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The hexosamine biosynthetic pathway can mediate myocardial apoptosis in a rat model of diet‐induced insulin resistance
Author(s) -
Rajamani U.,
Joseph D.,
Roux S.,
Essop M. F.
Publication year - 2011
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2011.02275.x
Subject(s) - insulin resistance , medicine , endocrinology , insulin , apoptosis , phosphorylation , biology , cytochrome c , oxidative phosphorylation , caspase 3 , biochemistry , programmed cell death
Aims: Type 2 diabetes is characterized by deranged metabolic pathways that may result in cardiovascular complications. For example, hyperglycaemia promotes flux through the hexosamine biosynthetic pathway (HBP) leading to greater O ‐GlcNAcylation of target proteins, with pathophysiological outcomes. This study investigated mechanisms whereby increased HBP flux elicits myocardial apoptosis in a rat model of diet‐induced hyperglycaemia/insulin resistance. Methods: Four‐week‐old male Wistar rats were fed a high‐fat diet (86 days) after which insulin resistance was assessed vs. matched controls. Oxidative stress was evaluated, and apoptotic peptide levels, BAD phosphorylation and overall O ‐GlcNAcylation assessed by immunoblotting. Protein‐specific O ‐GlcNAcylation and BAD‐Bcl‐2 dimerization were determined by immunoprecipitation and Western blotting. Results: Rats consuming the high‐fat diet exhibited a moderate elevation in body weight, higher fasting insulin and glucose levels, and insulin resistance vs. controls. Overall protein O ‐GlcNAcylation was increased in hyperglycaemic/insulin‐resistant hearts. In parallel, myocardial peptide levels of apoptotic markers (caspase‐3, cytochrome‐c, BAD) were significantly higher with insulin resistance. To gain mechanistic insight into our findings, we evaluated O ‐GlcNAcylation of BAD, a pro‐apoptotic Bcl‐2 homolog. Here we found increased BAD O ‐GlcNAcylation and decreased BAD phosphorylation (Ser136) in hyperglycaemic/insulin‐resistant rat hearts. These data are in agreement with competition by phosphorylation and O ‐GlcNAcylation for the same or neighbouring site(s) on target proteins. Moreover, we observed increased BAD‐Bcl‐2 dimerization in hyperglycaemic/insulin‐resistant hearts. Conclusion: The main finding of this study is that increased apoptosis in hyperglycaemic/insulin‐resistant hearts can also be mediated through HBP‐induced BAD O ‐GlcNAcylation and greater formation of BAD‐Bcl‐2 dimers (pro‐apoptotic).