O‐GlcNAcylation Mediates Glucose‐Induced Alterations in Endothelial Cell Phenotype in Human Diabetes Mellitus

BACKGROUND: Posttranslational protein modification with O‐linked N‐acetylglucosamine (O‐GlcNAc) is linked to high glucose levels in type 2 diabetes mellitus (T2DM) and may alter cellular function. We sought to elucidate the involvement of O‐GlcNAc modification in endothelial dysfunction in patients with T2DM. METHODS AND RESULTS: Freshly isolated endothelial cells obtained by J‐wire biopsy from a forearm vein of patients with T2DM (n=18) was compared with controls (n=10). Endothelial O‐GlcNAc levels were 1.8‐ford higher in T2DM patients than in nondiabetic controls (P=0.003). Higher endothelial O‐GlcNAc levels correlated with serum fasting blood glucose level (r=0.433, P=0.024) and hemoglobin A(1c) (r=0.418, P=0.042). In endothelial cells from patients with T2DM, normal glucose conditions (24 hours at 5 mmol/L) lowered O‐GlcNAc levels and restored insulin‐mediated activation of endothelial nitric oxide synthase, whereas high glucose conditions (30 mmol/L) maintained both O‐GlcNAc levels and impaired insulin action. Treatment of endothelial cells with Thiamet G, an O‐GlcNAcase inhibitor, increased O‐GlcNAc levels and blunted the improvement of insulin‐mediated endothelial nitric oxide synthase phosphorylation by glucose normalization. CONCLUSIONS: Taken together, our findings indicate a role for O‐GlcNAc modification in the dynamic, glucose‐induced impairment of endothelial nitric oxide synthase activation in endothelial cells from patients with T2DM. O‐GlcNAc protein modification may be a treatment target for vascular dysfunction in T2DM.