Heart Plasticity in Response to Pressure- and Volume-Overload: A Review of Findings in Compensated and Decompensated Phenotypes

Multiscale Finite Element Modeling of Left Ventricular Growth in Simulations of Valve Disease

Multiscale models of the cardiovascular system are emerging as effective tools for investigating the mechanisms that drive ventricular growth and remodeling. These models can predict how molecular-level mechanisms impact organ-level structure and function and could provide new insights that help improve patient care. MyoFE is a multiscale computer framework that bridges molecular and organ-level mechanisms in a finite element model of the left ventricle that is coupled with the systemic circulation. In this study, we extend MyoFE to include a growth algorithm, based on volumetric growth theory, to simulate concentric growth (wall thickening/thinning) and eccentric growth (chamber dilation/constriction) in response to valvular diseases. Specifically in our model, concentric growth is controlled by time-averaged total stress along the fiber direction over a cardiac cycle while eccentric growth responds to time-averaged intracellular myofiber passive stress over a cardiac cycle. The new framework correctly predicted different forms of growth in response to two types of valvular diseases, namely aortic stenosis and mitral regurgitation. Furthermore, the model predicted that LV size and function are nearly restored (reversal of growth) when the disease-mimicking perturbation was removed in the simulations for each valvular disorder. In conclusion, the simulations suggest that time-averaged total stress along the fiber direction and time-averaged intracellular myofiber passive stress can be used to drive concentric and eccentric growth in simulations of valve disease.

Disruption of the interaction between caveolae and Piezo1 promotes pressure overload-induced cardiac remodeling

Piezo1 channels are activated by mechanical stress and play a significant role in cardiac hypertrophy and fibrosis. However, the molecular mechanisms underlying Piezo1 activation on the cell membrane following pressure overload remain unclear. Caveolae are known to mitigate mechanical forces and regulate Piezo1 function. Therefore, this study aimed to investigate the interaction between caveolae and Piezo1 in the development of pressure overload-induced cardiac remodeling. We observed reduced colocalization between Piezo1 and Caveolin-3 in hypertrophic cardiomyocytes following abdominal aortic constriction and Angiotensin-II treatment, accompanied by increased Piezo1 function and expression. Furthermore, enhanced Piezo1 function was also noted upon caveolae disruption using methyl-beta-cyclodextrin (mβCD). Thus, our findings suggested that pressure overload led to Piezo1 translocation from caveolae, thereby augmenting its function and expression, which may contribute to cardiac remodeling.

Enriched housing differentially alters allostatic load and cardiopulmonary responses to wildfire-related smoke in male and female mice

Living conditions are an important modifier of individual health outcomes and may lead to higher allostatic load (AL). However, housing-induced cardiovascular and immune effects contributing to altered environmental responsiveness remain understudied. This investigation was conducted to examine the influence of enriched (EH) versus depleted housing (DH) conditions on cardiopulmonary functions, systemic immune responses, and allostatic load in response to a single wildfire smoke (WS) exposure in mice. Male and female C57BL/6J mice were divided into EH or DH for 22 weeks, and cardiopulmonary assessments measured before and after exposures to either one-hr filtered air (FA) or flaming eucalyptus WS exposure. Male and female DH mice exhibited increased heart rate (HR) and left ventricular mass (LVM), as well as reduced stroke volume and end diastolic volume (EDV) one week following exposure to WS. Female DH mice displayed significantly elevated levels of IL-2, IL-17, corticosterone and hemoglobin A1c (HbA1c) following WS, while female in EH mice higher epinephrine levels were detected. Female mice exhibited higher AL than males with DH, which was potentiated post-WS exposure. Thus, DH increased susceptibility to extreme air pollution in a gender-dependent manner suggesting that living conditions need to be evaluated as a modifier of toxicological responses.

Beyond prevalence: significance and differential impact of echocardiographic abnormalities in dialysis patients

BACKGROUND

Echocardiography is commonly used to assess hydratation status and cardiac function in kidney failure patients, but the impact of structural or functional abnormalities on the prognosis of kidney failure patients was yet to be investigated. This study aimed to investigate the prevalence and clinical significance of echocardiographic abnormalities in kidney failure patients.

METHODS

This study included 857 kidney failure patients who underwent echocardiography at dialysis initiation. Patients were followed up for a median of 4.2 years for the occurrence of major adverse cardiovascular events (MACE) and all-cause mortality.

RESULTS

Among the 857 patients studied, 77% exhibited at least one echocardiographic abnormality. The most common abnormalities were left ventricular hypertrophy and left atrial enlargement, but they were not significantly correlated with poor outcomes. Instead, the primary predictors of both major adverse cardiovascular events and mortality in kidney failure patients were left ventricular systolic function, right ventricular systolic function, left ventricular volume index, and valvular abnormalities. Although diastolic dysfunction was linked to major adverse cardiovascular events, it was not associated with mortality. Furthermore, the study revealed that increased left ventricular volume index and left ventricular systolic dysfunction had a more significant impact on peritoneal dialysis (PD) patients than on hemodialysis (HD) patients.

CONCLUSION

This study provides insights into the echocardiographic abnormalities and their association with adverse outcomes in kidney failure patients, which can help clinicians optimize the management of patients and closely monitor possible high-risk populations.

Circular RNA regulatory role in pathological cardiac remodelling

Cardiac remodelling involves structural, cellular and molecular alterations in the heart after injury, resulting in progressive loss of heart function and ultimately leading to heart failure. Circular RNAs (circRNAs) are a recently rediscovered class of non-coding RNAs that play regulatory roles in the pathogenesis of cardiovascular diseases, including heart failure. Thus, a more comprehensive understanding of the role of circRNAs in the processes governing cardiac remodelling may set the ground for the development of circRNA-based diagnostic and therapeutic strategies. In this review, the current knowledge about circRNA origin, conservation, characteristics and function is summarized. Bioinformatics and wet-lab methods used in circRNA research are discussed. The regulatory function of circRNAs in cardiac remodelling mechanisms such as cell death, cardiomyocyte hypertrophy, inflammation, fibrosis and metabolism is highlighted. Finally, key challenges and opportunities in circRNA research are discussed, and orientations for future work to address the pharmacological potential of circRNAs in heart failure are proposed.

Management of Chronic Heart Failure in Dialysis Patients: A Challenging but Rewarding Path

Chronic heart failure (CHF) is a common complication and cause of death in dialysis patients. Although several clinical guidelines and expert consensus on heart failure (HF) in the general population have been issued in China and abroad, due to abnormal renal function or even no residual renal function (RRF) in dialysis patients, the high number of chronic complications, as well as the specificity, variability, and limitations of hemodialysis (HD) and peritoneal dialysis (PD) treatments, there are significant differences between dialysis patients and the general population in terms of the treatment and management of HF. The current studies are not relevant to all dialysis-combined HF populations, and there is an urgent need for high-quality studies on managing HF in dialysis patients to guide and standardize treatment. After reviewing the existing guidelines and literature, we focused on the staging and diagnosis of HF, management of risk factors, pharmacotherapy, and dialysis treatment in patients on dialysis. Based on evidence-based medicine and clinical trial data, this report reflects new perspectives and future trends in the diagnosis and treatment of HF in dialysis patients, which will further enhance the clinicians' understanding of HF in dialysis patients.

Knockdown of ANGPTL2 promotes left ventricular systolic dysfunction by upregulation of NOX4 in mice

Background: Angiopoietin-like 2 (ANGPTL2) is a pro-inflammatory and pro-oxidant circulating protein that predicts and promotes chronic inflammatory diseases such as atherosclerosis in humans. Transgenic murine models demonstrated the deleterious role of ANGPTL2 in vascular diseases, while deletion of ANGPTL2 was protective. The nature of its role in cardiac tissues is, however, less clear. Indeed, in adult mice knocked down (KD) for ANGPTL2, we recently reported a mild left ventricular (LV) dysfunction originating from a congenital aortic valve stenosis, demonstrating that ANGPTL2 is essential to cardiac development and function. Hypothesis: Because we originally demonstrated that the KD of ANGPTL2 protected vascular endothelial function via an upregulation of arterial NOX4, promoting the beneficial production of dilatory H2O2, we tested the hypothesis that increased cardiac NOX4 could negatively affect cardiac redox and remodeling and contribute to LV dysfunction observed in adult Angptl2-KD mice. Methods and results: Cardiac expression and activity of NOX4 were higher in KD mice, promoting higher levels of cardiac H2O2 when compared to wild-type (WT) mice. Immunofluorescence showed that ANGPTL2 and NOX4 were co-expressed in cardiac cells from WT mice and both proteins co-immunoprecipitated in HEK293 cells, suggesting that ANGPTL2 and NOX4 physically interact. Pressure overload induced by transverse aortic constriction surgery (TAC) promoted LV systolic dysfunction in WT mice but did not further exacerbate the dysfunction in KD mice. Importantly, the severity of LV systolic dysfunction in KD mice (TAC and control SHAM) correlated with cardiac Nox4 expression. Injection of an adeno-associated virus (AAV9) delivering shRNA targeting cardiac Nox4 expression fully reversed LV systolic dysfunction in KD-SHAM mice, demonstrating the causal role of NOX4 in cardiac dysfunction in KD mice. Targeting cardiac Nox4 expression in KD mice also induced an antioxidant response characterized by increased expression of NRF2/KEAP1 and catalase. Conclusion: Together, these data reveal that the absence of ANGPTL2 induces an upregulation of cardiac NOX4 that contributes to oxidative stress and LV dysfunction. By interacting and repressing cardiac NOX4, ANGPTL2 could play a new beneficial role in the maintenance of cardiac redox homeostasis and function.

Timing of Surgery for Asymptomatic Primary Mitral Regurgitation: Possible Value of Early, Serial Measurements of Left Ventricular Sphericity

Asymptomatic primary mitral regurgitation due to myxomatous degeneration of the mitral valve leaflets may remain so for long periods, even as left ventricular function progresses to a decompensated stage. During the early compensated stage, the ventricle's initial response to the volume overload is an asymmetric increase in the diastolic short axis dimension, accomplished by a diastolic shift of the interventricular septum into the right ventricular cavity, creating a more spherical left ventricular diastolic shape, increasing diastolic filling and stroke volume. Early valve repair is recommended to reduce postoperative left ventricular dysfunction. Early serial measurements of left ventricular sphericity index [LV-Si]. during the compensated stage of mitral regurgitation might identify subtle changes in left ventricular shape and assist in determining the optimal earliest timing for surgical intervention.

Mathematical modeling of active contraction of the human cardiac myocyte: A review

Background and objective

In this present research paper, a mathematical model has been developed to study myocyte contraction in the human cardiac muscle, using the Land model. Different parts of the human heart with a focus on the composition of the myocyte cells have been explored numerically to enabling us to determine the interaction of various parameters in the heart muscle. The main objective of the work is to direct the study of the Land model, which has been exploited to simulate the contraction of real human myocytes.

Methods

Mathematical models has been developed based on the Hill model and Huxley model. Myocyte contraction for different scenarios, such as in isometric tension and isotonic tension have been studied.

Results

It is found that increase in stretch, the peak active tension increases, in line with well-established length-dependent tension generation. Five parameters are selected: [Ca2+]T50, Tref, TRPN50, β0, and β1, which have been varied in between the range of -50%-100%, to examine the isometric effects of each parameter on the behavior of the tension developed in the intact myocyte cells, with the most sensitive parameter being [Ca2+]T50.

Conclusion

In conclusion, it is found that the Land model provides a good platform for the analysis of the active contraction of the human cardiac myocyte.

Proteomic profiling of sudden cardiac death with acquired cardiac hypertrophy

BACKGROUND

Cardiac hypertrophy, which develops in middle-aged and older individuals as a consequence of hypertension and obesity, is an established risk factor for sudden cardiac death (SCD). However, it is sometimes difficult to differentiate SCD with acquired cardiac hypertrophy (SCH) from compensated cardiac hypertrophy (CCH), at autopsy. We aimed to elucidate the proteomic alteration in SCH, which can be a guideline for future postmortem diagnosis.

METHODS

Cardiac tissues were sampled at autopsy. SCH group consisted of ischemic heart failure, hypertensive heart failure, and aortic stenosis. CCH group included cases of non-cardiac death with cardiac hypertrophy. The control group comprised cases of non-cardiac death without cardiac hypertrophy. All patients were aged > 40 years, and hypertrophic cardiomyopathy was not included in this study. We performed histological examination and shotgun proteomic analysis, followed by quantitative polymerase chain reaction analysis.

RESULTS

Significant obesity and myocardial hypertrophy, and mild myocardial fibrosis were comparable in SCH and CCH cases compared to control cases. The proteomic profile of SCH cases was distinguishable from those of CCH and control cases, and many sarcomere proteins were increased in SCH cases. Especially, the protein and mRNA levels of MYH7 and MYL3 were significantly increased in SCH cases.

CONCLUSION

This is the first report of cardiac proteomic analysis in SCH and CCH cases. The stepwise upregulation of sarcomere proteins may increase the risk for SCD in acquired cardiac hypertrophy before cardiac fibrosis progresses significantly. These findings can possibly aid in the postmortem diagnosis of SCH in middle-aged and older individuals.

Cardiac mechanics and reverse remodelling under mechanical support from left ventricular assist devices

In recent years, development of mechanical circulatory support devices has proved to be a new treatment modality, in addition to standard pharmacological therapy, for patients with heart failure or acutely depressed cardiac function. These include left ventricular assist devices, which mechanically unload the heart when implanted. As a result, they profoundly affect the acute cardiac mechanics, which in turn, carry long-term consequences on myocardial function and structural function. Multiple studies have shown that, when implanted, mechanical circulatory assist devices lead to reverse remodelling, a process whereby the diseased myocardium reverts to a healthier-like state. Here, we start by first providing the reader with an overview of cardiac mechanics and important hemodynamic parameters. We then introduce left ventricular assist devices and describe their mode of operation as well as their impact on the hemodynamics. Changes in cardiac mechanics caused by device implantation are then extrapolated in time, and the long-term consequences on myocardial phenotype, as well as the physiological basis for these, is investigated.

Using urinary metabolomics to identify metabolic pathways linked to cardiac structural alterations in young adults: The African-PREDICT study

BACKGROUND AND AIMS

Risk factor exposure from young ages was shown to contribute to cardiovascular events - cardiac hypertrophy, which may be accompanied by an altered metabolism. To determine how early metabolic alterations associate with myocardial structural changes, we profiled urinary metabolites in young adults with cardiovascular disease (CVD) risk factor(s) and a control group without CVD risk factors.

METHODS AND RESULTS

We included healthy adults (N = 1202), aged 20-30 years, stratified based on risk factors, i.e., obesity, physical inactivity, elevated blood pressure (BP), hyperglycemia, dyslipidemia, low socio-economic status, smoking and excessive alcohol use - forming the CVD risk group (N = 1036) and the control group (N = 166). Relative wall thickness (RWT) and left ventricular mass index (LVMi) were measured using echocardiography. Targeted metabolomics data were obtained using a liquid chromatography-tandem mass spectrometry method. Clinic systolic BP, 24 h BP and RWT were higher in the CVD risk group compared to the control group (all P ≤ 0.031). Exclusively in the CVD risk group, RWT associated with creatine and dodecanoylcarnitine; while LVMi associated with glycine, serine, glutamine, threonine, alanine, citrulline, creatine, proline, pyroglutamic acid and glutamic acid (all P ≤ 0.040). Exclusively in the control group, LVMi associated with propionylcarnitine and butyrylcarnitine (all P ≤ 0.009).

CONCLUSION

In young adults without CVD, but with CVD risk factors, LVMi and RWT associated with metabolites linked energy metabolism (shifting from solely fatty acid oxidation to glycolysis, with impaired creatine kinase activity) and oxidative stress. Our findings support early onset metabolic changes accompanying cardiac structural alterations due to lifestyle and behavioural risk factors.

Association of the rs3039851 Insertion/Deletion in the Gene PPP3R1, Which Encodes the Regulatory Calcineurin Subunit B Type 1, with Left Ventricular Mass in Polish Full-Term Newborns

BACKGROUND

The five base-pair (bp) insertion/deletion (rs3039851) polymorphism in the PPP3R1 gene, which encodes calcineurin subunit B type 1, has been found to be associated with left ventricular hypertrophy (LVH) in hypertensive patients and in athletes. The aim of this study is to analyze the possible association between PPP3R1:rs3039851 polymorphism and left ventricular mass (LVM) in full-term healthy newborns.

METHODS

The study group consisted of 162 consecutive, full-term, healthy newborns. Two-dimensional M-mode echocardiography was used to assess LVM. The PPP3R1:rs3039851 polymorphism was identified by PCR-RFLP in genomic DNA extracted from cord blood leukocytes.

RESULTS

No significant differences were found between newborns homozygous for the reference allele (5I/5I, n = 135) and newborns carrying at least one 5D allele (n = 27) for LVM standardized for body mass, body length or body surface area (LVM/BM, LVM/BL or LVM/BSA, respectively). However, the frequency of PPP3R1:rs3039851 genotypes with a 5D allele (5I/5D + 5D/5D) among newborns with the largest LVM/BM or LVM/BSA (upper tertile) was statistically significantly higher compared with the prevalence in individuals with the lowest values of both indices (lower tertile).

CONCLUSIONS

Our results suggest that the PPP3R1:rs3039851 polymorphism may contribute to subtle variation in left ventricular mass at birth.

Hypoxia-Inducible Factor 1-Alpha and Glucose Metabolism during Cardiac Remodeling Progression from Hypertrophy to Heart Failure

In pathological cardiac hypertrophy, the heart is more dependent on glucose than fatty acids. This shift in energy metabolism occurs due to several factors, including the oxygen deficit, which activates hypoxia-inducible factor-1α (HIF-1α), a critical molecule related to glucose metabolism. However, there are gaps regarding the behavior of key proteins in the glycolytic pathway and HIF-1α during the transition from hypertrophy to heart failure (HF). This study assesses the hypothesis that there is an early change and enhancement of HIF-1α and the glycolytic pathway, as well as an association between them during cardiac remodeling. Sham and aortic stenosis Wistar rats were analyzed at 2, 6, and 18 weeks and in HF (n = 10–18). Cardiac structure and function were investigated by echocardiogram. Myocardial glycolysis, the aerobic and anaerobic pathways and glycogen were analyzed by enzymatic assay, Western blot, and enzyme-linked immunosorbent assay (ELISA). The following were observed: increased left ventricular hypertrophy; early diastolic function change and severe systolic and diastolic dysfunction in HF; increased HIF-1α in the 2nd week and in HF; precocious alteration and intensification of glycolysis with a shift to anaerobic metabolism from the 6th week onwards; association between HIF-1α, glycolysis, and the anaerobic pathway. Our hypothesis was confirmed as there was an early change and intensification in glucose metabolism, alteration in HIF-1α, and an association between data during the progression from hypertrophy to heart failure.

DNA Methylation Analysis Identifies Novel Epigenetic Loci in Dilated Murine Heart upon Exposure to Volume Overload

Left ventricular (LV) dilatation, a prominent risk factor for heart failure (HF), precedes functional deterioration and is used to stratify patients at risk for arrhythmias and cardiac mortality. Aberrant DNA methylation contributes to maladaptive cardiac remodeling and HF progression following pressure overload and ischemic cardiac insults. However, no study has examined cardiac DNA methylation upon exposure to volume overload (VO) despite being relatively common among HF patients. We carried out global methylome analysis of LV harvested at a decompensated HF stage following exposure to VO induced by aortocaval shunt. VO resulted in pathological cardiac remodeling, characterized by massive LV dilatation and contractile dysfunction at 16 weeks after shunt. Although methylated DNA was not markedly altered globally, 25 differentially methylated promoter regions (DMRs) were identified in shunt vs. sham hearts (20 hypermethylated and 5 hypomethylated regions). The validated hypermethylated loci in Junctophilin-2 (Jph2), Signal peptidase complex subunit 3 (Spcs3), Vesicle-associated membrane protein-associated protein B (Vapb), and Inositol polyphosphate multikinase (Ipmk) were associated with the respective downregulated expression and were consistently observed in dilated LV early after shunt at 1 week after shunt, before functional deterioration starts to manifest. These hypermethylated loci were also detected peripherally in the blood of the shunt mice. Altogether, we have identified conserved DMRs that could be novel epigenetic biomarkers in dilated LV upon VO exposure.

Cardiac changes in spontaneously hypertensive rats: Modulation by aerobic exercise

Systemic arterial hypertension is a multifactorial clinical condition characterized by high and sustained levels of blood pressure. For a better understanding of the pathophysiology of hypertension, studies are conducted with spontaneously hypertensive animals, which allow the investigation of physiological changes that in most cases cannot be studied in humans. In these animals, myocardial remodeling, increased pro-inflammatory markers, redox imbalance and contractile dysfunctions that lead to changes in cardiac function can be observed. However, it can be inferring that aerobic training improves cardiac function and cardiomyocyte contractility, in addition to controlling inflammation and reducing oxidative stress in cardiac muscle, despite this, the precise mechanisms by which physical exercise improves cardiovascular control are not fully understood. In this review, we provide an overview of the pathophysiological changes that affect the heart of spontaneously hypertensive animals and their modulation by aerobic exercise.

Signaling network model of cardiomyocyte morphological changes in familial cardiomyopathy

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy.

Altered Cellular Protein Quality Control System Modulates Cardiomyocyte Function in Volume Overload-Induced Hypertrophy

Volume-induced hypertrophy is one of the risk factors for cardiac morbidity and mortality. In addition, mechanical and metabolic dysfunction, aging, and cellular redox balance are also contributing factors to the disease progression. In this study, we used volume overload (VO), which was induced by an aortocaval fistula in 2-month-old male Wistar rats, and sham-operated animals served as control. Functional parameters were measured by transthoracic echocardiography at termination 4- or 8-months after VO. The animals showed hypertrophic remodeling that was accompanied by mechanical dysfunction and increased cardiomyocyte stiffness. These alterations were reversible upon treatment with glutathione. Cardiomyocyte dysfunction was associated with elevated oxidative stress markers with unchanged inflammatory signaling pathways. In addition, we observed altered phosphorylation status of small heat shock proteins 27 and 70 and diminished protease expression caspases 3 compared to the matched control group, indicating an impaired protein quality control system. Such alterations might be attributed to the increased oxidative stress as anticipated from the enhanced titin oxidation, ubiquitination, and the elevation in oxidative stress markers. Our study showed an early pathological response to VO, which manifests in cardiomyocyte mechanical dysfunction and dysregulated signaling pathways associated with enhanced oxidative stress and an impaired protein quality control system.

What programs the size of animal cells?

The human body is programmed with definite quantities, magnitudes, and proportions. At the microscopic level, such definite sizes manifest in individual cells - different cell types are characterized by distinct cell sizes whereas cells of the same type are highly uniform in size. How do cells in a population maintain uniformity in cell size, and how are changes in target size programmed? A convergence of recent and historical studies suggest - just as a thermostat maintains room temperature - the size of proliferating animal cells is similarly maintained by homeostatic mechanisms. In this review, we first summarize old and new literature on the existence of cell size checkpoints, then discuss additional advances in the study of size homeostasis that involve feedback regulation of cellular growth rate. We further discuss recent progress on the molecules that underlie cell size checkpoints and mechanisms that specify target size setpoints. Lastly, we discuss a less-well explored teleological question: why does cell size matter and what is the functional importance of cell size control?

Computational modelling of multi-temporal ventricular-vascular interactions during the progression of pulmonary arterial hypertension

A computational framework is developed to consider the concurrent growth and remodelling (G&R) processes occurring in the large pulmonary artery (PA) and right ventricle (RV), as well as ventricular-vascular interactions during the progression of pulmonary arterial hypertension (PAH). This computational framework couples the RV and the proximal PA in a closed-loop circulatory system that operates in a short timescale of a cardiac cycle, and evolves over a long timescale due to G&R processes in the PA and RV. The framework predicts changes in haemodynamics (e.g. 68.2% increase in mean PA pressure), RV geometry (e.g. 38% increase in RV end-diastolic volume) and PA tissue microstructure (e.g. 90% increase in collagen mass) that are consistent with clinical and experimental measurements of PAH. The framework also predicts that a reduction in RV contractility is associated with long-term RV chamber dilation, a common biomarker observed in the late-stage PAH. Sensitivity analyses on the G&R rate constants show that large PA stiffening (both short and long term) is affected by RV remodelling more than the reverse. This framework can serve as a foundation for the future development of a more predictive and comprehensive cardiovascular G&R model with realistic heart and vascular geometries.

The RalGAPα1-RalA signal module protects cardiac function through regulating calcium homeostasis

Sarcoplasmic/endoplasmic reticulum calcium ATPase SERCA2 mediates calcium re-uptake from the cytosol into sarcoplasmic reticulum, and its dysfunction is a hallmark of heart failure. Multiple factors have been identified to modulate SERCA2 activity, however, its regulation is still not fully understood. Here we identify a Ral-GTPase activating protein RalGAPα1 as a critical regulator of SERCA2 in cardiomyocytes through its downstream target RalA. RalGAPα1 is induced by pressure overload, and its deficiency causes cardiac dysfunction and exacerbates pressure overload-induced heart failure. Mechanistically, RalGAPα1 regulates SERCA2 through direct interaction and its target RalA. Deletion of RalGAPα1 decreases SERCA2 activity and prolongs calcium re-uptake into sarcoplasmic reticulum. GDP-bound RalA, but not GTP-bound RalA, binds to SERCA2 and activates the pump for sarcoplasmic reticulum calcium re-uptake. Overexpression of a GDP-bound RalAS28N mutant in the heart preserves cardiac function in a mouse model of heart failure. Our findings have therapeutic implications for treatment of heart failure.

Evaluation of the Reliability of Electrocardiographic Criteria for Cardiac Hypertrophy Based on Echocardiographic Data

Background.

Left ventricular hypertrophy (LVH) regardless of other risk factors may be associated with an increased risk of mortality from cardiovascular diseases. Therefore, timely diagnosis for LVH is important in order to avoid possible complications. One of the simplest and cheapest methods to diagnose LVH is electrocardiography (ECG). Although a number of ECG criteria for LVH is known, their reliability varies in many studies.

Aim.

To evaluate the reliability of ECG criteria for LVH based on transthoracic echocardiography (TTE) data.

Methods.

The study included all consecutive patients in Kaunas Clinical Hospital Department of Cardiology from December 2019 until March 2020 and from September until October 2020, after applying the inclusion and exclusion criteria. The sensitivity and specificity of the ECG criteria for LVH were assessed based on TTE measurements performed during the same inpatient setting. The reliability of the ECG criteria for LVH was assessed using ROC curves. Reliability differences in gender, age and nutritional status groups were assessed using ANOVA statistical method.

Results.

Data from 95 patients were analyzed (63.2% were women and 36.8% were men). The sensitivity, specificity and AUC of Sokolow–Lyon criterion were 9.38%, 85.71% and 0.44 (p = 0.034), R in aVL – 6.25%, 90.48% and 0.51 (p = 0.038), Cornell – 21.88%, 100 % and0.69 (p = 0.084), Cornell product – 31.25%, 95.24% and 0.72 (p = 0.070), Peguero–Lo Presti – 31.25%, 85.71% and 0.68 (p = 0.053), respectively. No statistically significant differences were observed among the individual gender, age and nutritional status groups.

Conclusions.

Sokolow–Lyon and RaVL criteria were not statistically significantly reliable in LVH diagnosis compared to TTE, unlike the Cornell, Cornell product, and Peguero–Lo Presti criteria.

Ca2+/calmodulin-dependent protein kinase II and protein kinase G oxidation contributes to impaired sarcomeric proteins in hypertrophy model

Aims

Volume overload (VO) induced hypertrophy is one of the hallmarks to the development of heart diseases. Understanding the compensatory mechanisms involved in this process might help preventing the disease progression.

Methods and results

Therefore, the present study used 2 months old Wistar rats, which underwent an aortocaval fistula to develop VO‐induced hypertrophy. The animals were subdivided into four different groups, two sham operated animals served as age‐matched controls and two groups with aortocaval fistula. Echocardiography was performed prior termination after 4‐ and 8‐month. Functional and molecular changes of several sarcomeric proteins and their signalling pathways involved in the regulation and modulation of cardiomyocyte function were investigated.

Results

The model was characterized with preserved ejection fraction in all groups and with elevated heart/body weight ratio, left/right ventricular and atrial weight at 4‐ and 8‐month, which indicates VO‐induced hypertrophy. In addition, 8‐months groups showed increased left ventricular internal diameter during diastole, RV internal diameter, stroke volume and velocity‐time index compared with their age‐matched controls. These changes were accompanied by increased Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness in 8‐month VO rats compared with other groups. The altered cardiomyocyte mechanics was associated with phosphorylation deficit of sarcomeric proteins cardiac troponin I, myosin binding protein C and titin, also accompanied with impaired signalling pathways involved in phosphorylation of these sarcomeric proteins in 8‐month VO rats compared with age‐matched control group. Impaired protein phosphorylation status and dysregulated signalling pathways were associated with significant alterations in the oxidative status of both kinases CaMKII and PKG explaining by this the elevated Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness and perhaps the development of hypertrophy.

Conclusions

Our findings showed VO‐induced cardiomyocyte dysfunction via deranged phosphorylation of myofilament proteins and signalling pathways due to increased oxidative state of CaMKII and PKG and this might contribute to the development of hypertrophy.

New Progress in the Molecular Regulations and Therapeutic Applications in Cardiac Oxidative Damage Caused by Pressure Overload

Chronic pressure overload is a key risk factor for mortality due to its subsequent development of heart failure, in which the underlying molecular mechanisms remain vastly undetermined. In this review, we updated the latest advancements for investigating the role and relevant mechanisms of oxidative stress involved in the pathogenesis of pressure-overload-induced cardiomyopathy and cardiac dysfunction, focusing on significant biological sources of reactive oxygen species (free radical) production, antioxidant defenses, and their association with the cardiac metabolic remodeling in the stressed heart. We also summarize the newly developed preclinical therapeutic approaches in animal models for pressure-overload-induced myocardial damage. This review aims to enhance the current understanding of the mechanisms of chronic hypertensive heart failure and potentially improve the development of better therapeutic strategies for the associated diseases.

Remodelling of adult cardiac tissue subjected to physiological and pathological mechanical load in vitro

AIMS

Cardiac remodelling is the process by which the heart adapts to its environment. Mechanical load is a major driver of remodelling. Cardiac tissue culture has been frequently employed for in vitro studies of load-induced remodelling; however, current in vitro protocols (e.g. cyclic stretch, isometric load, and auxotonic load) are oversimplified and do not accurately capture the dynamic sequence of mechanical conformational changes experienced by the heart in vivo. This limits translational scope and relevance of findings.

METHODS AND RESULTS

We developed a novel methodology to study chronic load in vitro. We first developed a bioreactor that can recreate the electromechanical events of in vivo pressure-volume loops as in vitro force-length loops. We then used the bioreactor to culture rat living myocardial slices (LMS) for 3 days. The bioreactor operated based on a 3-Element Windkessel circulatory model enabling tissue mechanical loading based on physiologically relevant parameters of afterload and preload. LMS were continuously stretched/relaxed during culture simulating conditions of physiological load (normal preload and afterload), pressure-overload (normal preload and high afterload), or volume-overload (high preload & normal afterload). At the end of culture, functional, structural, and molecular assays were performed to determine load-induced remodelling. Both pressure- and volume-overloaded LMS showed significantly decreased contractility that was more pronounced in the latter compared with physiological load (P < 0.0001). Overloaded groups also showed cardiomyocyte hypertrophy; RNAseq identified shared and unique genes expressed in each overload group. The PI3K-Akt pathway was dysregulated in volume-overload while inflammatory pathways were mostly associated with remodelling in pressure-overloaded LMS.

CONCLUSION

We have developed a proof-of-concept platform and methodology to recreate remodelling under pathophysiological load in vitro. We show that LMS cultured in our bioreactor remodel as a function of the type of mechanical load applied to them.

Myofibril orientation as a metric for characterizing heart disease

Myocyte disarray is a hallmark of many cardiac disorders. However, the relationship between alterations in the orientation of individual myofibrils and myofilaments to disease progression has been largely underexplored. This oversight has predominantly been because of a paucity of methods for objective and quantitative analysis. Here, we introduce a novel, less-biased approach to quantify myofibrillar and myofilament orientation in cardiac muscle under near-physiological conditions and demonstrate its superiority as compared with conventional histological assessments. Using small-angle x-ray diffraction, we first investigated changes in myofibrillar orientation at increasing sarcomere lengths in permeabilized, relaxed, wild-type mouse myocardium from the left ventricle by assessing the angular spread of the 1,0 equatorial reflection (angle σ). At a sarcomere length of 1.9 μm, the angle σ was 0.23 ± 0.01 rad, decreased to 0.19 ± 0.01 rad at a sarcomere length of 2.1 μm, and further decreased to 0.15 ± 0.01 rad at a sarcomere length of 2.3 μm (p < 0.0001). Angle σ was significantly larger in R403Q, a MYH7 hypertrophic cardiomyopathy model, porcine myocardium (0.24 ± 0.01 rad) compared with wild-type myocardium (0.14 ± 0.005 rad; p < 0.0001), as well as in human heart failure tissue (0.19 ± 0.006 rad) when compared with nonfailing samples (0.17 ± 0.007 rad; p = 0.01). These data indicate that diseased myocardium suffers from greater myofibrillar disorientation compared with healthy controls. Finally, we showed that conventional, histology-based analysis of disarray can be subject to user bias and/or sampling error and lead to false positives. Our method for directly assessing myofibrillar orientation avoids the artifacts introduced by conventional histological approaches that assess myocyte orientation and only indirectly evaluate myofibrillar orientation, and provides a precise and objective metric for phenotypically characterizing myocardium. The ability to obtain excellent x-ray diffraction patterns from frozen human myocardium provides a new tool for investigating structural anomalies associated with cardiac diseases.

Emerging therapeutic targets for cardiac hypertrophy

INTRODUCTION

Cardiac hypertrophy is associated with adverse outcomes across cardiovascular disease states. Despite strides over the last three decades in identifying molecular and cellular mechanisms driving hypertrophy, the link between pathophysiological stress stimuli and specific myocyte/heart growth profiles remains unclear. Moreover, the optimal strategy for preventing pathology in the setting of hypertrophy remains controversial.

AREAS COVERED

This review discusses molecular mechanisms underlying cardiac hypertrophy with a focus on factors driving the orientation of myocyte growth and the impact on heart function. We highlight recent work showing a novel role for the spectrin-based cytoskeleton, emphasizing regulation of myocyte dimensions but not hypertrophy per se. Finally, we consider opportunities for directing the orientation of myocyte growth in response to hypertrophic stimuli as an alternative therapeutic approach. Relevant publications on the topic were identified through Pubmed with open-ended search dates.

EXPERT OPINION

To define new therapeutic avenues, more precision is required when describing changes in myocyte and heart structure/function in response to hypertrophic stimuli. Recent developments in computational modeling of hypertrophic networks, in concert with more refined experimental approaches will catalyze translational discovery to advance the field and further our understanding of cardiac hypertrophy and its relationship with heart disease.

Gene expression profiling and functional analysis of ventricular tissues from murine transverse aortic constriction

BACKGROUND

Transverse aortic constriction (TAC) model is widely used to study pressure overload-induced cardiac remodeling. However, the conserved transcriptional features of TAC model and the underlying regulatory mechanisms remain unclear.

METHODS

In this study, we screened out the high-quality microarray data for ventricular tissue from murine TAC model. The transcriptional changes in ventricular tissue were analyzed by identifying the common differently expressed genes (DEGs) and enriched gene sets. We also analyzed the protein-protein interaction and mRNA-mRNA association of DEGs. Furthermore, the potential regulatory elements of the DEGs were explored through comparative analysis between mouse and human.

RESULTS

265 common DEGs and 45 enriched canonical pathways were identified in murine TAC model. 201 DEGs had the protein-protein interaction, whereas 96 DEGs had mRNA-mRNA association. 99 transcription factor (TF)-mRNA and 2997 microRNA (miRNA)-mRNA regulatory relationships were retrieved.

CONCLUSIONS

In pressure overload-induced cardiac remodeling, inflammation, fibrosis, metabolic remodeling and hypoxia were significant features. Approaches to intervene these phenomena may have therapeutic values. TFs and miRNAs are important regulator elements of DEGs in both mouse and human. Examination of miRNAs is a promising tool to detect the occurrence of pressure overload-induced cardiac remodeling in patients.

Dapagliflozin has No Protective Effect on Experimental Pulmonary Arterial Hypertension and Pulmonary Trunk Banding Rat Models

Sodium-glucose cotransporter-2 (SGLT2) inhibitors, a novel class of hypoglycemic drugs, show excellent cardiovascular benefits, and have further improved heart failure outcomes, significantly reducing cardiovascular and all-cause mortality irrespective of diabetes status. However, the efficacy of SGLT2 inhibitors in pulmonary arterial hypertension (PAH) and right ventricular (RV) dysfunction remains unknown. This study aimed to evaluate the effects of dapagliflozin in rats with PAH and RV dysfunction. PAH was induced in rats by monocrotaline (MCT) subcutaneous injection (60 mg/kg). Isolated RV dysfunction was induced in another group of rats by pulmonary trunk banding (PTB). Dapagliflozin (1.5 mg/kg) was administered daily via oral gavage one day (prevention groups) or two weeks (reversal groups) after modeling. Echocardiography and hemodynamic assessments were used to observe pulmonary vascular resistance and RV function. Histological staining was used to observe pulmonary vascular and RV remodeling. As compared with MCT group, dapagliflozin treatment did not significantly improve the survival of rats. Pulmonary arterial media wall thickness in MCT group was significantly increased, but dapagliflozin did not significantly improved vascular remodeling both in the prevention group and reversal group. In MCT group, RV hypertrophy index, RV area, the fibrosis of RV increased significantly, and RV function decreased significantly. Consistently, dapagliflozin did not show protective effect on the RV remodeling and function. In the PTB model, we also did not find the direct effect of dapagliflozin on the RV. This is a negative therapeutic experiment, suggesting human trials with dapagliflozin for PAH or RV failure should be cautious.

Multiscale simulations of left ventricular growth and remodeling

Cardiomyocytes can adapt their size, shape, and orientation in response to altered biomechanical or biochemical stimuli. The process by which the heart undergoes structural changes-affecting both geometry and material properties-in response to altered ventricular loading, altered hormonal levels, or mutant sarcomeric proteins is broadly known as cardiac growth and remodeling (G&R). Although it is likely that cardiac G&R initially occurs as an adaptive response of the heart to the underlying stimuli, prolonged pathological changes can lead to increased risk of atrial fibrillation, heart failure, and sudden death. During the past few decades, computational models have been extensively used to investigate the mechanisms of cardiac G&R, as a complement to experimental measurements. These models have provided an opportunity to quantitatively study the relationships between the underlying stimuli (primarily mechanical) and the adverse outcomes of cardiac G&R, i.e., alterations in ventricular size and function. State-of-the-art computational models have shown promise in predicting the progression of cardiac G&R. However, there are still limitations that need to be addressed in future works to advance the field. In this review, we first outline the current state of computational models of cardiac growth and myofiber remodeling. Then, we discuss the potential limitations of current models of cardiac G&R that need to be addressed before they can be utilized in clinical care. Finally, we briefly discuss the next feasible steps and future directions that could advance the field of cardiac G&R.

The CR9 element is a novel mechanical load-responsive enhancer that regulates natriuretic peptide genes expression

Enhancers regulate gene expressions in a tissue- and pathology-specific manner by altering its activities. Plasma levels of atrial and brain natriuretic peptides, encoded by the Nppa and Nppb, respectively, and synthesized predominantly in cardiomyocytes, vary depending on the severity of heart failure. We previously identified the noncoding conserved region 9 (CR9) element as a putative Nppb enhancer at 22-kb upstream from the Nppb gene. However, its regulatory mechanism remains unknown. Here, we therefore investigated the mechanism of CR9 activation in cardiomyocytes using different kinds of drugs that induce either cardiac hypertrophy or cardiac failure accompanied by natriuretic peptides upregulation. Chronic treatment of mice with either catecholamines or doxorubicin increased CR9 activity during the progression of cardiac hypertrophy to failure, which is accompanied by proportional increases in Nppb expression. Conversely, for cultured cardiomyocytes, doxorubicin decreased CR9 activity and Nppb expression, while catecholamines increased both. However, exposing cultured cardiomyocytes to mechanical loads, such as mechanical stretch or hydrostatic pressure, upregulate CR9 activity and Nppb expression even in the presence of doxorubicin. Furthermore, the enhancement of CR9 activity and Nppa and Nppb expressions by either catecholamines or mechanical loads can be blunted by suppressing mechanosensing and mechanotransduction pathways, such as muscle LIM protein (MLP) or myosin tension. Finally, the CR9 element showed a more robust and cell-specific response to mechanical loads than the -520-bp BNP promoter. We concluded that the CR9 element is a novel enhancer that responds to mechanical loads by upregulating natriuretic peptides expression in cardiomyocytes.

Decoding the complexity of circular RNAs in cardiovascular disease

Circular RNAs (circRNAs) are a new class of covalently circularized noncoding RNAs widely expressed in the human heart. Emerging evidence suggests they have a regulatory role in a variety of cardiovascular diseases (CVDs). This review's current focus includes our understanding of circRNA classification, biogenesis, function, stability, degradation mechanisms, and their roles in various cardiovascular disease conditions. Our knowledge of circRNA, the relatively recent member of the noncoding RNA family, is still in its infancy; however, recent literature proposes circRNAs may be promising targets for the understanding and treatment of CVD.

Mineralocorticoid Receptor in Smooth Muscle Contributes to Pressure Overload-Induced Heart Failure

BACKGROUND

Mineralocorticoid receptor (MR) antagonists decrease heart failure (HF) hospitalization and mortality, but the mechanisms are unknown. Preclinical studies reveal that the benefits on cardiac remodeling and dysfunction are not completely explained by inhibition of MR in cardiomyocytes, fibroblasts, or endothelial cells. The role of MR in smooth muscle cells (SMCs) in HF has never been explored.

METHODS

Male mice with inducible deletion of MR from SMCs (SMC-MR-knockout) and their MR-intact littermates were exposed to HF induced by 27-gauge transverse aortic constriction versus sham surgery. HF phenotypes and mechanisms were measured 4 weeks later using cardiac ultrasound, intracardiac pressure measurements, exercise testing, histology, cardiac gene expression, and leukocyte flow cytometry.

RESULTS

Deletion of MR from SMC attenuated transverse aortic constriction-induced HF with statistically significant improvements in ejection fraction, cardiac stiffness, chamber dimensions, intracardiac pressure, pulmonary edema, and exercise capacity. Mechanistically, SMC-MR-knockout protected from adverse cardiac remodeling as evidenced by decreased cardiomyocyte hypertrophy and fetal gene expression, interstitial and perivascular fibrosis, and inflammatory and fibrotic gene expression. Exposure to pressure overload resulted in a statistically significant decline in cardiac capillary density and coronary flow reserve in MR-intact mice. These vascular parameters were improved in SMC-MR-knockout mice compared with MR-intact littermates exposed to transverse aortic constriction.

CONCLUSIONS

These results provide a novel paradigm by which MR inhibition may be beneficial in HF by blocking MR in SMC, thereby improving cardiac blood supply in the setting of pressure overload-induced hypertrophy, which in turn mitigates the adverse cardiac remodeling that contributes to HF progression and symptoms.

Fibroblast Growth Factor 23 and Left Ventricular Hypertrophy in Chronic Kidney Disease-A Pediatric Perspective

Cardiovascular diseases (CVD) are a hallmark in pediatric patients with chronic kidney disease (CKD) contributing to an enhanced risk of all-cause and CV morbidity and mortality in these patients. The bone-derived phosphaturic hormone fibroblast growth factor (FGF) 23 progressively rises with declining kidney function to maintain phosphate homeostasis, with up to 1,000-fold increase in patients with kidney failure requiring dialysis. FGF23 is associated with the development of left ventricular hypertrophy (LVH) and thereby accounts to be a CVD risk factor in CKD. Experimentally, FGF23 directly induces hypertrophic growth of cardiac myocytes in vitro and LVH in vivo. Further, clinical studies in adult CKD have observed cardiotoxicity associated with FGF23. Data regarding prevalence and determinants of FGF23 excess in children with CKD are limited. This review summarizes current data and discusses whether FGF23 may be a key driver of LVH in pediatric CKD.

Neonatal Heart Responds to Pressure Overload With Differential Alterations in Various Cardiomyocyte Maturation Programs That Accommodate Simultaneous Hypertrophy and Hyperplasia

Pressure overload is one of the pathophysiological conditions commonly associated with right-sided congenital heart disease (CHD). Patients suffer from this condition right after birth. However, little is known about how neonatal heart reacts to it. We have previously established a pulmonary artery banding (PAB) model in neonatal rat. Here we show that PAB accelerated transition of mononuclear cardiomyocytes into multinucleated cells to promote hypertrophic growth in neonatal heart. The elevated afterload significantly increased the mitotic activities of neonatal cardiomyocytes. Consistent with the proliferative potential, the elevated pressure overload also increased cytokinetic marker counts of cardiomyocytes. Using cardiomyocyte-specific lineage tracing, we noticed a clonal expansion of rare unlabeled cardiomyocytes in the PAB group, revealing a subgroup of cardiomyocytes with a strong capability of proliferation. In addition, PAB hearts at post-banding day 7 didn’t have the accumulation of macrophages, which is an immune response essential for neonatal heart regeneration in injury models. Transcriptomic analyses revealed that neonatal PAB induced an expression profile featuring both cardiomyocyte hypertrophy, such as highly activated translation, oxidative phosphorylation, and mitochondrial biogenesis programs etc., and immature cardiomyocyte, such as enhanced cell cycle activities and glycolytic metabolism, down-regulated cytoskeleton and ion channel gene expression, and maintenance of fetal-specific sarcomeric isoforms etc. It indicates that pressure overload has differential impacts on various cardiomyocyte maturation (CM) programs that may contribute to the concurrent cardiomyocyte hypertrophy and hyperplasia. The bivalent status of transcriptional profile highlights the plasticity of neonatal cardiomyocytes that can be exploited to adapt the postnatal environment.

Biological Context Linking Hypertension and Higher Risk for COVID-19 Severity

The coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), represents a public health crisis of major proportions. Advanced age, male gender, and the presence of comorbidities have emerged as risk factors for severe illness or death from COVID-19 in observation studies. Hypertension is one of the most common comorbidities in patients with COVID-19. Indeed, hypertension has been shown to be associated with increased risk for mortality, acute respiratory distress syndrome, need for intensive care unit admission, and disease progression in COVID-19 patients. However, up to the present time, the precise mechanisms of how hypertension may lead to the more severe manifestations of disease in patients with COVID-19 remains unknown. This review aims to present the biological plausibility linking hypertension and higher risk for COVID-19 severity. Emphasis is given to the role of the renin-angiotensin system and its inhibitors, given the crucial role that this system plays in both viral transmissibility and the pathophysiology of arterial hypertension. We also describe the importance of the immune system, which is dysregulated in hypertension and SARS-CoV-2 infection, and the potential involvement of the multifunctional enzyme dipeptidyl peptidase 4 (DPP4), that, in addition to the angiotensin-converting enzyme 2 (ACE2), may contribute to the SARS-CoV-2 entrance into target cells. The role of hemodynamic changes in hypertension that might aggravate myocardial injury in the setting of COVID-19, including endothelial dysfunction, arterial stiffness, and left ventricle hypertrophy, are also discussed.

Defective Autophagy in Vascular Smooth Muscle Cells Alters Vascular Reactivity of the Mouse Femoral Artery

Autophagy is an important cellular survival process that enables degradation and recycling of defective organelles and proteins to maintain cellular homeostasis. Hence, defective autophagy plays a role in many age-associated diseases, such as atherosclerosis, arterial stiffening and hypertension. Recently, we showed in mice that autophagy in vascular smooth muscle cells (VSMCs) of large elastic arteries such as the aorta is important for Ca²⁺ mobilization and vascular reactivity. Whether autophagy plays a role in the smaller muscular arteries, such as the femoral artery, and thereby contributes to for example, blood pressure regulation is currently unknown. Therefore, we determined vascular reactivity of femoral artery segments of mice containing a VSMC specific deletion of the essential autophagy gene Atg7 (Atg7^F/F SM22α-Cre⁺) and compared them to femoral artery segments of corresponding control mice (Atg7^+/+ SM22α-Cre⁺). Our results indicate that similar to the aorta, femoral artery segments showed enhanced contractility. Specifically, femoral artery segments of Atg7^F/F SM22α-Cre⁺ mice showed an increase in phasic phenylephrine (PE) induced contractions, together with an enhanced sensitivity to depolarization induced contractions. In addition, and importantly, VSMC sensitivity to exogenous nitric oxide (NO) was significantly increased in femoral artery segments of Atg7^F/F SM22α-Cre⁺ mice. Notwithstanding the fact that small artery contractility is a significant pathophysiological determinant for the development of hypertension, 7 days of treatment with angiotensin II (AngII), which increased systolic blood pressure in control mice, was ineffective in Atg7^F/F SM22α-Cre⁺ mice. It is likely that this was due to the increased sensitivity of VSMCs to NO in the femoral artery, although changes in the heart upon AngII treatment were also present, which could also be (partially) accountable for the lack of an AngII-induced rise in blood pressure in Atg7^F/F SM22α-Cre⁺ mice. Overall, our study indicates that apart from previously shown effects on large elastic arteries, VSMC autophagy also plays a pivotal role in the regulation of the contractile and relaxing properties of the smaller muscular arteries. This may suggest a role for autophagy in vascular pathologies, such as hypertension and arterial stiffness.

A practical guide for investigating cardiac physiology using living myocardial slices

Ex vivo multicellular preparations are essential tools to study tissue physiology. Among them, the recent methodological and technological developments in living myocardial slices (LMS) are attracting increasing interest by the cardiac research field. Despite this, this research model remains poorly perceived and utilized by most research laboratories. Here, we provide a practical guide on how to use LMS to interrogate multiple aspects of cardiac function, structure and biochemistry. We discuss issues that should be considered to conduct successful experiments, including experimental design, sample preparation, data collection and analysis. We describe how laboratory setups can be adapted to accommodate and interrogate this multicellular research model. These adaptations can often be achieved at a reasonable cost with off-the-shelf components and operated reliably using well-established protocols and freely available software, which is essential to broaden the utilization of this method. We will also highlight how current measurements can be improved to further enhance data quality and reliability to ensure inter-laboratory reproducibility. Finally, we summarize the most promising biomedical applications and envision how living myocardial slices can lead to further breakthroughs.

Updating the Risk Stratification for Sudden Cardiac Death in Cardiomyopathies: The Evolving Role of Cardiac Magnetic Resonance Imaging. An Approach for the Electrophysiologist

The prevention of sudden cardiac death (SCD) in cardiomyopathies (CM) remains a challenge. The current guidelines still favor the implantation of devices for the primary prevention of SCD only in patients with severely reduced left ventricular ejection fraction (LVEF) and heart failure (HF) symptoms. The implantation of an implantable cardioverter-defibrillator (ICD) is a protective barrier against arrhythmic events in CMs, but the benefit does not outweigh the cost in low risk patients. The identification of high risk patients is the key to an individualized prevention strategy. Cardiac magnetic resonance (CMR) provides reliable and reproducible information about biventricular function and tissue characterization. Furthermore, late gadolinium enhancement (LGE) quantification and pattern of distribution, as well as abnormal T1 mapping and extracellular volume (ECV), representing indices of diffuse fibrosis, can enhance our ability to detect high risk patients. CMR can also complement electro-anatomical mapping (EAM), a technique already applied in the risk evaluation and in the ventricular arrhythmias ablation therapy of CM patients, providing a more accurate assessment of fibrosis and arrhythmic corridors. As a result, CMR provides a new insight into the pathological substrate of CM. CMR may help identify high risk CM patients and, combined with EAM, can provide an integrated evaluation of scar and arrhythmic corridors in the ablative therapy of ventricular arrhythmias.