线粒体与多潜能干细胞功能

线粒体是细胞内重要的细胞器,主要功能是通过氧化磷酸化为细胞生命活动提供能量。近年来,研究表明,在多潜能干细胞（Pluripotent stem cells, PSCs）中线粒体表现出独有的特征,即在多能性状态下,PSCs主要依靠糖酵解提供能量,其分化期间线粒体氧化磷酸化代谢能力逐渐增强。相反,体细胞重编程为多潜能干细胞期间,线粒体氧化磷酸化向糖酵解途径的转变是其成功重编程必需的代谢过程。另外,线粒体通过生物合成和形态结构的动态重塑维持了PSCs多能性、诱导分化及诱导多能干细胞（Induced pluripotent stem cells, iPSCs）的重编程。因此,本文综述了PSCs线粒体形态结构及其在调控PSCs多能性、合成代谢、氧化还原状态的平衡、分化及重新编程中的作用,为深入了解线粒体调控PSCs功能的作用提供理论基础。     

Iron uncouples oxidative phosphorylation in brain mitochondria isolated from vitamin E-deficient rats

Few, if any, studies have examined the effect of vitamin E deficiency on brain mitochondrial oxidative phosphorylation. The latter was studied using brain mitochondria isolated from control and vitamin E-deficient rats (13 months of deficiency) after exposure to iron, an inducer of oxidative stress. Mitochondria were treated with iron (2 to 50 microM) added as ferrous ammonium sulfate. Rates of state 3 and state 4 respiration, respiratory control ratios, and ADP/O ratios were not affected by vitamin E deficiency alone. However, iron uncoupled oxidative phosphorylation in vitamin E-deficient mitochondria, but not in controls. In vitamin E-deficient mitochondria, iron decreased ADP/O ratios and markedly stimulated state 4 respiration; iron had only a modest effect on these parameters in control mitochondria. Thus, vitamin E may have an important role in sustaining oxidative phosphorylation. Low concentrations of iron (2 to 5 microM) oxidized mitochondrial tocopherol that exists in two pools. The release of iron in brain may impair oxidative phosphorylation, which would be exacerbated by vitamin E deficiency. The results are important for understanding the pathogenesis of human brain disorders known to be associated with abnormalities in mitochondrial function as well as iron homeostasis (e.g., Parkinson's disease).     

Emerging role of SIRT3 in endothelial metabolism,angiogenesis, and cardiovascular disease

Sirtuin 3 (SIRT3) a mitochondrial enzyme that plays an important role in energy homeostasis, cardiac remodeling, and heart failure (HF). The expression of SIRT3 declines with advanced age, cardiovascular, and metabolic diseases. Accumulating evidence suggests that SIRT3 plays a critical role in protecting the heart from cardiac hypertrophy, cardiac dysfunction associated with HF, and in the protection of cardiac cells from stress-mediated cell death. Clinical studies have demonstrated that HF with preserved ejection fraction (HFpEF) in patients present with abnormalities in coronary microcirculation related to endothelial dysfunction and coronary microvascular rarefaction. Although SIRT3-mediated regulation of mitochondrial homeostasis and heart function has been intensively investigated, the effect of SIRT3 on endothelial cell (EC) glycolytic metabolism and microvascular function has not been well studied. ECs utilize glycolysis for generating ATP rather than oxidative phosphorylation to maintain their normal functions and promote angiogenesis and EC–cardiomyocyte interactions. Emerging evidence indicates that SIRT3 is involved in the regulation of endothelial metabolism and angiogenesis and thus affects the development of cardiovascular diseases associated with aging. This review will discuss the current knowledge of SIRT3 and its functional role on endothelial metabolism, cardiac function, and cardiovascular diseases.     

膜蛋白ATAD3A在线粒体质量控制中的作用

线粒体质量控制对于线粒体网络的稳态和线粒体功能的正常发挥具有重要意义。三磷酸腺苷酶家族蛋白3A(ATAD3A)是同时参与调节线粒体结构功能、线粒体动力学和线粒体自噬等重要生物学过程的线粒体膜蛋白之一。近期研究表明,ATAD3A既可与Mic60/Mitofilin和线粒体转录因子A (TFAM)等因子相互作用以维持线粒体嵴的形态和氧化磷酸化功能,又能与发动蛋白相关蛋白1 (Drp1)结合而正性/负性调节线粒体分裂,还可作为线粒体外膜转位酶（TOM）复合物和线粒体内膜转位酶（TIM）复合物之间的桥接因子而介导PTEN诱导激酶（PINK1）输入线粒体进行加工,显示出促自噬或抗自噬活性。本文对ATAD3A在调控线粒体质量控制中的作用及其机制进行了综述。     

线粒体蛋白质组及蛋白质量控制

线粒体是哺乳动物细胞内重要细胞器,不仅通过氧化磷酸化产生ATP为细胞提供能量,也参与调节钙离子稳态、活性氧(reactive oxygen species,ROS)的产生、细胞应激反应和细胞死亡等过程,其功能障碍不仅导致多种人类疾病的发生,而且也能降低动物卵母细胞质量和早期胚胎发育能力.大量证据表明,线粒体的功能依赖于...     

How mitochondrial damage affects cell function

The pathophysiology of mitochondrial DNA (mtDNA) diseases is caused by increased cell death and dysfunction due to the accumulation of mutations to mtDNA. While the disruption of oxidative phosphorylation is central to mtDNA diseases, many other factors, such as Ca²⁺ dyshomeostasis, increased oxidative stress and defective turnover of mitochondrial proteins, may also contribute. The relative importance of these processes in causing cell dysfunction and death is uncertain. It is also unclear whether these damaging processes lead to the disease phenotype through affecting cell function, increasing cell death or a combination of both. These uncertainties limit our understanding of mtDNA disease pathophysiology and our ability to develop rational therapies. Here, we outline how the accumulation of mtDNA mutations can lead to cell dysfunction by altering oxidative phosphorylation, Ca²⁺ homeostasis, oxidative stress and protein turnover and discuss how these processes affect cell function and susceptibility to cell death. A better understanding of these processes will eventually clarify why particular mtDNA mutations cause defined syndromes in some cases but not in others and why the same mutation can lead to different phenotypes.     

Resveratrol improves mitochondrial function and protects against metabolic disease by activating SIRT1 and PGC-1alpha

Diminished mitochondrial oxidative phosphorylation and aerobic capacity are associated with reduced longevity. We tested whether resveratrol (RSV), which is known to extend lifespan, impacts mitochondrial function and metabolic homeostasis. Treatment of mice with RSV significantly increased their aerobic capacity, as evidenced by their increased running time and consumption of oxygen in muscle fibers. RSV's effects were associated with an induction of genes for oxidative phosphorylation and mitochondrial biogenesis and were largely explained by an RSV-mediated decrease in PGC-1alpha acetylation and an increase in PGC-1alpha activity. This mechanism is consistent with RSV being a known activator of the protein deacetylase, SIRT1, and by the lack of effect of RSV in SIRT1(-/-) MEFs. Importantly, RSV treatment protected mice against diet-induced-obesity and insulin resistance. These pharmacological effects of RSV combined with the association of three Sirt1 SNPs and energy homeostasis in Finnish subjects implicates SIRT1 as a key regulator of energy and metabolic homeostasis.     

Oxidative stress-mediated mitochondrial fission promotes hepatic stellate cell activation via stimulating oxidative phosphorylation

Previous studies have demonstrated dysregulated mitochondrial dynamics in fibrotic livers and hepatocytes. Little is currently known about how mitochondrial dynamics are involved, nor is it clear how mitochondrial dynamics participate in hepatic stellate cell (HSC) activation. In the present study, we investigated the role of mitochondrial dynamics in HSC activation and the underlying mechanisms. We verified that mitochondrial fission was enhanced in human and mouse fibrotic livers and active HSCs. Moreover, increased mitochondrial fission driven by fis1 overexpression could promote HSC activation. Inhibiting mitochondrial fission using mitochondrial fission inhibitor-1 (Mdivi-1) could inhibit activation and induce apoptosis of active HSCs, indicating that increased mitochondrial fission is essential for HSC activation. Mdivi-1 treatment also induced apoptosis in active HSCs in vivo and thus ameliorated CCl₄-induced liver fibrosis. We also found that oxidative phosphorylation (OxPhos) was increased in active HSCs, and OxPhos inhibitors inhibited activation and induced apoptosis in active HSCs. Moreover, increasing mitochondrial fission upregulated OxPhos, while inhibiting mitochondrial fission downregulated OxPhos, suggesting that mitochondrial fission stimulates OxPhos during HSC activation. Next, we found that inhibition of oxidative stress using mitoquinone mesylate (mitoQ) and Tempol inhibited mitochondrial fission and OxPhos and induced apoptosis in active HSCs, suggesting that oxidative stress contributes to excessive mitochondrial fission during HSC activation. In conclusion, our study revealed that oxidative stress contributes to enhanced mitochondrial fission, which triggers OxPhos during HSC activation. Importantly, inhibiting mitochondrial fission has huge prospects for alleviating liver fibrosis by eliminating active HSCs.Subject terms: Endocrine system and metabolic diseases, Cell biology     

Energy crisis: The role of oxidative phosphorylation in acute inflammation and sepsis

Mitochondrial dysfunction is increasingly recognized as an accomplice in most of the common human diseases including cancer, neurodegeneration, diabetes, ischemia/reperfusion injury as seen in myocardial infarction and stroke, and sepsis. Inflammatory conditions, both acute and chronic, have recently been shown to affect mitochondrial function. We here discuss the role of oxidative phosphorylation (OxPhos), focusing on acute inflammatory conditions, in particular sepsis and experimental sepsis models. We discuss mitochondrial alterations, specifically the suppression of oxidative metabolism and the role of mitochondrial reactive oxygen species in disease pathology. Several signaling pathways including metabolic, proliferative, and cytokine signaling affect mitochondrial function and appear to be important in inflammatory disease conditions. Cytochrome c oxidase (COX) and cytochrome c, the latter of which plays a central role in apoptosis in addition to mitochondrial respiration, serve as examples for the entire OxPhos system since they have been studied in more detail with respect to cell signaling. We propose a model in which inflammatory signaling leads to changes in the phosphorylation state of mitochondrial proteins, including Tyr304 phosphorylation of COX catalytic subunit I. This results in an inhibition of OxPhos, a reduction of the mitochondrial membrane potential, and consequently a lack of energy, which can cause organ failure and death as seen in septic patients.     

Drosophila Clueless Is Highly Expressed in Larval Neuroblasts,Affects Mitochondrial Localization and Suppresses Mitochondrial Oxidative Damage

Mitochondria are critical for neuronal function due to the high demand of ATP in these cell types. During Drosophila development, neuroblasts in the larval brain divide asymmetrically to populate the adult central nervous system. While many of the proteins responsible for maintaining neuroblast cell fate and asymmetric cell divisions are known, little is know about the role of metabolism and mitochondria in neuroblast division and maintenance. The gene clueless (clu) has been previously shown to be important for mitochondrial function. clu mutant adults have severely shortened lifespans and are highly uncoordinated. Part of their lack of coordination is due to defects in muscle, however, in this study we have identified high levels of Clu expression in larval neuroblasts and other regions of the dividing larval brain. We show while mitochondria in clu mutant neuroblasts are mislocalized during the cell cycle, surprisingly, overall brain morphology appears to be normal. This is explained by our observation that clu mutant larvae have normal levels of ATP and do not suffer oxidative damage, in sharp contrast to clu mutant adults. Mutations in two other genes encoding mitochondrial proteins, technical knockout and stress sensitive B, do not cause neuroblast mitochondrial mislocalization, even though technical knockout mutant larvae suffer oxidative damage. These results suggest Clu functions upstream of electron transport and oxidative phosphorylation, has a role in suppressing oxidative damage in the cell, and that lack of Clu’s specific function causes mitochondria to mislocalize. These results also support the previous observation that larval development relies on aerobic glycolysis, rather than oxidative phosphorylation. Thus Clu’s role in mitochondrial function is not critical during larval development, but is important for pupae and adults.     

Mutations in the mitochondrial methionyl-tRNA synthetase cause a neurodegenerative phenotype in flies and a recessive ataxia (ARSAL) in humans

An increasing number of genes required for mitochondrial biogenesis, dynamics, or function have been found to be mutated in metabolic disorders and neurological diseases such as Leigh Syndrome. In a forward genetic screen to identify genes required for neuronal function and survival in Drosophila photoreceptor neurons, we have identified mutations in the mitochondrial methionyl-tRNA synthetase, Aats-met, the homologue of human MARS2. The fly mutants exhibit age-dependent degeneration of photoreceptors, shortened lifespan, and reduced cell proliferation in epithelial tissues. We further observed that these mutants display defects in oxidative phosphorylation, increased Reactive Oxygen Species (ROS), and an upregulated mitochondrial Unfolded Protein Response. With the aid of this knowledge, we identified MARS2 to be mutated in Autosomal Recessive Spastic Ataxia with Leukoencephalopathy (ARSAL) patients. We uncovered complex rearrangements in the MARS2 gene in all ARSAL patients. Analysis of patient cells revealed decreased levels of MARS2 protein and a reduced rate of mitochondrial protein synthesis. Patient cells also exhibited reduced Complex I activity, increased ROS, and a slower cell proliferation rate, similar to Drosophila Aats-met mutants.     

Mitochondrial dysfunction in epilepsy

Mitochondrial dysfunction has been identified as one potential cause of epileptic seizures. Impaired mitochondrial function has been reported for the seizure focus of patients with temporal lobe epilepsy and Ammon's horn sclerosis and of adult and immature animal models of epilepsy. Since mitochondrial oxidative phosphorylation provides the major source of ATP in neurons and mitochondria participate in cellular Ca(2+) homeostasis and generation of reactive oxygen species, their dysfunction strongly affects neuronal excitability and synaptic transmission. Therefore, mitochondrial dysfunction is proposed to be highly relevant for seizure generation. Additionally, mitochondrial dysfunction is known to trigger neuronal cell death, which is a prominent feature of therapy-resistant epilepsy. For this reason mitochondria have to be considered as promising targets for neuroprotective strategies in epilepsy.     

Lack of oxidative phosphorylation and low mitochondrial membrane potential decrease susceptibility to apoptosis and do not modulate the protective effect of Bcl-x(L) in osteosarcoma cells

We explored the role of low mitochondrial membrane potential (DeltaPsim) and the lack of oxidative phosphorylation in apoptosis by assessing the susceptibility of osteosarcoma cell lines with and without mitochondrial DNA to staurosporine-induced death. Our cells without mitochondrial DNA had low DeltaPsim and no functional oxidative phosphorylation. Contrary to our expectation, these cells were more resistant to staurosporine-induced death than were the parental cells. This reduced susceptibility was associated with decreased activation of caspase 3 but not with the mitochondrial permeability transition pore or cytochrome c release from the mitochondria. Apoptosis in both cell lines was associated with an increase in DeltaPsim. Bcl-x(L) could protect both cell types against caspase 3 activation and apoptosis by a mechanism that does not appear to be mediated by mitochondrial function or modulation of DeltaPsim. Nevertheless, we found that Bcl-x(L) expression can stimulate cell respiration in cells with mitochondrial DNA. Our results showed that the lack of functional oxidative phosphorylation and/or low mitochondrial membrane potential are associated with an antiapoptotic effect, possibly contributing to the development of some types of cancer. It also reinforces a model in which Bcl-x(L) can exert an antiapoptotic effect by stimulating oxidative phosphorylation and/or inhibiting caspase activation.     

The mitochondria-targeted imidazole substituted oleic acid ‘TPP-IOA’ affects mitochondrial bioenergetics and its protective efficacy in cells is influenced by cellular dependence on aerobic metabolism

A variety of mitochondria-targeted small molecules have been invented to manipulate mitochondrial redox activities and improve function in certain disease states. 3-Hydroxypropyl-triphenylphosphonium-conjugated imidazole-substituted oleic acid (TPP-IOA) was developed as a specific inhibitor of cytochrome c peroxidase activity that inhibits apoptosis by preventing cardiolipin oxidation and cytochrome c release to the cytosol. Here we evaluate the effects of TPP-IOA on oxidative phosphorylation in isolated mitochondria and on mitochondrial function in live cells. We demonstrate that, at concentrations similar to those required to achieve inhibition of cytochrome c peroxidase activity, TPP-IOA perturbs oxidative phosphorylation in isolated mitochondria. In live SH-SY5Y cells, TPP-IOA partially collapsed mitochondrial membrane potential, caused extensive fragmentation of the mitochondrial network, and decreased apparent mitochondrial abundance within 3 h of exposure. Many cultured cell lines rely primarily on aerobic glycolysis, potentially making them less sensitive to small molecules disrupting oxidative phosphorylation. We therefore determined the anti-apoptotic efficacy of TPP-IOA in SH-SY5Y cells growing in glucose or in galactose, the latter of which increases reliance on oxidative phosphorylation for ATP supply. The anti-apoptotic activity of TPP-IOA that was observed in glucose media was not seen in galactose media. It therefore appears that, at concentrations required to inhibit cytochrome c peroxidase activity, TPP-IOA perturbs oxidative phosphorylation. In light of these data it is predicted that potential future therapeutic applications of TPP-IOA will be restricted to highly glycolytic cell types with limited reliance on oxidative phosphorylation.     

Roles of sirtuins in the regulation of antioxidant defense and bioenergetic function of mitochondria under oxidative stress

Abstract

In addition to serving as the power house of mammalian cells, mitochondria are crucial for the maintenance of cellular homeostasis in response to physiological or environmental changes. Several lines of evidence suggest that posttranslational modification (PTM) of proteins plays a pivotal role in the regulation of the bioenergetic function of mitochondria. Among them, reversible lysine acetylation of mitochondrial proteins has been established as one of the key mechanisms in cellular response to energy demand by modulating the flux of a number of key metabolic pathways. In this article, we focus on the role of Sirt3-mediated deacetylation in: (1) flexibility of energy metabolism, (2) activation of antioxidant defense, and (3) maintenance of cellular redox status in response to dietary challenge and oxidative stress. We suggest that oxidative stress-elicited down-regulation of Sirt3 plays a role in the pathophysiology of diabetes, cardiac hypotrophy, mitochondrial diseases, and age-related diseases. Besides, the physiological role of newly identified lysine acylation mediated by Sirt5 and its biochemical effects on oxidative metabolism are also discussed. Moreover, we have integrated the regulatory function of several protein kinases that are involved in the phosphorylation of mitochondrial enzymes during oxidative stress. Finally, the functional consequence of the synergistic regulation through diverse protein modifications is emphasized on the maintenance of the bioenergetic homeostasis and metabolic adaptation of the animal and human cells. Together, we have provided an updated review of PTM in mitochondrial biology and their implications in aging and human diseases through an intricate regulation of energy metabolism under oxidative stress.     

Mitochondrial redox system,dynamics, and dysfunction in lung inflammaging and COPD

Myriad forms of endogenous and environmental stress disrupt mitochondrial function by impacting critical processes in mitochondrial homeostasis, such as mitochondrial redox system, oxidative phosphorylation, biogenesis, and mitophagy. External stressors that interfere with the steady state activity of mitochondrial functions are generally associated with an increase in reactive oxygen species, inflammatory response, and induction of cellular senescence (inflammaging) potentially via mitochondrial damage associated molecular patterns (DAMPS). Many of these are the key events in the pathogenesis of chronic obstructive pulmonary disease (COPD) and its exacerbations. In this review, we highlight the primary mitochondrial quality control mechanisms that are influenced by oxidative stress/redox system, including role of mitochondria during inflammation and cellular senescence, and how mitochondrial dysfunction contributes to the pathogenesis of COPD and its exacerbations via pathogenic stimuli.     

Mouse models of oxidative phosphorylation defects: powerful tools to study the pathobiology of mitochondrial diseases

Defects in the oxidative phosphorylation system (OXPHOS) are responsible for a group of extremely heterogeneous and pleiotropic pathologies commonly known as mitochondrial diseases. Although many mutations have been found to be responsible for OXPHOS defects, their pathogenetic mechanisms are still poorly understood. An important contribution to investigate the in vivo function of several mitochondrial proteins and their role in mitochondrial dysfunction, has been provided by mouse models. Thanks to their genetic and physiologic similarity to humans, mouse models represent a powerful tool to investigate the impact of pathological mutations on metabolic pathways. In this review we discuss the main mouse models of mitochondrial disease developed, focusing on the ones that directly affect the OXPHOS system.     

Comprehensive application of an mtDsRed2-Tg mouse strain for mitochondrial imaging

Mitochondria are essential for many cellular functions such as oxidative phosphorylation and calcium homeostasis; consequently, mitochondrial dysfunction could cause many diseases, including neurological disorders. Recently, mitochondrial dynamics, such as fusion, fission, and transportation, have been visualized in living cells by using time-lapse imaging systems. The changes in mitochondrial morphology could be an indicator for estimating the activity of mitochondrial biological function. Here, we report a transgenic mouse strain, mtDsRed2-Tg, which expresses a red fluorescent protein, DsRed2, exclusively in mitochondria. Mitochondrial morphology could be clearly observed in various tissues of this strain under confocal microscope. Recently, many transgenic mouse strains in which enhanced green fluorescent protein (EGFP)-tagged proteins of interest are expressed have been established for physiological analysis in vivo. After mating these strains with mtDsRed2-Tg mice, red-colored mitochondria and green-colored proteins were detected simultaneously using fluorescent imaging systems, and the interactions between mitochondria and those proteins could be morphologically analyzed in cells and tissues of the F₁ hybrids. Thus, mtDsRed2-Tg mice can be a powerful tool for bioimaging studies on mitochondrial functions.     

Mitochondrial quality control in cardiac cells: Mechanisms and role in cardiac cell injury and disease

Mitochondria play an important role in maintaining cardiac homeostasis by supplying the major energy required for cardiac excitation–contraction coupling as well as controlling the key intracellular survival and death pathways. Healthy mitochondria generate ATP molecules through an aerobic process known as oxidative phosphorylation (OXPHOS). Mitochondrial injury during myocardial infarction (MI) impairs OXPHOS and results in the excessive production of reactive oxygen species (ROS), bioenergetic insufficiency, and contributes to the development of cardiovascular diseases. Therefore, mitochondrial biogenesis along with proper mitochondrial quality control machinery, which removes unhealthy mitochondria is pivotal for mitochondrial homeostasis and cardiac health. Upon damage to the mitochondrial network, mitochondrial quality control components are recruited to segregate the unhealthy mitochondria and target aberrant mitochondrial proteins for degradation and elimination. Impairment of mitochondrial quality control and accumulation of abnormal mitochondria have been reported in the pathogenesis of various cardiac disorders and heart failure. Here, we provide an overview of the recent studies describing various mechanistic pathways underlying mitochondrial homeostasis with the main focus on cardiac cells. In addition, this review demonstrates the potential effects of mitochondrial quality control dysregulation in the development of cardiovascular disease.