Beclin 1与mTOR对心肌缺血/再灌注损伤中自噬的交互调控机制

自噬是一个进化上高度保守的受损或功能障碍的蛋白质聚集体或细胞器降解的过程。在心肌缺血/再灌注(I/R)过程中,可以通过多种因素诱导细胞的自噬活动,而且越来越多的证据表明,自噬在心肌缺血/再灌注损伤(MIRI)中可能起“双刃剑”的作用,适度自噬可促进细胞存活;而不适当的激活自噬可能会加速细胞死亡。Beclin 1介导的自噬/凋亡互反馈信号通路和哺乳动物雷帕霉素靶蛋白(mTOR)介导的自噬与mTOR的互反馈信号通路,是两条经典的自噬激活信号途径,也可能是调控自噬“双刃剑”转向促进细胞存活的重要调控机制。本文将重点综述上述两条信号通路对自噬的交互式调控作用。速发挥作用。因此,Z盘部位实质上成为心肌细胞中的信号转导中心。     

The relationship between p38 mitogen-activated protein kinase and AMP-activated protein kinase during myocardial ischemia

OBJECTIVE: p38 mitogen-activated protein kinase (p38 MAPK) and AMP-activated protein kinase (AMPK) are activated by, and influence sensitivity to, myocardial ischemia. Recently a number of studies have suggested that AMPK may participate in the activation of p38 MAPK. We therefore examined whether AMPK may be the principal "ischemia sensor" responsible for p38 MAPK activation during myocardial ischemia. METHODS: We used a variety of approaches to alter AMPK activity during ischemia and studied the repercussions on p38 MAPK activation. RESULTS: The activities of AMPK and p38 MAPK were temporally related in adult rat ventricular myocytes (ARVM) subjected to simulated ischemia and in isolated mouse hearts subjected to no-flow ischemia. However p38 MAPK activation was unaltered in mouse hearts lacking the predominant or minor myocardial isoforms, AMPKalpha2 or AMPKalpha1 respectively. Likewise, in ARVM, adenoviral-driven expression of the minor myocardial isoform AMPKalpha1, in a constitutively active or dominant negative form reducing AMPK activity, did not alter p38 MAPK activation under basal conditions or during simulated ischemia. Finally, pharmacological inhibition of AMPK during ischemia with compound C did not attenuate the coincident activation of p38 MAPK. CONCLUSIONS: Although AMPK and p38 MAPK are both activated during myocardial ischemia, the activation of p38 MAPK occurs independently of AMPK.     

腺苷酸活化蛋白激酶在脑缺血中的作用

腺苷酸活化蛋白激酶(adenosine monophosphate-activated protein kinase,AMPK)是一种丝氨酸/苏氨酸蛋白激酶,为机体细胞内能量调节的开关.在营养缺乏、缺血等情况下,AMPK系统激活,作为代谢和应激信号转导元件调节下游靶蛋白表达.急性脑缺血后,AMPK被激活并加重神经元凋亡,而给予AMPK抑制剂则可减轻脑缺血损伤.卒中后,AMPK激活可导致脑源性神经生长因子表达上调和内皮型一氧化氮合酶活化,对神经元再生和修复起着保护作用.文章对AMPK在实验性脑缺血中作用的研究进展进行了综述.     

AMP-activated protein kinase: a key stress signaling pathway in the heart

AMP-activated protein kinase (AMPK) is activated during exercise and ischemia and is emerging as an important regulatory mechanism in the heart. AMPK promotes adenosine triphosphate-generating pathways, including glucose transport, glycolysis, and fatty acid oxidation, while inhibiting energy-consuming anabolic pathways. After ischemia-reperfusion, AMPK-deficient hearts from transgenic mice have severe left ventricular contractile dysfunction with increased apoptosis and necrosis. Mutations in the AMPKgamma(2) subunit lead to cardiac glycogen overload, Wolff-Parkinson-White syndrome, arrhythmias, and heart failure. This review focuses on the molecular mechanisms of activation and cardiovascular actions of AMPK in the heart.     

AMP-activated protein kinase control of energy metabolism in the ischemic heart

Myocardial ischemia produces an energy-deficient state in heart muscle, which if not corrected can lead to cardiomyocyte death. AMP-activated protein kinase (AMPK) is a key kinase that can increase energy production in the ischemic heart. During ischemia a rapid activation of AMPK occurs, resulting in an activation of both myocardial glucose uptake and glycolysis, as well as an increase in fatty acid oxidation. This activation of AMPK has the potential to increase energy production, thereby protecting the heart during ischemic stress. However, at clinically relevant high levels of fatty acids, ischemia-induced activation of AMPK also stimulates fatty acid oxidation during and following ischemia. This can contribute to ischemic injury secondary to an inhibition of glucose oxidation, which results in a decrease in cardiac efficiency. As a result, AMPK activation has the potential to be either beneficial or harmful in the ischemic heart.     

AMP-activated protein kinase in the brain

Since its discovery as an important regulator of fuel utilization in the periphery, AMP-activated protein kinase (AMPK) has become a contender for many important cell-intrinsic and organismal roles regarding energy balance in the central nervous system. The challenge will be to delineate the mechanisms by which neuronal AMPK can respond to cellular energy requirements as well as whole body energy demands. Thus, under physiological conditions in the brain, hypothalamic AMPK responds to changes in energy balance/food intake, whereas under pathological conditions, AMPK responds globally in the brain to energy challenge. Modulation of fatty acid metabolism affects energy balance in a context-specific manner and may provide an insight into other mechanisms for selective activation or inhibition of AMPK activity for therapeutic applications.     

自噬在脑缺血中的双重作用

自噬是一种细胞内成分降解过程,分为启动、延伸、成熟以及自噬体降解等不同阶段,其作用与细胞损伤程度有关.自噬在饥饿、低氧等情况下适度激活,可促进细胞存活;而在脑缺血时过度激活,可导致细胞裂解和促进细胞死亡.预处理可能通过适当激活自噬而产生缺血耐受作用.自噬受到多种蛋白激酶、凋亡分子以及氧化应激通路的严格调控.     

The role of AMP-activated protein kinase in fuel selection by the stressed heart

The heart responds to energetic stress with both acute and chronic changes in substrate metabolism. Recent work has demonstrated that the metabolic stress kinase AMP-activated protein kinase (AMPK) plays an important role in the acute regulation of carbohydrate and fatty acid metabolism in the setting of acute energetic stressors, such as ischemia/reperfusion, or increased workload, through covalent and noncovalent regulation of enzymes involved in intermediary metabolism. In addition, chronic activation of AMPK has been shown to affect the expression of key proteins regulating carbohydrate and fatty acid metabolism. Characterizing the effects of AMPK will provide important insights into its function in the normal heart and might provide new metabolic therapies for ischemic heart disease and heart failure.     

AMP-activated protein kinase activates p38 mitogen-activated protein kinase by increasing recruitment of p38 MAPK to TAB1 in the ischemic heart

AMP-activated protein kinase (AMPK) promotes glucose transport, maintains ATP stores, and prevents injury and apoptosis during ischemia. AMPK has several direct molecular targets in the heart but also may interact with other stress-signaling pathways. This study examined the role of AMPK in the activation of the p38 mitogen-activated protein kinase (MAPK). In isolated heart muscles, the AMPK activator 5-aminoimidazole-4-carboxy-amide-1-beta-D-ribofuranoside (AICAR) increased p38 MAPK activation. In AMPK-deficient mouse hearts, expressing a kinase-dead (KD) alpha2 catalytic subunit, p38 MAPK activation was markedly reduced during low-flow ischemia (2.3- versus 7-fold in wild-type hearts, P<0.01) and was similarly reduced during severe no-flow ischemia in KD hearts (P<0.01 versus ischemic wild type). Knockout of the p38 MAPK upstream kinase, MAPK kinase 3 (MKK3), did not affect ischemic activation of either AMPK or p38 MAPK in transgenic mkk3(-/-) mouse hearts. Ischemia increased p38 MAPK recruitment to transforming growth factor-beta-activated protein kinase 1-binding protein 1 (TAB1), a scaffold protein that promotes p38 MAPK autophosphorylation. Moreover, TAB1 was associated with the alpha2 catalytic subunit of AMPK. p38 MAPK recruitment to TAB1/AMPK complexes required AMPK activation and was reduced in ischemic AMPK-deficient transgenic mouse hearts. The potential role of p38 MAPK in mediating the downstream action of AMPK to promote glucose transport was also assessed. The p38 MAPK inhibitor SB203580 partially inhibited both AICAR- and hypoxia-stimulated glucose uptake and GLUT4 translocation. Activation of p38 MAPK by anisomycin also increased glucose transport in heart muscles. Thus, AMPK has an important role in promoting p38 MAPK activation in the ischemic heart by inducing p38 MAPK autophosphorylation through interaction with the scaffold protein TAB1.     

心肌缺血/再灌损伤时TXNIP表达水平升高并增加心肌自噬

目的 探讨心肌缺血/再灌注（MI/R）时硫氧还蛋白相互结合蛋白（TXNIP）表达及对心肌细胞自噬水平的影响。 方法 构建TXNIP敲除鼠及TXNIP过表达小鼠,制作上述小鼠MI/R模型,观察MI/R后心肌TXNIP表达水平是否与心肌损伤及自噬有关。 结果 与假手术组（Sham）小鼠相比,小鼠心肌TXNIP表达水平在缺血及再灌注损伤过程中持续升高（P<0.01）。在小鼠MI/R后,心脏超声证实与野生型（WT）小鼠相比,TXNIP过表达小鼠LVEF（%）值更低（P<0.05）;伊文氏蓝/TTC染色同样证实TXNIP过表达小鼠心肌梗死面积更大（P<0.05）。而TXNIP敲除鼠MI/R后心脏LVEF（%）值（P<0.05）及心肌梗死面积（P<0.05）均较WT小鼠显著减轻。通过免疫印迹（LC3Ⅱ/LC3I及P62表达）及电子显微镜观察自噬小体检测发现,相比WT小鼠,TXNIP敲除小鼠心肌自噬程度更轻（P<0.05）,TXNIP过表达小鼠则心肌自噬程度更重（P<0.05）。 结论 上述结果证实了在MI/R后TXNIP升高导致心脏功能的降低,心肌梗死面积的增加及心肌细胞自噬的增多。     

Effects of electroacupuncture at different time during reperfusion on the expression of Bcl-2and Beclin1 in myocardial tissue in rats with myocardial ischemia reperfusion injury

<正>Objective To compare the effects of electroacupuncture (EA) at different time during reperfusion on the expression of autophagy-related protein Bcl-2 and Beclin1in myocardial tissue in rats with myocardial ischemia reperfusion injury (MIRI),and to explore the autophagy-related mechanism of EA on protecting MIRI. Methods A total of 72 SD rats were randomly divided into a     

Oxygen-derived free radicals related injury in the heart during ischemia and reperfusion

It has been suggested recently that oxygen-derived free radicals may play an important role in the genesis of reperfusion injury and arrhythmias. Free radicals have a very short half-life (ranging from mili- to microseconds), hence almost all the reports supporting the free radical hypothesis of reperfusion cell injury have been indirect. We have applied electrone spin resonance spectrometry to measure directly the amount of free radicals generated during ischemia and reperfusion. The concentration of free radicals in mitochondria increased significantly during ischemia (for 20 and 40 min). The concentration of free radicals after reperfusion was higher than that during ischemia, and a large amount of free radical generation occurred within the first 60 sec of reperfusion and returned to the level of prereperfusion at 5 min after reperfusion. The concentration of free radicals in the reperfusion-induced ventricular fibrillation group was significantly higher than that in the non-occurrence group. The administration of liposomal superoxide dismutase reduced the incidence of reperfusion-induced ventricular fibrillation and that prevented the free radical generation during reperfusion. This study showed that enhanced generation of free radicals occurred at the onset of ventricular fibrillation and that free radical scavenger prevented the development of arrhythmias and free radical generation during reperfusion. We have obtained more circumstantial evidence for an involvement of free radicals in the genesis of reperfusion injury and arrhythmias.     

New progress in roles of nitric oxide during hepatic ischemia reperfusion injury

Hepatic ischemia reperfusion injury(HIRI) is a clinical condition which may lead to cellular injury and organ dysfunction. The role of nitric oxide(NO) in HIRI is complicated and inconclusive. NO produced by endothelial nitric oxide synthase(e NOS) activation plays a protective role during early HIRI. But e NOS overexpression and the resulting excessive NO bioavailability can aggravate liver injury. NO induced by inducible nitric oxide synthase(i NOS) may have either a protective or a deleterious effect during the early phase of HIRI, but it may protect the liver during late HIRI. Here, we reviewed the latest findings on the role of NO during HIRI:(1) NO exerts a protective effect against HIRI by increasing NO bioavailability, downregulating p53 gene expression, decreasing inflammatory chemokines, reducing ROS via inhibiting the mitochondrial respiratory chain, activating s GCGTP-c GMP signal pathway to reduce liver cell apoptosis, and regulating hepatic immune functions;(2) e NOS protects against HIRI by increasing NO levels, several e NOS/NO signal pathways(such as Akt-e NOS/NO, AMPK-e NOS/NO and HIF-1α-e NOS/NO) participating in the anti-HIRI process, and inhibiting over-expression of e NOS also protects against HIRI; and(3) the inhibition of i NOS prevents HIRI. Thus, the adverse effects of NO should be avoided, but its positive effect in the clinical treatment of diseases associated with HIRI should be recognized.     

AMP-activated protein kinase: Role in metabolism and therapeutic implications

AMP-activated protein kinase (AMPK) is an enzyme that works as a fuel gauge which becomes activated in situations of energy consumption. AMPK functions to restore cellular ATP levels by modifying diverse metabolic and cellular pathways. In the skeletal muscle, AMPK is activated during exercise and is involved in contraction-stimulated glucose transport and fatty acid oxidation. In the heart, AMPK activity increases during ischaemia and functions to sustain ATP, cardiac function and myocardial viability. In the liver, AMPK inhibits the production of glucose, cholesterol and triglycerides and stimulates fatty acid oxidation. Recent studies have shown that AMPK is involved in the mechanism of action of metformin and thiazolidinediones, and the adipocytokines leptin and adiponectin. These data, along with evidence that pharmacological activation of AMPK in vivo improves blood glucose homeostasis, cholesterol concentrations and blood pressure in insulin-resistant rodents, make this enzyme an attractive pharmacological target for the treatment of type 2 diabetes, ischaemic heart disease and other metabolic diseases.     

Temporal changes in the subcellular distribution of protein kinase C in rabbit heart during global ischemia

Our recent studies utilizing an in vivo regional ischemia model revealed no changes in the subcellular distribution of protein kinase C (PKC) in dog and rabbit hearts after repeated 5 min episodes of preconditioning ischemia/reperfusion. However, 10 min of sustained ischemia resulted in an increase in PKC activity in the membrane fraction. These findings indicate that prolonged ischemia may cause changes in the subcellular distribution of PKC. However, the detailed time course of these changes during sustained severe ischemia is poorly resolved. Thus, our objective was to study temporal changes in PKC distribution in the cytosolic, nuclear, and membrane fractions isolated from globally ischemic rabbit heart. Hearts were removed under deep anesthesia, placed into normal saline at 37°C, and repeatedly sampled from apex to base at baseline, 2, 5, and 10 min into global ischemia, with matched samples obtained in every heart. PKC activity was increased at 2 min into global ischemia in both the nuclear fraction (1069±75 vs 893±49 pmol/min/g at baseline; p=0.05) and the membrane fraction (1374±95 vs 1187±59 pmol/min/g at baseline; p<0.05) with persistent translocation observed at 5 and 10 min into the protocol. Thus, direct biochemical determination of PKC activity in the isolated rabbit heart revealed increased activity in the nuclear and the membrane fractions as early as 2 min into global ischemia. Received: 27 August 1997, Returned for revision: 17 September 1997, Revision received: 13 October 1997, Accepted: 6 November 1997