Myofibrillar remodeling in cardiac hypertrophy, heart failure and cardiomyopathies

The role of p130Cas/BCAR1 adaptor protein in the pathogenesis of cardiovascular diseases: A literature review

Breast cancer anti-estrogen resistance-1 (p130Cas/BCAR1) is an adaptor protein of the cas(Cas) family. This protein regulates multiple complex pathways in different organs including bones, pancreas, and immune and cardiovascular systems. Although previous research well demonstrated the role of p130Cas/BCAR1 in different diseases especially cancers, a precise review study on the various effects of p130Cas/BCAR1 on cardiovascular diseases is missing. In this study, we reviewed mechanisms of action for p130Cas/BCAR1 impact, on cardiac embryonic development defects, hypertrophy and remodeling, pulmonary artery hypertension (PAH), and atherosclerosis. Also, we suggest feature direction for research and potential therapeutic implications. This study showed that p130Cas/BCAR1 can affect cardiovascular diseases in various mechanisms including actin stress fiber formation, attachment to focal adhesion kinase (FAK) and angiotensin II (Ang II), generation of reactive oxygen species (ROS), and growth factor signaling through amplifying receptor tyrosine kinase (RTKs).

Role of Vasoactive Hormone-Induced Signal Transduction in Cardiac Hypertrophy and Heart Failure

Heart failure is the common concluding pathway for a majority of cardiovascular diseases and is associated with cardiac dysfunction. Since heart failure is invariably preceded by adaptive or maladaptive cardiac hypertrophy, several biochemical mechanisms have been proposed to explain the development of cardiac hypertrophy and progression to heart failure. One of these includes the activation of different neuroendocrine systems for elevating the circulating levels of different vasoactive hormones such as catecholamines, angiotensin II, vasopressin, serotonin and endothelins. All these hormones are released in the circulation and stimulate different signal transduction systems by acting on their respective receptors on the cell membrane to promote protein synthesis in cardiomyocytes and induce cardiac hypertrophy. The elevated levels of these vasoactive hormones induce hemodynamic overload, increase ventricular wall tension, increase protein synthesis and the occurrence of cardiac remodeling. In addition, there occurs an increase in proinflammatory cytokines and collagen synthesis for the induction of myocardial fibrosis and the transition of adaptive to maladaptive hypertrophy. The prolonged exposure of the hypertrophied heart to these vasoactive hormones has been reported to result in the oxidation of catecholamines and serotonin via monoamine oxidase as well as the activation of NADPH oxidase via angiotensin II and endothelins to promote oxidative stress. The development of oxidative stress produces subcellular defects, Ca2+-handling abnormalities, mitochondrial Ca2+-overload and cardiac dysfunction by activating different proteases and depressing cardiac gene expression, in addition to destabilizing the extracellular matrix upon activating some metalloproteinases. These observations support the view that elevated levels of various vasoactive hormones, by producing hemodynamic overload and activating their respective receptor-mediated signal transduction mechanisms, induce cardiac hypertrophy. Furthermore, the occurrence of oxidative stress due to the prolonged exposure of the hypertrophied heart to these hormones plays a critical role in the progression of heart failure.

Molecular mechanisms underlying sarcopenia in heart failure

The loss of skeletal muscle, also known as sarcopenia, is an aging-associated muscle disorder that is disproportionately present in heart failure (HF) patients. HF patients with sarcopenia have poor outcomes compared to the overall HF patient population. The prevalence of sarcopenia in HF is only expected to grow as the global population ages, and novel treatment strategies are needed to improve outcomes in this cohort. Multiple mechanistic pathways have emerged that may explain the increased prevalence of sarcopenia in the HF population, and a better understanding of these pathways may lead to the development of therapies to prevent muscle loss. This review article aims to explore the molecular mechanisms linking sarcopenia and HF, and to discuss treatment strategies aimed at addressing such molecular signals.

Status of β1-Adrenoceptor Signal Transduction System in Cardiac Hypertrophy and Heart Failure

Although β 1-adrenoceptor ( β 1-AR) signal transduction, which maintains cardiac function, is downregulated in failing hearts, the mechanisms for such a defect in heart failure are not fully understood. Since cardiac hypertrophy is invariably associated with heart failure, it is possible that the loss of β 1-AR mechanisms in failing heart occurs due to hypertrophic process. In this regard, we have reviewed the information from a rat model of adaptive cardiac hypertrophy and maladaptive hypertrophy at 4 and 24 weeks after inducing pressure overload as well as adaptive cardiac hypertrophy and heart failure at 4 and 24 weeks after inducing volume overload, respectively. Varying degrees of alterations in β 1-AR density as well as isoproterenol-induced increases in cardiac function, intracellular Ca 2 + -concentration in cardiomyocytes and adenylyl cyclase activity in crude membranes have been reported under these hypertrophic conditions. Adaptive hypertrophy at 4 weeks of pressure or volume overload showed unaltered or augmented increases in the activities of different components of β 1-AR signaling. On the other hand, maladaptive hypertrophy due to pressure overload and heart failure due to volume overload at 24 weeks revealed depressions in the activities of β 1-AR signal transduction pathway. These observations provide evidence that β 1-AR signal system is either unaltered or upregulated in adaptive cardiac hypertrophy and downregulated in maladaptive cardiac hypertrophy or heart failure. Furthermore, the information presented in this article supports the concept that downregulation of β 1-AR mechanisms in heart failure or maladaptive cardiac hypertrophy is not due to hypertrophic process per se. It is suggested that a complex mechanism involving the autonomic imbalance may be of a critical importance in determining differential alterations in non-failing and failing hearts.

Adverse effects of copper, manganese and mercury, alone and in mixtures on the aorta and heart of Spraque-Dawley rats

Cardiovascular diseases (CVD) are a common global cause of death and are therefore a major health concern. Inhaled or ingested environmental heavy metals contribute to the development of CVD. The aim of this study was to address the limited information available on the effect of relevant dosages of metals in mixtures. Three metals with reported effects on the cardiovascular system (CVS) were identified, and these metals were copper (Cu), manganese (Mn) and mercury (Hg). In Sprague-Dawley rats, the adverse effects of copper (Cu), manganese (Mn) and mercury (Hg), alone and as part of mixtures, on the blood parameters, the aorta and heart were investigated. Forty-eight male Sprague-Dawley rats were randomly divided into eight groups (n = 6): control, Cu, Mn, Hg, Cu + Mn, Cu + Hg, Mn + Hg and Cu, Mn + Hg. The seven experimental groups received the metal mixtures at 100 times the World Health Organisation (WHO) safety limit for drinking water (2 mg/L for Cu, 0.4 mg/L for Mn and 0.06 mg/L for Hg) via oral gavage for 28 days. After 28 days, compared with the control, red blood cell levels were increased for Cu + Hg. All other measured blood parameters were unchanged. Morphological changes in the tunica media were connective tissue deposition and an abundance of collagen type I in the metal exposed aortic tissues. In the cardiac tissue of metal-exposed rats, changes in the cardiomyocyte and myofibrillar arrangement, with an increase in collagen type I and III was observed. Ultrastructurally, the aortic collagen and elastin band arrangement and the cardiac mitochondrial and myofibrillar arrangement and structures were altered in the experimental groups. These changes indicated that exposure to these metals in rats caused minor changes in the blood parameters, however, the changes in tissue and cellular structure indicated an increased risk for the development of CVD.

Using the Proteomics Toolbox to Resolve Topology and Dynamics of Compartmentalized cAMP Signaling

cAMP is a second messenger that regulates a myriad of cellular functions in response to multiple extracellular stimuli. New developments in the field have provided exciting insights into how cAMP utilizes compartmentalization to ensure specificity when the message conveyed to the cell by an extracellular stimulus is translated into the appropriate functional outcome. cAMP compartmentalization relies on the formation of local signaling domains where the subset of cAMP signaling effectors, regulators and targets involved in a specific cellular response cluster together. These domains are dynamic in nature and underpin the exacting spatiotemporal regulation of cAMP signaling. In this review, we focus on how the proteomics toolbox can be utilized to identify the molecular components of these domains and to define the dynamic cellular cAMP signaling landscape. From a therapeutic perspective, compiling data on compartmentalized cAMP signaling in physiological and pathological conditions will help define the signaling events underlying disease and may reveal domain-specific targets for the development of precision medicine interventions.

Targeting mitochondrial impairment for the treatment of cardiovascular diseases: From hypertension to ischemia-reperfusion injury, searching for new pharmacological targets

Mitochondria and mitochondrial proteins represent a group of promising pharmacological target candidates in the search of new molecular targets and drugs to counteract the onset of hypertension and more in general cardiovascular diseases (CVDs). Indeed, several mitochondrial pathways result impaired in CVDs, showing ATP depletion and ROS production as common traits of cardiac tissue degeneration. Thus, targeting mitochondrial dysfunction in cardiomyocytes can represent a successful strategy to prevent heart failure. In this context, the identification of new pharmacological targets among mitochondrial proteins paves the way for the design of new selective drugs. Thanks to the advances in omics approaches, to a greater availability of mitochondrial crystallized protein structures and to the development of new computational approaches for protein 3D-modelling and drug design, it is now possible to investigate in detail impaired mitochondrial pathways in CVDs. Furthermore, it is possible to design new powerful drugs able to hit the selected pharmacological targets in a highly selective way to rescue mitochondrial dysfunction and prevent cardiac tissue degeneration. The role of mitochondrial dysfunction in the onset of CVDs appears increasingly evident, as reflected by the impairment of proteins involved in lipid peroxidation, mitochondrial dynamics, respiratory chain complexes, and membrane polarization maintenance in CVD patients. Conversely, little is known about proteins responsible for the cross-talk between mitochondria and cytoplasm in cardiomyocytes. Mitochondrial transporters of the SLC25A family, in particular, are responsible for the translocation of nucleotides (e.g., ATP), amino acids (e.g., aspartate, glutamate, ornithine), organic acids (e.g. malate and 2-oxoglutarate), and other cofactors (e.g., inorganic phosphate, NAD⁺, FAD, carnitine, CoA derivatives) between the mitochondrial and cytosolic compartments. Thus, mitochondrial transporters play a key role in the mitochondria-cytosol cross-talk by leading metabolic pathways such as the malate/aspartate shuttle, the carnitine shuttle, the ATP export from mitochondria, and the regulation of permeability transition pore opening. Since all these pathways are crucial for maintaining healthy cardiomyocytes, mitochondrial carriers emerge as an interesting class of new possible pharmacological targets for CVD treatments.

Monoamine oxidase A-dependent ROS formation modulates human cardiomyocyte differentiation through AKT and WNT activation

During embryonic development, cardiomyocytes undergo differentiation and maturation, processes that are tightly regulated by tissue-specific signaling cascades. Although redox signaling pathways involved in cardiomyogenesis are established, the exact sources responsible for reactive oxygen species (ROS) formation remain elusive. The present study investigates whether ROS produced by the mitochondrial flavoenzyme monoamine oxidase A (MAO-A) play a role in cardiomyocyte differentiation from human induced pluripotent stem cells (hiPSCs). Wild type (WT) and MAO-A knock out (KO) hiPSCs were generated by CRISPR/Cas9 genome editing and subjected to cardiomyocyte differentiation. Mitochondrial ROS levels were lower in MAO-A KO compared to the WT cells throughout the differentiation process. MAO-A KO hiPSC-derived cardiomyocytes (hiPSC-CMs) displayed sarcomere disarray, reduced α- to β-myosin heavy chain ratio, GATA4 upregulation and lower macroautophagy levels. Functionally, genetic ablation of MAO-A negatively affected intracellular Ca2+ homeostasis in hiPSC-CMs. Mechanistically, MAO-A generated ROS contributed to the activation of AKT signaling that was considerably attenuated in KO cells. In addition, MAO-A ablation caused a reduction in WNT pathway gene expression consistent with its reported stimulation by ROS. As a result of WNT downregulation, expression of MESP1 and NKX2.5 was significantly decreased in MAO-A KO cells. Finally, MAO-A re-expression during differentiation rescued expression levels of cardiac transcription factors, contractile structure, and intracellular Ca2+ homeostasis. Taken together, these results suggest that MAO-A mediated ROS generation is necessary for the activation of AKT and WNT signaling pathways during cardiac lineage commitment and for the differentiation of fully functional human cardiomyocytes.

Future scope and challenges for congestive heart failure: Moving towards development of pharmacotherapy

Heart failure is invariably associated with cardiac hypertrophy and impaired cardiac performance. Although several drugs have been developed to delay the progression of heart failure, none of the existing interventions have shown beneficial effects in reducing morbidity and mortality. In order to determine specific targets for future drug development, we have discussed different mechanisms involving both cardiomyocytes and non-myocyte (extracellular matrix) alterations for the transition of cardiac hypertrophy to heart failure as well as for the progression of heart failure. We have emphasized the role of oxidative stress, inflammatory cytokines, metabolic alterations and Ca2+-handling defects in adverse cardiac remodeling and heart dysfunction in hypertrophied myocardium. Alterations in the regulatory process due to several protein kinases as well as participation of mitochondrial Ca2+-overload, activation of proteases and phospholipases and changes in gene expression for subcellular remodeling have also been described for the occurrence of cardiac dysfunction. Association of cardiac arrhythmia with heart failure has been explained as a consequence of catecholamine oxidation products. Since these multifactorial defects in extracellular matrix and cardiomyocytes are evident in the failing heart, it is a challenge for experimental cardiologists to develop appropriate combination drug therapy for improving cardiac function in heart failure.

Myocardial Afterload Is a Key Biomechanical Regulator of Atrioventricular Myocyte Differentiation in Zebrafish

Heart valve development is governed by both genetic and biomechanical inputs. Prior work has demonstrated that oscillating shear stress associated with blood flow is required for normal atrioventricular (AV) valve development. Cardiac afterload is defined as the pressure the ventricle must overcome in order to pump blood throughout the circulatory system. In human patients, conditions of high afterload can cause valve pathology. Whether high afterload adversely affects embryonic valve development remains poorly understood. Here we describe a zebrafish model exhibiting increased myocardial afterload, caused by vasopressin, a vasoconstrictive drug. We show that the application of vasopressin reliably produces an increase in afterload without directly acting on cardiac tissue in zebrafish embryos. We have found that increased afterload alters the rate of growth of the cardiac chambers and causes remodeling of cardiomyocytes. Consistent with pathology seen in patients with clinically high afterload, we see defects in both the form and the function of the valve leaflets. Our results suggest that valve defects are due to changes in atrioventricular myocyte signaling, rather than pressure directly acting on the endothelial valve leaflet cells. Cardiac afterload should therefore be considered a biomechanical factor that particularly impacts embryonic valve development.

Mechanisms for the development of heart failure and improvement of cardiac function by angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, are well-known for the treatments of cardiovascular diseases, such as heart failure, hypertension and acute coronary syndrome. Several of these inhibitors including captopril, enalapril, ramipril, zofenopril and imidapril attenuate vasoconstriction, cardiac hypertrophy and adverse cardiac remodeling, improve clinical outcomes in patients with cardiac dysfunction and decrease mortality. Extensive experimental and clinical research over the past 35 years has revealed that the beneficial effects of ACE inhibitors in heart failure are associated with full or partial prevention of adverse cardiac remodeling. Since cardiac function is mainly determined by coordinated activities of different subcellular organelles, including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils, for regulating the intracellular concentration of Ca2+ and myocardial metabolism, there is ample evidence to suggest that adverse cardiac remodelling and cardiac dysfunction in the failing heart are the consequence of subcellular defects. In fact, the improvement of cardiac function by different ACE inhibitors has been demonstrated to be related to the attenuation of abnormalities in subcellular organelles for Ca2+-handling, metabolic alterations, signal transduction defects and gene expression changes in failing cardiomyocytes. Various ACE inhibitors have also been shown to delay the progression of heart failure by reducing the formation of angiotensin II, the development of oxidative stress, the level of inflammatory cytokines and the occurrence of subcellular defects. These observations support the view that ACE inhibitors improve cardiac function in the failing heart by multiple mechanisms including the reduction of oxidative stress, myocardial inflammation and Ca2+-handling abnormalities in cardiomyocytes.

Involvement of phospholipase C in the norepinephrine-induced hypertrophic response in Cardiomyocytes

Norepinephrine (NE) is known to mediate cardiomyocyte hypertrophy through the G protein coupled a1 -adrenoceptor (a1 -AR) and the activation of the phosphoinositide-specific phospholipase C (PLC). Since the by-products of PLC activity are important downstream signal transducers for cardiac hypertrophy, the role of and the regulatory mechanisms involved in the activation of PLC isozymes in cardiac hypertrophy are highlighted in this review. The discussion is focused to underscore PLC in different experimental models of cardiac hypertrophy, as well as in isolated adult and neonatal cardiomyocytes treated with NE. Particular emphasis is laid concerning the a1 -AR-PLC-mediated hypertrophic signalling pathway. From the information provided, it is evident that the specific activation of PLC isozymes is a primary signalling event in the a1 -AR mediated response to NE as well as initiation and progression of cardiac hypertrophy. Furthermore, the possibility of PLC involvement in the perpetuation of cardiac hypertrophy is also described. It is suggested that specific PLC isozymes may serve as viable targets for the prevention of cardiac hypertrophy in patient population at-risk for the development of heart failure.

Functional and structural phenotyping of cardiomyocytes in the 3D organization of embryoid bodies exposed to arsenic trioxide

Chronic exposure to environmental pollutants threatens human health. Arsenic, a world-wide diffused toxicant, is associated to cardiac pathology in the adult and to congenital heart defects in the foetus. Poorly known are its effects on perinatal cardiomyocytes. Here, bioinformatic image-analysis tools were coupled with cellular and molecular analyses to obtain functional and structural quantitative metrics of the impairment induced by 0.1, 0.5 or 1.0 µM arsenic trioxide exposure on the perinatal-like cardiomyocyte component of mouse embryoid bodies, within their 3D complex cell organization. With this approach, we quantified alterations to the (a) beating activity; (b) sarcomere organization (texture, edge, repetitiveness, height and width of the Z bands); (c) cardiomyocyte size and shape; (d) volume occupied by cardiomyocytes within the EBs. Sarcomere organization and cell morphology impairment are paralleled by differential expression of sarcomeric α-actin and Tropomyosin proteins and of acta2, myh6 and myh7 genes. Also, significant increase of Cx40, Cx43 and Cx45 connexin genes and of Cx43 protein expression profiles is paralleled by large Cx43 immunofluorescence signals. These results provide new insights into the role of arsenic in impairing cytoskeletal components of perinatal-like cardiomyocytes which, in turn, affect cell size, shape and beating capacity.

Expression of atrial‑fetal light chains in cultured human cardiomyocytes after chemical ischemia‑reperfusion injury

Atrial light chains (ALC1) are naturally present in adult heart atria, while ventricular light chains (VLC1) are predominant in ventricles. Degradation of VLC1 and re-expression of ALC1 in heart ventricles are associated with heart disorders in response to pressure overload. The aim of the current study was to investigate changes in myosin light chain expression after simulated ischemia and simulated reperfusion (sI/sR). Human cardiomyocytes (HCM) isolated from adult heart ventricles were subjected to chemical ischemia. The control group was maintained under aerobic conditions. Myocyte injury was determined by testing lactate dehydrogenase (LDH) activity. The gene expression of ALC1, VLC1 and MMP-2 were assessed by reverse transcription-quatitive PCR. Additionally, protein synthesis was measured using ELISA kits and MMP-2 activity was measured by zymography. The results revealed that LDH activity was increased in sI/sR cell-conditioned medium (P=0.02), confirming the ischemic damage of HCM. ALC1 gene expression and content in HCM were also increased in the sI/sR group (P=0.03 and P<0.001, respectively), while VLC1 gene expression after sI/sR was decreased (P=0.008). Furthermore, MMP-2 gene expression and synthesis were lower in the sI/sR group when compared with the aerobic control group (P<0.001 and P=0.03, respectively). MMP-2 activity was also increased in sI/sR cell-conditioned medium (P=0.006). In conclusion, sI/sR treatment led to increased ALC1 and decreased VLC1 expression in ventricular cardiomyocytes, which may constitute an adaptive mechanism to altered conditions and contribute to the improvement of heart function.

Role of angiotensin II in the development of subcellular remodeling in heart failure

The development of heart failure under various pathological conditions such as myocardial infarction (MI), hypertension and diabetes are accompanied by adverse cardiac remodeling and cardiac dysfunction. Since heart function is mainly determined by coordinated activities of different subcellular organelles including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils for regulating the intracellular concentration of Ca2+, it has been suggested that the occurrence of heart failure is a consequence of subcellular remodeling, metabolic alterations and Ca2+-handling abnormalities in cardiomyocytes. Because of the elevated plasma levels of angiotensin II (ANG II) due to activation of the renin-angiotensin system (RAS) in heart failure, we have evaluated the effectiveness of treatments with angiotensin converting enzyme (ACE) inhibitors and ANG II type 1 receptor (AT1R) antagonists in different experimental models of heart failure. Attenuation of marked alterations in subcellular activities, protein content and gene expression were associated with improvement in cardiac function in MI-induced heart failure by treatment with enalapril (an ACE inhibitor) or losartan (an AT1R antagonist). Similar beneficial effects of ANG II blockade on subcellular remodeling and cardiac performance were also observed in failing hearts due to pressure overload, volume overload or chronic diabetes. Treatments with enalapril and losartan were seen to reduce the degree of RAS activation as well as the level of oxidative stress in failing hearts. These observations provide evidence which further substantiate to support the view that activation of RAS and high level of plasma ANG II play a critical role in inducing subcellular defects and cardiac dys-function during the progression of heart failure.

Hypertrophic cardiomyopathy β-cardiac myosin mutation (P710R) leads to hypercontractility by disrupting super relaxed state

Hypertrophic cardiomyopathy (HCM) is the most common inherited form of heart disease, associated with over 1,000 mutations, many in β-cardiac myosin (MYH7). Molecular studies of myosin with different HCM mutations have revealed a diversity of effects on ATPase and load-sensitive rate of detachment from actin. It has been difficult to predict how such diverse molecular effects combine to influence forces at the cellular level and further influence cellular phenotypes. This study focused on the P710R mutation that dramatically decreased in vitro motility velocity and actin-activated ATPase, in contrast to other MYH7 mutations. Optical trap measurements of single myosin molecules revealed that this mutation reduced the step size of the myosin motor and the load sensitivity of the actin detachment rate. Conversely, this mutation destabilized the super relaxed state in longer, two-headed myosin constructs, freeing more heads to generate force. Micropatterned human induced pluripotent derived stem cell (hiPSC)-cardiomyocytes CRISPR-edited with the P710R mutation produced significantly increased force (measured by traction force microscopy) compared with isogenic control cells. The P710R mutation also caused cardiomyocyte hypertrophy and cytoskeletal remodeling as measured by immunostaining and electron microscopy. Cellular hypertrophy was prevented in the P710R cells by inhibition of ERK or Akt. Finally, we used a computational model that integrated the measured molecular changes to predict the measured traction forces. These results confirm a key role for regulation of the super relaxed state in driving hypercontractility in HCM with the P710R mutation and demonstrate the value of a multiscale approach in revealing key mechanisms of disease.

Hypertrophic cardiomyopathy β-cardiac myosin mutation (P710R) leads to hypercontractility by disrupting super relaxed state

Hypertrophic cardiomyopathy (HCM) is the most common inherited form of heart disease, associated with over 1,000 mutations, many in β-cardiac myosin (MYH7). Molecular studies of myosin with different HCM mutations have revealed a diversity of effects on ATPase and load-sensitive rate of detachment from actin. It has been difficult to predict how such diverse molecular effects combine to influence forces at the cellular level and further influence cellular phenotypes. This study focused on the P710R mutation that dramatically decreased in vitro motility velocity and actin-activated ATPase, in contrast to other MYH7 mutations. Optical trap measurements of single myosin molecules revealed that this mutation reduced the step size of the myosin motor and the load sensitivity of the actin detachment rate. Conversely, this mutation destabilized the super relaxed state in longer, two-headed myosin constructs, freeing more heads to generate force. Micropatterned human induced pluripotent derived stem cell (hiPSC)-cardiomyocytes CRISPR-edited with the P710R mutation produced significantly increased force (measured by traction force microscopy) compared with isogenic control cells. The P710R mutation also caused cardiomyocyte hypertrophy and cytoskeletal remodeling as measured by immunostaining and electron microscopy. Cellular hypertrophy was prevented in the P710R cells by inhibition of ERK or Akt. Finally, we used a computational model that integrated the measured molecular changes to predict the measured traction forces. These results confirm a key role for regulation of the super relaxed state in driving hypercontractility in HCM with the P710R mutation and demonstrate the value of a multiscale approach in revealing key mechanisms of disease.

Zebrafish as a New Tool in Heart Preservation Research

Heart transplantation became a reality at the end of the 1960s as a life-saving option for patients with end-stage heart failure. Static cold storage (SCS) at 4-6 °C has remained the standard for heart preservation for decades. However, SCS only allows for short-term storage that precludes optimal matching programs, requires emergency surgeries, and results in the unnecessary discard of organs. Among the alternatives seeking to extend ex vivo lifespan and mitigate the shortage of organs are sub-zero or machine perfusion modalities. Sub-zero approaches aim to prolong cold ischemia tolerance by deepening metabolic stasis, while machine perfusion aims to support metabolism through the continuous delivery of oxygen and nutrients. Each of these approaches hold promise; however, complex barriers must be overcome before their potential can be fully realized. We suggest that one barrier facing all experimental efforts to extend ex vivo lifespan are limited research tools. Mammalian models are usually the first choice due to translational aspects, yet experimentation can be restricted by expertise, time, and resources. Instead, there are instances when smaller vertebrate models, like the zebrafish, could fill critical experimental gaps in the field. Taken together, this review provides a summary of the current gold standard for heart preservation as well as new technologies in ex vivo lifespan extension. Furthermore, we describe how existing tools in zebrafish research, including isolated organ, cell specific and functional assays, as well as molecular tools, could complement and elevate heart preservation research.

Tissue Expression of Atrial and Ventricular Myosin Light Chains in the Mechanism of Adaptation to Oxidative Stress

Ischemia/reperfusion (I/R) injury induces post-translational modifications of myosin light chains (MLCs), increasing their susceptibility to degradation by matrix metalloproteinase 2 (MMP-2). This results in the degradation of ventricular light chains (VLC1) in heart ventricles. The aim of the study was to investigate changes in MLCs content in the mechanism of adaptation to oxidative stress during I/R. Rat hearts, perfused using the Langendorff method, were subjected to I/R. The control group was maintained in oxygen conditions. Lactate dehydrogenase (LDH) activity and reactive oxygen/nitrogen species (ROS/RNS) content were measured in coronary effluents. Atrial light chains (ALC1) and ventricular light chains (VLC1) gene expression were examined using RQ-PCR. ALC1 and VLC1 protein content were measured using ELISA tests. MMP-2 activity was assessed by zymography. LDH activity as well as ROS/RNS content in coronary effluents was higher in the I/R group (p = 0.01, p = 0.04, respectively), confirming heart injury due to increased oxidative stress. MMP-2 activity in heart homogenates was also higher in the I/R group (p = 0.04). ALC1 gene expression and protein synthesis were significantly increased in I/R ventricles (p < 0.01, 0.04, respectively). VLC1 content in coronary effluents was increased in the I/R group (p = 0.02), confirming the increased degradation of VLC1 by MMP-2 and probably an adaptive production of ALC1 during I/R. This mechanism of adaptation to oxidative stress led to improved heart mechanical function.

Chronic Occupational Exposure to Ionizing Radiation Induces Alterations in the Structure and Metabolism of the Heart: A Proteomic Analysis of Human Formalin-Fixed Paraffin-Embedded (FFPE) Cardiac Tissue

Epidemiological studies on workers employed at the Mayak plutonium enrichment plant have demonstrated an association between external gamma ray exposure and an elevated risk of ischemic heart disease (IHD). In a previous study using fresh-frozen post mortem samples of the cardiac left ventricle of Mayak workers and non-irradiated controls, we observed radiation-induced alterations in the heart proteome, mainly downregulation of mitochondrial and structural proteins. As the control group available at that time was younger than the irradiated group, we could not exclude age as a confounding factor. To address this issue, we have now expanded our study to investigate additional samples using archival formalin-fixed paraffin-embedded (FFPE) tissue. Importantly, the control group studied here is older than the occupationally exposed (>500 mGy) group. Label-free quantitative proteomics analysis showed that proteins involved in the lipid metabolism, sirtuin signaling, mitochondrial function, cytoskeletal organization, and antioxidant defense were the most affected. A histopathological analysis elucidated large foci of fibrotic tissue, myocardial lipomatosis and lymphocytic infiltrations in the irradiated samples. These data highlight the suitability of FFPE material for proteomics analysis. The study confirms the previous results emphasizing the role of adverse metabolic changes in the radiation-associated IHD. Most importantly, it excludes age at the time of death as a confounding factor.

Progressive Myofibril Reorganization of Human Cardiomyocytes on a Dynamic Nanotopographic Substrate

Cardiomyocyte (CM) alignment with striated myofibril organization is developed during early cardiac organogenesis. Previous work has successfully achieved in vitro CM alignment using a variety of biomaterial scaffolds and substrates with static topographic features. However, the cellular processes that occur during the response of CMs to dynamic surface topographic changes, which may provide a model of in vivo developmental progress of CM alignment within embryonic myocardium, remains poorly understood. To gain insights into these cellular processes involved in the response of CMs to dynamic topographic changes, we developed a dynamic topographic substrate that employs a shape memory polymer coated with polyelectrolyte multilayers to produce a flat-to-wrinkle surface transition when triggered by a change in incubation temperature. Using this system, we investigated cellular morphological alignment and intracellular myofibril reorganization in response to the dynamic wrinkle formation. Hence, we identified the progressive cellular processes of human-induced pluripotent stem cell-CMs in a time-dependent manner, which could provide a foundation for a mechanistic model of cardiac myofibril reorganization in response to extracellular microenvironment changes.

The Pathogenic Role of Very Low Density Lipoprotein on Atrial Remodeling in the Metabolic Syndrome

Atrial fibrillation (AF) is the most common persistent arrhythmia, and can lead to systemic thromboembolism and heart failure. Aging and metabolic syndrome (MetS) are major risks for AF. One of the most important manifestations of MetS is dyslipidemia, but its correlation with AF is ambiguous in clinical observational studies. Although there is a paradoxical relationship between fasting cholesterol and AF incidence, the benefit from lipid lowering therapy in reduction of AF is significant. Here, we reviewed the health burden from AF and MetS, the association between two disease entities, and the metabolism of triglyceride, which is elevated in MetS. We also reviewed scientific evidence for the mechanistic links between very low density lipoproteins (VLDL), which primarily carry circulatory triglyceride, to atrial cardiomyopathy and development of AF. The effects of VLDL to atria suggesting pathogenic to atrial cardiomyopathy and AF include excess lipid accumulation, direct cytotoxicity, abbreviated action potentials, disturbed calcium regulation, delayed conduction velocities, modulated gap junctions, and sarcomere protein derangements. The electrical remodeling and structural changes in concert promote development of atrial cardiomyopathy in MetS and ultimately lead to vulnerability to AF. As VLDL plays a major role in lipid metabolism after meals (rather than fasting state), further human studies that focus on the effects/correlation of postprandial lipids to atrial remodeling are required to determine whether VLDL-targeted therapy can reduce MetS-related AF. On the basis of our scientific evidence, we propose a pivotal role of VLDL in MetS-related atrial cardiomyopathy and vulnerability to AF.

Ethanol and its metabolites: update on toxicity, benefits, and focus on immunomodulatory effects

This article summarizes recent experimental and epidemiological data on the toxic and beneficial effects of ethanol and its metabolites (acetaldehyde), and focuses on their immunomodulatory effects. The section dealing with the toxic effects of alcohol focuses on its chronic toxicity (liver disorders, carcinogenic effects, cardiovascular disorders, neuropsychic disorders, addiction and withdrawal syndrome, hematologic disorders, reprotoxicity, osteoporosis) although acute toxicity is considered. The role of oxidative metabolism of ethanol by alcohol dehydrogenase, cytochrome P450 2E1, and aldehyde dehydrogenase, as well as the impact of genetic polymorphism in its physiopathology are also highlighted. The section dealing with the beneficial effects of low to moderate alcohol consumption (on cardiovascular system, diabetes, the nervous system and sensory organs, autoimmune diseases, and rheumatology) highlights the importance of anti-inflammatory and immunomodulatory effects in these observations. This knowledge, enriched by a focus on the immunomodulatory effects of ethanol and its metabolites, in particular on the NLRP3 inflammasome pathway, might facilitate the development of treatments that can reduce ethanol's harmful effects or accentuate its beneficial effects.

Very Low-Density Lipoproteins of Metabolic Syndrome Modulates STIM1, Suppresses Store-Operated Calcium Entry, and Deranges Myofilament Proteins in Atrial Myocytes

Individuals with metabolic syndrome (MetS) are at high risk for atrial myopathy and atrial fibrillation. Very low-density lipoproteins (VLDLs) of MetS (MetS-VLDLs) are cytotoxic to atrial myocytes in vivo and in vitro. The calcineurin-nuclear factor of activated T-cells (NFAT) pathway, which is regulated by stromal interaction molecule 1 (STIM1)/ calcium release-activated calcium channel protein 1 (Orai1)-mediated store-operated Ca²⁺ entry (SOCE), is a pivotal mediator of adaptive cardiac hypertrophy. We hypothesized that MetS-VLDLs could affect SOCE and the calcineurin-NFAT pathway. Normal-VLDL and MetS-VLDL samples were isolated from the peripheral blood of healthy volunteers and individuals with MetS. VLDLs were applied to HL-1 atrial myocytes for 18 h and were also injected into wild-type C57BL/6 male mouse tails three times per week for six weeks. After the sarcoplasmic reticulum (SR) Ca²⁺ store was depleted, SOCE was triggered upon reperfusion with 1.8 mM of Ca²⁺. SOCE was attenuated by MetS-VLDLs, along with reduced transcriptional and membranous expression of STIM1 (P = 0.025), and enhanced modification of O-GlcNAcylation on STIM1 protein, while Orai1 was unaltered. The nuclear translocation and activity of calcineurin were both reduced (P < 0.05), along with the alteration of myofilament proteins in atrial tissues. These changes were absent in normal-VLDL-treated cells. Our results demonstrated that MetS-VLDLs suppressed SOCE by modulating STIM1 at the transcriptional, translational, and post-translational levels, resulting in the inhibition of the calcineurin-NFAT pathway, which resulted in the alteration of myofilament protein expression and sarcomere derangement in atrial tissues. These findings may help explain atrial myopathy in MetS. We suggest a therapeutic target on VLDLs to prevent atrial fibrillation, especially for individuals with MetS.

Advanced Evolution of Pathogenesis Concepts in Cardiomyopathies

Cardiomyopathy is a group of heterogeneous cardiac diseases that impair systolic and diastolic function, and can induce chronic heart failure and sudden cardiac death. Cardiomyopathy is prevalent in the general population, with high morbidity and mortality rates, and contributes to nearly 20% of sudden cardiac deaths in younger individuals. Genetic mutations associated with cardiomyopathy play a key role in disease formation, especially the mutation of sarcomere encoding genes and ATP kinase genes, such as titin, lamin A/C, myosin heavy chain 7, and troponin T1. Pathogenesis of cardiomyopathy occurs by multiple complex steps involving several pathways, including the Ras-Raf-mitogen-activated protein kinase-extracellular signal-activated kinase pathway, G-protein signaling, mechanotransduction pathway, and protein kinase B/phosphoinositide 3-kinase signaling. Excess biomechanical stress induces apoptosis signaling in cardiomyocytes, leading to cell loss, which can induce myocardial fibrosis and remodeling. The clinical features and pathophysiology of cardiomyopathy are discussed. Although several basic and clinical studies have investigated the mechanism of cardiomyopathy, the detailed pathophysiology remains unclear. This review summarizes current concepts and focuses on the molecular mechanisms of cardiomyopathy, especially in the signaling from mutation to clinical phenotype, with the aim of informing the development of therapeutic interventions.

Autologous endothelial progenitor cell therapy improves right ventricular function in a model of chronic thromboembolic pulmonary hypertension

BACKGROUND

Right ventricular (RV) failure is the main prognostic factor in pulmonary hypertension, and ventricular capillary density (CD) has been reported to be a marker of RV maladaptive remodeling and failure. Our aim was to determine whether right intracoronary endothelial progenitor cell (EPC) infusion can improve RV function and CD in a piglet model of chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

We compared 3 groups: sham (n = 5), CTEPH (n = 6), and CTEPH with EPC infusion (CTEPH+EPC; n = 5). After EPC isolation from CTEPH+EPC piglet peripheral blood samples at 3 weeks, the CTEPH and sham groups underwent right intracoronary infusion of saline, and the CTEPH+EPC group received EPCs at 6 weeks. RV function, pulmonary hemodynamics, and myocardial morphometry were investigated in the animals at 10 weeks.

RESULTS

After EPC administration, the RV fractional area change increased from 32.75% (interquartile range [IQR], 29.5%-36.5%) to 39% (IQR, 37.25%-46.50%; P = .030). The CTEPH+EPC piglets had reduced cardiomyocyte surface areas (from 298.3 μm² [IQR, 277.4-335.3 μm²] to 234.6 μm² (IQR, 211.1-264.7 μm²; P = .017), and increased CD31 expression (from 3.12 [IQR, 1.27-5.09] to 7.14 [IQR, 5.56-8.41; P = .017). EPCs were found in the RV free wall at 4 and 24 hours after injection but not 4 weeks later.

CONCLUSIONS

Intracoronary infusion of EPC improved RV function and CD in a piglet model of CTEPH. This novel cell-based therapy might represent a promising RV-targeted treatment in patients with pulmonary hypertension.

Cardiomyocyte-specific disruption of Cathepsin K protects against doxorubicin-induced cardiotoxicity

The lysosomal cysteine protease Cathepsin K is elevated in humans and animal models of heart failure. Our recent studies show that whole-body deletion of Cathepsin K protects mice against cardiac dysfunction. Whether this is attributable to a direct effect on cardiomyocytes or is a consequence of the global metabolic alterations associated with Cathepsin K deletion is unknown. To determine the role of Cathepsin K in cardiomyocytes, we developed a cardiomyocyte-specific Cathepsin K-deficient mouse model and tested the hypothesis that ablation of Cathepsin K in cardiomyocytes would ameliorate the cardiotoxic side-effects of the anticancer drug doxorubicin. We used an α-myosin heavy chain promoter to drive expression of Cre, which resulted in over 80% reduction in protein and mRNA levels of cardiac Cathepsin K at baseline. Four-month-old control (Myh-Cre^-; Ctsk^fl/fl) and Cathepsin K knockout (Myh-Cre⁺; Ctsk^fl/fl) mice received intraperitoneal injections of doxorubicin or vehicle, 1 week following which, body and tissue weight, echocardiographic properties, cardiomyocyte contractile function and Ca²⁺-handling were evaluated. Control mice treated with doxorubicin exhibited a marked increase in cardiac Cathepsin K, which was associated with an impairment in cardiac structure and function, evidenced as an increase in end-systolic and end-diastolic diameters, decreased fractional shortening and wall thickness, disruption in cardiac sarcomere and microfilaments and impaired intracellular Ca²⁺ homeostasis. In contrast, the aforementioned cardiotoxic effects of doxorubicin were attenuated or reversed in mice lacking cardiac Cathepsin K. Mechanistically, Cathepsin K-deficiency reconciled the disturbance in cardiac energy homeostasis and attenuated NF-κB signaling and apoptosis to ameliorate doxorubicin-induced cardiotoxicity. Cathepsin K may represent a viable drug target to treat cardiac disease.

Alcohol-Mediated Organ Damages: Heart and Brain

Alcohol is one of the most commonly abused substances in the United States. Chronic consumption of ethanol has been responsible for numerous chronic diseases and conditions globally. The underlying mechanism of liver injury has been studied in depth, however, far fewer studies have examined other organs especially the heart and the central nervous system (CNS). The authors conducted a narrative review on the relationship of alcohol with heart disease and dementia. With that in mind, a complex relationship between inflammation and cardiovascular disease and dementia has been long proposed but inflammatory biomarkers have gained more attention lately. In this review we examine some of the consequences of the altered cytokine regulation that occurs in alcoholics in organs other than the liver. The article reviews the potential role of inflammatory markers such as TNF-α in predicting dementia and/or cardiovascular disease. It was found that TNF-α could promote and accelerate local inflammation and damage through autocrine/paracrine mechanisms. Unraveling the mechanisms linking chronic alcohol consumption with proinflammatory cytokine production and subsequent inflammatory signaling pathways activation in the heart and CNS, is essential to improve our understanding of the disease and hopefully facilitate the development of new remedies.

Localization of transcripts, translation, and degradation for spatiotemporal sarcomere maintenance

The mechanisms responsible for maintaining macromolecular protein complexes, with their proper localization and subunit stoichiometry, are incompletely understood. Here we studied the maintenance of the sarcomere, the basic contractile macromolecular complex of cardiomyocytes. We performed single-cell analysis of cardiomyocytes using imaging of mRNA and protein synthesis, and demonstrate that three distinct mechanisms are responsible for the maintenance of the sarcomere: mRNAs encoding for sarcomeric proteins are localized to the sarcomere, ribosomes are localized to the sarcomere with localized sarcomeric protein translation, and finally, a localized E3 ubiquitin ligase allow efficient degradation of excess unincorporated sarcomeric proteins. We show that these mechanisms are distinct, required, and work in unison, to ensure both spatial localization, and to overcome the large variability in transcription. Cardiomyocytes simultaneously maintain all their sarcomeres using localized translation and degradation processes where proteins are continuously and locally synthesized at high rates, and excess proteins are continuously degraded.

VCP746, a novel A1 adenosine receptor biased agonist, reduces hypertrophy in a rat neonatal cardiac myocyte model

VCP746 is a novel A1 adenosine receptor (A1 AR) biased agonist previously shown to be cytoprotective with no effect on heart rate. The aim of this study was to investigate the potential anti-hypertrophic effect of VCP746 in neonatal rat cardiac myocytes (NCM). NCM hypertrophy was stimulated with interleukin (IL)-1β (10 ng/mL), tumour necrosis factor (TNF)-α (10 ng/mL) or Ang II (100 nmol/L) and was assessed by (3) H-leucine incorporation assay. VCP746 significantly inhibited IL-1β-, TNF-α- and Ang II-stimulated NCM hypertrophy as determined by (3) H-leucine incorporation. The anti-hypertrophic effect of VCP746 was also more potent than that of the prototypical A1 AR agonist, N(6) -cyclopentyladenosine (CPA). Further investigation with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay showed that neither CPA nor VCP746 had any effect on cell viability, confirming that the reduction in (3) H-leucine incorporation mediated by CPA and VCP746 was not due to a reduction in cell viability. IL-1β, TNF-α and Ang II were also shown to increase the mRNA expression of hypertrophy biomarkers, ANP, β-MHC and α-SKA in NCM. Treatment with VCP746 at concentrations as low as 1 nmol/L suppressed mRNA expression of ANP, β-MHC and α-SKA stimulated by IL-1β, TNF-α or Ang II, demonstrating the broad mechanistic basis of the potent anti-hypertrophic effect of VCP746. This study has shown that the novel A1 AR agonist, VCP746, is able to attenuate cardiac myocyte hypertrophy. As such, VCP746 is potentially useful as a pharmacological agent in attenuating cardiac remodelling, especially in the post-myocardial infarction setting, given its previously established cytoprotective properties.

Novel large-particle FACS purification of adult ventricular myocytes reveals accumulation of myosin and actin disproportionate to cell size and proteome in normal post-weaning development

RATIONALE

Quantifying cellular proteins in ventricular myocytes (MCs) is challenging due to tissue heterogeneity and the variety of cell sizes in the heart. In post-weaning cardiac ontogeny, rod-shaped MCs make up the majority of the cardiac mass while remaining a minority of cardiac cells in number. Current biochemical analyses of cardiac proteins do not correlate well the content of MC-specific proteins to cell type or size in normally developing tissue.

OBJECTIVE

To develop a new large-particle fluorescent-activated cell sorting (LP-FACS) strategy for the purification of adult rod-shaped MCs. This approach is developed to enable growth-scaled measurements per-cell of the MC proteome and sarcomeric proteins (i.e. myosin heavy chain (MyHC) and alpha-actin (α-actin)) content.

METHODS AND RESULTS

Individual cardiac cells were isolated from 21 to 94days old mice. An LP-FACS jet-in-air system with a 200-μm nozzle was defined for the first time to purify adult MCs. Cell-type specific immunophenotyping and sorting yielded ≥95% purity of adult MCs independently of cell morphology and size. This approach excluded other cell types and tissue contaminants from further analysis. MC proteome, MyHC and α-actin proteins were measured in linear biochemical assays normalized to cell numbers. Using the allometric coefficient α, we scaled the MC-specific rate of protein accumulation to growth post-weaning. MC-specific volumes (α=1.02) and global protein accumulation (α=0.94) were proportional (i.e. isometric) to body mass. In contrast, MyHC and α-actin accumulated at a much greater rate (i.e. hyperallometric) than body mass (α=1.79 and 2.19 respectively) and MC volumes (α=1.76 and 1.45 respectively).

CONCLUSION

Changes in MC proteome and cell volumes measured in LP-FACS purified MCs are proportional to body mass post-weaning. Oppositely, MyHC and α-actin are concentrated more rapidly than what would be expected from MC proteome accumulation, cell enlargement, or animal growth alone. LP-FACS provides a new standard for adult MC purification and an approach to scale the biochemical content of specific proteins or group of proteins per cell in enlarging MCs.

Iron overload exacerbates age-associated cardiac hypertrophy in a mouse model of hemochromatosis

Cardiac damage associated with iron overload is the most common cause of morbidity and mortality in patients with hereditary hemochromatosis, but the precise mechanisms leading to disease progression are largely unexplored. Here we investigated the effects of iron overload and age on cardiac hypertrophy using 1-, 5- and 12-month old Hfe-deficient mice, an animal model of hemochromatosis in humans. Cardiac iron levels increased progressively with age, which was exacerbated in Hfe-deficient mice. The heart/body weight ratios were greater in Hfe-deficient mice at 5- and 12-month old, compared with their age-matched wild-type controls. Cardiac hypertrophy in 12-month old Hfe-deficient mice was consistent with decreased alpha myosin and increased beta myosin heavy chains, suggesting an alpha-to-beta conversion with age. This was accompanied by cardiac fibrosis and up-regulation of NFAT-c2, reflecting increased calcineurin/NFAT signaling in myocyte hypertrophy. Moreover, there was an age-dependent increase in the cardiac isoprostane levels in Hfe-deficient mice, indicating elevated oxidative stress. Also, rats fed high-iron diet demonstrated increased heart-to-body weight ratios, alpha myosin heavy chain and cardiac isoprostane levels, suggesting that iron overload promotes oxidative stress and cardiac hypertrophy. Our findings provide a molecular basis for the progression of age-dependent cardiac stress exacerbated by iron overload hemochromatosis.

Proteomics of acute heart failure in a rat post-myocardial infarction model

The aim of the present study was to identify the mechanisms underlying the development of post-myocardial infarction (post-MI) heart failure. The left anterior descending coronary artery of rats was occluded to mimic human ischemic heart disease. Linear Trap Quadropole OrbiTrap mass spectrometry was used to profile the expressions of energy metabolism‑associated and calcium‑binding proteins in the post‑MI and control groups. Using the online Protein Analysis Through Evolutionary Relationships classification system, 78 differentially expressed proteins were identified, including 50 downregulated proteins and 28 upregulated proteins in post‑MI group when compared with the control group. The differentially expressed proteins were closely associated with energy metabolism, contractile function, calcium handling, pathological hypertrophy and cardiac remodeling. These results were further validated using western blotting. At different postoperative time points (1st and 14th day following surgery) during the progression of advanced heart failure post‑MI, dynamic alterations in differential protein expression were identified. The expression of the vitamin D protein was significantly upregulated on the 1st day post‑MI however, was then downregulated with progression of the disease on the 14th day post‑MI. These results identified various target proteins associated with the disease, which may be used as diagnostic markers.

A mathematical model for active contraction in healthy and failing myocytes and left ventricles

Cardiovascular disease is one of the leading causes of death worldwide, in particular myocardial dysfunction, which may lead to heart failure eventually. Understanding the electro-mechanics of the heart will help in developing more effective clinical treatments. In this paper, we present a multi-scale electro-mechanics model of the left ventricle (LV). The Holzapfel-Ogden constitutive law was used to describe the passive myocardial response in tissue level, a modified Grandi-Pasqualini-Bers model was adopted to model calcium dynamics in individual myocytes, and the active tension was described using the Niederer-Hunter-Smith myofilament model. We first studied the electro-mechanics coupling in a single myocyte in the healthy and diseased left ventricle, and then the single cell model was embedded in a dynamic LV model to investigate the compensation mechanism of LV pump function due to myocardial dysfunction caused by abnormality in cellular calcium dynamics. The multi-scale LV model was solved using an in-house developed hybrid immersed boundary method with finite element extension. The predictions of the healthy LV model agreed well with the clinical measurements and other studies, and likewise, the results in the failing states were also consistent with clinical observations. In particular, we found that a low level of intracellular Ca2+ transient in myocytes can result in LV pump function failure even with increased myocardial contractility, decreased systolic blood pressure, and increased diastolic filling pressure, even though they will increase LV stroke volume. Our work suggested that treatments targeted at increased contractility and lowering the systolic blood pressure alone are not sufficient in preventing LV pump dysfunction, restoring a balanced physiological Ca2+ handling mechanism is necessary.

Keratin mediated attachment of stem cells to augment cardiomyogenic lineage commitment

The objective of this work was to develop a simple surface modification technique using keratin derived from human hair for efficient cardiomyogenic lineage commitment of human mesenchymal stem cells (hMSCs). Keratin was extracted from discarded human hair containing both the acidic and basic components along with the heterodimers. The extracted keratin was adsorbed to conventional tissue culture polystyrene surfaces at different concentration. Keratin solution of 500μg/ml yielded a well coated layer of 12±1nm thickness with minimal agglomeration. The keratin coated surfaces promoted cell attachment and proliferation. Large increases in the mRNA expression of known cardiomyocyte genes such as cardiac actinin, cardiac troponin and β-myosin heavy chain were observed. Immunostaining revealed increased expression of sarcomeric α-actinin and tropomyosin whereas Western blots confirmed higher expression of tropomyosin and myocyte enhancer factor 2C in cells on the keratin coated surface than on the non-coated surface. Keratin promoted DNA demethylation of the Atp2a2 and Nkx2.5 genes thereby elucidating the importance of epigenetic changes as a possible molecular mechanism underlying the increased differentiation. A global gene expression analysis revealed a significant alteration in the expression of genes involved in pathways associated in cardiomyogenic commitment including cytokine and chemokine signaling, cell-cell and cell-matrix interactions, Wnt signaling, MAPK signaling, TGF-β signaling and FGF signaling pathways among others. Thus, adsorption of keratin offers a facile and affordable yet potent route for inducing cardiomyogenic lineage commitment of stem cells with important implications in developing xeno-free strategies in cardiovascular regenerative medicine.

Postinfarct Left Ventricular Remodelling: A Prevailing Cause of Heart Failure

Heart failure is a chronic disease with high morbidity and mortality, which represents a growing challenge in medicine. A major risk factor for heart failure with reduced ejection fraction is a history of myocardial infarction. The expansion of a large infarct scar and subsequent regional ventricular dilatation can cause postinfarct remodelling, leading to significant enlargement of the left ventricular chamber. It has a negative prognostic value, because it precedes the clinical manifestations of heart failure. The characteristics of the infarcted myocardium predicting postinfarct remodelling can be studied with cardiac magnetic resonance and experimental imaging modalities such as diffusion tensor imaging can identify the changes in the architecture of myocardial fibers. This review discusses all the aspects related to postinfarct left ventricular remodelling: definition, pathogenesis, diagnosis, consequences, and available therapies, together with experimental interventions that show promising results against postinfarct remodelling and heart failure.

Alcohol and the Heart: A Proteomics Analysis of Pericardium and Myocardium in a Swine Model of Myocardial Ischemia

BACKGROUND

Previous studies have demonstrated that moderate alcohol consumption is cardioprotective and reduces postoperative pericardial adhesions; however, the mechanism is not fully understood. Using proteomic analysis, we sought to objectively investigate the effects of daily moderate alcohol consumption in the pericardium and myocardium in a swine model of chronic myocardial ischemia.

METHODS

Fourteen swine underwent placement of an ameroid constrictor to induce chronic myocardial ischemia. Animals were supplemented with 90 mL of ethanol daily (ETOH) or 80 g of sucrose of equal caloric value (SUC). After 7 weeks, the ischemic myocardium and pericardium were harvested for proteomics analysis.

RESULTS

Pericardial proteomics analysis yielded 397 proteins, of which 23 were unique to SUC and 52 were unique to ETOH. Of the 322 common proteins, 71 were statistically significant and 23 were characterized (p < 0.05). Alcohol supplementation increased structural proteins, and decreased immune protease inhibitors and coagulation proteins in the pericardium (p < 0.01). Myocardial proteomics analysis yielded 576 proteins, of which 32 were unique to SUC and 21 were unique to ETOH. Of the 523 common proteins, 85 were significant, and 32 were characterized (p < 0.05). Alcohol supplementation decreased cardiac remodeling proteins, cell death proteins and motor proteins, and increased metabolic proteins (p < 0.05).

CONCLUSIONS

The results suggest that daily moderate alcohol consumption affects numerous pathways that contribute to cardioprotection, including cardiac remodeling, metabolism, and cell death. Our findings reveal the biosignature of myocardial and pericardial protein expression in the setting of chronic myocardial ischemia and daily moderate alcohol consumption.

Matrix elasticity regulates the optimal cardiac myocyte shape for contractility

Concentric hypertrophy is characterized by ventricular wall thickening, fibrosis, and decreased myocyte length-to-width aspect ratio. Ventricular thickening is considered compensatory because it reduces wall stress, but the functional consequences of cell shape remodeling in this pathological setting are unknown. We hypothesized that decreases in myocyte aspect ratio allow myocytes to maximize contractility when the extracellular matrix becomes stiffer due to conditions such as fibrosis. To test this, we engineered neonatal rat ventricular myocytes into rectangles mimicking the 2-D profiles of healthy and hypertrophied myocytes on hydrogels with moderate (13 kPa) and high (90 kPa) elastic moduli. Actin alignment was unaffected by matrix elasticity, but sarcomere content was typically higher on stiff gels. Microtubule polymerization was higher on stiff gels, implying increased intracellular elastic modulus. On moderate gels, myocytes with moderate aspect ratios (∼7:1) generated the most peak systolic work compared with other cell shapes. However, on stiffer gels, low aspect ratios (∼2:1) generated the most peak systolic work. To compare the relative contributions of intracellular vs. extracellular elasticity to contractility, we developed an analytical model and used our experimental data to fit unknown parameters. Our model predicted that matrix elasticity dominates over intracellular elasticity, suggesting that the extracellular matrix may potentially be a more effective therapeutic target than microtubules. Our data and model suggest that myocytes with lower aspect ratios have a functional advantage when the elasticity of the extracellular matrix decreases due to conditions such as fibrosis, highlighting the role of the extracellular matrix in cardiac disease.

Reversal of subcellular remodelling by losartan in heart failure due to myocardial infarction

This study tested the reversal of subcellular remodelling in heart failure due to myocardial infarction (MI) upon treatment with losartan, an angiotensin II receptor antagonist. Twelve weeks after inducing MI, rats were treated with or without losartan (20 mg/kg; daily) for 8 weeks and assessed for cardiac function, cardiac remodelling, subcellular alterations and plasma catecholamines. Cardiac hypertrophy and lung congestion in 20 weeks MI-induced heart failure were associated with increases in plasma catecholamine levels. Haemodynamic examination revealed depressed cardiac function, whereas echocardiographic analysis showed impaired cardiac performance and marked increases in left ventricle wall thickness and chamber dilatation at 20 weeks of inducing MI. These changes in cardiac function, cardiac remodelling and plasma dopamine levels in heart failure were partially or fully reversed by losartan. Sarcoplasmic reticular (SR) Ca²⁺-pump activity and protein expression, protein and gene expression for phospholamban, as well as myofibrillar (MF) Ca²⁺-stimulated ATPase activity and α-myosin heavy chain mRNA levels were depressed, whereas β-myosin heavy chain expression was increased in failing hearts; these alterations were partially reversed by losartan. Although SR Ca²⁺-release activity and mRNA levels for SR Ca²⁺-pump were decreased in failing heart, these changes were not reversed upon losartan treatment; no changes in mRNA levels for SR Ca²⁺-release channels were observed in untreated or treated heart failure. These results suggest that the partial improvement of cardiac performance in heart failure due to MI by losartan treatment is associated with partial reversal of cardiac remodelling as well as partial recovery of SR and MF functions.

C57BL/6 neuromuscular healthspan scoring system

Developing a scoring system based on physiological and functional measurements is critical to test the efficacy of potential interventions for sarcopenia and frailty in aging animal models; therefore, the aim of this study was to develop a neuromuscular healthspan scoring system (NMHSS). We examined three ages of male C57BL/6 mice: adults (6-7 months old, 100% survival), old (24-26 months old, 75% survival), and elderly group (>28 months old, ≤50% survival)-as well as mice along this age continuum. Functional performance (as determined by the rotarod and inverted-cling grip test) and in vitro muscle contractility were the determinants. A raw score was derived for each determinant, and the NMHSS was then derived as the sum of the individual determinant scores. In comparison with individual determinants, the NMHSS reduced the effect of individual variability within age groups, thus potentially providing an enhanced ability to detect treatment effects in future studies.

Cardiac remodeling and subcellular defects in heart failure due to myocardial infarction and aging

Although several risk factors including hypertension, cardiac hypertrophy, coronary artery disease, and diabetes are known to result in heart failure, elderly subjects are more susceptible to myocardial infarction and more likely to develop heart failure. This article is intended to discuss that cardiac dysfunction in hearts failing due to myocardial infarction and aging is associated with cardiac remodeling and defects in the subcellular organelles such as sarcolemma (SL), sarcoplasmic reticulum (SR), and myofibrils. Despite some differences in the pattern of heart failure due to myocardial infarction and aging with respect to their etiology and sequence of events, evidence has been presented to show that subcellular remodeling plays a critical role in the occurrence of intracellular Ca(2+)-overload and development of cardiac dysfunction in both types of failing heart. In particular, alterations in gene expression for SL and SR proteins induce Ca(2+)-handling abnormalities in cardiomyocytes, whereas those for myofibrillar proteins impair the interaction of Ca(2+) with myofibrils in hearts failing due to myocardial infarction and aging. In addition, different phosphorylation mechanisms, which regulate the activities of Ca(2+)-cycling proteins in SL and SR membranes as well as Ca(2+)-binding proteins in myofibrils, become defective in the failing heart. Accordingly, it is suggested that subcellular remodeling involving defects in Ca(2+)-handling and Ca(2+)-binding proteins as well as their regulatory mechanisms is intimately associated with cardiac remodeling and heart failure due to myocardial infarction and aging.

Cathepsin-L ameliorates cardiac hypertrophy through activation of the autophagy-lysosomal dependent protein processing pathways

BACKGROUND

Autophagy is critical in the maintenance of cellular protein quality control, the final step of which involves the fusion of autophagosomes with lysosomes. Cathepsin-L (CTSL) is a key member of the lysosomal protease family that is expressed in the murine and human heart, and it may play an important role in protein turnover. We hypothesized that CTSL is important in regulating protein processing in the heart, particularly under pathological stress.

METHODS AND RESULTS

Phenylephrine-induced cardiac hypertrophy in vitro was more pronounced in CTSL-deficient neonatal cardiomyocytes than in in controls. This was accompanied by a significant accumulation of autophagosomes, increased levels of ubiquitin-conjugated protein, as well as impaired protein degradation and decreased cell viability. These effects were partially rescued with CTSL1 replacement via adeno-associated virus-mediated gene transfer. In the in vivo murine model of aortic banding (AB), a deficiency in CTSL markedly exacerbated cardiac hypertrophy, worsened cardiac function, and increased mortality. Ctsl(-/-) AB mice demonstrated significantly decreased lysosomal activity and increased sarcomere-associated protein aggregation. Homeostasis of the endoplasmic reticulum was also altered by CTSL deficiency, with increases in Bip and GRP94 proteins, accompanied by increased ubiquitin-proteasome system activity and higher levels of ubiquitinated proteins in response to AB. These changes ultimately led to a decrease in cellular ATP production, enhanced oxidative stress, and increased cellular apoptosis.

CONCLUSIONS

Lysosomal CTSL attenuates cardiac hypertrophy and preserves cardiac function through facilitation of autophagy and proteasomal protein processing.

Role of neuropeptide Y and peroxisome proliferator-activated receptor γ coactivator-1α in stress cardiomyopathy

Death following situations of intense emotional stress has been linked to the cardiac pathology described as stress cardiomyopathy, whose pathomechanism is still not clear. In this study, we sought to determine, via an animal model, whether the transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1alpha (PGC-1α) and the amino peptide neuropeptide Y (NPY) play a role in the pathogenesis of this cardiac entity. Male Sprague-Dawley rats in the experimental group were subjected to immobilization in a plexy glass box for 1 h, which was followed by low voltage electric foot shock for about 1 h at 10 s intervals in a cage fitted with metallic rods. After 25 days the rats were sacrificed and sections of their hearts were processed. Hematoxylin-eosin staining of cardiac tissues revealed the characteristic cardiac lesions of stress cardiomyopathy such as contraction band necrosis, inflammatory cell infiltration and fibrosis. The semi-quantitative RT-PCR analysis for PGC-1α mRNA expression showed significant overexpression of PGC1-α in the stress-subjected rats (P<0.05). Fluorescence immunohistochemistry revealed a higher production of NPY in the stress-subjected rats as compared to the control rats (P=0.0027). Thus, we are led to conclude that following periods of intense stress, an increased expression of PGC1-α in the heart and an overflow of NPY may lead to stress cardiomyopathy and even death in susceptible victims. Moreover, these markers can be used to identify stress cardiomyopathy as the cause of sudden death in specific cases.

βIIPKC and εPKC isozymes as potential pharmacological targets in cardiac hypertrophy and heart failure

Cardiac hypertrophy is a complex adaptive response to mechanical and neurohumoral stimuli and under continual stressor, it contributes to maladaptive responses, heart failure and death. Protein kinase C (PKC) and several other kinases play a role in the maladaptative cardiac responses, including cardiomyocyte hypertrophy, myocardial fibrosis and inflammation. Identifying specific therapies that regulate these kinases is a major focus of current research. PKC, a family of serine/threonine kinases, has emerged as potential mediators of hypertrophic stimuli associated with neurohumoral hyperactivity in heart failure. In this review, we describe the role of PKC isozymes that is involved in cardiac hypertrophy and heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

β-adrenergic blockade attenuates cardiac dysfunction and myofibrillar remodelling in congestive heart failure

Although β-adrenoceptor (β-AR) blockade is an important mode of therapy for congestive heart failure (CHF), subcellular mechanisms associated with its beneficial effects are not clear. Three weeks after inducing myocardial infarction (MI), rats were treated daily with or without 20 and 75 mg/kg atenolol, a selective β₁-AR antagonist, or propranolol, a non-selective β-AR antagonist, for 5 weeks. Sham operated rats served as controls. All animals were assessed haemodynamically and echocardiographically and the left ventricle (LV) was processed for the determination of myofibrillar ATPase activity, α- and β-myosin heavy chain (MHC) isoforms and gene expression as well as cardiac troponin I (cTnI) phosphorylation. Both atenolol and propranolol at 20 and 75 mg/kg doses attenuated cardiac hypertrophy and lung congestion in addition to increasing LV ejection fraction and LV systolic pressure as well as decreasing heart rate, LV end-diastolic pressure and LV diameters in the infarcted animals. Treatment of infarcted animals with these agents also attenuated the MI-induced depression in myofibrillar Ca²⁺-stimulated ATPase activity and phosphorylated cTnI protein content. The MI-induced decrease in α-MHC and increase in β-MHC protein content were attenuated by both atenolol and propranolol at low and high doses; however, only high dose of propranolol was effective in mitigating changes in the gene expression for α-MHC and β-MHC. Our results suggest that improvement of cardiac function by β-AR blockade in CHF may be associated with attenuation of myofibrillar remodelling.