Extraction and purification of proteoglycans from mature bovine bone

Biglycan and chondroitin sulfate play pivotal roles in bone toughness via retaining bound water in bone mineral matrix

Recent in vitro evidence shows that glycosaminoglycans (GAGs) and proteoglycans (PGs) in bone matrix may functionally be involved in the tissue-level toughness of bone. In this study, we showed the effect of biglycan (Bgn), a small leucine-rich proteoglycan enriched in extracellular matrix of bone and the associated GAG subtype, chondroitin sulfate (CS), on the toughness of bone in vivo, using wild-type (WT) and Bgn deficient mice. The amount of total GAGs and CS in the mineralized compartment of Bgn KO mouse bone matrix decreased significantly, associated with the reduction of the toughness of bone, in comparison with those of WT mice. However, such differences between WT and Bgn KO mice diminished once the bound water was removed from bone matrix. In addition, CS was identified as the major subtype in bone matrix. We then supplemented CS to both WT and Bgn KO mice to test whether supplemental GAGs could improve the tissue-level toughness of bone. After intradermal administration of CS, the toughness of WT bone was greatly improved, with the GAGs and bound water amount in the bone matrix increased, while such improvement was not observed in Bgn KO mice or with supplementation of dermatan sulfate (DS). Moreover, CS supplemented WT mice exhibited higher bone mineral density and reduced osteoclastogenesis. Interestingly, Bgn KO bone did not show such differences irrespective of the intradermal administration of CS. In summary, the results of this study suggest that Bgn and CS in bone matrix play a pivotal role in imparting the toughness to bone most likely via retaining bound water in bone matrix. Moreover, supplementation of CS improves the toughness of bone in mouse models.

Induction of osteogenic differentiation by demineralized and decellularized bovine extracellular matrix derived hydrogels associated with barium titanate

Bone tissue-derive biomaterials have become of great interest to treat diseases of the skeletal system. Biological scaffolds of demineralized and decellularized extracellular matrices (ECM) have been developed and one of these options are ECM hydrogels derived from bovine bone. Nanomaterials may be able to regulate stem cell differentiation due to their unique physical-chemical properties. The present work aimed to evaluate the osteoinductive effects of ECM hydrogels associated with barium titanate nanoparticles (BTNP) on dental pulp cells derived from exfoliated teeth. The addition of BTNP in the ECM derived hydrogel did not affect cell proliferation and the formation of bone nodules. Furthermore, it increased the expression of bone alkaline phosphatase. The results demonstrated that the nanobiocomposites were able to promote the osteogenic differentiation, even in the absence of chemical inducing factors for osteogenic differentiation. In conclusion, bovine bone ECM hydrogel combined with BTNP presented and increased expression of markers of osteogenic differentiation in the absence of chemical inducing factors.

Production of Bone Broth Powder with Spray Drying Using Three Different Carrier Agents

The aim of this study is to determine the some physicochemical (proximate composition, pH and a_w values) and reconstitution (wettability, dispersibility and solubility index (SI)) properties of spray-dried bone broth powder (BBP) along with the effects of the addition of different carrier agents. Subsequently, the powdered products were stored to determine the storage stability (pH, lipid oxidation, color, browning index) for 3 mon at –18℃. For this purpose, firstly marrow-containing bones (Os femur and Os humerus) have been boiled to get the bone broth. Three different emulsions were respectively prepared (1) 20% maltodextrin (MD) added BBP, (2) 20% whey powder isolate (WPI) added BBP and (3) 10% MD and 10% WPI added BBP and the emulsions were dried using a spray-dryer with 185℃ inlet and 95℃ outlet temperature. The proximate composition and reconstitution properties of BBP were found statistically different (p<0.05) depending on the use of different carrier agents. MD added BBP showed uniform and smooth morphology. The color, browning index, thiobarbituric acid reactive substances (TBARS) and pH values of BBP significantly changed (p<0.05) during storage. In conclusion, both the results of physicochemical and storage period analyses showed that the most suitable encapsulation material in the production of the bone broth powder is MD.

AGE-RELATED DETERIORATION OF BONE TOUGHNESS IS RELATED TO DIMINISHING AMOUNT OF MATRIX GLYCOSAMINOGLYCANS (GAGS)

Hydration status significantly affects the toughness of bone. In addition to the collagen phase, recent evidence shows that glycosaminoglycans (GAGs) of proteoglycans (PGs) in the extracellular matrix also play a pivotal role in regulating the tissue-level hydration status of bone, thereby affecting the tissue-level toughness of bone. In this study, we hypothesized that the amount of GAGs in bone matrix decreased with age and such changes would lead to reduction in bound water and subsequently result in a decrease in the tissue-level toughness of bone. To test the hypothesis, nanoscratch tests were conducted to measure the tissue-level toughness of human cadaveric bone specimens, which were procured only from male donors in three different age groups: young (26 ± 6 years old), mid-aged (52 ± 5 years old) and elderly (73 ± 5 years old), with six donors in each group. Biochemical and histochemical assays were performed to determine the amount and major subtypes of GAGs and proteoglycans in bone matrix. In addition, low-field NMR measurements were implemented to determine bound water content in bone matrix. The results demonstrated that aging resulted in a statistically significant reduction (17%) of GAGs in bone matrix. Concurrently, a significant deterioration (20%) of tissue-level toughness of bone with age was observed. Most importantly, the deteriorated tissue-level toughness of bone was associated significantly with the age-related reduction (40%) of bound water, which was partially induced by the decrease of GAGs in bone matrix. Furthermore, we identified that chondroitin sulfate (CS) was a major subtype of GAGs and the amount of CS decreased with aging in accompany with a decrease of biglycan that is a major subtype of PGs in bone. The findings of this study suggests that reduction of GAGs in bone matrix is likely one of the molecular origins for age-related deterioration of bone quality.

Coupling Effect of Water and Proteoglycans on the In Situ Toughness of Bone

Proteoglycans (PGs) are one type of noncollagenous proteins in the extracellular matrix of bone that primarily contain a core protein and glycosaminoglycans (GAGs). GAGs are highly polar and negatively charged, thus have a strong tendency to attract water molecules into the matrix. We hypothesized in this study that PGs in bone play a pivotal role in sustaining the toughness of the tissue only when water is present. To test the hypothesis, we used a novel nanoscratch test to measure the in situ toughness of human cadaveric bone treated with and without peptide-N-glycosidase F (PNGase F), an enzyme that specifically removes the N-linked oligosaccharides of GAGs from core proteins. Cortical bone specimens were prepared from the posterior aspect of mid-diaphyseal femurs of six (n = 6) male human donors between 51.5 ± 5.17 years old. Biochemical and histochemical assays were used to verify whether N-linked oligosaccharides were removed from bone matrix by PNGase F. By testing wet and dehydrated bone specimens, the coupling effect between water and PGs on the in situ toughness of bone was investigated. The two-way ANOVA analyses showed that removal of GAGs had significant effects on the in situ toughness of wet bone samples. In contrast, the removal of GAGs did not show significant effects on the toughness of dry bone. The results of this study, for the first time, suggest that GAGs play a pivotal role in the in situ toughness of bone only when water is present, and vice versa, water functions as a plasticizer in bone only when GAGs are present. © 2015 American Society for Bone and Mineral Research.

Bone protein extraction without demineralization using principles from hydroxyapatite chromatography

Historically, extraction of bone proteins has relied on the use of demineralization to better retrieve proteins from the extracellular matrix; however, demineralization can be a slow process that restricts subsequent analysis of the samples. Here, we developed a novel protein extraction method that does not use demineralization but instead uses a methodology from hydroxyapatite chromatography where high concentrations of ammonium phosphate and ammonium bicarbonate are used to extract bone proteins. We report that this method has a higher yield than those with previously published small-scale extant bone extractions, with and without demineralization. Furthermore, after digestion with trypsin and subsequent high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis, we were able to detect several extracellular matrix and vascular proteins in addition to collagen I and osteocalcin. Our new method has the potential to isolate proteins within a short period (4h) and provide information about bone proteins that may be lost during demineralization or with the use of denaturing agents.

Computational model for the analysis of cartilage and cartilage tissue constructs

We propose a new non-linear poroelastic model that is suited to the analysis of soft tissues. In this paper the model is tailored to the analysis of cartilage and the engineering design of cartilage constructs. The proposed continuum formulation of the governing equations enables the strain of the individual material components within the extracellular matrix (ECM) to be followed over time, as the individual material components are synthesized, assembled and incorporated within the ECM or lost through passive transport or degradation. The material component analysis developed here naturally captures the effect of time-dependent changes of ECM composition on the deformation and internal stress states of the ECM. For example, it is shown that increased synthesis of aggrecan by chondrocytes embedded within a decellularized cartilage matrix initially devoid of aggrecan results in osmotic expansion of the newly synthesized proteoglycan matrix and tension within the structural collagen network. Specifically, we predict that the collagen network experiences a tensile strain, with a maximum of ~2% at the fixed base of the cartilage. The analysis of an example problem demonstrates the temporal and spatial evolution of the stresses and strains in each component of a self-equilibrating composite tissue construct, and the role played by the flux of water through the tissue.

Empirical evaluation of bone extraction protocols

The application of high-resolution analytical techniques to characterize ancient bone proteins requires clean, efficient extraction to obtain high quality data. Here, we evaluated many different protocols from the literature on ostrich cortical bone and moa cortical bone to evaluate their yield and relative purity using the identification of antibody-antigen complexes on enzyme-linked immunosorbent assay and gel electrophoresis. Moa bone provided an ancient comparison for the effectiveness of bone extraction protocols tested on ostrich bone. For the immunological part of this study, we focused on collagen I, osteocalcin, and hemoglobin because collagen and osteocalcin are the most abundant proteins in the mineralized extracellular matrix and hemoglobin is common in the vasculature. Most of these procedures demineralize the bone first, and then the remaining organics are chemically extracted. We found that the use of hydrochloric acid, rather than ethylenediaminetetraacetic acid, for demineralization resulted in the cleanest extractions because the acid was easily removed. In contrast, the use of ethylenediaminetetraacetic acid resulted in smearing upon electrophoretic separation, possibly indicating these samples were not as pure. The denaturing agents sodium dodecyl sulfate, urea, and guanidine HCl have been used extensively for the solubilization of proteins in non-biomineralized tissue, but only the latter has been used on bone. We show that all three denaturing agents are effective for extracting bone proteins. One additional method tested uses ammonium bicarbonate as a solubilizing buffer that is more appropriate for post-extraction analyses (e.g., proteomics) by removing the need for desalting. We found that both guanidine HCl and ammonium bicarbonate were effective for extracting many bone proteins, resulting in similar electrophoretic patterns. With the increasing use of proteomics, a new generation of scientists are now interested in the study of proteins from not only extant bone but also from ancient bone.

Bone Regeneration with BMP-2 Gene-modified Mesenchymal Stem Cells Seeded on Nano-hydroxyapatite/Collagen/ Poly(L-Lactic Acid) Scaffolds

In this study, the capacity of bone morphogenetic protein 2 (BMP-2) gene-transfected bone marrow-derived mesenchymal stem cells (MSCs) in combination with nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/ PLA) to improve the repair of bone defects in rabbit was explored. MSCs from New Zealand White rabbits were cultured and injected with pIRES2-EGFPhBMP-2 or pIRES2-EGFP by electroporation. After the transfer efficiency was determined through the expression of EGFP, the MSCs were seeded on scaffolds to generate an in vitro 3D cell/scaffold construct. The adhesion and proliferation of the MSCs cultured in the scaffold was assessed by SEM. The cellular constructs obtained were allografted into the 15 mm critical-sized segmental bone defects in the radius of New Zealand White rabbits for 12 weeks. The bone regeneration was assessed by radiographical and histological analyses. In vitro, nHAC/PLA facilitated MSC adhesion and proliferation on the scaffold, and gene transfer efficiency reached a maximum of 35.5 ± 3.8%. In vivo, the implantation of BMP-2 transfected MSCs/nHAC/PLA construct significantly enhanced the formation of new bone in the segmental defect, compared to the control groups. This novel 3D BMP-2 transfected MSCs/nHAC/PLA construct has the potential for bone repair by genetic tissue engineering approach.

Biological roles of dermatan sulphate proteoglycans

Dermatan sulphate-containing proteoglycans (DS-PGs) are widely distributed in the extracellular matrix of skin, sclera, tendon, cartilage and a variety of other connective tissues. Two species of dermatan sulphate proteoglycans, called DS-PGI and DS-PGII, have recently been isolated from mature bovine articular cartilages. In their monomeric forms, both DS-PGI and DS-PGII are polydisperse, have relative molecular masses (Mr) ranging from 80K to 140K, and possess protein cores with apparent Mr values of approximately 45K. DS-PGI readily self-associates whereas DS-PGII does not. Polyclonal and monoclonal antibodies against DS-PGII do not react with DS-PGI. DS-PGI and DS-PGII appear to possess different core proteins and represent two different species of dermatan sulphate proteoglycans. DS-PGs have dramatic effects on the biological functions of cells. For example, they inhibit the capacity of fibroblasts to adhere to a fibronectin substratum. BALB/c 3T3 cells were labelled with [3H]thymidine and plated onto dishes coated with plasma fibronectin, plasma fibronectin plus chondroitin sulphate proteoglycan (CS-PG, cartilage-specific proteoglycan monomer), or plasma fibronectin plus DS-PGs. In the absence of proteoglycan, approximately 55% of the cells were attached at 1 h. In the presence of CS-PG, cell attachment was slightly decreased. In the presence of DS-PGs, the adhesion of the fibroblasts to fibronectin was essentially abolished. Similar results were obtained if a plasma fibronectin substratum was preadsorbed with the DS-PGs and the DS-PGs were left in the attachment medium.

Osteogenic differentiation of rabbit mesenchymal stem cells in thermo-reversible hydrogel constructs containing hydroxyapatite and bone morphogenic protein-2 (BMP-2)

The aim of this study was to assess the efficacy of ectopic bone formation in a three-dimensional hybrid scaffold in combination with hydroxyapatite (HA) and poly(NiPAAm-co-AAc) as an injectable vehicle in the form of a supporting matrix for the osteogenic differentiation of rabbit mesenchymal stem cells (MSCs). Osteogenic differentiation of MSCs in the hybrid scaffold was greatly influenced by the addition of growth factors. When the osteoinduction activity of hybrid scaffold was studied following implantation into the back subcutis of nude mouse in terms of histological and biochemical examinations, significantly homogeneous bone formation was histologically observed throughout the hybrid scaffolds containing growth factor (BMP-2: bone morphogenic protein-2). The level of alkaline phosphatase activity and osteocalcin content at the implanted sites of hybrid scaffolds were significantly high for the perfusion group compared with those in static culture group. We conclude that combination of MSC-seeded hybrid scaffold containing BMP-2 was a promising method by which to enhance in vitro osteogenic differentiation of MSC and in vivo ectopic bone formation.

Age-related differences in the accumulation and size of hyaluronan in alginate culture

The alginate bead culture system has unique properties that make it possible to study the accumulation and turnover of macromolecules in two distinct matrix compartments of the cartilage matrix: the cell-associated matrix (CM) and the further removed matrix (FRM). Taking advantage of this culture system, the purpose of this study was to examine age-related changes in the metabolism of hyaluronan (HA) in these two compartments. Bovine chondrocytes, isolated from fetal, young adult, and old adult articular cartilage, were cultured in alginate beads. On Days 7 and 14 of culture, the alginate gel was solubilized, the CM and FRM were separated and macromolecules in both compartments were analyzed. When compared to the cells from fetal and old adult animals, the young adult cells proliferated at the fastest rate. Fetal cells produced a more abundant CM that was richer in proteoglycans (PGs) than the CM of young or old adult cells. With increasing age, there was an increased tendency for PG, collagen, and HA to escape incorporation into the CM and to become immobilized in the FRM. Very striking changes also were observed in the ratio of HA to PG, which increased markedly with age, and in the size of the HA molecules, which decreased markedly with age. The results suggest that the metabolism of HA in cartilage undergoes pronounced age-related changes, some of which are retained during culture in alginate gel. The findings also suggest that the previously documented age-related decrease in the size of HA in native bovine cartilage reflects, at least in part, a biochemical process occurring at the time or at least soon after the glycosaminoglycan chain is synthesized. It does not appear to simply be the result of age-related changes occurring slowly with time after synthesis, as was previously suggested to be the case for human articular cartilage.

Crystallinity and solubility characteristics of hydroxyapatite adsorbed amino acid

Hydroxyapatite (HAp) was synthesized in the presence of a variety of amino acids in order to investigate the effect of amino acid on the crystallinity and the solubility characteristics of HAp in the HAp-synthesizing condition. In the results of X-ray diffraction analysis, HAp synthesized in the presence of glycine (HAp-Gly), serine (HAp-Ser), aspartic acid (HAp-Asp) and glutamic acid (HAp-Glu) showed poor crystallinity compared with HAp synthesized in the absence of amino acid (HAp-con). The results of Fourier transform infrared spectroscopy suggested the adsorption of these amino acids on HAp. Scanning electron microphotographs showed that the size and morphology of HAp adsorbed amino acids changed significantly. Furthermore, the solubility of these HAps increased significantly compared to HAp-con, each differing in four amino acids. However, other amino acids did not affect the crystallinity and morphology of HAp and had no significant change in their solubility. Collectively, this study suggests that the crystallinity and the solubility of synthesized HAp are different owing to the variation of amino acids in the HAp synthesizing condition. It is expected that digestion-regulated HAp materials could be synthesized by using amino acid in their synthesizing condition.

Localizational alterations of calcium, phosphorus, and calcification-related organics such as proteoglycans and alkaline phosphatase during bone calcification

To further approach the mechanisms of bone calcification, embryonic rat calvariae were observed at electron microscopic level by the means of fine structures and various cytochemical localizations, including nonspecific proteoglycan (PG) stained by cuprolinic blue (CB), decorin, chondroitin sulfate, hyaluronan, and alkaline phosphatase (ALP), as well as the elemental mapping of calcium (Ca) and phosphorus (P) by energy-filtering transmission electron microscopy (EFTEM). In the calvariae, calcification advanced as the distance from osteoblasts increased. Closer to the osteoblasts, the osteoid was marked by an abundance of CB-positive PGs around collagen fibrils. After crystallization within matrix vesicles, calcified nodules formed and expanded, creating a coherent calcified matrix. The sizes of CB-positive PG-like structures diminished as calcification proceeded. Although small CB-positive structures were accumulated in early stage-calcified nodules, they were localized along the periphery of larger calcified nodules. Cytochemical tests for decorin, chondroitin sulfate, and hyaluronan determined their presence in the areas around collagen fibrils of the osteoid, as well as in and around calcified nodules, whereas ALP was found in the matrix vesicles, as well as in and around the calcified nodules. Ca tended to localize at the PG sites, while P often mapped to the collagen fibril structures, in the uncalcified matrix. In contrast, Ca/P colocalization was visible in and around the calcified nodules, where ALP and smaller CB-positive structures were observed. The difference in the localization patterns of Ca and P in uncalcified areas may limit the local [Ca2+][PO4(3-)] product, leading to the general inhibition of hydroxyapatite crystallization. The downsizing of CB-positive structures suggested enzymatic fragmentation of PGs. Such structural alterations would contribute to the preservation and transport of calcium. ALP possesses the ability to boost local phosphate anion concentration. Therefore, structurally altered PGs and ALP may cooperate in Ca/P colocalization, thus promoting bone calcification.

Differential effects of interleukin-1 on hyaluronan and proteoglycan metabolism in two compartments of the matrix formed by articular chondrocytes maintained in alginate

Phenotypically stable young adult bovine articular chondrocytes suspended in beads of alginate gel were first cultured for 5 days, using daily changes of medium containing 10% fetal bovine serum and supplements. The cells in the beads were then maintained in culture for a further 3 days in the presence or absence of interleukin-1alpha at 1 ng/ml in the daily change of medium. The exposure to interleukin-1alpha caused the incorporation of (35)S-sulfate into the predominant cartilage proteoglycan, aggrecan, to decrease by approximately 60%. In addition, proteoglycans that had accumulated into the cell-associated matrix during the first 5 days of culture in the absence of interleukin-1alpha moved into the matrix further removed from the cells and from there into the medium. In contrast, the exposure to interleukin-1alpha was found to markedly promote the rate of synthesis of hyaluronan, especially during the first 24 h. Over the 3 days of culture in the presence of interleukin-1alpha, a large proportion of the newly synthesized hyaluronan molecules, as well as those that had previously become residents of the cell-associated matrix, moved out of this compartment and appeared to become permanent residents of the further removed matrix. These results demonstrate that exposure of young adult articular chondrocytes to interleukin-1alpha has profound effects on the metabolism of hyaluronan, a molecule that plays a critical role in the retention of proteoglycan molecules in the matrix. Importantly, the results suggest that exposure of chondrocytes to interleukin-1 in inflamed joints, such as occurs in rheumatoid arthritis, leads to the rapid loss of coordination of the synthesis of aggrecan and hyaluronan, two of the critical constituents of the proteoglycan aggregate. In addition, we present evidence that these interleukin-1-induced effects differentially alter the metabolism of hyaluronan in the metabolically active cell-associated matrix and the metabolically inactive matrix further removed from the chondrocytes.

Effects of transforming growth factor-beta1 on the gene expression of decorin, biglycan, and alkaline phosphatase in osteoblast precursor cells and more differentiated osteoblast cells

In this study, the effects of incubating two clonal rat osteoblastic cell lines at different stages of differentiation, ROB-C26 (C26) and ROB-C20 (C20), with transforming growth factor-beta1 (TGF-beta1) on the gene expression of decorin, biglycan, and alkaline phosphatase were examined. C26 cells are a potential osteoblast precursor cell line that is also capable of differentiating into muscle cells and adipocytes and is differentiated into osteoblasts after treatment with bone morphogenetic protein-2. C20 cells are a more differentiated osteoblastic cell line. Our Northern blot studies demonstrated that after treatment with TGF-beta1 (0, 0.1, 1.0, 5.0, and 10 ng/ml), a dose- and time-dependent decrease in decorin mRNA expression was found in C26 cells. In contrast, the effect of decorin mRNA with TGF-beta1 was not determined in C20 cells, since decorin mRNA expression was extremely low in this cell line even in the absence or presence of TGF-beta1. Although TGF-beta1 treatment resulted in no appreciable effect on biglycan mRNA expression in both cell lines in a dose- and time-dependent manner, it decreased significantly the expression of alkaline phosphatase in both cell lines at the gene and protein level. Reverse transcriptase-polymerase chain reaction analysis revealed the gene expression of decorin, and TGF-beta type I and type II receptors in both cell lines. These results indicate that osteoblasts progenitor cells express both decorin and biglycan mRNAs. In contrast, more differentiated and mature osteoblastic cells express preferentially biglycan mRNA. TGF-beta1 exerts different effects on the expression of decorin and biglycan mRNAs, and is a potent inhibitor of the gene expression of alkaline phosphatase during osteoblast differentiation.

Effects of bone morphogenetic protein-2 and transforming growth factor-beta1 on gene expression of decorin and biglycan by cultured osteoblastic cells

The influence of bone morphogenetic protein-2 (BMP-2) and transforming growth factor beta (TGF-beta) on the expression of small proteoglycans, decorin and biglycan was investigated in a clonal rat osteoblastic cell line, ROS-C26 (C26) cells, which is a potential osteoblast precursor cell line and capable of differentiating into mature osteoblasts after treatment with recombinant BMP-2 (rhBMP-2). Following the culture of C26 cells for 3, 6, and 9 days in the presence or absence of rhBMP-2, alkaline phosphatase activity increased in the rhBMP-2 treated cells in direct proportion to their differentiation into more mature osteoblastic cells, whereas decorin mRNA decreased in the cells, when compared to control cells without rhBMP-2 treatment. These results were evident 6 days after treatment. However, rhBMP-2 treatment had no effect on biglycan mRNA expression in the cells. Subsequently, after removal of rhBMP-2 from the culture media, the cells were further cultured for 24 h with graded concentrations of TGF-beta1 (0, 0.1, 1.0, 5.0, and 10 ng/ml). TGF-beta1 decreased decorin mRNA expression in the cells dose dependently, but did not affect their biglycan mRNA expression. Furthermore, either removal of rhBMP-2 from the culture media or addition of TGF-beta1 significantly decreased alkaline phosphatase activity of rhBMP-2-induced cells. These results indicate that osteoblastic differentiation is accompanied by increased alkaline phosphatase activity and decreased expression of decorin mRNA, but continuous expression of biglycan mRNA. Both rhBMP-2 and TGF-beta1 inhibit decorin mRNA expression in osteoblasts at varying stages of differentiation, but their effects on biglycan mRNA expression and alkaline phosphatase are different.

Bone matrix proteins: isolation and characterization of a novel cell-binding keratan sulfate proteoglycan (osteoadherin) from bovine bone

A small cell-binding proteoglycan for which we propose the name osteoadherin was extracted from bovine bone with guanidine hydrochloride-containing EDTA. It was purified to homogeneity using a combination of ion-exchange chromatography, hydroxyapatite chromatography, and gel filtration. The Mof the proteoglycan was 85, 000 as determined by SDS-PAGE. The protein is rich in aspartic acid, glutamic acid, and leucine. Two internal octapeptides from the proteoglycan contained the sequences Glu-Ile-Asn-Leu-Ser-His-Asn-Lys and Arg-Asp-Leu-Tyr-Phe-Asn-Lys-Ile. These sequences are not previously described, and support the notion that osteoadherin belongs to the family of leucine-rich repeat proteins. A monospecific antiserum was raised in rabbits. An enzyme-linked immunosorbent assay was developed, and showed the osteoadherin content of bone extracts to be 0.4 mg/g of tissue wet weight, whereas none was found in extracts of various other bovine tissues. Metabolic labeling of primary bovine osteoblasts followed by immunoprecipitation showed the cells to synthesize and secrete the proteoglycan. Digesting the immunoprecipitated osteoadherin with N-glycosidase reduced its apparent size to 47 kD, thus showing the presence of several N-linked oligosaccharides. Digestion with keratanase indicated some of the oligosaccharides to be extended to keratan sulfate chains. In immunohistochemical studies of the bovine fetal rib growth plate, osteoadherin was exclusively identified in the primary bone spongiosa. Osteoadherin binds to hydroxyapatite. A potential function of this proteoglycan is to bind cells, since we showed it to be as efficient as fibronectin in promoting osteoblast attachment in vitro. The binding appears to be mediated by the integrin alphavbeta3, since this was the only integrin isolated by osteoadherin affinity chromatography of surface-iodinated osteoblast extracts.

Ultrastructural immunolocalization of bone sialoprotein in guinea-pig osteoarthritis

In diarthrodial joints, bone and cartilage are structurally and functionally inseparable as shown in osteoarthritis (OA), where subchondral bone changes are integral in the disease process. By ultrastructural immunohistochemistry using polyclonal antibodies against guinea-pig bone sialoprotein (BSP), we investigated the distribution of this matrix protein at the osteocartilaginous interface in Hartley guinea-pig knees at different stages of primary osteoarthritis. Between 6 and 12 months they developed moderate osteoarthritic changes predominantly in the medial condyle, progressing to severe OA at 30 months. In all age groups BSP labeling was concentrated to the osteocartilaginous interface at a 1 micron narrow zone at the interface. In the medial osteoarthritic condyle, BSP was increased as compared with the lateral nonosteoarthritic condyle, but only at 30 months, when cartilage fibrillation correlated to BSP. Our observations suggest that altered BSP abundance may be a potential bone marker for late stage OA, while early events in bone cannot be monitored. BSP is expressed early in osteogenesis and may have a role in biological mineralization and growth. Since a sharp zone of intense BSP labeling remains at a remarkably constant level throughout life in guinea-pigs, BSP may have an important structural and/or regulating role at the interface. The protein may act as an anchor of calcified articular cartilage to subchondral bone or by regulating mineralization at the osteocartilaginous interface.

A biochemical and immuno-electron microscopical analysis of chondroitin sulphate-rich proteoglycans in human alveolar bone

This study used biochemical and immunohistochemical methods to characterize the chondroitin sulphate-rich proteoglycans from human alveolar bone obtained from an oral source. Proteoglycans were extracted from bone by a sequential 4 M guanidine HCl extraction process, and purified by DEAE-ion exchange chromatography. SDS-PAGE and Western blot analysis, using CS-56 monoclonal antibody, demonstrated one major proteoglycan species with a core protein of 58 kDa, glycosaminoglycan chains of 45-66 kDa and a mean molecular weight of 205 kDa. This work confirmed the biochemistry of chondroitin sulphate-rich proteoglycans from a novel source of adult human alveolar bone, and pointed towards a proteoglycan with a high glutamate, glycine, aspartate, alanine, serine and leucine content. Sections of alveolar bone were embedded in LR White resin, labelled with CS-56 antibody and examined with the light and electron microscopes. At the light microscope level, labelling was restricted to the osteocyte lacunae and canaliculi. Ultrastructural observations showed that the labelling was localized to fine filamentous material in the walls of the osteocytes and canaliculi. Sparse labelling was associated with the collagen fibres immediately subjacent to the lamina limitans, but no labelling of the mineralized matrix was observed. These findings also indicated subtle differences in the distribution of chondroitin sulphate compared with previously reported work, which may indicate species or age differences in the samples used in this study. Ultrastructural analysis confirmed and extended observations of glycosaminoglycan localization at the osteocyte cell membrane of mature human alveolar bone.

Electrophoretic gels of dentin matrix proteins as diffusion media for in vitro mineralization

Non-collagenous proteins of dentin and bone have important effects on mineralization which have been studied by various in vitro systems. We developed an in vitro mineralization system using electrophoretic gels as diffusion media of calcium and phosphate ions. Calcium and phosphate ions were diffused naturally or propelled by electric potential. Calcium phosphate was precipitated in the gel, and the precipitation was affected by proteins in the gel which had been separated by electrophoresis. We applied this system to analysis of non-collagenous proteins of dentin. Among the proteins, phosphophoryns promoted calcium phosphate precipitation in the natural-diffusion system. A non-collagenous protein having a molecular mass of 60 kDa inhibited precipitation. The results were different, however, in the electric-diffusion system, in which phosphophoryns had a negative effect. The present system enabled us to compare the effects of plural proteins rapidly, even using unpurified material.

Nature and distribution of chondroitin sulphate and dermatan sulphate proteoglycans in rabbit alveolar bone

The type and distribution of mineral binding and collagenous matrix-associated chondroitin sulphate and dermatan sulphate proteoglycans in rabbit alveolar bone were studied biochemically and immunocytochemically, using three monoclonal antibodies (mAb 2B6, 3B3, and 1B5). The antibodies specifically recognize oligosaccharide stubs that remain attached to the core protein after enzymatic digestion of proteoglycans and identify epitopes in chondroitin 4-sulphate and dermatan sulphate; chondroitin 6-sulphate and unsulphated chondroitin; and unsulphated chondroitin, respectively. In addition, mAb 2B6 detects chondroitin 4-sulphate with chondroitinase ACII pre-treatment, and dermatan sulphate with chondroitinase B pre-treatment. Bone proteins were extracted from fresh specimens with a three-step extraction procedure: 4 M guanidine HCl (G-1 extract), 0.4 M EDTA (E-extract), followed by guanidine HCl (G-2 extract), to characterize mineral binding and collagenous matrix associated proteoglycans in E- and G2-extracts, respectively. Biochemical results using Western blot analysis of SDS-polyacrylamide gel electrophoresis of E- and G2-extracts demonstrated that mineral binding proteoglycans contain chondroitin 4-sulphate, chondroitin 6-sulphate, and dermatan sulphate, whereas collagenous matrix associated proteoglycans showed a predominance of dermatan sulphate with a trace of chondroitin 4-sulphate and no detectable chondroitin 6-sulphate or unsulphated chondroitin. Immunocytochemistry showed that staining associated with the mineral phase was limited to the walls of osteocytic lacunae and bone canaliculi, whereas staining associated with the matrix phase was seen on and between collagen fibrils in the remainder of the bone matrix. These results indicate that mineral binding proteoglycans having chondroitin 4-sulphate, dermatan sulphate, and chondroitin 6-sulphate were localized preferentially in the walls of the lacunocanalicular system, whereas collagenous associated dermatan sulphate proteoglycans were distributed over the remainder of the bone matrix.

EDTA-insoluble, calcium-binding proteoglycan in bovine bone

A calcium ion precipitable, trypsin-generated proteoglycan fragment has been isolated from the demineralized, EDTA-insoluble matrices of bone. The demineralized matrix was completely digested with trypsin, increasing concentrations of CaCl2 were added to the supernatant, and the resulting precipitates were analyzed. The amount of precipitate gradually increased with higher concentrations of calcium and was reversibly solubilized by EDTA. After molecular sieve and anion exchange chromatography, a proteoglycan-containing peak was obtained. Immunochemical analysis showed that this peak contained chondroitin 4-sulfate and possibly keratan sulfate. Amino acid analysis showed that this proteoglycan contained high amounts of aspartic acid/asparagine (Asx), serine (Ser), glutamic acid/glutamine (Glx), proline (Pro), and glycine (Gly); however, it contained little leucine (Leu) which suggests that it is not a member of the leucine-rich small proteoglycan family. In addition, significant amounts of phosphoserine (P-Ser) and hydroxyproline (Hyp) were identified in hydrolysates of this fraction. A single band (M(r) 59 kDa) was obtained on SDS-PAGE that stained with Stains-all but not with Coomassie Brilliant Blue R-250. If bone powder was trypsinized prior to demineralization, this proteoglycan-containing fraction was not liberated. Collectively, these results indicate that a proteoglycan occurs in the demineralized matrix that is precipitated with CaCl2 and is closely associated with both mineral and collagen matrices. Such a molecule might facilitate the structural network for the induction of mineralization in bone.

Isolation, characterization, and primary structure of a calcium-binding 63-kDa bone protein

A novel noncollagenous protein of the mineralized matrix of bovine bone was isolated by ion exchange and gel permeation chromatography. The apparent M(r) of the protein is 63,000 as determined by SDS-polyacrylamide gel electrophoresis. The protein is a rather minor constituent in bone and could not be detected in other connective tissues by enzyme-linked immunosorbent assay of guanidine HCl extracts. The 63-kDa protein was detected in the osteoid and around the osteocytes upon immuno-histochemical staining of bovine compact bone. The sequence of the 63-kDa protein was deduced from cDNA clones isolated from a rat calvaria lambda gt11 expression library. The protein contains two centrally located EF-hand Ca(2+)-binding domains. Seven heptad repeats are present indicating the ability of the protein for coiled-coil interactions. Ability to bind calcium was confirmed by 45Ca2+ binding to protein blotted onto nitrocellulose membrane. The protein was synthesized in calvaria explants as detected by immunoprecipitation of radiolabeled protein from the culture medium. Although the protein can be detected in biochemical amounts in bone only, varying amounts of mRNA for this protein were detected in several rat tissues by RNase protection assay with highest levels in rat calvaria. This extracellular protein corresponds to a mouse protein called nucleobindin.

The effects of vitamin D deficiency on proteoglycan and hyaluronate constituents of chick bone

The effect of vitamin D deficiency on proteoglycan and hyaluronate constituents of cortical diaphyseal chick bone was studied. Proteoglycans in rachitic bone showed no significant change with respect to their size, composition, or amount relative to other extractable macromolecular components. In contrast, bone hyaluronate levels were raised in chicks fed on diets that were either vitamin D-deficient or depleted in calcium or phosphate, a 7-fold increase being seen in hypocalcaemic vitamin D-deficient chicks. This increase in hyaluronate was not directly related either to the absence of vitamin D or to abnormal levels of blood calcium or phosphate per se; hyaluronate levels are probably regulated by another factor, not yet identified, that is responsive to changes in vitamin D and mineral metabolism.

An electron microscopic study on the presence of proteoglycans in the mineralized matrix of rat and human compact lamellar bone

The presence of proteoglycans (PGs) was studied in compact lamellar rat and human bone at the electron microscopic level. With the cationic dye cuprolinic blue (CB1), PGs could be demonstrated in the mineralized bone matrix. The amounts of PGs appeared to be equal in the different lamellae and osteons. More CBl-positive material was found in the outermost lamella of the cortex, in the perilacunar matrix around the osteocyte lacunae, and around the canaliculi. Enzyme digestion with chondroitinase ABC demonstrated that the CBl-positive rods consisted of PGs. These observations amplify biochemical studies in which PGs have been isolated from the mineralized bone matrix. The presence of CBl-positive rods in the mineralized matrix suggest that PGs do not have to be removed completely to make the matrix calcifiable.

Immunohistochemical localization of bone sialoprotein in foetal porcine bone tissues: comparisons with secreted phosphoprotein 1 (SPP-1, osteopontin) and SPARC (osteonectin)

Bone sialoprotein (BSP) is a prominent component of bone tissues that is expressed by differentiated osteoblastic cells. Affinity-purified antibodies to BSP were prepared and used in combination with biotin-conjugated peroxidase-labeled second antibodies to demonstrate the distribution of this protein in sections of demineralized foetal porcine tibia and calvarial bone. Staining for BSP was observed in the matrix of mineralized bone and also in the mineralized cartilage and associated cells of the epiphysis, but was not observed in the hypertrophic zone nor in any of the soft tissues including the periosteum. In comparison, SPP-1 (osteopontin) and SPARC (osteonectin), which are also major proteins in porcine bone, were observed in the cartilage as well as in the mineralized bone matrix. In addition, SPARC was also present in soft connective tissues. Although SPP-1 distribution was more restricted than SPARC, hypertrophic chondrocytes, periosteal cells and some stromal cells in the bone marrow spaces were stained in addition to osteoblastic cells. The variations in the distribution and cellular expression of BSP, SPARC and SPP-1 in bone and mineralizing cartilage indicate these proteins perform different functions in the formation and remodelling of mineralized connective tissues.

Biosynthesis of bone proteins by fetal porcine calvariae in vitro. Rapid association of sulfated sialoproteins (secreted phosphoprotein-1 and bone sialoprotein) and chondroitin sulfate proteoglycan (CS-PGIII) with bone mineral

To study the biosynthesis of bone proteins, fragments of fetal porcine calvariae were cultured in the presence of 50 micrograms/ml ascorbate and 10 mM beta-glycerophosphate and individual cultures labeled for either 4 h or 48 h with [35S]-methionine, Na2[35SO4], Na3[32PO4] or [14C]-glycine plus [14C]-proline. The radiolabeled proteins in tissue extracts were obtained by sequential extraction with 4 M GuHCl (G1-extract), 0.5 M EDTA (E-extract), and again with 4 M GuHCl (G2-extract) and analyzed together with the radiolabeled proteins secreted into the medium. SPP-1 (secreted phosphoprotein 1, osteopontin) was the major non-collagenous protein deposited into the bone matrix, with lesser amounts of BSP (bone sialoprotein), osteocalcin and chondroitin sulfate proteoglycans (CS-PG II and CS-PG III). SPP-1 was also the major phosphorylated protein and was recovered, together with several fragmented forms, almost entirely in the demineralizing extracts. Moreover, approximately one-half of the [35SO4] incorporated into E-extract proteins was present in SPP-1, the remainder being incorporated into PGs with smaller amounts associated with BSP. Over 65% of the [35SO4] in the proteoglycans of the demineralizing extracts was recovered in the small CS-PG III with less than 35% in CS-PG II, the bone homologue of DS-PG II (decorin). In contrast, CS-PG II was the predominant small proteoglycan in culture media and in guanidine extracts. Some sulfated BSP was also observed in guanidine extracts and small amounts appeared to bind to collagen. Radiolabeled SPARC (osteonectin), a prominent protein of fetal porcine bone, was not detected in the mineralized bone tissues but was prominent in the culture medium. These results demonstrate that following secretion, the major proteins expressed by osteoblastic cells are initially incorporated into different tissue compartments, with most of the sulfated sialoproteins and CS-PG III associating rapidly with the hydroxyapatite crystals. The initial distribution of these proteins is of importance in the evaluation of their role in bone formation and mineralization.

Localization of bone sialoprotein (BSP) expression to sites of mineralized tissue formation in fetal rat tissues by in situ hybridization

Bone sialoprotein (BSP) is a major protein in the mineralized matrix of bone and dentine. To study the relationship between the expression of BSP and the formation of mineralized connective tissues, a cDNA probe to rat BSP was prepared for in situ hybridization analysis of developing fetal rat bones and teeth. When used for Northern hybridization analysis of rat bone marrow cells induced to differentiate into osteogenic cells by dexamethasone, the BSP cDNA revealed a specific induction of 1.6- and 2.0-kb mRNA species of BSP. In tissue sections a strong hybridization signal associated with osteoblasts was observed in areas of endochondral bone formation in the long bone metaphysis and condylar cartilage, and in the intramembranous bone of the calvaria and mandible. Hybridization reflecting a lower degree of expression was evident in cells of the transitional zone of mineralizing cartilage and in odontoblasts forming incisor dentine. Expression of BSP was also demonstrated in the hypertrophic cartilage cells in the long bone and condylar process. In contrast, expression of BSP could not be detected in the reserve or proliferative chondrocytes, fibroblasts and muscle cells. These studies demonstrate that the expression of BSP in bones and teeth is essentially restricted to cells directly involved in the formation of mineralizing connective tissue matrices, indicating that BSP has a specific role in biological mineralization and that it is a useful marker of bone formation.

Proteoglycans of bovine cementum: isolation and characterization

The proteoglycans associated with the mineralized matrix of bovine cementum have been studied biochemically and their distribution within this tissue localized immunohistochemically. Both hyaluronate and proteoglycans were fractionated by DEAE-Sephacel ion-exchange chromatography. The proteoglycans eluted in three separate peaks of which two contained alkali labile protein associated with glycosaminoglycans, and one appeared as free glycosaminoglycan chains. Analysis of the glycosaminoglycans identified chondroitin sulfate as the predominant species, although minor quantities of dermatan sulfate and heparan sulfate were also identified. Agarose-acrylamide gel electrophoresis and Sepharose CL-6B molecular sieve chromatography of the proteoglycans indicated them to be smaller in size with respect to periodontal ligament and gingival proteoglycans, but similar to bone and dentine proteoglycans. Amino acid analyses indicated subtle differences between cementum and bone proteoglycans. Using a monoclonal antibody (9-A-2) which recognizes the unsaturated disaccharide of chondroitinase ACII-digested glycosaminoglycans, chondroitin sulfate was identified in the pericellular environment within the lacunae housing the cementoblasts as well as in the extracellular matrix of cementum.

Streaming potential of intact wet bone

The conversion of mechanical loads to bioelectrical signals in bone have been suggested to control repair and remodeling. These signals in wet bone are attributed to the electrokinetic behavior where mechanical forces cause electrical signals due to motion of an ion carrying extracellular fluid in the bone matrix (streaming potentials). Streaming potential experiments were performed on control and chemically treated intact wet bone plugs in aphosphate and phosphate buffers to examine the contribution of bone constituents to the electrokinetic behavior of bone tissue. Data indicate that the organic constituents of bone dominate streaming potentials. Slopes of streaming potential vs pressure are related to the electrokinetic (zeta) potential. The slopes should be analyzed in the low pressure region where data is mainly linear. Comparisons of estimated zeta potentials from streaming potentials with existing data obtained by particle electrophoresis showed similar trends.

The origin of electrokinetic potentials in bone tissue: the organic phase

The purpose of this study was to determine the relative contributions of the organic and mineral phases of cow cortical bone to its electrokinetic response at room temperature. The technique of particle electrophoresis permitted electrokinetic (zeta) potentials to be calculated and plotted as a function of pH. Control and demineralized bone particles exhibited similar isoelectric points at pH approximately 5.1 (pH at which the zeta potential is zero), well below the isoelectric point of the bone mineral (pH approximately 8.6). In addition, the use of phosphate-containing buffers resulted in a zeta potential sign reversal of the bone mineral but had no effect on both the control and demineralized bone. These key results form the basis from which we suggest that the bone mineral lies within the organic phase (e.g., the mineral is not exposed to the fluid phase) and that the electrokinetic behavior of bone tissue is dominated by its organic ultrastructure.

A biochemical and immunohistochemical study of the proteoglycans of alveolar bone

The purpose of this investigation was to study the proteoglycans in alveolar bone of three animal species. Alveolar bone was obtained from humans, pigs, and rabbits. Portions were fixed, sectioned, and stained with monoclonal antibodies against keratan sulfate and chondroitin sulfate. In other samples, biochemical analyses were performed. After removal of the organic matrix by 4 mol/L guanidinium HCl extraction in the presence of proteinase inhibitors, proteoglycans in the mineralized matrix were extracted with 4 mol/L guanidinium HCl/0.5 mol/L EDTA/proteinase inhibitors, and characterized on the basis of their glycosaminoglycan content (cellulose acetate membrane electrophoresis), charge (DEAE-Sephacel and hydroxylapatite chromatography), size (Sepharose CL-6B chromatography and agarose/polyacrylamide gel electrophoresis), and amino acid content. The results indicated that keratan sulfate could be detected immunohistochemically and biochemically in rabbit bone only. The predominant glycosaminoglycan in pig and human alveolar bone was chondroitin sulfate, although some hyaluronate, dermatan sulfate, and heparan sulfate were also detected. The proteoglycans were found to be slightly smaller than gingival proteoglycans, but similar to those in cementum, dentin, and other bones. In addition to intact proteoglycans, some free glycosaminoglycan chains were also extracted from the mineralized matrix. Amino acid analyses showed some subtle differences between alveolar bone proteoglycan and those of the soft tissues of the periodontium.

Light scattering studies of bovine skin proteodermatan sulfate

The proteodermatan sulfate (PDS) of bovine skin is a low molecular weight proteoglycan with a molecular structure consisting of a protein chain and a sulfated polysaccharide chain covalently linked at the 4-serine of the protein. Static and dynamic laser light scattering methods have been used to determine the weight-average molecular weight, Mw, zeta-average radius of gyration, Rg zeta, and zeta-average translational diffusion coefficient, Dto, zeta, of bovine skin PDS. We have also characterized the two components of PDS, i.e., the protein core and the dermatan sulfate (DS) chain. (The latter contained an N-terminal-linked penta- or tetrapeptide.) Interpretation of the PDS data is complicated by the block copolymer nature of its structure. When appropriate corrections are made, our results indicate that Mw for PDS monomer is 62,000 when dissolved in 4M guanidine hydrochloride (GdnHCl), and increases to 610,000 in 0.15M NaCl. Mw for the core protein in 4M GdnHCl is 39,000, and this also increases substantially to 650,000 in 0.15M NaCl. In contrast, Mw for the DS chain is 24,000 in 0.15M NaCl, indicating that there is minimal self-association of DS in 0.15M NaCl. Thus we conclude that the self-association of PDS involves the protein core. Comparison of Rg zeta and Rh, the average hydrodynamic radius, suggests that trace amounts of aggregation persist for the PDS and its core protein even in 4M GdnHCl. This conclusion is supported by evaluation of the second moments of the dynamic light scattering correlation function. Comparisons of the observed Dto, zeta for PDS with predicted values using hydrodynamic theory are consistent with a "lollipop" conformation for the molecule.

Glycosaminoglycans of human alveolar bone

Bone proteoglycan was extracted and the glycosaminoglycan (GAG) components identified. Chondroitin-4-sulphate was the major GAG detected and represented 93.8% of the total GAG extracted. In addition, hyaluronic acid (1.3%), dermatan sulphate (3.1%) and heparan sulphate (1.8%) were identified as minor constituents.

Characterization of porcine osteonectin extracted from foetal calvariae

Osteonectin, extracted from foetal porcine calvariae with 0.5 M-EDTA, was purified to homogeneity by using gel filtration and polyanion anion-exchange fast protein liquid chromatography under dissociative conditions without the need of reducing agents. The purified protein migrated with an Mr of 40,300 on SDS/polyacrylamide gels and was similar to bovine osteonectin in both amino acid composition and in its ability to bind to hydroxyapatite in the presence of 4 M-guanidinium hydrochloride (GdmCl). However, unlike the bovine protein, porcine osteonectin did not bind selectively to hydroxyapatite when EDTA tissue extracts were used. In addition, purified porcine osteonectin did not show any apparent affinity for either native or denatured type I collagen, but did bind to serum albumin. Primary sequence analysis revealed an N-terminal alanine residue, with approximately one-half of the subsequent 35 residues identified as small hydrophobic amino acids and one-quarter as acidic amino acids. The only significant difference between the N-terminal sequences of the bovine and porcine proteins was the deletion of the tripeptide Val-Ala-Glu in porcine osteonectin. In contrast with bovine osteonectin, far-u.v.c.d. of porcine osteonectin revealed considerable secondary structure, of which 27% was alpha-helix and 39% was beta-sheet. Cleavage of the molecule with CNBr under non-reducing conditions generated five fragments, of which two major fragments (Mr 27,900 and 12,400) stained blue with Stains All, a reagent that stains sialic-acid-rich proteins/phosphate-containing proteins and/or Ca2+-binding proteins blue while staining other proteins pink. The 12,400-Mr fragment bound 45Ca2+ selectively, indicating a Ca2+-binding site in this part of the molecule. The 27,900-Mr fragment did not bind Ca2+, and since biosynthetic studies with 32PO4(3-) did not show phosphorylation of porcine osteonectin, this fragment is likely to be highly acidic. The incomplete cleavage of the molecule with CNBr and the ability of the molecule to regain its secondary structure after exposure to 7 M-urea are features consistent with the molecule having a compact structure that is stabilized by numerous disulphide bridges. The chemical and binding properties of porcine osteonectin are closely similar to the recently described 'culture shock', SPARC and BM-40 proteins, indicating that these are homologous proteins.

The glycosaminoglycan constituents of alveolar and basal bone of the rabbit

Proteoglycan was extracted from alveolar and basal bone of New Zealand White rabbits using a sequential extraction procedure. Proteoglycans not associated with the bone mineral represented 1% of the total organic matrix whereas proteoglycans associated with the mineral represented 20% of the alveolar organic matrix and 12% of the basal organic matrix. Chondroitin-4-sulphate and keratan sulphate were identified in both alveolar and basal bone following protease treatment of the proteoglycan extracts and enzymic digestion with chondroitinase AC, ABC and keratanase. Differences were observed in the percentage of each glycosaminoglycan (GAG) in the total organic matrix. In alveolar bone samples, keratan sulphate and chondroitin-4-sulphate is present in equal proportions. In basal bone chondroitin-4-sulphate represents approximately half the value found in alveolar bone and keratan sulphate about a quarter. The extracts were examined by gel filtration on Sepharose 4B under associative conditions. The 280 nm absorbance profiles of proteoglycan from alveolar and basal bone were essentially similar with three main peaks evident, including molecular weight material in excess of 2 X 10(6). The bulk of the bone GAG appeared in the medium molecular weight range with trace amounts in lower molecular weight fractions.

Fibronectin-mediated adhesion of fibroblasts: inhibition by dermatan sulfate proteoglycan and evidence for a cryptic glycosaminoglycan-binding domain

Dermatan sulfate proteoglycans (DS-PGs) isolated from bovine articular cartilage have been examined for their effects on the adhesive responses of BALB/c 3T3 cells and bovine dermal fibroblasts on plasma fibronectin (pFN) and/or type I collagen matrices, and compared to the effects of the chondroitin sulfate/keratan sulfate proteoglycan monomers (CS/KS-PGs) from cartilage. DS-PGs inhibited the attachment and spreading of 3T3 cells on pFN-coated tissue culture substrata much more effectively than the cartilage CS/KS-PGs reported previously; in contrast, dermal fibroblasts were much less sensitive to either proteoglycan class unless they were pretreated with cycloheximide. Both cell types failed to adhere to substrata coated only with the proteoglycans; binding of the proteoglycans to various substrata has also been quantitated. While a strong inhibitory effect was obtained with the native intact DS-PGs, little inhibitory effect was obtained with isolated DS chains (liberated by alkaline-borohydride cleavage) or with core protein preparations (liberated by chondroitinase ABC digestion). In marked contrast, DS-PGs did not inhibit attachment or spreading responses of either 3T3 or dermal fibroblasts on type I collagen-coated substrata when the collagen was absorbed with pFN alone, DS-PGs alone, or the two in combination. These results support evidence for (a) collagen-dependent, fibronectin-independent mechanisms of adhesion of fibroblasts, and (b) different sites on the collagen fibrils where DS-PGs bind and where cell surface "receptors" for collagen bind. Experiments were developed to determine the mechanism(s) of inhibition. All evidence indicated that the mechanism using the intact pFN molecule involved the binding of the DS-PGs to the glycosaminoglycan (GAG)-binding sites of substratum-bound pFN, thereby inhibiting the interaction of the fibronectin with receptors on the cell surface. This was supported by affinity chromatography studies demonstrating that DS-PGs bind completely and effectively to pFN-Sepharose columns whereas only a subset of the cartilage CS/KS-PG binds weakly to these columns. In contrast, when a 120-kD chymotrypsin-generated cell-binding fragment of pFN (CBF which has no detectable GAG-binding activity as a soluble ligand) was tested in adhesion assays, DS-PGs inhibited 3T3 adherence on CBF more effectively than on intact pFN. A variety of experiments indicated that the mechanism of this inhibition also involved the binding of DS-PGs to only substratum-bound CBF due to the presence of a cryptic GAG-binding domain not observed in the soluble CBF.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical characterization of fracture callus proteoglycans

The changes in proteoglycan molecules during the initial stages of fracture healing in rats were characterized. Following extraction of callus proteoglycan components with dissociative solvents, the components were purified in a cesium chloride density gradient. The recovered proteoglycans were characterized with respect to their molecular size distribution using gel filtration chromatography and a centrifugal transport methodology. During this early healing period, a decrease was observed in the relative proportion of the aggregate and in the hydrodynamic size and sedimentation coefficients of these molecules. While some molecular degradation could have occurred during the early stages of fracture healing, the dominant change of the proteoglycan molecules seemed to be disaggregation. No significant difference was observed in the proportion of aggregates reformed when exogenous hyaluronate and link glycoproteins were allowed to interact with the two corresponding monomer preparations. The molecular changes of the proteoglycan molecules seem to parallel those occurring during endochondral calcification of rat epiphyseal cartilage.