Sustained versus transient ERK1/2 signaling underlies the anti- and proapoptotic effects of oxidative stress in human RPE cells.
OBJECTIVE
Oxidative stress is thought to contribute to the pathogenesis of age-related macular degeneration (AMD), which involves retinal pigmented epithelial (RPE) cell death. However, signaling pathways involved in the oxidative-stress-induced RPE cell death are poorly understood. This study was conducted to investigate the involvement of the MAP kinase pathways during the induction of RPE cell death by oxidative stress.


METHODS
ARPE-19 cells were exposed to the oxidant tert-butyl hydroperoxide (t-BHP). Cell viability was assessed by cell counting and MTT-staining, and apoptosis was quantified by TUNEL and flow cytometry. Activation of JNK1/3, p38 alphabeta MAPKs and ERK1/2 and their potential targets was detected by Western blot analysis and immunochemistry with specific anti-phospho protein antibodies. Specific pharmacologic inhibitors directed against the MAPKs were used to analyze the signaling involved in cell death of RPE cells exposed to t-BHP.


RESULTS
Exposure of RPE cells to t-BHP, associated with increase in reactive oxygen species and intracellular glutathione depletion, induced time- and concentration-dependent apoptosis, which was associated with the accumulation of inactive ERK1/2 in cell nuclei and a transient and weak ERK1/2 activation. This activation was accompanied by a deactivation of P90(RSK), the major target of ERK1/2 and consequently by the delayed activation of its transcription factor CREB. MEK1/2 inhibition completely suppressed the transient activation of ERK1/2 and completely blocked apoptosis, demonstrating the role of the MEK-ERK module in mediating oxidative-stress-induced RPE cell death. In contrast, neither JNKs nor p38 alphabeta MAPKs were involved in mediating t-BHP-induced apoptotic signaling in RPE cells.


CONCLUSIONS
The results suggest that inhibiting the MEK-ERK module may allow the development of selective methods for treating oxidative-stress-induced RPE degeneration, such as AMD.
Glotin
Anne-Lise
AL
Institut Biomédical des Cordeliers, INSERM (Institut National de la Santé et de la Recherche Médicale) Unité 598, Paris, France.
Calipel
Armelle
A
Brossas
Jean-Yves
JY
Faussat
Anne-Marie
AM
Tréton
Jacques
J
Mascarelli
Frédéric
F
D017209:Apoptosis; D015153:Blotting, Western; D002452:Cell Count; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048057:Mitogen-Activated Protein Kinase 10 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D010766:Phosphorylation; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020122:tert-Butylhydroperoxide / Q000633:toxicity*
D017382:Reactive Oxygen Species; D020122:tert-Butylhydroperoxide; D048057:Mitogen-Activated Protein Kinase 10; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048055:Mitogen-Activated Protein Kinase 8; D048051:p38 Mitogen-Activated Protein Kinases; D005978:Glutathione