The class A scavenger receptor binds to proteoglycans and mediates adhesion of macrophages to the extracellular matrix

The class A scavenger receptor (SR-A) binds modified lipoproteins and has been implicated in cholesterol ester deposition in macrophages. The SR-A also contributes to cellular adhesion. Using SR-A(+/+) and SR-A(-)/- murine macrophages, we found SR-A expression important for both divalent cation-dependent and -independent adhesion of macrophages to the human smooth muscle cell extracellular matrix. The SR-A mediated 65 and 85% of macrophage adhesion to the extracellular matrix in the presence and absence of serum, respectively. When EDTA was added to chelate divalent cations, the SR-A mediated 90 and 95% of the macrophage adhesion without and with serum, respectively. SR-A-mediated adhesion to the extracellular matrix was prevented by fucoidin, an SR-A antagonist. Biglycan and decorin, proteoglycans of the extracellular matrix, were identified as SR-A ligands. Compared with control cells, Chinese hamster ovary cells expressing the SR-A showed 5- and 6-fold greater cell association (binding and internalization) of (125)I-decorin and -biglycan, respectively. In competition studies, unlabeled proteoglycan or fucoidin competed for binding of (125)I-labeled decorin and -biglycan, and biglycan and decorin competed for the SR-A-mediated cell association and degradation of (125)I-labeled acetylated LDL, a well characterized ligand for the SR-A. These results suggest that the SR-A could contribute to the adhesion of macrophages to the extracellular matrix of atherosclerotic plaques.     

Murine macrophage heparanase: inhibition and comparison with metastatic tumor cells

Circulating macrophages and metastatic tumor cells can penetrate the vascular endothelium and migrate from the circulatory system to extravascular compartments. Both activated murine macrophages and different metastatic tumor cells (B16-BL6 melanoma; ESb T-lymphoma) attach, invade, and penetrate confluent vascular endothelial cell monlayer in vitro, by degrading heparan sulfate proteoglycans in the subendothelial extracellular matrix. The sensitivity of the enzymes from the various sources degrading the heparan sulfate proteoglycan was challenged and compared by a series of inhibitors. Activated macrophages demonstrate a heparanase with an endoglycosidase activity that cleaves from the [35S]O4 = -labeled heparan sulfate proteoglycans of the extracellular matrix 10 kDa glycosaminoglycan fragments. The macrophages do not store the heparanase intracellularly but it is instead found pericellularly and requires a continuous cell-matrix contact at the optimal pH for maintaining cell growth. The degradation of [35S]O4 = -labeled extracellular matrix proteoglycans by the macrophages' heparanase is significantly inhibited in the presence of heparan sulfate (10 micrograms/ml), arteparon (10 micrograms/ml), and heparin at a concentration of 3 micrograms/ml. In contrast, other glycosaminoglycans such as hyaluronic acid, dermatan sulfate, and chondroitin sulfate as well as the specific inhibitor of exo-beta-glucuronidase D-saccharic acid 1,4-lactone failed to inhibit the degradation of sulfated proteoglycans in the subendothelial extracellular matrix. Degradation of this heparan sulfate proteoglycan is a two-step sequential process involving protease activity followed by heparanase activity. However, the following antiproteases--alpha 2-macroglobulin, antithrombin III, leupeptin, and phenylmethylsulfony fluoride (PMSF)--failed to inhibit this degradation process, and only alpha 1-antitrypsin inhibited the heparanase activity. B16-BL6 metastatic melanoma cell heparanase, which is also a cell-associated enzyme, was inhibited by heparin to the same extent as the macrophage heparanase. On the other hand, heparanase of the highly metastatic variant (ESb) of a methylcholanthrene-induced T lymphoma, which is an extracellular enzyme released by the cells to the incubation medium, was more sensitive to heparin and arteparon than the macrophages' heparanase, inhibited at concentrations of 1 and 3 micrograms/ml, respectively. These results may indicate the potential use of heparin or other glycosaminoglycans as specific and differential inhibitors for the formation in certain cases of blood-borne tumor metastasis.     

Heparan sulfate depletion within pulmonary fibroblasts: implications for elastogenesis and repair

We investigated the role of sulfated proteoglycans in regulating extracellular matrix (ECM) deposition in pulmonary fibroblast cultures. Fibroblast cultures were subject to pharmacologic and enzymatic interventions to modify sulfated proteoglycan levels. Native and proteoglycan-depleted fibroblasts were treated with porcine pancreatic elastase at 2-4-day intervals and the elastase-mediated release of fibroblast growth factor 2 (FGF-2) and glycosaminoglycans was determined. Elastase treatment released significantly less FGF-2 and glycosaminoglycans (GAG) from PG-depleted fibroblasts with respect to native cells. Equilibrium ligand binding studies indicated that 125I FGF-2 binding at both cell surface receptor and heparan sulfate proteoglycan sites was reduced to different extents based on the method of proteoglycan depletion. Quantitation of elastin protein and message levels indicated that biological sulfation is required for the proper incorporation of tropoelastin into the extracellular matrix. These results suggest that sulfated proteoglycans play a central role in modulating pulmonary fibroblast extracellular matrix composition and are important mediators of elastolytic injury.     

Matrix-associated heparan sulfate proteoglycan: core protein-specific monoclonal antibodies decorate the pericellular matrix of connective tissue cells and the stromal side of basement membranes

Cultured human lung fibroblasts produce a large, nonhydrophobic heparan sulfate proteoglycan that accumulates in the extracellular matrix of the monolayer (Heremans, A., J. J. Cassiman, H. Van den Berghe, and G. David. 1988. J. Biol. Chem. 263: 4731-4739). A panel of four monoclonal antibodies, specific for four distinct epitopes on the 400-kD core protein of this extracellular matrix heparan sulfate proteoglycan, detects similar proteoglycans in human epithelial cell cultures. Immunohistochemistry of human tissues with the monoclonal antibodies reveals that these proteoglycans are concentrated at cell-matrix interfaces. Immunogold labeling of ultracryosections of human skin indicates that the proteoglycan epitopes are nonhomogeneously distributed over the width of the basement membrane. Immunochemical investigations and amino acid sequence analysis indicate that the proteoglycan from the fibroblast matrix shares several structural features with the large, low density heparan sulfate proteoglycan isolated from the Engelbreth-Holm-Swarm sarcoma. Thus, both epithelial cell sheets and individual mesenchymal cells accumulate a large heparan sulfate proteoglycan(s) at the interface with the interstitial matrix, where the proteoglycan may adopt a specific topological orientation with respect to this matrix.     

Production of proteoglycans by human lung fibroblasts (IMR-90) maintained in a low concentration of serum.

Maintenance of fibroblasts in 0.5% serum results in viable but non-proliferative cells that may be analogous to fibroblasts in vivo. The synthesis of proteoglycans by human embryo lung fibroblasts in Eagle's minimal essential medium with 0.5% newborn-bovine serum or with 10% serum has been compared. A similar amount of [35S]sulphate-labelled glycosaminoglycan per cell was secreted by fibroblasts in 10% or 0.5% serum. 35SO42-incorporation into sulphated glycosaminoglycans was enhanced in 0.5% serum when expressed per mg of cell protein, but [3H]glucosamine incorporation was decreased. The charge density of these glycosaminoglycans was not changed as determined by ion-exchange chromatography. It was concluded that decreased protein/ cell resulted in an apparent increase in 35S-labelled glycosaminoglycan synthesis/mg of cell protein, whereas decreased uptake of [3H]glucosamine resulted in a decrease in their glucosamine labelling. The proteoglycans secreted by fibroblasts in 0.5% serum were similar in glycosaminoglycan composition, chain length and buoyant density to the dermatan sulphate proteoglycan, which is the major secreted component of cells in 10% serum. Larger heparan sulphate and chondroitin sulphate proteoglycans, which comprise about 40% of the total secreted proteoglycans of cultures in 10% serum, were greatly diminished in the medium of cultures in 0.5% serum. The proteoglycan profile of medium from density-inhibited cultures in 10% serum resembles that of proliferating cultures, indicating that lack of proliferation was not responsible for the alteration. The dermatan sulphate proteoglycan, participating in extracellular matrix structure, may be the primary tissue product of lung fibroblasts in vivo.     

Heparin releasable and nonreleasable forms of heparan sulfate proteoglycan are found on the surfaces of cultured porcine aortic endothelial cells

Evidence suggests that endothelial cell layer heparan sulfate proteoglycans include a variety of different sized molecules which most likely contain different protein cores. In the present report, approximately half of endothelial cell surface associated heparan sulfate proteoglycan is shown to be releasable with soluble heparin. The remaining cell surface heparan sulfate proteoglycan, as well as extracellular matrix heparan sulfate proteoglycan, cannot be removed from the cells with heparin. The heparin nonreleasable cell surface proteoglycan can be released by membrane disrupting agents and is able to intercalate into liposomes. When the heparin releasable and nonreleasable cell surface heparan sulfate proteoglycans are compared, differences in proteoglycan size are also evident. Furthermore, the intact heparin releasable heparan sulfate proteoglycan is closer in size to proteoglycans isolated from the extracellular matrix and from growth medium than to that which is heparin nonreleasable. These data indicate that cultured porcine aortic endothelial cells contain at least two distinct types of cell surface heparan sulfate proteoglycans, one of which appears to be associated with the cells through its glycosaminoglycan chains. The other (which is more tightly associated) is probably linked via a membrane intercalated protein core.Abbreviations ECM extracellular matrix - HSPG heparan sulfate proteoglycan - PAE porcine aortic endothelial - PBS phosphate buffered saline     

Proteoglycans synthesized in vitro by nude and normal mouse peritoneal macrophages

Peritoneal macrophages from nude mice were found to be functionally similar to 'activated' macrophages from normal mice. The objective of the present study was to characterize the proteoglycans synthesized and secreted in vitro by peritoneal macrophages isolated from nude and normal Balb/c mice and to investigate the relationship between macrophage 'activation' and changes in the proteoglycan patterns. Macrophages obtained by peritoneal lavage were seeded in Petri dishes. After 2 h incubation at 37 degrees C, the adherent cells (macrophages) were exposed to [35S]sulphate for the biosynthetic labelling of proteoglycans. After incubation, the cell and medium fractions were collected and analysed for proteoglycans and glycosaminoglycans. The glycosaminoglycans were identified and characterized by a combination of agarose gel electrophoresis and enzymatic degradation with specific mucopolysaccharidases. It was shown that 3/4 of the total 35S-labelled glycosaminoglycans were in the extracellular compartment after 24-48 h. The macrophages synthesized dermatan sulphate (68%), chondroitin sulphate (7%) and heparan sulphate (25%). Both cell and medium fractions of normal and nude mouse macrophages contained glycosaminoglycans with the same ratios, although the nude mouse macrophages synthesized 2-fold less glycosaminoglycans than the normal mouse macrophages. Lower levels of 35S-proteoglycans were also obtained from in vitro 'activated' macrophages, but the ratios of dermatan sulphate:chondroitin sulphate: heparan sulphate were altered in these cells as compared to the control. Furthermore, all the 35S-macromolecules found in the extracellular compartment of nude and normal control cells were of proteoglycan nature, in contrast to the medium fractions of 'activated' macrophages, which contain both intact proteoglycans and 'free' glycosaminoglycan chains. These results indicate that, at least as regards the proteoglycans and glycosaminoglycans, the nude mouse macrophages are not identical to the 'activated' macrophages from normal mice.     

Effect of elastin peptides on human monocytes: Ca2+ mobilization, stimulation of respiratory burst and enzyme secretion

The effect of elastin peptides (Kappa-elastin) was investigated on human monocytes. The data presented here indicate that elastin peptides increase the intracellular Ca2+ level measured by Quin 2 fluorescence and mediate the release of beta glucuronidase and elastase. The O2 consumption and H2O2 release were stimulated in a dose-dependent manner. The early rise of cAMP was followed by a return to the original level at 30 min and by a concomitant increase of cGMP level. The action of elastin peptides on intracellular calcium level and cGMP levels may well be related to its previously demonstrated chemotactic activity. These activities may well play a role in the modifications of the extracellular matrix following elastin degradation as observed in atherosclerosis, emphysema and aging.     

Chondrodysplasias due to proteoglycan defects

The proteoglycans, especially the large chondroitin sulfate proteoglycan aggrecan, have long been viewed as important components of the extracellular matrix of cartilage. The drastic change in expression during differentiation from mesenchyme to cartilage, the loss of tissue integrity associated with proteoglycan degradation in several disease processes and, most important, the demonstration of abnormalities in proteoglycan production concomitant with the aberrant growth patterns exhibited by the brachymorphic mouse, the cartilage matrix deficient mouse, and the nanomelic chick provide the strongest evidence that the proteoglycan aggrecan is essential during differentiation and for maintenance of the skeletal elements. More recently, mutations associated with proteoglycans other than aggrecan, especially the heparan sulfate proteoglycans, glypican and perlecan, suggest an important role for these molecules in skeletal development as well. This review focuses on the molecular bases of the hereditary proteoglycan defects in animal models, as well as of some human chondrodysplasias, that collectively are providing a better understanding of the role of proteoglycans in the development and maintenance of the skeletal elements.     

Liberation of desmosine and isodesmosine as amino acids from insoluble elastin by elastolytic proteases

The development of atherosclerotic lesions and abdominal aortic aneurysms involves degradation and loss of extracellular matrix components, such as collagen and elastin. Releases of the elastin cross-links desmosine (DES) and isodesmosine (IDE) may reflect elastin degradation in cardiovascular diseases. This study investigated the production of soluble elastin cross-linking structures by proteinases implicated in arterial diseases. Recombinant MMP-12 and neutrophil elastase liberated DES and IDE as amino acids from insoluble elastin. DES and IDE were also released from insoluble elastin exposed to monocyte/macrophage cell lines or human primary macrophages derived from peripheral blood monocytes. Elastin oxidized by reactive oxygen species (ROS) liberated more unconjugated DES and IDE than did non-oxidized elastin when incubated with MMP-12 or neutrophil elastase. These results support the exploration of free DES and IDE as biomarkers of elastin degradation.     

Low density lipoprotein stimulation of human macrophage proteoglycan secretion

Lipoprotein trapping in arterial intima increases the risk for lipoprotein oxidation, foam cell formation, and inflammatory response in surrounding cells. Modified lipoproteins increase smooth muscle cell production of proteoglycans likely to retain lipoproteins in intimal extracellular matrix. We hypothesized that macrophage proteoglycan production is regulated in a similar manner, and characterized glycosaminoglycan side chains of secreted proteoglycans. Incubation with native low density lipoproteins (LDL) strongly stimulates total proteoglycan secretion in a time and concentration dependent manner. The main secretion product is small-sized (120 kDa) with unusually long galactosaminoglycan chains, predominantly chondroitin-6-O-sulfated. The effect appears specific for native LDL; oxidized LDL, very low density lipoproteins or phospholipid liposomes have only minor effects compared to control. These observations suggest that native LDL stimulate macrophages to secrete a chondroitin sulfate-rich proteoglycan moiety likely to have high capacity for vascular extracellular trapping of apolipoprotein B-containing lipoproteins.     

Extracellular matrix and the maintenance of the differentiated state: proteoglycans synthesized by replated chondrocytes and nonchondrocytes

It has been previously shown that undifferentiated stage 23 to 24 chick limb bud mesenchymal cells can be maintained in culture under conditions which promote chondrogenesis. As the chondrocytes mature in vitro, their proteoglycan synthesis progresses through a specific and reproducible biosynthetic program. By the eighth day of culture, the chondrocytes are making proteoglycans that are similar to proteoglycans isolated from adult animal tissues. Relative to the Day 8 proteoglycans, the proteoglycans synthesized by chick limb bud chondrocytes earlier in culture have a smaller monomer size, longer chondroitin sulfate chains, shorter keratan sulfate chains, a higher ratio of chondroitin-6-sulfate to chondroitin-4-sulfate, and a decreased ability to interact with hyaluronic acid. We have reported a procedure to remove the cells from Day 8 cultures and strip away most, if not all, of the extracellular matrix. In addition, the chondrocytes can be separated from the 40-50% nonchondrocytic cells normally found in Day 8 cultures, and the two cell populations replated separately. This report describes the analysis of the proteoglycans synthesized by replated cells; this analysis demonstrates quantitative and qualitative differences between chondrocyte and nonchondrocyte proteoglycans. The overall rate of proteoglycan synthesis is fourfold higher and the rate of synthesis of high buoyant density proteoglycans 30-fold higher for replated chondrocytes relative to nonchondrocytes. Qualitatively, more newly synthesized nonchondrocyte proteoglycans partition at lower buoyant density on CsCl equilibrium density gradients than do chondrocyte proteoglycans. Nonchondrocyte proteoglycans are of two major classes: One has a monomer size slightly smaller than that of Day 8 chondrocyte proteoglycan, but has much longer glycosaminoglycan chains. The other is considerably smaller than Day 8 chondrocyte proteoglycans, but has glycosaminoglycans of slightly larger size. In contrast, replated chondrocytes synthesize, even as soon as 4.5 hr after replating, proteoglycans that are identical to Day 8 chondrocyte proteoglycan in monomer size, in glycosaminoglycan chain size, in aggregability, and in the ratio of 6-sulfated to 4-sulfated chondroitin. Since denuding mature Day 8 chondrocytes of their extracellular matrix does not cause them to recapitulate their developmentally regulated program for the biosynthesis of proteoglycans, it is concluded that the quality of mature chondrocyte proteoglycan is not altered by the absence of extracellular matrix.     

Late preovulatory synthesis of proteoglycans by the human oocyte and cumulus cells and their secretion into the oocyte-cumulus-complex extracellular matrices

Light- and electron-microscope autoradiography using 3H-glucosamine and 3H-fucose as precursors was employed to investigate proteoglycan synthesis and secretion by late preovulatory human oocytes and cumulus cells. Both the oocyte and cumulus cells were found to be important cellular sources supplying proteoglycans to the oocyte-cumulus-complex extracellular matrices, i.e., the zona pellucida and the cumulus intercellular matrix. Both the oocyte and cumulus cells were shown to secrete labelled proteoglycans into the zona pellucida. Labelled proteoglycans were also detected in the cumulus intercellular matrix. Chase experiments revealed the labelled molecules to be relatively closely associated with both the zona pellucida and the cumulus intercellular matrix. Staining with chromic acid and phosphotungstic acid showed proteoglycan material to penetrate from the cumulus intercellular matrix into pores of the zona pellucida. This material is thought to be a structural equivalent of the newly synthesized proteoglycans secreted by cumulus cells and migrating into the zona pellucida (as detected by autoradiography). It is concluded that newly synthesized proteoglycans secreted by the oocyte and cumulus cells in the late preovulatory period are a component of the microenvironment in which fertilization takes place.     

Serum amyloid A, an acute-phase protein, modulates proteoglycan synthesis in cultured murine peritoneal macrophages.

Cultured peritoneal macrophages obtained from azocasein-injected mice were found to produce several fold more cell-associated and medium proteoglycans than peritoneal macrophages from untreated mice. Since serum amyloid A (an acute-phase protein) is also upregulated following injections of azocasein, we questioned whether its production was the immediate agent stimulating proteoglycan formation. Cultured peritoneal macrophages from untreated mice were then incubated with varying concentrations of SAA, resulting in a similar dose-dependent several fold increase in proteoglycan production. Of particular note was a disproportionate increase in cell-associated heparan sulfate proteoglycans in both experimental groups and of dermatan sulfate and chondroitin sulfate proteoglycans when cells were incubated in the presence of SAA in the culture medium. These results indicate a potentially important function of SAA in directing specific modifications in inflammatory conditions where increase in macrophage proteoglycans may play direct roles.     

Late preovulatory synthesis of proteoglycans by the human oocyte and cumulus cells and their secretion into the oocyte-cumulus-complex extracellular matrices

Summary Light- and electron-microscope autoradiography using ³H-glucosamine and ³H-fucose as precursors was employed to investigate proteoglycan synthesis and secretion by late preovulatory human oocytes and cumulus cells. Both the oocyte and cumulus cells were found to be important cellular sources supplying proteoglycans to the oocytecumulus-complex extracellular matrices, i.e., the zona pellucida and the cumulus intercellular matrix. Both the oocyte and cumulus cells were shown to secrete labelled proteoglycans into the zona pellucida. Labelled proteoglycans were also detected in the cumulus intercellular matrix. Chase experiments revealed the labelled molecules to be relatively closely associated with both the zona pellucida and the cumulus interecellular matrix. Staining with chromic acid and phosphotungstic acid showed proteoglycan material to penctrate from the cumulus intercellular matrix into pores of the zona pellucida. This material is thought to be a structural equivalent of the newly synthesized proteoglycans secreted by cumulus cells and migrating into the zona pellucida (as detected by autoradiography). It is concluded that newly synthesized proteoglycans secreted by the oocyte and cumulus cells in the late preovulatory period are a component of the microenvironment in which fertilization takes place.     

Inhibition of proteoglycan synthesis alters extracellular matrix deposition, proliferation, and cytoskeletal organization of rat aortic smooth muscle cells in culture

Arterial proteoglycans have been implicated in several important physiological processes ranging from lipid metabolism to regulation of smooth muscle cell growth. Vascular smooth muscle (VSM) cells are the major producers of proteoglycans in the medial layer of blood vessels. To study functional consequences of alterations in VSM proteoglycan metabolism we used 4-methylumbelliferyl-beta-D-xyloside to inhibit proteoglycan synthesis in primary and early passage cultures of rat aortic smooth muscle cells. Biochemical analysis of cultures labeled with 35SO4 showed the drug inhibited synthesis of different classes of proteoglycans by 50 to 62%. Inhibition of proteoglycan synthesis resulted in reduced accumulation of extracellular matrix, as shown by immunofluorescent staining with antibodies to chondroitin sulfate, fibronectin, thrombospondin, and laminin. There was also an inhibition of postconfluent (multilayered) growth of the smooth muscle cells, and a change in the morphology of the cells, with no apparent effect on subconfluent growth. In addition, in drug-treated cells there was a reduction in the number of cytoskeletal filaments that contained alpha-actin, the actin subtype synthesized by differentiated VSM cells. This occurred even though the total content of alpha-actin in the cells was not reduced. The effects of the inhibitor on growth and morphology could be reversed by switching the cultures to normal medium and could be prevented by growing the cells on preformed VSM extracellular matrix. These observations suggest the vascular extracellular matrix may play a role in regulating the growth and differentiation of smooth muscle cells.     

Extracellular matrix: differential influence on growth and biosynthesis patterns of vascular smooth muscle cells from SHR and WKY rats

Smooth muscle cells from spontaneously hypertensive rats (SHR) elaborated extracellular matrix (ECM) material in culture that was more stimulatory to growth of cells from normotensive (WKY) animals than their own matrix. Both cell types elaborated ECMs consisting of glycoconjugate material (proteoglycans, glycopeptides) elastin, and collagens, but there were differences in the relative proportions of the compounds synthesized. Cells from SHR produced an ECM richer in elastin than that synthesized by WKY derived cells (approximately 19% vs. 11%, respectively). However, the latter elaborated ECMs containing more (approximately 45% for WKY vs. 29% for SHR) glycoconjugate material than the former. The lysyloxidase-mediated cross-linking of elastin was more rapid in cultured cells from SHR animals than from their normotensive counterparts and may be as a consequence of increased substate (tropoelastin) availability in ECMs from SHR animals. The relative proportions and sulphate levels of the glycosaminoglycans associated with matrix material elaborated by the two cell types were similar. Radiolabelled glycoconjugate material was degraded by cells (SHR/WKY) when they were plated upon pre-formed ECMs, and their patterns of synthesis of new matrix was markedly altered under such conditions. New matrix material elaborated by cells plated upon ECM-coated dishes consisted predominantly of glycopeptide and proteoglycan matrix components. Epidermal growth factor promoted the incorporation of [3H]-thymidine into DNA by quiescent cells, and this was also markedly stimulated when cells were plated onto ECM-coated plasticware rather than onto plastic substratum.     

Deposition of tropoelastin into the extracellular matrix requires a competent elastic fiber scaffold but not live cells.

The initial steps of elastic fiber assembly were investigated using an in vitro assembly model in which purified recombinant tropoelastin (rbTE) was added to cultures of live or dead cells. The ability of tropoelastin to associate with preexisting elastic fibers or microfibrils in the extracellular matrix was then assessed by immunofluorescence microscopy using species-specific tropoelastin antibodies. Results show that rbTE can associate with elastic fiber components in the absence of live cells through a process that does not depend on crosslink formation. Time course studies show a transformation of the deposited protein from an initial globular appearance early in culture to a more fibrous structure as the matrix matures. Deposition required the C-terminal region of tropoelastin and correlated with the presence of preexisting elastic fibers or microfibrils. Association of exogenously added tropoelastin to the cellular extracellular matrix was inhibited by the addition of heparan sulfate but not chondroitin sulfate sugars. Together, these results suggest that the matrix elaborated by the cell is sufficient for the initial deposition of tropoelastin in the extracellular space and that elastin assembly may be influenced by the composition of sulfated proteoglycans in the matrix.     

细胞外间质

细胞外间质由四大家族组成,胶原蛋白,蛋白多糖。弹性蛋白和细胞外间质糖蛋白。细胞外间质成分不仅仅是细胞的惰性支持物,它具有活性的生物功能,例如细胞粘附及迁移,甚至涉及基因表达。细胞外间质研究是一个十分活跃的生物学领域。     

Complexes of low-density lipoproteins and arterial proteoglycan aggregates promote cholesteryl ester accumulation in mouse macrophages

We studied the effect of complexes of low-density lipoproteins (LDL) and different proteoglycan preparations from bovine aorta on LDL degradation and cholesteryl ester accumulation in mouse peritoneal macrophages. Native proteoglycan aggregate containing proteoglycan monomers, hyaluronic acid and link protein was isolated by associative extraction of aortic tissue, while proteoglycan monomer was obtained by dissociative isopycnic centrifugation of the native proteoglycan aggregate. In vitro proteoglycan aggregates were prepared by reaction of the proteoglycan monomer with exogenous hyaluronic acid. 125I-labeled LDL-proteoglycan complexes were formed in the presence of 30 mM Ca2+ and incubated with macrophages. At equivalent uronic acid levels in the proteoglycans the degradation of 125I-labeled LDL contained in the native proteoglycan aggregate complex was 3.7-7.5-fold greater than the degradation of the lipoprotein in the proteoglycan monomer complex. Degradation of 125I-LDL in the in vitro aggregate complex, while higher than that in the monomer complex, was markedly less than that in the native aggregate complex. The larger size and the greater complex-forming ability of the native proteoglycan aggregate might account for the greater capacity of the aggregate to promote LDL degradation in macrophages. The proteoglycan-stimulated degradation of LDL produced a marked increase in cholesteryl ester synthesis and content in macrophages. The LDL-proteoglycan complex was degraded with saturation kinetics, suggesting that these complexes are internalized through high-affinity receptors. Degradation was inhibited by the lysosomotropic agent, chloroquine. Acetyl-LDL, but not native LDL, competitively inhibited the degradation of the 125I-LDL component of the complex. Polyanionic compounds such as polyinosinic acid and fucoidin, while completely blocking the acetyl-LDL-stimulated cholesteryl ester formation, had no effect on the proteoglycan aggregate-stimulated cholesterol esterification. This suggests that LDL-proteoglycan complex and acetyl-LDL are not entering the cells through the same receptor pathway. These results demonstrate that the interaction of LDL with arterial wall proteoglycan aggregates results in marked cholesteryl ester accumulation in macrophages, a process likely to favor foam cell formation. A role for arterial proteoglycans in atherosclerosis is obvious.