Fibronectin stimulates macrophage uptake of low density lipoprotein-heparin-collagen complexes

Expression of O-glycosylated oncofetal fibronectin in alternatively activated human macrophages

Macrophage (Mϕ) polarization is an essential phenomenon for the maintenance of homeostasis and tissue repair, and represents the event by which Mϕ reach divergent functional phenotypes as a result to specific stimuli and/or microenvironmental signals. Mϕ can be polarized into two main phenotypes, M1 or classically activated and M2 or alternatively activated. These two categories diverge in many aspects, such as secreted cytokines, markers of cell surface, and biological functions. Over the last 10 years, many potential markers have been proposed for both M1 and M2 human Mϕ. However, there is scarce information regarding the glycophenotype adopted by these cells. Here, we show that M2- but not M1-polarized Mϕ expresses high levels of an unusual glycoform of fibronectin (FN), named O-glycosylated oncofetal FN (onf-FN), found in fetal/cancer cells, but not in healthy tissues. The onf-FN expression was confirmed in vitro by Western blot and real-time RT-qPCR in primary and cell line monocyte-derived Mϕ. onf-FN was induced by IL-4 and IL-13, but not by pro-inflammatory stimuli (LPS and INF-γ). RNA and protein analysis clearly demonstrated that it is specifically associated with the M2 polarization. In conclusion, we show by the first time that O-glycosylated onf-FN is expressed by M2-polarized Mϕ.

Lipoprotein(a) in Atherosclerotic Diseases: From Pathophysiology to Diagnosis and Treatment

Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL) cholesterol-like particle bound to apolipoprotein(a). Increased Lp(a) levels are an independent, heritable causal risk factor for atherosclerotic cardiovascular disease (ASCVD) as they are largely determined by variations in the Lp(a) gene (LPA) locus encoding apo(a). Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), and its role adversely affects vascular inflammation, atherosclerotic lesions, endothelial function and thrombogenicity, which pathophysiologically leads to cardiovascular (CV) events. Despite this crucial role of Lp(a), its measurement lacks a globally unified method, and, between different laboratories, results need standardization. Standard antilipidemic therapies, such as statins, fibrates and ezetimibe, have a mediocre effect on Lp(a) levels, although it is not yet clear whether such treatments can affect CV events and prognosis. This narrative review aims to summarize knowledge regarding the mechanisms mediating the effect of Lp(a) on inflammation, atherosclerosis and thrombosis and discuss current diagnostic and therapeutic potentials.

Affinity Selection of FGF2-Binding Heparan Sulfates for Ex Vivo Expansion of Human Mesenchymal Stem Cells

The future of human mesenchymal stem cells (hMSCs) as a successful cell therapy relies on bioprocessing strategies to improve the scalability of these cells without compromising their therapeutic ability. The culture-expansion of hMSCs can be enhanced by supplementation with growth factors, particularly fibroblast growth factor 2 (FGF2). The biological activity of FGF2 is controlled through interactions with heparan sulfate (HS) that facilitates ligand-receptor complex formation. We previously reported on an FGF2-interacting HS variant (termed HS2) isolated from embryonic tissue by anionic exchange chromatography that increased the proliferation and potency of hMSCs. Here, we detail the isolation of an FGF2 affinity-purified HS variant (HS8) using a scalable platform technology previously employed to generate HS variants with increased affinity for BMP-2 or VEGF₁₆₅ . This process used a peptide sequence derived from the heparin-binding domain of FGF2 as a substrate to affinity-isolate HS8 from a commercially available source of porcine mucosal HS. Our data show that HS8 binds to FGF2 with higher affinity than to FGF1, FGF7, BMP2, PDGF-BB, or VEGF₁₆₅ . Also, HS8 protects FGF2 from thermal destabilization and increases FGF signaling and hMSC proliferation through FGF receptor 1. Long-term supplementation of cultures with HS8 increased both hMSC numbers and their colony-forming efficiency without adversely affecting the expression of hMSC-related cell surface antigens. This strategy further exemplifies the utility of affinity-purifying HS variants against particular ligands important to the stem cell microenvironment and advocates for their addition as adjuvants for the culture-expansion of hMSCs destined for cellular therapy. J. Cell. Physiol. 232: 566-575, 2017. © 2016 Wiley Periodicals, Inc.

Fibronectin Splicing Variants Containing Extra Domain A Promote Atherosclerosis in Mice Through Toll-Like Receptor 4

OBJECTIVE

Cellular fibronectin containing extra domain A (EDA(+)-FN) is abundant in the arteries of patients with atherosclerosis. Several in vitro studies suggest that EDA(+)-FN interacts with Toll-like receptor 4 (TLR4). We tested the hypothesis that EDA(+)-FN exacerbates atherosclerosis through TLR4 in a clinically relevant model of atherosclerosis, the apolipoprotein E-deficient (Apoe(-/-)) mouse.

APPROACH AND RESULTS

The extent of atherosclerosis was evaluated in whole aortae and cross sections of the aortic sinus in male and female EDA(-/-)Apoe(-/-) mice (which lack EDA(+)-FN), EDA(fl/fl)Apoe(-/-) mice (which constitutively express EDA(+)-FN), and control Apoe(-/-) mice fed a high-fat Western diet for 14 weeks. Irrespective of sex, EDA(fl/fl)Apoe(-/-) mice exhibited a 2-fold increase in atherosclerotic lesions (aorta and aortic sinus) and macrophage content within plaques, whereas EDA(-/-)Apoe(-/-) mice exhibited reduced atherosclerotic lesions (P<0.05 versus Apoe(-/-), n=10-12 mice/group), although cholesterol and triglyceride levels and circulating leukocytes were similar. Genetic ablation of TLR4 partially reversed atherosclerosis exacerbation in EDA(fl/fl)Apoe(-/-) mice (P<0.05) but had no effect on atherosclerotic lesions in EDA(-/-)Apoe(-/-) mice. Purified cellular FN, which contains EDA, potentiated dose-dependent NFκB-mediated inflammation (increased phospho-NFκB p65/NFκB p65, tumor necrosis factor-α, and interleukin-1β) in bone marrow-derived macrophages from EDA(-/-)Apoe(-/-) mice but not from EDA(-/-)TLR4(-/-)Apoe(-/-) mice. Finally, using immunohistochemistry, we provide evidence for the first time that EDA(+)-FN colocalizes with macrophage TLR4 in murine aortic lesions and human coronary artery atherosclerotic plaques.

CONCLUSIONS

Our findings reveal that TLR4 signaling contributes to EDA(+)-FN-mediated exacerbation of atherosclerosis. We suggest that EDA(+)-FN could be a therapeutic target in atherosclerosis.

Lysosomal acid lipase: at the crossroads of normal and atherogenic cholesterol metabolism

Unregulated cellular uptake of apolipoprotein B-containing lipoproteins in the arterial intima leads to the formation of foam cells in atherosclerosis. Lysosomal acid lipase (LAL) plays a crucial role in both lipoprotein lipid catabolism and excess lipid accumulation as it is the primary enzyme that hydrolyzes cholesteryl esters derived from both low density lipoprotein (LDL) and modified forms of LDL. Evidence suggests that as atherosclerosis progresses, accumulation of excess free cholesterol in lysosomes leads to impairment of LAL activity, resulting in accumulation of cholesteryl esters in the lysosome as well as the cytosol in foam cells. Impaired metabolism and release of cholesterol from lysosomes can lead to downstream defects in ATP-binding cassette transporter A1 regulation, needed to offload excess cholesterol from plaque foam cells. This review focuses on the role LAL plays in normal cholesterol metabolism and how the associated changes in its enzymatic activity may ultimately contribute to atherosclerosis progression.

Aggregated LDL and lipid dispersions induce lysosomal cholesteryl ester accumulation in macrophage foam cells

Macrophage foam cells in atherosclerotic lesions accumulate substantial cholesterol stores within large, swollen lysosomes. Previous studies with mildly oxidized low density lipoprotein (OxLDL)-treated THP-1 macrophages suggest an initial buildup of free cholesterol (FC), followed by an inhibition of lysosomal cholesteryl ester (CE) hydrolysis and a subsequent lysosomal accumulation of unhydrolyzed lipoprotein CE. We examined whether other potential sources of cholesterol found within atherosclerotic lesions could also induce similar lysosomal accumulation. Biochemical analysis combined with microscopic analysis showed that treatment of THP-1 macrophages with aggregated low density lipoprotein (AggLDL) or CE-rich lipid dispersions (DISP) produced a similar lysosomal accumulation of both FC and CE. Co-treatment with an ACAT inhibitor, CP113,818, confirmed that the CE accumulation was primarily the result of the inhibition of lysosomal CE hydrolysis. The rate of unhydrolyzed CE buildup was more rapid with DISP than with AggLDL. However, with both treatments, FC appeared to accumulate in lysosomes before the inhibition in hydrolysis and CE accumulation, a sequence shared with mildly OxLDL. Thus, lysosomal accumulation of FC and CE can be attributable to more general mechanisms than just the inhibition of hydrolysis by oxidized lipids.

Fibronectin conformational changes induced by adsorption to liposomes

One of the major drawbacks of drug delivery techniques that utilize liposomes as carriers is that they are often cleared from the body before they can deliver their therapeutic cargo. It is well known that serum proteins can adsorb to these drug delivery vehicles and influence their uptake by phagocytic cells. For this reason, protein adsorption to liposomes has been extensively quantified, and strategies have been developed to minimize protein adsorption to improve drug delivery. However, the conformation of proteins on surfaces can play an even greater role in controlling cell behavior than the quantity of adsorbed protein. We have therefore used fluorescence resonance energy transfer (FRET) to measure changes in the structure of fibronectin (Fn)--a key serum protein involved in phagocytosis--upon interaction with phosphatidylcholine (PC) liposomes. Our experiments reveal that fibronectin opens up from its inactive, compact conformation upon interaction with gel phase PC liposomes. We also used FRET to estimate a physiologically relevant dissociation constant, KD=1.1 nM, for the interaction. Conformational changes in serum proteins may result in the exposure of otherwise concealed recognition sites and therefore influence the interaction of liposomes with phagocytic cells.

Ultrastructure of early lipid accumulation in ApoE-deficient mice

Apolipoprotein (apo) E-deficient mice develop severe hypercholesterolemia and have lesions that progress from fatty streaks to fibrous plaques distributed in lesion-prone areas throughout the aorta. Lesions develop in apoE-deficient mice on a regular chow diet and will occur faster on a diet higher in cholesterol. Examination of the aortas from these mice on a chow diet by high-resolution, freeze-etch electron microscopy demonstrated lipid retention in the intima by 3 weeks of age. Lipid was retained in the matrix as individual particles between 33 and 48 nm in diameter, aligned along the collagen fibrils and in aggregates consisting of lipid particles with average diameters of 33 and 68 nm. Larger particles seemed to have formed from fusion of smaller particles. Lipid retention was more widespread in 5- and 9-week-old mice. Monocyte attachment to endothelial cells was observed by electron microscopy at 5 weeks of age. The appearance of the intimal lipid was similar to that previously described in rabbit models and suggests that lipid interaction with matrix filaments and subsequent aggregation of lipid particles are critical first steps in the process of foam cell formation.

Aggregation of dimyristoylphosphatidylglycerol liposomes by human plasma low density lipoprotein

Turbidity (absorbance at 470 nm) measurements revealed human serum low density lipoprotein (LDL) to cause, within a few minutes and at physiological pH and [NaCl], the aggregation of liquid crystalline large unilamellar liposomes (LUVs) of dimyristoylphosphatidylglycerol (DMPG). No evidence for concomitant lipid or aqueous contents mixing was obtained with fluorescent assays for these processes, in keeping with the lack of fusion of LUVs. Involvement of apoB is implicated by the finding that tryptic digestion of LDL abrogates its ability to cause aggregation. Aggregation is not caused by VLDL, HDL2, or HDL3. Interestingly, also oxidised LDL failed to aggregate DMPG vesicles. Aggregation of DMPG LUVs by LDL did depend on the ionic strength of the medium as well as on the phase state of the lipid. More specifically, below the main transition temperature Tm maximal aggregation was seen in the presence of 25-100 mM NaCl, whereas slightly higher (up to 150 mM) [NaCl] were required when T>Tm. Aggregation due to LDL was also observed for dimyristoylphosphatidylserine as well as for dipalmitoylphosphatidylglycerol LUVs, whereas liposomes composed of either unsaturated acidic phospholipids or different phosphatidylcholines were not aggregated. Involvement of electrostatic attraction between the acidic phosphate of DMPG and cationic residues in apoB is suggested by the finding that increasing the content of dimyristoylphosphatidylcholine (DMPC) in DMPG liposomes reduced their aggregation and at XDMPC=0.50 no response was evident. Notably, increasing the mole fraction of 1-palmitoyl-2-oleyl-PG (POPG) in DMPG LUVs progressively reduced their aggregation by LDL and at XPOPG=0.50 there was complete inhibition. The latter effect of POPG is likely to be due to augmented hydration of the unsaturated lipid constituting a barrier for the contact between apoB and the vesicle surface. In keeping with this view, the presence of the strongly hygroscopic polymer, poly(ethylene glycol) at 1% (by weight) enhanced the aggregation and could partly reverse the inhibition by POPG.

Development of the lipid-rich core in human atherosclerosis

In recent years the role of the atherosclerotic core in promoting plaque rupture has become well recognized. A new insight into core development is its origination early in atherogenesis, before formation of the fibrous plaque. The early core is associated with accumulation of vesicular lipid rich in free cholesterol. Later in core development, lipid deposits become more diverse. The weight of evidence points toward a direct extracellular process, probably lipoprotein aggregation and fusion, as the chief pathway of cholesteryl ester accumulation, although foam cell death may also contribute cholesteryl ester. The mechanism or mechanisms of formation of vesicular, cholesterol-rich deposits are unknown. Since the increase in free cholesterol is likely to have deleterious effects on cells bordering the core, the further elucidation of cellular and biochemical pathways leading to and responding to free cholesterol accumulation is of great importance. Complement activation and cellular stress responses are prominent in the vicinity of core lipids, but their pathogenetic roles remain to be established. Since the core appears so early in atherogenesis, these as well as other, yet to be determined cellular responses to core lipids, oxidized and unoxidized, could have a considerable effect on overall lesion development. Much remains to be learned about macrophage and smooth muscle responses, calcification, capillarization, and matrix protein alterations in the evolution of the core and surrounding arterial intima.

Mast cell granule remnants carry LDL into smooth muscle cells of the synthetic phenotype and induce their conversion into foam cells

We report the effect of mast cells on the uptake of LDL by smooth muscle cells (SMCs) and their conversion into foam cells in vitro. The mast cells were stimulated to exocytose their cytoplasmic secretory granules, and the granule remnants formed were recovered from the extracellular fluid and added to cultures of SMCs of either the synthetic or contractile phenotype in LDL-containing medium. In the presence but not in the absence of granule remnants, SMCs of the synthetic phenotype took up LDL with ensuing stimulation of intracellular cholesteryl ester synthesis and cytoplasmic accumulation of neutral lipid droplets. Using methylated LDL (mLDL), a modified species of LDL that binds to granule remnants but not to LDL receptors, we demonstrated that this uptake (leading to foam cell formation) occurred only when LDL was bound to granule remnants. After the addition of colloidal gold-LDL and granule remnants to the incubation system, electron microscopy revealed that within phagosomes of the SMCs there were granule remnants (diameter, 0.5 to 1 micron) coated with LDL, confirming that LDL had been carried into the cells with the remnants. SMCs of the contractile phenotype were less efficient than their synthetic counterparts at phagocytosing LDL-coated granule remnants and were not converted into foam cells. This difference in the rate of phagocytosis of granule remnants was present even in the absence of LDL, revealing that the more active phagocytosis by SMCs of the synthetic phenotype was not specifically related to uptake of lipids but rather reflected a general phenotype characteristic of these cells. These observations indicate a phagocytic mechanism by which SMCs of the synthetic phenotype are converted into cholesteryl ester-filled foam cells, and they also suggest that degranulation of mast cells plays a role in the development of fatty streak lesions.

Regulation of the metabolism of lipoprotein-proteoglycan complexes in human monocyte-derived macrophages

Studies were performed to evaluate the effect of several factors on the metabolism of lipoprotein-proteoglycan complexes in human monocyte-derived macrophages. In vivo apoB-lipoprotein-proteoglycan complex was isolated from human aorta fibrous-plaque lesions and low-density lipoprotein (LDL)-proteoglycan complex was formed in vitro. Degradation of LDL-proteoglycan complex and cholesteryl ester synthesis mediated by the in vivo and in vitro complexes were lowest in freshly isolated monocytes. With the maturation of monocytes into macrophages, there was a dramatic rise in both. The degradation of the complex and the resultant stimulation of cholesterol esterification increased significantly with increasing cell density. Preincubation of macrophages in medium containing lipoprotein cholesterol did not down-regulate the subsequent degradation of LDL-proteoglycan complex. Macrophage-conditioned medium had a profound stimulatory effect on the degradation of LDL-proteoglycan complex and cholesterol esterification by mature macrophages and freshly isolated monocytes. The conditioned medium lost its stimulatory activity after boiling, dialysis and trypsin digestion. Macrophage activation with phorbol ester and bacterial lipopolysaccharide resulted in a marked suppression of the binding and degradation of the complex, as well as the complex-mediated cholesteryl ester synthesis. These results demonstrate that several factors regulate the metabolism of lipoprotein-proteoglycan complexes in human monocyte-derived macrophages.

Lipoprotein-proteoglycan complexes induce continued cholesteryl ester accumulation in foam cells from rabbit atherosclerotic lesions

We studied the metabolism of lipoprotein-proteoglycan complexes by macrophage-derived foam cells. Foam cells were isolated from atherosclerotic rabbit aortas. ApoB-lipoprotein-proteoglycan complex was isolated from human aorta fibrous plaque lesions and LDL-proteoglycan complex was formed in vitro. Both in vitro and in vivo complexes stimulated cholesteryl ester synthesis in foam cells by a dose-dependent, saturable process that resulted in the intracellular accumulation of cholesteryl ester. Stimulation of cholesteryl ester synthesis was linear with time over a 32-h period. Polyinosinic acid inhibited the stimulation of cholesteryl ester synthesis by the complexes by 32-37%, whereas cytochalasin D only produced a 6-16% inhibition. Foam cells degraded 125I-LDL-proteoglycan complex and 125I-acetyl LDL in a saturable, dose-dependent manner. Excess unlabeled acetyl-LDL inhibited the degradation of 125I-LDL-proteoglycan complex by 52%, while LDL had no effect. Similarly, excess unlabeled complex suppressed the degradation of 125I-acetyl-LDL by 48%. Foam cells degraded 125I-methyl-LDL-proteoglycan complex to the same extent as 125I-LDL-proteoglycan complex. These results show that foam cells from atherosclerotic lesions metabolize lipoprotein-proteoglycan complexes predominantly via receptor-mediated endocytosis and consequently continue to accumulate intracellular cholesteryl ester.

Altered susceptibility to in vitro oxidation of LDL in LDL complexes and LDL aggregates

Low density lipoprotein (LDL) is known to form complexes with polysulfated compounds, like heparin, dextran sulfate (DS), and chondroitin sulfate. In particular, chondroitin 6-sulfate (C6S)-rich proteoglycans of the arterial intima can associate with LDL, resulting in accumulation of LDL in atherosclerotic lesions. Besides LDL complex formation, LDL self-aggregation has been recently suggested to play a role in atherogenesis. Oxidative modification of LDL has also been implicated as a factor in the generation of the atherosclerotic plaque. Assuming that LDL self-aggregation may alter the molecule's susceptibility to oxidative modification, we have studied the sensitivity of LDL in LDL a aggregates as well as in insoluble and soluble LDL-C6S, LDL-heparin, and LDL-DS complexes to in vitro oxidation by cooper ions. Complexing the LDL with C6S and heparin resulted in an increased susceptibility of LDL to in vitro oxidation, whereas the oxidation of LDL complexed with DS was unaffected. In great contrast to the oxidation of LDL in LDL complexes, the in vitro oxidation of LDL in LDL aggregates (self-aggregation by denaturation) was strongly reduced. The results suggest that complex or aggregate formation may alter the susceptibility of the lipoprotein to oxidative modification and finally its metabolic fate or biological activity.

Monoclonal antibodies against LDL further enhance macrophage uptake of LDL aggregates

Self-aggregates of low density lipoprotein (LDL) are taken up and degraded more rapidly by macrophages than is native LDL. That enhanced uptake is attributable in part to phagocytosis via the LDL receptor pathway. However, arterial macrophages appear to express little LDL receptor activity. The present studies demonstrate an alternative mechanism by which LDL aggregates could contribute to foam cell formation. This could occur by the formation of large immune complexes that are taken up by macrophages via the Fc receptor. When immune complexes were formed with native, soluble LDL and MB47, a monoclonal antibody specific to the apoprotein B domain recognized by the LDL receptor, the subsequent uptake and degradation of the LDL by macrophages were inhibited 50-80% compared with native LDL alone. In contrast, when aggregated LDL was bound to MB47 at a similar molar ratio, the subsequent degradation of the insoluble immune complexes was two- to fivefold greater than that of aggregated LDL alone. The enhanced uptake was abolished when Fab or F(ab')2 fragments of MB47 were substituted for the intact antibody, indicating that the increased uptake was via the Fc receptor pathway. Furthermore, the uptake of the immune complexes of aggregated LDL was reduced by competition for the Fc receptor with heat-aggregated immunoglobulin. There was also an increase in the rate of cellular cholesterol esterification and an increase in macrophage cholesteryl ester mass. Since aggregates of LDL as well as autoantibodies against modified LDL have been demonstrated in atherosclerotic lesions, it is possible that immune complexes of aggregates of modified LDL may be generated in the intima.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta 1 is a heparin-binding protein: identification of putative heparin-binding regions and isolation of heparins with varying affinity for TGF-beta 1

Previous studies indicated that a major factor in heparin's ability to suppress the proliferation of vascular smooth muscle cells is an interaction with transforming growth factor-beta 1 (TGF-beta 1). Heparin appeared to bind directly to TGF-beta 1 and to prevent the association of TGF-beta 1 with alpha 2-macroglobulin (alpha 2-M). The present studies indicate that 20-70% of iodinated TGF-beta 1 binds to heparin-Sepharose and the retained fraction is eluted with approximately 0.37 M NaCl. Native, unlabelled platelet TGF-beta 1, however, is completely retained by heparin-Sepharose and eluted with 0.9-1.2 M NaCl. Using synthetic peptides, the regions of TGF-beta 1 that might be involved in the binding of heparin and other polyanions were examined. Sequence analysis of TGF-beta 1 indicated three regions with a high concentration of basic residues. Two of these regions had the basic residues arranged in a pattern homologous to reported consensus heparin-binding regions of other proteins. The third constituted a structurally novel pattern of basic residues. Synthetic peptides homologous to these three regions, but not to other regions of TGF-beta 1, were found to bind to heparin-Sepharose and were eluted with 0.15 M-0.30 M NaCl. Only two of these regions were capable of blocking the binding of heparin to 125I-TGF-beta. Immobilization of these peptides, followed by affinity purification of heparin, indicated that one peptide was capable of isolating subspecies of heparin with high and low affinity for authentic TGF-beta 1. The ability of TGF-beta 1 to bind to heparin or related proteoglycans under physiological conditions may be useful in understanding the biology of this pluripotent growth and metabolic signal. Conversely, a subspecies of heparin molecules with high affinity for TGF-beta 1 may be a factor in some of the diverse biological actions of heparin.

Fibronectin. A versatile matrix protein with roles in thoracic development, repair and infection

Fibronectin, a dimeric cell-adhesive extracellular matrix glycoprotein, is secreted by mesenchymal cells and assembled into insoluble matrices which have important biological functions in embryologic development as well as in tissue response to injury. Fibronectin interacts with numerous cell types including mesenchymal cells and inflammatory cells which bear appropriate fibronectin receptors. In vitro, fibronectin serves as an adhesive substrate and promotes cell proliferation and cytodifferentiation. During development, fibronectin-rich matrices are deposited in specific location and regulate the directional migration of embryonic cells. In particular, fibronectin matrices appear to be of critical importance to normal cardiopulmonary development. Following embryologic development, the tissue expression of fibronectin is greatly reduced, but increases markedly following tissue injury, where newly expressed fibronectin matrices appear critical to tissue repair. Recent evidence has documented increased expression of fibronectin in numerous pulmonary conditions including the adult respiratory distress syndrome (ARDS), bronchiolitis obliterans organizing pneumonia (BOOP) and idiopathic pulmonary fibrosis (IPF). Additionally, fibronectin also interacts with a large number of microorganisms and therefore also is potentially important in microbial adherence to airway epithelium and subsequent infections of the respiratory system.

Fucoidan is a non-anticoagulant inhibitor of intimal hyperplasia

We previously reported that heparin inhibits the proliferation of fibroblasts and vascular smooth muscle cells (SMC), in part, by binding to and increasing the antiproliferative activity of transforming growth factor-beta 1 (TGF-beta 1). We now report that certain other polyanions which are structurally distinct from heparin, such as fucoidan and polyinosinic acid, are more avid ligands for TGF-beta 1 and more potent antiproliferative agents than heparin. Fucoidan possessed more potent antiproliferative activity than heparin against rat and bovine aortic SMC in vitro, though possessing much lower anticoagulant activity than heparin. Furthermore, fucoidan suppressed in vivo intimal hyperplasia when continuously infused into rats subjected to balloon-catheter injury. Unlike heparin, which also suppressed intimal hyperplasia, fucoidan did not cause systemic anticoagulation. Thus, fucoidan may be useful as a non-anticoagulant inhibitor of post-angioplasty intimal hyperplasia.

High-density-lipoprotein-induced cholesterol efflux from arterial smooth muscle cell derived foam cells: functional relationship of the cholesteryl ester cycle and eicosanoid biosynthesis

Eicosanoids have been implicated in the regulation of arterial smooth muscle cell (SMC) cholesteryl ester (CE) metabolism. These eicosanoids, which include prostacyclin (PGI2), stimulate CE hydrolytic activities. High-density lipoproteins (HDL), which promote cholesterol efflux, also stimulate PGI2 production, suggesting that HDL-induced cholesterol efflux is modulated by eicosanoid biosynthesis. To ascertain the role of endogenously synthesized eicosanoids produced by arterial smooth muscle cells in the regulation of CE metabolism, we examined the effects of cyclooxygenase inhibition on CE hydrolytic enzyme activities, cholesterol efflux, and cholesterol content in normal SMC and SMC-derived foam cells following exposure to HDL and another cholesterol acceptor protein, serum albumin. Alterations of these activities were correlated with cholesterol efflux in response to HDL or bovine serum albumin (BSA) in the presence or absence of aspirin. HDL stimulated PGI2 synthesis and CE hydrolases in a dose-dependent manner. Eicosanoid dependency was established by demonstrating that HDL-induced acid cholesteryl ester hydrolase (ACEH) activity was blocked by aspirin. CE enrichment essentially abrogated HDL-induced PGI2 production in cells which also exhibited decreased lysosomal and cytoplasmic CE hydrolase activities. In CE-enriched cells whose cytoplasmic CE pool was metabolically labeled with [3H]oleate or cLDL containing [3H]cholesteryl linoleate, aspirin did not alter HDL- or BSA-induced net CE hydrolysis or efflux, respectively. Finally, aspirin treatment did not alter the mass of either free or esterified cholesterol content of untreated or CE-enriched SMC following exposure to acceptor proteins. These data demonstrated that CE enrichment significantly reduced HDL-induced activation of CE hydrolytic activity via inhibition of endogenous PGI2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta activity is potentiated by heparin via dissociation of the transforming growth factor-beta/alpha 2-macroglobulin inactive complex

The control of smooth muscle cell (SMC) proliferation is determined by the combined actions of mitogens, such as platelet-derived growth factor, and the opposing action of growth inhibitory agents, such as heparin and transforming growth factor-beta (TGF-beta). The present studies identify an interaction between heparin and TGF-beta in which heparin potentiates the biological action of TGF-beta. Using a neutralizing antibody to TGF-beta, we observed that the short term antiproliferative effect of heparin depended upon the presence of biologically active TGF-beta. This effect was observed in rat and bovine aortic SMC and in CCL64 cells, but not in human saphenous vein SMC. Binding studies demonstrated that the addition of heparin (100 micrograms/ml) to medium containing 10% plasma-derived serum resulted in a 45% increase in the specific binding of 125I-TGF-beta to cells. Likewise, heparin induced a twofold increase in the growth inhibitory action of TGF-beta at concentrations of TGF-beta near its apparent dissociation constant. Using 125I-labeled TGF-beta, we demonstrated that TGF-beta complexes with the plasma component alpha 2-macroglobulin, but not with fibronectin. Heparin increases the electrophoretic mobility of TGF-beta apparently by freeing TGF-beta from its complex with alpha 2-macroglobulin. Dextran sulfate, another highly charged antiproliferative molecule, but not chondroitin sulfate or dermatan sulfate, similarly modified TGF-beta's mobility. Relatively high, antiproliferative concentrations of heparin (1-100 micrograms/ml) were required to dissociate the TGF-beta/alpha 2-macroglobulin complex. Thus, it appears that the antiproliferative effect of heparin may be partially attributed to its ability to potentiate the biological activity of TGF-beta by dissociating it from alpha 2-macroglobulin, which normally renders it inactive. We suggest that heparin-like agents may be important regulators of TGF-beta's biological activity.