title: Oxidative Stress Induces Biphasic ERK1/2 Activation in the RPE with Distinct Effects on Cell Survival at Early and Late Activation.
abstract: OBJECTIVE
  Oxidative stress is considered a major factor in the deterioration of retinal pigment epithelium (RPE) cells in dry age-related macular degeneration (AMD). The MAPK ERK1/2 can be activated by oxidative stress, may exert both pro- and anti-apoptotic functions, and has recently been proposed as a major factor in RPE degeneration in atrophic changes. Nrf2 is a master regulator of oxidative stress defense and ERK1/2 is an upstream activator of Nrf2. In this study, we investigate the participation of ERK1/2 in oxidative stress pathways in connection with Nrf2.
  
  
  METHODS
  Nrf2 knock-out and wild-type primary RPE cells were prepared from mouse eyes. Oxidative stress was induced by different concentrations of t-butylhydroperoxide. Mitogen-activated protein kinases (MAPKs) were blocked by commercially available inhibitors (SB203580, U0126, SP600125). Cell viability was determined by MTT assay. ERK1/2 expression and activation were assessed by Western blotting.
  
  
  RESULTS
  Oxidative stress induced concentration dependent cell death, which occurred at lower concentrations in Nrf2 knock-out RPE. Western blot analysis displayed a biphasic activation of ERK1/2 in murine wild-type RPE and the inhibition of late, but not early activation of ERK1/2 exerted protection in wild-type murine RPE cells. The biphasic activation of ERK1/2 is lost in Nrf2 knock-out mice, and inhibition of ERK1/2 was generally protective. The inhibition of MAPK JNK or p38 exerted no protection, irrespective of Nrf2.
  
  
  CONCLUSIONS
  RPE cells display a biphasic activation of ERK1/2 after oxidative insult, of which the late activation is pro-apoptotic. The biphasic activation is lost in Nrf2 knock-outs, suggesting that early ERK1/2 activation may be connected to Nrf2 signaling. In addition, ERK1/2 activation in Nrf2 knock-outs mediates oxidative stress-induced cell death.
authors.affiliation: Department of Ophthalmology and.
authors.forename: Stefan
authors.initials: S
authors.lastname: Koinzer
authors.forename: Kirstin
authors.initials: K
authors.lastname: Reinecke
authors.forename: Thomas
authors.initials: T
authors.lastname: Herdegen
authors.forename: Johann
authors.initials: J
authors.lastname: Roider
authors.forename: Alexa
authors.initials: A
authors.lastname: Klettner
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002470:Cell Survival; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000502:physiology; D018384:Oxidative Stress; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D020122:tert-Butylhydroperoxide / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D020122:tert-Butylhydroperoxide; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases
keywords: Cell death; ERK1/2; Nrf2; oxidative stress; retinal pigment epithelium