Background:Phthalates are environmental contaminants commonly used as plasticizers in polyvinyl chloride (PVC) products. Recently, exposure to phthalates has been associated with preterm birth, low birth weight, and pregnancy loss. There is limited information about the possible mechanisms linking maternal phthalate exposure and placental development, but one such mechanism may be mediated by peroxisome proliferator–activated receptor γ (PPARγ). PPARγ belongs to the nuclear receptor superfamily that regulates, in a ligand-dependent manner, the transcription of target genes. Studies of PPARγ-deficient mice have demonstrated its essential role in lipid metabolism and placental development. In the human placenta, PPARγ is expressed in the villous cytotrophoblast (VCT) and is activated during its differentiation into syncytiotrophoblast.Objectives:The goal of this study was to investigate the action of mono(2-ethylhexyl) phthalate (MEHP) on PPARγ activity during in vitro differentiation of VCTs.Methods:We combined immunofluorescence, PPARγ activity/hCG assays, western blotting, and lipidomics analyses to characterize the impacts of physiologically relevant concentrations of MEHP (0.1, 1, and 10μM) on cultured VCTs isolated from human term placentas.Results:Doses of 0.1μM and 1μM MEHP showed significantly lower PPARγ activity and less VCT differentiation in comparison with controls, whereas, surprisingly, a 10μM dose had the opposite effect. MEHP exposure inhibited hCG production and significantly altered lipid composition. In addition, MEHP had significant effects on the mitogen-activated protein kinase (MAPK) pathway.Conclusions:This study suggests that MEHP has a U-shaped dose–response effect on trophoblast differentiation that is mediated by the PPARγ pathway and acts as an endocrine disruptor in the human placenta. https://doi.org/10.1289/EHP3730

The peroxisome-proliferator-activated-receptor-γ (PPARγ) is a member of the nuclear receptor superfamily that plays a critical role in diverse biological processes, including adipogenesis, lipid metabolism, and placental development. To study the activity of PPARγ, we constructed two new reporter genes: a fluorescent GFP-tagged histone-2B (PPRE-H2B-eGFP) and a secreted nanoluciferase (PPRE-pNL1.3[secNluc]). This study demonstrates their usage to monitor PPARγ activity in different cell types and screen for PPARγ's potential ligands.