Immunoelectron microscopic analysis of chondroitin sulfates during calcification in the rat growth plate cartilage

Molecular Mechanisms in Pathophysiology of Mucopolysaccharidosis and Prospects for Innovative Therapy

Mucopolysaccharidoses (MPSs) are a group of inborn errors of the metabolism caused by a deficiency in the lysosomal enzymes required to break down molecules called glycosaminoglycans (GAGs). These GAGs accumulate over time in various tissues and disrupt multiple biological systems, including catabolism of other substances, autophagy, and mitochondrial function. These pathological changes ultimately increase oxidative stress and activate innate immunity and inflammation. We have described the pathophysiology of MPS and activated inflammation in this paper, starting with accumulating the primary storage materials, GAGs. At the initial stage of GAG accumulation, affected tissues/cells are reversibly affected but progress irreversibly to: (1) disruption of substrate degradation with pathogenic changes in lysosomal function, (2) cellular dysfunction, secondary/tertiary accumulation (toxins such as GM2 or GM3 ganglioside, etc.), and inflammatory process, and (3) progressive tissue/organ damage and cell death (e.g., skeletal dysplasia, CNS impairment, etc.). For current and future treatment, several potential treatments for MPS that can penetrate the blood-brain barrier and bone have been proposed and/or are in clinical trials, including targeting peptides and molecular Trojan horses such as monoclonal antibodies attached to enzymes via receptor-mediated transport. Gene therapy trials with AAV, ex vivo LV, and Sleeping Beauty transposon system for MPS are proposed and/or underway as innovative therapeutic options. In addition, possible immunomodulatory reagents that can suppress MPS symptoms have been summarized in this review.

Annulus cells from more degenerated human discs show modified gene expression in 3D culture compared with expression in cells from healthier discs

BACKGROUND CONTEXT

Understanding gene expression patterns of disc cells in culture is important as we develop biologic therapies for disc degeneration. The objective of the present study was to determine if cells from more degenerated discs expressed different genes, or differed in their expression patterns, compared with patterns of cells from healthier discs.

PURPOSE

To determine if annulus cells from more degenerated discs expressed different gene expression patterns compared with patterns of cells from healthier discs using genome-wide analysis.

STUDY DESIGN

Cells from human annulus tissue were grown in three-dimensional (3D) culture and their gene expression patterns analyzed with Affymetrix microarray analysis. Gene expression patterns of cells from more degenerated discs (Thompson Grades IV and V) were compared with patterns from cells from healthier discs (Thompson Grades I, II, and III).

METHODS

After approval by our human subjects institutional review board, annulus cells were obtained from lumbar discs of seven subjects with Thompson Grades I, II, or III and from five subjects with discs of Thompson Grades IV and V. Cells were grown in 3D culture for 2 weeks; 3D cultures were used because this microenvironment more closely mimics the in vivo condition. mRNA was harvested, processed for Affymetrix genome-wide gene analysis, and data analyzed with p values adjusted so as to compensate for false discovery rates.

RESULTS

GeneSifter analyses showed that cells from more degenerated discs had 320 genes significantly upregulated, and 104 genes significantly downregulated compared with cells from healthier discs. Important genes included those related to: 1) the extracellular matrix (ECM) (keratin-associated protein 1-1, hyaluronan synthase 2, and nexin were upregulated; biglycan, collagen type VI alpha 2, thrombospondin 3, laminen alpha 1, fibronectin type III domain-containing protein 1, elastin microfibril interfacer 2, fibulin 2, and nidogen 1 and 2 were downregulated); 2) ECM proteolysis (ADAMTS6 was upregulated); 3) cell proliferation (never in mitosis gene 1-related kinase 3, cell division cycle 2-like 5 [cholinesterase-related cell division controller], RAB42 [member of RAS oncogene family], and cyclin-dependent kinase 6 were upregulated; RAS-like GTP-binding 1 was downregulated); 4) apoptosis (BCL2-like 11 and p53-inducible nuclear protein 1 were upregulated; caspase recruitment domain family, member 10, caspase-1 dominant-negative inhibitor pseudo-ICE, and caspase 9 and FADD-like apoptosis regulator were downregulated); and 5) growth factors, inflammatory mediators, and other genes (fibroblast growth factor 1, pregnancy-associated plasma protein-A, interleukin 1 alpha, and interleukin 7 were upregulated; TGF-beta-induced transcript 1, interleukin 26 and interleukin 1 receptor-like 1, tumor necrosis factor, alpha-induced protein 2, and chemokine (C-X3-C motif) ligand 1 were downregulated).

CONCLUSIONS

Data presented here show that annulus cells from more degenerated discs show modified gene expression in 3D culture. Important gene variations involved expression of interleukins, cytokines, ECM components, and apoptosis regulators. Results presented here have potential application in future cell-based biologic therapies for disc degeneration.

Asporin, a susceptibility gene in osteoarthritis, is expressed at higher levels in the more degenerate human intervertebral disc

Introduction

Asporin, also known as periodontal ligament-associated protein 1 (PLAP1), is a member of the family of small leucine-rich proteoglycan (SLRP) family. It is present within the cartilage extracellular matrix (ECM), and is reported to have a genetic association with osteoarthritis. Its D14 allele has recently been found to be associated with lumbar disc degeneration in Asian subjects. There have been no studies, however, of this gene's normal immunohistochemical localization within the human intervertebral disc, or of expression levels in Caucasian individuals with disc degeneration.

Methods

Studies were approved by our human subjects Institutional Review Board. Methods included immunohistochemical localization of asporin in the disc of humans and the sand rat (a small rodent with spontaneous age-related disc degeneration), and Affymetrix microarray analysis of asporin gene expression in vivo and in vitro.

Results

Immunohistochemical studies of human discs revealed that some, but not all, cells of the outer annulus expressed asporin. Fewer cells in the inner annulus contained asporin, and it was rarely present in cells in the nucleus pulposus. Similar patterns were found for the presence of asporin in lumbar discs of sand rats. Substantial relative gene expression levels were seen for asporin in both disc tissue and in annulus cells grown in three-dimensional culture. More degenerate human discs (Thompson grade 4) showed higher expression levels of asporin than did less degenerate (grade 1, 2 and 3) discs, P = 0.004.

Conclusions

In the discs of Caucasian subjects studied here, and in the sand rat, greater immunolocalization levels were found in the outer compared to inner annulus. Localization was rare in the nucleus. Gene expression studies showed greatest expression of asporin in the more degenerate human discs in vivo.

Gender-specific distribution of glycosaminoglycans during cartilage mineralization of human thyroid cartilage

The role of glycosaminoglycans (GAG) in the process of cartilage mineralization, especially in the hypertrophic zone of growth plates, is not yet fully understood. Human thyroid cartilage can serve as a model to observe matrix changes associated with cartilage mineralization because the processes follow a distinct route, progress very slowly and show sexual differences. Histochemical staining for low sulphated GAG (chondroitin-4- and -6-sulphates) was decreased in the interterritorial matrix of thyroid cartilage starting at the beginning of the fifth decade, but not in the pericellular or territorial matrix of chondrocytes. Because cartilage mineralization progressed in the interterritorial matrix it seems likely that a decreasing content of chondroitin-4- and -6-sulphates is involved in the mineralization process. This hypothesis is supported by the observation that immunostaining for chondroitin-4- and -6-sulphates was weaker in mineralized cartilage areas than in unmineralized areas, whereas there was no difference in staining for keratan sulphate. In all life decades, female thyroid cartilages contained more chondrocytes with a territorial rim of chondroitin-4- and -6-sulphates probably preventing cartilage mineralization compared with age-matched male specimens. Taken together, the characteristic distribution pattern of chondroitin-4- and -6-sulphates being more concentrated in female than in male thyroid cartilages provided evidence that these macromolecules decrease in cartilage mineralization.

In vitro analysis of anionic collagen scaffolds for bone repair

Collagen has been extensively described as a beneficial material in bone tissue engineering due to its biocompatibility, biodegradability, low antigenicity, and high tensile strength. However, collagen scaffolds in their pure form have some drawbacks and improvements in the physical, chemical, and biologic properties of collagen are necessary to overcome those inadequacies. Recently, the selective hydrolysis of carboxyamides of asparagine and glutamine residues of collagen has been employed to increase the number of negative sites and enhance the piezoelectric properties of collagen. Anionic collagen scaffolds were prepared by use of a hydrolysis treatment for either 24 h [bovine pericardium (BP 24)] or 48 h (BP 48). Bovine osteoblasts were cultured on them and on native matrices to understand the cellular interactions responsible for the good osteoconductivity and biocompatibility reported with in vivo tests. Based on the data obtained on cell adhesion, alkaline phosphatase (ALP) and extracellular matrix macromolecule production, and cellular proliferation through histological analysis, we may conclude that the materials tested reveal sufficient biocompatibility level for bone repair. Further, the evidence of some connection between ALP activity and the mineralization process should be emphasized. BP 48 presented the most promising results stimulating in vitro mineralization, ALP production, and possible osteoblast differentiation.

Characterization of sugar binding by osteoclast inhibitory lectin

Osteoclast inhibitory lectin (OCIL) is a membrane-bound C-type lectin that blocks osteoclast differentiation and, via binding to its cognate receptor NKRP1D, inhibits natural killer cell-mediated cytotoxicity. OCIL is a member of the natural killer cell receptor C-type lectin group that includes CD69 and NKRP1D. We investigated carbohydrate binding of soluble recombinant human and mouse OCIL in enzyme-linked immunosorbent assay-based assays. OCIL bound immobilized high molecular weight sulfated glycosaminoglycans, including fucoidan, lambda-carrageenan, and dextran sulfate, but not unsulfated dextran or sialated hyaluronic acid. Carbohydrate binding was Ca(2+)-independent. Binding of immobilized low molecular weight glycosaminoglycans, including chondroitin sulfate (A, B, and C forms) and heparin, was not observed. However, the soluble forms of these low molecular weight glycosaminoglycans competed for OCIL binding of immobilized fucoidan (as did soluble fucoidan, dextran sulfate, and lambda-carrageenan), indicating that OCIL does recognize these carbohydrates. Inhibition constants for chondroitin sulfate A and heparin binding were 380 and 5 nm, respectively. Immobilized and soluble monosaccharides did not bind OCIL. The presence of saturating levels of fucoidan, dextran sulfate, and lambda-carrageenan did not affect OCIL inhibition of osteoclast formation. The fucoidan-binding lectins Ulex europaeus agglutinin I and Anguilla anguilla agglutinin did not block osteoclast formation or affect the inhibitory action of OCIL. Although the osteoclast inhibitory action of OCIL is independent of sugar recognition, we have found that OCIL, a lectin widely distributed, but notably localized in bone, skin, and other connective tissues, binds a range of physiologically important glycosaminoglycans, and this property may modulate OCIL actions upon other cells.

Effects of zinc on cell proliferation and proteoglycan characteristics of epiphyseal chondrocytes

Zinc has been postulated as an important nutritional factor involved in growth promotion; however, the cellular mechanisms involved in the effects of zinc on linear growth remain to be elucidated. This study was conducted to evaluate the effects of zinc on the proliferation rate of epiphyseal growth plate chondrocytes and on the structural characteristics of the proteoglycans synthesized by these cells. For these purposes, hypertrophic and proliferating chondrocytes were isolated from the tibiae of 1- and 5-week-old chickens, respectively. Chondrocytes were cultured under serum-free conditions and primary cultures were used. The results showed that zinc stimulated proliferation by 40-50% above the baseline in the case of proliferating chondrocytes, but it had no effect on hypertrophic chondrocytes. Zinc had neither any effects on mean charge density of proteoglycans synthesized by hypertrophic chondrocytes nor in their hydrodynamic size. In contrast, zinc induced an increase in mean charge density and a decrease of hydrodynamic size of proteoglycans synthesized by proliferating chondrocytes. In both cell types zinc had no effect on the composition and hydrodynamic size of the glycosaminoglycan chains. The increased ability of proliferating chondrocytes cultured in the presence of zinc to synthesize 3'-phosphoadenosine 5'-phosphosulfate (PAPS) could be explained by the induction of enzymes participating in the sulfation pathway of proteoglycans. Therefore, the increase in mean charge density of proteoglycans observed in this study may be explained by an increase of the degree of sulfation of proteoglycan molecules. We speculate that the effect of zinc on linear growth may be explained at a cellular level by: a) an increase in proliferation rates of proliferating chondrocytes, and b) increased synthesis of highly charged proteoglycan molecules which decreases mineralization.

Biochemical basis of the pharmacologic action of chondroitin sulfates on the osteoarticular system

BACKGROUND

Chondroitin sulfates (CS) are involved in articular metabolism and could be used as therapeutic agents in degenerative articular diseases.

OBJECTIVES

To review the published reports describing both the metabolism of glycosaminoglycans (GAG) and their involvement in osteoarticular pathophysiology.

METHODS

MEDLINE search for relevant articles and review of cited references.

RESULTS

1) CS are formed of disaccharide units; sulfated galactosamine residues in position 4 or 6 are found in various ratios, depending on the age and the type of tissue. Binding to the core protein through N- and O-linkages leads to aggregates of monomers with high molecular weights. The proteoglycan aggregate exhibits viscoelastic and hydration properties and an ability to interact with the surrounding tissue through electric charges leading to protection of the cartilaginous tissues. 2) CS are synthesized both in chondrocytes and in bone cells by the action of specific glycosyl-transferases; their catabolism occurs in the matrix and involves numerous matrix (metalloproteinases) and lysosomal enzymes. 3) CS are inhibitors of extracellular proteases involved in the metabolism of connective tissues. In addition to their anti-inflammatory effects, CS in vitro stimulate proteoglycan production by chondrocytes; they also inhibit cartilage cytokine production and induce apoptosis of articular chondrocytes. CS increase the intrinsic viscosity of the synovial liquid. 4) In vivo in experimental arthritis, the number and severity of articular symptoms decreases after CS administration. In bones, CS accelerate the mineralization process and bone repair.

CONCLUSIONS

All these data suggest that CS play a role in articular and bone metabolism by controlling cartilaginous matrix integrity and bone mineralization.

Distribution of collagens and glycosaminoglycans in the joint capsule of the proximal interphalangeal joint of the human finger

BACKGROUND

The capsule of the proximal interphalangeal joint consists of the central slip of the extensor tendon dorsally, the collateral ligaments at the sides and the palmar ligament ventrally. Fibrocartilaginous menisci have been reported extending into the joint cavity and the central slip has a sesamoid fibrocartilage articulating with the proximal phalanx. This study relates ECM composition in the joint capsule to function.

METHODS

Each part of the capsule from 24 fingers amputated because of trauma, carcinoma, isthaemia, fixed-flexion deformities or Dupuytren's contracture, was dissected out. Sections were prepared for routine histology or immunolabelled with a panel of monoclonal and polyclonal antibodies against collagens and glycosaminoglycans using the avidin/biotin/peroxidase procedure.

RESULTS

All parts of the capsule consistently labelled for types I, III and VI collagens and for dermatan and keratan sulphate, though labelling was more pericellular in fibrocartilaginous regions. In contrast, only certain regions of the capsule in some fingers labelled for type II collagen, chondroitin 4 or 6 sulphate. The sesamoid fibrocartilage in the central slip showed the greatest degree of fibrocartilage differentiation, especially in fixed-flexion deformity fingers, and the palmar ligament the least.

CONCLUSIONS

The immunolabelling patterns suggest that there is an ordered sequence of matrix changes accompanying fibrocartilage differentiation. Chondroitin sulphate-containing proteoglycans accumulate first, and type II collagen appears later. The presence or absence of type II collagen probably relates to different levels of compressive loading. No fibrocartilaginous menisci were found in normal joints and those described previously are regarded as synovial folds.