A characteristic chondroitin sulfate trisaccharide unit with a sulfated fucose branch exhibits neurite outgrowth-promoting activity: Novel biological roles of fucosylated chondroitin sulfates isolated from the sea cucumber Apostichopus japonicus

Chondroitin sulfate (CS) is a class of sulfated glycosaminoglycan (GAG) chains that consist of repeating disaccharide unit composed of glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc). CS chains are found throughout the pericellular and extracellular spaces and contribute to the formation of functional microenvironments for numerous biological events. However, their structure-function relations remain to be fully characterized. Here, a fucosylated CS (FCS) was isolated from the body wall of the sea cucumber Apostichopus japonicus. Its promotional effects on neurite outgrowth were assessed by using isolated polysaccharides and the chemically synthesized FCS trisaccharide β-D-GalNAc(4,6-O-disulfate) (1-4)[α-l-fucose (2,4-O-disulfate) (1-3)]-β-D-GlcA. FCS polysaccharides contained the E-type disaccharide unit GlcA-GalNAc(4,6-O-disulfate) as a CS major backbone structure and carried distinct sulfated fucose branches. Despite their relatively lower abundance of E unit, FCS polysaccharides exhibited neurite outgrowth-promoting activity comparable to squid cartilage-derived CS-E polysaccharides, which are characterized by their predominant E units, suggesting potential roles of the fucose branch in neurite outgrowth. Indeed, the chemically synthesized FCS trisaccharide was as effective as CS-E tetrasaccharide in stimulating neurite elongation in vitro. In conclusion, FCS trisaccharide units with 2,4-O-disulfated fucose branches may provide new insights into understanding the structure-function relations of CS chains.

Pathophysiological Significance of Dermatan Sulfate Proteoglycans Revealed by Human Genetic Disorders

The indispensable roles of dermatan sulfate-proteoglycans (DS-PGs) have been demonstrated in various biological events including construction of the extracellular matrix and cell signaling through interactions with collagen and transforming growth factor-β, respectively. Defects in the core proteins of DS-PGs such as decorin and biglycan cause congenital stromal dystrophy of the cornea, spondyloepimetaphyseal dysplasia, and Meester-Loeys syndrome. Furthermore, mutations in human genes encoding the glycosyltransferases, epimerases, and sulfotransferases responsible for the biosynthesis of DS chains cause connective tissue disorders including Ehlers-Danlos syndrome and spondyloepimetaphyseal dysplasia with joint laxity characterized by skin hyperextensibility, joint hypermobility, and tissue fragility, and by severe skeletal disorders such as kyphoscoliosis, short trunk, dislocation, and joint laxity. Glycobiological approaches revealed that mutations in DS-biosynthetic enzymes cause reductions in enzymatic activities and in the amount of synthesized DS and also disrupt the formation of collagen bundles. This review focused on the growing number of glycobiological studies on recently reported genetic diseases caused by defects in the biosynthesis of DS and DS-PGs.

Histone deacetylase-mediated regulation of chondroitin 4-O-sulfotransferase-1 (Chst11) gene expression by Wnt/β-catenin signaling

Chondroitin sulfate (CS) proteoglycans are abundant extracellular and cell surface molecules that consist of a protein core to which highly sulfated CS chains are covalently attached. The CS backbone is composed of repeating disaccharide units [-GlcA-GalNAc-]_n, and during synthesis the CS chains acquire structural variability due to the action of sulfotransferases. Specific sulfation patterns are recognized by a large variety of proteins, including growth factors, morphogens, and extracellular matrix proteins, and these interactions regulate key events in development and normal physiology. Therefore, it is important to understand how gene expression of CS sulfotransferases is regulated. We previously found that Wnt signaling regulates the sulfation patterns of cell-associated CS chains by suppressing expression of chondroitin 4-O-sulfotaransferase-1 (C4ST-1), a CS biosynthetic enzyme. Here we investigated the mechanism underlying the regulation of C4ST-1 gene expression by Wnt/β-catenin signaling. Although C4ST-1 mRNA of 3'-UTR contains three binding sites for microRNAs (miRNA), these miRNAs played little role in controlling C4ST-1 gene expression. In contrast, the suppression of C4ST-1 gene expression by Wnt/β-catenin signaling can be recovered by treatment with trichostatin A, but not with 5'-aza-2'-deoxycytidine. These results suggest that the Wnt/β-catenin signal pathway controls C4ST-1 gene expression mainly through histone deacetylase.

Chondroitin 4-O-Sulfotransferase Is Indispensable for Sulfation of Chondroitin and Plays an Important Role in Maintaining Normal Life Span and Oxidative Stress Responses in Nematodes

Chondroitin sulfate (CS)/chondroitin (Chn) chains are indispensable for embryonic cell division and cytokinesis in the early developmental stages in Caenorhabditis elegans and mice, whereas heparan sulfate (HS) is essential for axon guidance during nervous system development. These data indicate that the fundamental functions of CS and HS are conserved from worms to mammals and that the function of CS/Chn differs from that of HS. Although previous studies have shown that C. elegans produces HS and non-sulfated Chn, whether the organism produces CS remains unclear. Here, we demonstrate that C. elegans produces a small amount of 4-O-sulfated Chn and report the identification of C41C4.1, an orthologue of the human chondroitin 4-O-sulfotransferase gene. Loss of C41C4.1 in C. elegans resulted in a decline in 4-O-sulfation of CS and an increase in the number of sulfated units in HS. C41C4.1 deletion mutants exhibited reduced survival rates after synchronization with sodium hypochlorite. Collectively, these results show for the first time that CS glycans are present in C. elegans and that the Chn 4-O-sulfotransferase responsible for the sulfation plays an important role in protecting nematodes from oxidative stress.

The role of specific Smad linker region phosphorylation in TGF-β mediated expression of glycosaminoglycan synthesizing enzymes in vascular smooth muscle

Hyperelongation of glycosaminoglycan chains on proteoglycans facilitates increased lipoprotein binding in the blood vessel wall and the development of atherosclerosis. Increased mRNA expression of glycosaminoglycan chain synthesizing enzymes in vivo is associated with the development of atherosclerosis. In human vascular smooth muscle, transforming growth factor-β (TGF-β) regulates glycosaminoglycan chain hyperelongation via ERK and p38 as well as Smad2 linker region (Smad2L) phosphorylation. In this study, we identified the involvement of TGF-β receptor, intracellular serine/threonine kinases and specific residues on transcription factor Smad2L that regulate glycosaminoglycan synthesizing enzymes. Of six glycosaminoglycan synthesizing enzymes, xylosyltransferase-1, chondroitin sulfate synthase-1, and chondroitin sulfotransferase-1 were regulated by TGF-β. In addition ERK, p38, PI3K and CDK were found to differentially regulate mRNA expression of each enzyme. Four individual residues in the TGF-β receptor mediator Smad2L can be phosphorylated by these kinases and in turn regulate the synthesis and activity of glycosaminoglycan synthesizing enzymes. Smad2L Thr220 was phosphorylated by CDKs and Smad2L Ser250 by ERK. p38 selectively signalled via Smad2L Ser245. Phosphorylation of Smad2L serine residues induced glycosaminoglycan synthesizing enzymes associated with glycosaminoglycan chain elongation. Phosphorylation of Smad2L Thr220 was associated with XT-1 enzyme regulation, a critical enzyme in chain initiation. These findings provide a deeper understanding of the complex signalling pathways that contribute to glycosaminoglycan chain modification that could be targeted using pharmacological agents to inhibit the development of atherosclerosis.

Emerging tools to study proteoglycan function during skeletal development

In the past 20years, appreciation for the varied roles of proteoglycans (PGs), which are specific types of sugar-coated proteins, has increased dramatically. PGs in the extracellular matrix were long known to impart structural functions to many tissues, especially articular cartilage, which cushions bones and allows mobility at skeletal joints. Indeed, osteoarthritis is a debilitating disease associated with loss of PGs in articular cartilage. Today, however, PGs have a demonstrated role in cell biological processes, such as growth factor signalling, prompting new perspectives on the etiology of PG-associated diseases. Here, we review diseases associated with defects in PG synthesis and sulfation, also highlighting current understanding of the underlying genetics, biochemistry, and cell biology. Since most research has analyzed a class of PGs called heparan sulfate PGs, more attention is paid here to studies of chondroitin sulfate PGs (CSPGs), which are abundant in cartilage. Interestingly, CSPG synthesis is tightly linked to the cell biological processes of secretion and lysosomal degradation, suggesting that these systems may be linked genetically. Animal models of loss of CSPG function have revealed CSPGs to impact skeletal development. Specifically, our work from a mutagenesis screen in zebrafish led to the hypothesis that cartilage PGs normally delay the timing of endochondral ossification. Finally, we outline emerging approaches in zebrafish that may revolutionize the study of cartilage PG function, including transgenic methods and novel imaging techniques. Our recent work with X-ray fluorescent imaging, for example, enables direct correlation of PG function with PG-dependent biological processes.

Glycosyltransferase complexes in eukaryotes: long-known, prevalent but still unrecognized

Glycosylation is the most common and complex cellular modification of proteins and lipids. It is critical for multicellular life and its abrogation often leads to a devastating disease. Yet, the underlying mechanistic details of glycosylation in both health and disease remain unclear. Partly, this is due to the complexity and dynamicity of glycan modifications, and the fact that not all the players are taken into account. Since late 1960s, a vast number of studies have demonstrated that glycosyltransferases typically form homomeric and heteromeric complexes with each other in yeast, plant and animal cells. To propagate their acceptance, we will summarize here accumulated data for their prevalence and potential functional importance for glycosylation focusing mainly on their mutual interactions, the protein domains mediating these interactions, and enzymatic activity changes that occur upon complex formation. Finally, we will highlight the few existing 3D structures of these enzyme complexes to pinpoint their individual nature and to emphasize that their lack is the main obstacle for more detailed understanding of how these enzyme complexes interact and function in a eukaryotic cell.

Basing RNA-seq explored the regulatory mechanism of the carbohydrate metabolism pathways during chicken male germ cell differentiation

Our study aimed to explore the regulatory mechanism of the carbohydrate metabolism signaling pathways and related genes during the differentiation of chicken embryonic stem cells to male germ cells, providing the basis for improving the efficiency of the in vitro induction system. Cell sorting was used to obtain highly purified embryonic stem cells (ESCs), primitive germ cells (PGCs), and spermatogonial stem cells (SSCs). The total RNA was then extracted from each cell type. The transcriptions of ESCs, PGCs, and SSCs were sequenced by DNA microarray and mRNA sequencing (RNA-seq). The results were analyzed by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database. The key pathways and genes of carbohydrate metabolism were screened during the differentiation process of chicken male germ cell. We concluded that 419 differentially expressed genes enriched to 26 carbohydrate metabolism pathways during the differentiation process of ESCs to SSCs, all of the chondroitin sulfate (CS) signaling pathway was significant. We screened the key genes CHSY3, B3GAT1, CHPF, and B4GALT7 which was significantly expressed in CS pathway. Quantitative RT-PCR showed that the expression trend of these genes is consistent with DNA Microarray and RNA-seq results. Our study supports the opinion that CS pathway is significantly different during the differentiation of chicken male germ cell (P < 0.05) and that CHSY3, B3GAT1, CHPF, and B4GALT7 are key genes.

Amino acid sequence surrounding the chondroitin sulfate attachment site of thrombomodulin regulates chondroitin polymerization

Thrombomodulin (TM) is a cell-surface glycoprotein and a critical mediator of endothelial anticoagulant function. TM exists as both a chondroitin sulfate (CS) proteoglycan (PG) form and a non-PG form lacking a CS chain (α-TM); therefore, TM can be described as a part-time PG. Previously, we reported that α-TM bears an immature, truncated linkage tetrasaccharide structure (GlcAβ1-3Galβ1-3Galβ1-4Xyl). However, the biosynthetic mechanism to generate part-time PGs remains unclear. In this study, we used several mutants to demonstrate that the amino acid sequence surrounding the CS attachment site influences the efficiency of chondroitin polymerization. In particular, the presence of acidic residues surrounding the CS attachment site was indispensable for the elongation of CS. In addition, mutants defective in CS elongation did not exhibit anti-coagulant activity, as in the case with α-TM. Together, these data support a model for CS chain assembly in which specific core protein determinants are recognized by a key biosynthetic enzyme involved in chondroitin polymerization.

Chondroitin sulfate-E mediates estrogen-induced osteoanabolism

Osteoporosis is an age-related disorder of bone remodeling in which bone resorption outstrips bone matrix deposition. Although anticatabolic agents are frequently used as first-line therapies for osteoporosis, alternative anabolic strategies that can enhance anabolic, osteogenic potential are actively sought. Sex steroid hormones, particularly estrogens, are bidirectional regulators for bone homeostasis; therefore, estrogen-mediated events are important potential targets for such anabolic therapies. Here, we show that estrogen-induced, osteoanabolic effects were mediated via enhanced production of chondroitin sulfate-E (CS-E), which could act as an osteogenic stimulant in our cell-based system. Conversely, estrogen deficiency caused reduced expression of CS-E-synthesizing enzymes, including GalNAc4S-6ST, and led to decreased CS-E production in cultures of bone marrow cells derived from ovariectomized mice. Moreover, Galnac4s6st-deficient mice had abnormally low bone mass that resulted from impaired osteoblast differentiation. These results indicated that strategies aimed at boosting CS-E biosynthesis are promising alternative therapies for osteoporosis.

GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate) is the preferred substrate for chondroitin N-acetylgalactosaminyltransferase-1

A deficiency in chondroitin N-acetylgalactosaminyltransferase-1 (ChGn-1) was previously shown to reduce the number of chondroitin sulfate (CS) chains, leading to skeletal dysplasias in mice, suggesting that ChGn-1 regulates the number of CS chains for normal cartilage development. Recently, we demonstrated that 2-phosphoxylose phosphatase (XYLP) regulates the number of CS chains by dephosphorylating the Xyl residue in the glycosaminoglycan-protein linkage region of proteoglycans. However, the relationship between ChGn-1 and XYLP in controlling the number of CS chains is not clear. In this study, we for the first time detected a phosphorylated tetrasaccharide linkage structure, GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate), in ChGn-1(-/-) growth plate cartilage but not in ChGn-2(-/-) or wild-type growth plate cartilage. In contrast, the truncated linkage tetrasaccharide GlcUAβ1-3Galβ1-3Galβ1-4Xyl was detected in wild-type, ChGn-1(-/-), and ChGn-2(-/-) growth plate cartilage. Consistent with the findings, ChGn-1 preferentially transferred N-acetylgalactosamine to the phosphorylated tetrasaccharide linkage in vitro. Moreover, ChGn-1 and XYLP interacted with each other, and ChGn-1-mediated addition of N-acetylgalactosamine was accompanied by rapid XYLP-dependent dephosphorylation during formation of the CS linkage region. Taken together, we conclude that the phosphorylated tetrasaccharide linkage is the preferred substrate for ChGn-1 and that ChGn-1 and XYLP cooperatively regulate the number of CS chains in growth plate cartilage.

Mechanisms for modulation of neural plasticity and axon regeneration by chondroitin sulphate

Chondroitin sulphate proteoglycans (CSPGs), consisting of core proteins linked to one or more chondroitin sulphate (CS) chains, are major extracellular matrix (ECM) components of the central nervous system (CNS). Multi-functionality of CSPGs can be explained by the diversity in structure of CS chains that undergo dynamic changes during development and under pathological conditions. CSPGs, together with other ECM components, form mesh-like structures called perineuronal nets around a subset of neurons. Enzymatic digestion or genetic manipulation of CSPGs reactivates neural plasticity in the adult brain and improves regeneration of damaged axons after CNS injury. Recent studies have shown that CSPGs not only act as non-specific physical barriers that prevent rearrangement of synaptic connections but also regulate neural plasticity through specific interaction of CS chains with its binding partners in a manner that depends on the structure of the CS chain.

Human genetic disorders and knockout mice deficient in glycosaminoglycan

Glycosaminoglycans (GAGs) are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases and sulfotransferases. The structural diversity of GAG polysaccharides, including their sulfation patterns and sequential arrangements, is essential for a wide range of biological activities such as cell signaling, cell proliferation, tissue morphogenesis, and interactions with various growth factors. Studies using knockout mice of enzymes responsible for the biosynthesis of the GAG side chains of proteoglycans have revealed their physiological functions. Furthermore, mutations in the human genes encoding glycosyltransferases, sulfotransferases, and related enzymes responsible for the biosynthesis of GAGs cause a number of genetic disorders including chondrodysplasia, spondyloepiphyseal dysplasia, and Ehlers-Danlos syndromes. This review focused on the increasing number of glycobiological studies on knockout mice and genetic diseases caused by disturbances in the biosynthetic enzymes for GAGs.

Metabolism of cartilage proteoglycans in health and disease

Cartilage proteoglycans are extracellular macromolecules with complex structure, composed of a core protein onto which a variable number of glycosaminoglycan chains are attached. Their biosynthesis at the glycosaminoglycan level involves a great number of sugar transferases well-orchestrated in Golgi apparatus. Similarly, their degradation, either extracellular or intracellular in lysosomes, involves a large number of hydrolases. A deficiency or malfunction of any of the enzymes participating in cartilage proteoglycan metabolism may lead to severe disease state. This review summarizes the findings regarding this topic.

Chondroitin sulfate proteoglycans: structure-function relationship with implication in neural development and brain disorders

Chondroitin sulfate proteoglycans (CSPGs) are extracellular matrix components that contain two structural parts with distinct functions: a protein core and glycosaminoglycan (GAG) side chains. CSPGs are known to be involved in important cell processes like cell adhesion and growth, receptor binding, or cell migration. It is recognized that the presence of CSPGs is critical in neuronal growth mechanisms including axon guidance following injury of nervous system components such as spinal cord and brain. CSPGs are upregulated in the central nervous system after injury and participate in the inhibition of axon regeneration mainly through their GAG side chains. Recently, it was shown that some CSPGs members like aggrecan, versican, and neurocan were strongly involved in brain disorders like bipolar disorder (BD), schizophrenia, and ADHD. In this paper, we present the chemical structure-biological functions relationship of CSPGs, both in health state and in genetic disorders, addressing methods represented by genome-wide and crystallographic data as well as molecular modeling and quantitative structure-activity relationship.

Age-dependent alterations of decorin glycosaminoglycans in human skin

Proteoglycans, a family of glycosaminoglycan (GAG) conjugated proteins, are important constituents of human skin connective tissue (dermis) and are essential for maintaining mechanical strength of the skin. Age-related alterations of dermal proteoglycans have not been fully elucidated. We quantified transcripts of 20 known interstitial proteoglycans in human skin and found that decorin was the most highly expressed. Decorin was predominantly produced by dermal fibroblasts. Decorin was localized in dermal extracellular matrix with GAG bound to type I collagen fibrils. Analysis of decorin extracted from young (21–30 years) and aged (>80 years) sun-protected human buttock skin revealed that decorin molecular size in aged skin is significantly smaller than in young skin. The average size of decorin protein did not alter, indicating size of GAG chain is reduced in aged, compared to young skin. This age-dependent alteration of decorin GAG may contribute to skin fragility of elderly people.

Alterations in the chondroitin sulfate chain in human osteoarthritic cartilage of the knee

OBJECTIVE

To determine whether the structure of chondroitin sulfate (CS) in cartilage is reflected by the degree of cartilage degeneration in patients with osteoarthritis (OA) of the knee and to determine how CS biosynthesis affects cartilage degeneration.

DESIGN

Two osteoarthritic cartilage samples were obtained from medial femoral condyle (MFC) and lateral femoral condyle (LFC) of 24 knees with end-stage OA. The samples were assigned to two groups as follows: lesion and remote cartilage were adjacent to and remote from the osteoarthritic cartilage, respectively. Histological grade was determined according to the Mankin score. The CS concentration and chain length were determined using high-performance liquid chromatography (HPLC) and gel filtration chromatography, respectively. Expression of the gene encoding CS glycosyltransferase was evaluated using a real-time quantitative polymerase chain reaction (qPCR) assay. These results were compared between lesion and remote cartilage.

RESULTS

The Mankin score indicated that lesion cartilage was more degraded compared with remote cartilage. Although the CS levels varied among individuals, the mean CS concentration and chain length were significantly lower and shorter in lesion cartilage than in remote cartilage, respectively (concentration: 12.04 vs 14.84 μg/mg wet weight, P = 0.021; chain length: 5.36 vs 6.19 kDa, P = 0.026). Three genes encoding CS glycosyltransferases (CHPF, CSGALNACT1, CSGALNACT2) were expressed at lower levels in lesion cartilage.

CONCLUSIONS

In the osteoarthritic knee, the CS concentration and chain length were reduced closer to the more degraded cartilage with decreasing CS glycosyltransferase gene expression. Inhibition of CS glycosyltransferase gene expression may reduce CS chain length, which may contribute to OA progression.

Chondroitin sulfate is indispensable for pluripotency and differentiation of mouse embryonic stem cells

Chondroitin sulfate (CS) proteoglycans are present on the surfaces of virtually all cells and in the extracellular matrix and are required for cytokinesis at early developmental stages. Studies have shown that heparan sulfate (HS) is essential for maintaining mouse embryonic stem cells (ESCs) that are primed for differentiation, whereas the function of CS has not yet been elucidated. To clarify the role of CS, we generated glucuronyltransferase-I-knockout ESCs lacking CS. We found that CS was required to maintain the pluripotency of ESCs and promoted initial ESC commitment to differentiation compared with HS. In addition, CS-A and CS-E polysaccharides, but not CS-C polysaccharides, bound to E-cadherin and enhanced ESC differentiation. Multiple-lineage differentiation was inhibited in chondroitinase ABC-digested wild-type ESCs. Collectively, these results suggest that CS is a novel determinant in controlling the functional integrity of ESCs via binding to E-cadherin.

Identification of phosphatase that dephosphorylates xylose in the glycosaminoglycan-protein linkage region of proteoglycans

Recently, we demonstrated that FAM20B is a kinase that phosphorylates the xylose (Xyl) residue in the glycosaminoglycan-protein linkage region of proteoglycans. The phosphorylation of Xyl residues by FAM20B enhances the formation of the linkage region. Rapid dephosphorylation is probably induced just after synthesis of the linker and just before polymerization initiates. Indeed, in vitro chondroitin or heparan sulfate polymerization does not occur when the Xyl residue of the tetrasaccharide linkage region is phosphorylated. However, the enzyme responsible for the dephosphorylation of Xyl remains unknown. Here, we identified a novel protein that dephosphorylates the Xyl residue and designated it 2-phosphoxylose phosphatase. The phosphatase efficiently removed the phosphate from the phosphorylated trisaccharide, Galβ1-3Galβ1-4Xyl(2-O-phosphate), but not from phosphorylated tetrasaccharide, GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate). Additionally, RNA interference-mediated inhibition of 2-phosphoxylose phosphatase resulted in increased amounts of GlcNAcα1-4GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate), Galβ1-3Galβ1-4Xyl(2-O-phosphate), and Galβ1-4Xyl(2-O-phosphate) in the cells. Gel filtration analysis of the glycosaminoglycan chains synthesized in the knockdown cells revealed that these cells produced decreased amounts of glycosaminoglycan chains and that the chains had similar lengths to those in the mock-transfected cells. Transcripts encoding this phosphatase were ubiquitously, but differentially, expressed in human tissues. Moreover, the phosphatase localized to the Golgi and interacted with the glucuronyltransferase-I involved in the completion of the glycosaminoglycan-protein linkage region. Based on these findings, we conclude that transient phosphorylation of the Xyl residue in the glycosaminoglycan-protein linkage region controls the formation of glycosaminoglycan chains of proteoglycans.

A chondroitin synthase-1 (ChSy-1) missense mutation in a patient with neuropathy impairs the elongation of chondroitin sulfate chains initiated by chondroitin N-acetylgalactosaminyltransferase-1

BACKGROUND

Previously, we identified two missense mutations in the chondroitin N-acetylgalactosaminyltransferase-1 gene in patients with neuropathy. These mutations are associated with a profound decrease in chondroitin N-acetylgalactosaminyltransferase-1 enzyme activity. Here, we describe a patient with neuropathy who is heterozygous for a chondroitin synthase-1 mutation. Chondroitin synthase-1 has two glycosyltransferase activities: it acts as a GlcUA and a GalNAc transferase and is responsible for adding repeated disaccharide units to growing chondroitin sulfate chains.

METHODS

Recombinant wild-type chondroitin synthase-1 enzyme and the F362S mutant were expressed. These enzymes and cells expressing them were then characterized.

RESULTS

The mutant chondroitin synthase-1 protein retained approximately 50% of each glycosyltransferase activity relative to the wild-type chondroitin synthase-1 protein. Furthermore, unlike chondroitin polymerase comprised of wild-type chondroitin synthase-1 protein, the non-reducing terminal 4-O-sulfation of GalNAc residues synthesized by chondroitin N-acetylgalactosaminyltransferase-1 did not facilitate the elongation of chondroitin sulfate chains when chondroitin polymerase that consists of the mutant chondroitin synthase-1 protein was used as the enzyme source.

CONCLUSIONS

The chondroitin synthase-1 F362S mutation in a patient with neuropathy resulted in a decrease in chondroitin polymerization activity and the mutant protein was defective in regulating the number of chondroitin sulfate chains via chondroitin N-acetylgalactosaminyltransferase-1. Thus, the progression of peripheral neuropathies may result from defects in these regulatory systems.

GENERAL SIGNIFICANCE

The elongation of chondroitin sulfate chains may be tightly regulated by the cooperative expression of chondroitin synthase-1 and chondroitin N-acetylgalactosaminyltransferase-1 in peripheral neurons and peripheral neuropathies may result from synthesis of abnormally truncated chondroitin sulfate chains.

Expression of chondroitin/dermatan sulfate glycosyltransferases during early zebrafish development

BACKGROUND

Chondroitin/dermatan sulfate (CS/DS) proteoglycans present in the extracellular matrix have important structural and regulatory functions.

RESULTS

Six human genes have previously been shown to catalyze CS/DS polymerization. Here we show that one of these genes, chpf, is represented by two copies in the zebrafish genome, chpfa and chpfb, while the other five human CS/DS glycosyltransferases csgalnact1, csgalnact2, chpf2, chsy1, and chsy3 all have single zebrafish orthologues. The putative zebrafish CS/DS glycosyltransferases are spatially and temporally expressed. Interestingly, overlapping expression of multiple glycosyltransferases coincides with high CS/DS deposition. Finally, whereas the relative levels of the related polysaccharide HS reach steady-state at around 2 days post fertilization, there is a continued relative increase of the CS amounts per larvae during the first 6 days of development, matching the increased cartilage formation.

CONCLUSIONS

There are 7 CS/DS glycosyltransferases in zebrafish, which, based on homology, can be divided into the CSGALNACT, CHSY, and CHPF families. The overlap between intense CS/DS production and the expression of multiple CS/DS glycosyltransferases suggests that efficient CS/DS biosynthesis requires a combination of several glycosyltransferases.

Decorin, lumican, and their GAG chain-synthesizing enzymes are regulated in myocardial remodeling and reverse remodeling in the mouse

On the basis of the role of small, leucine-rich proteoglycans (SLRPs) in fibrogenesis and inflammation, we hypothesized that they could be involved in cardiac remodeling and reverse remodeling as occurs during aortic stenosis and after aortic valve replacement. Thus, in a well-characterized aortic banding-debanding mouse model, we examined the SLRPs decorin and lumican and enzymes responsible for synthesis of their glycosaminoglycan (GAG) chains. Four weeks after banding of the ascending aorta, mice were subjected to a debanding operation (DB) and were subsequently followed for 3 or 14 days. Sham-operated mice served as controls. Western blotting revealed a 2.5-fold increase in the protein levels of glycosylated decorin in mice with left ventricular pressure overload after aortic banding (AB) with a gradual decrease after DB. Interestingly, protein levels of three key enzymes responsible for decorin GAG chain synthesis were also increased after AB, two of them gradually declining after DB. The inflammatory chemokine (C-X-C motif) ligand 16 (CXCL16) was increased after AB but was not significantly altered following DB. In cardiac fibroblasts CXCL16 increased the expression of the GAG-synthesizing enzyme chondroitin polymerizing factor (CHPF). The protein levels of lumican core protein with N-linked oligosaccharides increased by sevenfold after AB and decreased again 14 days after DB. Lumican with keratan sulfate chains was not regulated. In conclusion, this study shows alterations in glycosylated decorin and lumican core protein that might be implicated in myocardial remodeling and reverse remodeling, with a potential important role for CS/DS GAG chain-synthesizing enzymes.

Human genetic disorders caused by mutations in genes encoding biosynthetic enzymes for sulfated glycosaminoglycans

A number of genetic disorders are caused by mutations in the genes encoding glycosyltransferases and sulfotransferases, enzymes responsible for the synthesis of sulfated glycosaminoglycan (GAG) side chains of proteoglycans, including chondroitin sulfate, dermatan sulfate, and heparan sulfate. The phenotypes of these genetic disorders reflect disturbances in crucial biological functions of GAGs in human. Recent studies have revealed that mutations in genes encoding chondroitin sulfate and dermatan sulfate biosynthetic enzymes cause various disorders of connective tissues. This minireview focuses on growing glycobiological studies of recently described genetic diseases caused by disturbances in biosynthetic enzymes for sulfated GAGs.

Gene delivery to overcome astrocyte inhibition of axonal growth: an in vitro model of the glial scar

After injury to the central nervous system, a glial scar develops that physically and biochemically inhibits axon growth. In the scar, activated astrocytes secrete inhibitory extracellular matrix, of which chondroitin sulfate proteoglycans (CSPGs) are considered the major inhibitory component. An inhibitory interface of CSPGs forms around the lesion and prevents axons from traversing the injury, and decreasing CSPGs can enhance axon growth. In this report, we established an in vitro interface model of activated astrocytes and subsequently investigated gene delivery as a means to reduce CSPG levels and enhance axon growth. In the model, a continuous interface of CSPG producing astrocytes was created with neurons seeded opposite the astrocytes, and neurite crossing, stopping, and turning were evaluated as they approached the interface. We investigated the efficacy of lentiviral delivery to degrade or prevent the synthesis of CSPGs, thereby removing CSPG inhibition of neurite growth. Lentiviral delivery of RNAi targeting two key CSPG synthesis enzymes, chondroitin polymerizing factor and chondroitin synthase-1, decreased CSPGs, and reduced inhibition by the interface. Degradation of CSPGs by lentiviral delivery of chondroitinase also resulted in less inhibition and more neurites crossing the interface. These results indicate that the interface model provides a tool to investigate interventions that reduce inhibition by CSPGs, and that gene delivery can be effective in promoting neurite growth across an interface of CSPG producing astrocytes.

Involvement of Ext1 and heparanase in migration of mouse FBJ osteosarcoma cells

To know the involvement of glycosaminoglycans (GAGs) in the metastasis of mouse FBJ osteosarcoma cells, N(α)-lauroyl-O-(β-D-xylopyranosyl)-L-serinamide (Xyl-Ser-C12), which initiates elongation of GAG chains using the glycan biosynthesis system in cells, was administered to FBJ cells with different metastatic capacities. Production of glycosylated products derived from Xyl-Ser-C12, especially heparan sulfate (HS) GAG-type oligosaccharides such as GalNAc-GlcA-GlcNAc-GlcA-Gal-Gal-Xyl-Ser-C12, was indicated in poorly metastatic FBJ-S1 cells more than in highly metastatic FBJ-LL cells by LC-MS. The results of RT-PCR revealed that HS synthases, Ext1 and Ext2, were expressed in FBJ-S1 cells more than in FBJ-LL cells. Furthermore, siRNA against Ext1 suppressed the expression of HS and enhanced the motility of FBJ-S1 cells. In addition, the expression of heparanase (HPSE) was enhanced in Ext-1-knockdown FBJ-S1 cells, and responsible for the increase in cell motility caused by the down-regulation of Ext1 expression. Our data provide the first evidence that Ext1 regulates the expression of HPSE and also indicated that levels of Ext1 and HPSE influenced the motility of FBJ cells.

Proteoglycan synthesis and Golgi organization in polarized epithelial cells

A large number of complex glycosylation mechanisms take place in the Golgi apparatus. In epithelial cells, glycosylated protein molecules are transported to both the apical and the basolateral surface domains. Although the prevailing view is that the Golgi apparatus provides the same lumenal environment for glycosylation of apical and basolateral cargo proteins, there are indications that proteoglycans destined for the two opposite epithelial surfaces are exposed to different conditions in transit through the Golgi apparatus. We will here review data relating proteoglycan and glycoprotein synthesis to characteristics of the apical and basolateral secretory pathways in epithelial cells.

Chondroitin sulfate synthase-2 is necessary for chain extension of chondroitin sulfate but not critical for skeletal development

Chondroitin sulfate (CS) is a linear polysaccharide consisting of repeating disaccharide units of N-acetyl-D-galactosamine and D-glucuronic acid residues, modified with sulfated residues at various positions. Based on its structural diversity in chain length and sulfation patterns, CS provides specific biological functions in cell adhesion, morphogenesis, neural network formation, and cell division. To date, six glycosyltransferases are known to be involved in the biosynthesis of chondroitin saccharide chains, and a hetero-oligomer complex of chondroitin sulfate synthase-1 (CSS1)/chondroitin synthase-1 and chondroitin sulfate synthase-2 (CSS2)/chondroitin polymerizing factor is known to have the strongest polymerizing activity. Here, we generated and analyzed CSS2^−/− mice. Although they were viable and fertile, exhibiting no overt morphological abnormalities or osteoarthritis, their cartilage contained CS chains with a shorter length and at a similar number to wild type. Further analysis using CSS2^−/− chondrocyte culture systems, together with siRNA of CSS1, revealed the presence of two CS chain species in length, suggesting two steps of CS chain polymerization; i.e., elongation from the linkage region up to Mr ∼10,000, and further extension. There, CSS2 mainly participated in the extension, whereas CSS1 participated in both the extension and the initiation. Our study demonstrates the distinct function of CSS1 and CSS2, providing a clue in the elucidation of the mechanism of CS biosynthesis.

Chondroitin sulfate-E fine-tunes osteoblast differentiation via ERK1/2, Smad3 and Smad1/5/8 signaling by binding to N-cadherin and cadherin-11

Bone formation in the vertebrate skeleton occurs via the processes of endochondral and membranous ossification. Bone matrices contain chondroitin sulfate (CS) chains that regulate endochondral ossification. However, the function of CS in membranous ossification is unclear. Here, using preosteoblastic MC3T3-E1 cells we demonstrate that chondroitin sulfate-E (CS-E) promotes osteoblast differentiation by binding to both N-cadherin and cadherin-11. Differentiated MC3T3-E1 cells exhibited an increase in the total amount of CS and of E-disaccharide units of CS over time. In addition, CS-E polysaccharide, but not CS-A polysaccharide, bound to N-cadherin and cadherin-11 and enhanced osteoblast differentiation. In contrast, osteoblast differentiation was inhibited in chondroitinase ABC-digested MC3T3-E1 cells. Notably, CS-E polysaccharide and hexasaccharide activated intracellular signaling during osteoblast differentiation in non-contacting MC3T3-E1 cells, decreased ERK1/2 phosphorylation, and activated Smad3 and Smad1/5/8; these reactions were blocked by neutralizing antibodies against N-cadherin or cadherin-11, even though cell-cell adhesion is reported to be required for initiation of MC3T3-E1 cell differentiation. Furthermore, CS-E-unit overexpression in MC3T3-E1 cells increased adhesion of the cells to N-cadherin and cadherin-11, and promoted osteoblast differentiation. Collectively, these results suggest that CS-E is a selective ligand for the potential CS receptors, N-cadherin and cadherin-11, leading to osteoblast differentiation of MC3T3-E1 cells.

Chondroitin sulfate synthase 1 (Chsy1) is required for bone development and digit patterning

Joint and skeletal development is highly regulated by extracellular matrix (ECM) proteoglycans, of which chondroitin sulfate proteoglycans (CSPGs) are a major class. Despite the requirement of joint CSPGs for skeletal flexibility and structure, relatively little is understood regarding their role in establishing joint positioning or in modulating signaling and cell behavior during joint formation. Chondroitin sulfate synthase 1 (Chsy1) is one of a family of enzymes that catalyze the extension of chondroitin and dermatan sulfate glycosaminoglycans. Recently, human syndromic brachydactylies have been described to have loss-of-function mutations at the CHSY1 locus. In concordance with these observations, we demonstrate that mice lacking Chsy1, though viable, display chondrodysplasia and decreased bone density. Notably, Chsy1(-/-) mice show a profound limb patterning defect in which orthogonally shifted ectopic joints form in the distal digits. Associated with the digit-patterning defect is a shift in cell orientation and an imbalance in chondroitin sulfation. Our results place Chsy1 as an essential regulator of joint patterning and provide a mouse model of human brachydactylies caused by mutations in CHSY1.

Chondroitin 4-O-sulfotransferase-2 regulates the number of chondroitin sulfate chains initiated by chondroitin N-acetylgalactosaminyltransferase-1

Recently, it has been shown that a deficiency in ChGn-1 (chondroitin N-acetylgalactosaminyltransferase-1) reduced the numbers of CS (chondroitin sulfate) chains, leading to skeletal dysplasias in mice. Although these results indicate that ChGn-1 regulates the number of CS chains, the mechanism mediating this regulation is not clear. ChGn-1 is thought to initiate CS biosynthesis by transferring the first GalNAc (N-acetylgalactosamine) to the tetrasaccharide in the protein linkage region of CS. However, in vitro chondroitin polymerization does not occur on the non-reducing terminal GalNAc-linkage pentasaccharide structure. In the present study we show that several different heteromeric enzyme complexes composed of different combinations of four chondroitin synthase family members synthesized more CS chains when a GalNAc-linkage pentasaccharide structure with a non-reducing terminal 4-O-sulfation was the CS acceptor. In addition, C4ST-2 (chondroitin 4-O-sulfotransferase-2) efficiently transferred sulfate from 3′-phosphoadenosine 5′-phosphosulfate to position 4 of non-reducing terminal GalNAc-linkage residues, and the number of CS chains was regulated by the expression levels of C4ST-2 and of ChGn-1. Taken together, the results of the present study indicate that C4ST-2 plays a key role in regulating levels of CS synthesized via ChGn-1.

Electrospray ionization Fourier transform mass spectrometric analysis of intact bikunin glycosaminoglycan from normal human plasma

A mixture of glycosaminoglycan (GAG) chains from a plasma proteoglycan bikunin was fractionated using native, continuous-elution polyacrylamide gel electrophoresis, and the resulting fractions were analyzed by electrospray ionization Fourier transform mass spectrometry (ESI FTMS). Molecular mass analysis of the intact GAG afforded information about the length and composition of GAG chains in the mixture. Ambiguity in the interpretation of the intact GAG mass spectra was eliminated by conducting an additional experiment in which the GAG chains of known molecular mass were treated with a GAG-degrading enzyme, chondroitinase ABC, and the digestion products were analyzed by ESI FTMS. The plasma bikunin GAG chains consisted predominantly of odd number of saccharides, although few chains consisting of even number of saccharides were also detected. Majority of the analyzed chains were tetrasulfated or pentasulfated and comprised by 29 to 41 monosaccharides.

Chondroitin 4-O-sulfotransferase-1 regulates the chain length of chondroitin sulfate in co-operation with chondroitin N-acetylgalactosaminyltransferase-2

Previously, we demonstrated that sog9 cells, a murine L cell mutant, are deficient in the expression of C4ST (chondroitin 4-O-sulfotransferase)-1 and that they synthesize fewer and shorter CS (chondroitin sulfate) chains. These results suggested that C4ST-1 regulates not only 4-O-sulfation of CS, but also the length and amount of CS chains; however, the mechanism remains unclear. In the present study, we have demonstrated that C4ST-1 regulates the chain length and amount of CS in co-operation with ChGn-2 (chondroitin N-acetylgalactosaminyltransferase 2). Overexpression of ChGn-2 increased the length and amount of CS chains in L cells, but not in sog9 mutant cells. Knockdown of ChGn-2 resulted in a decrease in the amount of CS in L cells in a manner proportional to ChGn-2 expression levels, whereas the introduction of mutated C4ST-1 or ChGn-2 lacking enzyme activity failed to increase the amount of CS. Furthermore, the non-reducing terminal 4-O-sulfation of N-acetylgalactosamine residues facilitated the elongation of CS chains by chondroitin polymerase consisting of chondroitin synthase-1 and chondroitin-polymerizing factor. Overall, these results suggest that the chain length of CS is regulated by C4ST-1 and ChGn-2 and that the enzymatic activities of these proteins play a critical role in CS elongation.

Identification and molecular analysis of glycosaminoglycans in cutaneous lupus erythematosus and dermatomyositis

Glycosaminoglycans (GAGs), also known histologically as dermal mucin, accumulate in several inflammatory skin conditions. Because different GAG species have distinct immunologic effects, the authors examined two GAGs, hyaluronan (HA) and chondroitin sulfate (CS), using specific stains in cutaneous lupus erythematosus (CLE) and dermatomyositis (DM). In the dermis of one CLE subtype, tumid LE (TLE), they found only increased HA, but both HA and CS were significantly elevated in another CLE subtype, discoid LE (DLE). DM lesional dermis accumulated mainly CS but not HA. The authors then used glycomic gene expression microarrays to assess the expression of HA- and CS-related genes in CLE skin. Real-time quantitative PCR confirmed significantly increased expression of HAS2, CHSY1, and C4ST1 in the combined groups of CLE lesions (n = 8) compared to healthy controls (n = 4). Thus, the increase in HA in CLE presumably results from upregulation of HAS2, whereas CHSY1 and C4ST1 appear to contribute to increased CS. Based on their known immunomodulatory effects in other systems, HA and CS may thus participate in the pathophysiology of these inflammatory skin conditions.

Functions of chondroitin sulfate and heparan sulfate in the developing brain

Chondroitin sulfate and heparan sulfate proteoglycans are major components of the cell surface and extracellular matrix in the brain. Both chondroitin sulfate and heparan sulfate are unbranched highly sulfated polysaccharides composed of repeating disaccharide units of glucuronic acid and N-acetylgalactosamine, and glucuronic acid and N-acetylglucosamine, respectively. During their biosynthesis in the Golgi apparatus, these glycosaminoglycans are highly modified by sulfation and C5 epimerization of glucuronic acid, leading to diverse heterogeneity in structure. Their structures are strictly regulated in a cell type-specific manner during development partly by the expression control of various glycosaminoglycan-modifying enzymes. It has been considered that specific combinations of glycosaminoglycan-modifying enzymes generate specific functional microdomains in the glycosaminoglycan chains, which bind selectively with various growth factors, morphogens, axon guidance molecules and extracellular matrix proteins. Recent studies have begun to reveal that the molecular interactions mediated by such glycosaminoglycan microdomains play critical roles in the various signaling pathways essential for the development of the brain.

Proteoglycomics: recent progress and future challenges

Proteoglycomics is a systematic study of structure, expression, and function of proteoglycans, a posttranslationally modified subset of a proteome. Although relying on the established technologies of proteomics and glycomics, proteoglycomics research requires unique approaches for elucidating structure-function relationships of both proteoglycan components, glycosaminoglycan chain, and core protein. This review discusses our current understanding of structure and function of proteoglycans, major players in the development, normal physiology, and disease. A brief outline of the proteoglycomic sample preparation and analysis is provided along with examples of several recent proteoglycomic studies. Unique challenges in the characterization of glycosaminoglycan component of proteoglycans are discussed, with emphasis on the many analytical tools used and the types of information they provide.

Chondroitin sulfate N-acetylgalactosaminyltransferase-1 is required for normal cartilage development

CS (chondroitin sulfate) is a glycosaminoglycan species that is widely distributed in the extracellular matrix. To understand the physiological roles of enzymes involved in CS synthesis, we produced CSGalNAcT1 (CS N-acetylgalactosaminyltransferase 1)-null mice. CS production was reduced by approximately half in CSGalNAcT1-null mice, and the amount of short-chain CS was also reduced. Moreover, the cartilage of the null mice was significantly smaller than that of wild-type mice. Additionally, type-II collagen fibres in developing cartilage were abnormally aggregated and disarranged in the homozygous mutant mice. These results suggest that CSGalNAcT1 is required for normal CS production in developing cartilage.

The chondroitin/dermatan sulfate synthesizing and modifying enzymes in laryngeal cancer: expressional and epigenetic studies

Background

Significant biochemical changes are observed in glycosaminoglycans in squamous cell laryngeal carcinoma. The most characteristics are in chondroitin/dermatan sulfate fine structure and proportion, which might be due to differential expression of the enzymes involved in their biosynthesis. The aim of the present work was the investigation in expressional and epigenetic level of the enzymes involved in chondroitin/dermatan sulfate biosynthesis in laryngeal cancer.

Methods

Tissues subjected to total RNA and DNA isolation, and protein extraction. The techniques used in this study were RT-PCR analysis, western blotting and methylation specific PCR.

Results

We identified that many enzymes were expressed in the cancerous specimens intensively. Dermatan sulfate epimerase was expressed exclusively in the cancerous parts and in minor amounts in healthy tissues; in the macroscopically normal samples it was not detected. Furthermore, chondroitin synthase I and chondroitin polymerizing factor were strongly expressed in the cancerous parts compared to the corresponding normal tissues. Sulfotransferases, like chondroitin 6 sulfotransferase 3, were highly expressed mainly in healthy specimens.

Conclusions

The study of the various chondroitin/dermatan synthesizing enzymes revealed that they were differentially expressed in cancer, in human laryngeal cartilage, leading to specific chondroitin/dermatan structures which contributed to proteoglycan formation with specific features. The expression of the examined enzymes correlated with the glycosaminoglycan profile observed in previous studies.

Synthesis of the glycosaminoglycan-protein linkage tetraosyl peptide moieties of betaglycan, which serve as a hexosamine acceptor for enzymatic glycosyl transfer

Betaglycan, also known as TGF-β type III receptor, is a membrane-anchored proteoglycan, which has two glycosaminoglycan (GAG) attachment sites (López-Casillas, F.; Payne, H. M.; Andres, J. L.; Massagué, J. J.Cell Biol.1994, 124, 557-568). Chondroitin sulfate (CS) or heparan sulfate (HS) can attach to the first site, Ser(535), whereas only CS attaches to the second, Ser(546). Although the mechanism behind the assembly of CS and HS is not fully understood, it has been reported that the assembly of HS requires not only a cluster of acidic residues but also hydrophobic residues located near the Ser-Gly attachment sites (Esko, J. D. Zhang, L. Curr. Opin. Struct. Biol.1996, 6, 663-670). To further understand the effects of amino acids close to the Ser residues of the GAG-attachment sites on the glycosyltransferases, two tetraosyl peptides derived from the CS attachment sites of betaglycan, GlcA-Gal-Gal-Xyl-SerGlyAspAsnGly (1) and GlcA-Gal-Gal-Xyl-SerGlyAspAsnGlyPheProGly (2), were synthesized, and used as donor substrates for β1,4-N-acetylgalactosaminyltransferase-I (β4GalNAcT-I) and α1,4-N-acetylglucosaminyltransferase-I (α4GlcNAcT-I). Both the chemically synthesized linkage region tetrasaccharides were far better acceptors for β4GalNAcT-I than for α4GlcNAcT-I in vitro, although they also showed appreciable acceptor activity for α4GlcNAcT-I.

Chondroitin sulfate synthase-2/chondroitin polymerizing factor has two variants with distinct function

Chondroitin sulfate (CS) is a polysaccharide consisting of repeating disaccharide units of N-acetyl-D-galactosamine and d-glucuronic acid residues, modified with sulfated residues at various positions. To date six glycosyltransferases for chondroitin synthesis have been identified, and the complex of chondroitin sulfate synthase-1 (CSS1)/chondroitin synthase-1 (ChSy-1) and chondroitin sulfate synthase-2 (CSS2)/chondroitin polymerizing factor is assumed to play a major role in CS biosynthesis. We found an alternative splice variant of mouse CSS2 in a data base that lacks the N-terminal transmembrane domain, contrasting to the original CSS2. Here, we investigated the roles of CSS2 variants. Both the original enzyme and the splice variant, designated CSS2A and CSS2B, respectively, were expressed at different levels and ratios in tissues. Western blot analysis of cultured mouse embryonic fibroblasts confirmed that both enzymes were actually synthesized as proteins and were localized in both the endoplasmic reticulum and the Golgi apparatus. Pulldown assays revealed that either of CSS2A, CSS2B, and CSS1/ChSy-1 heterogeneously and homogeneously interacts with each other, suggesting that they form a complex of multimers. In vitro glycosyltransferase assays demonstrated a reduced glucuronyltransferase activity in CSS2B and no polymerizing activity in CSS2B co-expressed with CSS1, in contrast to CSS2A co-expressed with CSS1. Radiolabeling analysis of cultured COS-7 cells overexpressing each variant revealed that, whereas CSS2A facilitated CS biosynthesis, CSS2B inhibited it. Molecular modeling of CSS2A and CSS2B provided support for their properties. These findings, implicating regulation of CS chain polymerization by CSS2 variants, provide insight in elucidating the mechanisms of CS biosynthesis.

Platelet-derived growth factor differentially regulates the expression and post-translational modification of versican by arterial smooth muscle cells through distinct protein kinase C and extracellular signal-regulated kinase pathways

The synthesis of proteoglycans involves steps that regulate both protein and glycosaminoglycan (GAG) synthesis, but it is unclear whether these two pathways are regulated by the same or different signaling pathways. We therefore investigated signaling pathways involved in platelet-derived growth factor (PDGF)-mediated increases in versican core protein and GAG chain synthesis in arterial smooth muscle cells (ASMCs). PDGF treatment of ASMCs resulted in increased versican core protein synthesis and elongation of GAG chains attached to the versican core protein. The effects of PDGF on versican mRNA were blocked by inhibiting either protein kinase C (PKC) or the ERK pathways, whereas the GAG elongation effect of PDGF was blocked by PKC inhibition but not by ERK inhibition. Interestingly, blocking protein synthesis in the presence of cycloheximide abolished the PDGF effect, but not in the presence of xyloside, indicating that GAG synthesis that results from PKC activation is independent from de novo protein synthesis. PDGF also stimulated an increase in the chondroitin-6-sulfate to chondroitin-4-sulfate ratio of GAG chains on versican, and this effect was blocked by PKC inhibitors. These data show that PKC activation is sufficient to cause GAG chain elongation, but both PKC and ERK activation are required for versican mRNA core protein expression. These results indicate that different signaling pathways control different aspects of PDGF-stimulated versican biosynthesis by ASMCs. These data will be useful in designing strategies to interfere with the synthesis of this proteoglycan in various disease states.

Impairment of embryonic cell division and glycosaminoglycan biosynthesis in glucuronyltransferase-I-deficient mice

We have revealed that in Caenorhabditis elegans, non-sulfated chondroitin is required for normal cell division and cytokinesis at an early developmental stage, whereas heparan sulfate is essential for embryonic morphogenesis in the later stages of development. To clarify the roles of chondroitin sulfate and heparan sulfate in early embryogenesis in mammals, we generated glucuronyltransferase-I (GlcAT-I) knock-out mice by gene targeting. GlcAT-I is an enzyme required for the synthesis of both chondroitin sulfate and heparan sulfate. Here we report that mice with a deletion of GlcAT-I showed remarkable reduction of the synthesis of chondroitin sulfate and heparan sulfate and embryonic lethality before the 8-cell stage because of failed cytokinesis. In addition, treatment of wild-type 2-cell embryos with chondroitinase ABC had marked effects on cell division, although many heparitinase-treated embryos normally developed to blastocysts. Taken together, these results suggest that chondroitin sulfate in mammals, as with non-sulfated chondroitin in C. elegans, is indispensable for embryonic cell division.