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Increased JNK Phosphorylation and Oxidative Stress in Response to Increased Glucose Flux through Increased GLUT1 Expression in Rat Retinal Endothelial Cells

¹From the Departments of Internal Medicine and ⁵Physiology and the ⁶JDRF Center for Complications in Diabetes, University of Michigan Medical School, Ann Arbor, Michigan; the ²Department of Pharmaceutical Science, Toyama Medical and Pharmaceutical University, Toyama, Japan; the ³Department of Molecular Biopharmacy and Genetics, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan; and the ⁴Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana.

PURPOSE. To investigate whether increased glucose flux through increased glucose transporter1 (GLUT1) expression results in increased oxidative stress and increased c-jun N-terminal kinase (JNK) phosphorylation.

METHODS. GLUT1-overexpressing cells were established using a rat retinal endothelial cell line. The intracellular reactive oxygen species was detected by the oxidation of 5- (and -6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2-DCFDA). Western blot was performed to determine JNK phosphorylation and lipid peroxidation. Differentially expressed genes were detected by cDNA microarray analysis and confirmed by Northern blot analysis.

RESULTS. Clones overexpressing GLUT1 showed an approximate four- to eightfold increase in GLUT1 expression and a 44% increase in intracellular glucose concentrations. GLUT1-overexpressing cells had a 80% increase in DCF fluorescence and increased lipid peroxidation, as well as increased JNK phosphorylation. Analysis of differentially expressed genes in GLUT1-overexpressing cells showed increased expression of JNK interacting protein (JIP)-1, a scaffold protein necessary for JNK activation. Northern blot analysis confirmed upregulation of JIP-1. Immunoprecipitation showed that phosphorylated JNK, but not total JNK, coimmunoprecipitated with JIP-1 protein. At the cellular level, JIP-1 was predominantly localized in cytoplasm, especially in the perinuclear area in retinal endothelial cells.

CONCLUSIONS. GLUT1 overexpression and increased glucose flux result in increased oxidative stress and JNK phosphorylation in immortalized rat retinal endothelial cells. Further studies are needed to understand molecular events after increased glucose flux in retinal endothelial cells and the relation between increased oxidative stress and JNK phosphorylation.

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