Thromboxane A2 fails to induce proliferation of smooth muscle cells enriched with eicosapentaenoic acid and docosahexaenoic acid.

Thromboxane A2 (TXA2) released from aggregating platelets and injured vessel wall stimulates smooth muscle cell proliferation, which may contribute to the development of vascular lesion formation after percutaneous transluminal coronary angioplasty. Polyunsaturated fatty acids (n-3) present in the fish oils have been shown to have anti-atherosclerotic effects. In view of this, we examined the effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the active ingredients of fish oils on TXA2 induced smooth muscle cell proliferation. To find out the specificity of these fatty acids we used gamma-linolenic acid (n-6) and oleic acid (n-9) as controls. It was found that TXA2 failed to stimulate proliferation of smooth muscle cells preloaded with EPA or DHA but not with gamma-linolenic acid or oleic acid. Further, when smooth muscle cells were preloaded with both EPA and DHA, they acted together in preventing the TXA2 induced smooth muscle cell proliferation. These results demonstrate that one of the mechanisms by which fish oils may prevent neointima formation is by making smooth muscle cells less responsive to TXA2 induced proliferation of smooth muscle cells.     

Role of vascular smooth muscle cell in the inflammation of atherosclerosis

Atherosclerosis is a pathologic process occurring within the artery, in which many cell types, including T cell, macrophages, endothelial cells, and smooth muscle cells, interact, and cause chronic inflammation, in response to various inner- or outer-cellular stimuli. Atherosclerosis is characterized by a complex interaction of inflammation, lipid deposition, vascular smooth muscle cell proliferation, endothelial dysfunction, and extracellular matrix remodeling, which will result in the formation of an intimal plaque. Although the regulation and function of vascular smooth muscle cells are important in the progression of atherosclerosis, the roles of smooth muscle cells in regulating vascular inflammation are rarely focused upon, compared to those of endothelial cells or inflammatory cells. Therefore, in this review, we will discuss here how smooth muscle cells contribute or regulate the inflammatory reaction in the progression of atherosclerosis, especially in the context of the activation of various membrane receptors, and how they may regulate vascular inflammation. [BMB Reports 2014; 47(1): 1-7]     

Antisense oligonucleotides to stromelysin mRNA inhibit injury-induced proliferation of arterial smooth muscle cells.

Smooth muscle cell migration and proliferation are important events in the formation of intimal lesions associated with atherosclerosis and restenosis following balloon angioplasty. To make this possible, the smooth muscle cell has to change from a contractile to an activated repair cell with capacity to synthesize DNA and extracellular matrix components. There is now considerable evidence that the extracellular matrix has important functions in modulating the phenotypic properties of smooth muscle cells, but less is known about the role of the matrix metalloproteinases. The present study investigates the role of stromelysin in the modulation of rat aortic smooth muscle cell morphology and function following mechanical injury in vitro and in vivo. Antisense mRNA oligonucleotides were used to investigate the role of stromelysin expression in injury-induced phenotypic modulation and the subsequent migration and proliferation of vascular smooth muscle cells. Cultured rat aortic smooth muscle cells and balloon-injured rat carotid arteries were used as experimental models. Light- and electron microscopy were used to follow changes in smooth muscle cell phenotype and lesion formation and incorporation of 3H-thymidine to detect DNA synthesis. Injury-induced DNA synthesis and migration in vitro were inhibited by 72% and 36%, respectively, by adding stromelysin antisense oligonucleotides to the medium prior to injury. In primary cultures, 67% of the smooth muscle cells treated with stromelysin antisense were retained in a contractile phenotype as judged by analysis of cell fine structure, compared to 15% untreated cells and 40% in cells treated with mismatched oligonucleotides. Examination of the carotid arteries one week after balloon injury likewise demonstrated a larger fraction of contractile cells in the inner parts of the media in vessels treated with antisense oligonucleotides compared to those treated with mismatched oligonucleotides. The neointima was also distinctly thinner in antisense-treated than in mismatched-treated and control arteries at this time. These findings indicate that stromelysin mRNA antisense oligonucleotides inhibited phenotypic modulation of rat arterial smooth muscle cells and so caused a decrease in migration and proliferation and neointima formation in response to vessel wall injury.     

Cyclin D1 Is a Bona Fide Target Gene of NFATc1 and Is Sufficient in the Mediation of Injury-induced Vascular Wall Remodeling

Platelet-derived growth factor BB induced cyclin D1 expression in a time- and nuclear factor of activated T cells (NFAT)-dependent manner in human aortic smooth muscle cells (HASMCs), and blockade of NFATs prevented HASMC DNA synthesis and their cell cycle progression from G₁ to S phase. Selective inhibition of NFATc1 by its small interfering RNA also blocked HASMC proliferation and migration. Characterization of the cyclin D1 promoter revealed the presence of several NFAT binding sites, and the site at nucleotide −1333 was found to be sufficient in mediating platelet-derived growth factor BB-induced cyclin D1 promoter-luciferase reporter gene activity. In addition to its role in cell cycle progression, cyclin D1 mediated HASMC migration in an NFATc1-dependent manner. Balloon injury-induced cyclin D1-CDK4 activity requires NFAT activation, and adenovirus-mediated transduction of cyclin D1 was found to be sufficient to overcome the blockade effect of NFATs by VIVIT on balloon injury-induced vascular wall remodeling events, including smooth muscle cell migration from the medial to luminal region, their proliferation in the intimal region, and neointima formation. Together, these results provide more mechanistic evidence for the role of NFATs, particularly NFATc1, in the regulation of HASMC proliferation and migration as well as vascular wall remodeling. NFATc1 could be a potential therapeutic target against the renarrowing of artery after angioplasty.     

HOXB7 overexpression promotes differentiation of C3H10T1/2 cells to smooth muscle cells

The presence of immature smooth muscle cells and ectopic tissues such as fully-formed bone in atherosclerotic lesions, may result from recapitulation of embryonic mechanisms in the artery wall. We hypothesized that expression of homeobox genes is triggered in atherogenesis and that these regulate proliferation and differentiation of multipotential progenitor cells along one or more specific lineages. We identified expression of the homeobox gene HOXB7 in clones of bovine aortic medial cells previously shown to be multipotent. HOXB7 was subsequently detected in human atherosclerotic plaques by RT-PCR and in situ hybridization. Expression was localized to areas adjacent to calcification and scattered in media and neointima, which may be reflective of a role in either osteoblastic or smooth muscle cell differentiation. To differentiate between these possibilities, we overexpressed HOXB7 in C3H10T1/2 cells, a multipotent cell line able to differentiate into vascular smooth muscle cells (SMC), as well as osteogenic and chondrogenic lineages. Results showed that overexpression of HOXB7 increased proliferation 3.5-fold, and induced an SMC-like cell morphology. In addition, expression of the early SMC markers calponin and SM22alpha increased 4-fold and 3-fold respectively by semi-quantitative RT-PCR. Expression of the intermediate SMC marker smooth muscle myosin heavy chain (SM-MHC) did not change. No increase in osteogenic or chondrogenic differentiation was detected, neither in the C3H10T1/2 cells nor in M2 cells, a bone marrow stromal cell line used to confirm this result. These findings suggest that HOXB7 plays a role in expansion of immature cell populations or dedifferentiation of mature cells.     

Molecular mechanisms of cholesterol or homocysteine effect in the development of atherosclerosis: Role of vitamin E

The development of atherosclerosis is a multifactorial process in which both elevated plasma cholesterol levels and proliferation of smooth muscle cells play a central role. Numerous studies have suggested the involvement of oxidative processes in the pathogenesis of atherosclerosis and especially of oxidized low density lipoprotein. Some epidemiological studies have shown an association between high dietary intake and high serum concentrations of vitamin E and lower rates of ischemic heart disease. Cell culture studies have shown that alpha-tocopherol brings about inhibition of smooth muscle cell proliferation. This takes place via inhibition of protein kinase C activity. alpha-Tocopherol also inhibits low density lipoprotein induced smooth muscle cell proliferation and protein kinase C activity. The following animal studies showed that vitamin E protects development of cholesterol induced atherosclerosis by inhibiting protein kinase C activity in smooth muscle cells in vivo. Elevated plasma levels of homocysteine have been identified as an important and independent risk factor for cerebral, coronary and peripheral atherosclerosis. However the mechanisms by which homocysteine promotes atherosclerotic plaque formation are not clearly defined. Earlier reports have been suggested that homocysteine exert its effect via H2O2 produced during its metabolism. To evaluate the contribution of homocysteine in the pathogenesis of vascular diseases, we examined whether the homocysteine effect on vascular smooth muscle cell growth is mediated by H2O2. We show that homocysteine induces DNA synthesis and proliferation of vascular smooth muscle cells in the presence of peroxide scavenging enzyme, catalase. Our data suggest that homocysteine induces smooth muscle cell growth through the activation of an H2O2 independent pathway and accelerate the progression of atherosclerosis. The results indicate a cellular mechanism for the atherogenicity of cholesterol or homocysteine and protective role of vitamin E in the development of atherosclerosis.     

The Ran GTPase-Activating Protein (RanGAP1) Is Critically Involved in Smooth Muscle Cell Differentiation,Proliferation and Migration following Vascular Injury: Implications for Neointima Formation and Restenosis

Differentiation and dedifferentiation, accompanied by proliferation play a pivotal role for the phenotypic development of vascular proliferative diseases (VPD), such as restenosis. Increasing evidence points to an essential role of regulated nucleoporin expression in the choice between differentiation and proliferation. However, whether components of the Ran GTPase cycle, which is of pivotal importance for both nucleocytoplasmic transport and for mitotic progression, are subject to similar regulation in VPD is currently unknown. Here, we show that differentiation of human coronary artery smooth muscle cell (CASMC) to a contractile phenotype by stepwise serum depletion leads to significant reduction of RanGAP1 protein levels. The inverse event, dedifferentiation of cells, was assessed in the rat carotid artery balloon injury model, a well-accepted model for neointima formation and restenosis. As revealed by temporospatial analysis of RanGAP1 expression, neointima formation in rat carotid arteries was associated with a significant upregulation of RanGAP1 expression at 3 and 7 days after balloon injury. Of note, neointimal cells located at the luminal surface revealed persistent RanGAP1 expression, as opposed to cells in deeper layers of the neointima where RanGAP1 expression was less or not detectable at all. To gain first evidence for a direct influence of RanGAP1 levels on differentiation, we reduced RanGAP1 in human coronary artery smooth muscle cells by siRNA. Indeed, downregulation of the essential RanGAP1 protein by 50% induced a differentiated, spindle-like smooth muscle cell phenotype, accompanied by an upregulation of the differentiation marker desmin. Reduction of RanGAP1 levels also resulted in a reduction of mitogen induced cellular migration and proliferation as well as a significant upregulation of the cyclin-dependent kinase inhibitor p27^KIP1, without evidence for cellular necrosis. These findings suggest that RanGAP1 plays a critical role in smooth muscle cell differentiation, migration and proliferation in vitro and in vivo. Appropriate modulation of RanGAP1 expression may thus be a strategy to modulate VPD development such as restenosis.     

Influence of arterial wall compliance on the pressure drop across coronary artery stenoses under hyperemic flow condition

Hemodynamic endpoints such as flow and pressure drop are often measured during angioplasty procedures to determine the functional severity of a coronary artery stenosis. There is a lack of knowledge regarding the influence of compliance of the arterial wall-stenosis on the pressure drop under hyperemic flows across coronary lesions. This study evaluates the influence in flow and pressure drop caused by variation in arterial-stenosis compliance for a wide range of stenosis severities. The flow and pressure drop were evaluated for three different severities of stenosis and tested for limiting scenarios of compliant models. The Mooney-Rivlin model defined the non-linear material properties of the arterial wall and the plaque regions. The non-Newtonian Carreau model was used to model the blood flow viscosity. The fluid (blood)-structure (arterial wall) interaction equations were solved numerically using the finite element method. Irrespective of the stenosis severity, the compliant models produced a lower pressure drop than the rigid artery due to compliance of the plaque region. A wide variation in the pressure drop was observed between different compliant models for significant (90% area occlusion) stenosis with 41.0, 32.1, and 29.8 mmHg for the rigid artery, compliant artery with calcified plaque, and compliant artery with smooth muscle cell proliferation, respectively. When compared with the rigid artery for significant stenosis the pressure drop decreased by 27.7% and 37.6% for the calcified plaque and for the smooth muscle cell proliferation case, respectively. These significant variations in pressure drop for the higher stenosis may lead to misinterpretation and misdiagnosis of the stenosis severity.     

Expression of M-CSF receptor encoded by c-fms on smooth muscle cells derived from arteriosclerotic lesion.

Vascular smooth muscle cells in atherosclerotic lesions are phenotypically different from those in the normal arterial wall, and no expression of macrophage colony stimulating factor (M-CSF) receptor encoded by the proto-oncogene c-fms has been demonstrated in normal smooth muscle cells. In the present study, we demonstrated expression of c-fms and high affinity binding of M-CSF in smooth muscle cells isolated from an experimental rabbit model of arteriosclerosis (intimal smooth muscle cells), while no expression of c-fms was shown in medial smooth muscle cells. In the immunocytochemical analysis, both types of smooth muscle cells similarly reacted with an antibody specific to muscle cells (HHF 35) but did not react with an antibody specific to rabbit macrophages (RAM 11). In intimal smooth muscle cells, when cells were incubated with acetylated low density lipoproteins (LDL), the binding of acetylated LDL and foam cell formation were observed. In response to M-CSF, tyrosine-phosphorylation, as analyzed by the detection of anti-phosphotyrosine-reactive proteins, and an increased rate of cell proliferation were observed in intimal smooth muscle cells. These results indicated that intimal smooth muscle cells have the characteristics of monocyte-macrophages such as the expression of c-fms, which may be related to their proliferation and phenotypic conversion into foam cells in atheromatous lesions.     

Lipoprotein lipase in atherosclerosis: its presence in smooth muscle cells and absence from macrophages

The localization of lipoprotein lipase (LPL) in human atherosclerotic lesions was studied with immunocytochemical techniques. In the fibrous cap and surrounding intima of the plaque, where the smooth muscle cell is the dominating cell type, a high number of cells reacted with anti-LPL. A much lower number of stained cells was seen in the central lipid core region where the macrophages dominate. Further characterization of the LPL-containing cells in tissue sections showed that most of them were smooth muscle cells. Only a minor fraction of the macrophages in the plaque contained the enzyme. The results were confirmed on isolated cells from atherosclerotic tissue. Lipoprotein lipase was also detected in smooth muscle cells of non-atherosclerotic arteries. These findings suggest that the smooth muscle cells are the major source of LPL in the vascular wall. However, the enzyme was not present in some of the smooth muscle cells in the atherosclerotic lesion. This may imply that LPL synthesis is down-regulated in the atherosclerotic plaque.     

Nerve growth factor activation of Erk-1 and Erk-2 induces matrix metalloproteinase-9 expression in vascular smooth muscle cells.

In response to vascular injury, smooth muscle cells migrate from the media into the intima, where they contribute to the development of neointimal lesions. Increased matrix metalloproteinase (MMP) expression contributes to the migratory response of smooth muscle cells by releasing them from their surrounding extracellular matrix. MMPs may also participate in the remodeling of extracellular matrix in vascular lesions that could lead to plaque weakening and subsequent rupture. Neurotrophins and their receptors, the Trk family of receptor tyrosine kinases, are expressed in neointimal lesions, where they induce smooth muscle cell migration. We now report that nerve growth factor (NGF)-induced activation of the TrkA receptor tyrosine kinase induces MMP-9 expression in both primary cultured rat aortic smooth muscle cells and in a smooth muscle cell line genetically manipulated to express TrkA. The response to NGF was specific for MMP-9 expression, as the expression of MMP-2, MMP-3, or the tissue inhibitor of metalloproteinase-2 was not changed. Activation of the Shc/mitogen-activated protein kinase pathway mediates the induction of MMP-9 in response to NGF, as this response is abrogated in cells expressing a mutant TrkA receptor that does not bind Shc and by pretreatment of cells with the MEK-1 inhibitor, U0126. Thus, these results indicate that the neurotrophin/Trk receptor system, by virtue of its potent chemotactic activity for smooth muscle cells and its ability to induce MMP-9 expression, is a critical mediator in the remodeling that occurs in the vascular wall in response to injury.     

Abl regulates smooth muscle cell proliferation by modulating actin dynamics and ERK1/2 activation

Abl is a nonreceptor tyrosine kinase that has a role in regulating migration and adhesion of nonmuscle cells as well as smooth muscle contraction. The role of Abl in smooth muscle cell proliferation has not been investigated. In this study, treatment with endothelin-1 (ET-1) and platelet-derived growth factor (PDGF) increased Abl phosphorylation at Tyr(412) (an indication of Abl activation) in vascular smooth muscle cells. To assess the role of Abl in smooth muscle cell proliferation, we generated stable Abl knockdown cells by using lentivirus-mediated RNA interference. ET-1- and PDGF-induced cell proliferation was attenuated in Abl knockdown cells compared with cells expressing control shRNA and uninfected cells. Abl silencing also arrested cell cycle progression from G(0)/G(1) to S phase. Furthermore, activation of smooth muscle cells with ET-1 and PDGF induced phosphorylation of ERK1/2 and Akt. Abl knockdown attenuated ERK1/2 phosphorylation in smooth muscle cells stimulated with ET-1 and PDGF. However, Akt phosphorylation upon stimulation with ET-1 and PDGF was not reduced. Because Abl is known to regulate actin polymerization in smooth muscle, we also evaluated the effects of inhibition of actin polymerization on phosphorylation of ERK1/2. Pretreatment with the actin polymerization inhibitor latrunculin-A also blocked ERK1/2 phosphorylation during activation with ET-1 and PDGF. The results suggest that Abl may regulate smooth muscle cell proliferation by modulating actin dynamics and ERK1/2 phosphorylation during mitogenic activation.     

LncRNA LEF1-AS1 regulates the migration and proliferation of vascular smooth muscle cells by targeting miR-544a/PTEN axis

Long noncoding RNAs (lncRNAs) play important roles in endothelium development. A lncRNA, LEF1-AS1, is recently emerging as a potent mediator of the proliferation and migration of a number of cells, including smooth muscle cells. However, the effects of LEF1-AS1 in atherosclerosis remains largely unknown. Specimens from patients with coronary artery atherosclerosis were collected. The quantitative real-time polymerase chain reaction was used to analyze levels of LEF1-AS1 and microRNA-544a (miR-544a). Western blot analysis was used to assess PTEN, P-Akt, and T-Akt protein expression. Proliferation, migration, and invasion of cells were analyzed by cell counting kit-8 assay, scratch wound assay, and transwell assay, respectively. The interaction between LEF1-AS1, miR-544a, and PTEN was probed using bioinformatical analysis and dual-luciferase assay. In plasma and tissue of patients with coronary artery atherosclerosis, LEF1-AS1 was upregulated and miR-544a was downregulated. A negative correlation was found between LEF1-AS1 and miR-544a. miR-544a overexpression reversed the inhibition of LEF1-AS1 in smooth muscle cell proliferation and invasion, which were mediated through the PTEN pathway. LEF1-AS1 regulates smooth muscle cell proliferation and migration through the miR-544a/PTEN axis, indicating that LEF1-AS1 may be a potential therapeutic target in atherosclerosis.     

Expression of connexin43 gap functions between cultured vascular smooth muscle cells is dependent upon phenotype

The smooth muscle cell is the predominant cell type of the arterial media. In the adult vascular system, smooth muscle cells are found primarily in the contractile phenotype, but following injury or during atherosclerotic plaque formation the secretory synthetic phenotype is expressed. Recently it has been shown that gap junction connexin43 messenger RNA levels are six times higher in cultured smooth muscle cells in the synthetic phenotype than in intact aorta. We have modulated rabbit aortic smooth muscle cells in culture between the synthetic phenotype and one resembling the contractile phenotype, and correlated gap junction expression with phenotype. A dual labelling technique with antibodies against smooth muscle myosin and a synthetic peptide constructed to match a portion of the connexin43 gap junction protein was used for these experiments. Gap junctions are numerous between synthetic phenotype cells but few are observed between contractile cells. Rat aortic smooth muscle cells were also cultured and the growth and structure of gap junctions followed in the synthetic phenotype by use of freeze-fracture electron microscopy and immunohistochemical techniques. Junctional plaques are similar in structure to those observed in cardiac muscle, their size and number increasing with time in culture. The increased numbers of gap junctions between synthetic phenotype smooth muscle cells may be important during vessel development, following injury, or in atherosclerotic plaque formation.     

The degree of unsaturation of dietary fatty acids and the development of atherosclerosis (review)

Atherosclerosis is the principal contributor to the pathogenesis of myocardial and cerebral infarction, gangrene and loss of function in the extremities. It results from an excessive inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. Atherosclerotic lesions develop fundamentally in three stages: dysfunction of the vascular endothelium, fatty streak formation and fibrous cap formation. Each stage is regulated by the action of vasoactive molecules, growth factors and cytokines. This multifactorial etiology can be modulated through the diet. The degree of unsaturation of dietary fatty acids affects lipoprotein composition as well as the expression of adhesion molecules and other pro-inflammatory factors, and the thrombogenicity associated with atherosclerosis development. Thus, the preventive effects of a monounsaturated-fatty acid-rich diet on atherosclerosis may be explained by the enhancement of high-density lipoprotein-cholesterol levels and the impairment of low-density lipoprotein-cholesterol levels, the low-density lipoprotein susceptibility to oxidation, cellular oxidative stress, thrombogenicity and atheroma plaque formation. On the other hand, the increase of high-density lipoprotein cholesterol levels and the reduction of thrombogenicity, atheroma plaque formation and vascular smooth muscle cell proliferation may account for the beneficial effects of polyunsaturated fatty acid on the prevention of atherosclerosis. Thus, the advantages of the Mediterranean diet rich in olive oil and fish on atherosclerosis may be due to the modulation of the cellular oxidative stress/antioxidant status, the modification of lipoproteins and the down-regulation of inflammatory mediators.     

Maturation-dependent neointima formation in fowl aorta.

Fowl show spontaneous elevation of blood pressure (BP) and neointimal plaque formation in the abdominal aorta at young ages. Maturation/age-dependent modulation of vascular lesions and a causal relationship between elevated BP and neointima formation, however, have not been clarified. We therefore intended to characterize, first, maturation/age-dependent neointimal plaque formation and vascular lesions and, second, their relationship to BP elevation. The BP measured in conscious domestic fowl, Gallus gallus, White Leghorn breed, DeKalb strain, via an indwelling catheter inserted into the ischiadic artery, increased with maturation in males; and at plateau level, BP (mmHg) was significantly (P<0.01) higher in males (194.0+/-4.6, n=11) than in females (169.3+/-3.1, n=10). Neointimal plaques consisting of neointimal cells and abundant extracellular matrix appeared initially in the distal segment of the abdominal aorta (lesion-prone area) of chicks as early as 6 weeks old. The area (size) of neointimal plaques right above the ischiadic bifurcation increased with maturation, whereas the plaque area became smaller with some degenerative changes in adult birds. In some birds, diffuse subendothelial hyperplasia and more extensive plaque formation at the branching points of the aorta were observed. The plaque area appears to be larger in birds, particularly in males that have higher BP (r=0.68). The width of aortic smooth muscle (SM) layers, measured in regions with no plaque, increased with age, whereas the number of cells per unit of area decreased, suggesting that hypertrophy of vascular SM occurs in response to exposure of the vascular wall to high BP. The number of cells was significantly (P<0.01) higher in the plaque than in underlying aortic SM layers or in layers with no plaque formation. Both neointimal plaques and underlying SM layers are immunohistochemically positive for alpha SM actin, suggesting that neointimal cells are modulated SM cells, whereas the staining with SM myosin heavy chain antibody is low in neointimal plaques. Furthermore, plasma arginine levels dropped in accordance with the time of neointimal plaque formation, whereas plasma cholesterol levels showed an age-dependent increase. The results suggest that spontaneous development of neointimal plaques may be a consequence of exposure to high BP and associated local hemodynamic changes.     

A multiphase model of growth factor-regulated atherosclerotic cap formation

Atherosclerosis is characterised by the growth of fatty plaques in the inner artery wall. In mature plaques, vascular smooth muscle cells (SMCs) are recruited from adjacent tissue to deposit a collagenous cap over the fatty plaque core. This cap isolates the thrombogenic plaque content from the bloodstream and prevents the clotting cascade that leads to myocardial infarction or stroke. Despite the protective role of the cap, the mechanisms that regulate cap formation and maintenance are not well understood. It remains unclear why some caps become stable, while others become vulnerable to rupture. We develop a multiphase PDE model with non-standard boundary conditions to investigate collagen cap formation by SMCs in response to diffusible growth factor signals from the endothelium. Platelet-derived growth factor stimulates SMC migration, proliferation and collagen degradation, while transforming growth factor (TGF)-\(\beta \) stimulates SMC collagen synthesis and inhibits collagen degradation. The model SMCs respond haptotactically to gradients in the collagen phase and have reduced rates of migration and proliferation in dense collagenous tissue. The model, which is parameterised using in vivo and in vitro experimental data, reproduces several observations from plaque growth in mice. Numerical and analytical results demonstrate that a stable cap can be formed by a relatively small SMC population and emphasise the critical role of TGF-\(\beta \) in effective cap formation. These findings provide unique insight into the mechanisms that may lead to plaque destabilisation and rupture. This work represents an important step towards the development of a comprehensive in silico plaque model.

     

Quantitative historadioautographic analysis of the cellular proliferation characteristics of the aortic wall in rabbits with experimental atherosclerosis

Aortic intima cell proliferation has been studied in 49 rabbits with progressing experimental hypercholesterolemia, using 3H-thymidine. It has been shown that focal cell proliferation is related to infiltration sites of apo-B lipoproteins and can be observed already at pre-lipid stage of atherogenesis. 4 types of proliferating cells involved in the formation of lipid plaques have been identified: endothelial cells, smooth muscle cells, fibroblasts and macrophages, with the latter predominating in the atherosclerotic plaque cover.