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  • 1
    Electronic Resource
    Electronic Resource
    The inhibitory effect of cartilage proteoglycans on hydroxyapatite growth (1984)
    Springer
    Calcified tissue international 36 (1984), S. 285-290 
    Details
    ISSN: 1432-0827
    Keywords: Proteoglycans ; Chondroitin 4-sulfate ; Neutral dextran ; Hydroxyapatite growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The calcification of connective tissues, including cartilage, is under the control of many interacting systems. Proteoglycans are thought to retard the deposition of hydroxyapatite crystals, and modification of the proteoglycans presumably facilitates mineralization in those tissues that are actively calcifying. The mechanism underlying these regulations remains speculative. This study investigates this question by comparing the inhibitory effectiveness of several macromolecules at neutral pH and approximately physiological ionic strengths. Inhibitors tested include bovine nasal proteoglycan monomer A1D1D1 and aggregate-containing A1 fractions, glycosaminoglycan chains (chondroitin 4-sulfate), and neutral dextran (as an uncharged analog). Hydroxyapatite growth was assessed either by measuring the time-dependent decreases in solution calcium and phosphate concentrations, or by determining utilization of hydroxyl ion in a pH-Stat. All species studied inhibit hydroxyapatite growth, and the extent of inhibition for each class is concentration-dependent. The proteoglycan aggregate-containing A1 fraction is more effective than the proteoglycan monomer at the same concentration, and the proteoglycan monomer is more effective than chondroitin 4-sulfate. Neutral dextran inhibits hydroxyapatite growth less effectively than proteoglycans. These results suggest that inhibition of hydroxyapatite growth by proteoglycans critically depends on both status (aggregate, monomer, etc.) and hydrodynamic size of this macromolecule, supporting the hypothesis that modification of proteoglycansin vivo functions to modulate the effectiveness of proteoglycans as a hydroxyapatite growth inhibitor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405332
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of proteoglycans on in vitro hydroxyapatite formation (1979)
    Springer
    Calcified tissue international 27 (1979), S. 75-82 
    Details
    ISSN: 1432-0827
    Keywords: Proteoglycans ; Hydroxyapatite ; Amorphous calcium phosphate ; Nucleation ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Well-characterized bovine nasal proteoglycan A1 fraction (aggregate) and proteoglycan D1 fraction (subunit) have been shown to be effective inhibitors of hydroxyapatite (HA) formation in two in vitro test systems: (a) the transformation of amorphous calcium phosphate (ACP) to crystalline HA, and, (b) the direct precipitation of HA from low-concentration calcium phosphate solutions. A1 or D1 in solution slowed the transformation kinetics in system (a) without affecting the time to the onset of conversion. In system (b), A1 or D1 in solution increased the time to the onset of HA formation without affecting the HA formation kinetics. In both test systems A1 was a more effective inhibitor than D1, although the difference was not great. In both systems the inhibitory effect was proportional to the A1 or D1 solution concentration. The action of solutions of low and high molecular weight neutral dextrans on both test systems showed that high molecular weight and/or extended spatial molecular conformation has a much stronger correlation with inhibitory ability than solution viscosity. Proteoglycans have been implicated as playing a role in regulating biological mineralization particularly in the epiphyseal growth plate. Our study suggests that just enzymatic cleavage of aggregate into subunit is not sufficient to allow mineralization to occur, since we find that D1 itself is a potent inhibitor of HA formation. Further degradation and/or removal of D1 appears to be necessary for calcification to take place.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441164
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  • 3
    Electronic Resource
    Electronic Resource
    Age-Related changes in cartilage proteoglycans: Quantitative electron microscopic studies (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 28 (1994), S. 398-408 
    Details
    ISSN: 1059-910X
    Keywords: Aging ; Proteoglycans ; Electron microscopy ; Intervertebral disc ; Hyaline cartilage ; Nucleus pulposus ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Biochemical and biophysical studies have shown that the composition and sedimentation velocity of cartilage proteoglycans change with age, but these investigations cannot demonstrate the alterations in molecular structure responsible for these changes. Development of quantitative electron microscopic methods has made it possible to define the age-related structural changes in aggregating proteoglycans and to correlate the alterations in their structure with changes in tissue composition and morphology. Electron microscopic measurement of human and animal hyaline cartilage proteoglycans has shown that with increasing age the length of the chondroitin sulfate-rich region of aggregating proteoglycan monomers (aggrecan molecules) decreases, the variability in aggrecan length increases, the density of aggrecan keratan sulfate chains increases, the number of monomers per aggregate decreases, and the proportion of monomers that aggregate declines. Proteoglycans from the nucleus pulposus of the intervertebral disc show similar but more dramatic age-related alterations. At birth, nucleus pulposus aggrecan molecules are smaller and more variable in length than those found in articular cartilage. Within the first year of human life, the populations of aggregates and large aggrecan molecules analogous to those found in articular cartilage decline until few if any of these molecules remain in the central disc tissues of skeletally mature individuals. The mechanisms of the age-related changes in cartilage proteoglycans have not been fully explained, but measurement of proteoglycans synthesized by chondrocytes of different ages suggests that alterations in synthesis produce at least some of the age-related changes in aggrecan molecules. Degradation of aggrecan chondroitin sulfate-rich regions in the matrix probably also contributes to the structural changes seen by electron microscopy. Age-related changes in proteoglycan aggregation may be due to alterations in link protein function or inhibition of aggregation of newly synthesized aggrecan molecules by accumulation of degraded aggrecan molecules. © 1994 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1070280506
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  • 4
    Electronic Resource
    Electronic Resource
    Structural changes in reassembled growth plate aggregates (1986)
    Hoboken, NJ [u.a.] : Wiley-Blackwell
    Journal of Orthopaedic Research 4 (1986), S. 1-9 
    Details
    ISSN: 0736-0266
    Keywords: Proteoglycans ; Growth plate ; Mineralization ; Electron microscopy ; Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: To investigate possible structural changes in reassembled proteoglycan aggregates during cartilage mineralization, we examined the molecular architecture and dimensions of growth plate proteoglycan aggregates by electron microscopy. The ends of fetal bovine femurs and tibias were separated into three regions: the epiphysis; the cartilage growth plate, consisting of the proliferative zone and the unmineralized portion of the hypertrophic zone; and the calcified portion of the hypertrophic zone along with part of the metaphysis. Aggregates from all three regions had the same molecular architecture. They consisted of central hyaluronic filaments with multiple attached monomers. Monomers consisted of two segments: (a) a peripheral thick segment, which represents primarily the chondroitin sulfate-rich region, and (b) a thin segment attached directly to the hyaluronic acid filament. The length of aggregated monomers did not differ between the growth plate cartilage and the metaphysis, nor did the lengths of the thin and thick segments, indicating that the chondroitin sulfate-rich region of aggregated monomers is not degraded during cartilage mineralization. Between the growth plate cartilage and the metaphysis, aggregates became shorter and had fewer monomers and wider spacing between monomers. These structural alterations in proteoglycan aggregates may be one of the events that prepares the matrix for mineralization.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jor.1100040101
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  • 5
    Electronic Resource
    Electronic Resource
    Articular cartilage and intervertebral disc proteoglycans differ in structure: An electron microscopic study (1989)
    Hoboken, NJ [u.a.] : Wiley-Blackwell
    Journal of Orthopaedic Research 7 (1989), S. 146-151 
    Details
    ISSN: 0736-0266
    Keywords: Intervertebral disc ; Cartilage ; Proteoglycans ; Electron microscopy ; Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Articular cartilage and the intervertebral disc tissues have different material and biological properties and different patterns of aging and degeneration. To determine if the proteoglycans of these tissues differ in structure, we used the electron microscopic monolayer technique to compare baboon articular cartilage proteoglycans with baboon annulus fibrosus, transition zone, and nucleus pulposus proteoglycans. Intervertebral disc and articular cartilage porteoglycans differed signficantly. Articular cartilage contained large proteoglycan aggregates formed from hyaluronic acid central filaments, multiple monomers, and large nonaggregated monomers. These molecules were identical to those of nasal cartilage, growth plate cartilage, chondrosarcomas, or menisci. In contrast, the intervertebral disc tissues contained only nonaggregated proteoglycan monomers and clusters of monomers without apparent central filaments. Intervertebral disc nonaggregated monomers were shorter and more variable in length than those from articular cartilage, and nucleus pulposus nonaggregated monomers were even shorter and more variable in length than transition zone and annulus fibrosus monomers. These observations suggest that significant differences in proteoglycan metabolism exist between articular cartilage and intervertebral disc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jor.1100070121
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