Distribution of hyaluronan in articular cartilage as probed by a biotinylated binding region of aggrecan

Detection of Glycosaminoglycans in Pancreatic Islets and Lymphoid Tissues

In this chapter, we describe the detection of the glycosaminoglycans hyaluronan and heparan sulfate in pancreatic islets and lymphoid tissues. The identification of hyaluronan in tissues is achieved by utilizing a highly specific hyaluronan binding protein (HABP) probe that interacts with hyaluronan in tissue sections. The HABP probe is prepared by enzymatic digestion of the chondroitin sulfate proteoglycan aggrecan which is present in bovine nasal cartilage and is then biotinylated in the presence of bound hyaluronan and the link protein. Hyaluronan is then removed by gel filtration chromatography. The biotinylated HABP-link protein complex is applied to tissue sections, and binding of the complex to tissue hyaluronan is visualized by enzymatic precipitation of chromogenic substrates.To determine hyaluronan content in tissues, tissues are first proteolytically digested to release hyaluronan from the macromolecular complexes that this molecule forms with other extracellular matrix constituents. Digested tissue is then incubated with HABP . The hyaluronan-HABP complexes are extracted, and the hyaluronan concentration in the tissue is determined using an ELISA-like assay.Historically, heparan sulfate was identified in tissue sections using the cationic dye Alcian blue and histochemistry based on the critical electrolyte concentration principle of differential staining of glycosaminoglycans using salt solutions. For both human and mouse pancreas sections, the current optimal method for detecting heparan sulfate is by indirect immunohistochemistry using a specific anti-heparan sulfate monoclonal antibody. A peroxidase-conjugated secondary antibody is then applied, and its binding to the anti-heparan sulfate antibody is visualized by oxidation and precipitation of a chromogenic substrate.

Biomimetic molecules lower catabolic expression and prevent chondroitin sulfate degradation in an osteoarthritic ex vivo model

Aggrecan, the major proteoglycan in cartilage, serves to protect cartilage tissue from damage and degradation during the progression of osteoarthritis (OA). In cartilage extracellular matrix (ECM) aggrecan exists in an aggregate composed of several aggrecan molecules that bind to a single filament of hyaluronan. Each molecule of aggrecan is composed of a protein core and glycosaminoglycan sides chains, the latter of which provides cartilage with the ability to retain water and resist compressive loads. During the progression of OA, loss of aggrecan is considered to occur first, after which other cartilage matrix components become extremely susceptible to degradation. Proteolytic cleavage of the protein core of aggrecan by enzymes such as aggrecanases, prevent its binding to HA and lower cartilage mechanical strength. Here we present the use of HA-binding or collagen type II-binding molecules that functionally mimic aggrecan but lack known cleavage sites, protecting the molecule from proteolytic degradation. These molecules synthesized with chondroitin sulfate backbones conjugated to hyaluronan- or collagen type II- binding peptides, are capable of diffusing through a cartilage explant and adhering to the ECM of this tissue. The objective of this study was to test the functional efficacy of these molecules in an ex vivo osteoarthritic model to discern the optimal molecule for further studies. Different variations of chondroitin sulfate conjugated to the binding peptides were diffused through aggrecan depleted explants and assessed for their ability to enhance compressive stiffness, prevent CS degradation, and modulate catabolic (MMP-13 and ADAMTS-5) and anabolic (aggrecan and collagen type II) gene expression. A pilot in vivo study assessed the ability to retain the molecule within the joint space of an osteoarthritic guinea pig model. The results indicate chondroitin sulfate conjugated to hyaluronan-binding peptides is able to significantly restore equilibrium modulus and prevent CS degradation. All molecules demonstrated the ability to lower catabolic gene expression in aggrecan depleted explants. In order to enhance biosynthesis and regeneration, the molecules need to be coupled with an external stimulant such as a growth factor. The chondroitin sulfate molecule synthesized with HA-binding peptides demonstrated adherence to cartilage tissue and retention up to 6 hours in an ambulatory joint. Further studies will monitor the in vivo residence time and ability of the molecules to act as a disease-modifying agent.

The detection of glycosaminoglycans in pancreatic islets and lymphoid tissues

In this chapter, we describe the detection of the glycosaminoglycans hyaluronan and heparan sulfate in pancreatic islets and lymphoid tissues. The identification of hyaluronan in tissues is achieved by utilizing a highly specific hyaluronan binding protein (HABP) probe that interacts with hyaluronan in tissue sections. The HABP probe is prepared by enzymatic digestion of the chondroitin sulfate proteoglycan aggrecan which is present in bovine nasal cartilage, and is then biotinylated in the presence of bound hyaluronan and the link protein. Hyaluronan is then removed by gel filtration chromatography. The biotinylated HABP-link protein complex is applied to tissue sections and binding of the complex to tissue hyaluronan is visualized by enzymatic precipitation of chromogenic substrates. To determine hyaluronan content in tissues, tissues are first proteolytically digested to release hyaluronan from the macromolecular complexes that this molecule forms with other extracellular matrix constituents. Digested tissue is then incubated with HABP. The hyaluronan-HABP complexes are extracted and the hyaluronan concentration in the tissue is determined using an ELISA-like assay. Heparan sulfate is identified in mouse tissues by Alcian blue histochemistry and indirect immunohistochemistry. In human tissues, heparan sulfate is best detected by indirect immunohistochemistry using a specific anti-heparan sulfate monoclonal antibody. A biotinylated secondary antibody is then applied in conjunction with streptavidin-peroxidase and its binding to the anti-heparan sulfate antibody is visualized by enzymatic precipitation of chromogenic substrates.

Molecular adhesion between cartilage extracellular matrix macromolecules

In this study, we investigated the molecular adhesion between the major constituents of cartilage extracellular matrix, namely, the highly negatively charged proteoglycan aggrecan and the type II/IX/XI fibrillar collagen network, in simulated physiological conditions. Colloidal force spectroscopy was applied to measure the maximum adhesion force and total adhesion energy between aggrecan end-attached spherical tips (end radius R ≈ 2.5 μm) and trypsin-treated cartilage disks with undamaged collagen networks. Studies were carried out in various aqueous solutions to reveal the physical factors that govern aggrecan–collagen adhesion. Increasing both ionic strength and [Ca²⁺] significantly increased adhesion, highlighting the importance of electrostatic repulsion and Ca²⁺-mediated ion bridging effects. In addition, we probed how partial enzymatic degradation of the collagen network, which simulates osteoarthritic conditions, affects the aggrecan–collagen interactions. Interestingly, we found a significant increase in aggrecan–collagen adhesion even when there were no detectable changes at the macro- or microscales. It is hypothesized that the aggrecan–collagen adhesion, together with aggrecan–aggrecan self-adhesion, works synergistically to determine the local molecular deformability and energy dissipation of the cartilage matrix, in turn, affecting its macroscopic tissue properties.

Tissue distribution and subcellular localization of hyaluronan synthase isoenzymes

Hyaluronan synthases (HAS) are unique plasma membrane glycosyltransferases secreting this glycosaminoglycan directly to the extracellular space. The three HAS isoenzymes (HAS1, HAS2, and HAS3) expressed in mammalian cells differ in their enzymatic properties and regulation by external stimuli, but clearly distinct functions have not been established. To overview the expression of different HAS isoenzymes during embryonic development and their subcellular localization, we immunostained mouse embryonic samples and cultured cells with HAS antibodies, correlating their distribution to hyaluronan staining. Their subcellular localization was further studied by GFP-HAS fusion proteins. Intense hyaluronan staining was observed throughout the development in the tissues of mesodermal origin, like heart and cartilages, but also for example during the maturation of kidneys and stratified epithelia. In general, staining for one or several HASs correlated with hyaluronan staining. The staining of HAS2 was most widespread, both spatially and temporally, correlating with hyaluronan staining especially in early mesenchymal tissues and heart. While epithelial cells were mostly negative for HASs, stratified epithelia became HAS positive during differentiation. All HAS isoenzymes showed cytoplasmic immunoreactivity, both in tissue sections and cultured cells, while plasma membrane staining was also detected, often in cellular extensions. HAS1 had brightest signal in Golgi, HAS3 in Golgi and microvillous protrusions, whereas most of the endogenous HAS2 immunoreactivity was localized in the ER. This differential pattern was also observed with transfected GFP-HASs. The large proportion of intracellular HASs suggests that HAS forms a reserve that is transported to the plasma membrane for rapid activation of hyaluronan synthesis.

Hyal-1 but not Hyal-3 deficiency has an impact on ovarian folliculogenesis and female fertility by altering the follistatin/activin/Smad3 pathway and the apoptotic process

Ovarian follicle development is a process regulated by various endocrine, paracrine and autocrine factors that act coordinately to promote follicle growth. However, the vast majority of follicles does not reach the pre-ovulatory stage but instead, undergo atresia by apoptosis. We have recently described a role for the somatic hyaluronidases (Hyal-1, Hyal-2, and Hyal-3) in ovarian follicular atresia and induction of granulosa cell apoptosis. Herein, we show that Hyal-1 but not Hyal-3 null mice have decreased apoptotic granulosa cells after the induction of atresia and an increased number of retrieved oocytes after stimulation of ovulation. Furthermore, young Hyal-1 null mice had a significantly higher number of primordial follicles than age matched wild-type animals. Recruitment of these follicles at puberty resulted in an increased number of primary and healthy preantral follicles in Hyal-1 null mice. Consequently, older Hyal-1 deficient female mice have prolonged fertility. At the molecular level, immature Hyal-1 null mice have decreased mRNA expression of follistatin and higher levels of phospho-Smad3 protein, resulting in increased levels of phospho-Akt in pubertal mice. Hyal-1 null ovarian follicles did not exhibit hyaluronan accumulation. For Hyal-3 null mice, compensation by Hyal-1 or Hyal-2 might be related to the lack of an ovarian phenotype. In conclusion, our results demonstrate that Hyal-1 plays a key role in the early phases of folliculogenesis by negatively regulating ovarian follicle growth and survival. Our findings add Hyal-1 as an ovarian regulator factor for follicle development, showing for the first time an interrelationship between this enzyme and the follistatin/activin/Smad3 pathway.

The role of hyaluronan produced by Has2 gene expression in development of the spine

STUDY DESIGN

Histologic analysis of spine development in cartilage-specific knockout mice.

OBJECTIVE

To evaluate the role hyaluronan produced by hyaluronan synthase-2 (Has2) in spine development.

SUMMARY OF BACKGROUND DATA

The Has2 gene is responsible for most hyaluronan production throughout the body, including the skeleton. However, it is not possible to study the involvement of hyaluronan in skeletal development using constitutive Has2 knockout mice, as the embryonic mice die early before skeletal development has occurred. This problem can be overcome by the use of cartilage-specific knockout mice.

METHODS

Mice possessing floxed Has2 genes were crossed with mice expressing Cre recombinase under control of the type II collagen promoter to generate cartilage-specific Has2 knockout mice. Spine development was studied by histology.

RESULTS

Knockout mice died near birth and displayed severe abnormality in skeletal development. The spine showed defects in vertebral body size and the formation of the intervertebral discs. There was no evidence for the formation of an organized primary center of ossification within the vertebrae, and the appearance and organization of the hypertrophic chondrocytes was abnormal. Although no organized endochondral ossification appeared to be taking place, there was excessive bone formation at the center of the vertebrae. There was also a generalized increased cellularity of the vertebral cartilage and a corresponding decrease in the abundance of extracellular matrix. The nucleus pulposus of the intervertebral discs were less flattened than in the control mice and possessed an increased amount of large vacuolated cells. Remnants of the notochord could also be seen between adjacent discs.

CONCLUSION

Hyaluronan production by Has2 is essential for normal vertebral and intervertebral disc development within the spine, and the absence of this synthase impairs the organization of both soft and hard tissue elements.

Hyaluronan production by means of Has2 gene expression in chondrocytes is essential for long bone development

Mice possessing no Has2 expression in chondrocytes died near birth and displayed abnormalities throughout their skeleton. By embryonic day 18.5, the long bones were short and wide, and possessed excessive mineralization within their diaphysis, with little evidence of diaphyseal bone modeling. However, this does not appear to be associated with an absence of blood vessel invasion or the reduced presence of osteoclasts. There was no evidence for the formation of an organized growth plate between the epiphysis and diaphysis, and while hypertrophic chondrocytes were present in this region they were abnormal in both appearance and organization. There was also increased cellularity in the epiphyseal cartilage and a corresponding decrease in the abundance of extracellular matrix, but aggrecan was still present. Thus, hyaluronan production by chondrocytes is not only essential for formation of an organized growth plate and subsequent long bone growth but also for normal modeling of the diaphyseal bone.

A mouse model of human mucopolysaccharidosis IX exhibits osteoarthritis

Hyaluronidases are endoglycosidases that hydrolyze hyaluronan (HA), an abundant component of the extracellular matrix of vertebrate connective tissues. Six human hyaluronidase-related genes have been identified to date. Mutations in one of these genes cause a deficiency of hyaluronidase 1 (HYAL1) resulting in a lysosomal storage disorder, mucopolysaccharidosis (MPS) IX. We have characterized a mouse model of MPS IX and compared its phenotype with the human disease. The targeted Hyal1 allele in this model had a neomycin resistance cassette in exon 2 that replaced 753 bp of the coding region containing the predicted enzyme active site. As a result, Hyal1(-/-) animals had no detectable wild-type Hyal1 transcript, protein or serum activity. Hyal1 null animals were viable, fertile and showed no gross abnormalities at 1 year and 8 months of age. Histological studies of the knee joint showed a loss of proteoglycans occurring as early as 3 months that progressed with age. An increased number of chondrocytes displaying intense pericellular and/or cytoplasmic HA staining were detected in the epiphyseal and articular cartilage of null mice, demonstrating an accumulation of HA. Elevations of HA were not detected in the serum or non-skeletal tissues, indicating that osteoarthritis is the key disease feature in a Hyal1 deficiency. Hyal3 expression was elevated in Hyal1 null mice, suggesting that Hyal3 may compensate in HA degradation in non-skeletal tissues. Overall, the murine MPS IX model displays the key features of the human disease.

The effect of vestibular nerve section on the expression of the hyaluronan in the frog, Rana esculenta

Following postganglionic lesion of the eighth cranial nerve, the changes in the expression of hyaluronan (HA), one of the extracellular matrix macromolecules, were examined in the medial (MVN) and lateral (LVN) vestibular nuclei and in the entry or transitional zone (TZ) of the nerve in the frog. HA was detected in different survival times by using a specific biotinylated hyaluronan-binding probe. HA expression was defined by the area-integrated optical density (AIOD), calculated from pixel intensities of digitally captured images. During the first postoperative days the perineuronal net (PN), a HA-rich area around the neurons, was not distinguishable from the surrounding neuropil in the MVN and LVN, characterized by a bilateral drop of AIOD specifically on the operated side. From postoperative day 14 onwards AIOD increased whilst the PN reorganized. In contrast, the AIOD wobbled up and down bilaterally without any trend in the TZ. Statistical analysis indicated that AIOD changes in the structures studied ran parallel bilaterally presumably because of the operation. Our results demonstrated for the first time that (1) the lesion of the eighth cranial nerve is accompanied by the modification of AIOD reflected HA expression in the MVN, LVN and TZ, (2) different tendencies exist in the time course of AIOD in the structures studied and (3) these tendencies are similar on the intact and operated sides. Our findings may suggest an area dependent molecular mechanism of HA in the restoration of vestibular function.

Localization of CD44 and hyaluronan in the synovial membrane of the rat temporomandibular joint

Previous studies have pointed out a lack of adhesion structures in the synovial lining layer of the rat temporomandibular joint (TMJ) despite showing an epithelial arrangement. CD44, a major cell adhesion molecule, plays crucial roles as an anchor between cells and extracellular matrices by binding hyaluronan (HA) for the development of organs or the metastasis of tumors. The present study examined the localization of CD44 in the synovial membrane of the rat TMJ by immunocytochemistry for OX50, ED1, and Hsp25, which are markers for the rat CD44, macrophage-like type A, and fibroblast-like type B synoviocytes, respectively. Histochemistry for HA-binding protein (HABP) was also employed for the detection of HA. OX50 immunoreactions were found along the cell surface and, in particular, accumulated along the surface of the articular cavity. Observations by a double immunostaining and immunoelectron microscopy revealed that all the OX50-immunopositive cells were categorized as fibroblastic type B cells, which had many caveolae and a few vesicles reactive to intense OX50. However, the macrophage-like type A cells did not have any OX50 immunoreaction in the synovial lining layer. A strong HABP reaction was discernable in the extracellular matrix surrounding both OX50-positive and -negative cells in the synovial lining layers, exhibiting a meshwork distribution, but weak in its sublining layer. This localization pattern of CD44 and HABP might be involved in the formation of the epithelial arrangement of the synovial lining layer. Furthermore, OX50 immunonegativity in the type A cells suggests their low phagocytotic activity in the rat TMJ under normal conditions.

Localization of CD44 (hyaluronan receptor) and hyaluronan in rat mandibular condyle

CD44 is a multifunctional adhesion molecule that binds to hyaluronan (HA), type I collagen, and fibronectin. We investigated localization of CD44 and HA in mandibular condylar cartilage compared with the growth plate and the articular cartilage, to clarify the characteristics of chondrocytes. We also performed Western blotting using a lysate of mandibular condyle. In mandibular condyle, CD44-positive cells were seen in the surface region of the fibrous cell layer and in the proliferative cell layer. Western blotting revealed that the molecular weight of CD44 in condyle was 78 to 86 kD. Intense reactivity for HA was detected on the surface of the condyle and the lacunae of the hypertrophic cell layer. Moderate labeling was seen in cartilage matrix of the proliferative and maturative layer. Weak labeling was also seen in the fibrous cell layer. In growth plate and articular cartilage, HA was detected in all cell layers. However, chondrocytes of these cartilages did not exhibit reactivity for CD44. These results suggest that chondrocytes in the mandibular condylar cartilage differ in expression of CD44 from those in tibial growth plate and articular cartilage. Cell-matrix interaction between CD44 and HA may play an important role in the proliferation of chondrocytes in the mandibular condyle.

Direct quantification of the rupture force of single hyaluronan/hyaluronan binding protein bonds

The non-covalent bond between aggrecan and hyaluronan is critical for maintaining the normal structure and function of the extracellular matrix in articular cartilage. The failure of this bond can cause the loss of aggrecan and destruction of the extracellular matrix of articular cartilage. In this study, the rupture force of the single bond between hyaluronan and hyaluronan binding protein - the complex of the hyaluronan binding region of aggrecan and link protein - was directly measured with a nanomechanical testing system as 40+/-11 pN. The results were compared to a theoretical prediction based on a smart version of the Monte Carlo simulation.

Direct measurements of the compressive properties of single proteoglycan aggregates

Proteoglycan aggregate is a major component of the extracellular matrix in articular cartilage and is considered to be responsible for the resistance to compression of this tissue. The reduced stiffness of articular cartilage due to the loss of proteoglycan aggregate has been reported in osteoarthritis. In order to understand the mechanical properties of extracellular matrix in articular cartilage at molecular level, the compressive properties of 36 single molecules of proteoglycan aggregate were directly measured using a laser tweezers/interferometer system. The proteoglycan aggregates showed resistance when compressed to approximately 30% of their contour length. The stiffness of proteoglycan aggregates increased non-linearly from 2.6+/-3.8 pN/microm (compressed to 30-35% of their contour length) to 115.5+/-30.9 pN/microm (compressed to 2.5-5% of their contour length).

A method for testing compressive properties of single proteoglycan aggregates

This study presents a method for direct measurement of the compressive properties of single molecules of proteoglycan aggregate using a state-of-the-art laser tweezers/interferometer system previously developed to test the tensile properties of single molecules. A typical molecule of proteoglycan aggregate showed a highly non-linear resistance to compression after being compressed to about 25% of its original molecule length.

A comparative study of localization of heat shock protein 27 and heat shock protein 72 in the developmental and degenerative intervertebral discs

STUDY DESIGN

The lumbar intervertebral discs of 135 subjects after autopsy were immunostained with antihuman heat shock protein 27 (HSP27) monoclonal antibody and antihuman heat shock protein 72 (HSP72) polyclonal antibody.

OBJECTIVES

To present the data on metabolic changes that occurred in the chondrocytes of intervertebral discs during development and aging.

SUMMARY OF BACKGROUND DATA

Heat shock proteins have been implicated in the progressive degeneration of articular cartilage in joint disease, such as rheumatoid arthritis and osteoarthritis. However, the role and expression of heat shock proteins in human intervertebral discs have received little study.

METHODS

One hundred thirty-five specimens of human intervertebral discs were stained with hematoxylin and eosin, alcian blue, and Masson's trichrome and were immunostained with HSP27 and HSP72 by an indirect immunoperoxidase method. The relative amounts of HSP27 and HSP72 deposition were graded according to a semiquantitative scoring system.

RESULTS

Heat shock protein 72 accumulated in the cytoplasm of the chondrocytes of both endplate cartilage and nucleus pulposus during gestation and thereafter decreased with aging (age, </=60 years), and HSP72 immunoreactivity increased in the chondrocytes of degenerative discs. In addition, HSP72 was located in the nuclei of certain chondrocytes of the degenerated nucleus pulposus and anulus fibrosus, was highly expressed in the chondrocytes of endplate cartilage during gestation and childhood, and thereafter decreased with aging. Furthermore, with the progressive degeneration of the endplate cartilage, HSP27 immunoreactivity increased. The degree of HSP27 immunoreactivity did not change significantly according to age in either the nucleus pulposus or the anulus fibrosus.

CONCLUSIONS

Heat shock protein 27 and HSP72 are thus considered to be useful molecular indicators for degenerative change in intervertebral discs. Both HSP27 and HSP72 are presumed to play a role in cell protection from stress that is induced by mechanical and biologic factors causing intervertebral disc degeneration.

Anatomy, biochemistry, and physiology of articular cartilage

Articular cartilage serves as a load-bearing elastic material that is responsible for the frictionless movement of the surfaces of articulating joints. Its ability to undergo reversible deformation depends on its structural organization, including the specific arrangement of the matrix macromolecules and the chondrocytes. Interactions between the matrix and chondrocytes are responsible for the biological and mechanical properties of articular cartilage and enable it to respond by effecting a balance between anabolism and catabolism as well as continual internal remodeling. Age-related changes in the function of chondrocytes may contribute to the initiation and progression of osteoarthritis.

Immunohistochemistry of chondromodulin-I in the human intervertebral discs with special reference to the degenerative changes

The expression of the matrix protein chondromodulin-I has been studied in human intervertebral discs of 101 people using immunohistochemical analyses. The purpose of this report is to present data on the metabolic changes that were found to occur in the chondrocytes of intervertebral discs during development and aging. Chondromodulin-I was highly expressed during the gestational period and gradually decreased after maturation. It was detected in both the extracellular matrix and chondrocytes in the zone of hypertrophic cartilage, the zone of proliferative cartilage and the zone of resting cartilage in fetal discs. It was also present in the annulus fibrosus, nucleus pulposus and end-plate cartilage in mature discs. In degenerative discs, chondromodulin-1 immunoreactivity tended to be elevated in the remaining chondrocytes. Our findings suggest that the expression of the protein is developmentally regulated and upregulated through a defense mechanism against the degenerative processes of the aged intervertebral disc.

Hyaluronan distribution in the human and canine intervertebral disc and cartilage endplate

A biotinylated complex of aggrecan G1-domain and link protein was used to characterize the distribution of hyaluronan in paraffin-embedded sections of adult human and canine intervertebral disc and cartilage endplate. Limited chondroitinase ABC and trypsin digestions of the sections before staining was utilized to expose hyaluronan potentially masked by aggrecan. Hyaluronan concentration and hyaluronan to uronic acid ratio in different parts of the discs were measured as a background for the histological analysis. Hyaluronan staining was strong in the nucleus pulposus and inner parts of annulus fibrosus of both species, corroborated by biochemical assays of the same compartments. Particularly in human samples, hyaluronan in the interterritorial matrix of nucleus pulposus and annulus fibrosus was readily accessible to the probe without enzyme treatments. In contrast, the cell-associated hyaluronan signal was enhanced after trypsin or limited chondroitinase ABC-treatment of the sections, suggesting that pericellular hyaluronan was more masked by aggrecan than in the distant matrix. A puzzling feature of canine cartilage endplate cells was their intensive cell-associated hyaluronan signal, part of which appeared intracellular. Hyaluronan was abundant between the collagenous lamellae in annulus fibrosus, perhaps important in the plasticity of this tissue.