IGF-1 protects retinal ganglion cells from hypoxia-induced apoptosis by activating the Erk-1/2 and Akt pathways.
OBJECTIVE
Hypoxia-induced retinal ganglion cell (RGC) apoptosis has been implicated in many optic neuropathies. Insulin-like growth factor-1 (IGF-1) is important in maintaining neuronal survival, proliferation, and differentiation. The purpose of this study is to explore whether IGF-1 can protect RGCs from hypoxia-induced apoptosis and to determine the precise mechanisms that regulate this process.


METHODS
Purified RGC cultures were obtained from the retinas of neonatal Sprague Dawley (SD) rats using a two-step panning method. Primary cultured RGCs were cultured in a closed hypoxic chamber (5% O2, 5% CO2, and 90% N2) for 12 h with or without IGF-1. The degree of apoptosis in the RGCs was detected by caspase-3 expression and TUNEL and JC-1 staining assays. The expression and phosphorylation of protein kinase B (Akt), p44/42 mitogen-activated protein kinase (MAPK) (extracellular signal-regulated kinase-1/2 [Erk-1/2]), Bad, and caspase-3 was investigated with immunoblot analysis.


RESULTS
Hypoxia induces apoptosis in primary Sprague Dawley rat RGCs, as detected by caspase-3 expression and TUNEL and JC-1 staining assays, and that IGF-1 treatment could significantly reduce this effect in RGCs. Interestingly, pretreatment of RGCs with AG1024 (an IGF-1 inhibitor), U0126 (an Erk-1/2 inhibitor), and LY294002 (an Akt inhibitor) markedly attenuated the effects of IGF-1 treatment. Furthermore, western blot analysis suggested that the Erk-1/2 and Akt signaling pathways play a role in the protective effects of IGF-1 on RGCs exposed to hypoxia.


CONCLUSIONS
These data indicate that IGF-1 can protect primary cultured RGCs against hypoxia-induced apoptosis via the Erk-1/2 and Akt signaling pathways, suggesting that IGF-1 treatment is a potential therapeutic approach for treating hypoxia-induced neurodegeneration in the retina.
Department of Occupational Health, Third Military Medical University, Chongqing, China ; Institute of Tropical Medicine, Third Military Medical University, Chongqing, China.
Xuesen
X
Yang
Aimin
A
Wei
Yong
Y
Liu
Genlin
G
He
Zhou
Z
Zhou
Zhengping
Z
Yu
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects; D002478:Cells, Cultured; D019610:Cytoprotection / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D015398:Signal Transduction / Q000187:drug effects
D018696:Neuroprotective Agents; D047428:Protein Kinase Inhibitors; D007334:Insulin-Like Growth Factor I; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D053148:Caspase 3