Elevated placental histone H3K4 methylation via upregulated histone methyltransferases SETD1A and SMYD3 in preeclampsia and its possible involvement in hypoxia-induced pathophysiological process

Disturbance in placental epigenetic regulation contributes to the pathogenesis of preeclampsia (PE). Although aberrant placental DNA methylation status in PE has been thoroughly studied, the role of histone modifications, including histone methylation, in PE remains unclear. Moreover, no study has ever reported the association between PE and placental histone methylation status by focusing on histone methyltransferases. The present study aimed to investigate the possible involvement of placental epigenetic regulation by histone methylation via histone methyltransferases in the pathophysiology of PE. Placental mRNA expression of histone methyltransferases was examined using quantitative RT-PCR. Protein expression of histone methyltransferases and histone methylation status in placentas and trophoblast cell lines were assessed by immunoblotting and immunohistochemistry. Expression profile of histone methyltransferases in the placentas using quantitative RT-PCR revealed that the mRNA expression levels of histone 3 lysine 4 (H3K4) methyltransferases, SETD1A and SMYD3, were significantly increased in placentas from PE patients. Immunoblotting and immunohistochemistry revealed that not only protein expression levels of SETD1A and SMYD3, but also H3K4 methylation status was increased in the trophoblasts from PE placentas. In vitro studies using HTR-8/SV-neo and BeWo cells showed that hypoxia induced the expression levels of SETD1A and SMYD3, and subsequently enhanced H3K4 methylation. Furthermore, the overexpression of SETD1A and SMYD3 in HTR-8/SV-neo cells enhanced H3K4 methylation in response to hypoxia. Our study results suggest that placental epigenetic alteration by enhanced histone H3K4 methylation through upregulated SETD1A and SMYD3 might play a role in the pathophysiological process of PE associated with hypoxia.