Unique glycosylation of three keratan sulfate proteoglycan isoforms

Molecular cues for immune cells from small leucine-rich repeat proteoglycans in their extracellular matrix-associated and free forms

In this review we highlight emerging immune regulatory functions of lumican, keratocan, fibromodulin, biglycan and decorin, which are members of the small leucine-rich proteoglycans (SLRP) of the extracellular matrix (ECM). These SLRPs have been studied extensively as collagen-fibril regulatory structural components of the skin, cornea, bone and cartilage in homeostasis. However, SLRPs released from a remodeling ECM, or synthesized by activated fibroblasts and immune cells contribute to an ECM-free pool in tissues and circulation, that may have a significant, but poorly understood foot print in inflammation and disease. Their molecular interactions and the signaling networks they influence also require investigations. Here we present studies on the leucine-rich repeat (LRR) motifs of SLRP core proteins, their evolutionary and functional relationships with other LRR pathogen recognition receptors, such as the toll-like receptors (TLRs) to bring some molecular clarity in the immune regulatory functions of SLRPs. We discuss molecular interactions of fragments and intact SLRPs, and how some of these interactions are likely modulated by glycosaminoglycan side chains. We integrate findings on molecular interactions of these SLRPs together with what is known about their presence in circulation and lymph nodes (LN), which are important sites of immune cell regulation. Recent bulk and single cell RNA sequencing studies have identified subsets of stromal reticular cells that express these SLRPs within LNs. An understanding of the cellular source, molecular interactions and signaling consequences will lead to a fundamental understanding of how SLRPs modulate immune responses, and to therapeutic tools based on these SLRPs in the future.

An insight into new glycotherapeutics in glial inflammation: Understanding the role of glycosylation in mitochondrial function and acute to the chronic phases of inflammation

INTRODUCTION

Glycosylation plays a critical role during inflammation and glial scar formation upon spinal cord injury (SCI) disease progression. Astrocytes and microglia are involved in this cascade to modulate the inflammation and tissue remodeling from acute to chronic phases. Therefore, understating the glycan changes in these glial cells is paramount.

METHOD AND RESULTS

A lectin microarray was undertaken using a cytokine-driven inflammatory mixed glial culture model, revealing considerable differential glycosylation from the acute to the chronic phase in a cytokine-combination generated inflamed MGC model. It was found that several N- and O-linked glycans associated with glia during SCI were differentially regulated. Pearson's correlation hierarchical clustering showed that groups were separated into several clusters, illustrating the heterogenicity among the control, cytokine combination, and LPS treated groups and the day on which treatment was given. Control and LPS treatments were observed to be in dense clusters. This was further confirmed with lectin immunostaining in which GalNAc, GlcNAc, mannose, fucose and sialic acid-binding residues were detected in astrocytes and microglia. However, the sialyltransferase inhibitor inhibited this modification (upregulation of the sialic acid expression), which indeed modulates the mitochondrial functions.

CONCLUSIONS

The present study is the first functional investigation of glycosylation modulation in a mixed glial culture model, which elucidates the role of the glycome in neuroinflammation in progression and identified potential therapeutic targets for future glyco therapeutics in neuroinflammation.

Proteoglycan (Keratan Sulfate) Barrier in Developing Human Forebrain Isolates Cortical Epileptic Networks From Deep Heterotopia, Insulates Axonal Fascicles, and Explains Why Axosomatic Synapses Are Inhibitory

Axons from deep heterotopia do not extend through U-fibers, except transmantle dysplasias. Keratan sulfate (KS) in fetal spinal cord/brainstem median septum selectively repels glutamatergic axons while enabling GABAergic commissural axons. Immunocytochemical demonstration of KS in neocortical resections and forebrain at autopsy was studied in 12 fetuses and neonates 9-41 weeks gestational age (GA), 9 infants, children, and adolescents and 5 patients with focal cortical dysplasias (FCD1a). From 9 to 15 weeks GA, no KS is seen in the cortical plate; 19-week GA reactivity is detected in the molecular zone. By 28 weeks GA, patchy granulofilamentous reactivity appears in extracellular matrix and adheres to neuronal somata with increasing intensity in deep cortex and U-fibers at term. Perifascicular KS surrounds axonal bundles of both limbs of the internal capsule and within basal ganglia from 9 weeks GA. Thalamus and globus pallidus exhibit intense astrocytic reactivity from 9 weeks GA. In FCD1a, U-fiber reactivity is normal, discontinuous or radial. Ultrastructural correlates were not demonstrated; KS is not electron-dense. Proteoglycan barrier of the U-fiber layer impedes participation of deep heterotopia in cortical epileptic networks. Perifascicular KS prevents aberrant axonal exit from or entry into long and short tracts. KS adhesion to neuronal somatic membranes may explain inhibitory axosomatic synapses.

Keratan Sulphate in the Tumour Environment

Keratan sulphate (KS) is a bioactive glycosaminoglycan (GAG) of some complexity composed of the repeat disaccharide D-galactose β1→4 glycosidically linked to N-acetyl glucosamine. During the biosynthesis of KS, a family of glycosyltransferase and sulphotransferase enzymes act sequentially and in a coordinated fashion to add D-galactose (D-Gal) then N-acetyl glucosamine (GlcNAc) to a GlcNAc acceptor residue at the reducing terminus of a nascent KS chain to effect chain elongation. D-Gal and GlcNAc can both undergo sulphation at C6 but this occurs more frequently on GlcNAc than D-Gal. Sulphation along the developing KS chain is not uniform and contains regions of variable length where no sulphation occurs, regions which are monosulphated mainly on GlcNAc and further regions of high sulphation where both of the repeat disaccharides are sulphated. Each of these respective regions in the KS chain can be of variable length leading to KS complexity in terms of chain length and charge localization along the KS chain. Like other GAGs, it is these variably sulphated regions in KS which define its interactive properties with ligands such as growth factors, morphogens and cytokines and which determine the functional properties of tissues containing KS. Further adding to KS complexity is the identification of three different linkage structures in KS to asparagine (N-linked) or to threonine or serine residues (O-linked) in proteoglycan core proteins which has allowed the categorization of KS into three types, namely KS-I (corneal KS, N-linked), KS-II (skeletal KS, O-linked) or KS-III (brain KS, O-linked). KS-I to -III are also subject to variable addition of L-fucose and sialic acid groups. Furthermore, the GlcNAc residues of some members of the mucin-like glycoprotein family can also act as acceptor molecules for the addition of D-Gal and GlcNAc residues which can also be sulphated leading to small low sulphation glycoforms of KS. These differ from the more heavily sulphated KS chains found on proteoglycans. Like other GAGs, KS has evolved molecular recognition and information transfer properties over hundreds of millions of years of vertebrate and invertebrate evolution which equips them with cell mediatory properties in normal cellular processes and in aberrant pathological situations such as in tumourogenesis. Two KS-proteoglycans in particular, podocalyxin and lumican, are cell membrane, intracellular or stromal tissue-associated components with roles in the promotion or regulation of tumour development, mucin-like KS glycoproteins may also contribute to tumourogenesis. A greater understanding of the biology of KS may allow better methodology to be developed to more effectively combat tumourogenic processes.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

Determinants of Glycosaminoglycan (GAG) Structure

Proteoglycans (PGs) are glycosylated proteins of biological importance at cell surfaces, in the extracellular matrix, and in the circulation. PGs are produced and modified by glycosaminoglycan (GAG) chains in the secretory pathway of animal cells. The most common GAG attachment site is a serine residue followed by a glycine (-ser-gly-), from which a linker tetrasaccharide extends and may continue as a heparan sulfate, a heparin, a chondroitin sulfate, or a dermatan sulfate GAG chain. Which type of GAG chain becomes attached to the linker tetrasaccharide is influenced by the structure of the protein core, modifications occurring to the linker tetrasaccharide itself, and the biochemical environment of the Golgi apparatus, where GAG polymerization and modification by sulfation and epimerization take place. The same cell type may produce different GAG chains that vary, depending on the extent of epimerization and sulfation. However, it is not known to what extent these differences are caused by compartmental segregation of protein cores en route through the secretory pathway or by differential recruitment of modifying enzymes during synthesis of different PGs. The topic of this review is how different aspects of protein structure, cellular biochemistry, and compartmentalization may influence GAG synthesis.

Expression of fibromodulin in carotid atherosclerotic plaques is associated with diabetes and cerebrovascular events

AIMS

The small leucine-rich proteoglycans fibromodulin and lumican are functionally related extracellular matrix proteins involved in the regulation of collagen fiber formation. Fibromodulin-deficient apolipoprotein E-null mice have decreased vascular retention of lipids and reduced development of atherosclerosis suggesting that fibromodulin may influence the disease process. The aim of the present study was to investigate if fibromodulin and lumican are expressed in human carotid plaques and to determine if their expression is associated with the occurrence of preoperative symptoms and with risk for postoperative cardiovascular events.

METHODS AND RESULTS

153 plaques (51% symptomatic) obtained by carotid endarterectomy were included in this study. Plaque content was analyzed by immunohistochemistry and plaque cytokine content by multiplex technology. Fibromodulin and lumican were widely expressed in plaques and fibromodulin expression was significantly higher in symptomatic plaques. Expression of fibromodulin was significantly higher in plaques obtained from patients with diabetes and a high fibromodulin expression was associated with a higher incidence of post-operative cerebrovascular events, whereas no such associations were seen for lumican. Fibromodulin expression also correlated with plaque lipids and several pro-inflammatory cytokines. In addition, fibromodulin expression correlated with low levels of smooth muscle cells and the anti-inflammatory cytokine IL-10.

CONCLUSIONS

These observations support previous experimental findings in mice for a role of fibromodulin in atherosclerosis and provide clinical evidence of the involvement of fibromodulin in the inflammatory processes that characterize atherosclerotic plaque vulnerability. They also suggest that this is of particular importance in diabetes.

Human mesenchymal stem cells differentiate into keratocyte-like cells in keratocyte-conditioned medium

Culturing corneal keratocytes is difficult because keratocytes growing in a monolayer rapidly lose their stellate morphology and cease to express keratocyte markers such as keratocan, lumican and aldehyde dehydrogenase 1 family, member A1 (ALDH1A1). Conversely, mesenchymal stem cells (MSCs) can be easily expanded in cell culture, and they have a variety of differentiation pathways. We studied the feasibility of using MSCs as a source for corneal tissue engineering. Based on the observation that keratocytes have MSC-like properties, similar to bone marrow-derived MSCs (BM-MSCs), we hypothesized that MSCs would differentiate into corneal keratocyte-like cells in keratocyte-conditioned medium (KCM). We measured changes in the expression of keratocyte markers through quantitative real-time polymerase chain reaction (qRT-PCR) and found that human MSC's cultured in KCM expressed both keratocan and ALDH1A1. Western blot analysis demonstrated that human MSCs cultured in KCM steadily increased their expression of lumican and ALDH1A1, while they lost expression of α-smooth muscle actin (α-SMA). Immunocytochemistry indicated that human MSCs grown in KCM acquired characteristics similar to those of keratocytes. These results suggest that KCM can direct human MSCs to differentiate into keratocyte-like cells.

Enzymes responsible for synthesis of corneal keratan sulfate glycosaminoglycans

Keratan sulfate glycosaminoglycans are among the most abundant carbohydrate components of the cornea and are suggested to play an important role in maintaining corneal extracellular matrix structure. Keratan sulfate carbohydrate chains consist of repeating N-acetyllactosamine disaccharides with sulfation on the 6-O positions of N-acetylglucosamine and galactose. Despite its importance for corneal function, the biosynthetic pathway of the carbohydrate chain and particularly the elongation steps are poorly understood. Here we analyzed enzymatic activity of two glycosyltransferases, beta1,3-N-acetylglucosaminyltansferase-7 (beta3GnT7) and beta1,4-galactosyltransferase-4 (beta4GalT4), in the production of keratan sulfate carbohydrate in vitro. These glycosyltransferases produced only short, elongated carbohydrates when they were reacted with substrate in the absence of a carbohydrate sulfotransferase; however, they produced extended GlcNAc-sulfated poly-N-acetyllactosamine structures with more than four repeats of the GlcNAc-sulfated N-acetyllactosamine unit in the presence of corneal N-acetylglucosamine 6-O sulfotransferase (CGn6ST). Moreover, we detected production of highly sulfated keratan sulfate by a two-step reaction in vitro with a mixture of beta3GnT7/beta4GalT4/CGn6ST followed by keratan sulfate galactose 6-O sulfotransferase treatment. We also observed that production of highly sulfated keratan sulfate in cultured human corneal epithelial cells was dramatically reduced when expression of beta3GnT7 or beta4GalT4 was suppressed by small interfering RNAs, indicating that these glycosyltransferases are responsible for elongation of the keratan sulfate carbohydrate backbone.

Phenotypic responses to mechanical stress in fibroblasts from tendon, cornea and skin

Primary fibroblasts isolated from foetal mouse cornea, skin and tendon were subjected to linear shear stress and analysed for morphological parameters and by microarray, as compared with unstimulated controls. Approx. 350 genes were either up- or down-regulated by a significant amount, with 51 of these being common to all three cell types. Approx. 50% of altered genes in tendon and cornea fibroblasts were changed in common with one of the other cell types, with the remaining approx. 50% being specific to tendon or cornea. In skin fibroblasts, however, less than 25% of genes whose transcription was altered were specific only to skin. The functional spectrum of genes that were up- or down-regulated was diverse, with apparent house-keeping genes forming the major category of up-regulated genes. However, a significant number of genes associated with cell adhesion, extracellular matrix and matrix remodelling, as well as cytokines and other signalling factors, were also affected. Somewhat surprisingly, in these latter categories the trend was towards a reduction in mRNA levels. Verification of the mRNA quantity of a subset of these genes was performed by reverse transcriptase PCR and was found to be in agreement with the microarray analysis. These findings provide the first in-depth analysis of phenotypic differences between fibroblast cells from different tissue sources and reveal the responses of these cells to mechanical stress.

The mimecan gene expressed in human pituitary and regulated by pituitary transcription factor-1 as a marker for diagnosing pituitary tumors

CONTEXT

Mimecan, a secretory protein, belongs to a family of small leucine-rich proteoglycans (SLRPs). The physiological functions of mimecan have not been fully understood.

OBJECTIVE

We hypothesize that the mimecan gene expressed in the human pituitary and regulated by pituitary transcription factor-1 (Pit-1) might act as a marker for diagnosing pituitary tumors.

DESIGN

The clinical aspect of our work was a cross-sectional study.

SETTING AND PATIENTS

In total, 20 pituitary tumor samples were collected from January 1, 2002, to December 30, 2002, in Ruijin Hospital, Shanghai, China.

INTERVENTION

The number of pituitary tumors was limited. Collection of more pituitary tumor samples for additional observation will be necessary.

MAIN OUTCOME MEASURES

The main outcomes were measured by Northern blot, in situ hybridization, immunohistochemical analysis, and so on.

RESULTS

The mimecan gene was expressed at a moderate level in the mouse pituitary gland by Northern blot analysis. Expression of mimecan mRNA and protein is also observed in the human anterior pituitary gland. Luciferase reporter analysis and electrophoretic mobility shift assays show that Pit-1 activates the human mimecan promoter through Pit-1 response element sites. In addition, our data also show that almost all the ACTH- or GH-positive pituitary tumors likely express mimecan protein, and only a portion of prolactin-, TSH-, FSH-, and LH-positive pituitary tumors express mimecan protein.

CONCLUSIONS

This work provides insight into the regulating mechanism of mimecan in pituitary and suggests that mimecan may be an unidentified pituitary secretory protein, and certain pituitary cells secreting ACTH or GH also secrete mimecan.

Corneal keratocytes retain neural crest progenitor cell properties

Corneal keratocytes have a remarkable ability to heal the cornea throughout life. Given their developmental origin from the cranial neural crest, we asked whether this regenerative ability was related to the stem cell-like properties of their neural crest precursors. To this end, we challenged corneal stromal keratocytes by injecting them into a new environment along cranial neural crest migratory pathways. The results show that injected stromal keratocytes change their phenotype, proliferate and migrate ventrally adjacent to host neural crest cells. They then contribute to the corneal endothelial and stromal layers, the musculature of the eye, mandibular process, blood vessels and cardiac cushion tissue of the host. However, they fail to form neurons in cranial ganglia or branchial arch cartilage, illustrating that they are at least partially restricted progenitors rather than stem cells. The data show that, even at late embryonic stages, corneal keratocytes are not terminally differentiated, but maintain plasticity and multipotentiality, contributing to non-neuronal cranial neural crest derivatives.

Bone morphogenetic protein-1/tolloid-related metalloproteinases process osteoglycin and enhance its ability to regulate collagen fibrillogenesis

The mammalian bone morphogenetic protein-1 (BMP-1)/Tolloid-related metalloproteinases play key roles in regulating formation of the extracellular matrix (ECM) via biosynthetic processing of various precursor proteins into mature functional enzymes, structural proteins, and proteins involved in initiating the mineralization of hard tissue ECMs. They also have been shown to activate several members of the transforming growth factor-beta superfamily, and may serve to coordinate such activation with formation of the ECM in morphogenetic events. Osteoglycin (OGN), a small leucine-rich proteoglycan with unclear functions, is found in cornea, bone, and other tissues, and appears to undergo proteolytic processing in vivo. Here we have successfully generated recombinant OGN and have employed it to demonstrate that a pro-form of OGN is processed to varying extents by all four mammalian BMP-1/Tolloid-like proteinases, to generate a 27-kDa species that corresponds to the major form of OGN found in cornea. Moreover, whereas wild-type mouse embryo fibroblasts (MEFs) produce primarily the processed, mature form of OGN, MEFs homozygous null for genes encoding three of the four mammalian BMP-1/Tolloid-related proteinases produce only unprocessed pro-OGN. Thus, all detectable pro-OGN processing activity in MEFs is accounted for by products of these genes. We also demonstrate that both pro- and mature OGN can regulate type I collagen fibrillogenesis, and that processing of the prodomain by BMP-1 potentiates the ability of OGN to modulate the formation of collagen fibrils.

Keratocyte phenotype mediates proteoglycan structure: a role for fibroblasts in corneal fibrosis

In pathological corneas, accumulation of fibrotic extracellular matrix is characterized by proteoglycans with altered glycosaminoglycans that contribute to the reduced transparency of scarred tissue. During wound healing, keratocytes in the corneal stroma transdifferentiate into fibroblasts and myofibroblasts. In this study, molecular markers were developed to identify keratocyte, fibroblast, and myofibroblast phenotypes in primary cultures of corneal stromal cells and the structure of glycosaminoglycans secreted by these cells was characterized. Quiescent primary keratocytes expressed abundant protein and mRNA for keratocan and aldehyde dehydrogenase class 3 and secreted proteoglycans containing macromolecular keratan sulfate. Expression of these marker compounds was reduced in fibroblasts and also in transforming growth factor-beta-induced myofibroblasts, which expressed high levels of alpha-smooth muscle actin, biglycan, and the extra domain A (EDA or EIIIA) form of cellular fibronectin. Collagen types I and III mRNAs were elevated in both fibroblasts and in myofibroblasts. Expression of these molecular markers clearly distinguishes the phenotypic states of stromal cells in vitro. Glycosaminoglycans secreted by fibroblasts and myofibroblasts were qualitatively similar to and differed from those of keratocytes. Chondroitin/dermatan sulfate abundance, chain length, and sulfation were increased as keratocytes became fibroblasts and myofibroblasts. Fluorophore-assisted carbohydrate electrophoresis analysis demonstrated increased N-acetylgalactosamine sulfation at both 4- and 6-carbons. Hyaluronan, absent in keratocytes, was secreted by fibroblasts and myofibroblasts. Keratan sulfate biosynthesis, chain length, and sulfation were significantly reduced in both fibroblasts and myofibroblasts. The qualitatively similar expression of glycosaminoglycans shared by fibroblasts and myofibroblasts suggests a role for fibroblasts in deposition of non-transparent fibrotic tissue in pathological corneas.

An X-ray scattering investigation of corneal structure in keratocan-deficient mice

The transparency of the cornea has been closely linked with the characteristic size and arrangement of its constituent collagen fibrils. This arrangement, in turn, is thought to depend on interactions with intervening matrix proteoglycans. The purpose of this investigation was to examine fibrillar collagen organisation in the corneas of mice homozygous for a null mutation in keratocan, a keratan sulfate-containing proteoglycan. Low-angle synchrotron X-ray scattering techniques were used. We found that keratocan-deficient mice had corneal collagen fibrils with significantly larger diameters than those in wild-type littermates. Furthermore, there was an increase in the centre-to-centre spacing of the collagen fibrils that was accompanied by a decrease in nearest-neighbour fibrillar order. We hypothesise that a lack of keratocan might lower the number of keratan sulfate proteoglycans that associate with collagen, leading to alterations in their diameters and spatial arrangements. Alternatively, it might change the osmotic balance between the inside and outside of fibrils, causing them to swell and move further apart.

Proteoglycan expression during transforming growth factor beta -induced keratocyte-myofibroblast transdifferentiation

Keratocytes of the corneal stroma secrete a unique population of proteoglycan molecules considered essential for corneal transparency. In healing corneal wounds, keratocytes exhibit a myofibroblastic phenotype in response to transforming growth factor beta (TGF-beta), characterized by expression of alpha-smooth muscle actin. This study examined proteoglycan and collagen expression by keratocytes in vitro during the TGF-beta-induced keratocyte-myofibroblast transition. TGF-beta-treated primary bovine keratocytes developed myofibroblastic features, including actin stress fibers anchored to paxillin-containing focal adhesions, cell-associated fibronectin, alpha(5) integrin, and alpha-smooth muscle actin. Collagen I and III protein and mRNA increased in response to TGF-beta. Secretion of [(35)S]sulfate-labeled keratan sulfate proteoglycans decreased markedly in response to TGF-beta. Dermatan sulfate proteoglycans, however, increased in size and abundance. Protein and mRNA transcripts for normal stromal proteoglycans (lumican, keratocan, mimecan, and decorin) all decreased in response to TGF-beta, but protein expression and mRNA for biglycan, a proteoglycan present in fibrotic tissue, was markedly up-regulated. These results show that TGF-beta in vitro induces a proteoglycan expression pattern similar to that of corneal scars in vivo. This altered proteoglycan expression occurred coordinately with transdifferentiation of keratocytes to the myofibroblastic phenotype, implicating these cells as the source of fibrotic tissue in nontransparent corneal scars.

Human corneal GlcNac 6-O-sulfotransferase and mouse intestinal GlcNac 6-O-sulfotransferase both produce keratan sulfate

Human corneal N-acetylglucosamine 6-O-sulfotransferase (hCGn6ST) has been identified by the positional candidate approach as the gene responsible for macular corneal dystrophy (MCD). Because of its high homology to carbohydrate sulfotransferases and the presence of mutations of this gene in MCD patients who lack sulfated keratan sulfate in the cornea and serum, hCGn6ST protein is thought to be a sulfotransferase that catalyzes sulfation of GlcNAc in keratan sulfate. In this report, we analyzed the enzymatic activity of hCGn6ST by expressing it in cultured cells. A lysate prepared from HeLa cells transfected with an intact form of hCGn6ST cDNA or culture medium from cells transfected with a secreted form of hCGn6ST cDNA showed an activity of transferring sulfate to C-6 of GlcNAc of synthetic oligosaccharide substrates in vitro. When hCGn6ST was expressed together with human keratan sulfate Gal-6-sulfotransferase (hKSG6ST), HeLa cells produced highly sulfated carbohydrate detected by an anti-keratan sulfate antibody 5D4. These results indicate that hCGn6ST transfers sulfate to C-6 of GlcNAc in keratan sulfate. Amino acid substitutions in hCGn6ST identical to changes resulting from missense mutations found in MCD patients abolished enzymatic activity. Moreover, mouse intestinal GlcNAc 6-O-sulfotransferase had the same activity as hCGn6ST. This observation suggests that mouse intestinal GlcNAc 6-O-sulfotransferase is the orthologue of hCGn6ST and functions as a sulfotransferase to produce keratan sulfate in the cornea.

Fibroblast growth factor-2 promotes keratan sulfate proteoglycan expression by keratocytes in vitro

Keratocytes of the corneal stroma produce a specialized extracellular matrix responsible for corneal transparency. Corneal keratan sulfate proteoglycans (KSPG) are unique products of keratocytes that are down-regulated in corneal wounds and in vitro. This study used cultures of primary bovine keratocytes to define factors affecting KSPG expression in vitro. KSPG metabolically labeled with [(35)S]sulfate decreased during the initial 2-4 days of culture in quiescent cultures with low serum concentrations (0.1%). Addition of fetal bovine serum, fibroblast growth factor-2 (FGF-2), transforming growth factor beta, or platelet derived growth factor all stimulated cell division, but only FGF-2 stimulated KSPG secretion. Combined with serum, FGF-2 also prevented serum-induced KSPG down-regulation. KSPG secretion was lost during serial subculture with or without FGF-2. Expression of KSPG core proteins (lumican, mimecan, and keratocan) was stimulated by FGF-2, and steady state mRNA pools for these proteins, particularly keratocan, were significantly increased by FGF-2 treatment. KSPG expression therefore is supported by exogenous FGF-2 and eliminated by subculture of the cells in presence of serum. FGF-2 stimulates KSPG core protein expression primarily through an increase in mRNA pools.

Expression of the keratan sulfate proteoglycans lumican, keratocan and osteoglycin/mimecan during chick corneal development

The corneal proteoglycans belong to the Leu-rich proteoglycan (LRP) gene family and contain chondroitin/dermatan (CS/DS) or keratan sulfate (KS) chains. These proteoglycans play a critical role in generating and maintaining a transparent matrix within the corneal stroma. Decorin which has CS/DS chains and lumican which has KS chains, were first to be identified in the cornea. Two other corneal KS proteoglycans (KSPGs), keratocan and osteoglycin/mimecan were recently identified in bovine corneas. We cloned and sequenced chick osteoglycin/mimecan and found it to contain a stretch of 60 amino acids that showed no identity to the presumed mammalian homolog. The 177 base pair DNA coding for this unique sequence shows 47% identity to an 189 base pair sequence between exons 4 and 5 of the bovine osteoglycin/mimecan gene. This indicates that this cDNA represents an alternatively spliced form of osteoglycin/mimecan containing a unique N-terminal sequence. The expression of each of the three corneal KSPGs in the developing and mature chick cornea was investigated by competitive PCR and immuno-biochemical analysis of corneal extracts. Competitive PCR was used to determine the message levels for chick lumican, keratocan and osteoglycin in embryonic day 9, 12, 15, 18 and adult corneas. Results showed that lumican mRNA fluctuated during development but remained at a relatively high level while keratocan and osteoglycin message levels declined steadily from day 9 to adult. Additionally, lumican mRNA was present at higher levels, during all stages of corneal development, than keratocan and at much higher levels than osteoglycin. Antibodies shown to be specific for each KSPG were used to characterize proteoglycans isolated from embryonic and adult chick corneas. KSPGs from embryonic corneas eluted 1-2 fractions earlier on Q-Sepharose than KSPG from adult corneas. Additionally, Western blot analysis showed that embryonic KSPGs were more keratanase-resistant, endo-beta-galactosidase sensitive than adult KSPGs. The results of this study indicate an alteration in sulfation or the fine structure of the glycosaminoglycan chains occurs during corneal maturation for the 3 KSPGs.

Role of lumican in the corneal epithelium during wound healing

Lumican regulates collagenous matrix assembly as a keratan sulfate proteoglycan in the cornea and is also present in the connective tissues of other organs and embryonic corneal stroma as a glycoprotein. In normal unwounded cornea, lumican is expressed by stromal keratocytes. Our data show that injured mouse corneal epithelium ectopically and transiently expresses lumican during the early phase of wound healing, suggesting a potential lumican functionality unrelated to regulation of collagen fibrillogenesis, e. g. modulation of epithelial cell adhesion or migration. An anti-lumican antibody was found to retard corneal epithelial wound healing in cultured mouse eyes. Healing of a corneal epithelial injury in Lum(-/-) mice was significantly delayed compared with Lum(+/-) mice. These observations indicate that lumican expressed in injured epithelium may modulate cell behavior such as adhesion or migration, thus contributing to corneal epithelial wound healing.

The bovine mimecan gene. Molecular cloning and characterization of two major RNA transcripts generated by alternative use of two splice acceptor sites in the third exon

Mimecan is a proteoglycan expressed by many connective tissues. It was originally isolated in a truncated form as a bone-associated glycoprotein, osteoglycin, and was considered an osteoinductive factor. Recently, we demonstrated that the full-length translation product of the cDNA encoding mimecan is a corneal keratan sulfate proteoglycan present in other tissues without keratan sulfate chains. We also described multiple mimecan mRNA transcripts generated by differential splicing and alternative polyadenylation. In this study, we isolated genomic clones and determined the genomic organization of the bovine mimecan gene. The gene is spread over >33 kilobases of continuous DNA sequence and contains eight exons. The newly discovered first exon, identified by 5'-rapid amplification of cDNA ends, consists of a 5'-untranslated region and is enriched in C+G nucleotides. Two transcription initiation sites starting at the first and at the second exons were determined by primer extension. Molecular characterization shows that alternatively spliced RNA isoforms are generated by the use of two distinct splice acceptor sites in the third exon situated 278 base pairs apart. We determined a partial genomic structure of the human mimecan gene and demonstrated two alternatively spliced RNA transcripts that are generated likewise. Despite the diversity of mimecan transcripts, the primary structure of the core protein is encoded from exons 3 to 8 and remains unchanged, indicating its functional importance. Using ribonuclease protection assay, we analyzed the patterns of spliced RNA expressed in cultured bovine keratocytes. We demonstrated that their expression is differentially modulated in a temporal manner by basic fibroblast growth factor.

Cloning, characterization and tissue-specific expression of the gene encoding bovine keratocan, a corneal keratan sulfate proteoglycan

Keratocan is one of three major keratan sulfate proteoglycans characteristically expressed in cornea. We reported previously the sequence of bovine Kera cDNA. In this study, the complete bovine Kera gene was cloned and sequenced, and its expression pattern was determined. The Kera gene is composed of three exons and two introns that span 8.830kb of the bovine genome. The first exon contains 287 nucleotides of 5'-UTR sequence. Both of the two large introns of 1322 and 4178bp contain (CA)n repeats. The bovine Kera gene has a TATA box that is located 28bp upstream from tsp. Primer extension and S1 nuclease protection analyses were used to determine the major tsp. RPA indicate that cornea and sclera are the two tissues with the highest expression of Ktcn mRNA. This restricted expression in eye tissues, as well as the unique modification of keratocan with long keratan sulfate chains in cornea, suggests that this molecule may be important in developing and maintaining corneal transparency.

The cloning of mouse keratocan cDNA and genomic DNA and the characterization of its expression during eye development

Keratan sulfate proteoglycans (KSPGs) play a pivotal role in the development and maintenance of corneal transparency. Keratocan, lumican, and mimecan (osteoglycin) are the major KSPGs in vertebrate corneas. To provide a better understanding of the structure/function relationship of keratocan, we have cloned both the mouse keratocan gene and its cDNA. We have also examined its expression during embryonic development. The mouse keratocan gene spans approximately 6.5 kilobases of the mouse genome and contains three exons and two introns. Northern blotting and in situ hybridization were employed to examine keratocan gene expression during mouse development. Unlike lumican gene, which is expressed by many tissues other than cornea, keratocan mRNA is more selectively expressed in the corneal tissue of the adult mouse. During embryonic development, keratocan mRNA was first detected in periocular mesenchymal cells migrating toward developing corneas on embryonic day 13.5 (E13.5). Its expression was gradually restricted to corneal stromal cells on E14. 5 approximately E18.5. Interestingly, keratocan mRNA can be detected in scleral cells of E15.5 embryos, but not in E18.5 embryos. In adult eyes, keratocan mRNA can be detected in corneal keratocytes, but not in scleral cells.

Identification of the N-linked oligosaccharide sites in chick corneal lumican and keratocan that receive keratan sulfate

Corneal proteoglycans have chondroitin/dermatan and keratan sulfate (KS) chains and belong to the leucine-rich proteoglycan gene family. Corneal KS is N-linked to Asn of an NX(S/T) site through a complex oligosaccharide linkage region. Only some sites receive KS, whereas others remain in a high mannose form. To determine whether the attachment of KS was biased toward specific sites, we isolated trypsin-digested KS-containing fragments of chick corneal proteoglycans and sequenced the peptides. Results showed that all of the peptides sequenced aligned to the deduced amino acid sequence of either chick lumican or chick keratocan at the first, third, and fourth potential N-linked sites. Sites 1 and 4 in lumican and keratocan are in a homologous location. By analogy with the structure of ribonuclease inhibitor (a Leu-rich repeat containing protein), the KS chains would extend outward on the outer face of a horseshoe-like structure. The amino acid sequences surrounding the potential N-linked sites were also compared. Sites receiving KS tend to have a higher occurrence of aromatic residues, in particular Phe, located within 3 amino acids of NX(S/T). These conserved Phe residues may have a role in the conversion of high mannose N-linked oligosaccharides to polylactosamine and/or keratan sulfate.

Characterization and expression of the mouse lumican gene

Lumican is one of the major keratan sulfate proteoglycans (KSPG) in vertebrate corneas. We previously cloned the murine lumican cDNA. This study determines the structure of murine lumican gene (Lum) and its expression during mouse embryonic developments. The mouse lumican gene was isolated from a bacterial artificial chromosome mouse genomic DNA library and characterized by polymerase chain reaction and Southern hybridization. The lumican gene spans 6.9 kilobase pairs of mouse genome. The gene consists of three exons and two introns. Exon 1 constitutes 88 bases (b) of untranslated sequence. Exon 2 is 883 b and contains most of the coding sequence of lumican mRNA, and exon 3 has 152 b of coding sequence and 659 b of 3' noncoding sequence. The mouse lumican gene has a TATCA element, a presumptive TATA box, which locates 27 b 5'-upstream from the transcription initiation site. Northern hybridization and in situ hybridization indicate that in early stages of embryonic development, day 7 post coitus the embryo expresses little or no lumican. Thereafter, different levels of lumican mRNA can be detected in various organ systems, such as cornea stroma, dermis, cartilage, heart, lung, and kidney. The cornea and heart are the two tissues that have the highest expression in adult. Immunoblotting studies found that KSPG core proteins became abundant in the cornea and sclera by postnatal day 10 but that sulfated KSPG could not be detected until after the eyes open. These results indicate that lumican is widely distributed in most interstitial connective tissues. The modification of lumican with keratan sulfates in cornea is concurrent with eye opening and may contribute to corneal transparency.

Mimecan, the 25-kDa corneal keratan sulfate proteoglycan, is a product of the gene producing osteoglycin

Bovine cornea contains three unique keratan sulfate proteoglycans (KSPGs), of which two (lumican and keratocan) have been characterized using molecular cloning. The gene for the third protein (KSPG25) has not been identified. This study examined the relationship between the KSPG25 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein. The N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea. The osteoglycin amino acid sequence makes up the C-terminal 47% of the deduced sequence of the KSPG25 protein. Antibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratocan. KSPG25-related proteins, not modified with keratan sulfate, were also detected in several connective tissues. Northern blot analysis showed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues. Ribonuclease protection analysis detected several protected KSPG25 mRNA fragments, suggesting alternate splicing of KSPG25 transcripts. We conclude that the full-length translation product of the gene producing osteoglycin is a corneal keratan sulfate proteoglycan, also present in many non-corneal tissues without keratan sulfate chains. The multiple size protein products of this gene appear to result from in situ proteolytic processing and/or alternative splicing of mRNA. The name mimecan is proposed for this gene and its products.

Synthesis of corneal keratan sulfate proteoglycans by bovine keratocytes in vitro

Keratan sulfate proteoglycans (KSPGs) are the major proteoglycans of the cornea and are secreted by keratocytes in the corneal stroma. Previous studies have been able to show only transient secretion of KSPG in cell culture. In this study, cultures of bovine keratocytes were found to secrete the three previously characterized KSPG proteins into culture medium. Reactivity with monoclonal antibody I22 demonstrated substitution of these proteins with keratan sulfate chains. KSPG constituted 15% of the proteoglycan metabolically labeled with [35S]sulfate in keratocyte culture medium. This labeled KSPG contained keratan sulfate chains of 4700 Da compared to 21,000 Da for bovine corneal keratan sulfate. Labeled keratan sulfate from cultures contained nonsulfated, monosulfated, and disulfated disaccharides that were released by digestion with endo-beta-galactosidase or keratanase II. Nonsulfated disaccharides were relatively more abundant in keratan sulfate from culture than in corneal keratan sulfate. These results show that cultured bovine keratocytes maintain the ability to express all three of the known KSPG proteins, modified with keratan sulfate chains and sulfated on both N-acetylglucosamine and galactose moieties. KSPG made in vitro differs from that found in vivo in the length and sulfation of its keratan sulfate chains. The availability of cell cultures secreting corneal keratan sulfate proteoglycans provides an opportunity to examine biosynthesis and control of this important class of molecules.

Multiple non-reducing chain termini isolated from bovine corneal keratan sulfates

Keratan sulfate-containing proteoglycans were isolated from bovine cornea (15-month-old to 3-year-old animals) and digested with the enzyme, keratanase II. The released oligosaccharides, which included non-reducing termini and repeat region oligosaccharides but not linkage regions, were reduced with alkaline borohydride and fractionated on a Spherisorb column. These oligosaccharides were examined by 600-MHz 1H NMR spectroscopy using one- and two-dimensional methods and, in addition to some oligosaccharide alditols previously recovered from skeletal keratan sulfate, the following new capping structures were identified: NeuAcalpha2-6Galbeta1-4GlcNAc(S)-ol, NeuAcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc(S )-ol, NeuGcalpha2-6Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4Gl cNA c(S)-ol, NeuGcalpha2-3Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4Gl cNA c(S)-ol, NeuGcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc(S )-ol, NeuGcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-o l, Galalpha1-3Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc( S)-ol, Galalpha1-3Galbeta1-4GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)- ol, GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-ol, and GalNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-ol. These structures represent seven families of capping residues, whose relative molar proportions are given in parentheses: NeuAcalpha(2-3)- (12%), NeuAcalpha(2-6)- (41%), NeuGcalpha(2-3)- and NeuGcalpha(2-6)- families (12%), Galalpha(1-3)- (26%), GalNAc(S)beta(1-3)- (5%), and GlcNAc(S)beta(1-3)- (4%). It is not clear, at present, where each of these structures occurs on the bi-antennary N-linked corneal keratan sulfate chains, which themselves occur within three keratan sulfate proteoglycan species. However, examination of the relative proportions of the capping to the repeat structures and knowledge of the average molecular size suggests that the sum of these non-reducing termini represents the caps of two antennae.

Simultaneous expression of keratan sulphate epitope (a sulphated poly-N-acetyllactosamine) and blood group ABH antigens in papillary carcinomas of the human thyroid gland

The monoclonal antibody 5-D-4 recognizes heavily sulphated forms of keratan sulphate epitope. It reacted strongly with the cell surfaces of most thyroid papillary carcinomas from all the individuals examined, independently of the blood group of the patients. Cells of follicular variants of papillary carcinomas were also labelled by 5-D-4. In contrast, no labelling with this antibody was observed in other types of thyroid neoplasms, or in normal tissues. The reactivity of 5-D-4 with papillary carcinomas was markedly reduced or abolished by prior digestion with endo-beta-galactosidase, keratanase II, or N-glycosidase F. Although keratanase digestion had no effect on 5-D-4 labelling, it revealed the binding sites of Griffonia simplicifolia agglutinin II (GSA-II), which recognizes terminal N-acetylglucosamine in a limited number of carcinoma cells from some individuals. Blood group ABH antigens, which are simultaneously expressed together with keratan sulphate epitope in cancer cells, were eliminated by digestion with endo-beta-galactosidase and N-glycosidase F, but were resistant to keratanase and keratanase II treatment. These results indicate that keratan sulphate oligosaccharides are cancer-associated and are probably oncofoetal antigens, as are the blood group antigens in human thyroid glands. The results suggests that poly-N-acetyllactosamine, which is ubiquitously and consistently produced in papillary carcinomas, is modified in two different ways: sulphation on the 6-position of at least some units of either galactose or N-acetylglucosamine or both, and decoration of non-reducing termini with the blood group antigens. Along with the endo-beta-galactosidase-GSA-II labelling procedure, labelling with 5-D-4 may be a useful diagnostic means for distinguishing papillary carcinoma from other types of thyroid neoplasms.

Conformation, stability and interactions of corneal keratan sulfate proteoglycan

We have monitored the molecular conformation, stability, interaction and dynamics of keratan sulfate proteoglycan, the major structural protein component of the cornea, in solution, by studying the fluorescence spectral features of its tryptophan residues as component-specific intrinsic spectral probes (collagen, the other structural component of the cornea, has no tryptophans). Our study suggests that the Trp region of the molecule is in a motionally restricted environment as it exhibits a fluorescence red-edge effect and shows dipole relaxation. The extrinsic spectral probe 8-anilinonaphthalene 1-sulfonate reveals keratan sulfate proteoglycan to possess significant surface hydrophobicity. This dual character of keratan sulfate proteoglycan allows us to label it as an 'ambidextran' proteoglycan. The molecule is stable between pH 5-8 and has a Tm value of 72 degrees C. Disulfide bonds play a role in the stability of the molecule. KSPG is seen to interact with collagen and the model compound, poly(L-proline). Interaction of the proteoglycan with unilamellar vesicles appears to be more interfacial than penetrative. This dual interaction displayed by KSPG with collagen and with lipid assemblages suggests that it plays the role of a 'filler' in the extracellular matrix of the cornea.

Molecular cloning and tissue distribution of keratocan. Bovine corneal keratan sulfate proteoglycan 37A

Previous studies showed that the keratan sulfate-containing proteoglycans of bovine corneal stroma contain three unique core proteins designated 37A, 37B, and 25 (Funderburgh, J. L., Funderburgh, M. L., Mann, M. M., and Conrad, G. W. (1991) J. Biol. Chem. 266, 14226-14231). Degenerate oligonucleotides designed from amino acid sequences of the 37A protein were used to screen a cDNA expression library from cultured bovine keratocytes. A cDNA clone coding for keratocan, a 37A protein, was isolated and sequenced. The deduced keratocan amino acid sequence is unique but related to two other keratan sulfate-containing proteins, lumican (the 37B core protein) and fibromodulin. These three proteins share approximately 35% amino acid identity and a number of conserved structural features. Northern hybridization and immunoblotting of tissue extracts found keratocan distribution to be more limited than that of lumican or fibromodulin. Keratocan is abundant in cornea and sclera and detected in much lesser amounts in skin, ligament, cartilage, artery, and striated muscles. Only in cornea was keratocan found to contain large, sulfated keratan sulfate chains. Keratocan, like lumican, is a core protein of a major corneal proteoglycan but is present in non-corneal tissues primarily as a nonsulfated glycoprotein.

The human lumican gene. Organization, chromosomal location, and expression in articular cartilage

A human lumican cDNA sequence was derived by polymerase chain reaction techniques from RNA obtained from intestine, placenta, and articular cartilage. A contiguous sequence of 1729 bases was obtained corresponding to an observed message size of 1.8 kilobases (kb). The cDNA sequence consists of an 80-base pair (bp) 5'-untranslated region, a 1014-bp coding sequence, and a 618-bp 3'-untranslated region terminating in a 17-bp poly(A) tail. The deduced lumican protein sequence has 338 amino acids, including a putative 18-residue signal peptide. The human lumican gene was shown to be spread over about 7.5 kb of genomic DNA and to be located on chromosome 12q22. The gene consists of 3 exons separated by introns of 2.2 and 3.5 kb. The shorter 5'-intron resides 21 bases prior to the translation initiation codon, and the 3'-intron resides 152 bases prior to the translation termination codon. The lumican message is expressed at high levels in adult articular chondrocytes but at low levels in the young juvenile. This age-related trend in message level is not, however, common to all tissues in which the lumican gene is expressed. Lumican is present in the extracellular matrix of human articular cartilage at all ages, although its abundance is far greater in the adult. In the adult cartilage lumican exists predominantly in a glycoprotein form lacking keratan sulfate, whereas the juvenile form of the molecule is a proteoglycan.

Synthesis of stromal glycosaminoglycans in response to injury

Our goal is to examine the synthesis and deposition of corneal glycosaminoglycans (GAGs) in response to a wound created by the insertion of porous discs into stromal interlamellar pockets. The disc and the surrounding stromal tissue were assayed and compared to contralateral control stroma and to sham operated corneas at 14, 42, and 84 days. The tissue and/or discs were removed and labeled with 35S-sulfate for 18 h; GAGs were extracted with 4 M guanidine-HCl. Extracts were chromatographed on Q-Sepharose columns, bound proteoglycans were eluted with a linear salt gradient, and radioactive fractions were analyzed. Total GAG content was determined colorimetrically, using dimethylmethylene blue. Specific GAGs were determined using enzymatic digestion with selective polysaccharide lyases and protein cores were examined using SDS-PAGE. The nonbound fractions from the chromatography were assayed for TGF-beta using Western blot analysis and for hyaluronic acid using an 125I-radiometric assay. Specific GAGs were localized 42 days after the disc had been implanted in the stroma. The placement of the discs into the stroma resulted in a decrease in the total amount of GAG. However, the ratio of dermatan-chondroitin sulfate and heparan sulfate to keratan sulfate increased in the surrounding tissue and disc. Hyaluronic acid was elevated at day 14 in the surrounding tissue, and not until day 84 in the disc. Western blot analysis of surrounding tissue extracts revealed forms of TGF-beta that migrated with an apparent molecular mass of 63 and 43 kDa. The results indicate that the insertion of discs into interlamellar pockets causes changes in the sulfation and proportion of the glycosaminoglycans in the surrounding tissue and the disc. These changes are coincident with the appearance of TGF-beta. After 84 days, the population of glycosaminoglycans in the disc begins to resemble the surrounding stroma. This model will allow us to examine further the synthesis and deposition of proteins following an extensive wound in which cells must migrate to the wound site and then undergo extensive remodeling.

Spectroscopic characterisation of disaccharides derived from keratan sulfates

Skeletal keratan sulfates have been degraded by three independent techniques and the resultant, borohydride-reduced, disaccharides have been characterised by NMR spectroscopy. The 1H and 13C (where available) chemical shifts are reported for the following substances, where GalNAc-ol represents N-acetyl-galactosaminitol, GlcNAc-ol represents N-acetyl-glucosaminitol, GlcNAc(6S)-ol represents N-acetyl-glucosaminitol 6-O-sulfate and 2,5AnMan(6S)-ol represents 2,5-anhydro-D-mannitol 6-O-sulfate. (a) GlcNAc(6S)beta(1-3)Gal-ol, isolated after keratanase (from Pseudomonas sp.) digestion. (b) Gal beta(1-4)GlcNAc(6S)-ol and Gal(6S)beta(1-4) GlcNAc(6S)-ol, the 1H chemical shifts have been reported previously [Brown, G. M., Huckerby, T. N., Morris, H. G., Abram, B. L. & Nieduszynski, I. A. (1994) Biochemistry 33, 4836-4846; Brown, G. M., Huckerby, T. N. & Nieduszynski, I. A. (1994) Eur. J. Biochem. 224, 281-308], GlcNAc(6S)beta(1-6)GalNAc-ol, [formula: see text], [formula: see text], all isolated after keratanase II digestion. (c) Gal beta(1-4)2,5AnMan(6S)-ol and Gal(6S)beta(1-4)2,5AnMan(6S)-ol, isolated after hydrazinolysis and nitrous acid digestion. In addition, the model compounds Gal beta(1-4)GlcNAc-ol and Gal beta(1-6)GlcNAc-ol have also been examined by 1H and 13C NMR spectroscopy. The value of these data for microstructural analysis of keratan sulfate samples is discussed.