Cardio-Metabolic Research Group, Department of Physiological Sciences, Stellenbosch University, South Africa.
Acta Physiol (Oxf). 2011 Jun;202(2):151-7. doi: 10.1111/j.1748-1716.2011.02275.x. Epub 2011 Apr 19.
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.
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.
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.
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).
2 型糖尿病的特征是代谢途径紊乱，这可能导致心血管并发症。例如，高血糖会促进己糖胺生物合成途径（HBP）的通量增加，导致靶蛋白的 O-GlcNAc 化程度增加，从而产生病理生理后果。本研究旨在探讨在饮食诱导的高血糖/胰岛素抵抗大鼠模型中，增加 HBP 通量如何引发心肌细胞凋亡的机制。
4 周龄雄性 Wistar 大鼠在高脂饮食喂养 86 天后，与匹配的对照组相比，评估胰岛素抵抗情况。评估氧化应激，并通过免疫印迹法评估凋亡肽水平、BAD 磷酸化和整体 O-GlcNAc 化。通过免疫沉淀和 Western blot 测定蛋白质特异性 O-GlcNAc 化和 BAD-Bcl-2 二聚体化。
食用高脂饮食的大鼠体重中度增加，空腹胰岛素和血糖水平升高，胰岛素抵抗。高血糖/胰岛素抵抗的心脏中总蛋白 O-GlcNAc 化增加。与此平行，胰岛素抵抗时心肌凋亡标志物（caspase-3、细胞色素 c、BAD）的肽水平显著升高。为了深入了解我们的发现的机制，我们评估了 BAD 的 O-GlcNAc 化，BAD 是一种促凋亡的 Bcl-2 同源物。在这里，我们发现高血糖/胰岛素抵抗的大鼠心脏中 BAD 的 O-GlcNAc 化增加和 BAD 磷酸化（Ser136）减少。这些数据与磷酸化和 O-GlcNAc 化在靶蛋白的相同或相邻位点（s）上竞争一致。此外，我们观察到高血糖/胰岛素抵抗的心脏中 BAD-Bcl-2 二聚体化增加。
本研究的主要发现是，高血糖/胰岛素抵抗心脏中的凋亡增加也可以通过 HBP 诱导的 BAD O-GlcNAc 化和 BAD-Bcl-2 二聚体（促凋亡）的形成增加来介导。
