Differential transport kinetics of chondroitin sulfate and dermatan sulfate proteoglycan by monkey aorta smooth muscle cells

Osteogenic differentiation enhances the MC3T3-E1 secretion of glycosaminoglycans with an affinity for basic fibroblast growth factor and bone morphogenetic protein-2

Introduction

It is generally recognized that a wide variety of morphogens and growth factors bind to the glycosaminoglycans (GAG) of proteoglycans (PG) to affect their bioavailability to ligands. Many growth factors involving in osteogenic differentiation require the GAG side chains to facilitate their interaction to the cell surface receptors and the biosynthesis of osteogenic proteins. The objective of this study is to investigate the secretion of GAG from MC3T3-E1 pre-osteoblasts of a murine bone calvaria during the osteogenic differentiation.

Methods

When MC3T3-E1 cells were cultured in the differentiation medium (DM) containing bone morphogenetic protein (BMP)-2, the alkaline phosphatase activity, calcium content and the amount of basic fibroblast growth factor (bFGF)- or BMP-2-bound sulfated GAG were determined. Moreover, the disaccharide analysis of the GAG was performed.

Results

When MC3T3-E1 cells were cultured in the differentiation medium (DM) containing bone morphogenetic protein (BMP)-2, the alkaline phosphatase activity and calcium content were significantly enhanced compared with those of the BMP-2-free DM and normal medium with or without BMP-2. Significantly higher amount of GAG secreted was detected for cells cultured in the DM containing BMP-2, in contrast to other culture conditions. The GAG secreted had an affinity for BMP-2 and basic fibroblast growth factor (bFGF). The disaccharide analysis of GAG demonstrated that the percentage of ΔHexA α1,4GlcNSO₃ and ΔHexA (2-OSO₃) α1,4GlcNSO₃ increased, but that of ΔHexA α1,4GlcNSO₃(6-OSO₃) decreased (ΔHexA: unsaturated uronic acid residue, GlcNSO₃: N-sulfated glucosamine, ΔHexA (2-OSO₃): unsaturated uronic acid 2-sulfate residue, GlcNSO₃(6-OSO₃): N-sulfated glucosamine 6-sulfated).

Conclusion

It was found that the osteogenic differentiation allowed cells to enhance the secretion of GAG with an affinity for BMP-2 and bFGF.

Disruption of Heparan and Chondroitin Sulfate Signaling Enhances Mesenchymal Stem Cell-Derived Osteogenic Differentiation via Bone Morphogenetic Protein Signaling Pathways

Cell surface heparan sulfate (HS) and chondroitin sulfate (CS) proteoglycans have been implicated in a multitude of biological processes, including embryonic implantation, tissue morphogenesis, wound repair, and neovascularization through their ability to regulate growth factor activity and morphogenic gradients. However, the direct role of the glycosaminoglycan (GAG) sugar-side chains in the control of human mesenchymal stem cell (hMSC) differentiation into the osteoblast lineage is poorly understood. Here, we show that the abundant cell surface GAGs, HS and CS, are secreted in proteoglycan complexes that directly regulate the bone morphogenetic protein (BMP)-mediated differentiation of hMSCs into osteoblasts. Enzymatic depletion of the HS and CS chains by heparinase and chondroitinase treatment decreased HS and CS expression but did not alter the expression of the HS core proteins perlecan and syndecan. When digested separately, depletion of HS and CS chains did not effect hMSC proliferation but rather increased BMP bioactivity through SMAD1/5/8 intracellular signaling at the same time as increasing canonical Wnt signaling through LEF1 activation. Long-term culturing of cells in HS- and CS-degrading enzymes also increased bone nodule formation, calcium accumulation, and the expression of such osteoblast markers as alkaline phosphatase, RUNX2, and osteocalcin. Thus, the enzymatic disruption of HS and CS chains on cell surface proteoglycans alters BMP and Wnt activity so as to enhance the lineage commitment and osteogenic differentiation of hMSCs.

Decorin synthesized by arterial smooth muscle cells is retained in fibrin gels and modulates fibrin contraction

Fibrin serves as a provisional extracellular matrix (ECM) for arterial smooth muscle cells (ASMC) after vascular injury, yet little is known about the effect of fibrin on ECM remodeling by these cells. To address this question, monkey ASMC were grown on fibrin gels and tissue culture (TC) plastic, and proteoglycan synthesis and accumulation were assessed by radiolabeling. Initial rates of (35)S-sulfate incorporation into proteoglycans were identical for both groups, but increased proteoglycan accumulation was observed in cultures grown for 48 h on fibrin. This increased accumulation on fibrin was due to reduced proteoglycan turnover and retention within the fibrin gel. Decorin and biglycan constituted 40 and 14% of the total proteoglycan in the fibrin gels, whereas their combined contribution was only 12% in control matrices. To explore whether the retention of decorin in fibrin had any influence on the properties of the fibrin gel, ASMC-mediated fibrin contraction assays were performed. Both de novo synthesis of decorin as well as decorin added during polymerization inhibited the ability of the cells to contract fibrin. In contrast, decorin added exogenously to mature fibrin matrices had no effect on fibrin gel contraction. This study illustrates that decorin derived from ASMC selectively accumulates in fibrin and modifies fibrin architecture and mechanical properties. Such an accumulation may influence wound healing and the thrombotic properties of this provisional pro-atherosclerotic ECM.

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.

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.

Distinct rat aortic smooth muscle cells differ in versican/PG-M expression

Smooth muscle cells (SMCs) with distinct phenotypes are present in blood vessels, and distinct culture types appear when SMCs are maintained in vitro. For example, cultured SMCs from rat adult media grow as bipolar cells, which differ in gene expression from the predominantly cobblestone-shaped SMCs from rat pup aortas and rat neointimas that we call pi SMCs. Since proteoglycans are present at different concentrations in the normal intima and media and are elevated in atherosclerotic plaque, we sought to determine whether pi and adult medial SMC types synthesize different or unique proteoglycans that are characteristic of each phenotype. [35S]sulfate-labeled proteoglycans were purified by ion-exchange chromatography. An adult medial SMC line synthesized a large proteoglycan (0.2 Kav on Sepharose CL-2B) that was not detectable in a pi SMC line. Digestion of this proteoglycan with chondroitin ABC lyase revealed three core glycoproteins of 330, 370, and 450 kD. By Western blot analysis, the two smallest of these reacted with two antibodies to the human fibroblast proteoglycan versican. RNAs hybridizing to versican probes were found only in adult medial-type SMCs, including an adult medial type clone from pup aorta, by Northern blot analysis. Both SMC types synthesize RNAs that hybridize to probes for other proteoglycans, such as perlecan, biglycan, and decorin. We conclude that rat pi SMC cultures, unlike monkey, human, and rat adult medial SMC cultures, express little or no versican. This difference in expression may be responsible for the different morphologies and growth properties of the two cell types.

Heparin binding, internalization, and metabolism in vascular smooth muscle cells: II. Degradation and secretion in sensitive and resistant cells

Smooth muscle cell (SMC) proliferation plays a critical role in several pathological states, including atherosclerosis and hypertension. Heparin suppresses SMC proliferation in vivo and in culture, but the mechanism of action is still poorly understood. In an accompanying article in this issue (Letourneur et al. [1995] J. Cell Physiol., 165:676-686), we observed that heparin binding was up-regulated in heparin-sensitive SMC but was rapidly down-regulated in heparin-resistant SMC continuously exposed to heparin. In this communication, we examine the degradation and secretion of internalized heparin in sensitive and resistant SMC, using gel filtration chromatography to analyze heparin degradation products. Pulse-chase experiments using radiolabeled heparin indicate that sensitive and resistant SMC secrete heparin during the first few hours after exposure. Experiments in which cells are continuously exposed to heparin indicate that degradation and secretion occur in both sensitive and resistant SMC for approximately 5-8 hr. After that time, however, binding and internalization in resistant SMC rapidly decrease and degradation and secretion stop. In contrast, heparin binding and uptake continue in sensitive SMC; degradation and secretion also continue. Chloroquine prevents degradation in both sensitive and resistant SMC, suggesting that catabolism occurs in the lysosomal compartment. The results presented in this and the accompanying article (Letourneur et al. [1995] J. Cell. Physiol., 165:676-686) suggest that heparin acts to upregulate its receptors, and that increased binding of heparin is required for the antiproliferative response. Degradation and secretion kinetics parallel the internalization kinetics and appear to be strongly linked to the binding process.

Small proteoglycans

In this review the structure and functions of two non-related proteoglycan families are discussed. One family represents a group of extracellular matrix macromolecules characterized by core proteins with leucine-rich repeat motifs. Within this family special attention is given to those members which carry chondroitin or dermatan sulfate glycosaminoglycan chains. The second family is characterized by repeat sequences of serine and glycine. Their members are products of a single core protein gene and are characteristic constituents of secondary vesicles in cells of the haematopoietic lineage.

Small proteoglycans

In this review the structure and functions of two non-related proteoglycan families are discussed. One family represents a group of extracellular matrix macromolecules characterized by core proteins with leucine-rich repeat motifs. Within this family special attention is given to those members which carry chondroitin or dermatan sulfate glycosaminoglycan chains. The second family is characterized by repeat sequences of serine and glycine. Their members are products of a single core protein gene and are characteristic constituents of secretory vesicles in cells of the haematopoietic lineage.