tissue specificity and temporal changes in expression of five human endogenous retroviruses (HERVs), including syncytin/ERVWE1 and syncytin 2 . In the current study, we examined the cellular localization and quantified the transcripts of five HERVs, syncytin , syncytin 2 , HERV-H7/F(XA34), HERV-Fb1, and HERV-HML6-c14, in order to elucidate their physiological and etiological roles in the placenta and in pregnancy-induced hypertension (PIH), respectively. In situ hybridization revealed trophoblast-specific transcription of all five HERVs. Consistent with a previous immunohistochemical analysis, syncytin 2 transcripts were detected only in cytotrophoblasts. All the HERVs except HERV-HML6-c14 (HML6-c14) were predominantly localized in the cytoplasm of syncytiotrophoblasts and/or cytotrophoblasts. Quantitative analysis showed that transcriptional levels of these four HERVs were lower in placentas obtained from pregnant women with PIH ( n = 22) than in those from normotensive pregnant women ( n = 87) and that the differences were statistically significant ( p = 0.001, 0.01,