Cardiovascular calcification is currently viewed as an active disease process similar to embryonic bone formation. Cardiovascular calcification mainly affects the aortic valve and arteries and is associated with increased mortality risk. Aortic valve and arterial calcification share similar risk factors, including age, gender, diabetes, chronic renal disease, and smoking. However, the exact cellular and molecular mechanism of cardiovascular calcification is unknown. Late-stage cardiovascular calcification can be visualized with conventional imaging modalities such as echocardiography and computed tomography. However, these modalities are limited in their ability to detect the development of early calcification and the progression of calcification until advanced tissue mineralization is apparent. Due to the subsequent late diagnosis of cardiovascular calcification, treatment is usually comprised of invasive interventions such as surgery. The need to understand the process of calcification is therefore warranted and requires new imaging modalities which are able to visualize early cardiovascular calcification. This review focuses on the use of new imaging techniques to visualize novel concepts of cardiovascular calcification.
Hypoxia has been found in the atherosclerotic plaques of larger mammals, including humans. Whether hypoxia occurs in the plaques of standard mouse models with atherosclerosis has been controversial, given their small size. In this review, we summarize the findings of a recent report demonstrating that direct evidence of hypoxia can indeed be found in the plaques of mice deficient in apolipoprotein E (apoE−/−mice). Furthermore, studies in vitro showed that hypoxia promoted lipid synthesis and reduced cholesterol efflux through the ABCA1 pathway, and that the transcription factor HIF-1α mediated many, but not all, of the effects. These results are discussed in the context of the literature and clinical practice.
Netrins were initially identified as secreted ligands regulating axon guidance and migration through interaction with canonical receptors.
Netrins were then shown necessary for development of a range of tissues, including lung, mammary gland and the vasculature.
While new netrin receptors, as well as alternative ligands for classical netrin receptors, were described in the neuronal and epithelial fields, there was a singular focus on canonical netrin receptors in the vascular system, leading to controversy on netrin function and the nature of receptor-mediated netrin signaling in the endothelium.
Herein, we summarize the current state of knowledge on netrin ligands and receptors and discuss questions, controversies and perspectives surrounding netrin functions and receptor identity in the vasculature.
netrin; netrin receptor; endothelium; integrin
Reversible cysteine oxidative post-translational modifications (Ox-PTMs) represent an important mechanism to regulate protein structure and function. In mitochondria, redox-reactions can modulate components of the electron transport chain (ETC), the F1FO-ATP synthase complex and other matrix proteins/enzymes. Emerging evidence has linked Ox-PTMs to mitochondrial dysfunction and heart failure, highlighting some potential therapeutic avenues. Ox-PTMs can modify a variety of amino acid residues, including cysteine, and have the potential to modulate the function of a large number of proteins. Among this group, there is a selected subset of amino acid residues that can function as redox-switches. These unique sites are proposed to monitor the cell's oxidative balance through their response to the various Ox-PTMs. In this review, the role of Ox-PTMs in the regulation of the F1FO-ATP synthase complex is discussed in the context of heart failure and its possible clinical treatment.
Nanotechnology holds tremendous potential to advance the current treatment of coronary artery disease. Nanotechnology may assist medical therapies by providing a safe and efficacious delivery platform for a variety of drugs aimed at modulating lipid disorders, decreasing inflammation and angiogenesis within atherosclerotic plaques, and preventing plaque thrombosis. Nanotechnology may improve coronary stent applications by promoting endothelial recovery on a stent surface utilizing bio-mimetic nanofibrous scaffolds, and also by preventing in-stent restenosis using nanoparticle-based delivery of drugs that are decoupled from stents. Additionally, nanotechnology may enhance tissue-engineered graft materials for application in coronary artery bypass grafting by facilitating cellular infiltration and remodeling of a graft matrix.
Nanotechnology; coronary artery disease; atherosclerosis; percutaneous coronary intervention; coronary artery bypass graft
Cardiac gap junctions are specialized membrane structures comprised of arrays of intercellular channels responsible for propagation of the cardiac impulse. These channels are formed by oligomerization of individual protein subunits known as connexins. In response to a broad array of pathologic stressors, gap junction expression is disturbed, resulting in aberrant cardiac conduction and increased propensity for rhythm disturbances. In this article we review some of the recently identified molecular regulators of connexin assembly, membrane targeting and degradation, focusing on the role of post-translational phosphorylation of connexin43, the major gap junctional protein expressed in ventricular myocardium. We also describe efforts to engineer “designer” gap junctions that are resistant to pathologic remodeling.
Despite advances in cardiopulmonary resuscitation (CPR) methods including therapeutic hypothermia (TH), long-term neurological outcomes and survival after sudden cardiac arrest (CA) remains to be dismal. While nitric oxide (NO) prevents organ injury induced by ischemia and reperfusion (I/R), systemic vasodilation induced by intravenous NO-donor compounds typically precludes its use in post-CA patients in whom blood pressure is often low and unstable. Although developed as a selective pulmonary vasodilator, inhaled NO has systemic benefits in a variety of pre-clinical and clinical studies without causing potentially harmful systemic vasodilation. Breathing NO after CPR may prevent post-CA brain injury and improve long-term outcomes after CA and CPR.
Angiogenesis is a crucial process whereby new blood vessels are formed from pre-existing vessels and occurs under both normal and pathophysiological conditions. The process is precisely regulated through the balance between pro-angiogenic and anti-angiogenic mechanisms, and many of these mechanisms have been well-characterized through extensive research; however, little is known about how angiogenesis is regulated at the transcriptional level. We have recently shown that deletion of the Forkhead box (Fox) transcription factor Foxc1 in cells of neural crest (NC) lineage leads to aberrant vessel growth in the normally avascular corneas of mice, and that the effect is cell-type specific, because the corneas of mice lacking Foxc1 expression in vascular endothelial cells remained avascular. The NC-specific Foxc1 deletion was also associated with elevated levels of both pro-angiogenic factors, such as the matrix metalloproteases (MMPs) MMP-3, MMP-9, and MMP-19, and the angiogenic inhibitor soluble vascular endothelial growth factor receptor 1 (sVEGFR-1). Thus, FoxC1 appears to control angiogenesis by regulating two distinct and opposing mechanisms; if so, vascular development could be determined, at least in part, by a competitive balance between pro-angiogenic and anti-angiogenic FoxC1-regulated pathways. In this review, we describe the mechanisms by which FoxC1 regulates vessel growth and discuss how these observations could contribute to a more complete understanding of the role of FoxC1 in pathological angiogenesis.
Alternative splicing is a post-transcriptional mechanism that can substantially change the pattern of gene expression. Up to 95% of human genes have multi-exon alternative spliced forms, suggesting that alternative splicing is one of the most significant components of the functional complexity of the human genome. Nevertheless, alternative splicing regulation has received comparatively little attention in the study of cardiac diseases. When investigating SCN5A splicing abnormalities in heart failure, we found 47 of 181 known splicing regulators were upregulated in HF when compared to controls, which indicate that splicing regulation may play a key role in heart failure. Our results shows that AngII and hypoxia, signals common to HF, result in increased LUC7L3 and RBM25 splicing regulators, increased binding of RBM25 to SCN5A mRNA, increased SCN5A splice variant abundances, decreased full-length SCN5A mRNA and protein, and decreased Na+ current. These observations could shed light on a mechanism whereby cardiac function and arrhythmic risk are associated and allow for refined predictions of which patients may be at highest arrhythmic risk or suffer from Na+ channel blocking anti-arrhythmic drug complications.
Despite the well-documented influence of genetics on susceptibility to cardiovascular diseases, delineation of the full spectrum of the risk alleles had to await the development of modern Next Generation Sequencing technologies. The techniques provide unbiased approaches for identification of the DNA sequence variants (DSVs) in the entire genome (Whole Genome Sequencing) or the protein-coding exons (Whole Exome Sequencing). Each genome contains approximately 4 million DSVs and each exome about 13,000 single nucleotide variants (SNVs). The challenge facing the researchers and clinicians alike is to decipher biological and clinical significance of these variants and harness the information for the practice of medicine. The common DSVs typically exert modest effect sizes, as evidenced by the results of Genome-Wide association Studies (GWAS), and hence, modest or negligible clinical implications. The focus is on the rare variants with large effect sizes, which are expected to have stronger clinical implications, as in single gene disorders with Mendelian patterns of inheritance. However, the clinical implications of the rare variants for common complex cardiovascular diseases remain to be established. In our view, the most important contribution of the WES or WGS is in delineation of the novel molecular pathways involved in the pathogenesis of the phenotype, which would be expected to provide for preventive and therapeutic opportunities.
Cardiac Syndrome X; Microvascular Coronary Dysfunction
The importance of endothelial dysfunction in the development and clinical expression of cardiovascular disease is well recognized. Impaired endothelial function has been associated with an increased risk of cardiovascular events. Endothelial function may be evaluated in humans by assessing vasodilation in response to stimuli known to induce the release of nitric oxide. A novel pulse amplitude tonometry device noninvasively measures vasodilator function in the microcirculation of the finger. This article reviews the recent studies that support the utility of digital pulse amplitude tonometry as a relevant test of peripheral endothelial function.
The transcriptional co-activators PGC-1α and PGC-1β are master regulators of oxidative phosphorylation and fatty acid oxidation gene expression. Pressure overload hypertrophy and heart failure are associated with repressed PGC-1α and PGC-1β gene expression. Maintaining expression of PGC-1α and β preserves contractile function in response to a pathological increase in workload. Here we discuss the regulation of PGC-1 proteins under conditions of pressure overload hypertrophy and heart failure.
In normal and diseased vascular smooth muscle (SM), the RhoA pathway, which is activated by multiple agonists through G protein-coupled receptors (GPCRs), plays a central role in regulating basal tone and peripheral resistance. Multiple RhoA GTP exchange factors (GEFs) are expressed in SM raising the possibility that specific agonists coupled to specific GPCRs may couple to distinct RhoGEFs and provide novel therapeutic targets. This review will focus on the function and mechanisms of activation of p63RhoGEF (Arhgef 25; GEFT) recently identified in SM and its possible role in selective targeting of RhoA-mediated regulation of basal blood pressure through agonists that couple through Gαq/11.
For more than a half century, autoimmunity has been linked to a diverse array of heart diseases including rheumatic carditis, myocarditis, Chagas’ cardiomyopathy, post-myocardial infarction (Dressler’s) syndrome, and idiopathic dilated cardiomyopathy. Why the heart is targeted by autoimmunity in these seemingly unrelated conditions has remained enigmatic. Here, we discuss our recent studies indicating that this susceptibility is mediated by impaired negative selection of autoreactive α-myosin heavy chain -specific CD4+ T cells in the thymus of both mice and humans. We describe how this process may place the heart at increased risk for autoimmune attack following ischemic or infectious injury, providing a rationale for the development of antigen-specific tolerogenic therapies.
Mast cells (MCs) are implicated in the pathogenesis of atherosclerosis and abdominal aortic aneurysm (AAA). MC-specific chymase and tryptase play important roles in inducing endothelial cell expression of adhesion molecules and chemokines to promote leukocyte recruitment, degrading matrix proteins and activating protease-activated receptors to trigger smooth-muscle cell apoptosis, and activating other proteases to degrade medial elastin and to enhance angiogenesis. In experimental AAA, absence or pharmacological inhibition of chymase or tryptase reduced AAA formation and associated arterial pathologies, proving that these MC proteases participate directly in AAA formation. Increased levels of these proteases in human AAA lesions and in plasma from AAA patients suggest that these proteases are also essential to human AAA pathogenesis. Development of chymase or tryptase inhibitors or their antibodies may have therapeutic potential among affected human subjects.
The association between low exercise capacity and all-cause morbidity and mortality is statistically strong yet mechanistically unresolved. By connecting clinical observation with a theoretical base, we developed a working hypothesis that variation in capacity for oxygen metabolism is the central mechanistic determinant between disease and health (aerobic hypothesis). As an unbiased test, we show that two-way artificial selective breeding of rats for low and high intrinsic endurance exercise capacity also produces rats that differ for numerous disease risks including the metabolic syndrome, cardiovascular complications, premature aging, and reduced longevity. This contrasting animal model system may prove to be translationally superior, relative to more widely-used simplistic models for understanding geriatric biology and medicine.
Over the past hundred years, the fruit fly, Drosophila melanogaster, has provided tremendous insights into genetics and human biology. Drosophila-based research utilizes powerful, genetically-tractable approaches to identify new genes and pathways that potentially contribute to human diseases. New resources available in the fly research community have advanced the ability to examine genome-wide effects on cardiac function and facilitate the identification of structural, contractile, and signaling molecules that contribute to cardiomyopathies. This powerful model system continues to provide discoveries of novel genes and signaling pathways that are conserved among species and translatable to human pathophysiology.
Rapamycin is an FDA approved drug for the prevention of immunorejection following organ transplantation. Pharmacological studies suggest a potential new application of rapamycin in attenuating cardiomyopathy, but the potential for this application is not yet supported by genetic studies of genes in target of rapamycin (TOR) signaling in rodents. Recently, supporting genetic evidence was presented in zebrafish using two adult cardiomyopathy models. By characterizing a heterozygous zebrafish target of rapamycin (ztor) mutant, the therapeutic effect of long-term TOR signaling inhibition was demonstrated. Dose- and stage-dependent functions of TOR signaling provide an explanation for the seemingly contradictory results obtained in genetic studies of TOR components in rodents. The results from the zebrafish studies, together with the supporting preliminary clinical studies, suggested that TOR signaling inhibition should be further pursued as a novel therapeutic strategy for cardiomyopathy. Future directions for developing TOR-based therapy include assessing the long-term benefits of rapamycin as a candidate drug for heart failure patients, defining the dynamic activity of TOR, exploring the impacts of TOR signaling manipulation in different models of cardiomyopathies, and elucidating the downstream signaling branches that confer the therapeutic effects of TOR signaling inhibition.
Pannexins are a recently discovered protein family, with the isoform Panx1 ubiquitously expressed and therefore extensively studied. Panx1 proteins form membrane channels known to release purines such as ATP. Because ATP and more generally purinergic signaling plays an important role in the vasculature, it became evident that Panx1 could have a key role in vascular functions. This article review deals with recent findings on the pivotal role of Panx1 in smooth muscle cells in the contraction of arteries as well as recent insights in Panx1 channel regulation.
Vascular calcification is an independent risk factor for cardiovascular disease. Arterial calcification of the aorta, coronary, carotid and peripheral arteries becomes more prevalent with age. Genomewide association studies have identified regions of the genome linked to vascular calcification, and these same regions are linked to myocardial infarction risk. The 9p21 region linked to vascular disease and inflammation also associates with vascular calcification. In addition to these common variants, rare genetic defects can serve as primary triggers of accelerated and premature calcification. Infancy-associated calcific disorders are caused by loss of function mutations in ENPP1 an enzyme that produces extracellular pyrophosphate. Adult onset vascular calcification is linked to mutations NTE5, another enzyme that regulates extracellular phosphate metabolism. Common conditions that secondarily enhance vascular calcification include atherosclerosis, metabolic dysfunction, diabetes, and impaired renal clearance. Oxidative stress and vascular inflammation, along with biophysical properties, converge with these predisposing factors to promote soft tissue mineralization. Vascular calcification is accompanied by an osteogenic profile, and this osteogenic conversion is seen within the vascular smooth muscle itself as well as the matrix. Herein we will review the genetic causes of medial calcification in the smooth muscle layer, focusing on recent discoveries of gene mutations that regulate extracellular matrix phosphate production and the role of S100 proteins as promoters of vascular calcification.
vascular smooth muscle; calcification; S100/calgranulin
Stem cell therapies promise to regenerate the infarcted heart through the replacement of dead cardiac cells and stimulation of neovascularization. New research from our laboratory shows the transplantation of stem cells from human veins helps heart healing after an acute ischemic insult. Using a mouse model, we demonstrated that pericytes expanded from redundant human leg veins relocate around the vessels of the peri-infarct zone and release factors that promote reparative angiogenesis and cardiomyocyte survival and inhibit interstitial fibrosis. We plan to perform a first-in-man clinical trial with human pericytes in patients with refractory myocardial ischemia in the next 5 years.
Over the past 2 decades, stem cells have created enthusiasm as a regenerative therapy for ischemic heart disease (IHD). Transplantation of bone marrow stem cells, skeletal myoblasts, and endothelial progenitor cells has shown to improve myocardial function after infarction. More recently, attention has focused on the potential use of embryonic stem cells (ESC) and induced pluripotent stem cells (iPS), as they possess the capacity to differentiate into various cell types, including cardiac and endothelial cells. Clinical trials have shown positive effects on the functional recovery of heart after myocardial infarction (MI) and have answered questions on timing, dosage, and cell delivery route of stem cells such as those derived from bone marrow. Despite the current advances in stem cell research, one main hurdle remains the lack of reliable information about the fate of cell engraftment, survival, and proliferation after transplantation. This review will discuss the different cell types used in cardiac cell therapy as well as molecular imaging modalities relevant to survival issues.
In mouse heart, four connexins (Cxs), Cx30.2, Cx40, Cx43, and Cx45, form gap junction (GJ) channels for electric and metabolic cell-to-cell signaling. Extent and pattern of Cx isoform expression together with cytoarchitecture and excitability of cells determine the velocity of excitation spread in different regions of the heart. In the SA node, cell– cell coupling is mediated by Cx30.2 and Cx45, which form lowconductance (approximately 9 and 32 pS, respectively) GJ channels. In contrast, the working cardiomyocytes of atria and ventricles express mainly Cx40 and Cx43, which form GJ channels of high conductance (approximately 180 and 115 pS, respectively) that facilitate the fast conduction necessary for efficient mechanical contraction. In the AV node, cell–cell coupling is mediated by abundantly expressed Cx30.2 and Cx45 and Cx40, which is expressed to a lesser extent. Cx30.2 and Cx45 may determine higher intercellular resistance and slower conduction in the SA- and AV-nodal regions than in the ventricular conduction system or the atrial and ventricular working myocardium. Cx30.2 and its putative human ortholog, Cx31.9, under physiologic conditions form unapposed hemichannels in nonjunctional plasma membrane; these hemichannels have a conductance of approximately 20 pS and are permeable to cationic dyes up to approximately 400 Da in molecular mass. Genetic ablation of Cxs confirmed that Cx40 and Cx43 are important in determining the high conduction velocities in atria and ventricles, whereas the deletion of the Cx30.2 complementary DNA led to accelerated conduction in the AV node and reduced the Wenckebach period. We suggest that these effects are caused by (1) a dominant-negative effect of Cx30.2 on junctional conductance via formation of low-conductance homotypic and heterotypic GJ channels, and (2) open Cx30.2 hemichannels in non-junctional membranes, which shorten the space constant and depolarize the excitable membrane.