Keratan sulfate is a component of proteoglycans in the compressed region of adult bovine flexor tendon

Cartilage oligomeric matrix protein (COMP) levels in digital sheath synovial fluid and serum with tendon injury

Cartilage oligomeric matrix protein (COMP) is a noncollagenous extracellular matrix protein found predominantly in cartilage, but also in tendon, ligament and meniscus. Studies in man have demonstrated that it may be used as a prognostic marker in rheumatoid arthritis and osteoarthritis. The present study investigated whether tendon injury contributes to serum and tendon sheath synovial fluid levels of COMP in horses. COMP levels, analysed by competitive ELISA, in the digital sheath synovial fluid were more than 10-fold higher than in the serum. Levels were significantly raised when tendon damage or sepsis was present within the tendon sheath but showed only mild, statistically insignificant, elevation in cases of tenosynovitis alone. COMP concentrations in serum were found to vary with age. Foals (age < or = 1 year) had significantly (P<0.001) higher levels in comparison to older control horses. Total COMP concentrations in an age-matched group with tendinitis were not significantly different from the control group. Measurements of COMP levels in tendon sheath synovial fluid are therefore useful in depicting processes in tendon tissue, while elevated serum levels are likely to be more representative of joint disease than tendinitis.

Proteoglycan synthesis by fibroblasts from different regions of bovine tendon cultured in alginate beads

The ability of cell shape to modulate proteoglycan synthesis in tendon fibroblasts was investigated by placing freshly isolated tendon fibroblasts and chondrocytes into primary culture either as adherent cells on a polystyrene substratum or as rounded cells in alginate beads. Chondrocytes and cells from the compressed region of adult tendon synthesized predominantly large proteoglycan when maintained either as dense monolayers, where actin stress fibers in the cytoskeleton were prominent, or in alginate beads, where actin fibers could not be detected. After three rounds of proliferation as elongated adherent cells the synthesis of large proteoglycan was greatly reduced, i.e. the chondrocytic cells underwent 'dedifferentiation'. Cells from the tensional region of adult tendon synthesized predominantly small proteoglycan when in primary culture as a monolayer, after proliferation on a flat substratum, or as round cells in alginate beads. Fibroblasts from the tensional region of newborn tendon showed no tendency toward increased synthesis of large proteoglycan when maintained as round cells in alginate beads for 7 weeks. In tendon there appears to be a mechanically induced developmental transition from fibroblastic to chondrocytic cells. However, neither the change to a rounded cell shape nor the lack of organized cytoskeletal actin fibers was sufficient to induce chondrocyte-like proteoglycan synthesis in differentiated tendon fibroblasts in culture.

The distal tendon of the biceps brachii. Structure and clinical correlations

The structure and blood supply of 42 distal biceps tendons were investigated by means of light and electron microscopy as well as by immunohistochemistry. Possible structural causes for the rupture of the tendon are discussed. The distal biceps tendon wraps around the radius during pronation of the forearm. In this area the tendon is exposed to pressure and shearing forces in addition to those caused by tension. Two fibrocartilaginous areas were regularly observed. Large chondrocyte-like cells were found inside the fibrocartilage. As an expression of strain, the extracellular matrix is rich in acidic glycosaminoglycans and stains intensely with toluidine blue at pH 1. Electron microscopy showed a granular pericellular matrix that increases in size towards the gliding surface. Type I collagen is the main component of the distal biceps tendon. Type II collagen is found in tendon fibrocartilage but not in traction tendons. The gliding surface of the tendon is made up of reticular fibres that are equivalent to type III collagen. Monoclonal antibodies revealed the presence of dermatan-sulfate, keratansulfate and chondroitin-4- as well as chondroitin-6-sulfate. Blood vessels are usually absent in fibrocartilage, as was shown with a polyclonal antibody against the basement membrane component laminine. There are significant differences between the extracellular matrix of traction and gliding tendons, which may be responsible for the location of tendon rupture.

Aggrecan in bovine tendon

Large proteoglycans were purified by ion-exchange chromatography, gel filtration and CsCl gradient centrifugation from the compressed and tensional regions of adult bovine deep flexor tendon. Tryptic peptide maps of proteoglycan from the compressed region were very similar to maps of aggrecan from bovine articular cartilage, with evidence for the presence of all fifteen previously identified markers from the G1, G2 and G3 domains. The presence of aggrecan in these samples was confirmed by sequencing the G1 peptide YPIHTPR. The equivalent maps for large proteoglycan from tensional tendon were also consistent with the presence of aggrecan, and this was confirmed by sequencing three marker peptides from each of the G2 and G3 domains. However, G1 marker peptides were conspicuously absent from tensional samples. Northern blots for aggrecan mRNA showed high levels in cells from compressed tendon and articular cartilage. Extended exposure revealed a lower level of hybridization to RNA from tensional tendon as well. The results confirm that aggrecan, which is similar in core protein structure to articular cartilage aggrecan, is the predominant chondroitin sulfate-bearing large proteoglycan of compressed tendon. The results also indicate that aggrecan fragments lacking the G1 domain can account for the small amounts of chondroitin sulfate-bearing large proteoglycan in tensional regions of adult tendon.

Histochemical aspects of the proteoglycans of patellar tendon autografts used to replace the posterior cruciate ligament

In the female German black-faced sheep the posterior cruciate ligament was replaced by a free patellar tendon autograft and after 2, 6, 16, 26 and 52 weeks tissue samples of the graft's center (axial region far from bones) were removed for histochemistry and electron microscopy. To localize the proteoglycans Alcian Blue and 0.3 M MgCl2 were added to the fixative solution. The distribution of the proteoglycans in the graft was compared to that of a normal patellar tendon and of a normal posterior cruciate ligament. In the patellar tendon spindle-shaped cells predominated and proteoglycans appeared as short filaments at regular intervals between the collagen fibrils. In the posterior cruciate ligament chondroid cells and long filaments in a net-work-like arrangement were seen. In the patellar tendon autografts short interfibrillar filaments prevailed after 2, 6 and 16 weeks. After 26 weeks and particularly after 52 weeks long filaments also appeared. Digestion with Chondroitinase ABC, AC and Hyaluronidase suggested that the short filaments were PGs containing dermatan sulfate. In grafts, in the early phases the fibroblasts predominated, while in the late phases mainly chondroid cells were observed. The grafts showed aspects of the normal posterior cruciate ligament. However, differences remained, for example the thin collagen fibrils, which could represent one of the reasons for a secondary graft failure.

Proteoglycans in the compressed region of human tibialis posterior tendon and in ligaments

Proteoglycan content and tissue morphology were examined in tendons and ligaments from 24 cadavers, ranging in age at the time of death from 1.5 months to 83 years. The region of the human tibialis posterior tendon that passes under the medial malleolus was characterized by cells having a rounded shape, positive staining with alcian blue, and higher glycosaminoglycanuronic acid content than in the more proximal region of the same tendon. Analysis of proteoglycans by sodium dodecyl sulfate/polyacrylamide gel electrophoresis indicated that the predominant small proteoglycan of the proximal/tensional region was decorin, whereas two types of small proteoglycans (decorin and biglycan) and large proteoglycans were present in the region passing under the medial malleolus and presumably subjected to compressive and shear forces in addition to tension. The pattern of proteoglycan accumulation in the compressed region of tendon was basically similar for all individuals and showed no distinctive trends related to age after puberty. In terms of type and amount of proteoglycan, the patellar tendon was like the tensional region of the tibialis posterior. Glycosaminoglycan content in the lateral collateral ligament and anterior cruciate ligament, however, was twofold higher than in the tendons. The ligaments contained large as well as small proteoglycans, just as in the compressed region of tendon.

Healing of canine tendon in zones subjected to different mechanical forces

The effect of external force environment on the healing of a partial thickness injury to canine flexor tendon was studied. A 50% laceration was made in either the fibrocartilaginous (compressive) zone or in the tendinous (tensile) zone of canine flexor digitorum profundus tendons. After three or six weeks, the tendons were harvested. An optical method for determining zone-specific material properties showed that, in response to injury, the structural stiffness decreased in the tensile zone of the tendon but increased in the compressive zone. The mechanical properties and failure mechanism of canine tendon and their changes in response to injury vary according to tendon zone, and differences in the healing process in mechanically specialised zones of the flexor tendon are discussed.

Correlation of histopathological features of pannus with patterns of damage in different joints in rheumatoid arthritis

The cartilage-pannus junction has been studied in multiple sections from 23 rheumatoid joints. Changes suggesting a metaplastic reaction of the articular cartilage, termed transitional fibroblastic zone, were commonly found in hips and knees, but were rarely present in metatarsophalangeal joints, in which an invasive pannus with cartilage degradation in close association with inflammatory cells was seen. Thus when multiple sections from rheumatoid joints were examined a transitional fibroblastic zone was found in 1/15 (7%) sections from metatarsophalangeal joints compared with 29/57 (51%) and 15/48 (31%) sections from knee and hip joints respectively. In contrast, an invasive pannus occurred in 11/15 (73%) sections from metatarsophalangeal joints compared with 22/57 (39%) sections from knees and 19/48 (40%) sections from hips. These findings led to the suggestion that this pathological variation between different joints may explain the predominance of erosive change in small joints as compared with joint space narrowing with secondary osteoarthritis found in large joints in rheumatoid arthritis. Inappropriate comparisons between different joints may in part explain the variation in findings of previous histopathological studies.

Ultrastructure and proteoglycan composition in the developing fibrocartilaginous region of bovine tendon

Clear distinctions in morphology and proteoglycan composition have been described in regions of adult tendon that pass under bone and are subjected to compressive as well as tensional forces. In this study, developing bovine deep flexor tendon from early fetal stages through 6 months of age was examined biochemically and by light and electron microscopy. Longitudinal collagen fibers were seen in the tensional region of tendon throughout development; whereas a well established network arrangement of collagen fibers with wide interfibrillar spaces was seen in the compressed region by 7 months of fetal age. Collagen fibril diameters of both regions increased with age with the mean diameter in tensional tissue always greater than in compressed tissue. Glycosaminoglycan hexosamine content of the tensional region remained low throughout development (approximately 0.2% of dry tissue weight), but increased in the compressed region from 0.4% of dry weight at the 7-month fetal stage, to 1.0% dry weight at 6 months. Keratan sulfate was not detectable in tensional tendon at any age as measured by inhibition ELISA, but was found in increasing quantities in the pressure bearing region of tendon from young calves. Small proteoglycans predominated in both tensional and compressed regions throughout fetal and early neonatal development, and were of both PG I (biglycan) and PG II (decorin) types. Large proteoglycans represented only a small proportion of total proteoglycans in both regions of fetal tendon. By SDS/PAGE analysis, immunoreactivity, and molecular sieve chromatography, large proteoglycans of fetal compressed tendon were similar to large proteoglycans of adult tensional tendon in that they contained only chondroitin-6-sulfate, with little if any KS, and appeared to be slightly smaller than cartilage large proteoglycans.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chondroitinase-ABC on proteoglycans and swelling properties of fibrocartilage in bovine flexor tendon

Fibrocartilaginous regions of bovine deep flexor tendon were treated with chondroitinase-ABC and trypsin in order to extract proteoglycans from the extracellular matrix and thereby investigate the contribution of proteoglycan and collagen organization to tissue material properties. Chondroitinase-ABC digestion of tendon specimens for 24 h resulted in extraction of 60% of tissue glycosaminoglycan and leaching of the degraded large proteoglycan from the tissue residue. The totally degraded core protein of the small dermatan sulfate proteoglycan remained with the tissue residue, indicating that it is specifically associated with the tissue residue and that this association is not dependent on the glycosaminoglycan chains. Treatment of residues with trypsin after chondroitinase-ABC digestion depleted the specimens of proteoglycan. Bulk swelling tests on enzyme-extracted specimens showed that the distinct swelling properties of the fibrocartilaginous regions of the distal flexor tendon could be partially accounted for by elevated levels of proteoglycan. Swelling tests also showed that the distinct collagen organization of this region contributes significantly to the tissue's material properties. These results suggest that the fibrocartilaginous organization and composition of the articulating layer of distal tendon are adapted for mechanical requirements unique to this site, which receives compressive and frictional loads in addition to tensile loads.