Matricellular hevin regulates decorin production and collagen assembly

Matricellular proteins such as SPARC, thrombospondin 1 and 2, and tenascin C and X subserve important functions in extracellular matrix synthesis and cellular adhesion to extracellular matrix. By virtue of its reported interaction with collagen I and deadhesive activity on cells, we hypothesized that hevin, a member of the SPARC gene family, regulates dermal extracellular matrix and collagen fibril formation. We present evidence for an altered collagen matrix and levels of the proteoglycan decorin in the normal dermis and dermal wound bed of hevin-null mice. The dermal elastic modulus was also enhanced in hevin-null animals. The levels of decorin protein secreted by hevin-null dermal fibroblasts were increased by exogenous hevin in vitro, data indicating that hevin might regulate both decorin and collagen fibrillogenesis. We also report a decorin-independent function for hevin in collagen fibrillogenesis. In vitro fibrillogenesis assays indicated that hevin enhanced fibril formation kinetics. Furthermore, cell adhesion assays indicated that cells adhered differently to collagen fibrils formed in the presence of hevin. Our observations support the capacity of hevin to modulate the structure of dermal extracellular matrix, specifically by its regulation of decorin levels and collagen fibril assembly.

A role for decorin in cutaneous wound healing and angiogenesis

Decorin is known to influence tissue tensile strength and cellular phenotype. Therefore, decorin is likely to have an impact on tissue repair, including cutaneous wound healing. In this study, cutaneous healing of both excisional and incisional full-thickness dermal wounds was studied in decorin-deficient (Dcn(-/-)) animals. A statistically significant delay in excisional wound healing in the Dcn(-/-) mice occurred at 4 and 10 days postwounding and, in incisional wounds at 4, 10, and 18 days when compared with wild-type (Dcn(-/-)) controls. Fibrovascular invasion into polyvinylalcohol sponges was significantly increased by day 18 in Dcn(-/-) mice relative to Dcn(+/+) mice. The 18-day sponge implants in the Dcn(-/-) mice showed a marked accumulation of biglycan when compared with the corresponding implants in Dcn(+/+) mice. Thus, regulated production of decorin may serve as an excellent therapeutic approach for modifying impaired wound healing and harmful foreign body reactions.

Overexpression of hyaluronan synthases alters vascular smooth muscle cell phenotype and promotes monocyte adhesion

Hyaluronan (HA) accumulates in vascular disease but its functional role is not fully understood. To investigate the impact of HA enriched extracellular matrices (ECM) on cell phenotype, arterial smooth muscle cells (ASMCs) were transduced with retroviral constructs (LXSN) encoding murine has-1, has-2, and has-3. HA synthesis was significantly elevated in has transduced ASMCs. Metabolically labeled HA from has-1 and has-2 transduced cells was present mostly in high molecular weight (HWA) fractions (2-10x10(6) Da), whereas HA produced by has-3 and control cells was present in lower molecular weight fractions (approximately 2x10(6) Da). Both has-1 and has-3 transduced ASMCs accumulated more pericellular HA than has-2 transduced ASMCs. All has transduced ASMCs had attenuated growth and migration rates, and a decreased detachment response. Affinity histochemistry revealed that has-1 transduced ASMCs accumulated the greatest amount of HA containing ECM than the other transduced ASMCs. This ECM was hyaluronidase sensitive and bound a significantly greater number of monocytes than the ECM generated by has-2 or has-3 transduced ASMCs. Confocal microscopy showed CD44 positive monocytes bound to hyaluronidase sensitive ECM in has-1 transduced ASMCs. These data implicate specific has isoforms in the formation of HA enriched pro-inflammatory ECMs.

Progressive vascular smooth muscle cell defects in a mouse model of Hutchinson-Gilford progeria syndrome

Children with Hutchinson-Gilford progeria syndrome (HGPS) suffer from dramatic acceleration of some symptoms associated with normal aging, most notably cardiovascular disease that eventually leads to death from myocardial infarction and/or stroke usually in their second decade of life. For the vast majority of cases, a de novo point mutation in the lamin A (LMNA) gene is the cause of HGPS. This missense mutation creates a cryptic splice donor site that produces a mutant lamin A protein, termed "progerin," which carries a 50-aa deletion near its C terminus. We have created a mouse model for progeria by generating transgenics carrying a human bacterial artificial chromosome that harbors the common HGPS mutation. These mice develop progressive loss of vascular smooth muscle cells in the medial layer of large arteries, in a pattern very similar to that seen in children with HGPS. This mouse model should prove valuable for testing experimental therapies for this devastating disorder and for exploring cardiovascular disease in general.

Human tissue-engineered blood vessels for adult arterial revascularization

There is a crucial need for alternatives to native vein or artery for vascular surgery. The clinical efficacy of synthetic, allogeneic or xenogeneic vessels has been limited by thrombosis, rejection, chronic inflammation and poor mechanical properties. Using adult human fibroblasts extracted from skin biopsies harvested from individuals with advanced cardiovascular disease, we constructed tissue-engineered blood vessels (TEBVs) that serve as arterial bypass grafts in long-term animal models. These TEBVs have mechanical properties similar to human blood vessels, without relying upon synthetic or exogenous scaffolding. The TEBVs are antithrombogenic and mechanically stable for 8 months in vivo. Histological analysis showed complete tissue integration and formation of vasa vasorum. The endothelium was confluent and positive for von Willebrand factor. A smooth muscle-specific alpha-actin-positive cell population developed within the TEBV, suggesting regeneration of a vascular media. Electron microscopy showed an endothelial basement membrane, elastogenesis and a complex collagen network. These results indicate that a completely biological and clinically relevant TEBV can be assembled exclusively from an individual's own cells.

Inhibition of versican synthesis by antisense alters smooth muscle cell phenotype and induces elastic fiber formation in vitro and in neointima after vessel injury

The proteoglycan versican is implicated in several atherogenic events, including stimulation of vascular smooth muscle cell (VSMC) growth and migration, retention of lipoproteins, and promotion of thrombogenesis. A high content of intimal versican also correlates with a low content of elastin, suggesting an inhibitory role for versican in elastogenesis. To determine whether reduced production of versican can be used to enhance elastogenesis, we transduced Fischer rat VSMC (FRSMC) with a versican antisense sequence using the retroviral vector LXSN. Stable expression of versican antisense (LVaSN) significantly reduced versican production, induced a flattened morphology, reduced cell proliferation and migration, increased tropoelastin synthesis, increased elastin binding protein (S-Gal/EBP), and increased deposition of elastic fibers in long-term cultures. Add-back of chondroitin sulfate chains, or versican, decreased S-Gal/EBP and elastic fiber formation. LVaSN cells seeded into balloon catheter-injured rat carotid arteries formed neointimae containing low levels versican, increased amounts of S-Gal/EBP, and increased elastin deposits 7 days postinjury. At 4 weeks, neointimae formed from LVaSN cells were highly structured and contained multiple layers of elastic fibers and lamellae. These results indicate a central role for versican and its constituent chondroitin sulfate chains in controlling cell phenotype, elastogenesis, and intimal structure.

Transforming growth factor beta 1 induces neointima formation through plasminogen activator inhibitor-1-dependent pathways

OBJECTIVE

The mechanisms through which transforming growth factor (TGF)-beta1 promotes intimal growth, and the pathways through which TGF-beta1 expression is regulated in the artery wall, are incompletely understood. We used a mouse model to investigate mechanisms of TGF-beta1-induced intimal growth.

METHODS AND RESULTS

Adenovirus-mediated overexpression of TGF-beta1 in uninjured carotid arteries of wild-type mice induced formation of a cellular and matrix-rich intima. Intimal growth appeared primarily due to cell migration and matrix accumulation, with only a negligible contribution from cell proliferation. Overexpression of TGF-beta1 also stimulated expression of plasminogen activator inhibitor type 1 (plasminogen activator inhibitor [PAI]-1) in the artery wall. To test the hypothesis that PAI-1 is a critical downstream mediator of TGF-beta1-induced intimal growth, we transduced carotid arteries of PAI-1-deficient (Serpine1(-/-)) mice with the TGF-beta1-expressing vector. Overexpression of TGF-beta1 in Serpine1(-/-) arteries did not increase intimal growth, matrix accumulation, cell migration, or proliferation. Moreover, TGF-beta1-transduced arteries of Serpine1(-/-) mice secreted 6- to 10-fold more TGF-beta1 than did arteries of wild-type mice that were infused with the same concentration of the TGF-beta1-expressing vector.

CONCLUSIONS

PAI-1 is both a critical mediator of TGF-beta1-induced intimal growth and a key negative regulator of TGF-beta1 expression in the artery wall.

Antioxidants inhibit the ability of lysophosphatidylcholine to regulate proteoglycan synthesis

OBJECTIVE

We previously have shown that lysophosphatidylcholine (lysoPC) regulates proteoglycan synthesis by vascular smooth muscle cells (SMCs). Given the accumulating evidence for reactive oxygen species (ROS) as mediators of a variety of effects of lysoPC, the present study evaluates the potential role of ROS as intermediate molecules in the regulation of proteoglycan synthesis by lysoPC.

METHODS AND RESULTS

LysoPC (10 micromol/L) was found to stimulate rapid and sustained generation of ROS by SMC, as indicated using a fluorescent probe for measuring intracellular oxidants and fluorescence-activated cell sorting. This was not associated with cytotoxicity, as evaluated by fluorescence microscopy using MitoTracker Red or propidium iodide, cell number, cell protein, or lactate dehydrogenase release. Pretreatment with catalase or superoxide dismutase, specific scavengers of hydrogen peroxide and superoxide, respectively, blocked the ability of lysoPC to stimulate both accumulation of ROS and proteoglycan synthesis. Most importantly, these enzymatic antioxidants prevented lysoPC from stimulating the synthesis of proteoglycans with enhanced lipoprotein-binding properties, as quantified by a gel shift binding assay.

CONCLUSIONS

These findings strongly suggest that ROS are key mediators in the ability of lysoPC to regulate proteoglycan synthesis and that these effects can be inhibited by antioxidants.

Maintenance of chondroitin sulfation balance by chondroitin-4-sulfotransferase 1 is required for chondrocyte development and growth factor signaling during cartilage morphogenesis

Glycosaminoglycans (GAGs) such as heparan sulfate and chondroitin sulfate are polysaccharide chains that are attached to core proteins to form proteoglycans. The biosynthesis of GAGs is a multistep process that includes the attachment of sulfate groups to specific positions of the polysaccharide chains by sulfotransferases. Heparan-sulfate and heparan sulfate-sulfotransferases play important roles in growth factor signaling and animal development. However, the biological importance of chondroitin sulfation during mammalian development and growth factor signaling is poorly understood. We show that a gene trap mutation in the BMP-induced chondroitin-4-sulfotransferase 1 (C4st1) gene (also called carbohydrate sulfotransferase 11 - Chst11), which encodes an enzyme specific for the transfer of sulfate groups to the 4-O-position in chondroitin, causes severe chondrodysplasia characterized by a disorganized cartilage growth plate as well as specific alterations in the orientation of chondrocyte columns. This phenotype is associated with a chondroitin sulfation imbalance, mislocalization of chondroitin sulfate in the growth plate and an imbalance of apoptotic signals. Analysis of several growth factor signaling pathways that are important in cartilage growth plate development showed that the C4st1(gt/gt) mutation led to strong upregulation of TGFbeta signaling with concomitant downregulation of BMP signaling, while Indian hedgehog (Ihh) signaling was unaffected. These results show that chondroitin 4-O-sulfation by C4st1 is required for proper chondroitin sulfate localization, modulation of distinct signaling pathways and cartilage growth plate morphogenesis. Our study demonstrates an important biological role of differential chondroitin sulfation in mammalian development.

SPARC-thrombospondin-2-double-null mice exhibit enhanced cutaneous wound healing and increased fibrovascular invasion of subcutaneous polyvinyl alcohol sponges

Secreted protein acidic and rich in cysteine (SPARC) and thrombospondin-2 (TSP-2) are structurally unrelated matricellular proteins that have important roles in cell-extracellular matrix (ECM) interactions and tissue repair. SPARC-null mice exhibit accelerated wound closure, and TSP-2-null mice show an overall enhancement in wound healing. To assess potential compensation of one protein for the other, we examined cutaneous wound healing and fibrovascular invasion of subcutaneous sponges in SPARC-TSP-2 (ST) double-null and wild-type (WT) mice. Epidermal closure of cutaneous wounds was found to occur significantly faster in ST-double-null mice, compared with WT animals: histological analysis of dermal wound repair revealed significantly more mature phases of healing at 1, 4, 7, 10, and 14 days after wounding, and electron microscopy showed disrupted ECM at 14 days in these mice. ST-double-null dermal fibroblasts displayed accelerated migration, relative to WT fibroblasts, in a wounding assay in vitro, as well as enhanced contraction of native collagen gels. Zymography indicated that fibroblasts from ST-double-null mice also produced higher levels of matrix metalloproteinase (MMP)-2. These data are consistent with the increased fibrovascular invasion of subcutaneous sponge implants seen in the double-null mice. The generally accelerated wound healing of ST-double-null mice reflects that described for the single-null animals. Importantly, the absence of both proteins results in elevated MMP-2 levels. SPARC and TSP-2 therefore perform similar functions in the regulation of cutaneous wound healing, but fine-tuning with respect to ECM production and remodeling could account for the enhanced response seen in ST-double-null mice.

Microgrooved fibrillar collagen membranes as scaffolds for cell support and alignment

For several years, microgrooved substrates have been evaluated as a means to orient cells in engineered tissues. Recently, we fabricated thin (0.1-5.3 microm) planar and tubular collagen membranes (CMs) from air-dried hydrogels of native, fibrillar type I collagen (Vernon et al., Biomaterials 2004;26:1109-17). The CMs were strong, stable, and permeable and, hence, of potential use as scaffolds for tissue engineering. In the present study, planar CMs supported a robust attachment, spreading, and proliferation of human dermal fibroblasts (HDFs) and human umbilical artery smooth muscle cells (HUASMCs). Collagen hydrogels were air-dried onto microgrooved templates and subsequently removed in the form of grooved CMs with the potential to align cells. The grooved CMs were highly effective at inducing HDFs and HUASMCs to elongate and align, as revealed by scanning electron microscopy and by assays of f-actin and nuclear orientation. Alignment of cells was maintained at high cell densities. CMs with grooves of substantially different widths and depths were similarly effective in causing cell alignment; however, cells aligned poorly on CMs that had grooves less than 1 microm in depth. Grooved CMs with the capability to align cells might be of considerable use in the fabrication of tissue substitutes.

Native fibrillar collagen membranes of micron-scale and submicron thicknesses for cell support and perfusion

Fibrillar type I collagen is nontoxic, biocompatible, and possesses considerable strength and stability. In a study of scaffolds for use in laminated tissue substitutes, we examined the properties of membranes made from air-dried hydrogels of collagen fibrils that were polymerized from native, monomeric collagen. Planar collagen membranes (CMs) of 0.1-5.3 microm dry thickness were made by variation of the collagen concentration and/or the volume of the hydrogel. The planar CMs, which were comprised of a dense feltwork of long collagen fibrils 70-100 nm in diameter, showed considerable resistance to rupture and retained their membranous character after 6 weeks in tissue culture medium at 37 degrees C. CMs that were relatively thick when dry exhibited a greater proportional increase in rehydrated thickness and a greater diffusivity (when rehydrated) to 4.3 kDa dextran than did CMs that were relatively thin when dry. Hollow, tubular CMs of several configurations were prepared by embedment of solid, removable forms into collagen hydrogels prior to drying. By use of special fixtures, a planar CM that incorporated multiple, parallel tubes was fabricated. In summary, hydrogels of fibrillar collagen can be transformed into membranous structures suitable for tissue engineering applications.

Characterization of chondroitin/dermatan sulfate proteoglycans synthesized by bovine retinal pericytes in culture

Pericytes associate with the outside of endothelial cells in microvessels. Previous studies have shown that these cells synthesize glycosaminoglycans (GAGs) but the nature of the core proteins to which these GAGs are attached is unknown. In the present study, cultured bovine retinal pericytes were metabolically labeled with [(3)H]glucosamine, [(35)S]sodium sulfate or (35)S-labeled amino acids and the proteoglycans synthesized by these cells were purified by DEAE-Sephacel ion exchange and molecular sieve Sepharose CL-4B chromatography. Separated proteoglycans were digested with papain, heparitinase or chondroitin ABC lyase and the GAGs characterized by Sepharose CL-6B chromatography. Proteoglycans were also assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis before and after digestion with chondroitin ABC lyase. Pericytes predominantly synthesize and secrete chondroitin or dermatan sulfate proteoglycans (CS/DS PGs) rather than heparan sulfate proteoglycans (HSPGs). Two subclasses of CS/DS PGs are synthesized by pericytes; one is a high M(r) subclass with high charge density. This subclass eluted at the void volume of a Sepharose CL-4B molecular sieve column, was susceptible to chondroitin ABC lyase, and contained core proteins of ca. 550 and 450 kD which were recognized by antibody to versican. The other major subclass eluted at a K(av) ca. 0.45 on a Sepharose CL-4B molecular sieve column, was susceptible to chondroitin ABC lyase, and contained core proteins recognized by antibodies to either biglycan or decorin that separated as a broad band of ca. 50 kDa in SDS-PAGE. A small amount of HSPG was also synthesized by these cells and could be separated from the CS/DS PGs by DEAE-Sephacel chromatography using a linear gradient of 0.1-0.7 M NaCl. Release of GAG chains by protease digestion indicated that the length of GAG chains was approximately M(r) 45000 in biglycan and decorin, approximately M(r) 48000 in the small amount of HSPGs and approximately M(r) 66000 in versican. These proteoglycans resemble those synthesized by vascular smooth muscle cells but differ markedly from those synthesized by vascular endothelial cells.

Serum Amyloid A and Lipoprotein Retention in Murine Models of Atherosclerosis

Objective— Elevated serum amyloid A (SAA) levels are associated with increased cardiovascular risk in humans. Because SAA associates primarily with lipoproteins in plasma and has proteoglycan binding domains, we postulated that SAA might mediate lipoprotein retention on atherosclerotic extracellular matrix.

Methods and Results— Immunohistochemistry was performed for SAA, apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), and perlecan on proximal aortic lesions from chow-fed low-density lipoprotein receptor (LDLR) −/− and apoE −/− mice euthanized at 10, 50, and 70 weeks. SAA was detected on atherosclerotic lesion extracellular matrix at all time points in both strains. SAA area correlated highly with lesion areas (apoE −/− , r =0.76; LDLR −/− , r =0.86), apoA-I areas (apoE −/− , r =0.88; LDLR −/− , r =0.80), apoB areas (apoE −/− , r =0.74; LDLR −/− , r =0.89), and perlecan areas (apoE −/− , r =0.83; LDLR −/− , r =0.79) (all P <0.0001). In vitro, SAA enrichment increased high-density lipoprotein (HDL) binding to heparan sulfate proteoglycans, and immunoprecipitation experiments using plasma from apoE −/− and LDLR −/− mice demonstrated that SAA was present on both apoA-I–containing and apoB-containing lipoproteins.

Conclusions— In chow-fed apoE −/− and LDLR −/− mice, SAA is deposited in murine atherosclerosis at all stages of lesion development, and SAA immunoreactive area correlates highly with lesion area, apoA-I area, apoB area, and perlecan area. These findings are consistent with a possible role for SAA-mediated lipoprotein retention in atherosclerosis.

Smooth muscle cell biglycan overexpression results in increased lipoprotein retention on extracellular matrix: implications for the retention of lipoproteins in atherosclerosis

Lipoprotein retention on extracellular matrix (ECM) may play a central role in atherogenesis, and a specific extracellular matrix proteoglycan, biglycan, has been implicated in lipoprotein retention in human atherosclerosis. To test whether increased cellular biglycan expression results in increased retention of lipoproteins on ECM, rat aortic smooth muscle cells (SMCs) were transduced with a human biglycan cDNA-containing retroviral vector (LBSN) or with an empty retroviral vector (LXSN). To assess the importance of biglycan's glycosaminoglycan side chains in lipoprotein retention, ECM binding studies were also performed using RASMCs transduced with a retroviral vector encoding for a mutant, glycosaminoglycan-deficient biglycan (LBmutSN). Human biglycan mRNA and protein were confirmed in LBSN and LBmutSN RASMCs by Northern and Western blot analyses. HDL3+E binding to SMC ECM was increased significantly (as determined by 95% confidence intervals for binding curves) for LBSN as compared to either LXSN or LBmutSN cells; the increases for LBSN cell ECM were due primarily to an approximately 50% increase in binding sites (increased Bmax) versus LXSN cell ECM and of approximately 25% versus LBmutSN cell ECM. These results are consistent with the hypothesis that biglycan, through its glycosaminoglycan side chains, may mediate lipoprotein retention on atherosclerotic plaque ECM.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

V3 versican isoform expression alters the phenotype of melanoma cells and their tumorigenic potential

Versican is a large chondroitin sulfate proteoglycan produced by several tumor cell types, including malignant melanoma. The expression of increased amounts of versican in the extracellular matrix may play a role in tumor cell growth, adhesion and migration. We have expressed the V3 isoform of versican in human and canine melanoma cell lines. Retroviral overexpression of V3 did not change the morphology of any of the cell lines but markedly reduces cell growth in the V3 versican expressing melanoma cells. The V3-overexpressing melanoma cells retain their diminished growth potential in vivo because primary tumors arising from these cell lines growth more slowly than their vector only counterparts. This effect was accompanied by increases in cell adhesion on hyaluronan and an enhanced ability to migrate on hyaluronan-coated transwell chambers. This enhanced migration is blocked when cells are preincubated with soluble hyaluronan, or anti-CD44 antibodies, suggesting that V3 acts by altering the hyaluronan-CD44 interaction. Hyaluronan content and CD44 expression are not altered in V3-overexpressing cells compared to vector-transduced cells. Our results show that V3 overproduction modulates the in vitro behavior of human and canine melanoma cell lines and reduces their tumorigenicity in vivo.

Intracellular hyaluronan in arterial smooth muscle cells: association with microtubules, RHAMM, and the mitotic spindle

Although considered a pericellular matrix component, hyaluronan was recently localized in the cytoplasm and nucleus of proliferating cells, supporting earlier reports that hyaluronan was present in locations such as the nucleus, rough endoplasmic reticulum, and caveolae. This suggests that it can play roles both inside and outside the cell. Hyaluronan metabolism is coupled to mitosis and cell motility, but it is not clear if intracellular hyaluronan associates with cytoskeletal elements or plays a structural role. Here we report the distribution of intracellular hyaluronan, microtubules, and RHAMM in arterial smooth muscle cells in vitro. The general distribution of intracellular hyaluronan more closely resembled microtubule staining rather than actin filaments. Hyaluronan was abundant in the perinuclear microtubule-rich areas and was present in lysosomes, other vesicular structures, and the nucleolus. Partially fragmented fluorescein-hyaluronan was preferentially translocated to the perinuclear area compared with high-molecular-weight hyaluronan. In the mitotic spindle, hyaluronan colocalized with tubulin and with the hyaladherin RHAMM, a cell surface receptor and microtubule-associated protein that interacts with dynein and maintains spindle pole stability. Internalized fluorescein-hyaluronan was also seen at the spindle. Following telophase, an abundance of hyaluronan near the midbody microtubules at the cleavage furrow was also noted. In permeabilized cells, fluorescein-hyaluronan bound to RHAMM-associated microtubules. These findings suggest novel functions for hyaluronan in cellular physiology.

Fenofibrate modifies human vascular smooth muscle proteoglycans and reduces lipoprotein binding

AIMS/HYPOTHESIS

Vascular disease in type 2 diabetes is associated with an up-regulation of atherogenic growth factors, which stimulate matrix synthesis including proteoglycans. We have examined the direct actions of fenofibrate on human vascular smooth muscle cells (VSMCs) and have specifically investigated proteoglycan synthesis and binding to LDL.

METHODS

Proteoglycans synthesised by human VSMCs treated with fenofibrate (30 micromol/l) were assessed for binding to human LDL using a gel mobility shift assay, metabolically labelled with [(35)S]-sulphate and quantitated by cetylpyridinium chloride. They were then assessed for electrophoretic mobility by SDS-PAGE, for size by gel filtration, for sulphation pattern by fluorophore-assisted carbohydrate electrophoresis, and for glycosaminoglycan (GAG) composition by enzyme digestion.

RESULTS

Proteoglycans synthesised in the presence of fenofibrate showed an increase in the half-maximum saturation concentration of LDL from 36.8+/-12.4 microg/ml to 77.7+/-17 microg/ml under basal conditions, from 24.9+/-4.6 microg/ml to 39.1+/-6.1 microg/ml in the presence of TGF-beta1, and from 9.5+/-4.4 microg/ml to 31.1+/-3.4 microg/ml in the presence of platelet-derived growth factor/insulin. Fenofibrate treatment in the presence of TGF-beta1 inhibited the incorporation of [(35)S]-sulphate into secreted and cell-associated proteoglycans synthesised by human VSMCs by 59.2% (p<0.01) and 39.8% (p<0.01) respectively. The changes in sulphate incorporation following treatment with fenofibrate were associated with a concentration-related increase in the electrophoretic mobility due to a reduction in GAG length. There was no change in the sulphation pattern; however, there was an alteration in the disaccharide composition of the GAGs.

CONCLUSIONS/INTERPRETATION

Fenofibrate modifies the structure of vascular proteoglycans by reducing the length of the GAG chains and GAG composition, resulting in reduced binding to human LDL, a mechanism which may lead to a reduction of atherosclerosis and cardiovascular disease in people with diabetes treated with fenofibrate.

Decorin promotes aortic smooth muscle cell calcification and colocalizes to calcified regions in human atherosclerotic lesions

OBJECTIVE

Ectopic calcification localized to the intima of atherosclerotic plaque is a risk marker for cardiovascular events and increases the risk of aortic dissection during angioplasty. A variety of extracellular matrix molecules such as collagen type 1, bone sialoprotein, and osteopontin are known to regulate the biomineralization of bone and ectopic vascular calcification. In the present study, it was investigated whether decorin, a small leucine-rich proteoglycan expressed in bone and atherosclerotic plaque, is involved in arterial calcification.

METHODS AND RESULTS

Calcification was induced in cultured bovine aortic smooth muscle cell (BASMC) by the addition of beta-glycerophosphate or inorganic phosphate. Northern and Western analysis revealed that decorin expression was strongly upregulated in mineralizing BASMC. Furthermore, overexpression of decorin using a retroviral expression vector resulted in a 3- to 4-fold elevation of calcium deposited on the BASMC monolayer. Increased calcification in response to decorin could also be mimicked by adding exogenous decorin to the cultures. In addition, human coronary atherosclerotic lesions taken from sudden-death patients showed marked colocalization of calcium deposits with decorin.

CONCLUSIONS

Decorin induces calcification of arterial smooth muscle cell cultures and colocalizes to mineral deposition in human atherosclerotic plaque, suggesting that decorin functions as promoter of intimal calcification.

The accumulation of specific types of proteoglycans in eroded plaques: a role in coronary thrombosis in the absence of rupture

PURPOSE OF REVIEW

Although fibrous cap rupture is the primary cause of coronary thrombosis, plaque erosion is responsible for 30%-40% of acute thrombotic events. The interface of the eroded surface involves a denuded endothelium allowing direct contact of the platelet/fibrin thrombus with the underlying lesion. This review discusses the putative role of extracellular matrix molecules, in particular proteoglycans/hyaluronan, in the development of acute coronary thrombosis associated with erosion.

RECENT FINDINGS

The plaque/thrombus interface in erosion presents a unique surface since it consists of predominantly SMCs and proteoglycans with minimal or no inflammation. The lack of significant inflammation raises the possibility that erosion represents chronic wounding rather than true atherogenesis. The abundance of proteoglycan and hyaluronan matrix suggests their potential role in the development of thrombosis. Matrix changes may contribute to endothelial loss, the magnitude of the thrombotic event, or both. Versican facilitates platelet adhesion at low shear and cooperates with collagen to promote platelet aggregation. Further, versican may, in part, regulate water content and in turn support coagulation because water-dependent functionality of anticoagulation molecules. Finally, experimental models of plaque erosion are currently being developed guided by the premise that the loss of surface endothelium together with other procoagulant factors may underlie the development of platelet-rich thrombi.

SUMMARY

The loss of endothelium and exposure of a potentially procoagulant versican-hyaluronan matrix may be largely responsible for plaque erosion. The development of relevant animal models should allow further insight into the pathophysiology of coronary thrombosis in the absence of rupture.

Extracellular Matrix Changes in Stented Human Coronary Arteries

Background— Restenosis after stenting occurs secondary to the accumulation of smooth muscle cells (SMCs) and extracellular matrix (ECM), with the ECM accounting for >50% of the neointimal volume. The composition of the in-stent ECM has not been well characterized in humans.

Methods and Results— Postmortem human coronary arteries (n=45) containing stents underwent histological assessment of neointimal proteoglycans, hyaluronan, collagen (types I and III), SMCs, and CD44 (a cell surface receptor for hyaluronan). The mean duration of stent implantation was 18.7 months; stents in place ≥3 to <9 months (n=17) were assigned to group 1, stents ≥9 to <18 months old (n=19) to group 2, and stents ≥18 months old (n=9) to group 3. In groups 1 and 2, neointimal versican and hyaluronan staining was strongly positive, colocalized with α-actin-positive SMCs, and was greater in intensity compared with group 3. Conversely, decorin staining was greatest in group 3. The neointima of both group 1 and 2 stents was rich in type III collagen, with reduced staining in group 3. Type I collagen staining was weakest in group 1 stents, with progressively stronger staining in groups 2 and 3. SMC density and stent stenosis were significantly reduced in group 3 stents compared with groups 1 and 2. CD44 staining colocalized with macrophages and was associated with increased neointimal thickness.

Conclusions— The ECM within human coronary stents resembles a wound that is not fully healed until 18 months after deployment, followed by neointimal retraction. ECM contraction may be a target for therapies aimed at stent restenosis prevention.

Increase in serum amyloid a evoked by dietary cholesterol is associated with increased atherosclerosis in mice

BACKGROUND

Elevated serum amyloid A (SAA) levels are associated with increased cardiovascular risk. SAA levels can be increased by dietary fat and cholesterol. Moreover, SAA can cause lipoproteins to bind extracellular vascular proteoglycans, a process that is critical in atherogenesis. Therefore, we hypothesized that diet-induced increases in SAA would increase atherosclerosis independent of their effect on plasma cholesterol levels.

METHODS AND RESULTS

Female LDL-receptor-null (LDLR-/-) mice were fed high-saturated fat diets (21%, wt/wt), with or without added cholesterol (0.15%, wt/wt), for 10 weeks. Compared with chow-fed controls, the high-fat diets increased plasma SAA levels. Addition of cholesterol further increased SAA levels 2-fold (P<0.05) without further increasing plasma cholesterol levels. Addition of dietary cholesterol also increased atherosclerosis (P<0.05). Four lines of evidence suggest that SAA actually might cause atherosclerosis: (1) SAA levels when mice were euthanized correlated with the extent of atherosclerosis (r=0.49; P<0.02); (2) SAA levels after 5 weeks of diet correlated with the extent of atherosclerosis at 10 weeks (r=0.66; P<0.01); (3) binding of HDL from these animals to proteoglycans in vitro was related to the HDL-SAA content (r=0.65; P<0.01); and (4) immunoreactive SAA was present in lesion areas enriched with both proteoglycans and apolipoprotein A-I, the major HDL apolipoprotein.

CONCLUSIONS

Addition of cholesterol to a high-fat diet increased plasma SAA levels and atherosclerosis independent of an adverse effect on plasma lipoproteins, consistent with the hypothesis that SAA may promote atherosclerosis directly by mediating retention of SAA-enriched HDL to vascular proteoglycans.

Intracellular hyaluronan: a new frontier for inflammation?

A variety of obstacles have hindered the ultrastructural localization of hyaluronan (HA). These include a lack of adequate fixation techniques to prevent the loss of HA, the lack of highly sensitive and specific probes, and a lack of accessibility due to the masking of HA by HA-binding macromolecules such as proteoglycans and glycoproteins. Despite these problems, a number of studies, both biochemical and histochemical, have been published indicating that HA is not restricted to the extracellular milieu, but is also present intracellularly. This review focuses on the possible functions of intracellular HA, its potential relationships to extracellular HA structures, and implications for inflammatory processes.

Removal of heparan sulfate by heparinase treatment inhibits FGF-2-dependent smooth muscle cell proliferation in injured rat carotid arteries

Smooth muscle cells (SMC) of the rat carotid arterial media proliferate and migrate in response to injury during the formation of a neointima. The interaction of fibroblast growth factor (FGF-2), which is released at the site of injury, with heparan sulfate proteoglycans (HSPGs) is necessary to induce signaling, which elicits an FGF-dependent mitogenic response by arterial smooth muscle cells, and also serves as a mechanism for storage of the growth factor within the extracellular matrix. However, whether these interactions are critical during neointimal formation has not been directly tested. In this study, a model of FGF-2-dependent medial SMC mitogenic response in balloon-injured rat carotid artery was used to test the effect of degradation of vessel wall heparan sulfate on subsequent SMC proliferation. Treatment of balloon-catheterized rat carotid arteries with chondroitin ABC lyase and/or heparin lyases eliminated heparan sulfates in the vessel wall, as determined by immunoperoxidase staining. In contrast, the distribution in the carotid vessel wall of the large core protein of perlecan, a major vessel wall HSPG that binds FGF-2, is not decreased. The effect of glycosaminoglycan digestion in situ on medial SMC proliferation in response to a bolus injection of FGF-2 after injury was determined by measuring the percentage of SMC nuclei that incorporated 5-bromo-2'-deoxyuridine (BrdU) 48 h after injury. Enzymatic removal of heparan sulfate reduced BrdU incorporation into medial SMC by 60-70% (P < 0.001) at 48 h after injury. Moreover, pre-incubation of FGF-2 with heparin prior to injection restored SMC replication to the levels present in injured vessels treated with buffer alone (P < 0.01). These experiments indicate that endogenous HSPGs are essential to promote FGF-2-driven medial SMC proliferation following injury, and that heparinase treatment can abrogate FGF-2-dependent responses in vivo.

Proteoglycans in Atherosclerosis and Restenosis

The proteoglycan versican is one of several extracellular matrix (ECM) molecules that accumulate in lesions of atherosclerosis and restenosis. Its unique structural features create a highly interactive molecule that binds growth factors, enzymes, lipoproteins, and a variety of other ECM components to influence fundamental events involved in vascular disease. Versican is one of the principal genes that is upregulated after vascular injury and is a prominent component in stented and nonstented restenotic lesions. The synthesis of versican is highly regulated by specific growth factors and cytokines and the principal source of versican is the smooth muscle cell. Versican interacts with hyaluronan, a long chain glycosaminoglycan, to create expanded viscoelastic pericellular matrices that are required for arterial smooth muscle cell (ASMC) proliferation and migration. Versican is also prominent in advanced lesions of atherosclerosis, at the borders of lipid-filled necrotic cores as well as at the plaque-thrombus interface, suggesting roles in lipid accumulation, inflammation, and thrombosis. Versican influences the assembly of ECM and controls elastic fiber fibrillogenesis, which is of fundamental importance in ECM remodeling during vascular disease. Collectively, these studies highlight the critical importance of this specific ECM component in atherosclerosis and restenosis.

Thiazolidinediones reduce the LDL binding affinity of non-human primate vascular cell proteoglycans

AIMS/HYPOTHESIS

Retention of atherogenic lipoproteins in the artery wall by proteoglycans is a key step in the development of atherosclerosis. Thiazolidinediones have been shown to reduce atherosclerosis in mouse models. The aim of this study was to determine whether thiazolidinediones modify vascular proteoglycan synthesis in a way that decreases LDL binding.

METHODS

Primate aortic smooth muscle cells were exposed to troglitazone or rosiglitazone, or no stimulus at all for a 24-hour steady-state labelling period. Sulphate incorporation, size and LDL binding affinity of proteoglycans were determined. Proteoglycans secreted by cells in the presence or absence of troglitazone were separated into large and small classes by size exclusion chromatography, and LDL binding affinity was determined.

RESULTS

Proteoglycans synthesised by cells exposed to troglitazone or rosiglitazone were smaller, with decreased sulphate incorporation and decreased LDL binding affinity. However, troglitazone had a greater effect than rosiglitazone. Troglitazone reduced the LDL binding affinities of both the large and small proteoglycans compared with control. The binding differences persisted when glycosaminoglycan chains released from proteoglycans were incubated with LDL, indicating that troglitazone affects the glycosaminoglycan synthetic machinery of these cells.

CONCLUSIONS/INTERPRETATION

Thiazolidinediones decrease the LDL binding affinity of the proteoglycans synthesised by primate aortic smooth muscle cells. This could, in part, account for the reduced atherosclerosis observed in animal models.

Superficial pseudoaneurysms: clinicopathologic aspects and involvement of extracellular matrix proteoglycans

The distribution of proteoglycans in 21 temporal and two ulnar artery pseudoaneurysms was studied immunohistochemically. A history of trauma was elicited in six cases, and 16 of the lesions were pulsatile. The clinical diagnosis was aneurysm or cyst in 18 patients, possible arteritis in two patients, tumor in one patient, and unknown in the remaining patient. Histologically, there was a prominent myxoid neointimal response in the walls of each interrupted artery. The remnant arterial segment was often inconspicuous. Prominent smooth muscle cell proliferation and granulation tissue response with inflammation led to misdiagnosis of tumor or vasculitis, respectively, in 11 cases. Immunohistochemical staining for proteoglycans demonstrated abundant, diffuse versican in interrupted wall segments. Biglycan was confined to collagenized and vascularized areas. In some portions of medial disruption, in which angiogenesis was prominent, decorin was expressed within endothelial cells of neocapillaries. These findings demonstrate that superficial pseudoaneurysms may be mistaken clinically and pathologically for unrelated entities. The immunohistochemical studies confirm that versican is upregulated in areas of tensile stress. In addition, the presence of endothelial expression of decorin supports the concept of decorin's involvement in angiogenesis.

Glycosaminoglycans and proteoglycans in normal mitral valve leaflets and chordae: association with regions of tensile and compressive loading

This study was designed to identify the specific proteoglycans and glycosaminoglycans (GAGs) in the leaflets and chordae of the mitral valve and to interpret their presence in relation to the tensile and compressive loads borne by these tissues. Leaflets and chordae from normal human mitral valves (n = 31, obtained at autopsy) were weighed and selected portions digested using proteinase K, hyaluronidase, and chondroitinases. After fluorescent derivatization, fluorophore-assisted carbohydrate electrophoresis was used to separate and quantify the derivatized saccharides specific for each GAG type. In addition, the lengths of the chondroitin/dermatan sulfate chains were determined. Proteoglycans were identified by western blotting. The regions of the valve that experience tension, such as the chordae and the central portion of the anterior leaflet, contained less water, less hyaluronan, and mainly iduronate and 4-sulfated N-acetylgalactosamine with chain lengths of 50-70 disaccharides. These GAGs are likely associated with the small proteoglycans decorin and biglycan, which were found in abundance in the tensile regions. The valve regions that experience compression, such as the posterior leaflet and the free edge of the anterior leaflet, contained significantly more water, hyaluronan, and glucuronate and 6-sulfated N-acetylgalactosamine with chain lengths of 80-90 disaccharides. These GAGs are likely components of water-binding versican aggregates, which were abundant in the compressive loading regions. The relative amounts and distributions of these GAGs are therefore consistent with the tensile and compressive loads that these tissues bear. Finally, the concentrations of total GAGs and many different chondroitin/dermatan sulfate subclasses were significantly decreased with advancing age.

Extended life span is associated with insulin resistance in a transgenic mouse model of insulinoma secreting human islet amyloid polypeptide

Pancreatic amyloid is found in patients with insulinomas and type 2 diabetes. To study mechanisms of islet amyloidogenesis, we produced transgenic mice expressing the unique component of human islet amyloid, human islet amyloid polypeptide (hIAPP). These mice develop islet amyloid after 12 mo of high-fat feeding. To determine whether we could accelerate the rate of islet amyloid formation, we crossbred our hIAPP transgenic animals with RIP-Tag mice that develop islet tumors and die at 12 wk of age from hypoglycemia. At 12 wk of age, this new line of hIAPPxRIP-Tag mice was heavier (29.7 +/- 1.0 vs. 25.0 +/- 1.3 g, P < 0.05) and had increased plasma glucose levels (4.6 +/- 0.4 vs. 2.9 +/- 0.6 mmol/l, P < 0.05) compared with littermate RIP-Tag mice. However, the hIAPPxRIP-Tag mice did not display islet amyloid or amyloid fibrils despite high circulating hIAPP levels (24.6 +/- 7.0 pmol/l). Interestingly, hIAPPxRIP-Tag mice had a longer life span than RIP-Tag mice (121 +/- 8 vs. 102 +/- 5 days, P < 0.05). This increase in life span in hIAPPxRIP-Tag was positively correlated with body weight (r = 0.48, P < 0.05) and was associated with decreased insulin sensitivity compared with RIP-Tag mice. hIAPPxRIP-Tag mice did not develop amyloid during their 4-mo life span, suggesting that increased hIAPP secretion is insufficient for islet amyloid formation within such a short time. However, hIAPPxRIP-Tag mice did have an increase in life span that was associated with insulin resistance, suggesting that hIAPP has extrapancreatic effects, possibly on peripheral glucose metabolism.

Retrovirally mediated overexpression of versican v3 reverses impaired elastogenesis and heightened proliferation exhibited by fibroblasts from Costello syndrome and Hurler disease patients

The phenotypic resemblance of patients with Costello syndrome and Hurler disease has been linked to impaired formation of elastic fibers that coincides with elevated cellular proliferation. Impaired elastogenesis in these diseases associates with respective abnormal accumulation of chondroitin sulfate and dermatan sulfate proteoglycans that induce cell surface shedding of elastin-binding protein (EBP) normally required for intracellular chaperoning of tropoelastin and its assembly into elastic fibers. A variant of the chondroitin sulfate proteoglycan versican, V3, which lacks chondroitin sulfate, has recently been shown to stimulate elastic fiber assembly and decrease proliferation when expressed by retroviral transduction in arterial smooth muscle cells. However, the mechanism(s) by which V3 influences this phenotype is not known. We now demonstrate that transduction of skin fibroblasts from Costello syndrome and Hurler disease patients with cDNA to versican V3 completely reverses impaired elastogenesis and restores normal proliferation of these cells. This phenotypic reversal is accompanied by loss of chondroitin sulfate from the cell surface and increased levels of EBP. Versican V3 transduction of skin fibroblasts from GM(1)-gangliosidosis patients, which lack EBP, failed to restore impaired elastogenesis. These results suggest that induction of elastic fiber production by gene transfer of versican V3 in skin fibroblasts is mediated by rescue of the tropoelastin chaperone, EBP.

Pro- and anti-inflammatory factors cooperate to control hyaluronan synthesis in lung fibroblasts

Hyaluronan (HA) is an important constituent of the extracellular matrix and accumulates during inflammatory lung diseases like asthma. Little is known about the factors that regulate HA synthesis by lung cells. Accordingly, we investigated the effect of T-helper 1 (TH1) and 2 (TH2) cytokines and the anti-inflammatory agents fluticasone and salmeterol on HA synthesis in human lung fibroblasts. Interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF)-alpha were the most potent stimulators of HA synthesis and when combined, caused synergistic increases in HA accumulation. Time-course analysis of HA accumulation and [3H]-glucosamine incorporation into HA demonstrated continued synthesis over the 24 h of stimulation. Peak synthesis at 6-12 h coincided with an increased proportion of high molecular weight HA. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that IL-1beta and TNF-alpha induced HA synthase-2 messenger RNA (mRNA) 3 h following stimulation and remained elevated throughout the 24-h stimulation period. Fluticasone inhibited IL-1beta and TNF-alpha induced HA synthesis (44.5%) whereas salmeterol had no effect. When combined, fluticasone and salmeterol inhibited HA synthesis to a greater extent (85.2%). Further, fluticasone attenuated IL-1beta and TNF-alpha stimulated hyaluronan synthase-2 messenger RNA (mRNA), and the addition of salmeterol cooperatively enhanced this inhibition. These results indicate that enhanced synthesis of HA by the proinflammatory cytokines IL-1beta and TNF-alpha can be abrogated by specific corticosteroid and beta2 blocker combinations shown to be effective in the treatment of asthma.

Regulation of proteoglycan synthesis by leukotriene d4 and epidermal growth factor in bronchial smooth muscle cells

Extracellular matrix (ECM) expansion contributes to airway remodeling in asthma. This study examines the effect of leukotriene D4 (LTD4), combined with epidermal growth factor (EGF), on proteoglycan synthesis by cultured human bronchial smooth muscle cells (BSMCs). LTD4 plus EGF stimulated proliferation of BSMCs with increased versican synthesis. Further, versican mRNA splice variants, V0 and V1, were differently regulated in BSMCs by LTD4 plus EGF. Synthesis of [35S]-methionine labeled versican V0, as a percentage of total versican, was doubled. This upregulation was confirmed by Western analysis. Synthetic changes were paralleled by alterations in versican V0 mRNA. The effects of LTD4 and EGF on proteoglycan synthesis were inhibited by montelukast. Similar upregulation of versican V0 was observed in arterial smooth muscle cells (ASMCs) stimulated with LTD4 plus EGF as measured by western and reverse transcriptase-polymerase chain reaction analyses. Changes in ECM in the asthmatic airway may parallel those in atherosclerotic lesions where proliferating ASMCs synthesize a versican-rich expanded ECM. Inhibition of these processes could lead to reduced tissue expansion in the early phases of asthma progression.

The Regulated Synthesis of Versican, Decorin, and Biglycan: Extracellular Matrix Proteoglycans That Influence Cellular Phenotype

The principal extracellular matrix (ECM) chondroitin/dermatan sulfate proteoglycans include members of two gene families--the large aggregating chondroitin sulfate proteoglycans (lecticans) and the small leucine-rich proteoglycans (SLRPs). These families of proteoglycans are widely distributed within the interstitial matrix, where they are known to bind a variety of both soluble and insoluble ligands. Extensive structural studies and data concerning the synthesis of these proteoglycans have been published over the last few years. This review focuses on the regulation of the expression of the lectican, versican, and the SLRPs--decorin and biglycan, as well--studied and widely distributed examples of these families of ECM proteoglycans. In addition, the effects of these proteoglycans on the formation of the ECM and the response of cells to growth factors and cytokines are examined as mechanisms by which versican, decorin and biglycan, both directly and indirectly influence cellular proliferation, migration, and phenotype.

Overexpression of Decorin by Rat Arterial Smooth Muscle Cells Enhances Contraction of Type I Collagen In Vitro

OBJECTIVE

Overexpression of decorin reduces neointimal thickening in balloon-injured carotid arteries of rats by decreasing the volume of neointimal extracellular matrix (ECM). We examined the hypothesis that decorin regulates ECM volume by stimulating cell-mediated contraction of collagen-rich ECMs.

METHODS AND RESULTS

Rat arterial smooth muscle cells (ASMCs) transduced with bovine decorin cDNA by retroviral transfection (LDSN) exhibited enhanced contraction of collagen gels in vitro when compared with vector-only transduced (LXSN) cells. Addition of recombinant decorin to LXSN or LDSN cells did not stimulate contraction of collagen gels. Enhanced contraction of collagen by LDSN cells was unaffected by the metalloproteinase inhibitor GM6001. LDSN cells exhibited increased expression of type I collagen mRNA when compared with that of LXSN cells. Correspondingly, collagen gel contraction by LDSN cells was reduced by inhibition of collagen synthesis by 3,4-l-dehydroproline (L-DHP). Antibodies to alpha1beta1-integrin, but not to alpha2beta1-integrin, blocked collagen contraction by both LXSN and LDSN cells. However, LXSN and LDSN cells expressed similar levels of alpha1- and beta1-integrin mRNAs.

CONCLUSIONS

Decorin synthesized de novo by ASMCs increases type I collagen synthesis and enhances contraction of collagen gels. Regulated synthesis of decorin may be a useful therapeutic approach to reduce ECM volume in vascular disease.

Statin-exposed vascular smooth muscle cells secrete proteoglycans with decreased binding affinity for LDL

Retention of LDL in the artery intima is mediated by extracellular matrix proteoglycans and plays an important role in the initiation of atherosclerosis. Compared with quiescent cells, proliferating smooth muscle cells secrete proteoglycans with elongated glycosaminoglycan side chains, which have an increased binding affinity to LDL. Because 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors (statins) decrease smooth muscle cell proliferation, we hypothesized that statin exposure would decrease both the size and LDL binding affinity of vascular proteoglycans. Monkey aortic smooth muscle cells grown in culture were exposed to simvastatin (10 and 100 microM) and cerivastatin (0.1 and 1 microM), and newly secreted proteoglycans were quantified and characterized. Both simvastatin and cerivastatin caused a concentration-dependent reduction in cell growth and reduced 35SO4 incorporation into secreted proteoglycans, on both an absolute and a per cell basis. Interestingly, statin exposure increased the apparent molecular weight and hydrodynamic size of secreted proteoglycans. However, proteoglycans secreted from statin-exposed cells demonstrated a reduction in binding affinity to LDL. Thus, statins may induce atheroprotective changes in vascular proteoglycans and lower LDL retention in the vessel wall. These findings suggest a mechanism whereby statins may benefit atherosclerosis in a manner unrelated to serum LDL lowering.

Cell-associated and extracellular phospholipid transfer protein in human coronary atherosclerosis

BACKGROUND

Phospholipid transfer protein (PLTP) plays an important role in HDL particle metabolism and may modulate hepatic secretion of apolipoprotein B-containing lipoproteins. However, whether PLTP might participate directly in human atherosclerotic lesion formation is unknown.

METHODS AND RESULTS

The cellular and extracellular distributions of PLTP were determined in normal and atherosclerotic human coronary lesions with a monoclonal antibody to human PLTP. Cell types (smooth muscle cells [SMCs] or macrophages), apolipoproteins (apoA-I, apoB, and apoE), and extracellular matrix proteoglycans (biglycan and versican) were identified on adjacent sections with monospecific antibodies. Minimal extracellular PLTP was detected in nonatherosclerotic coronary arteries, but extracellular and cellular PLTP immunostaining was widespread in atherosclerotic lesions. PLTP was detected in foam cell SMCs and in foam cell macrophages, which suggests that cellular cholesterol accumulation might increase PLTP expression in both cell types. This was confirmed by in vitro studies demonstrating that cholesterol loading of macrophages leads to 2- to 3-fold increases in PLTP steady-state mRNA levels, protein expression, and activity. PLTP also was detected in an extracellular distribution, colocalizing with apoA-I, apoB, apoE, and the vascular proteoglycan biglycan. In gel mobility shift assays, both active and inactive recombinant PLTP markedly increased HDL binding to biglycan, which suggests that PLTP may mediate lipoprotein binding to proteoglycans independent of its phospholipid transfer activity.

CONCLUSIONS

PLTP is present in human atherosclerotic lesions, and its distribution suggests roles for PLTP in both cellular cholesterol metabolism and lipoprotein retention on extracellular matrix.

SPARC-null mice display abnormalities in the dermis characterized by decreased collagen fibril diameter and reduced tensile strength

Although collagen and elastic fibers are among the major structural constituents responsible for the mechanical properties of skin, proteins that associate with these components are also important for directing formation and maintaining the stability of these fibers. We present evidence that SPARC (secreted protein acidic and rich in cysteine) contributes to collagen fibril formation in the dermis. The skin of SPARC-null adult mice had approximately half the tensile strength as that of wild-type skin. Moreover, the collagen content of SPARC-null skin, as measured by hydroxyproline analysis, was substantially reduced in adult mice. At 2 weeks of age, no differences in collagen content were observed; within 2 months, however, the dermis of SPARC-null mice displayed a reduced collagen content that persisted through adulthood until approximately 20 months, when collagen levels of SPARC-null skin approximated those of wild-type controls. The collagen fibrils present in SPARC-null skin were smaller and more uniform in diameter, in comparison with those of wild-type skin. At 5 months of age, the average fibril diameter in SPARC-null versus wild-type skin was 60.2 nm versus 87.9 nm, respectively. Extraction of soluble dermal collagen revealed a relative increase in collagen VI, accompanied by a decrease in collagen I, in SPARC-null mice. A reduction in the relative amounts of higher-molecular weight collagen complexes was also observed in extracts of dermis from SPARC-null animals. Thus the absence of SPARC compromises the mechanical properties of the dermis, an effect that we attribute, at least in part, to the changes in the structure and composition of its collagenous extracellular matrix.

Propagation and control of T cell responses by heparan sulfate-bound IL-2

IL-2, a cytokine produced by T cells, is a key regulator of immune responses and T cell homeostasis. Controlling the availability of IL-2 is consequently of significant import to the immune system. Like other cytokines, IL-2 is thought to function as a soluble agonist, transiently present when secreted in response to appropriate stimuli. In this study, we show that the most salient properties of IL-2, propagation and control of T cell responses, are mediated in vivo by bound and not free cytokine and specifically by heparan sulfate-bound IL-2. These findings necessitate a new look at how IL-2 regulates immune responses and support the notion that the microenvironment plays a determining role in modulating the character of immune responses.

Proteoglycans synthesized and secreted by pancreatic islet beta-cells bind amylin

Pancreatic islet amyloid deposits in type 2 diabetes are associated with decreased islet beta-cell function. They contain both amylin (islet amyloid polypeptide), the beta-cell-derived unique fibrillogenic component, and heparan sulfate proteoglycans (HSPGs). We hypothesized that beta-cell HSPGs contribute to islet amyloidogenesis. [35S]Sulfate-labeled proteoglycans from islet-derived beta-TC3 cell cultures eluted from diethylaminoethyl Sephacel at 0.35M NaCl. Chromatography on Sepharose CL-4B and SDS-PAGE analysis revealed distinct populations of proteoglycans. Medium HSPGs eluted at K(av) approximately 0.18 and 0.50 with glycosaminoglycan chains of approximately 28 and 19 kDa, respectively. A third population containing chondroitin/dermatan sulfate eluted at K(av) approximately 0.70 with glycosaminoglycan chains of approximately 10 kDa. A single size class of heparan and chondroitin/dermatan sulfate proteoglycans in the cell layer eluted at K(av) approximately 0.40 with glycosaminoglycan chains of approximately 19 kDa. Medium and cell layer proteoglycans bound exclusively to fibrillogenic amylin, as determined by gel mobility shift assays, indicating a possible role for beta-cell-derived proteoglycans in islet amyloid formation.

Lysophosphatidylcholine regulates synthesis of biglycan and the proteoglycan form of macrophage colony stimulating factor

OBJECTIVE

We have shown that copper-oxidized LDL (Ox-LDL) regulates proteoglycan synthesis by arterial smooth muscle cells. Ox-LDL specifically upregulates biglycan expression while causing elongation of glycosaminoglycan chains on all of the major secreted proteoglycans (biglycan, decorin, and versican), resulting in enhanced lipoprotein-binding interactions. It is not known which component of Ox-LDL is responsible for these effects. This study investigated the ability of several bioactive components of Ox-LDL to regulate proteoglycan synthesis.

METHODS AND RESULTS

Those tested included 2 oxysterols (7-ketocholesterol and 7beta-hydroxycholesterol) and 2 lysolipids (lysophosphatidylcholine and lysophosphatidic acid) formed during LDL oxidation. 7-ketocholesterol, lysophosphatidylcholine, and lysophosphatidic acid all increased proteoglycan MWapp, which is correlated with chain elongation and enhanced lipoprotein-binding properties in vitro. Lysophosphatidylcholine mimics the ability of Ox-LDL to stimulate biglycan expression and also causes a marked induction of the core protein for the proteoglycan form of macrophage colony stimulating factor.

CONCLUSIONS

Multiple oxidized lipid molecules can modulate proteoglycan synthesis and may have important consequences to atherogenesis via processes that involve enhanced lipoprotein retention as well as the promotion of macrophage survival and differentiation.

Binding of interleukin-8 to heparan sulfate and chondroitin sulfate in lung tissue

Interleukin (IL)-8, a member of the CXC chemokine family, is a potent neutrophil chemotactic factor. Mechanisms that regulate the activity of chemokines in tissue are not clear. The goal of this study was to determine whether IL-8-glycosaminoglycan interactions are responsible for the binding of IL-8 in lung tissue. Experiments were performed with a quantitative tissue-binding assay to measure the amount of 125I-IL-8 binding and an in situ tissue-binding assay to characterize the location of IL-8 binding in lung tissue. Confocal microscopy demonstrated IL-8 binding to specific anatomic locations such as cell surfaces and extracellular matrix that were enriched with heparan sulfate and chondroitin sulfate. Removal of heparan sulfate or chondroitin sulfate from lung tissue significantly decreased the binding of 125I-IL-8. Two forms of IL-8 with single amino acid mutations in the glycosaminoglycan-binding domain showed decreased binding. In addition, studies with normal and monomeric IL-8 showed that dimerization increased the binding of 125I-IL-8 in lung tissue. These findings suggest that IL-8-glycosaminoglycan interactions determine the location where IL-8 binds in lung tissue and provides a site for the dimerization of IL-8, which increases the local concentration of IL-8 in the lungs.

Changes in perlecan expression during vascular injury: role in the inhibition of smooth muscle cell proliferation in the late lesion

OBJECTIVE

Vascular smooth muscle cells (SMCs), activated by growth factors after arterial injury, migrate and proliferate to expand the intima of the blood vessel. During intimal expansion, proliferation is suppressed and an increasingly large proportion of the neointimal mass is composed of newly synthesized extracellular matrix (ECM). We sough to determine whether the ECM heparan sulfate proteoglycan (HSPG) perlecan, which inhibits SMC proliferation in vitro, also accumulates and limits SMC proliferation during neointimal expansion.

METHODS AND RESULTS

Perlecan expression and accumulation were analyzed by immunohistochemistry and in situ hybridization during neointima formation after balloon catheter injury to the rat carotid artery. Perlecan expression was low in uninjured vessels and up to 7 days after injury, during maximal SMC proliferation. By 14 days after injury, perlecan was dramatically increased, and immunostaining remained heavy throughout the advanced lesion, 35 to 42 days after injury. Finally, explants of intimal tissue from 35- to 42-day neointimal lesions were digested with glycosaminoglycanases to determine whether endogenous HSPGs inhibit intimal SMC proliferation. SMCs within HS-depleted, but not chondroitinase ABC-treated or mock-incubated, explants were found to proliferate in response to platelet-derived growth factor BB.

CONCLUSIONS

HSPGs, such as perlecan, may inhibit the proliferative response of SMCs after vascular injury.

Characterization of ADAMTS-9 and ADAMTS-20 as a distinct ADAMTS subfamily related to Caenorhabditis elegans GON-1

We demonstrate that in humans, two metalloproteases, ADAMTS-9 (1935 amino acids) and ADAMTS-20 (1911 amino acids) are orthologs of GON-1, an ADAMTS protease required for gonadal morphogenesis in Caenorhabditis elegans. ADAMTS-9 and ADAMTS-20 have an identical modular structure, are distinct in possessing 15 TSRs and a unique C-terminal domain, and have a similar gene structure, suggesting that they comprise a new subfamily of human ADAMTS proteases. ADAMTS20 is very sparingly expressed, although it is detectable in epithelial cells of the breast and lung. However, ADAMTS9 is highly expressed in embryonic and adult tissues, and therefore we characterized the ADAMTS-9 protein further. Although the ADAMTS-9 zymogen has many proprotein convertase processing sites, pulse-chase analysis, site-directed mutagenesis, and amino acid sequencing demonstrated that maturation to the active form occurs by selective proprotein convertase (e.g. furin) cleavage of the Arg(287)-Phe(288) bond. Although lacking a transmembrane sequence, ADAMTS-9 is retained near the cell surface as well as in the ECM of transiently transfected COS-1 and 293 cells. COS-1 cells transfected with ADAMTS9 (but not vector-transfected cells) proteolytically cleaved bovine versican and aggrecan core proteins at the Glu(441)-Ala(442) bond of versican V1 and the Glu(1771)-Ala(1772) bond of aggrecan, respectively. In contrast, the ADAMTS-9 catalytic domain alone was neither localized to the cell surface nor able to confer these proteolytic activities on cells, demonstrating that the ancillary domains of ADAMTS-9, including the TSRs, are required both for specific extracellular localization and for its versicanase and aggrecanase activities.

Enhanced extracellular matrix accumulation in restenosis of coronary arteries after stent deployment

OBJECTIVES

The goal of this study was to evaluate the cellular and extracellular composition of human coronary arterial in-stent restenosis after various periods of time following stent deployment.

BACKGROUND

Neointimal in-growth rather than stent recoil is thought to be important for coronary arterial in-stent restenosis. There is only limited data on the cellular and extracellular composition changes with time after stent deployment.

METHODS

We analyzed 29 coronary arterial in-stent restenotic tissue samples (14 left anterior descending coronary artery, 10 right coronary artery, and 5 left circumflex artery) retrieved by using directional coronary atherectomy from 25 patients at 0.5 to 23 (mean, 5.7) months after deployment of Palmaz-Schatz stents employing histochemical and immunocytochemical techniques.

RESULTS

Cell proliferation was low (0% to 4%). Myxoid tissue containing extracellular matrix (ECM) enriched with proteoglycans was found in 69% of cases and decreased over time after stenting. Cell-depleted areas were found in 57% of cases and increased with time after stenting. Versican, biglycan, perlecan, and hyaluronan were present with varying individual distributions in all samples. Positive transforming growth factor-beta1 staining was found in 80% of cases. Immunostaining with alpha-smooth muscle actin identified the majority of cells as smooth muscle cells with occasional macrophages present (< or =12 cells per section).

CONCLUSIONS

These data suggest that enhanced ECM accumulation rather than cell proliferation contribute to later stages of in-stent restenosis. Balloon angioplasty of in-stent restenosis may, therefore, fail due to ECM changes during: 1) additional stent expansion, 2) tissue extrusion out of the stent, or 3) tissue compression.

ApoC-III content of apoB-containing lipoproteins is associated with binding to the vascular proteoglycan biglycan

Retention of apolipoprotein (apo)B and apoE-containing lipoproteins by extracellular vascular proteoglycans is critical in atherogenesis. Moreover, high circulating apoC-III levels are associated with increased atherosclerosis risk. To test whether apoC-III content of apoB-containing lipoproteins affects their ability to bind to the vascular proteoglycan biglycan, we evaluated the impact of apoC-III on the interaction of [(35)S]SO(4)-biglycan derived from cultured arterial smooth muscle cells with lipoproteins obtained from individuals across a spectrum of lipid concentrations. The extent of biglycan binding correlated positively with apoC-III levels within VLDL (r = 0.78, P < 0.01), IDL (r = 0.67, P < 0.01), and LDL (r = 0.52, P < 0.05). Moreover, the biglycan binding of VLDL, IDL, and LDL was reduced after depletion of apoC-III-containing lipoprotein particles in plasma by anti-apoC-III immunoaffinity chromatography. Since apoC-III does not bind biglycan directly, enhanced biglycan binding may result from a conformational change associated with increased apo C-III content by which apoB and/or apoE become more accessible to proteoglycans. This may be an intrinsic property of lipoproteins, since exogenous apoC-III enrichment of LDL and VLDL did not increase binding. ApoC-III content may thus be a marker for lipoproteins characterized as having an increased ability to bind proteoglycans.

Versican: a versatile extracellular matrix proteoglycan in cell biology

Versican is a large extracellular matrix proteoglycan that is present in a variety of tissues. Successful cloning of the gene in man, mouse, cow and chicken has revealed the existence of at least four splice variants of versican, which differ in the size of the core protein and the number of glycosaminoglycan chains. The highly interactive nature of versican provides a basis for its importance as a structural molecule, creating loose and hydrated matrices during key events in development and disease; and by interacting either directly with cells or indirectly with molecules that associate with cells to, in part, regulate cell adhesion and survival, cell proliferation, cell migration and extracellular matrix assembly. Several studies within the past two years have confirmed a significant role for versican in regulating cell phenotype.