Exosomes with major histocompatibility complex class II and co-stimulatory molecules are present in human BAL fluid

Exosomes are 30-100 nm diameter vesicles formed by inward budding of endosomal compartments and are produced by several cell types, including T-cells, B-cells and dendritic cells (DC)s. Exosomes from DCs express major histocompatibility complexes (MHC) class I and II, and co-stimulatory molecules on their surface, and can induce antigen-specific activation of T-cells. The aims of the present study were to investigate for the presence of exosomes in bronchoalveolar lavage fluid (BALF) from healthy individuals, and to establish if these exosomes bear MHC and co-stimulatory molecules. The authors analysed BALF taken from seven healthy volunteers and used exosomes from monocyte-derived DC (MDDC) cultures as a reference. After ultracentrifugation, exosomes were bound to anti-MHC class II coated magnetic beads and analysed by flow cytometry and electron microscopy. The authors report for the first time that exosomes are present in BALF. These exosomes are similar to MDDC derived exosomes as they express MHC class I and II, CD54, CD63 and the co-stimulatory molecule CD86. The results demonstrate that exosomes are present in the lung, and since they contain both major histocompatibility complex and co-stimulatory molecules it is likely that they are derived from antigen presenting cells and might have a regulatory role in local immune defence.

Cholesterol oxidase and the hydroxymethylglutaryl coenzyme A reductase inhibitor mevinolin perturb endocytic trafficking in cultured vascular smooth muscle cells

Cholesterol is a component of cellular membranes and especially abundant in caveolae (50-80 nm flask-shaped invaginations of the plasma membrane). Caveolae are highly numerous in vascular endothelial and smooth muscle cells and have been implicated in a variety of functions, including signal transduction, lipid transport and uptake of macromolecules. Here, the effects of cholesterol oxidase (an enzyme that oxidizes cholesterol in caveolae of living cells) and mevinolin (an inhibitor of cholesterol synthesis) on fine structure and internalization of exogenous markers were studied in rat aortic smooth muscle cells grown on a substrate of fibronectin in serum-free primary cultures. Cholesterol oxidase caused a growth in size of the endocytic compartment with accumulation of enlarged endosomes and lysosomes containing tracer molecules. In parallel, the number of caveolae was reduced by about one fifth. Moreover, the morphology of the Golgi complex was altered with swollen cisternae surrounded by empty-looking vacuoles. Mevinolin suppressed transition of the cells from a differentiated or contractile to a dedifferentiated or synthetic phenotype. In addition, contractile cells were found to ingest horseradish peroxidase (HRP) not only into endosomes and lysosomes but also into Golgi cisternae, especially on the convex/cis side of the stacks, and the endoplasmic reticulum. A similar pathway was noted in contractile cells exposed to cholera toxin B subunit (CTB)-HRP conjugates, a ligand that binds to ganglioside GM1 and at least in part is ingested via caveolae. Mevinolin did not prevent the transport of CTB-HRP to the Golgi complex, but the conjugates were in this case concentrated to the concave/trans side of the cisternal stacks. However, no clear effect on the number of caveolae was noted. The observations indicate an important role of cholesterol and caveolae in the control of endocytic traffic in smooth muscle cells. This function appears most significant when the cells are in a differentiated state.

Leptin induces vascular permeability and synergistically stimulates angiogenesis with FGF-2 and VEGF

Most endocrine hormones are produced in tissues and organs with permeable microvessels that may provide an excess of hormones to be transported by the blood circulation to the distal target organ. Here, we investigate whether leptin, an endocrine hormone, induces the formation of vascular fenestrations and permeability, and we characterize its angiogenic property in the presence of other angiogenic factors. We provide evidence that leptin-induced new blood vessels are fenestrated. Under physiological conditions, capillary fenestrations are found in the leptin-producing adipose tissue in lean mice. In contrast, no vascular fenestrations were detected in the adipose tissue of leptin-deficient ob/ob mice. Thus, leptin plays a critical role in the maintenance and regulation of vascular fenestrations in the adipose tissue. Leptin induces a rapid vascular permeability response when administrated intradermally. Further, leptin synergistically stimulates angiogenesis with fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF), the two most potent and commonly expressed angiogenic factors. These findings demonstrate that leptin has another new function-the increase of vascular permeability.

Prediction of amyloid fibril-forming proteins

In Alzheimer's disease and spongiform encephalopathies proteins transform from their native states into fibrils. We find that several amyloid-forming proteins harbor an alpha-helix in a polypeptide segment that should form a beta-strand according to secondary structure predictions. In 1324 nonredundant protein structures, 37 beta-strands with > or =7 residues were predicted in segments where the experimentally determined structures show helices. These discordances include the prion protein (helix 2, positions 179-191), the Alzheimer amyloid beta-peptide (Abeta, positions 16-23), and lung surfactant protein C (SP-C, positions 12-27). In addition, human coagulation factor XIII (positions 258-266), triacylglycerol lipase from Candida antarctica (positions 256-266), and d-alanyl-d-alanine transpeptidase from Streptomyces R61 (positions 92-106) contain a discordant helix. These proteins have not been reported to form fibrils but in this study were found to form fibrils in buffered saline at pH 7.4. By replacing valines in the discordant helical part of SP-C with leucines, an alpha-helix is found experimentally and by secondary structure predictions. This analogue does not form fibrils under conditions where SP-C forms abundant fibrils. Likewise, when Abeta residues 14-23 are removed or changed to a nondiscordant sequence, fibrils are no longer formed. We propose that alpha-helix/beta-strand-discordant stretches are associated with amyloid fibril formation.

Phenotypic modulation of arterial smooth muscle cells is associated with prolonged activation of ERK1/2

Arterial smooth muscle cells grown in primary culture on a substrate of fibronectin in serum-free medium are converted from a contractile to a synthetic phenotype. This process is dependent on integrin signaling and includes a major structural reorganization with loss of myofilaments and formation of a large secretory apparatus. Functionally, the cells lose their contractility and become competent to migrate, secrete extracellular matrix components, and proliferate in response to growth factor stimulation. Here, it is demonstrated that the mitogen-activated protein kinases ERK1/2 play a vital role in the fibronectin-mediated modification of rat aortic smooth muscle cells. Immunoblotting showed that phosphorylated ERK1/2 (p44/p42) were expressed throughout the period when the change in phenotypic properties of the cells took place. Moreover, phosphorylated ERK1/2 accumulated in the nucleus as revealed by immunocytochemical staining. Additional support for an active role of ERK1/2 in the shift in smooth muscle phenotype was obtained by the finding that PD98059, an inhibitor of the upstream kinase MEK1, potently suppressed both the expression of phosphorylated ERK1/2 and the fine structural rebuilding of the cells. In conclusion, the observations point to an important and multifaceted role of ERK1/2 in the regulation of differentiated properties and growth of vascular smooth muscle cells.

7beta-hydroxycholesterol induces Ca(2+) oscillations, MAP kinase activation and apoptosis in human aortic smooth muscle cells

In the present study, we characterize the early cytotoxic effects of 7beta-hydroxycholesterol, a major cytotoxin in oxidized LDL, in human aortic smooth muscle cells. Within a few minutes after addition, 7beta-hydroxycholesterol induced Ca(2+) oscillations with a frequency of approximately 0.3-0.4 min(-1). A few hours later, thapsigargin-sensitive Ca(2+) pools were depleted, indicating that 7beta-hydroxycholesterol perturbs intracellular Ca(2+) homeostasis. The mitogen-activated protein kinases (MAPKs) ERK1 and ERK2 (but not JNK) were activated within 5 min after addition of 7beta-hydroxycholesterol. The side-chain hydroxylated oxysterols 25-hydroxycholesterol and 27-hydroxycholesterol were more potent in inducing apoptosis than 7beta-hydroxycholesterol and cholesterol-5alpha,6alpha-epoxide, as determined by TUNEL staining. Addition of TNFalpha (10 ng/ml) and IFNgamma (20 ng/ml) enhanced the cytotoxicity of oxysterols and potentiated apoptosis. The cytokines alone were not toxic to smooth muscle cells at these concentrations. 25-Hydroxycholesterol and 7beta-hydroxycholesterol but not cholesterol inhibited protein synthesis at 4-8 h as determined by [35S]methionine incorporation assay. Morphologically, oxysterol-induced cell death was characterized by disorganization of the ER and Golgi membranes. The Ca(2+) and ERK signals preceded the ultrastructural changes induced by 7beta-hydroxycholesterol.

Fucoidan inhibits smooth muscle cell proliferation and reduces mitogen-activated protein kinase activity

OBJECTIVES AND DESIGN

fucoidan has previously been shown to inhibit the proliferation of arterial smooth muscle cells both in animal models and in vitro. However, the mechanisms behind the anti-proliferative effects of this polysulfated polysaccharide are not known in detail. Here, the inhibitory effect of fucoidan on rat aortic smooth muscle cell proliferation was examined and compared with the effects of heparin after stimulation with fetal calf serum, platelet-derived growth factor BB, basic fibroblast growth factor, heparin-binding epidermal growth factor, and angiotensin II.

MATERIALS AND METHODS

the cultures were analysed with respect to cell proliferation and DNA synthesis by cell counting and measurement of(3)H-thymidine incorporation. Phosphorylation of mitogen-activated protein kinase and nuclear translocation of phosphorylated mitogen-activated protein kinase were studied by immunoblotting and immunocytochemistry.

RESULTS

fucoidan was shown to be a more potent inhibitor of smooth muscle cell proliferation than heparin. Fucoidan also reduced growth factor-induced activation of mitogen-activated protein kinase and prevented nuclear translocation of phosphorylated mitogen-activated protein kinase.

CONCLUSION

fucoidan is a more potent anti-proliferative polysulphated polysaccharide than heparin and may mediate its effects through inhibition of the mitogen-activated protein kinase pathway in a similar manner as heparin.

The synthetic metalloproteinase inhibitor batimastat suppresses injury-induced phosphorylation of MAP kinase ERK1/ERK2 and phenotypic modification of arterial smooth muscle cells in vitro

Smooth muscle cell (SMC) migration and proliferation are important events in the formation of intimal lesions associated with atherosclerosis and restenosis following balloon angioplasty. The extracellular matrix has important functions in modulating SMC structure and function, but less is known about the role of the matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors. The present study investigates the effects of the synthetic MMP inhibitor batimastat (BB94) on vascular SMCs. As experimental model, rat aortic smooth muscle cells in primary and secondary cultures were employed. Electron microscopy was used to investigate the effects of BB94 on the overall phenotypic properties of the cells. Induction of DNA synthesis and migration was studied by thymidine autoradiography and counting of cells moving into an injured zone. Gelatin zymography was used for the detection of BB94-mediated inhibition of injury-induced MMP activity. Phosphorylation of the mitogen-activated protein kinases ERK1/ERK2, two potential mediators of the injury-induced activation of the cells, was measured by Western blotting. The results show that BB94 restrained the phenotypic modulation of vascular SMCs in primary cultures and suppressed injury-induced DNA synthesis and migration. Moreover, the upregulation of ERK1/ERK2 phosphorylation in injured secondary cultures and in cells treated with bFGF was markedly reduced by BB94, whereas TIMP-2 lacked a clear effect. Our data suggest that BB94 inhibits injury-induced activation of vascular SMCs by acting on MMPs as well as other targets.

Arteriosclerosis in rat aortic allografts: early changes in endothelial integrity and smooth muscle phenotype

BACKGROUND

Transplant arteriosclerosis remains a limiting factor for the long-term survival of transplanted organs and effective treatment is lacking. A rat model of aortic allografts was used to analyze this process by electron microscopy and further characterize the phenotypic properties of the cells involved.

METHODS

A segment of abdominal aorta was transplanted orthotopically from Fischer to Lewis rats. The animals were killed 1-12 weeks after the operation (four to six rats/group), and the grafts were removed and processed for microscopy.

RESULTS

The first changes (1 week) included detachment of endothelial cells, adhesion of degranulating platelets to the subendothelial matrix, and modification of smooth muscle cells in the media. The latter process was distinguished by loss of myofilaments and formation of a prominent endoplasmic reticulum and Golgi complex (shift from contractile to synthetic phenotype). Subsequently, modified smooth muscle cells invaded the intima. In parallel, lymphocytes and monocytes/macrophages infiltrated the intima and adventitia. The neointima grew in size by cell proliferation and production of extracellular matrix (4-8 weeks). Smooth muscle cells and monocytes/macrophages in the neointima and media were also noted to accumulate cytoplasmic lipid droplets and eventually turn into foam cells and die. Within the lipid-rich cell remnants, calcification occurred. Finally (12 weeks), the growth in mass of the intimal lesions ceased and in some places reformation of an endothelial lining was detected. Few viable smooth muscle cells remained in the media and the inflammatory infiltrate in the adventitia was reduced.

CONCLUSIONS

These observations highlight the importance of early changes in endothelial integrity and smooth muscle phenotype in the development of allograft vascular disease and form the basis for a partly modified model of the cellular mechanisms in this process.

STAT6 is required for the regulation of IL-4-induced cytoskeletal events in B cells

During lymphocyte activation, changes in cell morphology are commonly observed. This reflects cell functions important for the regulation of immune responses such as cell adhesion or cell migration. Notably, IL-4 has been shown to induce adhesion and locomotion in B cells, and we have recently described that IL-4 causes dramatic changes in B cell morphology. Thus, such B cells spread with dendritic cell protrusions and produce microvilli-like structures. The molecular mechanisms by which IL-4 induces these complex changes are currently unknown. Two signal transduction pathways are well described for IL-4, i.e. one involving insulin receptor substrate (IRS)-2 and a Janus kinase (JAK)/ signal transducer and activator of transcription (STAT) pathway mediated by STAT6. In this study we therefore used B cells from STAT6-deficient mice to address the question of a possible STAT6 dependence in IL-4-induced morphology changes. By light and electron microscopy, cell spreading and polarization were found to be severely impaired and microvilli formation was reduced. In contrast, only mild impairment was observed in cell adhesion in B cells from STAT6-deficient mice. Our results show that adhesion can be induced in the absence of STAT6. However, expression of STAT6 is necessary for optimal responses in both cell adhesion and microvilli induction. STAT6 is also essential to allow an IL-4-dependent spreading or polarization response. A possible interpretation of our results is that STAT6-dependent expression of a specific gene or genes is required for IL-4 to affect changes in B cell morphology.

Differences in caveolae dynamics in vascular smooth muscle cells of different phenotypes

Vascular smooth muscle cells shift between two major differentiated states with distinct morphological and functional properties, a contractile and a synthetic phenotype. Here, primary cultures were used to study caveolae expression and dynamics in these cells. The results demonstrate that caveolae are more numerous and more actively interact with intracellular organelles in contractile than in synthetic cells. Immunohistochemistry showed that caveolin-1 was mainly localized to caveolae in contractile cells and partly shifted to Golgi-associated vesicles in synthetic cells, whereas caveolin-2 chiefly appeared in cytoplasmic vesicles in both cases. Cholera toxin B subunit, a ligand of GM1 ganglioside, was internalized via caveolae and carried to endosomes and Golgi-associated vesicles. In contractile cells, it later moved into Golgi and endoplasmic reticulum (ER) cisternae and thus had access to the entire endocytic and exocytic pathways. In contrast, in synthetic cells, the tracer was restricted to the endocytic pathway. Filipin staining similarly disclosed that cholesterol was more widely distributed in contractile than in synthetic cells, with strong labeling of both caveolae and adjacent ER portions. Although no direct continuity between caveolae and ER was detected, it is suggested that cholesterol and other molecules may be translocated between these compartments. The observed differences in caveolae expression and dynamics are likely to be significant for the differences in proliferative capacity and cholesterol transport between contractile and synthetic smooth muscle cells.

Amyloid fibril formation by pulmonary surfactant protein C

Lung surfactant protein C (SP-C) is a lipopeptide that contains two fatty acyl (palmitoyl) chains bound via intrinsically labile thioester bonds. SP-C can transform from a monomeric alpha-helix into beta-sheet aggregates, reminiscent of structural changes that are supposed to occur in amyloid fibril formation. SP-C is here shown to form amyloid upon incubation in solution. Furthermore, one patient with pulmonary alveolar proteinosis (PAP, a rare disease where lung surfactant proteins and lipids accumulate in the airspaces) and six healthy controls have been studied regarding presence and composition of amyloid fibrils in the cell-free fraction of bronchoalveolar lavage (BAL) fluid. Abundant amyloid fibrils were found in BAL fluid from the patient with PAP and, in low amounts, in three of the six healthy controls. SDS-insoluble fibrillar material associated with PAP mainly consists of SP-C, in contrast to the fibrils found in controls. Fibrillated SP-C has to a significant extent lost the palmitoyl groups, and removal of the palmitoyl groups in vitro increases the rate of fibril formation.

Antisense oligonucleotides to stromelysin mRNA inhibit injury-induced proliferation of arterial smooth muscle cells

Smooth muscle cell migration and proliferation are important events in the formation of intimal lesions associated with atherosclerosis and restenosis following balloon angioplasty. To make this possible, the smooth muscle cell has to change from a contractile to an activated repair cell with capacity to synthesize DNA and extracellular matrix components. There is now considerable evidence that the extracellular matrix has important functions in modulating the phenotypic properties of smooth muscle cells, but less is known about the role of the matrix metalloproteinases. The present study investigates the role of stromelysin in the modulation of rat aortic smooth muscle cell morphology and function following mechanical injury in vitro and in vivo. Antisense mRNA oligonucleotides were used to investigate the role of stromelysin expression in injury-induced phenotypic modulation and the subsequent migration and proliferation of vascular smooth muscle cells. Cultured rat aortic smooth muscle cells and balloon-injured rat carotid arteries were used as experimental models. Light- and electron microscopy were used to follow changes in smooth muscle cell phenotype and lesion formation and incorporation of 3H-thymidine to detect DNA synthesis. Injury-induced DNA synthesis and migration in vitro were inhibited by 72% and 36%, respectively, by adding stromelysin antisense oligonucleotides to the medium prior to injury. In primary cultures, 67% of the smooth muscle cells treated with stromelysin antisense were retained in a contractile phenotype as judged by analysis of cell fine structure, compared to 15% untreated cells and 40% in cells treated with mismatched oligonucleotides. Examination of the carotid arteries one week after balloon injury likewise demonstrated a larger fraction of contractile cells in the inner parts of the media in vessels treated with antisense oligonucleotides compared to those treated with mismatched oligonucleotides. The neointima was also distinctly thinner in antisense-treated than in mismatched-treated and control arteries at this time. These findings indicate that stromelysin mRNA antisense oligonucleotides inhibited phenotypic modulation of rat arterial smooth muscle cells and so caused a decrease in migration and proliferation and neointima formation in response to vessel wall injury.

Effects of proteasome and calpain inhibitors on the structural reorganization and proliferation of vascular smooth muscle cells in primary culture

Vascular smooth muscle cells exhibit a striking plasticity and are able to change from a differentiated, contractile phenotype to a more immature, synthetic phenotype. This includes a prominent structural reorganization with loss of myofilaments and construction of a large secretory apparatus. As a result, the cells lose their contractility and become able to migrate, proliferate, and secrete extracellular matrix components. In vivo, this phenotypic shift is a chief factor behind the involvement of smooth muscle cells in formation of atherosclerotic and restenotic lesions. Here, the effects of the proteasome inhibitors carbobenzoxy-leucyl-leucyl-leucinal, N-acetyl-leucyl-leucyl-norleucinal, and lactacystin on the morphologic structure and growth of rat aortic smooth muscle cells in primary culture were examined. Electron microscopic analysis revealed that the volume density of myofilaments was higher and the volume density of the endoplasmic reticulum and the Golgi complex was lower in cells exposed to these drugs than in solvent-treated controls. Moreover, diffuse material representing incompletely degraded proteins gathered in the cytoplasm of exposed cells. Similar material was also found in lysosomes. Immunogold staining showed a positive reaction in the diffuse cytoplasmic aggregates with antibodies against ubiquitin-protein conjugates and proteasomes, whereas the material collecting in lysosomes reacted only with those against ubiquitin-protein conjugates. Moreover, weak staining for smooth muscle alpha-actin was noted in the cytoplasmic aggregates. Otherwise, reactivity for this protein was concentrated in myofilaments. In addition to the effects on cell structure described above, the proteasome inhibitors blocked cell multiplication. This was probably due to a decreased rate of transition into a synthetic state as well as direct interference with cell cycle progression in synthetic cells. These observations suggest that proteasomes have the major responsibility for protein degradation during transition of smooth muscle cells from a contractile to a synthetic phenotype. If proteasome activity is inhibited, undegraded material accumulates in the cytoplasm and is only partially taken up into lysosomes for digestion. These findings raise the possibility that proteasome inhibitors may have a beneficial effect on vascular pathologies associated with phenotypic modulation and proliferation of smooth muscle cells.

Presence of oxidized low density lipoprotein in nonrheumatic stenotic aortic valves

The aim of the present study was to analyze if LDL particles trapped in stenotic aortic valve tissue undergo oxidative modification. Degenerative aortic stenosis affects >3% of the population >75 years of age in the Western world. Recent studies have revealed the presence of a chronic inflammatory process similar to what has been described in other degenerative diseases such as atherosclerosis. However, the underlying disease mechanisms of degenerative aortic stenosis still remain largely unknown. Six tricuspid stenotic valves, obtained at valve replacement, were compared with 3 control valves collected from hearts taken out during transplantation. The stenotic valves and the control valves were examined by immunohistochemistry, using antibodies against apoB, 4-hydroxynonenal-modified LDL, leukocytes, and HLA-DR. All valves were also stained with oil red O for neutral lipids. Extracellular neutral lipids were found in all stenotic valves, extending from the bases along the fibrosa layer. This lipid colocalized with apoB- and 4-hydroxynonenal-modified LDL immunoreactivity. 4-Hydroxynonenal-modified LDLs were present around calcium deposits, subendothelially, and in the deeper layer of the fibrosa. There was also a colocalization with macrophages, T lymphocytes, and HLA-DR expression. Control valves had a thin area of neutral lipid accumulation, a small amount of apoB, but no signs of inflammation. A distinct colocalization between oxidized LDLs, T-lymphocyte accumulation, and calcium deposits suggests that oxidized lipids may play a role in the disease process.

A molecular model of Alzheimer amyloid beta-peptide fibril formation

Polymerization of the amyloid beta (Abeta) peptide into protease-resistant fibrils is a significant step in the pathogenesis of Alzheimer's disease. It has not been possible to obtain detailed structural information about this process with conventional techniques because the peptide has limited solubility and does not form crystals. In this work, we present experimental results leading to a molecular level model for fibril formation. Systematically selected Abeta-fragments containing the Abeta16-20 sequence, previously shown essential for Abeta-Abeta binding, were incubated in a physiological buffer. Electron microscopy revealed that the shortest fibril-forming sequence was Abeta14-23. Substitutions in this decapeptide impaired fibril formation and deletion of the decapeptide from Abeta1-42 inhibited fibril formation completely. All studied peptides that formed fibrils also formed stable dimers and/or tetramers. Molecular modeling of Abeta14-23 oligomers in an antiparallel beta-sheet conformation displayed favorable hydrophobic interactions stabilized by salt bridges between all charged residues. We propose that this decapeptide sequence forms the core of Abeta-fibrils, with the hydrophobic C terminus folding over this core. The identification of this fundamental sequence and the implied molecular model could facilitate the design of potential inhibitors of amyloidogenesis.

Role of microtubules in the organization of the Golgi complex

The Golgi complex of mammalian cells is composed of cisternal stacks that function in processing and sorting of membrane and luminal proteins during transport from the site of synthesis in the endoplasmic reticulum to lysosomes, secretory vacuoles, and the cell surface. Even though exceptions are found, the Golgi stacks are usually arranged as an interconnected network in the region around the centrosome, the major organizing center for cytoplasmic microtubules. A close relation thus exists between Golgi elements and microtubules (especially the stable subpopulation enriched in detyrosinated and acetylated tubulin). After drug-induced disruption of microtubules, the Golgi stacks are disconnected from each other, partly broken up, dispersed in the cytoplasm, and redistributed to endoplasmic reticulum exit sites. Despite this, intracellular protein traffic is only moderately disturbed. Following removal of the drugs, scattered Golgi elements move along reassembling microtubules back to the centrosomal region and reunite into a continuous system. The microtubule-dependent motor proteins cytoplasmic dynein and kinesin bind to Golgi membranes and have been implicated in vesicular transport to and from the Golgi complex. Microinjection of dynein heavy chain antibodies causes dispersal of the Golgi complex, and the Golgi complex of cells lacking cytoplasmic dynein is likewise spread throughout the cytoplasm. In a similar manner, kinesin antibodies have been found to inhibit Golgi-to-endoplasmic reticulum transport in brefeldin A-treated cells and scattering of Golgi elements along remaining microtubules in cells exposed to a low concentration of nocodazole. The molecular mechanisms in the interaction between microtubules and membranes are, however, incompletely understood. During mitosis, the Golgi complex is extensively reorganized in order to ensure an equal partitioning of this single-copy organelle between the daughter cells. Mitosis-promoting factor, a complex of cdc2 kinase and cyclin B, is a key regulator of this and other events in the induction of cell division. Cytoplasmic microtubules depolymerize in prophase and as a result thereof, the Golgi stacks become smaller, disengage from each other, and take up a perinuclear distribution. The mitotic spindle is thereafter put together, aligns the chromosomes in the metaphase plate, and eventually pulls the sister chromatids apart in anaphase. In parallel, the Golgi stacks are broken down into clusters of vesicles and tubules and movement of protein along the exocytic and endocytic pathways is inhibited. Using a cell-free system, it has been established that the fragmentation of the Golgi stacks is due to a continued budding of transport vesicles and a concomitant inhibition of the fusion of the vesicles with their target membranes. In telophase and after cytokinesis, a Golgi complex made up of interconnected cisternal stacks is recreated in each daughter cell and intracellular protein traffic is resumed. This restoration of a normal interphase morphology and function is dependent on reassembly of a radiating array of cytoplasmic microtubules along which vesicles can be carried and on reactivation of the machinery for membrane fusion.

Amyloid beta-peptide polymerization studied using fluorescence correlation spectroscopy

BACKGROUND

The accumulation of fibrillar deposits of amyloid beta-peptide (Abeta) in brain parenchyma and cerebromeningeal blood vessels is a key step in the pathogenesis of Alzheimer's disease. In this report, polymerization of Abeta was studied using fluorescence correlation spectroscopy (FCS), a technique capable of detecting small molecules and large aggregates simultaneously in solution.

RESULTS

The polymerization of Abeta dissolved in Tris-buffered saline, pH 7.4, occurred above a critical concentration of 50 microM and proceeded from monomers/dimers into two discrete populations of large aggregates, without any detectable amount of oligomers. The aggregation showed very high cooperativity and reached a maximum after 40 min, followed by an increase in the amount of monomers/dimers and a decrease in the size of the large aggregates. Electron micrographs of samples prepared at the time for maximum aggregation showed a mixture of an amorphous network and short diffuse fibrils, whereas only mature amyloid fibrils were detected after one day of incubation. The aggregation was reduced when Abeta was incubated in the presence of Abeta ligands, oligopeptides previously shown to inhibit fibril formation, and aggregates were partly dissociated after the addition of the ligands.

CONCLUSIONS

The polymerization of Abeta is a highly cooperative process in which the formation of very large aggregates precedes the formation of fibrils. The entire process can be inhibited and, at least in early stages, partly reversed by Abeta ligands.

Role of caveolae in cholesterol transport in arterial smooth muscle cells exposed to lipoproteins in vitro and in vivo

Arterial smooth muscle cells are able to shift between two major differentiated states with distinct morphologic and functional properties, a contractile phenotype and a synthetic phenotype. Recently, it was demonstrated that contractile smooth muscle cells have numerous caveolae and that these specialized regions of the plasma membrane, to a large extent, are lost when the cells are modified into a synthetic phenotype. At the same time, the levels of the cholesterol-binding membrane protein caveolin remained unchanged and caveolin was redistributed from the cell surface to the perinuclear cytoplasm. In the present investigation, electron microscopy was used to study how smooth muscle cells of different phenotypes react to exposure to low-density lipoprotein and other lipoproteins both in vitro and in vivo. Our findings indicate that contractile cells (present early in primary culture and in the media of normal arterial walls) do not accumulate lipids in the cytoplasm and release excess cholesterol by means of plasma membrane caveolae. Extracellularly, the expelled lipids were built into membranous configurations and piled up as myelin-like deposits. In synthetic cells (formed after a few days in primary culture and as a response to arterial injury), lipids gathered in cytoplasmic droplets and increased amounts of membranous inclusions appeared in endosomes and lysosomes. On the other hand, no signs of extracellular discharge of lipids were detected. The results suggest that contractile smooth muscle cells use caveolin and caveolae to free themselves of excess lipoprotein-derived cholesterol and so manage to maintain a balance in the influx and efflux of cholesterol. Synthetic smooth muscle cells show a Golgi-like immunostaining for caveolin but have an insufficient capacity to use this protein to transport cholesterol to the plasma membrane and out of the cell. Cholesterol will then rather be esterified and collect in lipid droplets, eventually leading to foam cell formation if the uptake of lipoprotein continues.

Phenotypic modulation of smooth muscle cells during formation of neointimal thickenings following vascular injury

Smooth muscle cells build up the media of mammalian arteries and constitute one of the principal cell types in atherosclerotic and restenotic lesions. Accordingly, they show a high degree of plasticity and are able to shift from a differentiated, contractile phenotype to a less differentiated, synthetic phenotype, and then back again. This modulation occurs as a response to vascular injury and includes a prominent structural reorganization with loss of myofilaments and formation of an extensive endoplasmic reticulum and a large Golgi complex. At the same time, the expression of cytoskeletal proteins and other gene products is altered. As a result, the cells lose their contractility and become able to migrate from the media to the intima, proliferate, and secrete extracellular matrix components, thereby contributing to the formation of intimal thickenings. The mechanisms behind this change in morphology and function of the smooth muscle cells are still incompletely understood. A crucial role has been ascribed to basement membrane proteins such as laminin and collagen type IV and adhesive proteins such as fibronectin. A significant role is also played by mitogenic proteins such as platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). An improved knowledge of the regulation of smooth muscle differentiated properties represents an important part in the search for new methods of prevention and treatment of vascular disease.

An animal model to study local oxidation of LDL and its biological effects in the arterial wall

Oxidized LDL (oxLDL) is present in atherosclerotic lesions and is believed to play a key role in atherogenesis. Mainly on the basis of cell culture studies, oxLDL has been shown to produce many biological effects that influence the atherosclerotic process. To study LDL oxidation in vivo, we have established a model in which Sprague-Dawley rats are given a single injection of unmodified human LDL (> or = 4 mg/kg body weight). Within 6 hours, an accumulation of apolipoprotein B and epitopes present on oxLDL are detected in the arterial endothelium and media. The presence of oxLDL is associated with activation of the transcription factor nuclear factor-kappaB in the endothelium as well as endothelial expression of intercellular adhesion molecule-1. Injection of LDL enriched with the antioxidant probucol resulted in arterial accumulation of apolipoprotein B, but the expression of oxLDL-specific epitopes was reduced at 24 hours. Thus, this simple model has the potential to analyze the mechanisms behind and biological effects of LDL oxidation in vivo.

Regulation of cell morphology in B lymphocytes by IL-4: evidence for induced cytoskeletal changes

Lymphocyte activation is often accompanied by changes in cell morphology, for example, in cell adhesion or motility. IL-4 is a cytokine exerting many effects on B lymphocytes. In this study, we show that stimulation with LPS in combination with IL-4, but not LPS or IL-4 alone, results in a pronounced dendritic morphology of B cells. Using a culture system in which Abs directed to B cell surface markers are immobilized on the tissue culture plastic, we find that cell spreading can be mediated by a variety of Abs, including anti-CD44, -CD23, -LFA-1, -VLA-4, -ICAM-1, and -Ig. B cells stimulated with anti-Ig Abs plus IL-4, or anti-CD40 Abs in the presence or absence of IL-4, are also induced to spread, while IL-2, IL-5, or IL-10 in combination with LPS or alone fail to induce this. Spreading correlates with induction of tight cell aggregation. It is sensitive to cytochalasin B, indicating a requirement for intact actin cytoskeleton. CD44 is selectively detected in the detergent-insoluble fraction of cell lysates prepared from LPS plus IL-4-stimulated B cell cultures after Ab cross-linking of CD44, suggesting a membrane protein-cytoskeleton interaction. Interestingly, electron microscopy studies reveal induction of microvilli-like structures on LPS plus IL-4-stimulated blasts, suggesting that IL-4 can influence cell morphology on an ultra-structural level. In summary, our data show that stimulation with LPS plus IL-4 or ligation of CD40 is capable of inducing dramatic morphologic changes in murine B cells, which correlates with in vitro induction of strong cell adhesion.

Tyrphostin A9 and wortmannin perturb the Golgi complex and block proliferation of vascular smooth muscle cells

To proliferate, vascular smooth muscle cells first convert from a contractile to a synthetic phenotype. Earlier studies indicate that this process is supported by fibronectin and accelerated by platelet-derived growth factor (PDGF). Here, the mechanisms in this transition were further explored. Isolated rat aortic smooth muscle cells were treated with tyrphostin A9, a PDGF receptor tyrosine kinase inhibitor, and wortmannin, a phosphoinositide 3-kinase inhibitor. Electron microscopy did not show any effect on the reorganization of the cells during the first days in culture, i.e. the loss of actin filaments and the formation of a large secretory apparatus. Conversely, both drugs caused hypertrophy of the Golgi complex, with large and partly vacuolized cisternal stacks. Nevertheless, a juxtanuclear staining pattern for the Golgi enzyme mannosidase II, the coat protein beta-COP, and the PDGF beta-receptor was retained. Moreover, the serum-induced proliferation of the cells was blocked. These findings suggest that signaling via PDGF receptor tyrosine kinases and phosphoinositide 3-kinases is not necessary for the shift of the smooth muscle cells from a contractile to a synthetic phenotype. On the other hand, these enzymes apparently carry out important functions in the control of intracellular membrane traffic and cell division.

Partitioning of cytoplasmic organelles during mitosis with special reference to the Golgi complex

During mitosis, not only the genetic material stored in the nucleus but also the constituents of the cytoplasm should be equally partitioned between the daughter cells. For this sake, the dividing cell goes through an extensive structural reorganization and transport along the endocytic and exocytic pathways is temporarily arrested. Early in prophase, the radiating array of cytoplasmic microtubules disassembles and the membrane systems of the secretory apparatus start to split up. In metaphase, the nuclear envelope fragments and the condensing chromosomes associate with the forming mitotic spindle. The cisternal and tubular elements of the endoplasmic reticulum and the Golgi complex break down into small vesicles, presumably as the result of an imbalance between vesicle budding and fusion. In anaphase, the two sets of chromosomes are pulled apart and a cleavage furrow forms halfway between the spindle poles. Since most organelles occur in multiple and widely dispersed copies at this stage, they will be evenly distributed between the daughter cells. During telophase and cytokinesis, the preceding fragmentation process is reversed. A nuclear envelope reappears around the chromosomes and cytoplasmic microtubules reassemble. The endoplasmic reticulum is rebuilt as a continuous system of flattened cisternae and tubules. Stacks of Golgi cisternae arise from small vesicles and are rearranged in an interconnected network. In parallel, the biosynthetic functions of the cell are normalized and intracellular membrane traffic is resumed.

Role of tyrosine kinases in extracellular matrix-mediated modulation of arterial smooth muscle cell phenotype

Fibronectin (FN) promotes the modulation of freshly isolated arterial smooth muscle cells (SMCs) from a contractile to a synthetic phenotype by interacting with integrins on the cell surface. This process is characterized by a structural and functional transformation of the cells, including a reorganization of the cytoskeleton, the formation of a large secretory apparatus, and the acquisition of proliferative capacity. In this study we have investigated the role of integrin signaling through tyrosine kinases in the structural changes that occur in SMCs during primary culture on FN. A gradual increase in phosphotyrosine staining in focal adhesions and a concomitant increase in tyrosine phosphorylation of proteins including focal adhesion kinase were observed. In contrast, cells seeded on laminin formed few focal adhesions, and tyrosine phosphorylation of proteins was less than in cells cultured on FN. Treatment of cells cultured on FN with the tyrosine kinase inhibitor genistein strongly suppressed focal adhesion formation, cell spreading, and cytoskeletal reorganization. In addition, electron microscopic analysis demonstrated that the phenotypic modulation was slowed down. These results indicate that the ability of extracellular matrix components to promote a change in the phenotypic properties of SMCs depends on the assembly of focal adhesions with associated tyrosine kinase activity.

Ca2+ channel blockers verapamil and nifedipine inhibit apoptosis induced by 25-hydroxycholesterol in human aortic smooth muscle cells

We have characterized the death of human aortic smooth muscle cells induced by 25-hydroxycholesterol, an oxidation product of cholesterol. Chromatin condensation characteristic of apoptosis was observed by enzymatic (TUNEL) staining of chromatin, and by electron microscopy. Fourteen percent of cells treated with 5 microg/ml of 25-hydroxycholesterol for 24 h displayed chromatin degradation as determined by positive TUNEL staining. Addition of TNF alpha (10 ng/ml) and IFN gamma (20 ng/ml) increased the proportion of TUNEL positive cells to 30%, whereas the cytokines alone were without effect. After 48 h, 40% of the cells treated with 5 microg/ml of 25-hydroxycholesterol were TUNEL positive, and 21% of the cells displayed chromatin condensation. Oligonucleosomal DNA fragmentation typical of apoptosis was demonstrated by agarose gel electrophoresis. Furthermore, activation of the ICE-like protease caspase 3 (CPP32) was observed in cells treated with 25-hydroxycholesterol. Addition of the Ca2+ entry blockers verapamil or nifedipine to the culture medium inhibited apoptosis by more than 70% and reduced cytotoxicity, while removal of Ca2+ from culture medium reduced apoptosis by 42%. Within a few minutes after addition, 25-hydroxycholesterol induced intracellular Ca2+ oscillations with a frequency of approximately 0.3-0.4 min(-1). Thus it appears that Ca2+ influx through plasma membrane channels is an important signal in oxysterol-induced apoptosis. Addition of TNF alpha and IFN gamma enhanced cytotoxicity and resulted in a higher proportion of apoptotic cells, suggesting that inflammatory cytokines can increase the cytotoxicity of lipid oxidation products.

DNA fragmentation and ultrastructural changes of degenerating cells in atherosclerotic lesions and smooth muscle cells exposed to oxidized LDL in vitro

Degeneration of smooth muscle cells in the fibrous cap of atherosclerotic lesions is an important factor in plaque rupture. Recent studies have suggested that many plaque cells are in a process of apoptosis as determined by positive deoxyribonucleotide-transferase-mediated dUTP end labeling. In this study, we demonstrate the existence of a colocalization between deoxyribonucleotide-transferase-mediated dUTP end labeling-positive smooth muscle cells and oxidized LDL immunoreactivity in human carotid plaques. Oxidized LDL was found to induce deoxyribonucleotide-transferase-mediated dUTP end labeling positivity in cultured human smooth muscle cells, but only in the presence of tumor necrosis factor-alpha and interferon-gamma. Electron microscopic analysis of cultured smooth muscle cells exposed to oxidized LDL in the absence of cytokines demonstrated cytoplasmic swelling and disruption of the plasma membrane, suggesting cell death by oncosis. Cells exposed to both oxidized LDL and cytokines were characterized by chromatin and cytoplasmic condensation compatible with cell death by apoptosis. These findings further support the notion that oxidized lipids play a role in plaque cell death.

Expression of caveolae on the surface of rat arterial smooth muscle cells is dependent on the phenotypic state of the cells

Both after vascular injury and when established in vitro, arterial smooth muscle cells pass through a characteristic change in phenotype. This process includes a prominent structural reorganization with partial loss of myofilaments and formation of a large endoplasmic reticulum and Golgi complex. As a result, the cells lose their contractility and become able instead to divide and to secrete extracellular matrix components. In the present study, the expression of plasma membrane caveolae in rat arterial smooth muscle cells was studied in primary culture and during the formation of neointimal thickenings after balloon injury. Electron microscopic analysis revealed that the number of caveolae (identified as flask-shaped invaginations of the plasma membrane) was reduced when the cells converted from a contractile to a synthetic phenotype (as defined morphologically) and then increased again when they readopted a more differentiated state. However, immunoblotting analysis did not show any changes in the cellular content of caveolin (a major protein component of caveolae) during the 1st week in culture. At the same time, immunocytochemical staining demonstrated a shift in the localization of caveolin from small spot-like structures dispersed over the cell surface to vesicular structures in the perinuclear cytoplasm. These findings indicate that the transition of smooth muscle cells from a contractile to a synthetic phenotype involves a marked decline in the number of plasma membrane caveolae. In parallel, caveolin is internalized and redistributed to Golgi-associated vesicles in the perinuclear cytoplasm. In context of the rapidly increasing awareness of the importance of caveolae both in signal transduction and intracellular cholesterol transport, it seems likely that the variations in the number of caveolae may be significant for the functional differences between smooth muscle cells in different phenotypes.

Phenotypic modulation of smooth muscle cells after arterial injury is associated with changes in the distribution of laminin and fibronectin

Earlier in vitro studies suggest opposing roles of laminin and fibronectin in regulation of differentiated properties of vascular smooth muscle cells. To find out if this may also be the case in vivo, we used immunoelectron microscopy to study the distribution of these proteins during formation of intimal thickening after arterial injury. In parallel, cell structure and content of smooth muscle alpha-actin was analyzed. The results indicate that the cells in the normal media are in a contractile phenotype with abundant alpha-actin filaments and an incomplete basement membrane. Within 1 week after endothelial denudation, most cells in the innermost layer of the media convert into a synthetic phenotype, as judged by loss of actin filaments, construction of a large secretory apparatus, and destruction of the basement membrane. Some of these cells migrate through fenestrae in the internal elastic lamina and invade a fibronectin-rich network deposited on its luminal surface. Within another few weeks a thick neointima forms, newly produced matrix components replace the stands of fibronectin, and a basement membrane reappears. Simultaneously, the cells resume a contractile phenotype, recognized by disappearance of secretory organelles and restoration of alpha-actin filaments. These findings support the notion that laminin and other basement membrane components promote the expression of a differentiated smooth muscle phenotype, whereas fibronectin stimulates the cells to adopt a proliferative and secretory phenotype.

Controlling amyloid beta-peptide fibril formation with protease-stable ligands

We have previously shown that short peptides incorporating the sequence KLVFF can bind to the approximately 40amino acid residue Alzheimer amyloid beta-peptide (Abeta) and disrupt amyloid fibril formation (Tjernberg, L. O., Näslund, J., Lindqvist, F., Johansson, J., Karlström, A. R., Thyberg, J., Terenius, L., and Nordstedt, C. (1996) J. Biol. Chem. 271, 8545-8548). Here, it is shown that KLVFF binds stereospecifically to the homologous sequence in Abeta (i.e. Abeta16-20). Molecular modeling suggests that association of the two homologous sequences leads to the formation of an atypical anti-parallel beta-sheet structure stabilized primarily by interaction between the Lys, Leu, and COOH-terminal Phe. By screening combinatorial pentapeptide libraries exclusively composed of D-amino acids, several ligands with a general motif containing phenylalanine in the second position and leucine in the third position were identified. Ligands composed of D-amino acids were not only capable of binding Abeta but also prevented formation of amyloid-like fibrils. These ligands are protease-resistant and may thus be useful as experimental agents against amyloid fibril formation in vivo.

Expression of phenotype- and proliferation-related genes in rat aortic smooth muscle cells in primary culture

OBJECTIVES

After endothelial injury, smooth muscle cells (SMCs) in the arterial media are modified from a contractile to a sympathetic phenotype. This process includes a prominent structural reorganization and makes the cells able to migrate into the intima, divide, and secrete extracellular matrix components. A similar change occurs in culture and then in vitro system has been established as a useful model in which to study the control of SMC differentiation. The purpose of this study was to analyze the expression of a number of phenotype- and proliferation-related genes in vascular SMCs during the first week in primary culture.

METHODS

SMCs were enzymatically isolated from rat aorta and seeded on substrates of fibronectin (an adhesive plasma protein) and laminin-collagen type IV (two major basement membrane proteins) in a serum-free medium or in uncoated dishes in a serum-containing medium. Total RNA was isolated from the cells after different times of culture and analyzed by Northern blotting for expression of specific gene transcripts. In part, expression of the corresponding proteins was also explored by Western blotting and indirect immunofluorescence microscopy.

RESULTS

The results indicate that the proto-oncogenes c-fos, c-jun and c-ets-1 were already activated during the isolation of the cells and then continued to be strongly expressed for a few days. Especially in the serum-free groups, there was also early activation of the genes for the matrix metalloproteinases, stromelysin (MMP-3) and type IV collagenase (MMP-2). In parallel, an increased expression of the genes for two extracellular matrix components was observed, with an early rise in osteopontin mRNA and a later rise in collagen type I mRNA. At the end of the test period, the corresponding proteins were deposited around the cells in a fibrillar pattern. Among the matrix receptors investigated, the beta 1 integrin subunit showed a high and persistent expression, whereas the alpha 5 and alpha 1 integrin subunits showed lower and more variable mRNA level. In support of the existence of an autocrine or paracrine platelet-derived growth factor (PDGF) loop, an early rise in expression of the PDGF A-chain gene and a subsequent rise in expression of the PDGF alpha-receptor gene were noted.

CONCLUSION

It is proposed that the coordinated shift in gene expression here described to take place in connection with the phenotypic modulation of vascular SMCs in primary culture is part of a predetermined genetic program that normally serves the function to engage the cells in a wound healing response.

Cell death in human atherosclerotic plaques involves both oncosis and apoptosis

The aim of the present study was to analyze the frequency and mechanism of cell-death in atherosclerotic plaques with a recent history (< 6 months) of rupture. Atherosclerotic plaques were obtained from patients with symptomatic ipsilateral carotid stenosis > 70% diameter reduction undergoing carotid endarterectomy. In situ tailing and nick translation of fragmented DNA, agarose gel electrophoresis of plaque DNA and electron microscopy were used to identify cell death by apoptosis (programmed cell death) and oncosis. The mean number of cells containing fragmented DNA in the plaques was 12.7 +/- 3.5% (n = 15). Focal accumulations of cells with DNA fragmentation occurred in the fibrous cap, at sites of rupture, close to lipid deposits and necrosis and was always accompanied by the presence of inflammatory cells. Electrophoretic separation of DNA isolated from part of plaques, where the presence of DNA fragmentation had previously been demonstrated by in situ DNA nick translation, resulted in multiple ladders of 180-200 base pairs characteristic of apoptosis. Electron microscopic analysis revealed presence of cells with morphological signs of degeneration in a frequency even higher than that found by in situ nick translation. Some of these cells had a characteristic apoptotic appearance with condensed chromatin and cytoplasm, but the large majority of the cells had an ultrastructure typical for cells undergoing cell death by oncosis with membrane disruption and swollen, disintegrating organelles. Thus, although apoptosis clearly takes place in atherosclerotic plaques, oncosis appears to be a much more common mechanism for cell death.

Generation of Alzheimer amyloid beta peptide through nonspecific proteolysis

Polymerization of Alzheimer amyloid beta peptide (Abeta) into amyloid fibrils is associated with resistance to proteolysis and tissue deposition. Here, it was investigated whether Abeta might be generated as a protease-resistant core from a polymerized precursor. A 100-amino acid C-terminal fragment of the Alzheimer beta-amyloid precursor protein (C100), containing the Abeta and cytoplasmic domains, polymerized both when inserted into membranes and after purification. When subjected to digestion using the nonspecific enzyme proteinase K, the cytoplasmic domain of C100 was degraded, whereas the Abeta domain remained intact. In contrast, dissociated C100 polymers were almost completely degraded by proteinase K. Mammalian cells transfected with the human Alzheimer beta-amyloid precursor gene contained a fragment corresponding to C100, which needed similar harsh conditions to be dissolved, as did polymers formed by purified C100. Hence, it was concluded that C100 polymers are formed in mammalian cells. These results suggest that the C terminus of Abeta can be generated by nonspecific proteases, acting on a polymerized substrate, rather than a specific gamma-secretase. This offers an explanation of how the Abeta peptide can be formed in organelles containing proteases capable of cleaving most peptide bonds.

Arrest of beta-amyloid fibril formation by a pentapeptide ligand

Polymerization of amyloid beta-peptide (Abeta) into amyloid fibrils is a critical step in the pathogenesis of Alzheimer's disease. Here, we show that peptides incorporating a short Abeta fragment (KLVFF; Abeta16-20) can bind full-length Abeta and prevent its assembly into amyloid fibrils. Through alanine substitution, it was demonstrated that amino acids Lys16, Leu17, and Phe20 are critical for binding to Abeta and inhibition of Abeta fibril formation. A mutant Abeta molecule, in which these residues had been substituted, had a markedly reduced capability of forming amyloid fibrils. The present data suggest that residues Abeta16-20 serve as a binding sequence duringA beta polymerization and fibril formation. Moreover, the present KLVFF peptide may serve as a lead compound for the development of peptide and non-peptide agents aimed at inhibiting Abeta amyloidogenesis in vivo.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Inhibitors of ADP-ribosylation suppress phenotypic modulation and proliferation of smooth muscle cells cultured from rat aorta

The effects of hexamethylenebisacetamide (HMBA), an inhibitor of poly-ADP-ribosylation, and meta-iodobenzylguanidine (MIBG), an inhibitor of mono-ADP-ribosylation, on the phenotypic properties and proliferation of cultured rat aortic smooth muscle cells were studied using a combination of structural and chemical methods. The results show that HMBA and MIBG both slowed down the transition of the cells from a contractile to a synthetic phenotype in primary culture. While the control cells rapidly lost most of their myofilaments and built up an extensive endoplasmic reticulum and Golgi complex, a conspicuous fraction of the drug-treated cells retained a characteristic smooth muscle morphology for at least 6 days. Moreover, most of the treated cells remained positive for smooth muscle alpha-actin and desmin throughout this period. In contrast, the drugs lacked distinct effects on cell morphology and cytoskeletal organization in secondary cultures. Nevertheless, they strongly inhibited serum-stimulated cell growth both in primary and secondary cultures. The ability of serum-starved cells to synthesize DNA after exposure to platelet-derived growth factor or serum was also restrained. Notably, the drugs could be added several hours after the mitogens without loss of effect, suggesting that they did not prevent the entrance into but rather the progression through the cell cycle. Accordingly, the expression of early response genes like c-fos, c-jun and c-myc was not blocked by the drugs. On the other hand, HMBA reduced the expression of transcripts for smooth muscle alpha-actin, type IV collagenase, collagen type I, and osteopontin both in primary and secondary cultures. Weaker and more variable effects were obtained with MIBG. Taken together, the findings support the notion that poly- and mono-ADP-ribosylation of proteins are involved in the control of smooth muscle cell differentiation and growth.

Phenotypic modulation of smooth muscle cells during the formation of neointimal thickenings in the rat carotid artery after balloon injury: an electron-microscopic and stereological study

The formation of neointimal thickenings in the rat carotid artery after balloon injury was studied by a combination of electron-microscopic and stereological methods. All smooth muscle cells in the normal media had a contractile phenotype, the cytoplasm being dominated by myofilaments. Seven days after endothelial denudation, the smooth muscle cells in the innermost part of the media had assumed a synthetic phenotype by loss of myofilaments and formation of a large endoplasmic reticulum and Golgi complex. These cells moved through fine openings in the internal elastic lamina and gave rise to a growing neointima by proliferation and secretion of extracellular matrix components. Fourteen days after the operation, the neointima had almost reached its final size, and mitoses were no longer noted. Nevertheless, the cells maintained a synthetic phenotype with prominent secretory organelles, although myofilaments had started to become more abundant again. They were surrounded by an extracellular matrix made up of collagen fibrils and coalescing patches of elastin. Thirty-five days after the operation, an endothelial cell layer had reformed and covered most of the luminal vessel surface. In parallel, the smooth muscle cells in the neointima had returned to a contractile phenotype with a cytoplasm dominated by myofilaments. These findings provide a morphological basis for further analysis of the cellular and molecular interactions involved in the formation of neointimal thickenings after endothelial injury, and for the search for agents interfering with this process.

Characterization of stable complexes involving apolipoprotein E and the amyloid beta peptide in Alzheimer's disease brain

Genetic evidence suggests a role for apolipoprotein E (apoE) in Alzheimer's disease (AD) amyloidogenesis. Here, amyloid-associated apoE from 32 AD patients was purified and characterized. We found that brain amyloid-associated apoE apparently exists not as free molecules but as complexes with polymers of the amyloid beta peptide (A beta). Brain A beta-apoE complexes were detected irrespective of the apoE genotype, and similar complexes could be mimicked in vitro. The fine structure of purified A beta-apoE complexes was fibrillar, and immunogold labeling revealed apoE immunoreactivity along the fibrils. Thus, we conclude that A beta-apoE complexes are principal components of AD-associated brain amyloid and that the data presented here support a role for apoE in the pathogenesis of AD.

The Alzheimer A beta peptide develops protease resistance in association with its polymerization into fibrils

An intriguing property of the polypeptide constituents of amyloid is that they apparently can escape the proteolytic mechanisms that normally catalyze turnover and prevent abnormal tissue accumulation of polypeptides. Here, we demonstrate that the A beta peptide, the principal component of cerebrovascular amyloid deposits in Alzheimer's disease, becomes resistant to an array of proteases as a result of structural changes associated with its polymerization into amyloid fibrils. It is further demonstrated that fibril formation per se does not lead to protease resistance but probably structural changes associated with polymerization. The results suggest that higher order structural changes, regulated by the primary structure, enable amyloidogenic polypeptides to escape proteolytic degradation and accumulate in tissues.

The metabolic pathway generating p3, an A beta-peptide fragment, is probably non-amyloidogenic

The Alzheimer a beta amyloid precursor protein is metabolized by at least two secretory pathways. One generates the A beta peptide and the other a N-terminally truncated A beta fragment termed p3 that is considered non-amyloidogenic. However, direct evidence is missing. We have undertaken to synthesize and purify p3. Pure p3 polymerizes in vitro, forming a lattice with an ultrastructure distinct from the linear fibrils of A beta. In contrast to amyloid, polymerized p3 does not bind thioflavine T. It is therefore concluded that amino acids in the N-terminal part of the A beta molecule are required for formation of typical amyloid fibrils and that the metabolic pathway generating p3 probably is non-amyloidogenic

Fibronectin and the basement membrane components laminin and collagen type IV influence the phenotypic properties of subcultured rat aortic smooth muscle cells differently

A substrate of the extracellular matrix protein fibronectin has previously been found to promote the modulation of freshly isolated rat aortic smooth muscle cells from a contractile to a synthetic phenotype early in primary culture. In contrast, substrates of the basement membrane proteins laminin and collagen type IV were found to retain the cells in a contractile phenotype. Here, we have studied whether rat aortic smooth muscle cells tht have already adopted a synthetic phenotype are also affected differently by these proteins. For this sake, subcultured cells were detached with trypsin, seeded on substrates of either fibronectin or laminin plus collagen type IV, and incubated in a serum-free medium for one to three days. RNA blot and immunoblot analyses indicated that cells grown on laminin plus collagen type IV expressed smooth muscle alpha-actin transcripts and protein at higher levels than cells grown on fibronectin. Moreover, immunocytochemical and electron-microscopic analyses revealed that cells positively stained for smooth muscle alpha-actin and cells with a cytoplasm dominated by large microfilament bundles were more numerous on laminin plus collagen type IV than on fibronectin. Finally, thymidine autoradiography showed that the DNA synthetic response to stimulation with platelet-derived growth factor or serum was weaker in cells grown on laminin plus collagen type IV than in cells grown on fibronectin. These findings confirm the notion that a substrate of laminin and collagen type IV stimulates the in vitro expression of differentiated smooth muscle traits at a higher level than does a substrate of fibronectin.(ABSTRACT TRUNCATED AT 250 WORDS)

Human neutrophil phagocytic granules contain a truncated soluble form of the Alzheimer beta/A4 amyloid precursor protein (APP)

We have characterized the molecular species and subcellular distribution of Alzheimer beta/A4 amyloid precursor protein (APP) in neutrophilic granulocytes purified from human peripheral blood. APP was readily detectable in these cells. Immunochemical analysis with a panel of antibodies revealed that this APP species lacked the transmembrane and cytoplasmic domains previously demonstrated in cell-associated APP. However, it contained a protease inhibitor domain of the Kunitz type, indicating that neutrophil APP is a potent inhibitor of certain serine proteases. Upon subcellular fractionation, APP was primarily localized to azurophilic granules, which are neutrophil-specific phagocytic organelles assigned to enzymatic digestion of invading microbes and dead or injured tissue. Apparently, in the neutrophil, a nonsecretory organelle stores truncated, soluble APP, a species previously found only in blood plasma and cerebrospinal fluid or in conditioned medium of cultured cells. Soluble APP in neutrophils may therefore have intracellular functions in addition to its previously described extracellular functions. These findings also indicate that there are previously uncharacterized cell-specific differences in processing, trafficking, and storage of the APP molecule. Finally, the precise subcellular localization of APP to neutrophil-specific phagocytic organelles is suggestive of a role for APP in the nonimmunological host defense.

Functions of the Golgi complex in cell division: formation of cell-matrix contacts and cell-cell communication channels in the terminal phase of cytokinesis

The Golgi complex of mammalian cells is disorganized into dispersed vesicular and tubular elements during mitosis and is then reorganized into an interconnected system of cisternal stacks in each daughter cell during cytokinesis. Recent studies further indicate that the Golgi complex is typically relocated from the proximal to the distal side of the nucleus in the terminal phase of cytokinesis (as related to the intercellular bridge). Here, the functional role of this shift in position was approached using rat embryo fibroblasts synchronized with thymidine and nocodazole. Mitotic cells were collected by shaking and seeded in medium without or with brefeldin A (a fungal metabolite that inhibits protein secretion). They were fixed after one or two hours and stained for immunocytochemical demonstration of mannosidase II (a Golgi protein), fibronectin (an extracellular matrix protein), the fibronectin receptor (a member of the integrin family of proteins), and connexin 43 (a member of the connexin family of gap junction proteins). One hour after seeding, the cells had completed mitosis and progressed into cytokinesis. The Golgi complex was now usually located on the proximal side of the nucleus and overlapping fibrillar arrays of fibronectin and fibronectin receptors were observed in the contact zone between the daughter cells, while connexin 43 mainly occurred in fine dispersed spots. Two hours after seeding, the cells had spread out on the substrate and started to move apart. The Golgi complex was now usually located on the distal side of the nucleus. Moreover, fibronectin and fibronectin receptors were found to codistribute both in the contact zone between the daughter cells and in adhesive contacts beneath them, while connexin 43 was concentrated to plaques in the former zone. After treatment with brefeldin A, there was a diffuse cytoplasmic staining for mannosidase II and fibronectin and no distinct extracellular staining for fibronectin was noted. In addition, the connexin 43 positive plaques were reduced in size and number. Although the cells completed cytokinesis in the presence of the drug, they showed an increased tendency to detach from the substrate and locate on top of each other rather than to move apart normally. Taken together, the observations suggest that the change in position of the Golgi complex during cytokinesis serves the function to direct transport of secretory proteins as well as membrane constituents to different parts of the cell surface at different times.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship between the Golgi complex and microtubules enriched in detyrosinated or acetylated alpha-tubulin: studies on cells recovering from nocodazole and cells in the terminal phase of cytokinesis

Double immunofluorescence microscopy was used to study the relationship between the Golgi complex and microtubules enriched in posttranslationally modified tubulins in cultured mouse L929 fibroblasts. In interphase cells, the elements of the Golgi complex were grouped around the microtubule-organizing center. From here, tyrosinated microtubules extended to the periphery of the cells, whereas the distribution of detyrosinated and acetylated microtubules largely overlapped with that of the Golgi complex. Treatment of cells with 10 microM nocodazole led to the disruption of all microtubules and dispersion of the Golgi elements. Following withdrawal of the drug, tyrosinated microtubules reformed first, followed by acetylated and then detyrosinated microtubules. In parallel, the Golgi elements moved back toward the juxtanuclear region and reestablished a close spatial relationship first with the acetylated and later also with the detyrosinated microtubules. Long-term recovery in the presence of 0.15 or 0.3 microM nocodazole allowed partial reformation of tyrosinated and acetylated microtubules, whereas no or only a few detyrosinated microtubules were detected. At the same time, the Golgi elements were grouped closer together around or on one side of the nucleus in close relation to acetylated microtubules. In synchronized cells released from a mitotic block, a radiating array of tyrosinated microtubules was first formed, followed by acetylated and detyrosinated microtubules. The Golgi elements initially came together in a few groups and thereafter took an overall morphology similar to that in interphase cells. During this reunification, they showed a close spatial relationship to acetylated microtubules, whereas detyrosinated microtubules appeared only later. Microtubules enriched in acetylated and/or detyrosinated tubulin thus appear to take part in establishing and maintaining the organization of the Golgi elements within an interconnected supraorganellar system. Whether the acetylation and detyrosination of tubulin are directly involved in this process or merely represent two modifications within this subpopulation of microtubules remains unknown.

Cervical ripening with mifepristone (RU 486) in first trimester abortion. An electron microscope study

Mifepristone (RU 486) is a steroid that binds to the progesterone receptor and acts as a progesterone antagonist. It has been used clinically to terminate an early pregnancy. In the present investigation, the effects of mifepristone on the fine structure of the cervix were evaluated in two groups of women undergoing a first trimester abortion, using a triple-blind randomized protocol. In group I (n = 18), a cervical biopsy was taken after two doses of 100 mg mifepristone or placebo orally 24 and 12 h before vacuum aspiration. In group II (n = 20), cervical biopsies were taken before and after two doses of 100 mg mifepristone or placebo orally 48 and 36 h before vacuum aspiration. Smooth muscle cells, fibroblasts and an extracellular matrix with large bundles of collagen fibrils were the main structural components in all cervical biopsies. In group I, an increased number of mast cells and signs of new blood capillary formation and collagenolysis were observed in several of the biopsies after mifepristone treatment (67% correctly classified). In group II, the effects were less evident and in most of the cases (70%) no definite differences were noted between the biopsies taken before and after mifepristone treatment. Nevertheless, mifepristone treatment had induced softening in the cervical tissue, as judged by the decrease in resistance to mechanical dilatation.