miR-99 family is potential target to reverse cerium dioxide nanoparticle-induced placental cell dysfunction

Cerium dioxide nanoparticles (CeO₂ NPs) are increasingly used as diesel additive, causing a lot of concern about their toxic effects when released into the atmosphere. To date, there is little knowledge about the toxic effects of CeO₂ NPs on the female reproductive system.

The morphology and size distribution of CeO₂ NPs was observed by transmission electronic microscope (TEM) and Zetasizer Nano, respectively. The uptake of CeO₂ NPs by cells was also observed by TEM after treatment. The cytotoxicity of CeO₂ NPs was studied by Cell Counting Kit-8 (CCK-8), the cellular invasive and migratory ability was examined by transwell assay, the cell apoptosis and reactive oxygen species (ROS) were studied by flow cytometry (FCM), and the mRNAs and proteins expressions were revealed by quantitative real-time PCR (qRT-PCR) and western blotting. The cytoskeletons and autophagy levels were revealed by immunofluorescence. The target regulation of miR-99 to mammalian target of rapamycin (mTOR) was proved by dual luciferase reporter assay after transfection.

We studied the cytotoxic effects of CeO₂ NPs on human trophoblastic cells (HTR-8/Svneo) and found that the invasive and migratory abilities of HTR-8/SVneo cells were decreased after CeO₂ NPs exposure. Immunofluorescence assays showed that the cellular microtubule networks and microfilament arrangement were obviously altered, and although the expression of cytoskeleton proteins (α-tubulin, β-tubulin, actin) did not change, the protein levels of invasion- and migration-related factors [matrix metalloproteinase 2 (MMP2), protein kinases B (AKT), mTOR] were decreased in exposed cells. Accordingly, the expression level of miR-99 family members (miR-99a, miR-99b, miR-100), which can regulate mTOR, was significantly increased after CeO₂ NPs exposure. Dual luciferase reporter assay indicated that the miR-99 family members directly targeted mTOR.

CeO₂ NPs impaired the invasive and migratory abilities, which play an important role in embryo implantation, as well as determining placental function and embryonic development.