Acrolein Inhalation Alters Myocardial Synchrony and Performance at and Below Exposure Concentrations that Cause Ventilatory Responses

Acrolein is an irritating aldehyde generated during combustion of organic compounds. Altered autonomic activity has been documented following acrolein inhalation, possibly impacting myocardial synchrony and function. Given the ubiquitous nature of acrolein in the environment, we sought to better define the immediate and delayed functional cardiac effects of acrolein inhalation in vivo. We hypothesized that acrolein inhalation would increase markers of cardiac mechanical dysfunction, i.e., myocardial dyssynchrony and performance index in mice. Male C57Bl/6J mice were exposed to filtered air (FA) or acrolein (0.3 or 3.0 ppm) for 3 h in whole-body plethysmography chambers (n = 6). Echocardiographic analyses were performed 1 day before exposure and at 1 and 24 h post-exposure. Speckle tracking echocardiography revealed that circumferential strain delay (i.e., dyssynchrony) was increased at 1 and 24 h following exposure to 3.0 ppm, but not 0.3 ppm, when compared to pre-exposure and/or FA exposure. Pulsed wave Doppler of transmitral blood flow revealed that acrolein exposure at 0.3 ppm, but not 3.0 ppm, increased the Tei index of myocardial performance (i.e., decreased global heart performance) at 1 and 24 h post-exposure compared to pre-exposure and/or FA exposure. We conclude that short-term inhalation of acrolein can acutely modify cardiac function in vivo and that echocardiographic evaluation of myocardial synchrony and performance following exposure to other inhaled pollutants could provide broader insight into the health effects of air pollution.

The Impact of Chronic Glycogen Synthase Kinase-3 Inhibition on Remodeling of Normal and Pre-Diabetic Rat Hearts

PURPOSE

There is an ongoing search for new drugs and drug targets to treat diseases like Alzheimer's disease, cancer and type 2 diabetes (T2D). Both obesity and T2D are characterized by the development of a cardiomyopathy associated with increased hypertension and compensatory left ventricular hypertrophy. Small, specific glycogen synthase kinase-3 (GSK-3) inhibitors were developed to replace lithium chloride for use in psychiatric disorders. In addition, they were advocated as treatment for T2D since GSK-3 inhibition improves blood glucose handling. However, GSK-3 is a regulator of hypertrophic signalling in the heart via phosphorylation of NFATc3 and β-catenin respectively. In view of this, we hypothesized that chronic inhibition of GSK-3 will induce myocardial hypertrophy or exacerbate existing hypertrophy.

METHODS

Rats with obesity-induced prediabetes were treated orally with GSK-3 inhibitor (CHIR118637 (CT20026)), 30 mg/kg/day for the last 8 weeks of a 20-week diet high in sugar content vs a control diet. Biometric and biochemical parameters were measured, echocardiography performed and localization and co-localization of NFATc3 and GATA4 determined in cardiomyocytes.

RESULTS

Obesity initiated myocardial hypertrophy, evidenced by increased ventricular mass (1.158 ± 0.029 vs 0.983 ± 0.03 g) and enlarged cardiomyocytes (18.86 ± 2.25 vs 14.92 ± 0.50um(2)) in association with increased end-diastolic diameter (EDD = 8.48 ± 0.11 vs 8.15 ± 0.10 mm). GSK-3 inhibition (i) increased ventricular mass only in controls (1.075 ± 0.022 g) and (ii) EDD in both groups (controls: 8.63 ± 0.07; obese: 8.72 ± 0.15 mm) (iii) localized NFATc3 and GATA4 peri-nuclearly.

CONCLUSION

Indications of onset of myocardial hypertrophy in both control and obese rats treated with a GSK-3 inhibitor were found. It remains speculation whether these changes were adaptive or maladaptive.

Myocardial oxidative stress correlates with left ventricular dysfunction on strain echocardiography in a rodent model of sepsis

BACKGROUND

Recognition of cardiomyopathy in sepsis can be challenging due to the limitations of conventional measures such as ejection fraction (EF) and fractional shortening (FS) in the context of variable preload and afterload conditions. This study correlates myocardial function using strain echocardiography (SE) with cardiomyocyte oxidative stress in a murine model of sepsis.

METHODS

C57BL/6J mice were randomized into control (n = 10), sham (n = 25), and a cecal ligation and puncture (CLP) (n = 33) model of sepsis. Echocardiography was performed pre-, 12, 24, and 48 h post-injury. Cardiac pro-inflammatory cytokines and mitochondrial redox scavenger expression were evaluated in a subset of each arm. To evaluate the influence of redox scavenger upregulation on oxidative injury and cardiac function, CLP was performed on mitochondrial catalase-upregulated C57BL/6J MCAT^+/+ mice (n = 12) and wild-type (WT) animals for comparison.

RESULTS

Septic C57BL/6J mice exhibited depressed longitudinal strain (LS) when compared to sham and control at 24 h (p < 0.01) and 48 h (p = 0.04) post-CLP despite having a preserved EF. Furthermore, there was a significant association between increased odds of mortality and depressed LS (OR = 1.23, p = 0.04). Septic C57BL/6J mice concomitantly demonstrated increased expression of cardiomyocyte pro-inflammatory cytokines and decreased expression of redox scavengers at 24 and 48 h. When comparing C57Bl/6 MCAT ^+/+ mice and C57BL/6J WT mice, a significant decrease in LS was identified in the WT mice at 24 h (MCAT = -23 ± 5% vs. WT = -15 ± 4% p < 0.01) and 48 h (MCAT = -23 ± 7% vs. WT = -15 ± 4.3% p = 0.04) post-CLP which correlated with significant increase in the level of cardiac oxidative stress following CLP.

CONCLUSIONS

In this sepsis model, SE identified cardiomyopathy despite normal EF. SE depression temporally coincides with upregulation of inflammatory cytokines and decreases expression of key mitochondrial ROS scavengers. Upregulation of redox scavenger (CAT) abrogates oxidative stress and cardiac dysfunction in this sepsis model.

Antioxidant Treatment Improves Cardiac Dysfunction in a Murine Model of Premature Aging

Bmal1-(brain and muscle ARNT-like protein-1) deficient (Bmal1) mice prematurely age because of an increased reactive oxygen species (ROS) production. These mice also show a decline in cardiac function with age. We investigated whether an antioxidant treatment can ameliorate the declining cardiac function in prematurely aged Bmal1 mice. Male Bmal1 and wild-type (Bmal1) mice were exposed for 15 weeks to a high fat and high cholesterol diet with or without the antioxidant 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL; 5 mmol/L; in drinking water during the last 10 weeks). Echocardiographic analysis revealed that TEMPOL treatment of Bmal1 mice normalized cardiac function, as evidenced by a decrease in left ventricular diastolic and systolic internal diameters, and by an increase in fractional shortening and ejection fraction. The antioxidant did not affect cardiac function in Bmal1 mice. Although TEMPOL did not influence cardiac ROS levels in Bmal1 mice, it significantly protected Bmal1 cardiac telomeres from oxidation, as evidenced by a reduction in the telomere damage score (0.11 ± 0.012% vs. 0.16 ± 0.015%; P = 0.028). Thus, antioxidant treatment normalized cardiac function of Bmal1 mice, probably in part by scavenging ROS.

The Probability of Inconstancy in Assessment of Cardiac Function Post-Myocardial Infarction in Mice

In the present study, we explore the inherent variability that leads to overlaps in cardiac functional parameters between control and post-myocardial infarction (MI) mice. Heart failure was induced by Left Coronary Artery (LCA) ligation in mice. Average Ejection Fraction (EF) measured by echocardiography was lower in MI mice compared to control, but exhibited higher Standard Deviation (SD) and Standard Error (SEM), notably in 2D mode. Fractional Shortening (FS) showed a higher degree of overlap between MI and control mice even though the mean values were significantly different. Hemodynamic measurements of EF resulted in greater SD, SEM, ± 95% confidence intervals, and effect size. In comparing echocardiography at different time points, EF and FS were consistent by mean, but had apparent fluctuation in individual tracks, which were more obvious in MI than control mice. Hemodynamic measurements showed more complexity in data collection in mice in vivo. MI size showed variability that correlated with severity of cardiac function. These studies show that there is inherent variability in functional cardiac parameters after induction of heart failure by MI in mice. Analysis of these parameters by traditional statistical methods is insufficient, and we propose a more robust statistical analysis for proper data interpretation.

Imaging Reveals the Connection Between Spontaneous Coronary Plaque Ruptures, Atherothrombosis, and Myocardial Infarctions in HypoE/SRBI-/- Mice

The hyperlipidemic mouse model HypoE/SRBI(-/-) has been shown to develop occlusive coronary atherosclerosis followed by myocardial infarctions and premature deaths in response to high-fat, high-cholesterol diet (HFC). However, the causal connection between myocardial infarctions and atherosclerotic plaque rupture events in the coronary arteries has not been investigated so far. The objective of this study was to assess whether diet-induced coronary plaque ruptures trigger atherothrombotic occlusions, resulting in myocardial infarctions in HFC-fed HypoE/SRBI(-/-) mice.

METHODS

HypoE/SRBI(-/-) mice were characterized with respect to the individual dynamics of myocardial infarctions and features of infarct-related coronary atherosclerosis by serial noninvasive molecular and functional imaging, histopathology, and a pharmaceutical intervention. Detailed histologic analysis of whole mouse hearts was performed when spontaneously occurring acute myocardial infarctions were diagnosed by imaging.

RESULTS

Using the imaging-triggered approach, we discovered thrombi in 32 (10.8%) of all 296 atherosclerotic coronary plaques in 14 HFC-fed HypoE/SRBI(-/-) mice. These thrombi typically were found in arteries presenting with inflammatory plaque phenotypes. Acetylsalicylic acid treatment did not attenuate the development of atherosclerotic coronary plaques but profoundly reduced the incidence of premature deaths, the number of thrombi (7 in 249 plaques), and also the degree of inflammation in the culprit lesions.

CONCLUSION

HFC-induced ruptures of coronary plaques trigger atherothrombosis, vessel occlusions, myocardial infarctions, and sudden death in these mice. Thus, the HypoE/SRBI(-/-) mouse model mimics major features of human coronary heart disease and might therefore be a valuable model for the investigation of molecular and cellular parameters driving plaque rupture-related events and the development of new interventional approaches.

Modulation of myocardial injury and collagen deposition following ischaemia-reperfusion by linagliptin and liraglutide, and both together

Studies have indicated that dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists reduce infarct size after myocardial ischaemia. Whether these agents modify cardiac remodelling after ischaemia is unclear. Furthermore, it is not known if combination of the two types of drugs is superior to either agent alone. We investigated the modulatory effect of the DPP-4 inhibitor linagliptin alone, the GLP-1 activator liraglutide alone, or the two agents together on myocardial infarct size, left ventricular contractile function and cardiac remodelling signals after a brief period of left coronary artery (LCA) occlusion. C57BL/6 mice were treated with vehicle, the DPP-4 inhibitor linagliptin, the GLP-1 activator liraglutide, or both agents together for 5 days, and then subjected to LCA occlusion (1 h) and reperfusion (3 h). Ischaemia-reperfusion increased reactive oxygen species (ROS) generation and expression of NADPH oxidase (p47(phox), p22(phox) and gp91(phox) subtypes), collagens, fibronectin and proinflammatory cytokines (interleukin 6, tumour necrosis factor α and monocyte chemoattractant protein-1) in the LCA-supplied regions. Pre-treatment with linagliptin or liraglutide reduced infarct size, protected cardiomyocytes from injury and preserved cardiac contractile function in a similar fashion. It is interesting that profibrotic (collagen deposition) signals were expressed soon after ischaemia-reperfusion. Both linagliptin and liraglutide suppressed ROS generation, NADPH oxidase and proinflammatory signals, and reduced collagen deposition. Addition of linagliptin or liraglutide had no significant additive effect above and beyond that of liraglutide and linagliptin given alone. In conclusion, linagliptin and liraglutide can improve cardiac contractile function and indices of cardiac remodelling, which may be related to their role in inhibition of ROS production and proinflammatory cytokines after ischaemia.

Left ventricular function measurements in a mouse myocardial infarction model. Comparison between 3D-echocardiography and ECG-gated SPECT

AIM

To assess the accuracy of ECG-gated micro (µ)-SPECT in a mouse myocardial infarction (MI) model in comparison to 3D-echocardiography.

ANIMALS, METHODS

In a mouse (Swiss mice) MI model we compared the accuracy of technetium-99m sestamibi (99mTc-sestamibi) myocardial perfusion, electrocardiogram (ECG) gated µSPECT to 3D-echocardiography in determining left ventricular function. 3D-echocardiography and myocardial perfusion ECG-gated µSPECT data were acquired in the same animal at baseline (n = 11) and 7 (n = 8) and 35 (n = 9) days post ligation of the left anterior descending coronary artery (LAD). Sham operated mice were used as a control (8, 6 and 7 mice respectively). Additionally, after day 35 µSPECT scans, hearts were harvested and 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) staining and autoradiography was performed to determine infarct size.

RESULTS

In both infarcted and sham-operated mice we consistently found comparable values for the end-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF) obtained by 3D-echocardiography and ECG-gated µSPECT. Excellent correlations between measurements from 3D-echocardiography and ECG-gated µSPECT were found for EDV, ESV and EF (r = 0.9532, r = 0.9693 respectively and r = 0.9581) in infarcted mice. Furthermore, comparable infarct size values were found at day 35 post MI by TTC staining and autoradiography (27.71 ± 1.80% and 29.20 ± 1.18% with p = 0.43).

CONCLUSION

We have demonstrated that ECG-gated µSPECT imaging provides reliable left ventricular function measurements in a mouse MI model. Obtained results were comparable to the highly accurate 3D-echocardiography. This, in addition to the opportunity to simultaneously image multiple biological processes during a single acquisition makes µSPECT imaging a serious option for studying cardiovascular disease in small animals.

A microRNA-Hippo pathway that promotes cardiomyocyte proliferation and cardiac regeneration in mice

In contrast to lower vertebrates, the mammalian heart has limited capacity to regenerate after injury in part due to ineffective reactivation of cardiomyocyte proliferation. We show that the microRNA cluster miR302-367 is important for cardiomyocyte proliferation during development and is sufficient to induce cardiomyocyte proliferation in the adult and promote cardiac regeneration. In mice, loss of miR302-367 led to decreased cardiomyocyte proliferation during development. In contrast, increased miR302-367 expression led to a profound increase in cardiomyocyte proliferation, in part through repression of the Hippo signal transduction pathway. Postnatal reexpression of miR302-367 reactivated the cell cycle in cardiomyocytes, resulting in reduced scar formation after experimental myocardial infarction. However, long-term expression of miR302-367 induced cardiomyocyte dedifferentiation and dysfunction, suggesting that persistent reactivation of the cell cycle in postnatal cardiomyocytes is not desirable. This limitation can be overcome by transient systemic application of miR302-367 mimics, leading to increased cardiomyocyte proliferation and mass, decreased fibrosis, and improved function after injury. Our data demonstrate the ability of microRNA-based therapeutic approaches to promote mammalian cardiac repair and regeneration through the transient activation of cardiomyocyte proliferation.

Overexpressing superoxide dismutase 2 induces a supernormal cardiac function by enhancing redox-dependent mitochondrial function and metabolic dilation

During heightened cardiac work, O2 consumption by the heart benefits energy production via mitochondria. However, some electrons leak from the respiratory chain and yield superoxide, which is rapidly metabolized into H2O2 by SOD2. To understand the systemic effects of the metabolic dilator, H2O2, we studied mice with cardiac-specific SOD2 overexpression (SOD2-tg), which increases the H2O2 produced by cardiac mitochondria. Contrast echocardiography was employed to evaluate cardiac function, indicating that SOD2-tg had a significantly greater ejection fraction and a lower mean arterial pressure (MAP) that was partially normalized by intravenous injection of catalase. Norepinephrine-mediated myocardial blood flow (MBF) was significantly enhanced in SOD2-tg mice. Coupling of MBF to the double product (Heart Rate×MAP) was increased in SOD2-tg mice, indicating that the metabolic dilator, "spilled" over, inducing systemic vasodilation. The hypothesis that SOD2 overexpression effectively enhances mitochondrial function was further evaluated. Mitochondria of SOD2-tg mice had a decreased state 3 oxygen consumption rate, but maintained the same ATP production flux under the basal and L-NAME treatment conditions, indicating a higher bioenergetic efficiency. SOD2-tg mitochondria produced less superoxide, and had lower redox activity in converting cyclic hydroxylamine to stable nitroxide, and a lower GSSG concentration. EPR analysis of the isolated mitochondria showed a significant decrease in semiquinones at the SOD2-tg Qi site. These results support a more reductive physiological setting in the SOD2-tg murine heart. Cardiac mitochondria exhibited no significant differences in the respiratory control index between WT and SOD2-tg. We conclude that SOD2 overexpression in myocytes enhances mitochondrial function and metabolic vasodilation, leading to a phenotype of supernormal cardiac function.

IL-18 neutralization during alveolar hypoxia improves left ventricular diastolic function in mice

AIM

In patients, an association exists between pulmonary diseases and diastolic dysfunction of the left ventricle (LV). We have previously shown that alveolar hypoxia in mice induces LV diastolic dysfunction and that mice exposed to hypoxia have increased levels of circulating interleukin-18 (IL-18), suggesting involvement of IL-18 in development of diastolic dysfunction. IL-18 binding protein (IL-18BP) is a natural inhibitor of IL-18. In this study, we hypothesized that neutralization of IL-18 during alveolar hypoxia would improve LV diastolic function.

METHODS

Mice were exposed to 10% oxygen for 2 weeks while treated with IL-18BP or vehicle. Cardiac function and morphology were measured using echocardiography, intraventricular pressure measurements and magnetic resonance imaging (MRI). For characterization of molecular changes in the heart, both real-time PCR and Western blotting were performed. ELISA technique was used to measure levels of circulating cytokines.

RESULTS

As expected, exposure to hypoxia-induced LV diastolic dysfunction, as shown by prolonged time constant of isovolumic relaxation (τ). Improved relaxation with IL-18BP treatment was demonstrated by a significant reduction towards control τ values. Decreased levels of phosphorylated phospholamban (P-PLB) in hypoxia, but normalization by IL-18BP treatment suggest a role for IL-18 in regulation of calcium-handling proteins in hypoxia-induced diastolic dysfunction. In addition, MRI showed less increase in right ventricular (RV) wall thickness in IL-18BP-treated animals exposed to hypoxia, indicating an effect on RV hypertrophy.

CONCLUSION

Neutralization of IL-18 during alveolar hypoxia improves LV diastolic function and partly prevents RV hypertrophy.

Osteoglycin Prevents Cardiac Dilatation and Dysfunction After Myocardial Infarction Through Infarct Collagen Strengthening

Rationale:

To maintain cardiac mechanical and structural integrity after an ischemic insult, profound alterations occur within the extracellular matrix. Osteoglycin is a small leucine-rich proteoglycan previously described as a marker of cardiac hypertrophy.

Objective:

To establish whether osteoglycin may play a role in cardiac integrity and function after myocardial infarction (MI).

Methods and Results:

Osteoglycin expression is associated with collagen deposition and scar formation in mouse and human MI. Absence of osteoglycin in mice resulted in significantly increased rupture-related mortality with tissue disruption, intramyocardial bleeding, and increased cardiac dysfunction, despite equal infarct sizes. Surviving osteoglycin null mice had greater infarct expansion in comparison with wild-type mice because of impaired collagen fibrillogenesis and maturation in the infarcts as revealed by electron microscopy and collagen polarization. Absence of osteoglycin did not affect cardiomyocyte hypertrophy in the remodeling remote myocardium. In cultured fibroblasts, osteoglycin knockdown or supplementation did not alter transforming growth factor-β signaling. Adenoviral overexpression of osteoglycin in wild-type mice significantly improved collagen quality, thereby blunting cardiac dilatation and dysfunction after MI. In osteoglycin null mice, adenoviral overexpression of osteoglycin was unable to prevent rupture-related mortality because of insufficiently restoring osteoglycin protein levels in the heart. Finally, circulating osteoglycin levels in patients with heart failure were significantly increased in the patients with a previous history of MI compared with those with nonischemic heart failure and correlated with survival, left ventricular volumes, and other markers of fibrosis.

Conclusions:

Increased osteoglycin expression in the infarct scar promotes proper collagen maturation and protects against cardiac disruption and adverse remodeling after MI. In human heart failure, osteoglycin is a promising biomarker for ischemic heart failure.

High throughput phenotyping of left and right ventricular cardiomyopathy in calcineurin transgene mice

Consistent protocols for the assessment of diastolic and systolic cardiac function to assure the comparability of existing data on preclinical models are missing. Calcineurin transgene (CN) mice are a preclinical model for hypertrophic and failing hearts. We aimed at evaluating left and right ventricular structural and functional remodeling in CN hearts with an optimized phenotyping protocol. We developed a protocol using techniques and indices comparable to those from human diagnostics for comprehensive in vivo cardiac screening using high-frequency echocardiography, Doppler, electrocardiography and cardiac magnetic resonance (CMR) techniques. We measured left and right ventricular dimensions and function, pulmonary and mitral flow pattern and the hearts electrophysiology non-invasively in <1 h per mouse. We found severe biventricular dilation and a drastic decline in performance in accordance with a condition of heart failure (HF), diastolic dysfunction and defects in electrical conduction in 8-week-old calcineurin transgenic mice. Echocardiography of the left ventricle was performed with and without anesthesia. In all cases absolute values on echocardiography compared with CMR were smaller for LV dimension and wall thickness, resulting in higher fractional shorting and ejection fraction. The study protocol described here opens opportunities to assess the added value of combined echocardiography, Doppler, CMR and ECG recording techniques for the diagnosis of biventricular cardiac pathologies i.e. of HF and to study symptom occurrence and disease progression non-invasively in high-throughput. Phenotyping CN hearts revealed new symptom occurrence and allowed insights into the diverse phenotype of hypertrophic failing hearts.

Effect of lactation on maternal postpartum cardiac function and adiposity: a murine model

OBJECTIVE

Lactation is associated with reduction in maternal metabolic disease and hypertension later in life; however, findings in humans may be confounded by socioeconomic factors. We sought to determine the independent contribution of lactation on cardiovascular parameters and adiposity in a murine model.

STUDY DESIGN

Following delivery, CD-1 female mice were randomly divided into 2 groups: lactated (L; nursed pups for 3 weeks, n = 10), and nonlactated (NL; pups were removed after birth, n = 12). Blood pressure (BP) was assessed prepregnancy and at 1 and 2 months' postpartum. Visceral and subcutaneous adipose tissue determined by computed tomography and left ventricular ejection fraction, cardiac output, and the E/A ratio determined by microultrasound were evaluated at 1 and 2 months' postpartum. The results were analyzed using a Student t test (significance at P < .05).

RESULTS

We observed a significantly different maternal BP at 2 months' postpartum with relatively greater BP in NL (systolic BP: NL, 122.2 ± 7.2 vs L, 96.8 ± 9.8 mm Hg; P = .04; diastolic BP: NL, 87.0 ± 6.8 vs L, 65.9 ± 6.2 mm Hg; P = .04). Visceral adipose tissue was significantly increased in NL mice at 1 (22.0 ± 4.1% vs 10.7 ± 1.8%, P = .04) and 2 months' postpartum (22.9 ± 3.5% vs 11.2 ± 2.2%, P = .02), whereas subcutaneous adipose tissue did not differ between the groups. At 2 months' postpartum, ejection fraction (51.8 ± 1.5% vs 60.5 ± 3.8%; P = .04), cardiac output (14.2 ± 1.0 vs 18.0 ± 1.3 mL/min; P = .02) and mitral valve E/A ratio (1.38 ± 0.06 vs 1.82 ± 0.13; P = .04) were significantly lower in NL mice than L mice.

CONCLUSION

Our data provide evidence that interruption of lactation adversely affects postpartum maternal cardiovascular function and adiposity.

Normal electrocardiographic and echocardiographic (M-mode and two-dimensional) values in Polish Landrace pigs

BACKGROUND

Swine are recognized animal models of human cardiovascular diseases. Normal values of cardiac morphology and function have been published for swine but for smaller number of pigs and not for swine whose weights ranged up 100 kg. In order to improve the value of results of an investigation on cardiac morphology and function in swine when such data are extrapolated to humans, the aim of this study was to document electrocardiographic and echocardiographic measures of cardiac morphology and function in swine. The study comprised 170 single and repeated measurements that were made in 132 healthy domestic swine (Sus domesticus) whose weights ranged between 20-160 kg and were used as controls in three different experiments. All electrocardiographic and echocardiographic measurements in all swine were done under general anaesthesia.

RESULTS

Statistically significant correlations were found between body weight and heart rate (HR), the duration of the P-wave, the duration of the QRS interval, the duration of the QT interval, and the corrected QT ratio (QTc). Since body weight was positively correlated with age, statistically significant correlations were also found between age and HR, the duration of the P-wave, the duration of the QRS interval, the duration of the QT interval, and the QTc. We found that the thickness of the left ventricular wall and the internal diameter of the left ventricle increased with age and body weight. We also found positive trends between body weight and ejection fraction and body weight and fractional shortening. We also found a positive relationship between age, body weight, and the ratio of the left ventricular internal diameter to its wall thickness, as well as the relative left atrial size.

CONCLUSION

Many electro- and echocardiographic measures of cardiac morphology and function of healthy swine are related to their body weight. When the electro- and echocardiographic measures of domestic swine and humans are compared, the most comparable electrocardiographic values are those that were determined in swine whose body weights are not greater than 70 kg. In contrast, the most comparable echocardiographic measures are those that were determined in swine with a body weight of 40-110 kg.

Targeted inactivation of Cerberus like-2 leads to left ventricular cardiac hyperplasia and systolic dysfunction in the mouse

Previous analysis of the Cerberus like 2 knockout (Cerl2^−/−) mouse revealed a significant mortality during the first day after birth, mostly due to cardiac defects apparently associated with randomization of the left-right axis. We have however, identified Cerl2-associated cardiac defects, particularly a large increase in the left ventricular myocardial wall in neonates that cannot be explained by laterality abnormalities. Therefore, in order to access the endogenous role of Cerl2 in cardiogenesis, we analyzed the embryonic and neonatal hearts of Cerl2 null mutants that did not display a laterality phenotype. Neonatal mutants obtained from the compound mouse line Cer2^−/−::Mlc1v-nLacZ24⁺, in which the pulmonary ventricle is genetically marked, revealed a massive enlargement of the ventricular myocardium in animals without laterality defects. Echocardiography analysis in Cerl2^−/− neonates showed a left ventricular systolic dysfunction that is incompatible with a long lifespan. We uncovered that the increased ventricular muscle observed in Cerl2^−/− mice is caused by a high cardiomyocyte mitotic index in the compact myocardium which is mainly associated with increased Ccnd1 expression levels in the left ventricle at embryonic day (E) 13. Interestingly, at this stage we found augmented left ventricular expression of Cerl2 levels when compared with the right ventricle, which may elucidate the regionalized contribution of Cerl2 to the left ventricular muscle formation. Importantly, we observed an increase of phosphorylated Smad2 (pSmad2) levels in embryonic (E13) and neonatal hearts indicating a prolonged TGFβs/Nodal-signaling activation. Concomitantly, we detected an increase of Baf60c levels, but only in Cerl2^−/− embryonic hearts. These results indicate that independently of its well-known role in left-right axis establishment Cerl2 plays an important role during heart development in the mouse, mediating Baf60c levels by exerting an important control of the TGFβs/Nodal-signaling pathway.

Treatment of established left ventricular hypertrophy with fibroblast growth factor receptor blockade in an animal model of CKD

BACKGROUND

Activation of fibroblast growth factor receptor (FGFR)-dependent signalling by FGF23 may contribute to the complex pathogenesis of left ventricular hypertrophy (LVH) in chronic kidney disease (CKD). Pan FGFR blockade by PD173074 prevented development of LVH in the 5/6 nephrectomy rat model of CKD, but its ability to treat and reverse established LVH is unknown.

METHODS

CKD was induced in rats by 5/6 nephrectomy. Two weeks later, rats began treatment with vehicle (0.9% NaCl) or PD173074, 1 mg/kg once-daily for 3 weeks. Renal function was determined by urine and blood analyses. Left ventricular (LV) structure and function were determined by echocardiography, histopathology, staining for myocardial fibrosis (Sirius-Red) and investigating cardiac gene expression profiles by real-time PCR.

RESULTS

Two weeks after inducing CKD by 5/6 nephrectomy, rats manifested higher (mean ± SEM) systolic blood pressure (208 ± 4 versus 139 ± 3 mmHg; P < 0.01), serum FGF23 levels (1023 ± 225 versus 199 ± 9 pg/mL; P < 0.01) and LV mass (292 ± 9 versus 220 ± 3 mg; P < 0.01) when compared with sham-operated animals. Thereafter, 3 weeks of treatment with PD173074 compared with vehicle did not significantly change blood pressure, kidney function or metabolic parameters, but significantly reduced LV mass (230 ± 14 versus 341 ± 33 mg; P < 0.01), myocardial fibrosis (2.5 ± 0.7 versus 5.4 ± 0.95% staining/field; P < 0.01) and cardiac expression of genes associated with pathological LVH, while significantly increasing ejection fraction (18 versus 2.5% post-treatment increase; P < 0.05).

CONCLUSIONS

FGFR blockade improved cardiac structure and function in 5/6 nephrectomy rats with previously established LVH. These data support FGFR activation as a potentially modifiable, blood pressure-independent molecular mechanism of LVH in CKD.

High-throughput phenotypic assessment of cardiac physiology in four commonly used inbred mouse strains

Mice with genetic alterations are used in heart research as model systems of human diseases. In the last decade there was a marked increase in the recognition of genetic diversity within inbred mouse strains. Increasing numbers of inbred mouse strains and substrains and analytical variation of cardiac phenotyping methods require reproducible, high-throughput methods to standardize murine cardiovascular physiology. We describe methods for non-invasive, reliable, easy and fast to perform echocardiography and electrocardiography on awake mice. This method can be used for primary screening of the murine cardiovascular system in large-scale analysis. We provide insights into the physiological divergence of C57BL/6N, C57BL/6J, C3HeB/FeJ and 129P2/OlaHsd mouse hearts and define the expected normal values. Our report highlights that compared to the other three strains tested C57BL/6N hearts reveal features of heart failure such as hypertrophy and reduced contractile function. We found several features of the mouse ECG to be under genetic control and obtained several strain-specific differences in cardiac structure and function.

Deficiency of cardiac Acyl-CoA synthetase-1 induces diastolic dysfunction, but pathologic hypertrophy is reversed by rapamycin

In mice with temporally-induced cardiac-specific deficiency of acyl-CoA synthetase-1 (Acsl1(H-/-)), the heart is unable to oxidize long-chain fatty acids and relies primarily on glucose for energy. These metabolic changes result in the development of both a spontaneous cardiac hypertrophy and increased phosphorylated S6 kinase (S6K), a substrate of the mechanistic target of rapamycin, mTOR. Doppler echocardiography revealed evidence of significant diastolic dysfunction, indicated by a reduced E/A ratio and increased mean performance index, although the deceleration time and the expression of sarco/endoplasmic reticulum calcium ATPase and phospholamban showed no difference between genotypes. To determine the role of mTOR in the development of cardiac hypertrophy, we treated Acsl1(H-/-) mice with rapamycin. Six to eight week old Acsl1(H-/-) mice and their littermate controls were given i.p. tamoxifen to eliminate cardiac Acsl1, then concomitantly treated for 10weeks with i.p. rapamycin or vehicle alone. Rapamycin completely blocked the enhanced ventricular S6K phosphorylation and cardiac hypertrophy and attenuated the expression of hypertrophy-associated fetal genes, including α-skeletal actin and B-type natriuretic peptide. mTOR activation of the related Acsl3 gene, usually associated with pathologic hypertrophy, was also attenuated in the Acsl1(H-/-) hearts, indicating that alternative pathways of fatty acid activation did not compensate for the loss of Acsl1. Compared to controls, Acsl1(H-/-) hearts exhibited an 8-fold higher uptake of 2-deoxy[1-(14)C]glucose and a 35% lower uptake of the fatty acid analog 2-bromo[1-(14)C]palmitate. These data indicate that Acsl1-deficiency causes diastolic dysfunction and that mTOR activation is linked to the development of cardiac hypertrophy in Acsl1(H-/-) mice.

Bioluminescence imaging of cardiomyogenic and vascular differentiation of cardiac and subcutaneous adipose tissue-derived progenitor cells in fibrin patches in a myocardium infarct model

BACKGROUND

Adipose tissue-derived progenitor cells (ATDPCs) isolated from human cardiac adipose tissue are useful for cardiac regeneration in rodent models. These cells do not express cardiac troponin I (cTnI) and only express low levels of PECAM-1 when cultured under standard conditions. The purpose of the present study was to evaluate changes in cTnI and PECAM-1 gene expression in cardiac ATDPCs following their delivery through a fibrin patch to a murine model of myocardial infarction using a non-invasive bioluminescence imaging procedure.

METHODS AND RESULTS

Cardiac and subcutaneous ATDPCs were doubly transduced with lentiviral vectors for the expression of chimerical bioluminescent-fluorescent reporters driven by constitutively active and tissue-specific promoters (cardiac and endothelial for cTnI and PECAM-1, respectively). Labeled cells mixed with fibrin were applied as a 3-D fibrin patch over the infarcted tissue. Both cell types exhibited de novo expression of cTnI, though the levels were remarkably higher in cardiac ATDPCs. Endothelial differentiation was similar in both ATDPCs, though cardiac cells induced vascularization more effectively. The imaging results were corroborated by standard techniques, validating the use of bioluminescence imaging for in vivo analysis of tissue repair strategies. Accordingly, ATDPC treatment translated into detectable functional and morphological improvements in heart function.

CONCLUSIONS

Both ATDPCs differentiate to the endothelial lineage at a similar level, cardiac ATDPCs differentiated more readily to the cardiomyogenic lineage than subcutaneous ATDPCs. Non-invasive bioluminescence imaging was a useful tool for real time monitoring of gene expression changes in implanted ATDPCs that could facilitate the development of procedures for tissue repair.

Cardiac assessment in pediatric mice: strain analysis as a diagnostic measurement

Echocardiography is a robust tool for assessing cardiac function in both humans and laboratory animals. Conventional echocardiographic measurements, including chamber dimensions, wall thickness, and ejection fraction are routinely obtained to assess cardiac function in mice. Recently, myocardial strain and strain rate measurements have been added to functional assessments to provide additional details on regional abnormalities that are not evident using conventional measurements. To date, all studies of strain and strain rate in mice or rats have involved adult animals. This study serves to outline methods for acquiring echocardiographic images in pediatric mice and to provide myocardial strain and strain rate values for healthy C57BL/6J mice between 3 and 11 weeks old. Between weeks 3 and 11, left ventricular radial strain ranged from 32 to 43% and longitudinal strain ranged from -15 to -19%, with analysis over time showing no significant changes with aging (radial strain, P = 0.192 and longitudinal strain, P = 0.264; n = 4 for each time point evaluated). In conclusion, myocardial strain analysis in pediatric mice is technically feasible and has potential application in studying the pathophysiology of pediatric cardiovascular disease.

Rapamycin extends murine lifespan but has limited effects on aging

Aging is a major risk factor for a large number of disorders and functional impairments. Therapeutic targeting of the aging process may therefore represent an innovative strategy in the quest for novel and broadly effective treatments against age-related diseases. The recent report of lifespan extension in mice treated with the FDA-approved mTOR inhibitor rapamycin represented the first demonstration of pharmacological extension of maximal lifespan in mammals. Longevity effects of rapamycin may, however, be due to rapamycin's effects on specific life-limiting pathologies, such as cancers, and it remains unclear if this compound actually slows the rate of aging in mammals. Here, we present results from a comprehensive, large-scale assessment of a wide range of structural and functional aging phenotypes, which we performed to determine whether rapamycin slows the rate of aging in male C57BL/6J mice. While rapamycin did extend lifespan, it ameliorated few studied aging phenotypes. A subset of aging traits appeared to be rescued by rapamycin. Rapamycin, however, had similar effects on many of these traits in young animals, indicating that these effects were not due to a modulation of aging, but rather related to aging-independent drug effects. Therefore, our data largely dissociate rapamycin's longevity effects from effects on aging itself.

Cardiac-respiratory self-gated cine ultra-short echo time (UTE) cardiovascular magnetic resonance for assessment of functional cardiac parameters at high magnetic fields

BACKGROUND

To overcome flow and electrocardiogram-trigger artifacts in cardiovascular magnetic resonance (CMR), we have implemented a cardiac and respiratory self-gated cine ultra-short echo time (UTE) sequence. We have assessed its performance in healthy mice by comparing the results with those obtained with a self-gated cine fast low angle shot (FLASH) sequence and with echocardiography.

METHODS

2D self-gated cine UTE (TE/TR = 314 μs/6.2 ms, resolution: 129 × 129 μm, scan time per slice: 5 min 5 sec) and self-gated cine FLASH (TE/TR = 3 ms/6.2 ms, resolution: 129 × 129 μm, scan time per slice: 4 min 49 sec) images were acquired at 9.4 T. Volume of the left and right ventricular (LV, RV) myocardium as well as the end-diastolic and -systolic volume was segmented manually in MR images and myocardial mass, stroke volume (SV), ejection fraction (EF) and cardiac output (CO) were determined. Statistical differences were analyzed by using Student t test and Bland-Altman analyses.

RESULTS

Self-gated cine UTE provided high quality images with high contrast-to-noise ratio (CNR) also for the RV myocardium (CNRblood-myocardium = 25.5 ± 7.8). Compared to cine FLASH, susceptibility, motion, and flow artifacts were considerably reduced due to the short TE of 314 μs. The aortic valve was clearly discernible over the entire cardiac cycle. Myocardial mass, SV, EF and CO determined by self-gated UTE were identical to the values measured with self-gated FLASH and showed good agreement to the results obtained by echocardiography.

CONCLUSIONS

Self-gated UTE allows for robust measurement of cardiac parameters of diagnostic interest. Image quality is superior to self-gated FLASH, rendering the method a powerful alternative for the assessment of cardiac function at high magnetic fields.

BMPER regulates cardiomyocyte size and vessel density in vivo

BACKGROUND

BMPER, an orthologue of Drosophila melanogaster Crossveinless-2, is a secreted factor that regulates bone morphogenetic protein activity in endothelial cell precursors and during early cardiomyocyte differentiation. Although previously described in the heart, the role of BMPER in cardiac development and function remain unknown.

METHODS

BMPER-deficient hearts were phenotyped histologically and functionally using echocardiography and Doppler analysis. Since BMPER -/- mice die perinatally, adult BMPER +/- mice were challenged to pressure-overload-induced cardiac hypertrophy and hindlimb ischemia to determine changes in angiogenesis and regulation of cardiomyocyte size.

RESULTS

We identify for the first time the cardiac phenotype associated with BMPER haploinsufficiency. BMPER messenger RNA and protein are present in the heart during cardiac development through at least E14.5 but is lost by E18.5. BMPER +/- ventricles are thinner and less compact than sibling wild-type hearts. In the adult, BMPER +/- hearts present with decreased anterior and posterior wall thickness, decreased cardiomyocyte size and an increase in cardiac vessel density. Despite these changes, BMPER +/- mice respond to pressure-overload-induced cardiac hypertrophy challenge largely to the same extent as wild-type mice.

CONCLUSION

BMPER appears to play a role in regulating both vessel density and cardiac development in vivo; however, BMPER haploinsufficiency does not result in marked effects on cardiac function or adaptation to pressure overload hypertrophy.

Prion protein as a mediator of neurocardiosympathetic interactions

A proteomic approach to study cardiovascular disease includes the examination of proteins associated with risk factors such as left ventricular hypertrophy (LVH). PrP(C) is a host-coded membrane-bound glycoprotein found in most cell types, including myocardium, and whose physiological function is uncertain. We have taken a selective proteomic approach and performed mechanistic studies to determine whether PrP(C) levels are related to left ventricular (LV) structure or function. Echocardiograms were performed at baseline in 65 mice comprising three strains of the same C57Bl/6J × 129SV genetic background but expressing different levels of PrP(C) (wild-type mice (WT), PrP(-/-) , and PrP(C) over-expressing transgenic mice (tga20)). There were no significant differences in LV mass or LV ejection fraction between the three groups. Either normal saline (n = 60) or isoproterenol (n = 55) was then administered intraperitoneally (50 mg/kg/day) for 5 days/wk for two consecutive weeks to induce LVH. Body weight decreased significantly in the PrP(-/-) group (18%). On multivariate analysis, higher LV mass index posttreatment was independently associated with the tga20 group (versus PrP(-/-) versus WT, p = 0.002) after adjusting for treatment (isoproterenol versus saline), and weight change (r(2) = 0.13 for model, p = 0.016). Therefore, PrP(C) appears unrelated to LV mass and function in the basal state. Isoproterenol causes transient enhancement of PrP(C) expression in WT mice and a more pronounced increase in tga20 mice at 2 h posttreatment. Overexpression of PrP(C) in the tga20 group may be associated with higher LV mass after a 2 wk regimen of isoproterenol.

Application of echocardiography on transgenic mice with cardiomyopathies

Cardiomyopathies are common cardiac disorders that primarily affect cardiac muscle resulting in cardiac dysfunction and heart failure. Transgenic mouse disease models have been developed to investigate the cellular mechanisms underlying heart failure and sudden cardiac death observed in cardiomyopathy cases and to explore the therapeutic outcomes in experimental animals in vivo. Echocardiography is an essential diagnostic tool for accurate and noninvasive assessment of cardiac structure and function in experimental animals. Our laboratory has been among the first to apply high-frequency research echocardiography on transgenic mice with cardiomyopathies. In this work, we have summarized our and other studies on assessment of systolic and diastolic dysfunction using conventional echocardiography, pulsed Doppler, and tissue Doppler imaging in transgenic mice with various cardiomyopathies. Estimation of embryonic mouse hearts has been performed as well using this high-resolution echocardiography. Some technical considerations in mouse echocardiography have also been discussed.

Mice with cardiac overexpression of peroxisome proliferator-activated receptor γ have impaired repolarization and spontaneous fatal ventricular arrhythmias

BACKGROUND

Diabetes mellitus and obesity, which confer an increased risk of sudden cardiac death, are associated with cardiomyocyte lipid accumulation and altered cardiac electric properties, manifested by prolongation of the QRS duration and QT interval. It is difficult to distinguish the contribution of cardiomyocyte lipid accumulation from the contribution of global metabolic defects to the increased incidence of sudden death and electric abnormalities.

METHODS AND RESULTS

In order to study the effects of metabolic abnormalities on arrhythmias without the complex systemic effects of diabetes mellitus and obesity, we studied transgenic mice with cardiac-specific overexpression of peroxisome proliferator-activated receptor γ 1 (PPARγ1) via the cardiac α-myosin heavy-chain promoter. The PPARγ transgenic mice develop abnormal accumulation of intracellular lipids and die as young adults before any significant reduction in systolic function. Using implantable ECG telemeters, we found that these mice have prolongation of the QRS and QT intervals and spontaneous ventricular arrhythmias, including polymorphic ventricular tachycardia and ventricular fibrillation. Isolated cardiomyocytes demonstrated prolonged action potential duration caused by reduced expression and function of the potassium channels responsible for repolarization. Short-term exposure to pioglitazone, a PPARγ agonist, had no effect on mortality or rhythm in WT mice but further exacerbated the arrhythmic phenotype and increased the mortality in the PPARγ transgenic mice.

CONCLUSIONS

Our findings support an important link between PPARγ activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality.

Ultrasound biomicroscopy in small animal research: applications in molecular and preclinical imaging

Ultrasound biomicroscopy (UBM) is a noninvasive multimodality technique that allows high-resolution imaging in mice. It is affordable, widely available, and portable. When it is coupled to Doppler ultrasound with color and power Doppler, it can be used to quantify blood flow and to image microcirculation as well as the response of tumor blood supply to cancer therapy. Target contrast ultrasound combines ultrasound with novel molecular targeted contrast agent to assess biological processes at molecular level. UBM is useful to investigate the growth and differentiation of tumors as well as to detect early molecular expression of cancer-related biomarkers in vivo and to monitor the effects of cancer therapies. It can be also used to visualize the embryological development of mice in uterus or to examine their cardiovascular development. The availability of real-time imaging of mice anatomy allows performing aspiration procedures under ultrasound guidance as well as the microinjection of cells, viruses, or other agents into precise locations. This paper will describe some basic principles of high-resolution imaging equipment, and the most important applications in molecular and preclinical imaging in small animal research.

Coronary artery ligation and intramyocardial injection in a murine model of infarction

Mouse models are a valuable tool for studying acute injury and chronic remodeling of the myocardium in vivo. With the advent of genetic modifications to the whole organism or the myocardium and an array of biological and/or synthetic materials, there is great potential for any combination of these to assuage the extent of acute ischemic injury and impede the onset of heart failure pursuant to myocardial remodeling.

Here we present the methods and materials used to reliably perform this microsurgery and the modifications involved for temporary (with reperfusion) or permanent coronary artery occlusion studies as well as intramyocardial injections. The effects on the heart that can be seen during the procedure and at the termination of the experiment in addition to histological evaluation will verify efficacy.

Briefly, surgical preparation involves anesthetizing the mice, removing the fur on the chest, and then disinfecting the surgical area. Intratracheal intubation is achieved by transesophageal illumination using a fiber optic light. The tubing is then connected to a ventilator. An incision made on the chest exposes the pectoral muscles which will be cut to view the ribs. For ischemia/reperfusion studies, a 1 cm piece of PE tubing placed over the heart is used to tie the ligature to so that occlusion/reperfusion can be customized. For intramyocardial injections, a Hamilton syringe with sterile 30gauge beveled needle is used. When the myocardial manipulations are complete, the rib cage, the pectoral muscles, and the skin are closed sequentially. Line block analgesia is effected by 0.25% marcaine in sterile saline which is applied to muscle layer prior to closure of the skin. The mice are given a subcutaneous injection of saline and placed in a warming chamber until they are sternally recumbent. They are then returned to the vivarium and housed under standard conditions until the time of tissue collection. At the time of sacrifice, the mice are anesthetized, the heart is arrested in diastole with KCl or BDM, rinsed with saline, and immersed in fixative. Subsequently, routine procedures for processing, embedding, sectioning, and histological staining are performed.

Nonsurgical intubation of a mouse and the microsurgical manipulations described make this a technically challenging model to learn and achieve reproducibility. These procedures, combined with the difficulty in performing consistent manipulations of the ligature for timed occlusion(s) and reperfusion or intramyocardial injections, can also affect the survival rate so optimization and consistency are critical.

Syndecan-4 signalling inhibits apoptosis and controls NFAT activity during myocardial damage and remodelling

AIMS

Myocardial infarction (MI) results in acute impairment of left ventricular (LV) function through the initial development of cardiomyocyte death and subsequent progression of LV remodelling. The expression of syndecan-4 (Sdc4), a transmembrane proteoglycan, is up-regulated after MI, but its function in the heart remains unknown. Here, we characterize the effects of Sdc4 deficiency in murine myocardial ischaemia and permanent infarction.

METHODS AND RESULTS

Targeted deletion of Sdc4 (Sdc4(-/-)) leads to increased myocardial damage after ischaemic-reperfusion injury due to enhanced cardiomyocyte apoptosis associated with reduced activation of extracellular signal-regulated kinase in cardiomyocytes in vitro and in vivo. After ischaemic-reperfusion injury and permanent infarction, we observed an increase in cardiomyocyte area, nuclear translocation of nuclear factor of activated T cells (NFAT), and transcription of the NFAT target rcan1.4 in wild-type mice. NFAT pathway activation was enhanced in Sdc4(-/-) mice. In line with the in vivo data, NFAT activation and hypertrophy occurs in isolated cardiomyocytes with reduced Sdc4 expression during phenylephrine stimulation in vitro. Despite the initially increased myocardial damage, echocardiography revealed improved LV geometry and function in Sdc4(-/-) mice 7 days after MI.

CONCLUSION

Interception of the Sdc4 pathway enhances infarct expansion and hypertrophic remodelling during early infarct healing in ischaemic-reperfusion injury and permanent infarction mouse models and exerts net beneficial effects on LV function.

Effects of heart rate and anesthetic timing on high-resolution echocardiographic assessment under isoflurane anesthesia in mice

OBJECTIVE

Anesthesia provides sedation and immobility, facilitating echocardiography in mice, but it influences cardiovascular function and therefore outcomes of measurement. This study aimed to determine the effect of the optimal heart rate (HR) and anesthetic timing on echocardiographic reproducibility under isoflurane anesthesia.

METHODS

Male C57BL/6J mice underwent high-resolution echocardiography with relative fixed HRs and anesthetic timing. The same experiment was repeated once again after 1 week.

RESULTS

Echocardiography was highly reproducible in repeated measurements under low-HR (350-400 beats per minute [bpm]) and high-HR (475-525 bpm) conditions except some M-mode parameters under low-HR conditions. With similar anesthetic timing, mice with a high HR had decreased preload indices and increased ejection phase and Doppler indices. Inversely, when the HR was similar, the echocardiographic results of mice under short anesthetic timing showed little difference from the ones under long anesthetic timing.

CONCLUSIONS

This study shows that echocardiographic assessment is greatly reproducible under a high HR. The HR is more important than anesthetic timing for echocardiographic evaluation in mice.

Characterization and in vivo pharmacological rescue of a Wnt2-Gata6 pathway required for cardiac inflow tract development

Little is understood about the molecular mechanisms underlying the morphogenesis of the posterior pole of the heart. Here we show that Wnt2 is expressed specifically in the developing inflow tract mesoderm, which generates portions of the atria and atrio-ventricular canal. Loss of Wnt2 results in defective development of the posterior pole of the heart, resulting in a phenotype resembling the human congenital heart syndrome complete common atrio-ventricular canal. The number and proliferation of posterior second heart field progenitors is reduced in Wnt2(-/-) mutants. Moreover, these defects can be rescued in a temporally restricted manner through pharmacological inhibition of Gsk-3beta. We also show that Wnt2 works in a feedforward transcriptional loop with Gata6 to regulate posterior cardiac development. These data reveal a molecular pathway regulating the posterior cardiac mesoderm and demonstrate that cardiovascular defects caused by loss of Wnt signaling can be rescued pharmacologically in vivo.