Mitochondrial DNA damage triggers mitochondrial-superoxide generation and apoptosis
Department of Pharmacolgy, College of Medicine, University of South Alabama, Mobile, AL 36688, USA. AJP Cell Physiology
(Impact Factor: 3.78).
03/2008; 294(2):C413-22. DOI: 10.1152/ajpcell.00362.2007
Recently, it has become apparent that mitochondrial DNA (mtDNA) damage can rapidly initiate apoptosis independent of mutations, although the mechanism involved remains unclear. To elucidate this mechanism, angiotensin II-mediated apoptosis was studied in cells that were transduced with a lentiviral vector to overexpress the DNA repair enzyme 8-oxoguanine glycosylase or were treated with inhibitors known to block angiotensin II-induced mtDNA damage. Cells exhibiting angiotensin II-induced mtDNA damage showed two phases of superoxide generation, the first derived from NAD(P)H oxidase and the second of mitochondrial origin, whereas cells prevented from experiencing mtDNA damage importantly exhibited only the first phase. Furthermore, cells with mtDNA damage demonstrated impairments in mitochondrial protein expression, cellular respiration, and complex 1 activity before the onset of the second phase of oxidation. After the second phase, the mitochondrial membrane potential collapsed, cytochrome c was released, and the cells underwent apoptosis, all of which were prevented by disrupting mtDNA damage. Collectively, these data reveal a novel mechanism of apoptosis that is initiated when mtDNA damage triggers mitochondrial superoxide generation and ultimately the activation of the mitochondrial permeability transition. This novel mechanism may play an important pathological role.
Available from: plosone.org
- "This secondary production of ROS and lipid oxidation is most likely due to damage to the mitochondrial electron transport chain and/or the induction of NADPH oxidases. H2O2 has been shown to damage mitochondrial DNA and lipids as well as disrupt the electron transport chain, causing an increase in mitochondrial superoxide production , . In addition, recent evidence has emerged implicating H2O2 as a signaling molecule capable of stimulating ROS production via NADPH oxidases , . "
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ABSTRACT: The Nrf2 (NF-E2 related factor 2)-ARE (antioxidant response element) pathway controls a powerful array of endogenous cellular antioxidant systems and is an important pathway in the detoxification of reactive oxygen species (ROS) in the brain. Using a combination of quantitative proteomics and siRNA screening, we have identified novel protective mechanisms of the Nrf2-ARE pathway against oxidative stress in astrocytes. Studies from our lab and others have shown Nrf2 overexpression protects astrocytes from oxidative stress. However, the exact mechanisms by which Nrf2 elicits these effects are unknown. In this study, we show that induction of Nrf2 reduces levels of reactive oxygen species (ROS) produced by various oxidative stressors and results in robust cytoprotection. To identify the enzymes responsible for these effects, we used stable isotope labeling by amino acids in cell culture (SILAC) and quantitative shotgun proteomics to identify 72 Nrf2-regulated proteins in astrocytes. We hypothesized a subset of these proteins might play a critical role in Nrf2 protection. In order to identify these critical proteins, we used bioinformatics to narrow our target list of proteins and then systematically screened each candidate with siRNA to assess the role of each in Nrf2 protection. We screened each target against H2O2, tert-butyl hydroperoxide, and 4-hydroxynonenal and subsequently identified three enzymes-catalase, prostaglandin reductase-1, and peroxiredoxin-6-that are critical for Nrf2-mediated protection in astrocytes.
Available from: Julio Sergio Marchini
- "So, considering the critical role of oxidative stress in cardiac remodeling, we suggest that oxidative stress is associated with the cardiac dysfunction observed in our study. Oxidative stress has direct effects on cellular structure and function, and it can activate signaling molecules that are involved in cardiac remodeling, including apoptotic cascade , . In previous studies, taurine has been shown to promote antioxidant activity, regulating the rate of ROS generation by the mitochondria . "
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ABSTRACT: Micronutrient deficiency is observed in heart failure patients. Taurine, for example, represents 50% of total free amino acids in the heart, and in vivo studies have linked taurine deficiency with cardiomyopathy.
Thirty-four male Wistar rats (body weight = 100 g) were weighed and randomly assigned to one of two groups: Control (C) or taurine-deficient (T (-)). Beta-alanine at a concentration of 3% was added to the animals' water to induce taurine deficiency in the T (-) group. On day 30, the rats were individually submitted to echocardiography; morphometrical and histopathological evaluation and metalloproteinase activity, oxidative stress and inflammation evaluation were performed. Tissue samples were collected to determine the taurine concentration in the heart.
Taurine deficiency led to decreases in: ventricular wall thickness, left ventricle dry weight, myocyte sectional area, left ventricle posterior wall thickness and ventricular geometry. With regard to heart function, the velocity of the A wave, the ratio between the E and A wave, the ejection fraction, fractional shortening and cardiac output values were decreased in T (-) rats, suggesting abnormal diastolic and systolic function. Increased fibrosis, inflammation and increased activation of metalloproteinases were not observed. Oxidative stress was increased in deficient animals.
These data suggest that taurine deficiency promotes structural and functional cardiac alterations with unique characteristics.
Available from: Vasundhara Kain
- "This Ca 2 + overload and ROS production in mitochondria may act as a stimulus to trigger the apoptotic cascade or damage the integrity of the mitochondrial membrane to activate the death pathway. Various other stimuli like angiotensin II or isoproterenol injury independently or in conjunction with high-glucose treatment also activate ROS, RNS and calcium accumulation . It is therefore likely that these stimuli may also activate similar cell death signaling pathways which involves mobilization of cytosolic and mitochondrial calcium and ROS generation. "
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ABSTRACT: Cardiac cell apoptosis is the initiating factor of cardiac complications especially diabetic cardiomyopathy. Mitochondria are susceptible to the damaging effects of elevated glucose condition. Calcium overload and oxidative insult are the two mutually non-exclusive phenomena suggested to cause cardiac dysfunction. Here, we examined the effect of high-glucose induced calcium overload in calpain-1 mediated cardiac apoptosis in an in vitro setting.
H9c2, rat ventricular myoblast cell line was treated with elevated glucose condition and the cellular consequences were studied. Intracellular calcium trafficking, ROS generation, calpain-1 activation and caspase-12 and caspase-9 pathway were studied using flow cytometry, confocal microscopy and Western blot analysis.
High-glucose treatment resulted in increased intracellular calcium ([Ca2+]i) which was mobilized to the mitochondria. Concomitant intra-mitochondrial calcium ([Ca2+]m) increase resulted in enhanced reactive oxygen and nitrogen species generation. These events led to mitochondrial dysfunction and apoptosis. Cardiomyocyte death exhibited several classical markers of apoptosis, including activation of caspases, appearance of annexin V on the outer plasma membrane, increased population of cells with sub-G0/G1 DNA content and nuclear condensation. Key findings include elucidation of cell signaling mechanism of high-glucose induced calcium-dependent cysteine protease calpain-1 activation, which triggers non-conventional caspases as alternate mode of cell death.
This information increases the understanding of cardiac cell death under hyperglycemic condition and can possibly be extended for designing new therapeutic strategies for diabetic cardiomyopathy.
The novel findings of the study reveal that high glucose induces apoptosis by both mitochondria-dependent and independent pathways via concomitant rise in intracellular calcium.
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