Glucose deprivation induced increase in O‐GlcNAc levels in cardiomyocytes is not mediated via increased OGT expression

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O‐Linked N‐acetylglucosamine (O‐GlcNAc) is a post‐translational modification of proteins that plays an important role in mediating the response of cells to stress. Previous studies in human hepatocellular carcinoma and Neuro‐2a neuroblastoma cells demonstrated that glucose deprivation increased O‐GlcNAc levels by up‐regulation of O‐GlcNAc transferase (OGT) in an AMP‐activated protein kinase‐dependent manner. The goal of this study was to examine the effect of glucose deprivation (GD) on O‐GlcNAc levels in neonatal rat ventricular cardiomyocytes (NRVM). GD significantly increased NRVM O‐GlcNAc levels within 1‐2 hours and O‐GlcNAc levels continued to increase over the next 6 hours. GD increased p38 and Akt phosphorylation, but had no effect OGT protein levels. Increasing hexosamine biosynthesis with glucosamine (5mM) significantly attenuated the effects of GD; however, inhibition of OGT (Alloxan, 5mM or TT04, 5µM) or O‐GlcNAcase (PUGNAc or NAG‐Bt, 100µM) had no effect. Surprisingly, inhibition of capacitative calcium entry (CCE) with SKF 96365 (5μM) markedly inhibited GD‐induced increase in O‐GlcNAc. These results demonstrate that GD rapidly increases O‐GlcNAc levels in NRVM independent of changes in OGT expression. The mechanism underlying the GD‐induced increase in O‐GlcNAcylation in NRVMs remains to be determined; however, it appears to be mediated at least in part via hexosamine biosynthesis and CCE. (Supported by NIH grants: HL067464 and HL079364)