糖原合成酶激酶-3β和心肌肥厚的负性调控

心肌肥大和心力衰竭是大多数心血管疾病的严重和终末阶段,研究其信号转导机制具有重要意义。目前,治疗心肌肥厚的药物主要是以促肥厚的信号分子作为靶点,例如血管紧张素转化酶抑制剂、B肾上腺素阻断剂,能够减少肥厚反应,但不能完全逆转肥厚。因此,开发另一类作用机制完全不同但能有效阻断病理性心肌肥厚的药物就显得十分必要。日益增多的证据表明,探索心肌肥大的负性调控机制和研究心肌肥大的致病机制一样重要。     

Sarcoplasmic reticular and mitochondrial calcium transport in cardiac hypertrophy

To evaluate changes in Ca2+ transport activities in the cardiac sarcoplasmic reticulum (microsomes) and mitochondria, cardiac hypertrophy was induced in rabbits by constricting the abdominal aorta. The animals showed a stable non-failing left heart hypertrophy between 16-22 weeks after the operation. ATP-dependent Ca2+ uptake and Ca2+ binding activities were depressed in microsomes from hypertrophied rabbits in comparison with sham-operated controls (P less than 0.05). These changes were seen at different concentrations of free Ca2+ (10(-7) to 10(-4)M) and were accompanied by alterations in the phospholipid content of the microsomal fraction. Mitochondrial Ca2+ transport activities and phospholipid content remained unchanged in the hypertrophied heart. The results of this study identify a specific lesion in the sarcotubular membrane and suggest that the depressed Ca2+ transport activity in the microsomal fraction from the hypertrophied myocardium may be due to changes in its phospholipid composition.     

Autophagy in cardiac myocyte homeostasis, aging, and pathology

Autophagy, an intralysosomal degradation of cells' own constituents that includes macro-, micro-, and chaperone-mediated autophagy, plays an important role in the renewal of cardiac myocytes. This cell type is represented by long-lived postmitotic cells with very poor (if any) replacement through differentiation of stem cells. Macroautophagy, the most universal form of autophagy, is responsible for the degradation of various macromolecules and organelles including mitochondria and is activated in response to stress, promoting cell survival. This process is also involved in programmed cell death when injury is irreversible. Even under normal conditions, autophagy is somewhat imperfect, underlying gradual accumulation of defective mitochondria and lipofuscin granules within aging cardiac myocytes. Autophagy is involved in the most important cardiac pathologies including myocardial hypertrophy, cardiomyopathies, and ischemic heart disease, a fact that has led to increasing attention to this process.     

A role for the mitochondrial deacetylase Sirt3 in regulating energy homeostasis

Here, we demonstrate a role for the mitochondrial NAD-dependent deacetylase Sirt3 in the maintenance of basal ATP levels and as a regulator of mitochondrial electron transport. We note that Sirt3^−/− mouse embryonic fibroblasts have a reduction in basal ATP levels. Reconstitution with wild-type but not a deacetylase-deficient form of Sirt3 restored ATP levels in these cells. Furthermore in wild-type mice, the resting level of ATP correlates with organ-specific Sirt3 protein expression. Remarkably, in mice lacking Sirt3, basal levels of ATP in the heart, kidney, and liver were reduced >50%. We further demonstrate that mitochondrial protein acetylation is markedly elevated in Sirt3^−/− tissues. In addition, in the absence of Sirt3, multiple components of Complex I of the electron transport chain demonstrate increased acetylation. Sirt3 can also physically interact with at least one of the known subunits of Complex I, the 39-kDa protein NDUFA9. Functional studies demonstrate that mitochondria from Sirt3^−/− animals display a selective inhibition of Complex I activity. Furthermore, incubation of exogenous Sirt3 with mitochondria can augment Complex I activity. These results implicate protein acetylation as an important regulator of Complex I activity and demonstrate that Sirt3 functions in vivo to regulate and maintain basal ATP levels.     

SIRT3 regulation of mitochondrial oxidative stress

Mitochondria play a central role in the production of reactive oxygen species as byproducts of metabolism and energy production. In order to protect cellular structures from oxidative stress-induced damage, cells have evolved elegant mechanisms for mitochondrial ROS detoxification. The mitochondrial sirtuin, SIRT3, is emerging as a pivotal regulator of oxidative stress by deacetylation of substrates involved in both ROS production and detoxification. This review will summarize recent findings on the regulation of mitochondrial ROS homeostasis by SIRT3.     

Alterations in mitochondrial function in cardiac hypertrophy and heart failure

Normal cardiac function requires high and continuous supply with ATP. As mitochondria are the major source of ATP production, it is apparent that mitochondrial function and cardiac function need to be closely related to each other. When subjected to overload, the heart hypertrophies. Initially, the development of hypertrophy is a compensatory mechanism, and contractile function is maintained. However, when the heart is excessively and/or persistently stressed, cardiac function may deteriorate, leading to the onset of heart failure. There is considerable evidence that alterations in mitochondrial function are involved in the decompensation of cardiac hypertrophy. Here, we review metabolic changes occurring at the mitochondrial level during the development of cardiac hypertrophy and the transition to heart failure. We will focus on changes in mitochondrial substrate metabolism, the electron transport chain and the role of oxidative stress. We will demonstrate that, with respect to mitochondrial adaptations, a clear distinction between hypertrophy and heart failure cannot be made because most of the findings present in overt heart failure can already be found in the various stages of hypertrophy.     

间歇有氧运动训练上调SIRT3改善衰老心肌线粒体功能

目的 探讨间歇有氧运动训练（AIT）对调节SIRT3介导的抗氧化酶系统改善老年小鼠心肌线粒体功能的影响。方法 采用C57小鼠（20月龄）20只,随机分为AIT组和非运动组,每组10只。以成年野生型C57小鼠非运动组(4月龄,10只)为对照组。建立间歇有氧运动训练12周小鼠模型,跑台训练由3部分构成:10 min热身运动,7 min间歇训练（4 min高强度和3 min低强度训练）及1 min冷却。每日训练1 h,每周训练5 d,训练时间为12周。应用蛋白免疫印迹法(Western blot)检测心肌线粒体抗氧化酶相关蛋白的表达。结果 AIT显著上调衰老心肌中线粒体去乙酰化酶sirtuin-3（SIRT3）表达水平,提高AMP依赖的蛋白激酶(AMPK)的磷酸化水平(P<0.05);AIT可改善老年组小鼠心肌线粒体抗氧化酶(MnSOD、Catalase)的活性,有效减少衰老心肌脂质过氧化损伤(P<0.05);AIT训练显著提高衰老心肌线粒体生物合成能力改善了线粒体的功能(均P<0.05)。结论 有氧间歇运动训练可有效地上调衰老小鼠心肌细胞SIRT3水平,有效提高衰老小鼠心肌线粒体功能,其机制可能与激活心肌SIRT3所介导的抗氧化酶系统有关。     

SIRT3在AGEs诱导的心肌老化中的角色及机制研究

目的：研究晚期糖基化终产物（AGEs）诱导心肌老化的机制,沉默信息调节因子SRIT3是否参与,探索黄山药总皂苷(TSDP )改善心肌老化下游机制。方法：原代心肌细胞分对照组,AGEs+NC SiRNA组,AGEs及+SIRT3 SiRNA共干预组,用western-blot测P16,P53及SOD2表达水平,用活性氧试剂盒测细胞内活性氧,用半乳糖苷酶（SA-β-Gal）染色试剂盒测细胞老化。另对照组,AGEs+NC SiRNA组,TSDP+AGEs+NC SiRNA组,及 TSDP+AGEs+SIRT3 SiRNA组,用SA-β-Gal测老化。结果： AGEs+NC SiRNA组较对照组SIRT3蛋白水平下降,AGEs+NC SiRNA,和AGEs+SIRT3 SiRNA共干预组较对照组P53增加,SOD2减少,SA-β-Gal比例及活性氧增加。SIRT3 SiRNA共干预组较AGEs+NC SiRNA组P53增加,P16及SA-β-Gal比例不变。TSDP预干预AGEs组较AGEs+NC SiRNA组SA-β-Gal活性降低,敲降SIRT3后SA-β-Gal活性降低现象消失。结论：AGEs可能是通过下调SIRT3的表达水平,减少抗氧化物蛋白SOD2的表达,加重线粒体氧化应激,促进AGEs诱导的心肌老化进程。TSDP可能通过调控 SIRT3的表达水平而影响老化。     

The role of mitochondrial DNA mutations in aging and sarcopenia: implications for the mitochondrial vicious cycle theory of aging

Aging is associated with a progressive loss of skeletal muscle mass and strength and the mechanisms mediating these effects likely involve mitochondrial DNA (mtDNA) mutations, mitochondrial dysfunction and the activation of mitochondrial-mediated apoptosis. Because the mitochondrial genome is densely packed and close to the main generator of reactive oxygen species (ROS) in the cell, the electron transport chain (ETC), an important role for mtDNA mutations in aging has been proposed. Point mutations and deletions in mtDNA accumulate with age in a wide variety of tissues in mammals, including humans, and often coincide with significant tissue dysfunction. Here, we examine the evidence supporting a causative role for mtDNA mutations in aging and sarcopenia. We review experimental outcomes showing that mtDNA mutations, leading to mitochondrial dysfunction and possibly apoptosis, are causal to the process of sarcopenia. Moreover, we critically discuss and dispute an important part of the mitochondrial 'vicious cycle' theory of aging which proposes that accumulation of mtDNA mutations may lead to an enhanced mitochondrial ROS production and ever increasing oxidative stress which ultimately leads to tissue deterioration and aging. Potential mechanism(s) by which mtDNA mutations may mediate their pathological consequences in skeletal muscle are also discussed.     

Increased sensitivity of mitochondrial respiration to inhibition by nitric oxide in cardiac hypertrophy

Cardiac hypertrophy is a significant risk factor for the development of congestive heart failure (CHF). Mitochondrial defects are reported in CHF, but no consistent mitochondrial alterations have yet been identified in hypertrophy. In this study selective metabolic inhibitors were used to determine thresholds for respiratory inhibition and to reveal novel mitochondrial defects in hypertrophy. Cardiac hypertrophy was produced in rats by aortic banding. Mitochondria were isolated from left ventricular tissue and the effects of inhibiting respiratory complexes I and IV on mitochondrial oxygen consumption were measured. At 8 weeks post-surgery, 65+/-2% complex IV inhibition was required to inhibit respiration half maximally in control mitochondria. In contrast, only 52+/-6% complex IV inhibition was required to inhibit respiration half maximally in mitochondria from hypertrophied hearts (P=0.046). This effect persisted at 22 weeks post-surgery and was accompanied by a significant upregulation of inducible nitric oxide synthase (iNOS, 3.0+/-0.7-fold, P=0.006). We conclude that respiration is more sensitive to complex IV inhibition in hypertrophy. Nitric oxide is a well documented inhibitor of complex IV, and thus the combination of increased NO(.)from iNOS and an increased sensitivity to inhibition of one of its targets could result in a bioenergetic defect in hypertrophy that may be a harbinger of CHF.     

The role of mitochondrial DNA rearrangements in aging and human diseases.

Instabilities and point mutations of the high molecular weight mitochondrial DNA (mtDNA) were shown to be correlated with various degenerative processes in both lower eukaryotes as well as in mammals. In filamentous fungi, circular and linear plasmids were demonstrated to be involved in mtDNA rearrangements and in the genetic control of senescence. In addition, in these eukaryotic microorganisms, which have proved to be ideal model systems in experimental gerontology, a number of nuclear genes were identified controlling the stability of the mitochondrial genome. Although the mitochondrial genome of mammals, including humans, appears to be quite stable in comparison to other species, mtDNA instabilities of the type described in fungi were observed in mitochondria of patients with different mitochondrial degenerative disorders (CPEO, KSS, Pearson syndrome, LHON, MERRF, MELAS). It was later demonstrated that such mtDNA rearrangements appear to accumulate progressively during aging in human subjects. These data suggest that instabilities of the mitochondrial genome may play an important role in the control of life span not only in lower eukaryotes, but also in humans.     

The mitochondrial biogenesis regulatory program in cardiac adaptation to ischemia--a putative target for therapeutic intervention

The resurgence of mitochondrial biology research stems from the realization that the distinct regulation of mitochondria to meet diverse homeostatic demands is driven by exquisite biochemical and molecular control mechanisms. This program termed mitochondrial biogenesis is integral to orchestrating mitochondrial function and appears to exhibit adaptive remodeling following biomechanical and oxidative stress. The major bioenergetic function of mitochondria partitions the final utilization of oxygen between oxidative phosphorylation and reactive oxygen species. As disruption in oxidative phosphorylation and excessive reactive oxygen species contribute to cardiac ischemia-reperfusion injury, we hypothesize that the mitochondrial biogenesis regulatory program is an explicit target for cardiac therapeutic interventions. The objectives of this review are to (a) define the advances in understanding the mitochondrial biogenesis regulatory program integrated to its control of mitochondrial bioenergetics and oxygen utilization, (b) reveal how this program is modulated by chronic hypoxia and ischemic preconditioning, and (c) examine the therapeutic potential of modulating the regulation of mitochondrial biogenesis as a strategy to attenuate ischemia-reperfusion injury.     

Old and new tools to dissect calcineurin's role in pressure-overload cardiac hypertrophy

In the last several years, a number of experiments have implicated a pivotal role of the calcium/calmodulin-calcineurin dependent pathway as a final common signaling mechanism by which diverse hypertrophic stimuli converge to mediate hypertrophic responses in cardiomyocytes. Calcineurin inhibitors, i.e. cyclosporine A (CsA) and FK506, can interrupt the pathway, thereby preventing cardiac hypertrophy. The data that convincingly support this novel hypothesis were derived either from in vitro studies in cultured cardiomyocytes or from in vivo studies in transgenic mice. However, when the hypothesis was tested in clinically relevant animal models of cardiac hypertrophy, controversial results and conclusions emerged. In conventional models of cardiac hypertrophy, two questions remain to be answered: (1) whether calcineurin is activated in hypertrophied cardiac muscle, and (2) whether calcineurin inhibitors prevent cardiac hypertrophy. In addition, clinical observations have revealed that calcineurin inhibitors appear to exert pro-hypertrophic effects in organ transplant recipients. The controversies suggest that current calcineurin inhibitors are blunt tools for testing the hypothesis in pressure-overload hypertrophy in vivo, because there are so many confounding effects that are associated with systemic administration of the drugs. As such, new genetic approaches may overcome some of the problems associated with pharmacological inhibitors. This invited review will focus on the controversies surrounding the ability of calcineurin inhibition to prevent conventional (pressure-overload) cardiac hypertrophy and the new genetic approaches to address the question.     

Regulation of the mPTP by SIRT3-mediated deacetylation of CypD at lysine 166 suppresses age-related cardiac hypertrophy

Cardiac failure is a leading cause of age-related death, though its root cause remains unknown. Mounting evidence implicates a decline in mitochondrial function due to increased opening of the mitochondrial permeability transition pore (mPTP). Here we report that the NAD+-dependent deacetylase SIRT3 deacetylates the regulatory component of the mPTP, cyclophilin D (CypD) on lysine 166, adjacent to the binding site of cyclosporine A, a CypD inhibitor. Cardiac myocytes from mice lacking SIRT3 exhibit an age-dependent increase in mitochondrial swelling due to increased mPTP opening, a phenotype that is rescued by cyclosporine A. SIRT3 knockout mice show accelerated signs of aging in the heart including cardiac hypertrophy and fibrosis at 13 months of age. SIRT3 knockout mice are also hypersensitive to heart stress induced by transverse aortic constriction (TAC), as evidenced by cardiac hypertrophy, fibrosis, and increased mortality. Together, these data show for the first time that SIRT3 activity is necessary to prevent mitochondrial dysfunction and cardiac hypertrophy during aging and shed light on new pharmacological approaches to delaying aging and treating diseases in cardiac muscle and possibly other post-mitotic tissues.