Activation of Autophagic Flux against Xenoestrogen Bisphenol-A-induced Hippocampal Neurodegeneration via AMP kinase (AMPK)/Mammalian Target of Rapamycin (mTOR) Pathways

J Biol Chem. 2015 Aug 21;290(34):21163-84. doi: 10.1074/jbc.M115.648998. Epub 2015 Jul 2.

Abstract

The human health hazards related to persisting use of bisphenol-A (BPA) are well documented. BPA-induced neurotoxicity occurs with the generation of oxidative stress, neurodegeneration, and cognitive dysfunctions. However, the cellular and molecular mechanism(s) of the effects of BPA on autophagy and association with oxidative stress and apoptosis are still elusive. We observed that BPA exposure during the early postnatal period enhanced the expression and the levels of autophagy genes/proteins. BPA treatment in the presence of bafilomycin A1 increased the levels of LC3-II and SQSTM1 and also potentiated GFP-LC3 puncta index in GFP-LC3-transfected hippocampal neural stem cell-derived neurons. BPA-induced generation of reactive oxygen species and apoptosis were mitigated by a pharmacological activator of autophagy (rapamycin). Pharmacological (wortmannin and bafilomycin A1) and genetic (beclin siRNA) inhibition of autophagy aggravated BPA neurotoxicity. Activation of autophagy against BPA resulted in intracellular energy sensor AMP kinase (AMPK) activation, increased phosphorylation of raptor and acetyl-CoA carboxylase, and decreased phosphorylation of ULK1 (Ser-757), and silencing of AMPK exacerbated BPA neurotoxicity. Conversely, BPA exposure down-regulated the mammalian target of rapamycin (mTOR) pathway by phosphorylation of raptor as a transient cell's compensatory mechanism to preserve cellular energy pool. Moreover, silencing of mTOR enhanced autophagy, which further alleviated BPA-induced reactive oxygen species generation and apoptosis. BPA-mediated neurotoxicity also resulted in mitochondrial loss, bioenergetic deficits, and increased PARKIN mitochondrial translocation, suggesting enhanced mitophagy. These results suggest implication of autophagy against BPA-mediated neurodegeneration through involvement of AMPK and mTOR pathways. Hence, autophagy, which arbitrates cell survival and demise during stress conditions, requires further assessment to be established as a biomarker of xenoestrogen exposure.

Keywords: hippocampus; neural stem cell (NSC); neurodegeneration; toxicology; xenobiotic.

Publication types

  • Research Support, Non-U.S. Gov't
  • Retracted Publication

MeSH terms

  • Androstadienes / pharmacology
  • Animals
  • Animals, Newborn
  • Apoptosis Regulatory Proteins / antagonists & inhibitors
  • Apoptosis Regulatory Proteins / genetics
  • Apoptosis Regulatory Proteins / metabolism
  • Autophagy / drug effects*
  • Autophagy / genetics
  • Beclin-1
  • Benzhydryl Compounds / antagonists & inhibitors
  • Benzhydryl Compounds / toxicity*
  • Environmental Pollutants / antagonists & inhibitors
  • Environmental Pollutants / toxicity*
  • Gene Expression Regulation
  • Heat-Shock Proteins / genetics
  • Heat-Shock Proteins / metabolism
  • Hippocampus / drug effects*
  • Hippocampus / metabolism
  • Hippocampus / pathology
  • Humans
  • Macrolides / pharmacology
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • Neurons / drug effects*
  • Neurons / metabolism
  • Neurons / pathology
  • Oxidative Stress
  • Phenols / antagonists & inhibitors
  • Phenols / toxicity*
  • Primary Cell Culture
  • Protein Kinases / genetics
  • Protein Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Rats
  • Rats, Wistar
  • Reactive Oxygen Species / metabolism
  • Sequestosome-1 Protein
  • Signal Transduction
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases / genetics
  • TOR Serine-Threonine Kinases / metabolism*
  • Wortmannin

Substances

  • Androstadienes
  • Apoptosis Regulatory Proteins
  • Beclin-1
  • Becn1 protein, rat
  • Benzhydryl Compounds
  • Environmental Pollutants
  • Heat-Shock Proteins
  • LC3 protein, rat
  • Macrolides
  • Microtubule-Associated Proteins
  • Phenols
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Sequestosome-1 Protein
  • Sqstm1 protein, rat
  • bafilomycin A1
  • Protein Kinases
  • AMP-activated protein kinase kinase
  • TOR Serine-Threonine Kinases
  • mTOR protein, rat
  • bisphenol A
  • Sirolimus
  • Wortmannin