Effects of platelet-derived growth factor and transforming growth factor-beta 1 on the synthesis of a large versican-like chondroitin sulfate proteoglycan by arterial smooth muscle cells

Vascular proliferation and transforming growth factor-beta expression in pre- and early stage of diabetes mellitus in Otsuka Long-Evans Tokushima fatty rats

The roles of transforming growth factor (TGF)-beta 1 in vascular proliferation, atherosclerosis, and plaque still remain controversial. TGF-beta 1 has been previously reported to inhibit the proliferation and migration of vascular smooth muscle cells and endothelial cells, in vitro. On the other hand, administration or transgenic overexpression of TGF-beta 1 enhances extracellular matrix synthesis and cellular hyperplasia of the intima and media in the normal artery and injured artery in vivo. We evaluated the correlation of arterial proliferation with plasma levels of TGF-beta 1 and TGF-beta receptor type II, respectively, in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a new strain of spontaneous non-insulin-dependent diabetes mellitus (NIDDM) models. OLETF rats (n=30) were divided into three groups aged 5,15, and 30 weeks. Long-Evans Tokushima Otsuka (LETO) rats (n=30) were used as age-matched non-diabetic controls. Plasma TGF-beta1 and insulin were determined by enzyme-linked immunosorbent assay. Immunoreactive TGF-beta receptor type II antigen was detected by immunohistochemistry on the thoracic artery. Arterial media area was measured microscopically. Oral glucose tolerance test was performed to examine the stage of diabetes mellitus. The thoracic aorta wall section area increased significantly from the age of 15 weeks in OLETF rats, versus LETO rats. In both OLETF and LETO rats, plasma TGF-beta 1 increased significantly from the age of 15 weeks. In OLETF rats, plasma TGF-beta 1 increased significantly over that in LETO rats (P<0.001). Furthermore, TGF-beta receptor type II was detected on aortic wall as strong signals in OLETF rats, but only weakly in LETO rats. OLETF rats showed hyperinsulinemia and insulin resistance from the age of 15 weeks. With oral glucose tolerance test, from the age of 15 weeks, the high glucose level in OLETF rats was prolonged to 2 h after loading, and the insulin levels at both fasting and after loading were significantly higher than those of LETO rats (P<0.001). There are significant linear relations between plasma TGF-beta 1 antigen and aorta wall section area, and plasma TGF-beta 1 antigen and fasting insulin level (P<0.001, respectively). We found that plasma TGF-beta 1 and vascular TGF-beta type II receptors existed to a greater extent in pre- and early stages of diabetes mellitus (DM) in OLETF rats compared with LETO rats. The greater extent of each in OLETF rats was associated with hyperinsulinemia and/or vascular thickening.

The extracellular matrix on atherogenesis and diabetes-associated vascular disease

Atherosclerosis is remarkably increased in type 2 diabetes suggesting that mechanisms causing arterial lesion are enhanced by the metabolic disturbances of insulin resistance (IR) and diabetes. Several lines of research suggest that processes taking place in the arterial intima extracellular matrix may be part of a shared pathogenic mechanism. The intima extracellular matrix is where atherogenesis takes place. This layer contains fibrilar macromolecules like collagens, proteoglycans (PGs), hyaluronate, and extracellular multi-domain proteins. Specific interaction of lysine, arginine-rich segments of the apoB-100 lipoproteins, LDL, IDL and Lp (a), with the negatively charged glycosaminoglycans (GAGs) of PGs cause retention of the lipoproteins, one of the initiation process of atherogenesis. Such interactions cause structural modifications of the lipid and protein moieties of the lipoproteins that appear to increase their susceptibility to proteases, phospholipases and free radical-mediated processes. The association of apoB-lipoproteins, specially small and dense LDL, with intima PGs increases their uptake by macrophages and human arterial smooth muscle cells (HASMC) leading to 'foam cell' formation. In vitro, elevated levels of non-esterified fatty acids (NEFA) alter the matrix of endothelial cells basement membrane making them more permeable to macromolecules. NEFA cause changes in the expression of genes controlling the PGs composition of the PGs secreted by HASMC causing formation of a matrix with high affinity for LDL. These results lead us to speculate that an important component of the dyslipidemia of IR and type 2 diabetes, chronic high NEFA, may contribute to cellular alterations that cause changes of the arterial intima extracellular matrix. Such changes may increase the atherogenicity of the retention of apoB lipoproteins in the intima and contribute to the systemic alteration of the arterial wall frequently observed in IR and type 2 diabetes.

Differential effects of gemfibrozil on migration, proliferation and proteoglycan production in human vascular smooth muscle cells

The aim of this study was to determine, if gemfibrozil has anti-atherogenic actions on human vascular smooth muscle cells (SMCs) and whether these actions are affected by high glucose concentrations, which mimic the hyperglycemia of diabetes. Proliferation of SMCs treated with gemfibrozil was estimated by cell counting (Coulter Counter) and [3H]thymidine incorporation, migration in a scrape-wound assay, proteoglycan (PG) biosynthesis and glycosaminoglycan (GAG) synthesis on xyloside by [35S]sulfate labeling and sizing by sodium dodecyl sulphide-polyacrylamide gel electrophoresis (SDS-PAGE). Gemfibrozil (100 micromol/l) did not affect migration in low or high glucose media. Gemfibrozil caused concentration-dependent inhibition of proliferation in low glucose media (24% inhibition at 100 micromol/l, P<0.01) and inhibited the re-initiation of DNA synthesis by 33.3% (100 micromol/l, P<0.05) in low glucose and 31.4% (100 micromol/l, P<0.001) in high glucose conditions. In low and high glucose media, gemfibrozil (100 micromol/l) reduced total PG production in the presence of TGF-beta 1, which was associated with a decrease in the apparent size of PGs. Gemfibrozil and another PPAR-alpha ligand, WY-14643, significantly inhibited basal and TGF-beta1 stimulated GAG synthesis. We conclude that some SMCs properties associated with atherogenesis are favorably affected by gemfibrozil. Hence, direct vascular actions of gemfibrozil observed in this study may contribute to the reduction in cardiovascular disease observed in clinical studies with gemfibrozil.

Basement membrane and beta amyloid fibrillogenesis in Alzheimer's disease

High-resolution ultrastructural and immunohistochemical studies revealed that in situ beta amyloid fibrils of Alzheimer's disease were made up of a core consisting of a solid column of amyloid P component (AP) and associated chondroitin sulfate proteoglycan, and a heparan sulfate proteoglycan surface layer with externally associated fine filaments of beta protein. The main body of beta amyloid fibrils closely resembled that of microfibrils. Abundant microfibrils were reported to be present at the basement membrane of capillaries with "leaky" blood-urine or blood-air barriers. Similarly, abundant microfibril-like beta amyloid fibrils are formed at the microvascular basement membrane in cerebrovascular amyloid angiopathy with altered blood-brain barrier. Since AP is an indispensable major component of microfibrils and microfibril-like structures, the formation of microfibrils may depend on, among other factors, the availability of AP. Thus, in beta amyloid fibrillogenesis fibrils may be built around AP which continuously leaks out from circulation into vascular basement membrane, and beta amyloid fibrils may be regarded as pathologically altered basement membrane-associated microfibrils. With no source of AP around them, senile plaque fibrils may also be derived from perivascular amyloid.

Increased plasmin and serine proteinase activity during flow-induced intimal atrophy in baboon PTFE grafts

High blood flow causes intimal atrophy and loss of extracellular matrix in PTFE aortoiliac grafts. We have investigated whether matrix-degrading proteinases are altered in this baboon model of atrophy using zymography, western analysis, and a versican degradation assay. After four days of high flow, urokinase was increased and plasminogen activator inhibitor-1 was decreased in the intima. Plasminogen was increased after seven days. Pro-matrix metalloproteinase (MMP)-2, activated MMP-2, and proMMP-9 levels were modestly increased by high flow at 7 days, whereas MMP-3 and tissue inhibitor of metalloproteinases-1 were not altered. Extracts of 4-day high-flow intimas degraded more 35S-methionine-labeled versican than low-flow intimal extracts, and this activity was inhibited by AEBSF, a serine proteinase inhibitor, and a plasmin antibody. In contrast, this activity was not inhibited by the MMP inhibitor, BB-94 (Batimastat). These data suggest that serine proteinases, including plasmin, may be largely responsible for extracellular matrix degradation in this primate model of flow-induced intimal atrophy.

Differential effects of cadmium on proteoglycan synthesis of arterial smooth muscle cells: increase in small dermatan sulfate proteoglycans, biglycan and decorin, in the extracellular matrix at low cell density

Proteoglycans (PGs), especially chondroitin/dermatan sulfate proteoglycans (CS/DSPGs), accumulate and their composition variously changes in atherosclerotic vascular walls. Since cadmium causes atherosclerosis in experimental animals, PGs synthesized by cultured vascular smooth muscle cells after exposure to cadmium were characterized in the present study. Sparse and dense cultures of the cells were metabolically labeled with [35S]sulfate for 24 h in the presence of cadmium chloride at noncytotoxic levels (0.2 microM or less). The incorporation of [35S]sulfate into glycosaminoglycans was determined by the cetylpyridinium chloride precipitation method. The labeled PGs were characterized by DEAE-Sephacel ion exchange chromatography and Sepharose CL-4B molecular sieve chromatography. The M(r) and the glycosaminoglycan composition of small CS/DSPGs were analyzed by SDS-polyacrylamide gel electrophoresis and Sepharose CL-6B chromatography, respectively, before and after digestion with chondroitin ABC lyase or papain. The core proteins were identified by Western blot analysis. These experiments indicate that cadmium differentially acts on the PG synthesis when vascular smooth muscle cell density is low. Specifically, cadmium increased the accumulation of small CS/DSPGs identified as biglycan and decorin in the cell layer of sparse cells. However, the hydrodynamic size and the length of chondroitin/dermatan sulfate chains in the PGs were unaffected by cadmium. On the other hand, cadmium decreased other cell layer-associated PGs that were separated from biglycan and decorin by DEAE-Sephacel chromatography in the sparse cells; as the result, whole glycosaminoglycans were decreased in both the cell layer and the conditioned medium. It is therefore concluded that cadmium may change the composition of PGs in atherosclerotic plaques through induction of biglycan and decorin synthesis and inhibition of other PG synthesis in vascular smooth muscle cells.

Proteoglycans synthesized by arterial smooth muscle cells in the presence of transforming growth factor-beta1 exhibit increased binding to LDLs

The "response-to-retention" hypothesis of atherogenesis states that atherogenic lipoproteins, such as low density lipoprotein (LDL), are retained in vessels by proteoglycans and undergo proatherosclerotic modifications. Transforming growth factor (TGF)-beta1 has been identified in atherosclerotic vessels and has been shown to stimulate the synthesis of chondroitin sulfate- and dermatan sulfate-containing proteoglycans by arterial smooth muscle cells (ASMCs), but whether it promotes lipid retention has not been addressed. We investigated whether TGF-beta1 modulates the biosynthesis of proteoglycans by ASMCs in a manner that promotes binding to LDL. Proteoglycans isolated from TGF-beta1-treated ASMCs exhibited enhanced binding to native LDL compared with the binding of proteoglycans isolated from control cultures (K(d) 18 microg/mL LDL versus 81 microg/mL LDL, respectively). The increase in proteoglycan-LDL binding caused by TGF-beta1 could be attributed primarily to the glycosaminoglycan portion of the proteoglycans, since the glycosaminoglycan chains liberated from the core proteins of these proteoglycans synthesized in the presence of TGF-beta1 exhibited increased LDL binding as well. Furthermore, glycosaminoglycan chains initiated on xyloside (an initiator of glycosaminoglycan synthesis) in the presence of TGF-beta1 were longer and displayed enhanced binding to LDL compared with the LDL binding of xyloside-initiated glycosaminoglycan chains from control cultures. These results indicate that TGF-beta1 promotes LDL-proteoglycan interaction primarily by its effects on the glycosaminoglycan synthetic machinery of the ASMCs. Therefore, this study supports a proatherogenic role for TGF-beta1.

Overexpression of the V3 variant of versican alters arterial smooth muscle cell adhesion, migration, and proliferation in vitro

Versican is an extracellular matrix proteoglycan produced by many cells. Although versican is generally known as a large chondroitin sulfate proteoglycan (CSPG), the smallest splice variant, V3, consists only of the amino- and carboxy-terminal globular domains and is therefore predicted to be a small glycoprotein, lacking CS chains. The large size, negative charge, and ability of versican variants to form pericellular coats with hyaluronan are responsible for many of its effects. V3, lacking the large size and high charge density, but retaining the hyaluronan-binding domain of the larger isoforms, may have different effects on cell phenotype. To determine whether V3 alters cell phenotype, Fisher rat arterial smooth muscle cells (ASMCs), which express the larger CSPG versican splice forms (V0 and V1) were retrovirally transduced with the rat V3 cDNA. Northern analysis for versican RNAs confirmed that cells transduced with V3 retrovirus, but not cells tranduced with the empty vector, expressed RNA of the size expected for V3/neo(r) bicistronic RNA. V3 overexpressing cells were more spread on tissue culture plastic, had a smaller length-to-breadth ratio and were more resistant to release from the culture dish by trypsin. Interference reflection microscopy of sparsely plated cells showed larger areas of close contact between the V3 expressing cells and the coverslip, in comparison to control cells. Focal contacts in the periphery of V3 expressing cells were larger. Growth and migration studies revealed that V3 transduced cells grow slower and migrate a shorter distance in a scratch wound assay. The increased adhesion and the inhibition of migration and proliferation resulting from V3 overexpression are the opposites of the known and predicted effects of the other variants of versican. V3 may exert these effects through changes in pericellular coat formation, either by competing with larger isoforms for hyaluronan-binding, or by altering other components of the pericellular matrix.

Arterial wall chondroitin sulfate proteoglycans: diverse molecules with distinct roles in lipoprotein retention and atherogenesis

Chondroitin sulfate proteoglycans (CSPGs) of the arterial wall are generally considered to be atherogenic because of their ability to trap cholesterol-rich lipoproteins in vitro. Nevertheless, CSPGs are a diverse group of molecules with a long evolutionary history and distinct biologic functions. The three principal CSPGs in the arterial wall are versican, which is part of the hyalectan gene family; and decorin and biglycan, which are members of a separate gene family, the small leucine-rich proteoglycans. Importantly, there is now substantial evidence that the different molecular species of CSPGs participate unequally in lipoprotein retention, and that they exert unequal regulatory effects that are related to atherogenesis. Recently available murine models with genetic manipulations that affect CSPGs now allow causal studies of the roles of these molecules to be conducted in vivo, with occasionally surprising results. Moreover, tools are being developed to examine human genetic variations that are relevant to CSPGs, which may provide additional important insights into the human disease. The era in which proteoglycans are regarded as a nondescript backdrop, playing purely nonspecific structural roles, is over. Studies in manipulated animals and in human populations will continue to reveal precise, dynamic roles for these fascinating and ancient molecules.

Platelet-derived growth factor stimulates the formation of versican-hyaluronan aggregates and pericellular matrix expansion in arterial smooth muscle cells

Hyaluronan and versican-rich pericellular matrices form around arterial smooth muscle cells (ASMC) preferentially during the detachment phase of proliferation and migration. PDGF is a potent mitogen and chemotactic agent for ASMC and also stimulates the production of extracellular matrix molecules which may regulate the proliferative and migratory capacity of the cells. We have examined the effect of PDGF on the formation of hyaluronan-dependent pericellular matrices, and on the synthesis and interaction of several major pericellular coat constituents. As demonstrated using a particle exclusion assay, PDGF stimulated the formation of pericellular matrices and was seen both in an increased proportion of cells with a coat and a greater coat size. This increase was accompanied by a transient increase in hyaluronan synthase 2 (HAS2) expression and an increase in hyaluronan synthesis and polymer length. PDGF also increased the synthesis of versican and link protein as measured at the mRNA and protein levels. The amount of native versican-hyaluronan aggregates and link-stabilized aggregate was also increased following PDGF treatment. Time lapse imaging showed that pericellular matrix formation occurred around trailing cell processes prior to their detachment. These data suggest that PDGF modulates the synthesis and organization of ASMC pericellular coat-forming molecules such as versican, hyaluronan, and link protein, which leads to extracellular matrix expansion and alterations in ASMC phenotype.

Isolation and characterization of fibroblasts derived from regenerating human periodontal defects

In an attempt to understand better the cells responsible for periodontal regeneration, cells from human gingiva, periodontal ligament and regenerating periodontal defects treated with expanded polytetrafluorethylene membranes were isolated, cultured and characterized. Guided tissue regeneration procedures were carried out on three human volunteers around molar teeth destined for extraction. After a 6-week 'healing phase', fibroblast cell cultures were established from explants of the regenerating soft connective tissue (RTF), as well as from the associated periodontal ligament (PLF) and gingiva (GF). Following stimulation with platelet-derived growth factor-beta (PDGF) and insulin-like growth factor-1 (IGF-1), [3H]thymidine-uptake and dye-binding assays were used to assess the rate of DNA synthesis and cell proliferation, respectively. Northern blotting was used to measure the expression of mRNA for the extracellular matrix proteoglycans decorin, biglycan and versican. The results show that the GF and RTF proliferated more quickly than the PLF. PDGF and IGF-1 were mitogenic for all three cell types. Decorin mRNA expression was stronger in the GF than the RTF and PLF, whereas versican mRNA expression was stronger in the GF and PLF than the RTF. Biglycan mRNA expression was strong in the PLF, moderate in the GF and weak in the RTF. The growth factors did not affect the mRNA expression for biglycan, but they upregulated versican and downregulated decorin mRNA. It can be concluded that RTF exhibits properties characteristic of a reparative phenotype. More specifically, it proliferates faster than PLF, from which it is derived, while exhibiting a unique pattern of proteoglycan mRNA expression. Therefore, this study demonstrates that fibroblasts obtained from the regenerating periodontal defects exhibit characteristics consistent with their ability to facilitate periodontal regeneration.

Retroviral overexpression of decorin differentially affects the response of arterial smooth muscle cells to growth factors

Decorin is a member of the family of small leucine-rich proteoglycans that are present in blood vessels and synthesized by arterial smooth muscle cells (ASMCs). This proteoglycan accumulates in topographically defined regions of atherosclerotic lesions and may play a role in the development of this disease. However, little is known about whether decorin has specific effects on the cellular events that contribute to atherosclerotic lesion formation. In the present study, rat ASMCs were transduced with a retroviral vector (LDSN) that carries the bovine decorin gene. Compared with vector control cells (LXSN), these cells constitutively overexpress decorin, as verified by Northern and Western analysis and by metabolic labeling. Experiments were performed to examine the responsiveness of decorin-overexpressing rat ASMCs to platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1), 2 growth factors that affect cell proliferation and extracellular matrix production in atherosclerosis. Decorin-overexpressing cells had decreased [(3)H]thymidine incorporation into DNA and increased the levels of the cyclin-dependent kinase inhibitors p21 and p27 in the first 24 hours of response to serum and PDGF-BB. However, these effects of decorin were not apparent at 48 or 72 hours after plating and did not result in reduced growth of decorin-overexpressing cells in response to serum and PDGF-BB. In contrast, the growth response of decorin-overexpressing ASMCs to TGF-beta1, as well as the expression of TGF-beta1-responsive genes, such as plasminogen activator inhibitor-1 and versican (an extracellular matrix proteoglycan), was diminished. These results indicate that decorin selectively inhibits the responsiveness of rat ASMCs to TGF-beta1 and suggests that the induction of constitutive decorin overexpression by ASMCs in vivo may have therapeutic value in the inhibition of TGF-beta1-mediated effects on the development of atherosclerotic lesions.

Mechanical strain induces specific changes in the synthesis and organization of proteoglycans by vascular smooth muscle cells

In the mechanically active environment of the artery, cells sense mechanical stimuli and regulate extracellular matrix structure. In this study, we explored the changes in synthesis of proteoglycans by vascular smooth muscle cells in response to precisely controlled mechanical strains. Strain increased mRNA for versican (3.2-fold), biglycan (2.0-fold), and perlecan (2.0-fold), whereas decorin mRNA levels decreased to a third of control levels. Strain also increased versican, biglycan, and perlecan core proteins, with a concomitant decrease in decorin core protein. Deformation did not alter the hydrodynamic size of proteoglycans as evidenced by molecular sieve chromatography but increased sulfate incorporation in both chondroitin/dermatan sulfate proteoglycans and heparan sulfate proteoglycans (p < 0.05 for both). Using DNA microarrays, we also identified the gene for the hyaluronan-linking protein TSG6 as mechanically induced in smooth muscle cells. Northern analysis confirmed a 4.0-fold increase in steady state mRNA for TSG6 following deformation. Size exclusion chromatography under associative conditions showed that versican-hyaluronan aggregation was enhanced following deformation. These data demonstrate that mechanical deformation increases specific vascular smooth muscle cell proteoglycan synthesis and aggregation, indicating a highly coordinated extracellular matrix response to biomechanical stimulation.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Human abdominal aortic aneurysm is characterized by decreased versican concentration and specific downregulation of versican isoform V(0)

Abdominal aortic aneurysm (AAA) is a common disease of human aorta with increased incidence. It is a complication to atherosclerosis and it is closely associated with alterations in extracellular macromolecules. In this study, the levels of mRNA for versican--the major extracellular arterial proteoglycan (PG)--present in AAA and normal aortas were evaluated by reverse-transcriptase polymerase chain reaction. The concentration of versican was also examined in corresponding tissue samples. Versican was almost completely extracted with 4 M guanidine hydrochloride in the presence of Triton X-100, isolated by chromatography on DEAE-Sephacel and characterized using treatment with specific chondro-/dermato-lyases and agarose gel electrophoresis. Versican localization in tissue as well as the variation and distribution of smooth muscle cells (SMCs) and macrophages were also investigated immunohistochemically. The mRNAs coding for versican isoforms V(0) and V(1) were identified in both tissues, whereas V(2) was absent. The expression of V(0) was decreased 40% in aneurysmal vessel wall, whereas that for V(1) remained constant. This change was simultaneous with a significant decrease in versican concentration by 89%. In normal aortas, most versican was seen in the intima, whereas in AAA, this layer is characterized by advanced atherosclerotic lesion, rich in lipids and macrophages but poor in versican. The decreased transcription and the still lower amount of versican in the AAA may correlate to (i) a decrease in density of SMCs, these cells being the major source of versican in aorta, and (ii) the presence of macrophages, which may induce versican degradation and modulate versican synthesis. It is proposed that the decreased synthesis and increased degradation of versican, particularly of isoform V(0), and the resulting low concentration in the intima are crucial factors contributing to the altered viscoelastic and compressive properties and thereby to the deformity and dilatation of aorta.

Up-regulation of extracellular matrix proteoglycans and collagen type I in human crescentic glomerulonephritis

BACKGROUND

The pathogenesis of crescentic glomerulonephritis (CGN) involves cellular migration and proliferation in the urinary space, frequently followed by fibrous organization. Extracellular matrix proteoglycans (PGs) may regulate these events via effects on cellular migration, interactions with growth factors, including transforming growth factor-beta (TGF-beta), and control of collagen fibrillogenesis. The expression of PG in human CGN is unknown.

METHODS

Renal tissues from 18 patients with CGN were examined immunohistochemically for versican, decorin, biglycan and collagen type I, and were compared with morphologically normal tissues from six tumor nephrectomies. Synthesis of decorin, biglycan, and procollagen type I mRNAs was evaluated by in situ hybridization.

RESULTS

Versican was strongly expressed in cellular crescents and periglomerular areas, whereas decorin and biglycan accumulated in collagen type I-enriched regions, including fibrocellular and fibrous crescents, and interstitial fibrosis. PG and collagen type I accumulation colocalized with myofibroblasts in crescents, periglomerular areas, and interstitium.

CONCLUSIONS

The temporal and spatial patterns of expression demonstrated in this study provide evidence to support pathogenic roles for PG in the evolution of CGN. Based on known biological properties of this molecule, versican may facilitate migration of cells in developing crescents. Decorin and biglycan may contribute to progression of CGN, perhaps via interactions with collagen type I in the remodeled extracellular matrix.

Comparison of deposits of versican, biglycan and decorin in saphenous vein and internal thoracic, radial and coronary arteries: correlation to patency

BACKGROUND

Matrix proteoglycans versican, biglycan and decorin are important determinants of vessel-wall structure and pathology. Thickened myxoid intimas typical of restenosis and early atherosclerosis are enriched in versican and biglycan, proteoglycans that promote proliferation and migration of smooth muscle cells and bind lipoproteins. In contrast, compact fibrous intimas are characterized by decorin.

OBJECTIVE

To compare the distribution patterns of these matrix proteoglycans, and changes induced by organ culture in coronary artery, saphenous vein, internal thoracic artery (ITA), and radial artery, and correlate differences to patency.

METHODS

Vessels were collected at the time of bypass surgery and heart transplantation and either fixed for immunohistochemistry or prepared for organ culture. Vessels in culture were labelled with [3H]-glucosamine and processed for autoradiography and immunohistochemistry. Distribution patterns for proteoglycans and radio-labelling were determined morphometrically.

RESULTS

Distribution profiles in coronary artery and saphenous vein were similar, with relatively high levels of subendothelial versican and biglycan and low levels of decorin. In culture subendothelial incorporation of [3H]-glucosamine and immunostaining for versican and biglycan, but not decorin, were significantly increased. In contrast, the thin intima of the ITA was relatively enriched in decorin compared with the medial layers and in culture intimal staining for decorin increased markedly compared with a modest increase for biglycan and no change for versican. There was an even distribution in radial artery of all three proteoglycans across the intima without subendothelial accumulations. In culture there was an increase in staining intensity for proteoglycans of the radial artery. Neither the ITA nor radial artery exhibited an increase in subendothelial incorporation of [3H]-glucosamine in culture.

CONCLUSIONS

The distributions of proteoglycans, and responses to culture correlate to the known differences in patency between grafted saphenous vein and ITA and predict that the radial artery will outperform the saphenous vein but might not be as good as the ITA for long-term patency.

Binding of a large chondroitin sulfate/dermatan sulfate proteoglycan, versican, to L-selectin, P-selectin, and CD44

Here we show that a large chondroitin sulfate proteoglycan, versican, derived from a renal adenocarcinoma cell line ACHN, binds L-selectin, P-selectin, and CD44. The binding was mediated by the interaction of the chondroitin sulfate (CS) chain of versican with the carbohydrate-binding domain of L- and P-selectin and CD44. The binding of versican to L- and P-selectin was inhibited by CS B, CS E, and heparan sulfate (HS) but not by any other glycosaminoglycans tested. On the other hand, the binding to CD44 was inhibited by hyaluronic acid, chondroitin (CH), CS A, CS B, CS C, CS D, and CS E but not by HS or keratan sulfate. A cross-blocking study indicated that L- and P-selectin recognize close or overlapping sites on versican, whereas CD44 recognizes separate sites. We also show that soluble L- and P-selectin directly bind to immobilized CS B, CS E, and HS and that soluble CD44 directly binds to immobilized hyaluronic acid, CH, and all the CS chains examined. Consistent with these results, structural analysis showed that versican is modified with at least CS B and CS C. Thus, proteoglycans sufficiently modified with the appropriate glycosaminoglycans should be able to bind L-selectin, P-selectin, and/or CD44.

Interaction of native and modified low-density lipoproteins with extracellular matrix

Lipoprotein-matrix interactions play an important role in arterial disease. Extracellular matrix proteoglycans bind and retain specific positively charged domains on apolipoproteins B- and E-containing lipoproteins during atherogenesis. Retained lipoproteins can undergo several modifications, which may alter their interaction with extracellular matrix molecules. Growth factors, cytokines and oxidized low density lipoproteins influence proteoglycan structure, rendering them more likely to bind and retain lipoproteins during atherogenesis. Lipoproteins, native and modified, also can modulate the expression of several of the matrix degrading enzymes present in vascular tissue, thereby influencing plaque stability. Thus, the interaction of atherogenic lipoproteins with arterial wall matrix molecules can influence the genesis and progression of atherosclerosis and its complications.

Microvascular pericytes express aggrecan message which is regulated by BMP-2

Multipotential mesenchymal stem cells capable of chondro-osseous induction contribute to the endochondral callus of healing fractured bone. Microvascular pericytes serving the role of multipotential mesenchymal stem cells are considered osteoprogenitors because they express type I collagen, alkaline phosphatase enzyme activity, osteocalcin immunoreactivity, and bone sialoprotein mRNA. Previous electron microscopic studies indicate that this cell type has a contribution to the fracture callus. Limited data suggest that pericytes may also assume a chondrogenic phenotype. We undertook in vitro studies to understand how the chondro-osseous phenotype of the pericyte might be regulated. Using Northern analysis and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we found that cultured pericytes produce aggrecan and type II collagen mRNA indicating their chondrogenic potential. Aggrecan message is elevated by BMP-2 as analyzed by both Northern hybridization and RT-PCR. This finding suggests a regulatory role for this morphogen on this phenotype in pericytes. RT-PCR amplified versican product was also associated with pericyte cultures but was not affected by BMP-2. Our data strongly support a chondrogenic role for the pericyte and that the phenotype is regulated at least in part by BMP.

Oxidized low density lipoproteins regulate synthesis of monkey aortic smooth muscle cell proteoglycans that have enhanced native low density lipoprotein binding properties

Oxidized low density lipoproteins (Ox-LDL) affect several biological processes involved in atherogenesis. However, it is not known whether Ox-LDL can regulate proteoglycan expression and thus affect arterial wall lipoprotein retention. This study evaluated whether Ox-LDL, as compared with native LDL, regulates proteoglycan expression by monkey arterial smooth muscle cells in vitro and whether proteoglycans synthesized in the presence of Ox-LDL exhibit altered lipoprotein binding properties. Ox-LDL stimulated glycosaminoglycan synthesis, as measured by (35)SO(4) incorporation, by 30-50% over that of native LDL. The effect was maximal after 72 h of exposure to 5 microg/ml of Ox-LDL. The molecular sizes of versican, biglycan, and decorin increased in response to Ox-LDL, as indicated by size exclusion chromatography and SDS-polyacrylamide gel electrophoresis. These effects could be mimicked by the lipid extract of Ox-LDL. These size increases were largely due to chain elongation and not to alterations in the ratio of (35)SO(4) to [(3)H]glucosamine incorporation. Affinity chromatography indicated that Ox-LDL stimulated the synthesis of proteoglycans with high affinity for native LDL. Ox-LDL also specifically stimulated mRNA expression for biglycan (but not versican or decorin), which was correlated with increased expression of secreted biglycan. Thus, Ox-LDL may influence lipoprotein retention by regulating synthesis of biglycan and also by altering glycosaminoglycan synthesis of vascular proteoglycans so as to enhance lipoprotein binding properties.

Low-density lipoprotein stimulates mesangial cell proteoglycan and hyaluronan synthesis

BACKGROUND

Hyperlipidaemia leads to glomerulosclerosis in small mammals and may contribute to progressive renal disease in man. One prominent feature of lipid-induced glomerular injury in animal models is the accumulation of mesangial matrix. These studies were designed to investigate whether low-density lipoprotein (LDL) enhanced mesangial cell (MC) matrix deposition by modulating the production of proteoglycans (PG) and hyaluronan (HA).

METHODS

Growth arrested human MC were metabolically labelled with either 50 microCi/ml Na(2)[(35)S]sulphate or 25 microCi/ml [(3)H]glucosamine and stimulated with LDL (10-100 microg/ml). The radiolabelled PG and HA extracted from the cell layer and the culture medium were isolated, quantified and characterized. Comparison of the PG core proteins synthesized by MC was carried out using Western blot analysis.

RESULTS

LDL stimulation led to a dose- and time-dependent increase in [(35)S]sulphate incorporation into PG in the culture medium and to a lesser extent in the cell layer. Analysis of the glycosaminoglycan (GAG) chains showed no difference in either their size or charge. Enzyme digestion studies demonstrated that the synthesis of both chondroitin sulphate PG (CSPG) and heparan sulphate PG (HSPG) was enhanced as was the production of the core proteins of versican (a large CSPG), perlecan (a basement membrane HSPG) and to a lesser extent decorin (a small dermatan sulphate PG (DSPG)). An increase in HA synthesis was also demonstrated in [(3)H]glucosamine labelled cells following LDL stimulation.

CONCLUSION

LDL selectively enhances the synthesis of specific PG and HA by mesangial cells. Such effects may contribute to the expansion of the mesangial matrix and modify cell-matrix interactions in lipid-induced renal damage.

Cell density-dependent regulation of proteoglycan synthesis by transforming growth factor-beta(1) in cultured bovine aortic endothelial cells

The regulation of vascular endothelial cell behavior during angiogenesis and in disease by transforming growth factor-beta(1) (TGF-beta(1)) is complex, but it clearly involves growth factor-induced changes in extracellular matrix synthesis. Proteoglycans (PGs) synthesized by endothelial cells contribute to the formation of the vascular extracellular matrix and also influence cellular proliferation and migration. Since the effects of TGF-beta(1) on vascular smooth muscle cell growth are dependent on cell density, it is possible that TGF-beta(1) also directs different patterns of PG synthesis in endothelial cells at different cell densities. In the present study, dense and sparse cultures of bovine aortic endothelial cells were metabolically labeled with [(3)H]glucosamine, [(35)S]sulfate, or (35)S-labeled amino acids in the presence of TGF-beta(1). The labeled PGs were characterized by DEAE-Sephacel ion exchange chromatography and Sepharose CL-4B molecular sieve chromatography. The glycosaminoglycan M(r) and composition were analyzed by Sepharose CL-6B chromatography, and the core protein M(r) was analyzed by SDS-polyacrylamide gel electrophoresis, before and after digestion with papain, heparitinase, or chondroitin ABC lyase. These experiments indicate that the effect of TGF-beta(1) on vascular endothelial cell PG synthesis is dependent on cell density. Specifically, TGF-beta(1) induced an accumulation of small chondroitin/dermatan sulfate PGs (CS/DSPGs) with core proteins of approximately 50 kDa in the medium of both dense and sparse cultures, but a cell layer-associated heparan sulfate PG with a core protein size of approximately 400 kDa accumulated only in dense cultures. Moreover, only in the dense cell cultures did TGF-beta(1) cause CS/DSPG hydrodynamic size to increase, which was due to the synthesis of CS/DSPGs with longer glycosaminoglycan chains. The heparan sulfate PG and CS/DSPG core proteins were identified as perlecan and biglycan, respectively, by Western blot analysis. The present data suggest that TGF-beta(1) promotes the synthesis of both perlecan and biglycan when endothelial cell density is high, whereas only biglycan synthesis is stimulated when the cell density is low. Furthermore, glycosaminoglycan chains are elongated only in biglycan synthesized by the cells at a high cell density.

Lipoprotein lipase enhances the binding of native and oxidized low density lipoproteins to versican and biglycan synthesized by cultured arterial smooth muscle cells

Retention of low density lipoproteins (LDL) by vascular proteoglycans and their subsequent oxidation are important in atherogenesis. Lipoprotein lipase (LPL) can bind LDL and proteoglycans, although the effect of different proteoglycans to influence the ability of LPL to act as a bridge in the formation of LDL-proteoglycan complexes is unknown. Using an electrophoretic gel mobility shift assay, [(35)S]SO(4)-labeled versican and biglycan, two extracellular proteoglycans secreted by vascular cells, bound native LDL in a saturable fashion. The addition of bovine milk LPL dose-dependently increased the binding of native LDL to both versican and biglycan, approaching saturation at 30-40 microgram/ml LPL for versican and 20 microgram/ml LPL for biglycan. LDL was oxidized by several methods, including copper, 2, 2-azo-bis(2-amidinopropane)-2HCl and hypochlorite. Extensively copper- and hypochlorite-oxidized LDL bound poorly to versican and biglycan. Proteoglycan binding to LDL was correlated inversely with the extent of LDL; however, the addition of LPL to oxidized LDL together with biglycan or versican allowed the oxidized LDL to bind the proteoglycans in an LPL dose-dependent manner. Addition of LPL had a greater relative effect on the binding of extensively oxidized LDL to proteoglycans compared with native LDL. LPL had a slightly greater effect on increasing the binding of native and oxidized LDL to biglycan than versican. Thus, LPL in the artery wall might increase the atherogenicity of oxidized LDL, since it enables its binding to vascular biglycan and versican.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Versican/PG-M isoforms in vascular smooth muscle cells

The expression of increased amounts of proteoglycans in the extracellular matrix may play a role in vascular stenosis and lipid retention. The large chondroitin sulfate proteoglycan versican is synthesized by vascular smooth muscle cells (SMCs), accumulates during human atherosclerosis and restenosis, and has been shown to bind LDLs. We recently demonstrated that adult rat aortic SMCs express several versican mRNAs. Four versican splice variants, V0, V1, V2, and V3, have recently been described, which differ dramatically in length. These variants differ in the extent of modification by glycosaminoglycan chains, and V3 may lack glycosaminoglycan chains. In this study, we characterized versican RNAs from rat SMCs by cloning, sequencing, and hybridization with domain-specific probes. DNA sequence was obtained for the V3 isoform, and for a truncated V0 isoform. By hybridization of polyadenylated RNA with domain-specific probes, we determined that the V0, V1, and V3 isoforms are present in vascular SMCs. We confirmed the presence of the V3 isoform in polyadenylated RNA and in RT-PCR products by hybridization with an oligonucleotide that spans the splice junction between the hyaluronan-binding domain and the epidermal growth factor-like domain. In addition, a novel splice variant was cloned by PCR amplification from both rat and human SMC RNA. This appears to be an incompletely spliced variant, retaining the final intron. PCR analysis shows that this intron can be retained in both V1 and V3 isoforms. The predicted translation product of this variant would have a different carboxy-terminus than previously described versican isoforms.

The sulfate moieties of glycosaminoglycans are critical for the enhancement of beta-amyloid protein fibril formation

Our previous studies have demonstrated that perlecan and perlecan-derived glycosaminoglycans (GAGs) not only bind beta-amyloid protein (Abeta) 1-40 and 1-42, but are also potent enhancers of Abeta fibril formation and stabilize amyloid fibrils once formed. However, it was not determined which moieties in perlecan heparan sulfate GAG chains may be responsible for the observed effects and whether other GAGs were also capable of a similar enhancement of Abeta fibril formation as observed with perlecan GAGs. In the present study, thioflavin T fluorometry (over a 1-week period) was used to extend our previous studies and to test the hypothesis that the sulfate moiety is critical for the enhancing effects of heparin/heparan sulfate GAGs on Abeta 1-40 fibrillogenesis. This hypothesis was confirmed when removal of all sulfates from heparin (i.e., completely desulfated N-acetylated heparin) led to a complete loss in the enhancement of Abeta fibrillogenesis as demonstrated in both thioflavin T fluorometry and Congo red staining studies. On the other hand, removal of O-sulfate from heparin (i.e., completely desulfated N-sulfated heparin), and to a lesser extent N-sulfate (i.e., N-desulfated N-acetylated heparin), resulted in only a partial loss of the enhancement of Abeta 1-40 fibril formation. These studies indicate that the sulfate moieties of GAGs are critical for enhancement of Abeta amyloid fibril formation. In addition, other sulfated molecules such as chondroitin-4-sulfate, dermatan sulfate, dextran sulfate, and pentosan polysulfate all significantly enhanced (greater than twofold by 3 days) Abeta amyloid fibril formation. These latter findings indicate that deposition and accumulation of other GAGs at sites of Abeta amyloid deposition in Alzheimer's disease brain may also participate in the enhancement of Abeta amyloidosis.

Formation of hyaluronan- and versican-rich pericellular matrix is required for proliferation and migration of vascular smooth muscle cells

The accumulation of hyaluronan (HA) and the HA-binding proteoglycan versican around smooth muscle cells in lesions of atherosclerosis suggests that together these molecules play an important role in the events of atherogenesis. In this study we have examined the formation of HA- and versican-rich pericellular matrices by human aortic smooth muscle cells in vitro, using a particle-exclusion assay, and the role of the pericellular matrix in cell proliferation and migration. The structural dependence of the pericellular matrix on HA can be demonstrated by the complete removal of the matrix with Streptomyces hyaluronidase. The presence of versican in the pericellular matrix was confirmed immunocytochemically. By electron microscopy, the cell coat was seen as a tangled network of hyaluronidase-sensitive filaments decorated with ruthenium red-positive proteoglycan granules. Ninety percent of migrating cells in wounded cultures, and virtually all mitotic cells, displayed abundant HA- and versican-rich coats. Time-lapse video imaging revealed that HA- and versican-rich pericellular matrix formation is dynamic and rapid, and coordinated specifically with cell detachment and mitotic cell rounding. HA oligosaccharides, which inhibit the binding of HA to the cell surface and prevent pericellular matrix formation, significantly reduced proliferation and migration in response to platelet-derived growth factor, whereas larger HA fragments and high molecular weight HA had no effect. Treatment with HA oligosaccharides also led to changes in cell shape from a typical fusiform morphology to a more spread and flattened appearance. These data suggest that organization of HA- and versican-rich pericellular matrices may facilitate migration and mitosis by diminishing cell surface adhesivity and affecting cell shape through steric exclusion and the viscous properties of HA proteoglycan gels.

Effect of hypoxia and hypoxia/reoxygenation on proteoglycan metabolism by vascular smooth muscle cells

Hypoxia and hypoxia/reoxygenation are known to affect vascular smooth muscle cell physiology. In this study, we first investigated proteoglycan synthesis by human aortic smooth muscle cells exposed to normoxia, hypoxia, or hypoxia/reoxygenation. We then compared the newly synthesized proteoglycans from normoxic and hypoxic-reoxygenation cultures for their ability to bind low density lipoprotein (LDL). Confluent smooth muscle cells under normoxia, hypoxia, or hypoxia/reoxygenation were pulsed with [35S]sulfate, and secreted and cell-associated proteoglycans were analyzed. Secreted proteoglycans in cultures exposed to hypoxia (4 h)/reoxygenation (19 h) increased 28% over those of cells continuously exposed to normoxia. Cell-associated proteoglycans did not differ significantly between the two groups. In contrast, hypoxia (4 h) followed by a 30-min reoxygenation produced a 37% decrease in newly synthesized proteoglycans. Hypoxia alone also resulted in a 24% decrease in secreted proteoglycans and a 20% decrease in cell-associated proteoglycans. Proteoglycans newly synthesized by smooth muscle cells exposed to normoxia and hypoxia/reoxygenation did not differ in their charge densities and molecular size but did differ in glycosaminoglycan composition. Exposure of smooth muscle cells to hypoxia/reoxygenation produced a 60% increase in a proteoglycan subfraction that bound LDL with very high affinity. The incorporation of [3H]leucine into total cellular protein decreased significantly following exposure of smooth muscle cells to hypoxia as well as hypoxia/reoxygenation. These results indicate that hypoxia and hypoxia/reoxygenation cause major alterations in proteoglycan metabolism by vascular smooth muscle cells.

Transcriptional and posttranscriptional regulation of proteoglycan gene expression

Proteoglycans are among the most complex and sophisticated molecules of mammalian systems in terms of their protein and carbohydrate moieties. These macromolecules are in a continuous interplay with each other and the cell surface signal-transducing pathways, some of which are beginning to be elucidated. Because of their domain structure, catalytic potential, and diversity, these molecules appear to be designed for integrating numerous signaling events. For example, some proteoglycans interact with hyaluronan and lectins, thereby linking cell surfaces and distant matrix molecules. Some interact with collagen during the complex process of fibrillogenesis and regulate this biological process fundamental to animal life. Others interact with growth factors and serve as depot available during growth or tissue remodeling. In this review, we center on the most recent developments of proteoglycan biology, focusing primarily on genomic organization and transcriptional and posttranscriptional control. We discuss only those proteoglycans whose gene and promoter elements have been characterized and proved to be functional. When possible, we correlate the effects of growth factors and cytokines on proteoglycan gene expression with the topology of cis-acting elements in their genomic control regions. The analysis leads to a comprehensive critical appraisal of the principles that underlie the regulation of proteoglycan gene expression and to the delineation of common regulatory mechanisms.

The soft tissue cover of the mandibular condyle. Differentiation in histological forms and age-related changes of aggrecan- and versican-like proteoglycans

Age-related changes of the composition of the extracellular matrix of the soft tissue cover of the mandibular condyle (STC), especially of the large proteoglycans, have been investigated. Proteoglycans were extracted from the STC of neonatal, juvenile and adult domestic pigs, fractionated by density gradient centrifugation and analyzed by electrophoresis/Western blotting. Experiments revealed firstly that a large CS/KS proteoglycan (aggrecan) is an essential constituent of the STC at all ages. This proteoglycan is required for nutrition of avascular tissues, and age-related changes in its average size and substitution with KS (keratan sulfate) may be a response to altered functional loading and tissue architecture of the STC. Secondly it was shown that a large CS/DS (chondroitin sulfate/dermatan sulfate) proteoglycan characterized by a doublet of core proteins at 200 and 250 kDa, thereby resembling perlecan, is present in the tissue of adults, but not of neonates and juveniles. Thirdly a large CS/DS proteoglycan characterized by core proteins at 350, 450 and 550 kDa, thereby resembling versican, was present in juveniles. It was detectable only weakly in neonates and not in adults. Results of core protein analysis were confirmed by results of agarose gel electrophoresis/Western blotting of the undigested proteoglycans isolated directly from the tissue extracts. Versican is believed to destabilize cell-matrix interactions required for cell proliferation and differentiation. In this context, presence of versican-like proteoglycans in the STC of growing individuals and its disappearance in adults appears to be related to the growth potential of the mandibular condyle.

Matrix proteoglycans: from molecular design to cellular function

The proteoglycan superfamily now contains more than 30 full-time molecules that fulfill a variety of biological functions. Proteoglycans act as tissue organizers, influence cell growth and the maturation of specialized tissues, play a role as biological filters and modulate growth-factor activities, regulate collagen fibrillogenesis and skin tensile strength, affect tumor cell growth and invasion, and influence corneal transparency and neurite outgrowth. Additional roles, derived from studies of mutant animals, indicate that certain proteoglycans are essential to life whereas others might be redundant. The review focuses on the most recent genetic and molecular biological studies of the matrix proteoglycans, broadly defined as proteoglycans secreted into the pericellular matrix. Special emphasis is placed on the molecular organization of the protein core, the utilization of protein modules, the gene structure and transcriptional control, and the functional roles of the various proteoglycans. When possible, proteoglycans have been grouped into distinct gene families and subfamilies offering a simplified nomenclature based on their protein core design. The structure-function relationship of some paradigmatic proteoglycans is discussed in depth and novel aspects of their biology are examined.

Pathogenesis of abdominal aortic aneurysms: possible role of differential production of proteoglycans by smooth muscle cells

PURPOSE

In vivo and in vitro observations strongly suggest that marked differences exist in the phenotype, growth, and matrix-producing capabilities of distinct smooth muscle cell subpopulations. An earlier study from our laboratory showed differences in matrix metalloproteinase expression patterns in cultures of medial smooth muscle cells from tissue affected by abdominal aortic aneurysm (AAA) or atherosclerotic occlusive disease and from normal arterial tissue. In this study we were interested in ascertaining whether smooth muscle cells from the same sample groups also synthesized different proteoglycan profiles that correlated with vascular disease.

METHODS

Proteoglycans from smooth muscle cell monolayer cultures from tissue affected by AAA or atherosclerotic occlusive disease and from normal arterial tissue were examined by means of immunoblotting and affinity-blotting composite agarose polyacrylamide gel electrophoresis (CAPAGE) and sodium dodecyl sulphate PAGE. Enzyme-linked immunosorbent assay (ELISA) was used to quantitate perlecan levels in smooth muscle cell monolayer media samples.

RESULTS

Versican, perlecan, and biglycan levels were significantly elevated in AAA smooth muscle cell cultures. Two populations of smooth muscle cell versican were identified by means of CAPAGE-immunoblotting and by means of a novel affinity-blotting technique with biotinylated hyaluronan. A small keratan sulfate-substituted proteoglycan was present in similar levels in all smooth muscle cell cultures. This proteoglycan had a free core protein of about 55 kd after keratanase digestion and had a relatively high charge-to-mass ratio, as was evident from its electrophoretic mobility in CAPAGE; this proteoglycan was tentatively identified as keratocan. Immunoblotting with monoclonal antibodies 3-G-10 (anti-delta heparan sulfate, heparan sulfate stubs generated by heparitinase treatment) and 10-E-4 (anti-native heparan sulfate chains) helped identify several smooth muscle cell heparan sulfate-substituted proteoglycans. Elevated levels of intact and processed perlecan core protein were identified in AAA cultures by means of immunoblotting with a monoclonal antibody to perlecan core protein (A76). ELISA measurements confirmed that perlecan levels were significantly higher in AAA smooth muscle cell cultures compared with the normal arterial tissue and tissue affected by atherosclerotic occlusive disease.

CONCLUSIONS

Because heparan sulfate proteoglycans can bind growth factors, their elevated synthesis by AAA smooth muscle cells in combination with an increased expression of matrix metalloproteinases may at least partly explain the differential proliferative capacity of the AAA smooth muscle cells examined and may govern the pattern of abnormal cellular proliferation and matrix protein synthesis observed in the pathogenesis of vascular disease.

Ozone alters the distribution of beta1 integrins in cultured primate bronchial epithelial cells

The effects of 0.5 ppm ozone exposure for 6 h on the synthesis and distribution of beta1 integrins were examined in bronchial epithelial cells cultured at an air-cell interface. Ozone exposure damaged cilia and caused significant cell loss. Immunocytochemical localization and quantification of the beta1 subunit in the remaining attached cells using scanning laser cytometry demonstrated time-dependent changes in beta1 distribution in response to ozone. Although no changes were detected immediately after exposure, beta1 immunoreactivity increased 23 +/- 5% and 66 +/- 6% at 6 and 24 h, respectively. The increased immunostaining was localized at the apical surfaces and, to a lesser extent, at cell-cell contacts of cultured cells. Furthermore, integrin redistribution was not due to increased messenger RNA (mRNA) levels and protein synthesis because levels of beta1 mRNA and newly synthesized beta1 protein did not change after ozone exposure. However, immunoprecipitation analysis of beta1 integrins in lysates from equal numbers of cells showed that ozone-exposed cells contained 90 +/- 15% more total beta1 subunit at 24 h after exposure. In addition, our results demonstrated the presence of the alpha5beta1 integrin complex in bronchial epithelial cells and that the detergent-soluble amount of its associated beta1 subunit increased 60 +/- 10% in lysates of ozone-exposed cells. In conclusion, ozone altered cellular distribution of beta1 integrins in the remaining attached cells subsequent to cell injury and loss. The changes in beta1 distribution might be due to increased detergent extractibility of beta1 integrins rather than a real increase in the synthesis of beta1 integrins.

Association of apo B lipoproteins with arterial proteoglycans: pathological significance and molecular basis

Retention of apo B-100 lipoproteins, low density lipoprotein (LDL) and probably lipoprotein(a), Lp(a), by intima proteoglycans (PGs) appears to increase the residence time needed for their structural, hydrolytic and oxidative modifications. If the rate of LDL entry exceeds the tissue capacity to eliminate the modified products, this process may be a contributor to atherogenesis and lesion advancement. LDL binds to PGs of the intima, by association of specific positive segments of the apo B-100 with the negatively-charged glycosaminoglycans (GAGs) made of chondroitin sulfate (CS), dermatan sulfate (DS) and probably heparan sulfate (HS). Small, dense LDL has a higher affinity for CS-PGs than large buoyant particles, probably because they expose more of the segments binding the GAGs than larger LDL. PGs cause irreversible structural alterations of LDL that potentiate hydrolytic and oxidative modifications. These alterations also increase LDL uptake by macrophages and smooth muscle cells. These in vitro data suggest that part of the atherogenicity of LDL may depend on its tendency to form complexes with arterial PGs in vivo. Ex vivo results support this hypothesis. Subjects with coronary heart disease have LDL with significantly higher affinity for arterial PGs. This is also a characteristic of subjects with the atherogenic lipoprotein phenotype, with high levels of small, dense LDL. The LDL-PG affinity, however can be modified by dietary or pharmacological interventions that change the composition and size of LDL. Lesion-prone intima contain PGs with a high affinity for LDL. Increased LDL entrapment at these sites may be a key step in a cyclic atherogenic process.

Human chondroitin 6-sulfotransferase: cloning, gene structure, and chromosomal localization

Chondroitin 6-sulfotransferase (C6ST) is the key enzyme in the biosynthesis of chondroitin 6-sulfate, a glycosaminoglycan implicated in chondrogenesis, neoplasia, atherosclerosis, and other processes. C6ST catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to carbon 6 of the N-acetylgalactosamine residues of chondroitin. Based on the previously published avian sequence, we searched the database of expressed sequence tags (dbEST) and obtained partial-length cDNAs that we completed by 5'-RACE using human chondrosarcoma and endothelial-cell RNA as template. Stable transfection of our full-length expression construct into CHO-K1 cells resulted in marked increases in C6ST and keratan sulfate sulfotransferase (KSST) enzymatic activities in cell homogenates. The predicted 411 amino acid sequence of human C6ST contains an N-terminal hydrophobic domain consistent with membrane insertion, four potential sites for N-linked glycosylation, several consensus sequences for protein phosphorylation, and one RGD sequence. The human and chick C6ST cDNA share 51% nucleotide identity, 40% amino acyl identity, and 75% amino acyl conservation. The human C6ST gene structure has been elucidated and exhibits an intron-less coding region, and the gene has been mapped to human chromosome 11 by radiation hybrid panel mapping.

Human monocyte-derived macrophages secrete two forms of proteoglycan-macrophage colony-stimulating factor that differ in their ability to bind low density lipoproteins

This study evaluated whether human monocyte-derived macrophages synthesize specific types of proteoglycans with lipoprotein-binding capability that could contribute to lipid retention in the arterial wall. After labeling with either [35S]SO4 or [35S]methionine, macrophages secreted a high molecular mass proteoglycan, with glycosaminoglycan chains of approximately 18 kDa and core protein bands of approximately 100 and 55 kDa. Both core protein bands were recognized by an antibody to PG-100, an antibody that recognizes the proteoglycan form of macrophage colony-stimulating factor (PG-100/PG-MCSF). The interaction between PG-100/PG-MCSF and low density lipoproteins (LDL) was examined by gel mobility shift. In this system, PG-100/PG-MCSF was resolved further into two forms. The two forms had the same core proteins but differed in their overall size and glycosaminoglycan content. The larger form contained glycosaminoglycan chains that were entirely chondroitin ABC lyase-sensitive, whereas the smaller form contained chains that were sensitive to both chondroitin ABC lyase and heparinase. Both forms bound native LDL with high affinity, but the larger form bound LDL with higher affinity than the smaller form. The glycosaminoglycan chains of PG-100/PG-MCSF, but not the core proteins, were responsible for binding to native LDL. Mildly oxidized LDL and methyl-LDL, which have an electrophoretic charge similar to that of native LDL, also bound PG-100/PG-MCSF. In contrast, extensively oxidized LDL and acetyl-LDL, which are more electronegative than native LDL, did not bind to either form of PG-100/PG-MCSF. The demonstration of two forms of human monocyte-derived macrophage PG-100/PG-MCSF which bind LDL may represent an additional role for macrophages in the extracellular trapping of lipoproteins in atherosclerosis.

Matrix protein mRNA levels in canine meniscus cells in vitro

The resident cells of the meniscus synthesize a fibrocartilaginous extracellular matrix in vivo composed predominantly of type I collagen fibers. To increase our understanding of matrix biosynthesis by meniscus cells in vitro, we examined matrix protein mRNA levels in cultured meniscus cells isolated from skeletally mature dogs. The mRNA levels of five matrix protein genes (COL1A1, COL2A1, aggrecan, COL6A1, and fibronectin) were measured in meniscus cells by Northern blotting and compared with those of patellar tendon fibroblasts and femoral articular cartilage chondrocytes. In freshly isolated cells (Day 0 cells), COL1A1, COL2A1, and aggrecan mRNA levels were low or undetectable in both meniscus cells and tendon fibroblasts. In intact meniscus tissue, COL1A1 mRNA levels were also low or undetectable. COL2A1 and aggrecan mRNA transcripts were readily observed, however, in Day 0 articular chondrocytes. The levels of expression of COL6A1 and fibronectin mRNA transcripts in Day 0 meniscus cells were intermediate between higher articular chondrocyte levels and lower tendon fibroblast levels. After 1 week in monolayer culture (Day 7 cells), meniscus cells expressed readily detectable levels of COL1A1 mRNA transcripts, similar to that observed for cultured tendon fibroblasts. COL1A1 mRNA transcripts were either not detected or detected at very low levels in monolayer cultures of articular chondrocytes. COL2A1 and aggrecan mRNA transcripts were readily detected in cultured articular chondrocytes but not in meniscus cells or in tendon fibroblasts. All three types of cells continued to express COL6A1 and fibronectin mRNA transcripts after 1 week in culture. These results demonstrate that the patterns of expression of COL1A1 and COL2A1 mRNA transcripts by meniscus cells are similar to those of tendon fibroblasts and dissimilar to those of articular chondrocytes both in freshly isolated cells and in monolayer cultured cells. This mRNA expression pattern supports the idea that monolayer culture of meniscus cells results in the expression of a predominantly fibroblastic phenotype.

Age-related changes in populations of aortic glycosaminoglycans: species with low affinity for plasma low-density lipoproteins, and not species with high affinity, are preferentially affected

Glycosaminoglycans were extracted from the intima and media layers of normal human thoracic aortas from donors of different ages. The arterial segments were devoid of macroscopically visible lesions obtained from patients who had no clinically evident cardiovascular disease. Total glycosaminoglycan content increases during the first 40 years of life. Changes in the content of hyaluronic acid and heparan sulfate are less noticeable. The content of chondroitin sulfate (mainly the 6-isomer) increases, whereas dermatan sulfate remains constant. Plasma LDL-affinity chromatography of dermatan sulfate+chondroitin 4/6-sulfate fractions allowed the separation of LDL high- and low-affinity glycosaminoglycan species. Remarkably, only glycosaminoglycan species with low affinity for plasma LDL increase with age in the disease-free areas of human thoracic aortas studied. These results suggest that age-related changes in glycosaminoglycan composition of the arterial wall do not contribute to increased deposition of plasma LDL. However, the alternative explanation that individuals with arterial glycosaminoglycans that avidly bind LDL would develop early and severe cardiovascular disease and would thus be excluded from our analysis cannot be ruled out.

Growth factor modulation of mitogenic responses and proteoglycan synthesis by human periodontal fibroblasts

In order to understand the relationship between specific growth factors and matrix synthesis by periodontal cells, we have investigated the effects of platelet-derived growth factor BB (PDGF-BB), insulin-like growth factor-I (IGF-1), and growth hormone on DNA and proteoglycan synthesis by cultured human gingival and periodontal ligament fibroblasts in vitro. PDGF-BB and IGF-1, but not growth hormone, were mitogenic for both periodontal ligament fibroblasts and gingival fibroblasts, although the periodontal ligament cells responded more strongly. The mitogenic response was accompanied by alterations in expression of matrix proteoglycan mRNA. For both the gingival and periodontal ligament cells, there was a decrease in mRNA for decorin and an increase in mRNA for versican following exposure to IGF-1 and PDGF-BB. Although no change was seen in response to PDGF, biglycan mRNA level was increased by IGF-1 in periodontal ligament fibroblasts. With the gingival fibroblasts, biglycan mRNA levels were unaffected by IGF-1, PDGF-BB, or growth hormone. These findings suggest variable responses of fibroblasts to growth factors depending upon anatomical site within the periodontium. Moreover, there appears to be a correlation between cell proliferation and the types of proteoglycan synthesised with decorin expression being suppressed, and versican being increased during fibroblast proliferation.

Elevated expression of proteoglycans in proliferating vascular smooth muscle cells

Smooth muscle cell (SMC) proliferation and increased production of arterial wall proteoglycans (PG) are implicated in atherogenesis. We investigated the effect of SMC proliferation on the biosynthesis of PG and the ability of the newly synthesized PG to bind low density lipoprotein (LDL). Proliferating and quiescent human aortic SMC were pulsed with [35S]sulfate for 24 h. Secreted and cell-associated PG were then analyzed. When SMC plated at a low density were induced to proliferate, PG synthesis increased significantly in comparison with quiescent cells. This was the net result of a 2.7-fold increase in secreted PG and a 1.3-fold increase in cell-associated PG. The increased PG synthesis in proliferating SMC correlated with a significant increase in the steady-state level of mRNA for perlecan and biglycan, and a modest increase in the versican-specific mRNA. The mRNA for decorin showed a 40% decrease. The increased PG secretion in proliferating cultures was due to increases in heparan sulfate PG, dermatan sulfate PG, and chondroitin sulfate PG secretion. Quiescent SMC at confluency produced 50% less PG than the corresponding SMC plated at a low density. Although confluent SMC stimulated to proliferate also had increased PG synthesis, this was 50% less than the PG synthesis by proliferating SMC that were initially plated at a low density. The PG synthesized by proliferating and quiescent SMC did not differ in charge density and molecular size. Secreted PG from both quiescent and proliferating cultures contained subfractions that bound LDL with high affinity. However, compared with quiescent cultures, the proliferating cultures produced more of a PG subfraction that exhibited very high affinity to LDL (31.6% in quiescent cultures versus 40.8% in proliferating cultures). These results indicate that PG metabolism is altered significantly in proliferating human SMC which might have implications in the pathophysiology of atherosclerosis.

Identification, partial characterization, and distribution of versican and link protein in bovine dental pulp

The dynamics of changes in the cellularity and extracellular matrix composition of dental pulp varies considerably during tooth development and maturation. In this paper, we studied matrix proteoglycans where we hypothesized that they played important roles in structural, spatial, and transport aspects of pulpal development and maintenance. The pulpal tissue was collected from partially erupted bovine incisors, pulverized, and then extracted with 6 M guanidine-HCl. The extract was subjected to anion column chromatography (DEAE-8HR), and the fractions collected were screened by dot-blot immunoassay by means of monoclonal antibodies generated against 4- and 6-sulfated chondroitin sulfate isomers, and keratan sulfate, 2-B-6, 3-B-3, and 5-D-4, respectively. The chondroitin-6-sulfate was the major glycosaminoglycan species and occurred as a large-molecular-weight proteoglycan (> 500 kDa). After further purification, it was subjected to agarose/acrylamide composite gel electrophoresis, and it migrated as a single band stained with Stains-All. The band was immunopositive against antibody 3-B-3 by Western blot analysis. The partial amino acid sequence analyses of the core protein clearly indicated this molecule to be versican. The presence of link protein was also confirmed by Western blot analysis with an anti-link protein monoclonal antibody, 8-A-4. Furthermore, immunohistochemical study indicated that the distributions of versican and link protein coincide in the dental pulp and are enriched in the peripheral area of the tissue just beneath the odontoblast layer. Since the dental pulp contains hyaluronan, versican may bind to hyaluronan via its hyaluronan-binding domain, where this association is stabilized by link protein. This complex, then, could form large hydrated proteoglycan aggregates that fill the extracellular space, support odontoblasts, and/or facilitate the transport function of metabolites and nutrients within the tissue.

Cellular consequences of the association of apoB lipoproteins with proteoglycans. Potential contribution to atherogenesis

Many of the discussed results come from empirical experiments performed with in vitro models whose relevance to the complex environment of the intima is limited. However, they are consistent with the line of reasoning that intima PGs interact specifically with apoB lipoproteins and contribute to their retention. This could provide the residence time and the initial alterations of the lipoproteins that favor their further modifications by oxidative processes and hydrolytic enzymes. Products of such modifications, and the modified particles, may be stimuli for changes in the functionality of endothelium, smooth muscle cells, and macrophages. The focal synthesis of PGs with high affinity for apoB lipoproteins could make the phenomena chronic. Clinical and laboratory studies indicate that dense LDL, poor in surface polar lipids, is associated with an atherogenic phenotype. Particles with these properties may contribute to the disease via its high affinity for arterial PGs. This affinity can be modulated by diet, lifestyle, and lipid-lowering drugs.