ERK- and Akt-dependent neuroprotection by erythropoietin (EPO) against glyoxal-AGEs via modulation of Bcl-xL, Bax, and BAD.
OBJECTIVE
To characterize the neuroprotective mechanisms of erythropoietin (EPO) against the stress of glyoxal-advanced glycation end products (AGEs) in retinal neuronal cells.


METHODS
Rat retinal organ culture, primary retinal neuron culture, and retinal cell line (R28 cell) culture under glyoxal-AGEs insult were used as in vitro models. Exogenous EPO was applied to these models. Retinal neuronal cell death was assessed by TUNEL, ethidium bromide/acridine orange staining, and cell viability assay. R28 cell proliferation was evaluated by BrdU incorporation and propidium iodide staining. Real-time RT-PCR and Western blot analysis were used to detect Bcl-xL, Bcl-2, Bax, BAD, and products of extracellular signal regulated kinase (ERK) and Akt pathways. Specific inhibitors and plasmids were used to pinpoint the roles of ERK and Akt pathways. Results. EPO protected the retinal cells from glyoxal-AGE-induced injury in a time- and dose-dependent fashion. The protective function of EPO was proved to be antiapoptotic, not pro-cell proliferative. Glyoxal upregulated Bax expression but suppressed Bcl-xL expression and BAD phosphorylation. In contrast, EPO enhanced BAD phosphorylation and Bcl-xL expression but downregulated Bax. The regulation of these apoptosis-related proteins by EPO was through ERK and Akt pathways.


CONCLUSIONS
These data demonstrate that exogenous EPO significantly attenuates the retinal neuronal cell death induced by glyoxal-AGEs by promoting antiapoptotic and suppressing apoptotic proteins. EPO/EPO receptor signaling through ERK and Akt pathways is pivotal in EPO neuroprotective mechanisms.
Shen
Jianfeng
J
Laboratory of Clinical Visual Sciences, Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Wu
Yalan
Y
Xu
Jing-Ying
JY
Zhang
Jingfa
J
Sinclair
Stephen H
SH
Yanoff
Myron
M
Xu
Guoxu
G
Li
Weiye
W
Xu
Guo-Tong
GT
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004921:Erythropoietin / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D005434:Flow Cytometry; D017127:Glycation End Products, Advanced / Q000633:toxicity; D006037:Glyoxal / Q000633:toxicity*; D020287:In Situ Nick-End Labeling; D008297:Male; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009924:Organ Culture Techniques; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D055351:Retinal Neurons / Q000187:drug effects* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494821:Bad protein, rat; C494828:Bax protein, rat; C494813:Bcl2l1 protein, rat; D017127:Glycation End Products, Advanced; D018696:Neuroprotective Agents; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; D004921:Erythropoietin; D006037:Glyoxal; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases