IDENTIFICATION AND CHARACTERIZATION OF A GENE REGULATING ENZYMATIC GLYCOSYLATION WHICH IS INDUCED BY DIABETES AND HYPERGLYCEMIA SPECIFICALLY IN RAT CARDIAC TISSUE

Primary cardiac abnormalities have been frequently reported in patient s with diabetes probably due to metabolic consequences of the disease, Approximately 2,000 mRNA species from the heart of streptozotocin-ind uced diabetic and control rats were compared by the mRNA differential display method, two of eight candidate clones thus isolated (DH1 and 1 3) were confirmed by Northern blot analysis, The expression of clone 1 3 was increased in the heart by 3.5-fold (P < 0.05) and decreased in t he aorta by twofold (P < 0.05) in diabetes as compared to control, Seq uence analysis showed that clone 13 is a rat mitochondrial gene, DH1 w as predominantly expressed in the heart with an expression level 6.8-f old higher in the diabetic rats than in control (P < 0.001), Insulin t reatment significantly (P < 0.001) normalized the expression of DH1 in the hearts of diabetic rats, DH1 expression was observed in cultured rat cardiomyocytes, but not in aortic smooth muscle cells or in cardia c derived fibroblasts, The expression in cardiomyocytes was regulated by insulin and glucose concentration of culture media, The full length cDNA of DH1 had a single open-reading frame with 85 and 92% amino aci d identity to human and mouse UDP-GlcNAc:Gal beta 1-3GalNAc alpha R be ta 1-6 N-acetylglucosaminyltransferase (core 2 GlcNAc-T), respectively , a key enzyme determining the structure of O-linked glycosylation, Tr ansient transfection of DH1 cDNA into Cos7 cells conferred core 2 GlcN Ac-T enzyme activity, In vivo, core 2 GlcNAc-T activity was increased by 82% (P < 0.05) in diabetic hearts vs controls, while the enzymes Gl cNAc-TI and GlcNAc-TV responsible for N-linked glycosylation were unch anged, These results suggest that core 2 GlcNAc-T is specifically indu ced in the heart by diabetes or hyperglycemia. The induction of this e nzyme may be responsible for the increase in the deposition of glycoco njugates and the abnormal functions found in the hearts of diabetic ra ts.