4-hydroxy-2-nonenal and Hypertrophy--Left-Ventricular

Reactive oxygen species (ROS) are elevated in the heart in response to hemodynamic and metabolic stress and promote hypertrophic signaling. ROS also mediate the formation of lipid peroxidation-derived aldehydes that may promote myocardial hypertrophy. One lipid peroxidation by-product, 4-hydroxy-trans-2-nonenal (HNE), is a reactive aldehyde that covalently modifies proteins thereby altering their function. HNE adducts directly inhibit the activity of LKB1, a serine/threonine kinase involved in regulating cellular growth in part through its interaction with the AMP-activated protein kinase (AMPK), but whether this drives myocardial growth is unclear. We tested the hypothesis that HNE promotes myocardial protein synthesis and if this effect is associated with impaired LKB1-AMPK signaling. In adult rat ventricular cardiomyocytes, exposure to HNE (10 μM for 1h) caused HNE-LKB1 adduct formation and inhibited LKB1 activity. HNE inhibited the downstream kinase AMPK, increased hypertrophic mTOR-p70S6K-RPS6 signaling, and stimulated protein synthesis by 27.1 ± 3.5%. HNE also stimulated Erk1/2 signaling, which contributed to RPS6 activation but was not required for HNE-stimulated protein synthesis. HNE-stimulated RPS6 phosphorylation was completely blocked using the mTOR inhibitor rapamycin. To evaluate if LKB1 inhibition by itself could promote the hypertrophic signaling changes observed with HNE, LKB1 was depleted in adult rat ventricular myocytes using siRNA. LKB1 knockdown did not replicate the effect of HNE on hypertrophic signaling or affect HNE-stimulated RPS6 phosphorylation. Thus, in adult cardiac myocytes HNE stimulates protein synthesis by activation of mTORC1-p70S6K-RPS6 signaling most likely mediated by direct inhibition of AMPK. Because HNE in the myocardium is commonly increased by stimuli that cause pathologic hypertrophy, these findings suggest that therapies that prevent activation of mTORC1-p70S6K-RPS6 signaling may be of therapeutic value.

Topics: Aldehydes; AMP-Activated Protein Kinases; Animals; Cells, Cultured; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Hypertrophy, Left Ventricular; Lipid Peroxidation; Male; Mechanistic Target of Rapamycin Complex 1; Multiprotein Complexes; Myocardium; Myocytes, Cardiac; Phosphorylation; Protein Biosynthesis; Protein Serine-Threonine Kinases; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Ribosomal Protein S6; Ribosomal Protein S6 Kinases, 70-kDa; RNA Interference; RNA, Small Interfering; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Increasing evidence suggests a critical role for mitochondrial aldehyde dehydrogenase 2 (ALDH2) in protection against cardiac injuries; however, the downstream cytosolic actions of this enzyme are largely undefined.. Proteomic analysis identified a significant downregulation of mitochondrial ALDH2 in the heart of a rat heart failure model after myocardial infarction. The mechanistic insights underlying ALDH2 action were elucidated using murine models overexpressing ALDH2 or its mutant or with the ablation of the ALDH2 gene (ALDH2 knockout) and neonatal cardiomyocytes undergoing altered expression and activity of ALDH2. Left ventricle dilation and dysfunction and cardiomyocyte death after myocardial infarction were exacerbated in ALDH2-knockout or ALDH2 mutant-overexpressing mice but were significantly attenuated in ALDH2-overexpressing mice. Using an anoxia model of cardiomyocytes with deficiency in ALDH2 activities, we observed prominent cardiomyocyte apoptosis and increased accumulation of the reactive aldehyde 4-hydroxy-2-nonenal (4-HNE). We subsequently examined the impacts of mitochondrial ALDH2 and 4-HNE on the relevant cytosolic protective pathways. Our data documented 4-HNE-stimulated p53 upregulation via the phosphorylation of JNK, accompanying increased cardiomyocyte apoptosis that was attenuated by inhibition of p53. Importantly, elevation of 4-HNE also triggered a reduction of the cytosolic HSP70, further corroborating cytosolic action of the 4-HNE instigated by downregulation of mitochondrial ALDH2.. Downregulation of ALDH2 in the mitochondria induced an elevation of 4-HNE, leading to cardiomyocyte apoptosis by subsequent inhibition of HSP70, phosphorylation of JNK, and activation of p53. This chain of molecular events took place in both the mitochondria and the cytosol, contributing to the mechanism underlying heart failure.

Topics: Aldehyde Dehydrogenase; Aldehyde Dehydrogenase, Mitochondrial; Aldehydes; Animals; Animals, Newborn; Apoptosis; Cells, Cultured; Disease Models, Animal; Down-Regulation; Heart Failure; HSP70 Heat-Shock Proteins; Humans; Hypertrophy, Left Ventricular; JNK Mitogen-Activated Protein Kinases; Male; Mice, Inbred C57BL; Mice, Knockout; Mitochondria, Heart; Mitochondrial Proteins; Mutation; Myocardial Infarction; Myocardium; Phosphorylation; Rats, Sprague-Dawley; RNA Interference; Signal Transduction; Time Factors; Transfection; Tumor Suppressor Protein p53; Ventricular Dysfunction, Left; Ventricular Function, Left

Mitochondria are a principal site for generation of reactive oxygen species (ROS) in the heart. Peroxisome proliferator activated receptor gamma coactivator 1 alpha (PGC-1 alpha) plays an important role in regulating mitochondrial biogenesis and myocardial metabolism, but whether PGC-1 alpha can simultaneously upregulate myocardial mitochondrial antioxidants has not been studied. In the present study, we examined the effect of PGC-1 alpha deficiency (PGC-1 alpha(-/-)) on oxidative stress and expression of a group of mitochondrial antioxidants in normal hearts and in hearts exposed to chronic systolic pressure overload produced by transverse aortic constriction (TAC). We found that PGC-1 alpha(-/-) caused moderate but significant decreases of myocardial mitochondrial antioxidant enzymes such as SOD2, and thioredoxin (Trx2), but had no effect on expression of myocardial oxidative stress markers and left ventricular (LV) function under basal conditions. However, in response to TAC for 6 weeks, PGC-1 alpha(-/-) mice showed greater increases of myocardial oxidative stress markers 3'-nitrotyrosine and 4-hydroxynonenal, more severe LV hypertrophy and dilatation, pulmonary congestion, and a greater reduction of LV fractional shortening and dP/dt(max) than did wild-type hearts. SOD mimetic MnTMPyP treatment (6 mg/kg/day) significantly attenuated TAC-induced LV hypertrophy and dysfunction in PGC-1 alpha(-/-) mice. These data indicate that PGC-1 alpha plays an important role in regulating expression of myocardial mitochondrial antioxidants SOD2 and Trx2 and in protecting hearts against TAC-induced myocardial oxidative stress, hypertrophy, and dysfunction.

Topics: Aldehydes; Animals; Antioxidants; Heart Failure; Hypertension; Hypertrophy, Left Ventricular; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitochondria, Heart; Myocardial Contraction; Myocardium; Nitroso Compounds; Oxidative Stress; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Reactive Oxygen Species; Superoxide Dismutase; Systole; Thioredoxins; Trans-Activators; Transcription Factors; Tyrosine

Master regulators of protein synthesis such as mammalian target of rapamycin (mTOR) and p70S6 kinase contribute to left ventricular hypertrophy. These prohypertrophic pathways are modulated by a number of kinase cascades, including the hierarchical LKB1/AMP-activated protein kinase (AMPK) energy-sensing pathway. Because oxidative stress inhibits the LKB1/AMPK signaling axis to promote abnormal cell growth in cancer cells, we investigated whether oxidative stress associated with hypertension also results in the inhibition of this kinase circuit to contribute to left ventricular hypertrophy.. In the spontaneously hypertensive rat, a well-established genetic model of hypertension and subsequent cardiac hypertrophy, the development of left ventricular hypertrophy is associated with an increase in the electrophilic lipid peroxidation byproduct 4-hydroxy-2-nonenal (HNE). Using isolated cardiomyocytes, we show that elevated levels of HNE result in the formation of HNE-LKB1 adducts that inhibit LKB1 and subsequent AMPK activity. Consistent with inhibition of the LKB1/AMPK signaling pathway, the mTOR/p70S6 kinase system is activated, which is permissive for cardiac myocyte cell growth. Treatment of cardiomyocytes with resveratrol prevents HNE modification of the LKB1/AMPK signaling axis and blunts the prohypertrophic p70S6 kinase response. Furthermore, administration of resveratrol to spontaneously hypertensive rats results in increased AMPK phosphorylation and activity and reduced left ventricular hypertrophy.. Our data identify a molecular mechanism in the cardiomyocyte involving the oxidative stress-derived lipid peroxidation byproduct HNE and the LKB1/AMPK signaling pathway that contributes to the development of left ventricular hypertrophy. We also suggest that resveratrol may be a potential therapy for patients at risk for developing pathological cardiac hypertrophy by preventing this prohypertrophic process.

Topics: Aldehydes; AMP-Activated Protein Kinase Kinases; AMP-Activated Protein Kinases; Animals; Cardiomegaly; Cells, Cultured; Hypertension; Hypertrophy, Left Ventricular; Lipid Peroxidation; Myocytes, Cardiac; Oxidative Stress; Protein Kinases; Protein Serine-Threonine Kinases; Rats; Rats, Inbred SHR; Resveratrol; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Stilbenes; TOR Serine-Threonine Kinases

Elevated superoxide formation in cardiac extracts of apolipoprotein E-knockout (apoE-KO) mice has been reported. In addition, we previously reported that hypoxia increased oxidative stress in the aortas of apoE-KO mice, although we did not examine the effect of hypoxia on the heart. The aim of this study was to investigate the effect of chronic hypoxia on the left ventricular (LV) remodeling in apoE-KO mice treated with or without an angiotensin II receptor blocker. Male apoE-KO mice (n=83) and wild-type mice (n=34) at 15 weeks of age were kept under hypoxic conditions (oxygen, 10.0+/-0.5%) and treated with olmesartan (3 mg/kg/day) or vehicle for 3 weeks. Although LV pressure was not changed, hypoxia caused hypertrophy of cardiomyocytes and increased interstitial fibrosis in the LV myocardium. Furthermore, nuclear factor-kappaB (NF-kappaB) and matrix metalloproteinase (MMP)-9 activities were increased in apoE-KO mice exposed to chronic hypoxia. Olmesartan effectively suppressed the 4-hydroxy-2-nonenal protein expression and NF-kappaB and MMP-9 activities, and preserved the fine structure of the LV myocardium without affecting the LV pressure. In conclusion, olmesartan reduced oxidative stress, and attenuated the hypoxia-induced LV remodeling, in part through the inhibition of NF-kappaB and MMP-9 activities, in apoE-KO mice.

Topics: Aldehydes; Angiotensin II Type 1 Receptor Blockers; Animals; Apolipoproteins E; Heart Ventricles; Hypertrophy, Left Ventricular; Hypoxia; Imidazoles; Male; Matrix Metalloproteinase 9; Matrix Metalloproteinase Inhibitors; Mice; Mice, Knockout; Myocytes, Cardiac; NADPH Oxidases; NF-kappa B; Oxidative Stress; Superoxides; Tetrazoles; Ventricular Remodeling

Although NO derived from endothelial NO synthase (eNOS) is thought to be cardioprotective, the role of inducible NO synthase (iNOS) remains controversial. Using mice lacking iNOS (iNOS-/-), we studied (1) whether development of hypertension, cardiac hypertrophy, and dysfunction after deoxycorticosterone acetate (DOCA)-salt would be less severe compared with wild-type controls (WT; C57BL/6J), and (2) whether the cardioprotection attributable to lack of iNOS is mediated by reduced oxidative stress. Mice were uninephrectomized and received either DOCA-salt (30 mg/mouse SC and 1% NaCl+0.2% KCl in drinking water) or vehicle (tap water) for 12 weeks. Systolic blood pressure (SBP) was measured weekly. Left ventricular (LV) ejection fraction (EF) by echocardiography and cardiac response to isoproterenol (50 ng/mouse IV) were studied at the end of the experiment. Expression of eNOS and iNOS as well as the oxidative stress markers 4-hydroxy-2-nonenal (4-HNE, a marker of lipid peroxidation) and nitrotyrosine (a marker for peroxynitrite) were determined by Western blot and immunohistochemical staining, respectively. DOCA-salt increased SBP and LV weight similarly in both strains and decreased EF in WT but not in iNOS-/-. Cardiac contractile and relaxation responses to isoproterenol were greater, 4-HNE and nitrotyrosine levels were lower, and eNOS expression tended to be higher in iNOS-/-. We conclude that lack of iNOS leads to better preservation of cardiac function, which may be mediated by reduced oxidative stress and increased eNOS; however, it does not seem to play a significant role in preventing DOCA-salt-induced hypertension and hypertrophy.

Topics: Aldehydes; Animals; Blood Pressure; Cardiotonic Agents; Desoxycorticosterone; Heart; Hypertension; Hypertrophy, Left Ventricular; Isoproterenol; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Myocardium; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxidative Stress; Sodium Chloride; Tyrosine