Cardiovascular functional phenotypes and pharmacological responses in apolipoprotein E deficient mice

Aerobic exercise attenuates dysautonomia, cardiac diastolic dysfunctions, and hemodynamic overload in female mice with atherosclerosis

Cardiovascular risk increases during the aging process in women with atherosclerosis and exercise training is a strategy for management of cardiac risks in at-risk populations. Therefore, the aims of this study were to evaluate: (1) the influence of the aging process on cardiac function, hemodynamics, cardiovascular autonomic modulation, and baroreflex sensitivity in females with atherosclerosis at the onset of reproductive senescence; and (2) the impact of exercise training on age-related dysfunctions in this model. Eighteen Apolipoprotein-E knockout female mice were divided equally into young (Y), middle-aged (MA), and trained middle-aged (MAT). Echocardiographic exams were performed to verify cardiac morphology and function. Cannulation for direct recording of blood pressure and heart rate, and analysis of cardiovascular autonomic modulation, baroreflex sensitivity were performed. The MA had lower cardiac diastolic function (E'/A' ratio), and higher aortic thickness, heart rate and mean arterial pressure, lower heart rate variability and baroreflex sensitivity compared with Y. There were no differences between Y and MAT in these parameters. Positive correlation coefficients were found between aortic wall thickness with hemodynamics data. The aging process causes a series of deleterious effects such as hemodynamic overload and dysautonomia in female with atherosclerosis. Exercise training was effective in mitigating aged-related dysfunctions.

The improvement of homocysteine-induced myocardial inflammation by vitamin D depends on activation of NFE2L2 mediated MTHFR

OBJECTIVES

Myocardial inflammation underlies a broad spectrum of conditions that cause damage to the myocardium and lead to structural and functional defects. Homocysteine (Hcy) is closely related to the occurrence and development of cardiovascular diseases. We investigated the mechanism underlying the effects of vitamin D as a prophylactic treatment for Hcy-induced cardiac inflammation.

METHODS

The levels of 25(OH)D3 and Hcy were assessed using ELISA kits. Expression levels of the vitamin D receptor (VDR), NFE2 like bZIP transcription factor 2 (NFE2L2), methylenetetrahydrofolate reductase (MTHFR) and inflammatory factors were examined by Western blotting, immunohistochemistry and real time polymerase chain reaction. NFE2L2/MTHFR-knockdown HL-1 cells and NFE2L2+/- mouse were used to test the effects of vitamin D.

RESULTS

We found the levels of Hcy in the serum and myocardial tissue of mice in the Hcy + CCE group were lower than in the Hcy groups, which was opposed to the trend exhibited by the serum 25(OH)D3 level of mice. The mRNA and protein expression levels of the inflammatory factors in cardiac tissues and cardiomyocytes were strongly decreased by the Hcy treatment, compared to the Hcy + CCE/Hcy + 1,25(OH)2D3 groups. Moreover, the results revealed that the level of nuclear NFE2L2 in Hcy + CCE/Hcy + 1,25(OH)2D3 group was increased compared to Hcy group with a reciprocal decrease in the level of cytosolic NFE2L2 in vivo and in vitro. Similarly, the MTHFR mRNA and protein expression in the Hcy + CCE group was higher than the Hcy group. We determined that NFE2L2 promoted the expression of MTHFR. However, based on Hcy treatment, the combination of 1,25(OH)2D3 and MTHFR-/- reversed the decline in IL-6 and TNFα expression caused by 1,25(OH)2D3 alone. Chromatin immunoprecipitation and luciferase reporter assays showed the up-regulation effect of VDR on NFE2L2 and NFE2L2 on MTHFR.

CONCLUSIONS

Our findings indicate that vitamin D/VDR could improve Hcy-induced myocardial inflammation through activation of NFE2L2 mediated MTHFR.

ApoE/NOS3 Knockout Mice as a Novel Cardiovascular Disease Model of Hypertension and Atherosclerosis

Hypertension is an independent risk factor for atherosclerosis. However, few models of hypertensive atherosclerosis have been established in medical research. In this study, we crossed the ApoE knockout (ApoE-KO; ApoE-/-) atherosclerotic mouse model with the NOS3 knockout (NOS3-KO; NOS3-/-) hypertensive mouse model to establish an ApoE/NOS3 double knockout (ApoE/NOS3-KO; ApoE/NOS3-/-) hypertensive atherosclerosis mouse model. We found that ApoE/NOS3-/- mice reproduced normally, had a blood pressure of 133.00 ± 3.85 mmHg, and developed hypertensive fundus retinopathy and hypertensive nephropathy. In addition, serum total cholesterol (TC) and low-density lipoprotein (LDL) levels in the blood were abnormally elevated, steatosis was observed in the liver cells, and atherosclerotic lesions were observed in the aortic vessels in ApoE/NOS3-/- adult mice. In conclusion, ApoE/NOS3-/- adult mice are a satisfactory model of hypertension and atherosclerosis and can be utilized for studies on cardiovascular diseases.

Cardiac Mitochondria Dysfunction in Dyslipidemic Mice

Dyslipidemia triggers many severe pathologies, including atherosclerosis and chronic inflammation. Several lines of evidence, including our studies, have suggested direct effects of dyslipidemia on cardiac energy metabolism, but details of these effects are not clear. This study aimed to investigate how mild dyslipidemia affects cardiac mitochondria function and vascular nucleotide metabolism. The analyses were performed in 3- and 6-month-old knock-out mice for low-density lipoprotein receptor (Ldlr−/−) and compared to wild-type C57Bl/6J mice (WT). Cardiac isolated mitochondria function was analyzed using Seahorse metabolic flux analyzer. The mechanical function of the heart was measured using echocardiography. The levels of fusion, fission, and mitochondrial biogenesis proteins were determined by ELISA kits, while the cardiac intracellular nucleotide concentration and vascular pattern of nucleotide metabolism ecto-enzymes were analyzed using reverse-phase high-performance liquid chromatography. We revealed the downregulation of mitochondrial complex I, together with a decreased activity of citrate synthase (CS), reduced levels of nuclear respiratory factor 1 and mitochondrial fission 1 protein, as well as lower intracellular adenosine and guanosine triphosphates’ pool in the hearts of 6-month Ldlr−/− mice vs. age-matched WT. The analysis of vascular ecto-enzyme pattern revealed decreased rate of extracellular adenosine monophosphate hydrolysis and increased ecto-adenosine deaminase activity (eADA) in 6-month Ldlr−/− vs. WT mice. No changes were observed in echocardiography parameters in both age groups of Ldlr−/− mice. Younger hyperlipidemic mice revealed no differences in cardiac mitochondria function, CS activity, intracellular nucleotides, mitochondrial biogenesis, and dynamics but exhibited minor changes in vascular eADA activity vs. WT. This study revealed that dysfunction of cardiac mitochondria develops during prolonged mild hyperlipidemia at the time point corresponding to the formation of early vascular alterations.

Comparison of the Physical Characteristics and Behavior in ABC Transporter A1, A7 or Apolipoprotein E Knockout Mice with Lipid Transport Dysfunction

The physical characteristics and behavior of the ATP-binding cassette (ABC) A1, A7, and apolipoprotein (apo) E knockout (KO) mice with lipid transport dysfunction were investigated. These KO mice exhibited adequate growth, and their body masses increased steadily. No remarkable changes were observed in their blood pressure and heart rate. However, there was a slight increase in the heart rate of the ABCA7 KO mice compared with that of the wild-type (WT) mice. ABCA1 and apoE KO mice showed hypo- and hyper-cholesterol concentrations in the plasma, respectively. With regard to the cerebrum, however, the weight of the ABCA1 KO mice was lighter than those of the other genotypes. Furthermore, the cholesterol, triglyceride and phospholipid concentrations, and fatty acid composition were generally similar. Compared with the WT mice, ABCA1 KO mice stayed for a shorter time in the closed arm of the elevated plus maze, and performed worse in the initial stage of the Morris water maze. To thermal stimuli, the ABCA1 and apoE KO mice showed hyper- and hypo-sensitivities, respectively. Only the response of the ABCA1 KO mice was significantly inhibited by pretreatment with indomethacin. A low concentration of the prostaglandin E metabolites was detected in the plasma of the ABCA1 KO mice. Thus, ABCA1 is thought to play a specific role in the neural function.

Chitin-glucan and pomegranate polyphenols improve endothelial dysfunction

The vascular dysfunction is the primary event in the occurrence of cardio-vascular risk, and no treatment exists until now. We tested for the first time the hypothesis that chitin-glucan (CG) - an insoluble fibre with prebiotic properties- and polyphenol-rich pomegranate peel extract (PPE) can improve endothelial and inflammatory disorders in a mouse model of cardiovascular disease (CVD), namely by modulating the gut microbiota. Male Apolipoprotein E knock-out (ApoE-/-) mice fed a high fat (HF) diet developed a significant endothelial dysfunction attested by atherosclerotic plaques and increasing abundance of caveolin-1 in aorta. The supplementation with CG + PPE in the HF diet reduced inflammatory markers both in the liver and in the visceral adipose tissue together with a reduction of hepatic triglycerides. In addition, it increased the activating form of endothelial NO-synthase in mesenteric arteries and the heme-nitrosylated haemoglobin (Hb-NO) blood levels as compared with HF fed ApoE-/- mice, suggesting a higher capacity of mesenteric arteries to produce nitric oxide (NO). This study allows to pinpoint gut bacteria, namely Lactobacillus and Alistipes, that could be implicated in the management of endothelial and inflammatory dysfunctions associated with CVD, and to unravel the role of nutrition in the modulation of those bacteria.

Poly(ADP-ribose) Polymerase (PARP) and PARP Inhibitors: Mechanisms of Action and Role in Cardiovascular Disorders

Poly(ADP-ribosyl)ation is an immediate cellular repair response to DNA damage and is catalyzed primarily by poly(ADP-ribose)polymerase-1 (PARP1), which is the most abundant of the 18 different PARP isoforms and accounts for more than 90% of the catalytic activity of PARP in the cell nucleus. Upon detection of a DNA strand break, PARP1 binds to the DNA, cleaves nicotinamide adenine dinucleotide between nicotinamide and ribose and then modifies the DNA nuclear acceptor proteins by formation of a bond between the protein and the ADP-ribose residue. This generates ribosyl-ribosyl linkages that act as a signal for other DNA-repairing enzymes and DNA base repair. Extensive DNA breakage in cells results in excessive activation of PARP with resultant depletion of the cellular stores of nicotinamide adenine dinucleotide (NAD+) which slows the rate of glycolysis, mitochondrial electron transport, and ultimately ATP formation in these cells. This paper focuses on PARP in DNA repair in atherosclerosis, acute myocardial infarction/reperfusion injury, and congestive heart failure and the role of PARP inhibitors in combating the effects of excessive PARP activation in these diseases. Free oxygen radicals and nitrogen radicals in arteries contribute to disruption of the vascular endothelial glycocalyx, which increase the permeability of the endothelium to inflammatory cells and also low-density lipoproteins and the accumulation of lipid in the vascular intima. Mild inflammation and DNA damage within vascular cells promote PARP1 activation and DNA repair. Moderate DNA damage induces caspase-dependent PARP cleavage and vascular cell apoptosis. Severe DNA damage due to vascular inflammation causes excessive activation of PARP1. This causes endothelial cell depletion of NAD+ and ATP, downregulation of atheroprotective SIRT1, necrotic cell death, and ultimately atherosclerotic plaque disruption. Inhibition of PARP decreases vascular endothelial cell adhesion P-selectin and ICAM-1 molecules, inflammatory cells, pro-death caspase-3, and c-Jun N-terminal kinase (JNK) activation and upregulates prosurvival extracellular signal-regulated kinases and AKT, which decrease vascular cell apoptosis and necrosis and limit atherosclerosis and plaque disruption. In myocardial infarction with coronary occlusion then reperfusion, which occurs with coronary angioplasty or thrombolytic therapy, reperfusion injury occurs in as many as 31% of patients and is caused by inflammatory cells, free oxygen and nitrogen radicals, the rapid transcriptional activation of inflammatory cytokines, and the activation of PARP1. Inhibition of PARP attenuates neutrophil infiltration and inflammatory cytokine expression in the reperfused myocardium and preserves myocardial NAD+ and ATP. In addition, PARP inhibition increases the activation of myocyte survival enzymes protein kinase B (Akt) and protein kinase C epsilon (PKCε), and decreases the activity of myocardial ventricular remodeling enzymes PKCα/β, PKCζ/λ, and PKCδ. As a consequence, cardiomyocyte and vascular endothelial cell necrosis is decreased and myocardial contractility is preserved. In heart failure and circulatory shock in animal models, PARP inhibition significantly attenuates decreases in left ventricular systolic pressure, ventricular contractility and relaxation, stroke volume, and increases survival by limiting or preventing upregulation of adhesion molecules, proinflammatory cytokines, myocardial mononuclear cell infiltration, and PKCα/β and PKC λ/ζ. In this manner, PARP inhibition partially restores the myocardial concentrations of NAD+, limits ventricular remodeling and fibrosis, and prevents significant decreases in myocardial contractility. Based primarily on investigations in preclinical models of atherosclerosis, myocardial infarction, and heart failure, PARP inhibition appears to be beneficial in limiting or inhibiting cardiovascular dysfunction. These studies indicate that investigations of acute and chronic PARP inhibition are warranted in patients with atherosclerotic coronary artery disease.

Assessment of local pulse wave velocity distribution in mice using k-t BLAST PC-CMR with semi-automatic area segmentation

BACKGROUND

Local aortic pulse wave velocity (PWV) is a measure for vascular stiffness and has a predictive value for cardiovascular events. Ultra high field CMR scanners allow the quantification of local PWV in mice, however these systems are yet unable to monitor the distribution of local elasticities.

METHODS

In the present study we provide a new accelerated method to quantify local aortic PWV in mice with phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) at 17.6 T. Based on a k-t BLAST (Broad-use Linear Acquisition Speed-up Technique) undersampling scheme, total measurement time could be reduced by a factor of 6. The fast data acquisition enables to quantify the local PWV at several locations along the aortic blood vessel based on the evaluation of local temporal changes in blood flow and vessel cross sectional area. To speed up post processing and to eliminate operator bias, we introduce a new semi-automatic segmentation algorithm to quantify cross-sectional areas of the aortic vessel. The new methods were applied in 10 eight-month-old mice (4 C57BL/6J-mice and 6 ApoE (-/-)-mice) at 12 adjacent locations along the abdominal aorta.

RESULTS

Accelerated data acquisition and semi-automatic post-processing delivered reliable measures for the local PWV, similiar to those obtained with full data sampling and manual segmentation. No statistically significant differences of the mean values could be detected for the different measurement approaches. Mean PWV values were elevated for the ApoE (-/-)-group compared to the C57BL/6J-group (3.5 ± 0.7 m/s vs. 2.2 ± 0.4 m/s, p < 0.01). A more heterogeneous PWV-distribution in the ApoE (-/-)-animals could be observed compared to the C57BL/6J-mice, representing the local character of lesion development in atherosclerosis.

CONCLUSION

In the present work, we showed that k-t BLAST PC-MRI enables the measurement of the local PWV distribution in the mouse aorta. The semi-automatic segmentation method based on PC-CMR data allowed rapid determination of local PWV. The findings of this study demonstrate the ability of the proposed methods to non-invasively quantify the spatial variations in local PWV along the aorta of ApoE (-/-)-mice as a relevant model of atherosclerosis.

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.

Nutritional depletion in n-3 PUFA in apoE knock-out mice: A new model of endothelial dysfunction associated with fatty liver disease

SCOPE

Western diets are characterized by low intake of n-3 PUFA compensated by constant amounts of n-6 PUFA. Reduced intake of n-3 PUFA is associated with increased cardiovascular risk, as observed in nonalcoholic fatty liver disease patients. The study aimed to evaluating the impact of dietary n-3 PUFA depletion on endothelial function, an early key event of cardiovascular diseases.

METHODS AND RESULTS

C57Bl/6J or apolipoprotein E knock-out (apoE^-/- ) were fed control (CT) or n-3 PUFA-depleted diets (DEF) for 12 wks. Mice fed n-3 DEF diet developed a hepatic steatosis, linked to changes in hepatic expression of genes controlled by Sterol Regulatory Element Binding Protein-1 and -2. Vascular function was assessed on second- and third-order mesenteric arteries and n-3 PUFA-depleted apoE^-/- mice presented endothelial dysfunction characterized by decreased vasorelaxation in response of acetylcholine. The presence of a nitric oxide synthase (NOS) inhibitor blunted the relaxation in each groups and heme-nitrosylated hemoglobin blood (Hb-NO) level was significantly lower in n-3 PUFA-depleted apoE^-/- mice.

CONCLUSION

Twelve weeks of n-3 DEF diet promote steatosis and accelerate the process of endothelial dysfunction in apoE^-/- mice by a mechanism involving the NOS/NO pathway. We propose n-3 PUFA-depleted apoE^-/- mice as a new model to study endothelial dysfunction related to hepatic steatosis independently of obesity.

Exercise capacity and cardiac hemodynamic response in female ApoE/LDLR(-/-) mice: a paradox of preserved V'O2max and exercise capacity despite coronary atherosclerosis

We assessed exercise performance, coronary blood flow and cardiac reserve of female ApoE/LDLR^−/− mice with advanced atherosclerosis compared with age-matched, wild-type C57BL6/J mice. Exercise capacity was assessed as whole body maximal oxygen consumption (V’O_2max), maximum running velocity (v_max) and maximum distance (DIST_max) during treadmill exercise. Cardiac systolic and diastolic function in basal conditions and in response to dobutamine (mimicking exercise-induced cardiac stress) were assessed by Magnetic Resonance Imaging (MRI) in vivo. Function of coronary circulation was assessed in isolated perfused hearts. In female ApoE/LDLR^−/− mice V’O_2max, v_max and DIST_max were not impaired as compared with C57BL6/J mice. Cardiac function at rest and systolic and diastolic cardiac reserve were also preserved in female ApoE/LDLR^−/− mice as evidenced by preserved fractional area change and similar fall in systolic and end diastolic area after dobutamine. Moreover, endothelium-dependent responses of coronary circulation induced by bradykinin (Bk) and acetylcholine (ACh) were preserved, while endothelium-independent responses induced by NO-donors were augmented in female ApoE/LDLR^−/− mice. Basal COX-2-dependent production of 6-keto-PGF_1α was increased. Concluding, we suggest that robust compensatory mechanisms in coronary circulation involving PGI₂- and NO-pathways may efficiently counterbalance coronary atherosclerosis-induced impairment in V’O_2max and exercise capacity.

Intermedin1-53 Protects Against Myocardial Fibrosis by Inhibiting Endoplasmic Reticulum Stress and Inflammation Induced by Homocysteine in Apolipoprotein E-Deficient Mice

AIM

Endoplasmic reticulum stress (ERS) and inflammation participate in cardiac fibrosis. Importantly, a novel paracrine/autocrine peptide intermedin_1-53 (IMD_1-53) in the heart inhibits myocardial fibrosis in rats. However, the mechanisms are yet to be fully elucidated.

METHODS

Myocardial fibrosis in apolipoprotein E-deficient (ApoE -/-) mice and neonatal rat cardiac fibroblasts (CFs) were induced using homocysteine (Hcy).

RESULTS

IMD_1-53 inhibited myocardial fibrosis in vivo and in vitro. Picrosirius red staining showed that IMD_1-53 reduced myocardial interstitial collagen deposition in ApoE-/- mice treated with Hcy and decreased the expression of myocardial collagen I and III, which was further verified in rat CFs. IMD_1-53 attenuated myocardial hypertrophy, as shown by cardiomyocyte cross-sectional area, ratio of heart weight to body weight, and mRNA levels of atrial natriuretic peptide and brain natriuretic peptide. IMD_1-53 inhibited the upregulation of ERS hallmarkers such as glucose-regulated protein 78 (GRP78), GRP94, activating transcription factor 6 (ATF6), ATF4, inositol-requiring enzyme 1α, spliced-X-box-binding protein-1, protein kinase receptor-like ER kinase, and eukaryotic translation initiation factor 2α in mouse myocardium and rat CFs treated with Hcy. In addition, IMD_1-53 decreased the production of inflammatory factors such as tumor necrosis factor-α, monocyte chemotactic protein-1, interleukin-6 (IL-6), and IL-1β in the mouse myocardium and rat CFs treated with Hcy. Concurrently, IMD_1-53 ameliorated the expression of nuclear factor-κB, transforming growth factor-β1, and c-Jun N-terminal kinase in the mouse myocardium and rat CFs treated with Hcy.

CONCLUSIONS

IMD potentially protects against myocardial fibrosis induced by Hcy in ApoE-/- mice, possibly via attenuating myocardial ERS and inflammation.

The effects of fish oil consumption on cardiovascular remodeling in ApoE deficient mice

Owing to their spontaneous development of atherosclerosis, apolipoprotein E knockout mice (ApoE(KO)) are one of the best studied animal models for this disease. Little is known about the utility of various omega-3 fatty acid regimens, in particular fish oils, in preventing cardiac disease in ApoE(KO) mice. The purpose of this study was to determine the cardiovascular effects of omega-3 fatty acid supplementation with either safflower oil (control), fish oil, flaxseed oil, or designed oil in ApoE(KO) mice fed a high-fat diet for a total of 16 weeks. In-vivo cardiac function was assessed weekly using murine echocardiography. Blood pressure, plasma lipid levels, and brain natriuretic peptide (BNP) were serially measured. The results show that ApoE(KO) mice fed fish oil demonstrated an increase in left ventricular wall thickness as a result of increased afterload. Despite chronic treatment with fish oil over 16 weeks, blood pressure increased in ApoE(KO) mice by 20% compared with the baseline. Both echocardiographic evidence of left ventricular hypertrophy and biochemical increase in BNP levels confirmed diastolic dysfunction in ApoE(KO) mice fed fish oil. This suggests that high-fat diet supplemented with fish oil may lead to adverse cardiovascular effects in ApoE deficient mice.

Sex Differences in Presynaptic Density and Neurogenesis in Middle-Aged ApoE4 and ApoE Knockout Mice

Atherosclerosis and apolipoprotein E ε4 (APOE4) genotype are risk factors for Alzheimer's disease (AD) and cardiovascular disease (CVD). Sex differences exist in prevalence and manifestation of both diseases. We investigated sex differences respective to aging, focusing on cognitive parameters in apoE4 and apoE knockout (ko) mouse models of AD and CVD. Presynaptic density and neurogenesis were investigated immunohistochemically in male and female apoE4, apoE ko, and wild-type mice. Middle-aged female apoE4 mice showed decreased presynaptic density in the inner molecular layer of the dentate gyrus of the hippocampus. Middle-aged female apoE ko mice showed a trend towards increased neurogenesis in the hippocampus compared with wild-type mice. No differences in these parameters could be observed in middle-aged male mice. Specific harmful interactions between apoE4 and estrogen could be responsible for decreased presynaptic density in female apoE4 mice. The trend of increased neurogenesis found in female apoE ko mice supports previous studies suggesting that temporarily increased amount of synaptic contacts and/or neurogenesis is a compensatory mechanism for synaptic failure. To our knowledge, no other studies investigating presynaptic density in aging female apoE4 or apoE ko mice are available. Sex-specific differences between APOE genotypes could account for some sex differences in AD and CVD.

DDDAS Design of Drug Interventions for the Treatment of Dyslipidemia in ApoE-/- Mice

Computational models of complex systems, such as signaling networks and biological systems, can be used to explain the behavior of such systems under various conditions. The large number of integrated processes and variables, and the nonlinearities inherent in the fundamental processes, make it difficult for scientists unassisted by computer simulations to effectively predict the consequences of a particular intervention. For this reason, computer simulation has become an important tool for generating hypotheses about the behavior of these systems that can then be tested in the laboratory and clinic. A dynamic data-driven application simulation (DDDAS) was designed by Biospherics to model complex metabolic disease pathways by testing potential binary therapies in simulations at various combinations of two points in the pathways. Since DDDAS chooses the most effective pair-wise combinations, this data-driven system allows for the implementation of real-time data to model or predict a measurement or event. By incorporating data dynamically rather than statically, the predictions and measurements become more reliable. Dyslipidemia, a common precursor to atherosclerosis, can be manifested by high triglycerides, increased apolipoprotein (Apo) B, high levels of LDL, and low levels of HDL. SPX106 and D-tagatose is a combination drug therapy composed of a carbohydrate (D-tagatose) and SPX106. D-tagatose has been studied for the treatment of diabetes for several years, and has the ability to lower blood insulin levels and to decrease glycogen formation. SPX106 is a natural substance that accelerates lipid catabolism and inhibits dyslipidemia. In apolipoprotein E knockout mice (ApoE^-/-), this drug combination has been shown to significantly lower both the amount of atherosclerosis and blood cholesterol levels. This study used 26 male ApoE^-/- mice (n=13 in each group, control and treated). The control group received the normal "Western" diet (Harlan TD88137) and the treatment group received a modified version in which the sucrose was replaced with D-tagatose and 1g of SPX106 was added for every kilogram of chow. Mice were fed the diet for 8 weeks and then sacrificed via cardiac puncture. Blood serum was analyzed for cholesterol concentration. A significant difference was observed between the control and treated groups for total cholesterol levels. FPLC separations were done on fractions from both control and treated groups. A significant difference between VLDL and HDL levels was found between the treated and control mice (p<0.05 for both). Aortas were also taken and preserved in formalin to be quantified for atherosclerosis. Aortic sinuses were frozen in OCT and sectioned using a cryostat and then quantified for atherosclerosis. Treated mice showed statistically significant reduction in atherosclerosis in the aortic arch (p<0.01), the thoracic aorta (p<0.05), and the aortic sinus (p<0.05) as well as a reduction of cholesterol (p<0.05).

Cysteinyl leukotriene signaling aggravates myocardial hypoxia in experimental atherosclerotic heart disease

Background

Cysteinyl-leukotrienes (cys-LT) are powerful spasmogenic and immune modulating lipid mediators involved in inflammatory diseases, in particular asthma. Here, we investigated whether cys-LT signaling, in the context of atherosclerotic heart disease, compromises the myocardial microcirculation and its response to hypoxic stress. To this end, we examined Apoe^−/− mice fed a hypercholesterolemic diet and analysed the expression of key enzymes of the cys-LT pathway and their receptors (CysLT1/CysLT2) in normal and hypoxic myocardium as well as the potential contribution of cys-LT signaling to the acute myocardial response to hypoxia.

Methods and principal findings

Myocardial biopsies from Apoe^−/− mice demonstrated signs of chronic inflammation with fibrosis, increased apoptosis and expression of IL-6, as compared to biopsies from C57BL/6J control mice. In addition, we found increased leukotriene C₄ synthase (LTC₄S) and CysLT1 expression in the myocardium of Apoe^−/− mice. Acute bouts of hypoxia further induced LTC₄S expression, increased LTC₄S enzyme activity and CysLT1 expression, and were associated with increased extension of hypoxic areas within the myocardium. Inhibition of cys-LT signaling by treatment with montelukast, a selective CysLT1 receptor antagonist, during acute bouts of hypoxic stress reduced myocardial hypoxic areas in Apoe^−/− mice to levels equal to those observed under normoxic conditions. In human heart biopsies from 14 patients with chronic coronary artery disease mRNA expression levels of LTC₄S and CysLT1 were increased in chronic ischemic compared to non-ischemic myocardium, constituting a molecular basis for increased cys-LT signaling.

Conclusion

Our results suggest that CysLT1 antagonists may have protective effects on the hypoxic heart, and improve the oxygen supply to areas of myocardial ischemia, for instance during episodes of sleep apnea.

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.

Endothelial damage and regeneration: the role of the renin-angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is part of the blood pressure regulating system. Its main effector peptide is angiotensin II (Ang II). Although it may induce hypertension, the proinflammatory, profibrotic, and prothrombotic effects are mainly mediated by effects of Ang II on the cellular and molecular level that are independent of blood pressure. Therefore, pharmacotherapeutic intervention within the RAAS is an important treatment modality for patients suffering from cardiovascular diseases, even those who are not hypertensive. In addition to the blood pressure lowering and vasculoprotective (pleiotropic) effects of angiotensin II type 1 (AT(1)) receptor blockers (ARBs), and angiotensin-converting enzyme (ACE) inhibitors, regenerative progenitor cell therapy emerges as an auxiliary therapy to improve regeneration of the vascular endothelium. This review focuses on the growing knowledge about regenerating vascular cells, their response to RAAS effectors, and RAAS-modulating pharmacotherapy in the context of endothelial cell damage and regeneration.

Regional in vivo transit time measurements of aortic pulse wave velocity in mice with high-field CMR at 17.6 Tesla

BACKGROUND

Transgenic mouse models are increasingly used to study the pathophysiology of human cardiovascular diseases. The aortic pulse wave velocity (PWV) is an indirect measure for vascular stiffness and a marker for cardiovascular risk.

RESULTS

This study presents a cardiovascular magnetic resonance (CMR) transit time (TT) method that allows the determination of the PWV in the descending murine aorta by analyzing blood flow waveforms. Systolic flow pulses were recorded with a temporal resolution of 1 ms applying phase velocity encoding. In a first step, the CMR method was validated by pressure waveform measurements on a pulsatile elastic vessel phantom. In a second step, the CMR method was applied to measure PWVs in a group of five eight-month-old apolipoprotein E deficient (ApoE(-/-)) mice and an age matched group of four C57Bl/6J mice. The ApoE(-/-) group had a higher mean PWV (PWV = 3.0 ± 0.6 m/s) than the C57Bl/6J group (PWV = 2.4 ± 0.4 m/s). The difference was statistically significant (p = 0.014).

CONCLUSIONS

The findings of this study demonstrate that high field CMR is applicable to non-invasively determine and distinguish PWVs in the arterial system of healthy and diseased groups of mice.

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.

Preview. Adult neurogenesis is altered by GABAergic imbalance in models of Alzheimer's disease

Early stages of Alzheimer's disease (AD) affect hippocampal function. In this issue of Cell Stem Cell, Li et al. (2009) and Sun et al. (2009) propose abnormal GABA signaling as a trigger for impaired network plasticity in the AD hippocampus.

Opposing roles of PARP-1 in MMP-9 and TIMP-2 expression and mast cell degranulation in dyslipidemic dilated cardiomyopathy

INTRODUCTION

Previously, we demonstrated that inhibition of poly(ADP-ribose) polymerase (PARP) exerts protective effects against high-fat (HF) diet-induced atherogenesis in part by increasing tissue inhibitor of metalloproteinase (TIMP)-2 expression. Given that characteristics of dilated cardiomyopathy closely associate with atherosclerosis and are mediated by an imbalance between matrix metalloproteinases (MMPs) and TIMPs, we hypothesized that PARP-1 gene deletion may protect against HF-induced cardiac hypertrophy and dilatations by altering TIMP-2/MMPs balance in favor of a maintenance of tissue homeostasis.

METHODS AND RESULTS

Hemodynamic parameters determined by echocardiography were similar in ApoE(-/-) mice and PARP-1-deficient ApoE(-/-) mice (DKO) fed a regular diet (RD). However, histological analysis revealed that cardiomyocytes of ApoE(-/-) mice on RD were hypertrophied, displaying an enlarged cell body and nucleus, traits that were absent in DKO animals. HF diet-fed ApoE(-/-) mice exhibited increased interventricular septum, left ventricular (LV) internal dimension, LV volume, and LV mass in addition to a separation of myocardial fibers suggestive of dilated cardiomyopathy. PARP-1 gene deletion protected against these degenerative changes. MMP activity was dramatically increased in hearts of ApoE(-/-) mice on HF diet and was accompanied by increased collagen degradation, mast cell degranulation, and increased myocyte cell death. PARP-1 gene knockout was associated with increased TIMP-2 expression antagonizing, as a result, the damaging effects of active MMPs.

CONCLUSIONS

The present study demonstrates that PARP-1 gene deletion exerts protective effects against HF diet-induced dilated cardiomyopathy by maintaining increased expression of TIMP-2. With additional protective effects against cell death and inflammation, PARP-1 deficiency preserves cardiac tissue homeostasis.

Cardiac hypertrophy during hypercholesterolemia and its amelioration with rosuvastatin and amlodipine

Hypercholesterolemia is a common accompaniment of atherosclerosis and may be associated with cardiac hypertrophy. To define the mechanistic basis of cardiac hypertrophy in hypercholesterolemia, we fed low-density lipoprotein receptor knockout (LDLR KO) mice regular diet or high cholesterol (HC) diet for 26 weeks. There was clear evidence of cardiomyocyte hypertrophy and collagen deposition in the hearts of LDLR KO mice fed with HC diet, confirmed by histopathology (hematoxylin and eosin and Picrosirius staining) and upregulation of genes for brain natriuretic peptide, alpha-tubulin, transforming growth factor beta1, and connective tissue growth factor (CTGF). These changes were independent of change in blood pressure. The hypercholesterolemic mice hearts showed an upregulation of LOX-1, an oxidized low-density lipoprotein receptor, and angiotensin II type 1 receptor (AT1R) at messenger RNA level. In addition, there was a marked upregulation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and nuclear factor kappaB (NF-kappaB) messenger RNA, indicating overexpression of markers of oxidant stress. A separate group of LDLR KO mice were fed HC diet along with a potent 3-hydroxy-3-methylglutarylcoenzyme A reductase inhibitor rosuvastatin or a dihydropyridine calcium channel blocker amlodipine. Administration of rosuvastatin or amlodipine reduced the overexpression of genes for LOX-1 and AT1R and associated NADPH oxidase and NF-kappaB. These phenomena were associated with a marked decrease in cardiomyocyte hypertrophy and collagen deposits in and around the cardiomyocytes. In conclusion, this study provides evidence of cardiac hypertrophy and fibrosis in hypercholesterolemia independent of blood pressure change LOX-1 and AT1R act as possible signals for oxidant stress leading to alterations in cardiac structure during hypercholesterolemia. Most importantly, rosuvastatin and amlodipine ameliorate cardiomyocyte hypertrophy and fibrosis.

Protective effects of PARP-1 knockout on dyslipidemia-induced autonomic and vascular dysfunction in ApoE mice: effects on eNOS and oxidative stress

The aims of this study were to investigate the role of poly(ADP-ribose) polymerase (PARP)-1 in dyslipidemia-associated vascular dysfunction as well as autonomic nervous system dysregulation. Apolipoprotein (ApoE)^−/− mice fed a high-fat diet were used as a model of atherosclerosis. Vascular and autonomic functions were measured in conscious mice using telemetry. The study revealed that PARP-1 plays an important role in dyslipidemia-associated vascular and autonomic dysfunction. Inhibition of this enzyme by gene knockout partially restored baroreflex sensitivity in ApoE^−/− mice without affecting baseline heart-rate and arterial pressure, and also improved heart-rate responses following selective blockade of the autonomic nervous system. The protective effect of PARP-1 gene deletion against dyslipidemia-induced endothelial dysfunction was associated with preservation of eNOS activity. Dyslipidemia induced PARP-1 activation was accompanied by oxidative tissue damage, as evidenced by increased expression of iNOS and subsequent protein nitration. PARP-1 gene deletion reversed these effects, suggesting that PARP-1 may contribute to vascular and autonomic pathologies by promoting oxidative tissue injury. Further, inhibition of this oxidative damage may account for protective effects of PARP-1 gene deletion on vascular and autonomic functions. This study demonstrates that PARP-1 participates in dyslipidemia-mediated dysregulation of the autonomic nervous system and that PARP-1 gene deletion normalizes autonomic and vascular dysfunctions. Maintenance of eNOS activity may be associated with the protective effect of PARP-1 gene deletion against dyslipidemia-induced endothelial dysfunction.

Pulse wave imaging of normal and aneurysmal abdominal aortas in vivo

The abdominal aortic aneurysm (AAA) is a common vascular disease. The current clinical criterion for treating AAAs is an increased diameter above a critical value. However, the maximum diameter does not correlate well with aortic rupture, the main cause of death from AAA disease. AAA disease leads to changes in the aortic wall mechanical properties. The pulse-wave velocity (PWV) may indicate such a change. Because of limitations in temporal and spatial resolution, the widely used foot-to-foot method measures the global, instead of regional, PWV between two points at a certain distance in the circulation. However, mechanical properties are nonuniform along the normal and pathological (e.g., the AAA and atherosclerosis) arteries; thus, such changes are typically regional. Pulse-wave imaging (PWI) has been developed by our group to map the pulse-wave propagation along the abdominal aorta in mice in vivo. By using a retrospective electrocardiogram (ECG) gating technique, the radio-frequency (RF) signals over one cardiac cycle were obtained in murine aortas at the extremely high frame rate of 8 kHz and with a field-of-view (FOV) of 12 x 12 mm(2). The velocities of the aortic wall were estimated using an RF-based speckle tracking method. An Angiotensin II (AngII) infusion-based AAA model was used to simulate the human AAA case. Sequences of wall velocity images can noninvasively and quantitatively map the propagation of the pulse wave along the aortic wall. In the normal and sham aortas, the propagation of the pulse wave was relatively uniform along the wall, while in the AngII-treated aortas, the propagation was shown to be nonuniform. There was no significant difference ( p > 0.05) in the PWV between sham (4.67 +/- 1.15 m/s, n=5) and AngII-treated (4.34 +/- 1.48 m/s, n=17) aortas. The correlation coefficient of the linear regression was significantly higher ( p < 0.005) in the sham aortas (0.89 +/- 0.03, n=5 ) than in the AngII-treated ones (0.61 +/- 0.15, n=17). The wall velocities induced by the pulse wave were lower and the pulse wave moved nonuniformly along the AngII-treated aorta ( p < 0.005), with the lowest velocities at the aneurysmal regions. The discrepancy in the regional wall velocity and the nonuniform pulse-wave propagation along the AngII-treated aorta indicated the inhomogeneities in the aortic wall properties, and the reduced wall velocities indicated stiffening of the aneurysmal wall. This novel technique may thus constitute an early detection tool of vascular degeneration as well as serve as a suitable predictor of AAA rupture, complementary to the current clinical screening practice.

In vivo comparison of atherosclerotic plaque progression with vessel wall strain and blood flow velocity in apoE(-/-) mice with MR microscopy at 17.6 T

OBJECT

At present, in vivo plaque characterization in mice by MRI is typically limited to the visualization of vascular lesions with no accompanying analysis of vessel wall function. The aim of this study was to analyze the influence of atherosclerotic plaque development on the morphological and mechanical characteristics of the aortic vessel wall in a pre-clinical murine model of atherosclerosis.

MATERIALS AND METHODS

Groups of apolipoprotein E-deficient (apoE(-/-)) and C57BL/6J control mice fed a high-fat diet were monitored over a 12-week time period by high-field MRI. Multi-Slice-Multi-Spin-Echo and Phase-Contrast MRI sequences were employed to track changes to aortic vessel wall area, blood flow velocity and distensibility.

RESULTS

After 6- and 12-weeks, significant changes in vessel wall area and circumferential strain were detected in the apoE(-/-) mice relative to the control animals. Blood flow velocity and intravascular lumen remained unchanged in both groups, findings that are in agreement with the theory of positive remodeling of the ascending aorta during plaque progression.

CONCLUSION

This study has demonstrated the application of high-field MRI for characterizing the temporal progression of morphological and mechanical changes to murine aortic vasculature associated with atherosclerotic lesion development.

Effects of rosuvastatin on cardiovascular morphology and function in an ApoE-knockout mouse model of atherosclerosis

This study investigated the effects of rosuvastatin on plaque progression and in vivo coronary artery function in apolipoprotein E-knockout (ApoE-KO) mice, using noninvasive high-resolution ultrasound techniques. Eight-week-old male ApoE-KO mice (n = 20) were fed a high-fat diet with or without rosuvastatin (10 micromol.kg(-1).day(-1)) for 16 wk. When compared with control, rosuvastatin reduced total cholesterol levels (P < 0.05) and caused significant retardation of lesion progression in the brachiocephalic artery, as visualized in vivo using an ultrasound biomicroscope (P < 0.05). Histological analysis confirmed the reduction of brachiocephalic atherosclerosis and also revealed an increase in collagen content in the statin-treated group (P < 0.05). Coronary volumetric flow was measured by simultaneous recording of Doppler velocity signals and left coronary artery morphology before and during adenosine infusion. The hyperemic flow in response to adenosine was significantly greater in left coronary artery following 16 wk of rosuvastatin treatment (P < 0.001), whereas the baseline flow was similar in both groups. In conclusion, rosuvastatin reduced brachiocephalic artery atherosclerotic plaques in ApoE-KO mice. Coronary artery function assessed using recently developed in vivo ultrasound-based protocols, also improved.

Effects of isoflurane on coronary blood flow velocity in young, old and ApoE(-/-) mice measured by Doppler ultrasound

The commonly used anesthetic agent isoflurane (ISO) is a potent coronary vasodilator that could potentially be used in the assessment of coronary reserve, but its effects on coronary blood flow in mice are unknown. Coronary reserve is reduced by age, coronary artery disease and other cardiac pathologies in man, and some of these conditions can now be modeled in mice. Accordingly, we used Doppler ultrasound to measure coronary flow velocity in mice anesthetized with low (1%) and high (2.5%) levels of ISO to generate baseline (B) and elevated hyperemic (H) coronary flows, respectively. A 20-MHz Doppler probe was mounted in a micromanipulator and pointed trans-thoracically toward the origin of the left main coronary arteries of 10 6-wk (Young [Y]), 10 2-y (Old [O]) and 20 2-y apolipoprotein-E null (ApoE(-/-)) atherosclerotic (A) mice. In each mouse, we measured (B) and (H) peak diastolic velocities. B was 35.4 +/- 1.4 cm/s (Y), 24.8 +/- 1.6 (O) and 51.7 +/- 6.4 (A); H was 83.5 +/- 1.3 (Y), 86.5 +/- 1.9 (O) and 120 +/- 16.9 (A) and H/B was 2.4 +/- 0.1 (Y), 3.6 +/- 0.2 (O) and 2.5 +/- 0.2 (A). The differences in baseline velocities and H/B between O and Y and between A and O were significant (p < 0.01), whereas the differences in hyperemic velocities were not (p > 0.05). H/B was higher in old mice as a result of decreased baseline flow rather than increased hyperemic flow velocity. In contrast, ApoE(-/-) mice have increased baseline and hyperemic velocities, perhaps because of coronary lesions. The differences in baseline velocities between young and old mice could be the result of age-related changes in basal metabolism or to differential sensitivity to isoflurane. We conclude that Doppler ultrasound combined with coronary vasodilation via isoflurane could provide a convenient and noninvasive method to estimate coronary reserve in mice, but also that care must be taken when assessing coronary flow in mice under isoflurane anesthesia because of its potent coronary vasodilator properties.