Proteoglycan populations of baboon (Papio papio) articular cartilage

Common structures of the core proteins of interstitial proteoglycans

Connective tissues, with few exceptions, contain easily distinguishable large and small proteoglycans with chondroitin sulphate or dermatan sulphate side-chains. One group consists of the large aggregating proteoglycans that have the capacity to interact specifically with hyaluronate, thereby forming very large aggregates. These proteoglycans can be divided into two families which can be separated by electrophoresis. Preliminary results indicate that one of these may be derived from the other by processing in the extracellular matrix. Although most prominent in cartilage, similar proteoglycans are present in many types of tissue, such as aorta, sclera and tendon. Another population are the large non-aggregating proteoglycans, identified in cartilage. These proteoglycans show structural features partially different from any of the others. They may represent a distinct population of molecules present in many connective tissues. Many tissues contain major populations of small, non-aggregating proteoglycans. These can be divided into two major groups, differing in the composition of their core proteins, while having similar types of side-chain constituents. One group is represented by proteoglycans from nasal cartilage and aorta, while the other is represented by proteoglycans from tendon, bone, sclera and cornea.

Non-collagenous protein screening in the human chondrodysplasias: link proteins, cartilage oligomeric matrix protein (COMP), and fibromodulin

A gel-electrophoretic screening for link proteins, cartilage oligomeric matrix protein (COMP), and fibromodulin abnormalities was performed in fetuses, newborn infants, and children with various types of chondrodysplasia. Microdissected freeze-dried sections of upper tibial growth cartilage were extracted with 4M guanidinium chloride in the presence of proteolysis inhibitors. After dialysis against 8M urea, the extracts were submitted to stepwise ion-exchange chromatography to separate the large proteoglycans (aggrecans) from the other components. The latter were analyzed by gel electrophoresis, electrotransferred onto nitrocellulose membranes, and reacted with specific antibodies. Control samples from individuals with apparently normal growth were analyzed in the same runs. Two link protein bands with abnormal electrophoretic migration were found in a sporadic case of spondylometaphyseal dysplasia, Kozlowski type. Three link protein bands with the same migration as in the control samples were found in thanatophoric dysplasia, homozygous achondroplasia, achondrogenesis type II, hypochondrogenesis, Goldblatt syndrome, Desbuquois dysplasia, pseudoachondroplasia, and diastrophic dysplasia. In several pathologic cases with normal electrophoretic pattern of the link proteins, small link protein fragments appeared after reduction. The gel electrophoretic pattern of COMP was studied in thanatophoric dysplasia, diastrophic dysplasia, homozygous achondroplasia, fibrochondrogenesis, hypochondrogenesis, Goldblatt syndrome, and Kniest dysplasia. In all these cases the pattern was the same as in the control samples. The main band of fibromodulin had a normal migration rate in fibrochondrogenesis, Desbuquois dysplasia, Kniest dysplasia, and pseudoachondroplasia. It was delayed in diastrophic dysplasia.

Multiple epiphyseal dysplasia, Fairbank type: morphologic and biochemical study of cartilage

We have performed histochemical, immunohistochemical, electron microscopic, and biochemical studies on the upper tibial cartilage from a case of multiple epiphyseal dysplasia, Fairbank type. Most chondrocytes had intracytoplasmic inclusions which took the stains for proteins and were resistant to microbial collagenase digestion. The electron microscopic study showed that the inclusions are dilatations of the rough endoplasmic reticulum containing a material with alternately wide electron dense and electron lucent layers. Both in optical and in electron microscopy the inclusions fixed antibodies against the core protein of the large cartilage proteoglycans (aggrecans). They didn't stain with antibodies against type II collagen. The gel electrophoretic pattern of the large proteoglycans was different from normal controls. The morphologic and biochemical alterations found in multiple epiphyseal dysplasia are similar to those already described in pseudoachondroplasia (Stanescu et al.: Eur J Pediatr 138:121-225, 1982; Stanescu et al.: J Bone Joint Surg 66A:817-836, 1984). However, the inclusions are smaller and the growth cartilage much less disorganized in multiple epiphyseal dysplasia. The similarity of morphologic and biochemical abnormalities strongly suggests that the two diseases have a similar pathogenesis and belong to the same bone dysplasia family.

Variability in the G3 domain content of bovine aggrecan from cartilage extracts and chondrocyte cultures

The content of the globular domains G1, G2 and G3 on the core protein of high-density (A1D1) aggrecan isolated from newborn and mature bovine cartilage and from cultures of bovine chondrocytes was examined. Quantitation based on the 220 nm absorbance of tryptic marker peptides from each domain isolated by reversed-phase HPLC showed that while the content of G1 and G2 was essentially the same for all samples, the content of G3 varied markedly. The molar yield of G3 and G1 marker peptides indicated that approximately 55% of the G1-bearing aggrecan from immature cartilage carried the G3 domain, while for mature cartilage this figure was markedly reduced, at about 35%. Aggrecan prepared from the cell layer matrix of calf chondrocyte cultures had an apparent G3 content similar to newborn cartilage (55%), whereas aggrecan prepared from the medium of these cultures had a markedly higher G3 content, at about 80%. The high content of G3 in cell medium samples compared to cartilage extracts was supported by electron microscopic analysis of A1D1 preparations. The G3 content of the two subpopulations of aggrecan present in mature cartilage and separable by flat bed agarose gel electrophoresis was also determined at about 45% (Band I) and 20% (Band II) respectively. These results are discussed in terms of the likely origin of the marked variability in the G3 domain content of aggrecan.

Immunological detection of the EGF-like domain of the core proteins of large proteoglycans from human and baboon cartilage

Recent data from the literature have shown that cDNA clones for the carboxyterminal domain of the core protein of large proteoglycan monomers from human cartilage contain an EGF-like domain, which appears to undergo alternative splicing. In the present study we have found that articular proteoglycans from human and baboon separated on agarose flat-bed gels and blotted onto nitrocellulose react with a rabbit antiserum to mouse EGF. In addition both forms of the proteoglycans (band I and band II) seen on these gels are reactive. Reactivity is seen with proteoglycans extracted from human articular cartilage of various ages (fetal, newborn, young and aged) and with proteoglycans extracted from cartilage of thanatophoric dysplasia and homozygous achondroplasia. Reactivity is dependent on prior digestion of the nitrocellulose blot with Chase ABC, suggesting masking of epitope by chondroitin sulfate. Reactivity of the EGF antiserum with cartilage proteoglycan core protein was also demonstrated in an ELISA system with core protein as coating antigen. The reactivity appears to reside in a tryptic peptide generated from Chase/keratanase digested core protein. The immunoreactive species migrates as a 68 KDa species on gradient gels. Immunological detection and quantitative analysis of the EGF-like domain could be useful for analysis of various proteoglycan samples.

The influence of scoliosis and ageing on proteoglycan heterogeneity in the human intervertebral disc

Proteoglycans (PGs) purified from 19-year-old male (19M), 53-year-old female (53F), and 15-16-year-old adolescent idiopathic scoliotic (AIS) disc tissues were characterised by their aggregation properties with hyaluronic acid (HA), glycosaminoglycan (GAG), and amino acid composition, electrophoretic mobilities by composite agarose polyacrylamide gel electrophoresis (CAPGE), and hydrodynamic size by Sepharose CL2B gel permeation chromatography. Proteoglycan levels were similar in the AIS and 53F discs, but considerably higher levels were found in the 19M discs. Proteoglycan populations assessed by the aforementioned criteria demonstrated a similar level of heterogeneity in the AIS and 53F discs but this differed with the 19M sample. Two small Mr, low buoyant density PG species were particularly prominent in AIS and 53F discs: these were similar to two nonaggregating PG species formerly reported by di Fabio et al.; however, the corresponding PG species in 19M discs were of somewhat different composition. Collectively, these data suggest similar processing of PGs in the AIS and 53F discs. Furthermore, the pattern of normal age changes in the PGs from AIS discs appears to be disturbed, most likely arising as a consequence of the abnormal biomechanical forces intrinsic to the deformity.

The small proteoglycans of cartilage matrix

The small proteoglycans (PGs) of cartilage matrix represent a small fraction of the total mass of PGs, but with a small size they can be present in equivalent moles to the large PGs. Three types of PGs with a wide skeletal and extraskeletal distribution, biglycan (PGI), decorin (PGII) and fibromodulin have distinct but homologous core proteins containing leucin-rich sequences. Carbohydrate substituants (one or two chondroitin sulfate/dermatan sulfate chains for decorin and biglycan respectively, chains of keratan sulfate for fibromodulin and oligosaccharides) present variations from tissue to tissue and with age and other factors. Decorin and fibromodulin appear to interact with collagen and to participate in the regulation of collagen matrices. In vitro experiments indicate a role for small PGs in adhesion, multiplication, differentiation, and migration of cells. Recent data on molecular biology of the small PGs contribute to a better understanding of their functions and make the evaluation of their role in hereditary diseases.

Homozygous achondroplasia: morphologic and biochemical study of cartilage

We have performed histochemical, immunohistochemical, electron microscopic, and biochemical studies on the upper tibial cartilage from a case of homozygous achondroplasia. The growth zone was narrow and disorganized. Columnization was absent except for a few areas with short rows of cells. Hypertrophy was reduced to scattered clusters of cells. The provisional calcification was patchy and primary trabeculae were thick and irregularly arranged. Islands of fibrous or fibrocartilagineous tissue were found along the growth zone. The matrix did not stain with safranin O and lacked metachromasia, except for pericellular rims around the hypertrophic cell clusters. Staining with antibodies against the large proteoglycan monomers and chondroitin-4-sulfate was weakly positive. Electron microscopic examination showed that only a few cells had degenerative signs. In most areas of the matrix, proteoglycan granules were absent. Areas with dense collagen fibers were seen. In contrast to the growth zone, the cartilage of the remaining epiphyses had normal histochemical, immunohistochemical, and electron microscopic appearance. The large proteoglycan monomers had a normal composition and hydrodynamic size. Type II and XI collagen, pepsin fragments of type IX collagen, and several noncollagenous proteins extracted from cartilage had a normal electrophoretic migration. It is suggested that a mutation affecting a matrix component or a regulatory pathway present only or predominantly in the growth area of the chondroepiphysis might explain the findings.

Micromechanical spectroscopy of cartilage proteoglycans: hydration

Proteoglycan subunits extracted from calf cartilage have been studied with a high resolving power mechanical spectroscopy: the Thermostimulated Creep (TSC). The influence of hydration on TSC spectra shows the existence of two types of bound water: the weakly bound water increases the inertia of proteoglycan and stiffens their structure; the strongly bound water is responsible to a compensation law indicating the existence of a resonance phenomenon at the physiological temperature. Because of the looseness of bonds in weakly bound water, an increase of the local pressure may induce, in vivo, a release of water in tissues. This hypothesis explains perfectly the role of a water pump of proteoglycans in cartilage.

Proteoglycan profiles obtained by electrophoresis and triple immunoblotting

Using synovial fluid of individuals with osteoarthritis as a prototypic biologic fluid containing one part proteoglycan per 100 to 1000 parts of other protein, profiles of proteoglycan were produced without preliminary purification through agarose-acrylamide gel electrophoresis, transfer to nitrocellulose, and triple immunoblotting. Chondroitin sulfate, keratan sulfate, and a hyaluronic acid binding region appear to be present on individual synovial fluid proteoglycans in variable amounts, and consequently a triple immunoblot using monoclonal antibodies to these three epitopes has the potential for developing a proteoglycan profile. The profile is assembled by means of densitometric scans of autoradiograms obtained after use of 125I-labeled anti-mouse immunoglobulin. By contrast to the profile of a relatively homogeneous proteoglycan purified from articular cartilage extracts, the proteoglycans of synovial fluid appeared to be quite heterogeneous with the bulk of keratan sulfate epitopes migrating ahead of the bulk of the chondroitin sulfate epitopes. Most of the proteoglycans appeared to possess a hyaluronate binding region.

Proteoglycans of the human intervertebral disc. Electrophoretic heterogeneity of the aggregating proteoglycans of the nucleus pulposus

Nuclei pulposi were dissected from lumbar discs of radiologically normal human spines of cadavers aged 17, 20 and 21 years. Proteoglycans were extracted with 4 M guanidine hydrochloride (dissociative conditions) with proteinase inhibitors and isolated as A1 fractions by associative density-gradient centrifugation. Aggregating and non-aggregating proteoglycans were separated by Sepharose 2B chromatography. Both aggregating and non-aggregating proteoglycans contained a keratan sulphate-rich region as isolated by chondroitinase/trypsin/chymotrypsin digestion and Sepharose CL-6B chromatography. Agarose/acrylamide-gel electrophoresis of individual fractions of a Bio-Gel A-50m dissociative-column separation of the aggregating proteoglycans revealed two, well-separated bands: S and F, the slower and faster migrating bands respectively. The non-aggregating proteoglycan fractions were eluted under associative conditions (0.5 M-sodium acetate, pH 6.8) and migrated as a single band in the electrophoretic system. The gel-electrophoretic heterogeneity of the aggregating proteoglycans was still evident after hydroxylamine fragmentation and removal of the hyaluronate-binding portion of the molecule. Dissociative density-gradient centrifugation of the aggregating proteoglycans partially separated the Band-S proteoglycans from the Band-F population. Subsequent dissociative chromatography of the high-buoyant-density Band F proteoglycans permitted discrimination of this band into two gel-electrophoresis-distinguishable populations (Bands F-1 and F-2). Enzyme-linked immunosorbent assays with a monoclonal antibody that recognized keratan sulphate demonstrated that the D1 fraction containing the Band F-1 proteoglycans was enriched in keratan sulphate compared with the total aggregating or non-aggregating pool of proteoglycans. The proteoglycans of young adult nucleus pulposus could then be ascribed to one of four structurally and/or electrophoretically distinct populations: (1) the non-aggregating population, which comprised about 70% of the total extractable proteoglycans; (2) the aggregating pool, comprising: (a) Band F-1 proteoglycans, which had a relatively large hydrodynamic size, uronate/protein weight ratio, were enriched in keratan sulphate and had a high buoyant density; (b) Band S proteoglycans, which migrated slower in agarose/acrylamide gels, had a smaller hydrodynamic size, lower buoyant density and a lower uronate/protein ratio than the Band F-1 population; (c) Band F-2 proteoglycans, which were lower in buoyant density, smaller in hydrodynamic size and slightly faster in electrophoretic mobility than the Band F-1 proteoglycans.

Age-related changes in small proteoglycans of low buoyant density of human articular cartilage

Proteoglycans extracted from articular cartilage of large joints of humans aged 4, 11, 70 and 75, were fractionated on associative density gradients. The top fraction (A3) was purified by ion-exchange chromatography and subsequent gel filtration on Sepharose CL 4B in 4 M GuCl, 0.5% Triton x 100. Proteoglycans from young cartilages yielded a narrow rapid migrating band on gel electrophoresis, had a Kav of 0.43 and 0.44 on Sepharose CL 4B, a glucosamine/galactosamine ratio of 0.11 and 0.12 and a glycoprotein core rich in aspartic acid and leucine with a Mr of about 47,000. Proteoglycans from old cartilages gave a wider and slower migrating band on gel electrophoresis, had a wide peak with a Kav of 0.38 and 0.40 on Sepharose CL 4B, a glucosamine/galactosamine ratio of 5.1 and 3.2, a glycoprotein core rich in glutamic acid and glycine, and with a Mr of about 170,000-180,000. Analysis using monoclonal antibodies detected epitopes of keratarn sulfate and of hyaluronic acid binding region in the fractions from old but not in those from young cartilages. Small proteoglycans not derived from the large monomers are the major component of low-buoyant-density fractions of proteoglycans from young cartilages. Fragments of large monomers containing keratan sulfate and hyaluronic acid binding region are the major component of similar fractions from old cartilage.

Preparative electrophoresis on agarose submerged gels of two aggregating proteoglycan monomers from articular cartilage

Analytical electrophoresis on polyacrylamide-agarose gels of aggregating proteoglycan monomers from baboon articular cartilage produces two distinct bands, corresponding to two different aggregating monomer populations. A preparative electrophoresis procedure is described for isolating the two monomers. Proteoglycans were extracted from young baboon articular cartilage in 4 M guanidinium chloride containing proteolysis inhibitors and aggregated after hyaluronic acid addition. The aggregates were separated from non-aggregated proteoglycans by isopycnic centrifugation, followed by gel chromatography on Sepharose CL-2B. The monomers of the aggregates were obtained by isopycnic centrifugation under dissociative conditions. Two monomers were separated by preparative electrophoresis on 0.8 % agarose submerged gels. Approximately 60 % of the proteoglycans were recovered from the gel using a freeze-squeeze procedure. Aliquots of the separated monomers gave single bands when submitted to analytical polyacrylamide-agarose gel electrophoresis. Their migration and appearance were similar to that of the two bands present in the non separated preparation of monomers.

Proteoglycan electrophoresis on horizontal submerged polyacrylamide-agarose gels

A method of proteoglycan electrophoresis on submerged horizontal polyacrylamide-agarose gels is described. Several preparations of purified proteoglycans extracted from fetal and young baboon articular cartilage and from mandibular dog-fish cartilage were analyzed. Discrete bands corresponding to proteoglycan monomers of different size were obtained. The results were similar to those obtained using the more tedious electrophoretic separation on cylindrical gel rods.

The protein core of the largest proteoglycan monomer of articular cartilage. Gel electrophoretic pattern and tryptophanyl peptide bond cleavage

The largest proteoglycan monomer of baboon (Papio papio) articular cartilage was isolated and the protein rich core was obtained after chondroitinase AC II and keratanase digestions. On SDS-PAGE the core yielded a single band with apparent Mr of 290,000. Tryptophanyl peptide bond cleavage of the core with N-chlorosuccinimide/urea gave 4 peptides with apparent Mr of 105,000, 66,000, 62,000 and 56,000

Monoclonal antibodies to different protein-related epitopes of human articular cartilage proteoglycans

Monoclonal antibodies produced against chondroitinase-treated human adult cartilage proteoglycans were selected for their ability to recognize epitopes on native proteoglycans. Binding analyses revealed that four of these monoclonal antibodies (BCD-4, BCD-7, EFG-4 and KPC-190) each recognized a different epitope on the same proteoglycan molecule which represents a subpopulation of a high buoyant density (D1) fraction of human articular cartilage proteoglycans (10, 30, 50 and 60% in fetal-newborn, 1.5 years old, 15 years old and 52-56 years old cartilages, respectively). Analysis of epitope specificities revealed that BCD-7 and EFG-4 monoclonal antibodies recognized epitopes on proteoglycan monomer which are associated with the protein structure in that they are sensitive to cleavage by Pronase, papain and alkali treatment and do not include keratan sulphate, chondroitin sulphate or oligosaccharides. The BCD-4 and KPC-190 epitopes also proved to be sensitive to Pronase or papain digestion or to alkali treatment, but keratanase or endo-beta-galactosidase also reduced the immunoreactivity of these epitopes. These observations indicate that the BCD-4 and KPC-190 epitopes represent peptides substituted with keratan sulphate or keratan sulphate-like structures. The BCD-4 epitope is, however, absent from a keratan sulphate-rich fragment of human adult proteoglycan, while the other three epitopes were detected in this fragment. None of these four epitopes were detected in the link proteins of human cartilage, in the hyaluronic acid-binding region of human newborn cartilage proteoglycan, in Swarm rat chondrosarcoma proteoglycan, in chicken limb bud proteoglycan monomer and in the small dermatan sulphate-proteoglycan of bovine costal cartilage. EFG-4 and KPC-190 epitopes were not detected in human fetal cartilage proteoglycans, although fetal molecules contained trace amounts of epitopes reactive with BCD-4 and BCD-7 antibodies.

Gel electrophoresis of proteoglycan monomers of baboon articular cartilage separated by zonal rate centrifugation in sucrose gradients

Proteoglycan monomers from articular cartilage of young baboons and of a baboon foetus were submitted to zonal rate centrifugation in sucrose gradients. The peaks obtained were analyzed by gel electrophoresis on polyacrylamide-agarose gels. The proteoglycan monomers corresponding to the bands obtained by gel-electrophoresis of unfractionated proteoglycans were separated in the gradients and the sedimentation distance correlated with the electrophoretic mobility.

Assay of proteoglycan populations using agarose-polyacrylamide gel electrophoresis

The agarose-polyacrylamide gel electrophoresis procedure for the analysis of proteoglycans originally described by C. A. McDevitt and H. Muir (1971, Anal. Biochem. 44, 612-622) has been modified to minimize trailing and to allow the analysis of crude samples, i.e., tissue extracts. A slab gel system was used, permitting reproducible analysis of many samples. Procedures are described that can be used to separate and quantify several subpopulations of proteoglycans and also to quantify the proportion of proteoglycans capable of aggregating with hyaluronic acid. Applications of the procedure include transfer to nitrocellulose paper followed by immunological detection of proteoglycans as well as fluorography of separated, radiolabeled proteoglycans.

Separation and characterization of two populations of aggregating proteoglycans from cartilage

Intermediary gel immunoelectrophoresis was used to show that purified aggregating cartilage proteoglycans from 2-year-old steers contain two distinct populations of molecules and that only one of these is immunologically related to non-aggregating cartilage proteoglycans. The two types of aggregating proteoglycans were purified by density-gradient centrifugation in 3.5M-CsCl/4M-guanidinium chloride and separated by zonal rate centrifugation in sucrose gradients. The higher-buoyant-density faster-sedimenting proteoglycan represented 43% of the proteoglycans in the extract. It had a weight-average Mr of 3.5 X 10(6), did not contain a well-defined keratan sulphate-rich region, had a quantitatively dominant chondroitin sulphate-rich region and contained 5.9% protein and 23% hexosamine. The lower-buoyant-density, more slowly sedimenting, proteoglycan represented 15% of the proteoglycans in the extract. It had a weight-average Mr of 1.3 X 10(6), contained both the keratan sulphate-rich and the chondroitin sulphate-rich regions and contained 7.3% protein and 23% hexosamine. Each of the proteoglycan preparations showed only one band on agarose/polyacrylamide-gel electrophoresis. The larger proteoglycan had a lower mobility than the smaller. The distribution of chondroitin sulphate chains along the chondroitin sulphate-rich region was similar for the two types of proteoglycans. The somewhat larger chondroitin sulphate chains of the larger proteoglycan could not alone account for the larger size of the proteoglycan. Peptide patterns after trypsin digestion of the proteoglycans showed great similarities, although the presence of a few peptides not shared by both populations indicates that the core proteins are partially different.

Opsismodysplasia: a new type of chondrodysplasia with predominant involvement of the bones of the hand and the vertebrae

The name opsismodysplasia is proposed for a new chondrodysplasia, which was studied in three patients. Clinically, the condition is recognized at birth on the basis of shortness, short hands, and facial abnormalities with a short nose and a depressed bridge of nose. The most characteristic radiographic signs are: very retarded bone maturation; marked shortness of the bones of the hands and of the feet with concave metaphyses; and thin, lamellar vertebral bodies. The growth cartilage studied in one case showed a wide hypertrophic area containing thick connective tissue septa, irregular provisional calcification, and vascular invasion. Type I collagen was detected in the hypertrophic area by immunohistochemical and microchemical tests. The transmission of opsismodysplasia is probably autosomal recessive.

The use of caesium sulphate density gradient centrifugation to analyse proteoglycans from human articular cartilages of different ages

Proteoglycan subunits from human articular cartilage were fractionated by caesium sulphate density gradient centrifugation. A single heterogeneous population of molecules was produced whose average density decreased with increasing age of the individual from which they were obtained. At no density did the carbohydrate composition of any adult fraction resemble that of any newborn fraction, although there was considerable overlap in density. However, there was a similarity in amino acid composition between the most dense proteoglycans from the adult and those of least density from the newborn. The carbohydrate content of a 2-year-old proteoglycan was intermediate in composition, with high density fractions resembling the newborn and low density fractions resembling the adult. In addition, the proteoglycans of lowest density in both the newborn and two year preparations showed additional bands on agarose/polyacrylamide gel electrophoresis resembling the adult material. These results indicate that while a core protein of adult composition may occur in the juvenile proteoglycan it need not necessarily be glycosylated in an adult manner, suggesting that glycosylation is to some extent independent of the origin of core protein heterogeneity.

A comparison of the proteoglycans produced by rabbit articular chondrocytes in monolayer and spinner culture and those of bovine nasal cartilage

The structural and immunological properties of the glycosaminoglycans and the core proteins of bovine nasal cartilage proteoglycan and the proteoglycans produced by rabbit articular chondrocytes in spinner and monolayer culture were compared. Culture medium with 35SO4- or 3H-serine-labeled proteoglycan was mixed with bovine nasal cartilage 4M guanidine-HCl extract and digested with trypsin. The proteoglycan fragments were then isolated by DEAE-cellulose chromatography and fractionated by dissociative CsCl density gradient centrifugation. Approximately 90% of the 35SO4 incorporated into proteoglycan by the cultured chondrocytes was in chondroitin sulfates and about 5% in keratan sulfate. Although there was considerable overlap in the Sepharose 4B elution of the tryptic proteoglycan fragments of highest buoyant density, some monolayer-produced proteoglycan fragments eluted earlier and some spinner-produced proteoglycan fragments eluted later than the proteoglycan fragments from bovine nasal cartilage. These differences in apparent fragment size could relate to differences in glycosaminoglycan chain length, since the glycosaminoglycans released by treatment with alkali from monolayer-produced proteoglycan in part eluted from Sepharose 4B earlier and those from spinner-produced proteoglycan in part eluted later than the chondroitin sulfate chains released from bovine cartilage proteoglycan. After digestion with chondroitinase ABC, 3H-serine-labeled high density tryptic proteoglycan fragments from monolayer and spinner culture yielded Sepharose 6B elution profiles which were similar to each other but did not coincide with the peaks of carbazole reactivity found with similarly treated fragments of bovine nasal cartilage proteoglycan. Cross-reactivity was demonstrated by radioimmunoautography between bovine cartilage and rabbit chondrocyte proteoglycan fragments restricted to gradient fractions of low buoyant density, but immunological cross-reactivity was not found for the antigens associated with the keratan sulfate-rich and chondroitin sulfate-bearing tryptic fragments of bovine nasal cartilage proteoglycan. These studies indicate that the proteoglycan core proteins produced by rabbit articular chondrocytes in monolayer and spinner culture are, in part, different from the core protein of bovine nasal cartilage proteoglycan and that the three proteoglycans differ in the length of some of their chondroitin sulfate chains.

Noncollagenous proteins in cartilage of normal subjects and patients with degenerative joint disease. A gel electrophoretic study

Normal articular cartilage from subjects of various ages and cartilage from patients with degenerative joint disease were extracted with 4M guanidinium chloride. After dialysis against 8M urea pH 6.8, a 0.2M NaCl fraction was obtained by ion exchange chromatography on DE-52 in 8M urea. This fraction was concentrated, reduced, and analyzed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (7% gels). Six major noncollagenous protein bands (P1-P6) were found; 2 were identified as the link proteins. The approximate molecular weights of P1-P6 were: 87,000, 64,000, 56,000, 46,000, 41,000, and 27,000. A similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern of P1-P6 was found in young baboons, in normal young and aged humans, and in patients with degenerative joint disease. Peaks corresponding to extracted collagen were decreased in older patients and increased in patients with degenerative joint disease, even those of advanced age.

Immunodiffusion studies of the tryptic fragments of bovine nasal-cartilage proteoglycan monomer of high buoyant density

Tryptic fragments of bovine nasal-cartilage proteoglycan, fractionated by dissociative density-gradient ultracentrifugation, were made to react by immunodiffusion against antiserum to a hyaluronidase-digest subfraction of cartilage proteoglycan monomer. This reaction produced two families of partly superimposed precipitin lines. One family was restricted to gradient fractions of medium or low buoyant density and included the immunoprecipitation reaction attributed to the hyaluronic acid-binding region of the cartilage proteoglycan monomer. The second family of precipitin lines was present alone in gradient fractions of high buoyant density. Immunodiffusion studies with antisera to relatively homogeneous keratan sulphate-rich and chondroitin sulphate-bearing fragment subfractions isolated from the gradient fraction of highest density indicated that both subfractions contained the antigenic determinants responsible for the second family of precipitin lines. Additional immunodiffusion studies, with the use of multispecific antisera to chondroitinase ABC digest and hyaluronidase digest of proteoglycan monomer, confirmed that the two subfractions shared antigenic determinants, and, in addition, indicated that these determinants were on one molecular species in the keratan sulphate-rich fragment subfraction and divided among at least three in the chondroitin sulphate-bearing fragment subfraction. Although an unprecedentedly large number of cartilage proteoglycan antigens could be recognized with the antisera employed in this cartilage proteoglycan antigens could be recognized with the antisera employed in this study, it was not possible to identify antigenic determinants unambiguously specific for the three structurally and functionally distinct regions of the cartilage proteoglycan monomer.

Isolation and biochemical characterization of the tryptic fragments of bovine nasal-cartilage proteoglycan monomer of high buoyant density

Relatively homogeneous fractions of proteoglycan fragments were prepared from tryptic digests of the 4M-guanidinium chloride extract of bovine nasal cartilage. Glycosaminoglycan-containing fragments were separated from non-proteoglycan contaminants by ion-exchange chromatography and fractionated by equilibrium density-gradient centrifugation under dissociative conditions. The fractions of highest buoyant density were chromatographed on a column of Sepharose 4B, digested with chondroitinase ABC and chromatographed on a column of Sepharose 6B, yielding two distinct fractions: fraction B/6B-4 contained fragments from the chondroitin sulphate-bearing region of the proteoglycan monomer, and fraction B/6B-2 fragments from the keratan sulphate-rich region, most probably including a chondroitin sulphate-bearing monomer segment. By dansyl chloride analysis, fraction B/6B-2 had alanine and leucine as sole and fraction B/6B-4 had isoleucine and leucine as greatly predominant N-terminal amino acids, indicative of the relative homogeneity of these preparations of cartilage proteoglycan monomer fragments.

Immunochemical analysis of cartilage proteoglycans. Cross-reactivity of molecules isolated from different species

Antibodies directed against whole bovine nasal-cartilage proteoglycan and against the hyaluronic acid-binding region and chondroitin sulphate peptides from the same molecule were used in immunodiffusion and immunoelectromigration experiments. Proteoglycans from bovine nasal and tracheal cartilage showed immunological identity, with all three antisera. Proteoglycans from pig hip articular cartilage, dog hip articular cartilage, human tarsal articular cartilage and rat chondrosarcoma reacted with all the antisera and showed immunological identity with the corresponding structures isolated from bovine nasal-cartilage proteoglycans. In contrast, proteoglycans from rabbit articular cartilage, rabbit nasal cartilage and cultured chick limb buds did not react with the antibodies directed against the hyaluronic acid-binding region, though reacting with antibodies raised against whole proteoglycan monomer and against chondroitin sulphate peptides. All the proteoglycans gave two precipitation lines with the anti-(chondroitin sulphate peptide) antibodies. Similarly, the proteoglycans reacting with the anti-(hyaluronic acid-binding region) antibodies gave two precipitation lines. The results indicate the presence of at least two populations of aggregating proteoglycan monomers in cartilage. The relative affinity of the antibodies for cartilage proteoglycans and proteoglycan substructures from various species was determined by radioimmunoassay. The affinity of the anti-(hyaluronic acid-binding region) antibodies for the proteoglycans decreased in the order bovine, dog, human and pig cartilage. Rat sternal-cartilage and rabbit articular-cartilage proteoglycans reacted weakly, whereas chick limb-bud and chick sternal-cartilage proteoglycans did not react. In contrast, the affinity of antibodies to chondroitin sulphate peptides for proteoglycans increased in the order bovine cartilage, chick limb bud and chick sternal cartilage, dog cartilage, rat chondrosarcoma, human cartilage, pig cartilage, rat sternal cartilage and rabbit cartilage.

A novel low-molecular weight chondroitin sulphate proteoglycan isolated from cartilage

Proteoglycans were isolated from cartilage by extraction with 4M-guanidinium chloride followed by direct centrifugation in 4M-guanidinium chloride/CsCl at a low starting density, 1.34 g/ml. N-Ethylmaleimide was included in the extraction solvent as a precaution against contamination of proteoglycans with unrelated proteins mediated by disulphide exchange. A novel, discrete, low-buoyant-density proteoglycan (1.40--1.35 g/ml) was demonstrated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Its proteoglycan nature was revealed by the shift in the molecular size observed on gel electrophoresis after treatment with chondroitinase ABC. The core protein was monodisperse. The proteoglycan was further purified by gel chromatography with and without addition of hyaluronate. The proteoglycan constitutes less than 2% (by weight) of the total extracted proteoglycans and is not capable of interacting with hyaluronate. The same proteoglycan was purified in larger quantities by sequential associative and dissociative CsCl-density-gradient centrifugation, zonal rate sedimentation in a sucrose gradient and gel chromatography on Sepharose CL-4B. The pure proteoglycan had a molecular weight of 76 300 determined by sedimentation-equilibrium centrifugation and an apparent partial specific volume of 0.59 ml/g. It contained about 25% protein (of dry weight) and had remarkably high contents of leucine and cysteine as compared with other proteoglycans. The proteoglycan contained two to three large chondroitin sulphate chains and some oligosaccharides.

Age-related changes in the chemical composition of bovine articular cartilage. The structure of high-density proteoglycans

Proteoglycans were extracted from the articular cartilage of foetal, calf and adult bovine metacarpal-phalangeal joints with 4m-guanidinium chloride. After extraction, the high-density proteoglycans (PG-I fractions) were prepared by sedimentation in two sequential CsCl-density-gradient procedures [Swann, Powell & Sotman (1979) J. Biol. Chem.254, 945-954]. The PG-I fractions from foetal, calf and adult tissues accounted for 75%, 52% and 46% respectively of the extracted components. The glucosamine, galactose, N-acetylneuraminic acid and protein contents increased with age. The overall amino acid compositions of PG-I fractions were similar. Fractionation of PG-I-fraction samples on a Bio-Gel A-50m column indicated that the molecular weight decreased with age. The PG-I fractions were specifically (3)H-labelled by treatment with galactose oxidase followed by reduction with NaB(3)H(4). The (3)H radioactivity was incorporated into both galactose and galactosamine residues of different carbohydrate side chains. The elution profiles of alkaline borohydride-treated foetal, calf and adult PG-I-fraction samples on a Sepharose 6B column showed that the molecular weights of chondroitin sulphate chains were 13500, 12000 and 10500 in foetal, calf and adult tissues respectively. Fractionation of the alkaline borohydride-treated foetal, calf and adult PG-I-fraction samples and (3)H-labelled calf and adult PG-I-fraction samples on a Bio-Gel P-10 column showed that there was an inverse relationship between the low-molecular-weight O-linked oligosaccharides and the higher-molecular-weight sialic acid-containing constituents at different ages. The oligosaccharide components of foetal, calf and adult PG-I-fraction samples represented 79%, 69% and 36% respectively of the total sialic acid content of the proteoglycans. Similarly in the (3)H-labelled calf and adult samples 75% and 30% of the total radioactivity were present in the oligosaccharide components respectively. Digestion with chondroitinase AC-II and infrared analyses showed that the PG-I-fraction F and C samples contained primarily chondroitin 4-sulphate chains whereas PG-I-fraction sample A was 6-sulphated. These studies show that the major proteoglycans (PG-I fractions) in the articular cartilage of foetal, calf and adult animals differ in the content, types and structure of the chondroitin sulphate, keratan sulphate and oligosaccharide constituents. These changes in proteoglycan structure reflect the gross age-related changes in the chemical composition of the tissue.

Link-proteins and non-collagenous proteins from normal and chondrodysplastic cartilages

Baboon and human articular and growth cartilage was extracted with 4M guanidinium chloride in the presence of proteolysis inhibitors. After dialysis against 8M urea pH 6.8 the proteins were separated from proteoglycans by ion-exchange chromatography. The concentrated and reduced protein fractions was analyzed by SDS-PAGE. Bands corresponding to collagen and to 6 major non-collegenous proteins were found. Two of the latter were identified with the link-proteins. By using small columns and microconcentration procedures, a gel-electrophoretic analysis of link-proteins extracted from small pieces of cartilage was performed and ten cases of osteochondrodysplasias were studied. No abnormalities were detected in the following syndromes: achondroplasia, diastrophic dwarfism, thanatophoric dwarfism, Jeune disease, spondyloepiphyseal dysplasia congenita, Kozlowski syndrome, osteogenesis imperfecta, polyepiphyseal dysplasia with diabetes mellitus.

Immunochemical analysis of cartilage proteoglycans. Antigenic determinants of substructures

Antibodies were raised in rabbits by injection of cartilage proteoglycan monomers, isolated hyaluronic acid-binding region, polysaccharide-peptides prepared by trypsin digestion of proteoglycans and link-protein. The rabbits injected with the proteoglycan monomers made antibodies reacting with the intact proteoglycan. The antiserum contained antibodies specific for, and also reacting with, the isolated hyaluronic acid-binding region and the keratan sulphate-rich region. In addition there were probably antibodies reacting with other structures of the proteoglycan monomer. When isolated hyaluronic acid-binding region was used for immunization the antibodies obtained reacted specifically with the hyaluronic acid-binding region. The antibodies obtained from rabbits immunized with the polysaccharide-peptides reacted with the proteoglycan monomers and showed a reaction identical with that of the chondroitin sulphate-peptides isolated after trypsin digestion of proteoglycans. The antibodies prepared with the link-protein as the antigen reacted only with the link-protein and not with any preparation from the proteoglycan monomer. Neither did any of the antisera raised against the proteoglycan monomer or its substructures react with the link-protein. Separately it was shown that the peptide 'maps' prepared from trypsin digests of the link-protein and the hyaluronic acid-binding region were different. Therefore it appears that the link-protein is not structurally related to the proteoglycan or the hyaluronic acid-binding region. Digestion of proteoglycan monomers or isolated hyaluronic acid-binding region with trypsin did not destroy the antigenic sites of the hyaluronic acid-binding region. In contrast trypsin digests of previously reduced and alkylated preparations did not react with the anti-(hyaluronic acid-binding region). The trypsin digests, however, reacted with both the antibodies directed against the chondroitin sulphate-peptides and those against the keratan sulphate-peptides. Trypsin digestion of the link-proteins destroyed the antigenic site and the reactivity with the antibodies. By combining immunoassay of proteoglycan preparations before and after trypsin digestion it is feasible to quantitatively determine its substructures by using the antisera described above.

Age-related changes in the composition and structure of human articular-cartilage proteoglycans

1. Analysis of the purified proteoglycans extracted from normal human articular cartilage with 4M-guanidinium chloride showed that there was an age-related increase in their content of protein and keratan sulphate. 2. The hydrodynamic size of the dissociated proteoglycans also decreased with advancing age, but there was little change in the proportion that could aggregate. 3. Results suggested that some extracts of aged-human cartilage had an increased content of hyaluronic acid compared with specimens from younger patients. 4. Dissociated proteoglycans, from cartilage of all age groups, bind to hyaluronic acid and form aggregates in direct proportion to the hyaluronic acid concentration. 5. Electrophoretic heterogeneity of the dissociated proteoglycans was demonstrated on polyacrylamide/agarose gels. The number of proteoglycan species observed was also dependent on the age of the patient.

A comparative study of the proteoglycan of growth cartilage of normal and rachitic chicks

1. Proteoglycan was isolated from growth cartilage of normal and rachitic chicks. 2. The proteoglycan from normal cartilage showed differences in chemical composition and physical properties from a comparable fraction isolated from bovine nasal cartilage. 3. The proteoglycan from rachitic-chick cartilage was of smaller size than tis normal counterpart, though of similar average chemical composition. 4. Differences between proteoglycan from normal and rachitic cartilages can be explained in terms of limited proteolytic cleavage.