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1.  Mitochondrial oxidative stress mediates Angiotensin II-induced cardiac hypertrophy and Gαq overexpression-induced heart failure 
Circulation research  2011;108(7):837-846.
Rationale
Mitochondrial dysfunction has been implicated in several cardiovascular diseases; however, the roles of mitochondrial oxidative stress and DNA damage in hypertensive cardiomyopathy are not well understood.
Objective
We evaluated the contribution of mitochondrial reactive oxygen species (ROS) to cardiac hypertrophy and failure by using genetic mouse models overexpressing catalase targeted to mitochondria and to peroxisomes.
Methods and Results
Angiotensin II increases mitochondrial ROS in cardiomyocytes, concomitant with increased mitochondrial protein carbonyls, mitochondrial DNA deletions, increased autophagy and signaling for mitochondrial biogenesis in hearts of Angiotensin II treated mice. The causal role of mitochondrial ROS in Angiotensin II-induced cardiomyopathy is shown by the observation that mice that overexpress catalase targeted to mitochondria, but not mice that overexpress wild-type peroxisomal catalase, are resistant to cardiac hypertrophy, fibrosis and mitochondrial damage induced by Angiotensin II, as well as heart failure induced by overexpression of Gαq. Furthermore, primary damage to mitochondrial DNA, induced by zidovudine administration or homozygous mutation of mitochondrial polymerase gamma, is also shown to contribute directly to the development of cardiac hypertrophy, fibrosis and failure.
Conclusions
These data indicate the critical role of mitochondrial ROS in cardiac hypertrophy and failure and support the potential use of mitochondrial-targeted antioxidants for prevention and treatment of hypertensive cardiomyopathy.
doi:10.1161/CIRCRESAHA.110.232306
PMCID: PMC3785241  PMID: 21311045
mitochondria; reactive oxygen species; angiotensin; cardiomyopathy; heart failure
2.  Mitochondrial targeted antioxidant peptide ameliorates hypertensive cardiomyopathy 
Objectives
We investigated the effect of reducing mitochondrial oxidative stress by the mitochondrial-targeted antioxidant peptide SS-31 in hypertensive cardiomyopathy.
Background
Oxidative stress has been implicated in hypertensive cardiovascular diseases. Mitochondria and NADPH oxidase have been proposed as primary sites of reactive oxygen species (ROS) generation.
Methods
The mitochondrial targeted antioxidant peptide SS-31 was used to determine the role of mitochondrial oxidative stress in Angiotensin II (Ang)-induced cardiomyopathy, as well as in Gαq overexpressing mice with heart failure.
Results
Angiotensin II induces mitochondrial ROS in neonatal cardiomyocytes, which is prevented by SS-31, but not the non-targeted antioxidant N-acetyl cysteine (NAC). Continuous administration of Ang for 4 weeks in mice significantly increased both systolic and diastolic blood pressure, and this was not affected by SS-31 treatment. Ang was associated with upregulation of NADPH oxidase 4 (NOX4) expression, increased cardiac mitochondrial protein oxidative damage and induced the signaling for mitochondrial biogenesis. Reducing mitochondrial ROS by SS-31 substantially attenuated Ang-induced NOX4 upregulation, mitochondrial oxidative damage, upregulation of mitochondrial biogenesis, phosphorylation of p38 MAP kinase, and prevented apoptosis, concomitant with amelioration of Ang induced cardiac hypertrophy, diastolic dysfunction, and fibrosis, despite the absence of blood pressure lowering effect. NAC did not show any beneficial effect. SS-31 administration for 4 weeks also partially rescued the heart failure phenotype of Gαq overexpressing mice.
Conclusions
Mitochondrial targeted peptide SS-31 ameliorates cardiomyopathy resulting from prolonged Ang stimulation as well as Gαq overexpression, suggesting its potential clinical application for target organ protection in hypertensive cardiovascular diseases.
doi:10.1016/j.jacc.2010.12.044
PMCID: PMC3742010  PMID: 21620606
mitochondria; hypertension; cardiomyopathy
3.  Mitochondrial targeted catalase suppresses invasive breast cancer in mice 
BMC Cancer  2011;11:191.
Background
Treatment of invasive breast cancer has an alarmingly high rate of failure because effective targets have not been identified. One potential target is mitochondrial generated reactive oxygen species (ROS) because ROS production has been associated with changes in substrate metabolism and lower concentration of anti-oxidant enzymes in tumor and stromal cells and increased metastatic potential.
Methods
Transgenic mice expressing a human catalase gene (mCAT) were crossed with MMTV-PyMT transgenic mice that develop metastatic breast cancer. All mice (33 mCAT positive and 23 mCAT negative) were terminated at 110 days of age, when tumors were well advanced. Tumors were histologically assessed for invasiveness, proliferation and metastatic foci in the lungs. ROS levels and activation status of p38 MAPK were determined.
Results
PyMT mice expressing mCAT had a 12.5 per cent incidence of high histological grade primary tumor invasiveness compared to a 62.5 per cent incidence in PyMT mice without mCAT. The histological grade correlated with incidence of metastasis with 56 per cent of PyMT mice positive for mCAT showing evidence of pulmonary metastasis compared to 85.4 per cent of PyMT mice negative for mCAT with pulmonary metastasis (p ≤ 0.05). PyMT tumor cells expressing mCAT had lower ROS levels and were more resistant to hydrogen peroxide-induced oxidative stress than wild type tumor cells, suggesting that mCAT has the potential of quenching intracellular ROS and subsequent invasive behavior. The metastatic tumor burden in PyMT mice expressing mCAT was 0.1 mm2/cm2 of lung tissue compared with 1.3 mm2/cm2 of lung tissue in PyMT mice expressing the wild type allele (p ≤ 0.01), indicating that mCAT could play a role in mitigating metastatic tumor progression at a distant organ site. Expression of mCAT in the lungs increased resistance to hydrogen peroxide-induced oxidative stress that was associated with decreased activation of p38MAPK suggesting ROS signaling is dependent on p38MAPK for at least some of its downstream effects.
Conclusion
Targeting catalase within mitochondria of tumor cells and tumor stromal cells suppresses ROS-driven tumor progression and metastasis. Therefore, increasing the antioxidant capacity of the mitochondrial compartment could be a rational therapeutic approach for invasive breast cancer.
Please see related commentary article: http://www.biomedcentral.com/1741-7015/9/62
doi:10.1186/1471-2407-11-191
PMCID: PMC3123323  PMID: 21605372
4.  Mitochondrial proteome remodelling in pressure overload-induced heart failure: the role of mitochondrial oxidative stress 
Cardiovascular Research  2011;93(1):79-88.
Aims
We investigate the role of mitochondrial oxidative stress in mitochondrial proteome remodelling using mouse models of heart failure induced by pressure overload.
Methods and results
We demonstrate that mice overexpressing catalase targeted to mitochondria (mCAT) attenuate pressure overload-induced heart failure. An improved method of label-free unbiased analysis of the mitochondrial proteome was applied to the mouse model of heart failure induced by transverse aortic constriction (TAC). A total of 425 mitochondrial proteins were compared between wild-type and mCAT mice receiving TAC or sham surgery. The changes in the mitochondrial proteome in heart failure included decreased abundance of proteins involved in fatty acid metabolism, an increased abundance of proteins in glycolysis, apoptosis, mitochondrial unfolded protein response and proteolysis, transcription and translational control, and developmental processes as well as responses to stimuli. Overexpression of mCAT better preserved proteins involved in fatty acid metabolism and attenuated the increases in apoptotic and proteolytic enzymes. Interestingly, gene ontology analysis also showed that monosaccharide metabolic processes and protein folding/proteolysis were only overrepresented in mCAT but not in wild-type mice in response to TAC.
Conclusion
This is the first study to demonstrate that scavenging mitochondrial reactive oxygen species (ROS) by mCAT not only attenuates most of the mitochondrial proteome changes in heart failure, but also induces a subset of unique alterations. These changes represent processes that are adaptive to the increased work and metabolic requirements of pressure overload, but which are normally inhibited by overproduction of mitochondrial ROS.
doi:10.1093/cvr/cvr274
PMCID: PMC3243039  PMID: 22012956
Mitochondria; Oxidative stress; Proteome; Pressure overload; Cardiomyopathy
5.  Age-Dependent Cardiomyopathy in Mitochondrial Mutator Mice is Attenuated by Overexpression of Catalase Targeted to Mitochondria 
Aging Cell  2010;9(4):536-544.
Mitochondrial defects have been found in aging and several age-related diseases. Mice with a homozygous mutation in the exonuclease encoding domain of mitochondrial DNA polymerase gamma (Polgm/m) are prone to age-dependent accumulation of mitochondrial DNA mutations and have shown a broad spectrum of aging-like phenotypes. However, the mechanism of cardiac phenotypes in relation to the role of mitochondrial DNA mutations and oxidative stress in this mouse model has not been fully addressed. We demonstrate age-dependent cardiomyopathy in Polgm/m mice, which by 13-14 months of age displays marked cardiac hypertrophy and dilatation, impairment of systolic and diastolic function and increased cardiac fibrosis. This age-dependent cardiomyopathy is associated with increases in mitochondrial DNA (mtDNA) deletions and protein oxidative damage, increased expression of apoptotic and senescence markers, as well as a decline in signaling for mitochondrial biogenesis. The relationship of these changes to mitochondrial reactive oxygen species (ROS) was tested by crossing Polgm/m mice with mice that overexpress mitochondrial targeted catalase (mCAT). All of the above phenotypes were partially rescued in Polgm/m/mCAT mice. These data indicate that accumulation of mitochondrial DNA damage with age can lead to cardiomyopathy, and that this phenotype is partly mediated by mitochondrial oxidative stress.
doi:10.1111/j.1474-9726.2010.00581.x
PMCID: PMC3265170  PMID: 20456298
mitochondria; mutation; aging; cardiomyopathy; oxidative stress
6.  Cardiac Aging in Mice and Humans: the Role of Mitochondrial Oxidative Stress 
Trends in cardiovascular medicine  2009;19(7):213-220.
Age is a major risk factor for cardiovascular diseases, not only because it prolongs exposure to several other cardiovascular risks, but also owing to intrinsic cardiac aging, which reduces cardiac functional reserve, predisposes the heart to stress and contributes to increased cardiovascular mortality in the elderly. Intrinsic cardiac aging in the murine model closely recapitulates age-related cardiac changes in humans, including left ventricular hypertrophy, fibrosis and diastolic dysfunction. Cardiac aging in mice is accompanied by accumulation of mitochondrial protein oxidation, increased mitochondrial DNA mutations, increased mitochondrial biogenesis, as well as decreased cardiac SERCA2 protein. All of these age-related changes are significantly attenuated in mice overexpressing catalase targeted to mitochondria (mCAT). These findings demonstrate the critical role of mitochondrial reactive oxygen species (ROS) in cardiac aging and support the potential application of mitochondrial antioxidants to cardiac aging and age-related cardiovascular diseases.
doi:10.1016/j.tcm.2009.12.004
PMCID: PMC2858758  PMID: 20382344
7.  Extension of mouse lifespan by overexpression of catalase 
Age  2006;28(2):209-218.
The free radical theory of aging was originally proposed 50 years ago, and is arguably the most popular mechanism explaining the aging process. According to this theory, aging results from the progressive decline in organ function due to the damage generated by reactive oxygen species (ROS). These chemical species are a normal part of metabolism, and a group of enzymes exists to protect cells against their toxic effects. One of these species is hydrogen peroxide (H2O2), which can be degraded by catalase. To determine the role of hydrogen peroxide in aging and its importance in different subcellular compartments, transgenic mice were developed with increased catalase activities localized to the peroxisome (PCAT), nucleus (NCAT), or mitochondrion (MCAT). The largest effect on lifespan was found in MCAT animals, with a 20% increase in median lifespan and a 10% increase in the maximum lifespan. A more modest effect was seen in PCAT animals, and no significant change was found in NCAT animals. Upon further examination of the MCAT mice, it was found that H2O2 production and H2O2-induced aconitase inactivation were attenuated, oxidative damage and the development of mitochondrial deletions were reduced, and cardiac pathology and cataract development were delayed. These results are consistent with a role of H2O2 in the development of pathology and in the limitation of mouse lifespan. They also demonstrate the importance of mitochondria as a source, and possible target, of ROS.
doi:10.1007/s11357-006-9010-z
PMCID: PMC2464724  PMID: 19943142
aconitase; aging; catalase; hydrogen peroxide; lifespan; mitochondria; mitochondrial DNA; reactive oxygen species; superoxide dismutase
8.  Overexpression of catalase targeted to mitochondria attenuates murine cardiac aging 
Circulation  2009;119(21):2789-2797.
Background:
Age is a major risk for cardiovascular diseases. Although mitochondrial reactive oxygen species (ROS) have been proposed as one of the causes of aging, their role in cardiac aging remains unclear. We have previously shown that overexpression of catalase targeted to mitochondria (mCAT) prolongs murine median lifespan by 17-21%.
Methods and Results:
We used echocardiography to study cardiac function in aging cohorts of wild type (WT) and mCAT mice. Changes found in WT mice recapitulate human aging: age-dependent increases in left ventricular mass index (LVMI) and left atrial dimension, worsening of the myocardial performance index (MPI), and a decline in diastolic function. Cardiac aging in mice is accompanied by accumulation of mitochondrial protein oxidation, increased mitochondrial DNA mutations and deletions and mitochondrial biogenesis, increased ventricular fibrosis, enlarged myocardial fiber size, decreased cardiac SERCA2 protein and activation of the calcineurin-NFAT pathway. All of these age-related changes were significantly attenuated in mCAT mice. Analysis of survival of 130 mice demonstrated that echocardiographic cardiac aging risk scores were significant predictors of mortality. The estimated attributable risk to mortality for these two parameters was 55%.
Conclusion:
This study shows that cardiac aging in the mouse closely recapitulates human aging and demonstrates the critical role of mitochondrial ROS in cardiac aging and the impact of cardiac aging on survival. These findings also support the potential application of mitochondrial antioxidants in ROS-related cardiovascular diseases.
doi:10.1161/CIRCULATIONAHA.108.822403
PMCID: PMC2858759  PMID: 19451351
aging; diastole; mitochondria; oxidant stress; survival
9.  Cathepsin E Deficiency Impairs Autophagic Proteolysis in Macrophages 
PLoS ONE  2013;8(12):e82415.
Cathepsin E is an endosomal aspartic proteinase that is predominantly expressed in immune-related cells. Recently, we showed that macrophages derived from cathepsin E-deficient (CatE−/−) mice display accumulation of lysosomal membrane proteins and abnormal membrane trafficking. In this study, we demonstrated that CatE−/− macrophages exhibit abnormalities in autophagy, a bulk degradation system for aggregated proteins and damaged organelles. CatE−/− macrophages showed increased accumulation of autophagy marker proteins such as LC3 and p62, and polyubiquitinated proteins. Cathepsin E deficiency also altered autophagy-related signaling pathways such as those mediated by the mammalian target of rapamycin (mTOR), Akt, and extracellular signal-related kinase (ERK). Furthermore, immunofluorescence microscopy analyses showed that LC3-positive vesicles were merged with acidic compartments in wild-type macrophages, but not in CatE−/− macrophages, indicating inhibition of fusion of autophagosome with lysosomes in CatE−/− cells. Delayed degradation of LC3 protein was also observed under starvation-induced conditions. Since the autophagy system is involved in the degradation of damaged mitochondria, we examined the accumulation of damaged mitochondria in CatE−/− macrophages. Several mitochondrial abnormalities such as decreased intracellular ATP levels, depolarized mitochondrial membrane potential, and decreased mitochondrial oxygen consumption were observed. Such mitochondrial dysfunction likely led to the accompanying oxidative stress. In fact, CatE−/− macrophages showed increased reactive oxygen species (ROS) production and up-regulation of oxidized peroxiredoxin-6, but decreased antioxidant glutathione. These results indicate that cathepsin E deficiency causes autophagy impairment concomitantly with increased aberrant mitochondria as well as increased oxidative stress.
doi:10.1371/journal.pone.0082415
PMCID: PMC3855462  PMID: 24340026
10.  Mitochondria-targeted catalase reduces abnormal APP processing, amyloid β production and BACE1 in a mouse model of Alzheimer's disease: implications for neuroprotection and lifespan extension 
Human Molecular Genetics  2012;21(13):2973-2990.
The purpose of this study was to investigate the protective effects of the mitochondria-targeted antioxidant catalase (MCAT) and lifespan extension in mice that express amyloid beta (Aβ). Using immunoblotting and immunostaining analyses, we measured the production of full-length amyloid precursor protein (APP), soluble APPα, C-terminal fragments CTF99 and CTF83, monomeric and oligomeric Aβ, Aβ deposits and beta site amyloid precursor protein cleaving enzyme 1 (BACE1), in different stages of disease progression in MCAT/AβPP and AβPP mice. Using quantitative reverse transcriptase polymerase chain reaction and immunostaining analyses, we studied the expression of catalase, BACE1, the Alzheimer's disease (AD) markers, synaptophysin, APP, neprilysin, insulin-degrading enzyme and transthyretin in MCAT, AβPP, MCAT/AβPP and wild-type (WT) mice. Using the high pressure liquid chromatography analysis of 8-hydroxy-2-deoxyguanosine, we measured oxidative DNA damage in the cerebral cortical tissues from MCAT, AβPP, MCAT/AβPP and WT mice. We found that the AβPP transgenic mice that carried the human MCAT gene lived 5 months longer than did the AβPP mice. We also found that the overexpression of MCAT in the brain sections from the MCAT/AβPP transgenic mice significantly correlated with a reduction in the levels of full-length APP, CTF99, BACE1, Aβ levels (40 and 42), Aβ deposits and oxidative DNA damage relative to the brain sections from the AβPP mice. Interestingly, we found significantly increased levels of soluble APPα and CTF83 in the MCAT/AβPP mice, relative to the AβPP mice. These data provide direct evidence that oxidative stress plays a primary role in AD etiopathology and that in MCAT mice express Aβ, MCAT prevents abnormal APP processing, reduces Aβ levels and enhances Aβ-degrading enzymes in mice at different ages, corresponding to different stages of disease progression. These findings indicate that mitochondria-targeted molecules may be an effective therapeutic approach to treat patients with AD.
doi:10.1093/hmg/dds128
PMCID: PMC3373244  PMID: 22492996
11.  Cardiac Aging: From Molecular Mechanisms to Significance in Human Health and Disease 
Antioxidants & Redox Signaling  2012;16(12):1492-1526.
Abstract
Cardiovascular diseases (CVDs) are the major causes of death in the western world. The incidence of cardiovascular disease as well as the rate of cardiovascular mortality and morbidity increase exponentially in the elderly population, suggesting that age per se is a major risk factor of CVDs. The physiologic changes of human cardiac aging mainly include left ventricular hypertrophy, diastolic dysfunction, valvular degeneration, increased cardiac fibrosis, increased prevalence of atrial fibrillation, and decreased maximal exercise capacity. Many of these changes are closely recapitulated in animal models commonly used in an aging study, including rodents, flies, and monkeys. The application of genetically modified aged mice has provided direct evidence of several critical molecular mechanisms involved in cardiac aging, such as mitochondrial oxidative stress, insulin/insulin-like growth factor/PI3K pathway, adrenergic and renin angiotensin II signaling, and nutrient signaling pathways. This article also reviews the central role of mitochondrial oxidative stress in CVDs and the plausible mechanisms underlying the progression toward heart failure in the susceptible aging hearts. Finally, the understanding of the molecular mechanisms of cardiac aging may support the potential clinical application of several “anti-aging” strategies that treat CVDs and improve healthy cardiac aging.
I. Introduction
II. Aging and Epidemiology of CVDs
III. Physiology of Cardiac Aging
A. Ventricular changes
B. Valvular changes
IV. Animal Models of Cardiac Aging
A. Rodents
B. Drosophila
C. Canines
D. Nonhuman primates
V. Mitochondria and the Free Radical Theory of Aging
A. ROS and aging
B. Pleiotropy of ROS
C. Mitochondrial hormesis in aging
D. Mitochondrial turnover in aging
VI. Molecular Mechanisms of Cardiac Aging
A. Mitochondrial oxidative stress in cardiac aging
B. Neurohormonal regulation of cardiac aging
1. Renin-angiotensin system in cardiac aging
2. B-adrenergic signaling
3. Insulin/insulin-like growth factor 1/PI3K signaling
4. Natriuretic peptides signaling
C. Nutrient signaling in cardiac aging
D. Cardiac stem cell aging and telomeres
VII. Aging, Oxidative Stress, and CVDs
A. Oxidative stress and mitochondria in CVDs
1. The central role of mitochondrial oxidative stress and redox status in hypertension and heart failure
2. The role of mitochondria and oxidative stress in IR injury
B. Mechanisms of progression to heart failure in the aged hypertrophic heart
1. Increased cardiomyocyte death
2. ECM remodeling
3. Alteration of calcium handling proteins
4. Hypoxic response and angiogenesis
5. Mitochondrial dysfunction and abnormalities in energetics
VIII. Exercise, Cardiovascular Risks, and Cardiac Aging
IX. Emerging “Anti-Aging” Interventional Strategies for Cardiac Aging and CVDs
A. Dietary restriction
B. Antioxidant interventions
1. Nontargeted antioxidants
2. Mitochondrial-targeted antioxidants
a. TPP+conjugated antioxidants
b. Szeto-schiller peptides
C. Resveratrol and SIRTs activators
X. Conclusion and Future Directions
doi:10.1089/ars.2011.4179
PMCID: PMC3329953  PMID: 22229339
12.  Mitochondrial Turnover and Aging of Long-Lived Postmitotic Cells: The Mitochondrial–Lysosomal Axis Theory of Aging 
Antioxidants & Redox Signaling  2010;12(4):503-535.
Abstract
It is now generally accepted that aging and eventual death of multicellular organisms is to a large extent related to macromolecular damage by mitochondrially produced reactive oxygen species, mostly affecting long-lived postmitotic cells, such as neurons and cardiac myocytes. These cells are rarely or not at all replaced during life and can be as old as the whole organism. The inherent inability of autophagy and other cellular-degradation mechanisms to remove damaged structures completely results in the progressive accumulation of garbage, including cytosolic protein aggregates, defective mitochondria, and lipofuscin, an intralysosomal indigestible material. In this review, we stress the importance of crosstalk between mitochondria and lysosomes in aging. The slow accumulation of lipofuscin within lysosomes seems to depress autophagy, resulting in reduced turnover of effective mitochondria. The latter not only are functionally deficient but also produce increased amounts of reactive oxygen species, prompting lipofuscinogenesis. Moreover, defective and enlarged mitochondria are poorly autophagocytosed and constitute a growing population of badly functioning organelles that do not fuse and exchange their contents with normal mitochondria. The progress of these changes seems to result in enhanced oxidative stress, decreased ATP production, and collapse of the cellular catabolic machinery, which eventually is incompatible with survival. Antioxid. Redox Signal. 12, 503–535.
Introduction
ROS, Mitochondrial Damage, and Aging
Biomolecular damage under normal conditions
Imperfect turnover of damaged biologic structures
Major targets of ROS attack: mitochondria and lysosomes
Mitochondrial Fusion, Fission, and Biogenesis
The role of mitochondrial dynamics
Mitochondrial fusion
Mitochondrial fission
Mitochondrial biogenesis
Mitochondrial Proteolytic Systems
Mitochondrial Turnover by Autophagy
The main functions of the lysosomal compartment
Autophagy
Autophagic degradation of mitochondria (mitophagy)
Lipofuscin Formation and Its Influence on Autophagy
Influence of labile iron and ROS on lipofuscin formation
Consequences of the nondegradability of lipofuscin
Disease-related accumulation of intralysosomal and extralysosomal waste
Imperfect Mitochondrial Turnover and Postmitotic Cellular Aging
Age-related accumulation of defective mitochondria within postmitotic cells
Age-related decline in autophagy and Lon protease activity accelerates mitochondrial damage
Enlarged mitochondria are resistant to degradation and do not fuse with normal ones
Mechanisms of the age-related accumulation of mitochondria with homoplasmic mtDNA mutations
Decreased mitochondrial biogenesis in aged cells
Summary and Conclusions
doi:10.1089/ars.2009.2598
PMCID: PMC2861545  PMID: 19650712
13.  Targeted Expression of Catalase to Mitochondria Prevents Age-Associated Reductions in Mitochondrial Function and Insulin Resistance 
Cell metabolism  2010;12(6):668-674.
SUMMARY
Aging-associated muscle insulin resistance has been hypothesized to be due to decreased mitochondrial function, secondary to cumulative free radical damage, leading to increased intramyocellular lipid content. To directly test this hypothesis we examined both in vivo and in vitro mitochondrial function, intramyocellular lipid content and insulin action in lean healthy mice with targeted overexpression of the human catalase gene to mitochondria (MCAT mice). Here we show that MCAT mice are protected from age-induced decrease in muscle mitochondrial function (~30%), energy metabolism (~7%) and lipid-induced muscle insulin resistance. This protection from age-induced reduction in mitochondrial function was associated with reduced mitochondrial oxidative damage, preserved mitochondrial respiration and muscle ATP synthesis and AMP-activated protein kinase-induced mitochondrial biogenesis. Taken together these data suggest that the preserved mitochondrial function maintained by reducing mitochondrial oxidative damage may prevent age-associated whole body energy imbalance and muscle insulin resistance.
doi:10.1016/j.cmet.2010.11.004
PMCID: PMC3013349  PMID: 21109199
14.  Bnip3-mediated mitochondrial autophagy is independent of the mitochondrial permeability transition pore 
Autophagy  2010;6(7):855-862.
Bnip3 is a pro-apoptotic BH3-only protein which is associated with mitochondrial dysfunction and cell death. Bnip3 is also a potent inducer of autophagy in many cells. In this study, we have investigated the mechanism by which Bnip3 induces autophagy in adult cardiac myocytes. Overexpression of Bnip3 induced extensive autophagy in adult cardiac myocytes. Fluorescent microscopy studies and ultrastructural analysis revealed selective degradation of mitochondria by autophagy in myocytes overexpressing Bnip3. Oxidative stress and increased levels of intracellular Ca2+ have been reported by others to induce autophagy, but Bnip3-induced autophagy was not abolished by antioxidant treatment or the Ca2+ chelator BAPTA-AM. We also investigated the role of the mitochondrial permeability transition pore (mPTP) in Bnip3-induced autophagy. Although the mPTP has previously been implicated in the induction of autophagy and selective removal of damaged mitochondria by autophagosomes, mitochondria sequestered by autophagosomes in Bnip3-treated cardiac myocytes had not undergone permeability transition and treatment with the mPTP inhibitor cyclosporine A did not inhibit mitochondrial autophagy in cardiac myocytes. Moreover, cyclophilin D (cypD) is an essential component of the mPTP and Bnip3 induced autophagy to the same extent in embryonic fibroblasts isolated from wild-type and cypD-deficient mice. These results support a model where Bnip3 induces selective removal of the mitochondria in cardiac myocytes and that Bnip3 triggers induction of autophagy independent of Ca2+, ROS generation and mPTP opening.
doi:10.4161/auto.6.7.13005
PMCID: PMC3039735  PMID: 20668412
Bnip3; autophagy; cardiac myocytes; mitochondria; permeability transition pore; cyclophilin D
15.  Cardiac-Specific Overexpression of Catalase Attenuates Lipopolysaccharide-Induced Myocardial Contractile Dysfunction: Role of Autophagy 
Free radical biology & medicine  2012;53(6):1327-1338.
Lipopolysaccharide (LPS) from Gram-negative bacteria is a major initiator of sepsis, leading to cardiovascular collapse. Accumulating evidence has indicated a role of reactive oxygen species (ROS) in cardiovascular complication in sepsis. This study was designed to examine the effect of cardiac-specific overexpression of catalase in LPS-induced cardiac contractile dysfunction and the underlying mechanism(s) with a focus on autophagy. Catalase transgenic and wild-type FVB mice were challenged with LPS (6 mg/kg) and cardiac function was evaluated. Levels of oxidative stress, autophagy, apoptosis and protein damage were examined using fluorescence microscopy, Western blot, TUNEL assay, caspase-3 activity and carbonyl formation. Kaplan-Meier curve was constructed for survival following LPS treatment. Our results revealed a lower mortality in catalase mice compared with FVB mice following LPS challenge. LPS injection led to depressed cardiac contractile capacity as evidenced by echocardiography and cardiomyocyte contractile function, the effect of which was ablated by catalase overexpression. LPS treatment induced elevated TNF-α level, autophagy, apoptosis (TUNEL, caspase-3 activation, cleaved caspase-3), production of ROS and O2−, and protein carbonyl formation, the effects of which were significantly attenuated by catalase overexpression. Electron microscopy revealed focal myocardial damage characterized by mitochondrial injury following LPS treatment, which was less severe in catalase mice. Interestingly, LPS-induced cardiomyocyte contractile dysfunction was prevented by antioxidant NAC and the autophagy inhibitor 3-methyladenine. Taken together, our data revealed that catalase protects against LPS-induced cardiac dysfunction and mortality, which may be associated with inhibition of oxidative stress and autophagy.
doi:10.1016/j.freeradbiomed.2012.07.084
PMCID: PMC3495589  PMID: 22902401
lipopolysaccharide; cardiac; contractile function; oxidative stress; autophagy
16.  Cyclophilin D is required for mitochondrial removal by autophagy in cardiac cells 
Autophagy  2010;6(4):462-472.
Autophagy is a highly regulated intracellular degradation process by which cells remove cytosolic long-lived proteins and damaged organelles. The mitochondrial permeability transition (MPT) results in mitochondrial depolarization and increased reactive oxygen species production, which can trigger autophagy. Therefore, we hypothesized that the MPT may have a role in signaling autophagy in cardiac cells. Mitochondrial membrane potential was lower in HL-1 cells subjected to starvation compared to cells maintained in full medium. Mitochondrial membrane potential was preserved in starved cells treated with cyclosporin A (CsA), suggesting the MPT pore is associated with starvation-induced depolarization. Starvation-induced autophagy in HL-1 cells, neonatal rat cardiomyocytes and adult mouse cardiomyocytes was inhibited by CsA. Starvation failed to induce autophagy in CypD-deficient murine cardiomyocytes, whereas in myocytes from mice overexpressing CypD the levels of autophagy were enhanced even under fed conditions. Collectively, these results demonstrate a role for CypD and the MPT in the initiation of autophagy. We also analyzed the role of the MPT in the degradation of mitochondria by biochemical analysis and electron microscopy. HL-1 cells subjected to starvation in the presence of CsA had higher levels of mitochondrial proteins (by Western blot), more mitochondria and less autophagosomes (by electron microscopy) then cells starved in the absence of CsA. Our results suggest a physiologic function for CypD and the MPT in the regulation of starvation-induced autophagy. Starvation-induced autophagy regulated by CypD and the MPT may represent a homeostatic mechanism for cellular and mitochondrial quality control.
doi:10.4161/auto.6.4.11553
PMCID: PMC3768271  PMID: 20364102
autophagy; cardiac myocyte; cyclophilin D; mitochondrial permeability transition
17.  Attenuation of Angiotensin II-induced Vascular Dysfunction and Hypertension by Overexpression of Thioredoxin-2 
Hypertension  2009;54(2):338-344.
Reactive oxygen species (ROS) increase in the cardiovascular system during hypertension and in response to angiotensin II. As mitochondria contribute to ROS-generation we sought to investigate the role of thioredoxin-2, a mitochondria specific antioxidant enzyme.
Mice were created with overexpression of human thioredoxin-2 (TghTrx2 mice) and backcrossed to C57BL/6J mice for at least 6 generations. 12 week old male TghTrx2 or littermate wild-type mice were made hypertensive by infusion of angiotensin II (400ng/kg per min) for 14 days using osmotic minipumps. Systolic arterial blood pressure was not different between TghTrx2 and wild-type animals under baseline conditions (101±1 resp. 102±1 mmHg). The angiotensin II-induced hypertension in wild-type (145±2 mmHg) was significantly attenuated in TghTrx2 mice (124±1 mmHg, p<0.001). Aortic endothelium-dependent relaxation was significantly reduced in wild-type following angiotensin II infusion, but nearly unchanged in transgenic mice. Elevated vascular superoxide and hydrogen peroxide levels as well as expression of NADPH oxidase subunits in response to angiotensin II infusion were significantly attenuated in TghTrx2 mice. Mitochondrial superoxide anion levels were augmented after angiotensin II infusion in wild-type mice, this was blunted in TghTrx2 mice. Angiotensin II infusion significantly increased myocardial superoxide formation, heart weight and cardiomyocyte size in wild-type, but not in TghTrx2 mice.
These data indicate a major role for mitochondrial thioredoxin-2 in the development of cardiovascular alterations and hypertension during chronic angiotensin II infusion. Thioredoxin-2 may represent an important therapeutic target for the prevention and treatment of hypertension and oxidative stress.
doi:10.1161/HYPERTENSIONAHA.108.127928
PMCID: PMC2752391  PMID: 19506101
angiotensin II; endothelial function; hypertension; mitochondria; thioredoxin-2; reactive oxygen species
18.  Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity 
Autophagy  2013;9(3):328-344.
Autophagy is a cellular self-digestion process that mediates protein quality control and serves to protect against neurodegenerative disorders, infections, inflammatory diseases and cancer. Current evidence suggests that autophagy can selectively remove damaged organelles such as the mitochondria. Mitochondria-induced oxidative stress has been shown to play a major role in a wide range of pathologies in several organs, including the heart. Few studies have investigated whether enhanced autophagy can offer protection against mitochondrially-generated oxidative stress. We induced mitochondrial stress in cardiomyocytes using antimycin A (AMA), which increased mitochondrial superoxide generation, decreased mitochondrial membrane potential and depressed cellular respiration. In addition, AMA augmented nuclear DNA oxidation and cell death in cardiomyocytes. Interestingly, although oxidative stress has been proposed to induce autophagy, treatment with AMA did not result in stimulation of autophagy or mitophagy in cardiomyocytes. Our results showed that the MTOR inhibitor rapamycin induced autophagy, promoted mitochondrial clearance and protected cardiomyocytes from the cytotoxic effects of AMA, as assessed by apoptotic marker activation and viability assays in both mouse atrial HL-1 cardiomyocytes and human ventricular AC16 cells. Importantly, rapamycin improved mitochondrial function, as determined by cellular respiration, mitochondrial membrane potential and morphology analysis. Furthermore, autophagy induction by rapamycin suppressed the accumulation of ubiquitinylated proteins induced by AMA. Inhibition of rapamycin-induced autophagy by pharmacological or genetic interventions attenuated the cytoprotective effects of rapamycin against AMA. We propose that rapamycin offers cytoprotection against oxidative stress by a combined approach of removing dysfunctional mitochondria as well as by degrading damaged, ubiquitinated proteins. We conclude that autophagy induction by rapamycin could be utilized as a potential therapeutic strategy against oxidative stress-mediated damage in cardiomyocytes.
doi:10.4161/auto.22971
PMCID: PMC3590254  PMID: 23298947
oxidative stress; mitochondrial dysfunction; autophagy; cardiomyocytes; rapamycin; MTOR
19.  Calorie Restriction Increases Muscle Mitochondrial Biogenesis in Healthy Humans 
PLoS Medicine  2007;4(3):e76.
Background
Caloric restriction without malnutrition extends life span in a range of organisms including insects and mammals and lowers free radical production by the mitochondria. However, the mechanism responsible for this adaptation are poorly understood.
Methods and Findings
The current study was undertaken to examine muscle mitochondrial bioenergetics in response to caloric restriction alone or in combination with exercise in 36 young (36.8 ± 1.0 y), overweight (body mass index, 27.8 ± 0.7 kg/m2) individuals randomized into one of three groups for a 6-mo intervention: Control, 100% of energy requirements; CR, 25% caloric restriction; and CREX, caloric restriction with exercise (CREX), 12.5% CR + 12.5% increased energy expenditure (EE). In the controls, 24-h EE was unchanged, but in CR and CREX it was significantly reduced from baseline even after adjustment for the loss of metabolic mass (CR, −135 ± 42 kcal/d, p = 0.002 and CREX, −117 ± 52 kcal/d, p = 0.008). Participants in the CR and CREX groups had increased expression of genes encoding proteins involved in mitochondrial function such as PPARGC1A, TFAM, eNOS, SIRT1, and PARL (all, p < 0.05). In parallel, mitochondrial DNA content increased by 35% ± 5% in the CR group (p = 0.005) and 21% ± 4% in the CREX group (p < 0.004), with no change in the control group (2% ± 2%). However, the activity of key mitochondrial enzymes of the TCA (tricarboxylic acid) cycle (citrate synthase), beta-oxidation (beta-hydroxyacyl-CoA dehydrogenase), and electron transport chain (cytochrome C oxidase II) was unchanged. DNA damage was reduced from baseline in the CR (−0.56 ± 0.11 arbitrary units, p = 0.003) and CREX (−0.45 ± 0.12 arbitrary units, p = 0.011), but not in the controls. In primary cultures of human myotubes, a nitric oxide donor (mimicking eNOS signaling) induced mitochondrial biogenesis but failed to induce SIRT1 protein expression, suggesting that additional factors may regulate SIRT1 content during CR.
Conclusions
The observed increase in muscle mitochondrial DNA in association with a decrease in whole body oxygen consumption and DNA damage suggests that caloric restriction improves mitochondrial function in young non-obese adults.
Anthony Civitarese and colleagues observed an increase in mitochondrial DNA in muscle and a decrease in whole body oxygen consumption in healthy adults who underwent caloric restriction.
Editors' Summary
Background.
Life expectancy (the average life span) greatly increased during the 20th century in most countries, largely due to improved hygiene, nutrition, and health care. One possible approach to further increase human life span is “caloric restriction.” A calorie-restricted diet provides all the nutrients necessary for a healthy life but minimizes the energy (calories) supplied in the diet. This type of diet increases the life span of mice and delays the onset of age-related chronic diseases such as heart disease and stroke. There are also hints that people who eat a calorie-restricted diet might live longer than those who overeat. People living in Okinawa, Japan, have a lower energy intake than the rest of the Japanese population and an extremely long life span. In addition, calorie-restricted diets beneficially affect several biomarkers of aging, including decreased insulin sensitivity (a precursor to diabetes). But how might caloric restriction slow aging? A major factor in the age-related decline of bodily functions is the accumulation of “oxidative damage” in the body's proteins, fats, and DNA. Oxidants—in particular, chemicals called “free radicals”—are produced when food is converted to energy by cellular structures called mitochondria. One theory for how caloric restriction slows aging is that it lowers free-radical production by inducing the formation of efficient mitochondria.
Why Was This Study Done?
Despite hints that caloric restriction might have similar effects in people as in rodents, there have been few well-controlled studies on the effect of good quality calorie-reduced diets in healthy people. It is also unknown whether an energy deficit produced by increasing physical activity while eating the same amount of food has the same effects as caloric restriction. Finally, it is unclear how caloric restriction alters mitochondrial function. The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) organization is investigating the effect of caloric restriction interventions on physiology, body composition, and risk factors for age-related diseases. In this study, the researchers have tested the hypothesis that short-term caloric deficit (with or without exercise) increases the efficiency of mitochondria in human muscle.
What Did the Researchers Do and Find?
The researchers enrolled 36 healthy overweight but non-obese young people into their study. One-third of them received 100% of their energy requirements in their diet; the caloric restriction (CR) group had their calorie intake reduced by 25%; and the caloric restriction plus exercise (CREX) group had their calorie intake reduced by 12.5% and their energy expenditure increased by 12.5%. The researchers found that a 25% caloric deficit for six months, achieved by diet alone or by diet plus exercise, decreased 24-hour whole body energy expenditure (i.e., overall calories burned for body function), which suggests improved mitochondrial function. Their analysis of genes involved in mitochondria formation indicated that CR and CREX both increased the number of mitochondria in skeletal muscle. Both interventions also reduced the amount of DNA damage—a marker of oxidative stress—in the participants' muscles.
What Do These Findings Mean?
These results indicate that a short-term caloric deficit, whether achieved by diet or by diet plus exercise, induces the formation of “efficient mitochondria” in people just as in rodents. The induction of these efficient mitochondria in turn reduces oxidative damage in skeletal muscles. Consequently, this adaptive response to caloric restriction might have the potential to slow aging and increase longevity in humans as in other animals. However, this six-month study obviously provides no direct evidence for this, and, by analogy with studies in rodents, an increase in longevity might require lifelong caloric restriction. The results here suggest that even short-term caloric restriction can produce beneficial physiological changes, but more research is necessary before it becomes clear whether caloric restriction should be recommended to healthy individuals.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040076.
The CALERIE (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy) Web site contains information on the study and how to participate
American Federation for Aging Research includes information on aging with pages on the biology of aging and on caloric restriction
The Okinawa Centenarian Study is a population-based study on long-lived elderly people in Okinawa, Japan
US Government information on nutrition
MedlinePlus encyclopedia pages on diet and calories
The Calorie Restriction Society, a nonprofit organization that provides information on life span and caloric restriction
Wikipedia pages on calorie restriction and on mitochondria (note: Wikipedia is an online encyclopedia that anyone can edit)
doi:10.1371/journal.pmed.0040076
PMCID: PMC1808482  PMID: 17341128
20.  Interaction of TNF with Angiotensin II Contributes to Mitochondrial Oxidative Stress and Cardiac Damage in Rats 
PLoS ONE  2012;7(10):e46568.
Recent evidence suggests that tumor necrosis factor alpha (TNF) and angiotensin II (ANGII) induce oxidative stress contribute to cardiovascular disease progression. Here, we examined whether an interaction between TNF and ANGII contributes to altered cardiac mitochondrial biogenesis and ATP production to cause cardiac damage in rats. Rats received intraperitoneal injections of TNF (30 µg/kg), TNF + losartan (LOS, 1 mg/kg), or vehicle for 5 days. Left ventricular (LV) function was measured using echocardiography. Rats were sacrificed and LV tissues removed for gene expression, electron paramagnetic resonance and mitochondrial assays. TNF administration significantly increased expression of the NADPH oxidase subunit, gp91phox, and the angiotensin type 1 receptor (AT-1R) and decreased eNOS in the LV of rats. Rats that received TNF only had increased production rates of superoxide, peroxynitrite and total reactive oxygen species (ROS) in the cytosol and increased production rates of superoxide and hydrogen peroxide in mitochondria. Decreased activities of mitochondrial complexes I, II, and III and mitochondrial genes were observed in rats given TNF. In addition, TNF administration also resulted in a decrease in fractional shortening and an increase in Tei index, suggesting diastolic dysfunction. TNF administration with concomitant LOS treatment attenuated mitochondrial damage, restored cardiac function, and decreased expression of AT1-R and NADPH oxidase subunits. Mitochondrial biogenesis and function is severely impaired by TNF as evidenced by downregulation of mitochondrial genes and increased free radical production, and may contribute to cardiac damage. These defects are independent of the downregulation of mitochondrial gene expression, suggesting novel mechanisms for mitochondrial dysfunction in rats given TNF.
doi:10.1371/journal.pone.0046568
PMCID: PMC3467241  PMID: 23056347
21.  High glucose-induced oxidative stress promotes autophagy through mitochondrial damage in rat notochordal cells 
International Orthopaedics  2013;37(12):2507-2514.
Purpose
Diabetes mellitus is associated with an increased risk of intervertebral disc degeneration (IDD). Reactive oxygen species (ROS), oxidative stressors, play a key role in autophagy of diabetes-associated diseases. Mitochondria are known to be the main source of endogenous ROS in most mammalian cell types. The authors therefore conducted the following study to evaluate the effects of high glucose concentrations on the induction of oxidative stress and autophagy through mitochondrial damage in rat notochordal cells.
Methods
Rat notochordal cells were isolated, cultured, and placed in either 10 % fetal bovine serum (normal control) or 10 % fetal bovine serum plus two different high glucose concentrations (0.1 M and 0.2 M) (experimental conditions) for one and three days, respectively. We identified and quantified the mitochondrial damage (mitochondrial transmembrane potential) and the generation of ROS and antioxidants (manganese superoxide dismutase [MnSOD] and catalase). We also investigated expressions and activities of autophagy markers (beclin-1, light chain3-I [LC3-I] and LC3-II, autophagy-related gene [Atg] 3, 5, 7, and 12).
Results
An enhanced disruption of mitochondrial transmembrane potential, which indicates mitochondrial damage, was identified in rat notochordal cells treated with both high glucose concentrations. Both high glucose concentrations increased production of ROS by rat notochordal cells in a dose- and time-dependent manner. The two high glucose solutions also enhanced rat notochordal cells’ compensatory expressions of MnSOD and catalase in a dose- and time-dependent manner. The proautophagic effects of high glucose concentrations were manifested in the form of enhanced rat notochordal cells’ expressions of beclin-1, LC3-II, Atg3, 5, 7, and 12 in a dose- and time-dependent manner. The ratio of LC3-II/LC3-I expression was also increased in a dose- and time-dependent manner.
Conclusions
The findings from this study demonstrate that high glucose-induced oxidative stress promotes autophagy through mitochondrial damage of rat notochordal cells in a dose- and time-dependent manner. These results suggest that preventing the generation of oxidative stress might be a novel therapeutic target by which to prevent or to delay IDD in patients with diabetes mellitus.
doi:10.1007/s00264-013-2037-8
PMCID: PMC3843215  PMID: 23907350
Autophagy; Mitochondral damage; Diabetes; High glucose concentration; Oxidative stress; Intervertebral disc degeneration; Reactive oxygen species
22.  ROCK1 plays an essential role in the transition from cardiac hypertrophy to failure in mice 
Pathological cardiac hypertrophy caused by diverse etiologies eventually leads to cardiac dilation and functional decompensation. We have recently reported that genetic deletion of Rho-associated coiled-coil containing protein kinase 1 (ROCK1) inhibited several pathological events including cardiomyocyte apoptosis in compensated hypertrophic hearts. The present study investigated whether ROCK1 deficiency can prevent the transition from hypertrophy to heart failure. Transgenic mice with cardiac-restricted overexpression of Gαq develop compensated cardiac hypertrophy at young ages, but progress into lethal cardiomyopathy accompanied by increased apoptosis after pregnancy or at old ages. The studies were first carried out using age- and pregnancy-matched wild-type (WT), Gαq, ROCK1−/−, and Gαq/ROCK1−/− mice. The potent beneficial effect of ROCK1 deletion is demonstrated by abolishment of peripartum mortality, and significant attenuation of left ventricular (LV) dilation, wall thinning, and contractile dysfunction in the peripartum Gαq transgenic mice. Increase in cardiomyocyte apoptosis was suppressed by ROCK1 deletion, associated with increased extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) activation and inhibition of mitochondrial translocation of Bax. In addition, ROCK1 deficiency also improved survival, inhibited cardiomyocyte apoptosis, and preserved LV dimension and function in old Gαq mice at 12 months. Furthermore, transgenic overexpression of ROCK1 increased cardiomyocyte apoptosis and accelerated hypertrophic decompensation in Gαq hearts in the absence of pregnancy stress. The present study provides for the first time in vivo evidence for the long-term beneficial effects of ROCK1 deficiency in hypertrophic decompensation and suggests that ROCK1 may be an attractive therapeutic target to limit heart failure progression.
doi:10.1016/j.yjmcc.2010.08.008
PMCID: PMC2949495  PMID: 20709073
Rho kinase; ROCK1; apoptosis; Gαq; ERK/MAPK; Bax; heart failure
23.  Mitochondria Oxidative Stress, Connexin43 Remodeling, and Sudden Arrhythmic Death 
Background
Previously, we showed a mouse model (ACE8/8) of cardiac renin-angiotensin system (RAS) activation has a high rate of spontaneous ventricular tachycardia (VT) and sudden cardiac death (SCD) secondary to a reduction in connexin43 (Cx43) level. Angiotensin-II activation increases reactive oxygen species (ROS) production, and ACE8/8 mice show increased cardiac ROS. We sought to determine the source of ROS and if ROS played a role in the arrhythmogenesis.
Methods and Results
Wild-type and ACE8/8 mice with and without two weeks of treatment with L-NIO (nitric oxide synthase inhibitor), sepiapterin (precursor of tetrahydrobiopterin), MitoTEMPO (mitochondria-targeted antioxidant), TEMPOL (a general antioxidant), apocynin (NADPH oxidase inhibitor), allopurinol (xanthine oxidase inhibitor), and ACE8/8 crossed with P67 dominant negative mice to inhibit the NADPH oxidase were studied. Western blotting, detection of mitochondrial ROS by MitoSOX Red, electron microscopy, immunohistochemistry, fluorescent dye diffusion technique for functional assessment of Cx43, telemetry monitoring, and in-vivo electrophysiology studies were performed. Treatment with MitoTEMPO reduced SCD in ACE8/8 mice (from 74% to 18%, P<0.005), decreased spontaneous ventricular premature beats, decreased VT inducibility (from 90% to 17%, P<0.05), diminished elevated mitochondrial ROS to the control level, prevented structural damage to mitochondria, resulted in 2.6 fold increase in Cx43 level at the gap junctions, and corrected gap junction conduction. None of the other antioxidant therapies prevented VT and SCD in ACE8/8 mice.
Conclusions
Mitochondrial oxidative stress plays a central role in angiotensin II-induced gap junction remodeling and arrhythmia. Mitochondria-targeted antioxidants may be effective antiarrhythmic drugs in cases of RAS activation.
doi:10.1161/CIRCEP.112.976787
PMCID: PMC3716298  PMID: 23559673
sudden cardiac death; ventricular tachycardia; oxidative stress; mitochondria
24.  Therapeutic Targeting of Mitochondrial Superoxide in Hypertension 
Circulation research  2010;107(1):106-116.
Rationale:
Superoxide (O2∸) has been implicated in the pathogenesis of many human diseases including hypertension, however commonly employed antioxidants have proven ineffective in clinical trials. It is possible that these agents are not adequately delivered to the subcellular sites of superoxide production.
Objective:
Because the mitochondria are important sources of reactive oxygen species, we postulated that mitochondrial targeting of superoxide scavenging would have therapeutic benefit.
Methods and Results:
In this study, we found that the hormone angiotensin II increased endothelial mitochondrial superoxide production. Treatment with the mitochondrial targeted antioxidant mitoTEMPO decreased mitochondrial O2∸, inhibited the total cellular O2∸, reduced cellular NADPH oxidase activity and restored the level of bioavailable NO. These effects were mimicked by overexpressing the mitochondrial MnSOD (SOD2), while SOD2 depletion with siRNA increased both basal and angiotensin II-stimulated cellular O2∸. Treatment of mice in vivo with mitoTEMPO attenuated hypertension when given at the onset of angiotensin II infusion and decreased blood pressure by 30 mm Hg following establishment of both angiotensin II-induced and DOCA-salt hypertension, while a similar dose of non-targeted TEMPOL was not effective. In vivo, mitoTEMPO decreased vascular O2∸, increased vascular NO• production and improved endothelial-dependent relaxation. Interestingly, transgenic mice overexpressing mitochondrial SOD2 demonstrated attenuated angiotensin II-induced hypertension and vascular oxidative stress similar to mice treated with mitoTEMPO.
Conclusions:
These studies show that mitochondrial O2∸ is important for the development of hypertension and that antioxidant strategies specifically targeting this organelle could have therapeutic benefit in this and possibly other diseases.
doi:10.1161/CIRCRESAHA.109.214601
PMCID: PMC2901409  PMID: 20448215
hypertension; mitochondria; superoxide; mitochondrial targeted antioxidant
25.  Hearts from Mice Fed a Non-Obesogenic High-Fat Diet Exhibit Changes in Their Oxidative State, Calcium and Mitochondria in Parallel with Increased Susceptibility to Reperfusion Injury 
PLoS ONE  2014;9(6):e100579.
Rationale
High-fat diet with obesity-associated co-morbidities triggers cardiac remodeling and renders the heart more vulnerable to ischemia/reperfusion injury. However, the effect of high-fat diet without obesity and associated co-morbidities is presently unknown.
Objectives
To characterize a non-obese mouse model of high-fat diet, assess the vulnerability of hearts to reperfusion injury and to investigate cardiac cellular remodeling in relation to the mechanism(s) underlying reperfusion injury.
Methods and Results
Feeding C57BL/6J male mice high-fat diet for 20 weeks did not induce obesity, diabetes, cardiac hypertrophy, cardiac dysfunction, atherosclerosis or cardiac apoptosis. However, isolated perfused hearts from mice fed high-fat diet were more vulnerable to reperfusion injury than those from mice fed normal diet. In isolated cardiomyocytes, high-fat diet was associated with higher diastolic intracellular Ca2+ concentration and greater damage to isolated cardiomyocytes following simulated ischemia/reperfusion. High-fat diet was also associated with changes in mitochondrial morphology and expression of some related proteins but not mitochondrial respiration or reactive oxygen species turnover rates. Proteomics, western blot and high-performance liquid chromatography techniques revealed that high-fat diet led to less cardiac oxidative stress, higher catalase expression and significant changes in expression of putative components of the mitochondrial permeability transition pore (mPTP). Inhibition of the mPTP conferred relatively more cardio-protection in the high-fat fed mice compared to normal diet.
Conclusions
This study shows for the first time that high-fat diet, independent of obesity-induced co-morbidities, triggers changes in cardiac oxidative state, calcium handling and mitochondria which are likely to be responsible for increased vulnerability to cardiac insults.
doi:10.1371/journal.pone.0100579
PMCID: PMC4065057  PMID: 24950187

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