Increased expression of β-N-acetylglucosaminidase in erythrocytes from individuals with pre-diabetes and diabetes

OBJECTIVE - O-linked β-N-acetylglucosamine (O-GlcNAc) plays an important role in the development of insulin resistance and glucose toxicity. O-GlcNAcylation is regulated by O-GlcNAc transferase (OGT), which attaches O-GlcNAc to serine and/or threonine residues of proteins and by O-GlcNAcase, which removes O-Glc-NAc. We investigated the expression of these two enzymes in erythrocytes of human subjects with diabetes or pre-diabetes. RESEARCH DESIGN AND METHODS - Volunteers with normal condition, pre-diabetes, and diabetes were recruited through a. Digestive and Kidney Diseases) study and at the Johns Hopkins Comprehensive Diabetes Center. Erythrocyte proteins were extracted and hemoglobins were depleted. Global O-GlcNAcylation of erythrocyte proteins was confirmed by Western blotting using an O-GlcNAc-specific antibody. Relative OGT and O-GlcNAcase protein amounts were determined by Western blot analysis. Relative expression of O-GlcNAcase was compared with the level of A1C. RESULTS - Erythrocyte proteins are highly O-GlcNAcylated. O-GlcNAcase expression is significantly increased in erythrocytes from both individuals with pre-diabetes and diabetes compared with normal control subjects. Unlike O-GlcNAcase, protein levels of OGT did not show significant changes. CONCLUSIONS - O-GlcNAcase expression is increased in erythrocytes from both individuals with pre-diabetes and individuals with less well-controlled diabetes. These findings, together with the previous study that demonstrated the increased site-specific O-GlcNAcylation of certain erythrocyte proteins, suggest that the upregulation of O-GlcNAcase might be an adaptive response to hyperglycemia-induced increases in O-GlcNAcylation, which are likely deleterious to erythrocyte functions. In any case, the early and substantial upregulation of O-GlcNAcase in individuals with pre-diabetes may eventually have diagnostic utility.