Significance of quiescent smooth muscle migration in the injured rat carotid artery

Three-Dimensional Bioprinting in Vascular Tissue Engineering and Tissue Vascularization of Cardiovascular Diseases

In the 21st century, significant progress has been made in repairing damaged materials through material engineering. However, the creation of large-scale artificial materials still faces a major challenge in achieving proper vascularization. To address this issue, researchers have turned to biomaterials and three-dimensional (3D) bioprinting techniques, which allow for the combination of multiple biomaterials with improved mechanical and biological properties that mimic natural materials. Hydrogels, known for their ability to support living cells and biological components, have played a crucial role in this research. Among the recent developments, 3D bioprinting has emerged as a promising tool for constructing hybrid scaffolds. However, there are several challenges in the field of bioprinting, including the need for nanoscale biomimicry, the formulation of hydrogel blends, and the ongoing complexity of vascularizing biomaterials, which requires further research. On a positive note, 3D bioprinting offers a solution to the vascularization problem due to its precise spatial control, scalability, and reproducibility compared with traditional fabrication methods. This paper aims at examining the recent advancements in 3D bioprinting technology for creating blood vessels, vasculature, and vascularized materials. It provides a comprehensive overview of the progress made and discusses the limitations and challenges faced in current 3D bioprinting of vascularized tissues. In addition, the paper highlights the future research directions focusing on the development of 3D bioprinting techniques and bioinks for creating functional materials.

Tissue-Engineered Endothelial Cells Induce Sustained Vascular Healing Through Early Induction of Vascular Repair

Background

Perivascular implantation of tissue-engineered endothelial cells (TEEC) after vascular injury profoundly inhibits neointimal hyperplasia. However, the time course and mechanism by which this effect occurs remain unknown. By developing genetically modified TEEC that express a “suicide gene,” we can control the time during which the TEEC could exert their effect and determine the length of time TEEC need to be present following vascular injury to exert their inhibitory effect on long-term neointimal hyperplasia.

Methods

Bovine aortic endothelial cells (BAE) were transfected with the human herpes simplex virus thymidine kinase (tk) gene to render them sensitive to ganciclovir (GCV). These BAE+tk were grown to confluence on Gelfoam and shown to have the same growth kinetics and biologic potency as control cells but were sensitive to GCV at low concentrations. The BAE+tk were grown on Gelfoam and placed in the perivascular space around balloon-injured rat carotid arteries. Rats randomly received BAE-tk, BAE+tk, or nothing (control) after balloon injury. GCV was administered early (days 1–7), late (days 5–11), or not at all.

Results

Two weeks after injury, extensive neointimal hyperplasia was observed in control animals with an intima:media (I:M) area ratio of 0.80 ± 0.19. Early administration of GCV killed the BAE in constructs with TK sensitivity and eliminated the impact of TEEC regulation of intimal hyperplasia (0.45 ± 0.06). Intimal hyperplasia was still effectively reduced in animals with implants containing BAE-tk or BAE+tk which received GCV late (0.11 ± 0.04 and 0.19 ± 0.05). Immunohistochemistry demonstrated the lethal effect of GCV on TK-sensitive cells.

Conclusions

The application of perivascular TEEC for only the first few days after injury had a significant inhibitory effect on intimal hyperplasia. This is in contrast to the results obtained in this same animal model with the infusion of isolated anti-smooth muscle cell proliferative agents. This suggests that the mechanism of action of TEEC may be upstream from smooth muscle cell proliferation. Moreover, the use of this technique to further elucidate biologic mechanisms will prove invaluable in the tissue engineering field.

Lay Summary

We report a novel, genetically altered tissue-engineered endothelial cell (TEEC) implant that inhibits neointimal hyperplasia after experimental vascular injury. The viability of these implants can be carefully controlled and suggest a putative mechanism by which TEEC recapitulate control over the vascular response to injury.

Effect of Extracellular Vesicles From Multiple Cells on Vascular Smooth Muscle Cells in Atherosclerosis

Atherosclerosis (AS)-related diseases are still the main cause of death in clinical patients. The phenotype switching, proliferation, migration, and secretion of vascular smooth muscle cells (VSMCs) have a pivotal role in atherosclerosis. Although numerous research studies have elucidated the role of VSMCs in AS, their potential functional regulations continue to be explored. The formation of AS involves various cells, such as endothelial cells, smooth muscle cells, and macrophages. Therefore, intercellular communication of blood vessels cannot be ignored due to closely connected endothelia, media, and adventitia. Extracellular vesicles (EVs), as the vectors of cell-to-cell communication, can deliver proteins and nucleic acids of parent cells to the recipient cells. EVs have emerged as being central in intercellular communication and play a vital role in the pathophysiologic mechanisms of AS. This review summarizes the effects of extracellular vesicles (EVs) derived from multiple cells (endothelial cells, macrophages, mesenchymal stem cells, etc.) on VSMCs in AS. The key findings of this review are as follows: 1) endothelial cell–derived EVs (EEVs) have anti- or pro-atherogenic effects on VSMCs; 2) macrophage-derived EVs (MEVs) aggravate the proliferation and migration of VSMCs; 3) mesenchymal stem cells can inhibit VSMCs; and 4) the proliferation and migration of VSMCs can be inhibited by the treatment of EVs with atherosclerosis-protective factors and promoted by noxious stimulants. These results suggested that EVs have the same functional properties as treated parent cells, which might provide vital guidance for treating AS.

Elevated H3K4me3 Through MLL2-WDR82 upon Hyperglycemia Causes Jagged Ligand Dependent Notch Activation to Interplay with Differentiation State of Endothelial Cells

Endothelial-to-mesenchymal transition (EndMT) is a hallmark of diabetes-associated vascular complications. Epigenetic mechanisms emerged as one of the key pathways to regulate diabetes-associated complications. In the current study, we aimed to determine how abrupt changes in histone 3 lysine 4 tri-methylation (H3K4me3) upon hyperglycemia exposure reprograms endothelial cells to undergo EndMT. Through in vitro studies, we first establish that intermittent high-glucose exposure to EC most potently induced partial mesenchyme-like characteristics compared with transient or constant high-glucose-challenged endothelial cells. In addition, glomerular endothelial cells of BTBR Ob/Ob mice also exhibited mesenchymal-like characteristics. Intermittent hyperglycemia-dependent induction of partial mesenchyme-like phenotype of endothelial cells coincided with an increase in H3K4me3 level in both macro- and micro-vascular EC due to selective increase in MLL2 and WDR82 protein of SET1/COMPASS complex. Such an endothelial-specific heightened H3K4me3 level was also detected in intermittent high-glucose-exposed rat aorta and in kidney glomeruli of Ob/Ob mice. Elevated H3K4me3 enriched in the promoter regions of Notch ligands Jagged1 and Jagged2, thus causing abrupt expression of these ligands and concomitant activation of Notch signaling upon intermittent hyperglycemia challenge. Pharmacological inhibition and/or knockdown of MLL2 in cells in vitro or in tissues ex vivo normalized intermittent high-glucose-mediated increase in H3K4me3 level and further reversed Jagged1 and Jagged2 expression, Notch activation and further attenuated acquisition of partial mesenchyme-like phenotype of endothelial cells. In summary, the present study identifies a crucial role of histone methylation in hyperglycemia-dependent reprograming of endothelial cells to undergo mesenchymal transition and indicated that epigenetic pathways contribute to diabetes-associated vascular complications.

Emerging Concepts of Vascular Cell Clonal Expansion in Atherosclerosis

Clonal expansion is a process that can drive pathogenesis in human diseases, with atherosclerosis being a prominent example. Despite advances in understanding the etiology of atherosclerosis, clonality studies of vascular cells remain in an early stage. Recently, several paradigm-shifting preclinical studies have identified clonal expansion of progenitor cells in the vasculature in response to atherosclerosis. This review provides an overview of cell clonality in atherosclerotic progression, focusing particularly on smooth muscle cells and macrophages. We discuss key findings from the latest research that give insight into the mechanisms by which clonal expansion of vascular cells contributes to disease pathology. The further probing of these mechanisms will provide innovative directions for future progress in the understanding and therapy of atherosclerosis and its associated cardiovascular diseases.

17R/S-Benzo-RvD1, a synthetic resolvin D1 analogue, attenuates neointimal hyperplasia in a rat model of acute vascular injury

BACKGROUND

Persistent inflammation following vascular injury drives neointimal hyperplasia (NIH). Specialized lipid mediators (SPM) mediate resolution which attenuates inflammation and downstream NIH. We investigated the effects of a synthetic analogue of resolvin D1 (RvD1) on vascular cells and in a model of rat carotid angioplasty.

METHODS

Human venous VSMC and endothelial cells (EC) were employed in migration, cell shape, toxicity, proliferation and p65 nuclear translocation assays. Murine RAW 264.7 cells were utilized to test the effect of pro-resolving compounds on phagocytic activity. A model of rat carotid angioplasty was used to evaluate the effects of 17R/S-benzo-RvD1 (benzo-RvD1) and 17R-RvD1 applied to the adventitia via 25% Pluronic gel. Immunostaining was utilized to examine Ki67 expression and leukocyte recruitment. Morphometric analysis was performed on arteries harvested 14 days after injury.

RESULTS

Exposure to benzo-RvD1 attenuated PDGF- stimulated VSMC migration across a range of concentrations (0.1-100 nM), similar to that observed with 17R-RvD1. Pre-treatment with either Benzo-RvD1 or 17R-RvD1 (10, 100nM) attenuated PDGF-BB-induced VSMC cytoskeletal changes to nearly baseline dimensions. Benzo-RvD1 demonstrated modest anti-proliferative activity on VSMC and EC at various concentrations, without significant cytotoxicity. Benzo-RvD1 (10nM) inhibited p65 nuclear translocation in cytokine-stimulated EC by 21% (p<0.05), similar to 17R-RvD1. Consistent with pro-resolving activities of other SPM, both 17R-RvD1 and benzo-RvD1 increased the phagocytic activity of RAW 264.7 cells against S. Aureus and Zymosan particles. There were no significant differences in Ki-67 or CD45 staining observed on day 3 after angioplasty. Periadventitial treatment with benzo-RvD1 reduced carotid neointimal area at 14 days compared to control (0.08 mm2 v. 0.18 mm2; p<0.05), with similar efficacy to 17R-RvD1.

CONCLUSIONS

17R/S-benzo-RvD1 and 17R-RvD1 exhibit similar pro-resolving and anti-migratory activity in cell-based assays, and both compounds attenuated NIH following acute arterial injury in rats. Further studies of the mechanisms of resolution following vascular injury, and the translational potential of SPM analogues, are indicated.

Vascular Tissue Engineering: Challenges and Requirements for an Ideal Large Scale Blood Vessel

Since the emergence of regenerative medicine and tissue engineering more than half a century ago, one obstacle has persisted: the in vitro creation of large-scale vascular tissue (>1 cm³) to meet the clinical needs of viable tissue grafts but also for biological research applications. Considerable advancements in biofabrication have been made since Weinberg and Bell, in 1986, created the first blood vessel from collagen, endothelial cells, smooth muscle cells and fibroblasts. The synergistic combination of advances in fabrication methods, availability of cell source, biomaterials formulation and vascular tissue development, promises new strategies for the creation of autologous blood vessels, recapitulating biological functions, structural functions, but also the mechanical functions of a native blood vessel. In this review, the main technological advancements in bio-fabrication are discussed with a particular highlights on 3D bioprinting technologies. The choice of the main biomaterials and cell sources, the use of dynamic maturation systems such as bioreactors and the associated clinical trials will be detailed. The remaining challenges in this complex engineering field will finally be discussed.

Vascular smooth muscle cells in atherosclerosis: time for a re-assessment

Vascular smooth muscle cells (VSMCs) are key participants in both early and late-stage atherosclerosis. VSMCs invade the early atherosclerotic lesion from the media, expanding lesions, but also forming a protective fibrous cap rich in extracellular matrix to cover the 'necrotic' core. Hence, VSMCs have been viewed as plaque-stabilizing, and decreased VSMC plaque content-often measured by expression of contractile markers-associated with increased plaque vulnerability. However, the emergence of lineage-tracing and transcriptomic studies has demonstrated that VSMCs comprise a much larger proportion of atherosclerotic plaques than originally thought, demonstrate multiple different phenotypes in vivo, and have roles that might be detrimental. VSMCs down-regulate contractile markers during atherosclerosis whilst adopting alternative phenotypes, including macrophage-like, foam cell-like, osteochondrogenic-like, myofibroblast-like, and mesenchymal stem cell-like. VSMC phenotypic switching can be studied in tissue culture, but also now in the media, fibrous cap and deep-core region, and markedly affects plaque formation and markers of stability. In this review, we describe the different VSMC plaque phenotypes and their presumed cellular and paracrine functions, the regulatory mechanisms that control VSMC plasticity, and their impact on atherogenesis and plaque stability.

H3K4 Methyltransferase Smyd3 Mediates Vascular Smooth Muscle Cell Proliferation, Migration, and Neointima Formation

[Figure: see text].

Smooth muscle cells in atherosclerosis: clones but not carbon copies

Our knowledge of the contribution of vascular smooth muscle cells (SMCs) to atherosclerosis has greatly advanced in the previous decade with the development of techniques allowing for the unambiguous identification and phenotypic characterization of SMC populations within the diseased vascular wall. By performing fate mapping or single-cell transcriptomics studies, or a combination of both, the field has made key observations: SMCs populate atherosclerotic lesions by the selective expansion and investment of a limited number of medial SMCs, which undergo profound and diverse modifications of their original phenotype and function. Thus, if SMCs residing within atherosclerotic lesions and contributing to the disease are clones, they are not carbon copies and can play atheroprotective or atheropromoting roles, depending on the nature of their phenotypic transitions. Tremendous progress has been made in identifying the transcriptional mechanisms biasing SMC fate. In the present review, we have summarized the recent advances in characterizing SMC investment and phenotypic diversity and the molecular mechanisms controlling SMC fate in atherosclerotic lesions. We have also discussed some of the remaining questions associated with these breakthrough observations. These questions include the underlying mechanisms regulating the phenomenon of SMC oligoclonal expansion; whether single-cell transcriptomics is reliable and sufficient to ascertain SMC functions and contributions during atherosclerosis development and progression; and how SMC clonality and phenotypic plasticity affects translational research and the therapeutic approaches developed to prevent atherosclerosis complications. Finally, we have discussed the complementary approaches the field should lean toward by combining single-cell phenotypic categorization and functional studies to understand further the complex SMC behavior and contribution in atherosclerosis.

Factors Controlling Growth of Arterial Cells following Injury*

The proliferation of vascular smooth muscle cells is a key event in the development of arterial lesions. In experimental models, loss of arterial endothelium followed by platelet adherence does not necessarily stimulate smooth muscle cell proliferation. Furthermore, using animals deficient in platelets, smooth muscle cell proliferation was induced to an equal extent as in control animals following injury with a balloon catheter. Modulation of the smooth muscle response, however, was achieved by totally denuding arteries with a technique which did not traumatize medial cells. These data suggested that injury and cell death might induce proliferation of cells by release of endogenous mitogen. Basic FGF is present in the arterial wall and addition of this mitogen to denuded arteries was found to cause a highly significant increase in smooth muscle cell proliferation. These studies suggest that smooth muscle cell proliferation could be induced by factors present in the arterial wall and does not require exogenous factors. Smooth muscle cell proliferation following balloon catheter injury is significantly reduced by administration of calcium antagonists. Repeated administration of nifedipine caused a significant reduction in intimal lesion size induced by injury. The anti-proliferative. effect was not observed in other tissues. Influx of Ca++ ions into medial smooth muscle cells may therefore be an obligatory step for replication.

Smooth Muscle Diversity in Arterial Wound Repair*

Repair of arterial injury results in formation of a new structure, a neointima, that causes luminal narrowing. Smooth muscle cell (SMC) properties required for neointima formation are also found in nascent SMCs of developing blood vessels in the embryo (e.g., proliferation, extracellular matrix synthesis, cell migration). We isolated 2 distinct types of SMC from aortic media of newborn rats that were distinguished by cell shape, secretion of platelet-derived growth factor (PDGF) and insulin-like growth factor-1 (IGF-1), and expression of PDGF-B and PDGF α-receptor genes. These two SMC types did not interconvert over many cell generations in vitro. Adult rat aorta yields only one SMC type, suggesting that the “pup” SMC variant is developmentally regulated. However, SMC with the “pup” phenotype reappear in the adult artery wall during neointima formation after balloon catheter injury. These observations raise the possibility that SMC proliferation and arterial remodeling during development, repair and disease of the artery wall might depend upon a SMC subpopulation with special properties.

Smooth Muscle Cell Phenotypic Diversity

Vascular smooth muscle cells (SMC) play a critical role in controlling blood pressure and blood distribution, as well as maintaining the structural integrity of the blood vessel. SMC also participate in physiological and pathological vascular remodeling due to their remarkable ability to dynamically modulate their phenotype. During the past decade, the development of in vivo fate mapping systems for unbiased identification and tracking of SMC and their progeny has led to major discoveries as well as the reevaluation of well-established concepts about the contribution of vascular SMC in major vascular diseases including atherosclerosis. Lineage tracing studies revealed that SMC undergoes multiple phenotypic transitions characterized by the expression of markers of alternative cell types (eg, macrophage-like and mesenchymal-stem cell-like) and populate injured or diseased vessels by oligoclonal expansion of a limited number of medial SMC. With the development of high-throughput transcriptomics and single-cell RNA sequencing (scRNAseq), the field is moving forward towards in-depth SMC phenotypic characterization. Herein, we review the major observations put forth by lineage and clonality tracing studies and the evidence in support for SMC phenotypic diversity in healthy and diseased vascular tissue. We will also discuss the opportunities and remaining challenges of combining lineage tracing and single-cell transcriptomics technologies, as well as studying the functional relevance of SMC phenotypic transitions and identifying the mechanisms controlling them.

Migration versus proliferation as contributor to in vitro wound healing of vascular endothelial and smooth muscle cells

Wound closure, as a result of collective cell growth, is an essential biological response to injury. In the field of vascular biology, the response of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) to injury and substrate surface is important in therapeutic clinical treatment interventions such as angioplasty and atherectomy. Specifically, the mechanism by which cells close wounds (i.e. proliferation versus migration) in response to injury stimuli is of interest to better modulate recurrent vascular stenosis, prevent thrombus formation, occlusion, and life-threatening cardiovascular events. Here, we examine growth extent and temporal sequence of events following wound or gap introduction to a confluent monolayer of vascular SMCs or ECs. Significant differences in the preferred mechanisms of these cells to close wounds or gaps were observed; after 48 h, 73% of SMC wound closure was observed to be due to proliferation, while 75% of EC wound closure resulted from migration. These mechanisms were further modulated via addition or removal of extracellular matrix substrate and injury, with ECs more responsive to substrate composition and less to injury, in comparison to SMCs. Our results indicate that ECs and SMCs heal wounds differently, and that the time and mode of injury and associated substrate surface all impact this response.

An Ex Vivo Vessel Injury Model to Study Remodeling

Objective:

Invasive coronary interventions can fail due to intimal hyperplasia and restenosis. Endothelial cell (EC) seeding to the vessel lumen, accelerating re-endothelialization, or local release of mTOR pathway inhibitors have helped reduce intimal hyperplasia after vessel injury. While animal models are powerful tools, they are complex and expensive, and not always reflective of human physiology. Therefore, we developed an in vitro 3D vascular model validating previous in vivo animal models and utilizing isolated human arteries to study vascular remodeling after injury. Approach: We utilized a bioreactor that enables the control of intramural pressure and shear stress in vessel conduits to investigate the vascular response in both rat and human arteries to intraluminal injury.

Results:

Culturing rat aorta segments in vitro, we show that vigorous removal of luminal ECs results in vessel injury, causing medial proliferation by Day-4 and neointima formation, with the observation of SCA1⁺ cells (stem cell antigen-1) in the intima by Day-7, in the absence of flow. Conversely, when endothelial-denuded rat aortae and human umbilical arteries were subjected to arterial shear stress, pre-seeding with human umbilical ECs decreased the number and proliferation of smooth muscle cell (SMC) significantly in the media of both rat and human vessels.

Conclusion:

Our bioreactor system provides a novel platform for correlating ex vivo findings with vascular outcomes in vivo. The present in vitro human arterial injury model can be helpful in the study of EC-SMC interactions and vascular remodeling, by allowing for the separation of mechanical, cellular, and soluble factors.

Photodynamic therapy of balloon-injured rat carotid arteries using indocyanine green

Photodynamic therapy (PDT) has been used to inhibit intimal hyperplasia in injured arteries. Because of the limited tissue penetration of visible light, an endovascular light source with a guided wire is often required for effective treatment. Indocyanine green (ICG), a near-infrared (NIR) photosensitizer, has been used in PDT for cancers. An extracorporeal light source may be used for shallow tissue because of the better tissue penetration of NIR light. The aim of this study was to evaluate the effect of ICG-PDT using extracorporeal NIR light on the inhibition of intimal hyperplasia in balloon-injured carotid arteries. A balloon injury (BI) model was used to induce intimal hyperplasia of carotid artery. Sprague-Dawley rats were divided into control, BI, BI + 1 × PDT, and BI + 2 × PDT groups. The control group underwent a sham procedure. PDT was performed 7 days after BI. In the BI + 1 × PDT group, ICG was administered 1 h before light irradiation. External illumination with 780-nm light-emitting diode light at a fluence of 4 J/cm² was applied. For the BI + 2 × PDT group, PDT was performed again at day 7, following the first PDT. Hematoxylin and eosin (H & E) staining was performed to assess vessel morphology. Arterial wall thickness was significantly larger in the BI group compared with the control group. ICG-PDT significantly reduced arterial wall thickness compared with the BI group. Repeated PDT further decreased arterial wall thickness to the level of the control group. These findings indicate a promising approach for the treatment of restenosis of carotid arteries.

A New Technique to Induce Experimental Myointimal Hyperplasia

BACKGROUND

Arterial myointimal hyperplasia (MIH) has a significant impact on the long-term outcomes of vascular procedures such as bypass surgery and angioplasty. In this study, we describe a new and innovative technique to induce MIH using a dental flossing cachet in Wistar rats.

METHODS

The intimal damage in the common carotid artery was induced by inserting the tip of the dental flossing cachet through the external carotid artery into the common carotid artery and turning it on for 3 rounds of 20 s each (n = 10). After 2 weeks, the rats were anesthetized and the common carotid arteries of the experimental side and the contralateral side (control) were harvested and preserved for histopathological studies.

RESULTS

The experimental carotid arteries showed significant intimal proliferation and thickening compared to the controls. The intima/media ratio of the experimental and normal (control) common carotid arteries were 1.274 ± 0.162 and 0.089 ± 0.023 (mean ± SEM), respectively (p < 0.001).

CONCLUSION

This technique is simple, inexpensive, and highly reproducible and it induces sufficient MIH to study this phenomenon in animal models.

Distinct Cellular Mechanisms Underlie Smooth Muscle Turnover in Vascular Development and Repair

Supplemental Digital Content is available in the text.

Rationale:

Vascular smooth muscle turnover has important implications for blood vessel repair and for the development of cardiovascular diseases, yet lack of specific transgenic animal models has prevented it’s in vivo analysis.

Objective:

The objective of this study was to characterize the dynamics and mechanisms of vascular smooth muscle turnover from the earliest stages of embryonic development to arterial repair in the adult.

Methods and Results:

We show that CD146 is transiently expressed in vascular smooth muscle development. By using CRISPR-Cas9 genome editing and in vitro smooth muscle differentiation assay, we demonstrate that CD146 regulates the balance between proliferation and differentiation. We developed a triple-transgenic mouse model to map the fate of NG2⁺CD146⁺ immature smooth muscle cells. A series of pulse-chase experiments revealed that the origin of aortic vascular smooth muscle cells can be traced back to progenitor cells that reside in the wall of the dorsal aorta of the embryo at E10.5. A distinct population of CD146⁺ smooth muscle progenitor cells emerges during embryonic development and is maintained postnatally at arterial branch sites. To characterize the contribution of different cell types to arterial repair, we used 2 injury models. In limited wire-induced injury response, existing smooth muscle cells are the primary contributors to neointima formation. In contrast, microanastomosis leads to early smooth muscle death and subsequent colonization of the vascular wall by proliferative adventitial cells that contribute to the repair.

Conclusions:

Extensive proliferation of immature smooth muscle cells in the primitive embryonic dorsal aorta establishes the long-lived lineages of smooth muscle cells that make up the wall of the adult aorta. A discrete population of smooth muscle cells forms in the embryo and is postnatally sustained at arterial branch sites. In response to arterial injuries, existing smooth muscle cells give rise to neointima, but on extensive damage, they are replaced by adventitial cells.

Diverse cellular architecture of atherosclerotic plaque derives from clonal expansion of a few medial SMCs

Fibrous cap smooth muscle cells (SMCs) protect atherosclerotic lesions from rupturing and causing thrombosis, while other plaque SMCs may have detrimental roles in plaque development. To gain insight into recruitment of different plaque SMCs, we mapped their clonal architecture in aggregation chimeras of eGFP+Apoe-/- and Apoe-/- mouse embryos and in mice with a mosaic expression of fluorescent proteins in medial SMCs that were rendered atherosclerotic by PCSK9-induced hypercholesterolemia. Fibrous caps in aggregation chimeras were found constructed from large, endothelial-aligned layers of either eGFP+ or nonfluorescent SMCs, indicating substantial clonal expansion of a few cells. Similarly, plaques in mice with SMC-restricted Confetti expression showed oligoclonal SMC populations with little intermixing between the progeny of different medial SMCs. Phenotypes comprised both ACTA2+ SMCs in the cap and heterogeneous ACTA2- SMCs in the plaque interior, including chondrocyte-like cells and cells with intracellular lipid and crystalline material. Fibrous cap SMCs were invariably arranged in endothelium-aligned clonal sheets, confirming results in the aggregation chimeras. Analysis of the clonal structure showed that a low number of local medial SMCs partake in atherosclerosis and that single medial SMCs can produce several different SMC phenotypes in plaque. The combined results show that few medial SMCs proliferate to form the entire phenotypically heterogeneous plaque SMC population in murine atherosclerosis.

MicroRNA-761 inhibits Angiotensin II-induced vascular smooth muscle cell proliferation and migration by targeting mammalian target of rapamycin

Aberrant vascular smooth muscle cell (VSMC) proliferation and migration are a major pathological phenomenon in vascular disease characterized by intimal thickening. The important role of the mammalian target of rapamycin (mTOR) signaling in VSMC proliferation has been previously reported. Consequently, down-regulation of mTOR pathway may be an effective way of controlling excessive VSMC proliferation. Since microRNAs (miRNA) are newly emerging regulators of virtually all the biological processes including cellular proliferation, miRNAs targeting mTOR pathway may be utilized to suppress aberrant VSMC proliferation during pathologic conditions. Thus, in the present study, we screened miRNAs targeting mTOR, and we identified miR-761 as a new mTOR targeting miRNA. Luciferase assay using luciferase vector containing 3'UTR of mTOR indicated that miR-761 directly targets mTOR mRNA leading to suppression of mTOR protein expression. Our data also indicate that miR-761 expression decreases during angiotensin II (AngII)-induced proliferation of VSMCs, and exogenous miR-761 delivery effectively inhibit the AngII-induced VSMC proliferation. Additionally, the results of migration tests demonstrate that down-regulation of mTOR using exogenous miR-761 suppresses AngII-induced migration of VSMCs as well. Taken together, the present study provided evidence that miR-761 can be a potent anti-proliferative agent for vascular diseases such as atherosclerosis and restenosis, and warrants further studies to validate the effectiveness of miR-761 in vivo.

Preclinical Restenosis Models: Challenges and Successes

Coronary artery disease remains a major problem for Western societies. The advent of percutaneous interventions, including stents has brought clinical care to a new level of efficacy, yet problems remain. Restenosis following stenting in human coronary arteries appears at last to be yielding to therapeutic strategies, especially drug eluting stents. Because therapeutic percutaneous coronary intervention is widely dominated by the intracoronary stent, restenosis therapies must include the stented coronary artery. Animal models and in particular the porcine coronary model seem to represent the human coronary artery reaction to stenting. It mimics several clinical conditions including thrombosis and neointimal formation. A key question in the era of intravascular technologies is how well this and other models can predict clinical events. This paper discusses the models and their application.

DNA Methylation Signature of Post-injury Neointimal Cells During Vascular Remodeling in the Rat Balloon Injury Model

Vascular smooth muscle cell (VSMC) accumulation in the neointimal is a common feature in vascular diseases such as atherosclerosis, transplant arteriosclerosis and restenosis. In this study, we isolated the neointimal cells and uninjured residential vascular smooth muscle cells by laser micro dissection and carried out single-cell whole-genome methylation sequencing. We also sequenced the bisulfite converted genome of circulating bone-marrow-derived cells such as peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC). We found totally 2,360 differential methylation sites (DMS) annotated to 1,127 gene regions. The majority of differentially methylated regions (DMRs) were located in intergenic regions, outside those CpG islands and island shores. Interestingly, exons have less DMRs than promotors and introns, and CpG islands contain more DMRs than islands shores. Pearson correlation analysis showed a clear clustering of neointimal cells with PBMC/BMMC. Gene set enrichment analysis of differentially methylated CpG sites revealed that many genes were important for regulation of VSMC differentiation and stem cell maintenance. In conclusion, our results showed that neointimal cells are more similar to the progenitor cells in methylation profile than the residential VSMCs at the 30^th day after the vascular injury.

Lysophosphatidic acid-induced vascular neointimal formation in mouse carotid arteries is mediated by the matricellular protein CCN1/Cyr61

Vascular smooth muscle cell (SMC) migration is an essential step involved in neointimal formation in restenosis and atherosclerosis. Lysophosphatidic acid (LPA) is a bioactive component of oxidized low-density lipoprotein and is produced by activated platelets, implying that LPA influences vascular remodeling. Our previous study revealed that matricellular protein CCN1, a prominent extracellular matrix (ECM) protein, mediates LPA-induced SMC migration in vitro. Here we examined the role of CCN1 in LPA-induced neointimal formation. By using LPA infusion of carotid artery in a mouse model, we demonstrated that LPA highly induced CCN1 expression (approximately six- to sevenfold) in neointimal lesions. Downregulation of CCN1 expression with the specific CCN1 siRNA in carotid arteries blocked LPA-induced neointimal formation, indicating that CCN1 is essential in LPA-induced neointimal formation. We then used LPA receptor knockout (LPA₁-/-, LPA₂-/-, and LPA₃-/-) mice to examine LPA receptor function in CCN1 expression in vivo and in LPA-induced neointimal formation. Our data reveal that LPA₁ deficiency, but not LPA₂ or LPA₃ deficiency, prevents LPA-induced CCN1 expression in vivo in mouse carotid arteries. We also observed that LPA₁ deficiency blunted LPA infusion-induced neointimal formation, indicating that LPA₁ is the major mediator for LPA-induced vascular remodeling. Our in vivo model of LPA-induced neointimal formation established a key role of the ECM protein CCN1 in mediating LPA-induced neointimal formation. Our data support the notion that the LPA₁-CCN1 axis may be the central control for SMC migration and vascular remodeling. CCN1 may serve as an important vascular disease marker and potential target for vascular therapeutic intervention.

Extensive Proliferation of a Subset of Differentiated, yet Plastic, Medial Vascular Smooth Muscle Cells Contributes to Neointimal Formation in Mouse Injury and Atherosclerosis Models

Supplemental Digital Content is available in the text.

Rationale:

Vascular smooth muscle cell (VSMC) accumulation is a hallmark of atherosclerosis and vascular injury. However, fundamental aspects of proliferation and the phenotypic changes within individual VSMCs, which underlie vascular disease, remain unresolved. In particular, it is not known whether all VSMCs proliferate and display plasticity or whether individual cells can switch to multiple phenotypes.

Objective:

To assess whether proliferation and plasticity in disease is a general characteristic of VSMCs or a feature of a subset of cells.

Methods and Results:

Using multicolor lineage labeling, we demonstrate that VSMCs in injury-induced neointimal lesions and in atherosclerotic plaques are oligoclonal, derived from few expanding cells. Lineage tracing also revealed that the progeny of individual VSMCs contributes to both alpha smooth muscle actin (aSma)–positive fibrous cap and Mac3-expressing macrophage-like plaque core cells. Costaining for phenotypic markers further identified a double-positive aSma+ Mac3+ cell population, which is specific to VSMC-derived plaque cells. In contrast, VSMC-derived cells generating the neointima after vascular injury generally retained the expression of VSMC markers and the upregulation of Mac3 was less pronounced. Monochromatic regions in atherosclerotic plaques and injury-induced neointima did not contain VSMC-derived cells expressing a different fluorescent reporter protein, suggesting that proliferation-independent VSMC migration does not make a major contribution to VSMC accumulation in vascular disease.

Conclusions:

We demonstrate that extensive proliferation of a low proportion of highly plastic VSMCs results in the observed VSMC accumulation after injury and in atherosclerotic plaques. Therapeutic targeting of these hyperproliferating VSMCs might effectively reduce vascular disease without affecting vascular integrity.

The Effect of Nonporous PTFE-Covered Stents on Intimal Hyperplasia following Balloon Arterial Injury in Minipigs

Purpose:

To report an experimental study investigating the ability of nonporous polytetrafluoroethylene (PTFE) covering on a metallic stent to retard the development of neointimal hyperplasia (NIH).

Methods:

Three groups of Hanford miniature swine underwent standardized balloon injury to both external iliac arteries. Group I animals (control) received balloon injuries only. Group II had the site of balloon injury supported by a properly sized, balloon-expandable Palmaz stent placed directly over the injury site. Group III animals received a Palmaz stent covered with PTFE graft. All animals underwent arteriography immediately after intervention and again prior to sacrifice and specimen harvest at 4 weeks. The specimens were examined grossly and histologically at the proximal, middle, and distal segments for NIH development.

Results:

Uncovered stents developed significantly more NIH (p < 0.0001) and greater luminal narrowing (p < 0.001) than the controls. PTFE-covered stents (group III) exhibited less NIH (p < 0.001) and luminal reduction (p < 0.01) than bare stents (group II) at the middle portion of the stent-graft, but the PTFE cover had no effect on NIH and lumen reduction at the proximal or distal ends of the prosthesis.

Conclusions:

PTFE-covered stents retarded NIH at 4 weeks, but only at the midportion of the devices; the covering did not prevent neointimal pannus ingrowth at the proximal and distal ends.

Anti-atherogenic and anti-inflammatory properties of glucagon-like peptide-1, glucose-dependent insulinotropic polypepide, and dipeptidyl peptidase-4 inhibitors in experimental animals

We reported that native incretins, liraglutide and dipeptidyl peptidase‐4 inhibitors (DPP‐4i) all confer an anti‐atherosclerotic effect in apolipoprotein E‐null (Apoe^−/−) mice. We confirmed the anti‐atherogenic property of incretin‐related agents in the mouse wire injury model, in which the neointimal formation in the femoral artery is remarkably suppressed. Furthermore, we showed that DPP‐4i substantially suppresses plaque formation in coronary arteries with a marked reduction in the accumulation of macrophages in cholesterol‐fed rabbits. DPP‐4i showed an anti‐atherosclerotic effect in Apoe^−/− mice mainly through the actions of glucagon‐like peptide‐1 and glucose‐dependent insulinotropic polypepide. However, the dual incretin receptor antagonists partially attenuated the suppressive effect of DPP‐4i on atherosclerosis in diabetic Apoe^−/− mice, suggesting an incretin‐independent mechanism. Exendin‐4 and glucose‐dependent insulinotropic polypepide elicited cyclic adenosine monophosphate generation, and suppressed the lipopolysaccharide‐induced gene expression of inflammatory molecules, such as interleukin‐1β, interleukin‐6 and tumor necrosis factor‐α, in U937 human monocytes. This suppressive effect, however, was attenuated by an inhibitor of adenylate cyclase and mimicked by 8‐bromo‐cyclic adenosine monophosphate or forskolin. DPP‐4i substantially suppressed the lipopolysaccharide‐induced expression of inflammatory cytokines without affecting cyclic adenosine monophosphate generation or cell proliferation. DPP‐4i more strongly suppressed the lipopolysaccharide‐induced gene expression of inflammatory molecules than incretins, most likely through inactivation of CD26. Glucagon‐like peptide‐1 and glucose‐dependent insulinotropic polypepide suppressed oxidized low‐density lipoprotein‐induced macrophage foam cell formation in a receptor‐dependent manner, which was associated with the downregulation of acyl‐coenzyme A cholesterol acyltransferase‐1 and CD36, as well as the up‐regulation of adenosine triphosphate‐binding cassette transporter A1. Our studies strongly suggest that incretin‐related agents have favorable effects on macrophage‐driven atherosclerosis in experimental animals.

Perivascular delivery of resolvin D1 inhibits neointimal hyperplasia in a rat model of arterial injury

OBJECTIVE

Lipid mediators derived from omega-3 polyunsaturated fatty acids such as resolvin D1 (RvD1) accelerate the resolution of inflammation and have potential as vascular therapeutics. The objective of this study was to evaluate local perivascular delivery of RvD1 as a means to attenuate neointimal hyperplasia in a rat model of arterial injury.

METHODS

Smooth muscle cells were harvested from rat aortas to study the effects of RvD1 on rat arterial vascular smooth muscle cell responses in vitro, with focus on inflammation, proliferation, migration, cytoskeletal changes, and cytotoxicity. The safety and efficacy of perivascular delivery of RvD1 through thin biodegradable three-layered poly(lactic-co-glycolic acid) wraps or 25% Pluronic F127 gels were studied in a rat model of carotid angioplasty. A total of 200 ng of RvD1 was loaded into each construct for perivascular delivery after injury. Morphometric and histologic analyses were performed 3 and 14 days after injury.

RESULTS

RvD1 attenuated rat arterial vascular smooth muscle cell inflammatory pathways, proliferation, migration, and mitogen-induced cytoskeletal changes in vitro, without evidence of cytotoxicity. RvD1-loaded wraps reduced neointimal formation after carotid angioplasty by 59% vs no-wrap controls (P = .001) and by 45% vs vehicle-wrap controls (P = .002). RvD1-loaded Pluronic gels similarly reduced neointimal formation by 49% vs no-gel controls (P = .02) and by 52% vs vehicle-gel controls (P = .02). No group was associated with infection, thrombosis, or negative vessel remodeling. Wraps were found to be easier to apply than gel constructs. Ki67 proliferation index was significantly lower in RvD1-loaded wrap-treated arteries compared with both no-wrap and vehicle-wrap controls at both 3 and 14 days after injury (65% vs no-wrap group and 70% vs vehicle-wrap group at day 3, 49% vs both control groups at day 14; P < .05). Similarly, oxidative stress (30% and 29%; P < .05) and nuclear factor κB activation (42% and 45%; P < .05) were significantly lower in the RvD1-loaded wrap group compared with both no-wrap and vehicle-wrap controls at 3 days after injury.

CONCLUSIONS

Local perivascular delivery of RvD1 attenuates formation of neointimal hyperplasia without associated toxicity in a rat model of carotid angioplasty. This effect is likely due to attenuation of inflammatory pathways as well as decreased arterial smooth muscle cell proliferation and migration.

Thrombomodulin Induces a Quiescent Phenotype and Inhibits Migration in Vascular Smooth Muscle Cells In Vitro

BACKGROUND

Loss of critical endothelial cell function and subsequent vascular smooth muscle cell (VSMC) migration is central to the pathology of injury-induced neointimal hyperplasia and recurrent stenosis. Thrombomodulin (TM), well known for its function as an endothelial surface anticoagulant, may have an unknown direct effect on VSMC physiology that would be lost after injury. Here, we examined a novel effect of TM on VSMC by testing the hypothesis that direct application of TM induces favorable changes to the morphology of VSMC and inhibits their migration.

METHODS

Primary human VSMC were harvested using the explant technique and used in early passage (1-4) for all experiments. Laser-scanning confocal fluorescent imaging was performed to assess the effect of soluble TM on VSMC morphology. In vitro, migration of VSMC was measured using: (1) a 4-hr modified Boyden chemotaxis assay and (2) a 24-hr electric cell-substrate impedance sensing injury migration assay. Migration experiments were conducted with VSMC exposed to increasing doses of soluble recombinant TM. Recombinant thrombin served as a positive control and serum-free media as a negative control for all experimentation. Data were analyzed using a Student's t-test or repeated measures analysis of variance where appropriate (α < 0.05).

RESULTS

VSMC exposed to TM clearly demonstrated a quiescent morphology with organized stress fibers consistent with a quiescent, differentiated, contractile phenotype; whereas, thrombin stimulation led to an activated, dedifferentiated, synthetic phenotype. VSMC demonstrated a low, baseline level of migration in unstimulated serum-free conditions. Thrombin significantly stimulated VSMC migration as expected. TM, independent of thrombin, significantly inhibited baseline VSMC migration in a dose-response fashion. The maximal inhibition was observed at (5 μg/mL) with 70% reduction (56 ± 1.7 vs. 18 ± 3.5 cells/5 high-power fields, P = 0.0005).

CONCLUSIONS

TM has a direct effect on VSMC resulting in a quiescent, differentiated and contractile phenotype, and inhibition of migration. This effect is independent of the presence of thrombin. These findings provide new knowledge in understanding the pathophysiology of vascular injury and support a strategy focused on restoring key endothelial function to prevent intimal hyperplasia.

Optimal blood pressure in patients with peripheral artery disease following endovascular therapy

This study examined the associations between blood pressure (BP) and event incidence to define optimal BP after endovascular therapy (EVT) in patients who underwent EVT. BP was monitored every 6 months for 5 years, and the patients were divided into two groups by average BP: ≥ 140/90 mmHg and < 140/90 mmHg. The association of BP with several events was examined. Although no significant differences in total mortality were observed between the groups, restenosis rates were significantly higher among patients who did not achieve target BP (36.2%) than among those who did (18.2%) (p < 0.01). The percentage of patients with glycosylated haemoglobin > 7.0% was significantly higher among those who did not achieve target BP in the restenosis group (42.9%) than in the other group (10.8%) (p < 0.01). In the restenosis group, there was a significantly higher percentage of patients taking metformin (p < 0.01) than in the other group. Metformin seemed to be administered to patients with more severe diabetes mellitus. In conclusion, it is important to manage hypertension and diabetes to prevent restenosis after EVT.

A Novel Approach against Vascular Intimal Hyperplasia Through the Suppression of Girdin

Intimal hyperplasia is an impediment to patency in both arteries after percutaneous angioplasty (PTA) and veingraft. It is well known that migration and proliferation of vascular smooth muscle cells (SMCs) influence the vascular remodeling process, there are no therapies to prevent intimal hyperplasia of post-PTA arteries and vein grafts. Girdin (girders of actin filaments), also known as Gα-interacting vesicle associated protein (GIV) is a novel actin-binding Akt substrate.Girdin is highly expressed in limited types of cells such as smooth muscle cells, neuroblasts, and cancer cells. Girdin is involved in the cell migration, proliferation and remodeling of actin filaments. This study revealed that Girdin is involved with intimal hyperplasia in carotid arteries after balloon injury and vein grafts and vascular SMCs migration and proliferation. There are suggestions that Girdin has pivotal roles in migration and proliferation of vascular SMCs and that gene therapy targeting Girdin could be a novel therapeutic strategy for restenosis after PTA and vein graft failure.

New Endoplasmic Reticulum Stress Regulator, Gipie, Regulates the Survival of Vascular Smooth Muscle Cells and the Neointima Formation After Vascular Injury

Objective—

The accumulation of unfolded protein in the endoplasmic reticulum (ER) initiates an adaptive stress response, termed the unfolded protein response. Previous studies suggested that ER stress might be involved in the formation of neointima after vascular injury. We recently discovered a novel regulator of ER stress, 78-kDa glucose-regulated protein–interacting protein induced by ER stress (Gipie). The objective of this study was to elucidate the role of Gipie using models of vascular disease.

Approach and Results—

We investigated the functions of Gipie in cultured vascular smooth muscle cells (VSMCs) and in a vascular injury model of a rat carotid artery. The expression of Gipie was predominantly detected in synthetic VSMCs and to a much lesser extent in contractile VSMCs, which was augmented by treatment with thapsigargin. Gipie knockdown increased the phosphorylation levels of c-Jun N-terminal kinase and the number of apoptotic cells under ER stress. Moreover, Gipie knockdown decreased the mature form of collagen I in synthetic VSMCs. The expression of Gipie was rarely detected in the medial VSMCs of the intact carotid artery, whereas it was detected in most of the neointimal cells and some of the medial VSMCs after balloon injury. Depletion of Gipie in the rat carotid artery attenuated the neointimal thickening, which was accompanied by increased cell death in the neointima. Conversely, overexpression of Gipie augmented the neointimal thickening.

Conclusions—

Gipie participates in the ER stress response in VSMCs and plays an important role in neointima formation after vascular injury.

Surgical marking pen dye inhibits saphenous vein cell proliferation and migration in saphenous vein graft tissue

OBJECTIVE

Markers containing dyes such as crystal violet (CAS 548-62-9) are routinely used on the adventitia of vein bypass grafts to avoid twisting during placement. Because little is known about how these dyes affect vein graft healing and function, we determined the effect of crystal violet on cell migration and proliferation, which are responses to injury after grafting.

METHODS

Fresh human saphenous veins were obtained as residual specimens from leg bypass surgeries. Portions of the vein that had been surgically marked with crystal violet were analyzed separately from those that had no dye marking. In the laboratory, they were split into easily dissected inner and outer layers after removal of endothelium. This cleavage plane was within the circular muscle layer of the media. Cell migration from explants was measured daily as either (1) percentage of migration-positive explants, which exclusively measures migration, or (2) number of cells on the plastic surrounding each explant, which measures migration plus proliferation. Cell proliferation and apoptosis (Ki67 and TUNEL staining, respectively) were determined in dye-marked and unmarked areas of cultured vein rings. The dose-dependent effects of crystal violet were measured for cell migration from explants as well as for proliferation, migration, and death of cultured outer layer cells. Dye was extracted from explants with ethanol and quantified by spectrophotometry.

RESULTS

There was significantly less cell migration from visibly blue compared with unstained outer layer explants by both methods. There was no significant difference in migration from inner layer explants adjacent to blue-stained or unstained sections of vein because dye did not penetrate to the inner layer. Ki67 staining of vein in organ culture, which is a measure of proliferation, progressively increased up to 6 days in nonblue outer layer and was abolished in the blue outer layer. Evidence of apoptosis (TUNEL staining) was present throughout the wall and not different in blue-stained and unstained vein wall segments. Blue outer layer explants had 65.9 ± 8.0 ng dye/explant compared with 2.1 ± 1.3 for nonblue outer layer explants. Dye applied in vitro to either outer or inner layer explants dose dependently inhibited migration (IC50∼10 ng/explant). The IC50s of crystal violet for outer layer cell proliferation and migration were 0.1 and 1.2 μg/mL, whereas the EC50 for death was between 1 and 10 μg/mL.

CONCLUSIONS

Crystal violet inhibits venous cell migration and proliferation, indicating that alternative methods should be considered for marking vein grafts.

Identification of PI3K regulatory subunit p55γ as a novel inhibitor of vascular smooth muscle cell proliferation and neointimal formation

AIMS

Phosphatidylinositol 3 kinases (PI3Ks) play a pivotal role in vascular physiology and pathophysiology. We aimed to investigate the role of p55γ, a regulatory subunit of PI3Ks, in vascular smooth muscle cell (VSMC) proliferation and neointimal formation.

METHODS AND RESULTS

We identified p55γ as an important factor that suppresses VSMC proliferation and injury-evoked neointimal formation. Western blot and mRNA analyses showed that p55γ expression declined in balloon-injured rat carotid arteries and in response to PDGF-BB and serum treatment in cultured VSMCs. Overexpression of p55γ inhibited, whereas short hairpin RNA knockdown of p55γ promoted PDGF-BB- and serum-induced VSMC proliferation. Importantly, in vivo adenoviral gene transfer of p55γ into carotid arteries attenuated, while knockdown of p55γ enhanced balloon injury-induced neointimal formation. Furthermore, p55γ sequentially up-regulated p53 and p21, resulting in cell-cycle arrest in S phase; small-interfering RNA knockdown of either p53 or p21 blocked p55γ-induced VSMC growth arrest. Mechanistically, p55γ interacted with and stabilized p53 protein by blocking mouse double minute 2 homologue-mediated p53 ubiquitination and degradation, subsequently activating its target gene p21. Concurrently, p55γ up-regulated Bcl-xl expression, resulting in non-apoptotic growth arrest effect.

CONCLUSION

These findings mark p55γ as a novel upstream regulator of the p53-p21 signalling pathway that negatively regulates VSMC proliferation, suggesting that malfunction of p55γ may trigger vascular proliferative disorders.

Smooth muscle-specific drug targets for next-generation drug-eluting stent

The occurrence of stent thrombosis is one of the major obstacles limiting the long-term clinical efficacy of percutaneous coronary intervention. The anti-smooth muscle proliferation drugs coated on drug-eluting stents (DES) often indistinguishably block re-endothelialization, an essential step toward successful vascular repair, due to their nonspecific effect on endothelial cells (ECs). Therefore, identification of therapeutic targets that differentially regulate vascular smooth muscle cell (VSMC) and EC proliferation may lead to the development of ideal drugs for the next-generation DES. Our recent studies have shown that CTP synthase 1 (CTPS1) differentially regulates the proliferation of VSMC and EC after vascular injury. Therefore, CTPS1 inhibitors are promising agents for DES. In addition to CTPS1, other factors have also shown cell-specific effects on VSMC and/or EC proliferation and thus may become potential molecular targets for developing drugs to coat stents.

Short-term vasculoprotective effects of imatinib mesylate on intimal hyperplasia of arterial anastomosis: An experimental study using a rabbit model

BACKGROUND

Since the beginning of the 'microvascular era', the success rates of microvascular procedures have increased to more than 90% in most series. The main reason for failure, however, is the healing of microarterial anastomosis, which is dependent on the status of endothelial cells and affects the rate of arterial thrombosis. In 80% of arterial thrombosis cases, complications are primarily observed during the first 72 h after surgery. Healing of arterial anastomosis results in intimal hyperplasia in which myofibroblasts comprise the predominant cell type. Intimal hyperplasia has been described previously as an adaptive process that occurs in response to hemodynamic stress or injuries to the vascular bed. During wound healing, fibroblasts proliferate, migrate and differentiate into myofibroblasts - a process that takes one to three days. Imatinib mesylate (ST1571-Gleevec, Novartis, Germany) is a specific platelet-derived growth factor receptor blocker that has found use as an adjunct to sirolimus in cardiovascular surgery for restenosis. However, its potential utility in preventing arterial thrombosis in microvascular surgery has not been evaluated in routine plastic surgery practice.

METHODS

Twenty-four randomly selected, male, white New Zealand rabbits were divided into six groups (A to F), and the femoral artery model was used for arterial anastomosis. Following anastomosis, groups A, B and C received phosphate-buffered saline orogastrically. In groups D, E and F, imatinib mesylate was administered via an orogastric tube twice per day at a dose of 10 mg/kg starting two days before arterial anastomosis. Following anastomosis, imatinib mesylate was administered for one, three and seven days, and the regression of intimal hyperplasia was recorded.

RESULTS

In groups administered imatinib mesylate (ie, groups D, E and F), intimal hyperplasia decreased by up to 50%, which represented a statistically significant difference. Histological analysis confirmed smooth muscle cell migration from the tunica intima to media on days 3 and 7 in groups E and F.

CONCLUSION

The present study revealed that imatinib mesylate, which was initiated as a prophylactic, systemic pretreatment and continued for seven days, gradually decreased intimal hyperplasia at the anastomosis site.

Implications of autophagy for vascular smooth muscle cell function and plasticity

Vascular smooth muscle cells (VSMCs) are fundamental in regulating blood pressure and distributing oxygen and nutrients to peripheral tissues. They also possess remarkable plasticity, with the capacity to switch to synthetic, macrophage-like, or osteochondrogenic phenotypes when cued by external stimuli. In arterial diseases such as atherosclerosis and restenosis, this plasticity seems to be critical and, depending on the disease context, can be deleterious or beneficial. Therefore, understanding the mechanisms regulating VSMC phenotype and survival is essential for developing new therapies for vascular disease as well as understanding how secondary complications due to surgical interventions develop. In this regard, the cellular process of autophagy is increasingly being recognized as a major player in vascular biology and a critical determinant of VSMC phenotype and survival. Although autophagy was identified in lesional VSMCs in the 1960s, our understanding of the implications of autophagy in arterial diseases and the stimuli promoting its activation in VSMCs is only now being elucidated. In this review, we highlight the evidence for autophagy occurring in VSMCs in vivo, elaborate on the stimuli and processes regulating autophagy, and discuss the current understanding of the role of autophagy in vascular disease.

Vein graft failure

After the creation of an autogenous lower extremity bypass graft, the vein must undergo a series of dynamic structural changes to stabilize the arterial hemodynamic forces. These changes, which are commonly referred to as remodeling, include an inflammatory response, the development of a neointima, matrix turnover, and cellular proliferation and apoptosis. The sum total of these processes results in dramatic alterations in the physical and biomechanical attributes of the arterialized vein. The most clinically obvious and easily measured of these is lumen remodeling of the graft. However, although somewhat less precise, wall thickness, matrix composition, and endothelial changes can be measured in vivo within the healing vein graft. Recent translational work has demonstrated the clinical relevance of remodeling as it relates to vein graft patency and the systemic factors influencing it. By correlating histologic and molecular changes in the vein, insights into potential therapeutic strategies to prevent bypass failure and areas for future investigation are explored.

CTP synthase 1, a smooth muscle-sensitive therapeutic target for effective vascular repair

OBJECTIVE

Vascular remodeling as a result of smooth muscle cell (SMC) proliferation and neointima formation is a major medical challenge in cardiovascular intervention. However, antineointima drugs often indistinguishably block re-endothelialization, an essential step toward successful vascular repair, because of their nonspecific effect on endothelial cells (ECs). The objective of this study is to identify a therapeutic target that differentially regulates SMC and EC proliferation.

APPROACH AND RESULTS

Using both rat balloon injury and mouse wire injury models, we identified CTP synthase 1 (CTPS1) as one of the potential targets that may be used for developing therapeutics for treating neointima-related disorders. CTPS1 was induced in proliferative SMCs in vitro and neointima SMCs in vivo. Blockade of CTPS1 expression by small hairpin RNA or activity by cyclopentenyl cytosine suppressed SMC proliferation and neointima formation. Surprisingly, cyclopentenyl cytosine had much less effect on EC proliferation. Of importance, blockade of CTPS1 in vivo sustained the re-endothelialization as a result of induction of CTP synthesis salvage pathway enzymes nucleoside-diphosphate kinase A and B in ECs. Diphosphate kinase B seemed to preserve EC proliferation via use of extracellular cytidine to synthesize CTP. Indeed, blockade of both CTPS1 and diphosphate kinase B suppressed EC proliferation in vitro and the re-endothelialization in vivo.

CONCLUSIONS

Our study uncovered a fundamental difference in CTP biosynthesis between SMCs and ECs during vascular remodeling, which provided a novel strategy by using cyclopentenyl cytosine or other CTPS1 inhibitors to selectively block SMC proliferation without disturbing or even promoting re-endothelialization for effective vascular repair after injury.

Statins attenuate the development of atherosclerosis and endothelial dysfunction induced by exposure to urban particulate matter (PM10)

Exposure to ambient air particulate matter (particles less than 10μm or PM10) has been shown to be an independent risk factor for the development and progression of atherosclerosis. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have well-established anti-inflammatory properties. The aim of this study was to determine the impact of statins on the adverse functional and morphological changes in blood vessels induced by PM10. New Zealand White rabbits fed with a high fat diet were subjected to balloon injury to their abdominal aorta followed by PM10/saline exposure for 4weeks±lovastatin (5mg/kg/day) treatment. PM10 exposure accelerated balloon catheter induced plaque formation and increased intimal macrophages and lipid accumulation while lovastatin attenuated these changes and promoted smooth muscle cell recruitment into plaques. PM10 impaired vascular acetylcholine (Ach) responses and increased vasoconstriction induced by phenylephrine as assessed by wire myograph. Supplementation of nitric oxide improved the impaired Ach responses. PM10 increased the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in blood vessels and increased the plasma levels of endothelin-1 (ET-1). Incubation with specific inhibitors for iNOS, COX-2 or ET-1 in the myograph chambers significantly improved the impaired vascular function. Lovastatin decreased the expression of these mediators in atherosclerotic lesions and improved endothelial dysfunction. However, lovastatin was unable to reduce blood lipid levels to the baseline level in rabbits exposed to PM10. Taken together, statins protect against PM10-induced cardiovascular disease by reducing atherosclerosis and improving endothelial function via their anti-inflammatory properties.

Apoptosis signal-regulating kinase 1 deficiency attenuates vascular injury-induced neointimal hyperplasia by suppressing apoptosis in smooth muscle cells

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase that plays a crucial role in stress-induced apoptosis. Recently, we have reported that suppressed macrophage apoptosis in ASK1 and apolipoprotein E double-knockout mice accelerates atheromatous plaques in the hyperlipidemia-induced atherosclerotic model. However, the pathogenic role of smooth muscle cell (SMC) apoptosis in atherosclerosis still remains unclear. We investigated neointimal remodeling in ligated carotid arteries of ASK1-deficient mice (ASK1(-/-)) for 3 weeks. ASK1(-/-) mice had significantly more suppressed intimal formation, inversely manifesting as potential anti-atherogenic aspects of ASK1 deficiency, characterized by fewer SMCs and less collagen synthesis; and fewer apoptotic SMCs, infiltrating T lymphocytes, and microvessels, associated with decreased apoptosis of luminal endothelial cells, compared with those of wild-type mice. Injured arteries of ASK1(-/-) mice also showed significantly down-regulated expression of pro-apoptotic markers, adhesion molecules, and pro-inflammatory signaling factors. Moreover, tumor necrosis factor-α-induced apoptosis was markedly suppressed in cultured aortic SMCs from ASK1(-/-) mice. These findings suggest that ASK1 accelerates mechanical injury-induced vascular remodeling with activated SMC migration via increased neovascularization and/or enhanced SMC and endothelial cell apoptosis. ASK1 expression, especially in the SMCs, might be crucial, and reciprocally responsible for various pro-atherogenic functions, and SMC apoptosis seems to be detrimental in this model.