Collagen and elastin cross-linking: a mechanism of constrictive remodeling after arterial injury

Review paper: The importance of consideration of collagen cross-links in computational models of collagen-based tissues

Collagen as the main protein in Extra Cellular Matrix (ECM) is the main load-bearing component of fibrous tissues. Nanostructure and architecture of collagen fibrils play an important role in mechanical behavior of these tissues. Extensive experimental and theoretical studies have so far been performed to capture these properties, but none of the current models realistically represent the complexity of network mechanics because still less is known about the collagen's inner structure and its effect on the mechanical properties of tissues. The goal of this review article is to emphasize the significance of cross-links in computational modeling of different collagen-based tissues, and to reveal the need for continuum models to consider cross-links properties to better reflect the mechanical behavior observed in experiments. In addition, this study outlines the limitations of current investigations and provides potential suggestions for the future work.

Elastin stabilization prevents impaired biomechanics in human pulmonary arteries and pulmonary hypertension in rats with left heart disease

Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.

Cardiovascular Disease in Myeloproliferative Neoplasms: JACC: CardioOncology State-of-the-Art Review

Myeloproliferative neoplasms are associated with increased risk for thrombotic complications. These conditions most commonly involve somatic mutations in genes that lead to constitutive activation of the Janus-associated kinase signaling pathway (eg, Janus kinase 2, calreticulin, myeloproliferative leukemia protein). Acquired gain-of-function mutations in these genes, particularly Janus kinase 2, can cause a spectrum of disorders, ranging from clonal hematopoiesis of indeterminate potential, a recently recognized age-related promoter of cardiovascular disease, to frank hematologic malignancy. Beyond thrombosis, patients with myeloproliferative neoplasms can develop other cardiovascular conditions, including heart failure and pulmonary hypertension. The authors review the pathophysiologic mechanisms of cardiovascular complications of myeloproliferative neoplasms, which involve inflammation, prothrombotic and profibrotic factors (including transforming growth factor-beta and lysyl oxidase), and abnormal function of circulating clones of mutated leukocytes and platelets from affected individuals. Anti-inflammatory therapies may provide cardiovascular benefit in patients with myeloproliferative neoplasms, a hypothesis that requires rigorous evaluation in clinical trials.

Depletion of LOXL2 improves respiratory capacity: From air-breathing fish to mammal under hypoxia

Air-breathing fish are fascinating because of their ability to survive under hypoxia for a long time by using air-breathing organs (ABOs). Fish ABOs are thought to resemble the mammal lung all along. However, the link between the two has not been studied in depth. Here, we reported a markedly improved respiratory capacity in mice under hypoxia by inhibiting lysyl oxidase-like 2 (LOXL2), inspired from the intestinal air-breathing of loach (Misgurnus anguillicaudatus). Moreover, a posterior intestine (an ABO) transcriptome analysis revealed that the deletion of Loxl2b obviously inhibited PI3K-AKT and TGF-β signaling, meanwhile, induced VEGF signaling, which could cause vasodilation and angiogenesis to improve the air-breathing ability of loach. The same phenomenon was found in LOXL2-inhibition mice under hypoxia, which significantly prolonged their living period relative to wild-type (WT) mice. In addition, compared with WT loach, Loxl2b^-/- loach presented enhanced anaerobic metabolism, which could also make itself to better survive in hypoxic environment. This should be the magic of air-breathing fish! Supplied from air-breathing fish, this study provides a novel means of improving respiratory capacity in mammal under hypoxia.

An Investigation of the Altered Textural Property in Woody Breast Myopathy Using an Integrative Omics Approach

Woody breast (WB) is a myopathy observed in broiler Pectoralis major (PM) characterized by its tough and rubbery texture with greater level of calcium content. The objective of this study was to investigate the functionality/integrity of WB sarcoplasmic reticulum (SR), which may contribute to the elevated calcium content observed in WB and other factors that may influence WB texture. Fourteen Ross line broiler PM [7 severe WB and 7 normal (N)] were selected, packaged, and frozen at −20°C at 8 h postmortem from a commercial processing plant. Samples were used to measure pH, sarcomere length, proteolysis, calpain activity, collagenase activity, collagen content, collagen crosslinks density, and connective tissue peak transitional temperature. Exudate was also collected from each sample to evaluate free calcium concentration. The SR fraction of the samples was separated and utilized for proteomic and lipidomic analysis. The WB PM had a higher pH, shorter sarcomeres, lower % of intact troponin-T, more autolyzed μ/m calpain, more activated collagenase, greater collagen content, greater mature collagen crosslinks density, and higher connective tissue peak transitional temperature than the N PM (p ≤ 0.05). Exudate from WB PM had higher levels of free calcium than those from N PM (p < 0.05). Proteomics data revealed an upregulation of calcium transport proteins and a downregulation of proteins responsible for calcium release (p < 0.05) in WB SR. Interestingly, there was an upregulation of phospholipase A2 (PLA2), and cholinesterase exhibited a 7.6-fold increase in WB SR (p < 0.01). Lipidomics data revealed WB SR had less relative % of phosphatidylcholine (PC) and more lysophosphatidylcholine (LPC; p < 0.05). The results indicated that upregulation of calcium transport proteins and downregulation of calcium-release proteins in WB SR may be the muscle’s attempt to regulate this proposed excessive signaling of calcium release due to multiple factors, such as upregulation of PLA2 resulting in PC hydrolysis and presence of cholinesterase inhibitors in the system prolonging action potential. In addition, the textural abnormality of WB may be the combined effects of shorter sarcomere length and more collagen with greater crosslink density being deposited in the broiler PM.

Plasticity and Enzymatic Degradation Coupled With Volumetric Growth in Pulmonary Hypertension Progression

Pulmonary hypertension (PH) is one of the least understood and highly elusive cardiovascular conditions associated with elevated pulmonary arterial pressure. Although the disease mechanisms are not completely understood, evidence has accumulated from human and animal studies that irreversible processes of pulmonary arterial wall damage, compensated by stress-mediated growth, play critical roles in eliciting the mechanisms of disease progression. The aim of this study is to develop a thermodynamic modeling structure of the pulmonary artery to consider coupled plastic-degradation-growth irreversible processes to investigate the mechanical roles of the dissipative phenomena in the disease progression. The proposed model performs a model parameter study of plastic deformation and degradation processes coupled with dissipative growth subjected to elevated pulmonary arterial pressure and computationally generates in silico simulations of PH progression using the clinical features of PH, found in human morphological and mechanical data. The results show that considering plastic deformation can provide a much better fitting of the ex vivo inflation tests than a widely used pure hyperelastic model in higher pressure conditions. In addition, the parameter sensitivity study illustrates that arterial damage and growth cause the increased stiffness, and the full simulation (combining elastic-plastic-degradation-growth models) reveals a key postpathological recovery process of compensating vessel damage by vascular adaptation by reducing the rate of vessel dilation and mediating vascular wall stress. Finally, the simulation results of luminal enlargement, arterial thickening, and arterial stiffness for an anisotropic growth are found to be close to the values from the literature.

Epigenetic Regulation of Vascular Smooth Muscle Cell Phenotype Switching in Atherosclerotic Artery Remodeling: A Mini-Review

Atherosclerosis is a chronic inflammatory disease characterized by extensive remodeling of medium and large-sized arteries. Inward remodeling (=lumen shrinkage) of the vascular walls is the underlying cause for ischemia in target organs. Therefore, inward remodeling can be considered the predominant feature of atherosclerotic pathology. Outward remodeling (=lumen enlargement) is a physiological response compensating for lumen shrinkage caused by neointimal hyperplasia, but as a pathological response to changes in blood flow, outward remodeling leads to substantial arterial wall thinning. Thinned vascular walls are prone to rupture, and subsequent thrombus formation accounts for the majority of acute cardiovascular events. Pathological remodeling is driven by inflammatory cells which induce vascular smooth muscle cells to switch from quiescent to a proliferative and migratory phenotype. After decades of intensive research, the molecular mechanisms of arterial remodeling are starting to unfold. In this mini-review, we summarize the current knowledge of the epigenetic and transcriptional regulation of vascular smooth muscle cell phenotype switching from the contractile to the synthetic phenotype involved in arterial remodeling and discuss potential therapeutic options.

Molecular imaging of extracellular matrix proteins with targeted probes using magnetic resonance imaging

The extracellular matrix (ECM) consists of proteins and carbohydrates that supports different biological structures and processes such as tissue development, elasticity, and preservation of organ structure. Diseases involving inflammation, fibrosis, tumor invasion, and injury are all attributed to the transition of the ECM from homeostasis to remodeling, which can significantly change the biochemical and biomechanical features of ECM components. While contrast agents have played an indispensable role in facilitating clinical diagnosis of diseases using magnetic resonance imaging (MRI), there is a strong need to develop novel biomarker-targeted imaging probes for in vivo visualization of biological processes and pathological alterations at a cellular and molecular level, for both early diagnosis and monitoring drug treatment. Herein, we will first review the pathological accumulation and characterization of ECM proteins recognized as important molecular features of diseases. Developments in MRI probes targeting ECM proteins such as collagen, fibronectin, and elastin via conjugation of existing contrast agents to targeting moieties and their applications to various diseases, are also reviewed. We have also reviewed our progress in the development of collagen-targeted protein MRI contrast agent with significant improvement in relaxivity and metal binding specificity, and their applications in early detection of fibrosis and metastatic cancer. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Anti-lysyl oxidase combined with a vacuum device induces penile lengthening by remodeling the tunica albuginea

This study aimed to explore whether and how anti-lysyl oxidase (anti-LOX) combined with a vacuum device (VD) could promote penile lengthening and to evaluate the effect on erectile function. This study was performed on four groups of adult rats: control, anti-LOX, VD (negative pressure value of −300 mmHg), and anti-LOX + VD. Penile length was measured by a modified VD method and verified on exposed length data. Intracavernous pressure (ICP) and maximum ICP/mean arterial pressure (MAP) ratio were recorded to assess erectile function. For corpus cavernosum, LOX activity and concentrations of pyridinoline, desmosine, hydroxyproline, and elastin were analyzed; transmission electron microscope and Hart's elastin staining were performed to monitor microstructural changes. Anti-LOX and VD significantly lengthened the penis by 10.8% (3.75 mm) and 8.2% (2.48 mm) compared with the control group, respectively, while anti-LOX + VD achieved the longest penile size (40.58 ± 0.40 mm) which was 17.4% longer than the control group (34.58 ± 0.54 mm). After 1-week washout, no penile retraction was observed. Meanwhile, exposed penile length data confirmed that the penis in the anti-LOX + VD group was also significantly longer. Anti-LOX inhibited LOX activity to reduce pyridinoline level, which led the penile tunica albuginea remodeling. However, it had no effect on hydroxyproline, desmosine, and elastin levels. Moreover, anti-LOX had no impact on erectile function, which was determined by ICP and ICP/MAP ratio. These results suggest that anti-LOX elongates the penis by reducing pyridinoline, which induces tunica albuginea remodeling. This lengthening effect was more obvious when combined with a VD. All procedures had no impact on erectile function.

Co-administration of resveratrol and beta-aminopropionitrile attenuates liver fibrosis development via targeting lysyl oxidase in CCl4-induced liver fibrosis in rats

Objectives: In the current study, we aimed to investigate the effect of administration of resveratrol (RES) and beta-aminopropionitrile (BAPN) separately and together on the liver fibrosis progression via regulation of the gene expression and protein level of lysyl oxidase (LOX).Materials and methods: The six-week old Wistar rats received carbon tetrachloride (CCl₄) intraperitoneally and RES and BAPN were administrated orally for eight weeks. The hepatoprotective effects of RES, BAPN, and combination treatment were evaluated. Then the hepatic protein and gene expression levels of LOX were measured.Results: Both RES and BAPN showed the antifibrotic effect through the reduction of collagen fiber bundles, hepatic hydroxyproline content, and protein level of LOX. The antifibrotic effect increased when RES and BAPN up-taken together.Conclusion: The co-administration of RES and BAPN can be considered as a promising therapeutic approach via targeting LOX.

Emerging Roles of Lysyl Oxidases in the Cardiovascular System: New Concepts and Therapeutic Challenges

Lysyl oxidases (LOX and LOX-likes (LOXLs) isoenzymes) belong to a family of copper-dependent enzymes classically involved in the covalent cross-linking of collagen and elastin, a pivotal process that ensures extracellular matrix (ECM) stability and provides the tensile and elastic characteristics of connective tissues. Besides this structural role, in the last years, novel biological properties have been attributed to these enzymes, which can critically influence cardiovascular function. LOX and LOXLs control cell proliferation, migration, adhesion, differentiation, oxidative stress, and transcriptional regulation and, thereby, their dysregulation has been linked to a myriad of cardiovascular pathologies. Lysyl oxidase could modulate virtually all stages of the atherosclerotic process, from endothelial dysfunction and plaque progression to calcification and rupture of advanced and complicated plaques, and contributes to vascular stiffness in hypertension. The alteration of LOX/LOXLs expression underlies the development of other vascular pathologies characterized by a destructive remodeling of the ECM, such as aneurysm and artery dissections, and contributes to the adverse myocardial remodeling and dysfunction in hypertension, myocardial infarction, and obesity. This review examines the most recent advances in the study of LOX and LOXLs biology and their pathophysiological role in cardiovascular diseases with special emphasis on their potential as therapeutic targets.

LOXL1 Is Regulated by Integrin α11 and Promotes Non-Small Cell Lung Cancer Tumorigenicity

Integrin α11, a stromal collagen receptor, promotes tumor growth and metastasis of non-small cell lung cancer (NSCLC) and is associated with the regulation of collagen stiffness in the tumor stroma. We have previously reported that lysyl oxidase like-1 (LOXL1), a matrix cross-linking enzyme, is down-regulated in integrin α11-deficient mice. In the present study, we investigated the relationship between LOXL1 and integrin α11, and the role of LOXL1 in NSCLC tumorigenicity. Our results show that the expression of LOXL1 and integrin α11 was correlated in three lung adenocarcinoma patient datasets and that integrin α11 indeed regulated LOXL1 expression in stromal cells. Using cancer-associated fibroblast (CAF) with either a knockdown or overexpression of LOXL1, we demonstrated a role for LOXL1 in collagen matrix remodeling and collagen fiber alignment in vitro and in vivo in a NSCLC xenograft model. As a consequence of collagen reorganization in NSCLC tumor stroma, we showed that LOXL1 supported tumor growth and progression. Our findings demonstrate that stromal LOXL1, under regulation of integrin α11, is a determinant factor of NSCLC tumorigenesis and may be an interesting target in this disease.

Current and Emerging Preclinical Approaches for Imaging-Based Characterization of Atherosclerosis

Atherosclerotic plaques can remain quiescent for years, but become life threatening upon rupture or disruption, initiating clot formation in the vessel lumen and causing acute myocardial infarction and ischemic stroke. Whether and how a plaque ruptures is determined by its macroscopic structure and microscopic composition. Rupture-prone plaques usually consist of a thin fibrous cap with few smooth muscle cells, a large lipid core, a dense infiltrate of inflammatory cells, and neovessels. Such lesions, termed high-risk plaques, can remain asymptomatic until the thrombotic event. Various imaging technologies currently allow visualization of morphological and biological characteristics of high-risk atherosclerotic plaques. Conventional protocols are often complex and lack specificity for high-risk plaque. Conversely, new imaging approaches are emerging which may overcome these limitations. Validation of these novel imaging techniques in preclinical models of atherosclerosis is essential for effective translational to clinical practice. Imaging the vessel wall, as well as its biological milieu in small animal models, is challenging because the vessel wall is a small structure that undergoes continuous movements imposed by the cardiac cycle as it is adjacent to circulating blood. The focus of this paper is to provide a state-of-the-art review on techniques currently available for preclinical imaging of atherosclerosis in small animal models and to discuss the advantages and limitations of each approach.

Copper transporter ATP7A interacts with IQGAP1, a Rac1 binding scaffolding protein: role in PDGF-induced VSMC migration and vascular remodeling

Vascular smooth muscle cell (VSMC) migration contributes to neointimal formation after vascular injury. We previously demonstrated that copper (Cu) transporter ATP7A is involved in platelet-derived growth factor (PDGF)-induced VSMC migration in a Cu- and Rac1-dependent manner. The underlying mechanism is still unknown. Here we show that ATP7A interacts with IQGAP1, a Rac1 and receptor tyrosine kinase binding scaffolding proteins, which mediates PDGF-induced VSMC migration and vascular remodeling. In cultured rat aortic SMCs, PDGF stimulation rapidly promoted ATP7A association with IQGAP1 and Rac1 and their translocation to the lipid rafts and leading edge. Cotransfection assay revealed that ATP7A directly bound to NH₂-terminal domain of IQGAP1. Functionally, either ATP7A or IQGAP1 depletion using siRNA significantly inhibited PDGF-induced VSMC migration without additive effects, suggesting that IQGAP1 and ATP7A are in the same axis to promote migration. Furthermore, IQGAP1 siRNA blocked PDGF-induced ATP7A association with Rac1 as well as its translocation to leading edge, while PDGF-induced IQGAP1 translocation was not affected by ATP7A siRNA or Cu chelator. Overexpression of mutant IQGAP1 lacking a Rac1 binding site prevented PDGF-induced translocation of Rac1, but not ATP7A, to the leading edge, thereby inhibiting lamellipodia formation and VSMC migration. In vivo, ATP7A colocalized with IQGAP1 at neointimal VSMCs in a mice wire injury model, while neointimal formation and extracellular matrix deposition induced by vascular injury were inhibited in ATP7A mutant mice with reduced Cu transporter function. In summary, IQGAP1 functions as ATP7A and Rac1 binding scaffolding protein to organize PDGF-dependent ATP7A translocation to the lamellipodial leading edge, thereby promoting VSMC migration and vascular remodeling.

Lysyl oxidase (LOX) limits VSMC proliferation and neointimal thickening through its extracellular enzymatic activity

Lysyl oxidase (LOX) plays a critical role in extracellular matrix maturation and limits VSMC proliferation and vascular remodeling. We have investigated whether this anti-proliferative effect relies on the extracellular catalytically active LOX or on its biologically active propeptide (LOX-PP). High expression levels of both LOX and LOX-PP were detected in the vascular wall from transgenic mice over-expressing the full-length human LOX cDNA under the control of SM22α promoter (TgLOX), which targets the transgene to VSMC without affecting the expression of mouse LOX isoenzymes. TgLOX VSMC also secrete high amounts of both mature LOX and LOX-PP. Wild-type (WT) mouse VSMC exposed to VSMC supernatants from transgenic animals showed reduced proliferative rates (low [³H]-thymidine uptake and expression of PCNA) than those incubated with conditioned media from WT cells, effect that was abrogated by β-aminopropionitrile (BAPN), an inhibitor of LOX activity. Lentiviral over-expression of LOX, but not LOX-PP, decreased human VSMC proliferation, effect that was also prevented by BAPN. LOX transgenesis neither impacted local nor systemic inflammatory response induced by carotid artery ligation. Interestingly, in this model, BAPN normalized the reduced neointimal thickening observed in TgLOX mice. Therefore, extracellular enzymatically active LOX is required to limit both VSMC proliferation and vascular remodeling.

Tropoelastin: A novel marker for plaque progression and instability

Background

Elastolysis and ineffective elastogenesis favor the accumulation of tropoelastin, rather than cross-linked elastin, in atherosclerotic plaques. We developed gadolinium-labeled tropoelastin-specific magnetic resonance contrast agents (Gd-TESMAs) for tropoelastin imaging in animal models.

Methods and Results

Two peptides, VVGSPSAQDEASPLS and YPDHVQYTHY were selected to target tropoelastin. In vitro binding, relaxivity, and biodistribution experiments enabled characterization of the probes and selecting the best candidate for in vivo MRI. MRI was performed in atherosclerotic apolipoprotein E-deficient (ApoE^-/-) mice and New Zealand white rabbits with stable and rupture-prone plaques using Gd-TESMA. Additionally, human carotid endarterectomy specimens were imaged ex vivo. The VVGSPSAQDEASPLS-based probe discriminated between tropoelastin and cross-linked elastin (64±7% vs 1±2%, P=0.001), had high in vitro relaxivity in solution (r_1-free=11.7±0.6mM^-1s^-1, r_{1-bound to tropoelastin} = 44±1mM^-1s^-1) and favorable pharmacokinetics. In vivo mice vascular enhancement (4wks=0.13±0.007mm², 8wks=0.22±0.01mm², 12wks=0.33±0.01mm², P<0.001) and R₁ relaxation rate (4wks=0.90±0.01 s^-1, 8wks=1.40±0.03 s^-1, 12wks=1.87±0.04s^-1, P<0.001) increased with atherosclerosis progression after Gd-TESMA injection. Conversely, statin-treated (0.13±0.01mm², R₁ =1.37±0.03s^-1) and control (0.10±0.005mm², R₁ =0.87±0.05s^-1) mice showed less enhancement. Rupture-prone rabbit plaques had higher R₁ relaxation rate compared with stale plaques (R₁=2.26±0.1s^-1vs R₁=1.43±0.02s^-1, P=0.001), after administration of Gd-TESMA that allowed detection of rupture-prone plaques with high sensitivity (84.4%) and specificity (92.3%). Increased vascular R₁ relaxation rate was observed in carotid endarterectomy plaques after soaking (R_1pre= 1.1±0.26 s^-1 vs R_1post= 3.0±0.1s^-1, P=0.01). Ex vivo analyses confirmed the MRI findings and showed uptake of the contrast agent to be specific for tropoelastin.

Conclusions

MRI of tropoelastin provides a novel biomarker for atherosclerotic plaque progression and instability.

Immunological challenges associated with artificial skin grafts: available solutions and stem cells in future design of synthetic skin

The repair or replacement of damaged skins is still an important, challenging public health problem. Immune acceptance and long-term survival of skin grafts represent the major problem to overcome in grafting given that in most situations autografts cannot be used. The emergence of artificial skin substitutes provides alternative treatment with the capacity to reduce the dependency on the increasing demand of cadaver skin grafts. Over the years, considerable research efforts have focused on strategies for skin repair or permanent skin graft transplantations. Available skin substitutes include pre- or post-transplantation treatments of donor cells, stem cell-based therapies, and skin equivalents composed of bio-engineered acellular or cellular skin substitutes. However, skin substitutes are still prone to immunological rejection, and as such, there is currently no skin substitute available to overcome this phenomenon. This review focuses on the mechanisms of skin rejection and tolerance induction and outlines in detail current available strategies and alternatives that may allow achieving full-thickness skin replacement and repair.

Can thrombus age guide thrombolytic therapy?

Venous thrombosis (VT) is a common yet complex clinical condition that has shown minimal alteration in clinical management for decades. It is well known that thrombus evolves structurally over time, with complex changes resulting from the interplay between coagulation factors, cytokines, leukocytes and a myriad of other factors. Our current treatment options are most effective in the acute thrombus, which is composed predominantly of a loose mesh of fibrin and red blood cells (RBCs), making current anticoagulation therapies and thrombolytics quite effective in treatment. Later stages of thrombus are more cellular containing leukocytes, and develop a fibrotic collagenous framework that is more resistant to our current treatments. Understanding the biology of an evolving thrombus will allow us to tailor our treatment and optimize outcomes, as well as focus on novel therapies for the treatment of chronic thrombus. Given the morbidity and mortality of both post thrombotic syndrome (PTS) in patients with deep VT, as well as chronic thromboembolic pulmonary hypertension (CTEPH) in patients with pulmonary embolism (PE), new and innovative therapies must continue to be explored to help prevent these potentially devastating conditions.

Human hepatocyte growth factor inhibits early neointima formation in rabbit abdominal aortae following ultrasound-guided balloon injury

The present study investigated the effects of in vivo gene transfer of human hepatocyte growth factor (hHGF) on neointima formation in rabbit abdominal aortae following ultrasound‑guided balloon injury. New Zealand white rabbits were randomly divided into four groups: endothelium injury alone (EI), endothelium injury with control vector transfection (EI‑V), endothelium injury with hHGF transfection (EI‑HGF), and hHGF transfection alone without endothelium injury (HGF). Endothelial injury was established by scraping the abdominal aortic wall using a balloon catheter under the guidance of a transabdominal ultrasound. hHGF gene transfer was performed 7 days following injury. hHGF mRNA and protein expression levels were determined at 3, 7, 14 and 21 days following transfection. Neointima formation was assessed by histopathological analysis at 14 and 28 days following injury. hHGF mRNA and protein expression levels were detected in the target abdominal aortae in EI‑HGF and HGF groups with the greatest levels observed 3 days following transfection, and their levels dropped below detection limits at 21 days following transfection. hHGF was not detectable in the EI and EI‑V groups throughout the experiment. The neointimal area and the neointima to media ratio in the EI‑HGF group were significantly decreased compared with those in the EI or EI‑V group at 14 days following injury. However, no differences were observed at 28 days following injury. The present study demonstrated that in vivo hHGF gene transfer inhibits the early formation of neointima in balloon‑injured rabbit abdominal aortae.

Molecular imaging of the extracellular matrix in the context of atherosclerosis

This review summarizes the current status of molecular imaging of the extracellular matrix (ECM) in the context of atherosclerosis. Apart from cellular components, the ECM of the atherosclerotic plaque plays a relevant role during the initiation of atherosclerosis and its' subsequent progression. Important structural and signaling components of the ECM include elastin, collagen and fibrin. However, the ECM not only plays a structural role in the arterial wall but also interacts with different cell types and has important biological signaling functions. Molecular imaging of the ECM has emerged as a new diagnostic tool to characterize biological aspects of atherosclerotic plaques, which cannot be characterized by current clinically established imaging techniques, such as X-ray angiography. Different types of molecular probes can be detected in vivo by imaging modalities such as magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT). The modality specific signaling component of the molecular probe provides information about its spatial location and local concentration. The successful introduction of molecular imaging into clinical practice and guidelines could open new pathways for an earlier detection of disease processes and a better understanding of the disease state on a biological level. Quantitative in vivo molecular parameters could also contribute to the development and evaluation of novel cardiovascular therapeutic interventions and the assessment of response to treatment.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Suppression of Phosphatidylinositol 3-Kinase/Akt Signaling Attenuates Hypoxia-Induced Pulmonary Hypertension Through the Downregulation of Lysyl Oxidase

Lysyl oxidase (LOX) is a copper-dependent enzyme that catalyzes covalent cross-linking of collagen. In response to hypoxia, phosphatidylinositol 3-kinase (PI3K) pathway is activated and contributes to pulmonary arterial hypertension (PAH). However, potential role of LOX in hypoxia-induced PAH is poorly understood. In this study, we explored the mechanism responsible for the development of hypoxia-induced PAH. Potent inhibitors of PI3K/Akt and LOX, wortmannin and β-aminopropionitrile (β-APN), were administrated in rat model of hypoxia-induced PAH. The cross-linking of collagen was assessed by the determination of hydroxyproline. LOX, LOXL-1, LOXL-2, LOXL-3, LOXL-4, Akt, and phospho-Akt expression was detected by real-time polymerase chain reaction and western blot analysis. We observed that collagen cross-linking and LOX activity were elevated in hypoxia-exposed rat lung tissue, but these effects were reversed by β-APN and wortmannin. In addition, exposure to hypoxia enhanced mRNA and protein expression and activity of LOX and LOXL-1 in a PI3K/Akt-dependent manner and induced the development of PAH. After the administration of wortmannin, the upregulation of LOX and cross-linking of collagen were significantly reversed in hypoxia-exposed rat pulmonary artery tissue. Taken together, the present study demonstrated that the upregulation of LOX expression and collagen cross-linking is PI3K/Akt dependent in rat with hypoxia-induced PAH. Suppression of PI3K/Akt pathway may alleviate hypoxia-induced PAH through the downregulation of LOX.

The lysyl oxidase inhibitor β-aminopropionitrile reduces body weight gain and improves the metabolic profile in diet-induced obesity in rats

Extracellular matrix (ECM) remodelling of the adipose tissue plays a pivotal role in the pathophysiology of obesity. The lysyl oxidase (LOX) family of amine oxidases, including LOX and LOX-like (LOXL) isoenzymes, controls ECM maturation, and upregulation of LOX activity is essential in fibrosis; however, its involvement in adipose tissue dysfunction in obesity is unclear. In this study, we observed that LOX is the main isoenzyme expressed in human adipose tissue and that its expression is strongly upregulated in samples from obese individuals that had been referred to bariatric surgery. LOX expression was also induced in the adipose tissue from male Wistar rats fed a high-fat diet (HFD). Interestingly, treatment with β-aminopropionitrile (BAPN), a specific and irreversible inhibitor of LOX activity, attenuated the increase in body weight and fat mass that was observed in obese animals and shifted adipocyte size toward smaller adipocytes. BAPN also ameliorated the increase in collagen content that was observed in adipose tissue from obese animals and improved several metabolic parameters – it ameliorated glucose and insulin levels, decreased homeostasis model assessment (HOMA) index and reduced plasma triglyceride levels. Furthermore, in white adipose tissue from obese animals, BAPN prevented the downregulation of adiponectin and glucose transporter 4 (GLUT4), as well as the increase in suppressor of cytokine signaling 3 (SOCS3) and dipeptidyl peptidase 4 (DPP4) levels, triggered by the HFD. Likewise, in the TNFα-induced insulin-resistant 3T3-L1 adipocyte model, BAPN prevented the downregulation of adiponectin and GLUT4 and the increase in SOCS3 levels, and consequently normalised insulin-stimulated glucose uptake. Therefore, our data provide evidence that LOX plays a pathologically relevant role in the metabolic dysfunction induced by obesity and emphasise the interest of novel pharmacological interventions that target adipose tissue fibrosis and LOX activity for the clinical management of this disease.

Highlighted Article: Lysyl oxidase (LOX) could play a role in the metabolic dysfunction induced by obesity, and consequently the inhibition of LOX activity could be a valuable strategy to ameliorate obesity-related metabolic disturbances.

A novel photochemical cross-linking technology to improve luminal gain, vessel compliance, and buckling post-angioplasty in porcine arteries

Development of substituted 1,8-naphthalimides for photochemical cross-linking of biomolecules is the focus of this research. This study describes limited cross-linking of collagen in the artery wall to control recoil and buckling in arteries following balloon angioplasty. Isolated porcine arteries were overstretched (25%) with balloon angioplasty (BA) +/- light-activated naphthalimide treatment (NVS). Lumen size and recoil were measured as retention of stretch after angioplasty. Cross-sectional compliance and distensibility coefficients were measured as slope of cross-sectional area versus increasing hydrostatic pressure. Buckling was measured, with 30% axial pre-stretch and 200 mmHg, as deviation from the center line. Electron microscopy evaluation of collagen fibers was conducted.

RESULTS

Uninjured arteries have low compliance and low levels of buckling, whereas the BA-injured arteries demonstrated much greater compliance and buckling behavior. Treatment of the injured artery with NVS reduced buckling and demonstrated compliance midway between the two groups while retaining the increased luminal diameter imparted by angioplasty compared to untreated vessels. In summary, limited collagen cross-linking with NVS treatment resulted in lumen retention, as well as improved compliance without the accompanying rigidity and stiffness of conventional stent therapy or current cross-linking materials. This treatment shows great promise for dilation, repair and strengthening of arteries damaged by injury or vascular disease.

Vascular wall extracellular matrix proteins and vascular diseases

Extracellular matrix proteins form the basic structure of blood vessels. Along with providing basic structural support to blood vessels, matrix proteins interact with different sets of vascular cells via cell surface integrin or non-integrin receptors. Such interactions induce vascular cell de novo synthesis of new matrix proteins during blood vessel development or remodeling. Under pathological conditions, vascular matrix proteins undergo proteolytic processing, yielding bioactive fragments to influence vascular wall matrix remodeling. Vascular cells also produce alternatively spliced variants that induce vascular cell production of different matrix proteins to interrupt matrix homeostasis, leading to increased blood vessel stiffness; vascular cell migration, proliferation, or death; or vascular wall leakage and rupture. Destruction of vascular matrix proteins leads to vascular cell or blood-borne leukocyte accumulation, proliferation, and neointima formation within the vascular wall; blood vessels prone to uncontrolled enlargement during blood flow diastole; tortuous vein development; and neovascularization from existing pathological tissue microvessels. Here we summarize discoveries related to blood vessel matrix proteins within the past decade from basic and clinical studies in humans and animals - from expression to cross-linking, assembly, and degradation under physiological and vascular pathological conditions, including atherosclerosis, aortic aneurysms, varicose veins, and hypertension.

Lysyl oxidase (LOX) in vascular remodelling. Insight from a new animal model

Lysyl oxidase (LOX) is an extracellular matrix-modifying enzyme that seems to play a critical role in vascular remodelling. However, the lack of viable LOX-deficient animal models has been an obstacle to deep in LOX biology. In this study we have developed a transgenic mouse model that over-expresses LOX in vascular smooth muscle cells (VSMC) to clarify whether LOX could regulate VSMC phenotype and vascular remodelling. The SM22α proximal promoter drove the expression of a transgene containing the human LOX cDNA. Two stable transgenic lines, phenotypically indistinguishable, were generated by conventional methods (TgLOX). Transgene expression followed the expected SMC-specific pattern. In TgLOX mice, real-time PCR and immunohistochemistry evidenced a strong expression of LOX in the media from aorta and carotid arteries, coincident with a higher proportion of mature collagen. VSMC isolated from TgLOX mice expressed high levels of LOX pro-enzyme, which was properly secreted and processed into mature and bioactive LOX. Interestingly, cell proliferation was significantly reduced in cells from TgLOX mice. Transgenic VSMC also exhibited low levels of Myh10 (marker of SMC phenotypic switching), PCNA (marker of cell proliferation) and MCP-1, and a weak activation of Akt and ERK1/2 in response to mitogenic stimuli. Accordingly, neointimal thickening induced by carotid artery ligation was attenuated in TgLOX mice that also displayed a reduction in PCNA and MCP-1 immunostaining. Our results give evidence that LOX plays a critical role in vascular remodelling. We have developed a new animal model to study the role of LOX in vascular biology.

Molecular MRI of atherosclerosis

Despite advances in prevention, risk assessment and treatment, coronary artery disease (CAD) remains the leading cause of morbidity and mortality in Western countries. The lion's share is due to acute coronary syndromes (ACS), which are predominantly triggered by plaque rupture or erosion and subsequent coronary thrombosis. As the majority of vulnerable plaques does not cause a significant stenosis, due to expansive remodeling, and are rather defined by their composition and biological activity, detection of vulnerable plaques with x-ray angiography has shown little success. Non-invasive vulnerable plaque detection by identifying biological features that have been associated with plaque progression, destabilization and rupture may therefore be more appropriate and may allow earlier detection, more aggressive treatment and monitoring of treatment response. MR molecular imaging with target specific molecular probes has shown great promise for the noninvasive in vivo visualization of biological processes at the molecular and cellular level in animals and humans. Compared to other imaging modalities; MRI can provide excellent spatial resolution; high soft tissue contrast and has the ability to simultaneously image anatomy; function as well as biological tissue composition and activity.

Cardiovascular protection by ApoE and ApoE-HDL linked to suppression of ECM gene expression and arterial stiffening

Arterial stiffening is a risk factor for cardiovascular disease, but how arteries stay supple is unknown. Here, we show that apolipoprotein E (apoE) and apoE-containing high-density lipoprotein (apoE-HDL) maintain arterial elasticity by suppressing the expression of extracellular matrix genes. ApoE interrupts a mechanically driven feed-forward loop that increases the expression of collagen-I, fibronectin, and lysyl oxidase in response to substratum stiffening. These effects are independent of the apoE lipid-binding domain and transduced by Cox2 and miR-145. Arterial stiffness is increased in apoE null mice. This stiffening can be reduced by administration of the lysyl oxidase inhibitor BAPN, and BAPN treatment attenuates atherosclerosis despite highly elevated cholesterol. Macrophage abundance in lesions is reduced by BAPN in vivo, and monocyte/macrophage adhesion is reduced by substratum softening in vitro. We conclude that apoE and apoE-containing HDL promote healthy arterial biomechanics and that this confers protection from cardiovascular disease independent of the established apoE-HDL effect on cholesterol.

Three-dimensional imaging of the aortic vessel wall using an elastin-specific magnetic resonance contrast agent

OBJECTIVE

The aim of this study was to demonstrate the feasibility of high-resolution 3-dimensional aortic vessel wall imaging using a novel elastin-specific magnetic resonance contrast agent (ESMA) in a large animal model.

MATERIALS AND METHODS

The thoracic aortic vessel wall of 6 Landrace pigs was imaged using a novel ESMA and a nonspecific control agent. On day 1, imaging was performed before and after the administration of a nonspecific control agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA; Bayer Schering AG, Berlin, Germany). On day 3, identical scans were repeated before and after the administration of a novel ESMA (Lantheus Medical Imaging, North Billerica, Massachusetts). Three-dimensional inversion recovery gradient echo delayed-enhancement imaging and magnetic resonance (MR) angiography of the thoracic aortic vessel wall were performed on a 1.5-T MR scanner (Achieva; Philips Medical Systems, the Netherlands). The signal-to-noise ratio and the contrast-to-noise ratio of arterial wall enhancement, including the time course of enhancement, were assessed for ESMA and Gd-DTPA. After the completion of imaging sessions, histology, electron microscopy, and inductively coupled plasma mass spectroscopy were performed to localize and quantify the gadolinium bound to the arterial vessel wall.

RESULTS

Administration of ESMA resulted in a strong enhancement of the aortic vessel wall on delayed-enhancement imaging, whereas no significant enhancement could be measured with Gd-DTPA. Ninety to 100 minutes after the administration of ESMA, significantly higher signal-to-noise ratio and contrast-to-noise ratio could be measured compared with the administration of Gd-DTPA (45.7 ± 9.6 vs 13.2 ± 3.5, P < 0.05 and 41.9 ± 9.1 vs 5.2 ± 2.0, P < 0.05). A significant correlation (0.96; P < 0.01) between area measurements derived from ESMA scans and aortic MR angiography scans could be found. Electron microscopy and inductively coupled plasma mass spectroscopy confirmed the colocalization of ESMA with elastic fibers.

CONCLUSION

We demonstrate the feasibility of aortic vessel wall imaging using a novel ESMA in a large animal model under conditions resembling a clinical setting. Such an approach could be useful for the fast 3-dimensional assessment of the arterial vessel wall in the context of atherosclerosis, aortic aneurysms, and hypertension.

Mechanisms of post-intervention arterial remodelling

It has been appreciated over the past two decades that arterial remodelling, in addition to intimal hyperplasia, contributes significantly to the degree of restenosis that develops following revascularization procedures. Remodelling appears to be an adventitia-based process that is contributed to by multiple factors including cytokines and growth factors that regulate extracellular matrix or phenotypic transformation of vascular cells including myofibroblasts. In this review, we summarize the currently available information from animal models as well as clinical investigations regarding arterial remodelling. The factors that contribute to this process are presented with an emphasis on potential therapeutic methods to enhance favourable remodelling and prevent restenosis.

Intrauterine growth restriction promotes vascular remodelling following carotid artery ligation in rats

Epidemiological studies revealed an association between IUGR (intrauterine growth restriction) and an increased risk of developing CVDs (cardiovascular diseases), such as atherosclerosis or hypertension, in later life. Whether or not IUGR contributes to the development of atherosclerotic lesions, however, is unclear. We tested the hypothesis that IUGR aggravates experimentally induced vascular remodelling. IUGR was induced in rats by maternal protein restriction during pregnancy (8% protein diet). To detect possible differences in the development of vascular injury, a model of carotid artery ligation to induce vascular remodelling was applied in 8-week-old intrauterine-growth-restricted and control rat offspring. Histological and immunohistochemical analyses were performed in the ligated and non-ligated carotid arteries 8 weeks after ligation. IUGR alone neither caused overt histological changes nor significant dedifferentiation of VSMCs (vascular smooth muscle cells). After carotid artery ligation, however, neointima formation, media thickness and media/lumen ratio were significantly increased in rats after IUGR compared with controls. Moreover, dedifferentiation of VSMCs and collagen deposition in the media were more prominent in ligated carotids from rats after IUGR compared with ligated carotids from control rats. We conclude that IUGR aggravates atherosclerotic vascular remodelling induced by a second injury later in life.

Transfer of bone-marrow-derived mesenchymal stem cells influences vascular remodeling and calcification after balloon injury in hyperlipidemic rats

Bone-marrow-derived mesenchymal stem cells (BM-MSCs) were found to markedly increase atherosclerotic lesion size. The aim of this paper was to investigate whether BM-MSCs contribute to vascular remodeling and calcification after balloon injury in hyperlipidemic rats. Labeled BM-MSCs were found in the lesion of hyperlipidemic rats after balloon injury. Comparing injury group, transferred BM-MSCs significantly triggered vascular negative remodeling, characterized by the changes of remodeling index (0.628 ± 0.0293 versus 0.544 ± 0.0217), neointimal area (0.078 ± 0.015 mm² versus 0.098 ± 0.019 mm²), PCNA index (23.91 ± 6.59% versus 43.11 ± 5.31%), and percentage of stenosis (18.20 ± 1.09% versus 30.58 ± 1.21%). Apparent vascular calcification was detected in medial layers at 6 weeks after balloon angioplasty, which may be associated with upregulation of bone morphogenetic protein-2 (BMP-2). Our data indicated that unselected BM-MSCs transfer may induce vascular remodeling and calcification after balloon injury in hyperlipidemic rats.

Value of MR contrast media in image-guided body interventions

In the past few years, there have been multiple advances in magnetic resonance (MR) instrumentation, in vivo devices, real-time imaging sequences and interventional procedures with new therapies. More recently, interventionists have started to use minimally invasive image-guided procedures and local therapies, which reduce the pain from conventional surgery and increase drug effectiveness, respectively. Local therapy also reduces the systemic dose and eliminates the toxic side effects of some drugs to other organs. The success of MR-guided procedures depends on visualization of the targets in 3D and precise deployment of ablation catheters, local therapies and devices. MR contrast media provide a wealth of tissue contrast and allows 3D and 4D image acquisitions. After the development of fast imaging sequences, the clinical applications of MR contrast media have been substantially expanded to include pre- during- and post-interventions. Prior to intervention, MR contrast media have the potential to localize and delineate pathologic tissues of vital organs, such as the brain, heart, breast, kidney, prostate, liver and uterus. They also offer other options such as labeling therapeutic agents or cells. During intervention, these agents have the capability to map blood vessels and enhance the contrast between the endovascular guidewire/catheters/devices, blood and tissues as well as direct therapies to the target. Furthermore, labeling therapeutic agents or cells aids in visualizing their delivery sites and tracking their tissue distribution. After intervention, MR contrast media have been used for assessing the efficacy of ablation and therapies. It should be noted that most image-guided procedures are under preclinical research and development. It can be concluded that MR contrast media have great value in preclinical and some clinical interventional procedures. Future applications of MR contrast media in image-guided procedures depend on their safety, tolerability, tissue specificity and effectiveness in demonstrating success of the interventions and therapies.

The effect of maternal hypercholesterolemia on the placenta and fetal arteries in rabbits

PURPOSE: To investigate the degree of placental permeability in dyslipidemic rabbits and the consequent vascular dysfunction in fetuses of female rabbits with high lipoprotein levels. METHODS: Fifteen adult females New Zealand White rabbits were divided into two groups. Group 1(n=5) - hypercholesterolemic diet with 0.5% cholesterol, and Group 2 (n=10) - control. On day 30, the levels of plasma lipoproteins and triglycerides were analyzed in the mothers, and the presence of collagen was analyzed in the placenta as well as in fetal coronary and aorta. Statistical analyses used the Student's t and the Mann-Whitney tests. RESULTS: Lipoprotein levels were significantly different (p=0.02 to p<0.001) in experimental and control groups. In the hypercholesterolemic group, total cholesterol levels were in average 793mg/dl; triglycerides were in average 257mg/dl; HDL-C was 48mg/dl, and LDL-C was in average 692mg/dl. The amount of collagen per micrometers square (mµ²) in samples from hypercholesterolemic animals was significantly higher than in the control group. CONCLUSIONS: The study confirmed placental permeability to lipoproteins, shown by increased amounts of collagen in fetal tissues. This alteration results in increased susceptibility to atherosclerosis in adult life, representing a risk factor for the early development of disease, which may appear even in the prenatal period.

Detection of altered extracellular matrix in surface layers of unstable carotid plaque: an optical spectroscopy, birefringence and microarray genetic analysis

Erosion and rupture of surface layers in atherosclerotic plaque can cause heart attack and stroke; however, changes in luminal surface composition are incompletely defined. Laser-induced fluorescence spectroscopy (LIFS), with limited tissue penetration, was used to investigate the surface of unstable carotid plaque and correlated with microscopy, birefringence and gene expression. Arterial matrix collagens I, III and elastin were assessed in unstable plaques (n = 25) and reference left internal mammary arteries (LIMA, n = 10). LIFS in addition to selective histological staining with picrosirius red, Movat pentachrome and immunostaining revealed decreased elastin and increased collagen I and III (P < 0.05) in carotid plaque when compared with LIMA. Within plaque, collagen I was elevated in the internal carotid region versus the common carotid region. Polarized light microscopy detected layers of aligned collagen and associated mechanical rigidity of the fibrous cap. Microarray analysis of three carotid and three LIMA specimens confirmed up-regulation of collagen I, III and IV, lysyl oxidase and MMP-12. In conclusion, LIFS analysis coupled with microscopy revealed marked regional differences in collagen I, III and elastin in surface layers of carotid plaque; indicative of plaque instability. Birefringence measurements demonstrated mechanical rigidity and weakening of the fibrous cap with complementary changes in ECM gene expression.

MRI of coronary wall remodeling in a swine model of coronary injury using an elastin-binding contrast agent

BACKGROUND

The extracellular matrix (ECM) plays an important role in the pathogenesis of atherosclerosis and in-stent restenosis. Elastin is an essential component of the ECM. ECM degradation can lead to plaque destabilization, whereas enhanced synthesis typically leads to vessel wall remodeling resulting in arterial stenosis or in-stent restenosis after stent implantation. The objective of this study was to demonstrate the feasibility of MRI of vascular remodeling using a novel elastin-binding contrast agent (BMS-753951).

METHODS AND RESULTS

Coronary injury was induced in 6 pigs by endothelial denudation and stent placement. At day 28, delayed-enhancement MRI coronary vessel wall imaging was performed before and after injection of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA). Two days later, DE-MRI was repeated after administration of BMS-753951. Contrast-to-noise-ratio and areas of enhancement were determined. Delayed-enhancement MRI with BMS-753951 caused strong enhancement of the aortic, pulmonary artery, and injured coronary artery walls, whereas Gd-DTPA did not. Delayed-enhancement MRI of the stented coronary artery with BMS-753951 yielded a 3-fold higher contrast-to-noise-ratio when compared with the balloon-injured and control coronary artery (21±6 versus 7±3 versus 6±4; P<0.001). The area of enhancement correlated well with the area of remodeling obtained from histological data (R(2)=0.86, P<0.05).

CONCLUSIONS

We demonstrate the noninvasive detection and quantification of vascular remodeling in an animal model of coronary vessel wall injury using an elastin-specific MR contrast agent. This novel approach may be useful for the assessment of coronary vessel wall remodeling in patients with suspected coronary artery disease. Further studies in atherosclerotic animal models and degenerative ECM disease are now warranted.

Assessment of atherosclerotic plaque burden with an elastin-specific magnetic resonance contrast agent

Atherosclerosis and its consequences remain the main cause of mortality in industrialized and developing nations. Plaque burden and progression have been shown to be independent predictors for future cardiac events by intravascular ultrasound. Routine prospective imaging is hampered by the invasive nature of intravascular ultrasound. A noninvasive technique would therefore be more suitable for screening of atherosclerosis in large populations. Here we introduce an elastin-specific magnetic resonance contrast agent (ESMA) for noninvasive quantification of plaque burden in a mouse model of atherosclerosis. The strong signal provided by ESMA allows for imaging with high spatial resolution, resulting in accurate assessment of plaque burden. Additionally, plaque characterization by quantifying intraplaque elastin content using signal intensity measurements is possible. Changes in elastin content and the high abundance of elastin during plaque development, in combination with the imaging properties of ESMA, provide potential for noninvasive assessment of plaque burden by molecular magnetic resonance imaging (MRI).

Characterization of vascular strain during in-vitro angioplasty with high-resolution ultrasound speckle tracking

Background

Ultrasound elasticity imaging provides biomechanical and elastic properties of vascular tissue, with the potential to distinguish between tissue motion and tissue strain. To validate the ability of ultrasound elasticity imaging to predict structurally defined physical changes in tissue, strain measurement patterns during angioplasty in four bovine carotid artery pathology samples were compared to the measured physical characteristics of the tissue specimens.

Methods

Using computational image-processing techniques, the circumferences of each bovine artery specimen were obtained from ultrasound and pathologic data.

Results

Ultrasound-strain-based and pathology-based arterial circumference measurements were correlated with an R² value of 0.94 (p = 0.03). The experimental elasticity imaging results confirmed the onset of deformation of an angioplasty procedure by indicating a consistent inflection point where vessel fibers were fully unfolded and vessel wall strain initiated.

Conclusion

These results validate the ability of ultrasound elasticity imaging to measure localized mechanical changes in vascular tissue.

Unexpected role of the copper transporter ATP7A in PDGF-induced vascular smooth muscle cell migration

RATIONALE

Copper, an essential nutrient, has been implicated in vascular remodeling and atherosclerosis with unknown mechanism. Bioavailability of intracellular copper is regulated not only by the copper importer CTR1 (copper transporter 1) but also by the copper exporter ATP7A (Menkes ATPase), whose function is achieved through copper-dependent translocation from trans-Golgi network (TGN). Platelet-derived growth factor (PDGF) promotes vascular smooth muscle cell (VSMC) migration, a key component of neointimal formation.

OBJECTIVE

To determine the role of copper transporter ATP7A in PDGF-induced VSMC migration.

METHODS AND RESULTS

Depletion of ATP7A inhibited VSMC migration in response to PDGF or wound scratch in a CTR1/copper-dependent manner. PDGF stimulation promoted ATP7A translocation from the TGN to lipid rafts, which localized at the leading edge, where it colocalized with PDGF receptor and Rac1, in migrating VSMCs. Mechanistically, ATP7A small interfering RNA or CTR small interfering RNA prevented PDGF-induced Rac1 translocation to the leading edge, thereby inhibiting lamellipodia formation. In addition, ATP7A depletion prevented a PDGF-induced decrease in copper level and secretory copper enzyme precursor prolysyl oxidase (Pro-LOX) in lipid raft fraction, as well as PDGF-induced increase in LOX activity. In vivo, ATP7A expression was markedly increased and copper accumulation was observed by synchrotron-based x-ray fluorescence microscopy at neointimal VSMCs in wire injury model.

CONCLUSIONS

These findings suggest that ATP7A plays an important role in copper-dependent PDGF-stimulated VSMC migration via recruiting Rac1 to lipid rafts at the leading edge, as well as regulating LOX activity. This may contribute to neointimal formation after vascular injury. Our findings provide insight into ATP7A as a novel therapeutic target for vascular remodeling and atherosclerosis.

Arterial gene transfer of the TGF-beta signalling protein Smad3 induces adaptive remodelling following angioplasty: a role for CTGF

AIMS

Although transforming growth factor-beta (TGF-beta) is believed to stimulate intimal hyperplasia after arterial injury, its role in remodelling remains unclear. We investigate whether Smad3, a TGF-beta signalling protein, might facilitate its effect on remodelling.

METHODS AND RESULTS

Using the rat carotid angioplasty model, we assess Smad3 expression following arterial injury. We then test the effect of arterial Smad3 overexpression on the response to injury, and use a conditioned media experimental design to confirm an Smad3-dependent soluble factor that mediates this response. We use small interfering RNA (siRNA) to identify this factor as connective tissue growth factor (CTGF). Finally, we attempt to replicate the effect of medial Smad3 overexpression through adventitial application of recombinant CTGF. Injury induced medial expression of Smad3; overexpression of Smad3 caused neointimal thickening and luminal expansion, suggesting adaptive remodelling. Smad3 overexpression, though exclusively medial, caused adventitial changes: myofibroblast transformation, proliferation, and collagen production, all of which are associated with adaptive remodelling. Supporting the hypothesis that Smad3 initiated remodelling and these adventitial changes via a secreted product of medial smooth muscle cells (SMCs), we found that media conditioned by Smad3-expressing recombinant adenoviral vector (AdSmad3)-infected SMCs stimulated adventitial fibroblast transformation, proliferation, and collagen production in vitro. This effect was attenuated by pre-treatment of SMCs with siRNA specific for CTGF, abundantly produced by AdSmad3-infected SMCs, and significantly up-regulated in Smad3-overexpressing arteries. Moreover, periadventitial administration of CTGF replicated the effect of medial Smad3 overexpression on adaptive remodelling and neointimal hyperplasia.

CONCLUSION

Medial gene transfer of Smad3 promotes adaptive remodelling by indirectly influencing the behaviour of adventitial fibroblasts. This arterial cell-cell communication is likely to be mediated by Smad3-dependent production of CTGF.

Vascular remodeling in ApoE-deficient mice: diet dependent modulation after carotid ligation

Vascular remodeling is influenced by trauma and proatherogenic factors such as cholesterol. It has been shown that cholesterol exerts a direct effect on vessel wall structure. In this study we evaluated the effects of vascular trauma and cholesterol treatment on vascular remodeling and plaque integrity in carotid ligated ApoE-deficient mice. The right carotid artery was ligated in mice fed regular chow or cholesterol and fat containing diet. After 4 weeks left (non-ligated) and right (ligated) carotids were prepared. For studying vascular remodeling the vascular areas were evaluated morphometrically by calculating the areas from circumference measurements on Verhoff-van Gieson stains. The cellular and structural features of the plaque were analyzed by histological staining and immunohistochemistry. Under regular chow total vessel area decreased by 35% (p<0.001); cholesterol-rich diet led to an increase by 20% (p<0.05). In both feeding groups ligated carotids presented neointima development. The medial area increased only in mice fed regular chow. The luminal area was reduced by 80% (regular chow: p<0.001) and by 90% (cholesterol-rich diet: p<0.01). Regular chow led to structured plaques showing the typical features of stable plaques. Under cholesterol diet well defined plaque structures were missing. These lesions were characterized by numerous macrophages, few mostly PCNA positive smooth muscle cell (SMC) and less collagen particularly in the shoulder region. Our data indicate that in ApoE-deficient mice both direction of the remodeling response and lesion integrity are due to the diet applied: regular chow led to constrictive remodeling, whereas cholesterol and fat containing diet was associated with an adaptive response. Our data further indicate that the direction of response is not only related to the macrophage content but also to a proliferative intimal SMC-phenotype. Our data implicate that high serum cholesterol levels are not only inducers of plaque instability but also of the so far "positively recorded" compensatory remodeling.

Regulation of lysyl oxidase in vascular cells: lysyl oxidase as a new player in cardiovascular diseases

Lysyl oxidase (LOX) plays a crucial role in the maintenance of extracellular matrix stability and could participate in vascular remodelling associated with cardiovascular diseases. Evidence from in vitro and in vivo studies shows that LOX downregulation is associated with the endothelial dysfunction characteristic of earlier stages of the atherosclerotic process. Conversely, upregulation of this enzyme in vascular cells could induce neointimal thickening in atherosclerosis and restenosis. In fact, LOX is chemotactic for vascular smooth muscle cells and monocytes, is modulated by proliferative stimulus in these cells, and could control other cellular processes such as gene expression and cell transformation. Furthermore, it is conceivable that LOX downregulation could underlie plaque instability and contribute to the destructive remodelling that takes place during aneurysm development. Overall, LOX could play a key role in vascular homeostasis and, hence, it emerges as a new player in cardiovascular diseases. This review addresses the experimental evidence related to the role of LOX in vascular disorders and the potential benefits of controlling its expression and function.

Lysyl oxidase propeptide inhibits smooth muscle cell signaling and proliferation

Lysyl oxidase is required for the normal biosynthesis and maturation of collagen and elastin. It is expressed by vascular smooth muscle cells, and its increased expression has been previously found in atherosclerosis and in models of balloon angioplasty. The lysyl oxidase propeptide (LOX-PP) has more recently been found to have biological activity as a tumor suppressor, and it inhibits Erk1/2 Map kinase activation. We reasoned that LOX-PP may have functions in normal non-transformed cells. We, therefore, investigated its effects on smooth muscle cells, focusing on important biological processes mediated by Erk1/2-dependent signaling pathways including proliferation and matrix metalloproteinase-9 (MMP-9) expression. In addition, we investigated whether evidence for accumulation of LOX-PP could be found in vivo in a femoral artery injury model. Recombinant LOX-PP was expressed and purified, and was found to inhibit primary rat aorta smooth muscle cell proliferation and DNA synthesis by more than 50%. TNF-alpha-stimulated MMP-9 expression and Erk1/2 activation were both significantly inhibited by LOX-PP. Immunohistochemistry studies carried out with affinity purified anti-LOX-PP antibody showed that LOX-PP epitopes were expressed at elevated levels in vascular lesions of injured arteries. These novel data suggest that LOX-PP may provide a feedback control mechanism that serves to inhibit properties associated with the development of vascular pathology.

Genetic and molecular mechanisms of chemical atherogenesis

Injury to the cellular components of the vascular wall and blood by endogenous and exogenous chemicals has been associated with atherosclerosis in humans and experimental systems. The genetic and molecular mechanisms responsible for initiation and promotion of atherosclerotic changes include modulation of extracellular matrix-integrin axis, genes involved in the regulation of growth and differentiation and possibly, genomic stability. This review summarizes seminal studies over the past 20 years that shed light on critical gene-gene and gene-environment interactions mediating the atherogenic response to chemical injury.

Matrix metalloproteinases and atherogenesis in dependence of age

BACKGROUND

Changes in the proteoglycan metabolism of the intima of arteries belong to the initial lesions of atherosclerosis (AS). The accumulation of proteoglycans, alterations of pericellular glycoproteins and modulations of collagen turnover also play a fundamental role in the progression of AS. They influence lipid retention, cell behavior and calcinosis. The decisive role played by the matrix metalloproteinases (MMPs) and their inhibiting factors (tissue inhibitors of metalloproteinases [TIMPs]) in these processes is not yet fully understood and therefore the subject of this overview. The causes of the abrupt change of a long-term existing stabile AS to a vulnerable plaque as well as the participation of age-related vascular wall remodeling in the progression of AS also remain open questions.

DISCUSSION

Apart from the well-known risk factors for AS, less well-known influences like the disturbances of gene expression in vascular smooth muscle cells affect an MMP/TIMP imbalance. The various consequences of this imbalance range from intima cell proliferation as an early change in AS as well as accelerated progression to the destabilization of fibrous plaques by increased collagenolysis as well as the formation of aneurysms. Infectious or toxic influences may trigger these mechanisms; an involvement of age-related vessel wall changes should also be considered. The prognostic significance of circulating MMP concentrations for the existence of instabile plaques are of great interest, as is the plaque stabilizing effect of statins by suppression of MMPs.

CONCLUSIONS

MMPs navigate the behavior of vascular wall cells in different AS stages, in adaptive remodeling, in normal aging and in non-atherosclerotic vessel disease. The clinical relevance of a disturbance in the MMP/TIMP balance is demonstrated firstly by the initiation of AS due to migration and proliferation of intima cells and secondly in the collagenolysis, necrotic transformation and apoptosis of existing fibrous lesions resulting in instabile rupture proned plaques. Investigations into the genetic typing of MMPs and the results of experimental gene deficiency models have significantly contributed to the clarification of these facts.