Inhibitory Effects of Bisphenol-A on Neural Stem Cells Proliferation and Differentiation in the Rat Brain Are Dependent on Wnt/β-Catenin Pathway

Abstract

Neurogenesis, a process of generation of new neurons, occurs throughout the life in the hippocampus and sub-ventricular zone (SVZ). Bisphenol-A (BPA), an endocrine disrupter used as surface coating for packaged food cans, injures the developing and adult brain. However, the effects of BPA on neurogenesis and underlying cellular and molecular mechanism(s) are still unknown. Herein, we studied the effect(s) of prenatal and early postnatal exposure of low dose BPA on Wnt/β-catenin signaling pathway that controls different steps of neurogenesis such as neural stem cell (NSC) proliferation and neuronal differentiation. Pregnant rats were treated with 4, 40, and 400 μg BPA/kg body weight orally daily from gestational day 6 to postnatal day 21. Both in vivo and in vitro studies showed that BPA alters NSC proliferation and differentiation. BPA impaired NSC proliferation (5'-bromo-2'-deoxyuridine (BrdU(+)) and nestin(+) cells) and neuronal differentiation (BrdU/doublecortin(+) and BrdU/neuronal nuclei (NeuN(+)) cells) in the hippocampus and SVZ as compared to control. It significantly altered expression/protein levels of neurogenic genes and the Wnt pathway genes in the hippocampus. BPA reduced cellular β-catenin and p-GSK-3β levels and decreased β-catenin nuclear translocation, and cyclin-D1 and TCF/LEF promoter luciferase activity. Specific activation and blockage of the Wnt pathway suggested involvement of this pathway in BPA-mediated inhibition of neurogenesis. Further, blockage of GSK-3β activity by SB415286 and GSK-3β small interfering RNA (siRNA) attenuated BPA-induced downregulation of neurogenesis. Overall, these results suggest significant inhibitory effects of BPA on NSC proliferation and differentiation in the rat via the Wnt/β-catenin signaling pathway.

Dynamin-related Protein 1 Inhibition Mitigates Bisphenol A-mediated Alterations in Mitochondrial Dynamics and Neural Stem Cell Proliferation and Differentiation

“…previous studies demonstrated that BPA exposure inhibits NSC proliferation and differentiation and also causes neurodegeneration in the hippocampus (1)(2)(3). In the present study, we found increased mitochondrial fission, increased oxidative stress, and apoptosis.…”

“…Hippocampal NSC Culture-Hippocampus-derived NSC culture was carried out following our previous studies (2,3,62). Briefly, pregnant Wistar rats were deeply anesthetized with a mixture of ketamine and xylazine (3:1 ratio) and dissected cautiously to remove the embryos at embryonic day 12.…”

“…BPA Treatment and Neurosphere Growth Kinetics Assay-To study the effects of BPA on multipotent NSC proliferation and neurosphere formation, the neurosphere growth kinetics assay was performed as described in our previous studies (2,62). Briefly, hippocampal single-cell suspension was plated in a 12-well plate at a density of 5 ϫ 10 4 cells/well in neurobasal medium containing B-27, N-2 supplement, basic FGF, and EGF.…”

“…Fluorescent images were acquired using an inverted fluorescent microscope. The quantification of proliferating and differentiating cells was carried out following our previously published studies (2,3,62,68). Co-localization of Drp-1 and TOMM20, in terms of % Drp-1 mitochondrial translocation was quantified using ImageJ (National Institutes of Health) employing the JACoP plugin (1, 69).…”

“…Our recent study suggests that the adverse consequences of BPA vary with the duration of its exposure, such as activation of autophagic flux takes place after the transient exposure of BPA in the hippocampus region of the rat brain to ameliorate its neurotoxicity (1). Contrarily, prolonged and chronic exposure of BPA impairs autophagy as well as neurogenesis in the hippocampus, leading to neurodegeneration and cognitive impairments (1)(2)(3). Several studies have reported the association between toxic effects of BPA and pathogenesis of neurodegenerative disorders and other diseases (4 -7).…”