Diabetic cardiomyopathy is characterized by impaired cardiac contractility leading to poor myocardial performance. We investigated the role that the
hexosamine pathway, and especially altered nuclear O-Glc-NAcylation, plays in the development of
diabetic cardiomyopathy. Incubating neonatal rat cardiomyocytes in high
glucose (25 mM) resulted in prolonged
calcium transients when compared with myocytes incubated in normal
glucose (5.5 mM), which is consistent with delayed myocardial relaxation. High
glucose-treated myocytes also exhibited reduced sarcoendoplasmic reticulum Ca(2+)-
ATPase 2a (SERCA2a)
mRNA and
protein expression, decreased SERCA2a promoter activity, and increased O-GlcNAcylation of
nuclear proteins compared with myocytes treated with normal
glucose. Exposure of myocytes to 8 mM
glucosamine or an adenovirus expressing
O-GlcNAc-transferase (OGT) resulted in prolonged
calcium transient decays and significantly reduced SERCA2a
protein levels, whereas treatment with an adenovirus encoding
O-GlcNAcase (GCA) resulted in improved
calcium transients and SERCA2a
protein levels in myocytes exposed to high
glucose. Effects of elevated
glucose or altered O-GlcNAcylation were also observed on essential
transcription factors involved in cardiomyocyte function. High
glucose-treated myocytes (with or without OGT adenovirus) exhibited increased levels of O-GlcNAcylated specificity
protein 1 compared with control myocytes, whereas infecting high
glucose-treated myocytes with GCA adenovirus reduced the degree of specificity
protein 1 Glc-NAcylation. Treatment of myocytes with 25 mM
glucose, 8 mM
glucosamine, or OGT adenovirus also significantly reduced levels of myocytes enhancer factor-2A
protein compared with control myocytes, whereas
infection with GCA adenovirus resulted in improved myocytes enhancer factor-2 expression. Our results suggest that the
hexosamine pathway, and O-GlcNAcylation in particular, is important in impaired cardiac myocyte function and the development of
diabetic cardiomyopathy.