ECHO parameters of diastolic dysfunction

PathoClock and PhysioClock in mice recapitulate human multimorbidity and heterogeneous aging

BACKGROUND

Multimorbidity is a public health concern and an essential component of aging and healthspan but understudied because investigative tools are lacking that can be translatable to capture similarities and differences of the aging process across species and variability between individuals and individual organs.

METHODS

To help address this need, body organ disease number (BODN) borrowed from human studies was applied to C57BL/6 (B6) and CB6F1 mouse strains at 8, 16, 24, and 32 months of age, as a measure of systems morbidity based on pathology lesions to develop a mouse PathoClock resembling clinically-based Body Clock in humans, using Bayesian inference. A mouse PhysioClock was also developed based on measures of physiological domains including cardiovascular, neuromuscular, and cognitive function in the same two mouse strains so that alignment with BODN was predictable.

RESULTS

Between- and within-age variabilities in PathoClock and PhysioClock, as well as between-strain variabilities. Both PathoClock and PhysioClock correlated with chronological age more strongly in CB6F1 than C57BL/6. Prediction models were then developed, designated as PathoAge and PhysioAge, using regression models of pathology and physiology measures on chronological age. PathoAge better predicted chronological age than PhysioAge as the predicted chronological and observed chronological age for PhysioAge were complex rather than linear.

CONCLUSION

PathoClock and PhathoAge can be used to capture biological changes that predict BODN, a metric developed in humans, and compare multimorbidity across species. These mouse clocks are potential translational tools that could be used in aging intervention studies.

Guidelines for measuring cardiac physiology in mice

Cardiovascular disease is a leading cause of death, and translational research is needed to understand better mechanisms whereby the left ventricle responds to injury. Mouse models of heart disease have provided valuable insights into mechanisms that occur during cardiac aging and in response to a variety of pathologies. The assessment of cardiovascular physiological responses to injury or insult is an important and necessary component of this research. With increasing consideration for rigor and reproducibility, the goal of this guidelines review is to provide best-practice information regarding how to measure accurately cardiac physiology in animal models. In this article, we define guidelines for the measurement of cardiac physiology in mice, as the most commonly used animal model in cardiovascular research.

Listen to this article’s corresponding podcast at http://ajpheart.podbean.com/e/guidelines-for-measuring-cardiac-physiology-in-mice/.

Acute Catecholamine Exposure Causes Reversible Myocyte Injury Without Cardiac Regeneration

RATIONALE

Catecholamines increase cardiac contractility, but exposure to high concentrations or prolonged exposures can cause cardiac injury. A recent study demonstrated that a single subcutaneous injection of isoproterenol (ISO; 200 mg/kg) in mice causes acute myocyte death (8%-10%) with complete cardiac repair within a month. Cardiac regeneration was via endogenous cKit(+) cardiac stem cell-mediated new myocyte formation.

OBJECTIVE

Our goal was to validate this simple injury/regeneration system and use it to study the biology of newly forming adult cardiac myocytes.

METHODS AND RESULTS

C57BL/6 mice (n=173) were treated with single injections of vehicle, 200 or 300 mg/kg ISO, or 2 daily doses of 200 mg/kg ISO for 6 days. Echocardiography revealed transiently increased systolic function and unaltered diastolic function 1 day after single ISO injection. Single ISO injections also caused membrane injury in ≈10% of myocytes, but few of these myocytes appeared to be necrotic. Circulating troponin I levels after ISO were elevated, further documenting myocyte damage. However, myocyte apoptosis was not increased after ISO injury. Heart weight to body weight ratio and fibrosis were also not altered 28 days after ISO injection. Single- or multiple-dose ISO injury was not associated with an increase in the percentage of 5-ethynyl-2'-deoxyuridine-labeled myocytes. Furthermore, ISO injections did not increase new myocytes in cKit(+/Cre)×R-GFP transgenic mice.

CONCLUSIONS

A single dose of ISO causes injury in ≈10% of the cardiomyocytes. However, most of these myocytes seem to recover and do not elicit cKit(+) cardiac stem cell-derived myocyte regeneration.

Left Ventricular Diastolic Dysfunction Assessed by Conventional Echocardiography and Spectral Tissue Doppler Imaging in Adolescents With Arterial Hypertension

Compared to conventional echocardiography, spectral tissue Doppler imaging (s-TDI) allows more precise evaluation of diastolic cardiac function. The purpose of this study was to conduct s-TDI to analyze the slow movement of the left ventricular (LV) myocardium in adolescents with systemic arterial hypertension (HT) and to determine whether patients with HT suffer from LV diastolic dysfunction. The study group comprised 69 consecutive patients (48 boys and 21 girls aged 14-17 years [mean, 15.5 ± 1.1 years]) with primary HT, and the control group comprised 48 healthy participants (24 boys and 24 girls aged 14-17 years [mean, 15.8 ± 1.3 years]). Physical examinations, 24-hour arterial blood pressure monitoring, conventional 2-dimensional and Doppler echocardiography, and s-TDIs were performed. Analysis revealed that study group participants were significantly heavier and had greater LV mass indices than controls (P < 0.001). There were no differences between the velocities of E waves (peak early filling of mitral inflow), but the deceleration times of the mitral E waves were significantly shorter whereas the A waves survived longer in the study group than in the control group. The velocities of A waves (peak late filling of mitral inflow) were elevated (P = 0.041), and the E/A wave pattern (E/A = 1.8 ± 0.4) was normal. These results suggest pseudonormalization, a type of LV diastolic dysfunction in adolescents with HT.In the study group, when the sample volume was positioned at the septal or lateral insertion site of the mitral leaflet, the e' wave velocity was significantly depressed whereas the a' wave velocity was elevated, compared to those of the control group (P < 0.001).The e'/a' ratios from the septal and lateral insertion sites were lower, whereas the E/e' ratio from the septal insertion site was significantly higher in the study group, similar to that seen in atrial reversal velocity (P < 0.001).These findings indicate that using sTDI to find and measure diastolic LV failure is valuable when the probe is placed at the septal and lateral mitral valve annuli during examination.Changes in the myocardium appear similar to those seen in adults.

The role of 1.5 tesla MRI and anesthetic regimen concerning cardiac analysis in mice with cardiomyopathy

Accurate assessment of left ventricular function in rodent models is essential for the evaluation of new therapeutic approaches for cardiac diseases. In our study, we provide new insights regarding the role of a 1.5 Tesla (T) magnetic resonance imaging (MRI) device and different anesthetic regimens on data validity. As dedicated small animal MRI and echocardiographic devices are not broadly available, we evaluated whether monitoring cardiac function in small rodents with a clinical 1.5 T MRI device is feasible. On a clinical electrocardiogram (ECG) synchronized 1.5 T MRI scanner we therefore studied cardiac function parameters of mice with chronic virus-induced cardiomyopathy. Thus, reduced left ventricular ejection fraction (LVEF) could be verified compared to healthy controls. However, our results showed a high variability. First, anesthesia with medetomidine, midazolam and fentanyl (MMF) led to depressed cardiac function parameters and more variability than isoflurane gas inhalation anesthesia, especially at high concentrations. Furthermore, calculation of an average ejection fraction value from sequenced scans significantly reduced the variance of the results. To sum up, we introduce the clinical 1.5 T MRI device as a new tool for effective analysis of left ventricular function in mice with cardiomyopathy. Besides, we suggest isoflurane gas inhalation anesthesia at high concentrations for variance reduction and recommend calculation of an average ejection fraction value from multiple sequenced MRI scans to provide valid data and a solid basis for further clinical testing.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

Echocardiographic Characterization of Postnatal Development in Mice with Reduced Arterial Elasticity

PURPOSE

Decreased expression of elastin results in smaller, less compliant arteries and high blood pressure. In mice, these differences become more significant with postnatal development. It is known that arterial size and compliance directly affect cardiac function, but the temporal changes in cardiac function have not been investigated in elastin insufficient mice. The aim of this study is to correlate changes in arterial size and compliance with cardiac function in wildtype (WT) and elastin haploinsufficient (Eln^+/- ) mice from birth to adulthood.

METHODS

Ultrasound scans were performed at the ages of 3, 7, 14, 21, 30, 60, and 90 days on male and female WT and Eln^+/- mice. 2-D ultrasound and pulse wave Doppler images were used to measure the dimensions and function of the left ventricle (LV), ascending aorta and carotid arteries.

RESULTS

Eln^+/- arteries are smaller and less compliant at most ages, with significant differences from WT as early as 3 days old. Surprisingly, there are no correlations (R² < 0.2) between arterial size and compliance with measures of LV hypertrophy or systolic function. There are weak correlations (0.2 < R² < 0.5) between arterial size and compliance with measures of LV diastolic function.

CONCLUSIONS

Eln^+/- mice have similar cardiac function to WT throughout postnatal development, demonstrating the remarkable ability of the developing cardiovascular system to adapt to mechanical and hemodynamic changes. Correlations between arterial size and compliance with diastolic function show that these measures may be useful indicators of early diastolic dysfunction.

Increased myofilament Ca2+ sensitivity and diastolic dysfunction as early consequences of Mybpc3 mutation in heterozygous knock-in mice

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in MYBPC3 encoding cardiac myosin-binding protein C (cMyBP-C). The mechanisms leading from gene mutations to the HCM phenotype remain incompletely understood, partially because current mouse models of HCM do not faithfully reflect the human situation and early hypertrophy confounds the interpretation of functional alterations. The goal of this study was to evaluate whether myofilament Ca(2+) sensitization and diastolic dysfunction are associated or precede the development of left ventricular hypertrophy (LVH) in HCM. We evaluated the function of skinned and intact cardiac myocytes, as well as the intact heart in a recently developed Mybpc3-targeted knock-in mouse model carrying a point mutation frequently associated with HCM. Compared to wild-type, 10-week old homozygous knock-in mice exhibited i) higher myofilament Ca(2+) sensitivity in skinned ventricular trabeculae, ii) lower diastolic sarcomere length, and faster Ca(2+) transient decay in intact myocytes, and iii) LVH, reduced fractional shortening, lower E/A and E'/A', and higher E/E' ratios by echocardiography and Doppler analysis, suggesting systolic and diastolic dysfunction. In contrast, heterozygous knock-in mice, which mimic the human HCM situation, did not exhibit LVH or systolic dysfunction, but exhibited higher myofilament Ca(2+) sensitivity, faster Ca(2+) transient decay, and diastolic dysfunction. These data demonstrate that myofilament Ca(2+) sensitization and diastolic dysfunction are early phenotypic consequences of Mybpc3 mutations independent of LVH. The accelerated Ca(2+) transients point to compensatory mechanisms directed towards normalization of relaxation. We propose that HCM is a model for diastolic heart failure and this mouse model could be valuable in studying mechanisms and treatment modalities.