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]     

Regulation of smooth muscle cell accumulation in diabetes-accelerated atherosclerosis

Diabetes leads to accelerated formation/progression of lesions of atherosclerosis. Cardiovascular disease thus develops earlier in people with type 1 or type 2 diabetes compared to people without diabetes, and cardiovascular (macrovascular) disease is the major cause of death in adults with diabetes. The molecular and cellular mechanisms leading to diabetes-accelerated atherosclerosis are not well understood. The arterial smooth muscle cell (SMC), one of the three or four principal cell types in atherosclerosis, has been extensively studied over the years. Proliferation and accumulation of SMCs are believed to play important roles in the progression of macrophage-rich lesions to fibroatheromas. Further progression of these atheromas into complicated vulnerable lesions that are likely to cause the acute clinical symptoms of atherosclerosis (myocardial infarction and stroke) may involve cell death and loss of SMCs from the fibrous cap of the lesion. Recent animal studies have shown that diabetes causes a marked increase in SMC accumulation and proliferation in atheromas. Hyperglycemia, advanced glycation end-products, insulin and lipid abnormalities associated with the diabetic environment have been suggested to increase SMC accumulation. Indeed, it is becoming increasingly clear that macrovascular disease associated with diabetes is a multifactorial disease. We review the factors and mechanisms that may regulate SMC proliferation and accumulation in different stages of lesion progression in diabetes. We propose that lipid abnormalities associated with diabetes can act in combination with growth factors present in the diabetic environment to increase SMC accumulation and accelerate lesion progression.     

The smooth muscle cell. III. Elastin synthesis in arterial smooth muscle cell culture

Primate arterial smooth muscle cells and skin fibroblasts were examined for their ability to synthesize elastin in culture. In the presence of the lathyrogen beta-aminopropionitrile, the smooth muscle cells incorporate [3H]lysine into a lysyl oxidase substrate that was present in the medium and associated with the cell layer. A component having a mol wt of 72,000 and an electrophoretic mobility similar to that of authentic tropoelastin was isolated from the labeled smooth muscle cells by coacervation and fractionation with organic solvents. In the absence of beta-aminopropionitrile, long-term cultures of smooth muscle cells incorporated [14C]lysine into desmosine and isodesmosine, the cross-link amino acids unique to elastin. In contrast, no desmosine formation occurred in the fibroblast cultures. These characteristics demonstrate that arterial smooth muscle cells are capable of synthesizing both soluble and cross-lined elastin in culture.     

Association of smooth membranes with spindle microtubules in the arterial smooth muscle cell

Smooth membrane-limited vesicles and cisternae are closely associated with spindle microtubules in mitotic pulmonary trunk smooth muscle cells of the rabbit. This may play a regulatory role in the structure-function integrity of the spindle.     

Smooth muscle and endothelial cell function in the pathogenesis of atherosclerosis.

Although clinical studies have been very useful in identifying factors that accelerate the development of atherosclerotic vascular disease, the pathogenesis of the vascular lesions remains unknown. Studies carried out in the last 10 years have shown that smooth muscle and endothelial cells of the vascular wall play a very important role in atherogenesis. It has become apparent that these cells are very active metabolically during the initiation and subsequent growth of the plaques, and that the materials that these cells produce and secrete are important in the composition and growth of the plaques. In addition, there are important interactions at the vessel wall-blood interface that involve endothelial cells, hemodynamic forces and many constituents of the blood, including platelets, lipoproteins, coagulation factors, fibrinolytic agents and leukocytes. In this article the numerous functions of both smooth muscle and endothelial cells are discussed and the effects of known atherogenic agents on these cellular functions are reviewed. Emphasis is placed on the important interactions that take place both within the vessel wall and at the vessel wall-blood interface. Understanding of the regulation of smooth muscle and endothelial cell function during the development and subsequent growth of fibrofatty plaques may be useful in designing appropriate therapeutic interventions to control atherosclerotic disease.     

A model of smooth muscle cell synchronization in the arterial wall

Vasomotion is a rhythmic variation in microvascular diameter. Although known for more than 150 years, the cellular processes underlying the initiation of vasomotion are not fully understood. In the present study a model of a single cell is extended by coupling a number of cells into a tube. The simulated results point to a permissive role of cGMP in establishing intercellular synchronization. In sufficient concentration, cGMP may activate a cGMP-sensitive calcium-dependent chloride channel, causing a tight spatiotemporal coupling between release of sarcoplasmic reticulum calcium, membrane depolarization, and influx of extracellular calcium. Low [cGMP] is associated only with unsynchronized waves. At intermediate concentrations, cells display either waves or whole cell oscillations, but these remain unsynchronized between cells. Whole cell oscillations are associated with rhythmic variation in membrane potential and flow of current through gap junctions. The amplitude of these oscillations in potential grows with increasing [cGMP], and, past a certain threshold, they become strong enough to entrain all cells in the vascular wall, thereby initiating sustained vasomotion. In this state there is a rhythmic flow of calcium through voltage-sensitive calcium channels into the cytoplasm, making the frequency of established vasomotion sensitive to membrane potential. It is concluded that electrical coupling through gap junctions is likely to be responsible for the rapid synchronization across a large number of cells. Gap-junctional current between cells is due to the appearance of oscillations in the membrane potential that again depends on the entrainment of sarcoplasmic reticulum and plasma membrane within the individual cell.     

Role of oxidized human plasma low density lipoproteins in atherosclerosis: effects on smooth muscle cell proliferation

The effects of oxidized human plasma low density lipoproteins (Ox-LDL) on the proliferation of cultured aortic smooth muscle cells was studied, employing viable cell counting, [³H] thymidine incorporation into DNA, and the release of lactate dehydrogenase (LDH) into the medium. Oxidized LDL (prepared by incubation of LDL with copper sulfate) exerted a concentration-dependent stimulation (2 fold, compared to control) of aortic smooth muscle cell proliferation at low concentrations (0.1 µg – 10 µg/ml medium). On the other hand, at high concentrations (25–200 µg/ml), Ox-LDL produced a pronounced decrease in viable cells, a decrease in the incorporation of [³H] thymidine into DNA, and an increase in the release of LDH in the medium. In this report, the previously postulated biological roles of oxidized-LDL in atherosclerosis are discussed in view of these findings.Abbreviations Ox-LDL Oxidized human plasma Low Density Lipoproteins - SMC Smooth Muscle Cells - LDH Lactate Dehydrogenase - LPC Lysophosphatidycholine - PC Phosphatidylcholine - TNF Tumor Necrosis Factor     

Vascular smooth muscle cell proliferation in the pathogenesis of atherosclerotic cardiovascular diseases

Atherosclerosis is the principal cause of myocardial infarction, stroke, and peripheral vascular disease, accounting for nearly half of all mortality in developed countries. For example, it has been estimated that atherosclerosis leads to approximately 500,000 deaths from coronary artery disease and 150,000 deaths from stroke every year in the United States (American Heart Association, 1996). Percutaneous transluminal angioplasty has become a well-established technique for revascularization of occluded arteries. However, the long-term efficacy of the procedure remains limited by progressive vessel renarrowing (restenosis) within the following few months after angioplasty. Abnormal vascular smooth muscle cell (VSMC) proliferation is thought to play an important role in the pathogenesis of both atherosclerosis and restenosis. Accordingly, considerable effort has been devoted to elucidate the mechanisms that regulate cell cycle progression in VSMCs. In the present article, we will review the different factors that are involved in the control of VSMC proliferation, especially in the context of cardiovascular disease. Ultimately, a thorough understanding of these regulatory networks may lead to the development of novel drug and gene therapies for the treatment of cardiovascular diseases. Therapeutic approaches that targeted specific cell-cycle control genes or growth regulatory molecules which effectively inhibited neointimal lesion formation will be also discussed.     

Role of thrombin in the pathogenesis of atherosclerosis

Atherosclerosis is an arterial disease associated with inflammation. Thrombin is a procoagulant and proinflammatory serine protease that contributes to the pathology of atherosclerosis by enhancing the expression of cell adhesion molecules, inducing the secretion of proinflammatory cytokines, activating inflammatory responses in atherosclerotic plaques, stimulating proliferation of aortic smooth muscle cells, and exacerbating vascular lesions at sites of injury. Hence, thrombin appears to be an important target for treatment of atherosclerosis and thrombin pharmacological inhibitors have significant therapeutic potency for suppressing inflammatory responses in cardiovascular diseases. This review summarizes the proinflammatory signaling functions of thrombin as well as the therapeutic potency of thrombin inhibitors in the pathogenesis of atherosclerosis and hence their potential therapeutic value in this condition.     

Role of calcium-phosphate deposition in vascular smooth muscle cell calcification

In this work we are studying whether calcium phosphate deposition (CPD) during vascular calcification is a passive or a cell-mediated mechanism. Passive CPD was studied in fixed vascular smooth muscle cells (VSMC), which calcify faster than live cells in the presence of 1.8 mM Ca2(+) and 2 mM P(i). CPD seems to be a cell-independent process that depends on the concentration of calcium, phosphate, and hydroxyl ions, but not on Ca × P(i) concentration products, given that deposition is obtained with 2 × 2 and 4 × 1 Ca × P(i) mM2 but not with 2 × 1 or 1 × 4 Ca × P(i) mM2. Incubation with 4 mM P(i) without CPD (i.e., plus 1 mM Ca) does not induce osteogene expression. Increased expression of bone markers such as Bmp2 and Cbfa1 is only observed concomitantly with CPD. Hydroxyapatite is the only crystalline phase in both lysed and live cells. Lysed cell deposits are highly crystalline, whereas live cell deposits still contain large amounts of amorphous calcium. High-resolution transmission electron microscopy revealed a nanostructure of rounded crystallites of 5-10 nm oriented at random in lysed cells, which is compatible with spontaneous precipitation. The nanostructure in live cells consisted of long fiber crystals, 10-nm thick, embedded in an amorphous matrix. This structure indicates an active role of cells in the process of hydroxyapatite crystallization. In conclusion, our data suggest that CPD is a passive phenomenon, which triggers the osteogenic changes that are involved in the formation of a well organized, calcified crystalline structure.     

Role of Nrf2 in the pathogenesis of atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vascular arterial walls. A number of studies have revealed the biological and genetic bases of atherosclerosis, and over 100 genes influence atherosclerosis development. Nrf2 plays an important role in oxidative stress response and drug metabolism, but the Nrf2 signaling pathway is closely associated with atherosclerosis development. During atherosclerosis progression, Nrf2 signaling modulates many physiological and pathophysiological processes, such as lipid homeostasis regulation, foam cell formation, macrophage polarization, redox regulation and inflammation. Interestingly, Nrf2 exhibits both pro- and anti-atherogenic effects in experimental animal models. These observations make the Nrf2 pathway a promising target to prevent atherosclerosis.     

Defective autophagy in vascular smooth muscle cells enhances cell death and atherosclerosis

Macroautophagy/autophagy is considered as an evolutionarily conserved cellular catabolic process. In this study, we aimed to elucidate the role of autophagy in vascular smooth muscle cells (SMCs) on atherosclerosis. SMCs cultured from mice with SMC-specific deletion of the essential autophagy gene atg7 (Atg7cKO) showed reduced serum-induced cell growth, increased cell death, and decreased cell proliferation rate. Furthermore, 7-ketocholestrerol enhanced apoptosis and the expression of CCL2 (chemokine [C-C motif] ligand 2) with the activation of TRP53, the mouse ortholog of human and rat TP53, in SMCs from Atg7cKO mice. In addition, Atg7cKO mice crossed with Apoe (apolipoprotein E)-deficient mice (apoeKO; Atg7cKO:apoeKO) showed reduced medial cellularity and increased TUNEL-positive cells in the descending aorta at 10 weeks of age. Intriguingly, Atg7cKO: apoeKO mice fed a Western diet containing 1.25% cholesterol for 14 weeks showed a reduced survival rate. Autopsy of the mice demonstrated the presence of aortic rupture. Analysis of the descending aorta in Atg7cKO:apoeKO mice showed increased plaque area, increased TUNEL-positive area, decreased SMC-positive area, accumulation of macrophages in the media, and adventitia and perivascular tissue, increased CCL2 expression in SMCs in the vascular wall, medial disruption, and aneurysm formation. In conclusion, our data suggest that defective autophagy in SMCs enhances atherosclerotic changes with outward arterial remodeling.     

Characteristics of human arterial smooth muscle cell cultures infected with cytomegalovirus

Summary Distinct, sequential events occurring during the destruction and simultaneous regrowth of human arterial smooth muscle cell (SMC) cultures infected with cytomegalovirus (CMV, AD169 strain) were characterized. The events were influenced by the typical phenotypic diversity reflecting relative states of differentiation of the SMC cultures. Progenitors of regeneration were a surviving population of small, undifferentiated or relatively undifferentiated SMCs. As these cells reached confluence focally, the number of cells reactive with antismooth muscle serum, i.e. differentiating, increased, and in some postconfluent foci the organization of SMCs resembled the topography of uninfected cultures. Thus, infected SMC cultures had a limited capacity to repopulate, to organize typically, and to differentiate. However, continuing cytopathic effects gradually destroyed much of the regrowth, and a relatively large, nondividing SMC with prominent cytoplasmic filaments, similar to SMCs in terminal, uninfected cultures, predominated. Infected cultures consisting overwhelmingly of the large terminal phenotype were far less productive of infectious CMV than cultures populated by SMCs with continuing capacity to divide. Gradually, cultures consisting of the terminal phenotype deteriorated as a result of sporadic cytopathic effects of CMV and an effect resembling “senescent” degeneration in uninfected, nondividing cultures in late passage. The infected, terminal phenotype could be a latent or persistent source of CMV antigen or nucleic acid-positive cells detected by different investigators in normal and in atheromatous, human tissue, assuming that it exists and survives for an extended period in vivo after infection of vascular SMC. The derivation of smooth muscle cell lines used in this investigation was supported through National Research and Demonstration Center grant HL-17269-07 from the National Heart, Lung and Blood Institute, Bethesda, MD.     

Phosphorylation of caldesmon in arterial smooth muscle

We have isolated caldesmon (Mr = 145,000), by immunoprecipitation, from [32P]orthophosphate-loaded porcine carotid arteries. In resting muscles, caldesmon was phosphorylated to 0.45 mol of PO4/mol protein, while the 20,000-dalton myosin regulatory light chain (LC20) was phosphorylated to less than 0.05 mol/mol. After stimulation by KCl (110 mM) for 75 min and phorbol 12,13-dibutyrate (PDBu, 1 microM) for 60 min, caldesmon phosphorylation levels rose to 0.96 and 1.1 mol/mol, respectively. LC20 phosphorylation increased to 0.49 mol/mol at 1 min of stimulation by KCl and decreased to 0.17 mol/mol at 60 min. With PDBu, phosphate incorporation into LC20 rose only slightly, reaching 0.09 mol/mol after 90 min. Muscles contracted with histamine (10 microM) or ouabain (1 microM) also demonstrated elevated levels of phosphate incorporation into caldesmon. In these muscles, LC20 phosphorylation levels were less than 0.05 mol/mol. Three major phosphopeptides of indistinguishable mobility were identified on maps of caldesmon from resting, KCl-stimulated, and PDBu-stimulated muscles. There was, however, little similarity between the phosphopeptide maps of caldesmon phosphorylated in intact tissue and maps of purified caldesmon phosphorylated in vitro by protein kinase C (Ca2+/phospholipid-dependent enzyme) or Ca2+/calmodulin kinase II.     

Proteoglycans in arterial smooth muscle cell cultures: an ultrastructural histochemical analysis

The extracellular matrix in cultures of arterial smooth muscle cells has been examined by ultrastructural histochemistry using each of the following cationic dyes: ruthenium red, Alcian blue, acridine orange, and safranin O. All dyes exhibited an affinity for a structural component that was either preserved as a granule with ruthenium red or Alcian blue, or as an extended filament or bottlebrush structure with acridine orange or safranin O. Both granules and filaments were removed when the cultures were pretreated with chondroitinase ABC, an enzyme that degrades the glycosaminoglycan moiety of some proteoglycans. These structural components of the extracellular matrix were not observed when cultures were prepared in the absence of the cationic dyes. Labeling experiments (35S-sulfate) revealed that approximately 40% of the total labeled proteoglycans were lost during routine processing for electron microscopy (i.e., fixation through dehydration). Inclusion of any one of the cationic dyes during fixation reduced the losses to less than 1%. The extended filamentous structure preserved by safranin O and acridine orange resembled the structure of purified proteoglycans prepared from the same cultures and spread on cytochrome c monolayer films. These observations suggest that proteoglycans exist as extended bottlebrush structures within the extracellular matrix, and support the interpretation that the granular deposits observed in the ruthenium red and Alcian blue preparations most likely represent individual proteoglycan monomers that have undergone molecular collapse during processing. In addition, the dyes also exhibited an affinity for chords of fine fibrils that contained small granules and/or filaments. Both the fibrillar material and the associated granular and filamentous structures enmeshed in the fibrils resisted digestion with chondroitinase ABC.     

Force-velocity relationships in hypertensive arterial smooth muscle

Increased total peripheral resistance is the cardinal haemodynamic disorder in essential hypertension. This could be secondary to alterations in the mechanical properties of vascular smooth muscle. Adequate study has not been made of the force-velocity (F-V) relationship in hypertensive arterial smooth muscle. Increased shortening in arterial smooth muscle would result in greater narrowing of arteries. The objectives of this investigation were to see if there is (i) increased shortening or increased maximum change in muscle length (delta Lmax where L stands for muscle length), (ii) an increased maximum velocity of shortening (Vmax) measured in l omicron per second where l omicron is the optimal muscle length for tension development, and (iii) a difference in maximum isometric tension (P omicron) developed in spontaneously hypertensive rat (SHR; N = 6) compared with normotensive Wistar Kyoto rat (WKY;N = 5) caudal artery strips. An electromagnetic muscle lever was employed in recording force-velocity data. Analysis of these data revealed the following: (a) the SHR mean P omicron of 6.21 +/- 1.01 N/cm2 was not different from the mean WKY P omicron of 6.97 +/- 1.64 N/cm2 (p greater than 0.05); (b) the SHR preparations showed greater shortening for all loads imposed; (c) the SHR Vmax of 0.016 l omicron/s was greater than the WKY Vmax of 0.013 l omicron/s (p less than 0.05). This study provides evidence that while hypertensive arterial smooth muscle is not able to produce more force than normotensive arterial smooth muscle, it is capable of faster and greater shortening. The latter could result in increased narrowing of hypertensive arteries and increased blood pressure.