Role of extracellular signal-regulated kinase in glutamate-stimulated apoptosis of rat retinal ganglion cells.
OBJECTIVE
To investigate the involvement of the extracellular signal-regulated kinase (ERK) signaling pathway after intravitrevous injection of glutamate in rat retina.


METHODS
Three groups of five Sprague-Dawley rats each were studied. Group I was a normal control group, intravitreal saline injections. In Group II, one eye received an intravitreal glutamate injection (375 nmol, dissolved in saline) while the contralateral eye served as control. In Group III, intravitreal PD98059 (100 micro mol, an inhibitor of ERK) injections were administered 1 hr before glutamate injections. Seven days after injections, phosphorylated (activated) ERK in retina was localized by immunohistochemistry and fluorescent double labeling of retinal cryosections. Specific ERK blockade was documented to assess the functional significance of activated ERK. TUNEL staining was performed to assess apoptotic cell death.


RESULTS
Expression of phosphorylated ERK in rat retina was observed in the inner nuclear layer, the outer nuclear layer, and the nerve fiber layer after 3 days intravitreous injection of glutamate, increasing significantly after 7 days. Double immunofluorescence labling demonstrated that the increased retinal immunostaining for phospho-ERK was predominantly localized to the retinal Müller cells after 7 days intravitreous injection of glutamate. Moreover, blocking activation of ERK significantly improved the number of TUNEL-positive cells in the eyes receiving intravitreal PD98059 injections compared with the eyes receiving glutamate injections.


CONCLUSIONS
The ERK pathway is involved in signal transduction in the retina after excessive stimulation by glutamate, which may contribute to the antiapoptotic role in retinal ganglion cell death induced by glutamate.
Zhou
Run-Hai
RH
Department of Ophthalmology, Tangdu Hospital, Fourth Military Medical University, Xi'an, China.
Yan
Hong
H
Wang
Bai-Ren
BR
Kuang
Fang
F
Duan
Xiao-Li
XL
Xu
Z
Z
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D005419:Flavonoids / Q000494:pharmacology; D019084:Fluorescent Antibody Technique, Indirect; D018698:Glutamic Acid / Q000494:pharmacology*; D007124:Immunoenzyme Techniques; D020287:In Situ Nick-End Labeling; D007267:Injections; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012165:Retinal Ganglion Cells / Q000201:enzymology / Q000473:pathology*; D015398:Signal Transduction / Q000502:physiology*; D014822:Vitreous Body
D005419:Flavonoids; D018698:Glutamic Acid; D048049:Extracellular Signal-Regulated MAP Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one