title: Nrf2-Keap1 antioxidant defense and cell survival signaling are upregulated by 17β-estradiol in homocysteine-treated dopaminergic SH-SY5Y cells.
abstract: OBJECTIVE
  A recent neuroimaging study discovered the neurotoxicity effects of homocysteine (Hcy), which is only seen in elderly women. Estrogens exert a variety of actions on brain function that influence cognitive function, mood, and neuroprotection. The Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant defense pathway has been well-known to afford neuroprotection. Here, we first demonstrate the roles of Nrf2-Keap1 in 17β-estradiol (E2) cytoprotection and Hcy toxicity and the protective mechanisms of E2 on Hcy cytotoxicity in human dopaminergic SH-SY5Y cells.
  
  
  METHODS
  Cell viability was determined by trypan blue method. Protein expression was determined by Western blot analysis. Superoxide dismutase (SOD) activity was determined by ELISA. Reactive oxygen species (ROS) production was determined by flow cytometry.
  
  
  RESULTS
  In Hcy-treated SH-SY5Y cells, E2 increased cell viability, attenuated ROS production, activated Akt signaling and inhibited glycogen synthase kinase-3β (GSK-3β), a kinase known to participate in neurodegeneration. Moreover, E2 treatment led to Nrf2 dissociation from Keap1, the main negative regulator of Nrf2 activity in the cytoplasm, and increased the protein level of Nrf2 in the nucleus, with a significant increase in HO-1 expression and SOD activity in Hcy-treated cells. E2-induced Nrf2 activation was attenuated by the PI3K inhibitor LY294002 and the estrogen receptor antagonist ICI 182,780. Further, E2 decreased Hcy-induced apoptotic death by upregulating the antiapoptotic protein Bcl-2, decreasing cytochrome c release from mitochondria, and attenuating apoptotic cascade activation (Bax, caspase-9, and caspase-3).
  
  
  CONCLUSIONS
  E2 activates cell survival signaling and Nrf2-Keap1 antioxidant defense pathway and attenuates Hcy cytotoxicity.
authors.affiliation: Department of Psychiatry, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan, ROC.
authors.forename: Cheng-Sheng
authors.initials: CS
authors.lastname: Chen
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Tseng
authors.forename: Ya-Yun
authors.initials: YY
authors.lastname: Hsu
authors.forename: Yi-Ching
authors.initials: YC
authors.lastname: Lo
mesh_terms: D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000494:pharmacology; D000077267:Fulvestrant; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006710:Homocysteine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D000072019:Kelch-Like ECH-Associated Protein 1; D009025:Morpholines / Q000494:pharmacology; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013482:Superoxide Dismutase / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000975:Antioxidants; D002867:Chromones; D004965:Estrogen Antagonists; D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D009025:Morpholines; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D047428:Protein Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D006710:Homocysteine; D000077267:Fulvestrant; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004958:Estradiol; D045304:Cytochromes c; D013482:Superoxide Dismutase; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3