VEGF Stimulates the ERK 1/2 signaling pathway and apoptosis in cerebral endothelial cells after ischemic conditions.
OBJECTIVE
Cerebral endothelial cells that line microvessels play an important role in maintaining blood flow homeostasis within the brain-forming part of the blood-brain barrier. These cells are injured by hypoxia-induced reperfusion, leading to blood-brain barrier breakdown and exacerbation of ischemic injury. We investigated the roles of vascular endothelial growth factor (VEGF) and the downstream extracellular signal-regulated kinase (ERK) protein after oxygen-glucose deprivation (OGD) in primary endothelial cells.


METHODS
Primary mouse endothelial cells were isolated and subjected to OGD. Western analysis of VEGF and ERK 1/2 protein levels was performed. Cells were transfected with VEGF small interference RNA. A terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay and DNA fragmentation assay were used on mouse endothelial cells that overexpress copper/zinc-superoxide dismutase (SOD1).


RESULTS
VEGF protein expression was induced and its receptor, Flk-1, was stimulated by OGD. Phosphorylation of ERK 1/2 protein levels was upregulated. Inhibition of phosphorylated ERK (pERK) expression by U0126 reduced endothelial cell death by OGD. Transfection of small interfering RNA for VEGF also inhibited an increase in pERK, suggesting that VEGF acts via ERK. The TUNEL and DNA fragmentation assays showed a significant decrease in TUNEL-positivity in the SOD1-overexpressing endothelial cells compared with wild-type cells after OGD.


CONCLUSIONS
Our data suggest that OGD induces VEGF signaling via its receptor, Flk-1, and activates ERK via oxidative-stress-dependent mechanisms. Our study shows that in cerebral endothelial cells the ERK 1/2 signaling pathway plays a significant role in cell injury after OGD.
Narasimhan
Purnima
P
Department of Neurosurgery, Stanford University School of Medicine, Stanford, Calif 94305-5487, USA.
Liu
Jing
J
Song
Yun Seon
YS
Massengale
Justin L
JL
Chan
Pak H
PH
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001812:Blood-Brain Barrier / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D066298:In Vitro Techniques; D002546:Ischemic Attack, Transient / Q000378:metabolism* / Q000473:pathology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology; D010100:Oxygen / Q000494:pharmacology; D034741:RNA, Small Interfering; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005947:Glucose; D010100:Oxygen