Preeclampsia is a severe pregnancy disease causing significant maternal and perinatal morbidity and mortality. Term preeclampsia (diagnosis>37 gestation weeks) accounts for 80% of the overall disease burden. However, due to our poor understanding of its underlying etiology, we still lack early prediction and prevention methods. Whether deficient early placentation contributes to term preeclampsia is hotly debated and has never been experimentally proven.
Our previous multi-omics on early pregnancy placental biopsies revealed melanophilin as associated with term preeclampsia. RNA sequencing data showed melanophilin is significantly downregulated in placental tissue from term preeclampsia compared to uncomplicated pregnancies. Melanophilin is well characterized as a key regulator of hair, skin, and eye colour, but more recently it is shown to regulate insulin granule release and enhance cancer progression. However, melanophilin has never been investigated in the placenta. We investigated the localization and expression of melanophilin in human decidua and placenta across gestation by qPCR and immunohistochemistry. siRNA knockdown of melanophilin in trophoblast cell lines (HTR8 and trophoblast stem cells [hTSC], n=4/group) was used to determine its role in gene expression (qPCR) and adhesion/proliferation (xCELLigence/MTT assay).
Melanophilin localized to extravillous trophoblast in decidua and syncytiotrophoblast, cytotrophoblast, stromal, endothelial and Hofbauer cells in placental villus. Melanophilin mRNA expression in placental villus was highest in the 1st trimester, reducing by 200% to be almost absent in the second trimester and at term (p<0.05). In vitro, melanophilin loss significantly promoted trophoblast adhesion (HTR8 1.3-fold; p<0.05) and proliferation (at 24h: HTR8 1.5-fold; hTSC 1.3-fold; p<0.05). Melanophilin knockdown in hTSC reduced mRNA expression of PlGF (0.4-fold) and regulated genes associated with trophoblast differentiation (HLAG, bhCG, GATA3, EOMES).
Here we show melanophilin was highly expressed in first trimester placenta and regulates trophoblast adhesion, proliferation and gene expression. Loss of melanophilin may contribute to the diminished trophoblast differentiation seen in preeclampsia.