Proteoglycans: an overview

The microstructure and micromechanics of the tendon-bone insertion

The exceptional mechanical properties of the load-bearing connection of tendon to bone rely on an intricate interplay of its biomolecular composition, microstructure and micromechanics. Here we identify that the Achilles tendon-bone insertion is characterized by an interface region of ∼500 μm with a distinct fibre organization and biomolecular composition. Within this region, we identify a heterogeneous mechanical response by micromechanical testing coupled with multiscale confocal microscopy. This leads to localized strains that can be larger than the remotely applied strain. The subset of fibres that sustain the majority of loading in the interface area changes with the angle of force application. Proteomic analysis detects enrichment of 22 proteins in the interfacial region that are predominantly involved in cartilage and skeletal development as well as proteoglycan metabolism. The presented mechanisms mark a guideline for further biomimetic strategies to rationally design hard-soft interfaces.

Effects of Freeze-Thaw Cycle with and without Proteolysis Inhibitors and Cryopreservant on the Biochemical and Biomechanical Properties of Articular Cartilage

OBJECTIVE

We investigated the effects of freeze-thawing on the properties of articular cartilage.

DESIGN

The reproducibility of repeated biomechanical assay of the same osteochondral sample was first verified with 11 patellar plugs from 3 animals. Then, 4 osteochondral samples from 15 bovine patellae were divided into 4 groups. The reference samples were immersed in phosphate-buffered saline (PBS) containing proteolysis inhibitors and biomechanically tested before storage for further analyses. Samples of group 1 were biomechanically tested before and after freeze-thawing in PBS in the absence and those of group 2 in the presence of inhibitors. Samples of the group 3 were biomechanically tested in PBS-containing inhibitors, but frozen in 30% dimethyl sulfoxide/PBS and subsequently tested in PBS supplemented with the inhibitors. Glycosaminoglycan contents of the samples and immersion solutions were analyzed, and proteoglycan structures examined with SDS-agarose gel electrophoresis.

RESULTS

Freeze-thawing decreased slightly dynamic moduli in all 3 groups. The glycosaminoglycan contents and proteoglycan structures of the cartilage were similar in all experimental groups. Occasionally, the diffused proteoglycans were partly degraded in group 1. Digital densitometry revealed similar staining intensities for the glycosaminoglycans in all groups. Use of cryopreservant had no marked effect on the glycosaminoglycan loss during freeze-thawing.

CONCLUSION

The freeze-thawed cartilage samples appear suitable for the biochemical and biomechanical studies.

Influence of extremely low frequency, low energy electromagnetic fields and combined mechanical stimulation on chondrocytes in 3-D constructs for cartilage tissue engineering

Articular cartilage, once damaged, has very low regenerative potential. Various experimental approaches have been conducted to enhance chondrogenesis and cartilage maturation. Among those, non-invasive electromagnetic fields have shown their beneficial influence for cartilage regeneration and are widely used for the treatment of non-unions, fractures, avascular necrosis and osteoarthritis. One very well accepted way to promote cartilage maturation is physical stimulation through bioreactors. The aim of this study was the investigation of combined mechanical and electromagnetic stress affecting cartilage cells in vitro. Primary articular chondrocytes from bovine fetlock joints were seeded into three-dimensional (3-D) polyurethane scaffolds and distributed into seven stimulated experimental groups. They either underwent mechanical or electromagnetic stimulation (sinusoidal electromagnetic field of 1 mT, 2 mT, or 3 mT; 60 Hz) or both within a joint-specific bioreactor and a coil system. The scaffold-cell constructs were analyzed for glycosaminoglycan (GAG) and DNA content, histology, and gene expression of collagen-1, collagen-2, aggrecan, cartilage oligomeric matrix protein (COMP), Sox9, proteoglycan-4 (PRG-4), and matrix metalloproteinases (MMP-3 and -13). There were statistically significant differences in GAG/DNA content between the stimulated versus the control group with highest levels in the combined stimulation group. Gene expression was significantly higher for combined stimulation groups versus static control for collagen 2/collagen 1 ratio and lower for MMP-13. Amongst other genes, a more chondrogenic phenotype was noticed in expression patterns for the stimulated groups. To conclude, there is an effect of electromagnetic and mechanical stimulation on chondrocytes seeded in a 3-D scaffold, resulting in improved extracellular matrix production.

Changes in the myocardial interstitium and contribution to the progression of heart failure

The myocardial interstitium is highly organized and orchestrated, whereby small disruptions in composition, spatial relationships, or content lead to altered myocardial systolic and/or diastolic performance. These changes in extracellular matrix structure and function are important in the progression to heart failure in pressure overload hypertrophy, dilated cardiomyopathy, and ischemic heart disease. The myocardial interstitium is not a passive entity, but rather a complex and dynamic microenvironment that represents an important structural and signaling system within the myocardium.

Temperature effects in articular cartilage biomechanics

Articular cartilage is the soft tissue that covers contacting surfaces of bones in synovial joints. Cartilage is composed of chondrocytes and an extracellular matrix containing numerous biopolymers, cations and water. Healthy cartilage functions biomechanically to provide smooth and stable joint movement. Degenerative joint diseases such as osteoarthritis involve cartilage deterioration, resulting in painful and cumbersome joint motion. Temperature is a fundamental quantity in mechanics, yet the effects of temperature on cartilage mechanical behavior are unknown. This study addressed the questions of whether cartilage stiffness and stress relaxation change with temperature. Samples of middle-zone bovine calf patellofemoral cartilage were tested in unconfined compression first at 24°C and then again after heating to 60°C. The data reveal that when temperature increases: (1) both peak and equilibrium stiffness increase by 150 and 8%, respectively, and (2) stress relaxation is faster at higher temperature, as shown by a 60% decrease in the time constant. The increases in temperature-dependent stiffness are consistent with polymeric mechanisms of matrix viscoelasticity but not with interstitial fluid flow. The changes in the time constant are consistent with a combination of both fluid flow and matrix viscoelasticity. Furthermore, we discovered a novel phenomenon: at stress-relaxation equilibrium, compressive stress increased with temperature. These data demonstrate a rich area of cartilage mechanics that has previously been unexplored and emphasize the role of polymer dynamics in cartilage viscoelasticity. Further studies of cartilage polymer dynamics may yield additional insight into mechanisms of cartilage material behavior that could improve treatments for cartilage degeneration.

Tissue mechanics, animal models, and pelvic organ prolapse: a review

Pelvic floor disorders such as pelvic organ prolapse, urinary incontinence, and fecal incontinence affect a large number of women each year. The pelvic floor can be thought of as a biomechanical structure due to the complex interaction between the vagina and its supportive structures that are designed to withstand the downward descent of the pelvic organs in response to increases in abdominal pressure. Although previous work has highlighted the biochemical changes that are associated with specific risk factors (i.e. parity, menopause, and genetics), little work has been done to understand the biomechanical changes that occur within the vagina and its supportive structures to prevent the onset of these pelvic floor disorders. Human studies are often limited due to the challenges of obtaining large tissue samples and ethical concerns. Therefore, it is necessary to investigate the use of animal models and their importance in understanding how different risk factors affect the biomechanical properties of the vagina and its supportive structures. In this review paper, we will discuss the different animal models that have been previously used to characterize the biomechanical properties of the vagina: including non-human primates, rodents, rabbits, and sheep. The anatomy and preliminary biomechanical findings are discussed along with the importance of considering experimental conditions, tissue anisotropy, and viscoelasticity when characterizing the biomechanical properties of vaginal tissue. Although there is not a lot of biomechanics research related to the vagina and pelvic floor, the future is exciting due to the significant potential for scientific findings that will improve our understanding of these conditions and hopefully lead to improvements in the prevention and treatment of pelvic disorders.

Effects of 24R,25- and 1α,25-dihydroxyvitamin D3 on mineralizing growth plate chondrocytes

Time- and dosage-dependent effects of 1,25(OH)(2)D(3) and 24,25(OH)(2)D(3) on primary cultures of pre- and post-confluent avian growth plate (GP) chondrocytes were examined. Cultures were grown in either a serum-containing culture medium designed to closely mimic normal GP extracellular fluid (DATP5) or a commercially available serum-free media (HL-1) frequently used for studying skeletal cells. Hoechst DNA, Lowry protein, proteoglycan (PG), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP) activity and calcium and phosphate mineral deposition in the extracellular matrix were measured. In preconfluent cultures grown in DATP5, physiological levels of 24,25(OH)(2)D(3) (0.10-10 nM) increased DNA, protein, and LDH activity significantly more than did 1,25(OH)(2)D(3) (0.01-1.0 nM). However, in HL-1, the reverse was true. Determining ratios of LDH and PG to DNA, protein, and each other, revealed that 1,25(OH)(2)D(3) specifically increased PG, whereas 24,25(OH)(2)D(3) increased LDH. Post-confluent cells were generally less responsive, especially to 24,25(OH)(2)D(3). The positive anabolic effects of 24,25(OH)(2)D(3) required serum-containing GP-fluid-like culture medium. In contrast, effects of 1,25(OH)(2)D(3) were most apparent in serum-free medium, but were still significant in serum-containing media. Administered to preconfluent cells in DATP5, 1,25(OH)(2)D(3) caused rapid, powerful, dosage-dependent inhibition of Ca(2+) and Pi deposition. The lowest level tested (0.01 nM) caused >70% inhibition during the initial stages of mineral deposition; higher levels of 1,25(OH)(2)D(3) caused progressively more profound and persistent reductions. In contrast, 24,25(OH)(2)D(3) increased mineral deposition 20-50%; it required >1 week, but the effects were specific, persistent, and largely dosage-independent. From a physiological perspective, these effects can be explained as follows: 1,25(OH)(2)D(3) levels rise in hypocalcemia; it stimulates gut absorption and releases Ca(2+) from bone to correct this deficiency. We now show that 1,25(OH)(2)D(3) also conserves Ca(2+) by inhibiting mineralization. The slow anabolic effects of 24,25(OH)(2)D(3)are consistent with its production under eucalcemic conditions which enable bone formation. These findings, which implicate serum-binding proteins and accumulation of PG in modulating accessibility of the metabolites to GP chondrocytes, also help explain some discrepancies previously reported in the literature.

Crystallization and preliminary X-ray diffraction studies of the cartilage link protein from bovine trachea

Cartilage extracellular matrix link protein, having molecular mass of approximately 40 kDa, is a metalloprotein that binds divalent cations and is only soluble in low ionic strength solutions. The link protein was purified from bovine trachea and has been crystallized by a vapor diffusion method using PEG 3350 as precipitant. The crystal symmetry is P1, and the unit cell dimensions are a = 43.55, b = 53.11, c = 60.10 A, alpha = 90.44, beta = 106.21, gamma = 101.51 degrees. The VM of 1.8 A3/Da is consistent with the presence of two molecules of the link protein in the asymmetric unit. The crystals diffract X-rays from a synchrotron source to 1.7 A resolution.

Developmental expression of proteoglycans in the tectorial and basilar membrane of the gerbil cochlea

The appearance and distribution of specific proteoglycans (PGs) was assessed during development and maturation of the tectorial (TM) and basilar membranes (BM) in the gerbil cochlea. At birth, monoclonal antibodies against keratan sulfate (KSPG) and chondroitin 4- or 6-sulfate (4S CSPG, 6S CSPG) reacted with the upper fibrous layer of the TM with staining for anti-KSPG predominating. Reactivity for 4S CSPG remained constant whereas that for 6S CSPG increased through day 20 when it exceeded that of 4S CSPG. The region of Köllikers organ near the developing tunnel of Corti stained positively with all three PG antibodies from birth through day 8. In contrast, cells in the developing inner spiral sulcus lacked immunoreactive KSPG but expressed CSPG. PGs were first detectable in the BM of the basal turn at day 8 and increased to near adult levels by 16 days after birth. Anti-KSPG again showed the strongest staining with labeling density for 4S and 6S CSPG being about equal at maturity. Staining with all three antibodies was localized along the margins of the BM. Reactivity of the TM and BM in the upper turns lagged behind that of the basal turns by 24-48 h. Our results show that the TM is relatively mature at birth, needing only minor changes in its PG content to reach adult levels. In contrast, the BM showed a marked increase in its content of PGs during a period corresponding to the onset and rapid development of auditory function.

Immunohistochemical localization of keratan sulfate and chondroitin 4- and 6-sulfate proteoglycans in subregions of the tectorial and basilar membranes

Proteoglycans containing keratan sulfate (KSPG) and 4- and 6-sulfated epitopes of chondroitin sulfate (CSPG) were identified in distinct domains of the tectorial and basilar membranes by ultrastructural immunogold labeling with monoclonal antibodies. In the tectorial membrane (TM), the highest concentration of gold particles was present in the upper fibrous layers of the limbal, middle and marginal zones with all three antibodies. Reactivity with anti-KSPG exceeded that with anti-4S and anti-6S CSPG, especially in the marginal zone. The cover net showed no reactivity for any antibody. Labeling density of gold particles with all three antibodies increased markedly from base to apex. In the basilar membrane (BM), all three PGs were most highly concentrated in regions of amorphous ground substance bordering the upper and lower filamentous bands. As in the TM, reactivity for anti-KSPG in the BM exceeded that for either CSPG antibody and staining with all three antibodies was stronger and more widespread in the apical as compared to the basal turns. These results provide the first ultrastructural demonstration of KSPG and CSPG in distinct subregions of the TM and BM. The preferential distribution and marked increase in PGs from base to apex in both TM and BM supports a role for these macromolecules in regulating structural and mechanical properties of these highly specialized extracellular membranes.

Identity of the core proteins of the large chondroitin sulphate proteoglycans synthesized by skeletal muscle and prechondrogenic mesenchyme

Large, chondroitin sulphate-containing proteoglycans are synthesized by three prominent tissue in the embryonic chick limb. One of these proteoglycans is aggrecan, the phenotype-specific proteoglycan of cartilage. Another, PG-M, is produced by prechondrogenic mesenchymal cells. The third, M-CSPG, is made by developing skeletal muscle cells. While the carbohydrate components of PG-M and M-CSPG share some similarities, both of these proteoglycans clearly have different carbohydrate moieties from those of aggrecan. To compare these three proteoglycans at another level, their core protein structures were analysed in three ways: by the presence or absence of monoclonal antibody epitopes, by one-dimensional peptide display of the cyanogen bromide-cleaved core proteins and by electron microscopic imaging of the molecules. Monoclonal antibodies whose epitopes are present in aggrecan core protein were tested with core protein preparations from M-CSPG and PG-M. One of these, 7D1, recognizes both PG-M and M-CSPG, while another, 1C6, shows no reactivity for the non-cartilage proteoglycans. The absence of 1C6 reactivity is of interest, as its epitope is in a region of the aggrecan core protein known to have a functional homologue in the core proteins of PG-M and M-CSPG. The cyanogen bromide-fragmented peptide pattern of M-CSPG is the same as that of PG-M, and both are different from that of aggrecan. The aggrecan pattern has one prominent large band (molecular mass 130 kDa), some less prominent large bands (molecular mass 70-100 kDa) and several smaller bands. In contrast, the PG-M and M-CSPG patterns show no bands with molecular masses > 73 kDa, and the smaller bands (molecular mass < 40 kDa) have a different pattern to that of the smaller bands from aggrecan. The electron microscopic images of aggrecan show a core protein with one end having two globular regions separated by a short linear segment; adjacent to this is a long linear segment, which sometimes contains a third globular region at the end of the core protein opposite the end with the double-globe structure. M-CSPG and PG-M core proteins never show images with the double-globe structure. Instead, one end of the molecule has a single globular domain, and a second globular region is variably present at the opposite end of the core protein. Thus, by all three methods, the core proteins of PG-M and M-CSPG appear to be the same and both differ from the core protein of aggrecan.

Biochemistry of articular cartilage in health and disease

Articular cartilage covers the ends of long bones in synovial joints, providing smooth articulation and cushioning of the underlying bone during joint movement. The tissue can be viewed as a viscoelastic, composite material composed of collagen type II (and smaller amounts of other collagens) entrapping compressed (underhydrated) proteoglycan aggregates which generate a high osmotic/swelling pressure. This abundant extracellular matrix (ECM) is synthesized and turned over by relatively few cells, the chondrocytes. These cells produce a compartmentalized ECM, the components of which are heterogeneous and vary with anatomical location. They also undergo changes with age and altered functional requirements. Articular cartilage contains no separating basement membranes, nerves, lymphatics, or blood vessels. Access to nutrients and elimination of waste products occur via diffusion through the extracellular matrix. The turnover of collagen is much slower than that of proteoglycans. Products of the metabolic turnover of the matrix macromolecules are released continuously into the synovial cavity and ultimately reach the blood circulation where they can be measured as "markers" of metabolic changes.

Carbohydrate and amino acid analyses of Giardia muris cysts

Intact Giardia muris cysts were subjected to consecutive chloroform/methanol and 2% sodium dodecyl sulfate (SDS) extractions, and to amyloglucosidase treatment. The SDS-insoluble, amyloglucosidase-fast cyst walls (ACW) were further incubated with chymotrypsin, trypsin, papain, or pronase. Low voltage scanning electron microscopy revealed no discernible change in the ultrastructure of the filamentous layer of the cyst wall following any of these treatments. Affinity for cyst wall-specific monoclonal antibody (Meridian Diagnostics, Cincinnati, OH) was also retained after all treatments. Periodic acid-Schiff staining and gas chromatography/mass spectrometry (GC/MS) of intact and treated cyst hydrolysates showed a significant reduction in the amount of glucose associated with the cyst (72 nmoles/10(6) intact cysts vs 1.9 nmoles/10(6) ACW) as a result of amyloglucosidase treatment, indicating that glucose is stored within Giardia as an SDS-insoluble polymer. Galactosamine was identified by GC/MS as the predominant sugar associated with both the ACW and the proteinase treated ACW (42 nmoles/10(6) ACW). High performance liquid chromatographic analysis of amino acids from intact and treated cyst hydrolysates revealed a marked reduction, but not elimination, of detectable quantities of identifiable amino acid residues (255 nmoles/10(6) intact cysts vs 6.8 nmoles/10(6) proteinase treated ACW). These results suggest that the filamentous layer of the cyst wall is primarily a carbohydrate peptide complex.

The endocytic hyaluronan receptor in rat liver sinusoidal endothelial cells is Ca(+2)-independent and distinct from a Ca(+2)-dependent hyaluronan binding activity

Isolated and cultured rat liver sinusoidal endothelial cells (LECs) retain the ability to specifically bind 125I-hyaluronan (HA) and internalize it using a coated pit pathway [Biochem J, 257:875-884, 1989]. Here we have determined the effect of Ca+2 on the binding and endocytosis of HA by LECs. 125I-HA binding to intact LECs at 4 degrees C occurred both in the absence (10 mM EGTA) or the presence of physiologic concentrations of Ca+2 (1.8 mM). However, the specific binding of 125I-HA to LECs increased linearly with increasing Ca+2 concentrations. After permeabilization with the nonionic detergent digitonin, the Ca(+2)-independent HA binding activity increased approximately 743%, while the Ca(+2)-dependent binding activity was enhanced only approximately 46%. Therefore, the Ca(+2)-dependent HA binding activity appears not to be intracellular, whereas the Ca(+2)-independent HA receptor is found both inside LECs and on the cell surface. When LECs were allowed to endocytose 125I-HA at 37 degrees C in 10 mM EGTA or in 1.8 mM Ca+2, no differences were seen in the extent or rate of endocytosis. When LECs were allowed to endocytose 125I-HA in the presence of 10 mM Ca+2, the amount of cell-associated radioactivity increased approximately 20-50-fold. However, this additional cell-associated 125I-HA was not sensitive to hyperosmolarity and was removed by washing the cells in 10 mM EGTA at 4 degrees C. Therefore, the Ca(+2)-dependent cell-associated 125I-HA had accumulated on the cell surface and had not been internalized. From these studies we conclude that LECs have at least two types of specific HA binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-related effects of 1,25-dihydroxyvitamin D3 on growth, modeling, and morphology of fetal mouse metatarsals cultured in serum-free medium

A serum-free, fetal bone organ culture model that permits the simultaneous determination of modeling and growth parameters was used to examine the effects of a near physiologic and a pharmacologic dose of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3]. The fetuses of pregnant mice were removed on day 17 of gestation, and three medial metatarsal rudiments were cleaned and after preculturing were cultured as pair-matched groups for 4 days in MEM supplemented with 0.2% BSA. 1,25-(OH)2D3 was added to the cultures at concentrations of 10(-12) or 10(-6) M. Cultures treated with the carrier and devitalized bones served as controls. For resorption studies, pregnant mice were given 45Ca on day 17 of pregnancy and fetal metatarsals harvested 24 h later. Resorption was determined by the amount of 45Ca released into the media. DNA synthesis was estimated by determining the incorporation of [3H]thymidine, collagen synthesis by measuring the incorporation of [3H]proline, mineralization by the incorporation of 45Ca, and proteoglycan synthesis by the incorporation of 35S. The amount of radiolabel was detected in media, as well as in noncultured, dead, and cultured rudiments. The total length of the rudiments and length of the calcified diaphyses were measured daily. In addition, rudiments from all experimental groups were prepared for light and electron microscopy. The high dose (10(-6) M) of 1,25-(OH)2D3 suppressed total rudiment growth but not the growth of the calcified diaphysis, 1,25-(OH)2D3 also decreased DNA, collagen, and proteoglycan synthesis, reduced calcification, and increased bone resorption in a dose-related manner. There were morphologic and ultrastructural changes in the osseous tissues and cells, particularly with the high dose of vitamin D, that supported the biochemical findings of suppressed activity of the osteogenic and chondrogenic cells. However, the suppression of collagen production and bone cell proliferation observed with the pharmacologic dose of vitamin D may be partially attributable to the decrease in bone mass (from increased resorption), thus resulting in less osseous tissue surface for these events to occur as endochondral osteogenesis progressed. The lower dose of vitamin D, however, had effects on 35S and 45Ca incorporation that could not be attributed to a decreased osseous tissue mass. This study emphasizes the importance of measuring specialized activities of the various cell populations in bone rudiment culture models to more fully understand the changes in tissue metabolism that result in changes in rudiment growth and modeling.

Connective tissues of the periodontium. Research and clinical implications

The periodontium is a complex anatomical site composed of a variety of hard and soft connective tissues. The site is subjected to enormous daily chemical and mechanical abuse, yet, for the most part remains relatively intact. Nonetheless, when breakdown does occur, the ability of the periodontium to regenerate is sometimes limited. This review considers the various components of the periodontium and how they might be involved in not only the pathology of periodontal diseases but also the various reparative and regenerative processes required during wound healing. In addition, the importance of external factors such as a variety of commonly prescribed medications on these events is discussed.

Immunohistochemical identification of proteoglycans in gelatinous membranes of cat and gerbil inner ear

Proteoglycans have been identified in gelatinous membranes of adult cat and gerbil inner ears using highly specific histochemical techniques. The tectorial and otoconial membranes and cupula of both species stained strongly with high iron diamine which is specific for sulfate esters and with monoclonal antibody against keratan sulfate proteoglycan (KSPG). The cat tectorial membrane also showed strong immunoreactivity with monoclonal antibody against chondroitin sulfate proteoglycan (CSPG) but the gerbil tectorial membrane reacted only weakly with this antibody. Otoconial membranes and the cupula of both species showed little if any immunostaining with antibodies against CSPG. Supporting cells in the vestibular neurosensory epithelium and planum semilunatum cells in the ampullae of the cat stained strongly with anti-KSPG, demonstrating the origin of KSPG in the cat. These cell types failed to stain in the gerbil, however, suggesting a different mechanism of secretion or a slower rate of turnover of membraneous KSPG in the gerbil. Interdental cells of both species failed to react with either antibody, leaving the origin of tectorial membrane proteoglycans in question. The approach used here provides a highly sensitive and reliable means of assessing the contribution of specific proteoglycans to inner ear structure and function.

Human aortic proteoglycans of subjects from districts of high and low prevalence of atherosclerosis in China

The contents of three species of proteoglycans (PGs), heparan sulfate PG(HSPG), chondroitin sulfate PG(CSPG) and dermatan sulfate chondroitin sulfate PG(DSCSPG), in human thoracic aortas of subjects from districts of high (Beijin, in North China) and low (Nanning, in South China) prevalence of atherosclerosis in China were quantitated. Higher aortic HSPG and DSCSPG (but lower DS) in samples from Nanning than those from Beijing might be implicated in the lower prevalence of atherosclerosis in the former.

Ultrastructure of proteoglycans in the tectorial membrane

The ultrastructure of proteoglycans (PGs) in the tectorial membrane (TM) of the mature chinchilla cochlea was investigated using the cationic dye Cuprolinic blue. When used at a high critical electrolyte concentration, Cuprolinic blue has been shown specifically to bind to the glycosaminoglycan residues of sulfated PGs. After Cuprolinic blue treatment, PGs were observed in the TM which were represented as rod-shaped, electron-dense structures. A perifibrillar, primarily orthogonal, array of PGs was associated with the type A protofibrils. These PGs were distributed in 50 nm intervals along the length of the type A protofibrils. A less common orientation was parallel to the axis of the type A protofibrils. PGs did not appear to be associated with the type B protofibrils. Based upon previous results by other investigators, the TM contains types II and IX collagen, and it appears likely that the type A protofibrils are composed of collagen type II. PGs visualized in the TM in this study thus may represent the glycosaminoglycan residue of type IX collagen which is associated with the type II collagen fibrils. Alternatively, the TM PGs may be small dermatan or chondroitin sulfate PGs.

Correlations between age and rat dermis modifications. Ultrastructural-morphometric evaluations and lysyl oxidase activity

The extracellular matrix is a complex, integrated macromolecular system which plays a crucial role in the economy of each organ. In this study we focused our attention on the correlations between age and rat skin dermis. The latter was chosen as a model of the connective tissue, and was analyzed by means of electron microscopy and by measurement of the activity of lysyl oxidase, the enzyme involved in collagen and elastin crosslink formation. Ultrastructural and morphometric evaluations associated to body weight growth, showed a progressive increase in the amounts of extracellular components and a progressive reduction in the cell density. Skin from adult animals appeared characterized by a well organized matrix; by contrast, in old rats, we observed several degenerative features such as the disorganization of collagen bundles, the vacuolization of elastic fibers, and the atrophy of the mesenchimal cells. Morphometric evaluations in old animals showed a slight but significant reduction in the percentage of the total collagen measured, a fair stability in the area occupied by the elastin fibers, and an increase of the apparently non-structured matrix. The fact that lysyl oxidase activity was diminished in old rats does not corroborate the observation by several authors that increased collagen insolubility is a consequence of higher intra- and intermolecular crosslinking. This would suggest that other chemical modifications, such as crosslink oxidation or non enzymatic glycosylation, might be involved during the aging of connective tissue. The qualitative and quantitative modifications observed at all ages illustrate the correlation between connective tissue modifications and structural and/or functional properties of the skin.

Mechanical stimulation by intermittent compression stimulates sulfate incorporation and matrix mineralization in fetal mouse long-bone rudiments under serum-free conditions

Mechanical stimulation evoked by intermittent hydrostatic compression (IC) in a closed culture system has been shown to stimulate calcification of fetal long-bone rudiments in the presence of serum [6]. We have studied effects of IC on sulfate metabolism and matrix mineralization under serum-free conditions, in short-term (24 hours) cultures of mineralizing long-bone rudiments in alpha minimum essential medium (MEM) + 0.2% bovine serum albumen (BSA). Exposure to IC for 24 hours stimulated radiosulfate incorporation into the papain-digestible pool in the noncalcifying epiphyses and, to a larger extent, in the calcifying diaphysis. The percentage release of 35S from prelabeled rudiments was stimulated in the epiphyses, but inhibited in the diaphyses. The changes in sulfate metabolism of matrix mineralization, in hypertrophic cartilage, and the diaphyseal bone collar, were judged from the increase in length of the diaphysis. This study shows that under serum-free conditions, mechanical stimulation by IC increases sulfate content while stimulating mineralization in calcifying cartilage of fetal long-bone rudiments. Mechanical stimulation seems to be an important regulator of cartilage calcification.

Cytochemical changes in a human arterial proteoglycan related to atherosclerosis

The cuprolinic blue (CB) staining method has been used to visualize and characterize proteoglycans (PG) in the extracellular matrix (ECM) of normal and atherosclerotic human arteries. Arterial tissues of 13 individuals (1-83 years of age) were obtained by autopsy. For electron microscopic visualization of PGs staining with CB was performed in the presence of a critical electrolyte concentration of 0.3 M MgCl2. Under these conditions CB selectively interacts with the polysulfated glycosaminoglycan (GAG) side chains of the molecules. Removal of PG side chains by GAG-degrading enzymes prior to CB staining selectively prevented the formation of chondroitin sulfate (CS)-rich and dermatan sulfate (DS)-rich PG-CB precipitates. The DS-rich type of PG is mainly associated with collagen fibrils, the CS-rich type of PG is preferentially localized in nonfibrous areas of the ECM (soluble matrix). When normal arterial tissues are compared with those affected by atherosclerosis quantitative and qualitative changes of PG-CB precipitates are detected. In fibrous plaques a strong accumulation of a large CS-rich type of precipitate close by smooth muscle cells (SMC) and foam cells is observed. In addition, these precipitates are significantly longer in fibrous plaques than in adjacent normal media (116 nm vs. 100 nm; P less than 0.001). This alteration is independent of the age of the donor. Small DS-rich PG-CB precipitates associated with collagen fibrils show strong variations in their length, but not a significant tendency towards elongated precipitates in atherosclerosis. The present results demonstrate that ultracytochemical and morphometric analysis are useful in providing information on the diverse types, locations, interactions, and possibly of molecular changes of PGs in normal and atherosclerotic human arteries.

Growth hormone stimulates insulin-like growth factor I actions on adult articular chondrocytes

We report effects of adding insulin-like growth factor I (IGF-I) and methionyl human growth hormone (GH), alone or in combination, to adult bovine articular chondrocytes plated at high density. Purified human and synthetic IGF-I stimulated chondrocyte DNA and proteoglycan synthesis. GH had no effect on either process. However, GH added in combination with IGF-I increased proteoglycan, cell-associated proteoglycan, and keratan sulfate synthesis over levels observed with IGF-I alone. IGF-I and GH did not alter the hydrodynamic size of proteoglycans or synthesis of collagen. Our results show that GH and IGF-I act together to stimulate adult chondrocyte extracellular matrix synthesis.

Paracoccidioidomycosis: a sequential histopathologic study of lesions in experimentally-infected rats

Female albino rats were used for the sequential histopathological study of experimental paracoccidioidomycosis. The animals were inoculated intraperitoneally with a strain of Paracoccidioides brasiliensis in the yeast-like phase, and sacrificed at given intervals from 1 to 168 days after inoculation; each animal received an inoculum of 4 x 10(6) cells in 0.8 ml of saline. The control group received saline containing scrapings of the culture medium. Tissue from the inoculation site was examined. The cellular population, the extracellular matrix, and the presence and characteristics of fungi were analysed in the inflammatory granulomatous process by light microscopy. The results allowed to separate the kinetic of the inflammatory response into three stages: 1) neutrophilic or macrophagic-neutrophilic; 2) pre-granulomatous; 3) granulomatous. Synthesis of the extracellular matrix began with the depositing of fibrin-like material, and increased gradually with deposits of collagen, proteoglycans, and glycoproteins. Parasites were present in all of the examined periods. Recurrences of the disease were clearly shown through the concurrence of recently-formed granulomas with older granulomas, implying that this type of granulomatous process does not eliminate the disease, nor is it able to limit fungal dissemination over a prolonged period of time.

Connective matrix organization in chronic granulomas of experimental paracoccidioidomycosis

The histological and ultrastructural aspects of chronic granulomas from rats infected intraperitoneally with Paracoccidioides brasiliensis are described with special emphasis on the composition of the extracellular matrix. The granulomas were structurally arranged in two zones, one central containing fungi, and the other peripheral. The extracellular matrix was composed of collagen types I and III, proteoglycans, glycoprotein, and an undefined amorphous substance. The main cellular population was represented by macrophages, epithelioid cells, and giant cells in the central zone, and fibroblasts in the peripheral zone. The fibrotic process was a critical event in this stage of the infection, and showed a centrifugal direction. This might be provoked by direct stimulus from the fungi or by macrophage-fibroblastic interaction.

Ultrastructure of complex carbohydrates of rodent and monkey ependymal glycocalyx and meninges

The surfaces of the brain offer metabolic and mechanical support to the underlying parenchyma. Mouse, rat, and monkey brains were fixed by immersion in a glutaraldehyde fixative or glutaraldehyde with cetylpyridinium chloride, followed by block staining for complex carbohydrates using alcian blue with OsO4 postfixation, or OsO4 postfixative solution containing ruthenium red, or alcian blue and then ruthenium red-OsO4 treatment. The ependyma in these species had a glycocalyx extending into the ventricular fluid as a finely filamentous network when stained with alcian blue or with alcian blue followed by ruthenium red-OsO4. Mice in the middle age range had stained material in this glycocalyx resembling the hyaluronic acid reported in the ocular vitreous body. Similar material was seen in the arachnoidal space of these mice and in the inner connective tissue matrix of the dura mater. Both the mouse and monkey had a cell-free zone, termed the inner dural matrix zone, between the thick fibrous dura and its innermost cellular layer. This zone contained filamentous and globular alcian blue-stained material. The complex carbohydrates of the mouse ependymal glycocalyx and inner dural matrix zone underwent changes developmentally. Aged rats were injected intraventricularly with latex beads, which, along with extravasated erythrocytes, were seen to adhere to the ependymal glycocalyx. A similar adhesion of erythrocytes was seen in the mouse and monkey ependymal glycocalyx and in the filamentous network of the mouse and monkey inner dural matrix zone. The ependymal glycocalyx, formed in part of complex carbohydrates, is much thicker than previously demonstrated. Some activities related to the ependymal lining of the ventricles, including the movement of cells or particles, the penetration of metabolites or serum-protein fractions (e.g., immunoglobulins), and cell-surface hydration, probably depend in part on complex carbohydrates that provide a sticky, electrically negative, hydrophilic environment. The complex carbohydrates in the inner dural matrix zone might provide mechanical buffering. Complex carbohydrates in the arachnoidal space may help to maintain a loose tissue that needs not only to be hydrated, but also to be open enough to provide cerebrospinal fluid circulation.

The effects of proteoglycans from different cartilage types on in vitro hydroxyapatite proliferation

Proteoglycans extracted from nasal and articular cartilages have previously been shown to inhibit hydroxyapatite proliferation in vitro. This study now demonstrates that proteoglycans isolated (dissociatively extracted and reaggregated in vitro) from bovine fetal growth plate and bovine occipital condyle, as well as those from bovine nasal cartilage, all retard hydroxyapatite seeded-growth in vitro. On a weight basis (1 mg/ml), the growth plate proteoglycan preparation had a significantly greater inhibitory effect. The greater inhibitory effect of the growth plate proteoglycans as compared to the other cartilage proteoglycan preparations may be related to the unique properties of the proteoglycans in the growth plate, a tissue that undergoes physiological calcification.