"Vulnerable plaques" — ticking of the time bomb

Residual risks and evolving atherosclerotic plaques

Atherosclerotic disease of the coronary and carotid arteries is the primary global cause of significant mortality and morbidity. The chronic occlusive diseases have changed the epidemiological landscape of health problems both in developed and the developing countries. Despite the enormous benefit of advanced revascularization techniques, use of statins, and successful attempts of targeting modifiable risk factors, like smoking and exercise in the last four decades, there is still a definite "residual risk" in the population, as evidenced by many prevalent and new cases every year. Here, we highlight the burden of the atherosclerotic diseases and provide substantial clinical evidence of the residual risks in these diseases despite advanced management settings, with emphasis on strokes and cardiovascular risks. We critically discussed the concepts and potential underlying mechanisms of the evolving atherosclerotic plaques in the coronary and carotid arteries. This has changed our understanding of the plaque biology, the progression of unstable vs stable plaques, and the evolution of plaque prior to the occurrence of a major adverse atherothrombotic event. This has been facilitated using intravascular ultrasound, optical coherence tomography, and near-infrared spectroscopy in the clinical settings to achieve surrogate end points. These techniques are now providing exquisite information on plaque size, composition, lipid volume, fibrous cap thickness and other features that were previously not possible with conventional angiography.

Biomechanical characteristics of isolated carotid atherosclerotic plaques assessed by ultrasonography

BACKGROUND

The aim of this study was to assess the biomechanical characteristics of carotid atherosclerotic plaques using intima-media thickness (IMT) automatic tracking combined with acoustic densitometry (AD) imaging, and to elucidate the relationship between biomechanical characteristics and inflammatory activity of corresponding plaques evaluated by 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT).

METHODS

Sixty-one patients with isolated carotid atherosclerotic plaques underwent conventional carotid ultrasonography, IMT automatic tracking, and acoustic densitometry (AD) imaging. Following these assessments, patients received an 18F-FDG PET/CT scan within 24 hours. We quantified biomechanical and AD parameters including IMT strain rate (SR), IMT time strain rate (TR), and corrected average image intensity value (AIIc%) on the upstream, fibrous cap top, and downstream regions of the plaque and compared them to the reference area(normal intima adjacent to the upstream of the assessed plaque). Target background ratio (TBR) was acquired by 18F-FDG PET/CT for evaluating the inflammatory activity of corresponding plaques. We further divided all participants into an inflammatory group (TBR≥1.25) and non-inflammatory group (TBR<1.25) measures of SR/TR and AIIc% in the two groups were compared and analyzed.

RESULTS

SR/TR were significantly lower in the plaque group when compared to reference area. SR/TR at the cap top area (CTA) and downstream area (DA) of the plaques were lower than those in the reference area (P<0.05) while there was no statistically significant difference in SR or TR of the upstream area (UA) between the plaque and reference area. SR/TR were significantly greater for UA than CTA and DA (P<0.05 for both). AIIc% was significantly lower for UA and CTA than that for DA (P<0.05). The SR/TR of plaque regions were negatively correlated with corresponding AIIc% (r=-0.74, r=-0.75, P<0.05). TR in the inflammatory group was significantly lower than in the non-inflammatory group (P<0.05), while SR and AIIc% showed no statistically significant difference. TR demonstrated a significant negative correlation with TBR (r=-0.83, P<0.05). Receiver operating characteristic curve (ROC) analysis showed that the area under the curve (AUC) of TR was 0.87. Furthermore, TR less than 75.06‰ demonstrated a sensitivity of 88.0% and a specificity of 80.6% for the identification of inflammatory plaques.

CONCLUSIONS

IMT automatic tracking, combined with AD imaging, can be applied to identify the anisotropic biomechanical features of carotid plaques. This novel imaging modality may be used to provide an early assessment of the biomechanical characteristics of carotid plaques. Additionally, the TR parameter was associated with plaque inflammation reaction, possibly providing a new indicator for the early identification of plaque vulnerability.

Autophagy dysfunction and regulatory cystatin C in macrophage death of atherosclerosis

Autophagy dysfunction in mouse atherosclerosis models has been associated with increased lipid accumulation, apoptosis and inflammation. Expression of cystatin C (CysC) is decreased in human atheroma, and CysC deficiency enhances atherosclerosis in mice. Here, we first investigated the association of autophagy and CysC expression levels with atheroma plaque severity in human atherosclerotic lesions. We found that autophagy proteins Atg5 and LC3β in advanced human carotid atherosclerotic lesions are decreased, while markers of dysfunctional autophagy p62/SQSTM1 and ubiquitin are increased together with elevated levels of lipid accumulation and apoptosis. The expressions of LC3β and Atg5 were positively associated with CysC expression. Second, we investigated whether CysC expression is involved in autophagy in atherosclerotic apoE-deficient mice, demonstrating that CysC deficiency (CysC(-/-) ) in these mice results in reduction of Atg5 and LC3β levels and induction of apoptosis. Third, macrophages isolated from CysC(-/-) mice displayed increased levels of p62/SQSTM1 and higher sensitivity to 7-oxysterol-mediated lysosomal membrane destabilization and apoptosis. Finally, CysC treatment minimized oxysterol-mediated cellular lipid accumulation. We conclude that autophagy dysfunction is a characteristic of advanced human atherosclerotic lesions and is associated with reduced levels of CysC. The deficiency of CysC causes autophagy dysfunction and apoptosis in macrophages and apoE-deficient mice. The results indicate that CysC plays an important regulatory role in combating cell death via the autophagic pathway in atherosclerosis.

Autophagy Induction Protects Against 7-Oxysterol-induced Cell Death via Lysosomal Pathway and Oxidative Stress

7-Oxysterols are major toxic components in oxidized low-density lipoprotein and human atheroma lesions, which cause lysosomal membrane permeabilization (LMP) and cell death. Autophagy may function as a survival mechanism in this process. Here, we investigated whether 7-oxysterols mixed in an atheroma-relevant proportion induce autophagy, whether autophagy induction influences 7-oxysterol-mediated cell death, and the underlying mechanisms, by focusing on cellular lipid levels, oxidative stress, and LMP in 7-oxysterol-treated macrophages. We found that 7-oxysterols induced cellular lipid accumulation, autophagy dysfunction, and cell death in the form of both apoptosis and necrosis. Exposure to 7-oxysterols induced autophagic vacuole synthesis in the form of increased autophagy marker microtubule-associated protein 1A/1B-light chain 3 (LC3) and LC3-phosphatidylethanolamine conjugate (LC3-II) and autophagic vacuole formation. This led to an accumulation of p62, indicating a reduction in autophagic vacuole degradation. Importantly, autophagy induction significantly reduced 7-oxysterol-mediated cell death by diminishing LMP and oxidative stress. Moreover, autophagy induction minimized cellular lipid accumulation induced by 7-oxysterols. These findings highlight the importance of autophagy in combating cellular stress, LMP, and cell death in atherosclerosis. Therefore, activation of the autophagy pathway may be a potential therapeutic strategy for prevention of necrotic core formation in atherosclerotic lesions.

XBP1 mRNA splicing triggers an autophagic response in endothelial cells through BECLIN-1 transcriptional activation

Sustained activation of X-box-binding protein 1 (XBP1) results in endothelial cell (EC) apoptosis and atherosclerosis development. The present study provides evidence that XBP1 mRNA splicing triggered an autophagic response in ECs by inducing autophagic vesicle formation and markers of autophagy BECLIN-1 and microtubule-associated protein 1 light chain 3β (LC3-βII). Endostatin activated autophagic gene expression through XBP1 mRNA splicing in an inositol-requiring enzyme 1α (IRE1α)-dependent manner. Knockdown of XBP1 or IRE1α by shRNA in ECs ablated endostatin-induced autophagosome formation. Importantly, data from arterial vessels from XBP1 EC conditional knock-out (XBP1eko) mice demonstrated that XBP1 deficiency in ECs reduced the basal level of LC3β expression and ablated response to endostatin. Chromatin immunoprecipitation assays further revealed that the spliced XBP1 isoform bound directly to the BECLIN-1 promoter at the region from nt -537 to -755. BECLIN-1 deficiency in ECs abolished the XBP1-induced autophagy response, whereas spliced XBP1 did not induce transcriptional activation of a truncated BECLIN-1 promoter. These results suggest that XBP1 mRNA splicing triggers an autophagic signal pathway through transcriptional regulation of BECLIN-1.

Isolation, bulk cultivation, and characterization of coronary microvascular pericytes: the second most frequent myocardial cell type in vitro

Densely arranged pericytes engird the endothelial tube of all coronary microvessels. Since the experimental access to these abundant cells in situ is difficult, a prerequisite for broader investigation is the availability of sufficient numbers of fully differentiated pericytes in homogenous culture. To reach this goal, we applied strictly standardized cell isolation techniques, optimized culture methods and specific histological staining. Approximately 1,000-fold enriched pericytes were proteolytically detached from highly purified coronary microvascular networks (density gradient centrifugation) of eight mammalian species including human. Addition of species-autologous fetal or neonatal serum (10-20% vol/vol) was a precondition for longer term survival of homogenous pericyte cultures. This ensured optimal growth (doubling time <14 h) and full expression of pericyte-specific markers. In 3-mo, 10(10) pericytes (15 g) could be cultivated from 1 bovine heart. Pericytes could be stored in liquid N(2), recultured, and passaged repeatedly without loss of typical features. In cocultures with EC or vascular smooth muscle cells, pericytes transferred fluorescent calcein to each other and to EC via their antler-like extensions, organized angiogenetic sprouting of vessels, and rapidly activated coagulation factors X and II via tissue factor and prothrombinase. The interconnected pericytes of the coronary system are functionally closely correlated with the vascular endothelium and may play key roles in the adjustment of local blood flow, the regulation of angiogenic processes, and the induction of procoagulatory processes. Their successful bulk cultivation enables direct experimental access under defined in vitro conditions and the isolation of pericyte specific antigens for the production of specific antibodies.

In vivo mapping of vascular inflammation using multimodal imaging

BACKGROUND

Plaque vulnerability to rupture has emerged as a critical correlate to risk of adverse coronary events but there is as yet no clinical method to assess plaque stability in vivo. In the search to identify biomarkers of vulnerable plaques an association has been found between macrophages and plaque stability--the density and pattern of macrophage localization in lesions is indicative of probability to rupture. In very unstable plaques, macrophages are found in high densities and concentrated in the plaque shoulders. Therefore, the ability to map macrophages in plaques could allow noninvasive assessment of plaque stability. We use a multimodality imaging approach to noninvasively map the distribution of macrophages in vivo. The use of multiple modalities allows us to combine the complementary strengths of each modality to better visualize features of interest. Our combined use of Positron Emission Tomography and Magnetic Resonance Imaging (PET/MRI) allows high sensitivity PET screening to identify putative lesions in a whole body view, and high resolution MRI for detailed mapping of biomarker expression in the lesions.

METHODOLOGY/PRINCIPAL FINDINGS

Macromolecular and nanoparticle contrast agents targeted to macrophages were developed and tested in three different mouse and rat models of atherosclerosis in which inflamed vascular plaques form spontaneously and/or are induced by injury. For multimodal detection, the probes were designed to contain gadolinium (T1 MRI) or iron oxide (T2 MRI), and Cu-64 (PET). PET imaging was utilized to identify regions of macrophage accumulation; these regions were further probed by MRI to visualize macrophage distribution at high resolution. In both PET and MR images the probes enhanced contrast at sites of vascular inflammation, but not in normal vessel walls. MRI was able to identify discrete sites of inflammation that were blurred together at the low resolution of PET. Macrophage content in the lesions was confirmed by histology.

CONCLUSIONS/SIGNIFICANCE

The multimodal imaging approach allowed high-sensitivity and high-resolution mapping of biomarker distribution and may lead to a clinical method to predict plaque probability to rupture.

Correlation between cathepsin D serum concentration and carotid intima-media thickness in hemodialysis patients

AIM

Cardiovascular (CV) disease is the leading cause of death in hemodialysis (HD) patients, and approximately half of mortalities in HD patients are attributed to CV disease. Atherosclerosis is the most frequent cause of CV complications in patients with end-stage renal disease (ESRD). Based on recent studies, cathepsin D has been suggested as a potential marker of atherosclerosis, and we hypothesized that there is an association between serum concentration of cathepsin D and carotid intima-media thickness (CIMT) in hemodialysis patients.

METHODS

Thirty-one hemodialysis patients (18 men and 13 women) were enrolled in this study. Serum levels of soluble cathepsin D were measured with an enzyme-linked immunosorbant assay (ELISA) kit. CIMT was determined in each patient.

RESULTS

The data showed that there was a positive significant correlation between serum concentration of cathepsin D and CIMT by using Pearson correlation (P value <0.05).

CONCLUSION

Based on the results of this study, cathepsin D could be suggested to have a role in the development of atherosclerotic plaques.

Pericytes in the macrovascular intima: possible physiological and pathogenetic impact

The frequently observed de-endothelialization of venous coronary bypass grafts prepared using standard methods exposes subendothelial prothrombotic cells to blood components, thus endangering patients by inducing acute thromboembolic infarction or long-term proliferative stenosis. Our aim was to gain deeper histological and physiological insight into these relations. An intricate network of subendothelial cells, characterized by histological features specific for true pericytes, was detected even in healthy vessels and forms, coupled to the luminal endothelium, a second leaflet of the macrovascular intima. These cells, and particularly those in the venous intima, express enormous concentrations of tissue factor and can recruit additional amounts of up to the 25-fold concentration within 1 h during preincubation with serum (intimal pericytes of venous origin activate 30.71 +/- 4.07 pmol coagulation factor x.min(-1).10(-6) cells; n = 15). Moreover, decoupled from the endothelium, they proliferate rapidly (generation time, 15 +/- 2.1 h, n = 8). Central regions of atherosclerotic plaques, as well as of those of restenosed areas of coronary vein grafts, consist almost completely of these cells. In stark contrast with the prothrombogenicity of the intimal pericytes, intact luminal endothelium recruits high concentrations of thrombomodulin (CD 141) specifically within its intercellular junctions, activates Protein C rapidly (42 +/- 5.1 pmol/min.10(6) venous endothelial cells at thrombin saturation; n = 15), can thus actively prevent coagulatory processes, and never expresses histologically detectable and functionally active tissue factor. Given this strongly prothrombotic potential of the intimal pericytes and their overshooting growth behavior in endothelium-denuded vascular regions, they may play important roles in the development of atherosclerosis, thrombosis, and saphenous vein graft disease.

Death receptors and their ligands in atherosclerosis

Atherosclerosis is characterized by the accumulation of a fibro-fatty plaque consisting of immune cells, vascular smooth muscle cells (VSMCs), vascular endothelial cells (ECs), and extracellular matrix, surrounding a lipid-rich core. The complexity of atherosclerosis is highlighted by the multifaceted effects that apoptosis and proliferation of specific cell types can have on vessels at different stages of the disease. Death receptors are membrane-bound protein complexes that on binding their cognate ligand, activate an intracellular signaling cascade that results in apoptosis. More recently, signaling from these receptors has been shown to activate multiple other processes, including cell proliferation. This review summarizes our current understanding of signaling events after death receptor activation and the role of death receptors and their ligands in atherosclerosis.

The involvement of lysosomes in myocardial aging and disease

The myocardium is mainly composed of long-lived postmitotic cells with, if there is any at all, a very low rate of replacement through the division and differentiation of stem cells. As a consequence, cardiac myocytes gradually undergo pronounced age-related alterations which, furthermore, occur at a rate that inversely correlates with the longevity of species. Basically, these alterations represent the accumulation of structures that have been damaged by oxidation and that are useless and often harmful. These structures (so-called 'waste' materials), include defective mitochondria, aberrant cytosolic proteins, often in aggregated form, and lipofuscin, which is an intralysosomal undegradable polymeric substance. The accumulation of 'waste' reflects the insufficient capacity for autophagy of the lysosomal compartment, as well as the less than perfect functioning of proteasomes, calpains and other cellular digestive systems. Senescent mitochondria are usually enlarged, show reduced potential over their inner membrane, are deficient in ATP production, and often produce increased amounts of reactive oxygen species. The turnover of damaged cellular structures is hindered by an increased lipofuscin loading of the lysosomal compartment. This particularly restricts the autophagic turnover of enlarged, defective mitochondria, by diverting the flow of lysosomal hydrolases from autophagic vacuoles to lipofuscin-loaded lysosomes where the enzymes are lost, since lipofuscin is not degradable by lysosomal hydrolases. As a consequence, aged lipofuscin-rich cardiac myocytes become overloaded with damaged mitochondria, leading to increased oxidative stress, apoptotic cell death, and the gradual development of heart failure. Defective lysosomal function also underlies myocardial degeneration in various lysosomal storage diseases, while other forms of cardiomyopathies develop due to mitochondrial DNA mutations, resulting in an accumulation of abnormal mitochondria that are not properly eliminated by autophagy. The degradation of iron-saturated ferritin in lysosomes mediates myocardial injury in hemochromatosis, an acquired or hereditary disease associated with iron overload. Lysosomes then become sensitized to oxidative stress by the overload of low mass, redox-active iron that accumulates when iron-saturated ferritin is degraded following autophagy. Lysosomal destabilization is of importance in the induction and/or execution of programmed cell death (either classical apoptotic or autophagic), which is a common manifestation of myocardial aging and a variety of cardiac pathologies.

Matrix vesicles in the fibrous cap of atherosclerotic plaque: possible contribution to plaque rupture

Plaque rupture is the most common type of plaque complication and leads to acute ischaemic events such as myocardial infarction and stroke. Calcification has been suggested as a possible indicator of plaque instability. Although the role of matrix vesicles in the initial stages of arterial calcification has been recognized, no studies have yet been carried out to examine a possible role of matrix vesicles in plaque destabilization. Tissue specimens selected for the present study represented carotid specimens obtained from patients undergoing carotid endarterectomy. Serial frozen cross-sections of the tissue specimens were cut and mounted on glass slides. The thickness of the fibrous cap (FCT) in each advanced atherosclerotic lesion, containing a well developed lipid/necrotic core, was measured at its narrowest sites in sets of serial sections. According to established criteria, atherosclerotic plaque specimens were histologically subdivided into two groups: vulnerable plaques with thin fibrous caps (FCT <100 μm) and presumably stable plaques, in which fibrous caps were thicker than 100 μm. Twenty-four carotid plaques (12 vulnerable and 12 presumably stable plaques) were collected for the present analysis of matrix vesicles in fibrous caps. In order to provide a sufficient number of representative areas from each plaque, laser capture microdissection (LCM) was carried out. The quantification of matrix vesicles in ultrathin sections of vulnerable and stable plaques revealed that the numbers of matrix vesicles were significantly higher in fibrous caps of vulnerable plaques than those in stable plaques (8.908±0.544 versus 6.208±0.467 matrix vesicles per 1.92 μm² standard area; P= 0.0002). Electron microscopy combined with X-ray elemental microanalysis showed that some matrix vesicles in atherosclerotic plaques were undergoing calcification and were characterized by a high content of calcium and phosphorus. The percentage of calcified matrix vesicles/microcalcifications was significantly higher in fibrous caps in vulnerable plaques compared with that in stable plaques (6.705±0.436 versus 5.322±0A94; P= 0.0474). The findings reinforce a view that the texture of the extracellular matrix in the thinning fibrous cap of atherosclerotic plaque is altered and this might contribute to plaque destabilization.

Circulating Apoptotic Progenitor Cells

BACKGROUND

Progenitor CD34 cells are capable of differentiating into endothelial cells and play a role in neoangiogenesis. Circulating CD34+ cells and endothelial progenitor cells are increased in acute coronary syndrome (ACS) patients possibly because of peripheral mobilization. We tested the hypothesis that circulating apoptotic progenitors are detectable in healthy subjects and altered in ACS patients.

METHODS AND RESULTS

Peripheral blood mononuclear cells were isolated by Ficoll density gradient from 53 patients with ACS undergoing coronary angiography and 27 healthy subjects. Apoptosis in progenitor CD34+ cells was assessed using the Annexin V-PE/7-AAD detection kit, and fluorescence-activated cell sorter analysis was performed with triple staining for CD34, annexin-V, and 7-AAD. The percentage of apoptotic CD34+ progenitors was determined in the 2 subject groups and correlated with clinical characteristics. The percentage of apoptotic CD34+ progenitor cells was significantly increased in patients with ACS as compared with healthy subjects and was associated with the extent of coronary stenosis by angiography. There was no significant correlation between apoptotic progenitor CD34+ cells and the other parameters that we examined (age, smoking, hypertension, hyperlipidemia, diabetes mellitus, ejection fraction, creatinine levels, or taking any of the various medications, including beta blockers, thiazides, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium blockers, nitrates, or statins).

CONCLUSION

We established for the first time to our knowledge an assay to detect circulating apoptotic progenitor cells using fluorescein isothiocyanate-anti-CD34 MAb, annexin V-PE, and 7-AAD and found that apoptotic CD34+ cells are increased in ACS patients and in patients with more extensive coronary artery disease. This novel assay may shed new light on the factors governing the hemostasis of progenitor CD34+ cells.

Noninvasive two-dimensional strain imaging of arteries: validation in phantoms and preliminary experience in carotid arteries in vivo

Cardiac disease and stroke are the major causes of death in the Western World. Atherosclerosis of the carotid artery is the most important predictor of stroke. Elastography is a technique to assess the composition and vulnerability of an atherosclerotic plaque. Contrary to intravascular applications, the ultrasound beam and radial strain are not aligned in noninvasive acquisitions. In this study, 2D displacement and strain images were determined and used to calculate the radial and circumferential strain. Rf-data were acquired using a Philips SONOS 7500 live 3D ultrasound system, equipped with an 11_3L (3 to 11 MHz) linear array transducer and rf-interface. A homogeneous, hollow cylinder phantom [20% gelatin, 1% SiC scatterers (10 microM)] was measured in a water tank at different intraluminal pressures. In addition, measurements in patients (n = 12) were made to evaluate the in vivo applicability of the technique. Longitudinal and cross-sectional recordings were made, both in phantoms and patients. Strain along the ultrasound beam (axial strain) was determined using cross-correlation analysis for signal-windows from both the pre- and post-compression data. For lateral strain, new ultrasound lines were generated between the acquired lines using interpolation. A cross-correlation based search algorithm was applied to determine lateral displacement and strain. Longitudinal axial strain images in the phantom showed a decreasing strain from the lumen- vessel wall interface to the outer region that can be described by a 1 over r(2) relationship. The lateral strain image showed no strain in this direction indicating a plane strain situation. In the cross-sectional view, compression of the material in regions at 12 and 6 o'clock was observed, whereas expansion was observed in regions at 3 and 9 o'clock. This pattern is in accordance with theory, but can only be partly corrected for: in the transition regions, zero axial strain was measured. The lateral strain image showed a complementary pattern. In patients, low strain was observed in nonatherosclerotic artery walls. High and low strain regions were found in atherosclerotic plaques. High quality elastograms were generated both in longitudinal and cross-sectional views. In conclusion, 2D noninvasive elastography of atherosclerotic carotid plaques is feasible. Phantom studies revealed elastograms in accordance with theory. Additional in vivo validation is needed to assess the value of this technique for identifying plaque vulnerability and composition.

Insulin-like growth factor-I receptors in atherosclerotic plaques of symptomatic and asymptomatic patients with carotid stenosis: effect of IL-12 and IFN-γ

The balance between apoptosis and survival of vascular smooth muscle cells (VSMCs) in the fibrous cap appears to best correlate with plaque instability or stability and is controlled by growth factors and cytokines. We recently reported the inhibition of insulin-like growth factor (IGF)-I-induced proliferation and increase in apoptosis of VSMCs by atheroma-associated cytokines. Here we assessed the expression of IGF-I receptor (IGF-IR) in atherosclerotic plaques and in plaque VSMCs of asymptomatic and symptomatic patients with carotid stenosis and examined the effect of IGF-I, IL-12, and IFN-γ on the expression of IGF-IR and IGF-binding protein (IGFBP)-3 in plaque VSMCs. We observed significantly lower density of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive apoptotic nuclei and increased positive immunoreactivity to IGF-IR and mRNA transcripts of endogenous IGF-I and IGF-IR in asymptomatic than in symptomatic plaque VSMCs. Positive correlation was found between apoptosis and IGF-IR expression in asymptomatic ( r2= 0.942) and symptomatic ( r2= 0.908) plaque VSMCs. The specific binding of125I-labeled IGF-I was 3.7-fold higher in plaque VSMCs of asymptomatic patients than in symptomatic patients. IGF-I increased both IGF-IR mRNA transcripts and expression of IGFBP-3 in VSMCs of asymptomatic plaques. IL-12 and IFN-γ decreased IGF-IR mRNA transcripts and further increased the expression of IGFBP-3 in asymptomatic VSMCs but had no effect in symptomatic VSMCs. These data suggest that the decreased expression of IGF-IR mRNA and increased expression of IGFBP-3 in carotid plaques of symptomatic patients could be due to atheroma-associated cytokines and this could result in plaque instability.

Increased expression of inhibitor of apoptosis proteins in atherosclerotic plaques of symptomatic patients with carotid stenosis

Vascular remodeling and atheromatous lesion formation are determined in part by the balance between apoptosis and survival of vascular smooth muscle cells (VSMCs). In the chronic stages, apoptosis of VSMCs in the atherosclerotic plaques contributes to the weakening and potential rupture of the plaque causing pathologies such as acute coronary syndrome. The higher incidence of apoptosis in the plaques of symptomatic than in asymptomatic patients has been demonstrated, but the expression of survival proteins, including the inhibitor of apoptosis proteins (IAPs), has not been thoroughly examined. The aim of this study was to investigate the immunohistochemical expression of cellular inhibitor of apoptosis protein-2 (cIAP2), x-linked inhibitor of apoptosis protein (XIAP), and survivin in normal carotid arteries, and carotid endarterectomy specimens of symptomatic and asymptomatic patients with carotid stenosis. The results demonstrated stronger immunopositivity to smooth muscle myosin heavy chain antigen (SM-MHC) (sm2), proliferating cell nuclear antigen (PCNA), and p50 subunit of NF-kappabeta in the asymptomatic plaques than in symptomatic plaques. Furthermore, there was higher expression of cIAP2, XIAP, and survivin in the symptomatic than in the asymptomatic plaques and this paralleled caspase-3 expression. The increased expression of IAPs in symptomatic plaques could be due to endogenous defense mechanism to protect against the pro-apoptotic effect of the inflammatory stimuli that are released in the plaques. This could be involved in the stabilization of symptomatic atheromatous plaques and may prove a potential therapeutic target.

Insulin-like growth factor-1 and TNF-alpha regulate autophagy through c-jun N-terminal kinase and Akt pathways in human atherosclerotic vascular smooth cells

A balance between programmed cell death and survival of vascular smooth muscle cells (VSMC) in the fibrous cap, which is primarily composed of VSMC and extracellular matrix, appears to best correlate with plaque instability or stability and is controlled by growth factors and cytokines. Autophagy is also involved in programmed cell death. We assessed the effect of TNF-alpha and insulin-like growth factor-1 (IGF-1) on the expression of autophagic genes, microtubule-associated protein 1 light chain 3 (MAPLC-3) and Beclin-1 in VSMC isolated from atherosclerotic plaques. Transmission electron microscopy showed a significantly higher number of vacuolated cells in the TNF-alpha-treated VSMC and a markedly lower number in the IGF-1-treated VSMC when compared with the untreated control group. TNF-alpha-induced MAPLC-3 mRNA expression through c-jun N-terminal kinase and protein kinase B pathways and induced Beclin-1 protein expression through the c-jun N-terminal kinase pathway. Expression of MAPLC-3 and Beclin-1 correlated with autophagic cell death of plaque VSMC. IGF-1 inhibited MAPLC-3 mRNA transcripts through the Akt pathway. These findings suggest that the expression of autophagy genes can be influenced by IGF-1 and TNF-alpha through c-jun N-terminal kinase or Akt pathways and autophagy might be involved in the regulation of plaque stability.

Differential effects of insulin-like growth factor-1 and atheroma-associated cytokines on cell proliferation and apoptosis in plaque smooth muscle cells of symptomatic and asymptomatic patients with carotid stenosis

Morbidity and mortality from atherosclerosis are associated with complicated atherosclerotic lesions due to plaque rupture, which is regulated by a balance between proliferation and apoptosis of vascular smooth muscle cells (VSMC). We examined insulin-like growth factor-1 (IGF-1)-induced survival of plaque VSMC from carotid endarterectomy specimens and investigated the underlying cellular mechanisms in the presence and absence of IL-12 and IFN-gamma. Both IL-12 and IFN-gamma were strongly expressed in symptomatic atherosclerotic plaques as compared with asymptomatic plaques. In asymptomatic plaque VSMC, IGF-1 induced the survival and proliferation of VSMC and accelerated VSMC into S-phase. IL-12 or IFN-gamma inhibited proliferation and VSMC were arrested in the G0-G1 phase. IGF-1 markedly inhibited the expression of p27(kip) and p21(cip) and significantly induced cyclin E and cyclin D. Both cytokines by themselves increased the expression of p27(kip) and p21(cip) and inhibited cyclin E and cyclin D. On the contrary, in symptomatic VSMC there was already increased apoptosis of VSMC and there was no significant effect of IGF-1 or inflammatory cytokines on proliferation, apoptosis or the expression of p27(kip) and p21(cip) and cyclin D and E. These data suggest that IGF-1 is more potent in inducing the survival of VSMC from the endarterectomy specimens of asymptomatic patients as compared to that of symptomatic subjects and cytokines associated with atheroma lesions decrease the activity of IGF-1-induced survival in the VSMC of asymptomatic plaques. The different expression and activity of cell cycle regulatory proteins could be responsible for apoptosis of VSMC and destabilization of atherosclerotic plaques.