Muscle Cell Death Research Articles

Farnesoid X Receptor Ligands Inhibit Vascular Smooth Muscle Cell Inflammation and Migration

The farnesoid X receptor/bile acid receptor (FXR; NR1H4) is a ligand-activated transcription factor that regulates bile acid and lipid homeostasis, and is highly expressed in enterohepatic tissue. FXR is also expressed in vascular tissue. We have investigated whether FXR regulates inflammation and migration in vascular smooth muscle cells. The FXR target gene, small heterodimer partner (SHP), was induced in vascular smooth muscle cells after treatment with synthetic FXR ligands, GW4064, or 6alpha-ethyl-chenodeoxycholic acid. FXR ligands induced smooth muscle cell death and downregulated interleukin (IL)-1beta-induced inducible nitric oxide synthase and cyclooxygenase-2 expression. In addition, FXR ligands suppressed smooth muscle cell migration stimulated by platelet-derived growth factor-BB. Reporter gene assays showed that FXR ligands activated an FXR reporter gene and suppressed IL-1beta-induced nuclear factor (NF)-kappaB activation and iNOS in a manner that required functional FXR and SHP. Our observations suggest that a FXR-SHP pathway may be a novel therapeutic target for vascular inflammation, remodeling, and atherosclerotic plaque stability.

Oxygen regulation of arterial smooth muscle cell proliferation and survival

The purpose of this study was to determine if hypoxia elicits different proliferative and apoptotic responses in systemic arterial smooth muscle cells incubated under conditions that do or do not result in cellular ATP depletion and whether these effects are relevant to vascular remodeling in vivo. Gene expression profiling was used to identify potential regulatory pathways. In human aortic smooth muscle cells (HASMCs) incubated at 3% O(2), proliferation and progression through the G1/S interphase are enhanced. Incubation at 1% O(2) reduced proliferation, delayed G1/S transition, increased apoptotic cell death, and is associated with mitochondrial membrane depolarization and reduced cellular ATP levels. In aorta and mesenteric artery from rats exposed to hypoxia (10% O(2), 48 h), both proliferation and apoptosis are increased, as are medial nuclear density and smooth muscle cell content. Although nuclear levels of hypoxia-inducible factor 1-alpha (HIF-1alpha) are increased to a similar extent in HASMCs incubated at 1 and 3% O(2), expression of tumor protein p53, its transcriptional target p21, as well as their regulatory factors and downstream effectors, are differentially affected under these two conditions, suggesting that the bidirectional effects of hypoxia are mediated by this pathway. We conclude that hypoxia induces a state of enhanced cell turnover through increased rates of both smooth muscle cell proliferation and death. This confers the ability to remodel the vasculature in response to changing tissue metabolic needs while avoiding the accumulation of mutations that may lead to malignant transformation or the formation of abnormal vascular structures.

A mutation in CHN-1/CHIP suppresses muscle degeneration in Caenorhabditis elegans

Duchenne muscular dystrophy (DMD) is one of the most severe X-linked, inherited diseases of childhood, characterized by progressive muscle wasting and weakness as the consequence of mutations in the dystrophin gene. The protein encoded by dystrophin is a huge cytosolic protein that links the intracellular F-actin filaments to the members of the dystrophin–glycoprotein–complex (DGC). Dystrophin deficiency results in the absence or reduction of complex components that are degraded through an unknown pathway. We show here that muscle degeneration in a Caenorhabditis elegans DMD model is efficiently reduced by downregulation of chn-1, encoding the homologue of the human E3/E4 ubiquitylation enzyme CHIP. A deletion mutant of chn-1 delays the cell death of body-wall muscle cells and improves the motility of animals carrying mutations in dystrophin and MyoD. Elimination of chn-1 function in the musculature, but not in the nervous system, is sufficient for this effect, and can be phenocopied by proteasome inhibitor treatment. This suggests a critical role of CHIP/CHN-1-mediated ubiquitylation in the control of muscle wasting and degeneration and identifies a potential new drug target for the treatment of this disease.

Involvement of c-Jun NH2-terminal kinase and nitric oxide-mediated mitochondria-dependent intrinsic pathway signaling in cardiotoxin-induced muscle cell death: role of testosterone

To test the hypothesis that c-Jun NH2-terminal kinase (JNK) and nitric oxide (NO)-mediated signaling plays an important role in muscle cell apoptosis, we examined the contribution of these molecules in muscle cell apoptosis during cardiotoxin (ctx)-induced muscle injury in mice. Compared to controls, where no apoptosis was detected, the percent of muscle cell apoptosis rose significantly (P < 0.05) at 4 h (27%) after ctx-treatment and increased further progressively up to 16 h posttreatment (80%), before it fell again at 24 h posttreatment (38%). Initiation of apoptosis was preceded by JNK activation and elevated levels of B-cell lymphoma-2 (BCL-2) in the mitochondrial fractions (BAX levels remained unaffected). Ctx treatment also resulted in the inactivation of BCL-2 through phosphorylation at serine 70, thereby perturbing the BAX/BCL-2 rheostat, and the subsequent activation of the cytochrome c-mediated death pathway. Concomitant administration of SP600125, a selective JNK inhibitor, or aminoguanidine (AG), a selected inducible nitric oxide synthase (iNOS) inhibitor, effectively diminished BCL-2 phosphorylation, suppressed cytochrome c release from mitochondria and caspase activation, and significantly prevented ctx-induced muscle cell apoptosis. In additional studies, we examined the role of testosterone in preventing such ctx-induced muscle cell apoptosis. Collectively, the present study emphasizes the role of a new signal transduction pathway involving JNK and iNOS that promotes ctx-induced myocyte apoptosis by provoking BCL-2 phosphorylation, leading to its inactivation, and subsequent activation of the intrinsic pathway signaling. Testosterone therapy has no protective effect in acute muscle injury associated with increased muscle cell death after ctx-treatment.

Emodin Induces Growth Arrest and Death of Human Vascular Smooth Muscle Cells Through Reactive Oxygen Species and p53

Percutaneous coronary intervention is the main therapy for revascularization of occluded coronary arteries. However, a progressive artery restenosis caused by abnormal proliferation and migration of vascular smooth muscle cells (VSMC) hinders the effective treatment. In this study, we examined the effect of emodin, a natural anthraquinoid compound, on cultured VSMC. Lower doses of emodin suppressed cell proliferation and induced unscheduled DNA synthesis. Higher doses of emodin increased lumpy chromatin condensation and lysosomes in VSMC, suggesting the occurrence of apoptosis and autophagy. Emodin increased production of reactive oxygen species (ROS), which was abolished by an NADPH oxidase inhibitor diphenylene iodonium (DPI). DPI could also decrease the number of apoptosis induced by emodin, suggesting the involvement of ROS in emodin-induced apoptosis. Emodin upregulated the protein levels of p53 in a dose-dependent manner. Laser confocal microscope showed most of emodin scattering in the cytoplasms and a little within the nuclei. These findings collectively indicated that emodin induces both growth arrest and death of human VSMCs in 2 independent manners, implying it as a promising therapy for preventing restenosis.

Physiological Smooth Muscle Cell Apoptosis Contributes to the Uterine Vascular Remodeling in Human Early Pregnancy

See related article, pages 834–841 Although equipped with the entire machinery driving cell proliferation and cell death, the turnover of the vascular smooth muscle cell (VSMC) layer within the vascular wall is quite low throughout the adult normal body. Vascular wall remodeling with VSMC apoptosis is routinely considered as associated with vascular diseases. This includes the development and regression of vascular thickening in hypertension, in advanced atherosclerotic plaques where VSMC apoptosis promotes plaque rupture, after angioplasty-induced arterial injury, as well as in arterial aneurysm where apoptosis is responsible for excessive slackening and rupture of the vessel media.1 Furthermore, in several animal studies, early pregnancy is a physiological situation where vessel wall remodeling plays a vital role. Indeed, in the first trimester of human pregnancy, vascular wall remodeling through degenerative changes converts the uterine spiral arteries located within the decidua basilis into toneless, widely opened arteries, thus enabling abundant blood supply to the maternal-fetal exchange area within the placenta. It is known that extravillous cytotrophoblasts deriving from fetal cytotrophoblastic shell migrate into segments of the spiral artery wall, through retrograde endovascular (intravasation) and interstitial migratory pathways (extravasation) into the decidua basilis to trigger the disappearance of endothelial and VSMC. In this process, trophoblasts become buried intramurally within a fibrinoid layer, which replaces the original muscular medial layer. Such trophoblast invasion converts the ends of spiral arteries into a wide caliber vessel that can better deliver maternal blood to the expanding intervillous space of the placenta (Figure 1A). Defective or incomplete trophoblast invasion can result in pathological pregnancies, including preeclampsia and intrauterine growth restriction.2,3 Therefore, understanding the cellular mechanisms governing the interaction between intramural trophoblast and vascular wall cells is yet to be determined. Oversimplified schematic depicting the trophoblasts invading the spiral artery traveling from myometrium up to …

Is Pathologic Intimal Thickening the Key to Understanding Early Plaque Progression in Human Atherosclerotic Disease?

The term “ P athologic I ntimal T hickening” (PIT) was recently introduced to define an early stage of atherosclerosis described in human coronary lesions found at autopsies of sudden death victims.1 This descriptive identifier is based on the AHA type III (intermediate) lesion and, as originally presented by Stary and collegues, it’s believed to be the morphological and chemical bridge to more advanced plaques.2 The precise histological features and clinical relevance of PIT remains unsettled, and use of the term is still far from widespread. In short, PIT identifies a lesion with an extracellular lipid pool with intimal smooth muscle cell loss typically adjacent to the medial wall in addition to varying degrees of macrophage infiltration near the lumen. These morphological features indicate a progressive lesion in the earlier stages of atherosclerosis, although there is yet the presence of a necrotic core. As recently studied by Nakashima and colleagues in this issue of Arteriosclerosis, Thrombosis, and Vascular Biology , it may provide a key in settling the chicken-versus-egg debate of atherosclerotic plaque progression: does lipid come first, or do macrophages?3 Is PIT the precursor lesion of fibroatheroma? The study in this issue uses 3-dimensional histology to attempt to address some of these issues, and, in doing so, may raise as many questions as it answers. See page 1159 Although there are many detailed autopsy studies describing various lesion morphologies, little is known how human atherosclerosis progresses from early to more advanced plaques, marked by the formation of a necrotic core. This important question remains, in part, from a lack of direct experimental testing in prospective models of human disease. Moreover, potentially relevant finding in animals are difficult to associate with humans because the pathologic change of atherosclerosis in man cannot be definitely equated with animals. Although …

Mitochondrial dysfunction in the pathogenesis of Ullrich congenital muscular dystrophy and prospective therapy with cyclosporins.

Ullrich congenital muscular dystrophy is a severe genetically and clinically heterogeneous muscle disorder linked to collagen VI deficiency. The pathogenesis of the disease is unknown. To assess the potential role of mitochondrial dysfunction in the onset of muscle fiber death in this form of dystrophy, we studied biopsies and myoblast cultures obtained from patients with different genetic defects of collagen VI and variable clinical presentations of the disease. We identified a latent mitochondrial dysfunction in myoblasts from patients with Ullrich congenital muscular dystrophy that matched an increased occurrence of spontaneous apoptosis. Unlike those in myoblasts from healthy donors, mitochondria in cells from patients depolarized upon addition of oligomycin and displayed ultrastructural alterations that were worsened by treatment with oligomycin. The increased apoptosis, the ultrastructural defects, and the anomalous response to oligomycin could be normalized by Ca(2+) chelators, by plating cells on collagen VI, and by treatment with cyclosporin A or with the specific cyclophilin inhibitor methylAla(3)ethylVal(4)-cyclosporin, which does not affect calcineurin activity. Here we demonstrate that mitochondrial dysfunction plays an important role in muscle cell wasting in Ullrich congenital muscular dystrophy. This study represents an essential step toward a pharmacological therapy of Ullrich congenital muscular dystrophy with cyclosporin A and methylAla(3)ethylVal(4) cyclosporin.

Myosin Phosphatase Regulatory Pathways

In many ways, the smooth muscle cell (SMC) has been at the forefront in defining cellular signaling pathways. For example, the initial description of agonist-dependent intracellular calcium ([Ca2+]i) transients was made on vertebrate vascular SMC using aqueorin as the indicator.1 Delineation of nitric oxide (NO) and cGMP signaling was first accomplished in smooth muscle.2,3 And more recently, insights into the general mechanisms of gene transcription that dictate phenotypic traits of cells are being defined by smooth muscle specific gene expression.4,5 It should come as no surprise then that the interactions among many signaling pathways in cells should be explained first in the SMC. Perhaps the reason for the central position of the SMC in defining paradigms in cellular biology is that there are well-defined physiologic end points amenable to measurement (ie, contractile force) and even better described and easily quantified biochemical pathways that underlie said physiologic end points (ie, myosin regulatory light chain phosphorylation). From a historical perspective, the role of protein phosphorylation in smooth muscle contraction as a paradigm for cell signaling follows only that for the control of glycogen metabolism (see 6,7 for reviews). Increases in the levels of cytosolic [Ca2+]i initiate smooth muscle contraction by binding to the universal intracellular Ca2+ receptor protein, calmodulin (CaM), which in turn binds to and activates smooth muscle myosin light chain kinase (MLCK). Activated MLCK catalyzes the phosphorylation serine-19 of the regulatory myosin light chain (MLC) thereby increasing cross-bridge cycling and the rate of tension development. Dephosphorylation of MLC is catalyzed by smooth muscle specific myosin light chain phosphatase (MLCP). Decreases in cytosolic [Ca2+]i and MLC dephosphorylation are considered salient events in smooth muscle relaxation. What has become apparent only within the last decade is the fact that …

Human antimicrobial peptide LL-37 is present in atherosclerotic plaques and induces death of vascular smooth muscle cells: a laboratory study

BackgroundDeath of smooth muscle cells in the atherosclerotic plaques makes the plaques more prone to rupture, which can initiate an acute ischemic event. The development of atherosclerosis includes the migration of immune cells e.g. monocytes/macrophages and T lymphocytes into the lesions. Immune cells can release antimicrobial peptides. One of these, human cathelicidin antimicrobial peptide hCAP-18, is cleaved by proteinase 3 generating a 4.5 kDa C-terminal fragment named LL-37, which has been shown to be cytotoxic. The aim of the study was to explore a potential role of LL-37 in the pathophysiology of atherosclerosis.MethodsWe investigated the presence of LL-37 in human atherosclerotic lesions obtained at autopsy using immunohistochemistry. The direct effects of LL-37 on cultured vascular smooth muscle cells and isolated neutrophil granulocytes were investigated with morphological, biochemical and flow cytometry analysis.ResultsThe neointima of atherosclerotic plaques was found to contain LL-37-like immunoreactivity, mainly in macrophages. In cultured smooth muscle cells, LL-37 at 30 μg/ml caused cell shrinkage, membrane blebbing, nuclear condensation, DNA fragmentation and an increase in caspase-3 activity as studied by microscopy, ELISA and enzyme activity assay, respectively. Flow cytometry demonstrated that LL-37 in a subset of the cells caused a small but rapidly developing increase in membrane permeability to propidium iodide, followed by a gradual development of FITC-annexin V binding. Another cell population stained heavily with both propidium iodide and FITC-annexin V. Neutrophil granulocytes were resistant to these effects of LL-37.ConclusionThis study shows that LL-37 is present in atherosclerotic lesions and that it induces death of vascular smooth muscle cells. In a subset of cells, the changes indicate the development of apoptosis triggered by an initial mild perturbation of plasma membrane integrity. The findings suggest a role for LL-37 as a mediator of immune cell-induced death of vascular smooth muscle cells in atherosclerosis.

Posttranslational nitrotyrosination of α-tubulin induces cell cycle arrest and inhibits proliferation of vascular smooth muscle cells

Hyperproliferation of vascular smooth muscle cells is a hallmark of atherosclerosis and related vascular complications. Microtubules are important for many aspects of mammalian cell responses including growth, migration and signaling. α-Tubulin, a component of the microtubule cytoskeleton, is unique amongst cellular proteins in that it undergoes a reversible posttranslational modification whereby the C-terminal tyrosine residue is removed (Glu-tubulin) and re-added (Tyr-tubulin). Whereas the reversible detyrosination/tyrosination cycle of α-tubulin has been implicated in regulating various aspects of cell biology, the precise function of this posttranslational modification has remained poorly characterized. Herein, we provide evidence suggesting that α-tubulin detyrosination is a required event in the proliferation of vascular smooth muscle cells. Proliferation of rat aortic smooth muscle cells in response to serum was temporally associated with the detyrosination of α-tubulin, but not acetylation of α-tubulin; Glu-tubulin reached maximal levels between 12 and 18 h following cell cycle initiation. Inclusion of 3-nitro- l-tyrosine (NO 2Tyr) in the culture medium resulted in the selective nitrotyrosination of α-tubulin, that was paralleled by decreased elaboration of Glu-tubulin, decreased expression of cyclins A and E, decreased association of the microtubule plus-end binding protein EB1, and inhibited cell proliferation. Nitrotyrosination of α-tubulin did not induce necrotic or apoptotic death of rat aortic smooth muscle cells, but instead led to cell cycle arrest at the G 1/S boundary coincident with decreased DNA synthesis. Collectively, these results suggest that the C-terminus of α-tubulin and its detyrosination are functionally important as a molecular switch that regulates cell cycle progression in vascular smooth muscle cells.

Insulin‐like growth factor‐1 and TNF‐α 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.

Melatonin reduces ischemia/reperfusion‐induced superoxide generation in arterial wall and cell death in skeletal muscle

The purpose of this study was to determine the effect of melatonin on superoxide generation in arterial wall at an early phase of reperfusion and on endothelial dysfunction of microvasculature and cell viability of cremaster muscle at late phase of reperfusion (24 hr) after prolonged ischemia. Bilateral vascular pedicles which supply blood flow to the cremaster muscle were exposed. After surgical preparation, microvascular clamps were applied on the right iliac, femoral and spermatic arteries to create 4 hr of ischemia in both feeding vessels and the unexposed cremaster muscle. The vascular clamping was omitted on the left iliac, femoral and spermatic arteries and served as an internal control. Melatonin or Vehicle was via by intravenous injection at 10 min prior to reperfusion and 10 min after reperfusion. In the first experiment, the vascular pedicle was harvested after reperfusion to measure superoxide generation in real time by lucigenin-derived chemiluminescence. In the second experiment, endothelial-dependent and -independent vasodilatation was examined in the terminal arteriole of cremaster muscle which was then harvested to examine cell viability by WST-1 assay on day 2. Superoxide generation in arterial wall peaked at first 5-min of reperfusion and declined to near baseline after 60 min of reperfusion. Melatonin treatment significantly reduced superoxide generation in arterial walls and improved cell viability in cremaster muscles. Melatonin treatment also significantly reduced microvascular endothelial dysfunction which was still observable in the microcirculation of cremaster muscle after 24 hr of reperfusion. Melatonin reduces superoxide generation in the early phase of reperfusion resulting in attenuating endothelial dysfunction and muscle cell death in the late phase of reperfusion.

Activation of apoptotic pathways at muscle fiber synapses is circumscribed and reversible in a slow-channel syndrome model

In the slow-channel syndrome (SCS) mutant acetylcholine receptors elicit calcium overload and myonuclear degeneration at the neuromuscular junction (NMJ), without muscle fiber death. Activated caspases are present at SCS motor endplates. We hypothesized that SCS represents a limited form of apoptosis. We found condensed chromatin and occasional single-strand DNA nicks in degenerating synaptic nuclei. Cleaved forms of caspases-3 and -9 were present in mouse SCS muscle homogenates and were specifically localized to NMJs. Finally, interruption of cholinergic activity by axotomy markedly reduced NMJ caspase activity and improved the morphological features of apoptosis at NMJs. These results demonstrate that in SCS processes leading to apoptosis may remain compartmentalized and reversible. Use of cysteine protease inhibitors may aid in treatment of this and other dystrophic muscle and excitotoxic disorders. Identification of extrasynaptic factors that prevent the spread of apoptosis in SCS muscle fibers may aid in developing treatments for neurological disorders characterized by excitotoxicity or apoptosis.

MRI visualized neo-intimal dissection and co-localization of novel apoptotic markers apolipoprotein C-1, ceramide and caspase-3 in a Watanabe hyperlipidemic rabbit model

Purpose Apoptotic arterial wall vascular smooth muscle cell death is known to contribute to plaque vulnerability and rupture. Novel apoptotic markers like apolipoprotein C-I have been implicated in apoptotic human vascular smooth muscle cell death via recruiting a neutral sphingomyelinase (N-SMase)-ceramide pathway. In vivo relevance of these observations in an animal model of plaque rupture has not been shown. Methods and Results Using Watanabe rabbits, we investigated three different groups (group 1, three normal Watanabe rabbits; group 2, six Watanabe rabbits fed with high cholesterol diet for 3 months; group 3, five Watanabe rabbits with similar diet but additional endothelial denudation). We followed progression of atherosclerosis to pharmacologically induced plaque rupture non-invasively using novel 3D magnetic resonance Fast-Field-Echo angiography (TR = 7.2, TE = 3.6 ms, matrix = 512 × 512) and Fast-Spin-Echo vessel wall imaging methods (TR = 3 heart beats, TE = 10.5 ms, matrix = 304 × 304) on 1.5 T MRI. MRI provided excellent image quality with good MRI versus histology vessel wall thickness correlation ( r = 0.8). In six animals of group 2/3 MRI detected neo-intimal dissection in the abdominal aorta which was accompanied by immuno-histochemical demonstration of concomitant aforementioned novel apoptotic markers, previously implicated in the apoptotic smooth muscle cell death in vitro. Conclusions Our studies suggest a potential role for the signal transduction pathway involving apolipoprotein C-I for in vivo apoptosis and atherosclerotic plaque rupture visualized by MRI.

Abstract no.: 9 Nitric oxide donors and oxysterol‐induced smooth muscle cell death

Objective Macrophage‐derived mediators (nitric oxide (NO), TNFα) and environmental factors (oxysterols) can induce smooth muscle cell (SMC) death in atherosclerotic plaques, thereby increasing the risk of plaque rupture. Since NO donors are used by angina pectoris patients, we investigated their effects on vascular SMC death induced by 7‐ketocholesterol (7‐KC).Methods SMCs derived from the rabbit aorta (150 000; passage 2–6) were seeded in six well plates in HAM F10 with 10% foetal bovine serum (FBS). The next day, they were exposed to 25 μM7‐KC and various concentrations of S‐nitroso‐N‐acetyl‐penicilamine (SNAP), SIN‐1 (linsidomine) or spermine‐NONOate (SPNO) in the presence of 2% FBS. Uptake of neutral red (0.01%, added 16 h later) was measured for 2 h as viability index; the protein content of the adherent SMCs was measured using the BCA method.Results 7‐KC caused 50.7 ± 1.5% (n = 12) decrease of viability, SMC loss was less pronounced (control 90 ± 2, 7‐KC 74 ± 2 μg protein/monolayer, n = 12). Exposure to 100 μM SIN‐1 or SNAP for 2 or 18 h did not change viability or protein content, either alone or in combination with 25 μM 7‐KC. In contrast, 100 μM SPNO caused a transient viability loss in control cells (from 100% to 74 ± 4% at 2 h and 95 ± 3% at 18 h) and in SMCs treated with 7‐KC (from 51 ± 3% to 39 ± 2% at 2 h and 49 ± 3% at 18 h). Interestingly, the effect of SPNO was less pronounced in SMCs treated with 7‐KC, particularly at higher concentrations (e.g. decrease of viability at 300 μM SPNO 25 ± 5% in control, and 3 ± 3% in 7‐KC‐treated SMCs).Conclusion The results indicate that effects of NO donors on SMC viability in an atherogenic environment cannot be predicted from experiments with normal SMCs. S‐Nitrosylation of the catalytic cysteine residue of caspases, thereby suppressing apoptosis, could explain why the effects of 7‐KC and SPNO were not additive.

Abstract no.: 1 Statins and oxysterol‐induced vascular smooth muscle cell death

Objective The strength of the fibrous cap of an atherosclerotic plaque is maintained by smooth muscle cells (SMCs). 7‐Ketocholesterol (7‐KC), and other oxysterols formed inside plaques, are known to induce SMC death, thereby increasing the risk of rupture and myocardial infarction (MI). Statins are known to protect patients from MI, but paradoxically they induce apoptosis in vascular SMCs as well. The aim of this study was to investigate the cell death effects of statins in 7‐KC‐treated SMCs.Methods Rabbit aorta SMCs (50 000; passage 2–6) were seeded in 24 well plates in HAM F10 with 10% foetal bovine serum (FBS). The next day, they were exposed to 25 μM 7‐KC and 10−8–10−4 M of fluvastatin (fluva), simvastatin (simva) or pravastatin (prava) in the presence of 2% FBS. Uptake of neutral red (0.01%, added 16 h later) was measured for 2 h as viability index.Results SMC viability decreased from 100% to 55 ± 3% (n = 28) upon 18 h exposure to 25 μM 7‐KC. High concentrations of fluva (≥ 10 μM) or simva (≥ 1 μM) also induced a concentration‐dependent loss of SMC viability; prava was always without effect. Interestingly, fluva and simva partly reversed the viability loss evoked by 7‐KC. Similar effects were seen when mitochondrial function was assessed using the succinate dehydrogenase substrate MTT. Fluva and simva alone were without effect, but they attenuated the mitochondrial dysfunction induced by 7‐KC. In contrast, both statins and 7‐KC enhanced the conversion of the caspase substrate DEVD‐R110 by SMC monolayers.Conclusions The results confirm that 7‐KC and high concentrations of lipophilic statins induce SMC death and activate caspases. Yet, in 7‐KC treated SMCs statins paradoxically attenuated viability loss and mitochondrial dysfunction. This clearly illustrates that drug effects seen in normal SMCs are not necessarily predictive of their action in an atherosclerotic setting.

Association of Gln222Arg polymorphism in the deoxyribonuclease I (DNase I) gene with myocardial infarction in Japanese patients

We have recently reported that serum deoxyribonuclease I (DNase I) activity, which may be involved in apoptosis, increases abruptly in the early phase of acute myocardial infarction (MI) [Kawai Y, Yoshida M, Arakawa K, Kumamoto T, Morikawa N, Masamura K, Tada H, Ito S, Hoshizaki H, Oshima S, Taniguchi K, Terasawa H, Miyamori I, Kishi K, Yasuda T. Diagnostic use of serum deoxyribonuclease I activity as a novel early-phase marker in acute myocardial infarction. Circulation 2004;109:2398-2400]. Death of vascular smooth muscle cells, in part because of apoptosis, is postulated to heighten susceptibility to disruption of vulnerable plaque, resulting in onset of MI. The present study evaluated the possibility that Gln222Arg polymorphism of the DNase I gene may be one of the factors involved in predisposition to MI. We assessed 611 Japanese patients: 311 with MI and 300 with stable angina pectoris (AP). Three common phenotypes determined by two common codominant alleles, DNASE1*1 and *2, whose corresponding gene products exhibit different properties, were found in these patient groups. The prevalence of DNASE1*2 was significantly higher in patients with MI than in those with AP (0.543 vs. 0.428, P < 0.001), being confirmed by phenotyping of the second study population. Multiple logistic regression analysis showed that the odds ratio of DNASE1*2 was 1.51 [95% confidence interval (CI) 1.04-2.18]. The association of the DNASE1*2 allele with MI was statistically significant, being independent of other conventional risk factors. Our data demonstrate that Gln222Arg polymorphism in the DNase I gene is associated with MI in the Japanese patients.

Widespread tissue distribution and diverse functions of corticotropin-releasing factor and related peptides

Peptides of the corticotropin-releasing factor (CRF) family are expressed throughout the central nervous system (CNS) and in peripheral tissues where they play diverse roles in physiology, behavior, and development. Current data supports the existence of four paralogous genes in vertebrates that encode CRF, urocortin/urotensin 1, urocortin 2 or urocortin 3. Corticotropin-releasing factor is the major hypophysiotropin for adrenocorticotropin, and also functions as a thyrotropin-releasing factor in non-mammalian species. In the CNS, CRF peptides function as neurotransmitters/neuromodulators. Recent work shows that CRF peptides are also expressed at diverse sites outside of the CNS in mammals, and we found widespread expression of CRF and urocortins, CRF receptors and CRF binding protein (CRF-BP) genes in the frog Xenopus laevis. The functions of CRF peptides expressed in the periphery in non-mammalian species are largely unexplored. We recently found that CRF acts as a cytoprotective agent in the X. laevis tadpole tail, and that the CRF-BP can block CRF action and hasten tail muscle cell death. The expression of the CRF-BP is strongly upregulated in the tadpole tail at metamorphic climax where it may neutralize CRF bioactivity, thus promoting tail resorption. Corticotropin-releasing factor and urocortins are also known to be cytoprotective in mammalian cells. Thus, CRF peptides may play diverse roles in physiology and development, and these functions likely arose early in vertebrate evolution.

Disruptive T cells

A study on page 239 shows that death-inducing T cells kill smooth muscle cells in atherosclerotic plaques. Sato et al. show that this lethal T cell activity is heightened in patients with heart disease, which could destabilize the plaques in these patients and make them more prone to rupture. Figure 1 TRAIL-expressing CD4+ T cells trigger apoptosis of vascular smooth muscle cells (red) in atherosclerotic plaques The narrowing of arteries is a natural process caused by the gradual deposition of fat and cholesterol into artery walls. The buildup of arterial plaques (atherosclerosis) is a long-term process that, for some, culminates in acute coronary syndromes (ACSs) such as heart attack and cardiac arrest. These acute attacks are caused by the sudden rupture of atherosclerotic plaques—an event that may happen more readily in some individuals than in others. Plaques that contain immune cells such as macrophages and T cells are the most vulnerable to rupture, although the mechanism behind this observation is not well understood. Now, Sato and colleagues show that CD4+ T cells that infiltrate atherosclerotic plaques trigger the death of vascular smooth muscle cells (VSMCs), a process proposed to destabilize the plaques. The plaque-infiltrating T cells expressed high levels of TRAIL, a death receptor normally used by T cells and NK cells to destroy cancerous cells. The expression of this receptor was required for T cells to induce apoptosis in VSMCs (which expressed the TRAIL receptor DR5) both in vitro and in vivo. CD4+ T cells from patients with ACS expressed higher levels of TRAIL when activated and were more adept at triggering VSMC apoptosis in vitro compared with T cells from healthy individuals, possibly explaining why these individuals developed acute disease while others were spared. What causes plaque-residing VSMCs to express DR5 and why T cells infiltrate the plaques in some individuals is not yet known. These results demonstrate that the TRAIL pathway—previously thought to induce death only in cancer cells—can also trigger apoptosis in nontransformed cells. A recombinant form of TRAIL is currently in clinical trials for the treatment of certain cancers, a therapeutic approach that might need reevaluation in light of its potential negative effects on patients with atherosclerosis.