Monoclonal antibodies reactive with keratan sulfate-bearing tryptic fragments of bovine nasal cartilage proteoglycan

Monoclonal antibody-producing cell lines were derived from BALB/c mice immunized with a testicular hyaluronidase digest of tryptic fragments of bovine nasal cartilage proteoglycan. Sera and hybridoma culture supernatants were screened by solid-phase immunoassay for reactivity against a chondroitinase ABC digest of the same proteoglycan fragment fraction. Antibody specificity was determined by competitive inhibition with purified proteoglycan fragment subfractions and their enzymatically modified derivatives. Two monoclonal antibodies were produced which reacted with keratan sulfate-rich fragments from bovine nasal and human articular cartilage proteoglycan. One, monoclonal LC8.13, is directed against keratan sulfate itself, but differs from 5-D-4, a previously described monoclonal antibody to keratan sulfate, in its lesser reactivity with keratanase-treated fragments. The second, monoclonal F1.2, appears to be directed against a conformation-dependent determinant on the core protein of this segment of the cartilage proteoglycan monomer. Monoclonal F1.2 does not react with the keratan sulfate species in human and fetal calf serum and can therefore detect the production of keratan sulfate-bearing proteoglycan by chondrocytes cultured in serum-containing media.     

Monoclonal antibodies reacting with endo-beta-galactosidase-resistant epitopes on keratan sulfate-bearing fragments of bovine nasal cartilage proteoglycan.

Six monoclonal antibody-producing cell lines were derived from mice immunized with keratan sulfate (KS)-bearing tryptic fragments of the core protein of bovine nasal cartilage proteoglycan monomer digested with KS-specific endo-beta-galactosidase. The monoclonal antibodies were characterized by solid-phase ELISA competition studies and SDS-PAGE immunoblotting. Two of them resemble previously described monoclonal antibodies that are directed to epitopes containing both KS and core protein. In contrast, the remaining four monoclonal antibodies are unprecedented in being directed to epitopes whose reactivity is unaffected or enhanced by endo-beta-galactosidase degradation of KS. SDS-PAGE immunoblots revealed two large KS-bearing tryptic fragments of cartilage proteoglycan and a heterogeneous population of smaller fragments not evident by non-immunological techniques. Some of the antibodies used react with all KS-bearing fragments, others react only with the two largest fragments.     

The effect of contaminant proteases in testicular hyaluronidase preparations on the immunological properties of bovine nasal cartilage proteoglycan.

Commercial testicular hyaluronidase preparations are contaminated by a small amount of protease activity which is partially inhibited by serine-protease inhibitors or pepstatin. These protease inhibitors can be shown by Sepharose gel column chromatography to abolish or reduce hyaluronidase-induced degradation of bovine nasal cartilage proteoglycan subunit without affecting the ability of the enzyme to degrade chondroitin sulfate. In addition, immunodiffusion studies indicate that pretreatment of hyaluronidase with these protease inhibitors reduces or abolishes the ability of the enzyme to produce a second "link-related" immunoprecipitin line upon digestion of link protein-containing proteoglycan fractions. Thus, the enhancement of immune reactivity and the unmasking of an additional antigen noted after digestion of cartilage proteoglycan with testicular hyaluronidase are most likely due to the exposure of additional antigenic sites or the the release of more highly immunoreactive fragments by the contaminant proteases rather than to the action of hyaluronidase itself.     

A comparison of bovine nasal cartilage proteoglycan core protein produced by chondroitinase and hyaluronidase: the possible role of protease contaminants.

The basic subunit of cartilage proteoglycan consists of multiple glycosaminoglycan chains covalently attached to a core protein. It is unclear as to whether there is a single core protein or multiple different core proteins, since previous studies using either chondroitinase or testicular hyaluronidase to enzymatically remove chondroitin sulfate side chains from the proteoglycan subunit have yielded conflicting results. In the present study, a chondroitinase-produced core protein preparation isolated as a single peak on Sepharose gel chromatography was found to contain at least two immunologically distinct components. Hyaluronidase-produced core protein from the same proteoglycan subunit fraction was found to contain multiple components nearly all of which were smaller than the components in the chondroitinase digest. A possible explanation of these findings is that they resulted from proteolytic degradation of the core protein in the course of the enzymatic removal of its chondroitin sulfate. The presence of small amounts of protease contaminants in several commercial chondroitinase and hyaluronidase preparations was detected by an extremely sensitive radioassay. Until proteases can be rigorously excluded from enzyme preparations used to degrade the proteoglycan subunit, it will not be possible to determine whether it consists of a single or several different core proteins.     

Effects of electromagnetic fields on proteoglycan metabolism of bovine articular cartilage explants

Electromagnetic field (EMF) exposure has been proposed for the treatment of osteoarthritis. In this study, we investigated the effects of EMF (75 Hz, 2,3 mT) on proteoglycan (PG) metabolism of bovine articular cartilage explants cultured in vitro, both under basal conditions and in the presence of interleukin-1beta (IL-1beta) in the culture medium. Proteoglycan synthesis and the residual PG tissue content resulted significantly higher in EMF-exposed explants than in controls, whereas no effect was observed on PG release and nitric oxide (NO) production. IL-1beta induced both a reduction in PG synthesis and an increase in PG release, related to a strong stimulation of NO production, which resulted in a net loss of tissue PG content. In IL-1beta-treated explants, EMF increased PG synthesis, whereas in spite of a slight stimulation of NO production EMF did not modify PG release. This resulted in the residual PG tissue content being maintained at the control level. In both experimental conditions, the effects of EMF were associated with an increase in lactate production. The results of our study show that EMFs are able to promote anabolic activities and PG synthesis in bovine articular cartilage explants. This effect also is maintained in the presence of IL-1beta, thus counteracting the catabolic activity of the cytokine. Altogether, these data suggest that EMF exposure exerts a chondroprotective effect on articular cartilage in vitro.     

Isolation and characterization of glycoproteins in proteoglycan aggregates of calf rib cartilage

Proteoglycan aggregates were prepared under associative conditions from calf rib cartilage extracts isolated with 4 M guanidine . HCl in the presence of proteinase inhibitors. Five Coomassie blue positive bands including two link proteins could be detected after treatment of proteoglycan aggregates with 2-mercaptoethanol. After dissociating these proteoglycan aggregates with 4 M guanidine . HCl three fractions were obtained by chromatography on Sepharose 2B under the same conditions. A large complex obtained in the excluded volume was partially soluble in the presence of 0.1% sodium dodecyl sulfate, but did not enter 7.5% polyacrylamide gel. It split into seven bands; five of them were not found in proteoglycan aggregates after 2-mercaptoethanol treatment. Neither link proteins nor hyaluronate could be detected in this complex, but chondroitin sulfate was present. Proteoglycan monomers and one included fraction were isolated in addition to this complex. From the included fraction, 8 glycoproteins including 2 link proteins were isolated by preparative polyacrylamide gel electrophoresis and their amino acid and sugar contents determined. These glycoproteins possessed the ability to bind hyaluronate. These results indicate the presence of other glycoproteins besides the two link proteins and a glycoprotein-proteoglycan complex in proteoglycan aggregates of calf rib cartilage.     

Isolation and characterization of an abundant elastase inhibitor from NaCl extracts of bovine nasal septa and articular cartilage.

Extracts of cartilage have been reported to inhibit many serine proteinases and metalloenzymes. Such inhibition may be important in protecting cartilage against degradation by chondrocytic proteinases such as collagenase, stromelysin and by leukocytic proteases, such as elastase. We report here isolation and partial characterization of a 17-kD elastase inhibitor from 0.5 M NaCl extracts of both nasal septum cartilage and articular cartilage, which inhibits elastase and represents 0.08% of the weight of nasal cartilage and 0.002% of the weight of articular cartilage. The protein was highly specific for elastase and did not inhibit cartilage metalloproteinases, suggesting that it may be mainly directed toward protecting cartilage against leukocytic proteases. The inhibitor had a blocked amino-terminus, was high in serine and glycine and lacked carbohydrate. The ease with which the inhibitor was extracted from cartilage suggests that it may function in vivo as a highly abundant elastase inhibitor which is secreted into synovial fluid from cartilage. The inhibitor was shown to be synthesized by bovine articular cartilage in explant culture and nearly all of the metabolically labeled material was secreted into the culture media. The inhibitor cross-reacted with polyclonal antibodies to bovine neck ligament alpha-elastin and antibodies to the inhibitor reacted with bovine neck ligament elastin. The properties of this inhibitor are different than those of any other reported cartilage derived inhibitor.     

Anti-aging effects of high molecular weight proteoglycan from salmon nasal cartilage in hairless mice

Proteoglycans comprise a family of complex macromolecules consisting of a core protein with covalently attached glycosaminoglycan (GAG) chains. The skin anti-aging effects of oral administration of proteoglycan fractions with different molecular weights from salmon nasal cartilage were investigated in a hairless mouse model of skin aging; aging was caused by repeated ultraviolet B (UVB) irradiation. Three proteoglycan fractions of different molecular weights were prepared from salmon nasal cartilage water extract by ion-exchange column chromatography and gel filtration column chromatography. Physiological and histological analysis of the skin indicated that oral administration of high molecular weight proteoglycan inhibited UVB-induced skin aging, defined as increased erythema, increased transepidermal water loss (TEWL), decreased hydration, and epidermal and dermal hypertrophies. The serum and dorsal skin inflammatory cytokine levels indicated that high molecular weight proteoglycan acts on gut immunity and improves skin by inhibiting surplus inflammatory cytokines produced by UVB irradiation. These results suggest that high molecular weight proteoglycan from salmon nasal cartilage is effective in preventing skin aging.     

The potential use of implanted radiolabelled bovine nasal cartilage in dialysis tubing to evaluate agents affecting cartilage degradationin vivo

Cartilage which undergoes extensive autolysisin vitro (spontaneous or stimulated) is characterized by proteoglycan loss. Experimental conditions and inhibitor profils studies suggest neutral metalloproteinases induce the autolysis.In these preliminary studies we compared the degradation of Na₂ ³⁵SO₄ labeled bovine nasal cartilage (BNC) plugs placed in dialysis tubingin vitro andin vivo. The dialysis tubing was used to exclude large molecules (molecular weights greater than 2000) like proteinases, and proteinase inhibitors (e.g. ₂-macroglobulin) but not potential test agents from the implanted cartilage. Cartilage autolysis occurred with live tissue but not with heat-killed tissue in both thein vitro andin vivo systems. In addition retinoic acid and phenanthroline were effective when placed inside or outside the dialysis tubing. A potentially useful procedure to evaluate agents which affect cartilage degradation is described.     

Structure and regulation of articular cartilage proteoglycan expression]

Beyond aggrecan, the major proteoglycan present in articular cartilage that confers resistance to compressive load and viscoelasticity to the tissue, other proteoglycan families have been described in cartilage. Among them, decorin, biglycan and fibromodulin which belong to the small leucine-rich proteoglycans family bind to matrix components, specially to collagen fibrils and thus regulate fibrillogenesis in cartilage and matrix integrity. These small proteoglycans can also interact with TGF-beta and modulate its bioavailability and stability. The third family is composed by cell surface proteoglycans as syndecans, glypican-1 and betaglycan. These molecules interact with various components of cell environment (growth factors, proteases, matrix components, etc.) and mediate numerous cell functions. Some modifications of one of these proteoglycan expression occur during degenerative pathologies and may lead to alteration of the functional properties of the tissue as well as variations in growth factor bioavailability. These factors are involved in the attempt of cartilage repair initiated by chondrocytes in the early stages of osteoarthritis.     

Identification and functional characterization of a bovine orthologue to DC-SIGN

Dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) C-type lectin is almost exclusively expressed at the cell surface of DC. In addition to its normal function facilitating contact of DC with T cells, DC-SIGN has been shown to bind a variety of pathogens, including Mycobacterium bovis, and HIV-1 envelope protein gp120. In this study, we identified the bovine ortholog of the human DC-SIGN gene within the bovine genome, which exists as a single copy. PCR amplified a product, showing a 100% match with the predicted sequences as well as a sequence predicted to be similar to that of SIGNR7. Furthermore, a protein with the same molecular weight as human DC-SIGN was detected by Western blot in cell lysate derived from bovine DC. To characterize this molecule functionally, the uptake of FITC-labeled OVA and FITC-labeled gp120 (FITC-gp120) by bovine and human DC was assessed. FITC-gp120 was shown to bind to bovine DC in a time- and temperature-dependent manner. Binding was blocked by a polyclonal anti-DC-SIGN antibody but not by a control antibody. Furthermore, blocking of this molecule also reduced the binding of M. bovis bacillus Calmette-Guerin expressing GFP. Confocal microscopy showed that DC-SIGN was expressed on the surface of bovine DC. Subsequent pulse-chase studies revealed that FITC-gp120 was internalized by bovine monocyte-derived DC as early as 10 min. Thus, there is evidence of a DC-SIGN-like molecule expressed specifically by bovine DC. This molecule may play an important role in the infection of bovine (DC) cells with M. bovis.     

Identification and characterization of Thy-1 homologues from bovine thymocytes

Two forms of Thy-1 homologues of apparent mol. wt of 25,000 (designated BTp25) and 45,000 (designated BTp45) were isolated from bovine thymocyte membrane by solubilization, affinity chromatography with Con A, and preparative SDS-PAGE. Both forms reacted with a rabbit antiserum to murine Thy-1 in an enzyme-linked immunosorbent assay (ELISA). BTp45 is most likely a dimer of BTp25, since the two are indistinguishable in their amino acid compositions. Comparison of amino acid compositions of BTp25 and BTp45 to that of rodent and human Thy-1 by the S delta Q index revealed significant relatedness among these molecules. BTp25 and BTp45 demonstrate more structural homology to rodent Thy-1 than to human Thy-1. Detailed chemical analyses indicate that bovine Thy-1 homologues contain neutral sugars and fatty acids covalently bound to the polypeptide chain; therefore, they are lipoglycoproteins.     

Osteogenic protein-1 (OP-1) blocks cartilage damage caused by fibronectin fragments and promotes repair by enhancing proteoglycan synthesis

OBJECTIVE AND DESIGN: The abilities of osteogenic protein-1 (OP-1) and TGF-beta1 to affect cartilage damage caused by fibronectin fragments (Fn-fs) that are known to greatly enhance cartilage proteoglycan (PG) degradation were compared. MATERIAL: Articular cartilage was obtained from 18 month old bovines. TREATMENT: To test blocking of damage, cartilage was cultured with or without OP-1 or TGF-beta in the presence of 100 nM Fn-fs. To test restoration of PG, cartilage was first cultured with Fn-fs and the cartilage then treated with factors. METHODS: Cartilage PG content was measured in papain digests using the dimethylmethylene blue assay. PG synthesis was measured by incorporation of 35S labeled sulfate. RESULTS: OP-1 blocked damage and restored PG in damaged cartilage, apparently due to enhanced PG synthesis. However, TGF-beta1 alone decreased PG content. CONCLUSIONS: These results clearly demonstrate differences between OP-1 and TGF-beta1, both members of the TGF-beta superfamily and illustrate the efficacy of OP- in blocking Fn-f mediated damage.     

Identification and characterization of a Candida albicans-binding proteoglycan secreted from rat submandibular salivary glands.

A previously identified Candida albicans-binding glycoprotein secreted from rat submandibular glands (RSMG) has been further purified from an aqueous RSMG extract by ion-exchange chromatography and gel filtration. Biochemical analysis of the glycoprotein revealed high levels of uronic acid and sulfate, suggesting that it was a proteoglycan. Its amino acid and carbohydrate compositions were similar to those observed for other proteoglycans and differed significantly from those of RSMG mucin, the major secretory glycoprotein of RSMG. In addition, the apparent molecular weight of the glycoprotein was reduced following treatment with either chondroitinase ABC or heparitinase, demonstrating the presence of chondroitin sulfate and heparan sulfate. On the basis of its structure and anatomical source, the glycoprotein is referred to as submandibular gland secreted proteoglycan 1 (SGSP1). SGSP1 also binds monoclonal antibody 1F9, which recognizes the human blood group A carbohydrate epitope found on RSMG mucin. Hence, SGSP1 appears to be a hybrid molecule with carbohydrate structures found in both proteoglycans and RSMG mucin. Enzymatic digestion of SGSP1, followed by its interaction with a radiolabelled C. albicans strain in a filter-binding assay, demonstrated that binding to this strain appears to be mediated primarily via the heparan sulfate side chains of SGSP1 and not via the blood group A oligosaccharide.     

Rhein reduces proteoglycan loss during the autolytic breakdown of cultured cartilage

Rhein (R: 1,8-dihydroxy-3-carboxyanthraquinone) is the active metabolite of the drug diacerhein (DAR), an anthraquinone molecule which has recently been proposed for the long-term treatment of osteoarthrosis. In the present study we have examined the effects of rhein, as compared to indomethacin or hydrocortisone, on an in-vitro model of cartilage degradation, represented by the autolytic breakdown of the articular cartilage excised from rabbit knee and cultured for seven days. During this period there is a spontaneous loss of proteoglycans. At the end of the period we measured the amount of proteoglycans which remained bound to the cartilage. The samples treated with R revealed dose-dependent modifications in the amounts of cartilage-bound proteoglycans, with a 40% increase as compared with non-treated samples at the dose of 7 x 10(-5) M. We conclude that R shows a protective effect on the articular cartilage, and that at least a part of the beneficial effect that DAR has shown in the course of clinical trials in osteoarthrosis may be due to direct effects of its active metabolite (R) on cartilaginous tissue.