Characterization of chondroitin sulfate isolated from trypsin-chymotrypsin digests of cartilage proteoglycans

Future proofing of chondroitin sulphate production: Importance of sustainability and quality for the end-applications

Chondroitin sulphates (CSs) are the most well-known glycosaminoglycans (GAGs) found in any living organism, from microorganisms to invertebrates and vertebrates (including humans), and provide several health benefits. The applications of CSs are numerous including tissue engineering, osteoarthritis treatment, antiviral, cosmetics, and skincare applications. The current commercial production of CSs mostly uses animal, bovine, porcine, and avian tissues as well as marine organisms, marine mammals, sharks, and other fish. The production process consists of tissue hydrolysis, protein removal, and purification using various methods. Mostly, these are chemical-dependent and are complex, multi-step processes. There is a developing trend for abandonment of harsh extraction chemicals and their substitution with different green-extraction technologies, however, these are still in their infancy. The quality of CSs is the first and foremost requirement for end-applications and is dependent on the extraction and purification methodologies used. The final products will show different bio-functional properties, depending on their origin and production methodology. This is a comprehensive review of the characteristics, properties, uses, sources, and extraction methods of CSs. This review emphasises the need for extraction and purification processes to be environmentally friendly and gentle, followed by product analysis and quality control to ensure the expected bioactivity of CSs.

Hyaluronic acid and Chondroitin sulfate from marine and terrestrial sources: Extraction and purification methods

Hyaluronic acid (HA) and chondroitin sulfate (CS) are valuable bioactive polysaccharides that have been highly used in biomedical and pharmaceutical applications. Extensive research was done to ensure their efficient extraction from marine and terrestrial by-products at a high yield and purity, using specific techniques to isolate and purify them. In general, the cartilage is the most common source for CS, while the vitreous humor is main used source of HA. The developed methods were based in general on tissue hydrolysis, removal of proteins and purification of the target biopolymers. They differ in the extraction conditions, enzymes and/or solvents used and the purification technique. This leads to specific purity, molecular weight and sulfation pattern of the isolated HA and CS. This review focuses on the analysis and comparison of different extraction and purification methods developed to isolate these valuable biopolymers from marine and terrestrial animal by-products.

Articular cartilage changes in maturing athletes: new targets for joint rejuvenation

Context:

Articular cartilage has a unique functional architecture capable of providing a lifetime of pain-free joint motion. This tissue, however, undergoes substantial age-related physiologic, mechanical, biochemical, and functional changes that reduce its ability to overcome the effects of mechanical stress and injury. Many factors affect joint function in the maturing athlete—from chondrocyte survival and metabolism to structural composition and genetic/epigenetic factors governing cartilage and synovium. An evaluation of age-related changes for joint homeostasis and risk for osteoarthritis is important to the development of new strategies to rejuvenate aging joints.

Objective:

This review summarizes the current literature on the biochemical, cellular, and physiologic changes occurring in aging articular cartilage.

Data Sources:

PubMed (1969-2013) and published books in sports health, cartilage biology, and aging.

Study Selection:

Keywords included aging, athlete, articular cartilage, epigenetics, and functional performance with age.

Study Design:

Systematic review.

Level of Evidence:

Level 3.

Data Extraction:

To be included, research questions addressed the effect of age-related changes on performance, articular cartilage biology, molecular mechanism, and morphology.

Results:

The mature athlete faces challenges in maintaining cartilage health and joint function due to age-related changes to articular cartilage biology, morphology, and physiology. These changes include chondrocyte loss and a decline in metabolic response, alterations to matrix and synovial tissue composition, and dysregulation of reparative responses.

Conclusion:

Although physical decline has been regarded as a normal part of aging, many individuals maintain overall fitness and enjoy targeted improvement to their athletic capacity throughout life. Healthy articular cartilage and joints are needed to maintain athletic performance and general activities. Genetic and potentially reversible epigenetic factors influence cartilage physiology and its response to mechanical and injurious stimuli. Improved understandings of the physical and molecular changes to articular cartilage with aging are important to develop successful strategies for joint rejuvenation.

Structure and biology of the intervertebral disk in health and disease

The intervertebral disks along the spine provide motion and protection against mechanical loading. The 3 structural components, nucleus pulposus, annulus fibrosus, and cartilage endplate, function as a synergistic unit, though each has its own role. The cells within each of these components have distinct origins in development and morphology, producing specific extracellular matrix proteins that are organized into unique architectures fit for intervertebral disk function. This article focuses on various aspects of intervertebral disk biology and disruptions that could lead to diseases such as intervertebral disk degeneration.

The glycosaminoglycan attachment regions of human aggrecan

Aggrecan possesses both chondroitin sulfate (CS) and keratan sulfate (KS) chains attached to its core protein, which reside mainly in the central region of the molecule termed the glycosaminoglycan-attachment region. This region is further subdivided into the KS-rich domain and two adjacent CS-rich domains (CS1 and CS2). The CS1 domain of the human is unique in exhibiting length polymorphism due to a variable number of tandem amino acid repeats. The focus of this work was to determine how length polymorphism affects the structure of the CS1 domain and whether CS and KS chains can coexist in the different glycosaminoglycan-attachment domains. The CS1 domain possesses several amino acid repeat sequences that divide it into three subdomains. Variation in repeat number may occur in any of these domains, with the consequence that CS1 domains of the same length may possess different amino acid sequences. There was no evidence to support the presence of KS in either the CS1 or the CS2 domains nor the presence of CS in the KS-rich domain. The structure of the CS chains was shown to vary between the CS1 and CS2 domains, particularly in the adult, with variation occurring in chain length and the sulfation of the non-reducing terminal N-acetyl galactosamine residue. CS chains in the adult CS2 domain were shorter than those in the CS1 domain and possessed disulfated terminal residues in addition to monosulfated residues. There was, however, no change in the sulfation pattern of the disaccharide repeats in the CS chains from the two domains.

Thyroid hormone enhances aggrecanase-2/ADAM-TS5 expression and proteoglycan degradation in growth plate cartilage

Effects of thyroid hormone on proteoglycan degradation in various regions of cartilage were investigated. In propylthiouracil-treated rats with hypothyroidism, proteoglycan degradation in epiphyseal cartilage during endochondral ossification was markedly suppressed. However, injections of T(4) reversed this effect of propylthiouracil on proteoglycan degradation. In pig growth plate explants, T(3) also induced breakdown of proteoglycan. T(3) increased the release of aggrecan monomer and core protein from the explants into the medium. Accordingly, the level of aggrecan monomer remaining in the tissue decreased after T(3) treatment, and the monomer lost hyaluronic acid-binding capacity, suggesting that the cleavage site is in the interglobular domain. The aggrecan fragment released from the T(3)-exposed explants underwent cleavage at Glu(373)-Ala(374), the major aggrecanase-cleavage site. The stimulation of proteoglycan degradation by T(3) was less prominent in resting cartilage explants than in growth plate explants and was barely detectable in articular cartilage explants. Using rabbit growth plate chondrocyte cultures, we explored proteases that may be involved in T(3)-induced aggrecan degradation and found that T(3) enhanced the expression of aggrecanase-2/ADAM-TS5 (a disintegrin and a metalloproteinase domain with thrombospondin type I domains) mRNA, whereas we could not detect any enhancement of stromelysin, gelatinase, or collagenase activities or any aggrecanase-1/ADAM-TS4 mRNA expression. We also found that the aggrecanse-2 mRNA level, but not aggrecanase-1, increased at the hypertrophic stage during endochondral ossification. These findings suggest that aggrecanse-2/ADAM-TS5 is involved in aggrecan breakdown during endochondral ossification, and that thyroid hormone stimulates the aggrecan breakdown partly via the enhancement of aggrecanase-2/ADAM-TS5.

Hyaluronan, a common thread

Hyaluronan, nature's simplest, but still exceptionally versatile glycosaminoglycan, is currently the focus of attention across a wide front of research; from cell biology, morphogenesis, matrix organization, pathobiology to tissue engineering. This macromolecule has entangled me in a number of puzzling and challenging projects over the past 3 decades. These entertaining encounters are outlined in this retrospective.

Structurally Specific Heparan Sulfates Support Primitive Human Hematopoiesis by Formation of a Multimolecular Stem Cell Niche

Stem cell localization, conservation, and differentiation is believed to occur in niches in the marrow stromal microenvironment. Our recent observation that long-term in vitro human hematopoiesis requires a stromal heparan sulfate proteoglycan (HSPG) led us to hypothesize that such HSPG may orchestrate the formation of the stem cell niche. We compared the structure and function of HS from M2-10B4, a hematopoiesis-supportive cell line, with HS from a nonsupportive cell line, FHS-173-We. Long-term culture-initiating cell (LTC-IC) maintenance was enhanced by PG from supportive cells but not by PG from nonsupportive cells (P < .005). The supportive HS were significantly larger and more highly sulfated than the nonsupportive HS. Specifically, supportive HS contained higher 6-O-sulfation on the glucosamine residues. In agreement with these observations, purified 6-O-sulfated heparin and highly 6-O-sulfated bovine kidney HS similarly maintained LTC-IC. In contrast, completely desulfated heparin, N-sulfated heparin, and unmodified heparin did not support LTC-IC maintenance. Moreover, the supportive HS promoted LTC-IC maintenance but not differentiation of CD34+/HLA-DR−cells into colony-forming cells (CFCs) and mature blood cells. The supportive HS but not the nonsupportive HS bound both cytokines and matrix components critical for hematopoiesis, including interleukin-3 (IL-3), macrophage inflammatory protein-1 (MIP-1), and thrombospondin (TSP). Significantly more CD34+ cells adhered directly to immobilized O-sulfated heparin than to N-sulfated or desulfated heparin. Thus, hematopoiesis-supportive stromal HSPG possessing large, highly 6-O-sulfated HS mediate the juxtaposition of hematopoietic progenitors with stromal cells, specific growth-promoting (IL-3) and growth-inhibitory (MIP-1 and platelet factor 4 [PF4]) cytokines, and extracellular matrix (ECM) proteins such as TSP. We conclude that the structural specificity of stromal HSPG that determines the selective colocalization of cytokines and ECM components leads to the formation of discrete niches, thereby orchestrating the controlled growth and differentiation of stem cells. These findings may have important implications for ex vivo expansion of and gene transfer into primitive hematopoietic progenitors.

Structurally Specific Heparan Sulfates Support Primitive Human Hematopoiesis by Formation of a Multimolecular Stem Cell Niche

Stem cell localization, conservation, and differentiation is believed to occur in niches in the marrow stromal microenvironment. Our recent observation that long-term in vitro human hematopoiesis requires a stromal heparan sulfate proteoglycan (HSPG) led us to hypothesize that such HSPG may orchestrate the formation of the stem cell niche. We compared the structure and function of HS from M2-10B4, a hematopoiesis-supportive cell line, with HS from a nonsupportive cell line, FHS-173-We. Long-term culture-initiating cell (LTC-IC) maintenance was enhanced by PG from supportive cells but not by PG from nonsupportive cells (P < .005). The supportive HS were significantly larger and more highly sulfated than the nonsupportive HS. Specifically, supportive HS contained higher 6-O-sulfation on the glucosamine residues. In agreement with these observations, purified 6-O-sulfated heparin and highly 6-O-sulfated bovine kidney HS similarly maintained LTC-IC. In contrast, completely desulfated heparin, N-sulfated heparin, and unmodified heparin did not support LTC-IC maintenance. Moreover, the supportive HS promoted LTC-IC maintenance but not differentiation of CD34+/HLA-DR−cells into colony-forming cells (CFCs) and mature blood cells. The supportive HS but not the nonsupportive HS bound both cytokines and matrix components critical for hematopoiesis, including interleukin-3 (IL-3), macrophage inflammatory protein-1 (MIP-1), and thrombospondin (TSP). Significantly more CD34+ cells adhered directly to immobilized O-sulfated heparin than to N-sulfated or desulfated heparin. Thus, hematopoiesis-supportive stromal HSPG possessing large, highly 6-O-sulfated HS mediate the juxtaposition of hematopoietic progenitors with stromal cells, specific growth-promoting (IL-3) and growth-inhibitory (MIP-1 and platelet factor 4 [PF4]) cytokines, and extracellular matrix (ECM) proteins such as TSP. We conclude that the structural specificity of stromal HSPG that determines the selective colocalization of cytokines and ECM components leads to the formation of discrete niches, thereby orchestrating the controlled growth and differentiation of stem cells. These findings may have important implications for ex vivo expansion of and gene transfer into primitive hematopoietic progenitors.

Progressive polyarthritis induced in BALB/c mice by aggrecan from normal and osteoarthritic human cartilage

OBJECTIVE

To find an "unlimited" source of antigenic material (aggrecan) for arthritis induction in BALB/c mice; to analyze the specificities of immune reactions to aggrecan and type II collagen in 2 arthritis-susceptible murine strains, BALB/c mice for proteoglycan (aggrecan)-induced arthritis and DBA/1j mice for collagen-induced arthritis; to compare the histopathologic features of arthritis induced by purified aggrecans or total extracts of osteoarthritic (OA) cartilage; and to determine arthritis susceptibility in various BALB/c colonies.

METHODS

Aggrecans from total extracts of human fetal, normal adult, OA, and rheumatoid cartilage samples and from osteophytes were isolated, purified by gradient centrifugation, deglycosylated, characterized, and tested for arthritis induction. Purified type II collagen and salt-soluble collagens from OA cartilage were denatured, stromelysin treated, and used for immunization and arthritis induction in arthritis-susceptible (DBA/1j and BALB/c) murine strains.

RESULTS

Chondrocytes from OA cartilage synthesize predominantly fetal-type aggrecan, which is the most efficient antigenic material for arthritis induction in BALB/c mice. The critical autoimmune/arthritogenic T cell epitopes of aggrecan are located in the G1 domain. Although most of the aggrecan molecules are heavily degraded and lost from OA cartilage, the G1 domain-containing fragments accumulate in OA cartilage. The amount of G1-containing fragments is approximately twice as much in OA than in normal adult articular cartilage, and the arthritogenic epitope(s) remains intact in G1-containing fragments retained in cartilage. Thus, total extracts of OA cartilage (without additional purification), if deglycosylated appropriately, can be used as arthritogenic material in BALB/c mice.

CONCLUSION

Predominantly G1 domain-containing fragments of aggrecan accumulate in OA cartilage, and these are the fragments which induce arthritis in BALB/c mice. Arthritis induction is highly specific for aggrecan epitopes and dictated by the genetic background of the BALB/c strain.

Effect of proteoglycan removal on solute mobility in articular cartilage

Transport of nutrients, cytokines, pharmacologic agents, and matrix components through articular cartilage is critical for the viability and structural integrity of the tissue. To understand the role of the extracellular matrix in regulating this process, we measured the diffusivity of three uncharged solutes of different molecular size (glucose, MW 180; inulin, MW 5000; dextran, MW 70,000) into intact cartilage and cartilage that had its proteoglycan (PG) component removed. Solute diffusivity was measured by performing transient (nonsteady state) one-dimensional diffusion tests using radiolabelled solutes. Compared to intact cartilage, the diffusivity of glucose was unchanged after PG removal, inulin was unchanged but dextran increased by 1.7 times after 71% PG removal, and both inulin and dextran increased by 1.6 and 2.0 times, respectively, after 93% PG removal. The diffusivities of inulin and dextran were inversely proportional to the PG content. While no change was found in the tissue's bulk fluid content, PG depletion resulted in an increase in fluid content in the upper regions of the tissue and a decrease in the lower regions. These results indicate that in intact tissue small uncharged solutes have free mobility through the inter-molecular and intra-molecular PG volumes, larger molecules have limited intra-molecular mobility, and very large molecules are excluded from the intra-molecular space.

Structure of the human aggrecan gene: exon-intron organization and association with the protein domains

The complete exon-intron organization of the human aggrecan gene has been defined, and the exon organization has been compared with the individual domains of the protein core. A yeast artificial chromosome containing the aggrecan gene was selected from the Centre d'Etude du Polymorphisme Humaine yeast artificial chromosome library. A cosmid sulibrary was created from this, and direct sequencing of individual cosmids was used to provide the exon-intron organization. The human aggrecan gene was found to be composed of 19 exons ranging in size from 77 to 4224 bp. Exon 1 is non-coding, whereas exons 2-19 code for a protein core of 2454 amino acids with a calculated mass of 254379 Da. Intron 1 of the gene is at least 13 kb. Overall, the sizes of the 18 introns range from 0.5 to greater than 13 kb. Each intron begins with a GT and ends with an AG, thus obeying the GT/AG rule of splice-junction sequences. The entire coding region is contained in 39.4 kb of the gene. The organization of exons is strongly related to the specific domains of the protein core. The A loop of G1 and the interglobular domain are encoded by exons 3 and 7 respectively. The B and B' loops of G1 are encoded by exons 4-6, and those of G2 are encoded by exons 8-10. These sets of exons, coding for the B and B' loops, are identical in size and organization. This is supported by the intron classes associated with these exons. Exon 11 codes for the 5' half of the keratan sulphate-rich region, and exon 12 codes for the 3' half of the keratan sulphate-rich region as well as the entire chondroitin sulphate-rich region. G3 is encoded by exons 13-18, including the alternatively spliced epidermal growth factor-like and complement regulatory protein-like domains. The correspondence between the exon organization and the protein domains argues strongly for modular assembly of the aggrecan gene.

Isolation and partial characterization of a cell-surface heparan sulfate proteoglycan from embryonic rat spinal cord

Cell-surface heparan sulfate proteoglycans (HSPGs) are potential mediators of neuronal cell adhesion, spreading, and neurite outgrowth on various extra-cellular matrix molecules. One possible site of HSPG attachment is a heparin binding domain of fibronectin, which is present in the synthetic peptide FN-C/H II. In this study, HSPGs extracted from embryonic rat spinal cord by detergent were purified by ion-exchange chromatography, gel filtration, and affinity chromatography on an agarose column coupled with FN-C/H II conjugated to ovalbumin (OA). Heparitinase treatment of the iodinated HSPG fraction led to the appearance of a major protein core with a molecular size of 72 kDa, as determined by reducing SDS-PAGE. The intact proteoglycan has a molecular size of approximately 150-165 kDa, containing heparan sulfate glycosaminoglycan chains of about 10-15 kDa. Anti-HSPG antibodies recognized the 72 kDa core protein by immunoblotting, and stained the surface of spinal cord neurons, oligodendrocytes, and a subset of astrocytes. These results identify a cell-surface HSPG that may mediate neuron-substratum or neuron-glia interactions in embryonic central nervous system.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Monoclonal antibodies directed against epitopes within the core protein structure of the large aggregating proteoglycan (aggrecan) from the swarm rat chondrosarcoma

The core protein of the large hyaline cartilage proteoglycan, aggrecan, is composed of six distinct domains: globular 1 (G1), interglobular, globular 2 (G2), keratan sulfate attachment, chondroitin sulfate (CS) attachment, and globular 3 (G3). Monoclonal antibodies that recognize epitopes in these domains were raised against Swarm rat chondrosarcoma aggrecan that was either denatured through reduction and alkylation or partially deglycosylated through chondroitinase ABC digestion or alkali elimination, the latter with or without sulfite addition. Monoclonal antibodies were further characterized for reactivity to purified aggrecan substructures including rat chondrosarcoma G1 and CS attachment domains, a recombinant rat chondrosarcoma G3 domain fusion protein, bovine articular cartilage G2 domain, and rat chondrosarcoma link protein (LP). Biochemical characterization of the specificities of these monoclonal antibodies indicated that one (1C6) recognized an epitope shared by both the G1 and the G2 domains; one (5C4) recognized an epitope shared by both LP and the G1 domain; one (7D1) recognized an epitope shared by both the G1 and the CS attachment domains; two (14A1 and 15B2) recognized epitopes in the CS attachment domain; one (14B4) recognized an epitope in the G3 domain; and one (13D1) recognized a ubiquitous epitope shared by the G1, G2, G3, and CS attachment domains of aggrecan and also LP. Collectively the specificities of these antibodies confirm the occurrence of multiple repeated epitopes (both carbohydrate and protein in nature) throughout the different domain structures of aggrecan. These antibodies have been proven to be useful for identifying aggrecan-like molecules in several connective tissues other than cartilage.

Antigenic properties of keratan sulfate: influence of antigen structure, monoclonal antibodies, and antibody valency

The influence of (a) antigen structure, (b) type of monoclonal antibody, and (c) antibody bivalency on the immunochemical detection and quantification of keratan sulfate (KS) from aggrecan has been studied. Apparent KS epitope levels were determined by immunoglobulin G (IgG)-enzyme-linked immunosorbent assay (ELISA) in preparations of human aggrecan and in a defined series of lower molecular weight proteoglycan preparations generated by proteolytic and alkali treatment of aggrecan. Gel filtration chromatography showed KS epitope to be preferentially detected in the higher molecular weight fragments of the preparations. In single KS chains the epitope was detected in the chains of higher M(r). The ability of the proteoglycan to inhibit in the IgG-ELISA decreased with a reduction in proteoglycan fragment size, ranging between 6- and 260-fold, depending on the antibody used. This was considered to be a cooperative binding effect. With most antibodies, the sensitivity of the IgG-ELISA (represented by the steepness of the inhibition slope) was also reduced with smaller inhibitor sizes. The lowest limit of detectability (the amount of KS required to generate 20% inhibition) varied by up to 60-fold depending on the antibody used. The use of monovalent Fab fragments instead of the whole IgG anti-KS antibody in the ELISA showed that the bivalency of the antibody also affected the quantitation of the assay. In the Fab-ELISA the assay was found to have an increased detectability (by 9.5-fold with aggrecan as the inhibitor), and the proteoglycan fragments and aggrecan all generated parallel inhibition curves. Although the Fab-ELISA was somewhat influenced by the structural presentation of the KS, this was not apparent for small fragments and single chains. Thus the effects of cooperative binding and antibody valency could be overcome and quantitative data could be obtained for all samples, using papain-digested samples and the Fab-ELISA. Application of this assay to analysis of body fluids showed the KS-containing fragments in synovial fluid, serum, and urine were of different sizes and could be quantified.

Cell surface phosphatidylinositol-anchored heparan sulfate proteoglycan initiates mouse melanoma cell adhesion to a fibronectin-derived, heparin-binding synthetic peptide

Cell surface heparan sulfate proteoglycan (HSPG) from metastatic mouse melanoma cells initiates cell adhesion to the synthetic peptide FN-C/H II, a heparin-binding peptide from the 33-kD A chain-derived fragment of fibronectin. Mouse melanoma cell adhesion to FN-C/H II was sensitive to soluble heparin and pretreatment of mouse melanoma cells with heparitinase. In contrast, cell adhesion to the fibronectin synthetic peptide CS1 is mediated through an alpha 4 beta 1 integrin and was resistant to heparin or heparitinase treatment. Mouse melanoma cell HSPG was metabolically labeled with [35S]sulfate and extracted with detergent. After HPLC-DEAE purification, 35S-HSPG eluted from a dissociative CL-4B column with a Kav approximately 0.45, while 35S-heparan sulfate (HS) chains eluted with a Kav approximately 0.62. The HSPG contained a major 63-kD core protein after heparitinase digestion. Polyclonal antibodies generated against HSPG purified from mouse melanoma cells grown in vivo also identified a 63-kD core protein. This HSPG is an integral plasma membrane component by virtue of its binding to Octyl Sepharose affinity columns and that anti-HSPG antibody staining exhibited a cell surface localization. The HSPG is anchored to the cell surface through phosphatidylinositol (PI) linkages, as evidenced in part by the ability of PI-specific phospholipase C to eliminate binding of the detergent-extracted HSPG to Octyl Sepharose. Furthermore, the mouse melanoma HSPG core protein could be metabolically labeled with 3H-ethanolamine. The involvement of mouse melanoma cell surface HSPG in cell adhesion to fibronectin was also demonstrated by the ability of anti-HSPG antibodies and anti-HSPG IgG Fab monomers to inhibit mouse melanoma cell adhesion to FN-C/H II. 35S-HSPG and 35S-HS bind to FN-C/H II affinity columns and require 0.25 M NaCl for elution. However, heparitinase-treated 125I-labeled HSPG failed to bind FN-C/H II, suggesting that HS, and not HSPG core protein, binds FN-C/H II. These data support the hypothesis that a phosphatidylinositol-anchored HSPG on mouse melanoma cells (MPIHP-63) initiates recognition to FN-C/H II, and implicate PI-associated signal transduction pathways in mediating melanoma cell adhesion to this defined ligand.

Modulation of glomerular proteoglycans by insulin-like growth factor-1

Effect of insulin-like growth factor-1 (IGF) on the synthesis of glomerular proteoglycans (PGs) in an ex vivo recirculating organ perfusion system was investigated. Kidneys were perfused with a medium (approximately 80 ml) containing [35S]-sulfate (250 microCi/ml) and IGF (62.5 to 625 ng/ml). After radiolabeling, a small cortical piece was saved for tissue autoradiography, and the remaining kidney and the perfusion medium were utilized for biochemical studies. The glomeruli were isolated; their PGs extracted and characterized. A two- to threefold increase of the total radioactivities in tissue and media fractions was observed with the exposure to IGF. By Sepharose CL-6B chromatography, the tissue PGs eluted as two peaks (A and B) with Kav = 0.24 and 0.48, and the majority of the radioactivity was confined to peak A. This peak contained intact PGs while peak B included glycosaminoglycan (GAG) chains. Elution profiles of the glomerular PGs were similar in the control and IGF groups. However, there was a disproportionate increase of chondroitin/dermatan sulfate in the IGF group. The media fractions also had two peaks, and most of the radioactivity was associated with peak B containing GAG chains. A remarkable accentuation of peak B along with significant increase in the chondroitin/dermatan sulfate were observed in the IGF group. By DEAE-Sephacel chromatography, the PGs/GAGs of IGF group eluted at a relatively lower salt concentration as compared to the control. Autoradiography revealed a relatively high concentration of radioactivity over the mesangium as compared to the other cell types of the glomerulus. [35S]-methionine studies revealed a generalized increase of protein synthesis in the IGF group, but comparatively much less than that of PGs/GAGs. These results indicate that IGF enhances the biosynthesis of PGs/GAGs by various cell types of the renal glomerulus, especially that of the mesangial cell, as reflected by the selective increase of chondroitin/dermatan sulfate.

Effect of puromycin on metanephric differentiation: morphological, autoradiographic and biochemical studies

Effect of aminonucleoside of puromycin (PAN) on metanephric development and proteoglycans (PGs) was investigated. Murine metanephric tissues, obtained on the thirteenth day of gestation, were exposed to PAN in a culture medium for one to seven days and processed for morphological, histochemical and immunofluorescent studies. For tissue autoradiographic and biochemical studies, kidneys were labelled with a precursor product of PGs, that is, [35S]-sulfate. A generalized decrease in the glomerular population along with swelling and deformation in the ureteric bud branches was observed. These changes were accompanied with a diminution in the total incorporated radioactivity and a reduction in the autoradiographic grains, especially over the tips of ureteric bud branches. Sepharose CL-4B chromatography revealed a major high molecular weight PG (Mr greater than 2.5 x 10(6], and a relative increase in the chondroitinase-ABC sensitive PGs. The media PGs were of relatively smaller size. Immunoprecipitation experiments with [35S]-methionine-labeled tissues and immunofluorescent studies revealed a significant decrease of PGs in metanephric tissues, while type IV collagen and laminin were relatively unaffected. Significant glomerular changes included failure in differentiation of the visceral epithelial foot processes, formation of villi and in maturation of glomerular basement membrane. The latter was seen as fragments of extracellular matrices interspersed among undifferentiated podocytes and had reduced staining with ruthenium red--a dye marker for the PGs. This deficiency of PGs was confirmed by electron microscopic autoradiography, where a reduction in the number of silver grains was observed. The fact that the PAN-induced cellular and extracellular alterations were associated with perturbances in biosynthesis of PGs, suggests that the morphogenetic regulators, that is, PGs play a vital role in various differentiation processes involved during metanephric development.

Purification and characterization of iduronic acid-rich and glucuronic acid-rich proteoglycans implicated in human post-burn keloid scar

Small proteoglycans (PGs), extracted from human keloid scar tissue with 4M guanidinium chloride and fractionated by DEAE-cellulose chromatography, were separated by ethanol precipitation into one L-iduronic acid-rich and one D-glucuronic acid-rich fraction. The size of the L-iduronic acid-rich PG was 102 kDa with a 27 kDa glycosaminoglycan chain, that of the D-glucuronic acid-rich PG was 90 kDa with a 26 kDa glycosaminoglycan chain, and the protein core of both PGs was 14.5 kDa. The two PGs carried sulfate groups mostly attached at C-4 of the 2-amino-2-deoxy-D-galactose units. The N-terminal amino acid sequence of both was similar to human bone PGII (decorin), normal and hypertrophic scar, and human dermal tissue PG.

Partial characterization of proteoglycans synthesized by human glomerular epithelial cells in culture

Confluent adult and fetal human glomerular epithelial cells were incubated for 24 h in the presence of [3H]-amino acids and [35S]sulfate. Two heparan-35SO4 proteoglycans were released into the culture medium. These 35S-labeled proteoglycans eluted as a single peak from anion exchange chromatographic columns, but were separable by gel filtration on Sepharose CL-6B columns. The larger heparan-35SO4 proteoglycan eluted with the column void volume and at a Kav of 0.26 from Sepharose CL-4B columns. The most abundant medium heparan-35SO4 proteoglycan was a high buoyant density proteoglycan similar in hydrodynamic size (Sepharose CL-6B Kav 0.23) to those previously described in glomerular basement membranes and isolated glomeruli. Heparan-35SO4 chains from both proteoglycans were 36 kDa. A smaller proportion of Sepharose CL-6B excluded dermatan-35SO4 proteoglycan was also synthesized by these cells. The predominant protein cores of both medium heparan-35SO4 proteoglycans were approximately 230 and 180 kDa. A hybrid chondroitin/dermatan-heparan-35SO4 proteoglycan with an 80-kDa protein core copurified with the smaller medium heparan-35SO4 proteoglycan. This 35S-labeled proteoglycan appeared as a diffuse, chondroitinase ABC sensitive 155-kDa fluorographic band in sodium dodecyl sulfate-polyacrylamide gels after the Sepharose CL-6B Kav 0.23 35S-labeled proteoglycan fraction was digested with heparitinase. The heparitinase generated heparan sulfate proteoglycan protein cores and the 155-kDa hybrid proteoglycan fragment had molecular weights similar to those previously identified in rat glomerular basement membrane and glomeruli using antibodies against a basement membrane tumor proteoglycan precursor (Klein et al. J. Cell Biol. 106, 963-970, 1988). Thus, human glomerular epithelial cells in culture are capable of synthesizing, processing, and releasing heparan sulfate proteoglycans which are similar to those synthesized in vivo and found in the glomerular basement membrane. These proteoglycans may belong to a family of related basement membrane proteoglycans.

Chondroitin sulfate proteoglycan synthesis and reutilization of beta-D-xyloside-initiated chondroitin/dermatan sulfate glycosaminoglycans in fetal kidney branching morphogenesis

Branching morphogenesis and chondroitin sulfate proteoglycan synthesis by explanted fetal mouse kidneys were previously shown to be inhibited by p-nitrophenyl beta-D-xylopyranoside (beta-D-xyloside) while glomerular development and heparan sulfate proteoglycan synthesis were unaffected. The metabolic fate of fetal kidney explant proteoglycans was investigated to determine whether or not recovery of proteoglycan synthesis and morphogenesis occur after exposure to beta-D-xyloside. Chondroitin sulfate proteoglycan synthesis resumed within 4 hr of removal of beta-D-xyloside and was enhanced once beta-D-xyloside-initiated chondroitin/dermatan-35SO4 glycosaminoglycans (GAGs) were released from the tissue. Radioactivity incorporated into beta-D-xyloside-initiated chondroitin/dermatan-35SO4 GAGs during labeling in the presence of beta-D-xyloside was reutilized in the synthesis of chondroitin-35SO4 proteoglycan during a 24-hr chase in nonradioactive medium without beta-D-xyloside. Further, highly purified beta-D-xyloside-initiated chondroitin/dermatan-35SO4 GAGs were taken up by kidneys more avidly than was free [35S]sulfate. These 35S-GAGs were degraded and reutilized in the synthesis of chondroitin-35SO4 proteoglycan. Ureteric bud branching resumed 48 hr after beta-D-xyloside was removed from the incubation medium. These findings support the idea that both chondroitin sulfate proteoglycan synthesis and proteoglycan processing may be involved in branching morphogenesis.

Structural characterization of chick embryonic skeletal muscle chondroitin sulfate proteoglycan

Embryonic chick skeletal muscle has been shown to synthesize a distinct proteoglycan of large size with relatively large, highly 6-sulfated chondroitin sulfate glycosaminoglycans. Further analysis of these proteoglycans indicates that tryptic digestion gives rise to fragments with an average of two chondroitin sulfate chains per peptide. The skeletal muscle chondroitin sulfate proteoglycan also contains oligosaccharides whose characteristics suggest the presence of both O-linked and N-linked oligosaccharides. These characteristics include the average hydrodynamic size of the oligosaccharides as well as their localization. Approximately 10% of the putative O-linked oligosaccharides reside on the same tryptic fragments which contain the chondroitin sulfate chains, while the presumptive N-linked oligosaccharides appear to be present at sites distant from the chondroitin sulfate. Further support for this identification comes from radioisotopic labeling with [3H]mannose, which is incorporated exclusively into the putative N-linked oligosaccharides. Some of the O-linked oligosaccharides which are not in close apposition to the chondroitin sulfate seem to occur in clusters. The skeletal muscle chondroitin sulfate proteoglycan has the ability to interact in a link protein-stabilized fashion with hyaluronic acid. This ability as well as the estimated number of chondroitin sulfate chains per cluster and the estimated number of oligosaccharides per chondroitin sulfate chain have implications about the structure of the core protein of the skeletal muscle proteoglycan. The information presented is used to construct a model of these molecules; with this detailed model, attention can now be directed at other aspects of the skeletal muscle chondroitin sulfate proteoglycan, such as its role in myogenesis.

Decreased de novo synthesis of proteoglycans in drug-induced renal cystic disease

Cellular and extracellular (tubular basement membrane, TBM) alterations in the proteoglycans (PGs) of the rat renal tubules in diphenylthiazole-induced cystic disease were investigated. The PGs of normal and cystic kidneys were labeled with [35S]sulfate in an organ-perfusion system. Extracted cellular and TBM PGs were characterized by Sepharose CL-6B chromatography before or after treatment with heparitinase (degrades heparan sulfate) or chondroitinase ABC (degrades chondroitin sulfate). Total radioactivities in cellular, TBM, and medium fractions of cystic kidneys were reduced by factors of 9, 7, and 3, respectively. The PGs obtained from cystic and normal kidneys had similar profiles, namely, two peaks of radioactivity with Kav values of 0.26 (Mr = 130,000-150,000) and 0.40 (Mr = 50,000-55,000). The peaks had variable proportions of radioactivity for cellular and TBM fractions. Besides heparan sulfate, an additional 15-20% of chondroitin sulfate was synthesized in all three fractions obtained from cystic kidneys. The PGs synthesized by cystic kidneys had lower charge-density characteristics as compared to controls by DEAE-Sephacel chromatography. The medium fractions contained mostly glycosaminoglycan chains (Kav = 0.47, Mr = 24,000-26,000) of heparan sulfate. Autoradiograms of tissue samples revealed approximately 50% and approximately 60% decreases of grain densities over the cellular and TBM compartments, respectively. This decrease in de novo PG synthesis may have some relationship in the pathogenesis of polycystic kidney disease.

Role of proteoglycans in renal development

The role of proteoglycans (PGs) in morphogenesis was investigated. Fetal kidneys were obtained from 13-day-old mouse embryos and maintained for 7 days in culture. The biosynthesis of PGs was perturbed by addition of p-nitrophenyl-beta-D-xylopyranoside in the culture medium. The kidneys were processed for morphological and biochemical studies. The morphological studies included staining of tissues with anti-basement membrane antibodies and ruthenium red. [35S]sulfate was used as the precursor product for biosynthetic and autoradiographic studies. The kidneys treated with xyloside had loose mesenchyme, inhibition of ureteric bud branching, diminution in the population of developing nephron elements, decreased immunofluorescence with anti-proteoglycan antibodies and staining with ruthenium red, and a reduced [35S]sulfate incorporation into poorly organized extracellular matrices. The biochemical studies included characterization of PGs/glycosaminoglycans (GAGs) by Sepharose CL-4B, -6B, and DEAE-Sephacel chromatographies and cellulose acetate electrophoresis. Under the influence of xyloside, the total radioactivities decreased 2 to 4-fold in tissues and increased 18 to 42-fold in media fractions. A reduction in the size of macromolecular form of PGs, i.e., from MW approximately 2.5 X 10(6) to approximately 2.5 X 10(4), was noted. The PGs/GAGs synthesized were mainly made up of heparan sulfate and small amounts of chondroitin sulfate. They eluted at a lower salt concentration as compared to the controls. A similar diminution in the size of media PGs, i.e., from MW approximately 1.8 X 10(5) to approximately 2.8 X 10(4), was observed. Additional studies with [3H]xyloside indicated that the chains initiated on xyloside residues were similar in size and composition to GAG-chains. These findings indicate that a perturbance in the biosynthesis of PGs/GAGs leads to abnormalities in renal organogenesis.

Isolation and partial characterization of dermatan sulfate proteoglycans from human post-burn scar tissues

Dermatan sulfate (DS) proteoglycans (PGs) were extracted from human post-burn scar (Sc) tissues with 4M guanidinium chloride and isolated from the extracts by DEAE-cellulose chromatography and by differential ethanol precipitation. The DS.PGs were further purified by Sepharose CL-6B column chromatography. The average molecular weight (Mr) of hypertrophic scar (HSc) tissue DS.PGs was 39,000 based on sedimentation equilibrium measurements. Alkaline borohydride treatment of DS.PGs liberated glycosaminoglycan (GAG) chains and the presence of xylitol indicated that these chains were attached to protein core by xylosyl residues. The average Mr of the DS.GAG chain from HSc and normal scar (NSc) samples were 23,500 and 20,000 respectively. After digestion of the HSc and NSc, DS.PGs with chondroitinase ABC in the presence of proteinase inhibitors, two peptide components with Mr values of 21,500 and 17,000 were detected by SDS-polyacrylamide gel electrophoresis using reducing conditions. Analysis of the protein core fractions derived from NSc and HSc DS.PGs by Sepharose CL-6B column chromatography showed the presence of a single NH2-terminal amino acid (aspartic acid) and also that the fractions with different KAV values had an identical NH2-terminal sequence (A1-A5). The A1-A23 sequence of NSc DS.PG (major fraction, C): NH2Asp-Glu-Ala-O-Gly-Ile-Gly-Pro-Glu-Val-Pro-Asp-Asp-Arg-Asp-Phe-G lu-Pro- Ser-Leu-Gly-Pro-Val was the same as reported for a DS.PG isolated from human fetal membrane (HFM) tissue (Brennan et al., 1984). ELISA inhibition assay using monoclonal antibodies raised in rabbit against the NH2-terminal peptide (containing 15 amino acids) of human fetal membrane tissue were found to cross-react with HSc and NSc DS.PGs. Monoclonal antibodies to bovine skin DS.PGs protein core (Pearson et al., 1983) did not show any cross-reactivity with scar DS.PGs. These results show that the scar DS.PGs described here are different from normal bovine skin DS.PGs in the size and type of the protein core, and that in all the samples, the peptide components have the same NH2-terminal amino acid sequence.

The detection of substructures within proteoglycan molecules. Electron-microscopic immuno-localization with the use of Protein A-gold

Proteoglycan monomers from pig laryngeal cartilage were examined by electron microscopy with benzyldimethylalkylammonium chloride as the spreading agent. The proteoglycans appeared as extended molecules with a beaded structure, representing the chondroitin sulphate chains collapsed around the protein core. Often a fine filamentous tail was present at one end. Substructures within proteoglycan molecules were localized by incubation with specific antibodies followed by Protein A-gold (diameter 4 nm). After the use of an anti-(binding region) serum the Protein A-gold (typically one to three particles) bound at the extreme end of the filamentous region. A small proportion of the labelled molecules (10-15%) showed the presence of gold particles at both ends. A monoclonal antibody specific for a keratan sulphate epitope (MZ15) localized a keratan sulphate-rich region at one end of the proteoglycan, but gold particles were not observed along the extended part of the protein core. This distribution was not changed by prior chondroitin AC lyase digestion of the proteoglycan. Localization with a different monoclonal antibody to keratan sulphate (5-D-4) caused a change in the spreading behaviour of a proportion (approx. 20%) of the proteoglycan monomers that lost their beaded structure and appeared with the chondroitin sulphate chains projecting from the protein core. In these molecules the Protein A-gold localized antibody (5-D-4) along the length of the protein core whereas in those molecules with a beaded appearance it labelled only at one end. Labelling with either of the monoclonal antibodies was specific, as it was inhibited by exogenously added keratan sulphate. The differential localization achieved may reflect structural differences within the proteoglycan population involving keratan sulphate and the protein core to which it is attached. The results showed that by this technique substructures within proteoglycan molecules can be identified by Protein A-gold labelling after the use of specific monoclonal or polyclonal antibodies.

Proteoglycan metabolism associated with mouse metanephric development: morphologic and biochemical effects of beta-D-xyloside

Morphology and de novo incorporation of [35S]sulfate into proteoglycans were studied in fetal mouse kidneys at the onset of organogenesis. Branching morphogenesis and nephron development in organ culture and in vivo were associated with de novo synthesis of chondroitin-SO4 and heparan-SO4 proteoglycans. The role of proteoglycan metabolism in metanephrogenesis was then studied by analysis of the effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on renal development and proteoglycan metabolism. Incubation of fetal kidneys in beta-D-xyloside at concentrations of 1.0 and 0.5 mM, but not at 0.1 mM, caused inhibition of ureteric branching and markedly diminished synthesis of a large Mr 2.0 X 10(6) Da chondroitin-SO4 proteoglycan. Incorporation of [35S]sulfate was stimulated at all beta-D-xyloside concentrations, reflecting synthesis of xyloside initiated dermatan-35SO4 chains. In contrast to dramatic effects on chondroitin-SO4 synthesis and ureteric branching, beta-D-xyloside had no effect on heparan-SO4 synthesis or on development of the glomerulus and glomerular basement membrane. We thus characterize the proteoglycans synthesized early in the course of renal organogenesis and describe observations which suggest an association between metabolism of chondroitin-SO4 proteoglycan and development of the ureter.

Proteoglycans synthesized by embryonic chicken retina in culture: composition and compartmentalization

Characteristics of the chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs) and heparan sulfate proteoglycans (HSPGs) from retinas of 14-day chicken embryos were examined following specific lyase digestion of the HSPG and CS/DSPG glycosaminoglycans, respectively. On the basis of gel exclusion chromatography the prevalent CS/DSPGs in the tissue were above Mr 400 X 10(3) with two or three glycosaminoglycan chains of Mr 60-70 X 10(3). The HSPGs existed in two distinct populations in the tissue. Those in the dominant population appeared to be in the range of Mr 250-300 X 10(3) with 9 to 12 glycosaminoglycan chains of Mr 15-25 X 10(3). The other population consisted of free heparan sulfate chains of Mr 15-25 X 10(3). The HSPGs in the medium tended to be intermediate in size. To examine the distribution of proteoglycans, tissues were sequentially homogenized and extracted in saline and reextracted with 4 M guanidine HCl (GdnHCl) and Triton X-100 (TX), or they were washed in heparin solution and dissociated to single cells with trypsin before sequential extraction in saline and GdnHCl with TX. Through comparison of the results of these two extraction methods, CS/DSPGs were found to be almost entirely within the medium or matrix or loosely associated with the cell surface, and most HSPGs were associated with either the basal lamina or the plasma membrane. The single heparan sulfate glycosaminoglycan chains appeared to be intracellular degradation products. These results support reports that CS/DSPGs may be present in the retina interphotoreceptor matrix and that HSPGs may be present in regions of synaptogenesis, associated with cell membranes.

The partial amino acid sequence of bovine cartilage proteoglycan, deduced from a cDNA clone, contains numerous Ser-Gly sequences arranged in homologous repeats

We have determined the sequence of a partial cDNA clone encoding the C-terminal region of bovine cartilage aggregating proteoglycan core protein. The deduced amino acid sequence contains a cysteine-rich region which is homologous with chicken hepatic lectin. This lectin-homologous region has previously been identified in rat and chicken cartilage proteoglycan. The bovine sequence presented here is highly homologous with the rat and chicken amino acid sequences in this apparently globular region. A region containing clusters of Ser-Gly sequences is located N-terminal to the lectin homology domain. These Ser-Gly-rich segments are arranged in tandemly repeated, approx. 100-residue-long, homology domains. Each homology domain consists of an approx. 75-residue-long Ser-Gly-rich region separated by an approx. 25-residue-long segment lacking Ser-Gly dipeptides. These dipeptides are arranged in 10-residue-long segments in the 100-residue-long homology domains. The shorter homologous segments are tandemly repeated some six times in each 100-residue-long homology domain. Serine residues in these repeats are potential attachment sites for chondroitin sulphate chains.

Xylosylated-proteoglycan-induced Golgi alterations

The effect of p-nitrophenyl beta-D-xylopyranoside on the Golgi apparatus and proteoglycans (PG) of the renal glomerulus was investigated in an isolated kidney organ perfusion system and monitored by utilizing [35S]sulfate as the PG precursor. By electron microscopy, a selective intracytoplasmic vesiculization of Golgi apparatus of visceral epithelium was observed in the beta-xyloside-treated kidneys. Electron microscopic autoradiography revealed most grains localized to the intracytoplasmic Golgi-derived vesicles, while very few grains were associated with the extracellular matrix membranes. Biochemically, a 2.3-fold increase in cellular matrix and a reduction by a factor of 1.7 in extracellular matrix of [35S]sulfate incorporation was observed. Besides a larger macromolecular form (Kavg = 0.25; Mr = 130,000), lower molecular weight PGs were recovered in the cellular (Kavg = 0.46, Mr = 30,000) and matrical (Kavg = 0.42, Mr = 45,000) compartments after xyloside treatment. The xyloside treatment increased the incorporated radioactivity, mostly included in free glycosaminoglycans and small PGs, in the media fraction by 3.8-fold. These data indicate that xyloside induces a dramatic imbalance in the de novo-synthesized PGs of cellular and extracellular compartments and that cellular accumulation of xylosylated (sulfated) PGs selectively alters the Golgi apparatus of the glomerular epithelial cell, the cell that actively synthesizes PGs.

Stereological studies on the epiphyseal growth cartilage and characterization of costal cartilage proteoglycans in the achondroplastic (cn/cn) mouse

The achondroplastic mouse is a dwarf mouse in which the endochondral growth of the skeleton is disturbed. The main morphological characteristic of the affected growth cartilage is an underdeveloped hypertrophic zone. The pattern of matrix mineralization seems to be unaffected, even in areas where hypertrophic chondrocytes are completely absent. The present stereological results indicate a disturbance of the cn/cn cartilage already in the proliferative zone. At the electron microscopical level a clearly abnormal spatial distribution of matrix vesicles was observed in the affected growth cartilage. The vesicle concentration of the cn/cn cartilage was increased, but the mineralizing cartilage showed a decrease of vesicles similar to that in the normal tissue. Parallel biochemical characterization of the proteoglycans and glycosaminoglycans of the cn/cn costal cartilage revealed normal conditions, also in the growth region, which was sampled as a separate tissue fraction. Thus the biochemical results provide no evidence of disturbed glycosaminoglycan metabolism.

Cloning and sequence analysis of a partial cDNA for chicken cartilage proteoglycan core protein

A chicken embryo sternal cartilage cDNA library, created in the plasmid expression vector pUC9, was screened for sequences coding for immunologically detectable core protein of the large, major proteoglycan of cartilage. A 1229-base-pair cDNA clone was isolated that contained only one extended open reading frame, which had sequences coding for a polypeptide of 379 amino acid residues. These deduced sequences corresponded to those anticipated from current models of proteoglycan structure; a deduced sequence encompassing 21 amino acids was almost identical to a known sequence of bovine nasal cartilage proteoglycan. Significant homology was found between the deduced amino acid sequence of the proteoglycan and two regions of a chicken hepatic lectin. Immunoprecipitation of the products of cell-free translation yielded a component of about 340 kDa, and transfer blot hybridization of sternal cartilage RNA showed a single mRNA of about 8.1 kilobases. Hybridizable mRNA sequences were readily detectable by dot-blot analyses of the cytoplasm of cartilaginous tissues of the chicken embryo, whereas similar analyses of prechondrogenic limb mesenchymal cells did not demonstrate such hybridizable mRNA signals.

Four classes of cell-associated proteoglycans in suspension cultures of articular-cartilage chondrocytes

The characteristics of cell-associated proteoglycans were studied and compared with those from the medium in suspension cultures of calf articular-cartilage chondrocytes. By including hyaluronic acid or proteoglycan in the medium during [35S]sulphate labelling the proportion of cell-surface-associated proteoglycans could be decreased from 34% to about 15% of all incorporated label. A pulse-chase experiment indicated that this decrease was probably due to blocking of the reassociation with the cells of proteoglycans exported to the medium. Three peaks of [35S]sulphate-labelled proteoglycans from cell extracts and two from the medium were isolated by gel chromatography on Sephacryl S-500. These were characterized by agarose/polyacrylamide-gel electrophoresis, by SDS/polyacrylamide-gel electrophoresis of core proteins, by glycosaminoglycan composition and chain size as well as by distribution of glycosaminoglycans in proteolytic fragments. The results showed that associated with the cells were (a) large proteoglycans, typical for cartilage, apparently bound to hyaluronic acid at the cell surface, (b) an intermediate-size proteoglycan with chondroitin sulphate side chains (this proteoglycan, which had a large core protein, was only found associated with the cells and is apparently not related to the large proteoglycans), (c) a small proteoglycan with dermatan sulphate side chains with a low degree of epimerization, and (d) a somewhat smaller proteoglycan containing heparan sulphate side chains. The medium contained a large aggregating proteoglycan of similar nature to the large cell-associated proteoglycan and small proteoglycans with dermatan sulphate side chains with a higher degree of epimerization than those of the cells, i.e. containing some 20% iduronic acid.

Undersulfated chondroitin sulfate in cartilage from a miniature poodle with spondyloepiphyseal dysplasia

In order to determine if either the proteoglycans or collagen in the cartilagenous epiphyses of a Miniature Poodle with spondyloepiphyseal dysplasia were abnormal, the cartilage was dissociatively extracted in 4 M guanidine HCl in the presence of protease inhibitors and subjected to isopycnic cesium chloride dissociative density gradient ultracentrifugation. Dissociative extraction solubilized 97% of the uronic acid and 88% of the protein. Uronic acid distributed anomalously in the density gradient in that about 1/3 was recovered in each of the D1 (1.58 g/ml), D2 (1.49 g/ml) and D3 (1.44 g/ml) fractions. Proteoglycans in the D1, D2 and D3 fractions also eluted from Sepharose CL-2B columns in a manner indicative of monomers of a smaller apparent hydrodynamic size than those from normal canine growth plate or articular cartilage. D1, D2 and D3 monomers subjected to the sodium borohydride reaction followed by chromatography on a Sepharose CL-6B column yielded glycosaminoglycan chain molecular weights of 10,200 (D1), 7600 (D2) and 6200 (D3). High pressure liquid chromatography on a Whatman Partisil 10PAC column of the chondroitinase AC II digests of D1, D2 and D3 fractions revealed that 60% of the D1, 81% of the D2 and 88% of the D3 unsaturated disaccharides eluted in the delta DiOS-delta DiHA position. Subsequent HPLC of the unsaturated disaccharides on the Hypersil APS column resulted in the recovery of 97% of the nonsulfated unsaturated disaccharides in the delta DiOS position. Associative extraction in 0.5 M guanidine followed by associative gradient ultracentrifugation resulted in the recovery of 27% of the uronic acid in the aA1 and 47% in the aA2 fractions. Two dimensional SDS gel electrophoresis of the CNBr peptides of the collagen isolated by pepsin digestion and 0.9 M NaCl precipitation revealed type II collagen. This study has demonstrated that spondyloepiphyseal dysplasia in a Miniature Poodle is characterized by cartilage containing undersulfated chondroitin sulfate proteoglycan.

The effects of trypsin treatment on proteoglycan biosynthesis by bovine articular cartilage

The effects of mild or severe trypsin treatment of bovine articular-cartilage slices in tissue culture were studied by monitoring the incorporation of [35S]sulphate into proteoglycans. Moderate trypsin treatment caused a subsequent marked inhibition of proteoglycan biosynthesis, which was reversible with time. Analysis on Sepharose CL-2B of the proteoglycan species synthesized showed that, directly after trypsin treatment, there was a 30% increase in the synthesis of the low-Mr proteoglycan (Kav. 0.71), and the total decrease in proteoglycan biosynthesis was reflected in a decrease in the synthesis of the high-Mr proteoglycan species (Kav. 0.31). The small proteoglycan was partially characterized and shown to be a true biosynthetic product and not a breakdown product. Trypsin treatment (20 micrograms/ml per 100 mg of tissue) of cartilage slices also resulted in an increase in the glycosaminoglycan chain size of the large proteoglycan, but not of the small proteoglycan.

Proteoglycans and glycosaminoglycans in cartilage from the brachymorphic (bm/bm) mouse

The brachymorphic (bm/bm) mouse is a disproportionate dwarf with a disturbance of the endochondral growth of the skeleton. Rib cartilage from 25-day-old affected animals and their normal siblings was analyzed for its contents and composition of proteoglycans. In addition to the previously reported undersulfation of chondroitin sulfate, it was demonstrated that one of the two types of aggregating proteoglycan and possibly the small ones are decreased in bm/bm costal cartilage, both in the growth region and in the remaining part. The molecular defect of the bm/bm condition is known to affect the synthesis of 3-phosphoadenosine 5-phosphosulfate (Sugahara and Schwartz, Proc. Natl. Acad. Sci. USA 76: 6615-6618, 1979). The above finding therefore suggests the existence of feedback mechanisms for the regulation of proteoglycan synthesis, whereby the undersulfation of glycosaminoglycans would result in decreased synthesis or increased turnover of certain proteoglycan subpopulations. Analysis of the glycosaminoglycan side chains indicated that mouse rib cartilage contains small amounts of keratan sulfate of extremely small size. The affected and control tissues, however, seemed to contain equal amounts of both glucosamine and galactosamine.

Chondrocyte-mediated depletion of articular cartilage proteoglycans in vitro

The degradation of proteoglycan was examined in cultured slices of pig articular cartilage. Pig leucocyte catabolin (10 ng/ml) was used to stimulate the chondrocytes and induce a 4-fold increase in the rate of proteoglycan loss from the matrix for 4 days. Material in the medium of both control and depleted cultures was mostly a degradation product of the aggregating proteoglycan. It was recovered as a very large molecule slightly smaller than the monomers extracted with 4M-guanidinium chloride and lacked a functional hyaluronate binding region. The size and charge were consistent with a very limited cleavage or conformational change of the core protein near the hyaluronate binding region releasing the C-terminal portion of the molecule intact from the aggregate. The 'clipped' monomer diffuses very rapidly through the matrix into the medium. The amount of proteoglycan extracted with 4M-guanidinium chloride decreased during culture from both the controls and depleted cartilage, and the average size of the molecules initially remained the same. However, the proportion of molecules with a smaller average size increased with time and was predominant in explants that had lost more than 70% of their proteoglycan. All of this material was able to form aggregates when mixed with hyaluronate, and glycosaminoglycans were the same size and charge as normal, indicating either that the core protein had been cleaved in many places or that larger molecules were preferentially released. A large proportion of the easily extracted and non-extractable proteoglycan remained in the partially depleted cartilage and the molecules were the same size and charge as those found in the controls. There was no evidence of detectable glycosidase activity and only very limited sulphatase activity. A similar rate of breakdown and final distribution pattern was found for newly synthesized proteoglycan. Increased amounts of latent neutral metalloproteinases and acid proteinase activities were present in the medium of depleted cartilage. These were not thought to be involved in the breakdown of proteoglycan. Increased release of proteoglycan ceased within 24h of removal of the catabolin, indicating that the effect was reversible and persisted only while the stimulus was present.

Proteoglycans and glycosaminoglycans of normal and strontium rachitic epiphyseal cartilage

An analytical protocol for the analysis of proteoglycans and proteins extracted from small sections of cartilage has been applied to the upper and lower parts of the epiphyseal growth plate of normal rats and rats with strontium-induced rickets. Only one polydisperse proteoglycan population was found in each of the four tissue portions. In strontium-induced rachitic animals the aggregability of proteoglycan monomers with hyaluronate was considerably increased in the lower part of the growth plate. The proteoglycans in the upper portion of the epiphysis contained somewhat less of chondroitin sulfate and keratan sulfate both in normal and strontium-induced rachitic rats. The chondroitin sulfate chains were somewhat larger in samples from strontium-induced rachitic rats compared with controls while in all groups about 90 per cent of the galactosamine in chondroitin sulfate was sulfated at position four. The findings of an altered composition of proteoglycans in strontium-induced rickets demonstrate that strontium not only prevents the mineral growth but may also induce the chondrocytes to produce a matrix with a different macromolecular composition.

Proteoglycans and glycosaminoglycans of epiphyseal cartilage in florid and healing low phosphate, vitamin D deficiency rickets

The composition of proteoglycans and glycosaminoglycans in two portions of the rat epiphyseal growth cartilage in florid and healing low phosphate, vitamin D deficiency rickets was studied. The concentration of both chondroitin sulfate and keratan sulfate was reduced with about 25 per cent in the lower (mineralizing) part of the growth plate in healing rickets compared to the lower (hypertrophic) part in florid rickets. In all samples about 85 per cent of the chondroitin sulfate chains had a sulfate ester group in the fourth position. Both in florid and healing rickets only one main population of polydisperse proteoglycans was found. In florid rickets the capacity to form aggregates with hyaluronic acid was the same in the upper and lower parts of the growth plate. With the onset of mineralization in healing rickets, however, a substantial decrease in this aggregability was demonstrated. These results give further support to the hypothesis that proteoglycans and, especially, proteoglycan aggregates, play a role in the mineralization process.