Exploring leukocyte O-GlcNAcylation as a novel diagnostic tool for the earlier detection of type 2 diabetes mellitus.

Abstract

Because current tests available for the diagnosis of diabetes have shortcomings, a novel screening method for the earlier and more efficient detection of type 2 diabetes would be a significant clinical advance. The hexosamine biosynthetic pathway usually acts as a fuel sensor, and its activation leads to O-linked β-N-acetylglucosamine (O-GlcNAc) modification of target proteins (O-GlcNAcylation) in a glucose-responsive manner. O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) are responsible for O-GlcNAc addition and removal, respectively. Because higher hexosamine biosynthetic pathway flux is linked to insulin resistance/type 2 diabetes, we hypothesized that increased O-GlcNAcylation of leukocyte proteins can detect the onset of pre- and overt diabetes. Seventy-four participants from Bellville and Stellenbosch (Western Cape, South Africa) were recruited and classified as normal, prediabetic, and diabetic individuals (American Diabetes Association criteria). Leukocytes isolated from study subjects were evaluated for O-GlcNAc, OGA, and O-GlcNAc transferase expression by flow cytometry and immunofluorescence microscopy. Flow cytometric analysis of leukocyte subtypes revealed increased O-GlcNAcylation in granulocytes vs. lymphocytes (P < 0.001). Diabetic individuals displayed higher leukocyte O-GlcNAcylation (P < 0.01), whereas granulocyte analysis showed an increase for prediabetic subjects (P < 0.01). However, OGA expression increased in leukocytes of diabetic subjects and is likely an adaptation to attenuate higher O-GlcNAcylation observed (P < 0.001). Together our data demonstrate that leukocyte (particularly granulocyte) O-GlcNAcylation could help detect pre- and overt diabetes and offer clinical value as unique markers for the earlier and more efficient detection of type 2 diabetes.