Chondroitin/Dermatan Sulfates in the Central Nervous System: Their Structures and Functions in Health and Disease

Enzymatic comparison of two homologous enzymes reveals N-terminal domain of chondroitinase ABC I regulates substrate selection and product generation

Chondroitinase ABC-type I (CSase ABC I), which can digest both chondroitin sulfate (CS) and dermatan sulfate (DS) in an endolytic manner, is an essential tool in structural and functional studies of CS/DS. Although a few CSase ABC I have been identified from bacteria, the substrate-degrading pattern and regulatory mechanisms of them have rarely been investigated. Herein, two CSase ABC I, IM3796 and IM1634, were identified from the intestinal metagenome of CS-fed mice. They show high sequence homology (query coverage: 88.00%, percent identity: 90.10%) except for an extra peptide (Met¹-His¹⁰⁹) at the N-terminus in IM1634, but their enzymatic properties are very different. IM3796 prefers to degrade 6-O-sulfated GalNAc residue-enriched CS into tetra- and disaccharides. In contrast, IM1634 exhibits nearly a thousand times more activity than IM3796, and can completely digest CS/DS with various sulfation patterns to produce disaccharides, unlike most CSase ABC I. Structure modeling showed that IM3796 did not contain an N-terminal domain composed of two β-sheets, which is found in IM1634 and other CSase ABC I. Furthermore, deletion of the N-terminal domain (Met¹-His¹⁰⁹) from IM1634 caused the enzymatic properties of the variant IM1634-T109 to be similar to those of IM3796, and conversely, grafting this domain to IM3796 increased the similarity of the variant IM3796-A109 to IM1634. In conclusion, the comparative study of the new CSase ABC I provides two unique tools for CS/DS-related studies and applications and, more importantly, reveals the critical role of the N-terminal domain in regulating the substrate binding and degradation of these enzymes.

Identification and Biochemical Characterization of a Surfactant-Tolerant Chondroitinase VhChlABC from Vibrio hyugaensis LWW-1

Chondroitinases, catalyzing the degradation of chondroitin sulfate (CS) into oligosaccharides, not only play a crucial role in understanding the structure and function of CS, but also have been reported as a potential candidate drug for the treatment of high CS-related diseases. Here, a marine bacterium Vibrio hyugaensis LWW-1 was isolated, and its genome was sequenced and annotated. A chondroitinase, VhChlABC, was found to belong to the second subfamily of polysaccharide lyase (PL) family 8. VhChlABC was recombinant expressed and characterized. It could specifically degrade CS-A, CS-B, and CS-C, and reached the maximum activity at pH 7.0 and 40 °C in the presence of 0.25 M NaCl. VhChlABC showed high stability within 8 h under 37 °C and within 2 h under 40 °C. VhChlABC was stable in a wide range of pH (5.0~10.6) at 4 °C. Unlike most chondroitinases, VhChlABC showed high surfactant tolerance, which might provide a good tool for removing extracellular CS proteoglycans (CSPGs) of lung cancer under the stress of pulmonary surfactant. VhChlABC completely degraded CS to disaccharide by the exolytic mode. This research expanded the research and application system of chondroitinases.

Rabbit PrP Is Partially Resistant to in vitro Aggregation Induced by Different Biological Cofactors

Prion diseases have been described in humans and other mammals, including sheep, goats, cattle, and deer. Since mice, hamsters, and cats are susceptible to prion infection, they are often used to study the mechanisms of prion infection and conversion. Mammals, such as horses and dogs, however, do not naturally contract the disease and are resistant to infection, while others, like rabbits, have exhibited low susceptibility. Infection involves the conversion of the cellular prion protein (PrP^C) to the scrapie form (PrP^Sc), and several cofactors have already been identified as important adjuvants in this process, such as glycosaminoglycans (GAGs), lipids, and nucleic acids. The molecular mechanisms that determine transmissibility between species remain unclear, as well as the barriers to transmission. In this study, we examine the interaction of recombinant rabbit PrP^C (RaPrP) with different biological cofactors such as GAGs (heparin and dermatan sulfate), phosphatidic acid, and DNA oligonucleotides (A1 and D67) to evaluate the importance of these cofactors in modulating the aggregation of rabbit PrP and explain the animal’s different degrees of resistance to infection. We used spectroscopic and chromatographic approaches to evaluate the interaction with cofactors and their effect on RaPrP aggregation, which we compared with murine PrP (MuPrP). Our data show that all cofactors induce RaPrP aggregation and exhibit pH dependence. However, RaPrP aggregated to a lesser extent than MuPrP in the presence of any of the cofactors tested. The binding affinity with cofactors does not correlate with these low levels of aggregation, suggesting that the latter are related to the stability of PrP at acidic pH. The absence of the N-terminus affected the interaction with cofactors, influencing the efficiency of aggregation. These findings demonstrate that the interaction with polyanionic cofactors is related to rabbit PrP being less susceptible to aggregation in vitro and that the N-terminal domain is important to the efficiency of conversion, increasing the interaction with cofactors. The decreased effect of cofactors in rabbit PrP likely explains its lower propensity to prion conversion.

Glycosaminoglycans

Glycosaminoglycans (GAGs) are important constituents of human glycome. They are negatively charged unbranched polysaccharides that are usually covalently attached to proteins, forming glycan-protein conjugates, called proteoglycans. Glycosaminoglycans play critical roles in numerous biological processes throughout individual development and are also involved in the pathological processes of various diseases. Based on their remarkable bioactivities and their universal involvement in disease progression, GAGs are applied as therapeutics or are being targeted or used in treating diseases. In this chapter, we introduce the characteristics of the four classes of GAGs that constitute the glycosaminoglycan family. The pathological roles of glycosaminoglycans in major diseases including innate disease, infectious disease, and cancer are discussed. The application of GAGs and their mimetics as therapeutics is introduced, as well as those therapeutic methods developed based on GAGs' role in pathogenesis. In addition, we provide a brief and overall lookback at the history of GAG research and sort out some critical techniques that facilitated GAG and glycomics studies.

Beware, commercial chondroitinases vary in activity and substrate specificity

Chondroitin sulfate (CS)and dermatan sulfate (DS) are negatively charged polysaccharides found abundantly in animal tissue and have been extensively described to play key roles in health and disease. The most common method to analyze their structure is by digestion into disaccharides with bacterial chondroitinases, followed by chromatography and/or mass spectrometry. While studying the structure of oncofetal CS, we noted a large variation in the activity and specificity of commercially available chondroitinases. Here studied the kinetics of the enzymes and used high-performance liquid chromatography-mass spectrometry to determine the di- and oligosaccharide products resulting from the digestion of commercially available bovine CS A, shark CS C and porcine DS, focusing on chondroitinases ABC, AC and B from different vendors. Application of a standardized assay setup demonstrated large variations in the enzyme-specific activity compared to the values provided by vendors, large variation in enzyme specific activity of similar enzymes from different vendors and differences in the extent of cleavage of the substrates and the generated products. The high variability of different chondroitinases highlights the importance of testing enzyme activity and monitoring product formation in assessing the content and composition of chondroitin and DSs in cells and tissues.

Proteoglycans in brain development and pathogenesis

Proteoglycans are diverse, complex extracellular/cell surface macromolecules composed of a central core protein with covalently linked glycosaminoglycan (GAG) chains; both of these components contribute to the growing list of important bio-active functions attributed to proteoglycans. Increasingly, attention has been paid to the roles of proteoglycans in nervous tissue development due to their highly regulated spatio/temporal expression patterns, whereby they promote/inhibit neurite outgrowth, participate in specification and maturation of various precursor cell types, and regulate cell behaviors like migration, axonal pathfinding, synaptogenesis and plasticity. These functions emanate from both the environments proteoglycans create around cells by retaining ions and water or serving as scaffolds for cell shaping or motility, and from dynamic interactions that modulate signaling fields for cytokines, growth factors and morphogens, which may bind to either the protein or GAG portions. Also, genetic abnormalities impacting proteoglycan synthesis during critical steps of brain development and response to environmental insults and injuries, as well as changes in microenvironment interactions leading to tumors in the central nervous system, all suggest roles for proteoglycans in behavioral and intellectual disorders and malignancies.

Dermatan 4-O-sulfotransferase1 ablation accelerates peripheral nerve regeneration

Chondroitin sulfate (CS) and dermatan sulfate (DS) proteoglycans are major components of the extracellular matrix implicated in neural development, plasticity and regeneration. While it is accepted that CS are major inhibitors of neural regeneration, the contributions of DS to regeneration have not been assessed. To enable a novel approach in studies on DS versus CS roles during development and regeneration, we generated a mouse deficient in the dermatan 4-O-sulfotransferase1 (Chst14(-/-)), a key enzyme in the synthesis of iduronic acid-containing modules found in DS but not CS. In wild-type mice, Chst14 is expressed at high levels in the skin and in the nervous system, and is enriched in astrocytes and Schwann cells. Ablation of Chst14, and the assumed failure to produce DS, resulted in smaller body mass, reduced fertility, kinked tail and increased skin fragility compared with wild-type (Chst14(+/+)) littermates, but brain weight and gross anatomy were unaffected. Neurons and Schwann cells from Chst14(-/-) mice formed longer processes in vitro, and Chst14(-/-) Schwann cells proliferated more than Chst14(+/+) Schwann cells. After femoral nerve transection/suture, functional recovery and axonal regrowth in Chst14(-/-) mice were initially accelerated but the final outcome 3months after injury was not better than that in Chst14(+/+) littermates. These results suggest that while Chst14 and its enzymatic products might be of limited importance for neural development, they may contribute to the regeneration-restricting environment in the adult mammalian nervous system.

Loss of dermatan sulfate epimerase (DSE) function results in musculocontractural Ehlers-Danlos syndrome

The sulfated polysaccharide dermatan sulfate (DS) forms proteoglycans with a number of distinct core proteins. Iduronic acid-containing domains in DS have a key role in mediating the functions of DS proteoglycans. Two tissue-specific DS epimerases, encoded by DSE and DSEL, and a GalNAc-4-O-sulfotransferase encoded by CHST14 are necessary for the formation of these domains. CHST14 mutations were previously identified for patients with the musculocontractural type of Ehlers-Danlos syndrome (MCEDS). We now identified a homozygous DSE missense mutation (c.803C>T, p.S268L) by the positional candidate approach in a male child with MCEDS, who was born to consanguineous parents. Heterologous expression of mutant full-length and soluble recombinant DSE proteins showed a loss of activity towards partially desulfated DS. Patient-derived fibroblasts also showed a significant reduction in epimerase activity. The amount of DS disaccharides was markedly decreased in the conditioned medium and the cell fraction from cultured fibroblasts of the patient when compared with a healthy control subject, whereas no apparent difference was observed in the chondroitin sulfate (CS) chains from the conditioned media. However, the total amount of CS disaccharides in the cell fraction from the patient was increased ∼1.5-fold, indicating an increased synthesis or a reduced conversion of CS chains in the cell fraction. Stable transfection of patient fibroblasts with a DSE expression vector increased the amount of secreted DS disaccharides. DSE deficiency represents a specific defect of DS biosynthesis. We demonstrate locus heterogeneity in MCEDS and provide evidence for the importance of DS in human development and extracellular matrix maintenance.

Endocan in cancers: a lesson from a circulating dermatan sulfate proteoglycan

As most proteoglycans exert their biological activities in the pericellular region, circulating Endocan has appeared since its discovery as an atypical dermatan sulfate proteoglycan, with distinctive structural and functional properties. Endocan is naturally expressed by endothelial cells, highly regulated in presence of proinflammatory and proangiogenic molecules, binds to matrix proteins, growth factors, integrin, and cells, and may be then considered as an accurate marker of endothelial activation. Consequently, Endocan expression has been associated with a growing number of pathological conditions where endothelium gets challenged and notably in highly vascularized cancers. In this context, Endocan has indeed been rapidly emerging as a promising tissue- and blood-based marker of the vascular growth and neoangiogenesis during cancer progression. Furthermore, very recent studies have reported an expression of Endocan by the tumor cells themselves. This highlights Endocan as a multifaceted molecule with a great interest for researchers and clinicians to better understand tumor development, from the bench to the clinics. With promising perspectives of clinical applications, Endocan thus appears as an exciting model for on going and future developments of proteoglycan-based approaches in cancer diagnostics and/or therapy.

Hyaluronidases Have Strong Hydrolytic Activity toward Chondroitin 4-Sulfate Comparable to that for Hyaluronan

Chondroitin sulfate (CS) chains are involved in the regulation of various biological processes. However, the mechanism underlying the catabolism of CS is not well understood. Hyaluronan (HA)-degrading enzymes, the hyaluronidases, are assumed to act at the initial stage of the degradation process, because HA is similar in structure to nonsulfated CS, chondroitin (Chn). Although human hyaluronidase-1 (HYAL1) and testicular hyaluronidase (SPAM1) can degrade not only HA but also CS, they are assumed to digest CS to only a limited extent. In this study, the hydrolytic activities of HYAL1 and SPAM1 toward CS-A, CS-C, Chn, and HA were compared. HYAL1 depolymerized CS-A and HA to a similar extent. SPAM1 degraded CS-A, Chn, and HA to a similar extent. CS is widely distributed from very primitive organisms to humans, whereas HA has been reported to be present only in vertebrates with the single exception of a mollusk. Therefore, a genuine substrate of hyaluronidases appears to be CS as well as HA.

Identification of amino acid residues required for the substrate specificity of human and mouse chondroitin sulfate hydrolase (conventional hyaluronidase-4)

Human hyaluronidase-4 (hHYAL4), a member of the hyaluronidase family, has no hyaluronidase activity, but is a chondroitin sulfate (CS)-specific endo-β-N-acetylgalactosaminidase. The expression of hHYAL4 is not ubiquitous but restricted to placenta, skeletal muscle, and testis, suggesting that hHYAL4 is not involved in the systemic catabolism of CS, but rather has specific functions in particular organs or tissues. To elucidate the function of hyaluronidase-4 in vivo, mouse hyaluronidase-4 (mHyal4) was characterized. mHyal4 was also demonstrated to be a CS-specific endo-β-N-acetylgalactosaminidase. However, mHyal4 and hHYAL4 differed in the sulfate groups they recognized. Although hHYAL4 strongly preferred GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate)-containing sequences typical in CS-D, where GlcUA represents d-glucuronic acid, mHyal4 depolymerized various CS isoforms to a similar extent, suggesting broad substrate specificity. To identify the amino acid residues responsible for this difference, a series of human/mouse HYAL4 chimeric proteins and HYAL4 point mutants were generated, and their preference for substrates was investigated. A combination of the amino acid residues at 261-265 and glutamine at 305 was demonstrated to be essential for the enzymatic activity as well as substrate specificity of mHyal4.

Evolution of glycosaminoglycans: Comparative biochemical study

Glycosaminoglycans, a major component of the extracellular matrix molecules in animal tissues, play important roles in various physiological events. Glycosaminoglycans are found in not only vertebrates but also many invertebrates, implying a conserved function in the animal kingdom. Here, we discuss the analysis of glycosaminoglycans in 11 invertebrate phyla focusing on structure as well as physiological functions elucidated in model organisms. Various sulfated structures of heparan sulfate are widely distributed from very primitive organisms to humans, indicating an involvement in fundamental biological processes. By contrast, chondroitin/dermatan sulfate from lower organisms is limited in its structural complexity and often associated with a particular function. The presence of hyaluronic acid outside of vertebrates has been reported only in a mollusk.

Congenital disorders of glycosylation with emphasis on loss of dermatan-4-sulfotransferase

The autosomal, recessively inherited, adducted thumb-clubfoot syndrome (ATCS) represents a generalized connective tissue disorder with congenital malformations, contractures of thumbs and feet, and a typical facial appearance. Cognitive development is normal in ATCS patients during childhood. ATCS is caused by homozygous nonsense and missense mutations in CHST14 which encodes an N-acetylgalactosamine 4-O-sulfotransferase 1 (D4ST1) that catalyzes the 4-O-sulfation of N-acetylgalactosamine in the repeating iduronic acid-alpha-1,3-N-acetylgalactosamine disaccharide sequence to form dermatan sulfate (DS). ATCS mutations lead to either a decrease or a loss of D4ST1 activity, as revealed by absence of DS and an excess of chondroitin sulfate (CS) in patient's fibroblasts. Either of these effects or their combination might cause the observed clinical symptoms by altering the physiological pattern of dermatan and CS chains on their corresponding proteoglycans (PGs). ATCS is the only recognized disorder resulting from a defect that is specific to DS biosynthesis, and thus represents another class of the congenital glycosylation disorders. Congenital disorders of glycosylation (CDG) include all genetic diseases that result from defects in the synthesis of glycans. These disorders cause a wide range of human diseases, with examples emanating from all medical subspecialties. ATCS is the first human disorder that emphasizes a role for DS in human development and extracellular matrix maintenance.

Identification of human hyaluronidase-4 as a novel chondroitin sulfate hydrolase that preferentially cleaves the galactosaminidic linkage in the trisulfated tetrasaccharide sequence

Human hyaluronidases have been considered to be the enzymes acting at the initial step in the catabolism of chondroitin sulfate (CS) in vivo. However, human hyaluronidase-1 digests CS more slowly than hyaluronan (HA), and its preferred substrate is HA rather than CS. We have identified a chondroitin hydrolase in Caenorhabditis elegans, which effectively degrades chondroitin but depolymerizes HA to a much lesser extent (Kaneiwa T, Yamada S, Mizumoto S, Montaño AM, Mitani S, Sugahara K. 2008. Identification of a novel chondroitin hydrolase in Caenorhabditis elegans. J Biol Chem. 283:14971-14979), suggesting the existence of CS-specific endoglycosidases in mammalian systems. In this study, human hyaluronidase-4 was demonstrated to be a CS-specific endo-beta-N-acetylgalactosaminidase. This is the first demonstration of a CS hydrolase in higher organisms. The specificity of a purified recombinant form of the enzyme was investigated in detail through the characterization of degradation products. The best substrate of the CS hydrolase was the galactosaminidic linkage in the sequence of a trisulfated tetrasaccharide GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate)-GlcUA-GalNAc(4-O- or 6-O-sulfate), where GlcUA and GalNAc represent D-glucuronic acid and N-acetyl-D-galactosamine, respectively. The disaccharide unit on the nonreducing side, GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate) (D unit), is rich in shark fin cartilage CS-D among various CS isoforms. CS hydrolase will be a useful tool for investigating CS-specific functions in tissues and cells. In addition, it may well be applicable to the treatment of acute spinal cord injuries as in the case of, or instead of, the bacterial CS lyase which has been used for recent clinical trials.

Dermatan sulfate epimerase 1-deficient mice have reduced content and changed distribution of iduronic acids in dermatan sulfate and an altered collagen structure in skin

Dermatan sulfate epimerase 1 (DS-epi1) and DS-epi2 convert glucuronic acid to iduronic acid in chondroitin/dermatan sulfate biosynthesis. Here we report on the generation of DS-epi1-null mice and the resulting alterations in the chondroitin/dermatan polysaccharide chains. The numbers of long blocks of adjacent iduronic acids are greatly decreased in skin decorin and biglycan chondroitin/dermatan sulfate, along with a parallel decrease in iduronic-2-O-sulfated-galactosamine-4-O-sulfated structures. Both iduronic acid blocks and iduronic acids surrounded by glucuronic acids are also decreased in versican-derived chains. DS-epi1-deficient mice are smaller than their wild-type littermates but otherwise have no gross macroscopic alterations. The lack of DS-epi1 affects the chondroitin/dermatan sulfate in many proteoglycans, and the consequences for skin collagen structure were initially analyzed. We found that the skin collagen architecture was altered, and electron microscopy showed that the DS-epi1-null fibrils have a larger diameter than the wild-type fibrils. The altered chondroitin/dermatan sulfate chains carried by decorin in skin are likely to affect collagen fibril formation and reduce the tensile strength of DS-epi1-null skin.

The mucopolysaccharidoses: a success of molecular medicine

The mucopolysaccharidoses represent a devastating group of lysosomal storage diseases affecting approximately 1 in 25 000 individuals. Advances in biochemistry and genetics over the past 25 years have resulted in the identification of the key hydrolases underlying the mucopolysaccharidoses, with subsequent isolation and characterisation of the genes involved. Ultimately these advances have led to the recent development of specific treatment regimens for some of the mucopolysaccharidoses, in the form of direct enzyme replacement. Direct replacement of the defective gene product has been attempted for very few genetic disorders, and thus the experience gained in the lysosomal storage diseases by the development, evaluation and integration of treatment regimens into healthcare is instructive for other rare genetic disorders. This review focuses on the pathophysiology of the mucopolysaccharidoses and highlights the complex biochemical and physiological perturbations that underlie the disease phenotype.