Impact of type‐2 diabetes on the hexosamine biosynthesis pathway and protein O‐glycosylation

Abstract

O-linked attachment of N-acetyl-glucosamine (O-GlcNAc) onto Ser/Thr residues plays an important role in the development of insulin resistance and diabetic complications. The goal of this study was to determine the effect of the development of Type-2 diabetes on O-GlcNAc levels in the heart. Hearts were isolated from 6-wk and 22-wk old obese Zucker diabetic fatty rats and age-matched lean littermates. UDP-GlcNAc, a precursor of O-GlcNAc was assessed by HPLC and protein O-GlcNAc and O-GlcNAc transferase (OGT) levels were assessed by immunoblot analysis. 6-wk old obese animals were hyperinsulinemic but normoglycemic; whereas by 22-wk of age the obese group was hyperglycemic. There were no differences in UDP-GlcNAc or O-GlcNAc levels between 6-wk old obese and lean groups; however, at 22 weeks, both UDP-GlcNAc and O-GlcNAc levels were significantly increased in the obese diabetic group compared to controls. OGT expression was unaffected between lean and obese groups at any age; however, there was a significant decrease in OGT expression and O-GlcNAc levels between 6 and 22 weeks in both control and the obese groups. These data suggest that the increase in O-GlcNAc levels in the 22-wk old obese diabetic group relative to lean controls was due to increased hexosamine biosynthesis flux rather than changes in OGT expression. In contrast the decrease in O-GlcNAc levels with age within both lean and obese groups appeared to be due to reduced OGT expression. Thus, cardiac O-GlcNAc levels appear to be modulated in opposing directions by age and diabetes. This work was supported by NIH grants HL076165, HL67464, HL077100.