ICAM-1 expression by vascular smooth muscle cells is phenotype-dependent

MiR-146a encapsulated liposomes reduce vascular inflammatory responses through decrease of ICAM-1 expression, macrophage activation, and foam cell formation

Vascular insults can create an inflammatory cascade involving endothelial cell, smooth muscle cell, and macrophage activation which can eventually lead to vascular disease such as atherosclerosis. Several studies have identified microRNA 146a's (miR-146a) anti-inflammatory potential based on its role in regulating the nuclear factor kappa beta (NF-κβ) pathway. Therefore, in this study, we introduced exogenous miR-146a encapsulated by liposomes to lipopolysaccharide (LPS) stimulated vascular cells and macrophages to reduce inflammatory responses. First, the miR-146a encapsulated liposomes showed uniform size (radius 96.4 ± 4.22 nm) and round shape, long term stability (at least two months), high encapsulation efficiency (69.73 ± 0.07%), and were well transfected to human aortic endothelial cells (HAECs), human aortic smooth muscle cells (SMCs), and human differentiated monocytes (U937 cells). In addition, we demonstrated that miR-146a encapsulated liposomes reduced vascular inflammation responses in HAECs and SMCs through inhibition of ICAM-1 expression and decreased monocyte adhesion. In macrophages, miR-146a liposome treatment demonstrated decreased production of proinflammatory cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β), as well as reduced oxidized low-density lipoprotein (ox-LDL) uptake and foam cell formation. Thus, based on these results, miR-146a encapsulated liposomes may be promising for reducing vascular inflammation by targeting its multiple associated mediators.

Effects of Glucagon-Like Peptide-1 Analogue and Fibroblast Growth Factor 21 Combination on the Atherosclerosis-Related Process in a Type 2 Diabetes Mouse Model

BACKGROUND

Glucagon-like peptide-1 (GLP-1) analogues regulate glucose homeostasis and have anti-inflammatory properties, but cause gastrointestinal side effects. The fibroblast growth factor 21 (FGF21) is a hormonal regulator of lipid and glucose metabolism that has poor pharmacokinetic properties, including a short half-life. To overcome these limitations, we investigated the effect of a low-dose combination of a GLP-1 analogue and FGF21 on atherosclerosis-related molecular pathways.

METHODS

C57BL/6J mice were fed a high-fat diet for 30 weeks followed by an atherogenic diet for 10 weeks and were divided into four groups: control (saline), liraglutide (0.3 mg/kg/day), FGF21 (5 mg/kg/day), and low-dose combination treatment with liraglutide (0.1 mg/kg/day) and FGF21 (2.5 mg/kg/day) (n=6/group) for 6 weeks. The effects of each treatment on various atherogenesisrelated pathways were assessed.

RESULTS

Liraglutide, FGF21, and their low-dose combination significantly reduced atheromatous plaque in aorta, decreased weight, glucose, and leptin levels, and increased adiponectin levels. The combination treatment upregulated the hepatic uncoupling protein-1 (UCP1) and Akt1 mRNAs compared with controls. Matric mentalloproteinase-9 (MMP-9), monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) were downregulated and phosphorylated Akt (p-Akt) and phosphorylated extracellular signal-regulated kinase (p-ERK) were upregulated in liver of the liraglutide-alone and combination-treatment groups. The combination therapy also significantly decreased the proliferation of vascular smooth muscle cells. Caspase-3 was increased, whereas MMP-9, ICAM-1, p-Akt, and p-ERK1/2 were downregulated in the liraglutide-alone and combination-treatment groups.

CONCLUSION

Administration of a low-dose GLP-1 analogue and FGF21 combination exerts beneficial effects on critical pathways related to atherosclerosis, suggesting the synergism of the two compounds.

Glucagon-like peptide-1 receptor agonist reduces di(2-ethylhexyl) phthalate-induced atherosclerotic processes in vascular smooth muscle cells

Glucagon-like peptide-1 receptor (GLP1R) agonist is an incretin hormone and regulates glucose metabolism. However, phthalates, known as endocrine disruptors, can interfere with hormone homeostasis. In the present study, we aimed to estimate the impact of GLP1R agonist on di(2 ethylhexyl) phthalate (DEHP)-induced atherosclerosis. For this purpose, the effects of GLP1R agonist on various atherogenesis-related cellular processes and pathways were assessed in vascular smooth muscle cells (VSMCs). DEHP-induced cell proliferation and migration were significantly decreased by GLP1R agonist in VSMCs. Protein levels of matrix metalloproteinase (MMP)-2 and MMP-9 were significantly decreased in cells exposed to GLP1R agonist, compared with DEHP-treated cells. Expression levels of intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 were also reduced in GLP1R agonist-treated cells. Similarly, DEHP-associated phosphorylation of protein kinase B and extracellular signal-regulated kinase 1/2 was decreased in GLP1R agonist-treated cells, compared with DEHP-treated cells. Our findings suggest that treatment with GLP1R agonist counteracts the activation of pathways related to atherosclerosis.

Inhibition of lysine-specific demethylase 1A suppresses neointimal hyperplasia by targeting bone morphogenetic protein 2 and mediating vascular smooth muscle cell phenotype

OBJECTIVES

Vascular disorders are associated with phenotypical switching of vascular smooth muscle cells (VSMCs). We investigated the effect of bone morphogenetic protein (BMP)-2 in controlling VSMC phenotype and vascular disorder progression. Lysine (K)-specific demethylase 1A (KDM1A) has been identified to target BMP-2 and is employed as a therapeutic means of regulating BMP-2 expression in VSMCs.

MATERIALS AND METHODS

VSMCs were stimulated with angiotensin II, and the expression of KDM1A and BMP-2 was detected. VSMC proliferation, apoptosis, and phenotype were evaluated. An in vivo aortic injury model was established, and VSMC behaviour was evaluated by the expression of key markers. The activation of BMP-2-associated signalling pathways was examined.

RESULTS

We confirmed the inhibitory effect of KDM1A on BMP-2 activity and demonstrated that KDM1A inhibition prevented VSMC transformation from a contractile to synthetic phenotype. In angiotensin II-treated VSMCs, KDM1A inhibition triggered a decrease in cell proliferation and inflammatory response. In vivo, KDM1A inhibition alleviated post-surgery neointimal formation and collagen deposition, preventing VSMCs from switching into a synthetic phenotype and suppressing disease onset. These processes were mediated by BMP-2 through canonical small mothers against decapentaplegic signalling, which was associated with the activation of BMP receptors 1A and 1B.

CONCLUSIONS

The regulatory correlation between KDM1A and BMP-2 offers insights into vascular remodelling and VSMC phenotypic modulation. The reported findings contribute to the development of innovative strategies against vascular disorders.

Platelet-Derived Growth Factor Receptor-β Regulates Vascular Smooth Muscle Cell Phenotypic Transformation and Neuroinflammation After Intracerebral Hemorrhage in Mice

OBJECTIVE

Platelet-derived growth factor-BB activates platelet-derived growth factor receptor-β and promotes vascular smooth muscle cell phenotypic transformation. Elevated levels of non-muscle myosin IIB (SMemb) are found in secretory smooth muscle cells along with inflammatory mediators, such as intercellular adhesion molecule-1, which can amplify neutrophil infiltration into the brain. In the present study, we investigated the role of platelet-derived growth factor-BB/platelet-derived growth factor receptor-β following intracerebral hemorrhage-induced brain injury in mice, with emphasis on its ability to promote vascular smooth muscle cell phenotypic transformation followed by increased intercellular adhesion molecule-1 expression and elevated neutrophil infiltration in the vicinity of the hematoma. We also determined the extent to which plasmin from the hematoma influences the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system subsequent to intracerebral hemorrhage.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred and fifty six eight-week-old male CD1 mice.

INTERVENTIONS

Brain injury was induced by autologous arterial blood or plasmin injection into mouse brains. Small interfering RNA targeting platelet-derived growth factor receptor-β was administered 24 hours before intracerebral hemorrhage. A platelet-derived growth factor receptor antagonist, Gleevec, was administered following intracerebral hemorrhage. A mitogen-activated protein kinase-activated protein kinase 2 inhibitor (KKKALNRQLGVAA) was delivered with platelet-derived growth factor-BB in naïve animals. Platelet-derived growth factor-BB was injected with a plasmin inhibitor (ε-aminocaproic acid) in intracerebral hemorrhage mice. Plasmin-injected mice were given platelet-derived growth factor receptor-β small interfering RNA 24 hours before the operation. Neurological deficits, brain edema, western blots, and immunofluorescence were evaluated.

MEASUREMENTS AND MAIN RESULTS

Platelet-derived growth factor receptor-β small interfering RNA attenuated SMemb and intercellular adhesion molecule-1 expression and neutrophil infiltration at 24 hours post injury and reduced neurological deficits and brain edema at 24 and 72 hours following intracerebral hemorrhage. The platelet-derived growth factor receptor antagonist, Gleevec, reduced SMemb and intercellular adhesion molecule-1 expression. Platelet-derived growth factor receptor-β activation led to increased expression of intercellular adhesion molecule-1 and was reversed by KKKALNRQLGVAA in naïve mice. Plasmin inhibition suppressed platelet-derived growth factor receptor-β activation and neutrophil infiltration, whereas exogenous platelet-derived growth factor-BB increased platelet-derived growth factor receptor-β activation, regardless of plasmin inhibition. Platelet-derived growth factor receptor-β small interfering RNA decreased the expression of intercellular adhesion molecule-1 by plasmin injection.

CONCLUSION

The platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system contributes to neuroinflammation through vascular smooth muscle cell phenotypic transformation near the hematoma via the p38 mitogen-activated protein kinase/mitogen-activated protein kinase-activated protein kinase 2 pathway following intracerebral hemorrhage. Plasmin is hypothesized to be upstream of the proposed neuroinflammatory system. The therapeutic intervention targeting the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β is a novel strategy to prevent plasmin-induced brain injury following intracerebral hemorrhage.

Nanoformulated copper/zinc superoxide dismutase attenuates vascular cell activation and aortic inflammation in obesity

OBJECTIVE

Endothelial cell (EC) oxidative stress can lead to vascular dysfunction which is an underlying event in the development of cardiovascular disease (CVD). The lack of a potent and bioavailable anti-oxidant enzyme is a major challenge in studies on antioxidant therapy. The objective of this study is to determine whether copper/zinc superoxide dismutase (CuZnSOD or SOD1) after nanoformulation (nanoSOD) can effectively reduce EC oxidative stress and/or vascular inflammation in obesity.

METHODS

Human aortic endothelial cells (HAECs) were treated with native- or nanoSOD for 6 h followed by treatment with linoleic acid (LA), a free fatty acid, for 6-24 h. To determine the in vivo relevance, the effectiveness of nanoSOD in reducing vascular cell activation was studied in a mouse model of diet-induced obesity.

RESULTS

We noted that nanoSOD was more effectively taken up by ECs than native SOD. Western blot analysis further confirmed that the intracellular accumulation of SOD1 protein was greatly increased upon nanoSOD treatment. Importantly, nanoSOD pretreatment led to a significant decrease in LA-induced oxidative stress in ECs which was associated with a marked increase in SOD enzyme activity in ECs. In vivo studies showed a significant decrease in markers of EC/vascular cell activation and/or inflammation in visceral adipose tissue (VAT), thoracic aorta, and heart collected from nanoSOD-treated mice compared to obese control mice. Interestingly, the expression of metallothionein 2, an antioxidant gene was significantly increased in nanoSOD-treated mice.

CONCLUSION

Our data show that nanoSOD is very effective in delivering active SOD to ECs and in reducing EC oxidative stress. Our data also demonstrate that nanoSOD will be a useful tool to reduce vascular cell activation in VAT and aorta in obesity which, in turn, can protect against obesity-associated CVD, in particular, hypertension.

Smooth muscle phenotypic modulation--a personal experience

The idea that smooth muscle cells can exist in multiple phenotypic states depending on the functional demands placed upon them has been around for >5 decades. However, much of the literature today refers to only recent articles, giving the impression that it is a new idea. At the same time, the current trend is to delve deeper and deeper into transcriptional regulation of smooth muscle genes, and much of the work describing the change in biology of the cells in the different phenotypic states does not appear to be known. This loss of historical perspective regarding the biology of smooth muscle phenotypic modulation is what the current article has tried to mitigate.

CD44 Expressed on Both Bone Marrow–Derived and Non–Bone Marrow–Derived Cells Promotes Atherogenesis in ApoE-Deficient Mice

Objective— The purpose of this study was to distinguish the contributions of CD44 expressed on bone marrow–derived and non–bone marrow–derived cells to atherosclerosis.

Methods and Results— Using bone marrow chimeras, we compared the contributions of CD44 expressed on bone marrow–derived cells versus non–bone marrow–derived cells to the vascular inflammation underlying atherosclerosis. We show that CD44 in both bone marrow–derived and non–bone marrow–derived compartments promotes atherosclerosis in apoE −/− mice and mediates macrophage and T cell recruitment to lesions in vivo. We also demonstrate that CD44 on endothelial cells (ECs) as well as on macrophages and T cells enhances leukocyte-endothelial cell adhesion and transendothelial migration in vitro. Furthermore, CD44 on vascular smooth muscle cells (VSMCs) regulates their hyaluronan (HA)-dependent migration. Interestingly, in mice lacking CD44 in both compartments, where we observed the least inflammation, we also observed enhanced fibrous cap formation.

Conclusions— CD44 expressed on bone marrow–derived and non–bone marrow–derived cells both promote atherosclerosis in apoE-deficient mice. Furthermore, CD44 plays a pivotal role in determining the balance between inflammation and fibrosis in atherosclerotic lesions which can impact clinical outcome in humans.

Inflammatory mechanisms: the molecular basis of inflammation and disease

Inflammation participates importantly in host defenses against infectious agents and injury, but it also contributes to the pathophysiology of many chronic diseases. Interactions of cells in the innate immune system, adaptive immune system, and inflammatory mediators orchestrate aspects of the acute and chronic inflammation that underlie diseases of many organs. A coordinated series of common effector mechanisms of inflammation contribute to tissue injury, oxidative stress, remodeling of the extracellular matrix, angiogenesis, and fibrosis in diverse target tissues. Atherosclerosis provides an example of a chronic disease that involves inflammatory mechanisms. Recruitment of blood leukocytes characterizes the initiation of this disease. Its progression involves many inflammatory mediators, modulated by cells of both innate and adaptive immunity. The complications of established atheroma, including plaque disruption and thrombosis, also intimately involve inflammation. Mastery of the inflammatory response should aid the development of novel strategies to predict disease susceptibility, target and monitor therapies, and ultimately develop new approaches to the prevention and treatment of chronic diseases associated with aging, such as atherosclerosis.

Smooth muscle cell phenotype alters cocultured endothelial cell response to biomaterial-pretreated leukocytes

Model in vitro culturing systems were developed to analyze roles of biomaterial-induced leukocyte activation on endothelial cell (EC) and smooth muscle cell (SMC) phenotype, and their crosstalk. Isolated monocytes or neutrophils were pretreated with model biomaterial beads and applied directly to "more secretory" (cultured in media containing 5% fetal bovine serum) or forced contractile (serum and growth factor starved) human aortic SMCs (HASMCs), or to the human aortic EC (HAEC) surface of HAEC/HASMC cocultures (HASMC phenotype varied to be "more or less secretory") for 5 or 24 h of static culture. Surface expression of proinflammatory [ICAM-1, VCAM-1, E-selectin], procoagulant (tissue factor), and anticoagulant (thrombomodulin) markers, as well as HAEC proliferation, were assessed by flow cytometry. Incubation of HAEC with biomaterial-pretreated monocytes (and neutrophils to lesser degree) suppressed HAEC proliferation and induced a proinflammatory/procoagulant HAEC phenotype. This HAEC phenotype was amplified in coculture with "more secretory" HASMCs and subdued in coculture with "less secretory" HASMCs. Direct incubation of biomaterial-pretreated monocytes or neutrophils with "more secretory" HASMCs further increased HASMC ICAM-1 and tissue factor expression. Direct incubation of biomaterial-pretreated monocytes or neutrophils with forced contractile HASMCs upregulated ICAM-1, VCAM-1, and tissue factor expression above the presence of serum-containing media alone.

Anti-atherogenic properties of fibrates may be largely due to their anti-inflammatory effects

Current understanding of the pathophysiology of atherosclerosis has undergone a remarkable evolution. Compelling evidence has evolved at both the basic science and clinical level for the importance of inflammation in the pathogenesis of atherosclerosis and its complications. Recent research has shown that both systemic and local inflammation plays a central role in all phases of the atherosclerotic process. Inflammatory cells dominate early atherosclerotic lesions, inflammatory cytokines accelerate progression of the lesions, and activation of inflammation can elicit acute coronary syndromes. Robust clinical studies have affirmed that fibrates are anti-atherogenic and can improve the cardiovascular risk profile. Fibrates not only modulate the serum concentrations of triglyceride and cholesterol, but also inhibit systemic inflammatory statue and inflammatory response in vascular cells. Fibrates act anti-inflammatory effects in monocyte/macrophage, T lymphocyte, endothelial cells, vascular smooth muscle cells and adipocytes. Since atherosclerosis is now regarded as an inflammatory disease and those inflammatory cells play critical important roles in the initiation and development of atherosclerosis, we hypothesize that anti-atherogenic properties of fibrates may be largely due to their anti-inflammatory effects.

Functional modulation of smooth muscle cells by the inflammatory mediator CAP37

CAP37, a neutrophil-derived protein, originally identified for its antimicrobial activity is now known to have strong immunoregulatory effects on host cells. Recently, we described its expression and localization within the vascular endothelium associated with atherosclerotic plaques. Since CAP37 is a potent activator of endothelial cells and monocytes, two of the key cellular components of the atherosclerotic plaque, this study was undertaken to determine whether CAP37 had functional effects on smooth muscle cells another important cellular participant in atherosclerosis. Sections from atherosclerotic lesions were stained for the presence of CAP37 and smooth muscle cell alpha actin. The effect of CAP37 on aorta smooth muscle cell migration and proliferation was investigated and the upregulation of adhesion molecules was determined. Immunocytochemistry indicated that CAP37 was present in a subset of smooth muscle cells within atherosclerotic lesions, but was absent in normal vessels. Flow cytometry using double labeling for the proliferation marker Ki-67 and CAP37 demonstrates that CAP37 is mainly expressed in proliferating smooth muscle cells. We show that CAP37 supports migration and proliferation of smooth muscle cells in vitro. Furthermore, CAP37-treated smooth muscle cells expressed higher levels of the cell adhesion molecule ICAM-1 when compared with untreated cells. We suggest that due to its localization to atherosclerotic plaques and its ability to modulate smooth muscle cells, CAP37 may play a role in the progression of this disease.

p53 activates ICAM-1 (CD54) expression in an NF-kappaB-independent manner

Intercellular adhesion molecule-1 (ICAM-1) is a crucial receptor in the cell-cell interaction, a process central to the reaction to all forms of injury. Its expression is upregulated in response to a variety of inflammatory/immune mediators, including cellular stresses. The NF-kappaB signalling pathway is known to be important for activation of ICAM-1 transcription. Here we demonstrate that ICAM-1 induction represents a new cellular response to p53 activation and that NF-kappaB inhibition does not prevent the effect of p53 on ICAM-1 expression after DNA damage. Induction of ICAM-1 is abolished after treatment with the specific p53 inhibitor pifithrin-alpha and is abrogated in p53-deficient cell lines. Furthermore, we map two functional p53-responsive elements to the introns of the ICAM-1 gene, and show that they confer inducibility to p53 in a fashion similar to other p53 target genes. These results support an NF-kappaB-independent role for p53 in ICAM-1 regulation that may link p53 to ICAM-1 function in various physiological and pathological settings.

Expression of interleukin-1 beta and interleukin-1 receptor antagonist in oxLDL-treated human aortic smooth muscle cells and in the neointima of cholesterol-fed endothelia-denuded rabbits

The migration of vascular smooth muscle cells (VSMCs) from the media to the intima and the proliferation of intimal VSMCs are key events in restenotic lesion development. These events, which are preceded and accompanied by inflammation, are modulated by the proinflammatory cytokine, interleukin-1 beta (IL-1 beta), which induces vascular smooth muscle cells to express adhesion molecules and to proliferate. IL-1 beta action is complex and regulated, in part, by its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1ra). Whether there was a temporal and spatial correlation between IL-1 beta and IL-1ra expression in, and release by, oxidized low density lipoproteins (oxLDL)-stimulated human aortic smooth muscle cells (HASMCs) was determined by using ELISA and Western blot. In addition, IL-1 beta and IL-1ra expression was detected in the neointima of endothelia-denuded cholesterol-fed New Zealand white rabbits by immunohistochemistry and Western blot. In HASMCs, oxLDL induced IL-beta and IL-1ra expression and release in a dose- and time-dependent manner. Treatment with 20 microg/ml oxLDL resulted in increased IL-1 beta release after 6 h, which peaked at 24 h, and in increased IL-1ra release, first seen after 12 h, but continuing to increase for at least 48 h. In the cells, IL-beta expression showed a similar pattern to release, whereas IL-1ra expression was seen in unstimulated cells and was not increased by oxLDL treatment. Confocal microscopy showed colocalization of IL-beta and IL-1ra expression in oxLDL-stimulated HASMCs. oxLDL caused significant induction of nuclear factor kappa B and activator protein-1 DNA binding activity in HASMCs (6.6- and 3.3-fold, respectively). In cholesterol-fed endothelia-denuded rabbits, the notably thickened intima showed significant IL-1 beta and IL-1ra expression. These results provide further support for the role of IL-1 system in the pathogenesis of restenosis. This is the first demonstration of IL-1 beta and IL-1ra expression and secretion of oxLDL-treated HASMCs and their expression in the rabbit neointima, suggesting that the smooth muscle cells of the intima are an important source of these factors.

A role for rho in smooth muscle phenotypic regulation

The role of the small GTP-binding protein Rho in the process of smooth muscle cell (SMC) phenotypic modulation was investigated using cultured rabbit aortic SMCs. Both Rho transcription and Rho protein expression were high for the first 3 days of culture ("contractile" state cells), with expression decreasing after change to the "synthetic" state and peaking upon return to the contractile phenotype. Activation of Rho (indicated by translocation to the membrane) also peaked upon return to the contractile state and was low in synthetic state SMCs. Transient transfection of synthetic state rabbit SMCs with constitutively active Rho (vall4rho) caused a dramatic decrease in cell size and reorganization of cytoskeletal proteins to resemble those of the contractile phenotype; alpha-actin and myosin adopted a tightly packed, highly organized arrangement, whereas vimentin localized to the immediate perinuclear region and focal adhesions were enlarged. Conversely, specific inhibition of endogenous Rho, by expression of C3 transferase, resulted in the complete loss of actin and myosin filaments without affecting the distribution of vimentin. Focal adhesions were reduced in number. Thus, Rho plays a key role in regulating SMC phenotypic expression.

The adhesion receptor CD44 promotes atherosclerosis by mediating inflammatory cell recruitment and vascular cell activation

Atherosclerosis causes most acute coronary syndromes and strokes. The pathogenesis of atherosclerosis includes recruitment of inflammatory cells to the vessel wall and activation of vascular cells. CD44 is an adhesion protein expressed on inflammatory and vascular cells. CD44 supports the adhesion of activated lymphocytes to endothelium and smooth muscle cells. Furthermore, ligation of CD44 induces activation of both inflammatory and vascular cells. To assess the potential contribution of CD44 to atherosclerosis, we bred CD44-null mice to atherosclerosis-prone apoE-deficient mice. We found a 50-70% reduction in aortic lesions in CD44-null mice compared with CD44 heterozygote and wild-type littermates. We demonstrate that CD44 promotes the recruitment of macrophages to atherosclerotic lesions. Furthermore, we show that CD44 is required for phenotypic dedifferentiation of medial smooth muscle cells to the "synthetic" state as measured by expression of VCAM-1. Finally, we demonstrate that hyaluronan, the principal ligand for CD44, is upregulated in atherosclerotic lesions of apoE-deficient mice and that the low-molecular-weight proinflammatory forms of hyaluronan stimulate VCAM-1 expression and proliferation of cultured primary aortic smooth muscle cells, whereas high-molecular-weight forms of hyaluronan inhibit smooth muscle cell proliferation. We conclude that CD44 plays a critical role in the progression of atherosclerosis through multiple mechanisms.

Vascular smooth muscle cell phenotypic modulation in culture is associated with reorganisation of contractile and cytoskeletal proteins

Smooth muscle cells (SMC) exhibit a functional plasticity, modulating from the mature phenotype in which the primary function is contraction, to a less differentiated state with increased capacities for motility, protein synthesis, and proliferation. The present study determined, using Western analysis, double-label immunofluorescence and confocal microscopy, whether changes in phenotypic expression of rabbit aortic SMC in culture could be correlated with alterations in expression and distribution of structural proteins. "Contractile" state SMC (days 1 and 3 of primary culture) showed distinct sorting of proteins into subcellular domains, consistent with the theory that the SMC structural machinery is compartmentalised within the cell. Proteins specialised for contraction (alpha-SM actin, SM-MHC, and calponin) were highly expressed in these cells and concentrated in the upper central region of the cell. Vimentin was confined to the body of the cell, providing support for the contractile apparatus but not co-localising with it. In line with its role in cell attachment and motility, beta-NM actin was localised to the cell periphery and basal cortex. The dense body protein alpha-actinin was concentrated at the cell periphery, possibly stabilising both contractile and motile apparatus. Vinculin-containing focal adhesions were well developed, indicating the cells' strong adhesion to substrate. In "synthetic" state SMC (passages 2-3 of culture), there was decreased expression of contractile and adhesion (vinculin) proteins with a concomitant increase in cytoskeletal proteins (beta-non-muscle [NM] actin and vimentin). These quantitative changes in structural proteins were associated with dramatic changes in their distribution. The distinct compartmentalisation of structural proteins observed in "contractile" state SMC was no longer obvious, with proteins more evenly distributed throughout the cytoplasm to accommodate altered cell function. Thus, SMC phenotypic modulation involves not only quantitative changes in contractile and cytoskeletal proteins, but also reorganisation of these proteins. Since the cytoskeleton acts as a spatial regulator of intracellular signalling, reorganisation of the cytoskeleton may lead to realignment of signalling molecules, which, in turn, may mediate the changes in function associated with SMC phenotypic modulation.