Aortic constriction exacerbates atherosclerosis and induces cardiac dysfunction in mice lacking apolipoprotein E

Stress, Vascular Smooth Muscle Cell Phenotype and Atherosclerosis: Novel Insight into Smooth Muscle Cell Phenotypic Transition in Atherosclerosis

PURPOSE OF REVIEW

Our work is to establish more distinct association between specific stress and vascular smooth muscle cells (VSMCs) phenotypes to alleviate atherosclerotic plaque burden and delay atherosclerosis (AS) progression.

RECENT FINDING

In recent years, VSMCs phenotypic transition has received significant interests. Different stresses were found to be associated with VSMCs phenotypic transition. However, the explicit correlation between VSMCs phenotype and specific stress has not been elucidated clearly yet. We discover that VSMCs phenotypic transition, which is widely involved in the progression of AS, is associated with specific stress. We discuss approaches targeting stresses to intervene VSMCs phenotypic transition, which may contribute to develop innovative therapies for AS.

Direct Cardiac Actions of the Sodium Glucose Co-Transporter 2 Inhibitor Empagliflozin Improve Myocardial Oxidative Phosphorylation and Attenuate Pressure-Overload Heart Failure

Background We determined if the sodium glucose co-transporter 2 inhibitor empagliflozin attenuates pressure overload-induced heart failure in non-diabetic mellitus mice by direct cardiac effects and the mechanisms involved. Methods and Results Male C57BL/6J mice (4-6 months of age) were subjected to sham surgeries or transverse aortic constriction to produce cardiac pressure overload. Two weeks after transverse aortic constriction, empagliflozin (10 mg/kg per day) or vehicle was administered daily for 4 weeks. Empagliflozin increased survival rate and significantly attenuated adverse left ventricle remodeling and cardiac fibrosis after transverse aortic constriction. Empagliflozin also attenuated left ventricular systolic and diastolic dysfunction, evaluated by echocardiography, and increased exercise endurance by 36% in mice with transverse aortic constriction-induced heart failure. Empagliflozin significantly increased glucose and fatty acid oxidation in failing hearts, while reducing glycolysis. These beneficial cardiac effects of empagliflozin occurred despite no significant changes in fasting blood glucose, body weight, or daily urine volume. In vitro experiments in isolated cardiomyocytes indicated that empagliflozin had direct effects to improve cardiomyocyte contractility and calcium transients. Importantly, molecular docking analysis and isolated perfused heart experiments indicated that empagliflozin can bind cardiac glucose transporters to reduce glycolysis, restore activation of adenosine monophosphate-activated protein kinase and inhibit activation of the mammalian target of rapamycin complex 1 pathway. Conclusions Our study demonstrates that empagliflozin may directly bind glucose transporters to reduce glycolysis, rebalance coupling between glycolysis and oxidative phosphorylation, and regulate the adenosine monophosphate-activated protein kinase mammalian target of rapamycin complex 1 pathway to attenuate adverse cardiac remodeling and progression of heart failure induced by pressure-overload in non-diabetic mellitus mice.

Atherosclerosis in Different Vascular Locations Unbiasedly Approached with Mouse Genetics

Atherosclerosis in different vascular locations leads to distinct clinical consequences, such as ischemic stroke and myocardial infarction. Genome-wide association studies in humans revealed that genetic loci responsible for carotid plaque and coronary artery disease were not overlapping, suggesting that distinct genetic pathways might be involved for each location. While elevated plasma cholesterol is a common risk factor, plaque development in different vascular beds is influenced by hemodynamics and intrinsic vascular integrity. Despite the limitation of species differences, mouse models provide platforms for unbiased genetic approaches. Mouse strain differences also indicate that susceptibility to atherosclerosis varies, depending on vascular locations, and that the location specificity is genetically controlled. Quantitative trait loci analyses in mice suggested candidate genes, including Mertk and Stab2, although how each gene affects the location-specific atherosclerosis needs further elucidation. Another unbiased approach of single-cell transcriptome analyses revealed the presence of a small subpopulation of vascular smooth muscle cells (VSMCs), which are “hyper-responsive” to inflammatory stimuli. These cells are likely the previously-reported Sca1⁺ progenitor cells, which can differentiate into multiple lineages in plaques. Further spatiotemporal analyses of the progenitor cells are necessary, since their distribution pattern might be associated with the location-dependent plaque development.

Pressure overload by suprarenal aortic constriction in mice leads to left ventricular hypertrophy without c-Kit expression in cardiomyocytes

Animal models of pressure overload are valuable for understanding hypertensive heart disease. We characterised a surgical model of pressure overload-induced hypertrophy in C57BL/6J mice produced by suprarenal aortic constriction (SAC). Compared to sham controls, at one week post-SAC systolic blood pressure was significantly elevated and left ventricular (LV) hypertrophy was evident by a 50% increase in the LV weight-to-tibia length ratio due to cardiomyocyte hypertrophy. As a result, LV end-diastolic wall thickness-to-chamber radius (h/R) ratio increased, consistent with the development of concentric hypertrophy. LV wall thickening was not sufficient to normalise LV wall stress, which also increased, resulting in LV systolic dysfunction with reductions in ejection fraction and fractional shortening, but no evidence of heart failure. Pathological LV remodelling was evident by the re-expression of fetal genes and coronary artery perivascular fibrosis, with ischaemia indicated by enhanced cardiomyocyte Hif1a expression. The expression of stem cell factor receptor, c-Kit, was low basally in cardiomyocytes and did not change following the development of robust hypertrophy, suggesting there is no role for cardiomyocyte c-Kit signalling in pathological LV remodelling following pressure overload.

Xuezhitong capsule, an extract of Allium macrostemon Bunge, exhibits reverse cholesterol transport and accompanies high-density lipoprotein levels to protect against hyperlipidemia in ApoE-/- mice

Background

Xuezhitong capsules (XZT) are derived from Xie Bai and used for abnormal lipid homeostasis treatment through maintained metabolic balance. However, their mechanisms are largely unknown. Here, we mainly assessed the contribution of reverse cholesterol transport (RCT) and the accompanying increase in the high-density lipoprotein (HDL) effects of XZT to cholesterol dysfunction amelioration in mice.

Methods

We assessed serum lipids by using enzymatic kits. We observed atherosclerotic plaque formation by hematoxylin-eosin (HE) and Oil Red O staining. We studied the lipid metabolism, fatty acid synthase (FAS), HDL, low-density lipoprotein receptor (LDLR), triglyceride (TG) metabolic enzyme expression levels, and RCT function in various tissues upon stimulation with high-fat diet, XZT, and some positive drugs by ELISA.

Results

After 34 weeks of high-fat diet administration, blood lipids levels increased because attenuated by XZT treatment (800 and 1,600 mg/kg, i.g.). XZT improved the lipid metabolism instability, induced RCT activation, and subsequently increased the HDL levels in hyperlipidemic mice (P<0.05). FAS (P<0.05) and LDLR (P<0.01) levels also remarkably improved. The effects of XZT were closely associated with RCT activation and the accompanying increase in the HDL levels, as characterized by XZT-induced preservation in ATP-binding cassette transporter member 1 (ABCA1), scavenger receptor class B type 1 (SRB1), acyl coenzyme A: cholesterol acyltransferase (ACAT), lecithin cholesterol acyltransferase (LCAT), apolipoprotein A I (ApoA1) and apolipoprotein B (ApoB). However, XZT showed no effect on high fat diet-activated TG metabolic enzyme expression levels (P>0.05).

Conclusions

XZT are promising drugs in balancing the cholesterol dysfunction from hyperlipidemia through RCT activation and accompanying increase in HDL levels.

Preserved heart function after left ventricular pressure overload in adult mice subjected to neonatal cardiac hypoplasia

Intrauterine growth restriction in animal models reduces heart size and cardiomyocyte number at birth. Such incomplete cardiomyocyte endowment is believed to increase susceptibility toward cardiovascular disease in adulthood, a phenomenon referred to as developmental programming. We have previously described a mouse model of impaired myocardial development leading to a 25% reduction of cardiomyocyte number in neonates. This study investigated the response of these hypoplastic hearts to pressure overload in adulthood, applied by abdominal aortic constriction (AAC). Echocardiography revealed a similar hypertrophic response in hypoplastic hearts compared with controls over the first 2 weeks. Subsequently, control mice develop mild left ventricular (LV) dilation, wall thinning and contractile dysfunction 4 weeks after AAC, whereas hypoplastic hearts fully maintain LV dimensions, wall thickness and contractility. At the cellular level, controls exhibit increased cardiomyocyte cross-sectional area after 4 weeks pressure overload compared with sham operated animals, but this hypertrophic response is markedly attenuated in hypoplastic hearts. AAC mediated induction of fibrosis, apoptosis or cell cycle activity was not different between groups. Expression of fetal genes, indicative of pathological conditions, was similar in hypoplastic and control hearts after AAC. Among various signaling pathways involved in cardiac hypertrophy, pressure overload induces p38 MAP-kinase activity in hypoplastic hearts but not controls compared with the respective sham operated animals. In summary, based on the mouse model used in this study, our data indicates that adult hearts after neonatal cardiac hypoplasia show an altered growth response to pressure overload, eventually resulting in better functional outcome compared with controls.

Crossroads between peripheral atherosclerosis, western-type diet and skeletal muscle pathophysiology: emphasis on apolipoprotein E deficiency and peripheral arterial disease

Atherosclerosis is a chronic inflammatory process that, in the presence of hyperlipidaemia, promotes the formation of atheromatous plaques in large vessels of the cardiovascular system. It also affects peripheral arteries with major implications for a number of other non-vascular tissues such as the skeletal muscle, the liver and the kidney. The aim of this review is to critically discuss and assimilate current knowledge on the impact of peripheral atherosclerosis and its implications on skeletal muscle homeostasis. Accumulating data suggests that manifestations of peripheral atherosclerosis in skeletal muscle originates in a combination of increased i)-oxidative stress, ii)-inflammation, iii)-mitochondrial deficits, iv)-altered myofibre morphology and fibrosis, v)-chronic ischemia followed by impaired oxygen supply, vi)-reduced capillary density, vii)- proteolysis and viii)-apoptosis. These structural, biochemical and pathophysiological alterations impact on skeletal muscle metabolic and physiologic homeostasis and its capacity to generate force, which further affects the individual's quality of life. Particular emphasis is given on two major areas representing basic and applied science respectively: a)-the abundant evidence from a well-recognised atherogenic model; the Apolipoprotein E deficient mouse and the role of a western-type diet and b)-on skeletal myopathy and oxidative stress-induced myofibre damage from human studies on peripheral arterial disease. A significant source of reactive oxygen species production and oxidative stress in cardiovascular disease is the family of NADPH oxidases that contribute to several pathologies. Finally, strategies targeting NADPH oxidases in skeletal muscle in an attempt to attenuate cellular oxidative stress are highlighted, providing a better understanding of the crossroads between peripheral atherosclerosis and skeletal muscle pathophysiology.

Osborne-Mendel rats simultaneously develop cardiac and renal dysfunction, left atrial thrombosis, peripheral artery occlusion, and ascending aortic dissection

Although chronic kidney disease (CKD) is strongly associated with onsets of cardiovascular disease (CVD), the pathogenic mechanism between these diseases has not been fully understood. To develop and validate new therapeutic strategies for this complication, appropriate experimental models that reflect the complexity of the underlying pathophysiology are needed. The Osborne-Mendel (OM) rat was identified as an atherosclerosis-prone and a premature-death rat strain among 16 inbred rat strains when fed high-cholesterol containing diet. When fed high-cholesterol diet, OM rats showed simultaneous occurrence of aortic aneurysm, aortic dissection, peripheral artery occlusion, and left atrial thrombosis. OM rats had significantly lower max dP/dt and higher min dP/dt than F344 rats did, indicating impaired left ventricle contractility and relaxation. OM rats developed renal dysfunction, showing increased urinary albumin excretion. OM rats also showed mild hypertension, decreased endothelial function, and enhanced coagulation and platelet aggregation, compared with F344 rats. We now report that OM rat would be a novel spontaneous animal model which simultaneously demonstrates cardiac and renal dysfunction, and CVD events. This model could be a useful model for the pre-clinical testing of pharmacological therapies and could provide new insight into potential targets and pathways for the treatment of CKD and CVD.

Comprehensive MRI for the detection of subtle alterations in diastolic cardiac function in apoE/LDLR(-/-) mice with advanced atherosclerosis

ApoE/LDLR(-/-) mice represent a reliable model of atherosclerosis. However, it is not clear whether cardiac performance is impaired in this murine model of atherosclerosis. Here, we used MRI to characterize cardiac performance in vivo in apoE/LDLR(-/-) mice with advanced atherosclerosis. Six-month-old apoE/LDLR(-/-) mice and age-matched C57BL/6J mice (control) were examined using highly time-resolved cine-MRI [whole-chamber left ventricle (LV) imaging] and MR tagging (three slices: basal, mid-cavity and apical). Global and regional measures of cardiac function included LV volumes, kinetics, time-dependent parameters, strains and rotations. Histological analysis was performed using OMSB (orceine with Martius, Scarlet and Blue) and ORO (oil red-O) staining to demonstrate the presence of advanced coronary atherosclerosis. MR-tagging-based strain analysis in apoE/LDLR(-/-) mice revealed an increased frequency of radial and circumferential systolic stretch (25% and 50% of segments, respectively, p ≤ 0.012), increased radial post-systolic strain index (45% of segments, p = 0.009) and decreased LV untwisting rate (-30.3° (11.6°)/cycle, p = 0.004) when compared with control mice. Maximal strains and LV twist were unchanged. Most of the cine-MRI-based LV functional and anatomical parameters also remained unchanged in apoE/LDLR(-/-) mice, with only a lower filling rate, longer filling time, shorter isovolumetric contraction time and slower heart rate observed in comparison with control mice. The coronary arteries displayed severe atherosclerosis, as evidenced by histological analysis. Using comprehensive MRI methods, we have demonstrated that, despite severe coronary atherosclerosis in six-month-old apoE/LDLR(-/-) mice, cardiac performance including global parameters, twist and strains, was well preserved. Only subtle diastolic alterations, possibly of ischemic background, were uncovered. Copyright © 2016 John Wiley & Sons, Ltd.

Serum neutrophil gelatinase-associated lipocalin concentration reflects severity of coronary artery disease in patients without heart failure and chronic kidney disease

Serum neutrophil gelatinase-associated lipocalin (NGAL) is recognized as a useful biomarker for acute kidney injury. Recently, elevated NGAL levels were reported in patients with heart failure and cardiac events, but the association between serum NGAL and severity of coronary artery disease (CAD) has not been investigated adequately. This study aimed to evaluate the association between serum NGAL concentration and CAD severity in patients without heart failure and chronic kidney disease. Two-hundred thirteen patients [mean age: 66.2 ± 9.2 (SD)] without heart failure and chronic kidney disease (estimated glomerular filtration rate >60 mL/min/1.73 m(2)) who underwent coronary angiography were retrospectively analyzed using the SYNTAX score. The mean concentration of serum NGAL was 134.3 ± 111.3 ng/mL. A statistically significant correlation was observed between serum NGAL levels and the SYNTAX score (R = 0.18, P = 0.0091). Multivariable analysis also showed elevated serum NGAL as an independent risk factor for a high SYNTAX score (P < 0.01). Moreover, we evaluated the association of serum NGAL and brain natriuretic peptide (BNP) with the SYNTAX score. Patients with high levels of serum NGAL (>100 ng/mL) and high levels of BNP (>25 pg/mL) had a higher SYNTAX score (low-low vs. high-high: 13.8 ± 13.4 vs. 20.8 ± 18.9, P < 0.05). Serum NGAL levels were positively and significantly associated with CAD severity, and the evaluation of both serum NGAL and BNP was useful for predicting CAD in patients without renal dysfunction and heart failure. Serum NGAL might be a biomarker for CAD severity.

FGF23 directly impairs endothelium-dependent vasorelaxation by increasing superoxide levels and reducing nitric oxide bioavailability

Fibroblast growth factor 23 (FGF23) is secreted primarily by osteocytes and regulates phosphate and vitamin D metabolism. Elevated levels of FGF23 are clinically associated with endothelial dysfunction and arterial stiffness in chronic kidney disease (CKD) patients; however, the direct effects of FGF23 on endothelial function are unknown. We hypothesized that FGF23 directly impairs endothelial vasorelaxation by hindering nitric oxide (NO) bioavailability. We detected expression of all four subtypes of FGF receptors (Fgfr1-4) in male mouse aortas. Exogenous FGF23 (90-9,000 pg/ml) did not induce contraction of aortic rings and did not relax rings precontracted with PGF2α. However, preincubation with FGF23 (9,000 pg/ml) caused a ∼36% inhibition of endothelium-dependent relaxation elicited by acetylcholine (ACh) in precontracted aortic rings, which was prevented by the FGFR antagonist PD166866 (50 nM). Furthermore, in FGF23-pretreated (9,000 pg/ml) aortic rings, we found reductions in NO levels. We also investigated an animal model of CKD (Col4a3(-/-) mice) that displays highly elevated serum FGF23 levels and found they had impaired endothelium-dependent vascular relaxation and reduced nitrate production compared with age-matched wild types. To elucidate a mechanism for the FGF23-induced impairment, we measured superoxide levels in endothelial cells and aortic rings and found that they were increased following FGF23 treatment. Crucially, treatment with the superoxide scavenger tiron reduced superoxide levels and also restored aortic relaxation to ACh. Therefore, our data suggest that FGF23 increases superoxide, inhibits NO bioavailability, and causes endothelial dysfunction in mouse aorta. Together, these data provide evidence that high levels of FGF23 contribute to cardiovascular dysfunction.

Protective effect of resveratrol against pressure overload-induced heart failure

Transverse aortic constriction (TAC)-induced pressure overload (PO) causes adverse cardiac remodeling and dysfunction that progresses to heart failure (HF). The purpose of this study was to determine whether the potent antioxidant, resveratrol, significantly attenuates PO-induced HF in wild-type mice. Male C57BL6 mice were subjected to either sham or TAC surgery. One group of TAC mice was given daily resveratrol treatment. Echocardiographic, biometric, and immunohistological analyses were performed on the three groups of mice. All echocardiographic parameters demonstrated significantly greater adverse cardiac remodeling and dysfunction in the TAC compared to the sham mice. Increases in the ratios of heart weight (HW)/body weight (BW) and lung weight (LW)/BW and a sharp decline in the percentage of ejection fraction and fractional shortening were found in TAC relative to sham mice. Likewise, the TAC protocol increased markers of oxidative stress, cardiac hypertrophy, inflammation, fibrosis, hypoxia, and apoptosis. These pathological changes were significantly attenuated by resveratrol treatment. Resveratrol treatment significantly attenuates the adverse cardiac remodeling and dysfunction produced by the TAC protocol in C57/BL6 mice and this activity is mediated, at least in part, by the inhibition of oxidative stress and inflammation indicating a therapeutic potential of resveratrol in HF.

Cathepsin K knockout alleviates pressure overload-induced cardiac hypertrophy

Evidence from human and animal studies has documented elevated levels of lysosomal cysteine protease cathepsin K in failing hearts. Here, we hypothesized that ablation of cathepsin K mitigates pressure overload-induced cardiac hypertrophy. Cathepsin K knockout mice and their wild-type littermates were subjected to abdominal aortic constriction, resulting in cardiac remodeling (heart weight, cardiomyocyte size, left ventricular wall thickness, and end diastolic and end systolic dimensions) and decreased fractional shortening, the effects of which were significantly attenuated or ablated by cathepsin K knockout. Pressure overload dampened cardiomyocyte contractile function along with decreased resting Ca2+ levels and delayed Ca2+ clearance, which were partly resolved by cathepsin K knockout. Cardiac mammalian target of rapamycin and extracellular signal-regulated kinases (ERK) signaling cascades were upregulated by pressure overload, the effects of which were attenuated by cathepsin K knockout. In cultured H9c2 myoblast cells, silencing of cathepsin K blunted, whereas cathepsin K transfection mimicked phenylephrine-induced hypertrophic response, along with elevated phosphorylation of mammalian target of rapamycin and ERK. In addition, cathepsin K protein levels were markedly elevated in human hearts of end-stage dilated cardiomyopathy. Collectively, our data suggest that cathepsin K ablation mitigates pressure overload-induced hypertrophy, possibly via inhibition of the mammalian target of rapamycin and ERK pathways.

Signaling pathways of apoE and its role of gene expression in glomerulus diseases

The roles of apolipoprotein E (apoE) in regulating plasma lipids and lipoproteins levels have been investigated for over several decades. However, in different tissues/cells, the role of apoE was different, such as that it was a risk factor for cancer, but some reports stated that apoE was a protective factor for renal diseases. At the moment, most of the studies find that apoE not only acts as a ligand for metabolism of lipids, but also plays as a factor to regulate lots of signaling pathways. There was rare review to sum up the signaling pathways for apoE, and there was also rare review to widely review the gene expression of apoE in glomerulus diseases. This review was performed to provide a relatively complete signaling pathways flowchart for apoE to the investigators who were interested in the roles of apoE in the pathogenesis of glomerulus diseases. In the past decades, some studies were also performed to explore the association of apoE gene expression with the risk of glomerulus diseases. However, the role of apoE in the pathogenesis of glomerulus diseases was controversial. Here, the signal transduction pathways of apoE and its role of gene expression in the pathogenesis of glomerulus diseases were reviewed.

mTOR-STAT3-notch signalling contributes to ALDH2-induced protection against cardiac contractile dysfunction and autophagy under alcoholism

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) has been shown to benefit myopathic changes following alcohol intake, although the precise mechanism is still unclear. This study was designed to evaluate the role of ALDH2 on chronic alcohol intake-induced myocardial geometric and functional damage with a focus on autophagic signalling. Wild-type friendly virus B (FVB) and transgenic mice overexpressing ALDH2 driven by chicken β-actin promoter were fed a 4% alcohol liquid diet for 12 weeks. Cardiac geometry and function were assessed using echocardiographic and IonOptix systems. Western blot analysis was used to evaluate the essential autophagy markers, Akt and AMP-dependent protein kinase (AMPK) as well as their downstream signalling mammalian target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3). Alcohol intake altered cardiac geometry and function as demonstrated by lessened LV wall and septal thickness, enlarged end systolic and diastolic diameters, decreased fractional shortening and cell shortening, the effects of which were mitigated by ALDH2 transgene. Chronic alcohol intake triggered myocardial autophagy as shown by LC3B II isoform switch, as well as decreased phosphorylation of mTOR, the effects of which were ablated by ALDH2. Chronic alcohol intake suppressed phosphorylation of Akt and AMPK, which was reconciled by ALDH2. Levels of Notch1 and STAT3 phosphorylation were dampened by chronic alcohol intake in FVB but not ALDH2 myocardium. Moreover, the γ-secretase Notch inhibitor N-[N-(3,5-difluorophenacetyl)-1-alany1]-S-phenyglycine t-butyl ester exacerbated ethanol-induced cardiomyocyte contractile dysfunction, apoptosis and autophagy. In summary, these findings suggested that ALDH2 elicits cardioprotection against chronic alcohol intake-induced cardiac geometric and functional anomalies by inhibition of autophagy possibly via restoring the Akt-mTOR-STAT3-Notch signalling cascade.

IGF-1 deficiency resists cardiac hypertrophy and myocardial contractile dysfunction: role of microRNA-1 and microRNA-133a

This study was designed to examine the impact of insulin-like growth factor-1 (IGF-1) deficiency on abdominal aortic constriction (AAC)-induced cardiac geometric and functional changes with a focus on microRNA-1, 133a and 208, which are specially expressed in hearts and govern cardiac hypertrophy and stress-dependent cardiac growth. Liver-specific IGF-1-deficient (LID) and C57/BL6 mice were subject to AAC. Echocardiographic and cardiomyocyte function were assessed 4 wks later. Haematoxylin and eosin staining was used to monitor myocardial morphology. Western blot and real-time PCR were used to detect protein and miR expression, respectively. Neonatal rat cardiomyocytes (NRCMs) were transfected with miRs prior to IGF-1 exposure to initiate cell proliferation. Immunohistochemistry and [³H] Leucine incorporation were used to detect cell surface area and protein abundance. C57 mice subject to AAC displayed increased ventricular wall thickness, decreased left ventricular end diastolic and end systolic dimensions and elevated cardiomyocyte shortening capacity, all of which were attenuated in LID mice. In addition, IGF-1 deficiency mitigated AAC-induced increase in atrial natriuretic factor, GATA binding protein 4, glucose transporter 4 (GLUT4) and Akt phosphorylation. In contrast, neither AAC treatment nor IGF-1 deficiency affected glycogen synthase kinase 3b, mammalian target of rapamycin, the Glut-4 translocation mediator Akt substrate of 160 kD (AS160) and protein phosphatase. Levels of miR-1 and -133a (but not miR-208) were significantly attenuated by AAC in C57 but not LID mice. Transfection of miR-1 and -133a obliterated IGF-1-induced hypertrophic responses in NRCMs. Our data suggest that IGF-1 deficiency retards AAC-induced cardiac hypertrophic and contractile changes via alleviating down-regulation of miR-1 and miR-133a in response to left ventricular pressure overload.

Cardiac and vascular phenotypes in the apolipoprotein E-deficient mouse

Cardiovascular death is frequently associated with atherosclerosis, a chronic multifactorial disease and a leading cause of death worldwide. Genetically engineered mouse models have proven useful for the study of the mechanisms underlying cardiovascular diseases. The apolipoprotein E-deficient mouse has been the most widely used animal model of atherosclerosis because it rapidly develops severe hypercholesterolemia and spontaneous atherosclerotic lesions similar to those observed in humans. In this review, we provide an overview of the cardiac and vascular phenotypes and discuss the interplay among nitric oxide, reactive oxygen species, aging and diet in the impairment of cardiovascular function in this mouse model.

Up-regulation of the cardiac lipid metabolism at the onset of heart failure

Chronic pressure overload and atherosclerosis are primary etiologic factors for cardiac hypertrophy and failure. However, mechanisms underlying the transition from hypertrophy to heart failure are incompletely understood. We analyzed the development of heart failure in mice with chronic pressure overload induced by aortic constriction and compared the results with aged apolipoprotein E-deficient mice suffering from advanced atherosclerosis. We combined cardiac function analysis by echocardiography and invasive hemodynamics with a comprehensive microarray gene expression study (GSE25765-8). The microarray data showed that the onset of heart failure induced by pressure overload or advanced atherosclerosis was accompanied by a strong up-regulation of key lipid metabolizing enzymes involved in fat synthesis, storage and oxidation. Cardiac lipid overload may be involved in the progression of heart failure by enhancing cardiomyocyte death. Up-regulation of the cardiac lipid metabolism was related to oxygen and ATP depletion of failing hearts because anti-ischemic treatment with ranolazine normalized the cardiac lipid metabolism and improved cardiac function. Vice versa, inhibition of cellular respiration and ATP generation by mild thiol-blocking with cystamine triggered the cardiac lipid metabolism and caused signs of heart failure. Cardiac tissue specimens of patients with heart failure also showed high protein levels of key fat metabolizing enzymes as well as lipid accumulation. Taken together, our data strongly indicate that up-regulation of the cardiac lipid metabolism and myocardial lipid overload are underlying the development of heart failure.

AMP-dependent kinase and autophagic flux are involved in aldehyde dehydrogenase-2-induced protection against cardiac toxicity of ethanol

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) alleviates ethanol toxicity although the precise mechanism is unclear. This study was designed to evaluate the effect of ALDH2 on ethanol-induced myocardial damage with a focus on autophagy. Wild-type FVB and transgenic mice overexpressing ALDH2 were challenged with ethanol (3g/kg/day, ip) for 3days and cardiac mechanical function was assessed using the echocardiographic and IonOptix systems. Western blot analysis was used to evaluate essential autophagy markers, Akt and AMPK, and the downstream signal mTOR. Ethanol challenge altered cardiac geometry and function as evidenced by enlarged ventricular end systolic and diastolic diameters, decreased cell shortening and intracellular Ca(2+) rise, prolonged relengthening and intracellular Ca(2+) decay, as well as reduced SERCA Ca(2+) uptake, which effects were mitigated by ALDH2. Ethanol challenge facilitated myocardial autophagy as evidenced by enhanced expression of Beclin, ATG7, and LC3B II, as well as mTOR dephosphorylation, which was alleviated by ALDH2. Ethanol challenge-induced cardiac defect and apoptosis were reversed by the ALDH2 agonist Alda-1, the autophagy inhibitor 3-MA, and the AMPK inhibitor compound C, whereas the autophagy inducer rapamycin and the AMPK activator AICAR mimicked or exacerbated ethanol-induced cell injury. Ethanol promoted or suppressed phosphorylation of AMPK and Akt, respectively, in FVB but not ALDH2 murine hearts. Moreover, AICAR nullified Alda-1-induced protection against ethanol-triggered autophagic and functional changes. Ethanol increased GFP-LC3 puncta in H9c2 cells, the effect of which was ablated by Alda-1 and 3-MA. Lysosomal inhibition using bafilomycin A1, E64D, and pepstatin A obliterated Alda-1- but not ethanol-induced responses in GFP-LC3 puncta. Our results suggest that ALDH2 protects against ethanol toxicity through altered Akt and AMPK signaling and regulation of autophagic flux.

Simvastatin inhibited cardiac hypertrophy and fibrosis in apolipoprotein E-deficient mice fed a "Western-style diet" by increasing PPAR α and γ expression and reducing TC, MMP-9, and Cat S levels

AIM

The examine the cardiac hypertrophy and fibrosis in apolipoprotein E-deficient mice (ApoE-/- mice) fed a "Western-style diet" and the effect of simvastatin intervention.

METHODS

Male ApoE-/- mice (n=36) were fed a "Western-style diet" from the age of 8 weeks. After 16 weeks, they were randomly given either simvastatin (25 mg·kg⁻¹·d⁻¹) or normal saline (control group) by gavage for 8, 16, or 24 weeks. The left ventricular (LV) wall thickness and diameter of the myocardial cells were determined with Hematoxylin-Eosin stain, and the level of fibrosis of the myocardial matrix was assessed with Masson stain. Real-time quantitative polymerase chain reaction and Western blotting analysis were used to determine the mRNA and protein expression of matrix metalloproteinase-9 (MMP-9), Cathepsin S (Cat S), and the peroxisome proliferator-activated receptors (PPARs) in the myocardium of ApoE-/- mice.

RESULTS

ApoE-/- mice fed a "Western-style diet" showed an significant age-dependent increase in total cholesterol (TC), LV wall thickness, myocardial cell diameter and LV collagen content (P<0.05). The simvastatin treatment group showed significantly reduced LV wall thickness, myocardial cell diameters and LV collagen content at 40 weeks when compared with the control group (P<0.05). Furthermore, treatment with simvastatin also significantly inhibited the mRNA and protein expressions of MMP-9 and Cat S as well as increased the mRNA and protein expressions of PPAR alpha and PPAR gamma at 32 and 40 weeks compared with the control group (P<0.05).

CONCLUSION

ApoE-/- mice fed a "Western-style diet" had cardiac hypertrophy and fibrosis, which worsened with age. Simvastatin treatment inhibits the development of cardiac hypertrophy and fibrosis, and this effect may be mediated through increased levels of PPAR alpha and PPAR gamma and reduced levels of TC, MMP-9, and Cat S.

An in vivo murine model of low-magnitude oscillatory wall shear stress to address the molecular mechanisms of mechanotransduction--brief report

OBJECTIVE

Current understanding of shear-sensitive signaling pathways has primarily been studied in vitro largely because of a lack of adequate in vivo models. Our objective was to develop a simple and well-characterized murine aortic coarctation model to acutely alter the hemodynamic environment in vivo and test the hypothesis that endothelial inflammatory protein expression is acutely upregulated in vivo by low-magnitude oscillatory wall shear stress (WSS).

METHODS AND RESULTS

Our model uses the shape memory response of nitinol clips to reproducibly induce an aortic coarctation and allow subsequent focal control over WSS in the aorta. We modeled the corresponding hemodynamic environment using computational fluid dynamics and showed that the coarctation produces low-magnitude oscillatory WSS distal to the clip. To assess the biological significance of this model, we correlated WSS to inflammatory protein expression and fatty streak formation. Vascular cell adhesion molecule-1 expression and fatty streak formation were both found to increase significantly in regions corresponding to acutely induced low-magnitude oscillatory WSS.

CONCLUSIONS

We have developed a novel aortic coarctation model that will be a useful tool for analyzing the in vivo molecular mechanisms of mechanotransduction in various murine models.

Hypercholesterolemia and myocardial function evaluated via tissue doppler imaging

OBJECTIVE

To establish a link between hypercholesterolemia and myocardial dysfunction.

BACKGROUND

Heart failure is a complex disease involving changes in systolic and diastolic function. Newer echocardiographic imaging modalities may be able to detect discreet changes in myocardial function associated with hypercholesterolemia. Therefore we sought to establish a link between hypercholesterolemia and myocardial dysfunction with tissue Doppler imaging (TDI).

METHODS

Twenty-seven rabbits were studied: 7 were fed normal chow (group 1) and 20 a high cholesterol diet (10 with ezetimibe, 1 mg/kg/day; group 2 and 10 without, group 3). Echocardiographic images were obtained under general anesthesia. Serum cholesterol levels were obtained at baseline, 3 and 6 months and myocardial cholesterol levels measured following euthanasia.

RESULTS

Doppler measurements, including E/A, E'/A' and S' were significantly lower in group 3 compared to both groups 1 and 2 but no significant differences were noted in chamber sizes or ejection fraction among the groups. Average serum cholesterol was higher in group 3 compared to groups 1 and 2 respectively (495 +/- 305 mg/dl vs. 114 +/- 95 mg/dl and 87 +/- 37 mg/dl; p < 0.01). Myocardial cholesterol content was also higher in group 3 compared to group 2 (0.10 +/- 0.04 vs. 0.06 mg/dl +/- 0.02; p = 0.05). There was significant correlation between S', E'/A', E/E' and serum cholesterol (r2 = 0.17 p = 0.04, r2 = 0.37 p = 0.001 and r2 = 0.24 p = 0.01).

CONCLUSION

Cholesterol load in the serum and myocardium was significantly associated with decreased systolic and diastolic function by TDI. Moreover, lipid lowering was protective.

Blood pressure is the major driving force for plaque formation in aortic-constricted ApoE−/− mice

OBJECTIVE

Using an aortic constriction model in mice, we studied whether the increase in pressure or the activation of the renin-angiotensin system (RAS) and its main receptors is the main driving force for plaque progression.

METHODS

Male ApoE mice underwent sham surgery or placement of a suprarenal silver clip around the aorta (AoC). Half the group was treated with the selective AT1 receptor antagonist losartan (30 mg/kg per day) for 4 weeks.

RESULTS

Anesthetized mean arterial pressure (MAP) was increased in AoC mice compared to sham (106 +/- 3 versus 90 +/- 1 mmHg, P < 0.001). Losartan reduced MAP in sham mice (78 +/- 2 mmHg, P < 0.01) but not in AoC (AoC losartan 104 +/- 2 mmHg). Plasma renin concentration (PRC) was increased in AoC mice compared to sham [1.6 +/- 0.3 versus 0.8 +/- 0.2 milliGoldblatt units (mGU)/ml, P < 0.001]. Losartan treatment augmented this difference (18.7 +/- 3.7 versus 4.6 +/- 1.7 mGU/ml, P < 0.01). AT2 receptor mRNA expression was increased 5.8-fold by aortic constriction in thoracic aorta (P < 0.05) and the major site for expression of the AT2 receptor protein was within the plaques. The plaque area was increased in AoC mice compared to sham (0.61 +/- 0.09 versus 0.07 +/- 0.01%, P < 0.001); however, losartan did not alter plaque area.

CONCLUSIONS

Our data do not support a role for the AT1 receptor in the progression of atherosclerosis in this model, since blockade with losartan did not alter plaque distribution. Furthermore, we found no support for the counteraction of atherogenesis by increased activity of the RAS acting on the AT2 receptor. Our data suggest that increased pressure is the main driving force for atherosclerosis in this model.

Molecular mechanisms of the vascular responses to haemodynamic forces

Blood vessels are permanently subjected to mechanical forces in the form of stretch, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow and shear stress. Significant variations in mechanical forces, of physiological or physiopathological nature, occur in vivo. These are accompanied by phenotypical modulation of smooth muscle cells and endothelial cells, producing structural modifications of the arterial wall. In all the cases, vascular remodelling can be allotted to a modification of the tensional strain or shear, and underlie a trend to reestablish baseline mechanical conditions. Vascular cells are equipped with numerous receptors that allow them to detect and respond to the mechanical forces generated by pressure and shear stress. The cytoskeleton and other structural components have an established role in mechanotransduction, being able to transmit and modulate tension within the cell via focal adhesion sites, integrins, cellular junctions and the extracellular matrix. Mechanical forces also initiate complex signal transduction cascades, including nuclear factor-kappaB and mitogen-activated protein kinase pathways, leading to functional changes within the cell.

Atherosclerotic lesions in the common coronary arteries of ApoE knockout mice

OBJECTIVE

The present study describes the distribution of atherosclerotic lesions in the coronary arteries of chow-fed 60-week-old male ApoE(-/-), 17-beta-estradiol-treated ApoE(-/-), and wild-type mice.

METHODS AND RESULTS

The histologic examination of coronary arteries in 12 ApoE(-/-) and 6 wild-type mice, in contrast to the distribution of atherosclerosis in human coronary arteries, reveals that the major lesions in the mouse are located in the valve sinus, including the origins of the coronary arteries. These retrovalvular lesions either stop abruptly at the orifice of the common coronary artery or extend a short distance onto the arterial trunks. The first segment and first branch of all the major coronary arteries, the usual sites of disease in humans, are protected from disease. Although the arterial trunks and the first level branches are free of disease, we found approximately four independent lesions per heart. Independent lesions are present in the heart in smaller, intramyocardial vessels. These lesions are comprised predominantly of macrophages and proteoglycan and exhibit little extracellular lipid. In some cases, the independent lesions occlude the lumen without evidence of myocardial infarct in the surrounding tissue.

CONCLUSIONS

The specificity of the localization of lesions in certain segments of the murine coronary tree suggests that fundamental properties found at different branch levels determine lesion location.

Assessment of cardiac function by echocardiography in conscious and anesthetized mice: importance of the autonomic nervous system and disease state

In this study, the authors sought to evaluate the mechanisms responsible for echocardiographically determined differences in cardiac structure and function between conscious and anesthetized mice to determine whether such differences were more or less evident in diseased states. Cardiac parameters were determined by transthoracic echocardiography. Mice anesthetized with a mixture of ketamine and xylazine showed reductions in heart rate (HR, 252 +/- 16 beats/min versus 734 +/- 9 beats/min) and fractional shortening (FS, 35% +/- 2% versus 59% +/- 2%) compared with conscious mice. Conscious mice responded little to the beta-agonist isoproterenol or atropine, but showed profound reductions in HR and FS in response to the beta(1)-antagonist atenolol. In contrast, both isoproterenol and atropine led to increases in HR and FS in anesthetized mice. The stress in conscious animals was reduced by the sedative midazolam, leading to partial restoration of responses to isoproterenol. Mice with constitutive activation of the beta-adrenergic system, due to cardiac overexpression of beta(2)-adrenergic receptors or with heart disease (myocardial infarct and pressure-overload hypertrophy) showed few differences in functional parameters between conscious and anesthetized states, attributable to pre-existing activation of the sympathetic and beta-adrenergic systems, even during anesthesia. The results indicate that the autonomic nervous system plays a critical role in the observed differences in cardiac structure and function between anesthetized and conscious mice.

Increased atherosclerosis and smooth muscle cell hypertrophy in natriuretic peptide receptor A-/-apolipoprotein E-/- mice

OBJECTIVE

Natriuretic peptide signaling is important in the regulation of blood pressure as well as in the growth of multiple cell types. To examine the role of natriuretic peptide signaling in atherosclerosis, we crossbred mice that lack natriuretic peptide receptor A (NPRA; Npr1-/-) with atherosclerosis-prone mice that lack apolipoprotein E (apoE; Apoe-/-).

METHODS AND RESULTS

Doubly deficient Npr1-/-Apoe-/- mice have increased blood pressure relative to Npr1+/+Apoe-/- mice (118+/-4 mm Hg compared with 108+/-2 mm Hg, P<0.05) that is coincident with a 64% greater atherosclerotic lesion size (P<0.005) and more advanced plaque morphology. Additionally, aortic medial thickness is increased by 52% in Npr1-/-Apoe-/- mice relative to Npr1+/+Apoe-/- mice (P<0.0001). Npr1-/-Apoe-/- mice also have significantly greater cardiac mass (9.0+/-0.3 mg/g body weight) than either Npr1+/+Apoe-/- mice (5.8+/-0.2 mg/g) or Npr1-/-Apoe+/+ mice (7.1+/-0.2 mg/g), suggesting that the lack of both NPRA and apoE synergistically enhances cardiac hypertrophy.

CONCLUSIONS

These data provide evidence that NPR1 is an atherosclerosis susceptibility locus and represents a potential link between atherosclerosis and cardiac hypertrophy. Our results also suggest roles for Npr1 as well as Apoe in regulation of hypertrophic cell growth.