Telomerase and myocardin co-expressing mesenchymal cells increase survival and induce cardiac and vascular markers in cardiac stromal cells undergoing simulated ischemia/reperfusion

Funding Acknowledgements

Type of funding sources: None.

Background

Cardiac stromal cells (CSCs) contain a pool of cells with supportive and paracrine functions. Various types of mesenchymal stromal cells (MSCs) can influence CSCs in the cardiac niche through their paracrine activity. Ischemia/reperfusion (I/R) leads to cell death and reduction of the paracrine activity of CSCs. The forced coexpression of telomerase reverse transcriptase (TERT) and myocardin (MYOCD), known to potentiate anti-apoptotic, pro-survival and pro-angiogenic activities of MSCs isolated from the adipose tissue (AT-MSCs), may increase CSC survival, favoring their paracrine activities.

Aim

To investigate the hypothesis that CSCs feature improved resistance to simulated I/R (SI/R) and increased commitment toward the cardiovascular lineage when preconditioned with conditioned media (CM) or extracellular vesicles (EV) released from AT-MSCs overexpressing TERT and MYOCD (T/M AT-MSCs).

Methods and Results

Murine CSCs were isolated with the cardiosphere (CSps) isolation technique.

T/M AT-MSCs and their secretome improved spontaneous intracellular calcium changes (Figure 1) and ryanodine receptor expression in aged CSps. The cytoprotective effect of AT-MSCs was tested in CSCs subjected to SI/R. SI/R induced cell death as compared to normoxia (28±4 vs 10±3%, p=0.02). Pretreatment with CM (15±2, p=0.02) or with the EV-enriched fraction (10±1%, p=0.02) obtained from mock-transduced AT-MSCs in normoxia reduced cell death after SI/R. The effect was more prononunced with CM (7±1%, p=0.01) or the EV-enriched fraction (2±1%, p=0.01) obtained from T/M AT-MSCs subjected to SI/R. In parallel, we observed lower expression of the apoptosis marker cleaved caspase-3 and higher expression of cardiac and vascular markers eNOS, sarcomeric α-actinin and cardiac actin.

Conclusions

The T/M AT-MSCs secretome exerts a cytoprotective effect and promotes development of CSCs undergoing SI/R towards a cardiovascular phenotype.

Cytotoxic terpenoids from Tripterygium hypoglaucum against human pancreatic cancer cells SW1990 by increasing the expression of Bax protein

ETHNOPHARMACOLOGICAL RELEVANCE

Tripterygium hypoglaucum (Kunmingshanhaitang in Chinese) is a plant of the genus Tripterygium which have been used as anti-tumor folk medicines in Yi and Bai ethnic groups in Yunnan province, China for hundreds of years. Terpenoids from T. hypoglaucum presented therapeutic effects on multiple tumors. But there were few studies about pancreatic cancer treatment of these terpenoids. Pancreatic cancer is an aggressive malignancy and lacked of specific drugs. Currently, anti-tumor drugs have poor therapeutic effect and prognosis for pancreatic cancer.

AIM OF THE STUDY

This study aimed to elucidate the terpenoids from T. hypoglaucum and illuminate their anti-pancreatic cancer bioactivities.

MATERIAL AND METHODS

Terpenoids were obtained through sequential chromatographic methods including silica gel, MCI gel, Sephadex LH-20, and preparative HPLC. Their structures were determined by HRESIMS, 1D and 2D NMR spectroscopic analysis. The absolute configurations of some new diterpenoids were assigned through comparison of experimental and calculated circular dichroism spectra. The cytotoxicity of isolates was measured using the MTT method on human pancreatic cancer cells SW1990. The effects on expressions of AKT, Erk1/2, p-AKT, p-Erk1/2, and Bax proteins in human pancreatic cancer cells SW1990 of these compounds were determined by western blotting assays.

RESULTS

Eleven new (compounds 1∼11) and fourteen known terpenoids (compounds 12∼25) were isolated from the underground parts of T. hypoglaucum. These compounds were belonged to abietane diterpenoids, isoprimara diterpenoids, ent-kaurane diterpenoids, oleanane triterpenoids, and friedelane triterpenoids. Compounds 5, 7, 8, 9, 16, 18, 22, 24, and 25 possessed significant cytotoxicity against SW1990 cells with IC₅₀ values of 19.28 ± 4.39, 9.91 ± 2.23, 27.32 ± 5.89, 56.43 ± 6.92, 0.16 ± 0.05, 0.58 ± 0.15, 0.81 ± 0.04, 0.48 ± 0.11, and 10.01 ± 1.39 μM respectively. After compounds 16, 22, and 24 been treated with the pancreatic cancer cells in medium and high doses, the protein expressions of AKT, p-AKT, Erk, and p-Erk were not remarkably reduced and the expressions of Bax protein were significantly increased.

CONCLUSION

This study indicated that terpenoids from T. hypoglaucum could inhibit human pancreatic cancer cells SW1990. Especially, compounds 16, 22, and 24 possessed significant cytotoxicity against SW1990 cells with low IC₅₀ values and could increase the expressions of Bax protein. These compounds shared a wide variety of structural characteristics which provided us more candidate molecules for the development of anti-pancreatic cancer drugs and further prompted us to investigate their anti-pancreatic mechanisms.

Telomerase and myocardin co-expressing mesenchymal cells increase survival and induce cardiac and vascular markers in cardiac stromal cells undergoing simulated ischemia/reperfusion

Background

Cardiac stromal cells (CSCs) contain a pool of cells with supportive and paracrine functions. Various types of mesenchymal stromal cells (MSCs) can influence CSCs in the cardiac niche through their paracrine activity. Ischemia/reperfusion (I/R) leads to cell death and reduction of the paracrine activity of CSCs. The forced coexpression of telomerase reverse transcriptase (TERT) and myocardin (MYOCD), known to potentiate anti-apoptotic, pro-survival and pro-angiogenic activities of MSCs isolated from the adipose tissue (AT-MSCs), may increase CSC survival, favoring their paracrine activities.

Aim

To investigate the hypothesis that CSCs feature improved resistance to simulated I/R (SI/R) and increased commitment toward the cardiovascular lineage when preconditioned with conditioned media (CM) or extracellular vesicles (EV) released from AT-MSCs overexpressing TERT and MYOCD (T/M AT-MSCs).

Methods and results

Murine CSCs were isolated with the cardiosphere (CSps) isolation technique.

T/M AT-MSCs and their secretome improved spontaneous intracellular calcium changes and ryanodine receptor expression in aged CSps. The cytoprotective effect of AT-MSCs was tested in CSCs subjected to SI/R. SI/R induced cell death as compared to normoxia (28±4 vs 10±3%, p=0.02). Pretreatment with CM (15±2, p=0.02) or with the EV-enriched fraction (10±1%, p=0.02) obtained from mock-transduced AT-MSCs in normoxia reduced cell death after SI/R. The effect was more prononunced with CM (7±1%, p=0.01) or the EV-enriched fraction (2±1%, p=0.01) obtained from T/M AT-MSCs subjected to SI/R. In parallel, we observed lower expression of the apoptosis marker cleaved caspase-3 and higher expression of cardiac and vascular markers eNOS, sarcomeric α-actinin and cardiac actin.

Conclusions

The T/M AT-MSCs secretome exerts a cytoprotective effect and promotes development of CSCs undergoing SI/R towards a cardiovascular phenotype.

Funding Acknowledgement

Type of funding sources: None.

[Analysis of treatment modalities and prognosis of patients with gallbladder cancer in China from 2010 to 2017]

Objective: To evaluate the clinical characteristics and prognosis of gallbladder cancer (GBC) patients in China. Methods: This retrospective multicenter cohort study enrolled 3 528 consecutive GBC patients diagnosed between January 2010 to December 2017 in 15 hospitals from 10 provinces. There were 1 345 (38.12%) males and 2 183 (61.88%) females.The age of diagnosis was (63.7±10.8) years old (range: 26 to 99 years old) .There were 213 patients (6.04%) in stage 0 to Ⅰ, whereas 1 059 (30.02%) in stage Ⅱ to Ⅲ, 1 874 (53.12%) in stage Ⅳ, and 382 (10.83%) unavailable. Surgery was performed on 2 255 patients (63.92%) . Three hundred and thirty-six patients received chemotherapy or radiotherapy (9.52%; of which 172 were palliative); 1 101 (31.21%) received only supportive treatment.The patient source, treatment and surgery, pathology, concomitant gallstone, and prognosis were analyzed. Results: Among the 3 528 GBC patients, 959 (27.18%) were from East China, 603 (17.09%) from East-North China, 1 533 (43.45%) from Central China, and 433(12.27%) from West China. Among the 1 578 resectable tumor, 665 (42.14%) underwent radical surgery, 913 (57.86%) underwent surgery that failed to follow the guidelines.Eight hundred and ninety-one (56.46%) patients were diagnosed before surgery, 254 (16.10%) during surgery, and 381 (24.14%) after surgery (time point of diagnosis couldn't be determined in 52 patients) .Among the 1 578 patients with resectable tumor, 759 (48.10%) had concomitant gallstone.Among the 665 patients underwent radical surgery, 69 (10.4%) showed positive resection margin, 510 (76.7%) showed negative resection margin, and 86 (12.9%) unreported margin status.The 5-year overall survival rate (5yOS) for the 3 528-patient cohort was 23.0%.The 5yOS for patients with resectable tumor was 39.6%, for patients with stage ⅣB tumor without surgery was 5.4%, and for patients with stage ⅣB tumor underwent palliative surgery was 4.7%. Conclusions: More than half GBC patients in China are diagnosed in stage Ⅳ.Curative intent surgery is valuable in improving prognosis of resectable GBC.The treatment of GBC needs further standardization.Effective comprehensive treatment for GBC is in urgent need.

CD1d-associated expression of NF-kB and cardiac dysfunction in diabetic and obese mice

In patients with obesity and diabetes mellitus, abnormal production of inflammatory factors may result in cardiovascular dysfunction. In the current study, we tested the impact of CD1d-mediated innate immune responses on the expression and activation of NFkB in the hearts of adipose diabetic (db/db) mice. Splenocytes from adult db/db and CD1d-knockout mice of both genders and their wild-type, C57BL/6 and Balb/C counterparts were examined for tumor necrosis factor (TNF)-alpha and TNF-alpha receptor type 1. The percentage of natural killer T (NKT) cells in CD3+ T cells was compared with that in nondiabetic control mice. Despite the absence of inflammatory infiltrates, the hearts of db/db mice showed alterations in TNF-alpha receptor-1 and NFkB activity, including increased expression of both the NFkB p52 and p65 subunits. In the hearts of CD1d-knockout mice, p52 expression was reduced, while p65 expression remained largely unchanged. On echocardiography, the ratio of E to A transmitral flow velocities (an indicator of diastolic function) was significantly decreased in db/db mice after they swam for 30 minutes. These results provide evidence for CD1d-mediated NFkB activation and diastolic dysfunction in the hearts of db/db mice. Therefore, CD1d-associated abnormalities of innate immune responses and TNF-alpha production in splenic tissue may contribute to NFkB activation and cardiac dysfunction in type 2 diabetes.

Large intervening non-coding RNA HOTAIR is associated with hepatocellular carcinoma progression

Increasing evidence suggests that large intervening non-coding RNAs (lincRNAs) regulate key pathways in cancer invasion and metastasis. In this observational retrospective study, the expression of the oncogenic lincRNA HOX transcript antisense RNA (HOTAIR) gene was measured in 63 patients with hepatocellular carcinoma (HCC) following hepatic resection. The HOTAIR gene was significantly overexpressed in HCC tissues compared with adjacent non-tumour tissues. Patients with high HOTAIR gene expression in their tumours had an increased risk of recurrence after hepatectomy. There was also a significant correlation between HOTAIR expression and lymph node metastasis. In vitro assays in the HCC cell line Bel7402 demonstrated that knockdown of HOTAIR lincRNA reduced cell proliferation and was associated with reductions in levels of matrix metalloproteinase-9 and vascular endothelial growth factor protein, which are important for cell motility and metastasis. In conclusion, HOTAIR lincRNA might be a potential biomarker for the existence of lymph node metastasis in HCC.

Dysregulated response to mycobacterial cord factor trehalose-6,6'-dimycolate in CD1D-/- mice

The biologic effects of the mycobacterial glycolipid trehalose-6,6'-dimycolate (TDM) include granuloma formation and macrophage activation and are dependent on physical conformation. In mice, the group II CD1 surface molecule CD1d has been implicated in glycolipid presentation. The importance of CD1d interactions in pathology has yet to be established. We hypothesized that mice lacking CD1d (CD1D(-/-)) would demonstrate dysregulated granulomatous response to TDM, compared with CD1D(+/-) heterozygous controls. Mice were intravenously injected with TDM-coated polystyrene-divinylbenzene beads and examined for histologic response and for changes in inflammatory cytokine and chemokine mRNA. Control CD1D heterozygous mice demonstrated a granulomatous response, which peaked at day 5. Increased mRNA for tumor necrosis factor-alpha (TNF-alpha) and macrophage inflammatory protein-1alpha (MIP-1alpha) correlated with development of granulomas, with very little change in interleukin-1beta (IL-1beta) and monocyte chemoattractant protein-1 (MCP-1). In contrast, the CD1D(-/-) mice revealed markedly different responses. Five days after administration, severe pulmonary hemorrhage was induced. The relative size of inflammation surrounding coated bead in the CD1D(-/-) mice was nearly double that induced in the CD1D(+/-) mice. CD1D(-/-) mice also demonstrated elevated mRNA for both inflammatory cytokines and chemokines by day 1 after administration, significantly earlier than responses seen in the heterozygous controls.

Molecular signal transduction in vascular cell apoptosis

Apoptosis is a form of genetically programmed cell death, which plays a key role in regulation of cellularity in a variety of tissue and cell types including the cardiovascular tissues. Under both physiological and pathophysiological conditions, various biophysiological and biochemical factors, including mechanical forces, reactive oxygen and nitrogen species, cytokines, growth factors, oxidized lipoproteins, etc., may influence apoptosis of vascular cells. The Fas/Fas ligand/caspase death-signaling pathway, Bcl-2 protein family/mitochondria, the tumor suppressive gene p53, and the proto-oncogene c-myc may be activated in atherosclerotic lesions, and mediates vascular apoptosis during the development of atherosclerosis. Abnormal expression and dysfunction of these apoptosis-regulating genes may attenuate or accelerate vascular cell apoptosis and affect the integrity and stability of atherosclerotic plaques. Clarification of the molecular mechanism that regulates apoptosis may help design a new strategy for treatment of atherosclerosis and its major complication, the acute vascular syndromes.

7-Ketocholesterol forms crystalline domains in model membranes and murine aortic smooth muscle cells

7-Ketocholesterol (7-keto) is one of the major oxygenated products found in oxidized low-density lipoproteins (LDL) and in atherosclerotic plaque, where it is believed to play a role in arterial pathology. We hypothesize that direct membrane effects independent of receptor binding may mediate its biological activity. To test this, small-angle x-ray diffraction approaches were used to examine the interactions of 7-keto with other membrane components in well-defined lipid vesicles and in murine aortic smooth muscle cell membranes. These data were compared with the interactions of 25-hydroxycholesterol (25-OHC) and cholesterol. Replacement of cholesterol with 7-keto in lipid vesicles produced distinct changes in membrane structure, including a marked increase in molecular volume associated with the hydrocarbon core (+/-0-8 A from the bilayer center). Additionally, there was an increase in electron density associated with the upper acyl chain region (+/-9-21 A), corresponding to the bilayer location of the steroid nucleus of 7-keto. In contrast, 25-OHC did not appear to intercalate into the membrane hydrocarbon core and did not form separate domains. Cells grown in the presence of the 7-keto developed extracellular crystals concomitant with the formation of membrane domains having a unit cell periodicity of 35.4 or 1.4 A greater than measured with cholesterol. Domains were formed within 4 h and persisted up to 72 h, after which cells showed signs of declining viability. We conclude that 7-keto is found in a membrane location distinct from cholesterol, does not condense phospholipids as efficiently as cholesterol and is able to self-associate into discrete intrabilayer domains. While these domains may decrease its cytotoxicity by inducing the formation of sterol crystals in smooth muscle cells, they may, in a broader capacity, contribute to the sterol crystals found in advanced atherosclerotic lesions.

Biologic effect and molecular regulation of vascular apoptosis in atherosclerosis

Apoptosis, a form of genetically programmed cell death, plays a key role in regulation of cellularity of the arterial wall. During atherogenesis, deregulated apoptosis may cause abnormalities of arterial morphogenesis, wall structural stability, and metabolisms. Many biophysiologic and biochemical factors, including mechanical forces, reactive oxygen and nitrogen species, cytokines, growth factors, oxidized lipoproteins, etc. may influence apoptosis of vascular cells. The Fas/Fas ligand/caspase death-signaling pathway, Bcl-2 protein family/mitochondria, the tumor suppressive gene p53, and the proto-oncogene c-myc may be activated in atherosclerotic lesions and mediate vascular apoptosis during the development of atherosclerosis. Abnormal expression and dysfunction of these apoptosis-regulating genes may attenuate or accelerate vascular cell apoptosis and affect the integrity and stability of plaques. Clarification of the molecular mechanism that regulates apoptosis may help design a new strategy for treatment of atherosclerosis and its major complication, the acute vascular syndromes.

Expression of class A scavenger receptor inhibits apoptosis of macrophages triggered by oxidized low density lipoprotein and oxysterol

The class A macrophage scavenger receptor (MSR-A) is a multifunctional trimeric glycoprotein involved in innate immune response as well as the development of lipid-laden foam cells during atherosclerosis. The MSR ligand, oxidized low density lipoprotein (oxLDL), is known to be cytotoxic to macrophages and other cell types. This study examined whether MSR mediates or modulates oxLDL-induced apoptosis. Treatment with oxLDL and its cytotoxic oxysterol, 7-ketocholesterol (7-KC), reduced viability and increased DNA fragmentation in human THP-1 cells, Chinese hamster ovary cells, and mouse peritoneal macrophages. However, cell death and DNA fragmentation were markedly diminished in the phorbol ester-differentiated MSR-expressing THP-1 cells and Chinese hamster ovary cells, with stable expression of MSR-AI after cDNA transfection when exposed to the same concentrations of oxLDL and 7-KC. Moreover, treatment with oxLDL and 7-KC induced much greater death and DNA fragmentation in MSR-A-deficient peritoneal macrophages compared with wild-type macrophages. Thus, MSR-A does not act as a receptor responsible for the apoptotic effect of oxLDL, and instead, expression of this receptor confers resistance of macrophages to the apoptotic stimulation by oxLDL and its cytotoxic lipid component. These results suggest that by preventing apoptosis, MSR-A may contribute to the long-term survival of macrophages and macrophage-derived lipid-laden foam cells in atherosclerotic lesions.

Peripheral vascular endothelial dysfunction and apoptosis in old monkeys

To determine the effects of aging on vasoactivity in a primate model (Macaca fascicularis), 13 young male monkeys (aged 7.1+/-0.4 years) and 9 old male monkeys (aged 19.8+/-0.6 years) were chronically instrumented for measurement of left ventricular and aortic pressures and cardiac output. Total cholesterol, triglyceride, and fasting blood sugar levels were not different between the 2 groups. There were no significant differences in baseline mean aortic pressure and total peripheral resistance (TPR) in the young monkeys versus the old monkeys. TPR fell less (P<0.05) with acetylcholine (1 microg/kg) in old monkeys (-25+/-1%) than in young monkeys (-34+/-2%), whereas decreases in TPR with sodium nitroprusside were similar in old and young monkeys. There was no evidence of atherosclerosis, but apoptosis of endothelial cells was enhanced (P<0.05) in the aortas and femoral arteries, but not in the media, of the old monkeys. There was a relationship (r=0.62, P=0.013) between the incidence of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive endothelial cells and endothelial cell density in the femoral artery. The reduced endothelial cell density was also correlated (r=0.82, P<0.01) with depressed TPR responses to acetylcholine. Thus, vascular endothelial dysfunction was present in old monkeys without evidence of atherosclerosis, which may be due to endothelial apoptosis and reduced endothelial cell density.

Determinants of the cardiomyopathic phenotype in chimeric mice overexpressing cardiac Gsalpha

Mice with overexpressed cardiac Gsalpha develop cardiomyopathy, characterized by myocyte hypertrophy and extensive myocardial fibrosis. The cardiomyopathy likely involves chronically enhanced beta-adrenergic signaling, because it can be blocked with long-term propranolol treatment. It remains unknown whether the genotype of the myocyte is solely responsible for the progressive pathological changes. A chimeric population in the heart should answer this question. Accordingly, we developed a chimeric animal, which combined cells from a transgenic overexpressed Gsalpha parent and a Rosa mouse containing the LacZ reporter gene, facilitating identification of the non-Gsalpha cells, which express a blue color with exposure to beta-galactosidase. We studied these animals at 14 to 17 months of age (when cardiomyopathy should have been present), with the proportion of Gsalpha cells in the myocardium ranging from 5% to 88%. beta-Galactosidase staining of the hearts demonstrated Gsalpha and Rosa cells, exhibiting a mosaic pattern. The fibrosis and hypertrophy, characteristic of the cardiomyopathy, were not distributed randomly. There was a direct correlation (r=0.85) between the extent of myocyte hypertrophy (determined by computer imaging) and the quantity of Gsalpha cells. The fibrosis, determined by picric acid Sirius red, was also more prominent in areas with the greatest Gsalpha cell density, with a correlation of r=0.88. Thus, the overexpressed Gsalpha can exert its action over the life of the animal, resulting in a local picture of cardiomyopathic damage in discrete regions of the heart, where clusters of the overexpressed Gsalpha cells reside, sparing the clusters of normal cells derived from the normal Rosa parent.

Dilated cardiomyopathy associated with simian AIDS in nonhuman primates

BACKGROUND

Cardiomyopathy is being recognized with increasing frequency in patients with AIDS, yet the relationship between HIV infection and cardiac contractile dysfunction remains obscure. The purpose of the present study was to determine if infection with simian immunodeficiency virus (SIV) in nonhuman primates is associated with cardiac dysfunction and myocardial injury.

METHODS AND RESULTS

Left ventricular size and function were determined by 2D echocardiography in 16 rhesus macaques before and at weekly intervals following infection with cloned pathogenic SIV(mac) 239 or the highly attenuated SIV(mac) 239 nef deletion mutant. A second group of 15 rhesus macaques chronically infected with pathogenic (n=6) or nonpathogenic (n=9) virus were studied at >2 years following infection. Cardiac tissues from 24 rhesus macaques chronically infected (>2 years) with pathogenic SIV were reviewed for evidence of cardiac pathology. Acute infection (<6 weeks) with either pathogenic or nonpathogenic SIV caused neither contractile dysfunction nor cardiac pathology. However, LV ejection fraction was significantly (P<0.05) depressed (43+/-7%) in rhesus macaques chronically infected with pathogenic SIV compared with rhesus macaques chronically infected with nonpathogenic SIV (61+/-3%). Furthermore, two thirds of rhesus macaques that succumbed to simian AIDS had myocardial pathology including lymphocytic myocarditis (n=9) and coronary arteriopathy (n=6), with complete vessel occlusion (n=4) and associated myocardial infarction and necrosis.

CONCLUSIONS

This unique model is valuable in understanding the pathogenesis of cardiac injury associated with retroviral infection in a relevant nonhuman primate model of AIDS.

Colocalization of beta-adrenergic receptors and caveolin within the plasma membrane

The rapid amplification of beta-adrenergic receptor signaling involves the sequential activation of multiple signaling molecules ranging from the receptor to adenylyl cyclase. The prevailing view of the agonist-induced interaction between signaling molecules is based on random collisions between proteins that diffuse freely in the plasma membrane. The recent identification of G protein alpha- and betagamma-subunits in caveolae and their functional interaction with caveolin suggests that caveolae may participate in G protein-coupled signaling. We have investigated the potential interaction of beta-adrenergic receptors with caveolin under resting conditions. beta1- and beta2-adrenergic receptors were recombinantly overexpressed in COS-7 cells. Caveolae were isolated using the detergent-free sucrose gradient centrifugation method. beta1- and beta2-adrenergic receptors were localized in the same gradient fractions as caveolin, where Gsalpha- and betagamma-subunits were detected as well. Immunofluorescence microscopy demonstrated the colocalization of beta-adrenergic receptors with caveolin, indicating a nonrandom distribution of beta-adrenergic receptors in the plasma membrane. Using polyhistidine-tagged recombinant proteins, beta-adrenergic receptors were copurified with caveolin, suggesting that they were physically bound. Our results suggest that, in addition to clathrin-coated pits, caveolae may act as another plasma membrane microdomain to compartmentalize beta-adrenergic receptors.

Cytotoxic cholesterol is generated by the hydrolysis of cytoplasmic cholesteryl ester and transported to the plasma membrane

The present study examines the fate and effects of free cholesterol (FC) generated by the hydrolysis of cytoplasmic cholesteryl esters (CE) in model macrophage foam cells. J774 or elicited mouse peritoneal macrophages (MPM) were enriched with CE by incubating with acetylated low density lipoprotein (acLDL) and FC/phospholipid dispersions, thus creating model foam cells. Treatment of the foam cells with the acyl coenzyme-A:cholesterol acyltransferase (ACAT) inhibitor, CP-113,818, in the absence of any extracellular cholesterol acceptors, resulted in cellular toxicity. This was accompanied by an increase in the amount of FC available for oxidation by an exogenous cholesterol oxidase. Furthermore, cellular toxicity was proportional to the size of the oxidase susceptible pool of FC over time. Morphological analysis and in situ DNA fragmentation assay demonstrated the occurrence of apoptosis in the ACAT inhibited cells. Co-treatment with the hydrophobic amine U18666A, an intracellular cholesterol transport inhibitor, led to a dose dependent reduction in cytotoxicity and apoptosis, and blocked the movement of FC into the oxidase susceptible pool. In addition, treating model foam cells with CP-113,818 plus chloroquine, a compound that inhibits the function of acidic vesicles, also diminished cellular toxicity. Staining with the cholesterol binding dye filipin revealed that the macrophages treated with CP-113,818 contained a cholesterol oxidase accessible pool of FC in the plasma membrane. These results suggest that FC generated by the hydrolysis of cytoplasmic CE is transported through acidic vesicles to the plasma membrane, and accumulation of FC in this pool triggers cell death by necrosis and apoptosis.

Beta-adrenergic receptor blockade arrests myocyte damage and preserves cardiac function in the transgenic G(salpha) mouse

Transgenic (TG) mice with cardiac G(salpha) overexpression exhibit enhanced inotropic and chronotropic responses to sympathetic stimulation, but develop cardiomyopathy with age. We tested the hypothesis that cardiomyopathy in TG mice with G(salpha) overexpression could be averted with chronic beta-adrenergic receptor (beta-AR) blockade. TG mice and age-matched wild-type littermates were treated with the beta-AR blocker propranolol for 6-7 months, starting at a time when the cardiomyopathy was developing but was not yet severe enough to induce significant cardiac depression (9.5 months of age), and ending at a time when cardiac depression and cardiomyopathy would have been clearly manifest (16 months of age). Propranolol treatment, which can induce cardiac depression in the normal heart, actually prevented cardiac dilation and the depressed left ventricular function characteristic of older TG mice, and abolished premature mortality. Propranolol also prevented the increase in myocyte cross-sectional area and myocardial fibrosis. Myocyte apoptosis, already apparent in 9-month-old TG mice, was actually eliminated by chronic propranolol. This study indicates that chronic sympathetic stimulation over an extended period is deleterious and results in cardiomyopathy. Conversely, beta-AR blockade is salutary in this situation and can prevent the development of cardiomyopathy.

CD1 expression in human atherosclerosis. A potential mechanism for T cell activation by foam cells

Atherosclerotic plaques are chronic inflammatory lesions composed of dysfunctional endothelium, smooth muscle cells, lipid-laden macrophages, and T lymphocytes. This study analyzed atherosclerotic tissue specimens for expression of CD1 molecules, a family of cell surface proteins that present lipid antigens to T cells, and examined the possibility that CD1+ lipid-laden macrophages might present antigen to T cells. Immunohistochemical studies using a panel of specific monoclonal antibodies demonstrated expression of each of the four previously characterized human CD1 proteins (CD1a, -b, -c, and -d) in atherosclerotic plaques. Expression of CD1 was not observed in normal arterial specimens and appeared to be restricted to the CD68+ lipid-laden foam cells of atherosclerotic lesions. CD1 molecules colocalized in areas of the arterial wall that also contained abundant T lymphocytes, suggesting potential interactions between CD1+ cells and plaque-infiltrating lymphocytes in situ. Using CD1-expressing foam cells derived from macrophages in vitro, we demonstrated the ability of such cells to present lipid antigens to CD1 restricted T cells. Given the abundant T cells, CD1+ macrophages, and lipid accumulation in atherosclerotic plaques, we propose a potential role for lipid antigen presentation by CD1 proteins in the generation of the inflammatory component of these lesions.

Transcriptional inhibition by interleukin-6 of the class A macrophage scavenger receptor in macrophages derived from human peripheral monocytes and the THP-1 monocytic cell line

Expression of the class A macrophage scavenger receptor (MSR) contributes to the uptake of modified low density lipoproteins (LDL) by macrophages and transformation of these cells into lipid-laden foam cells, which characterize atherosclerosis. Many environmental factors, in particular, proinflammatory cytokines and growth factors, can exert regulatory effects on MSR expression, whereas intracellular accumulation of cholesterol itself does not influence MSR levels to any considerable extent. In the present study, by using an in vitro model, we examined whether stimulation with interleukin-6 (IL-6), an immunoregulatory, multipotential cytokine, modulates the expression and activities of the MSR in macrophages. When treated with IL-6, macrophages derived from peripheral monocytes and phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 monocytic cells showed significantly reduced uptake and/or binding of the MSR ligand, acetylated LDL. This effect was paralleled by a reduction in the expression of MSR protein and mRNA. Analysis of MSR promoter activity in THP-1 cells transfected with an MSR promoter-reporter gene construct demonstrated decreased activity of the MSR promoter in IL-6-treated THP-1 macrophages. Electrophoretic mobility gel shift assay also showed a reduction in the binding of a transcription factor to the MSR promoter AP-1/ets elements in IL-6-treated cells. Thus, exposure to IL-6 may inhibit expression of the class A MSR in differentiated macrophages at transcriptional levels. This result suggests that this cytokine may modulate foam cell formation during atherogenesis.

An alpha-cardiac myosin heavy chain gene mutation impairs contraction and relaxation function of cardiac myocytes

Left Ventricular (LV) myocytes were isolated from 15-wk-old male mice bearing the Arg403 --> Gln alpha-cardiac myosin heavy chain missense mutation (alpha-MHC403/+), a model of familial hypertrophic cardiomyopathy. LV myocytes were classified morphologically: type I, rod shaped with parallel myofibrils; type II, irregularly shaped, shorter and wider than wild-type (WT) control cells, with parallel myofibrils; and type III, irregularly shaped with disoriented myofibrils. Compared with WT myocytes, alpha-MHC403/+ myocytes had fewer type I cells (WT = 74 +/- 3%, alpha-MHC403/+ = 41 +/- 4%, P < 0.01) and more type III cells (WT= 12 +/- 3%, alpha-MHC403/+ = 49 +/- 7%, P < 0.01). In situ histology also demonstrated marked myofibrillar disarray in the alpha-MHC403/+ hearts. With the use of video edge detection, myocytes were paced at 1 Hz (37 degrees C) to determine the effects of the mutation on myocyte function. End-diastolic length was reduced in mutant myocytes, but fractional shortening (% contraction) and sarcomere length were not. Velocity of contraction (-dL/dtmax) was depressed in mutant cells, but more in type II and III cells (-31%) than in type I cells (-18%). Velocity of relaxation (+dL/dt) was also depressed more in type II and III cells (-38%) than in type I cells (-16%). Using fura 2 dye with intracellular Ca2+ transients, we demonstrated that in alpha-MHC403/+ myocytes, the amplitude of the Ca2+ signal during contraction was unchanged but that the time required for decay of the signal to decrease 70% from its maximum was delayed significantly (WT = 159 +/- 8 ms; alpha-MHC403/+ = 217 +/- 14 ms, P < 0.01). Sarco(endo)plasmic reticulum Ca2+-ATPase mRNA levels in alpha-MHC403/+ and WT mice were similar. These data indicate that the altered cardiac dysfunction of alpha-MHC403/+ myocytes is directly due to defective myocyte function rather than to secondary changes in global cardiac function and/or loading conditions.

De novo expression of the class-A macrophage scavenger receptor conferring resistance to apoptosis in differentiated human THP-1 monocytic cells

The class-A macrophage scavenger receptor (MSR) is a trimeric multifunctional protein expressed selectively in differentiated monomyeloid phagocytes which mediates uptake of chemically modified lipoproteins and bacterial products. This study investigated whether MSR plays a role in the regulation of apoptosis, a model of genetically programmed cell death. De novo expression of MSR occurred in human THP-1 monocytic cells differentiated with phorbol esters, which activated a nuclear transcription factor binding to the Ap1/ets-like domain of the MSR promoter. The phorbol ester-stimulated THP-1 cells also expressed increased levels of the pro-apoptotic gene products, caspase-3 and Fas ligand, but the cells exhibited no change in apoptosis. Global activation of GTP-binding proteins with fluoride anions triggered apoptosis of THP-1 cells in a time- and concentration-dependent manner, demonstrated by nuclear shrinkage and fragmentation and internucleosomal DNA fragmentation. However, the MSR-expressing THP-1 macrophage-like cells showed a significant reduction in apoptosis compared to undifferentiated control THP-1 cells, which produce MSR at undetectable levels. Fluoride stimulation also triggered apoptosis of human Jurkat T cells. Stimulation with phorbol ester made no difference in apoptosis between treated and untreated Jurkat cells. Finally, Chinese hamster ovary (CHO) cells overexpressing the class-A MSR type I by cDNA transfection showed markedly increased resistance to G-protein-coupled apoptosis. Thus, de novo expression of MSR associated with monocyte maturation into macrophages appears to confer the resistance of macrophages to apoptotic stimulation by G-protein activation.

Apoptosis of cardiac myocytes in Gsalpha transgenic mice

-The stimulatory GTP-binding protein Gsalpha transmits signals from catecholamine receptors to activate adenylyl cyclase and thereby initiate a cascade leading to cardiac chronotropy and inotropy. Transgenic mice overexpressing the Gs alpha subunit (Gsalpha) selectively in their hearts exhibit increased cardiac contractility in response to beta-adrenergic receptor stimulation. However, with aging, these mice develop a cardiomyopathy. This study sought morphological and biochemical evidence that overexpression of Gsalpha is associated with increased myocyte apoptosis in the older animals and to determine whether such overexpression can promote apoptosis of isolated neonatal cardiac myocytes exposed to beta-adrenergic receptor agonists. In the hearts of 15- to 18-month-old Gsalpha transgenic mice, histochemistry and electron microscopy illustrated the existence of numerous myocytes with abnormal nuclei embedded in collagen-rich connective tissue. Terminal deoxyribonucleotide transferase-mediated dUTP nick-end labeling (TUNEL, for in situ labeling of DNA breaks) demonstrated that approximately 0.6% of myocyte nuclei contained fragmented DNA. Agarose gel electrophoresis provided further biochemical evidence of apoptosis by showing internucleosomal DNA fragmentation. Cultured cardiac myocytes from newborn Gsalpha transgenic mice showed increased TUNEL staining and internucleosomal DNA fragmentation compared with wild-type controls when treated with the beta-agonist isoproterenol. Thus, enhanced activation of beta-adrenergic signaling by overexpression of Gsalpha in the hearts of transgenic mice induces apoptosis of cardiac myocytes. This represents a potential mechanism that may contribute to the development of cardiomyopathy in this model.

Death of smooth muscle cells and expression of mediators of apoptosis by T lymphocytes in human abdominal aortic aneurysms

BACKGROUND

Thinning of the tunica media and rarefaction of smooth muscle cells (SMCs) characterize aneurysmal aortas. Apoptosis determines the cellularity and morphogenesis of tissue. Macrophages and T lymphocytes infiltrate the wall of abdominal aortic aneurysms (AAAs) and produce death-promoting proteins (perforin, Fas, and FasL). This study investigated whether apoptosis occurs in association with the expression of these proteins.

METHODS AND RESULTS

We examined signs of apoptosis and expression of death-promoting mediators in segments of AAAs from patients undergoing elective repair (n=20). Anti-alpha-actin immunostaining showed a reduced number of SMCs in AAAs. In situ terminal transferase-mediated dUTP nick end-labeling (TUNEL) showed higher levels of DNA fragmentation in AAAs than in controls (n=5). The AAA walls contained more cells bearing markers of apoptosis than normal aorta (P<0.05, Student's t test). Double immunostaining identified SMCs and macrophages as the principal cell types displaying fragmented DNA. Immunohistochemistry revealed that AAAs but not normal aorta contained CD4(+) and CD8(+) T cells that expressed well-characterized cytotoxic mediators: perforin, which produces membrane damage, and Fas, which acts by ligand-receptor interaction. Double immunostaining also identified SMCs that expressed Fas. Immunoblotting confirmed the presence and, in the case of Fas, activation of these proteins in aneurysmal tissue.

CONCLUSIONS

Many medial SMCs in AAAs bear markers of apoptosis and signals capable of initiating cell death. Apoptotic death may contribute to the reduction of cellularity and to the impaired repair and maintenance of the arterial extracellular matrix in AAAs. Macrophages and T lymphocytes infiltrate the wall of AAAs, where they can produce cytotoxic mediators such as cytokines, perforin, and Fas/FasL. These death-promoting products of activated immune cells may contribute to elimination of SMCs, a source of elastin and collagen, during the pathogenesis of AAAs.

Caspase-3-induced gelsolin fragmentation contributes to actin cytoskeletal collapse, nucleolysis, and apoptosis of vascular smooth muscle cells exposed to proinflammatory cytokines

Gelsolin, an 80 kDa actin-severing protein, has been recently identified as a substrate for the cell death-promoting cysteinyl protease caspase-3 (CPP32/apopain/YAMA). We investigated the role of gelsolin and its cleavage product in apoptosis of vascular smooth muscle cells (SMC) induced by the proinflammatory cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). Treatment with a combination of IFN-gamma and TNF-alpha reduced viability of SMC in a time- and concentration-dependent manner. Immunoblotting revealed that SMC treated with the cytokines generated a 41 kDa gelsolin fragment. The gelsolin fragmentation required activation of caspase-3, as the caspase-3 inhibitor diminished cytokine-induced cell death as well as the fragmentation. Gelsolin cleavage was accompanied by a reduction in F-actin content and by a marked disruption of cell structure. Adenovirus-mediated transfection of this N-terminal gelsolin fragment into SMC altered cell morphology, reduced cell viability, increased the number of TUNEL-positive cells, and promoted internucleosomal DNA fragmentation. Compared to wild-type cells, gelsolin-deficient SMC showed resistance to apoptosis induced by the inflammatory cytokines. These results suggest a mechanistic role for gelsolin cleavage during SMC apoptosis, a process implicated in vessel development as well as stability of atherosclerotic plaque.

Regulation of programmed cell death or apoptosis in atherosclerosis

Intimal thickening caused by accumulation of cells, lipids, and connective tissue characterizes atherosclerosis, an arterial disease that leads to cardiac and cerebral infarction. Apoptosis, or genetically programmed cell death, is important for the development and morphogenesis of organs and tissues. As in other tissues, cells of cardiovascular tissues can undergo apoptosis. Increased apoptosis has been found in both human and animal atherosclerotic lesions, mediating tissue turnover and lesion development. In addition to vascular cells, many activated immune cells, mainly macrophages and T cells, are present in atherosclerotic lesions, where these cells produce biologically active substances such as the proinflammatory cytokines tumor necrosis factor, interleukin-1 (IL-1), and interferon-gamma. Simultaneous exposure to these cytokines may trigger apoptosis of vascular smooth muscle cells. The products of death-regulating genes including Fas/Fas ligand, members of IL-1 beta cysteinyl protease (caspase) family, the tumor suppressive gene p53, and the protooncogene c-myc have been found in vascular cells and may participate in the regulation of vascular apoptosis during the development of atherosclerosis. Abnormal occurrence of apoptosis may take place in atherosclerotic lesions, including attenuation or acceleration of the apoptotic death process. The former may cause an increase in the cellularity of the lesions, and the latter can reduce cellular components important for maintaining the integrity and stability of the plaques. Clarification of the molecular mechanism that regulates apoptosis may help design a new strategy for treatment of patients with atherosclerosis and its major complications, heart attack and stroke.

Fas is expressed in human atherosclerotic intima and promotes apoptosis of cytokine-primed human vascular smooth muscle cells

The membrane protein Fas/Apo-1/CD95 signals programmed cell death or apoptosis in activated T lymphocytes. Vascular smooth muscle cells (SMCs) bear markers of programmed cell death or apoptosis in advanced atherosclerotic plaques that contain immune cells e.g., macrophages and T lymphocytes. This study tested the hypothesis that the Fas death-signaling pathway contributes to apoptosis of SMCs exposed to proinflammatory cytokines produced by these immune cells during atherogenesis. All atherosclerotic plaques examined (n = 14) contained immunoreactive Fas. The majority of the Fas+ SMCs localized in the intima of the plaques, whereas the medial SMCs expressed Fas antigen less prominently. Double staining for DNA fragments (TUNEL) and Fas or cell identification markers colocalized Fas with TUNEL+ SMCs in the areas that contained CD3+ T cells and CD68+ macrophages, suggesting a role for Fas in the induction of SMC apoptosis by activated T cells during atherogenesis. In culture, stimulation with interferon-gamma, tumor necrosis factor-alpha, and interleukin-1 beta increased expression of Fas in SMCs. Incubation with an activating anti-Fas antibody triggered apoptosis of the cytokine-primed but not the untreated SMCs, as demonstrated by TUNEL and electrophoresis of oligonucleosomal DNA fragments. These data suggest that activation of the Fas death-signaling pathway contributes to the induction of SMC apoptosis during atherogenesis and furnish a mechanism whereby immune cells and their cytokines promote this cell death process related to vascular remodeling and plaque rupture.

Macrophages and atherosclerotic plaque stability

Physical disruption of atheroma frequently causes coronary thrombosis. Ruptured plaques usually have thin fibrous caps overlying a large thrombogenic lipid core rich in lipid-laden macrophages. The biology of plaque monocyte-derived macrophages thus assumes critical importance in understanding plaque instability. Monocyte recruitment involves binding to leukocyte adhesion receptors on the endothelial surface such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Once adherent to the endothelial surface, monocytes enter the intima at sites of lesion predilection. This process probably requires directed migration of the mononuclear cells. A number of chemoattractant molecules, such as the monocyte chemoattractant molecule-1, may participate in signaling this entry of adherent monocytes into the artery wall. Once resident in the arterial intima, monocytes accumulate lipid, via increasingly well characterized receptor-mediated uptake, and transform into macrophage foam cells. These lesional macrophages also acquire other functional properties including production of the potent procoagulant, tissue factor, apolipoprotein E, and an increasing list of cytokines (protein mediators of information and immunity) that may participate importantly in autocrine and paracrine signaling among leukocytes and vascular endothelial and smooth muscle cells. Fatty streaks seldom cause clinical events but may evolve into complicated atheromatous plaques characterized by an accumulation of smooth muscle cells and extracellular matrix and formation of a central core containing extracellular lipid. Death of macrophages, including programmed cell death or apoptosis, probably promotes formation of this thrombogenic lipid pool whose size correlates with plaque instability. Lesion complication often culminates in rupture of the fibrous cap overlying this lipid core. The integrity of the fibrous cap, and thus its resistance to rupture, depends critically on the collagenous extracellular matrix of the plaque's fibrous cap. This aspect of plaque structure in turn depends upon the balance between synthesis and degradation of the macromolecules that comprise the extracellular matrix of the cap, principally interstitial forms of collagen derived from arterial smooth muscle cells. Collagen breakdown, however, appears to depend critically on macrophages. Plaque macrophages express a variety of matrix-degrading enzymes that can contribute to the weakening of the fibrous cap. In this way, macrophages can critically influence aspects of the biology of human atheroma related to lesion stability. We hypothesize that lipid-lowering reduces clinical events, as shown in recent trials, by stabilizing lesions in part by reversing some of the maladaptive functions of macrophages described above.

Apoptotic death of human leukemic cells induced by vascular cells expressing nitric oxide synthase in response to gamma-interferon and tumor necrosis factor-alpha

The host defense against tumor cells is in part based on the production of nitric oxide (NO) by activated macrophages. However, cells of the blood vessels can also participate in antitumor defense responses. They produce NO either constitutively [endothelial cells (ECs)] or after stimulation by proinflammatory cytokines (ECs and vascular smooth muscle cells). We have used a tumor cell-vascular cell coculture system to evaluate whether vascular cells can mediate cytotoxic effects on tumor cells. Treatment with IFN-gamma and tumor necrosis factor-alpha induced death of human erythroleukemic K562 cells cocultured with rodent vascular smooth muscle cells or ECs. The synergistic antitumor activity of the two cytokines depended on de novo gene expression of the inducible isoform of NO synthase and on synthesis of reactive nitrogen intermediates (RNIs) in the vascular cells. K562 cells did not produce any appreciable levels of NO, but they were targeted by RNIs released from the cytokine-stimulated vascular cells, as demonstrated by electron paramagnetic resonance spectrometry, which showed formation of nonheme iron-nitrosyl complexes in the tumor cells. Assays for mitochondrial respiration demonstrated that the tumor cells suffered from a block of the complexes I and II of the mitochondrial respiratory chain. Further analysis of the cytotoxic mechanism by fluorescent microscopy, flow cytometry, and DNA electrophoresis revealed that K562 cells attacked by NO-producing vascular cells underwent apoptosis with plasma membrane blebbing, cell volume reduction, condensation of cytoplasm and chromatin, and fragmentation of genomic DNA at internucleosomal sites. In contrast, only a few vascular cells exhibited these apoptotic changes, suggesting that these cells resist the RNI attack. Inhibition of NO production in vascular cells by NG-monomethyl-L-arginine, an inhibitor of NO synthases, significantly reduced the death of the K562 cells. These observations suggest that vascular cells induce apoptotic death of tumor cells by producing RNIs in response to cytokine stimulation.

Apoptosis of vascular smooth muscle cells induced by in vitro stimulation with interferon-gamma, tumor necrosis factor-alpha, and interleukin-1 beta

Recent studies have documented evidence for the death of smooth muscle cells (SMCs) within advanced human atheroma. These lesions contain macrophages and T lymphocytes in addition to SMCs. We therefore investigated whether interferon-gamma (IFN-gamma), a cytokine secreted by T lymphocytes, or interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), two cytokines characteristically produced by activated macrophages, can trigger apoptosis of vascular SMCs. Simultaneous treatment with IFN-gamma and TNF-alpha and/or IL-1 beta but not with each cytokine alone promoted death of human and rat SMCs. Exposure for 48 hours to a combination of IFN-gamma (400 U/mL), TNF-alpha (400 U/mL), and IL-1 beta (100 U/mL) significantly (P < .001) increased the accumulation of oligonucleosomes comprising DNA fragments and histones in human SMCs. Electrophoresis of genomic DNA showed internucleosomal fragments of genomic DNA isolated from the cytokine-cotreated SMCs of both humans and rats. These cells exhibited morphological changes typical of apoptosis, including cell shrinkage, membrane blebbing, chromatin condensation, and nuclear fragmentation. In situ 3' end labeling of DNA fragments with terminal transferase confirmed the fragmentation of genomic DNA in these cells. Simultaneous treatment with IFN-gamma and TNF-alpha or IL-1 beta induced elaboration of nitrite, an end product of nitric oxide, in rat but not human SMCs. NG-monomethyl-L-arginine inhibited nitrite accumulation and also partly blocked cytokine-induced apoptosis of rat SMCs but had little effect on human SMCs, suggesting operation of both nitric oxide-dependent and -independent mechanisms for cytokine-induced apoptosis in vascular SMCs. Production of immune cytokines by vascular cells and/or infiltrating leukocytes may regulate apoptotic death of SMCs during atherogenesis.

Expression of the macrophage scavenger receptor in atheroma. Relationship to immune activation and the T-cell cytokine interferon-gamma

Scavenger receptors mediate internalization of modified lipoproteins and foam cell transformation of monocyte-derived cytokines. We investigated macrophage scavenger receptor (MSR) expression in monocyte-macrophages from human peripheral blood and in atherosclerotic lesions and analyzed its relationship to T lymphocytes and immunoregulatory cytokines by immunohistochemistry and polymerase chain reaction (PCR). Antibodies specific for the two MSR isoforms were generated by immunizing rabbits with isoform-specific synthetic peptides conjugated to keyhole limpet hemocyanin. In human atherosclerotic plaques, these antibodies stained macrophages and foam cells in a pattern that corresponded to the distribution of the macrophage marker CD68. CD3-positive T cells and alpha-actin-positive smooth muscle cells exhibited no reactivity to the anti-MSR antibodies. The frequency of cells stained with antibodies to MSR type I was equal to that of cells stained for type II, suggesting that most macrophages coexpress both isoforms. Reverse transcription (RT)-PCR analysis confirmed that both MSR isoforms were expressed in all plaques examined. There was, however, a tendency toward a lower immunohistochemical staining intensity for MSR type I and a decreased number of lipid-rich foam cells in T cell-rich areas. The mRNAs for interleukin-2 and interferon-gamma, two major products of activated T cells, were detected by RT-PCR in all plaques tested. This indicates that activation of T lymphocytes occurs in atherosclerotic plaques. Since interferon-gamma downregulates MSR expression, these observations suggest a potential mechanism for local regulation of MSR expression in the atherosclerotic plaque.

High endothelial cells of postcapillary venules express the scavenger receptor in human peripheral lymph nodes

The macrophage scavenger receptor (MSR) is a multipotent receptor that mediates uptake of macromolecules with clustered negative charges, such as endotoxins and oxidized proteins and lipoproteins. It may also serve as an adhesion molecule for monocytes and macrophages. We have analysed MSR expression in human peripheral lymph nodes and show, by reverse transcription-PCR, that the type I isoform of MSR is abundantly expressed in this tissue. With the use of a new set of isoform-specific peptide antibodies, both isoforms of MSR were detected in the cuboidal endothelium of high-endothelial venules (HEV). MSR antibodies also stained macrophages and follicular dendritic cells of germinal centres. These data indicate that the MSR gene is expressed in HEV endothelium in vivo. It is suggested that MSR expression may be important for antigen uptake and leucocyte adhesion to HEV in the lymph node.

Evidence for apoptosis in advanced human atheroma. Colocalization with interleukin-1 beta-converting enzyme

This study sought evidence for apoptosis, a form of programmed cell death, in human atheromatous coronary and carotid arteries. Markers for apoptotic cells included in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), genomic DNA electrophoresis, and morphological analysis. Intimal lesions contained more TUNEL+ cells (34 +/- 6%, n = 8) than non-atherosclerotic arterial intima (8 +/- 3%, n = 5, P < 0.05). The tunica media of the diseased arteries had a percentage of TUNEL+ cells (5 +/- 1%) similar to that in the normal vessels (3 +/- 1%, N.S.). Oligonucleosomal DNA fragments were visualized in extracts from 12 atheromatous plaques but in none of 5 non-atherosclerotic vessels. Both smooth muscle cells (SMC) and macrophages, two major cell types in the atherosclerotic intima, bore markers of apoptosis, but with different patterns, as determined by double histochemical labeling for cell types and TUNEL. The TUNEL+ SMC localized mainly in the fibrotic portion of the atheroma, whereas TUNEL+ macrophages clustered near or within the lipid-rich core of the lesion. Atheromatous lesions expressed mRNA encoding interleukin-1 beta-converting enzyme (ICE), a mammalian cell death gene, as demonstrated by reverse transcriptase polymerase chain reaction. Immunohistochemistry revealed that ICE localized in regions of TUNEL+ SMC and macrophages. TUNEL- cells showed little or no immunoreactive ICE. These data point to a role for apoptosis in regulation of cell accumulation during atherogenesis and suggest involvement of ICE in SMC death in fibrous regions of complex atheroma, and in macrophage death in the lipid-rich core of the lesion. Apoptosis of vascular cells in fibrous cap may impede maintenance or repair of the matrix in this region and affect stability of the plaques.

Cytokine-induced expression of nitric oxide synthase results in nitrosylation of heme and nonheme iron proteins in vascular smooth muscle cells

Nitric oxide synthase (NOS) catalyzes the synthesis of the biomediator, nitric oxide (NO), from L-arginine. We have analyzed NOS induction and activity in cultured rat vascular smooth muscle cells (SMC), which respond to NO by relaxation and inhibition of mitochondrial respiration. Both interferon-gamma and tumor necrosis factor-alpha induced the expression of NOS mRNA and a combination of the two cytokines had a synergistic effect. An internal oligonucleotide complementary to murine macrophage NOS mRNA hybridized to polymerase chain reaction (PCR) products derived from SMC NOS but not brain NOS. Direct sequencing of the PCR products showed a high degree of homology between inducible NOS from SMC and macrophages. Analysis of NOS-dependent nitrite production demonstrated that the enzyme requires NADPH as a cofactor but not calcium for its activity. Cytokine treatment resulted in the development of electron paramagnetic resonance (EPR) signals characteristic for nitrosyl complexes, indicating nitrosylation of SMC molecules by enzymatically synthesized NO. De novo NOS gene transcription and protein synthesis are required for the cytokine-induced protein nitrosylation since addition of actinomycin D and cycloheximide abolished the cytokine effect. At an early stage of cytokine treatment and when low doses of cytokines were used, the EPR signal was dominated by a triplet hyperfine structure typical for hemenitrosyl complexes. With increasing incubation time and/or cytokine dose, the EPR spectra were gradually converted into a pattern resembling that of nonheme iron(II)-nitrosyl thiol complexes. Thereafter, the EPR signal shape no longer changed while the signal intensity increased quantitatively with NO synthesis, suggesting that considerable amounts of NO synthesized could be trapped in the cells by formation of nitrosyl complexes with intracellular molecules. Together, these results provide direct biochemical evidence for cytokine induction of NO synthesis and protein nitrosylation in SMC. This may represent an important second messenger system for cytokine effects on cellular metabolism in blood vessels.

Protein kinase C activation inhibits cytokine-induced nitric oxide synthesis in vascular smooth muscle cells

Vascular smooth muscle cells (SMC) respond by relaxation to nitric oxide (NO) released from the endothelium which expresses a constitutive, Ca(2+)-dependent NO synthase (cNOS). SMC can, however, produce NO themselves upon stimulation by proinflammatory cytokines which induce expression of an inducible, Ca(2+)-independent NO synthase (iNOS). Protein kinase C represents another important second messenger system involved in the regulation of SMC contraction. We have investigated iNOS expression and NO synthesis in rat vascular SMC treated with the cytokines, IFN gamma and TNF alpha, in the presence or absence of the activator of protein kinase C, beta-phorbol-12-myristate 13-acetate (PMA). Treatment with PMA did not induce any significant accumulation of nitrite, a major stable metabolite of NO, in SMC. When added simultaneously with the cytokines, PMA significantly reduced nitrite accumulation induced by cytokine stimulation in a dose-dependent fashion. This inhibitory effect was mediated by activation of PKC since calphostin C, a specific PKC inhibitor, abolished the PMA effect. Further analysis of iNOS mRNA with a rat iNOS cDNA probe demonstrated that addition of PMA reduced expression of SMC iNOS mRNA, indicating that the antagonism in induction of NO synthesis between PMA and the proinflammatory cytokines acts on the transcriptional level. The inhibitory effect of PMA may be mediated via induction of a suppressor of iNOS expression, since pretreatment with PMA reduced NO production after subsequent treatment with cytokines. These observations suggest that activation of the PKC pathway is involved in a negative regulation of iNOS gene expression and this is compatible with the observation that vascular SMC contraction can be induced by PKC activation.

cDNA cloning and expression of inducible nitric oxide synthase from rat vascular smooth muscle cells

Nitric oxide (NO) is an important signal molecule. In blood vessels, nitric oxide produced by the endothelium modulates vascular tone by inducing cGMP formation in smooth muscle cells. The latter cell type does not express NO synthase normally but expression is induced by the cytokines, interferon-gamma, tumor necrosis factor, and interleukin-1. We have constructed a cDNA library from cytokine-stimulated rat aortic smooth muscle cells and isolated a cDNA clone that contains the full-length sequence of inducible NO synthase. It is 4119 bp and confers NO synthesizing activity when transfected into COS-7 cells. The nucleotide sequence is 92% identical with inducible NO synthase of murine macrophages and contains a 497 bp untranslated 3' sequence with five conserved A(U)nA motifs that may be important in the regulation of mRNA turnover. This is supported by the short half-life (2.6 h) of smooth muscle NO synthase mRNA, which contrasts with brain and endothelial NO synthase.

Arterial smooth muscle cells express nitric oxide synthase in response to endothelial injury

Endothelial cells regulate vascular tone by secreting paracrine mediators that control the contractility of arterial smooth muscle cells. Nitric oxide (NO) is an important vasodilating agent that is generated from L-arginine by the enzyme nitric oxide synthase (NOS), which is expressed constitutively by the endothelium. NO also inhibits platelet aggregation, contributing to the antithrombotic properties of the endothelial surface. It would therefore be expected that loss of the endothelium during arterial injury would lead to vasospasm and thrombosis but instead, the neointima formed after injury has a nonthrombogenic surface and a maintained vascular patency. We report here that arterial smooth muscle cells in the neointima formed after a deendothelializing balloon injury to the rat carotid artery express the cytokine-inducible isoform of NOS. Expression was detectable by reverse transcription-polymerase chain reaction from day 1-14 after injury and in situ hybridization showed expression of NOS mRNA by neointimal smooth muscle cells, particularly at the surface of the lesion. This was associated with systemically detectable NO production as revealed by electron paramagnetic resonance spectroscopic analysis of nitrosylated red cell hemoglobin. Local NO production by intimal smooth muscle cells after endothelial injury could represent an important mechanism for the maintenance of arterial patency and nonthrombogenicity in the injured artery.

Interferon-gamma inhibits scavenger receptor expression and foam cell formation in human monocyte-derived macrophages

The scavenger receptor (ScR) mediates uptake of chemically modified low density lipoprotein (LDL) by human monocyte-derived macrophages. It is not down-regulated by high intracellular cholesterol levels, and exposure of macrophages to acetylated or oxidized LDL therefore leads to foam cell development. The hypothesis that this represents an important mechanism for intracellular cholesterol accumulation in atherosclerosis is supported by the finding of ScR expression in foam cells of atherosclerotic plaques. T lymphocytes are also present in such plaques and it is known that T cell products regulate macrophage activation. We have therefore studied the effect of interferon-gamma (IFN gamma), a lymphokine secreted by activated T lymphocytes, on the expression of ScR in human monocyte-derived macrophages. Binding and uptake of acetylated LDL were significantly reduced in macrophages exposed to recombinant IFN gamma or IFN gamma-containing lymphocyte-conditioned media. Competition experiments showed that the IFN gamma-regulated binding and uptake of acetylated LDL was mediated via ScR. IFN gamma exerted its effect on the saturable binding of acetylated LDL by reducing the number of cell surface binding sites without significantly affecting the affinity between acetylated LDL and its receptor. Northern analysis revealed that the type I ScR mRNA was significantly reduced in IFN gamma-treated cells. Finally, IFN gamma treatment reduced intracellular cholesteryl ester accumulation and inhibited the development of foam cells in the cultures. In conclusion, our data show that IFN gamma blocks the development of macrophage-derived foam cells by inhibiting expression of ScR. This suggests that macrophage-T lymphocyte interactions may reduce intracellular cholesterol accumulation in the atherosclerotic plaque.