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

Investigation of a Novel Cross-Linked Hyaluronan Hydrogel for Use as a Soft-Tissue Filler

Objective:

To investigate an innovative tyramine-based hyaluronan (TB-HA) biomaterial for soft-tissue augmentation. Specifically, to test: (1) the ability of the TB-HA biomaterial to be injected subcutaneously; and (2) to test the in vivo response of the TB-HA biomaterial in an immunocompetent animal model.

Introduction:

Hyaluronan (HA) is a normal component of most tissues and, as such, is nonimmunogenic, nontoxic, and noninflammatory. Cross-linked hydrogels are formed from HA by substitution (approximately 5%) with tyramine followed by enzymatic cross-linking with peroxidase in the presence of very dilute hydrogen peroxide. From a single formulation of tyramine-substituted HA (TS-HA), a full spectrum of biomaterial properties can be produced by varying the HA concentration before cross-linking. The properties of these biomaterials ranged from a soft, optically clear hydrogel (6.25 mg/mL), suitable for soft-tissue augmentation as an injectable material, to a paste-like material (12.5–25.0 mg/mL).

Materials and Methods:

The hydrogel was evaluated in vivo as an injectable material (6.25 mg/mL). The material was injected into the subcutaneous tissue of an adult Sprague-Dawley rat, harvested at 8 weeks, and evaluated grossly and histologically. The specimens were paraffin embedded, sectioned on a microtome, and stained with hematoxylin and eosin.

Results:

In vivo analysis of the TB-HA hydrogels at 8 weeks revealed that they were resistant to degradation. Histological analysis revealed no evidence of rejection or tissue inflammatory response.

Conclusions:

Novel enzymatic cross-linking of HA enables the development of a versatile new biomaterial that can be used for soft-tissue augmentation. Preliminary in vivo analysis in an immunocompetent rat model revealed that the hydrogel material resisted degradation and did not elicit a host inflammatory response.

The molecular composition of the extracellular matrix of the human iliolumbar ligament

BACKGROUND CONTEXT

The human iliolumbar ligament connects the transverse process of L5 to the iliac crest and contributes to lumbosacral stability and has been associated with low back pain. However, different opinions exist regarding the functional relevance of the ligament.

PURPOSE

In the present study, we analyze the regional molecular composition of the ligament extracellular matrix.

STUDY DESIGN

Special attention is given to the attachment sites, to determine whether the ligament is subjected to a certain mechanical environment.

METHODS

Iliolumbar ligament samples, extending from one enthesis to the other, were removed from 11 cadavers and fixed in methanol. Cryosections were immunolabeled with a panel of antibodies directed against collagens, glycosaminoglycans, proteoglycans, matrix proteins, and neurofilament.

RESULTS

The mid-substance of the ligament labeled for all the molecules normally found in dense fibrous connective tissue including types I, III, and VI collagen, versican, dermatan -, chondroitin 4 -, and keratan sulfate. However, both entheses were fibrocartilaginous and labeled for type II collagen, aggrecan, and chondroitin 6- sulfate. A common feature was fat between the fiber bundles near the entheses. Occasionally this fat contained nerve fibers.

CONCLUSIONS

The existence of fibrocartilaginous entheses suggests that the insertion sites of the ligament are subject to both tensile and compressive loading-probably because of insertional angle changes between ligament and bone during loading. Our findings support the suggestion that the iliolumbar ligament might play an important role in the stabilization of the lumbosacral junction.

Immunohistochemical composition of the human lunotriquetral interosseous ligament

PURPOSE

The human lunotriquetral ligament (LTL) is a functionally important intrinsic hand ligament, which is assumedly subjected to insertion angle changes at the entheses during movement. To clarify whether the current model of the ligament's mechanical environment is reflected in its structural composition, we determined the regional distribution of extracellular matrix-related antigens.

METHODS

The extracellular matrix was immunohistochemically investigated in 12 LTLs from both wrists of 6 human donors (Mean age: 60 y).

RESULTS

The dorsal, proximal, and volar portions of the ligament immunolabeled for type I, III collagen and versican. Both entheses labeled strongly for type II collagen, aggrecan, and link protein and were distinctly cartilaginous. The ligament midsubstance was positive for collagen II in 30%, for aggrecan in 40%, and for keratocan and lumican in 100% of specimens. In contrast, keratocan and lumican were absent from the fibrocartilaginous entheses and the articular cartilage. Ligament insertion at a carpal bone occurs either directly through fibrocartilage or indirectly through a bilayered configuration of fibrocartilage and hyaline-like cartilage. The hyaline-like cartilage is continuous with the neighboring articular cartilage.

CONCLUSIONS

The LTL has an extracellular matrix comparable with that of ligaments experiencing a combination of tensile and shear/compressive load at the attachment sites. All regions of the LTL exhibit fibrocartilaginous entheses; purely fibrous attachment sites are rare. The ligament midsubstance shows a more fibrous phenotype than the entheses and expresses keratocan and lumican, which previously have not been recorded in any human hand ligament.

Synthesis and characterization of tyramine-based hyaluronan hydrogels

Hyaluronan is particularly attractive for tissue engineering and repair because it: (1) is a normal component of the extracellular matrices of most mammalian tissues; (2) contributes to the biological and physical functions of these tissues; and (3) possesses excellent biocompatibility and physiochemical properties. In the present study, we characterize a two-step enzymatic cross-linking chemistry for production of tyramine-based hyaluronan hydrogels using fluorophore-assisted carbohydrate electrophoresis, enzymatic digestion, and spectroscopy including absorbance, fluorescence and (1)H NMR. Substitution on hyaluronan of tyramine and other adducts from unproductive side reactions depends on the molar ratio of tyramine to carbodiimide used during the substitution (step 1) reaction. Results indicate that relatively low tyramine substitution is required to form stable hydrogels, leaving the majority of hyaluronan disaccharides unmodified. Sufficient native HA structure is maintained to allow recognition and binding by b-HABP, a HA binding complex typically found in normal cartilage biology. Hydrogels were formed from tyramine-substituted hyaluronan through a peroxidase-dependent cross-linking (step 2) reaction at hyaluronan concentrations of 2.5 mg/ml and above. Uncross-linked tyramine-substituted hyaluronan was characterized after hyaluronidase SD digestion. Cross-linked hydrogels showed increased resistance to digestion by testicular hyaluronidase and hyaluronidase SD with increasing hyaluronan concentration. Cells directly encapsulated within the hydrogels during hydrogel cross-linking remained metabolically active during 7 days of culture similar to cells cultured in monolayer.

An immunohistochemical study of the triangular fibrocartilage complex of the wrist: regional variations in cartilage phenotype

The triangular fibrocartilage complex (TFCC) transmits load from the wrist to the ulna and stabilizes the distal radioulnar joint. Damage to it is a major cause of wrist pain. Although its basic structure is well established, little is known of its molecular composition. We have analysed the immunohistochemical labelling pattern of the extracellular matrix of the articular disc and the meniscal homologue of the TFCC in nine elderly individuals (age range 69-96 years), using a panel of monoclonal antibodies directed against collagens, glycosaminoglycans, proteoglycans and cartilage oligomeric matrix protein (COMP). Although many of the molecules (types I, III and VI collagen, chondroitin 4 sulphate, dermatan sulphate and keratan sulphate, the oversulphated epitope of chondroitin 6 sulphate, versican and COMP) were found in all parts of the TFCC, aggrecan, link protein and type II collagen were restricted to the articular disc and to entheses. They were thus not a feature of the meniscal homologue. The shift in tissue phenotype within the TFCC, from a fibrocartilaginous articular disc to a more fibrous meniscal homologue, correlates with biomechanical data suggesting that the radial region is stiff and subject to considerable stress concentration. The presence of aggrecan, link protein and type II collagen in the articular disc could explain why the TFCC is destroyed in rheumatoid arthritis, given that it has been suggested that autoimmunity to these antigens results in the destruction of articular cartilage. The differential distribution of aggrecan within the TFCC is likely to be reflected by regional differences in water content and mobility on the radial and ulnar side. This needs to be taken into account in the design of improved MRI protocols for visualizing this ulnocarpal complex of the wrist.

Binding and localization of recombinant lubricin to articular cartilage surfaces

Lubricin is a secreted, cytoprotective glycoprotein that contributes to the essential boundary lubrication mechanisms necessary for maintaining low friction levels at articular cartilage surfaces. Diminishment of lubricin function is thereby implicated as an adverse contributing factor in degenerative joint diseases such as osteoarthritis. Lubricin occurs as a soluble component of synovial fluid, and is synthesized and localized in the superficial layer of articular cartilage (and thus has also been described as "superficial zone protein", or SZP); however, defined interactions responsible for lubricin retention at this site are not well characterized. In the current studies, we identified molecular determinants that enable lubricin to effectively bind to articular cartilage surfaces. Efficient and specific binding to the superficial zone was observed for synovial lubricin, as well as for recombinant full-length lubricin and a protein construct comprising the lubricin C-terminal (hemopexin-like) domain (LUB-C, encoded by exons 7-12). A construct representing the N-terminal region of lubricin (LUB-N, encoded by exons 2-5) exhibited no appreciable cartilage-binding ability, but displayed the capacity to dimerize, and thus potentially influence lubricin aggregation. Disulfide bond disruption significantly attenuated recombinant lubricin and LUB-C binding to cartilage surfaces, demonstrating a requirement for protein secondary structure in facilitating the appropriate localization of lubricin at relevant tissue interfaces. These findings help identify additional key attributes contributing to lubricin functionality, which would be expected to be instrumental in maintaining joint homeostasis.

Expression of extracellular matrix molecules typical of articular cartilage in the human scapholunate interosseous ligament

The scapholunate interosseous ligament (SLIL) connects the scaphoid and lunate bones and plays a crucial role in carpal kinematics. Its rupture leads to carpal instability and impairment of radiocarpal joint function. As the ligament is one of the first structures affected in rheumatoid arthritis, we conducted an immunohistochemical study of cadaveric tissue to determine whether it contains known autoantigens for rheumatoid arthritis. We immunolabelled the ligament from one hand in 12 cadavers with monoclonal antibodies directed against a wide range of extracellular matrix (ECM) molecules associated with both fibrous and cartilaginous tissues. The labelling profile has also enabled us to comment on how the molecular composition of the ligament relates to its mechanical function. All regions of the ligament labelled for types I, III and VI collagens, chondroitin 4 and 6 sulphates, keratan sulphate, dermatan sulphate, versican, tenascin and cartilage oligomeric matrix protein (COMP). However, both entheses labelled strongly for type II collagen, aggrecan and link protein and were distinctly fibrocartilaginous. In some regions, the ligament attached to bone via a region of hyaline cartilage that was continuous with articular cartilage. Labelling for cartilage molecules in the midsubstance was most evident dorsally. We conclude that the SLIL has an ECM which is typical of other highly fibrocartilaginous ligaments that experience both tensile load and shear. The presence of aggrecan, link protein, COMP and type II collagen could explain why the ligament may be a target for autoantigenic destruction in some forms of rheumatoid arthritis.

Expression of versican in relation to chondrogenesis-related extracellular matrix components in canine mammary tumors

Versican plays a role in tumor cell proliferation and adhesion and may also regulate cell phenotype. Furthermore, it is one of the pivotal proteoglycans in mesenchymal condensation during prechondrogenesis. We have previously demonstrated accumulation of versican protein in myoepithelial-like spindle cell proliferations and myxoid tissues of complex and mixed mammary tumors of dogs. The objective of this study was to investigate whether the high expression of versican relates to prechondrogenesis in these tissues. Therefore, we aimed to identify cartilage markers, such as collagen type II and aggrecan both at mRNA and protein level in relation to versican. The neopitope of chondoitin-6-sulphate (3B3) known to be generated in developing cartilage has been investigated by immunohistochemisty and a panel of antibodies were used to characterize the phenotype of cells that are involved in cartilage formation. In addition, co-localization of versican with hyaluronan and link protein was studied. RT-PCR revealed upregulation of genes of versican, collagen type II and aggrecan in neoplastic tissues, especially in complex and mixed tumors. Immunohistochemistry showed the expression of cartilage biomarkers not only in the cartilagenous tissues of mixed tumors, but also in myoepitheliomas and in the myoepithelial-like cell proliferations and myxoid areas of complex and mixed tumors. The results show the cartilagenous differentiation of complex tumors and myoepitheliomas and indicate that the myxoid tissues and myoepithelial-like cell proliferations are the precursor tissues of the ectopic cartilage in mixed tumors. Furthermore, we suggest that cartilage formation in canine mammary tumors is a result of (myo)epithelial to mesenchymal transition.

An immunohistochemical study of the tissue bridging adult spondylolytic defects--the presence and significance of fibrocartilaginous entheses

Introduction Spondylolytic spondylolisthesis is an osseous discontinuity of the vertebral arch that predominantly affects the fifth lumbar vertebra. Biomechanical factors are closely related to the condition. An immunohistochemical investigation of lysis-zone tissue obtained from patients with isthmic spondylolisthesis was performed to determine the molecular composition of the lysis-zone tissue and enable interpretation of the mechanical demands to which the tissue is subject.

METHODS

During surgery, the tissue filling the spondylytic defects was removed from 13 patients. Twelve spondylolistheses were at the L5/S1 level with slippage being less than Meyerding grade II. Samples were methanol fixed, decalcified and cryosectioned. Sections were labelled with a panel of monoclonal antibodies directed against collagens, glycosaminoglycans and proteoglycans.

RESULTS

The lysis-zone tissue had an ordered collagenous structure with distinct fibrocartilaginous entheses at both ends. Typically, these had zones of calcified and uncalcified fibrocartilage labelling strongly for type II collagen and aggrecan. Labelling was also detected around bony spurs that extended from the enthesis into the lysis-zone. The entheses also labelled for types I, III and VI collagens, chondroitin four and six sulfate, keratan and dermatan sulfate, link protein, versican and tenascin.

CONCLUSIONS

Although the gap filled by the lysis tissue is a pathological feature, the tissue itself has hallmarks of a normal ligament-i.e. fibrocartilaginous entheses at either end of an ordered collagenous fibre structure. The fibrocartilage is believed to dissipate stress concentration at the hard/soft tissue boundary. The widespread occurrence of molecules typical of cartilage in the attachment of the lysis tissue, suggests that compressive and shear forces are present to which the enthesis is adapted, in addition to the expected tensile forces across the spondylolysis. Such a combination of tensile, shear and compressive forces must operate whenever there is any opening or closing of the spondylolytic gap.

Proteoglycans and catabolic products of proteoglycans present in ligament

The aim of the present study was to characterize the proteoglycans and catabolic products of proteoglycans present in the tensile region of ligament and explant cultures of this tissue, and to compare these with those observed in the tensile region of tendon. Approx. 90% of the total proteoglycans in fresh ligament was decorin, as estimated by N-terminal amino acid sequence analysis. Other species that were detected were biglycan and the large proteoglycans versican (splice variants V(0) and/or V1 and/or V2) and aggrecan. Approx. 23% of decorin detected in the matrix was degraded. Intact decorin and decorin fragments similar to those observed in the matrix that retained the N-terminus were also observed in the medium of ligament cultures. Intact biglycan core protein was detected in the matrix and medium of ligament cultures, and two fragments originating from the N-terminal region of biglycan were observed in the matrix of cultured ligament. Versican and versican fragments that retained the N-terminus of versican core protein were detected in fresh matrix and medium of tendon cultures. Approx. 42% of versican present in the fresh ligament was degraded. Aggrecan catabolites appearing in the culture medium were derived from aggrecanase cleavage of the core protein. An intact link protein and a degradation product from the N-terminal region of type XII collagen were also detected in the medium of the ligament explant.

An immunohistochemical study of the extracellular matrix of the tarsal plate in the upper eyelid in human beings

The superior tarsus is a plate of tissue that stiffens the upper eyelid, gives it support and determines its form. The purpose of the present study was to relate the composition of its extracellular matrix to its function and to report regional differences that may influence the activity of its Meibomian glands. Fourteen methanol-fixed specimens were cryosectioned for immunohistochemistry and labelled with a panel of monoclonal antibodies against a wide range of collagens, glycosaminoglycans and proteoglycans. Labelling was detected with avidin-biotin-peroxidase. A further six specimens were formalin-fixed for routine histology. The tarsal plate immunolabelled strongly for types I, III and VI collagen and for aggrecan, versican, tenascin, cartilage oligomeric matrix protein (COMP) together with a variety of glycosaminoglycans (notably chondroitin 6 sulphate). A region of strong labelling for aggrecan, dermatan sulphate and chondroitin 6 sulphate immediately surrounded the Meibomian glands. The site of labelling corresponded to a layer of acellular and amorphous matrix seen histologically that we have termed the 'territorial matrix'. The results suggested that the tarsal plate is a specialized connective tissue that is neither purely fibrous nor cartilaginous, yet has an aggrecan content that probably contributes to its stiffness. Its unique character highlights the challenge in choosing an ideal mechanical substitute. As patients with rheumatoid arthritis often have problems relating to tear film deficiency, the ability of aggrecan or COMP to act as autoantigens may be significant. An immune reaction directed against these molecules could alter tarsal gland function by interfering with the interaction between the glands and their territorial matrix.

Solid phase assays in glycoconjugate research: applications to the analysis of proteoglycans, glycosaminoglycans and metalloproteinases

Glycoconjugates are a class of macromolecules consisting of different constituents, one of which is sugar moieties. Glycoconjugates comprise the majority of tissue constituents, both intracellular and extracellular. Extracellular glycoconjugates (glycoproteins and proteoglycans) participate in a wide variety of interactions, through which they maintain tissue integrity. Therefore, their analysis or the study of their possible interactions would give evidence for the state of tissues. Since the amounts of some of the extracellular glycoconjugates are usually low or the amounts of tissue to be examined come from biopsies, specific analytical systems are developed for their study, the most familiar being solid phase assays, which have the advantages of analysis of multiple samples on the same time, cheap instrumentation and high specificity.

In situ hybridization and immunohistochemistry of versican, aggrecan and link protein, and histochemistry of hyaluronan in the developing mouse limb bud cartilage

We investigated the expression pattern of versican, aggrecan, link protein and hyaluronan in the developing limb bud cartilage of the fetal mouse using in situ hybridization and/or immunohistochemistry. Versican mRNA and immunostaining were detected in the mesenchymal cell condensation of the future digital bone at E13. Versican mRNA expression rapidly disappeared from the tibial cartilage, as cartilage formation progressed during E13-15, but the immunostaining was gradually replaced by aggrecan immunostaining from the diaphysis. Immunostaining for both molecules thus had a 'nega-posi' pattern and consequently versican immunostaining was still detected at the epiphyseal end at E15. This result indicated that versican functions as a temporary framework in newly formed cartilage matrix. An aggrecan-positive region within the cartilage invariably had intense hyaluronan staining, whereas a versican-positive region also had affinity for hyaluronan within the cartilage, but not in the mesenchymal cell condensation. Therefore, the presence of versican aggregates was not confirmed in the developing limb bud cartilage. Furthermore, although link protein was more closely related with aggrecan than versican during limb bud cartilage formation, there was a discrepancy between the expression of aggrecan and link protein in tibial cartilage at E15. In particular, only a link protein-positive region was present in the marginal area of the metaphysis and the epiphysis at this stage. This finding may indicate a novel role for link protein.

The establishment and characterization of an immortal cell line with a stable chondrocytic phenotype

A cell line was developed from the transplantable Swarm rat chondrosarcoma (RCS) and has been maintained in continuous monolayer tissue culture for a number of years. This long term-cultured (LTC) cell line exhibits the morphological and biochemical characteristics of chondrocytes and resembles the RCS tumor by electron and light microscopy. The cell line differs from the original tumor cells in that about 90% of the sulfated macromolecules are retained in the LTC extracellular matrix as compared to 30% by primary cultures of cells from the RCS tumor. An interesting and useful feature of this cell line is that it contains clonal populations of cells which differ in the quality and quantity of matrix produced. Two such clones serve to illustrate the diversity of cell types within the LTC cell line. One termed Rex accumulates an intensely staining matrix around it, while the other, Ng, accumulates a matrix, that remains virtually unstained. The chondrocytic nature and ease of cloning make these cells ideal for biochemical analysis of the chondrocyte and its extracellular matrix.

An immunohistochemical study of the rabbit suprapatella, a sesamoid fibrocartilage in the quadriceps tendon containing aggrecan

The rabbit suprapatella is a sesamoid fibrocartilage in the deep surface of the tendon of vastus intermedius and an integral part of the knee joint. We report the presence of a variety of proteoglycans (aggrecan and versican), glycosaminoglycans (chondroitin 4 and 6 sulfate, dermatan sulfate, keratan sulfate) and glycoproteins (tenascin) in its extracellular matrix and the intermediate filament vimentin in the fibrocartilage cells. The most significant finding is the presence of aggrecan in the extracellular matrix, along with its associated link protein and several of its integral glycosaminoglycans. Aggrecan probably enables the suprapatella to withstand compression. Although it can be assumed that aggrecan metabolites detected in synovial fluid from some human joints are predominantly associated with articular hyaline cartilage, the presence of aggrecan in the rabbit suprapatella means that this cannot be assumed for all animal knee joints. We conclude that it is important for orthopedic researchers who use animal models for arthritis research to check for the presence of a suprapatella when joint fluid analyses are interpreted.

Matrix metalloproteinases are involved in C-terminal and interglobular domain processing of cartilage aggrecan in late stage cartilage degradation

Monoclonal antibody (MAb) technology was used to examine aggrecan metabolites and the role of aggrecanases and matrix metalloproteinases (MMPs) in proteolysis of the interglobular domain (IGD) and C-terminus of aggrecan. An in vitro model of progressive cartilage degradation characterized by early proteoglycan loss and late stage collagen catabolism was evaluated in conjunction with a broad-spectrum inhibitor of MMPs. We have for the first time demonstrated that IGD cleavage by MMPs occurs during this late stage cartilage degeneration, both as a primary event in association with glycosaminoglycan (GAG) release from the tissue and secondarily in trimming of aggrecanase-generated G1 metabolites. Additionally, we have shown that MMPs were responsible for C-terminal catabolism of aggrecan and generation of chondroitin sulfate (CS) deficient aggrecan monomers and that this aggrecan truncation occurred prior to detectable IGD cleavage by MMPs. The onset of this later stage MMP activity was also evident by the generation of MMP-specific link protein catabolites in this model culture system. Recombinant MMP-1, -3 and -13 were all capable of C-terminally truncating aggrecan with at least two cleavage sites N-terminal to the CS attachment domains of aggrecan. Through analysis of aggrecan metabolites in pathological synovial fluids from human, canine and equine sources, we have demonstrated the presence of aggrecan catabolites that appear to have resulted from similar C-terminal processing of aggrecan as that induced in our in vitro culture systems. Finally, by developing a new MAb recognizing a linear epitope in the IGD of aggrecan, we have identified two novel aggrecan metabolites generated by an as yet unidentified proteolytic event. Collectively, these results suggest that C-terminal processing of aggrecan by MMPs may contribute to the depletion of cartilage GAG that leads to loss of tissue function in aging and disease. Furthermore, analysis of aggrecan metabolites resulting from both C-terminal and IGD cleavage by MMPs may prove useful in monitoring different stages in the progression of cartilage degeneration.

Cathepsin D cleaves aggrecan at unique sites within the interglobular domain and chondroitin sulfate attachment regions that are also cleaved when cartilage is maintained at acid pH

Bovine aggrecan was digested with bovine cathepsin D at pH 5.2 under conditions of partial digestion and the resulting aggrecan core protein fragments were separated by electrophoresis on gradient polyacrylamide gels. The fragments were characterized by their reactivity to specific antibodies and by N-terminal amino acid sequencing. It was also demonstrated that cathepsin D cleaved bovine aggrecan at five sites within the core protein, between residues Phe(342)-Phe(343) in the interglobular domain, Leu(1462)-Val(1463) between the chondroitin sulfate attachment regions 1 and 2 and Leu(1654)-Val(1655), Phe(1754)-Val(1755) and Leu(1854)-Ile(1855) that are located within the chondroitin sulfate attachment region 2 of the core protein. The time course of digestion showed that there was a continued degradation of aggrecan and there was no preferential cleavage of the core protein at any one site. It was shown that cathepsin D digested aggrecan over the pH range 5.2-6.5 resulting in the same products. When bovine cartilage was maintained in explant culture at pH 5.2 there was a rapid loss of both radiolabeled and chemical pools of sulfated glycosaminoglycans into the culture medium and this loss was inhibited by the inclusion in the medium of the aspartic proteinase inhibitor, pepstatin A. The aggrecan core protein fragments appearing in the medium of cultures maintained at pH 5.2 were characterized and it was shown that the fragments had N-terminal sequences starting at Phe(343), Ile(1855), and Val(1755) or Val(1463). This work demonstrates that cathepsin D present within the extracellular matrix of articular cartilage has the potential to contribute to the proteolytic processing of the core protein of aggrecan in this tissue.

Fibrocartilage in the transverse ligament of the human atlas

STUDY DESIGN

Immunohistochemical investigation.

OBJECTIVE

To determine whether molecules typical of articular cartilage are present in the transverse ligament and whether the ligament may be a target for an autoimmune response in rheumatoid arthritis.

SUMMARY OF BACKGROUND DATA

In chronic rheumatoid arthritis there is often a marked instability of the atlantoaxial complex, and the transverse ligament can show degenerative changes that compromise its mechanical function. In some rheumatoid patients there can be an autoimmune response to cartilage link protein, aggrecan, and Type II collagen.

METHODS

Transverse ligaments were removed from 13 cadavers and fixed in 90% methanol. Cryosections were immunolabeled with antibodies against proteoglycans (aggrecan, link protein, and versican), glycosaminoglycans (chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and keratan sulfate), and collagens (Types I, II, III, and VI).

RESULTS

Labeling for aggrecan and link protein was characteristic of the fibrocartilages, but versican was only detected in the fibrous regions. Equally, Types I, III, and VI collagens and keratan, dermatan, and chondroitin-4-sulfates were found throughout the ligament, but labeling for Type II collagen and chondroitin-6-sulfate was restricted to the fibrocartilages.

CONCLUSION

The presence of molecules typical of articular cartilage (aggrecan, link protein, and Type II collagen) in the transverse ligament explains why it can be a target for destruction in rheumatoid arthritis and also suggests that it is subject to constant compression against the dens rather than only at the extremes of movement.

An immunohistochemical study of the dorsal capsule of the lumbar and thoracic facet joints

STUDY DESIGN

The molecular composition of the extracellular matrix in the dorsal capsules of lumbar and thoracic facet joints was analyzed immunohistochemically.

OBJECTIVES

To determine whether the immunohistochemical profile of the lumbar joint capsule suggests a role of the capsule in limiting axial rotation of the lumbar motion segment.

SUMMARY OF BACKGROUND DATA

During axial rotation of the lumbar vertebrae, the axis of rotation shifts toward the facet joints in the direction of rotation. Thus, the capsule of the opposing joint should become tensed and wrap around the inferior articular process. Previous studies suggest that wrap-around ligaments are fibrocartilaginous. However, thoracic joint capsules are largely shielded from such loading and should be purely fibrous.

METHODS

Dorsal capsules were removed from lumbar and thoracic facet joints of six adult cadavers. Specimens were immunolabeled with monoclonal antibodies for collagens, chondroitin, dermatan and keratan sulfates, versican, tenascin, aggrecan and link protein. Antibody binding was detected using the Vectastain ABC 'Elite' peroxidase kit (Vector Laboratories, Inc., Burlingame, CA).

RESULTS

Both lumbar and thoracic joint capsules immunolabelled for most glycosaminoglycans and for Type I, III and VI collagens. However, labeling for Type II collagen, chondroitin-6-sulfate, aggrecan, and link protein was restricted to lumbar capsules. Such labeling was constantly seen at entheses and occasionally in the midsubstance.

CONCLUSIONS

The molecular composition of the lumbar joint capsule suggests that it acts as a fibrocartilaginous, 'wrap-around' ligament that withstands compression in addition to tension during torsional movements of the lumbar spine. It wraps around the inferior articular process as rotation occurs and limits further movement.

Fibrocartilage in the transverse ligament of the human acetabulum

Biomechanical experiments on isolated hip joints have suggested that the transverse ligament acts as a bridle for the lunate articular surface of the acetabulum during load bearing, but there are inherent limitations in such studies because the specimens are fixed artificially to testing devices and there are no modifying influences of muscle pull. Further evidence is thus needed to substantiate the theory. Here we argue that if the horns of the lunate surface are forced apart under load, the ligament would straighten and become compressed against the femoral head. It would thus be expected to share some of the features of tendons and ligaments that wrap around bony pulleys and yet previous work has suggested that the transverse ligament is purely fibrous. Transverse ligaments were removed from 8 cadavers (aged 17-39 y) and fixed in 90% methanol. Cryosections were immunolabelled with antibodies against collagens (types I, II, III, VI), glycosaminoglycans (chondroitins 4 and 6 sulphate, dermatan sulphate, keratan sulphate) and proteoglycans (aggrecan, link protein, versican, tenascin). A small sesamoid fibrocartilage was consistently present in the centre of each transverse ligament, near its inner surface at the site where it faced the femoral head. Additionally, a more prominent enthesis fibrocartilage was found at both bony attachments. All fibrocartilage regions, in at least some specimens, labelled for type II collagen, chondroitin 6 sulphate, aggrecan and link protein, molecules more typically associated with articular cartilage. The results suggest that the ligament should be classed as containing a 'moderately cartilaginous' sesamoid fibrocartilage, adapted to withstanding compression. This supports the inferences that can be drawn from previous biomechanical studies. We cannot give any quantitative estimate of the levels of compression experienced. All that can be said is that the ligament occupies an intermediate position in the spectrum of fibrocartilaginous tissues. It is more cartilaginous than some wrap-around tendons at the wrist, but less cartilaginous than certain other wrap-around ligaments, e.g. the transverse ligament of the atlas.

Histochemical localisation of versican, aggrecan and hyaluronan in the developing condylar cartilage of the fetal rat mandible

We investigated the histochemical localisation of versican, aggrecan and hyaluronan in the developing condylar cartilage of the fetal rat mandible at d 15-17 of gestation. At d 15 of gestation, immunostaining for versican was detected in the anlage of the future condylar process (condylar anlage), although the staining intensity showed a considerable regional variation. At d 16 of gestation, a metachromatically stained matrix firstly appeared in the condylar anlage. Aggrecan, hyaluronan and versican were simultaneously detected in this newly formed condylar cartilage. At d 17 of gestation, immunostaining for versican became restricted to the perichondrium and was barely detected in the cartilage. Colocalisation of versican and aggrecan was also seen in the cranial base cartilage at d 14 of gestation. These results indicate that although versican is replaced by aggrecan during the transition from prechondrogenic tissue to cartilage, both molecules were temporally colocalised in the newly formed cartilage. A hyaluronan-rich, low-versican area was identified in the posterior end of the condylar anlage during d 15-17 of gestation. The existence of this area is a unique structural feature of the developing condylar cartilage.

Marshall Urist Award. Interstitial collagenase gene expression correlates with in vitro invasion in human chondrosarcoma

Matrix metalloproteinases contribute to the processes of local invasion and metastasis by providing cells with the ability to traverse tissue boundaries. The levels of gene expression were quantitated for matrix metalloproteinases-1 and tissue inhibitors of metalloproteinases-1 in human chondrosarcoma cell lines, and the results were correlated with cell differentiation, collagenase activity, and in vitro invasion. Three well characterized human cell lines were used in this study, with the level of chondrocytic differentiation confirmed to be JJ012, FS090, and 105KC in increasing order on the basis of aggrecan and collagen gene expression. The matrix metalloproteinases-1/tissue inhibitors of metalloproteinases-1 ratio correlated with the level of differentiation in an inverse fashion. Collagenase activity paralleled matrix metalloproteinases-1/tissue inhibitors of metalloproteinases-1 gene expression and was associated with a more invasive phenotype in an in vitro assay. In this report, matrix metalloproteinase-1 and tissue inhibitors of metalloproteinases-1 expression in human chondrosarcoma tumor cell lines were quantitated, and it was shown that interstitial collagenase gene expression correlates inversely with chondrocytic differentiation. Differences in collagenase activity and in vitro invasion correlate inversely with the level of differentiation. These findings are consistent with the hypothesis that collagenase activity is associated with a poorer prognosis in chondrosarcoma by facilitating cell egress from the tumor matrix.

Fibrocartilage in the extensor tendons of the human metacarpophalangeal joints

The extensor tendons of the fingers cross both the metacarpophalangeal (MCP) and interphalangeal joints. Previous studies have shown that where the extensor tendons replace the capsule of the proximal interphalangeal (PIP) joint, they contain a sesamoid fibrocartilage that articulates with the proximal phalanx during flexion. The fibrocartilage labels immunohistochemically for a variety of glycosaminoglycans and collagens. In the current study, we investigate the molecular composition of the extensor tendons at the level of the MCP joints. This is of particular interest because the tendon has a greater moment arm at this location (and might thus be subject to greater compression), but is separated from the joint cavity by the capsule and peritendinous tissue. Six hands were removed from elderly cadavers (39-85 years of age) and the MCP joints were fixed in 90% methanol. The extensor tendons were dissected from all fingers, cryosectioned, and immunolabelled with a panel of monoclonal and polyclonal antibodies for types I, II, III, and VI collagens, chondroitin 4 and 6 sulphates, dermatan, and keratan sulphate and aggrecan. Antibody binding was detected with the Vectastain ABC 'Elite' avidin/biotin/peroxidase kit. The extensor tendons in all the fingers had a metachromatic sesamoid fibrocartilage on their deep surface which immunolabelled for types I, III, and VI collagens, and for all glycosaminoglycans and aggrecan. Labelling for type II collagen was also seen in some fibrocartilages and was a constant feature of all index fingers. This probably relates to the greater use of that digit and the higher loads to which its tendons are subject. Chondroitin 6 sulphate and type II collagen are the most consistent markers of the fibrocartilage phenotype and most of the chondroitin 6 sulphate is probably associated with aggrecan. It is concluded that the labelling profile of the tendon fibrocartilage in the different fingers at the MCP joints is broadly similar to that at the PIP joints. Thus, the potentially greater level of compression on the extensor tendons may be counterbalanced by the lack of fusion of the tendon with the joint capsule. It is suggested that the maintenance of a similar level of fibrocartilage differentiation at two different points along the length of the extensor tendon ensures that the tensile strength is the same in the two regions and that no weak link is present.

Characterization of collagens and proteoglycans at the insertion of the human Achilles tendon

This study provides a unique correlation between a molecular biological and biochemical analysis of the extracellular matrix (ECM) macromolecules in one half of 28 human Achilles tendons with an immunohistochemical study of the other. Both the insertion site and the mid-tendon were studied. The insertion (enthesis) is characterized by three distinctive fibrocartilages, two in the tendon (enthesial and sesamoid) and one on the heel bone (periosteal). Thus, its structure contrasts markedly with the fibrous character of the mid-tendon. RT-PCR analyses were performed on RNA extracted from mid-tendon and from the tendon fibrocartilages to investigate transcription of collagens and proteoglycans. Western blotting was also used to identify and characterize these macromolecules, and immunohistochemistry to localize their distribution. The results demonstrate striking differences in the ECM between the mid-tendon and its insertion. Types I, III, V and VI collagens, decorin, biglycan, fibromodulin and lumican were found in both the mid-tendon and the fibrocartilages, although their precise distribution often differed with site. mRNA for type II collagen was constantly present in the fibrocartilages, but it was only found in the mid-tendon of one specimen. The patterns of distribution for versican and aggrecan mRNA were complimentary - versican mRNA was present in the mid-tendon and absent from the fibrocartilages, while aggrecan mRNA was present in the fibrocartilages and absent from the mid-tendon. The range and distribution of ECM molecules detected in the Achilles tendon reflect the differing forces acting on it - the mid-tendon largely transmits tension and is characterized by molecules typical of fibrous tissues, but the fibrocartilages must also resist compression and thus contain, in addition, molecules typical of cartilage.

Developmental expression of keratan sulfate-like immunoreactivity distinguishes thalamic nuclei and cortical domains

Proteoglycans influence axonal outgrowth in several experimental paradigms, and their distribution during development suggests a role in axon guidance. We have used a monoclonal antibody, 5D4, that recognizes an epitope on sulfated keratans (KS), to define the distribution of keratan sulfate proteoglycans (KSPGs) in the developing thalamus and cortex of the rat. During development, 5D4 immunolabeling is present on thalamic axons as they grow through the internal capsule and subplate but is not present in the adjacent pathway for cortical efferent axons. Individual thalamic nuclei differ markedly in their expression of KSPGs; these distinctions persist throughout the period of developmentally regulated expression. Major cortical domains also differ in their expression of KSPGs, which are expressed throughout medial (cingulate and retrosplenial) cortex well before neocortex. Immunolabeling for KSPGs diminishes 2 weeks after birth; in the adult it is associated with small glia. The 5D4 epitope is present on several KSPGs (320, 220, and 160 kD) on Western blots during development but only in a broad 200-kD band in adult brain. Immunolabeling is degraded on sections and Western blots by keratanase II but not by keratanase I or chondroitinase ABC, confirming that the antibody recognizes KS. Bands identified by 5D4 on Western blots differ from those identified by antibodies to known KSPGs (aggrecan, claustrin, SV2, ABAKAN, phosphacan-KS), indicating that 5D4 is labeling KSPGs not previously described in the brain. The selective expression of KSPGs during development suggests that they may be a part of the molecular identity of thalamic nuclei and cortical domains that defines their connectivity.