An enzyme-linked immunoassay for the cartilage proteoglycan

Inflammatory bone loss in experimental periodontitis induced by Aggregatibacter actinomycetemcomitans in interleukin-1 receptor antagonist knockout mice

The interleukin-1 receptor antagonist (IL-1Ra) binds to IL-1 receptors and inhibits IL-1 activity. However, it is not clear whether IL-1Ra plays a protective role in periodontal disease. This study was undertaken to compare experimental periodontitis induced by Aggregatibacter actinomycetemcomitans in IL-1Ra knockout (KO) mice and wild-type (WT) mice. Computed tomography (CT) analysis and hematoxylin-and-eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining were performed. In addition, osteoblasts were isolated; the mRNA expression of relevant genes was assessed by real-time quantitative PCR (qPCR); and calcification was detected by Alizarin Red staining. Infected IL-1Ra KO mice exhibited elevated (P, <0.05) levels of antibody against A. actinomycetemcomitans, bone loss in furcation areas, and alveolar fenestrations. Moreover, protein for tumor necrosis factor alpha (TNF-α) and IL-6, mRNA for macrophage colony-stimulating factor (M-CSF), and receptor activator of NF-κB ligand (RANKL) in IL-1Ra KO mouse osteoblasts stimulated with A. actinomycetemcomitans were increased (P, <0.05) compared to in WT mice. Alkaline phosphatase (ALP), bone sialoprotein (BSP), osteocalcin (OCN)/bone gla protein (BGP), and runt-related gene 2 (Runx2) mRNA levels were decreased (P, <0.05). IL-1α mRNA expression was increased, and calcification was not observed, in IL-1 Ra KO mouse osteoblasts. In brief, IL-1Ra deficiency promoted the expression of inflammatory cytokines beyond IL-1 and altered the expression of genes involved in bone resorption in A. actinomycetemcomitans-infected osteoblasts. Alterations consistent with rapid bone loss in infected IL-Ra KO mice were also observed for genes expressed in bone formation and calcification. In short, these data suggest that IL-1Ra may serve as a potential therapeutic drug for periodontal disease.

Suppression of generation and replication of acyclovir-resistant herpes simplex virus by a sensitive virus

The role of acyclovir-sensitive herpes simplex virus (HSV) was analyzed in the process of its replacement by a resistant virus in vitro and in vivo in the aspect of acyclovir therapy. The mode of replacement of acyclovir-sensitive HSV with acyclovir-resistant HSV was examined by the passages of acyclovir-sensitive wild type HSV in Vero cells under acyclovir-treatment. The development of resistance was monitored more adequately by counting the number of acyclovir-resistant viruses in 10,000 plaque forming units than by the conventional susceptibility assay. The resistance increased with the proportion of thymidine kinase-deficient (TK(-)) viruses, when the susceptibilities of acyclovir-treated HSV population to 5'-iodo-2'deoxyuridine and phosphonoacetic acid were examined. The increased resistance was due to the increased proportion of acyclovir-resistant virus but not intermediately resistant virus. Infection with mixtures of TK(-) and acyclovir-sensitive strains rendered TK(-) sensitive to acyclovir, and virus yields were reduced to the levels of acyclovir-sensitive virus in Vero cells. Their yield reduction depended on the proportion of acyclovir-sensitive viruses and induction of TK activity. This reduction in virus yields of the mixture of TK(-) and acyclovir-sensitive strains was confirmed by acyclovir treatment in the skin of mice with cutaneous infection. Acyclovir treatment combined with superinfection of acyclovir-sensitive virus delayed the development of herpetic skin lesions due to acyclovir-resistant virus and reduced virus yields in the infected skin. Acyclovir-sensitive virus plays an important role in suppressing the generation and replication of acyclovir-resistant virus during acyclovir therapy.

Hydrostatic fluid pressure enhances matrix synthesis and accumulation by bovine chondrocytes in three-dimensional culture

Monolayer cell cultures and cartilage tissue fragments have been used to examine the effects of hydrostatic fluid pressure (HFP) on the anabolic and catabolic functions of chondrocytes. In this study, bovine articular chondrocytes (bACs) were grown in porous three-dimensional (3-D) collagen sponges, to which constant or cyclic (0.015 Hz) HFP was applied at 2.8 MPa for up to 15 days. The effects of HFP were evaluated histologically, immunohistochemically, and by quantitative biochemical measures. Metachromatic matrix accumulated around the cells within the collagen sponges during the culture period. There was intense intracellular, pericellular, and extracellular immunoreactivity for collagen type II throughout the sponges in all groups. The incorporation of [(35)S]-sulfate into glycosaminoglycans (GAGs) was 1.3-fold greater with constant HFP and 1.4-fold greater with cyclic HFP than in the control at day 5 (P < 0.05). At day 15, the accumulation of sulfated-GAG was 3.1-fold greater with constant HFP and 2.7-fold with cyclic HFP than the control (0.01). Quantitative immunochemical analysis of the matrix showed significantly greater accumulation of chondroitin 4-sulfate proteoglycan (C 4-S PG), keratan sulfate proteoglycan (KS PG), and chondroitin proteoglycan (chondroitin PG) than the control (P < 0.01). With this novel HFP culture system, 2.8 MPa HFP stimulated synthesis of cartilage-specific matrix components in chondrocytes cultured in porous 3-D collagen sponges.

Effects of medium perfusion on matrix production by bovine chondrocytes in three-dimensional collagen sponges

Various culture systems have been used for examining the anabolic and catabolic functions of isolated chondrocytes as well as for tissue engineering purposes. Perfusion or frequent medium change is beneficial for three-dimensional (3D) cultures of many cell types. In this study, bovine articular chondrocytes (bACs) were grown in 3D collagen sponges with or without medium perfusion (0.33 mL/min) for up to 15 days. The influence of medium perfusion was evaluated using markers of cartilage matrix accumulation, synthesis, and gene expression. Metachromatic matrix, collagen type II, and hyaluronan accumulated around the cells within the collagen sponges. Sulfated glycosaminoglycans (S-GAGs) that accumulated in the sponge exposed to nonperfused control were 130% of that in the perfused sponge at day 7. S-GAG accumulation after 15 days in the nonperfused control was 230% more than at day 7 (p < 0.01). (35)S-sulfate incorporation during the final 18 h of culture in the sponge exposed to nonperfusion was 180% greater than that in the perfused sponge (p < 0.01). Quantitative analyses show that at day 7, aggrecan and collagen type II gene expression were 350% and 240% greater, respectively, in the nonperfused culture than in the perfused one. These results indicate that perfused conditions that are beneficial for other cell types inhibit chondrogenesis by articular chondrocytes in 3D culture.

Emergence of resistance to acyclovir and penciclovir in varicella-zoster virus and genetic analysis of acyclovir-resistant variants

We have characterized the differential actions of acyclovir and penciclovir against varicella-zoster virus (VZV) in cell culture by comparing the frequency of appearance of resistant viruses followed by their characterization. Cells were infected with cell-free virus and the cultures were successively treated with increasing concentrations of acyclovir or penciclovir. Drug-resistant viruses were selected in the presence of 6 microg/ml of acyclovir or penciclovir. The emergence frequency of resistant viruses was significantly higher following acyclovir exposure than following penciclovir exposure (Fisher's exact test, P<0.0001), possibly reflecting virus growth differences under these experimental conditions. Based on antiviral drug susceptibility and thymidine kinase (TK) activity assays, 11 acyclovir-resistant variants from seven experiments using three virus strains (Kawaguchi strain, Oka varicella vaccine strain and a clinical isolate from a zoster patient) were found to be TK-deficient. Sequence analysis of TK-deficient variants of the Kawaguchi strain revealed deletions that caused frameshifts, resulting in premature termination in the TK gene.

Increased content of type-VI collagen epitopes in human osteoarthritic cartilage: quantitation by inhibition ELISA

Type-VI collagen is an integral part of the extracellular cartilage matrix. However, the exact amounts of type-VI collagen in normal and osteoarthritic human cartilage still are not known. In this study, we describe an inhibition enzyme-linked immunosorbent assay that was developed to quantitate type-VI collagen epitopes found in guanidinium chloride extracts from normal and osteoarthritic human cartilage. In 31 cartilage samples from various localizations of healthy adult human knees, type-VI collagen epitopes accounted for approximately 0.40% of the total collagen content. Interestingly, type-VI collagen epitopes increased about 4-fold in osteoarthritic cartilage. A statistically significant increase of type-VI collagen epitopes was found during early stages of the disease, with only a superficial roughening of the cartilage surface and a loss of proteoglycans. Thus, these findings indicate that type-VI collagen is a minor component of normal human articular cartilage and that the amount of type-VI collagen epitopes increases significantly during early stages of osteoarthritis.

Bovine aorta contains at least two related forms of heparan sulphate proteoglycan

1. The proteoglycan peak from anion exchange chromatography of an extract of bovine aorta was digested with chondroitinase ABC. The residual heparan sulphate proteoglycans were further purified by chromatography on Sepharose CL4B and DEAE-Sephacel to yield two species, of high and low charge density. 2. Higher molecular weight material had a higher proportion of high charge density proteoglycan, while the lower molecular weight species had a higher proportion of low charge density heparan sulphate proteoglycan. 3. The two species shared epitopes as they both reacted with an antibody to heparan sulphate proteoglycan from bovine glomerular basement membrane. 4. On electron microscopy, both high and low charge density proteoglycans were visualized as 'tadpole-like' molecules, which showed a tendency to aggregate via their globular heads. 5. Bovine aortic smooth muscle cells were cultured in the presence of [35S]sulphate and [3H]glucosamine. Proteoglycans were isolated from medium and cell layer extract by the methods outlined above. 6. The major HSPG species isolated from medium were significantly larger than those from cell layer and displayed substantial heterogeneity in both size of HS chain after papain digestion and size of protein core after heparitinase digestion. 7. The major cell layer species yielded two HS species of widely differing mol. wt after papain digestion, and a very small protein core after heparitinase digestion. Therefore cell layer-associated HSPGs show a good deal more homogeneity than those found in the medium. 8. Further ion-exchange chromatography after digestion with chondroitinase ABC revealed HSPG species of lower charge density, possibly derived from a hybrid chondroitin sulphate-dermatan sulphate proteoglycan (CS/DSPG) after removal of the CS/DS chains.

Murine tenascin: cDNA cloning, structure and temporal expression of isoforms

Mouse tenascin (TN)-encoding cDNA clones were isolated from a cDNA library of the 2H6GR mammary tumor cell line. Nucleotide (nt) and deduced amino acid (aa) sequences revealed the characteristic primary structure, which begins with a signal peptide and TN unique sequences, follows with 14 1/2 epidermal growth factor (EGF)-like repeats and 13 fibronectin type-III repeats (FN repeat), and concludes with fibrinogen-homologous sequences. Similar to chicken and human TN, the mouse TN cDNA contains five consecutive insertional FN repeats, as well as eight constitutive FN repeats. Three different cDNA clones that may have been generated by alternative splicing of these insertional FN repeats were identified and characterized. Based upon the deduced as sequence, a polyclonal antibody was produced against a synthetic TN peptide. It specifically recognized two TN isoforms of 230 kDNA and 190 kDa in protein extracts of mouse tissues. The tissue distributions of mouse TN mRNAs, revealed by Northern blot analysis, suggest that there is tissue-specific expression of TN isoforms. Two distinct mRNA transcripts (7 kb and 5.5 kg) were detected in brain, skeletal muscle, digestive tract and bladder, but only one was observed in lung, kidney (7 kg) and thymus (5.5 kg). TN mRNA expression was down-regulated 1 month after birth in most tissues. However, the 5.5-kb transcript persisted in cerebellum, thymus, and colon. The spatial and temporal patterns of TN expression seem to be controlled at the level of transcription, because analysis of various tissues by Western blots showed the same pattern as that seen in Northern blots.

Cartilage matrix glycoprotein is present in serum in experimental canine osteoarthritis

We have described previously a disulfide-bonded 550,000-D cartilage matrix glycoprotein (CMGP), which is found in normal hyaline cartilage, fibrocartilage, and the vitreous of the eye, and consists of subunits with apparent molecular weights of 130,000 in 4% gels (116,000 in 9% gels). In osteoarthritic cartilage from dogs subjected to transection of the anterior cruciate ligament (ACL), CMGP is cleaved to major immunoreactive fragments with apparent molecular weights of 65,000 and 75,000 after reduction with 2-mercaptoethanol. In the present study, using immunolocation analysis, a monoclonal antibody to CMGP did not react with serum from 8 of 12 dogs before ACL transection but did react with serum from seven of these animals 4 wk after surgery and with serum from 10 dogs at sacrifice, 8-14 wk after ACL transection. Serum from four dogs reacted with the monoclonal antibody before ACL transection. Serum from two dogs was negative at all time points. Immunolocation studies using a polyclonal antiserum to CMGP were performed in seven of these dogs and produced results identical with the monoclonal antibody in four dogs. In contrast, analysis of serial serum samples from three dogs with cartilage atrophy revealed no evidence of CMGP at any time point. These data suggest that CMGP may be a serum marker for osteoarthritis in this canine model.

Abnormal synthesis of cartilage-characteristic proteoglycan in azaserine-induced micromelial limbs

Administration of azaserine (250 micrograms) to day-4 chick embryos in ovo was shown to induce micromelial limbs. In the present study, biosynthesis of cartilage-characteristic proteoglycan H (PG-H) as an index of limb chondrogenesis was examined in normal and micromelial hind limbs from day-7 chick embryos by biochemical and immunological methods. (1) Metabolic labelling of the micromelial limbs with [6-3H]-glucose and [35S]sulphate, followed by analysis of labelled proteoglycans by glycerol-density-gradient centrifugation under dissociative conditions, showed a marked reduction in PG-H synthesis. (2) PG-H synthesized by micromelial limbs differed from that synthesized by normal limbs in possessing a slower sedimenting velocity and much lower amounts of chondroitin sulphates. (3) The amount of PG-H core protein in micromelial limbs was significantly decreased to about 19% on a per limb basis and about 42% on a per DNA basis of that in normal limbs, as determined by e.l.i.s.a. (4) The transition from PG-M to PG-H during limb formation was retarded in micromelial limbs as judged by an indirect immunofluorescence technique using antibodies against PG-M and PG-H. (5) The deficiency of incorporation of labelled glucose into chondroitin sulphate chains of PG-H in micromelial limbs was partially restored by using [6-3H]-glucosamine as a precursor, suggesting that the synthesis of UDP-N-acetylhexosamine, required for chondroitin sulphate chain synthesis of PG-H in micromelial limbs, was decreased. These results suggest that the reduction in the synthesis of PG-H as well as the production of an abnormal form of PG-H during a critical period of limb morphogenesis may be important factors in explaining the micromelia induced by azaserine.

Immunofluorescent localization of tenascin during development of the mouse urogenital sinus: possible involvement in genital duct morphogenesis

Tenascin is a compound of the mesenchymal extracellular matrix and has been proposed as a possible mediator in epithelial-mesenchymal interactions, because of its characteristic distribution in tissues during fetal development. In the present study, we have investigated by immunofluorescence the changes in the distribution of tenascin during development of the mouse urogenital sinus, a process in which tissue interactions were found to be essential. Tenascin first appears in dorsal mesenchyme on days 13-15 of gestation, coinciding with morphological changes of the epithelium. During male development, tenascin accumulates in the dorsal mesenchyme around the junction of Wolffian ducts, but not in the ventral mesenchyme, into which prostatic buds (prostate gland anlagen) project from the sinus epithelium. During female development, the mesenchyme that participates in the downgrowth of the vagina (derived from Müllerian ducts) stains intensively for tenascin. In both of these tenascin-positive areas, the epithelium undergoes conspicuous morphogenetic changes. The results suggest that mesenchymal tenascin could be involved in the epithelial morphogenesis of the sinus, especially in the morphogenesis of the genital ducts.

Probing the human B-cell repertoire: isolation of Epstein-Barr virus (EBV)-transformed human B lymphocytes making antibodies with a common idiotope that have different antigen-binding specificities

Human peripheral B lymphocytes were transformed with Epstein-Barr virus and probed with an antiidiotypic antibody made against a human monoclonal autoantibody. Six cell lines were isolated that produced antibodies bearing a common idiotope. Despite the presence of this common idiotope, the antibodies showed antigen-binding specificities different from that of the parental antibody to which the antiidiotypic antibody was made. By probing Epstein-Barr virus-transformed cells with well-characterized antiidiotypic antibodies, it should now be possible to isolate and determine the frequency of B cells bearing specific idiotopes in the human repertoire and to study the antigen-binding properties of these antibodies.

Basement membrane proteoglycan in various tissues: characterization using monoclonal antibodies to the Engelbreth-Holm-Swarm mouse tumor low density heparan sulfate proteoglycan

The Engelbreth-Holm-Swarm mouse tumor has been found to produce at least two molecular species of heparan sulfate proteoglycan, a low density one (LD) and a high density one, which differ not only in core proteins but also in glycosaminoglycan structures (Kato, M., Y. Koike, Y. Ito, S. Suzuki, and K. Kimata. 1987. J. Biol. Chem. 262:7180-7188). With aim at investigating their distribution and possible functions in tissues, monoclonal antibodies were produced. Hybridomas obtained by fusion of NS-1 mouse myeloma cells with spleen cells from the rat immunized with a mixture of these proteoglycans were selected by their ability to react with the antigen. Two of them secreted monoclonal antibodies (IgG2a), designated HK-84 and HK-102, that recognize specifically the core protein moiety of LD. Immunofluorescent staining of various tissues (skeletal muscle, cardiac muscle, lung, brain, and kidney) with these monoclonal antibodies has demonstrated that the antigen molecules were present in all basement membranes of these tissues. SDS-PAGE of heparitinase-treated proteoglycan fractions prepared from these tissues and subsequent immunoblotting using these monoclonal antibodies have confirmed that the antigen molecule was LD, and further suggested that there was a tissue-specific variation in the core molecular size. Based on these results, we propose that LD may be an essential component in all basement membranes.

Glomerular basement membrane proteoglycans are derived from a large precursor

The basement membrane heparan sulfate proteoglycan produced by the Englebreth-Holm-Swarm (EHS) tumor and by glomeruli were compared by immunological methods. Antibodies to the EHS proteoglycan immunoprecipitated a single precursor protein (Mr = 400,000) from [35S]methionine-pulsed glomeruli, the same size produced by EHS cells. These antibodies detected both heparan sulfate proteoglycans and glycoproteins in extracts of unlabeled glomeruli and glomerular basement membrane. The proteoglycans contained core proteins of varying size (Mr = 150,000 to 400,000) with a Mr = 250,000 species being predominant. The glycoproteins are fragments of the core protein which lack heparan sulfate side chains. Antibodies to glomerular basement membrane proteoglycan immunoprecipitated the precursor protein (Mr = 400,000) synthesized by EHS cells and also reacted with most of the proteolytic fragments of the EHS proteoglycan. This antibody did not, however, react with the P44 fragment, a peptide situated at one end of the EHS proteoglycan core protein. These data suggest that the glomerular basement membrane proteoglycan is synthesized from a large precursor protein which undergoes specific proteolytic processing.

Altered proteoglycan synthesis by micromelial limbs induced by 6-aminonicotinamide. Appearance of abnormal forms of cartilage-characteristic proteoglycan (PG-H)

Since administration of 6-aminonicotinamide (10 micrograms) to day-4 chick embryos in ovo was shown to induce micromelial limbs, biosynthesis of cartilage-characteristic proteoglycan-H (PG-H) as an important index of limb chondrogenesis was examined in day-7 normal and micromelial hind limbs by biochemical and immunological methods. (1) Metabolic labelling of the micromelial limbs with [6-3H]glucosamine and either [35S]sulphate or [35S]methionine, followed by analyses of labelled PG-H by glycerol density-gradient centrifugation under dissociative conditions, showed a marked reduction in the PG-H synthesis. (2) PG-H synthesized by the micromelial limbs was much lower than that synthesized by the normal limbs in the biosynthetic ratio of chondroitin sulphate to keratan sulphate and glycoprotein-type oligosaccharide, although no significant difference was observed in the immunological properties of these proteoglycans. (3) The degree of sulphation of chondroitin sulphates of PG-H was lowered in the micromelial limbs as judged by the increase of unsulphated disaccharide (delta Di-OS) released by chrondroitinase ABC digestion, although there were no significant differences between the normal and the micromelial limbs in the average molecular size (Mr = 38,000) of labelled chondroitin sulphates of PG-H. (4) Addition of beta-D-xyloside, an artificial initiator for chondroitin sulphate synthesis, to the micromelial limbs in culture recovered the incorporation of labelled glucosamine into chondroitin sulphate to that comparable with the normal control with beta-D-xyloside, although the incorporation of [35S]sulphate was lower in the micromelia than in the control with beta-D-xyloside. These results suggest that the reduction in the biosynthesis of the PG-H as well as the production of altered forms of PG-H induced by 6-aminonicotinamide during a critical period of limb morphogenesis may be an important factor for the micromelia.

An enzyme-linked immunosorbent assay (ELISA) of denatured cartilage link protein

Antiserum (MB007) was raised in rabbits to SDS-denatured cartilage link protein in order to develop an enzyme-linked immunosorbent assay (ELISA) to quantify link protein in cartilage extracts. The antibodies were characterized by using native and denatured link protein, either as the immobilised or the inhibiting antigen in the assay, and shown to bind more effectively to denatured link protein. At low concentrations, neither hyaluronate (0-30 micrograms/ml), proteoglycan (0-50 micrograms/ml) nor hyaluronate-binding region (0-3 micrograms/ml) competitively inhibited the link protein assay. However, at higher concentrations of proteoglycan (50 micrograms/ml-4 mg/ml) and hyaluronate-binding region (3-40 micrograms/ml) inhibition was observed. A more highly purified proteoglycan and a further purified hyaluronate-binding region preparation showed identical behaviour. The inhibition produced by proteoglycan and hyaluronate-binding region occurred at approximately equivalent molar concentrations (assuming Mr of 10(6) and 7 X 10(4), respectively). These results suggest that a significant proportion of these polyclonal antibodies recognize an epitope common to link protein and hyaluronate-binding region. However, the possibility that these effects are due to contamination with covalently bound link protein cannot be excluded. Trypsinated aggregates (0-10 micrograms/ml) produced no inhibition in the link protein ELISA, but as higher concentrations the inhibition was approximately 2000-fold lower than might have been expected from the link protein concentration present. Thus, the accessibility and/or binding of the antibodies to link protein was substantially decreased, illustrating masking of the link protein antigenic sites, as found by A. Ratcliffe and T.E. Hardingham (Biochem. J. 213 (1983) 371-378). These studies indicate that link protein in tissue extracts may be quantified in the concentration range 30-200 ng/ml and in the presence of hyaluronate, proteoglycan and hyaluronate-binding region, provided that both the immobilised and extracted link proteins are denatured.

Pancreatic islet cell surface glycoproteins containing Gal beta 1-4GlcNAc-R identified by a cytotoxic monoclonal autoantibody

To investigate the autoimmune pathogenesis of spontaneously occurring diabetes mellitus in BB rats, spleen cells of newly diagnosed diabetic BB rats were fused with mouse myeloma cells. Hybridoma supernatants were screened for antibodies by indirect immunofluorescence and by 51Cr-release assays using the RINm5F rat insulinoma cell line. One clone, E5C2, produced an IgM kappa antibody that was cytotoxic for RINm5F cells, but not for other rat cell lines nor for primary rat islet cells. However, treatment of primary rat islet cells with neuraminidase exposed surface antigens and rendered the cells susceptible to complement-mediated lysis by antibody E5C2. Using immunostaining of glycolipids separated by thin-layer chromatography, hapten inhibition assays with defined carbohydrates, and Western blots, the antigens recognized by E5C2 on RINm5F cells were identified as glycoproteins with molecular weights of 60,000 and 68,000. The antibody recognizes a carbohydrate antigen containing the sequence Gal beta 1-4GlcNAc-R, which on RINm5F cells is predominantly hidden by covalently bound sialic acid. These studies raise the possibility that hidden antigenic determinants on islet cells exposed by a variety of means may be the target of autoimmune attack.

Correction of abnormal matrix formed by cmd/cmd chondrocytes in culture by exogenously added cartilage proteoglycan

The cartilage matrix deficiency (cmd/cmd) mouse fails to synthesize the core protein of cartilage-characteristic proteoglycan (cartilage PG). Chondrocytes from the cmd/cmd cartilage cultured in vitro produced nodules with greatly reduced extracellular matrix. Immunofluorescence staining revealed that the nodules of mutant cells differed from the normal in lacking cartilage PG and in uneven and reduced deposition of type II collagen. Exogenously added cartilage PG prepared from either normal mouse cartilage or Swarm rat chondrosarcoma to the culture medium was incorporated exclusively into the extracellular matrices of the nodules, with a concurrent correction of the abnormal distribution pattern of type II collagen. The incorporation of cartilage PG into the matrix was disturbed by hyaluronic acid or decasaccharide derived therefrom, suggesting that the incorporation process involves the interaction of added proteoglycan with hyaluronic acid. Both the hyaluronic acid-binding region and the protein-enriched core molecule prepared from rat chondrosarcoma cartilage PG could also be incorporated but, unlike the intact cartilage PG, they were distributed equally in the surrounding zones where fibroblast-like cells predominate. The results indicate that the intact form of cartilage PG is required for specific incorporation into the chondrocyte nodules, and further suggest that cartilage PG plays a regulatory role in the assembly of the matrix macromolecules.

Heparan sulfate proteoglycans made by different basement-membrane-producing tumors have immunological and structural similarities

Using immunological assays, we determined the relationship between the heparan sulfate proteoglycans produced by two different murine basement-membrane-producing tumors, i.e., the mouse Engelbreth-Holm-Swarm (EHS) tumor and the L2 rat yolk-sac tumor. Antibodies prepared against the heparan sulfate proteoglycans obtained from these two sources immunoprecipitated the same precursor protein with a molecular mass of 400,000 daltons from 35S-methionine pulse-labeled cells of both tumors. Immunohistochemistry showed the heparan sulfate proteoglycan to be distributed in the extracellular matrix and also in the native basement membrane of surrounding normal murine tissues. Blocking and ELISA assays demonstrated that the antibodies recognized both antigens. Using techniques involving the chemical and enzymatic degradation of 35S-sulfate-labeled glycosaminoglycans, the mouse EHS tumor cells were found to produce mainly heparan sulfate (75%) along with smaller amounts of chondroitin sulfate (19%), whereas the L2 rat yolk-sac tumor produced mainly chondroitin sulfate (76%) with smaller amounts of heparan sulfate (21%). We conclude that these two murine basement-membrane-producing tumors elaborate an immunologically and structurally similar type of high-molecular-weight heparan sulfate proteoglycan which subsequently becomes incorporated into basement-membrane-like material.

Immunoenzymoassay of the hyaluronic acid-hyaluronectin interaction: application to the detection of hyaluronic acid in serum of normal subjects and cancer patients

The binding of a hyaluronic acid-binding glycoprotein, hyaluronectin (HN), isolated from human brain, to hyaluronic acid (HA) was investigated with the enzyme-linked immunosorbent assay technique using plastic microtest plates coated with a 50 mg/liter solution of HA in 0.1 M bicarbonate. Optimum conditions for HN binding to HA were in 0.2 M NaCl buffered with 0.1 M sodium phosphate at pH 7. An assay for HA in solution was set up exploiting the fact that HN binding could be inhibited by soluble HA. HA was preincubated for 1 h in a test tube with a 30-ng/ml HN solution (v/v) in the buffer containing 0.1% bovine serum albumin. Incubation on HA-coated microtest plate lasted 4 h and maximum sensitivity was achieved when incubation was carried out at 4 degrees C. HN bound to the plate was revealed by means of alkaline phosphatase-conjugated anti-HN antibodies. The test was used to measure HA inhibitory activity after depolymerization by ferrous ions. No difference was found between inhibitory activity or smaller fragments and that of high-molecular-weight HA. The assay was applied to determination of HA in sera. Specificity was demonstrated by Streptomyces hyaluronidase digestion of reactive material in sera. Other glycosaminoglycans did not interfere with the assay. Recovery of HA was good and intra- and interassay variation coefficients were 6 +/- 2.2 and 12%. In 103 blood donor sera, HA was found at 22.4 +/- 16.7 micrograms/liter. HA was elevated in most of the cancer patient sera tested.

Chondrogenesis in agarose gel culture. A model for chondrogenic induction, proliferation and differentiation

An in vitro model has been developed to study chondrogenic induction, proliferation and differentiation. Embryonic rat mesenchymal cells isolated from muscle and embedded in agarose were treated with a partially purified extract from bovine demineralized bone powder. Treated cells proliferated and synthesized matrix similar to differentiated chondrogenic cells in a dose-dependent manner. By employing an enzyme-linked immunosorbent assay (ELISA), cartilage-specific proteoglycan and type II collagen synthesis were quantitated. Of the cells tested, only embryonic mesenchymal cells from muscle responded to bone extract. Proteoglycan synthesis was sensitive to type of medium and cell density.

Purification and characterization of two cartilage-inducing factors from bovine demineralized bone

Two naturally occurring peptides that induce chondrogenesis in culture have been purified to apparent homogeneity. These cartilage-inducing factors (CIF-A and CIF-B) were isolated from bovine demineralized bone by dissociative extraction, gel filtration, cation-exchange chromatography, and reversed-phase HPLC. CIF-A and CIF-B at concentrations of 1-10 ng/ml each induce embryonic rat mesenchymal cells in culture to assume a cartilage morphology and synthesize cartilage-specific proteoglycan and type II collagen. The amino acid compositions of CIF-A and CIF-B are similar but not identical. Both factors have an apparent Mr of 26,000, as determined by NaDodSO4/PAGE. In the presence of 2-mercaptoethanol, both are converted to species of about one-half that Mr, indicating that they are dimers of identical or very similar chains.

Radioimmunoassay of proteoglycans

Human articular cartilage proteoglycan monomers (PG) were purified and used for developing a radioimmunoassay. Its analytical sensitivity is 0.6 ng/tube and its clinical sensitivity is 20 microliter/tube for serum and 0.12 microliter/tube for synovial fluid. The intra- and between-assay variation coefficient are less than 10 and 20%, respectively, in the linear part of the curve. There is a complete cross reaction with costal, vertebral disk and tracheal cartilage PGs and the PGs extracted from vein and artery. Concerning the latter, inhibition curves are not parallel. No cross reaction exists with PGs from various fetal tissues and small PGs from bone. However, large PGs from bone produce a weak cross reaction. Furthermore, the assay is species specific since cartilage PGs from dog, rat, chicken and calf embryos either do not or weakly cross react in the assay. Other constituents of cartilage: type II collagen, fibronectin, chondroitin sulfate and hyaluronic acid do not interfere with the assay. The antigenic determinants are localized on the protein core of the PG, as shown by the lack of cross reaction with glycosaminoglycans and PG treatment with various enzymes.

Appearance of distinct types of proteoglycan in a well-defined temporal and spatial pattern during early cartilage formation in the chick limb

Our recent studies have shown that chick embryo epiphyseal cartilage synthesizes three distinct species of proteoglycan (PG-H, PG-Lb, and PG-Lt) which are analogous in having glycosaminoglycan side chains of the chondroitin (dermatan) sulfate type but different from one another in regard to the structure of core protein. In the present report, the expression of PG-H and PG-Lb has been studied in developing chick hind limbs (stages 19-33), using antibodies specific for these substances in indirect immunofluorescence. At the onset of cartilage morphogenesis (stage 24), PG-H became recognizable in the cartilage primordia, whereas a parallel section stained for PG-Lb showed no reaction. The first evidence of PG-Lb appearance was seen in a stage 28 cartilage (e.g., tibia) in which the cells in the middiaphysis became elongated in a direction perpendicular to the long axis of the cartilage. The PG-Lb fluorescence was confined to the zone of these flattened, disc-like cells, whereas the fluorescence for PG-H was uniformly distributed throughout the cartilage. With further development of cartilage (stage 29 approximately), the zone of flattened cells spread proximally and distally, and simultaneously large hypertrophied cells appeared at the diaphyseal region. During these zonal changes of cell morphology, the PG-Lb fluorescence remained restricted to the zone of flattened cells. Parallel sections stained for PG-H, in contrast, showed an evenly distributed pattern of the PG-H fluorescence throughout the cartilage. The results indicate that the appearance of PG-Lb is closely associated with the zonal changes of cell shape and orientation along the proximal-distal axis of the developing limb cartilage, and further suggest that the flattened chondrocytes in this particular zone have undergone additional changes in gene expression to form an extracellular matrix of still another chemical property.

Characteristics of the core protein of the aggregating proteoglycan from the Swarm rat chondrosarcoma

A ternary complex of hyaluronic acid-binding region and link protein bound to hyaluronic acid was isolated from limit clostripain digests of proteoglycan aggregates isolated from the Swarm rat chondrosarcoma. Under these conditions, the hyaluronic acid-binding region has a molecular weight of approximately equal to 65,000 (HA-BR65). N-terminal amino acids in the complex were selectively 14C-carbamylated. The resulting derivatized HA-BR65 was isolated, and tryptic peptide maps were prepared and developed on two-dimensional TLC sheets. A single, labeled peptide was obtained which gave a Mr by approximately equal to 8,000 by SDS-PAGE. Chymotrypsin digestion of the ternary complex reduced the molecular weight of HA-BR65 to a polypeptide of approximately equal to 55,000 (HA-BR55) which still retains the same N-terminal tryptic peptide. Partial digestion of proteoglycan aggregates with clostripain generated a series of larger intermediates with the hyaluronic acid-binding region. Direct SDS-PAGE analysis revealed one major intermediate with approximately equal to 109,000 (HA-BR109) as well as HA-BR65. After chondroitinase digestion, two additional prominent intermediates were observed on a SDS-PAGE gel at Mr approximately equal to 120,000 (HA-BR120) and approximately equal to 140,000 (HA-BR140). All the intermediates were recognized by a monoclonal antibody specific for the hyaluronic acid-binding region, and all of them contained the same N-terminal tryptic peptide. The results indicate that the N terminus of the core protein is at the hyaluronic acid-binding end of the proteoglycan and that the chondroitin sulfate chains are first present on the core protein in a region between 109,000 and 120,000 molecular weight away from the N terminus.

In vitro induction of cartilage-specific macromolecules by a bone extract

An in vitro system has been developed to study the onset of chondrogenesis. Embryonic rat muscle mesenchymal cells, when treated in suspension culture with an extract of bovine bone matrix, synthesized cartilage-specific proteoglycan and type II collagen. The synthesis of these two macromolecules was assayed by the enzyme-linked immunosorbent assay inhibition technique. Further evidence of chondrogenesis was demonstrated by morphological changes of treated cells when cultured in firm agarose and stained for metachromatic matrix. Even with crude bone matrix extracts, the assay was sensitive at the microgram level and significant differences in cartilage macromolecules compared with controls were observed in 2-3 d. In vivo the same extract induced first cartilage and then bone.

Presence of link protein in cartilage from cmd/cmd (cartilage matrix deficiency) mice

Immunohistochemical and biochemical evidence that the cartilage from cmd/cmd mice, who have an autosomal recessive lethal mutation causing cartilage matrix deficiency, synthesizes link protein nearly at a normal level is provided. Since cartilage-characteristic proteoglycan is not synthesized in this mutant mouse (K. Kimata, H-J. Barrach, K. S. Brown, and J. P. Pennypacker (1981) J. Biol. Chem. 256, 6961-6968), link proteins are apparently not in conventional proteoglycan aggregate. However, the link proteins are functional and able to interact with exogenous cartilage-characteristic proteoglycan monomer and hyaluronic acid to form aggregates.

Immunological evidence for two distinct chondroitin sulfate proteoglycan core proteins: differential expression in cartilage matrix deficient mice

The expression and core protein structure of two proteoglycans, the major cartilage proteoglycan isolated from a rat chondrosarcoma and a small molecular weight chondroitin sulfate proteoglycan isolated from a rat yolk sac tumor, have been compared. The cartilage proteoglycan was not detectable in the cartilage tissue of cartilage matrix deficient (cmd/cmd) neonatal mice by immunofluorescence, but the cmd cartilage did react with antibodies against the core protein of the yolk sac tumor proteoglycan. Radioimmunoassays showed that the core proteins of these proteoglycans are not cross-reactive with each other. Analysis of the core proteins by sodium dodecyl sulfate/polyacrylamide gel electrophoresis after chondroitinase ABC treatment of the proteoglycan revealed a large difference in their sizes. The cartilage proteoglycan core protein had a molecular weight of about 200,000 while the yolk sac tumor proteoglycan core protein migrated with an apparent molecular weight of about 20,000. In addition, the cultured yolk sac tumor cells that make the small proteoglycan did not react with antiserum against the cartilage proteoglycan. These results indicate that the proteoglycan isolated from the yolk sac tumor is similar to the small chondroitin sulfate proteoglycan species found in cartilage and support the existence of at least two dissimilar and genetically independent chondroitin sulfate proteoglycan core proteins.