Genomic Profiling of BDE-47 Effects on Human Placental Cytotrophoblasts

Abstract

Despite gradual legislative efforts to phase out flame retardants (FRs) from the marketplace, polybrominated diphenyl ethers (PBDEs) are still widely detected in human maternal and fetal tissues, e.g., placenta, due to their continued global application in consumer goods and inherent biological persistence. Recent studies in rodents and human placental cell lines suggest that PBDEs directly cause placental toxicity. During pregnancy, trophoblasts play key roles in uterine invasion, vascular remodeling and anchoring of the placenta-fetal unit to the mother. Thus, to study the potential consequences of PBDE exposures on human placental development, we used an in vitro model: primary villous cytotrophoblasts (CTBs). Following exposures, the endpoints that were evaluated included cytotoxicity, function (migration, invasion), the transcriptome, and the methylome. In a concentration-dependent manner, common PBDE congeners, BDE-47 and -99, significantly reduced cell viability and increased death. Upon exposures to sub-cytotoxic concentrations (≤ 5µM), we observed BDE-47 accumulation in CTBs with limited evidence of metabolism. At a functional level, BDE-47 hindered the ability of CTBs to migrate and invade. Transcriptomic analyses of BDE-47 effects suggested concentration-dependent changes in gene expression, involving stress pathways, e.g., inflammation and lipid/cholesterol metabolism as well as processes underlying trophoblast fate, e.g., differentiation, migration, and vascular morphogenesis. In parallel assessments, BDE-47 induced low-level global increases in methylation of CpG islands, including a subset that were proximal to genes with roles in cell adhesion/migration. Thus, using a primary human CTB model, we showed that PBDEs induced alterations at cellular and molecular levels, which could adversely impact placental development.

Association of Polybrominated Diphenyl Ether (PBDE) Levels with Biomarkers of Placental Development and Disease during Mid-gestation

“…MMP1 was upregulated by exposing differentiating/invading CTBs to BDE-47 [40]. In agreement with previously published data [42], ITGA1 was upregulated in cell columns and primarily expressed in extravillous CTBs, especially in the interstitial and endovascular regions of the basal plate (iCTB and eCTB).…”

“…Perhaps upregulated CDH5 compensates for downregulated ITGA1. PBDEs may disrupt several pathways that regulate CTB differentiation, including, hormone, oxidative stress, inflammation, and placental developmental pathways [31,33,35,41,58], however, the direct interactions that lead to increased CDH5 expression as they invade is unknown and speculative at this point in the context of environmental exposures. Moreover, we were not able to account for other exposures.…”

“…Thus, the complexity of CTB invasion in the context of the exposome make it difficult to predict the outcome of experiments such as those described here. As to the MMP1 analyses, the effects of in vitro PBDE exposures were analyzed at the RNA level [40] as compared to the antibody-based protein approach we employed. Lack of correlation between transcriptomic and proteomic data is now a well-recognized phenomenon [60] Additionally, the effects of acute (in vitro) vs. chronic (in vivo) PBDE exposures are not well understood.…”

“…Perturbations to this developmental process contribute to preeclampsia and other complications usually clinically identified later in pregnancy or at term. Specifically, we examined the relationship between mid-gestational PBDE levels and biomarkers of placental development and disease, focusing on molecular and morphological features that: 1) correlate with normal placentation and pregnancy outcomes; 2) are adversely affected in pregnancy complications; and/or 3) are differentially expressed following exposure of primary human CTBs to PBDEs in vitro [40]. The molecules were stage-specific CTB antigens that correlate with differentiation and invasion: integrin alpha 1 (ITGA1), VE-cadherin (CDH5), and metalloproteinase 1 (MMP1).…”

Association of Polybrominated Diphenyl Ether (PBDE) Levels with Biomarkers of Placental Development and Disease during Mid-gestation

“…The results showed that PBDEs impaired the cells' ability to migrate and invade due to altered gene expression in CTB differentiation and environmental stress response pathways (Robinson et al, 2019). Together, these studies indicate a potential role for PBDEs in the pathophysiology of adverse pregnancy outcomes via effects on the placenta, and highlight functional and molecular perturbations to human placental development that can be evaluated in relation to PBDE exposures.…”