Diabetic hyperglycaemia activates CaMKII and arrhythmias by O-linked glycosylation
加州大学戴维斯分校(University of California, Davis)的药理学系主任、该研究的资深作者唐纳德·伯斯(Donald Bers)说:“我们发现的新的分子机制为保护糖尿病患者的心脏健康的新治疗策略铺平了道路。”
根据美国国家卫生研究院(National Institutes of Health)的数据，虽然心脏病在普通人群中很常见，但糖尿病患者的患心脏病的风险高达非糖尿病患者的四倍。美国心脏协会(American Heart Association)估计，至少65%的糖尿病患者死于心脏病或中风，并强调有必要对这一关系进行研究。
通过一系列的实验中,伯斯,他的团队,和他们的合作者约翰霍普金斯大学医学院显示糖尿病 人的中度到高的血糖水平特征导致了乙酰葡萄糖胺(O-linked N-acetylglucosamine,或O-GlcNAc)在心肌细胞结合到在一个被称为钙离子/钙调蛋白依赖的蛋白激酶2,或CaMKII蛋白质的特定部位。
“既然乙酰葡萄糖胺直接由葡萄糖和作为主要营养传感器调节大多数细胞过程, 这或许并不令人意外, 糖对蛋白质的结合正成为糖尿病中葡萄糖毒性的主要分子机制,”杰拉尔德·哈特说,教授和主任约翰霍普金斯大学医学院生物化学和伯斯的合作者之一。
How high blood sugar throws off heart rhythm
Posted by Karen Finney-UC Davis October 1st, 2013
Scientists have identified a biological pathway—activated by abnormally high blood sugar levels—that causes irregular heartbeats.
This condition is known as cardiac arrhythmia and is linked with heart failure and sudden cardiac death.
Reported online in the journal Nature, the discovery helps explain why diabetes is a significant independent risk factor for heart disease.
“The novel molecular understanding we have uncovered paves the way for new therapeutic strategies that protect the heart health of patients with diabetes,” says Donald Bers, chair of the pharmacology department at University of California, Davis and senior author of the study.
While heart disease is common in the general population, the risk is up to four times greater for diabetics, according to the National Institutes of Health. The American Heart Association estimates that at least 65 percent of people with diabetes die from heart disease or stroke and has emphasized the need for research focused on understanding this relationship.
Through a series of experiments, Bers, his team, and their collaborators at Johns Hopkins University School of Medicine show that the moderate to high blood glucose levels characteristic of diabetes caused a sugar molecule (O-linked N-acetylglucosamine, or O-GlcNAc) in heart muscle cells to fuse to a specific site on a protein known as calcium/calmodulin-dependent protein kinase II, or CaMKII.
CaMKII has important roles in regulating normal calcium levels, electrical activity, and pumping action of the heart, according to Bers. Its fusion with O-GlcNAc, however, led to chronic overactivation of CaMKII and pathological changes in the finely tuned calcium signaling system it controls, triggering full-blown arrhythmias in just a few minutes. The arrhythmias were prevented by inhibiting CaMKII or its union with O-GlcNAc.
“While scientists have known for a while that CaMKII plays a critical role in normal cardiac function, ours is the first study to identify O-GlcNAc as a direct activator of CaMKII with hyperglycemia,” says Bers.
The research encompassed detailed molecular experiments in rat and human proteins and tissues, calcium imaging in isolated rat cardiac myocytes exposed to high glucose, and assessments of whole heart arrhythmias with optical mapping in isolated hearts and in live diabetic rats.
This comprehensive approach allowed Bers and his team to identify the specific site of sugar attachment to CaMKII, along with how that attachment activated CaMKII and caused calcium-dependent arrhythmias.
“Since O-GlcNAc is directly made from glucose and serves as a major nutrient sensor in regulating most cellular processes, it is perhaps not surprising that attachment of this sugar to proteins is emerging as a major molecular mechanism of glucose toxicity in diabetes,” says Gerald Hart, professor and director of biological chemistry at Johns Hopkins University School of Medicine, and one of Bers’ collaborators.
“However, this represents the most clear-cut mechanistic study to date of how high glucose can directly affect the function of a critical regulatory protein,” says Hart.
“The Bers group’s findings undoubtedly will lead to development of treatments for diabetic cardiovascular disease and, potentially, therapeutics for glucose toxicity in other tissues that are affected by diabetes such as the retina, the nervous system and the kidney.”
In an additional experiment, the team found elevated levels of O-GlcNAc-modified CaMKII in both hearts and brains of deceased humans who were diagnosed with diabetes, with the highest levels in the hearts of patients who had both heart failure and diabetes.
“One key next step will be to determine if the fusion of O-GlcNAc to CaMKII contributes to neuropathies that are also common among diabetics,” says Bers.
The American Heart Association, National Science Foundation, Fondation Leducq Transatlantic CaMKII Alliance, and the National Institutes of Health funded the study.
Source: UC Davis
Original Study DOI: 10.1038/nature12537
Jeffrey R. Erickson, Laetitia Pereira, Lianguo Wang, Guanghui Han, Amanda Ferguson, Khanha Dao, Ronald J. Copeland, Florin Despa, Gerald W. Hart, Crystal M. Ripplinger & Donald M. Bers。
钙离子/钙调蛋白依赖性蛋白激酶II (CaMKII)是一种具有重要调节功能的酶，在心脏和大脑中，其慢性活化可能是一种病理状态。CaMKII激活在心力衰竭中可见，并可直接引起离子通道，钙离子处理和基因转录的病理改变。在这里，在人类、老鼠和老鼠中，我们发现了一种新的机制，将CaMKII和高血糖信号在糖尿病中联系起来，这是心脏病和神经退行性疾病的一个关键风险因素。急性高血糖导致CaMKII的共价修饰是乙酰葡萄糖胺(O-GlcNAc)。CaMKII的 乙酰葡萄糖胺修饰CaMKII，激活CaMKII，即使在Ca2+浓度下降后仍能产生分子记忆。 乙酰葡萄糖胺修饰CaMKII在糖尿病人和大鼠的心脏和大脑中增加。在心肌细胞中，葡萄糖浓度的增加显著提高了自发性内质网Ca2+释放事件，从而导致心脏机械功能障碍和心律失常。这些效应可以通过对 乙酰葡萄糖胺信号的药理抑制或CaMKII的基因消融术来预防。在完整的灌注心脏中，通过乙酰葡萄糖胺和camkii依赖的途径增加葡萄糖浓度，使心律失常加重。在糖尿病动物中，对 乙酰葡萄糖胺的急性阻断抑制了心律失常。因此，对CaMKII的乙酰葡萄糖胺修饰是一种新的信号通路，可能对糖尿病和其他疾病的心脏和神经病理生理学有贡献。
我们在CaMKII S279上通过乙酰葡萄糖糖胺修饰发现了一种新的激活CaMKII的机制(图4g)。急性细胞外葡萄糖升高，达到与糖尿病患者相似的水平，足以在完整的心肌细胞中通过这一途径激活CaMKII，并在完整的心脏和动物中导致心律失常。在糖尿病患者的心脏和大脑中，CaMKII 乙酰葡萄糖胺化升高，这可能导致心肌细胞和神经元的病理改变。实际上，这一途径可能通过磷酸化和氧化26与自主CaMKII激活相互协同，而磷酸化和氧化在许多细胞类型的信号传导中都很重要。CaMKIV与CaMKII有关，在S189中被乙酰葡糖胺化，通过CaM激酶激酶激酶15抑制其活化。在CaMKII中乙酰葡糖胺介导的活化与CaMKIV的抑制并不相似。
Diabetic hyperglycaemia activates CaMKII and arrhythmias by O-linked glycosylation
Jeffrey R. Erickson, Laetitia Pereira, Lianguo Wang, Guanghui Han, Amanda Ferguson, Khanha Dao, Ronald J. Copeland, Florin Despa, Gerald W. Hart, Crystal M. Ripplinger & Donald M. Bers
Nature volume 502, pages 372–376 (17 October 2013) | Download Citation
Ca2+/calmodulin-dependent protein kinase II (CaMKII) is an enzyme with important regulatory functions in the heart and brain, and its chronic activation can be pathological. CaMKII activation is seen in heart failure, and can directly induce pathological changes in ion channels, Ca2+ handling and gene transcription1. Here, in human, rat and mouse, we identify a novel mechanism linking CaMKII and hyperglycaemic signalling in diabetes mellitus, which is a key risk factor for heart2 and neurodegenerative diseases3,4. Acute hyperglycaemia causes covalent modification of CaMKII by O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAc modification of CaMKII at Ser 279 activates CaMKII autonomously, creating molecular memory even after Ca2+ concentration declines. O-GlcNAc-modified CaMKII is increased in the heart and brain of diabetic humans and rats. In cardiomyocytes, increased glucose concentration significantly enhances CaMKII-dependent activation of spontaneous sarcoplasmic reticulum Ca2+ release events that can contribute to cardiac mechanical dysfunction and arrhythmias1. These effects were prevented by pharmacological inhibition of O-GlcNAc signalling or genetic ablation of CaMKIIδ. In intact perfused hearts, arrhythmias were aggravated by increased glucose concentration through O-GlcNAc- and CaMKII-dependent pathways. In diabetic animals, acute blockade of O-GlcNAc inhibited arrhythmogenesis. Thus, O-GlcNAc modification of CaMKII is a novel signalling event in pathways that may contribute critically to cardiac and neuronal pathophysiology in diabetes and other diseases.
We also found higher in vivo arrhythmia susceptibility in normal and diabetic rats during challenge with caffeine and dobutamine (Fig. 4e, f). DON pre-treatment ablated arrhythmias induced by caffeine and dobutamine in diabetics, but had no effect on baseline or caffeine/dobutamine-induced arrhythmia in non-diabetic rats. We also confirmed that CaMKII activity is elevated in diabetic rat hearts, and that this effect is blunted by pre-treatment of rats with DON (Extended Data Fig. 6c), consistent with O-GlcNAc- and CaMKII-dependent hyperglycaemia-induced arrhythmogenesis.
We identified a novel mechanism for autonomous CaMKII activation by O-GlcNAc modification at CaMKII S279 (Fig. 4g). Acute extracellular glucose elevation, to levels that mimic those in diabetic patients, suffices to activate CaMKII through this pathway in intact cardiac myocytes and leads to arrhythmic events in intact hearts and animals. In diabetic hearts and brains CaMKII O-GlcNAcylation is elevated and this may contribute to pathological alterations in cardiac myocytes and neurons. Indeed, this pathway may synergize with autonomous CaMKII activation by phosphorylation8 and oxidation26, which are important in signalling in many cell types. CaMKIV, related to CaMKII, is O-GlcNAcylated at S189, which inhibits its activation by CaM kinase kinase15. O-GlcNAc-mediated activation in CaMKII is not analogous to the inhibition seen for CaMKIV.
Overactivation of CaMKII caused by hyperglycaemia during diabetes may lead to widespread and as yet unappreciated pathological consequences that merit exploration. It is already known that overactivation of CaMKII occurs in heart failure and neuronal excitotoxicity, and that this activated CaMKII can contribute to major dysfunction at the level of acute ion channel modulation that contributes to cardiac arrhythmias1,24, reduced contractility, neuronal damage27 and altered gene transcription1. In diabetes, these powerful CaMKII signalling pathways are likely to be activated by hyperglycaemia-induced O-GlcNAc modification of CaMKII, and this should be considered in future therapeutic strategies. This could also broaden the impact of CaMKII inhibitors in therapeutics in heart disease and beyond.