Smooth muscle cell phenotypes in atherosclerotic lesions

Extreme Diversity of the Human Vascular Mesenchymal Cell Landscape

Background Human mesenchymal cells are culprit factors in vascular (patho)physiology and are hallmarked by phenotypic and functional heterogeneity. At present, they are subdivided by classic umbrella terms, such as "fibroblasts," "myofibroblasts," "smooth muscle cells," "fibrocytes," "mesangial cells," and "pericytes." However, a discriminative marker-based subclassification has to date not been established. Methods and Results As a first effort toward a classification scheme, a systematic literature search was performed to identify the most commonly used phenotypical and functional protein markers for characterizing and classifying vascular mesenchymal cell subpopulation(s). We next applied immunohistochemistry and immunofluorescence to inventory the expression pattern of identified markers on human aorta specimens representing early, intermediate, and end stages of human atherosclerotic disease. Included markers comprise markers for mesenchymal lineage (vimentin, FSP-1 [fibroblast-specific protein-1]/S100A4, cluster of differentiation (CD) 90/thymocyte differentiation antigen 1, and FAP [fibroblast activation protein]), contractile/non-contractile phenotype (α-smooth muscle actin, smooth muscle myosin heavy chain, and nonmuscle myosin heavy chain), and auxiliary contractile markers (h1-Calponin, h-Caldesmon, Desmin, SM22α [smooth muscle protein 22α], non-muscle myosin heavy chain, smooth muscle myosin heavy chain, Smoothelin-B, α-Tropomyosin, and Telokin) or adhesion proteins (Paxillin and Vinculin). Vimentin classified as the most inclusive lineage marker. Subset markers did not separate along classic lines of smooth muscle cell, myofibroblast, or fibroblast, but showed clear temporal and spatial diversity. Strong indications were found for presence of stem cells/Endothelial-to-Mesenchymal cell Transition and fibrocytes in specific aspects of the human atherosclerotic process. Conclusions This systematic evaluation shows a highly diverse and dynamic landscape for the human vascular mesenchymal cell population that is not captured by the classic nomenclature. Our observations stress the need for a consensus multiparameter subclass designation along the lines of the cluster of differentiation classification for leucocytes.

The biology of vascular calcification

Vascular calcification (VC), characterized by different mineral deposits (i.e., carbonate apatite, whitlockite and hydroxyapatite) accumulating in blood vessels and valves, represents a relevant pathological process for the aging population and a life-threatening complication in acquired and in genetic diseases. Similarly to bone remodeling, VC is an actively regulated process in which many cells and molecules play a pivotal role. This review aims at: (i) describing the role of resident and circulating cells, of the extracellular environment and of positive and negative factors in driving the mineralization process; (ii) detailing the types of VC (i.e., intimal, medial and cardiac valve calcification); (iii) analyzing rare genetic diseases underlining the importance of altered pyrophosphate-dependent regulatory mechanisms; (iv) providing therapeutic options and perspectives.

Changes of the coronary arteries and cardiac microvasculature with aging: Implications for translational research and clinical practice

Aging results in functional and structural changes in the cardiovascular system, translating into a progressive increase of mechanical vessel stiffness, due to a combination of changes in micro-RNA expression patterns, autophagy, arterial calcification, smooth muscle cell migration and proliferation. The two pivotal mechanisms of aging-related endothelial dysfunction are oxidative stress and inflammation, even in the absence of clinical disease. A comprehensive understanding of the aging process is emerging as a primary concern in literature, as vascular aging has recently become a target for prevention and treatment of cardiovascular disease. Change of life-style, diet, antioxidant regimens, anti-inflammatory treatments, senolytic drugs counteract the pro-aging pathways or target senescent cells modulating their detrimental effects. Such therapies aim to reduce the ineluctable burden of age and contrast aging-associated cardiovascular dysfunction. This narrative review intends to summarize the macrovascular and microvascular changes related with aging, as a better understanding of the pathways leading to arterial aging may contribute to design new mechanism-based therapeutic approaches to attenuate the features of vascular senescence and its clinical impact on the cardiovascular system.

IGF-1 and cardiovascular disease

Atherosclerosis is an inflammatory arterial pathogenic condition, which leads to ischemic cardiovascular diseases, such as coronary artery disease and myocardial infarction, stroke, and peripheral arterial disease. Atherosclerosis is a multifactorial disorder and its pathophysiology is highly complex. Changes in expression of multiple genes coupled with environmental and lifestyle factors initiate cascades of adverse events involving multiple types of cells (e.g. vascular endothelial cells, smooth muscle cells, and macrophages). IGF-1 is a pleiotropic factor, which is found in the circulation (endocrine IGF-1) and is also produced locally in arteries (endothelial cells and smooth muscle cells). IGF-1 exerts a variety of effects on these cell types in the context of the pathogenesis of atherosclerosis. In fact, there is an increasing body of evidence suggesting that IGF-1 has beneficial effects on the biology of atherosclerosis. This review will discuss recent findings relating to clinical investigations on the relation between IGF-1 and cardiovascular disease and basic research using animal models of atherosclerosis that have elucidated some of the mechanisms underlying atheroprotective effects of IGF-1.

microRNA-21 and hypertension

Hypertension, a multifactorial disease, is a major risk factor for the development of stroke, coronary artery disease, heart failure, and chronic renal failure. However, its underlying cellular and molecular mechanisms remain largely elusive. Numerous studies have shown that microRNAs (miRNAs) are involved in a variety of cellular processes, including cellular proliferation, apoptosis, differentiation, and the development of diseases. microRNA-21 (miR-21), a conserved single-stranded non-coding RNA that is composed of approximately 22 nucleotides, is one of the most intensively studied miRNAs in recent years, and it can regulate gene expression at the post-transcriptional level. miR-21 is expressed in many kinds of tumors and in the cardiovascular system, and it plays an important role in the occurrence and development of cardiovascular diseases. In recent years, more and more evidence indicates that miR-21 plays an important role in hypertension. This article reviews the source, function, and altered levels of miR-21 in hypertension and the role of miR-21 in the pathogenesis of hypertension and target organ damage (TOD). The potential role of miR-21 as a new target for predicting and treating hypertension is also explored.

Role of lipids and intraplaque hypoxia in the formation of neovascularization in atherosclerosis

According to the current paradigm, chronic vascular inflammation plays a central role in the pathogenesis of atherosclerosis. The plaque progression is typically completed with rupture and subsequent acute cardiovascular complications. Previously, the role of adventitial vasa vasorum in atherogenesis was underestimated. However, investigators then revealed that vasa vasorum neovascularization can be observed when no clinical manifestation of atherosclerosis is present. Vasa vasorum is involved in various proatherogenic processes such as intimal accumulation of inflammatory leukocytes, intimal thickening, necrotic core formation, intraplaque haemorrhage, lesion rupture and atherothrombosis. Due to the destabilizing action of the intraplaque microenvironment, lesional vasa vasorum neovessels experience serious defects and abnormalities during development that leads to their immaturity, fragility and leakage. Indeed, intraplaque neovessels are a main cause of intraplaque haemorrhage. Visualization techniques showed that presence of neovascularization/haemorrhage can serve as a good indicator of lesion instability and higher risk of rupture. Vasa vasorum density is a strong predictor of acute cardiovascular events such as sudden death, myocardial infarction and stroke. At present, arterial vasa vasorum neovascularization is under intensive investigation along with development of therapeutic tools focused on the control of formation of vasa vasorum neovessels in order to prevent plaque haemorrhage/rupture and thromboembolism. KEY MESSAGE Neovascularization plays an important role in atherosclerosis, being involved in unstable plaque formation. Presence of neovascularization and haemorrhage indicates plaque instability and risk of rupture. Various imaging techniques are available to study neovascularization.

Intimal smooth muscle cells are a source but not a sensor of anti-inflammatory CYP450 derived oxylipins

Vascular pathologies are associated with changes in the presence and expression of morphologically distinct vascular smooth muscle cells. In particular, in complex human vascular lesions and models of disease in pigs and rodents, an intimal smooth muscle cell (iSMC) which exhibits a stable epithelioid or rhomboid phenotype in culture is often found to be present in high numbers, and may represent the reemergence of a distinct developmental vascular smooth muscle cell phenotype. The CYP450-oxylipin - soluble epoxide hydrolase (sEH) pathway is currently of great interest in targeting for cardiovascular disease. sEH inhibitors limit the development of hypertension, diabetes, atherosclerosis and aneurysm formation in animal models. We have investigated the expression of CYP450-oxylipin-sEH pathway enzymes and their metabolites in paired intimal (iSMC) and medial (mSMC) cells isolated from rat aorta. iSMC basally released significantly larger amounts of epoxy-oxylipin CYP450 products from eicosapentaenoic acid > docosahexaenoic acid > arachidonic acid > linoleic acid, and expressed higher levels of CYP2C12, CYP2B1, but not CYP2J mRNA compared to mSMC. When stimulated with the pro-inflammatory TLR4 ligand LPS, epoxy-oxylipin production did not change greatly in iSMC. In contrast, LPS induced epoxy-oxylipin products in mSMC and induced CYP2J4. iSMC and mSMC express sEH which metabolizes primary epoxy-oxylipins to their dihydroxy-counterparts. The sEH inhibitors TPPU or AUDA inhibited LPS-induced NFκB activation and iNOS induction in mSMC, but had no effect on NFκB nuclear localization or inducible nitric oxide synthase in iSMC; effects which were recapitulated in part by addition of authentic epoxy-oxylipins. iSMCs are a rich source but not a sensor of anti-inflammatory epoxy-oxylipins. Complex lesions that contain high levels of iSMCs may be more resistant to the protective effects of sEH inhibitors.

•

We examined oxylipin production in different SMC phenotypes.

•

Intimal SMC produced more oxylipins than medial SMC.

•

CYPs were differentially expressed and regulated by LPS in intimal and medial SMC.

•

sEH inhibitors reduce inflammation in medial but not intimal SMC.

•

Intimal SMC are a source but not sensor of epoxy-oxylipins.

Vasa vasorum in atherosclerosis and clinical significance

Atherosclerosis is a chronic inflammatory disease that leads to several acute cardiovascular complications with poor prognosis. For decades, the role of the adventitial vasa vasorum (VV) in the initiation and progression of atherosclerosis has received broad attention. The presence of VV neovascularization precedes the apparent symptoms of clinical atherosclerosis. VV also mediates inflammatory cell infiltration, intimal thickening, intraplaque hemorrhage, and subsequent atherothrombosis that results in stroke or myocardial infarction. Intraplaque neovessels originating from VV can be immature and hence susceptible to leakage, and are thus regarded as the leading cause of intraplaque hemorrhage. Evidence supports VV as a new surrogate target of atherosclerosis evaluation and treatment. This review provides an overview into the relationship between VV and atherosclerosis, including the anatomy and function of VV, the stimuli of VV neovascularization, and the available underlying mechanisms that lead to poor prognosis. We also summarize translational researches on VV imaging modalities and potential therapies that target VV neovascularization or its stimuli.

Effect of Transmural Transport Properties on Atheroma Plaque Formation and Development

We propose a mathematical model of atheroma plaque initiation and early development in coronary arteries using anisotropic transmural diffusion properties. Our current approach is on the process on plaque initiation and intimal thickening rather than in severe plaque progression and rupture phenomena. The effect of transport properties, in particular the anisotropy of diffusion properties of the artery, on plaque formation and development is investigated using the proposed mathematical model. There is not a strong influence of the anisotropic transmural properties on LDL, SMCs and collagen distribution and concentrations along the artery. On the contrary, foam cells distribution strongly depends on the value of the radial diffusion coefficient of the substances [Formula: see text] and the ratio [Formula: see text]. Decreasing [Formula: see text] or diffusion coefficients ratio means a higher concentration of the foam cells close to the intima. Due to the fact that foam cells concentration is associated to the necrotic core formation, the final distribution of foam cells is critical to evolve into a vulnerable or fibrotic plaque.

Mathematical modelling of atheroma plaque formation and development in coronary arteries

Atherosclerosis is a vascular disease caused by inflammation of the arterial wall, which results in the accumulation of low-density lipoprotein (LDL) cholesterol, monocytes, macrophages and fat-laden foam cells at the place of the inflammation. This process is commonly referred to as plaque formation. The evolution of the atherosclerosis disease, and in particular the influence of wall shear stress on the growth of atherosclerotic plaques, is still a poorly understood phenomenon. This work presents a mathematical model to reproduce atheroma plaque growth in coronary arteries. This model uses the Navier-Stokes equations and Darcy's law for fluid dynamics, convection-diffusion-reaction equations for modelling the mass balance in the lumen and intima, and the Kedem-Katchalsky equations for the interfacial coupling at membranes, i.e. endothelium. The volume flux and the solute flux across the interface between the fluid and the porous domains are governed by a three-pore model. The main species and substances which play a role in early atherosclerosis development have been considered in the model, i.e. LDL, oxidized LDL, monocytes, macrophages, foam cells, smooth muscle cells, cytokines and collagen. Furthermore, experimental data taken from the literature have been used in order to physiologically determine model parameters. The mathematical model has been implemented in a representative axisymmetric geometrical coronary artery model. The results show that the mathematical model is able to qualitatively capture the atheroma plaque development observed in the intima layer.

Molecular imaging to identify the vulnerable plaque--from basic research to clinical practice

Cardiovascular disease (CVD) is still the leading cause of death in the Western World. Adverse outcomes of CVD include stroke, myocardial infarction, and heart failure. Atherosclerosis is considered to be the major cause of CVD and is estimated to cause half of all deaths in developed countries. Atherosclerotic lesions of the vessel wall may obstruct blood flow mechanically through stenosis, but rupture of atherosclerotic plaques causing formation of occlusive thrombi is far more prevalent. Unfortunately, conventional diagnostic tools fail to assess whether a plaque is vulnerable to rupture. Research over the past decade identified the biological processes that are implicated in the course towards plaque rupture, like cell death and inflammation. Knowledge about plaque biology propelled the development of imaging techniques that target biologic processes in order to predict the vulnerable plaque. This paper discusses novel and existing molecular imaging targets and addresses advantages and disadvantages of these targets and respective imaging techniques in respect of clinical application and socio-economic impact.

Improvement in coronary heart disease risk factors during an intermittent fasting/calorie restriction regimen: Relationship to adipokine modulations

BACKGROUND

The ability of an intermittent fasting (IF)-calorie restriction (CR) regimen (with or without liquid meals) to modulate adipokines in a way that is protective against coronary heart disease (CHD) has yet to be tested.

OBJECTIVE

Accordingly, we examined the effects of an IFCR diet on adipokine profile, body composition, and markers of CHD risk in obese women.

METHODS

Subjects (n = 54) were randomized to either the IFCR-liquid (IFCR-L) or IFCR-food based (IFCR-F) diet for 10 weeks.

RESULTS

Greater decreases in body weight and waist circumference were noted in the IFCR-L group (4 ± 1 kg; 6 ± 1 cm) versus the IFCR-F group (3 ± 1 kg; 4 ± 1 cm). Similar reductions (P < 0.0001) in fat mass were demonstrated in the IFCR-L (3 ± 1 kg) and IFCR-F group (2 ± 1 kg). Reductions in total and LDL cholesterol levels were greater (P = 0.04) in the IFCR-L (19 ± 10%; 20 ± 9%, respectively) versus the IFCR-F group (8 ± 3%; 7 ± 4%, respectively). LDL peak particle size increased (P < 0.01) in the IFCR-L group only. The proportion of small LDL particles decreased (P < 0.01) in both groups. Adipokines, such as leptin, interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and insulin-like growth factor-1 (IGF-1) decreased (P < 0.05), in the IFCR-L group only.

CONCLUSION

These findings suggest that IFCR with a liquid diet favorably modulates visceral fat and adipokines in a way that may confer protection against CHD.

Transsignaling of interleukin-6 crucially contributes to atherosclerosis in mice

OBJECTIVE

Transsignaling of interleukin (IL)-6 is a central pathway in the pathogenesis of disorders associated with chronic inflammation, such as Crohn disease, rheumatoid arthritis, and inflammatory colon cancer. Notably, IL-6 also represents an independent risk factor for coronary artery disease (CAD) in humans and is crucially involved in vascular inflammatory processes.

METHODS AND RESULTS

In the present study, we showed that treatment with a fusion protein of the natural IL-6 transsignaling inhibitor soluble glycoprotein 130 (sgp130) and IgG1-Fc (sgp130Fc) dramatically reduced atherosclerosis in hypercholesterolemic Ldlr(-/-) mice without affecting weight gain and serum lipid levels. Moreover, sgp130Fc treatment even led to a significant regression of advanced atherosclerosis. Mechanistically, endothelial activation and intimal smooth muscle cell infiltration were decreased in sgp130Fc-treated mice, resulting in a marked reduction of monocyte recruitment and subsequent atherosclerotic plaque progression. Of note, patients with CAD exhibited significantly lower plasma levels of endogenous sgp130, suggesting that a compromised counterbalancing of IL-6 transsignaling may contribute to atherogenesis in humans.

CONCLUSIONS

These data clarify, for the first time, the critical involvement of, in particular, the transsignaling of IL-6 in CAD and warrant further investigation of sgp130Fc as a novel therapeutic for the treatment of CAD and related diseases.

A gene expression signature that classifies human atherosclerotic plaque by relative inflammation status

BACKGROUND

Atherosclerosis is a complex disease requiring improvements in diagnostic techniques and therapeutic treatments. Both improvements will be facilitated by greater exploration of the biology of atherosclerotic plaque. To this end, we carried out large-scale gene expression analysis of human atherosclerotic lesions.

METHODS AND RESULTS

Whole genome expression analysis of 101 plaques from patients with peripheral artery disease identified a robust gene signature (1514 genes) that is dominated by processes related to Toll-like receptor signaling, T-cell activation, cholesterol efflux, oxidative stress response, inflammatory cytokine production, vasoconstriction, and lysosomal activity. Further analysis of gene expression in microdissected carotid plaque samples revealed that this signature is differentially expressed in macrophage-rich and smooth muscle cell-containing regions. A quantitative PCR gene expression panel and inflammatory composite score were developed on the basis of the atherosclerotic plaque gene signature. When applied to serial sections of carotid plaque, the inflammatory composite score was observed to correlate with histological and morphological features related to plaque vulnerability.

CONCLUSIONS

The robust mRNA expression signature identified in the present report is associated with pathological features of vulnerable atherosclerotic plaque and may be useful as a source of biomarkers and targets of novel antiatherosclerotic therapies.

Chondro/osteoblastic and cardiovascular gene modulation in human artery smooth muscle cells that calcify in the presence of phosphate and calcitriol or paricalcitol

Vitamin D sterol administration, a traditional treatment for secondary hyperparathyroidism, may increase serum calcium and phosphorus, and has been associated with increased vascular calcification (VC). In vitro studies suggest that in the presence of uremic concentrations of phosphorus, vitamin D sterols regulate gene expression associated with trans-differentiation of smooth muscle cells (SMCs) to a chondro/osteoblastic cell type. This study examined effects of vitamin D sterols on gene expression profiles associated with phosphate-enhanced human coronary artery SMC (CASMC) calcification. Cultured CASMCs were exposed to phosphate-containing differentiation medium (DM) with and without calcitriol, paricalcitol, or the calcimimetic R-568 (10(-11)-10(-7) M) for 7 days. Calcification of CASMCs, determined using colorimetry following acid extraction, was dose dependently increased (1.6- to 1.9-fold) by vitamin D sterols + DM. In contrast, R-568 did not increase calcification. Microarray analysis demonstrated that, compared with DM, calcitriol (10(-8) M) + DM or paricalcitol (10(-8) M) + DM similarly and significantly (P < 0.05) regulated genes of various pathways including: metabolism, CYP24A1; mineralization, ENPP1; apoptosis, GIP3; osteo/chondrogenesis, OPG, TGFB2, Dkk1, BMP4, BMP6; cardiovascular, HGF, DSP1, TNC; cell cycle, MAPK13; and ion channels, SLC22A3 KCNK3. R-568 had no effect on CASMC gene expression. Thus, SMC calcification observed in response to vitamin D sterol + DM may be partially mediated through targeting mineralization, apoptotic, osteo/chondrocytic, and cardiovascular pathway genes, although some gene changes may protect against calcification. Further studies to determine precise roles of these genes in development of, or protection against VC and cardiovascular disease are required.

SHIP2 and its involvement in various diseases

IMPORTANCE OF THE FIELD

Inositol polyphosphate 5-phosphatase (SHIP2) is an important negative regulator of intracellular phosphatidylinositol phosphate, a key second messenger of various intracellular signaling pathways. The functional upregulation of SHIP2 results in signaling blockade, leading to related disorders.

AREAS COVERED IN THIS REVIEW

We first summarize the role of SHIP2 in the regulation of insulin signaling and type 2 diabetes, including remarkable advances in pharmacological approaches. In addition, this review highlights new findings regarding the involvement of SHIP2 in a number of diseases, including cancer, neurodegenerative diseases, and atherosclerosis.

WHAT THE READER WILL GAIN

Recently identified small-molecule inhibitors of SHIP2 phosphatase activity emphasize the potential therapeutic value of SHIP2. In addition, currently available evidence demonstrates the importance of the scaffolding-type protein function of SHIP2. Understanding this interesting function will help clarify the complicated involvement of SHIP2 in various disorders.

TAKE HOME MESSAGE

Recent studies have demonstrated that SHIP2 is a promising therapeutic target for not only type 2 diabetes, but also cancer, neurodegenerative diseases, and atherosclerosis. Targeting SHIP2 through specific small-molecule inhibitors will have beneficial effects on these diseases.

Smooth muscle LDL receptor-related protein-1 inactivation reduces vascular reactivity and promotes injury-induced neointima formation

OBJECTIVE

Defective smooth muscle expression of LDL receptor-related protein-1 (Lrp1) increases atherosclerosis in hypercholesterolemic mice. This study explored the importance of smooth muscle Lrp1 expression under normolipidemic conditions.

METHODS AND RESULTS

Smooth muscle cells isolated from control (smLrp1(+/+)) and smooth muscle-specific Lrp1 knockout (smLrp1(-/-)) mice were characterized based on morphology, smooth muscle marker protein expression levels, and growth rates in vitro. Vascular functions were assessed by aortic constrictive response to agonist stimulation in situ and neointimal hyperplasia to carotid arterial injury in vivo. The smLrp1(-/-) smooth muscle cells displayed reduced alpha-actin and calponin expression and an accelerated growth rate attribtuable to sustained phosphorylation of platelet-derived growth factor receptor (PRGFR) and protein kinase B/Akt. Vasoconstrictive response to agonist stimulation was impaired in aortic rings isolated from smLrp1(-/-) mice. Injury-induced neointimal hyperplasia was significantly increased in smLrp1(-/-) mice. The increase in neointima was associated with corresponding elevated activation of PDGFR signaling pathway.

CONCLUSIONS

Smooth muscle expression of Lrp1 is important in maintaining normal vascular functions under normolipidemic conditions. The absence of Lrp1 expression results in greater smooth muscle cell proliferation, deficient contractile protein expression, impairment of vascular contractility, and promotion of denudation-induced neointimal hyperplasia.

Proteomic screening of antioxidant effects exhibited by radix Salvia miltiorrhiza aqueous extract in cultured rat aortic smooth muscle cells under homocysteine treatment

AIM OF THE STUDY

Still little is known about the cellular mechanisms that contribute to the attenuated proliferation of aortic smooth muscle cells under the influence of the oxidative stress factors such as homocysteine (Hcy). Thus, we aimed to evaluate whether Salvia miltiorrhiza Bunge (Labiatae), a Chinese medicinal herb widely used in folk medicine for therapy of variety of human cardiovascular disorders would modulate this Hcy promoted growth effect in model animal aortic cells system.

MATERIALS AND METHODS

The Salvia miltiorrhiza roots aqueous extract (SMAE) containing 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenyl lactic acid and salvianolic acid B, as confirmed by narrow-bore HPLC analyses with binary gradient elution was used in variable concentrations for the treatment of the rat aortic smooth muscle A10 cells under Hcy stimulation. Two-dimensional electrophoresis (2-DE) coupled with MALDI-TOF mass spectrometry was applied for the elucidation of protein changes characterizing the response of the rat A10 cells into the Hcy-induced oxidative stress.

RESULTS

This study showed that a low dose (0.015 mg/mL) of the SMAE significantly inhibited growth (>60%, p<0.05) of the Hcy stimulated rat A10 cells. In addition, concentration of intracellular reactive oxygen species (ROS) obviously decreased in the rat A10 cells after its incubation with SMAE in terms of catalase increasing activity. Next, marked down-regulation of protein kinase C beta-1 (PKC beta-1) and phosphorylated mitogen-activated protein kinase (p-MAPK) expression suggest that observed inhibitory effect of the polyphenol-rich SMAE on the Hcy-induced growth of rat A10 cells was realized via the PKC/p44/42 MAPK-dependent pathway. The intensity changes of 10 protein spots in response of the rat A10 cells to the Hcy-induced oxidative damage as alpha-4-tropomyosin, vimentin, F1F0-ATP synthase (beta subunit), glucose regulated protein 75 (GRP75), actin (fragment), prohibitin, capping protein, plakoglobin, endoplasmic reticulum protein (ERp29), and peptidylprolyl isomerase A (PPIase A), were detected with statistical significance (p<0.05). Meanwhile, it was showed that used here SMAE resist carbonylation of specific cytoskeleton and chaperone proteins as vimentin, alpha-4-tropomyosin and GRP75, respectively, leading to phenotype transformations in the rat A10 cells.

CONCLUSION

These data suggest that applied here SMAE exerts its protective effect through circulating ROS suppression and subsequent modulation of protein carbonylation in rat aortic smooth muscle A10 cells. Redox-proteomics protocol highlighted in this study may be applicable in facilitating the assessing potential novel molecular therapeutic targets to reduce cardiovascular risk related with elevated Hcy levels in various human populations and elucidating new mechanisms through which protein functions can be regulated by the redox status with the use of naturally occurring antioxidants.

Differentiation patterning of vascular smooth muscle cells (VSMC) in atherosclerosis

To investigate the involvement of transdifferentiation and dedifferentiation phenomena inside atherosclerotic plaques, we analyzed the differentiation status of vascular smooth muscle cells (VSMC) in vitro and in vivo. Forty normal autoptic and 20 atherosclerotic carotid endarterectomy specimens as well as 20 specimens of infrarenal and suprarenal aortae were analyzed for the expression of cytokeratins 7 and 18 and beta-catenin as markers (epithelial transdifferentiation) as well as CD31 and CD34 (embryonic dedifferentiation) by conventional and double fluorescence immunohistochemistry and reverse transcription polymerase chain reaction. Looking at these markers, additional cell culture experiments with human aortic (HA)-VSMC were done under stimulation with IL-1beta, IL-6, and TNF-alpha. Cytokeratins and beta-catenin were expressed significantly higher in atherosclerotic than in normal carotids primarily localized in VSMC of the shoulder/cap region of atherosclerotic lesions. Additionally, heterogeneous cellular coexpression of CD31 and/or CD34 was observed in subregions of progressive atherosclerotic lesions by VSMC. The expression of those differentiation markers by stimulated HA-VSMC showed a time and cytokine dependency in vitro. Our findings show that (1) VSMC of progressive atheromas have the ability of differentiation, (2) that transdifferentiation and dedifferentiation phenomena are topographically diverse localized in the subregions of advanced atherosclerotic lesions, and (3) are influenced by inflammatory cytokines like IL-1beta, IL-6, and TNF-alpha.

Gene expression programs of human smooth muscle cells: tissue-specific differentiation and prognostic significance in breast cancers

Smooth muscle is present in a wide variety of anatomical locations, such as blood vessels, various visceral organs, and hair follicles. Contraction of smooth muscle is central to functions as diverse as peristalsis, urination, respiration, and the maintenance of vascular tone. Despite the varied physiological roles of smooth muscle cells (SMCs), we possess only a limited knowledge of the heterogeneity underlying their functional and anatomic specializations. As a step toward understanding the intrinsic differences between SMCs from different anatomical locations, we used DNA microarrays to profile global gene expression patterns in 36 SMC samples from various tissues after propagation under defined conditions in cell culture. Significant variations were found between the cells isolated from blood vessels, bronchi, and visceral organs. Furthermore, pervasive differences were noted within the visceral organ subgroups that appear to reflect the distinct molecular pathways essential for organogenesis as well as those involved in organ-specific contractile and physiological properties. Finally, we sought to understand how this diversity may contribute to SMC-involving pathology. We found that a gene expression signature of the responses of vascular SMCs to serum exposure is associated with a significantly poorer prognosis in human cancers, potentially linking vascular injury response to tumor progression.

Genetic and molecular mechanisms of chemical atherogenesis

Injury to the cellular components of the vascular wall and blood by endogenous and exogenous chemicals has been associated with atherosclerosis in humans and experimental systems. The genetic and molecular mechanisms responsible for initiation and promotion of atherosclerotic changes include modulation of extracellular matrix-integrin axis, genes involved in the regulation of growth and differentiation and possibly, genomic stability. This review summarizes seminal studies over the past 20 years that shed light on critical gene-gene and gene-environment interactions mediating the atherogenic response to chemical injury.

Calcification inhibitors and Wnt signaling proteins are implicated in bovine artery smooth muscle cell calcification in the presence of phosphate and vitamin D sterols

Administration of active vitamin D sterols to treat secondary hyperparathyroidism in patients with chronic kidney disease receiving dialysis has been associated with elevated serum calcium and phosphorus levels, which may lead to increased risk of vascular calcification. However, calcimimetics, by binding to the parathyroid gland calcium-sensing receptors, reduce serum parathyroid hormone, calcium, phosphorus, and the calcium-phosphorus product. Using cultured bovine aorta vascular smooth muscle cells (BASMCs), an in vitro model of vascular calcification, we compared calcification levels and gene expression profiles after exposure to the phosphate source ss-glycerolphosphate (BGP), the active vitamin D sterols calcitriol and paricalcitol, the calcimimetic R-568, or BGP with the active vitamin D sterols or R-568. Cells exposed to BGP (10 mM) alone or with calcitriol or paricalcitol showed dose-dependent BASMC calcification. No change in calcification was observed in cultures exposed to BGP with R-568, consistent with the observed lack of calcium-sensing receptor expression. Microarray analysis using total cellular RNA from cultures exposed to vehicle or BGP in the absence and presence of 10(-8) M calcitriol or paricalcitol for 7 days showed that cells exposed to BGP with calcitriol or BGP with paricalcitol had virtually identical gene expression profiles, which differed from those of cells treated with BGP or vehicle alone. Several osteoblast- and chondrocyte-associated genes were modulated by BGP and vitamin D exposure. In this study, exposure of BASMCs to phosphate and active vitamin D sterols induced calcification and changes in expression of genes associated with mineralized tissue.

Vascular smooth muscle cell phenotypic plasticity and the regulation of vascular calcification

Vascular smooth muscle cells (VSMCs) exhibit an extraordinary capacity to undergo phenotypic change during development, in vitro and in association with disease. Unlike other muscle cells they do not terminally differentiate. Development and maintenance of the mature contractile phenotype is regulated by a number of interacting transcription factors. In response to injury contractile VSMCs can be induced to change phenotype, proliferate and migrate to effect repair. On completion of the repair process VSMCs return to a nonproliferating contractile phenotype. In this way, in the context of atherosclerosis, a protective fibrous cap is formed and maintained at sites of injury. However in disease, when modulatory signals are perturbed, this phenotypic transition is dysregulated and VSMCs are induced to undergo inappropriate differentiation into cells with features of other mesenchymal lineages such as osteoblasts, chondrocytes and adipocytes. Moreover, evidence is accumulating that these aberrant phenotypic transitions contribute to the pathogenesis of vascular diseases such as atherosclerosis and Monckeberg's Sclerosis. Indeed, the osteo/chondrocytic conversion of VSMCs and the association of this phenotype with vascular calcification is a paradigm for how inappropriate differentiation can influence disease processes. Understanding of the mechanisms and signalling pathways involved in this particular phenotype change is well advanced offering the possibility for the design of successful therapeutic interventions in the future.

Phenotypic conversion leads to structural and functional changes of smooth muscle sarcolemma

Continuous changes in the length of smooth muscles require a highly organized sarcolemmal structure. Yet, smooth muscle cells also adapt rapidly to altered environmental cues. Their sarcolemmal plasticity must lead to profound changes which affect transmembrane signal transduction as well as contractility. We have established porcine vascular and human visceral smooth muscle cultures of epithelioid and spindle-shaped morphology and determined their plasma membrane properties. Epithelioid cells from both sources contain a higher ratio of cholesterol to glycerophospholipids, and express a less diverse range of lipid-associated annexins. These findings point to a reduction in efficiency of membrane segregation in epithelioid cells. Moreover, compared to spindle-shaped cells, cholesterol is more readily extracted from epithelioid cells with methyl-beta-cyclodextrin and its synthesis is more susceptible to inhibition with lovastatin. The inability of epithelioid cells to process vasoactive metabolites, such as angiotensin or nucleotides further indicates that contractile properties are impaired. Phenotypic plasticity extends beyond the loss of smooth muscle cell marker genes. The plasma membrane has undergone profound functional changes which are incompatible with cyclic foreshortening, but might be important in the development of vascular disease.

Role of Angiogenesis in Cardiovascular Disease

The role of angiogenesis in atherosclerosis and other cardiovascular diseases has emerged as a major unresolved issue. Angiogenesis has attracted interest from opposite perspectives. Angiogenic cytokine therapy has been widely regarded as an attractive approach both for treating ischemic heart disease and for enhancing arterioprotective functions of the endothelium; conversely, a variety of studies suggest that neovascularization contributes to the growth of atherosclerotic lesions and is a key factor in plaque destabilization leading to rupture. Here, we critically review the evidence supporting a role for angiogenesis and angiogenic factors in atherosclerosis and neointima formation, emphasizing the problems raised by some of the landmark studies and the suitability of animal models of atherosclerosis and neointimal thickening for investigating the role of angiogenesis. Because many of the relevant studies have focused on the role of vascular endothelial growth factor (VEGF), we consider this work in the wider context of VEGF biology and in light of recent experience from clinical trials of VEGF and other angiogenic cytokines for ischemic heart disease. Also discussed are recent findings suggesting that, although angiogenesis may contribute to neointimal growth, it is not required for the initiation of intimal thickening. Our assessment of the evidence leads us to conclude that, although microvessels are a feature of advanced human atherosclerotic plaques, it remains unclear whether angiogenesis either plays a central role in the development of atherosclerosis or is responsible for plaque instability. Furthermore, current evidence from clinical trials of both proangiogenic and antiangiogenic therapies does not suggest that inhibition of angiogenesis is likely to be a viable therapeutic strategy for cardiovascular disease.

Role of ceramide in activation of stress-associated MAP kinases by minimally modified LDL in vascular smooth muscle cells

Interaction of oxidized low-density lipoprotein (LDL) with arterial smooth muscle cells (SMC) is believed to play a key role in the development of atherosclerosis. Depending on the extent of oxidation, apolipoproteins and/or lipids in the particle may be modified and thus lead to different cellular responses (e.g. proliferation or cell death). Here we report on the signaling effects of LDL, in which only the lipids were oxidized. This so-called minimally modified LDL (mmLDL) mainly activated components involved in stress response and apoptotic cell death including p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase/stress-activated protein kinase (JNK) as well as neutral and acid sphingomyelinase. In contrast, proliferative signaling elements such as extracellular regulated kinase, AKT-kinase and phospho-BAD seem to play a minor role as they were only slightly stimulated by mmLDL. Ceramide, the hydrolysis product of sphingomyelin, seems to be a key mediator as it mimics mmLDL by inducing activation of the same signaling components. Moreover, mmLDL- and ceramide-associated effects on apoptotic protein kinases were abolished by NB6, a specific inhibitor of acid sphingomyelinase. Thus, acid sphingomyelinase is very likely to be primarily responsible for triggering intracellular signal transduction in SMC after exposure to mmLDL via formation of ceramide by an autocatalytic mechanism.

Adipocytic differentiation and liver x receptor pathways regulate the accumulation of triacylglycerols in human vascular smooth muscle cells

Lipid accumulation by vascular smooth muscle cells (VSMC) is a feature of atherosclerotic plaques. In this study we describe two mechanisms whereby human VSMC foam cell formation is driven by de novo synthesis of fatty acids leading to triacylglycerol accumulation in intracellular vacuoles, a process distinct from serum lipoprotein uptake. VSMC cultured in adipogenic differentiation medium accumulated lipids and were induced to express the adipocyte marker genes adipsin, adipocyte fatty acid-binding protein, C/EBPalpha, PPARgamma, and leptin. However, complete adipocyte differentiation was not observed as numerous genes present in mature adipocytes were not detected, and the phenotype was reversible. The rate of lipid accumulation was not affected by PPARgamma agonists, but screening for the effects of other nuclear receptor agonists showed that activation of the liver X receptors (LXR) dramatically promoted lipid accumulation in VSMC. Both LXRalpha and LXRbeta were present in VSMC, and their activation with TO901317 resulted in induction of the lipogenic genes fatty acid synthetase, sterol regulatory element binding protein (SREBP1c), and stearoyl-CoA desaturase. 27-Hydroxycholesterol, an abundant oxysterol synthesized by VSMC acted as an LXR antagonist and, therefore, may have a protective role in preventing foam cell formation. Immunohistochemistry showed that VSMC within atherosclerotic plaques express adipogenic and lipogenic markers, suggesting these pathways are present in vivo. Moreover, the development of an adipogenic phenotype in VSMC is consistent with their known phenotypic plasticity and may contribute to their dysfunction in atherosclerotic plaques and, thus, impinge on plaque growth and stability.

"Vulnerable plaques" — ticking of the time bomb

Atherosclerosis and its sequelae are one of the leading causes of morbidity and mortality, especially in the developed nations. Over the years, treatment protocols have changed with the changing understanding of the disease process. Inflammatory mechanisms have emerged as key players in the formation of the atherosclerotic plaque. For the majority of its life span, the plaque develops silently and only some exhibit overt clinical manifestations. The purpose of this review is to examine the inherent properties of some of these "vulnerable" or symptomatic plaques. Rupture of the plaque is related to the thickness of the fibrous cap overlying the necrotic lipid core. A thin cap is more likely to lead to rupture. Multiple factors broadly grouped as the "determinants of vulnerability" are responsible for directly or indirectly influencing the plaque dynamics. Apoptosis is considered an important underlying mechanism that contributes to plaque instability. Inflammatory reactions within the plaque trigger apoptosis by cell–cell contact and intra cellular death signaling. Once started, the apoptotic process affects all of the components that make up the plaque, including vascular smooth muscle cells, endothelial cells, and macrophages. Extensive research has identified many of the key cellular and molecular regulators that play a part in apoptosis within the atherosclerotic lesion. This information will help us to gain a better understanding of the underlying mechanisms at the cellular and molecular level and enable us to formulate better therapeutic strategies to combat this disease.Key words: apoptosis, atherosclerosis, inflammation, plaque stability, vulnerable plaques.

Human Smooth Muscle Cell Subpopulations Differentially Accumulate Cholesteryl Ester When Exposed to Native and Oxidized Lipoproteins

BACKGROUND

Vascular smooth muscle cells (SMCs) manifest diverse phenotypes and emerging evidence suggests this is caused by inherently distinct SMC subtypes. Recently, Li et al (Circ Res 2001;89:517-525) successfully cloned 2 uniquely responsive SMC subpopulations from a single human artery and we used this unique resource to test the hypothesis that distinct SMC subtypes are differential precursors of foam cell formation.

METHODS AND RESULTS

When challenged with human atherogenic native or oxidized hypertriglyceridemic very-low-density lipoprotein (HTG-VLDL), the larger, slower-growing, spindle-shaped HITB5 SMC clone accumulated significantly more cholesteryl ester (CE) and triglyceride (TG) than the smaller, faster-growing epithelioid-shaped HITA2 SMC clone (10 versus 2 microg CE/mg cell protein [PN] and 60 versus 7 microg TG/mg PN, P<0.05). Lipoprotein lipase (LPL), a key enzyme involved in lipoprotein uptake, was identified as one differentially expressed protein that altered the predisposition of HITA2 SMCs for lipid accumulation. Although HITB5 SMCs secreted significantly more LPL than did HITA2 SMCs (0.7 versus 0.2 U/mL media, P<0.05), the addition of bovine milk LPL to HITA2 SMCs, significantly increased native and oxidized HTG-VLDL-induced lipid accumulation.

CONCLUSIONS

Inherently distinct SMC subsets are differentially predisposed to lipoprotein-induced lipid accumulation. Moreover, the environment can influence the response of SMC subsets to atherogenic lipoproteins.

SM22α Modulates Vascular Smooth Muscle Cell Phenotype During Atherogenesis

The function of cytoskeletal proteins in the modulation of vascular smooth muscle cell (SMC) phenotype during vascular disease is poorly understood. In this report, we used a combination of gene targeting and Cre/lox-mediated cell fate mapping in mice to investigate the role of SM22α, an SMC-specific cytoskeletal protein of unknown function, in the development of atherosclerosis. In hypercholesterolemic ApoE-deficient mice, genetic ablation of SM22α resulted in increased atherosclerotic lesion area and a higher proportion of proliferating SMC-derived plaque cells. These results identify a role for SM22α in the regulation of SMC phenotype during atherogenesis.

Stromal cells of fibrodysplasia ossificans progressiva lesions express smooth muscle lineage markers and the osteogenic transcription factor Runx2/Cbfa-1: clues to a vascular origin of heterotopic ossification?

Fibrodysplasia ossificans progressiva (FOP) is a rare heritable genetic disorder, which is characterized pathologically by sporadic episodes of explosive growth of mesenchymal cells in skeletal muscle followed by cellular differentiation to heterotopic bone through an endochondral process. This study examined the histological origin and differentiation state of stromal cells in early FOP lesions and investigated the association between the phenotype of these FOP cells and bone formation. Interestingly, FOP lesional stromal cells were found to display characteristics of the smooth muscle (SM) cell lineage and are therefore potentially of vascular origin. These cells co-express multiple SM lineage markers along with multiple proteins associated with bone formation including the obligate osteogenic transcription factor Runx2/Cbfa-1. It is hypothesized that the stromal cells of early FOP lesions may be locally recruited vascular cells or cells of the bone marrow stroma and that these cells maintain the potential (given the correct environmental stimuli) to differentiate along an endochondral ossification pathway.

Genetic influence on cigarette-induced cardiovascular disease

Cigarette smoking as an addictive habit has accompanied human beings for more than 4 centuries. It is also one of the most potent and prevalent environmental health risks human beings are exposed to, and it is responsible for more than 1000 deaths each day in the United States. With recent research progress, it becomes clear that cigarette smoking can cause almost all major diseases prevalent today, such as cancer or heart disease. These detrimental effects are not only present in active smokers who choose the risk, but also to innocent bystanders, as passive smokers, who are exposed to cigarettes not-by-choice. While the cigarette-induced harm to human health is indiscriminate and severe, the degree of damage also varies from individual to individual. This intersubject variability in cigarette-induced pathologies is partly mediated by genetic variants of genes that may participate in detoxification process, eg, cytochrome P450 (CYP), cellular susceptibility to toxins, such as p53, or disease development. Through population studies, we have learned that certain CYP1A1 variants, such as Mspl polymorphism, may render the carriers more susceptible to cigarette-induced lung cancer or severe coronary atherosclerosis. The endothelial nitric oxide synthase intron 4 rare allele homozygotes are more likely to have myocardial infarction if they also smoke. In vitro experimental approach has further demonstrated that cigarettes may specifically regulate these genes in genotype-dependent fashion. While we still know little about genetic basis and molecular pathways for cigarette-induced pathological changes, understanding these mechanisms will be of great value in designing strategies to further reduce smoking in targeted populations, and to implement more effective measures in prevention and treatment of cigarette-induced diseases.

Differential effects of gemfibrozil on migration, proliferation and proteoglycan production in human vascular smooth muscle cells

The aim of this study was to determine, if gemfibrozil has anti-atherogenic actions on human vascular smooth muscle cells (SMCs) and whether these actions are affected by high glucose concentrations, which mimic the hyperglycemia of diabetes. Proliferation of SMCs treated with gemfibrozil was estimated by cell counting (Coulter Counter) and [3H]thymidine incorporation, migration in a scrape-wound assay, proteoglycan (PG) biosynthesis and glycosaminoglycan (GAG) synthesis on xyloside by [35S]sulfate labeling and sizing by sodium dodecyl sulphide-polyacrylamide gel electrophoresis (SDS-PAGE). Gemfibrozil (100 micromol/l) did not affect migration in low or high glucose media. Gemfibrozil caused concentration-dependent inhibition of proliferation in low glucose media (24% inhibition at 100 micromol/l, P<0.01) and inhibited the re-initiation of DNA synthesis by 33.3% (100 micromol/l, P<0.05) in low glucose and 31.4% (100 micromol/l, P<0.001) in high glucose conditions. In low and high glucose media, gemfibrozil (100 micromol/l) reduced total PG production in the presence of TGF-beta 1, which was associated with a decrease in the apparent size of PGs. Gemfibrozil and another PPAR-alpha ligand, WY-14643, significantly inhibited basal and TGF-beta1 stimulated GAG synthesis. We conclude that some SMCs properties associated with atherogenesis are favorably affected by gemfibrozil. Hence, direct vascular actions of gemfibrozil observed in this study may contribute to the reduction in cardiovascular disease observed in clinical studies with gemfibrozil.

Sialyltransferase activity of human plasma and aortic intima is enhanced in atherosclerosis

Sialyltransferase activity has been determined in membrane preparations containing the Golgi apparatus that were isolated from atherosclerotic and normal human aortic intima as well as in plasma of patients with documented atherosclerosis and healthy donors by measuring the transfer of N-acetylneuraminic acid (NeuAc) from CMP-NeuAc to asialofetuin. The asialofetuin sialyltransferase activity was found to be 2 times higher in the atherosclerotic intima as compared to the normal intima and 2-fold higher in patients' plasma than in that from healthy donors. The mean values of the apparent Michaelis constant (K(m)) for the sialylating enzyme for both tissues did not differ and were close for the intima and plasma. In contrast, the maximal velocity (V(max)) was 2 times higher for the atherosclerotic intima than for the normal intima and 3 times higher for patients' plasma than for that of the donors. These results suggest that the activity of asialofetuin sialyltransferases of aortal intima is enhanced in atherosclerosis as is the secretion of their soluble forms into patients' plasma.

Novel mechanisms of the antiproliferative effects of amlodipine in vascular smooth muscle cells from spontaneously hypertensive rats

The calcium channel blocker amlodipine continues to be of interest due to its potential proven ability to hinder the progression of atherosclerosis and reduce the number of clinical ischemic events. Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) are useful in the study of atherosclerosis because they show exaggerated growth with production of angiotensin II (Ang II) by conversion to the synthetic phenotype. To clarify mechanisms of the antiproliferative effects of amlodipine, we evaluated effects of the expression of growth factors, the changes in phenotype, and the proliferation of VSMC from SHR. Amlodipine significantly inhibited basal DNA synthesis and proliferation of VSMC from SHR. Amlodipine also inhibited expression of platelet-derived growth factor (PDGF) A-chain, transforming growth factor beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) mRNAs in VSMC from SHR. Decreases in levels of PDGF A-chain and bFGF mRNAs in VSMC from SHR were greater with amlodipine than with nifedipine. Amlodipine significantly inhibited expression of the synthetic phenotype markers osteopontin and matrix Gla mRNAs, indicating that it inhibited the exaggerated growth of VSMC from SHR and suppressed the change from the contractile phenotype to the synthetic phenotype. Thus, amlodipine may be a beneficial therapeutic agent for patients with hypertensive vascular diseases.

Heterogeneity of smooth muscle cells in advanced human atherosclerotic plaques: intimal smooth muscle cells expressing a fibroblast surface protein are highly activated by platelet-released products

BACKGROUND

In vascular disease, smooth muscle cells (SMC) undergo phenotypic modulation and may acquire properties resembling those of fibroblasts in tissue wound healing.

AIMS

We aimed to show the differential expression of a fibroblast surface protein (FSP) by SMC in atherosclerotic lesions.

RESULTS

In early human coronary atherosclerotic lesions the expression of FSP in the intima was absent. In contrast, 29 of 29 middle/advanced lesions contained intimal SMC expressing high levels of FSP. Fibroblast surface protein positive SMC were negative for desmin but expressed variable levels of alpha-SM actin, SM caldesmon, SM myosin heavy chain and vimentin. Explants from advanced atherosclerotic lesions yielded two main SMC subpopulations. SMC over-expressing FSP exhibited higher in vitro mitogenic response (premitotic DNA synthesis) to sera (2- to 8-fold) and platelet-released products (8- to 26-fold), especially from thrombin-activated platelets, than FSP-negative SMC.

CONCLUSIONS

Our results suggest that the expression of FSP in SMC could indicate an activated phenotype, and the presence of highly positive FSP cells in the atherosclerotic lesions might be indicative of an increased SMC responsiveness to processes that locally generate thrombin and activate platelets.

Telomere erosion and senescence in human articular cartilage chondrocytes

Aging and the degeneration of articular cartilage in osteoarthritis are distinct processes, but a strong association exists between age and the incidence and prevalence of osteoarthritis. We hypothesized that this association is due to in vivo replicative senescence, which causes age-related declines in the ability of chondrocytes to maintain articular cartilage. For this hypothesis to be tested, senescence-associated markers were measured in human articular chondrocytes from donors ranging in age from 1 to 87 years. These measures included in situ staining for senescence-associated beta-galactosidase activity, (3)H-thymidine incorporation assays for mitotic activity, and Southern blots for telomere length determinations. We found that senescence-associated beta-galactosidase activity increased with age, whereas both mitotic activity and mean telomere length declined. These findings indicate that chondrocyte replicative senescence occurs in vivo and support the hypothesis that the association between osteoarthritis and aging is due in part to replicative senescence. The data also imply that transplantation procedures performed to restore damaged articular surfaces could be limited by the inability of older chondrocytes to form new cartilage after transplantation.

Prevention of human smooth muscle cell proliferation without induction of apoptosis by the topoisomerase I inhibitor topotecan

Despite significant improvements in the treatment of atherosclerotic disease involving procedures such as angioplasty, bypass grafting, endartherectomy, or stent implantation, secondary failure due to late restenosis still occurs in 30-50% of individuals. Restenosis and later stages of atherosclerotic lesions arise from a complex series of fibroproliferative responses to vascular injury that are triggered by potent growth-regulatory molecules and finally result in vascular smooth muscle cell proliferation, migration, and neointima formation. The aim of this study was to investigate the antiproliferative effects of the topoisomerase I inhibitor topotecan on human arterial coronary smooth muscle cells. Following incubation of cells with different drug concentrations, mitotic indices were measured by bromodeoxyuridine incorporation, while cellular mitochondrial activity was evaluated using the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test. Continuous incubation with topotecan for 7 days resulted in a complete and dose-dependent reduction of smooth muscle cell proliferation, and topotecan inhibited cell proliferation in the presence of growth factors as well. In contrast, mitochondrial activity was only partially decreased. Remarkably, although even short-term incubations for 20 min were sufficient to induce a long-lasting growth inhibition, topotecan did not induce apoptosis. Our results therefore suggest that, based on its drug profile, the topoisomerase I inhibitor topotecan may be a promising drug to inhibit restenosis occurring after coronary angioplasty with local devices.

Inflammatory mechanisms

Traditional concepts of the pathogenesis of acute coronary syndromes have changed over the last few years. In particular it has been demonstrated that high-risk lesions are not necessarily angiographically severe. Rather, unstable high risk lesions are the ones composed of large lipid cores and thin fibrous caps. It is now widely accepted that plaque instability is related to the development of inflammation within the intima. A consequence of this is that stabilization of lesions provides a new therapeutic target. Furthermore, there is growing evidence that statins may stabilize lesions by altering the inflammatory response. A brief overview of these developments and their impact on clinical practice is presented.

A novel transgenic marker for migrating limb muscle precursors and for vascular smooth muscle cells

A unique pattern of LacZ expression was found in a transgenic mouse line, likely due to regulatory elements at the site of integration. Two new genes flanking the transgene were identified. At early stages of development, the transgene is transiently expressed in ventro-lateral demomyotomal cells migrating from the somites into the limb buds. At late developmental stages and in the adult, lacZ staining marks vascular smooth muscle cells throughout the vascular bed, with the exception of the major elastic arteries, and in pericytes. No expression was detected in skeletal and smooth muscles. Different patterns of expression in vascular smooth muscles was observed at distinct levels of the vascular tree, in arteries as well as in veins. Vessel injury, resulting in stimulation of smooth muscle cells proliferation and migration, is associated with transgene down-regulation. After the formation of neointima thickening, it is reactivated. This transgenic insertion may therefore be used as a useful marker to identify novel physiological cues or genetic elements involved in the regulation of the vascular smooth muscle phenotype(s). It may also provide an experimental tool for studying vasculature and the involvement of pericytes in regulating microvascular homeostasis.

Interferon-gamma induces secretory group IIA phospholipase A2 in human arterial smooth muscle cells. Involvement of cell differentiation, STAT-3 activation, and modulation by other cytokines

Increased expression of secretory non-pancreatic phospholipase A(2) (sPLA(2)-IIA) could be part of the inflammatory reaction in atherosclerosis. However, the factors controlling sPLA(2)-IIA production in human vascular cells are unknown. We investigated regulation of sPLA(2)-IIA expression and secretion by human arterial smooth muscle cells in culture (HASMC). SPLA(2)-IIA was induced after 3-14 days of culture in non-proliferating conditions. SPLA(2)-IIA was co-expressed with heavy caldesmon, a cytoskeleton protein, and p27, a G(1) cyclin inhibitor, proteins characteristically expressed by differentiated cells. Further incubation with 50-500 units/ml of interferon (IFN)-gamma significantly increased sPLA(2)-IIA mRNA and secretion. IFN-gamma-induced sPLA(2)-IIA was found to be active in cell media and associated with cell membrane proteoglycans. IFN-gamma induced sPLA(2)-IIA expression was antagonized by tumor necrosis factor (TNF)-alpha and interleukin (IL)-10. TNF-alpha added individually induced a significant but transient (4 h) increase in sPLA(2)-IIA secretion. IL-10 by itself did not affect sPLA(2)-IIA expression and secretion. IFN-gamma-stimulated sPLA(2)-IIA transcription involved STAT-3 protein. Interestingly, IL-6 but not IFN-gamma up-regulated the sPLA(2)-IIA expression in HepG2 cells, thus sPLA(2)-IIA induction by IFN-gamma response appears to be cell specific. In summary, conditions leading to cell differentiation induced sPLA(2)-IIA expression in HASMC and further exposure to IFN-gamma can up-regulate sPLA(2)-IIA transcription and secretion. This IFN-gamma stimulatory effect can be modulated by other cytokines.