The Effects of High Glucose Levels on Reactive Oxygen Species-Induced Apoptosis and Involved Signaling in Human Vascular Endothelial Cells

Abstract

This study investigated the effects of high glucose levels on human vascular endothelial cells and the expression of apoptosis-associated signaling molecules. Cell proliferation of human umbilical vein endothelial cells (HUVECs) was analyzed by colorimetric assay and cell number counting. Apoptosis was measured by Annexin V/FITC staining and flow cytometry. Gene knockdown was established by transfection of synthesized small interfering RNA. Caspase-3 activation was inhibited by a caspase-3 inhibitor. Protein expression of signaling molecules was measured by Western blot. Glucose significantly decreased HUVEC viability, induced cell apoptosis, and elevated levels of intracellular reactive oxygen species in a concentration and time-dependent manner. Glucose significantly upregulated the Nox4 isoform of nicotinamide adenine dinucleotide phosphate oxidase and phosphatase and tensin homolog (PTEN) protein expression, increased PTEN phosphorylation, and activated caspase-3 in a concentration-dependent manner. Silencing Nox4 and PTEN gene expression and inhibiting caspase-3 activation significantly protected HUVECs from glucose-induced cell apoptosis. Silencing Nox4 significantly normalized the levels of reactive oxygen species in glucose-treated cells; 20 mM glucose obviously upregulated Nox4, PTEN, phosphor-PTEN, and Bax levels, but significantly reduced integrin-linked kinase (ILK) activity, Bcl-2 (B cell lymphoma 2) expression, and protein kinase B (Akt) phosphorylation at serine 473. High glucose levels can reduce cell viability and induce apoptosis in HUVECs through Nox4-produced reactive oxygen species. Elevated levels of reactive oxygen species decreased Bcl-2 expression and increased PTEN expression and phosphorylation, which lead to the subsequent inhibition of ILK-Akt signaling, elevation of Bax expression, and activation of caspase-3.