Bisphenol A and Related Alkylphenols Exert Nongenomic Estrogenic Actions Through a G Protein-Coupled Estrogen Receptor 1 (Gper)/Epidermal Growth Factor Receptor (Egfr) Pathway to Inhibit Meiotic Maturation of Zebrafish Oocytes1

Abstract

Xenobiotic estrogens, such as bisphenol A (BPA), disrupt a wide variety of genomic estrogen actions, but their nongenomic estrogen actions remain poorly understood. We investigated nongenomic estrogenic effects of low concentrations of BPA and three related alkylphenols on the inhibition of zebrafish oocye maturation (OM) mediated through a G protein-coupled estrogen receptor 1 (Gper)-dependent epidermal growth factor receptor (Egfr) pathway. BPA (10-100 nM) treatment for 3 h mimicked the effects of estradiol-17beta (E2) and EGF, decreasing spontaneous maturation of defolliculated zebrafish oocytes, an effect not blocked by coincubation with actinomycin D, but blocked by coincubation with a Gper antibody. BPA displayed relatively high binding affinity (15.8% that of E2) for recombinant zebrafish Gper. The inhibitory effects of BPA were attenuated by inhibition of upstream regulators of Egfr, intracellular tyrosine kinase (Src) with PP2, and matrix metalloproteinase with ilomastat. Treatment with an inhibitor of Egfr transactivation, AG1478, and an inhibitor of the mitogen-activated protein kinase (MAPK) 3/1 pathway, U0126, increased spontaneous OM and blocked the inhibitory effects of BPA, E2, and the selective GPER agonist, G-1. Western blot analysis showed that BPA (10-200 nM) mimicked the stimulatory effects of E2 and EGF on Mapk3/1 phosphorylation. Tetrabromobisphenol A, 4-nonylphenol, and tetrachlorobisphenol A (5-100 nM) also inhibited OM, an effect blocked by cotreatment with AG1478, as well as with the GPER antagonist, G-15, and displayed similar binding affinities as BPA to zebrafish Gper. The results suggest that BPA and related alkylphenols disrupt zebrafish OM by a novel nongenomic estrogenic mechanism involving activation of the Gper/Egfr/Mapk3/1 pathway.

Neuroendocrine disruption in animal models due to exposure to bisphenol A analogues

“…Some of the effects of BPAF and BPS in the CNS and other systems might be due to non-genomic actions [68; 69; 70]. BPA has also been suggested to induce non-genomic affects when tested in rodent models and cells lines and zebrafish oocytes [95; 96; 97; 98]. …”

Mechanistic study of chlordecone-induced endocrine disruption: Based on an adverse outcome pathway network

“…One possible explaination for this is nongenomic estrogen action. For example, Fitzgerald et al (2015) reported that BPA can maintain meiotic arrest and prevent maturation of oocyte through a G-protein coupled estrogen receptor/epidermal growth factor receptor pathway. Further studies would be required to elabrate the nongenomic mechanism underlying chlordecone-induced endocrine disruptions and establish corresponding AOPs for chemical risk assessment.…”

Zebrafish in Toxicology and Environmental Health

“…Environmentally relevant doses of BPA were found to inhibit oocyte maturation by binding to the membrane estrogen receptor, Gper, and activating Egfr/Mapk3/1 signaling, which prevents resumption of meiosis (Fitzgerald, Peyton, Dong, & Thomas, 2015). Interestingly, this pathway is independent of signaling through the estrogen receptor (Fitzgerald et al, 2015).…”

“…Interestingly, this pathway is independent of signaling through the estrogen receptor (Fitzgerald et al, 2015). BPA is suggested to act through epigenetic mechanisms through histone modification and alteration of DNA methylation (Faulk et al, 2016; Kundakovic & Champagne, 2011; Santangeli et al, 2016), and zebrafish studies have provided key mechanistic insights.…”