Glutathione Regulates Endothelial Cell Function and VEGFR2 Signaling

Abstract

Under physiological and pathological conditions angiogenesis progresses in an idealized window of reactive oxygen species. Mice heterozygous for the Glutamate cysteine ligase modifier subunit knockout have augmented ischemic remodeling. During occlusion the ensuing ischemic milieu and accompanying vascular changes regulate the activity of vascular endothelial receptor 2 (VEGFR2). We hypothesized that cellular GSH concentration regulates endothelial cell function via altered VEGFR2 signaling.MethodsTo test this hypothesis, we first preformed mouse aortic endothelial cell (MAEC) outgrowth assays on aortic segments dissected from mice homozygous (KO) and heterozygous (Het) for GCLm knockout as well as wildtype controls (WT). VEGF stimulated chemotaxis was determined using the under‐agarose migration assay. Primary human aortic endothelial cells (HAEC) were purchased from Lonza and cultured following suppliers’ recomendations. Phospho‐Y1175 VEGFR2/total VEGFR2 and phospho‐Y416 proto‐oncogene c‐Src (Src)/total Src were determined by western blotting.ResultsOutgrowth area in the Het group was significantly larger than WT and KO at day 7 (2.15 fold, n=4, P<0.001). Het MAECs were 1.25 fold faster (n=4 p<0.001) while KO MAECs were 0.90 fold slower than WT (n=3, p<0.05) migrating towards VEGF‐A. Concurrently, we inhibited glutathione reductase in HAECs using 2‐acetylamino‐3‐[4‐(2‐acetylamino‐2‐carboxyethylsulfanylthiocarbonylamino)phenylthiocarbamoylsulfanyl]propionic acid (2‐AAPA). 2‐AAPA (75 µM) alone didn’t significantly activate VEGFR2. However, 2‐AAPA (75 µM) in combination with H2O2 (100 µM) induced a 5.5 fold (p<0.01, n=4) increase in the relative amount of active VEGFR2 compared to vehicle treated HAECs. 2‐AAPA both with and without H2O2 induced a significant increase in active Src, 5.3 and 9.0 fold (p<0.05, p<0.01, n=6) respectively. This effect was attenuated by the addition of Dithiothreitol (1mM). Furthermore, Src kinase inhibitor 1 (SKI) (200 nM) attenuated the effect of 2‐AAPA + H2O2 on VEGFR2. While the VEGFR2 kinase inhibitor SU1948 inhibited activation of VEGFR2, it had no significant effect on the 2‐AAPA + H2O2 mediated activation of Src. Glutathione S‐transferase P1 (GSTP1) catalyzes the enzymatic glutathionylation of proteins, The GSTP1 inhibitor TLK199 (50 µM) abrogated the effects of 2‐AAPA + H2O2 on VEGFR2.ConclusionCombined these data suggest Src mediates the 2‐AAPA + H2O2 activation of VEGFR2. And that glutathionylation is necessary for this effect, co‐immunoprecipitation experiments are underway to determine the glutathionylation status of Src in our system and its effect on the interaction of Src and VEGFR2.