Transcriptional and Epigenetic Mechanisms Underlying Enhanced in Vitro Adipocyte Differentiation by the Brominated Flame Retardant BDE-47

Abstract

Recent studies suggest that exposure to endocrine-disrupting compounds (EDCs) may play a role in the development of obesity. EDCs such as the flame retardant 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) have been shown to enhance adipocyte differentiation in the murine 3T3-L1 model. The mechanisms by which EDCs direct preadipocytes to form adipocytes are poorly understood. Here, we examined transcriptional and epigenetic mechanisms underlying the induction of in vitro adipocyte differentiation by BDE-47. Quantitative high content microscopy revealed concentration-dependent enhanced adipocyte differentiation following exposure to BDE-47 or the antidiabetic drug troglitazone (TROG). BDE-47 modestly activated the key adipogenic transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) in COS7 cells, transiently transfected with a GAL4 reporter construct. Increased gene expression was observed for Pparγ2, leptin (Lep), and glucose-6-phophatase catalytic subunit (G6pc) in differentiated 3T3-L1 cells after BDE-47 exposure compared to TROG. Methylation-sensitive high resolution melting (MS-HRM) revealed significant demethylation of three CpG sites in the Pparγ2 promoter after exposure to both BDE-47 and TROG in differentiated 3T3-L1 cells. This study shows the potential of BDE-47 to induce adipocyte differentiation through various mechanisms that include Pparγ2 gene induction and promoter demethylation accompanied by activation of PPARγ, and possible disruption of glucose homeostasis and IGF1 signaling.

Adipose Tissue as a Site of Toxin Accumulation

“…Moreover, di(2-ethylhexyl) phthalate (DEHP) or its metabolite mono-(2-ethylhexyl) phthalate (MEHP) increased adipocyte differentiation in 3T3-L1 cells, (142) (115), murine mesenchymal stem cells (44), and in vivo (142) (62). Few human studies have addressed effects of BFRs on obesity and metabolic syndrome; however, adipocyte differentiation was increased by the BFRs PDBE (397) and BDE-47 (185). These findings are supported by a recent study which reported increased body weight of obese mice treated with hexabromocyclododecane (HBCD) (431).…”

The Role of Epigenetics in the Latent Effects of Early Life Exposure to Obesogenic Endocrine Disrupting Chemicals

“…In 3T3-L1 cells, BDE-47 increased in Ppar␥2 expression levels, which was associated with a decrease in DNA methylation of the Ppar␥2 promoter. Also increased levels of several adipogenic genes were found after BDE-47 exposure, including Lep, but no changes in DNA methylation of the leptin promoter were found (36). Though perinatal exposure to BDE-47 resulted in increased body weight in rodents (37), to our knowledge, epigenetic analysis linking developmental exposure to the obesogenic effects of BDE-47 in vivo has not been performed.…”

“…BDE-47 binds and activates human PPAR␥ in vitro (36). In 3T3-L1 cells, BDE-47 increased in Ppar␥2 expression levels, which was associated with a decrease in DNA methylation of the Ppar␥2 promoter.…”

GSK Regulatory strategy for non-clinical safety assessment of vaccines intended for maternal immunization

“…Lipid accumulation and cell number were analysed according to a previously described method [3]. Zebrafish were exposed during early development (0-5 days) to MEHP and the internal concentration of secondary metabolites was defined to confirm metabolism of phthalates by the embryo.…”

“…Regulatory guidance for non-clinical safety studies to support the initiation of clinical trials involving pregnant subjects is available from FDA and WHO [3]. FDA guidance states that for products indicated specifically for immunization of pregnant women, data from non-clinical developmental toxicity studies should be available prior to initiation of clinical trials enrolling pregnant subjects.…”