Factors controlling smooth-muscle cell proliferation.

Injury to the arterial wall normally elicits a rapid and significant increase in smooth-muscle cell (SMC) replication with the subsequent development of intimal lesions. A variety of factors have been proposed to control SMC replication, but recent work has highlighted the role of basic fibroblast growth factor (bFGF) and platelet-derived growth factor in this process. In the carotid artery of the uninjured rat, we have shown that the SMCs express mRNA for bFGF and that bFGF can be readily extracted from these arteries. Following mechanical injury to the artery, ie, after balloon injury, we suggested that bFGF is released from damaged cells and then stimulates adjacent SMCs. In support of this concept, the infusion of a blocking antibody to bFGF was found to significantly inhibit the early SMC replication induced by use of a balloon catheter. The addition of the antibody at the time of injury, however, did not inhibit the development of intimal lesions. In contrast, studies by us and other investigators have shown that platelet-derived growth factor is not directly important for SMC replication after balloon injury, but that it plays a key role in stimulating the migration of SMCs into the intima. Intimal SMC replication was not inhibited with antibodies to either bFGF or platelet-derived growth factor. Therefore, while significant inroads have been made in understanding the initial events, we still do not fully understand all the processes involved in the proliferation of arterial intimal lesions.     

Intimal smooth muscle cell proliferation after balloon catheter injury. The role of basic fibroblast growth factor.

The localization and synthesis of basic fibroblast growth factor (bFGF) in the rat carotid artery were investigated at times of chronic smooth muscle cell proliferation. Immunocytochemical staining showed the presence of bFGF in the uninjured arterial wall, and after balloon injury, this cellular staining was decreased. Western and northern blot analyses likewise showed that the amount of bFGF protein and mRNA decreased after injury. A neutralizing antibody to bFGF was administered 4 and 5 days after injury and was found to have no effect on intimal smooth muscle cell proliferation. These data suggest that an increase in the expression of bFGF is not necessary for chronic smooth muscle cell proliferation observed after balloon catheter injury and that bFGF is not the major mitogen responsible for intimal smooth muscle cell proliferation.     

Endothelial Regulation of Vascular Repair: Role of bFGF in Paracrine Pathways

Vascular repair following injury is mediated by both endothelial and smooth muscle cells often through paracrine pathways. Basic fibroblast growth factor (bFGF) is present at sites of vascular injury. The role of bFGF in regulating reendothelialization through an effect on centrosome redistribution in cell migration is discussed. The role of bFGF in neointimal formation, especially as it relates to smooth muscle cell proliferation, is reviewed. It is concluded that bFGF appears to be an important agent regulating the early responses of the artery wall to injury. Presented in part at the Molecular Endocrine Pathology Symposium at the International Academy of Pathology XXI International Congress, Budapest, Hungary, October 20–25, 1996.     

Identification of platelet-derived growth factor A and B chains in human renal vascular rejection.

Platelet-derived growth factor (PDGF) exists as a dimer composed of two homologous but distinct peptides termed PDGF-A and -B chains, and may exist as AA, AB, and BB isoforms. The PDGF-B chain has been implicated as a mediator of renal vascular rejection by virtue of up-regulated expression of its receptor, PDGF beta-receptor, in affected arteries. A role for PDGF-A chain in mediating intimal proliferation has been suggested in human atherosclerosis (Rekhter MD, Gordon D: Does platelet-derived growth factor-A chain stimulate proliferation of arterial mesenchymal cells in human atherosclerotic plaques? Circ Res 1994, 75:410), but no studies of this molecule in human renal allograft injury have been reported to date. We used two polyclonal antisera to detect expression of PDGF-A chain and one monoclonal antibody to detect PDGF-B chain by immunohistochemistry in fixed, paraffin-embedded tissue from 1) normal adult kidneys, 2) a series of renal transplant biopsies chosen to emphasize features of vascular rejection, and 3) allograft nephrectomies. Immunohistochemistry was correlated with in situ hybridization on adjacent, formalin fixed tissue sections from nephrectomies utilizing riboprobes made from PDGF-A and -B chain cDNA. PDGF-A chain is widely expressed by medial smooth muscle cells of normal and rejecting renal arterial vessels of all sizes by immunohistochemistry and in situ hybridization. PDGF-A chain is also expressed by a population of smooth muscle cells (shown by double immunolabeling with an antibody to alpha-smooth muscle actin) comprising the intima in chronic vascular rejection. In arteries demonstrating acute rejection, up-regulated expression of PDGF-A chain by endothelial cells was detected by both immunohistochemistry and in situ hybridization. In contrast, PDGF-B chain was identified principally in infiltrating monocytes within the rejecting arteries, similar to its localization in infiltrating monocytes in human atherosclerosis. Although less prominent than the case for PDGF-A chain, PDGF-B chain also was present in medial and intimal smooth muscle cells in both rejecting and nonrejecting renal arteries. PDGF-A and -B chains have now been localized at both the mRNA and protein levels to the intimal proliferative lesions of vascular rejection. These peptides, which are known stimuli for smooth muscle cell migration and proliferation in experimental vascular injury, may have similar stimulatory effects on smooth muscle cells in an autocrine and/or paracrine manner to promote further intimal expansion and lesion progression in this form of human vasculopathy.     

藏红花素促进颈动脉损伤小鼠体内EPCs动员及损伤血管的再内皮化

目的:研究藏红花素对颈动脉损伤小鼠外周血中内皮祖细胞(endothelial progenitor cells,EPCs)动员的影响及其作用机制。方法:利用导丝损伤的方法构建C57BL/6小鼠颈动脉损伤模型,动物分为假手术组(sham组)、生理盐水处理模型组(model组)和藏红花素低、中、高剂量(10、50和100μmol·kg~(-1)·L~(-1))处理组。在3 d时,利用流式细胞术检测各组颈动脉损伤小鼠体内外周血中EPCs动员情况;7 d时,利用酶联免疫吸附法检测各组颈动脉损伤小鼠外周血血清中促血管修复因子——血管内皮生长因子(vascular endothelial growth factor,VEGF)、基质细胞衍生因子1(stromal-derived factor-1,SDF-1)、碱性成纤维细胞生长因子(basic fibroblast growth factor,bFGF)、表皮生长因子(epidermal growth factor,EGF)和基质金属蛋白酶9(matrix metalloproteinase-9,MMP-9)的含量变化;14 d时,利用依文思蓝和苏木精-伊红染色分别检测各组颈动脉损伤小鼠损伤血管再内皮化和内膜增生情况;同时采用real-time PCR检测各组颈动脉损伤小鼠损伤段血管中促修复因子相关受体——血管内皮生长因子受体2(vascular endothelial growth factor receptor 2,VEGFR-2)、CXC趋化因子受体4(CXC chemokine receptor-4,CXCR4)、碱性成纤维细胞生长因子受体(basic fibroblast growth factor receptor,bFGFR)和表皮生长因子受体(epidermal growth factor receptor,EGFR)的mRNA表达水平。结果:与sham组相比,model组颈动脉损伤小鼠外周血中EPCs动员量和促血管修复因子VEGF、SDF-1、bFGF、EGF、MMP-9的含量上升(P0.05);损伤血管再内皮化面积下降而增生内膜面积和增生内膜与中层膜面积比显著升高(P0.05);损伤段血管中促修复因子相关受体VEGFR-2、CXCR4、bFGFR和EGFR的表达水平亦上升(P0.05)。而与model组相比,不同浓度藏红花素处理组颈动脉损伤小鼠外周血中EPCs动员量和促血管修复因子VEGF、SDF-1、bFGF、EGF、MMP-9含量均显著上升(P0.05);损伤血管再内皮化面积逐渐上升而增生内膜面积和增生内膜与中层膜面积比逐渐下降(P0.05);损伤段血管中促修复因子相关受体基因VEGFR-2、CXCR4、bFGF-R和EGFR的表达水平随之逐渐上升(P0.05)。结论:藏红花素能够促进颈动脉损伤小鼠体内EPCs细胞动员及损伤血管的再内皮化,从而对损伤血管发挥修复作用。     

Fas ligand gene therapy for vascular intimal hyperplasia

Fas, a member of the tumor necrosis factor receptor super-family, is expressed in all cell types examined, while physiologic expression of Fas ligand (FasL) is found predominantly in activated T-lymphocytes, vascular endothelial cells, and "immune-privileged" tissues. Activation of Fas following FasL binding activates caspases, which results in apoptosis. In the vasculature, there may be a delicate balance between cell proliferation and apoptosis in vascular smooth muscle cells. Shifts in this balance could account for the accumulation of vascular smooth muscle cells in response to arterial injury, a major feature of vascular intimal hyperplasia. Intimal hyperplasia occurs in more than a third of patients receiving percutaneous transluminal balloon angioplasty. Stenting with or without coating significantly reduces the incidence rate of angiographic restenosis and that of target vessel revascularization. However, "in-stent" intimal hyperplasia/restenosis remains a challenge for clinical cardiologists. Although both the cell types and mechanisms that contribute to intimal hyperplasia in response to vascular injury remain controversial, vascular smooth muscle cell migration and proliferation appear to play an important role in the process. In animal models, cytotoxic and cytostatic gene therapy strategies targeted at the vascular smooth muscle cells have shown therapeutic potential for the treatment of vascular intimal hyperplasia. However, Fas ligand-based gene therapy appears to offer several advantages. In this review article, we will discuss the mode of FasL/Fas signaling in vascular smooth muscle cells and its therapeutic implications. We will also compare the relative merits of FasL with other cytotoxic and cytostatic gene therapy approaches for the treatment of intimal hyperplasia.     

Decorin inhibition of PDGF-stimulated vascular smooth muscle cell function: potential mechanism for inhibition of intimal hyperplasia after balloon angioplasty

Decorin is a small proteoglycan that binds to transforming growth factor-beta (TGF-beta) and inhibits its activity. However, its interaction with platelet-derived growth factor (PDGF), involved in arterial repair after injury, is not well characterized. The objectives of this study were to assess decorin-PDGF and decorin-PDGF receptor (PDGFR) interactions, the in vitro effects of decorin on PDGF-stimulated smooth muscle cell (SMC) functions and the in vivo effects of decorin overexpression on arterial repair in a rabbit carotid balloon-injury model. Decorin binding to PDGF was demonstrated by solid-phase binding and affinity cross-linking assays. Decorin potently inhibited PDGF-stimulated PDGFR phosphorylation. Pretreatment of rabbit aortic SMC with decorin significantly inhibited PDGF-stimulated cell migration, proliferation, and collagen synthesis. Decorin overexpression by adenoviral-mediated gene transfection in balloon-injured carotid arteries significantly decreased intimal cross-sectional area and collagen content by approximately 50% at 10 weeks compared to beta-galactosidase-transfected or balloon-injured, non-transfected controls. This study shows that decorin binds to PDGF and inhibits its stimulatory activity on SMCs by preventing PDGFR phosphorylation. Decorin overexpression reduces intimal hyperplasia and collagen content after arterial injury. Decorin may be an effective therapy for the prevention of intimal hyperplasia after balloon angioplasty.     

Doxycycline modulates smooth muscle cell growth, migration, and matrix remodeling after arterial injury

The tetracyclines function as antibiotics by inhibiting bacterial protein synthesis, but recent work has shown that they are pluripotent drugs that affect many mammalian cell functions including proliferation, migration, apoptosis, and matrix remodeling. Because all of these processes have been implicated in arterial intimal lesion development, the objective of these studies was to examine the effect of doxycycline treatment using a well-characterized model of neointimal thickening, balloon catheter denudation of the rat carotid artery. Rats were treated with 30-mg/kg/day doxycycline. Doxycycline reduced the activity of matrix metalloproteinase (MMP)-2 and MMP-9 in the arterial wall, and inhibited smooth muscle cell migration from media to intima by 77% at 4 days after balloon injury. Replication of smooth muscle cells in the intima at 7 days was reduced from 28.3 plus minus 2.5% in controls to 17.0 +/- 2.8% in doxycycline-treated rats. The synthesis of elastin and collagen was not affected, but accumulation of elastin was blocked in the doxycycline-treated rats. By contrast, collagen accumulation was not affected, which led to the formation of a more collagen-rich intima. At 28 days after injury, the intimal:medial ratio was significantly reduced from 1.67 +/- 0.09 in control rats to 1.36 +/- 0.06 in the doxycycline-treated rats. This study shows that doxycycline is an effective inhibitor of cell proliferation, migration, and MMP activity in vivo. Further study in more complicated models of atherosclerosis and restenosis is warranted.     

Response to injury and atherogenesis.

We postulate that the lesions of atherosclerosis arise as a result of some form of "injury" to arterial endothelium. This injury somehow results in alteration in endothelial cell-cell attachment or endothelial cell-connective tissue attachment, so that forces such as those derived from the shear in the flow of blood result in focal desquamation of endothelium. This is followed by adherence, aggregation, and release of platelets at the sites of focal injury. During the process of release, a mitogenic factor is secreted from the platelets which, together with plasma constituents, gains entry into the artery wall, resulting in focal intimal proliferation of smooth muscle cells. This intimal proliferation is accompanied by the synthesis of new connective tissue matrix proteins and often by the deposition of intracellular and extracellular lipids. Studies in cell culture of arterial smooth muscle have demonstrated that the principle mitogen present in blood serum is a platelet-derived factor that is present in all whole blood sera and missing in serum derived from platelet-free plasma. In the absence of the platelet factor, smooth muscle cells are quiescent in culture. This platelet mitogen is also active in vivo, since experimentally produced lesion of atherosclerosis induced mechanically by diet or by homocystine can be prevented if platelets are missing, as in thrombocytopenia, or if platelet function is impaired as a result of the use of platelet inhibitors such as dipyridamole. These studies point to the key role of the platelet in the stimulation of intimal smooth muscle proliferation that leads to the development of lesions of atherosclerosis.     

Kinetics of cellular proliferation after arterial injury. II. Inhibition of smooth muscle growth by heparin

Heparin inhibits intimal thickening after arterial injury. Whether this effect is due to inhibition of medial smooth muscle cell (SMC) migration, SMC proliferation in the intima, or synthesis and deposition of connective tissue has not been evident. In this study we have investigated these possibilities in a rat carotid balloon injury model. Heparin (0.3 mg/kg/hour) was administered intravenously by means of osmotic pumps to experimental animals, and controls received lactated Ringer's solution. Smooth muscle proliferation (thymidine index), intimal smooth muscle accumulation, and endothelial regeneration were measured at intervals between 0 and 28 days. Total smooth muscle growth as determined biochemically at 14 days was markedly inhibited by heparin if the pumps were placed 24 hours before or at the time of injury and less so if inserted 48 or 96 hours after injury. SMC thymidine indices were maximal in the media at 4 days and in the intima at 7 days for injured arteries of both heparin-treated and control rats; at each time point SMC proliferation and intimal thickening were less in heparin-treated rats. The volume of connective tissue in the intima was the same in both groups at 28 days. Medial SMC migration into the intima was diminished by heparin treatment, but endothelial regeneration was not affected. These results support the hypothesis that heparin is a specific inhibitor of SMC migration and proliferation and is most effective if started before SMC enter S-phase.     

A nonantibiotic chemically modified tetracycline (CMT-3) inhibits intimal thickening

Recent research has shown that the tetracycline antibiotics are pluripotent drugs that inhibit the activity of matrix metalloproteinases (MMPs) and affect many cellular functions including proliferation, migration, and matrix remodeling. We have shown that doxycycline inhibits MMP activity and intimal thickening after injury of the rat carotid artery, however we do not know whether these effects are because of the antibiotic, anti-MMP, or other actions of doxycycline. Recently, chemically modified tetracyclines have been synthesized that lack antibiotic activity but retain anti-MMP activity (CMT-3), or lack both antibiotic and anti-MMP activity (CMT-5). In the current study we have assessed the effects of treatment with CMT-3 or CMT-5 on intimal thickening after balloon catheter injury of the rat carotid artery. Rats were treated by oral gavage with 15 mg/kg/day CMT-3 or CMT-5. CMT-3 significantly reduced smooth muscle cell (SMC) proliferation in both the medial and intimal layers of the injured rat carotid artery compared to CMT-5. Furthermore, CMT-3 inhibited SMC migration from the media to the intima by 86% at 4 days after injury. CMT-3 also decreased MMP-2 activity. Finally, we found that CMT-3 treatment resulted in a significant reduction in intimal cross-sectional area from 0.23 +/- 0.01 mm(2) in the CMT-5 control group to 0.19 +/- 0.01 mm(2). There was also a reduction in elastin and collagen accumulation within the intima. We conclude that CMT-3 attenuated intimal thickening after arterial injury by inhibiting SMC proliferation, migration and MMP activity, and accumulation of extracellular matrix. The inhibitory effects of CMT-3 were independent of the antibiotic properties, but were dependent on the anti-MMP activity of the tetracycline family.     

Learning from vascular remodelling

The positioning of a hollow silicone collar around the carotid artery of a rabbit induces many changes of early atherosclerosis including intimal proliferation of smooth muscle cells. This occurs below an intact endothelium indicating that endothelial damage is not necessary for smooth muscle cell proliferation. The endothelium may in fact produce substances that control processes occurring in the intima. Vascular endothelial growth factor (VEGF) is an angiogenic agent that is produced by cultured vascular smooth muscle cells. The combination of hypoxia and factors such as platelet-derived growth factor, tumour necrosis factor alpha, basic fibroblast growth factor, and interleukin-1β lead to synergistic production of VEGF by cultured smooth muscle cells. VEGF receptors are present predominantly on the endothelium and may be an important target for modulating the response to damage, hypoxia and inflammation. Transfection of the gene for VEGF resulted in inhibition or regression of intimal hyperplasia induced by the silicone collar in the rabbit. Studies suggest that the two mediators responsible for this inhibition of smooth muscle cell proliferation are nitric oxide and prostacyclin, which are produced by cultured endothelial cells incubated with VEGF. Thus, VEGF produced by smooth muscle cells in response to hypoxia, damage or inflammation, acts on specific endothelial receptors to produce nitric oxide and prostacyclin, which inhibit smooth muscle cell proliferation. Failure of this process could give rise to intimal hyperplasia. Early clinical studies of VEGF transfection from the outside of human arteries using a biodegradable collar are in progress.     

Molecular mechanisms in intimal hyperplasia

Intimal hyperplasia is the process by which the cell population increases within the innermost layer of the arterial wall, such as occurs physiologically during closure of the ductus arteriosus and during involution of the uterus. It also occurs pathologically in pulmonary hypertension, atherosclerosis, after angioplasty, in transplanted organs, and in vein grafts. The underlying causes of intimal hyperplasia are migration and proliferation of vascular smooth muscle cells provoked by injury, inflammation, and stretch. This review discusses, at a molecular level, both the final common pathways leading to smooth muscle migration and proliferation and their (patho)-physiological triggers. It emphasizes the key roles played by growth factors and extracellular matrix-degrading metalloproteinases, which act in concert to remodel the extracellular matrix and permit cell migration and proliferation.     

碱性成纤维细胞生长因子对动脉粥样硬化大鼠脑基底动脉血管内皮功能与结构的影响

目的探讨碱性成纤维细胞生长因子(bFGF)对动脉粥样硬化(AS)模型大鼠脑基底动脉血管内皮功能与结构的影响。方法将48只雄性Wistar大鼠随机平均分成正常对照组、AS组与bFGF治疗组。除正常对照组外,在喂食开始时一次性腹腔注射维生素D3(6×105IU/kg)加高脂配方饲料喂养,6周后bFGF治疗组采用腹腔注射bFGF(9.5μg/kg,2次/d)治疗,连续2周后处死。观察不同组离体基底动脉对不同浓度乙酰胆碱(Ach)的舒张反应率;光镜观察血管形态结构的变化;ELISA与比色法分别测定血管壁一氧化氮(NO)与血清血管内皮生长因子(VEGF)含量变化;MTT法测体外培养内皮细胞的增殖活性;鬼笔环肽染色观察培养平滑肌细胞骨架微丝的变化。结果高脂饲料饲养6周后早期动脉粥样硬化形成;与AS组相比,经bFGF治疗2周后基底动脉对不同浓度Ach舒张反应百分率、动脉管壁NO与血清VEGF含量明显升高(P0.05);血管内皮细胞增殖活性也显著增强(P0.05);平滑肌细胞骨架微丝损伤明显改善。结论 AS对基底动脉血管内皮造成了损伤,而bFGF参与了损伤动脉血管结构与内皮功能的调节,这些变化提示bFGF对脑血管具有明显的保护作用。     

CD4+ mononuclear cells induce cytokine expression, vascular smooth muscle cell proliferation, and arterial occlusion after endothelial injury.

Studies of T cell-deficient or immunosuppressed animals undergoing arterial endothelial denudation have yielded conflicting results as to the contribution of the immune system to neointimal vascular smooth muscle cell accumulation and proliferation. We investigated the cell types and cytokine expression associated with intimal hyperplasia occurring 14 days after balloon angioplasty of the carotid artery in Sprague-Dawley rats. Immunohistological studies using monoclonal antibodies showed that the carotid luminal occlusion observed was associated with smooth muscle cell proliferation and neointimal accumulation of large numbers of CD4+, ED1+ mononuclear cells but no T cells. There was also wide-spread staining for the inflammatory cytokine interleukin-1B (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and IL-8, as well as dense expression of the potent smooth muscle mitogens platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), and protein S. The relationship of smooth muscle cell proliferation to monocyte/macrophage accumulation and cytokine expression was tested by daily intraperitoneal administration for 14 days of a rat CD4-specific monoclonal antibody, BWH-4 (500 micrograms/day). Morphometric analysis at day 14 showed that the intimal area of animals treated with CD4 monoclonal antibody comprised 7% +/- 4% of the arterial wall compared with 50% +/- 6% in control animals (n = 6/group, P < 0.001). In addition, immunohistological studies showed that CD4 monoclonal antibody treatment markedly reduced the intimal accumulation of mononuclear and smooth muscle cells and essentially abrogated expression of the cytokines PDGF-BB, TGF-beta, IL-1 beta, TNF-alpha, and IL-8, plus the anticoagulant molecule, protein S. Our results document the extensive expression in vivo of cytokines that in vitro promote vascular smooth muscle cell proliferation, and suggest that CD4+ mononuclear cells or their secreted products play a key role in the pathogenesis of intimal hyperplasia after endothelial injury. Furthermore, these observations may have clinical relevance in the development of novel strategies to prevent arteriosclerosis.     

Active cytomegalovirus infection in aortic smooth muscle cells from patients with abdominal aortic aneurysm

Cytomegalovirus (CMV) is associated with atherosclerosis and transplant vascular sclerosis. The aim of this study was to explore the hypothesis that active CMV infection in the vessel wall could be associated with abdominal aortic aneurysm (AAA). We examined the prevalence of CMV in AAA specimens from 22 patients undergoing surgery and, in five cases, characterized the function of smooth muscle cells (SMCs) from the aneurysm in vitro. Twenty-one (95%) of the 22 AAA specimens were CMV positive by a polymerase chain reaction assay, in situ hybridization, or a highly sensitive immunohistochemical staining technique. No positive cells were found in aortas from three CMV-seronegative organ donor cadavers. CMV immediate-early and late antigens were expressed in SMCs in the lesions and were associated with 5-lipoxygenase (5-LO) expression. CMV-positive intimal SMCs migrated 6.6 ± 1.5 times more efficiently than CMV-negative medial SMCs (p < 0.05). In vitro CMV infection of medial SMCs resulted in a 3.2 ± 1.2 times increase in migration (p < 0.05). The intimal migration was significantly inhibited by antibodies against basic fibroblast growth factor (bFGF; p < 0.05) in a dose-dependent fashion. Antibodies against platelet-derived growth factor (PDGF)-AB, insulin-like growth factor 1, vascular endothelial growth factor (VEGF), RANTES, monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein (MIP)-1α, or interleukin-1β did not significantly affect intimal SMC migration. However, intimal and medial SMCs secreted similar amounts of bFGF, MCP-1, MIP-1α, RANTES, PDGF-AB, PDGF-BB, epidermal growth factor, and VEGF. CMV infection in vitro of intimal and medial cells did not result in significant changes of bFGF or MCP-1 secretion. Since CMV infection can affect several functional parameters in SMCs, including several key factors in infected SMCs, our findings provide support for the hypothesis that CMV contributes to the pathogenesis of abdominal aortic aneurysm. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Sara Gredmark-Russ and Mensur Dzabic contributed equally to this work and share first co-authorship.     

Comparison of Artery Organ Culture and Co-culture Models for Studying Endothelial Cell Migration and Its Effect on Smooth Muscle Cell Proliferation and Migration

Arterial restenosis associated with intimal hyperplasia is the major cause of long-term failure of vascular interventions. Endothelium injury and the proliferation and migration of smooth muscle cells (SMC) are key events in the development of intimal hyperplasia. The objectives of this study were to develop an ex vivo artery injury model for studying endothelial cell (EC) migration and to compare it with an in vitro co-culture arterial wall injury model in terms of the effect of flow on EC migration and its effect on SMC migration and proliferation. Our results demonstrated that shear flow improves reendothelialization in the injured area by promoting EC migration. The migration distance of ECs is much smaller in the arteries than in an in vitro cell culture model (3.57 ± 1.29 mm vs. 5.2 ± 1.4 cm, p < 0.001). SMC proliferation was significantly less in the EC intact and reendothelialization areas than in the EC denuded areas indicating that reendothelialization suppresses SMC proliferation. Our models provide a new approach to study techniques to enhance endothelium healing.     

Endothelial regeneration. II. Restitution of endothelial continuity

With a modified balloon catheter the endothelium of rat thoracic aortae was completely removed to study the interaction between two important responses of the vessel wall to intimal injury: endothelial regeneration and formation of an intimal fibrocellular thickening. Endothelial cells deriving from the uninjured intercostal arteries regenerated by migration followed by proliferation and proceeded as a continuous sheet at a rate of approximately 0.07 mm. per day in the circumferential direction and approximately 6 times faster in the axial direction. Smooth muscle cells appeared in the intima only in areas which were not covered by regenerating endothelium 7 days after injury. The smooth muscle cells formed a multilayered fibrocellular intimal lesion which reached the maximal thickness after 3 weeks. The continuous sheet of regenerating endothelium covered the intimal smooth muscle cells at a slower rate; 6 weeks after injury large areas located most distant from the source of regenerating endothelium still showed modified smooth muscle cells lining the lumen. However, platelets did not adhere to these smooth muscle cells, and the total amount of intimal thickening did not increase between 3 and 6 weeks after injury. We conclude that, in response to intimal injury, endothelial regeneration precedes the accumulation of intimal smooth muscle cells, and that injured intimal areas, which are rapidly covered by continuous endothelium, are protected from the development of a fibrocellular intimal lesion.