Showing papers in "Circulation Research in 2011"

Mesenchymal Stem Cells Biology, Pathophysiology, Translational Findings, and Therapeutic Implications for Cardiac Disease

Abstract: Mesenchymal stem cells (MSCs) are a prototypical adult stem cell with capacity for self-renewal and differentiation with a broad tissue distribution. Initially described in bone marrow, MSCs have the capacity to differentiate into mesoderm- and nonmesoderm-derived tissues. The endogenous role for MSCs is maintenance of stem cell niches (classically the hematopoietic), and as such, MSCs participate in organ homeostasis, wound healing, and successful aging. From a therapeutic perspective, and facilitated by the ease of preparation and immunologic privilege, MSCs are emerging as an extremely promising therapeutic agent for tissue regeneration. Studies in animal models of myocardial infarction have demonstrated the ability of transplanted MSCs to engraft and differentiate into cardiomyocytes and vasculature cells, recruit endogenous cardiac stem cells, and secrete a wide array of paracrine factors. Together, these properties can be harnessed to both prevent and reverse remodeling in the ischemically injured ventricle. In proof-of-concept and phase I clinical trials, MSC therapy improved left ventricular function, induced reverse remodeling, and decreased scar size. This article reviews the current understanding of MSC biology, mechanism of action in cardiac repair, translational findings, and early clinical trial data of MSC therapy for cardiac disease.

Immunogenicity of Induced Pluripotent Stem Cells

Abstract: ### Immunogenicity of Induced Pluripotent Stem Cells Zhao et al Nature . 2011. doi:10.1038/nature10135 A new study shows the immunogenicity of induced pluripotent stem cells by the direct transplantation of undifferentiated cells into syngenic mice. The reprogramming of somatic cells into pluripotent stem cells has been reported after introducing a combination of several defined factors, such as OCT3/4, SOX2, KLF4, and c-MYC, into the cells.1 These artificially established cells are termed induced pluripotent stem cells (iPSCs). The iPSCs show unlimited growth while maintaining their potential for differentiation into various cell types of all 3 germ layers. Their pluripotency has been clearly shown by their contribution to chimeric animals and by the development of a full-term mouse during a tetraploid complementation experiment. These data also indicated that cells differentiated from iPSCs can at least partially replace the biological functions of various organs. Unlike embryonic stem cells (ESCs), iPSCs can be generated from a patient's own somatic cells. Therefore, the potential utility of iPSCs for regenerative medicine has been suggested. The development of iPSC-derived differentiated cells has been expected to provide personalized cells for cell-based therapy. However, the immunogenicity of these cells had not yet been strictly examined. Recently, Zhao et al. reported that the transplantation of immature iPSCs induced a T-cell–dependent immune response even in a syngenic mouse.2 When injected into immunodeficient mice, undifferentiated pluripotent cells grow locally, differentiate, and form teratomas that contain various cell types, including neurons, cartilage, keratinocytes, and intestinal epithelium. In this study, the authors investigated the immunoreactions …

Arterial Calcification in Chronic Kidney Disease: Key Roles for Calcium and Phosphate

Abstract: Vascular calcification contributes to the high risk of cardiovascular mortality in chronic kidney disease (CKD) patients. Dysregulation of calcium (Ca) and phosphate (P) metabolism is common in CKD patients and drives vascular calcification. In this article, we review the physiological regulatory mechanisms for Ca and P homeostasis and the basis for their dysregulation in CKD. In addition, we highlight recent findings indicating that elevated Ca and P have direct effects on vascular smooth muscle cells (VSMCs) that promote vascular calcification, including stimulation of osteogenic/chondrogenic differentiation, vesicle release, apoptosis, loss of inhibitors, and extracellular matrix degradation. These studies suggest a major role for elevated P in promoting osteogenic/chondrogenic differentiation of VSMC, whereas elevated Ca has a predominant role in promoting VSMC apoptosis and vesicle release. Furthermore, the effects of elevated Ca and P are synergistic, providing a major stimulus for vascular calcification in CKD. Unraveling the complex regulatory pathways that mediate the effects of both Ca and P on VSMCs will ultimately provide novel targets and therapies to limit the destructive effects of vascular calcification in CKD patients.

Microparticles in Hemostasis and Thrombosis

Abstract: Blood contains microparticles (MPs) derived from a variety of cell types, including platelets, monocytes, and endothelial cells. In addition, tumors release MPs into the circulation. MPs are formed from membrane blebs that are released from the cell surface by proteolytic cleavage of the cytoskeleton. All MPs are procoagulant because they provide a membrane surface for the assembly of components of the coagulation protease cascade. Importantly, procoagulant activity is increased by the presence of anionic phospholipids, particularly phosphatidylserine (PS), and the procoagulant protein tissue factor (TF), which is the major cellular activator of the clotting cascade. High levels of platelet-derived PS + MPs are present in healthy individuals, whereas the number of TF + , PS + MPs is undetectable or very low. However, levels of PS + , TF + MPs are readily detected in a variety of diseases, and monocytes appear to be the primary cellular source. In cancer, PS + , TF + MPs are derived from tumors and may serve as a useful biomarker to identify patients at risk for venous thrombosis. This review will summarize our current knowledge of the role of procoagulant MPs in hemostasis and thrombosis.

Growth of Engineered Human Myocardium With Mechanical Loading and Vascular Coculture

Abstract: Rationale: The developing heart requires both mechanical load and vascularization to reach its proper size, yet the regulation of human heart growth by these processes is poorly understood. Objective: We seek to elucidate the responses of immature human myocardium to mechanical load and vascularization using tissue engineering approaches. Methods and Results: Using human embryonic stem cell and human induced pluripotent stem cell–derived cardiomyocytes in a 3-dimensional collagen matrix, we show that uniaxial mechanical stress conditioning promotes 2-fold increases in cardiomyocyte and matrix fiber alignment and enhances myofibrillogenesis and sarcomeric banding. Furthermore, cyclic stress conditioning markedly increases cardiomyocyte hypertrophy (2.2-fold) and proliferation rates (21%) versus unconditioned constructs. Addition of endothelial cells enhances cardiomyocyte proliferation under all stress conditions (14% to 19%), and addition of stromal supporting cells enhances formation of vessel-like structures by ≈10-fold. Furthermore, these optimized human cardiac tissue constructs generate Starling curves, increasing their active force in response to increased resting length. When transplanted onto hearts of athymic rats, the human myocardium survives and forms grafts closely apposed to host myocardium. The grafts contain human microvessels that are perfused by the host coronary circulation. Conclusions: Our results indicate that both mechanical load and vascular cell coculture control cardiomyocyte proliferation, and that mechanical load further controls the hypertrophy and architecture of engineered human myocardium. Such constructs may be useful for studying human cardiac development as well as for regenerative therapy. # Novelty and Significance {#article-title-70}

Oxidation-Specific Epitopes Are Danger-Associated Molecular Patterns Recognized by Pattern Recognition Receptors of Innate Immunity

Abstract: Oxidation reactions are vital parts of metabolism and signal transduction. However, they also produce reactive oxygen species, which damage lipids, proteins and DNA, generating “oxidation-specific” epitopes. In this review, we discuss the hypothesis that such common oxidation-specific epitopes are a major target of innate immunity, recognized by a variety of “pattern recognition receptors” (PRRs). By analogy with microbial “pathogen-associated molecular patterns” (PAMPs), we postulate that host-derived, oxidation-specific epitopes can be considered to represent “danger (or damage)-associated molecular patterns” (DAMPs). We also argue that oxidation-specific epitopes present on apoptotic cells and their cellular debris provided the primary evolutionary pressure for the selection of such PRRs. Furthermore, because many PAMPs on microbes share molecular identity and/or mimicry with oxidation-specific epitopes, such PAMPs provide a strong secondary selecting pressure for the same set of oxidation-specific PRRs as well. Because lipid peroxidation is ubiquitous and a major component of the inflammatory state associated with atherosclerosis, the understanding that oxidation-specific epitopes are DAMPs, and thus the target of multiple arcs of innate immunity, provides novel insights into the pathogenesis of atherosclerosis. As examples, we show that both cellular and soluble PRRs, such as CD36, toll-like receptor-4, natural antibodies, and C-reactive protein recognize common oxidation-specific DAMPs, such as oxidized phospholipids and oxidized cholesteryl esters, and mediate a variety of immune responses, from expression of proinflammatory genes to excessive intracellular lipoprotein accumulation to atheroprotective humoral immunity. These insights may lead to improved understanding of inflammation and atherogenesis and suggest new approaches to diagnosis and therapy.

The Art of MicroRNA Research

Abstract: Originally identified as moderate biological modifiers, microRNAs have recently emerged as powerful regulators of diverse cellular processes with especially important roles in disease and tissue remodeling. The rapid pace of studies on microRNA regulation and function necessitates the development of suitable techniques for measuring and modulating microRNAs in different model systems. This review summarizes experimental strategies for microRNA research and highlights the strengths and weaknesses of different approaches. The development of more specific and sensitive assays will further illuminate the biology behind microRNAs and will advance opportunities to safely pursue them as therapeutic modalities.

Hydrogen Sulfide as Endothelium-Derived Hyperpolarizing Factor Sulfhydrates Potassium Channels

Abstract: Rationale:Nitric oxide, the classic endothelium-derived relaxing factor (EDRF), acts through cyclic GMP and calcium without notably affecting membrane potential. A major component of EDRF activity derives from hyperpolarization and is termed endothelium-derived hyperpolarizing factor (EDHF). Hydrogen sulfide (H2S) is a prominent EDRF, since mice lacking its biosynthetic enzyme, cystathionine γ-lyase (CSE), display pronounced hypertension with deficient vasorelaxant responses to acetylcholine. Objective:The purpose of this study was to determine if H2S is a major physiological EDHF. Methods and Results:We now show that H2S is a major EDHF because in blood vessels of CSE-deleted mice, hyperpolarization is virtually abolished. H2S acts by covalently modifying (sulfhydrating) the ATP-sensitive potassium channel, as mutating the site of sulfhydration prevents H2S-elicited hyperpolarization. The endothelial intermediate conductance (IKCa) and small conductance (SKCa) potassium channels mediate in part the effec...

Exosomes From Human CD34+ Stem Cells Mediate Their Proangiogenic Paracrine Activity

Abstract: Rationale: Transplantation of human CD34+ stem cells to ischemic tissues has been associated with reduced angina, improved exercise time, and reduced amputation rates in phase 2 clinical trials and has been shown to induce neovascularization in preclinical models. Previous studies have suggested that paracrine factors secreted by these proangiogenic cells are responsible, at least in part, for the angiogenic effects induced by CD34+ cell transplantation. Objective: Our objective was to investigate the mechanism of CD34+ stem cell–induced proangiogenic paracrine effects and to examine if exosomes, a component of paracrine secretion, are involved. Methods and Results: Exosomes collected from the conditioned media of mobilized human CD34+ cells had the characteristic size (40 to 90 nm; determined by dynamic light scattering), cup-shaped morphology (electron microscopy), expressed exosome-marker proteins CD63, phosphatidylserine (flow cytometry) and TSG101 (immunoblotting), besides expressing CD34+ cell lineage marker protein, CD34. In vitro, CD34+ exosomes replicated the angiogenic activity of CD34+ cells by increasing endothelial cell viability, proliferation, and tube formation on Matrigel. In vivo, the CD34+ exosomes stimulated angiogenesis in Matrigel plug and corneal assays. Interestingly, exosomes from CD34+ cells but not from CD34+ cell–depleted mononuclear cells had angiogenic activity. Conclusions: Our data demonstrate that human CD34+ cells secrete exosomes that have independent angiogenic activity both in vitro and in vivo. CD34+ exosomes may represent a significant component of the paracrine effect of progenitor cell transplantation for therapeutic angiogenesis. # Novelty and Significance {#article-title-11}

Multiple Facets of NF-κB in the Heart To Be or Not to NF-κB

Abstract: The progression from cardiac injury to symptomatic heart failure has been intensely studied over the last decade, and is largely attributable to a loss of functional cardiac myocytes through necrosis, intrinsic and extrinsic apoptosis pathways and autophagy. Therefore, the molecular regulation of these cellular programs has been rigorously investigated in the hopes of identifying a potential cell target that could promote cell survival and/or inhibit cell death to avert, or at least prolong, the degeneration toward symptomatic heart failure. The nuclear factor (NF)-κB super family of transcription factors has been implicated in the regulation of immune cell maturation, cell survival, and inflammation in many cell types, including cardiac myocytes. Recent studies have shown that NF-κB is cardioprotective during acute hypoxia and reperfusion injury. However, prolonged activation of NF-κB appears to be detrimental and promotes heart failure by eliciting signals that trigger chronic inflammation through enhanced elaboration of cytokines including tumor necrosis factor α, interleukin-1, and interleukin-6, leading to endoplasmic reticulum stress responses and cell death. The underlying mechanisms that account for the multifaceted and differential outcomes of NF-κB on cardiac cell fate are presently unknown. Herein, we posit a novel paradigm in which the timing, duration of activation, and cellular context may explain mechanistically the differential outcomes of NF-κB signaling in the heart that may be essential for future development of novel therapeutic interventions designed to target NF-κB responses and heart failure following myocardial injury.

Mitochondrial Oxidative Stress Mediates Angiotensin II–Induced Cardiac Hypertrophy and Gαq Overexpression–Induced Heart Failure

Abstract: Rationale: Mitochondrial dysfunction has been implicated in several cardiovascular diseases; however, the roles of mitochondrial oxidative stress and DNA damage in hypertensive cardiomyopathy are not well understood. Objective: We evaluated the contribution of mitochondrial reactive oxygen species (ROS) to cardiac hypertrophy and failure by using genetic mouse models overexpressing catalase targeted to mitochondria and to peroxisomes. Methods and Results: Angiotensin II increases mitochondrial ROS in cardiomyocytes, concomitant with increased mitochondrial protein carbonyls, mitochondrial DNA deletions, increased autophagy and signaling for mitochondrial biogenesis in hearts of angiotensin II–treated mice. The causal role of mitochondrial ROS in angiotensin II–induced cardiomyopathy is shown by the observation that mice that overexpress catalase targeted to mitochondria, but not mice that overexpress wild-type peroxisomal catalase, are resistant to cardiac hypertrophy, fibrosis and mitochondrial damage induced by angiotensin II, as well as heart failure induced by overexpression of Gαq. Furthermore, primary damage to mitochondrial DNA, induced by zidovudine administration or homozygous mutation of mitochondrial polymerase γ, is also shown to contribute directly to the development of cardiac hypertrophy, fibrosis and failure. Conclusions: These data indicate the critical role of mitochondrial ROS in cardiac hypertrophy and failure and support the potential use of mitochondrial-targeted antioxidants for prevention and treatment of hypertensive cardiomyopathy.

Mitochondrial Fusion is Essential for Organelle Function and Cardiac Homeostasis

Abstract: Rationale: Mitochondria constitute 30% of myocardial mass. Mitochondrial fusion and fission appear essential for health of most tissues. Mitochondrial fission occurs in neonatal cardiomycyte and is implicated in cardiomyocyte death. Mitochondrial fusion has not been observed in postmitotic myocytes of adult hearts, and its occurrence and function in this context are controversial. Objective: Determine the consequences on organelle and organ function of disrupting cardiomyocyte mitochondrial fusion in vivo. Methods and Results: The murine mfn1 and mfn2 genes, encoding mitofusins (Mfn) 1 and 2 that mediate mitochondrial tethering and outer mitochondrial membrane fusion, were interrupted by Cre-mediated excision of essential exons in neonatal (Nkx2.5-Cre) and adult (MYH6 modified estrogen receptor-Cre-modified estrogen receptor plus tamoxifen or Raloxifene) hearts. Embryonic combined Mfn1/Mfn2 ablation was lethal after e9.5. Conditional combined Mfn1/Mfn2 ablation in adult hearts induced mitochondrial fragmentation, cardiomyocyte and mitochondrial respiratory dysfunction, and rapidly progressive and lethal dilated cardiomyopathy. Before heart failure developed, cardiomyocyte shortening and calcium cycling were unaffected by absence of Mfn1 and Mfn2. Based on the time course over which fusion-defective mitochondrial size decreases, a mitochondrial fusion/fission cycle in adult mouse hearts occurs approximately every 16 days. Conclusions: Mitochondrial fusion in adult cardiac myocytes is necessary to maintain normal mitochondrial morphology and is essential for normal cardiac respiratory and contractile function. Interruption of mitochondrial fusion causes lethal cardiac failure at a time corresponding to 3 or 4 cycles of unopposed mitochondrial fission.

Intramyocardial, Autologous CD34+ Cell Therapy for Refractory Angina

Abstract: Rationale: A growing number of patients with coronary disease have refractory angina. Preclinical and early-phase clinical data suggest that intramyocardial injection of autologous CD34+ cells can improve myocardial perfusion and function. Objective: Evaluate the safety and bioactivity of intramyocardial injections of autologous CD34+ cells in patients with refractory angina who have exhausted all other treatment options. Methods and Results: In this prospective, double-blind, randomized, phase II study (ClinicalTrials.gov identifier: [NCT00300053][1]), 167 patients with refractory angina received 1 of 2 doses (1×105 or 5×105 cells/kg) of mobilized autologous CD34+ cells or an equal volume of diluent (placebo). Treatment was distributed into 10 sites of ischemic, viable myocardium with a NOGA mapping injection catheter. The primary outcome measure was weekly angina frequency 6 months after treatment. Weekly angina frequency was significantly lower in the low-dose group than in placebo-treated patients at both 6 months (6.8±1.1 versus 10.9±1.2, P =0.020) and 12 months (6.3±1.2 versus 11.0±1.2, P =0.035); measurements in the high-dose group were also lower, but not significantly. Similarly, improvement in exercise tolerance was significantly greater in low-dose patients than in placebo-treated patients (6 months: 139±151 versus 69±122 seconds, P =0.014; 12 months: 140±171 versus 58±146 seconds, P =0.017) and greater, but not significantly, in the high-dose group. During cell mobilization and collection, 4.6% of patients had cardiac enzyme elevations consistent with non-ST segment elevation myocardial infarction. Mortality at 12 months was 5.4% in the placebo-treatment group with no deaths among cell-treated patients. Conclusions: Patients with refractory angina who received intramyocardial injections of autologous CD34+ cells (105 cells/kg) experienced significant improvements in angina frequency and exercise tolerance. The cell-mobilization and -collection procedures were associated with cardiac enzyme elevations, which will be addressed in future studies. # Novelty and Significance {#article-title-35} [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00300053&atom=%2Fcircresaha%2F109%2F4%2F428.atom

Inherited Dysfunction of Sarcoplasmic Reticulum Ca2+ Handling and Arrhythmogenesis

Abstract: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease occurring in patients with a structurally normal heart: the disease is characterized by life-threatening arrhythmias elicited by stress and emotion. In 2001, the ryanodine receptor was identified as the gene that is linked to CPVT; shortly thereafter, cardiac calsequestrin was implicated in the recessive form of the same disease. It became clear that abnormalities in intracellular Ca2+ regulation could profoundly disrupt the electrophysiological properties of the heart. In this article, we discuss the molecular basis of the disease and the pathophysiological mechanisms that are impacting clinical diagnosis and management of affected individuals. As of today, the interaction between basic scientists and clinicians to understand CPVT and identify new therapeutic strategies is one of the most compelling examples of the importance of translational research in cardiology.

miR-15 Family Regulates Postnatal Mitotic Arrest of Cardiomyocytes

Abstract: Rationale:Mammalian cardiomyocytes withdraw from the cell cycle during early postnatal development, which significantly limits the capacity of the adult mammalian heart to regenerate after injury. The regulatory mechanisms that govern cardiomyocyte cell cycle withdrawal and binucleation are poorly understood. Objective:Given the potential of microRNAs (miRNAs) to influence large gene networks and modify complex developmental and disease phenotypes, we searched for miRNAs that were regulated during the postnatal switch to terminal differentiation. Methods and Results:Microarray analysis revealed subsets of miRNAs that were upregulated or downregulated in cardiac ventricles from mice at 1 and 10 days of age (P1 and P10). Interestingly, miR-195 (a member of the miR-15 family) was the most highly upregulated miRNA during this period, with expression levels almost 6-fold higher in P10 ventricles relative to P1. Precocious overexpression of miR-195 in the embryonic heart was associated with ventricular hypoplas...

Estrogen Signaling and Cardiovascular Disease

Abstract: Estrogen has pleiotropic effects on the cardiovascular system. The mechanisms by which estrogen confers these pleiotropic effects are undergoing active investigation. Until a decade ago, all estrogen signaling was thought to occur by estrogen binding to nuclear estrogen receptors (estrogen receptor-α and estrogen receptor-β), which bind to DNA and function as ligand-activated transcription factors. Estrogen binding to the receptor alters gene expression, thereby altering cell function. Estrogen also binds to nuclear estrogen receptors that are tethered to the plasma membrane, resulting in acute activation of signaling kinases such as PI3K. An orphan G-protein-coupled receptor, G-protein-coupled receptor 30, can also bind estrogen and activate acute signaling pathways. Thus, estrogen can alter cell function by binding to different estrogen receptors. This article reviews the different estrogen receptors and their signaling mechanisms, discusses mechanisms that regulate estrogen receptor levels and locations, and considers the cardiovascular effects of estrogen signaling.

Fetuin-A Regulation of Calcified Matrix Metabolism

Abstract: The final step of biomineralization is a chemical precipitation reaction that occurs spontaneously in supersaturated or metastable salt solutions. Genetic programs direct precursor cells into a mineralization-competent state in physiological bone formation (osteogenesis) and in pathological mineralization (ectopic mineralization or calcification). Therefore, all tissues not meant to mineralize must be actively protected against chance precipitation of mineral. Fetuin-A is a liver-derived blood protein that acts as a potent inhibitor of ectopic mineralization. Monomeric fetuin-A protein binds small clusters of calcium and phosphate. This interaction results in the formation of prenucleation cluster-laden fetuin-A monomers, calciprotein monomers, and considerably larger aggregates of protein and mineral calciprotein particles. Both monomeric and aggregate forms of fetuin-A mineral accrue acidic plasma protein including albumin, thus stabilizing supersaturated and metastable mineral ion solutions as colloids. Hence, fetuin-A is a mineral carrier protein and a systemic inhibitor of pathological mineralization complementing local inhibitors that act in a cell-restricted or tissue-restricted fashion. Fetuin-A deficiency is associated with soft tissue calcification in mice and humans.

Whole-Heart Modeling Applications to Cardiac Electrophysiology and Electromechanics

Abstract: Recent developments in cardiac simulation have rendered the heart the most highly integrated example of a virtual organ. We are on the brink of a revolution in cardiac research, one in which computational modeling of proteins, cells, tissues, and the organ permit linking genomic and proteomic information to the integrated organ behavior, in the quest for a quantitative understanding of the functioning of the heart in health and disease. The goal of this review is to assess the existing state-of-the-art in whole-heart modeling and the plethora of its applications in cardiac research. General whole-heart modeling approaches are presented, and the applications of whole-heart models in cardiac electrophysiology and electromechanics research are reviewed. The article showcases the contributions that whole-heart modeling and simulation have made to our understanding of the functioning of the heart. A summary of the future developments envisioned for the field of cardiac simulation and modeling is also presented. Biophysically based computational modeling of the heart, applied to human heart physiology and the diagnosis and treatment of cardiac disease, has the potential to dramatically change 21st century cardiac research and the field of cardiology.

Human Atherosclerotic Plaque Alternative Macrophages Display Low Cholesterol Handling but High Phagocytosis Because of Distinct Activities of the PPARγ and LXRα Pathways

Abstract: Rationale: A crucial step in atherogenesis is the infiltration of the subendothelial space of large arteries by monocytes where they differentiate into macrophages and transform into lipid-loaded foam cells. Macrophages are heterogeneous cells that adapt their response to environmental cytokines. Th1 cytokines promote monocyte differentiation into M1 macrophages, whereas Th2 cytokines trigger an “alternative” M2 phenotype. Objective: We previously reported the presence of CD68 + mannose receptor (MR) + M2 macrophages in human atherosclerotic plaques. However, the function of these plaque CD68 + MR + macrophages is still unknown. Methods and Results: Histological analysis revealed that CD68 + MR + macrophages locate far from the lipid core of the plaque and contain smaller lipid droplets compared to CD68 + MR − macrophages. Interleukin (IL)-4–polarized CD68 + MR + macrophages display a reduced capacity to handle and efflux cellular cholesterol because of low expression levels of the nuclear receptor liver x receptor (LXR)α and its target genes, ABCA1 and apolipoprotein E, attributable to the high 15-lipoxygenase activity in CD68 + MR + macrophages. By contrast, CD68 + MR + macrophages highly express opsonins and receptors involved in phagocytosis, resulting in high phagocytic activity. In M2 macrophages, peroxisome proliferator-activated receptor (PPAR)γ activation enhances the phagocytic but not the cholesterol trafficking pathways. Conclusions: These data identify a distinct macrophage subpopulation with a low susceptibility to become foam cells but high phagocytic activity resulting from different regulatory activities of the PPARγ-LXRα pathways.

MicroRNA-29 in Aortic Dilation: Implications for Aneurysm Formation

Abstract: Rationale:Aging represents a major risk factor for coronary artery disease and aortic aneurysm formation. MicroRNAs (miRs) have emerged as key regulators of biological processes, but their role in age-associated vascular pathologies is unknown. Objective:We aim to identify miRs in the vasculature that are regulated by age and play a role in age-induced vascular pathologies. Methods and Results:Expression profiling of aortic tissue of young versus old mice identified several age-associated miRs. Among the significantly regulated miRs, the increased expression of miR-29 family members was associated with a profound downregulation of numerous extracellular matrix (ECM) components in aortas of aged mice, suggesting that this miR family contributes to ECM loss, thereby sensitizing the aorta for aneurysm formation. Indeed, miR-29 expression was significantly induced in 2 experimental models for aortic dilation: angiotensin II-treated aged mice and genetically induced aneurysms in Fibulin-4R/R mice. More importa...

Microparticles, Vascular Function, and Atherothrombosis

Abstract: Membrane-shed submicron microparticles (MPs) are released after cell activation or apoptosis. High levels of MPs circulate in the blood of patients with atherothrombotic diseases, where they could serve as a useful biomarker of vascular injury and a potential predictor of cardiovascular mortality and major adverse cardiovascular events. Atherosclerotic lesions also accumulate large numbers of MPs of leukocyte, smooth muscle cell, endothelial, and erythrocyte origin. A large body of evidence supports the role of MPs at different steps of atherosclerosis development, progression, and complications. Circulating MPs impair the atheroprotective function of the vascular endothelium, at least partly, by decreased nitric oxide synthesis. Plaque MPs favor local inflammation by augmenting the expression of adhesion molecule, such as intercellular adhesion molecule -1 at the surface of endothelial cell, and monocyte recruitment within the lesion. In addition, plaque MPs stimulate angiogenesis, a key event in the transition from stable to unstable lesions. MPs also may promote local cell apoptosis, leading to the release and accumulation of new MPs, and thus creating a vicious circle. Furthermore, highly thrombogenic plaque MPs could increase thrombus formation at the time of rupture, together with circulating MPs released in this context by activated platelets and leukocytes. Finally, MPs also could participate in repairing the consequences of arterial occlusion and tissue ischemia by promoting postischemic neovascularization.

Calcium Regulates Key Components of Vascular Smooth Muscle Cell–Derived Matrix Vesicles to Enhance Mineralization

Abstract: Rationale:Matrix vesicles (MVs) are specialized structures that initiate mineral nucleation during physiological skeletogenesis. Similar vesicular structures are deposited at sites of pathological vascular calcification, and studies in vitro have shown that elevated levels of extracellular calcium (Ca) can induce mineralization of vascular smooth muscle cell (VSMC)–derived MVs. Objectives:To determine the mechanisms that promote mineralization of VSMC-MVs in response to calcium stress. Methods and Results:Transmission electron microscopy showed that both nonmineralized and mineralized MVs were abundantly deposited in the extracellular matrix at sites of calcification. Using cultured human VSMCs, we showed that MV mineralization is calcium dependent and can be inhibited by BAPTA-AM. MVs released by VSMCs in response to extracellular calcium lacked the key mineralization inhibitor matrix Gla protein and showed enhanced matrix metalloproteinase-2 activity. Proteomics revealed that VSMC-MVs share similarities...

The Emerging Role of Innate Immunity in the Heart and Vascular System For Whom the Cell Tolls

Abstract: Recent studies suggest that the heart possesses an innate immune system that is intended to delimit tissue injury, as well as orchestrate homoeostatic responses, within the heart. The extant literature suggests that this intrinsic stress response system is mediated, at least in part, by a family of pattern recognition receptors, most notably the Toll-like receptors. Although the innate immune system provides a short-term adaptive response to tissue injury, the beneficial effects of this phylogenetically ancient system may be lost if innate immune signaling becomes sustained and/or excessive; in which case, the salutary effects of activation of these pathways are contravened by the known deleterious effects of inflammatory signaling. Herein, the biology of innate immune signaling in the heart is reviewed, as well as the literature suggesting that the innate immune system is involved in the pathogenesis of atherosclerosis, acute coronary syndromes, stroke, viral myocarditis, sepsis, ischemia/reperfusion injury, and heart failure. The review concludes by discussing new therapies that are being developed to modulate the innate immune system.

Dabigatran Etexilate A New Oral Thrombin Inhibitor

Abstract: Long-term oral anticoagulation is indicated for several cardiovascular diseases, including the prevention of cardiac thromboembolism in patients with atrial fibrillation (AF),1 mechanical heart valves,2 and acute myocardial infarction (MI),3 as well as the secondary prevention of venous thromboembolism (VTE).4 For the past 60 years, oral vitamin K antagonists (eg, warfarin, acenocoumarol, phenprocoumon, fluindione) have been widely prescribed.5 However, their impact in preventing thromboembolism has been hampered by several limitations that compromise their effectiveness and safety and make them difficult to use (Table 1). Vitamin K antagonists have a delayed onset and offset of action that often prolong hospitalization, and thus increase healthcare costs. Their large interindividual variability in dose response and narrow therapeutic window demand regular monitoring of the international normalized ratio (INR) and result in complex individualized dosing. Despite careful dose adjustment, the INR is frequently outside the target therapeutic range, which increases the risk of thromboembolism and bleeding.6 Patients treated with a vitamin K antagonist require counseling about drug and food interactions, the need for routine monitoring, and the inherent risk of bleeding. To reduce some of the dose variability, an algorithm based on clinical and genetic data has been developed and validated for estimating the appropriate dose of warfarin,7 but evidence of the cost-effectiveness of pharmacogenetic testing to optimize warfarin dosing in routine clinical practice is lacking.8 View this table: Table 1. Limitations of Warfarin and Other Oral Vitamin K Antagonists As a consequence of the limitations of vitamin K antagonists, the quality of anticoagulant control is frequently suboptimal among those who receive the treatment, and many patients at risk of thromboembolism do not receive treatment; only 50% to 70% of patients with AF at risk of stroke who are eligible for anticoagulant therapy are treated with a vitamin K antagonist.9,– …

Transplantation of Human Pericyte Progenitor Cells Improves the Repair of Infarcted Heart Through Activation of an Angiogenic Program Involving Micro-RNA-132

Abstract: Rationale:Pericytes are key regulators of vascular maturation, but their value for cardiac repair remains unknown. Objective:We investigated the therapeutic activity and mechanistic targets of saphenous vein-derived pericyte progenitor cells (SVPs) in a mouse myocardial infarction (MI) model. Methods and Results:SVPs have a low immunogenic profile and are resistant to hypoxia/starvation (H/S). Transplantation of SVPs into the peri-infarct zone of immunodeficient CD1/Foxn-1nu/nu or immunocompetent CD1 mice attenuated left ventricular dilatation and improved ejection fraction compared to vehicle. Moreover, SVPs reduced myocardial scar, cardiomyocyte apoptosis and interstitial fibrosis, improved myocardial blood flow and neovascularization, and attenuated vascular permeability. SVPs secrete vascular endothelial growth factor A, angiopoietin-1, and chemokines and induce an endogenous angiocrine response by the host, through recruitment of vascular endothelial growth factor B expressing monocytes. The associat...

Human Atrial Action Potential and Ca2+ Model: Sinus Rhythm and Chronic Atrial Fibrillation

Abstract: Rationale: Understanding atrial fibrillation (AF) requires integrated understanding of ionic currents and Ca 2+ transport in remodeled human atrium, but appropriate models are limited. Objective: To study AF, we developed a new human atrial action potential (AP) model, derived from atrial experimental results and our human ventricular myocyte model. Methods and Results: Atria versus ventricles have lower I K1 , resulting in more depolarized resting membrane potential (≈7 mV). We used higher I to,fast density in atrium, removed I to,slow , and included an atrial-specific I Kur . I NCX and I NaK densities were reduced in atrial versus ventricular myocytes according to experimental results. SERCA function was altered to reproduce human atrial myocyte Ca 2+ transients. To simulate chronic AF, we reduced I CaL , I to , I Kur and SERCA, and increased I K1 ,I Ks and I NCX . We also investigated the link between Kv1.5 channelopathy, [Ca 2+ ] i , and AF. The sinus rhythm model showed a typical human atrial AP morphology. Consistent with experiments, the model showed shorter APs and reduced AP duration shortening at increasing pacing frequencies in AF or when I CaL was partially blocked, suggesting a crucial role of Ca 2+ and Na + in this effect. This also explained blunted Ca 2+ transient and rate-adaptation of [Ca 2+ ] i and [Na + ] i in chronic AF. Moreover, increasing [Na + ] i and altered I NaK and I NCX causes rate-dependent atrial AP shortening. Blocking I Kur to mimic Kv1.5 loss-of-function increased [Ca 2+ ] i and caused early afterdepolarizations under adrenergic stress, as observed experimentally. Conclusions: Our study provides a novel tool and insights into ionic bases of atrioventricular AP differences, and shows how Na + and Ca 2+ homeostases critically mediate abnormal repolarization in AF.

Intramyocardial Stem Cell Injection in Patients With Ischemic Cardiomyopathy: Functional Recovery and Reverse Remodeling

Abstract: Rationale: Transcatheter, intramyocardial injections of bone marrow–derived cell therapy produces reverse remodeling in large animal models of ischemic cardiomyopathy. Objective: We used cardiac MRI (CMR) in patients with left ventricular (LV) dysfunction related to remote myocardial infarction (MI) to test the hypothesis that bone marrow progenitor cell injection causes functional recovery of scarred myocardium and reverse remodeling. Methods and Results: Eight patients (aged 57.213.3 years) received transendocardial, intramyocardial injection of autologous bone marrow progenitor cells (mononuclear or mesenchymal stem cells) in LV scar and border zone. All patients tolerated the procedure with no serious adverse events. CMR at 1 year demonstrated a decrease in end diastolic volume (208.720.4 versus 167.47.32 mL; P0.03), a trend toward decreased end systolic volume (142.416.5 versus 107.67.4 mL; P0.06), decreased infarct size (P<0.05), and improved regional LV function by peak Eulerian circumferential strain in the treated infarct zone (8.11.0 versus 11.41.3; P0.04). Improvements in regional function were evident at 3 months, whereas the changes in chamber dimensions were not significant until 6 months. Improved regional function in the infarct zone strongly correlated with reduction of end diastolic volume (r 2 0.69, P0.04) and end systolic volume (r 2 0.83, P0.01). Conclusions: These data suggest that transcatheter, intramyocardial injections of autologous bone marrow progenitor cells improve regional contractility of a chronic myocardial scar, and these changes predict subsequent reverse remodeling. The findings support the potential clinical benefits of this new treatment strategy and ongoing randomized clinical trials. (Circ Res. 2011;108:792-796.)

Epicardial-Derived Cell Epithelial-to-Mesenchymal Transition and Fate Specification Require PDGF Receptor Signaling

Abstract: Rationale:In early heart development, platelet-derived growth factor (PDGF) receptor expression in the heart ventricles is restricted to the epicardium. Previously, we showed that PDGFRβ is require...

Malignant Tumor Formation After Transplantation of Short-Term Cultured Bone Marrow Mesenchymal Stem Cells in Experimental Myocardial Infarction and Diabetic Neuropathy

Abstract: Rationale:Bone marrow (BM)–derived mesenchymal stem cells (MSCs) hold great promise for cardiovascular cell therapy owing to their multipotency and culture expandability Objective:The aim of the study was to investigate whether MSCs can treat experimental acute myocardial infarction (MI) and diabetic neuropathy Methods and Results:We isolated mononuclear cells from mouse BM and cultured MSCs in a conventional manner Flow cytometry analyses of these cultured cells at passage 4 showed expression of typical MSC markers such as CD44 and CD29, but not hematopoietic markers such as c-kit, flk1, and CD34 To determine the therapeutic effects of MSCs, we injected MSCs into the peri-infarct area after ligation of the left anterior descending coronary arteries of mice and, as separate experiments, injected the same batch of MSCs into hindlimb muscles of mice with diabetic neuropathy During the follow-up at 4 to 8 weeks after cell transplantation, growing tumors were observed in 30% of hearts in the MI model, an

Calcific aortic valve stenosis: methods, models, and mechanisms.

Abstract: Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.