Postscript on possum cartilage and oxygen; what is keratan sulphate? A corrigendum to the addendum

The recent exchange on cartilage ultrastructure, the localisation of keratan sulphate (KS) therein and the influence of oxygen tension on both (Stockwell & Scott, 1997; Archer et al. 1997; Caterson, 1997) raised important issues which need clarification and extension. We wish to correct certain statements and to examine more rigorously principles which will establish a foundation for future discussion.

Leukemia inhibitory factor (LIF) binding protein attenuates the phlogistic and abolishes the chondral effects of LIF in goat joints

OBJECTIVE

To investigate the ability of murine leukemia inhibitory factor (LIF) binding protein (mLBP) to attenuate the effects of recombinant human LIF (rhLIF) in goat radiocarpal joints in vivo.

METHODS

Endotoxin-free saline (1 ml) containing either 0.5 or 1 microg of rhLIF was injected into the left and right radiocarpal joints of male angora goats. One hour later the right radiocarpal joints were injected with either 1 or 5 microg of naturally occurring mLBP in 1 ml saline, while the left radiocarpal joints (controls) received 1 ml saline vehicle alone. Goat joints were examined for clinical features of inflammation and synovial fluid (SF) was aspirated on Day 0 (before injection) and Days 2 and 6 postinjection. Leukocyte counts and concentrations of keratan sulfate were determined in the SF. Proteoglycan synthesis and proteoglycan content of cartilage was determined ex vivo in cartilage explants obtained at Day 6.

RESULTS

Preliminary time course studies in vitro showed that mLBP had to be added to cartilage explant cultures within 1 h of rhLIF for effective antagonism to occur. In joints injected with either 0.5 or 1 microg rhLIF significant increases in swelling, effusion volume, leukocyte counts, and SF keratan sulfate concentrations were observed relative to controls. Statistically significant depressions of ex vivo proteoglycan synthesis and in proteoglycan content of articular cartilage were also observed relative to controls. In joints injected with 1 microg rhLIF followed by 1 microg mLBP, statistically significant improvement was only observed in the rate of ex vivo cartilage proteoglycan synthesis. The observed rate did not differ significantly from that obtained in joints treated with vehicle alone. In contrast, in joints injected with 0.5 microg rhLIF followed by 5 microg mLBP, statistically significant improvement was observed in all variables. Treatment with 5 microg mLBP effectively negated the effects of rhLIF on joint swelling, effusion volume, leukocyte infiltration, and cartilage proteoglycan catabolism.

CONCLUSION

Murine LBP has the ability to attenuate the phlogistic effects of rhLIF in radiocarpal joints of goats and also abolishes the stimulatory effect of rhLIF on cartilage proteoglycan catabolism and depression of ex vivo proteoglycan synthesis. These antiinflammatory and chondral effects suggest that a humanized derivative of mLBP could be a clinically useful antagonist for LIF in inflammatory diseases.

Human corneal keratan sulfates

The keratan sulfate-containing proteoglycans were isolated from fourteen pooled human corneas (thirteen from 61- to 86-year-olds, plus one from a 12-year-old). These proteoglycans were subjected to digestion with the enzyme keratanase II, and the released oligosaccharides, which included nonreducing termini and repeat region oligosaccharides but not linkage regions, were reduced with alkaline borohydride and identified on two separate ion-exchange columns. Both of the latter had been calibrated with samples, most of which had been derived from bovine corneal keratan sulfate (Tai, G.-H., Huckerby, T. N., and Nieduszynski, I. A. (1996) J. Biol. Chem. 271, 23535-23546) and all of which had been fully characterized by NMR spectroscopic analysis. The capping structures identified in human corneal keratan sulfates occurred in the relative proportions: NeuAcalpha(2-6)- >NeuAcalpha(2-3)- >GalNAc(S)beta(1-3)-. The other groups of capping structures which had been identified in bovine corneal keratan sulfate, i.e. NeuGcalpha(2-3)-, NeuGcalpha(2-6)-, GlcNAc(S)beta(1-3)- were absent, although the possibility of the presence of some Galalpha(1-3)- structures could not be excluded. In addition, the human sample showed significantly higher levels of alpha(1-3)-fucosylated repeat region structures than did the bovine sample, and it is not clear whether this reflects a species or age dependence as the bovine corneas were from young animals, whereas the human corneas were predominantly from an older group. The charge densities and keratan sulfate chain sizes of the human and bovine keratan sulfate-containing proteoglycans were seen to be similar.

The natural history of the anterior cruciate ligament-deficient knee. Changes in synovial fluid cytokine and keratan sulfate concentrations

Restoring knee stability through reconstruction, while providing symptomatic relief, has not been shown to decrease the incidence of degenerative changes after rupture of the anterior cruciate ligament. This suggests that posttraumatic osteoarthritis may not be purely biomechanical in origin, but also biochemical. To test this, we measured the levels of seven cytokine modulators of cartilage metabolism in knee joint synovial fluid after anterior cruciate ligament rupture. We also measured keratan sulfate, a product of articular cartilage catabolism. The sample population consisted of patients with uninjured knee joints (N = 10), and patients with acute (N = 60), subacute (N = 18), and chronic (N = 8) anterior cruciate ligament-deficient knees. Synovial fluid samples were analyzed by enzyme-linked immunosorbent assays. Normal synovial fluids contained high levels of the interleukin-1 receptor antagonist but low concentrations of other cytokines. Immediately after ligament rupture there were large increases in interleukins 6 and 8, tumor necrosis factor alpha, and keratan sulfate. Interleukin-1 levels remained low throughout the course. As the injury became subacute and then chronic, interleukin-6, tumor necrosis factor-alpha, and keratan sulfate levels fell but remained considerably elevated 3 months after injury. Concentrations of interleukin-1Ra fell dramatically. Granulocyte-macrophage colony-stimulating factor concentrations were normal acutely and subacutely but by 3 months after injury were elevated 10-fold. Our data reveal a persistent and evolving disturbance in cytokine and keratan sulfate profiles within the anterior cruciate ligament-deficient knee, suggesting an important biochemical dimension to the development of osteoarthritis there.

Keratan sulphate in the trabecular meshwork and cornea

PURPOSE

A study was made of the distribution of keratan sulphate in the human anterior chamber.

METHODS

The monoclonal antibody, 5-D-4, was used in immuno-electron microscopy to visualise keratan sulphate distribution in the anterior chamber of 16 normal eyes, 7 Fuchs' dystrophy corneas, and a macular dystrophy cornea.

RESULTS

Keratan sulphate was detected in normal human aqueous humour and also on the surface of trabecular cells in the uveal meshwork. Normal corneal stroma showed an increase in keratan sulphate labelling from anterior to posterior, with marked labelling in the posterior region of Descemet's membrane. The apical surface of the corneal endothelium labelled positively, but showed considerable variation in the level of labelling from cell to cell. The macular dystrophy cornea had the classic histopathological features of a type I case, including a highly abnormal Descemet's membrane. No keratan sulphate was detected in the macular dystrophy patient's corneal stroma or serum. The Fuchs' endothelial dystrophy corneas showed a normal distribution of keratan sulphate labelling in the stroma. The Fuchs' endothelial cells labelled for keratan sulphate but were highly abnormal in appearance, often exhibiting long filopodia and appearing to be actively migrating.

CONCLUSIONS

This work has shown that keratan sulphate has a much wider distribution than was previously believed. The detection of keratan sulphate on the trabecular and endothelial cell surfaces also suggests a possible role for this molecule in cell adhesion and/or migration.

Macrophage receptors for lumican. A corneal keratan sulfate proteoglycan

PURPOSE

Keratan sulfate proteoglycans (KSPGs) of the cornea exhibit a characteristic change in glycosylation resulting from stromal inflammation and scarring. To examine potential roles for these molecules in the pathobiology of the cornea, the authors investigated interaction of inflammatory macrophages with KSPGs in vitro.

METHODS

Attachment and spreading of mouse peritoneal macrophages were examined on surfaces coated with corneal proteoglycans, intact or with modified glycosylation. Solution-phase interactions were demonstrated using soluble proteoglycans labeled with 125I-Iodine or with fluorescein. The affinity and specificity of these interactions were determined by competitive inhibition with unlabeled proteoglycans.

RESULTS

Macrophages did not adhere to intact corneal KSPGs but did attach and spread rapidly on the lumican core protein after the removal of keratan sulfate chains. Arterial lumican, a nonsulfated form of this proteoglycan, also stimulated macrophage attachment. Labeled arterial lumican specifically bound to macrophages with high affinity. Flow cytometry demonstrated a high proportion of macrophages binding lumican. Lumican binding was inhibited by divalent cation-chelators and by polyanions. Inhibition and kinetics of lumican binding were distinct from interaction of macrophages with maleated bovine serum albumin, collagen, laminin, and fibronectin.

CONCLUSIONS

The highly sulfated KSPGs of cornea do not promote macrophage adhesion; however, the low-sulfate lumican present in pathologic corneas may act to localize macrophages in regions of inflammation. The lumican receptor differs from macrophage scavenger receptors and from receptors for several other extracellular matrix molecules.

Developmental expression of keratan sulfate-like immunoreactivity distinguishes thalamic nuclei and cortical domains

Proteoglycans influence axonal outgrowth in several experimental paradigms, and their distribution during development suggests a role in axon guidance. We have used a monoclonal antibody, 5D4, that recognizes an epitope on sulfated keratans (KS), to define the distribution of keratan sulfate proteoglycans (KSPGs) in the developing thalamus and cortex of the rat. During development, 5D4 immunolabeling is present on thalamic axons as they grow through the internal capsule and subplate but is not present in the adjacent pathway for cortical efferent axons. Individual thalamic nuclei differ markedly in their expression of KSPGs; these distinctions persist throughout the period of developmentally regulated expression. Major cortical domains also differ in their expression of KSPGs, which are expressed throughout medial (cingulate and retrosplenial) cortex well before neocortex. Immunolabeling for KSPGs diminishes 2 weeks after birth; in the adult it is associated with small glia. The 5D4 epitope is present on several KSPGs (320, 220, and 160 kD) on Western blots during development but only in a broad 200-kD band in adult brain. Immunolabeling is degraded on sections and Western blots by keratanase II but not by keratanase I or chondroitinase ABC, confirming that the antibody recognizes KS. Bands identified by 5D4 on Western blots differ from those identified by antibodies to known KSPGs (aggrecan, claustrin, SV2, ABAKAN, phosphacan-KS), indicating that 5D4 is labeling KSPGs not previously described in the brain. The selective expression of KSPGs during development suggests that they may be a part of the molecular identity of thalamic nuclei and cortical domains that defines their connectivity.

Localization of types I, II and III collagen and glycosaminoglycans in the mandibular condyle of growing monkeys: an immunohistochemical study

In order to analyse the regional and age-related variations of primate condyles, immunohistochemical techniques were used to examine the localization of types I, II and III collagen and a variety of glycosaminoglycans in distinct anteroposterior regions of the mandibular condyle of two growing female rhesus monkeys (Macaca mulatta). In the juvenile monkey staining for types I and III collagen was weak in the fibrous tissue layer, intense in the pre-cartilaginous tissue layer and faint in the cartilaginous tissue layer; staining was significantly more intense in the posterosuperior and posterior regions than in the anterior region. Similarly, staining for cartilage-characteristic extracellular matrices, including type II collagen and keratan sulfate, was intense in the cartilaginous tissue layer of the posterior condyle. In contrast, in the late-adolescent monkey staining for the extracellular matrices was more intense in the anterior half of the condyle (i.e. from the anterior to the posterosuperior region) than in the posterior region, and most intense in the posterosuperior region. The results demonstrate that marked regional differences exist in the phenotypic expression of the extracellular matrices in the mandibular condyles of growing monkeys and that these differences vary between different developmental stages. The variations probably reflect the predominance of competing growth and articulatory functions in the mandibular condyles.

Macular corneal dystrophy type II: multiple studies on a cornea with low levels of sulphated keratan sulphate

We investigated an individual macular corneal dystrophy (MCD) type II cornea from a 42-year-old woman with markedly reduced antigenic keratan sulphate levels. A characteristic 4.6 A X-ray reflection was evident, and the mid-stroma contained 30% less sulphur than normal. Close packing of collagen was restricted to the superficial stroma. Abnormally large proteoglycan filaments were noted throughout the extracellular matrix and Descemet's membrane's posterior non-banded zone, but not its anterior banded zone. Small, collagen-associated stromal proteoglycans were susceptible to digestion with chondroitinase ABC, but not keratanase I or N-glycanase. On occasion, collagen fibrils ranged in size from 20 nm to 58 nm, with preferential diameters of 34 nm and 42 nm. Corneal guttae were evident, as were numerous endothelial inclusions, most probably due to intracellular fibrillogranular vacuoles similar to those found in the stroma. The endothelium expressed reduced anti-keratan sulphate labelling.

Biochemical, histochemical, and immunohistochemical characterization of distal tibial osteochondrosis in horses

OBJECTIVE

To compare the biochemical, histochemical, and immunohistochemical profiles of articular cartilage from horses with naturally acquired distal tibial osteochondrosis (OC) with cartilage from a similar location in clinically normal horses.

ANIMALS

9 affected horses (group 1, 16 OC lesions) and 4 control horses (group 2, 8 normal osteochondral specimens).

PROCEDURE

OC specimens were collected during arthroscopic removal of the fragment, and control specimens were collected by aseptic osteotomy. Uronic acid, total protein, total glycosaminoglycan (GAG), chondroitin sulfate (CS), and keratan sulfate (KS) contents were determined. Histomorphologic, histochemical, and immunohistochemical examinations were performed on specimens after snap freezing at -80 C and cryosectioning. Monoclonal antibodies (MAB) 3B3 and 5D4 were applied for location of epitopes of CS and KS, respectively.

RESULTS

OC lesions had significantly lower quantity of uronic acid, total GAG, and CS, compared with normal cartilage. OC cartilage had significantly less intense staining with toluidine blue, along with irregular cellularity and tidemark characteristics, compared with normal cartilage. Monoclonal antibodies 3B3 and 5D4 stained OC cartilage, whereas MAB 5D4 did not stain control cartilage. Additionally, MAB 3B3 and 5D4 stained the fibrous tissue that was found firmly attached to the OC lesion located between the parent distal portion of the tibia and OC fragment.

CONCLUSION

OC cartilage lesions of the distal intermediate ridge of the tibia in horses are biochemically, histochemically, and immunohistochemically distinct from normal cartilage from the same location. Results may reflect the inability of the chondrocyte of the developing joint to alter matrix components that would allow proper maturation and differentiation into bone.

Antibodies to the sulphated, high molecular mass mouse tectorin stain hair bundles and the olfactory mucus layer

Polyclonal antibodies were raised in chickens to the glycosylated forms of the high (H), medium (M) and low (L) molecular mass (MM) mouse tectorins. In the mouse cochlea, all three antibodies stained the tectorial membrane. Antibodies raised to HMM tectorin also stained the hair bundles of both inner and outer hair cells. A number of other mouse tissues were screened with the anti-tectorin antibodies to look for similar or antigenically related molecules. Staining was not observed in any other tissue type with the antibodies directed against the MMM and LMM tectorins. In the nose, the anti-HMM tectorin antibodies stained Bowman's glands and the mucus layer overlying the olfactory epithelium. The surface of the adjacent respiratory epithelium was not stained by these antibodies. HMM tectorin can be specifically radiolabelled by injecting neonatal mice with 35SO4 and undergoes a shift in electrophoretic mobility following treatment with keratanase, an endo-beta-galactosidase from Pseudomonas. However, when centrifuged on shallow CsCl gradients HMM tectorin has a buoyant density similar to that of glycoproteins and does not behave as a typical cartilage type proteoglycan. HMM tectorin does not react with mab 5D4, a monoclonal antibody that recognises keratan sulphate glycosaminoglycan from corneal and skeletal muscle proteoglycan. Unlike antibodies to HMM tectorin, mab 5D4 selectively stains the upper surface of the tectorial membrane, Hensen's stripe and the mucus layer overlying the respiratory epithelium. These studies indicate that the MMM and LMM tectorins may be unique to the cochlea, and that HMM may be a "light' keratan sulphate proteoglycan that is antigenically related to either the mucins or a more specific component of the olfactory mucus layer.

Proteoglycan metabolism of equine articular chondrocytes cultured in alginate beads

Equine chondrocytes were cultured in vitro for 30 days in ionically gelled alginate beads. The alginate polymerises into a stable gel in the presence of divalent cations (calcium), and rapid depolymerisation in the presence of a calcium chelator releases the viable chondrocytes. The chondrocytes maintained a spherical appearance for 30 days in culture, in marked contrast to monolayer cultures, which develop a dedifferentiated fibroblastic morphology. The major proteoglycan molecule produced by the encapsulated chondrocytes was aggrecan, of similar hydrodynamic size to aggrecan molecules present in the matrix of the articular cartilage from which the cells were harvested. Link protein, keratan sulphate and chondroitin sulphate were also synthesised by the chondrocytes, as demonstrated by immunohistochemistry. The proteoglycan secreted by the chondrocytes consisted of at least two pools, one remaining adjacent to the cell and forming a dense, cell-associated matrix, and another migrating more peripherally into the intercellular compartment. Newly synthesised proteoglycans extracted from the pericellular matrix and the intercellular matrix were similar in hydrodynamic size and aggregated in the presence of exogenous hyaluronan.

Association of N-acetylgalactosamine-6-sulfate sulfatase with the multienzyme lysosomal complex of beta-galactosidase, cathepsin A, and neuraminidase. Possible implication for intralysosomal catabolism of keratan sulfate

N-Acetylgalactosamine-6-sulfate sulfatase (GALNS) catalyzes the first step of intralysosomal keratan sulfate (KS) catabolism. In Morquio type A syndrome GALNS deficiency causes the accumulation of KS in tissues and results in generalized skeletal dysplasia in affected patients. We show that in normal cells GALNS is in a 1.27-MDa complex with three other lysosomal hydrolases: beta-galactosidase, alpha-neuraminidase, and cathepsin A (protective protein). GALNS copurifies with the complex by different chromatography techniques: affinity chromatography on both cathepsin A-binding and beta-galactosidase-binding columns, gel filtration, and chromatofocusing. Anti-human cathepsin A rabbit antiserum coprecipitates GALNS together with cathepsin A, beta-galactosidase, and alpha-neuraminidase in both a purified preparation of the 1. 27-MDa complex and crude glycoprotein fraction from human placenta extract. Gel filtration analysis of fibroblast extracts of patients deficient in either beta-galactosidase (beta-galactosidosis) or cathepsin A (galactosialidosis), which accumulate KS, demonstrates that the 1.27-MDa complex is disrupted and that GALNS is present only in free homodimeric form. The GALNS activity and cross-reacting material are reduced in the fibroblasts of patients affected with galactosialidosis, indicating that the complex with cathepsin A may protect GALNS in the lysosome. We suggest that the 1.27-MDa complex of lysosomal hydrolases is essential for KS catabolism and that the disruption of this complex may be responsible for the KS accumulation in beta-galactosidosis and galactosialidosis patients.

Strain-specific expression of microglial keratan sulfate proteoglycans in the normal rat central nervous system: inverse correlation with constitutive expression of major histocompatibility complex class II antigens

We have recently demonstrated that a novel type of keratan sulfate proteoglycan (KSPG) identified by the monoclonal antibody (mAb) 5D4 is expressed on ramified microglia but downregulated coincident with T-cell-mediated autoimmune inflammation of the spinal cord in Lewis (LEW) rats. In this study we show by immunocytochemistry and Western blot analysis that various inbred rat strains differ significantly in their constitutive expression of KSPG on ramified microglia in the normal CNS. Microglial KSPG was high in LEW and Fischer 344 rats but low in DA, Brown Norway (BN), and PVG rats. The KSPG low-expressing strains exhibited constitutive expression of major histocompatibility complex (MHC) class II antigens on ramified microglia that was not detectable in the KSPG high-expressing strains. Thus, an inverse correlation between constitutive KSPG and MHC class II expression was present. The KSPG-low-/MHC class II-positive phenotype is associated with resistance to experimental autoimmune encephalomyelitis in BN and PVG, but not DA rats. These findings suggest a significant impact of genetic factors on the molecular differentiation of resident macrophages in the CNS.

Chemonucleolytic effects of chondroitinase ABC on normal rabbit intervertebral discs. Course of action up to 10 days postinjection and minimum effective dose

STUDY DESIGN

This study demonstrated the chemonucleolytic effects of chondroitinase ABC and its histologic and biochemical background.

OBJECTIVES

To determine the course of chondroitinase ABC action on normal rabbit discs, and to find its minimum effective dosage.

SUMMARY OF BACKGROUND DATA

No previous study has assessed the chemonucleolytic action of chondroitinase ABC in a time- and dose-dependent manner. This study also investigated the biochemical causes of radiologic and histologic changes in the discs.

METHODS

Rabbits were injected with 4 U of pharmaceutical-grade chondroitinase ABC intradiscally. They were radiologically and histologically observed, and biochemical analyses of the discs were conducted on days 1, 3, 5, 7, and 10 postinjection in the time course study. Different doses of chondroitinase ABC were injected, and radiologic observations and water content of the discs were measured in the dose-finding study.

RESULTS

The time course study revealed that the chondroitin sulfate content of discs significantly decreased from day 1 postinjection until the end of the experimental period. The weight and water content of the nucleus pulposus decreased on day 3, and disc space narrowing was observed from the day after injection. The dose-finding study showed that a dose of 0.0002 U/disc still induced disc space narrowing and a decrease in water content.

CONCLUSIONS

Chondroitinase ABC is estimated to have a chemonucleolytic effect at least by day 3 postinjection at a dose level of 0.0002 U/disc or higher in rabbits.

Variation of an epitope of keratan sulphate and total glycosaminoglycans in normal equine joints

An epitope of keratan sulphate (KS) and total glycosaminoglycans (GAG) were measured in synovial fluid samples from joints of 53 horses immediately following humane destruction. Internal examination of the joints post mortem ensured that there was no gross evidence of osteoarthritis or other joint disease. Joints sampled were distal interphalangeal (DIP), proximal interphalangeal (PIP), metacarpophalangeal (MCP), metatarsophalangeal (MTP), tarsometatarsal (TMT), tarsocrural (TC), femoropatellar (FP) and antebrachiocarpal (ABC) joints. The age of each horse was assessed by examination of the teeth. Samples were analysed for the KS epitope using a monoclonal antibody 5D4 and an inhibition ELISA and for total GAG level by a direct dye binding technique. There was no significant correlation between KS or GAG concentration and age. However, there were significant differences in the concentrations of KS and GAG in different joints. The median level (+semi interquartile range) of KS:GAG ratio in the MCP was significantly lower than the PIP (0.25 [0.05] vs. 0.35 [0.08]; P < 0.007) and also the DIP joints (0.25 [0.05] vs. 0.47 [0.09] P < 0.001). This study provides information which is both valuable in the investigation of normal joint metabolism and essential in the interpretation of synovial fluid KS and GAG values in their potential role as aids in the evaluation of joint disease.

Viability of human corneal keratocytes during organ culture

The viability of human corneal keratocytes was assessed during four weeks of 'closed system' organ culture at 31 degrees C. After 28 days of culturing, the entire keratocyte population was still alive and viable because all cells incorporated uridine; a parameter for RNA-synthesis. During the first 14 days, mitoses were found in the anterior half of the stroma (0.23% mitoses per 48 h), while only few keratocytes were able to divide at day 28 (0.01% mitoses per 48 h). Metabolic parameters revealed a progressing acidosis in the medium with oxygen and glucose depletion. Immunological measurements of keratan sulphate proteoglycan suggested that approximately 1% of the total content was lost during the period. In conclusion, our current organ culture technique can maintain a viable keratocyte population for four weeks; a viable stroma can be grafted within this period.

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.

A chondroitin sulfate/keratan sulfate proteoglycan, PG-1000, forms complexes which are concentrated in the reticular laminae of electric organ basement membranes

Previously, we identified PG-1000 as part of a disulfide-linked complex of two large proteoglycans (PG-1000 and the beta component) and three smaller proteins purified from the extracellular matrix of elasmobranch electric organ (Iwata and Carlson, 1991, J. Biol. Chem. 266: 323-333). PG-1000 is a chondroitin sulfate/keratan sulfate proteoglycan with a molecular mass of about 1.2 x 16(6) daltons. When visualized in the electron microscope, PG-1000 has the typical "bottle-brush" appearance expected for a proteoglycan with an average total length of about 345 nm and about 20 chains of approximately 110 nm (Carlson and Wight, 1987, J. Cell Biol. 105: 3075-3086). Using immunocytochemical methods, we now demonstrate that PG-1000 is a component of the interstitial extracellular matrix of the electric organ. PG-1000 immunoreactivity is found throughout the interstitial matrix, but it is highly concentrated in that region of the matrix immediately adjacent to the basal lamina, the reticular lamina. The reticular and basal laminae together form the basement membrane. PG-1000 immunoreactivity is especially apparent on basal laminae that surround nerve fibers and nerve terminals. When the disulfide-linked PG-1000 complexes are purified and examined in the electron microscope following rotary shadowing, they appear as bottle-brush structures which are often attached at a central region and radiate like spokes of a wheel. These aggregates contain two to six proteoglycan monomers. We hypothesize that the PG-1000 complexes are disulfide-stabilized parts of an extended network of linked proteoglycans in the reticular lamina.

Changes in cartilage proteoglycan aggrecan after intra-articular injection of interleukin-1 in rabbits: studies of synovial fluid and articular cartilage

OBJECTIVE

To determine how acute but transient inflammation affects the cartilage proteoglycan aggrecan and the value of analyses of synovial fluid to study this.

METHODS

For 96 hours after a single intra-articular injection of rabbit knees with human interleukin-1 alpha (IL-1 alpha) or vehicle, articular cartilage and synovial fluid were examined using a putative indicator of aggrecan synthesis (aggrecan chondroitin sulphate epitope 846), immunoreactive keratan sulphate, and total glycosaminoglycan (GAG) content. Aggrecan extractability (with 0.5 M NaCl) followed by 4 M guanidine hydrochloride extraction permitted analyses of cartilage damage, total content and aggrecan heterogeneity. Aggrecan epitopes as well as GAG were assayed in synovial fluid. Changes were related to total joint leucocyte content in synovial fluid.

RESULTS

At 10 ng, IL-1 alpha produced a transient increase in synovial fluid leucocytes at six hours and 24 hours. This accompanied a reduction in content and increased extractability of GAG, which was greatest in the tibial medial compartment of the knee. Further studies of this compartment showed no change in keratan sulphate epitope content, but a transient increase in extractability in 0.5 M NaCl. Epitope 846 content and extractability were unchanged. Total contents and extractability for GAG were inversely correlated in both controls and joints injected with IL-1 alpha. These changes were accompanied by transient increases in GAG, keratan sulphate epitope, and 846 content in synovial fluid.

CONCLUSION

According to the aggrecan component measured, damage to the matrix of articular cartilage was sometimes reflected by a transient increased extractability and a net loss of aggrecan. There was always an increased release of GAG, and keratan sulphate, and 846 epitopes into synovial fluid. These studies show that changes in aggrecan epitopes and GAG in synovial fluid reflect changes in cartilage metabolism induced by acute transient inflammation.

Selective loss of cerebral keratan sulfate in Alzheimer's disease

Proteoglycans, especially heparan sulfate-substituted species, are known to be associated with the deposition of amyloid in Alzheimer's disease. We previously found that heparan sulfate from afflicted brains, and from control subjects, differed minimally in quantity and structure (Lindahl, B., Eriksson, L., and Lindahl, U.(1995) Biochem. J. 306, 177-184). In the present study, a glycosaminoglycan fraction, shown to contain heparan sulfate and keratan sulfate, was radiolabeled by partial N-deacetylation (hydrazinolysis) followed by re-N-acetylation using [3H]acetic anhydride. Quantitation of the 3H-labeled polysaccharides, based on digestion with heparitinase I from Flavobacterium heparinum and keratanase from Pseudomonas sp., revealed that the amounts of keratan sulfate in Alzheimer cerebral cortex are reduced to less than half of control values. Moreover, a monoclonal antibody against a highly sulfated keratan sulfate epitope bound to the majority of the neurons in normal cortex but not in the diseased tissue. The lack of highly sulfated keratan sulfate structures may reflect a specific functional defect of the cells.

Proteodermatan and proteokeratan sulfate (decorin, lumican/fibromodulin) proteins are horseshoe shaped. Implications for their interactions with collagen

The small proteoglycans proteodermatan and proteokeratan sulfates organize collagen fibrils in extracellular matrix [Scott, J. E. (1992) FASEB J. 6, 2639-2645], thus helping to maintain tissue shape. Their interaction with fibrils is probably via the protein. They have been examined by rotary shadowing-electron microscopy, which showed that these leucine-rich-repeat proteins are horseshoe shaped. Morphometry and comparison with polypeptide sequences suggest ways in which decorin could interact with tissue collagen fibrils. It is proposed that decorin is a bidentate ligand attached to two parallel neighboring collagen molecules in the fibril, helping to stabilize fibrils and orient fibrillogenesis.

Histologic Changes and Wound Healing Response Following 10-Pulse Noncontact Holmium:YAG Laser Thermal Keratoplasty

BACKGROUND

Noncontact holmium:YAG laser thermal keratoplasty (Ho:YAG LTK) is a promising new technology for correction of hyperopia and astigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters encompassing those used in clinical studies.

METHODS

We performed 10-pulse noncontact Ho:YAG LTK on three human corneas 1 day before their removal at penetrating keratoplasty and on six New Zealand white rabbit corneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry.

RESULTS

The amount of acute tissue injury increased according to the pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbits included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation.

CONCLUSIONS

Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response.

Macular corneal dystrophy in Iceland. A clinical, genealogic, and immunohistochemical study of 28 patients

BACKGROUND

The frequency of different types of macular corneal dystrophy (MCD) was determined in Iceland where MCD accounts for one third of every penetrating keratoplasty.

METHODS

The authors determined the serum levels of antigenic keratan sulfate (aKS) in 27 patients with MCD and 53 unaffected family members by an enzyme-linked immunosorbent assay that uses an anti-KS monoclonal antibody (5-D-4). The authors also stained sections from 37 corneal buttons (including 2 regrafts) from 23 patients with MCD by the avidin-biotin complex method using the same anti-KS monoclonal antibody.

RESULTS

Based on the serum analyses, 22 patients had MCD type I and 5 had MCD type II. The corneas from patients without detectable KS in the serum lacked immunohistochemical reactivity to the anti-KS antibody. Every MCD cornea examined from individuals with normal serum KS levels showed KS reactivity. All 53 unaffected siblings and parents carrying the recessive gene had normal serum KS levels.

CONCLUSIONS

Macular corneal dystrophy types I (78.6%) and II (21.4%) both occur in Iceland. Members of affected sibships had only one of these types, not both. Nine patients with MCD type I and four persons with MCD type II belonged to a large pedigree in which individuals have been traced as far back as the beginning of the 16th century. The linking of patients with MCD types I and II in an inbred pedigree suggests that both types may be manifestations of the same abnormal gene rather than independent entities. The serum KS levels were not helpful in detecting heterozygous MCD carriers.

Cell surface-associated keratan sulfate on normal and migrating corneal endothelium

PURPOSE

To investigate cell surface-associated keratan sulfate on the corneal endothelium.

METHODS

Immunolabeling techniques were used at the light, scanning, and transmission electron microscopic level to localize keratan sulfate on the corneal endothelium. The investigation included human, bovine, and rabbit corneal endothelia. A quantitative study of the relationship between cell size and keratan sulfate levels was conducted on normal bovine corneal endothelium. Changes in the distribution of keratan sulfate and chondroitin sulfate on endothelial cell surfaces were investigated on organ cultured bovine corneas during endothelial wound healing. Changes in the levels of keratan sulfate during endothelial wound healing were investigated in organ cultured human corneas and in vivo in rabbit corneas. Inhibition-enzyme-linked immunosorbent assay also was used to detect keratan sulfate in the aqueous humor.

RESULTS

A variegated distribution of keratan sulfate was revealed on normal human, bovine, and rabbit corneal endothelia. Some cells had high levels of keratan sulfate on their surfaces whereas others, sometimes immediately adjacent, had little or none. Wound healing experiments resulted in changes of keratan sulfate levels on the migrating endothelial cells in bovine, human, and rabbit. In wounded organ cultured bovine corneas, there was a decrease in keratan sulfate levels and an increase in chondroitin sulfate levels on migrating endothelial cells. Keratan sulfate was detected in bovine aqueous humor.

CONCLUSIONS

The pattern of occurrence of keratan sulfate and chondroitin sulfate on the corneal endothelial cells in normal and wounded cornea suggests that these glycosaminoglycans have differing roles in endothelial adhesion and migration.