Abstract 15762: Gapdh Interaction With Ape1 Endonuclease Protects Vascular Smooth Muscle Cells Against Apoptosis: Potential Role of These Enzymes in Prevention of Atherosclerotic Plaque Destabilization

Abstract

We have shown that oxidized lipids (OxLDL) co-localized with apoptotic vascular smooth muscle cells (VSMC) in atherosclerotic plaque and that OxLDL downregulated the major glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in cultured VSMC via H2O2-dependent mechanism. We hypothesized that maintenance of sufficient GAPDH levels is critical for cell survival under oxidative stress. H2O2 (220 uM, 12h) decreased GAPDH protein (55±5% decrease) and induced apoptosis (TUNEL assay) in human VSMC. Human VSMC transfection with pCMV-GAPDH increased GAPDH protein (3.5-fold) and prevented H2O2-induced apoptosis (74±4% decrease) vs. pCMV-GFP. We generated rat VSMC with constitutive 2-fold overexpression GAPDH (R3-VSMC). R3-VSMC had increased glycolysis (2.5 folds increase, pyruvate levels), ATP levels (38±2% increase) and reduced oxidative DNA damage (40±2% reduction in number of apurinic/apyrimidinic (AP) sites) and these effects correlated with suppressed H2O2-induced cell apoptosis (>90% reduction, TUNEL assay; 45.7±3.6% reduction, Cell Death ELISA). GAPDH-targeted siRNA reduced GAPDH protein (for 55%) and potentiated H2O2-induced apoptosis (9.4±0.3 folds increase, TUNEL; 8.6±0.4 folds increase, ELISA) in WT-VSMC and blocked anti-apoptotic effect seen in R3-VSMC. GAPDH known to bind apurinic/apyrimidinic (AP) endonuclease 1 (APE1), a major DNA repair enzyme. We found that GAPDH was co-immunoprecipitated and co-localized with APE1 in cytosolic/nuclear fraction and H2O2 induced further GAPDH-Ape1 co-localization and migration toward nuclei. APE1 specific activity was increased in H2O2-treated R3-VSMC vs. H2O2-treated WT VSMC, suggesting that GAPDH preserved APE1 activity under oxidative stress. APE1-targeted siRNA abrogated the protection of GAPDH overexpression against H2O2-induced apoptosis in VMSC. In summary, GAPDH downregulation mediates oxidant-induced VSMC apoptosis and forced expression of GAPDH protects VSMC from H2O2-induced cell death potentially via activation of APE1-dependent DNA repair. Our data suggest that preservation of GAPDH and APE1 activity in plaque VSMC could be a potential strategy to stabilize plaque and prevent acute coronary events.