Distinct Phenotypes Induced by Three Degrees of Transverse Aortic Constriction in Mice

Three-dimensional structure of entire hydrated murine hearts at histological resolution

Imaging the entire cardiomyocyte network in entire small animal hearts at single cell resolution is a formidable challenge. Optical microscopy provides sufficient contrast and resolution in 2d, however fails to deliver non-destructive 3d reconstructions with isotropic resolution. It requires several invasive preparation steps, which introduce structural artefacts, namely dehydration, physical slicing and staining, or for the case of light sheet microscopy also clearing of the tissue. Our goal is to provide 3d reconstructions of the cardiomyocyte network in entire hydrated murine hearts, and to develop a methodology for quantitative analysis of heart pathologies based on X-ray phase contrast computed tomography (XPCT). We have used XPCT at two beamlines of the extremely brilliant source (EBS) at the European Synchrotron Radiation Facility (ESRF) to scan wild-type murine hearts at high resolution, as well as a series of murine hearts of different pathological models, at reduced resolution and higher throughput. All hearts were obtained from the small animal facility of the university medical center in Göttingen. The hearts were fixed in formalin, stored and measured non-destructively in phosphate buffer solution. The high resolution dataset allows to discern individual cardiomyocytes in the tissue. All datasets have been analyzed using semi-automated image segmentation of the ventricles, rotation into a common coordinate system, classification into different anatomical compartments, and finally the structure tensor approach. A 3d streamline representation of the cardiomyocyte orientation vector field is provided. The different cardiovascular disease models are analysed based on metrics derived from the 3d structure tensor. An entire hydrated murine heart has been covered at an isotropic voxel size of 1.6 μ m (distributed over several volumes). A binned and fused dataset of this heart is available at 3.2 μ m, and has been analyzed by the structure tensor approach to yield the ventricular cardiomyocyte network or mesh, i.e. the aggregation of the cardiomyocyte chains in particular in the ventricular wall. Semi-automatic determination of structural metrics is already achieved and the corresponding tools and resulting data are made publically available. XPCT using extremely brilliant undulator radiation is close to achieve single cell reconstruction in an entire small animal organ.

Soy protein β-conglycinin ameliorates pressure overload-induced heart failure by increasing short-chain fatty acid (SCFA)-producing gut microbiota and intestinal SCFAs

BACKGROUND AND AIMS

Soybeans and their ingredients have antioxidant and anti-inflammatory effects on cardiovascular diseases. β-Conglycinin (β-CG), a major constituent of soy proteins, is protective against obesity, hypertension, and chronic kidney disease, but its effects on heart failure remain to be elucidated. We tested the effects of β-CG on left ventricular (LV) remodeling in pressure overload-induced heart failure.

METHODS

A transverse aortic constriction (TAC)-induced pressure overload was applied to the heart in 7-week-old C57BL6 male mice that were treated with β-CG, GlcNAc, or sodium propionate. Gut microbiota was analyzed by 16S rRNA sequencing. Fecal short-chain fatty acids (SCFAs) were quantified by GC-MS. The effects of oral antibiotics were examined in β-CG-fed mice.

RESULTS

β-CG ameliorated impaired cardiac contractions, cardiac hypertrophy, and myocardial fibrosis in TAC-operated mice. As β-CG is a highly glycosylated protein, we examined the effects of GlcNAc. GlcNAc had similar but less efficient effects on LV remodeling compared to β-CG. β-CG increased three major SCFA-producing intestinal bacteria, as well as fecal concentrations of SCFAs, in sham- and TAC-operated mice. Oral administration of antibiotics nullified the effects of β-CG in TAC-operated mice by markedly reducing SCFA-producing intestinal bacteria and fecal SCFAs. In contrast, oral administration of sodium propionate, one of SCFAs, ameliorated LV remodeling in TAC-operated mice to a similar extent as β-CG.

CONCLUSIONS

β-CG was protective against TAC-induced LV remodeling, which was likely to be mediated by increased SCFA-producing gut microbiota and increased intestinal SCFAs. Modified β-CG and/or derivatives arising from β-CG are expected to be developed as prophylactic and/or therapeutic agents to ameliorate devastating symptoms in heart failure.

The splicing factor hnRNPL demonstrates conserved myocardial regulation across species and is altered in heart failure

Heart failure (HF) is highly prevalent. Mechanisms underlying HF remain incompletely understood. Splicing factors (SF), which control pre-mRNA alternative splicing, regulate cardiac structure and function. This study investigated regulation of the splicing factor heterogeneous nuclear ribonucleoprotein-L (hnRNPL) in the failing heart. hnRNPL protein increased in left ventricular tissue from mice with transaortic constriction-induced HF and from HF patients. In left ventricular tissue, hnRNPL was detected predominantly in nuclei. Knockdown of the hnRNPL homolog Smooth in Drosophila induced cardiomyopathy. Computational analysis of predicted mouse and human hnRNPL binding sites suggested hnRNPL-mediated alternative splicing of tropomyosin, which was confirmed in C2C12 myoblasts. These findings identify hnRNPL as a sensor of cardiac dysfunction and suggest that disturbances of hnRNPL affect alternative splicing in HF.

Myocardial infarction augments sleep to limit cardiac inflammation and damage

Sleep is integral to cardiovascular health1,2. Yet, the circuits that connect cardiovascular pathology and sleep are incompletely understood. It remains unclear whether cardiac injury influences sleep and whether sleep-mediated neural outputs contribute to heart healing and inflammation. Here we report that in humans and mice, monocytes are actively recruited to the brain after myocardial infarction (MI) to augment sleep, which suppresses sympathetic outflow to the heart, limiting inflammation and promoting healing. After MI, microglia rapidly recruit circulating monocytes to the brain's thalamic lateral posterior nucleus (LPN) via the choroid plexus, where they are reprogrammed to generate tumour necrosis factor (TNF). In the thalamic LPN, monocytic TNF engages Tnfrsf1a-expressing glutamatergic neurons to increase slow wave sleep pressure and abundance. Disrupting sleep after MI worsens cardiac function, decreases heart rate variability and causes spontaneous ventricular tachycardia. After MI, disrupting or curtailing sleep by manipulating glutamatergic TNF signalling in the thalamic LPN increases cardiac sympathetic input which signals through the β2-adrenergic receptor of macrophages to promote a chemotactic signature that increases monocyte influx. Poor sleep in the weeks following acute coronary syndrome increases susceptibility to secondary cardiovascular events and reduces the heart's functional recovery. In parallel, insufficient sleep in humans reprogrammes β2-adrenergic receptor-expressing monocytes towards a chemotactic phenotype, enhancing their migratory capacity. Collectively, our data uncover cardiogenic regulation of sleep after heart injury, which restricts cardiac sympathetic input, limiting inflammation and damage.

Exploring in vivo and in vitro models for heart failure with biomarker insights: a review

BACKGROUND

Heart failure (HF) is a condition characterized by the heart's inability to meet the body's demands, resulting in various complications. Two primary types of HF exist, namely HF with preserved left ventricular ejection fraction (LVEF) and HF reduced with LVEF. The progression of HF involves compensatory mechanisms such as cardiac hypertrophy, fibrosis, and alterations in gene expression. Pressure overload and volume overload are common etiologies of HF, with pressure overload often stemming from conditions like hypertension, leading to left ventricular hypertrophy and fibrosis. In contrast, volume overload can arise from chronic valvular regurgitant disease, also inducing left ventricular hypertrophy.

MAIN BODY

In vitro cell culture techniques serve as vital tools in studying HF pathophysiology, allowing researchers to investigate cellular responses and potential therapeutic targets. Additionally, biomarkers, measurable biological characteristics, play a crucial role in diagnosing and predicting HF. Some notable biomarkers include adrenomedullin, B-type natriuretic peptide, copeptin, galectin-3, interleukin-6, matrix metalloproteinases (MMPs), midregional pro-atrial natriuretic peptide, myostatin, procollagen type I C-terminal propeptide, procollagen type III N-terminal propeptide and tissue inhibitors of metalloproteinases (TIMPs). These biomarkers aid in HF diagnosis, assessing its severity, and monitoring treatment response, contributing to a deeper understanding of the disease and potentially leading to improved management strategies and outcomes.

CONCLUSIONS

This review provides comprehensive insights into various in vivo models of HF, commonly utilized cell lines in HF research, and pivotal biomarkers with diagnostic relevance for HF. By synthesizing this information, researchers gain valuable resources to further explore HF pathogenesis, identify novel therapeutic targets, and enhance diagnostic and prognostic approaches.

The Extracellular Matrix and Cardiac Pressure Overload: Focus on Novel Treatment Targets

Heart failure is a significant health issue in developed countries, often stemming from conditions like hypertension, which imposes a pressure overload on the heart. Despite various treatment strategies for heart failure, many lack long-term effectiveness. A critical aspect of cardiac disease is the remodeling of the heart, where compensatory changes in the extracellular matrix exacerbate disease progression. This review explores the processes and changes occurring in the pressure-overloaded heart with respect to the extracellular matrix. It further summarizes current treatment strategies, and then focuses on novel treatment targets for maladaptive cardiac remodeling, derived from transverse aortic constriction-induced pressure overload animal models.

Cardiomyocyte-derived USP28 negatively regulates antioxidant response and promotes cardiac hypertrophy via deubiquitinating TRIM21

Rationale: Cardiac hypertrophy is an important pathological basis for heart failure. Most physiological activities of cardiomyocytes are regulated by proteins and their post-translational modification. Deubiquitinating enzymes (DUBs) are involved in protein stability maintenance and closely related to myocardial hypertrophy. In this study, we aimed to clarify the regulatory role of a DUB, ubiquitin-specific peptidase 28 (USP28), in cardiac hypertrophy and explore the molecular mechanism behind. Methods: Transcriptome and single-cell mRNA sequencing was used to demonstrate the association of USP28 and cardiac hypertrophy. Cardiomyocyte-specific USP28 knockout mice (USP28CKO) were subjected to angiotensin II (Ang II) infusion or transverse aortic constriction (TAC) models. Coimmunoprecipitation combined mass spectrum analysis (Co-IP/MS) was applied to screen out the substrate of USP28. Results: We first showed the up-regulation of USP28 in cardiac hypertrophy, and its cellular localization of cardiomyocytes. USP28CKO protects mouse heart against Ang II- or TAC-induced cardiac dysfunction and hypertrophy. Mechanistically, we identified tripartite motif-containing protein 21 (TRIM21) as the potential substrate of USP28 by Co-IP/MS analysis. Cardiomyocyte USP28 deubiquitinates and stabilizes TRIM21 to negatively regulate nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant response, increasing oxidative stress in cardiomyocytes and promoting cardiac hypertrophy and injury. Finally, using a selective USP28 inhibitor Otilonium Bromide, we confirmed the therapeutic effect of pharmacological inhibition of USP28 against TAC-induced established hypertrophic heart failure. Conclusion: Our study illustrates a cardiomyocyte-specific USP28-TRIM21 axis in regulating hypertrophic cardiomyopathy and presents USP28 as a potential target for the treatment of cardiac hypertrophy.

Loss of cardiomyocyte-specific adhesion G-protein-coupled receptor G1 (ADGRG1/GPR56) promotes pressure overload-induced heart failure

Adhesion G-protein-coupled receptors (AGPCRs), containing large N-terminal ligand-binding domains for environmental mechano-sensing, have been increasingly recognized to play important roles in numerous physiologic and pathologic processes. However, their impact on the heart, which undergoes dynamic mechanical alterations in healthy and failing states, remains understudied. ADGRG1 (formerly known as GPR56) is widely expressed, including in skeletal muscle where it was previously shown to mediate mechanical overload-induced muscle hypertrophy; thus, we hypothesized that it could impact the development of cardiac dysfunction and remodeling in response to pressure overload. In this study, we generated a cardiomyocyte (CM)-specific ADGRG1 knockout mouse model, which, although not initially displaying features of cardiac dysfunction, does develop increased systolic and diastolic LV volumes and internal diameters over time. Notably, when challenged with chronic pressure overload, CM-specific ADGRG1 deletion accelerates cardiac dysfunction, concurrent with blunted CM hypertrophy, enhanced cardiac inflammation and increased mortality, suggesting that ADGRG1 plays an important role in the early adaptation to chronic cardiac stress. Altogether, the present study provides an important proof-of-concept that targeting CM-expressed AGPCRs may offer a new avenue for regulating the development of heart failure.

Plasma concentrations of peptide hormones: Unrealistic levels of vasopressin (AVP), oxytocin (OXT), and brain natriuretic peptide (BNP)

Hormones are specific molecules measured in biological fluids by elaborate analytical systems requiring meticulous attention. Variation between laboratories can be expected. However, recently published measurements of AVP, OXT, and BNP in human plasma under basal/control conditions include numbers which, between publications, vary by 100-10 000-fold. Generally, the methods descriptions are scant, at best, and provide no information about quality control measures. Clearly, two results describing the same basal hormone concentration by numbers three orders of magnitude apart are incongruent providing reason for concern. Basal concentrations of bioactive AVP, OXT, and BNP in human plasma are in the order of 1-10 pmol/L. Therefore, assay systems applied to plasma must be able to measure concentrations of less than 1 pmol/L with appropriate specificity and accuracy. Basal concentrations of AVP, OXT, and BNP above 100 pmol/L should be reconsidered, as such results do not reflect bioactive hormone levels in humans, rats, or mice. Any concentration above 1000 pmol/L is of concern because such levels of bioactive hormone may be seen only under extreme conditions, if at all.

MYH11 rare variant augments aortic growth and induces cardiac hypertrophy and heart failure with pressure overload

Smooth muscle cell-specific myosin heavy chain, encoded by MYH11, is selectively expressed in smooth muscle cells (SMCs). Pathogenic variants in MYH11 predispose to a number of disorders, including heritable thoracic aortic disease associated with patent ductus arteriosus, visceral myopathy, and megacystis-microcolon-intestinal hypoperistalsis syndrome. Rare variants of uncertain significance occur throughout the gene, including MYH11 p.Glu1892Asp, and we sought to determine if this variant causes thoracic aortic disease in mice. Genomic editing was used to generate Myh11 E1892D/E1892D mice. Wild-type (WT) and mutant mice underwent cardiovascular phenotyping and with transverse aortic constriction (TAC). Myh11 E1892D/E1892D and WT mice displayed similar growth, blood pressure, root and ascending aortic diameters, and cardiac function up to 13 months of age, along with similar contraction and relaxation on myographic testing. TAC induced hypertension similarly in Myh11 E1892D/E1892D and WT mice, but mutant mice showed augmented ascending aortic enlargement and increased elastic fragmentation on histology. Unexpectedly, male Myh11 E1892D/E1892D mice two weeks post-TAC had decreased ejection fraction, stroke volume, fractional shortening, and cardiac output compared to similarly treated male WT mice. Importantly, left ventricular mass increased significantly due to primarily posterior wall thickening, and cardiac histology confirmed cardiomyocyte hypertrophy and increased collagen deposition in the myocardium and surrounding arteries. These results further highlight the clinical heterogeneity associated with MYH11 rare variants. Given that MYH11 is selectively expressed in SMCs, these results implicate a role of vascular SMCs in the heart contributing to cardiac hypertrophy and failure with pressure overload.

Cytotoxic T cells drive doxorubicin-induced cardiac fibrosis and systolic dysfunction

Doxorubicin, the most prescribed chemotherapeutic drug, causes dose-dependent cardiotoxicity and heart failure. However, our understanding of the immune response elicited by doxorubicin is limited. Here we show that an aberrant CD8+ T cell immune response following doxorubicin-induced cardiac injury drives adverse remodeling and cardiomyopathy. Doxorubicin treatment in non-tumor-bearing mice increased circulating and cardiac IFNγ+CD8+ T cells and activated effector CD8+ T cells in lymphoid tissues. Moreover, doxorubicin promoted cardiac CD8+ T cell infiltration and depletion of CD8+ T cells in doxorubicin-treated mice decreased cardiac fibrosis and improved systolic function. Doxorubicin treatment induced ICAM-1 expression by cardiac fibroblasts resulting in enhanced CD8+ T cell adhesion and transformation, contact-dependent CD8+ degranulation and release of granzyme B. Canine lymphoma patients and human patients with hematopoietic malignancies showed increased circulating CD8+ T cells after doxorubicin treatment. In human cancer patients, T cells expressed IFNγ and CXCR3, and plasma levels of the CXCR3 ligands CXCL9 and CXCL10 correlated with decreased systolic function.

Simultaneous Positron Emission Tomography and Molecular Magnetic Resonance Imaging of Cardiopulmonary Fibrosis in a Mouse Model of Left Ventricular Dysfunction

BACKGROUND

Aging-associated left ventricular dysfunction promotes cardiopulmonary fibrogenic remodeling, Group 2 pulmonary hypertension (PH), and right ventricular failure. At the time of diagnosis, cardiac function has declined, and cardiopulmonary fibrosis has often developed. Here, we sought to develop a molecular positron emission tomography (PET)-magnetic resonance imaging (MRI) protocol to detect both cardiopulmonary fibrosis and fibrotic disease activity in a left ventricular dysfunction model.

METHODS AND RESULTS

Left ventricular dysfunction was induced by transverse aortic constriction (TAC) in 6-month-old senescence-accelerated prone mice, a subset of mice that received sham surgery. Three weeks after surgery, mice underwent simultaneous PET-MRI at 4.7 T. Collagen-targeted PET and fibrogenesis magnetic resonance (MR) probes were intravenously administered. PET signal was computed as myocardium- or lung-to-muscle ratio. Percent signal intensity increase and Δ lung-to-muscle ratio were computed from the pre-/postinjection magnetic resonance images. Elevated allysine in the heart (P=0.02) and lungs (P=0.17) of TAC mice corresponded to an increase in myocardial magnetic resonance imaging percent signal intensity increase (P<0.0001) and Δlung-to-muscle ratio (P<0.0001). Hydroxyproline in the heart (P<0.0001) and lungs (P<0.01) were elevated in TAC mice, which corresponded to an increase in heart (myocardium-to-muscle ratio, P=0.02) and lung (lung-to-muscle ratio, P<0.001) PET measurements. Pressure-volume loop and echocardiography demonstrated adverse left ventricular remodeling, function, and increased right ventricular systolic pressure in TAC mice.

CONCLUSIONS

Administration of collagen-targeted PET and allysine-targeted MR probes led to elevated PET-magnetic resonance imaging signals in the myocardium and lungs of TAC mice. The study demonstrates the potential to detect fibrosis and fibrogenesis in cardiopulmonary disease through a dual molecular PET-magnetic resonance imaging protocol.

Tipifarnib Reduces Extracellular Vesicles and Protects From Heart Failure

BACKGROUND

Heart failure (HF) is one of the leading causes of mortality worldwide. Extracellular vesicles, including small extracellular vesicles or exosomes, and their molecular cargo are known to modulate cell-to-cell communication during multiple cardiac diseases. However, the role of systemic extracellular vesicle biogenesis inhibition in HF models is not well documented and remains unclear.

METHODS

We investigated the role of circulating exosomes during cardiac dysfunction and remodeling in a mouse transverse aortic constriction (TAC) model of HF. Importantly, we investigate the efficacy of tipifarnib, a recently identified exosome biogenesis inhibitor that targets the critical proteins (Rab27a [Ras associated binding protein 27a], nSMase2 [neutral sphingomyelinase 2], and Alix [ALG-2-interacting protein X]) involved in exosome biogenesis for this mouse model of HF. In this study, 10-week-old male mice underwent TAC surgery were randomly assigned to groups with and without tipifarnib treatment (10 mg/kg 3 times/wk) and monitored for 8 weeks, and a comprehensive assessment was conducted through performed echocardiographic, histological, and biochemical studies.

RESULTS

TAC significantly elevated circulating plasma exosomes and markedly increased cardiac left ventricular dysfunction, cardiac hypertrophy, and fibrosis. Furthermore, injection of plasma exosomes from TAC mice induced left ventricular dysfunction and cardiomyocyte hypertrophy in uninjured mice without TAC. On the contrary, treatment of tipifarnib in TAC mice reduced circulating exosomes to baseline and remarkably improved left ventricular functions, hypertrophy, and fibrosis. Tipifarnib treatment also drastically altered the miRNA profile of circulating post-TAC exosomes, including miR 331-5p, which was highly downregulated both in TAC circulating exosomes and in TAC cardiac tissue. Mechanistically, miR 331-5p is crucial for inhibiting the fibroblast-to-myofibroblast transition by targeting HOXC8, a critical regulator of fibrosis. Tipifarnib treatment in TAC mice upregulated the expression of miR 331-5p that acts as a potent repressor for one of the fibrotic mechanisms mediated by HOXC8.

CONCLUSIONS

Our study underscores the pathological role of exosomes in HF and fibrosis in response to pressure overload. Tipifarnib-mediated inhibition of exosome biogenesis and cargo sorting may serve as a viable strategy to prevent progressive cardiac remodeling in HF.

Soft robotic platform for progressive and reversible aortic constriction in a small-animal model

Our understanding of cardiac remodeling processes due to left ventricular pressure overload derives largely from animal models of aortic banding. However, these studies fail to enable control over both disease progression and reversal, hindering their clinical relevance. Here, we describe a method for progressive and reversible aortic banding based on an implantable expandable actuator that can be finely tuned to modulate aortic banding and debanding in a rat model. Through catheterization, imaging, and histologic studies, we demonstrate that our platform can recapitulate the hemodynamic and structural changes associated with pressure overload in a controllable manner. We leveraged soft robotics to enable noninvasive aortic debanding, demonstrating that these changes can be partly reversed because of cessation of the biomechanical stimulus. By recapitulating longitudinal disease progression and reversibility, this animal model could elucidate fundamental mechanisms of cardiac remodeling and optimize timing of intervention for pressure overload.

Treatment with αvβ3-integrin-specific 29P attenuates pressure-overload induced cardiac remodelling after transverse aortic constriction in mice

Heart failure remains one of the largest clinical burdens globally, with little to no improvement in the development of disease-eradicating therapeutics. Integrin targeting has been used in the treatment of ocular disease and cancer, but little is known about its utility in the treatment of heart failure. Here we sought to determine whether the second generation orally available, αvβ3-specific RGD-mimetic, 29P , was cardioprotective. Male mice were subjected to transverse aortic constriction (TAC) and treated with 50 μg/kg 29P or volume-matched saline as Vehicle control. At 3 weeks post-TAC, echocardiography showed that 29P treatment significantly restored cardiac function and structure indicating the protective effect of 29P treatment in this model of heart failure. Importantly, 29P treatment improved cardiac function giving improved fractional shortening, ejection fraction, heart weight and lung weight to tibia length fractions, together with partial restoration of Ace and Mme levels, as markers of the TAC insult. At a tissue level, 29P reduced cardiomyocyte hypertrophy and interstitial fibrosis, both of which are major clinical features of heart failure. RNA sequencing identified that, mechanistically, this occurred with concomitant alterations to genes involved molecular pathways associated with these processes such as metabolism, hypertrophy and basement membrane formation. Overall, targeting αvβ3 with 29P provides a novel strategy to attenuate pressure-overload induced cardiac hypertrophy and fibrosis, providing a possible new approach to heart failure treatment.

Cardiac fibroblasts in heart failure and regeneration

In heart disease patients, myocyte loss or malfunction invariably leads to fibrosis, involving the activation and accumulation of cardiac fibroblasts that deposit large amounts of extracellular matrix. Apart from the vital replacement fibrosis that follows myocardial infarction, ensuring structural integrity of the heart, cardiac fibrosis is largely considered to be maladaptive. Much work has focused on signaling pathways driving the fibrotic response, including TGF-β signaling and biomechanical strain. However, currently there are very limited options for reducing cardiac fibrosis, with most patients suffering from chronic fibrosis. The adult heart has very limited regenerative capacity. However, cardiac regeneration has been reported in humans perinatally, and reproduced experimentally in neonatal mice. Furthermore, model organisms such as the zebrafish are able to fully regenerate their hearts following massive cardiac damage into adulthood. Increasing evidence points to a transient immuno-fibrotic response as being key for cardiac regeneration to occur. The mechanisms at play in this context are changing our views on fibrosis, and could be leveraged to promote beneficial remodeling in heart failure patients. This review summarizes our current knowledge of fibroblast properties associated with the healthy, failing or regenerating heart. Furthermore, we explore how cardiac fibroblast activity could be targeted to assist future therapeutic approaches.

Comparative analysis of ventricular stiffness across species

Investigating ventricular diastolic properties is crucial for understanding the physiological cardiac functions in organisms and unraveling the pathological mechanisms of cardiovascular disorders. Ventricular stiffness, a fundamental parameter that defines ventricular diastolic functions in chordates, is typically analyzed using the end-diastolic pressure-volume relationship (EDPVR). However, comparing ventricular stiffness accurately across chambers of varying maximum volume capacities has been a long-standing challenge. As one of the solutions to this problem, we propose calculating a relative ventricular stiffness index by applying an exponential approximation formula to the EDPVR plot data of the relationship between ventricular pressure and values of normalized ventricular volume by the ventricular weight. This article reviews the potential, utility, and limitations of using normalized EDPVR analysis in recent studies. Herein, we measured and ranked ventricular stiffness in differently sized and shaped chambers using ex vivo ventricular pressure-volume analysis data from four animals: Wistar rats, red-eared slider turtles, masu salmon, and cherry salmon. Furthermore, we have discussed the mechanical effects of intracellular and extracellular viscoelastic components, Titin (Connectin) filaments, collagens, physiological sarcomere length, and other factors that govern ventricular stiffness. Our review provides insights into the comparison of ventricular stiffness in different-sized ventricles between heterologous and homologous species, including non-model organisms.

miR-222 inhibits pathological cardiac hypertrophy and heart failure

AIMS

Physiological cardiac hypertrophy occurs in response to exercise and can protect against pathological stress. In contrast, pathological hypertrophy occurs in disease and often precedes heart failure. The cardiac pathways activated in physiological and pathological hypertrophy are largely distinct. Our prior work demonstrated that miR-222 increases in exercised hearts and is required for exercise-induced cardiac hypertrophy and cardiomyogenesis. Here, we sought to define the role of miR-222 in pathological hypertrophy.

METHODS AND RESULTS

We found that miR-222 also increased in pathological hypertrophy induced by pressure overload. To assess its functional significance in this setting, we generated a miR-222 gain-of-function model through cardiac-specific constitutive transgenic miR-222 expression (TgC-miR-222) and used locked nucleic acid anti-miR specific for miR-222 to inhibit its effects. Both gain- and loss-of-function models manifested normal cardiac structure and function at baseline. However, after transverse aortic constriction (TAC), miR-222 inhibition accelerated the development of pathological hypertrophy, cardiac dysfunction, and heart failure. Conversely, miR-222-overexpressing mice had less pathological hypertrophy after TAC, as well as better cardiac function and survival. We identified p53-up-regulated modulator of apoptosis, a pro-apoptotic Bcl-2 family member, and the transcription factors, Hmbox1 and nuclear factor of activated T-cells 3, as direct miR-222 targets contributing to its roles in this context.

CONCLUSION

While miR-222 is necessary for physiological cardiac growth, it inhibits cardiac growth in response to pressure overload and reduces adverse remodelling and cardiac dysfunction. These findings support the model that physiological and pathological hypertrophy are fundamentally different. Further, they suggest that miR-222 may hold promise as a therapeutic target in pathological cardiac hypertrophy and heart failure.

A new approach to characterize cardiac sodium storage by combining fluorescence photometry and magnetic resonance imaging in small animal research

Cardiac myocyte sodium (Na+) homoeostasis is pivotal in cardiac diseases and heart failure. Intracellular Na+ ([Na+]i) is an important regulator of excitation-contraction coupling and mitochondrial energetics. In addition, extracellular Na+ ([Na+]e) and its water-free storage trigger collagen cross-linking, myocardial stiffening and impaired cardiac function. Therefore, understanding the allocation of tissue Na+ to intra- and extracellular compartments is crucial in comprehending the pathophysiological processes in cardiac diseases. We extrapolated [Na+]e using a three-compartment model, with tissue Na+ concentration (TSC) measured by in vivo 23Na-MRI, extracellular volume (ECV) data calculated from T1 maps, and [Na+]i measured by in vitro fluorescence microscopy using Na+ binding benzofuran isophthalate (SBFI). To investigate dynamic changes in Na+ compartments, we induced pressure overload (TAC) or myocardial infarction (MI) via LAD ligation in mice. Compared to SHAM mice, TSC was similar after TAC but increased after MI. Both TAC and MI showed significantly higher [Na+]i compared to SHAM (around 130% compared to SHAM). Calculated [Na+]e increased after MI, but not after TAC. Increased TSC after TAC was primarily driven by increased [Na+]i, but the increase after MI by elevations in both [Na+]i and [Na+]e.

Transcriptional changes during isoproterenol-induced cardiac fibrosis in mice

Introduction: β-adrenergic stimulation using β-agonists such as isoproterenol has been routinely used to induce cardiac fibrosis in experimental animal models. Although transcriptome changes in surgical models of cardiac fibrosis such as transverse aortic constriction (TAC) and coronary artery ligation (CAL) are well-studied, transcriptional changes during isoproterenol-induced cardiac fibrosis are not well-explored. Methods: Cardiac fibrosis was induced in male C57BL6 mice by administration of isoproterenol for 4, 8, or 11 days at 50 mg/kg/day dose. Temporal changes in gene expression were studied by RNA sequencing. Results and discussion: We observed a significant alteration in the transcriptome profile across the different experimental groups compared to the saline group. Isoproterenol treatment caused upregulation of genes associated with ECM organization, cell-cell contact, three-dimensional structure, and cell growth, while genes associated with fatty acid oxidation, sarcoplasmic reticulum calcium ion transport, and cardiac muscle contraction are downregulated. A number of known long non-coding RNAs (lncRNAs) and putative novel lncRNAs exhibited differential regulation. In conclusion, our study shows that isoproterenol administration leads to the dysregulation of genes relevant to ECM deposition and cardiac contraction, and serves as an excellent alternate model to the surgical models of heart failure.

Increased GIRK channel activity prevents arrhythmia in mice with heart failure by enhancing ventricular repolarization

Ventricular arrhythmia causing sudden cardiac death is the leading mode of death in patients with heart failure. Yet, the mechanisms that prevent ventricular arrhythmias in heart failure are not well characterized. Using a mouse model of heart failure created by transverse aorta constriction, we show that GIRK channel, an important regulator of cardiac action potentials, is constitutively active in failing ventricles in contrast to normal cells. Evidence is presented indicating that the tonic activation of M2 muscarinic acetylcholine receptors by endogenously released acetylcholine contributes to the constitutive GIRK activity. This constitutive GIRK activity prevents the action potential prolongation in heart failure ventricles. Consistently, GIRK channel blockade with tertiapin-Q induces QT interval prolongation and increases the incidence of arrhythmia in heart failure, but not in control mice. These results suggest that constitutive GIRK channels comprise a key mechanism to protect against arrhythmia by providing repolarizing currents in heart failure ventricles.

Circular RNA circSMAD4 regulates cardiac fibrosis by targeting miR-671-5p and FGFR2 in cardiac fibroblasts

Heart failure is a leading cause of death and is often accompanied by activation of quiescent cardiac myofibroblasts, which results in cardiac fibrosis. In this study, we aimed to identify novel circular RNAs that regulate cardiac fibrosis. We applied transverse aortic constriction (TAC) for 1, 4, and 8 weeks in mice. RNA sequencing datasets were obtained from cardiac fibroblasts isolated by use of a Langendorff apparatus and then further processed by use of selection criteria such as differential expression and conservation in species. CircSMAD4 was upregulated by TAC in mice or by transforming growth factor (TGF)-β1 in primarily cultured human cardiac fibroblasts. Delivery of si-circSMAD4 attenuated myofibroblast activation and cardiac fibrosis in mice treated with isoproterenol (ISP). si-circSmad4 significantly reduced cardiac fibrosis and remodeling at 8 weeks. Mechanistically, circSMAD4 acted as a sponge against the microRNA miR-671-5p in a sequence-specific manner. miR-671-5p was downregulated during myofibroblast activation and its mimic form attenuated cardiac fibrosis. miR-671-5p mimic destabilized fibroblast growth factor receptor 2 (FGFR2) mRNA in a sequence-specific manner and interfered with the fibrotic action of FGFR2. The circSMAD4-miR-671-5p-FGFR2 pathway is involved in the differentiation of cardiac myofibroblasts and thereby the development of cardiac fibrosis.

Measuring cardiomyocyte cellular characteristics in cardiac hypertrophy using diffusion-weighted MRI

PURPOSE

This paper presents a hierarchical modeling approach for estimating cardiomyocyte major and minor diameters and intracellular volume fraction (ICV) using diffusion-weighted MRI (DWI) data in ex vivo mouse hearts.

METHODS

DWI data were acquired on two healthy controls and two hearts 3 weeks post transverse aortic constriction (TAC) using a bespoke diffusion scheme with multiple diffusion times (Δ $$ \Delta $$ ), q-shells and diffusion encoding directions. Firstly, a bi-exponential tensor model was fitted separately at each diffusion time to disentangle the dependence on diffusion times from diffusion weightings, that is, b-values. The slow-diffusing component was attributed to the restricted diffusion inside cardiomyocytes. ICV was then extrapolated atΔ = 0 $$ \Delta =0 $$ using linear regression. Secondly, given the secondary and the tertiary diffusion eigenvalue measurements for the slow-diffusing component obtained at different diffusion times, major and minor diameters were estimated assuming a cylinder model with an elliptical cross-section (ECS). High-resolution three-dimensional synchrotron X-ray imaging (SRI) data from the same specimen was utilized to evaluate the biophysical parameters.

RESULTS

Estimated parameters using DWI data were (control 1/control 2 vs. TAC 1/TAC 2): major diameter-17.4μ $$ \mu $$ m/18.0μ $$ \mu $$ m versus 19.2μ $$ \mu $$ m/19.0μ $$ \mu $$ m; minor diameter-10.2μ $$ \mu $$ m/9.4μ $$ \mu $$ m versus 12.8μ $$ \mu $$ m/13.4μ $$ \mu $$ m; and ICV-62%/62% versus 68%/47%. These findings were consistent with SRI measurements.

CONCLUSION

The proposed method allowed for accurate estimation of biophysical parameters suggesting cardiomyocyte diameters as sensitive biomarkers of hypertrophy in the heart.

Effect of Danhong injection on heart failure in rats evaluated by metabolomics

Background

Heart failure (HF) is characterized by reduced ventricular filling or ejection function due to organic or non-organic cardiovascular diseases. Danhong injection (DHI) is a medicinal material used clinically to treat HF for many years in China. Although prior research has shown that Danhong injection can improve cardiac function and structure, the biological mechanism has yet to be determined.

Methods

Serum metabolic analysis was conducted via ultra-high-performance liquid chromatography-quadrupole time-of-flight/mass spectrometry (UHPLC-QE/MS) to explore underlying protective mechanisms of DHI in the transverse aortic constriction (TAC)-induced heart failure. Multivariate statistical techniques were used in the research, such as unsupervised principal component analysis (PCA) and orthogonal projection to latent structures discriminant analysis (OPLS-DA). MetaboAnalyst and Kyoto Encyclopedia of Genes and Genomes (KEGG) were employed to pinpoint pertinent metabolic pathways.

Results

After DHI treatment, cardiac morphology and function as well as the metabolism in model rats were improved. We identified 17 differential metabolites and six metabolic pathways. Two biomarkers, PC(18:3(6Z,9Z,12Z)/24:0) and L-Phenylalanine, were identified for the first time as strong indicators for the significant effect of DHI.

Conclusion

This study revealed that DHI could regulate potential biomarkers and correlated metabolic pathway, which highlighted therapeutic potential of DHI in managing HF.

Suppression of Heart Failure With PAR1 Pepducin Technology in a Pressure Overload Model in Mice

BACKGROUND

PAR1 (protease-activated receptor-1) contributes to acute thrombosis, but it is not clear whether the receptor is involved in deleterious inflammatory and profibrotic processes in heart failure. Here, we employ the pepducin technology to determine the effects of targeting PAR1 in a mouse heart failure with reduced ejection fraction model.

METHODS

After undergoing transverse aortic constriction pressure overload or sham surgery, C57BL/6J mice were randomized to daily sc PZ-128 pepducin or vehicle, and cardiac function, inflammation, fibrosis, and molecular analyses conducted at 7 weeks RESULTS: After 7 weeks of transverse aortic constriction, vehicle mice had marked increases in macrophage/monocyte infiltration and fibrosis of the left ventricle as compared with Sham mice. PZ-128 treatment significantly suppressed the inflammatory cell infiltration and cardiac fibrosis. Despite no effect on myocyte cell hypertrophy, PZ-128 afforded a significant reduction in overall left ventricle weight and completely protected against the transverse aortic constriction-induced impairments in left ventricle ejection fraction. PZ-128 significantly suppressed transverse aortic constriction-induced increases in an array of genes involved in myocardial stress, fibrosis, and inflammation.

CONCLUSIONS

The PZ-128 pepducin is highly effective in protecting against cardiac inflammation, fibrosis, and loss of left ventricle function in a mouse model.

New drug discovery of cardiac anti-arrhythmic drugs: insights in animal models

Cardiac rhythm regulated by micro-macroscopic structures of heart. Pacemaker abnormalities or disruptions in electrical conduction, lead to arrhythmic disorders may be benign, typical, threatening, ultimately fatal, occurs in clinical practice, patients on digitalis, anaesthesia or acute myocardial infarction. Both traditional and genetic animal models are: In-vitro: Isolated ventricular Myocytes, Guinea pig papillary muscles, Patch-Clamp Experiments, Porcine Atrial Myocytes, Guinea pig ventricular myocytes, Guinea pig papillary muscle: action potential and refractory period, Langendorff technique, Arrhythmia by acetylcholine or potassium. Acquired arrhythmia disorders: Transverse Aortic Constriction, Myocardial Ischemia, Complete Heart Block and AV Node Ablation, Chronic Tachypacing, Inflammation, Metabolic and Drug-Induced Arrhythmia. In-Vivo: Chemically induced arrhythmia: Aconitine antagonism, Digoxin-induced arrhythmia, Strophanthin/ouabain-induced arrhythmia, Adrenaline-induced arrhythmia, and Calcium-induced arrhythmia. Electrically induced arrhythmia: Ventricular fibrillation electrical threshold, Arrhythmia through programmed electrical stimulation, sudden coronary death in dogs, Exercise ventricular fibrillation. Genetic Arrhythmia: Channelopathies, Calcium Release Deficiency Syndrome, Long QT Syndrome, Short QT Syndrome, Brugada Syndrome. Genetic with Structural Heart Disease: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia, Dilated Cardiomyopathy, Hypertrophic Cardiomyopathy, Atrial Fibrillation, Sick Sinus Syndrome, Atrioventricular Block, Preexcitation Syndrome. Arrhythmia in Pluripotent Stem Cell Cardiomyocytes. Conclusion: Both traditional and genetic, experimental models of cardiac arrhythmias' characteristics and significance help in development of new antiarrhythmic drugs.

Pressure overload-induced systolic heart failure is associated with characteristic myocardial microRNA expression signature and post-transcriptional gene regulation in male rats

Although systolic function characteristically shows gradual impairment in pressure overload (PO)-evoked left ventricular (LV) hypertrophy (LVH), rapid progression to congestive heart failure (HF) occurs in distinct cases. The molecular mechanisms for the differences in maladaptation are unknown. Here, we examined microRNA (miRNA) expression and miRNA-driven posttranscriptional gene regulation in the two forms of PO-induced LVH (with/without systolic HF). PO was induced by aortic banding (AB) in male Sprague-Dawley rats. Sham-operated animals were controls. The majority of AB animals demonstrated concentric LVH and slightly decreased systolic function (termed as ABLVH). In contrast, in some AB rats severely reduced ejection fraction, LV dilatation and increased lung weight-to-tibial length ratio was noted (referred to as ABHF). Global LV miRNA sequencing revealed fifty differentially regulated miRNAs in ABHF compared to ABLVH. Network theoretical miRNA-target analysis predicted more than three thousand genes with miRNA-driven dysregulation between the two groups. Seventeen genes with high node strength value were selected for target validation, of which five (Fmr1, Zfpm2, Wasl, Ets1, Atg16l1) showed decreased mRNA expression in ABHF by PCR. PO-evoked systolic HF is associated with unique miRNA alterations, which negatively regulate the mRNA expression of Fmr1, Zfmp2, Wasl, Ets1 and Atg16l1.

The type of suture material affects transverse aortic constriction-induced heart failure development in mice: a repeated measures correlation analysis

Introduction

Transverse-aortic constriction (TAC) operation is a widely used animal model to induce hypertrophy and heart failure through left-ventricular pressure overload. In mice, the cardiac response to TAC exhibits considerable variability influenced by factors such as strain, sub-strain, age, sex and vendor.

Methods

To investigate the impact of suture material (silk versus prolene) and size (6-0 versus 7-0) on the TAC-induced phenotype, we performed surgeries on male C57BL6/N mice at 9 weeks of age defining the aortic constriction by a 27G needle, thereby employing most frequently used methodological settings. The mice were randomly assigned into four separate groups, 6-0 silk, 7-0 silk, 6-0 prolene and 7-0 prolene (10 mice per group). Echocardiography was conducted before TAC and every 4 weeks thereafter to monitor the development of heart failure. Repeated measures correlation analysis was employed to compare disease progression among the different groups.

Results

Our findings reveal a significant influence of the chosen suture material on TAC outcomes. Mice operated with prolene showed increased mortality, slower body weight gain, faster left-ventricular mass increase, and a faster decline in left-ventricular ejection fraction, fractional shortening and aortic pressure gradient compared to silk-operated mice. Moreover, despite non significant, using thinner suture threads (7-0) tended to result in a more severe phenotype compared to thicker threads (6-0) across all tested parameters.

Discussion

Collectively, our results highlight the importance of suture material selection in determining the cardiac phenotype induced by TAC and emphasize the need to consider this factor when comparing data across different research laboratories.

The immunology of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) now accounts for the majority of new heart failure diagnoses and continues to increase in prevalence in the United States. Importantly, HFpEF is a highly morbid, heterogeneous syndrome lacking effective therapies. Inflammation has emerged as a potential contributor to the pathogenesis of HFpEF. Many of the risk factors for HFpEF are also associated with chronic inflammation, such as obesity, hypertension, aging, and renal dysfunction. A large amount of preclinical evidence suggests that immune cells and their associated cytokines play important roles in mediating fibrosis, oxidative stress, metabolic derangements, and endothelial dysfunction, all potentially important processes in HFpEF. How inflammation contributes to HFpEF pathogenesis, however, remains poorly understood. Recently, a variety of preclinical models have emerged which may yield much needed insights into the causal relationships between risk factors and the development of HFpEF, including the role of specific immune cell subsets or inflammatory pathways. Here, we review evidence in animal models and humans implicating inflammation as a mediator of HFpEF and identify gaps in knowledge requiring further study. As the understanding between inflammation and HFpEF evolves, it is hoped that a better understanding of the mechanisms underlying immune cell activation in HFpEF can open up new therapeutic avenues.

T-Cell MyD88 Is a Novel Regulator of Cardiac Fibrosis Through Modulation of T-Cell Activation

BACKGROUND

Cardiac inflammation in heart failure is characterized by the presence of damage-associated molecular patterns, myeloid cells, and T cells. Cardiac damage-associated molecular patterns provide continuous proinflammatory signals to myeloid cells through TLRs (toll-like receptors) that converge onto the adaptor protein MyD88 (myeloid differentiation response 88). These induce activation into efficient antigen-presenting cells that activate T cells through their TCR (T-cell receptor). T-cell activation results in cardiotropism, cardiac fibroblast transformation, and maladaptive cardiac remodeling. T cells rely on TCR signaling for effector function and survival, and while they express MyD88 and damage-associated molecular pattern receptors, their role in T-cell activation and cardiac inflammation is unknown.

METHODS

We performed transverse aortic constriction in mice lacking MyD88 in T cells and analyzed remodeling, systolic function, survival, and T-cell activation. We profiled wild type versus Myd88-/- mouse T cells at the transcript and protein level and performed several functional assays.

RESULTS

Analysis of single-cell RNA-sequencing data sets revealed that MyD88 is expressed in mouse and human cardiac T cells. MyD88 deletion in T cells resulted in increased levels of cardiac T-cell infiltration and fibrosis in response to transverse aortic constriction. We discovered that TCR-activated Myd88-/- T cells had increased proinflammatory signaling at the transcript and protein level compared with wild type, resulting in increased T-cell effector functions such as adhesion, migration across endothelial cells, and activation of cardiac fibroblast. Mechanistically, we found that MyD88 modulates T-cell activation and survival through TCR-dependent rather than TLR-dependent signaling.

CONCLUSIONS

Our results outline a novel intrinsic role for MyD88 in limiting T-cell activation that is central to tune down cardiac inflammation during cardiac adaptation to stress.

A novel αB-crystallin R123W variant drives hypertrophic cardiomyopathy by promoting maladaptive calcium-dependent signal transduction

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disorder affecting 1 in 500 people in the general population. Characterized by asymmetric left ventricular hypertrophy, cardiomyocyte disarray and cardiac fibrosis, HCM is a highly complex disease with heterogenous clinical presentation, onset and complication. While mutations in sarcomere genes can account for a substantial proportion of familial cases of HCM, 40%-50% of HCM patients do not carry such sarcomere variants and the causal mutations for their diseases remain elusive. Recently, we identified a novel variant of the alpha-crystallin B chain (CRYABR123W) in a pair of monozygotic twins who developed concordant HCM phenotypes that manifested over a nearly identical time course. Yet, how CRYABR123W promotes the HCM phenotype remains unclear. Here, we generated mice carrying the CryabR123W knock-in allele and demonstrated that hearts from these animals exhibit increased maximal elastance at young age but reduced diastolic function with aging. Upon transverse aortic constriction, mice carrying the CryabR123W allele developed pathogenic left ventricular hypertrophy with substantial cardiac fibrosis and progressively decreased ejection fraction. Crossing of mice with a Mybpc3 frame-shift model of HCM did not potentiate pathological hypertrophy in compound heterozygotes, indicating that the pathological mechanisms in the CryabR123W model are independent of the sarcomere. In contrast to another well-characterized CRYAB variant (R120G) which induced Desmin aggregation, no evidence of protein aggregation was observed in hearts expressing CRYABR123W despite its potent effect on driving cellular hypertrophy. Mechanistically, we uncovered an unexpected protein-protein interaction between CRYAB and calcineurin. Whereas CRYAB suppresses maladaptive calcium signaling in response to pressure-overload, the R123W mutation abolished this effect and instead drove pathologic NFAT activation. Thus, our data establish the CryabR123W allele as a novel genetic model of HCM and unveiled additional sarcomere-independent mechanisms of cardiac pathological hypertrophy.

Deficiency of miR-409-3p improves myocardial neovascularization and function through modulation of DNAJB9/p38 MAPK signaling

Angiogenesis is critical for tissue repair following myocardial infarction (MI), which is exacerbated under insulin resistance or diabetes. MicroRNAs are regulators of angiogenesis. We examined the metabolic regulation of miR-409-3p in post-infarct angiogenesis. miR-409-3p was increased in patients with acute coronary syndrome (ACS) and in a mouse model of acute MI. In endothelial cells (ECs), miR-409-3p was induced by palmitate, while vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) decreased its expression. Overexpression of miR-409-3p decreased EC proliferation and migration in the presence of palmitate, whereas inhibition had the opposite effects. RNA sequencing (RNA-seq) profiling in ECs identified DNAJ homolog subfamily B member 9 (DNAJB9) as a target of miR-409-3p. Overexpression of miR-409-3p decreased DNAJB9 mRNA and protein expression by 47% and 31% respectively, while enriching DNAJB9 mRNA by 1.9-fold after Argonaute2 microribonucleoprotein immunoprecipitation. These effects were mediated through p38 mitogen-activated protein kinase (MAPK). Ischemia-reperfusion (I/R) injury in EC-specific miR-409-3p knockout (KO) mice (miR-409ECKO) fed a high-fat, high-sucrose diet increased isolectin B4 (53.3%), CD31 (56%), and DNAJB9 (41.5%). The left ventricular ejection fraction (EF) was improved by 28%, and the infarct area was decreased by 33.8% in miR-409ECKO compared with control mice. These findings support an important role of miR-409-3p in the angiogenic EC response to myocardial ischemia.

Atrioventricular node dysfunction in pressure overload-induced heart failure—Involvement of the immune system and transcriptomic remodelling

Heart failure is associated with atrioventricular (AV) node dysfunction, and AV node dysfunction in the setting of heart failure is associated with an increased risk of mortality and heart failure hospitalisation. This study aims to understand the causes of AV node dysfunction in heart failure by studying changes in the whole nodal transcriptome. The mouse transverse aortic constriction model of pressure overload-induced heart failure was studied; functional changes were assessed using electrocardiography and echocardiography and the transcriptome of the AV node was quantified using RNAseq. Heart failure was associated with a significant increase in the PR interval, indicating a slowing of AV node conduction and AV node dysfunction, and significant changes in 3,077 transcripts (5.6% of the transcriptome). Many systems were affected: transcripts supporting AV node conduction were downregulated and there were changes in transcripts identified by GWAS as determinants of the PR interval. In addition, there was evidence of remodelling of the sarcomere, a shift from fatty acid to glucose metabolism, remodelling of the extracellular matrix, and remodelling of the transcription and translation machinery. There was evidence of the causes of this widespread remodelling of the AV node: evidence of dysregulation of multiple intracellular signalling pathways, dysregulation of 109 protein kinases and 148 transcription factors, and an immune response with a proliferation of neutrophils, monocytes, macrophages and B lymphocytes and a dysregulation of 40 cytokines. In conclusion, inflammation and a widespread transcriptional remodelling of the AV node underlies AV node dysfunction in heart failure.

Nicorandil Suppresses Ischemia-Induced Norepinephrine Release and Ventricular Arrhythmias in Hypertrophic Hearts

PURPOSE

Ventricular arrhythmias (VAs) are a common cause of sudden death in acute myocardial infarction (MI), for which hypertension is a major risk factor. Nicorandil opens ATP-sensitive potassium (KATP) channels, which are expressed by nerve terminals and cardiomyocytes and regulate the release of norepinephrine (NE). However, the effects of nicorandil on ischemic NE release in cardiac tissue remain unclear. Therefore, we herein investigated whether nicorandil suppressed interstitial NE concentrations and VAs during acute MI in pressure overload-induced hypertrophic hearts.

METHODS

Rats were divided into two groups: an abdominal aortic constriction (AAC) group and sham-operated (Sham) group. Four weeks after constriction, cardiac geometry and functions were examined using echocardiography and hemodynamic analyses. Myocardial ischemia was induced by coronary artery occlusion for 100 min with or without the administration of nicorandil. VAs were assessed by electrocardiography, and NE concentrations in the ischemic region were measured using a micro-dialysis method.

RESULTS

AAC induced left ventricular hypertrophy with diastolic dysfunction. VAs markedly increased in the early phase (0-20 min) of ischemia in both groups and were more frequent in the AAC group. Cardiac interstitial NE concentrations were higher in the AAC group before ischemia and significantly increased during ischemia in both groups. Nicorandil significantly suppressed ischemia-induced VAs and NE increases in the AAC group.

CONCLUSION

Ischemia-induced VAs were more frequent in hypertrophic hearts and associated with high interstitial concentrations of NE. The attenuation of ischemia-induced increases in NE through neuronal KATP opening by nicorandil may suppress ischemia-induced VAs in hypertrophic hearts.

A time-series minimally invasive transverse aortic constriction mouse model for pressure overload-induced cardiac remodeling and heart failure

Transverse aortic constriction (TAC) is a widely-used animal model for pressure overload-induced cardiac hypertrophy and heart failure (HF). The severity of TAC-induced adverse cardiac remodeling is correlated to the degree and duration of aorta constriction. Most studies of TAC are performed with a 27-gauge needle, which is easy to cause a tremendous left ventricular overload and leads to a rapid HF, but it is accompanied by higher mortality attributed to tighter aortic arch constriction. However, a few studies are focusing on the phenotypes of TAC applied with a 25-gauge needle, which produces a mild overload to induce cardiac remodeling and has low post-operation mortality. Furthermore, the specific timeline of HF induced by TAC applied with a 25-gauge needle in C57BL/6 J mice remains unclear. In this study, C57BL/6 J mice were randomly subjected to TAC with a 25-gauge needle or sham surgery. Echocardiography, gross morphology, and histopathology were applied to evaluate time-series phenotypes in the heart after 2, 4, 6, 8, and 12 weeks. The survival rate of mice after TAC was more than 98%. All mice subjected to TAC maintained compensated cardiac remodeling during the first two weeks and began to exhibit heart failure characteristics after 4 weeks upon TAC. At 8 weeks post-TAC, the mice showed severe cardiac dysfunction, hypertrophy, and cardiac fibrosis compared to sham mice. Moreover, the mice raised a severe dilated HF at 12 weeks. This study provides an optimized method of the mild overload TAC-induced cardiac remodeling from the compensatory period to decompensatory HF in C57BL/6 J mice.

Sirtuin 1 aggravates hypertrophic heart failure caused by pressure overload via shifting energy metabolism

Sirtuin1 (SIRT1) is involved in regulating substrate metabolism in the cardiovascular system. Metabolic homeostasis plays a critical role in hypertrophic heart failure. We hypothesize that cardiac SIRT1 can modulate substrate metabolism during pressure overload-induced heart failure. The inducible cardiomyocyte Sirt1 knockout (icSirt1-/-) and its wild type littermates (Sirt1f/f) C57BL/6J mice were subjected to transverse aortic constriction (TAC) surgery to induce pressure overload. The pressure overload induces upregulation of cardiac SIRT1 in Sirt1f/f but not icSirt1-/- mice. The cardiac contractile dysfunctions caused by TAC-induced pressure overload occurred in Sirt1f/f but not in icSirt1-/- mice. Intriguingly, Sirt1f/f heart showed a drastic reduction in systolic contractility and electric signals during post-TAC surgery, whereas icSirt1-/- heart demonstrated significant resistance to pathological stress by TAC-induced pressure overload as evidenced by no significant changes in systolic contractile functions and electric properties. The targeted proteomics showed that the pressure overload triggered downregulation of the SIRT1-associated IDH2 (isocitrate dehydrogenase 2) that resulted in increased oxidative stress in mitochondria. Moreover, metabolic alterations were observed in Sirt1f/f but not in icSirt1-/- heart in response to TAC-induced pressure overload. Thus, SIRT1 interferes with metabolic homeostasis through mitochondrial IDH2 during pressure overload. Inhibition of SIRT1 activity benefits cardiac functions under pressure overload-related pathological conditions.

Proteomic Insights into Cardiac Fibrosis: From Pathophysiological Mechanisms to Therapeutic Opportunities

Cardiac fibrosis is a common pathophysiologic process in nearly all forms of heart disease which refers to excessive deposition of extracellular matrix proteins by cardiac fibroblasts. Activated fibroblasts are the central cellular effectors in cardiac fibrosis, and fibrotic remodelling can cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance. Recently, there is a rising focus on the proteomic studies of cardiac fibrosis for pathogenesis elucidation and potential biomarker mining. This paper summarizes the current knowledge of molecular mechanisms underlying cardiac fibrosis, discusses the potential of imaging and circulating biomarkers available to recognize different phenotypes of this lesion, reviews the currently available and potential future therapies that allow individualized management in reversing progressive fibrosis, as well as the recent progress on proteomic studies of cardiac fibrosis. Proteomic approaches using clinical specimens and animal models can provide the ability to track pathological changes and new insights into the mechanisms underlining cardiac fibrosis. Furthermore, spatial and cell-type resolved quantitative proteomic analysis may also serve as a minimally invasive method for diagnosing cardiac fibrosis and allowing for the initiation of prophylactic treatment.

Functional Impact and Regulation of Alternative Splicing in Mouse Heart Development and Disease

Alternative splicing (AS) plays a major role in the generation of transcript diversity. In the heart, roles have been described for some AS variants, but the global impact and regulation of AS patterns are poorly understood. Here, we studied the AS profiles in heart disease, their relationship with heart development, and the regulatory mechanisms controlling AS dynamics in the mouse heart. We found that AS profiles characterized the different groups and that AS and gene expression changes affected independent genes and biological functions. Moreover, AS changes, specifically in heart disease, were associated with potential protein-protein interaction changes. While developmental transitions were mainly driven by the upregulation of MBNL1, AS changes in disease were driven by a complex regulatory network, where PTBP1 played a central role. Indeed, PTBP1 over-expression was sufficient to induce cardiac hypertrophy and diastolic dysfunction, potentially by perturbing AS patterns.

Humanized Dsp ACM Mouse Model Displays Stress-Induced Cardiac Electrical and Structural Phenotypes

Arrhythmogenic cardiomyopathy (ACM) is an inherited disorder characterized by fibro-fatty infiltration with an increased propensity for ventricular arrhythmias and sudden death. Genetic variants in desmosomal genes are associated with ACM. Incomplete penetrance is a common feature in ACM families, complicating the understanding of how external stressors contribute towards disease development. To analyze the dual role of genetics and external stressors on ACM progression, we developed one of the first mouse models of ACM that recapitulates a human variant by introducing the murine equivalent of the human R451G variant into endogenous desmoplakin (DspR451G/+). Mice homozygous for this variant displayed embryonic lethality. While DspR451G/+ mice were viable with reduced expression of DSP, no presentable arrhythmogenic or structural phenotypes were identified at baseline. However, increased afterload resulted in reduced cardiac performance, increased chamber dilation, and accelerated progression to heart failure. In addition, following catecholaminergic challenge, DspR451G/+ mice displayed frequent and prolonged arrhythmic events. Finally, aberrant localization of connexin-43 was noted in the DspR451G/+ mice at baseline, becoming more apparent following cardiac stress via pressure overload. In summary, cardiovascular stress is a key trigger for unmasking both electrical and structural phenotypes in one of the first humanized ACM mouse models.

Mixed lineage kinase 3 requires a functional CRIB domain for regulation of blood pressure, cardiac hypertrophy, and left ventricular function

Mixed lineage kinase 3 (MLK3) modulates blood pressure and left ventricular function, but the mechanisms governing these effects remain unclear. In the current study, we therefore investigated the role of the MLK3 Cdc42/Rac interactive binding (CRIB) domain in cardiovascular physiology. We examined baseline and left ventricular pressure overload responses in a MLK3 CRIB mutant (MLK3C/C) mouse, which harbors point mutations in the CRIB domain to disrupt MLK3 activation by Cdc42. Male and female MLK3C/C mice displayed increased invasively measured blood pressure compared with wild-type (MLK3+/+) littermate controls. MLK3C/C mice of both sexes also developed left and right ventricular hypertrophy but normal baseline LV function by echocardiography and invasive hemodynamics. In LV tissue from MLK3C/C mice, map3k11 mRNA, which encodes MLK3, and MLK3 protein were reduced by 74 ± 6% and 73 ± 7%, respectively. After 1-wk LV pressure overload with 25-gauge transaortic constriction (TAC), male MLK3C/C mice developed no differences in LV hypertrophy but displayed reduction in the LV systolic indices ejection fraction and dP/dt normalized to instantaneous pressure. JNK activation was also reduced in LV tissue of MLK3C/C TAC mice. TAC induced MLK3 translocation from cytosolic fraction to membrane fraction in LV tissue from MLK3+/+ but not MLK3C/C mice. These findings identify a role of the MLK3 CRIB domain in MLK3 regulation of basal blood pressure and cardiac morphology, and in promoting the compensatory LV response to pressure overload.NEW & NOTEWORTHY Here, we identified that the presence of two discrete point mutations within the Cdc42/Rac interaction and binding domain of the protein MLK3 recapitulates the effects of whole body MLK3 deletion on blood pressure, cardiac hypertrophy, and left ventricular compensation after pressure overload. These findings implicate the CRIB domain, and thus MLK3 activation by this domain, as critical for maintenance of cardiovascular homeostasis.

Antigen presentation by cardiac fibroblasts promotes cardiac dysfunction

Heart failure (HF) is a leading cause of morbidity and mortality. Studies in animal models and patients with HF revealed a prominent role for CD4+ T cell immune responses in the pathogenesis of HF and highlighted an active crosstalk between cardiac fibroblasts and IFNγ producing CD4+ T cells that results in profibrotic myofibroblast transformation. Whether cardiac fibroblasts concomitantly modulate pathogenic cardiac CD4+ T cell immune responses is unknown. Here we show report that murine cardiac fibroblasts express major histocompatibility complex type II (MHCII) in two different experimental models of cardiac inflammation. We demonstrate that cardiac fibroblasts take up and process antigens for presentation to CD4+ T cells via MHCII induced by IFNγ. Conditional deletion of MhcII in cardiac fibroblasts ameliorates cardiac remodelling and dysfunction induced by cardiac pressure overload. Collectively, we demonstrate that cardiac fibroblasts function as antigen presenting cells (APCs) and contribute to cardiac fibrosis and dysfunction through IFNγ induced MHCII.

Neurogranin regulates calcium-dependent cardiac hypertrophy

Intracellular Ca2+-calmodulin (CaM) signaling plays an important role in Ca2+-CaM-dependent kinase (CaMKII) and calcineurin (CaN)-mediated cardiac biology. While neurogranin (Ng) is known as a major Ca2+-CaM modulator in the brain, its pathophysiological role in cardiac hypertrophy has never been studied before. In the present study, we report that Ng is expressed in the heart and depletion of Ng dysregulates Ca2+ homeostasis and promotes cardiac failure in mice. 10-month-old Ng null mice demonstrate significantly increased heart-to-body weight ratios compared to wild-type. Using histological approaches, we identified that depletion of Ng increases cardiac hypertrophy, fibrosis, and collagen deposition near perivascular areas in the heart tissue of Ng null mice. Ca2+ spark experiments revealed that cardiac myocytes isolated from Ng null mice have decreased spark frequency and width, while the duration of sparks is significantly increased. We also identified that a lack of Ng increases CaMKIIδ signaling and periostin protein expression in these mouse hearts. Overall, we are the first study to explore how Ng expression in the heart plays an important role in Ca2+ homeostasis in cardiac myocytes as well as the pathophysiology of cardiac hypertrophy and fibrosis.

Quantifying the impact of gut microbiota on inflammation and hypertensive organ damage

AIMS

Hypertension (HTN) can lead to heart and kidney damage. The gut microbiota has been linked to HTN, although it is difficult to estimate its significance due to the variety of other features known to influence HTN. In the present study, we used germ-free (GF) and colonized (COL) littermate mice to quantify the impact of microbial colonization on organ damage in HTN.

METHODS AND RESULTS

Four-week-old male GF C57BL/6J littermates were randomized to remain GF or receive microbial colonization. HTN was induced by subcutaneous infusion with angiotensin (Ang) II (1.44 mg/kg/d) and 1% NaCl in the drinking water; sham-treated mice served as control. Renal damage was exacerbated in GF mice, whereas cardiac damage was more comparable between COL and GF, suggesting that the kidney is more sensitive to microbial influence. Multivariate analysis revealed a larger effect of HTN in GF mice. Serum metabolomics demonstrated that the colonization status influences circulating metabolites relevant to HTN. Importantly, GF mice were deficient in anti-inflammatory fecal short-chain fatty acids (SCFA). Flow cytometry showed that the microbiome has an impact on the induction of anti-hypertensive myeloid-derived suppressor cells and pro-inflammatory Th17 cells in HTN. In vitro inducibility of Th17 cells was significantly higher for cells isolated from GF than conventionally raised mice.

CONCLUSIONS

Microbial colonization status of mice had potent effects on their phenotypic response to a hypertensive stimulus, and the kidney is a highly microbiota-susceptible target organ in HTN. The magnitude of the pathogenic response in GF mice underscores the role of the microbiome in mediating inflammation in HTN.

TRANSLATION PERSPECTIVE

To assess the potential of microbiota-targeted interventions to prevent organ damage in hypertension, an accurate quantification of microbial influence is necessary. We provide evidence that the development of hypertensive organ damage is dependent on colonization status and suggest that a healthy microbiota provides anti-hypertensive immune and metabolic signals to the host. In the absence of normal symbiotic host-microbiome interactions, hypertensive damage to the kidney in particular is exacerbated. We suggest that hypertensive patients experiencing perturbations to the microbiota, which are common in CVD, may be at a greater risk for target-organ damage than those with a healthy microbiome.

Animal Models to Study Cardiac Arrhythmias

Cardiac arrhythmias are a significant cause of morbidity and mortality worldwide, accounting for 10% to 15% of all deaths. Although most arrhythmias are due to acquired heart disease, inherited channelopathies and cardiomyopathies disproportionately affect children and young adults. Arrhythmogenesis is complex, involving anatomic structure, ion channels and regulatory proteins, and the interplay between cells in the conduction system, cardiomyocytes, fibroblasts, and the immune system. Animal models of arrhythmia are powerful tools for studying not only molecular and cellular mechanism of arrhythmogenesis but also more complex mechanisms at the whole heart level, and for testing therapeutic interventions. This review summarizes basic and clinical arrhythmia mechanisms followed by an in-depth review of published animal models of genetic and acquired arrhythmia disorders.

Biomedical Imaging in Experimental Models of Cardiovascular Disease

Major advances in biomedical imaging have occurred over the last 2 decades and now allow many physiological, cellular, and molecular processes to be imaged noninvasively in small animal models of cardiovascular disease. Many of these techniques can be also used in humans, providing pathophysiological context and helping to define the clinical relevance of the model. Ultrasound remains the most widely used approach, and dedicated high-frequency systems can obtain extremely detailed images in mice. Likewise, dedicated small animal tomographic systems have been developed for magnetic resonance, positron emission tomography, fluorescence imaging, and computed tomography in mice. In this article, we review the use of ultrasound and positron emission tomography in small animal models, as well as emerging contrast mechanisms in magnetic resonance such as diffusion tensor imaging, hyperpolarized magnetic resonance, chemical exchange saturation transfer imaging, magnetic resonance elastography and strain, arterial spin labeling, and molecular imaging.

Large and Small Animal Models of Heart Failure With Reduced Ejection Fraction

Heart failure (HF) describes a heterogenous complex spectrum of pathological conditions that results in structural and functional remodeling leading to subsequent impairment of cardiac function, including either systolic dysfunction, diastolic dysfunction, or both. Several factors chronically lead to HF, including cardiac volume and pressure overload that may result from hypertension, valvular lesions, acute, or chronic ischemic injuries. Major forms of HF include hypertrophic, dilated, and restrictive cardiomyopathy. The severity of cardiomyopathy can be impacted by other comorbidities such as diabetes or obesity and external stress factors. Age is another major contributor, and the number of patients with HF is rising worldwide in part due to an increase in the aged population. HF can occur with reduced ejection fraction (HF with reduced ejection fraction), that is, the overall cardiac function is compromised, and typically the left ventricular ejection fraction is lower than 40%. In some cases of HF, the ejection fraction is preserved (HF with preserved ejection fraction). Animal models play a critical role in facilitating the understanding of molecular mechanisms of how hearts fail. This review aims to summarize and describe the strengths, limitations, and outcomes of both small and large animal models of HF with reduced ejection fraction that are currently used in basic and translational research. The driving defect is a failure of the heart to adequately supply the tissues with blood due to impaired filling or pumping. An accurate model of HF with reduced ejection fraction would encompass the symptoms (fatigue, dyspnea, exercise intolerance, and edema) along with the pathology (collagen fibrosis, ventricular hypertrophy) and ultimately exhibit a decrease in cardiac output. Although countless experimental studies have been published, no model completely recapitulates the full human disease. Therefore, it is critical to evaluate the strength and weakness of each animal model to allow better selection of what animal models to use to address the scientific question proposed.

Mapping the cardiac vascular niche in heart failure

The cardiac vascular and perivascular niche are of major importance in homeostasis and during disease, but we lack a complete understanding of its cellular heterogeneity and alteration in response to injury as a major driver of heart failure. Using combined genetic fate tracing with confocal imaging and single-cell RNA sequencing of this niche in homeostasis and during heart failure, we unravel cell type specific transcriptomic changes in fibroblast, endothelial, pericyte and vascular smooth muscle cell subtypes. We characterize a specific fibroblast subpopulation that exists during homeostasis, acquires Thbs4 expression and expands after injury driving cardiac fibrosis, and identify the transcription factor TEAD1 as a regulator of fibroblast activation. Endothelial cells display a proliferative response after injury, which is not sustained in later remodeling, together with transcriptional changes related to hypoxia, angiogenesis, and migration. Collectively, our data provides an extensive resource of transcriptomic changes in the vascular niche in hypertrophic cardiac remodeling.

Angiotensin Receptor-Neprilysin Inhibitor Attenuates Cardiac Hypertrophy and Improves Diastolic Dysfunction in A Mouse Model of Heart Failure with Preserved Ejection Fraction

LCZ696, an angiotensin receptor-neprilysin inhibitor, has shown promising clinical efficacy in patients with heart failure (HF) with reduced ejection fraction. However, its potential effects on heart failure with preserved ejection fraction (HFpEF) are still not fully understood. We evaluated the effect of LCZ696 on HFpEF in transverse aortic constriction mice and compared it with the effect of the angiotensin receptor blocker valsartan. We found that LCZ696 improved cardiac diastolic function by reducing ventricular hypertrophy and fibrosis in mice with overload-induced diastolic dysfunction. In addition, there was superior inhibition of LCZ696 than stand-alone valsartan. As a potential underlying mechanism, we demonstrated that LCZ696 behaves as a potent suppressor of calcium-mediated calcineurin-NFAT signaling transduction pathways. Hence, we demonstrated the protective effects of LCZ696 in overload-induced HFpEF and provided a pharmaceutical therapeutic strategy for related diseases.