Changes in the expression of decorin and biglycan in human articular cartilage with age and regulation by TGF-beta

Biglycan reduces body weight by regulating food intake in mice and improves glucose metabolism through AMPK/AKT dual pathways in skeletal muscle

While biglycan (BGN) is suggested to direct diverse signaling cascades, the effects of soluble BGN as a ligand on metabolic traits have not been studied. Herein, we tested the effects of BGN on obesity in high-fat diet (HFD)-induced obese animals and glucose metabolism, with the underlying mechanism responsible for observed effects in vitro. Our results showed that BGN administration (1 mg/kg body weight, intraperitoneally) significantly prevented HFD-induced obesity, and this was mainly attributed to reduced food intake. Also, intracerebroventricular injection of BGN reduced food intake and body weight. The underlying mechanism includes modulation of neuropeptides gene expression involved in appetite in the hypothalamus in vitro and in vivo. In addition, BGN regulates glucose metabolism as shown by improved glucose tolerance in mice as well as AMPK/AKT dual pathway-driven enhanced glucose uptake and GLUT4 translocation in L6 myoblast cells. In conclusion, our results suggest BGN as a potential therapeutic target to treat risk factors for metabolic diseases.

Decorin-An Antagonist of TGF-β in Astrocytes of the Optic Nerve

During the pathogenesis of glaucoma, optic nerve (ON) axons become continuously damaged at the optic nerve head (ONH). This often is associated with reactive astrocytes and increased transforming growth factor (TGF-β) 2 levels. In this study we tested the hypothesis if the presence or absence of decorin (DCN), a small leucine-rich proteoglycan and a natural inhibitor of several members of the TGF family, would affect the expression of the TGF-βs and connective tissue growth factor (CTGF/CCN2) in human ONH astrocytes and murine ON astrocytes. We found that DCN is present in the mouse ON and is expressed by human ONH and murine ON astrocytes. DCN expression and synthesis was significantly reduced after 24 h treatment with 3 nM CTGF/CCN2, while treatment with 4 pM TGF-β2 only reduced expression of DCN significantly. Conversely, DCN treatment significantly reduced the expression of TGF-β1, TGF-β2 and CTGF/CCN2 vis-a-vis untreated controls. Furthermore, DCN treatment significantly reduced expression of fibronectin (FN) and collagen IV (COL IV). Notably, combined treatment with DCN and triciribine, a small molecule inhibitor of protein kinase B (AKT), attenuated effects of DCN on CTGF/CCN2, TGF-β1, and TGF-β2 mRNA expression. We conclude (1) that DCN is an important regulator of TGF-β and CTGF/CCN2 expression in astrocytes of the ON and ONH, (2) that DCN thereby regulates the expression of extracellular matrix (ECM) components and (3) that DCN executes its negative regulatory effects on TGF-β and CTGF/CCN2 via the pAKT/AKT signaling pathway in ON astrocytes.

Systemic transplantation of adult multipotent stem cells prevents articular cartilage degeneration in a mouse model of accelerated ageing

BACKGROUND

Osteoarthritis (OA) is one of the most prevalent joint diseases of advanced age and is a leading cause of disability worldwide. Ageing is a major risk factor for the articular cartilage (AC) degeneration that leads to OA, and the age-related decline in regenerative capacity accelerates OA progression. Here we demonstrate that systemic transplantation of a unique population of adult multipotent muscle-derived stem/progenitor cells (MDSPCs), isolated from young wild-type mice, into Zmpste24-/- mice (a model of Hutchinson-Gilford progeria syndrome, a condition marked by accelerated ageing), prevents ageing-related homeostatic decline of AC.

RESULTS

MDSPC treatment inhibited expression of cartilage-degrading factors such as pro-inflammatory cytokines and extracellular matrix-proteinases, whereas pro-regenerative markers associated with cartilage mechanical support and tensile strength, cartilage resilience, chondrocyte proliferation and differentiation, and cartilage growth, were increased. Notably, MDSPC transplantation also increased the expression level of genes known for their key roles in immunomodulation, autophagy, stress resistance, pro-longevity, and telomere protection. Our findings also indicate that MDSPC transplantation increased proteoglycan content by regulating chondrocyte proliferation.

CONCLUSIONS

Together, these findings demonstrate the ability of systemically transplanted young MDSPCs to preserve a healthy homeostasis and promote tissue regeneration at the molecular and tissue level in progeroid AC. These results highlight the therapeutic potential of systemically delivered multipotent adult stem cells to prevent age-associated AC degeneration.

TGF beta -1, -2 and -3 in the modulation of fibrosis in the cornea and other organs

The TGF beta-1, -2 and -3 isoforms are transcribed from different genes but bind to the same receptors and signal through the same canonical and non-canonical signal transduction pathways. There are numerous regulatory mechanisms controlling the action of each isoform that include the organ-specific cells producing latent TGF beta growth factors, multiple effectors that activate the isoforms, ECM-associated SLRPs and basement membrane components that modulate the activity and localization of the isoforms, other interactive cytokine-growth factor receptor systems, such as PDGF and CTGF, TGF beta receptor expression on target cells, including myofibroblast precursors, receptor binding competition, positive and negative signal transduction effectors, and transcription and translational regulatory mechanisms. While there has long been the view that TGF beta-1and TGF beta-2 are pro-fibrotic, while TGF beta-3 is anti-fibrotic, this review suggests that view is too simplistic, at least in adult tissues, since TGF beta-3 shares far more similarities in its modulation of fibrotic gene expression with TGF beta-1 and TGF beta-2, than it does differences, and often the differences are subtle. Rather, TGF beta-3 should be seen as a fibro-modulatory partner to the other two isoforms that modulates a nuanced and better controlled response to injury. The complex interplay between the three isoforms and numerous interactive proteins, in the context of the cellular milieu, controls regenerative non-fibrotic vs. fibrotic healing in a response to injury in a particular organ, as well as the resolution of fibrosis, when that occurs.

IGF-1 Upregulates Biglycan and Decorin by Increasing Translation and Reducing ADAMTS5 Expression

Proteoglycan (PG) is a glycosaminoglycan (GAG)-conjugated protein essential for maintaining tissue strength and elasticity. The most abundant skin PGs, biglycan and decorin, have been reported to decrease as skin ages. Insulin-like growth factor-1 (IGF-1) is important in various physiological functions such as cell survival, growth, and apoptosis. It is well known that the serum level of IGF-1 decreases with age. Therefore, we investigated whether and how IGF-1 affects biglycan and decorin. When primary cultured normal human dermal fibroblasts (NHDFs) were treated with IGF-1, protein levels of biglycan and decorin increased, despite no difference in mRNA expression. This increase was not inhibited by transcription blockade using actinomycin D, suggesting that it is mediated by IGF-1-induced enhanced translation. Additionally, both mRNA and protein expression of ADAMTS5, a PG-degrading enzyme, were decreased in IGF-1-treated NHDFs. Knockdown of ADAMTS5 via RNA interference increased protein expression of biglycan and decorin. Moreover, mRNA and protein expression of ADAMTS5 increased in aged human skin tissues compared to young tissue. Overall, IGF-1 increases biglycan and decorin, which is achieved by improving protein translation to increase synthesis and preventing ADAMTS5-mediated degradation. This suggests a new role of IGF-1 as a regulator for biglycan and decorin in skin aging process.

Relative Protein Abundances and Biological Ageing in Whole Skeletal Elements

Establishing biological age is an integral part of forensic investigations, currently achieved through morphological methods with varying degrees of accuracy. Furthermore, biological ageing is much easier in juveniles than in adults, at which point traditional ageing methods struggle. Therefore, biomolecular approaches are considered of great interest, with several protein markers already recognized for their potential forensic significance. However, previous studies have typically relied on subsampling different parts of skeletal elements. Here, we attempt to evaluate the proteome of complete elements using a rat model. In the analysis of specimens spanning beyond adulthood (1 week to 1.5 years), we observed 729 unique proteins across 33 samples (three for each sex for each of the five (female) or six (male)), five of which represent newly identified proteins in relation to age estimation: vimentin, osteopontin, matrilin-1, apolipoprotein A-I, and prothrombin. Most of these follow the trend of decreasing abundance through age, with the exception of prothrombin that increases. We consider the combined use of these relative abundances, along with those of previously noted fetuin-A, biglycan, albumin, and chromogranin-A signatures, as being of potential value to the development of an age estimation tool worthy of further evaluation in forensic contexts.

Biglycan and Decorin Expression and Distribution in Palatal Adhesion

Previous studies demonstrated that chondroitin sulfate proteoglycans (CSPGs) on apical surfaces of palatal medial edge epithelial (MEE) cells were necessary for palatal adhesion. In this study, we identified 2 proteoglycans, biglycan and decorin, that were expressed in the palatal shelves prior to adhesion. In addition, we established that these proteoglycans were dependent on transforming growth factor β (TGFβ) signaling. Laser capture microdissection was used to collect selected palatal epithelial cells from embryonic mouse embryos at various palate development stages. The expression of specific messenger RNA (mRNA) for biglycan and decorin was determined with quantitative real-time polymerase chain reaction. The TGFβrI kinase inhibitor (SB431542) was used in palatal organ cultures to determine if blocking TFGβ signaling changed biglycan and decorin distribution. Immunohistochemistry of both biglycan and decorin revealed expression on the apical and lateral surfaces of MEE cells. Biglycan protein and mRNA levels peaked as the palatal shelves adhered. Decorin was less abundant on the apical epithelial surface and also had reduced mRNA levels compared to biglycan. Their proteins were not expressed on MEE cells of palates treated with SB431542, an inhibitor of TGFβ signaling. The temporal expression of biglycan and decorin on the apical surface of MEE, combined with the evidence that these proteins were regulated through the TGFβ pathway, indicated that they may be important for adhesion.

Different combinations of growth factors for the tenogenic differentiation of bone marrow mesenchymal stem cells in monolayer culture and in fibrin-based three-dimensional constructs

Tendon injuries are severe burdens in clinics. The poor tendon healing is related to an ineffective response of resident cells and inadequate vascularization. Thanks to the high proliferation and multi-lineage differentiation capability, bone marrow-derived mesenchymal stem cells (BMSCs) are a promising cell source to support the tendon repair. To date, the association of various growth factors to induce the in vitro tenogenic differentiation of multipotent progenitor cells is poorly investigated. This study aimed to investigate the tenogenic differentiation of rabbit BMSCs by testing the combination of bone morphogenetic proteins (BMP-12 and 14) with transforming growth factor beta (TGF-β) and vascular endothelial growth factor (VEGF) both in 2D and 3D cultures within fibrin-based constructs. After 7 and 14 days, the tenogenic differentiation was assessed by analyzing cell metabolism and collagen content, the gene expression of tenogenic markers and the histological cell distribution and collagen deposition within 3D constructs. Our results demonstrated that the association of BMP-14 with TGF-β3 and VEGF enhanced the BMSC tenogenic differentiation both in 2D and 3D cultures. This study supports the use of fibrin as hydrogel-based matrix to generate spheroids loaded with tenogenic differentiated BMSCs that could be used to treat tendon lesions in the future.

A role for hedgehog signaling in the differentiation of the insertion site of the patellar tendon in the mouse

Tendons are typically composed of two histologically different regions: the midsubstance and insertion site. We previously showed that Gli1, a downstream effector of the hedgehog (Hh) signaling pathway, is expressed only in the insertion site of the mouse patellar tendon during its differentiation. To test for a functional role of Hh signaling, we targeted the Smoothened (Smo) gene in vivo using a Cre/Lox system. Constitutive activation of the Hh pathway in the mid-substance caused molecular markers of the insertion site, e.g. type II collagen, to be ectopically expressed or up-regulated in the midsubstance. This was confirmed using a novel organ culture method in vitro. Conversely, when Smo was excised in the scleraxis-positive cell population, the development of the fibrocartilaginous insertion site was affected. Whole transcriptome analysis revealed that the expression of genes involved in chondrogenesis and mineralization was down-regulated in the insertion site, and expression of insertion site markers was decreased. Biomechanical testing of murine adult patellar tendon, which developed in the absence of Hh signaling, showed impairment of tendon structural properties (lower linear stiffness and greater displacement) and material properties (greater strain), although the linear modulus of the mutant group was not significantly lower than controls. These studies provide new insights into the role of Hh signaling during tendon development.

Arterial retention of remnant lipoproteins ex vivo is increased in insulin resistance because of increased arterial biglycan and production of cholesterol-rich atherogenic particles that can be improved by ezetimibe in the JCR:LA-cp rat

BACKGROUND

Literature supports the "response-to-retention" hypothesis-that during insulin resistance, impaired metabolism of remnant lipoproteins can contribute to accelerated cardiovascular disease progression. We used the JCR:LA-cp rat model of metabolic syndrome (MetS) to determine the extent of arterial accumulation of intestinal-derived remnants ex vivo and potential mechanisms that contribute to exacerbated cholesterol deposition in insulin resistance.

METHODS AND RESULTS

Arteries from control and MetS (insulin-resistant) JCR:LA-cp rats were perfused ex vivo with Cy5-labeled remnant lipoproteins, and their arterial retention was quantified by confocal microscopy. Arterial proteoglycans were isolated from control and MetS rats at 6, 12, and 32 weeks of age. There was a significant increase in the arterial retention of remnants and in associated cholesterol accumulation in MetS rats as compared to control rats. Mechanistic studies reveal that increased cholesterol deposition is a result of greater arterial biglycan content; longer glycosaminoglycans and increased production of cholesterol-rich intestinal-derived remnants, as compared to controls. Additionally, perfusion of vessels treated with ezetimibe, alone or in combination with simvastatin, with remnants isolated from the respective treatment group reduced ex vivo arterial retention of remnant-derived cholesterol ex vivo as compared to untreated controls.

CONCLUSIONS

Increased progression of atherosclerotic cardiovascular disease in MetS and type 2 diabetes mellitus might be explained in part by an increase in the arterial retention of cholesterol-rich remnants. Furthermore, ezetimibe alone or in combination treatment with simvastatin could be beneficial in ameliorating atherosclerotic cardiovascular disease in insulin resistance and MetS.

Young adult chondrocytes proliferate rapidly and produce a cartilaginous tissue at the gel-media interface in agarose cultures

Primary chondrocytes cultured in agarose can escape the gel, accumulate at the interface between agarose and the culture medium, and form an outgrowing tissue. These outgrowths can appear as voluminous cartilage-like nodules that have never been previously investigated. In the present study, bovine articular chondrocytes from three age groups (fetal, young adult, aged) were seeded and cultured in agarose to test the hypothesis that hyaline-like cartilage outgrowths develop at the interface by appositional growth, in an age-dependant manner. Macroscopic appearance, cell content, cell division, cytoskeletal morphology, and extracellular matrix (ECM) composition were analyzed. Fetal chondrocytes produced a fibrous interfacial tissue while aged chondrocytes produced ECM-poor cell clusters. In contrast young adult chondrocytes produced large cartilaginous outgrowths, rich in proteoglycan and collagen II, where cells in the central region displayed a chondrocyte morphology. Cell proliferation was confined to the peripheral edge of these outgrowths, where elongated cell morphology, cell-cell contacts, and cell extensions toward the culture medium were seen. Thus these voluminous cartilaginous outgrowths formed in an appositional growth process and only for donor chondrocytes from young adult animals. This system offers an interesting ability to proliferate chondrocytes in a manner that results in a chondrocyte morphology and a cartilaginous ECM in central regions of the outgrowing tissue. It also provides an in vitro model system to study neocartilage appositional growth.

Fragmentation of decorin, biglycan, lumican and keratocan is elevated in degenerate human meniscus, knee and hip articular cartilages compared with age-matched macroscopically normal and control tissues

Introduction

The small leucine-rich proteoglycans (SLRPs) modulate tissue organization, cellular proliferation, matrix adhesion, growth factor and cytokine responses, and sterically protect the surface of collagen type I and II fibrils from proteolysis. Catabolism of SLRPs has important consequences for the integrity of articular cartilage and meniscus by interfering with their tissue homeostatic functions.

Methods

SLRPs were dissociatively extracted from articular cartilage from total knee and hip replacements, menisci from total knee replacements, macroscopically normal and fibrillated knee articular cartilage from mature age-matched donors, and normal young articular cartilage. The tissue extracts were digested with chondroitinase ABC and keratanase-I before identification of SLRP core protein species by Western blotting using antibodies to the carboxyl-termini of the SLRPs.

Results

Multiple core-protein species were detected for all of the SLRPs (except fibromodulin) in the degenerate osteoarthritic articular cartilage and menisci. Fibromodulin had markedly less fragments detected with the carboxyl-terminal antibody compared with other SLRPs. There were fewer SLRP catabolites in osteoarthritic hip than in knee articular cartilage. Fragmentation of all SLRPs in normal age-matched, nonfibrillated knee articular cartilage was less than in fibrillated articular cartilage from the same knee joint or total knee replacement articular cartilage specimens of similar age. There was little fragmentation of SLRPs in normal control knee articular cartilage. Only decorin exhibited a consistent increase in fragmentation in menisci in association with osteoarthritis. There were no fragments of decorin, biglycan, lumican, or keratocan that were unique to any tissue. A single fibromodulin fragment was detected in osteoarthritic articular cartilage but not meniscus. All SLRPs showed a modest age-related increase in fragmentation in knee articular and meniscal cartilage but not in other tissues.

Conclusion

Enhanced fragmentation of SLRPs is evident in degenerate articular cartilage and meniscus. Specific decorin and fibromodulin core protein fragments in degenerate meniscus and/or human articular cartilage may be of value as biomarkers of disease. Once the enzymes responsible for their generation have been identified, further research may identify them as therapeutic targets.

Expression and Regulation of the Osteoarthritis-associated Protein Asporin

Asporin (ASPN) is a small leucine-rich proteoglycan that is involved in pathological processes of osteoarthritis. Previously, we showed that asporin can inhibit transforming growth factor-beta1 (TGF-beta1)-mediated expression of cartilage matrix genes and chondrogenesis in vitro (Kizawa, H., Kou, I., Iida, A., Sudo, A., Miyamoto, Y., Fukuda, A., Mabuchi, A., Kotani, A., Kawakami, A., Yamamoto, S., Uchida, A., Nakamura, K., Notoya, K., Nakamura, Y., and Ikegawa, S. (2005) Nat. Genet. 37, 138-144). However, details about regulation of asporin itself are not yet known. Here, we examined ASPN expression in skeletal tissue and potential regulation of ASPN by TGF-beta. In situ hybridization revealed the presence of ASPN mRNA in the perichondrium/periosteum of long bones, but its absence in articular cartilage and growth plates. Immunohistochemical analysis also showed ASPN protein expression predominantly in the perichondrium/periosteum. TGF-beta1 induced endogenous ASPN mRNA expression over time in vitro, and this induction was suppressed by the TGF-beta type I receptor kinase inhibitor SB431542. Inhibition of Smad3 significantly reduced TGF-beta1-induced ASPN expression, whereas overexpression of Smad3 augmented the induction. Characterization of the human ASPN promoter region revealed a region from -126 to -82 that is sufficient for full promoter activity; however, TGF-beta1 failed to increase activity through the ASPN promoter. Our findings indicate that TGF-beta1 induces ASPN through Smad3 but that this induction is indirect.

Decorin regulates assembly of collagen fibrils and acquisition of biomechanical properties during tendon development

Tendon function involves the development of an organized hierarchy of collagen fibrils. Small leucine-rich proteoglycans have been implicated in the regulation of fibrillogenesis and decorin is the prototypic member of this family. Decorin-deficient mice demonstrate altered fibril structure and mechanical function in mature skin and tail tendons. However, the developmental role(s) of decorin needs to be elucidated. To define these role(s) during tendon development, tendons (flexor digitorum longus) were analyzed ultrastructurally from postnatal day 10 to 90. Decorin-deficient tendons developed abnormal, irregularly contoured fibrils. Finite mixture modeling estimated that the mature tendon was a three-subpopulation mixture of fibrils with characteristic diameter ranges. During development, in each subpopulation the mean diameter was consistently larger in mutant mice. Also, diameter distributions and the percentage of fibrils in each subpopulation were altered. Biomechanical analyses demonstrated that mature decorin-deficient tendons had significantly reduced strength and stiffness; however, there was no reduction in immature tendons. Expression of decorin and biglycan, a closely related family member, was analyzed during development. Decorin increased with development while biglycan decreased. Spatially, both had a comparable localization throughout the tendon. Biglycan expression increased substantially in decorin-deficient tendons suggesting a potential functional compensation. The accumulation of structural defects during fibril growth, a period associated with decorin expression and low biglycan expression, may be the cause of compromised mechanical function in the absence of decorin. Our findings indicate that decorin is a key regulatory molecule and that the temporal switch from biglycan to decorin is an important event in the coordinate regulation of fibrillogenesis and tendon development.

Kinetic analysis of the polymerization and depolymerization of β2-microglobulin-related amyloid fibrils in vitro

beta(2)-Microglobulin-related (Abeta(2)M) amyloidosis is a serious complication in patients on long-term dialysis, and partial unfolding of beta(2)-microglobulin (beta(2)-m) is believed to be prerequisite to its assembly into Abeta(2)M amyloid fibrils. Many kinds of amyloid-associated molecules (e.g., apolipoprotein E (apoE), glycosaminoglycans (GAGs), proteoglycans (PGs)) may contribute to the development of Abeta(2)M amyloidosis. The formation of Abeta(2)M amyloid fibrils in vitro was first observed at low pH (2.0-3.0). Very recently, low concentrations of 2,2,2-trifluoroethanol (TFE) and the sub-micellar concentration of sodium dodecyl sulfate, a model for anionic phospholipids, have been reported to cause the extension of Abeta(2)M amyloid fibrils at a neutral pH, inducing partial unfolding of beta(2)-m and stabilization of the fibrils. Moreover, apoE, GAGs and PGs were found to stabilize Abeta(2)M amyloid fibrils at a neutral pH, forming a stable complex with the fibrils. Some GAGs, especially heparin enhanced the fibril extension in the presence of TFE at a neutral pH. Some PGs, especially biglycan also induced the polymerization of acid-denatured beta(2)-m. These findings are consistent with the hypothesis that in vivo, specific molecules that affect the conformation and stability of beta(2)-m and amyloid fibrils will have significant effects on the deposition of Abeta(2)M amyloid fibrils.

Transforming growth factor beta stimulation of biglycan gene expression is potentially mediated by sp1 binding factors

Biglycan is a small leucine-rich proteoglycan which is localized in the extracellular matrix of bone and other specialized connective tissues. Both biglycan mRNA and protein are up-regulated by transforming growth factor-beta(1) (TGF-beta(1)) and biglycan appears to influence TGF-beta(1) activity. In this study, we have investigated the mechanism by which TGF-beta(1), TGF-beta(2) and TGF-beta(3) stimulate biglycan mRNA expression in the osteoblastic cell line MG-63. The cells were transfected with a series of deletional human biglycan promoter constructs and a region in the biglycan 5' DNA was found to respond to TGF-beta(1) with increased transcriptional activity in a dose-dependent manner. Also TGF-beta(2) and TGF-beta(3), two structurally highly related TGF-beta isoforms stimulated biglycan transcription. A TGF-beta responsive region was identified within the first 218 bp of the human biglycan promoter upstream from the transcriptional start site, which contained several binding sites for the transcription factor Sp1. Electrophoretic mobility shift assays with nuclear extracts from MG-63 cells showed binding of both Sp1 and Sp3 to a site at -216 to -208. When the biglycan promoter construct was co-transfected with Sp1 and Sp3 expression vectors in Sp1-deficient Drosophila Schneider-2 cells, Sp1 induced the transcriptional activity of biglycan. Addition of Sp3 augmented the effect of Sp1 on biglycan gene expression. Induction of biglycan mRNA expression in response to TGF-beta in MG-63 cells was abrogated by mithramycin, an inhibitor of Sp1 binding to GC-rich DNA sequences. A mutation in the Sp1 site at -216 to -208 within the -218 biglycan promoter construct substantially diminished the transcriptional up-regulation by TGF-beta(1). Taken together this data shows for the first time that TGF-beta(1) stimulation of human biglycan mRNA expression relies on increased transcription of the biglycan gene, and is mediated by members of the Sp1 family of transcription factors.

Molecular interactions in the formation and deposition of beta2-microglobulin-related amyloid fibrils

In beta2-microglobulin-related (A beta2M) amyloidosis, a serious complication in patients on long-term dialysis, partial unfolding of beta2-microglobulin (beta2-m) is believed to be prerequisite to its assembly into A beta2M amyloid fibrils. Many kinds of amyloid-associated molecules, (e.g., apolipoprotein E (apoE), glycosaminoglycans (GAGs), proteoglycans (PGs)) may contribute to the development of A beta2M amyloidosis. In 1990s, the formation of A beta2M amyloid fibrils in vitro was first observed at low pH (2.0-3.0). Very recently, low concentrations of 2,2,2-trifluoroethanol (TFE) and the sub-micellar concentration of sodium dodecyl sulfate, a model for anionic phospholipids, have been reported to cause the extension of A beta2M amyloid fibrils at a neutral pH, inducing partial unfolding of beta2-m and stabilization of the fibrils. Moreover, apoE, GAGs, and PGs were found to stabilize A beta2M amyloid fibrils at a neutral pH, forming a stable complex with the fibrils. Some GAGs, especially heparin, enhanced the fibril extension in the presence of TFE at a neutral pH. Some PGs, especially biglycan also induced the polymerization of acid-denatured beta2-m. These findings are consistent with the hypothesis that in vivo, specific molecules that affect the conformation and stability of beta2-m and amyloid fibrils will have significant effects on the deposition of A beta2M amyloid fibrils.

The pathophysiology of osteoarthritis

Osteoarthritis (OA) is a complex disease whose pathogenesis includes the contribution of biomechanical and metabolic factors which, altering the tissue homeostasis of articular cartilage and subchondral bone, determine the predominance of destructive over productive processes. A key role in the pathophysiology of articular cartilage is played by cell/extra-cellular matrix (ECM) interactions, which are mediated by cell surface integrins. In a physiologic setting, integrins modulate cell/ECM signaling, essential for regulating growth and differentiation and maintaining cartilage homeostasis. During OA, abnormal integrin expression alters cell/ECM signaling and modifies chondrocyte synthesis, with the following imbalance of destructive cytokines over regulatory factors. IL-1, TNF-alpha and other pro-catabolic cytokines activate the enzymatic degradation of cartilage matrix and are not counterbalanced by adequate synthesis of inhibitors. The main enzymes involved in ECM breakdown are metalloproteinases (MMPs), which are sequentially activated by an amplifying cascade. MMP activity is partially inhibited by the tissue inhibitors of MMPs (TIMPs), whose synthesis is low compared with MMP production in OA cartilage. Intriguing is the role of growth factors such as TGF-beta, IFG, BMP, NGF, and others, which do not simply repair the tissue damage induced by catabolic factors, but play an important role in OA pathogenesis.

Cross-Talk Between Interleukin-6 and Transforming Growth Factor-β3Regulates Extracellular Matrix Production by Human Fibroblasts from Subjects with Non-Syndromic Cleft Lip and Palate

BACKGROUND

Transforming growth factor-beta (TGF-beta) interference with interleukin 6 (IL-6) activity and the role of the latter in early human embryonic development prompted us to examine the effects IL-6 on matrix synthesis and the effects of TGF-beta3 on IL-6 expression human cleft lip and palate (CLP) fibroblasts.

METHODS

Collagen and glycosaminoglycan (GAG) synthesis were determined by radiolabeled precursors and biglycan expression by Northern blotting before and after adding IL-6. The effects of TGF-beta3 on IL-6 production were assayed by evaluating IL-6 transcript by Northern blotting and IL-6 protein secretion by enzyme-linked immunosorbent assay.

RESULTS

The results showed that IL-6 elicited an inhibitory effect on collagen and GAG levels in CLP fibroblasts by lowering hyaluronan and dermatan sulfate secretion. IL-6 up-regulated biglycan expression, but less strongly than TGF-beta3. TGF-beta3 significantly down-regulated IL-6 transcript and secretion in CLP fibroblasts.

CONCLUSIONS

These data suggest the increase in matrix components that characterize the CLP fibroblast phenotype might be due to a concerted TGF-beta3-IL-6 action. We hypothesize changes in cross-talk between TGF-beta3 and IL-6 signal transduction pathways are involved in the induction of cleft palate.

Glycosaminoglycan and proteoglycan inhibit the depolymerization of beta2-microglobulin amyloid fibrils in vitro

BACKGROUND

Although several kinds of evidence suggest that glycosaminoglycans (GAGs) and proteoglycans (PGs) may contribute to the development of beta2-microglobulin-related (Abeta2m) amyloidosis, the precise roles of these molecules for the development of Abeta2m amyloidosis are poorly understood.

METHODS

We investigated the effects of GAGs and PGs on the depolymerization of Abeta2m amyloid fibrils at a neutral pH, as well as on the formation of the fibrils at an acidic pH in vitro, using fluorescence spectroscopy with thioflavin T and electron microscopy.

RESULTS

Depolymerization of Abeta2m amyloid fibrils at pH 7.5 at 37 degrees C was inhibited dose-dependently by the presence of some GAGs (heparin, dermatan sulfate, or heparan sulfate) or PGs (biglycan, decorin, or keratan sulfate proteoglycan). Electron microscopy revealed that a significant amount of Abeta2m amyloid fibrils remained in the reaction mixture with some lateral aggregation. Second, when monomeric beta2m was incubated with aggrecan, biglycan, decorin, or heparin at pH 2.5 at 37 degrees C for up to 21 days, the thioflavin T fluorescence increased depending on dose and time. Electron microscopy revealed the formation of rigid and straight fibrils similar to Abeta2m amyloid fibrils in beta2m incubated with biglycan for 21 days.

CONCLUSION

These results suggest that some GAGs and PGs could enhance the deposition of Abeta2m amyloid fibrils in vivo, possibly by binding directly to the surface of the fibrils and stabilizing the conformation of beta2m in the fibrils, as well as by acting as a scaffold for the polymerization of beta2m into the fibrils.

The effect of link peptide on proteoglycan synthesis in equine articular cartilage

The basal rate of in vitro proteoglycan (PG) synthesis in explants of equine articular cartilage was subject to considerable variation in animals of the same age but was greater in younger than older animals. Synthesis of PGs in explant cultures was stimulated by a synthetic link peptide, identical in sequence to the N-terminus of the link protein (LP) of PG aggregates, in a similar manner to that demonstrated previously for human articular cartilage [Biochem. Soc. Trans. 25 (1997) 427; Arthritis Rheum. 41 (1998) 157]. Stimulation occurred in tissue from animals ranging from 1 to 30 years old but older animals required higher concentrations of peptide to produce a measurable response. Synthesis of PGs increased in a concentration-dependent manner and was paralleled by increases in the ability of aggrecan monomers to form aggregates with hyaluronan (HA). In addition to its effect on synthesis of PGs, link peptide also increased synthesis of both aggrecan and LP mRNA. Cartilage explant and chondrocyte cultures secreted small amounts of biologically active interleukin 1 (IL 1) and secretion of this cytokine was reduced considerably by the addition of link peptide. Reduction in the activity of this catabolic cytokine coupled with the increased synthesis of mRNA for aggrecan and link peptide may be the mechanism by which link peptide exerts its positive effect on the rate of PG synthesis in articular cartilage.

TGF beta 1 and biglycan, decorin, and fibromodulin metabolism in canine cartilage

OBJECTIVE

Small proteoglycans (PGs) may accumulate in late stage osteoarthritis even as aggrecan is lost. It is not clear what role transforming growth factor (TGF) beta has in this accumulation. Our goal was to investigate the ability of TGF beta 1 to modulate the synthesis and accumulation of decorin, biglycan, and fibromodulin in cartilage explants cultured under conditions in which aggrecan synthesis remains relatively constant.

DESIGN

Articular cartilage was cultured in the presence or absence of 4 ng/ml TGF beta 1 for up to 16 days. Material extracted from cartilage was assayed for 35SO(4)-large and small PGs and for total endogenous decorin, biglycan and fibromodulin.

RESULTS

The synthesis of 35SO(4)-small PGs increased during the 16 days in culture in response to TGF beta 1, but declined in control cultures. The difference in 35SO(4)-decorin between TGF beta 1 and control samples reached nine-fold after 16 days, while the difference in total endogenous decorin was less than 1.5-fold. 35SO(4)-decorin, which was present in TGF beta 1-treated cultures had an identical core protein, but a longer glycosaminoglycan chain than that of decorin in control cultures. No significant differences in endogenous biglycan were detected, but accumulation of fibromodulin in TGF beta 1 explants exceeded fibromodulin in controls, on average, by 3.8-fold. Fibromodulin was present in cartilage in both keratan sulfate- and non-sulfated oligosaccharide-substituted forms.

CONCLUSIONS

The accumulation of each of the three small PGs was affected to a different extent in response to TGF beta 1. Of the three, fibromodulin content was most rapidly augmented in response to TGF beta 1.

Age-related changes in the composition and mechanical properties of human nasal cartilage

Nasal cartilage is widely used in reconstructive surgery for the replacement of soft tissue defects and nasal reconstruction procedures. The ability to shape harvested tissue and the performance in the transplant site are related to the mechanical properties of nasal cartilage. Several studies have documented changes in composition and mechanical properties of other cartilages with age, but little is known about these processes in nasal cartilage. In this study, 45 human nasal septum specimens were gathered from patients 15-60 years of age after reconstructive surgery. Samples were cut to 6 mm in diameter and tested in confined compression to determine equilibrium modulus and hydraulic permeability and analyzed for glycosaminoglycan and hydroxyproline content. Equilibrium modulus decreased significantly with increasing donor age (P<0.01) while hydraulic permeability increased significantly (P<0.02). Glycosaminoglycan (GAG) content decreased significantly with age (P<0.05), while hydroxyproline content showed a slight, but not significant, increase with age (P>0.2). These trends are qualitatively similar to those observed in articular cartilage, suggesting the existence of a systemic process of cartilage degradation that is independent of mechanical loading. Further, the relationships between biochemical composition and mechanical properties were age-dependent, with cartilage from patients less than 30 years of age showing greater dependence of equilibrium modulus and hydraulic permeability on GAG and hydroxyproline content. This suggests that changes in matrix organization may accompany changes in tissue composition.

Interaction of bone proteoglycans and proteoglycan components with hydroxyapatite

The small leucine-rich proteoglycans (SLRPs) of bone interact with hydroxyapatite (HAP) and are proposed to play an important role in the regulation of the mineralisation process. The present study has examined the interaction of bone SLRPs, purified, liberated bone glycosaminoglycan (GAG) chains and core proteins, as well as commercial chondroitin 4-sulphate (C4S) with HAP. Isotherm data (0.02 M sodium acetate) revealed that the intact proteoglycans (PGs) and bone GAGs showed greater binding onto HAP with higher adsorption maxima than the constituent core proteins and commercial C4S. Adsorption was dependent on pH and ionic strength, increasing with decreasing pH and in the presence of calcium whilst decreasing in the presence of phosphate, suggesting that electrostatic effects are important. The data indicates that PG/GAG chemistry and conformation in solution are significant determinants in the adsorption process and provides important information concerning interfacial adsorption phenomena between the organic-inorganic phases of mineralised systems.

Time course of collagen and decorin changes in rat cardiac and skeletal muscle post-MI

We examined the temporal relationship between messages (type I and type III mRNAs) for the principal fibrillar procollagens and subsequent collagen accretion, cross-linking, and decorin expression in the left ventricle (LV) postmyocardial infarction (post-MI). We sought to determine 1) what role the proteoglycan decorin plays in extracellular matrix (ECM) remodeling known to take place as a consequence of MI and 2) the extent skeletal muscle ECM is altered early post-MI. Therefore, after surgically induced production of small- to moderate-sized infarcts (approximately 20% of LV mass), extent and time course of ECM remodeling was evaluated in remaining viable LV free wall and in slow- [soleus (SOL)] and fast-twitch [gastrocnemius (GAST)] skeletal muscles. Decorin, collagen, and hydroxylysylpyridinium cross-link concentrations and alpha1(I) (type I) and alpha1(III) (type III) procollagen mRNAs were measured in LVs from noninfarcted controls and at 72 h, 1, 2, 5, and 13 wk post-MI. These same data were collected in SOL and GAST muscles at all time points except 13 wk. Type I procollagen mRNA increased at both 72-h and 1-wk time points in LVs. Type III procollagen mRNA was elevated at 1 wk, returning to baseline by 2 wk post-MI. Collagen concentration was significantly increased by 1 wk, more than doubled by 5 wk, and was elevated 129% by 13 wk in the remaining viable LV. LV decorin expression was unaltered at early time points, but increased 38% at 5 wk post-MI and doubled by 13 wk post-MI. In skeletal muscle, procollagen mRNAs were transiently altered in SOL and GAST muscles without any demonstrable effect on the measured ECM parameters. This study reports, for the first time, the upregulation time course of decorin and its relationship to increased HP cross-linking and accumulation of collagen in viable myocardium post-MI.

Biglycan is overexpressed in pancreatic cancer and induces G1-arrest in pancreatic cancer cell lines

BACKGROUND & AIMS

Biglycan (PG-I), a component of the extracellular matrix (ECM), is overexpressed in pancreatic cancer. To determine possible matrix-tumor interactions, we investigated the effects of PG-I on pancreatic cancer.

METHODS

PG-I expression in cell lines and tissue samples was examined by Northern blot and immunofluorescence. The effect of PG-I on proliferation was determined by measuring activity of Ras, ERK, Rb, [(3)H]-thymidine incorporation, and cell cycle analysis. Expression of cyclin A, B1, D1, E1, G1, PCNA, p21, and p27 was analyzed by Northern and Western blots.

RESULTS

PG-I was overexpressed in the ECM of pancreatic cancer samples compared with normal pancreas or chronic pancreatitis tissues. Addition of transforming growth factor (TGF)-beta induced PG-I expression in HFL and HFFF2 fibroblasts as well as in the pancreatic cancer cell line PANC-1. PG-I inhibited growth of both TGF-beta-responsive and TGF-beta-unresponsive pancreatic cancer cells by inducing G1-arrest, which is accompanied by an increase of p27 and reduction of cyclin A and proliferating cell nuclear antigen. Furthermore, endogenous Ras and ERK activation was partly reduced by PG-I in vitro.

CONCLUSIONS

The ECM protein PG-I inhibits growth by arresting pancreatic cancer cells in G1 and may be part of a host defense mechanism aimed at slowing down pancreatic tumor progression.

Murine fibromodulin: cDNA and genomic structure, and age-related expression and distribution in the knee joint

The genomic structure of murine fibromodulin was determined, and its age-related expression and distribution were characterized in knee epiphyses, with decorin studied for reference. Fibromodulin, as well as decorin, have roles in collagen fibrillogenesis both in vitro and in vivo. The murine fibromodulin gene, Fmod, was similar with that in other species, with three exons and 86% of the translated sequence in exon 2. The 2.7 kb long cDNA contains an open reading frame of 1131 nt. Fibromodulin mRNA levels were highest in tissues rich in fibrillar collagens type I or type II. During growth, the distribution of fibromodulin mRNA was similar with that of type II collagen, with the highest levels between 5 days and 1 month of age. Thereafter, the expression of type II collagen declined to a level near the detection limit, whereas the fibromodulin expression decreased less markedly to a level of approx. 35% of maximum, and remained constant throughout the rest of the observation period. In contrast, decorin mRNA levels were the highest in old animals. Pericellular deposition of fibromodulin was strong around the late-hypertrophic chondrocytes of the secondary ossification centre and in the growth plate. In young epiphyses, both fibromodulin and decorin were found interterritorially, mainly in the uncalcified and deep-calcified cartilage. In the old mice, calcified cartilage became enriched with regard to fibromodulin, while, in contrast, decorin deposition diminished, particularly near the tidemark. In the subchondral bone trabeculae, decorin was found in the endosteum of growing, but not in the mature, epiphyses. Differences in the expression and distribution profiles suggest different roles for fibromodulin and decorin in the regulation of collagen fibrillogenesis, maintenance of the fibril organization and matrix mineralization. As fibromodulin is deposited closer to cells than decorin, it may have a primary role in collagen fibrillogenesis, whereas decorin might be involved in the maintenance of fibril structures in the interterritorial matrix.

Age-related changes in the synthesis and mRNA expression of decorin and aggrecan in human meniscus and articular cartilage

OBJECTIVE

To determine if the biosynthesis of aggrecan and decorin in the human meniscus and the potential of the cells to express these macromolecules (mRNA), is affected by the age of the individual and that if any changes are observed are they different to those measured in articular cartilage obtained from the same joint.

DESIGN

Radiolabelling of tissue explants, anion-exchange chromatography and agarose-polyacrylamide gel electrophoresis were used to analyze newly synthesized proteoglycans. A quantitative, competitive reverse-transcriptase polymerase chain reaction was developed and applied to the tissue to measure the expression of decorin and aggrecan mRNA.

RESULTS

Proteoglycan synthesis in the meniscus was higher in young donors (1-5 mmoles sulfate incorporated/h/mgDNA, under 20 years of age) than in adult tissues (0.5-1 mmoles incorporated/h/mgDNA, 20-62 years of age) and decorin was the major proteoglycan synthesized at this time. An age-related increase in the proportion of aggrecan synthesis in the meniscus was also observed using agarose-polyacrylamide gel electrophoresis. Both decorin (five-fold) and aggrecan (eight-fold) mRNA expression increased with age in meniscus whereas levels were relatively constant in articular cartilage. In addition, the synthesis of decorin and aggrecan and the expression of their mRNA was different in meniscus and articular cartilage from the same knee joint.

CONCLUSION

The synthesis and turnover of aggrecan and decorin in the human meniscus is influenced by the age of the individual and is not the same as that observed for articular cartilage.

Articular cartilage proteoglycan metabolism in avian degenerative joint disease: effects of strain selection and body weight

The effects of strain selection and body weight on proteoglycan metabolism and the onset of degenerative joint disease (DJD) were investigated in avian articular cartilage. Samples from the hock joint (proximal tarsometatarsus, PTM; distal tibiotarsus, DTT) of rapidly growing broiler fowl, fed either ad libitum or on a restricted-diet, were compared with those from a slow growing, light and non-selected strain (J-line). Synthesis and degradation of proteoglycans were investigated by radioactive pulse-chase studies, determination of total sulphated glycosaminoglycans and electrophoretic analysis. By gross morphology, degenerative changes in articular cartilage occurred solely in the DTT from ad libitum-fed broiler fowl, after 13 weeks. Differences in proteoglycan metabolism were also observed, most markedly in the DTT, where the rate of proteoglycan synthesis in the ad libitum-fed group was less than in age-matched J-line cartilage, and the proportions of both newly synthesised and resident proteoglycans released into the culture medium were greater. Results with the feed-restricted group were intermediate between ad libitum-fed and J-line. Electrophoretic analysis of proteoglycans in the culture media showed evidence of degradation solely in the ad libitum-fed group, with earliest onset in the DTT. The results indicate that proteoglycan metabolism in avian articular cartilage is similar to that in mammalian cartilage during the development of DJD, and that the onset of cartilage degeneration is linked with excessive load bearing.

Effects of interleukin-1beta and tumor necrosis factor-alpha on expression of matrix-related genes by cultured equine articular chondrocytes

OBJECTIVE

To determine the effects of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on expression and regulation of several matrix-related genes by equine articular chondrocytes.

SAMPLE POPULATION

Articular cartilage harvested from grossly normal joints of 8 foals, 6 yearling horses, and 8 adult horses.

PROCEDURE

Chondrocytes maintained in suspension cultures were treated with various doses of human recombinant IL-1beta or TNF-alpha. Northern blots of total RNA from untreated and treated chondrocytes were probed with equine complementary DNA (cDNA) probes for cartilage matrix-related genes. Incorporation of 35S-sulfate, fluorography of 14C-proline labeled medium, zymography, and western blotting were used to confirm effects on protein synthesis.

RESULTS

IL-1beta and TNF-alpha increased steady-state amounts of mRNA of matrix metalloproteinases 1, 3, and 13 by up to 100-fold. Amount of mRNA of tissue inhibitor of metalloproteinase-1 also increased but to a lesser extent (1.5- to 2-fold). Amounts of mRNA of type-II collagen and link protein were consistently decreased in a dose-dependent manner. Amount of aggrecan mRNA was decreased slightly; amounts of biglycan and decorin mRNA were minimally affected.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment of cultured equine chondrocytes with IL-1beta or TNF-alpha resulted in marked alterations in expression of various matrix and matrix-related genes consistent with the implicated involvement of these genes in arthritis. Expression of matrix metalloproteinases was increased far more than expression of their putative endogenous inhibitor. Results support the suggestion that IL-1beta and TNF-alpha play a role in the degradation of articular cartilage in arthritis.

An N-terminal peptide from link protein can stimulate biosynthesis of collagen by human articular cartilage

Previous studies have shown that a peptide identical in sequence to the N-terminal of link protein can function as a growth factor and up-regulate proteoglycan synthesis by human articular cartilage in explant culture (L. A. McKenna et al., Arthritis Rheum. 41, 157-162, 1998). The present study has extended these investigations to determine the effects of this peptide on the synthesis of collagen, another essential component of normal cartilage matrix. Explants from normal adult knee cartilage were maintained for periods of up to 8 days in medium with or without serum. Peptides were added during each day of culture. Synthesis of collagen was determined by the incorporation of [3H]proline into hydroxyproline and proteoglycans by incorporation of [35S]sulfate. The type of newly synthesized collagen was measured by SDS-polyacrylamide gel electrophoresis, fluorography, and immunoblotting. The link protein peptide stimulated synthesis of type II collagen in cartilage from a number of different subjects. Maximum up-regulation of synthesis was attained at a concentration of 100 ng/ml, similar to that observed previously for up-regulation of proteoglycan. Synthesis was up-regulated in both the presence and the absence of serum, although the overall rate of synthesis was greater when serum was added. The findings that this link peptide growth factor stimulated synthesis of proteins, including collagen, in a manner analogous to that shown previously for proteoglycans support the hypothesis that this peptide may have an important role in the feedback control of cartilage matrix synthesis.

Age-associated changes in decorin in rat mandibular condylar cartilage

The small proteoglycan decorin strongly binds the fibrils of collagen types I and II; this interaction is thought to play a part in the maintenance of tissue integrity and biomechanical properties. In limb articular cartilage, there is evidence that decorin synthesis increases with age and that it is elevated in response to increased loading or in osteoarthritic cartilage. The aim here was to characterize the presence and relative amount of decorin in the condylar cartilage of the temporomandibular joint (TMJ) with maturation by Western blotting, and to assess its tissue localization by immunohistochemistry. Comparative data were obtained from tibial articular cartilage, which has been extensively studied. Cartilage from the mandibular condyle and tibial plateau was harvested from 24-day-old (growing) and 161-day-old (young adult) female Sprague-Dawley rats. In growing animals, decorin appeared slightly more abundant in the mandibular condylar cartilage than in articular cartilage, whereas in young adult animals the decorin content in the TMJ cartilage was noticeably less than in limb articular cartilage. Although there was an increase in decorin abundance with age at the TMJ, the increase in decorin with age in limb articular cartilage was considerably more pronounced. These data indicate that, although decorin is present in mandibular condylar cartilage, its abundance in adults is less than in limb articular cartilage; thus, maturation-associated changes may be dissimilar in magnitude from those documented for limb articular cartilage.

TGFbeta isoforms and decorin gene expression are modified in fibroblasts obtained from non-syndromic cleft lip and palate subjects

Interaction between extracellular matrix (ECM) and cytokines is thought to be crucial for palatal development. The localization of transforming growth factors (TGFalpha and TGFbeta isoforms) in craniofacial tissues suggests that they carry out multiple functions during development. In the present report, we studied TGFalpha, TGFbeta1, and TGFbeta3 expressions and their effects on ECM macromolecule production of normal and cleft palatal fibroblasts in vitro, to investigate the mechanisms by which the phenotypic modulation of fibroblasts occurs during the cleft palate process. The results indicated that, while TGFalpha mRNA was not evidenced in CLP or normal fibroblasts, a reduced TGFbeta1 hybridization signal was detected in CLP fibroblasts. In addition, these secreted more active TGFbeta3 than TGFbeta1, as evaluated in a biological assay. The CLP phenotype, which differed from the normal one because of its higher PG decorin expression and greater production of GAG and collagen, was further modified by the addition of growth factors. In fact, in CLP fibroblasts, TGFalpha and TGFbeta1 down-regulated PG decorin transcript, TGFbeta1 increased collagen and GAG in both cellular and extracellular compartments, and TGFbeta3 promoted secretory processes of cells. In conclusion, the data represent the first report in a human model in vitro that TGFbeta1 and beta3 are differently expressed and are correlated to the CLP phenotype. Thus, strength is given to the hypothesis that TGFbeta isoforms are the potential inducers of phenotypic expression in palatal fibroblasts during development and that an autocrine growth factor production mechanism may be responsible for the phenotypic modifications.

Development and aging of the articular cartilage of the rabbit knee joint: Distribution of biglycan, decorin, and matrilin-1

We determined the distributions of the small proteoglycans biglycan and decorin and the glycoprotein matrilin-1 (cartilage matrix protein) during development and aging of articular cartilage in the rabbit knee joint. Before cavitation, the matrices of the interzone and the adjacent epiphyseal cartilage do not contain biglycan or decorin, but some chondrocytes express their mRNAs. Matrilin-1 is found only in the deeper epiphyseal cartilage. After cavitation, biglycan and decorin are detected in the presumptive articular cartilage, but there is no matrilin-1. All are present in the underlying epiphyseal cartilage. In the neonate, the epiphyseal cartilage is ossified and the articular cartilage becomes a discrete layer. Biglycan and decorin accumulate in the articular cartilage, but matrilin-1 remains confined to the residual epiphyseal cartilage. In the adult, the distributions of biglycan and decorin are highly variable. Decorin tends to be confined to the central region; matrilin-1 is absent. The findings indicate that the articular and epiphyseal cartilages are different from the earliest developmental stages. The epiphyseal cartilage can be identified by its possession of matrilin-1. Epiphyseal cartilage is removed during development to leave the articular cartilage. The relationships between the distributions of decorin and matrilin-1 and the fibrillar collagens are discussed. (J Histochem Cytochem 47:1603-1615, 1999)

Differential effects of interleukin-1 and transforming growth factor beta on the synthesis of small proteoglycans by rabbit articular chondrocytes cultured in alginate beads as compared to monolayers

Small proteoglycans (PGs) are supposed to play great roles in the assembly of cartilage matrix but the influence of cytokines and growth factors on their synthesis by articular chondrocytes is largely unknown. We investigated whether IL-1 and TGFbeta1 influence the production of small leucine-rich proteoglycans by chondrocytes cultured in a three-dimensional gel, as compared to the common monolayer system. Rabbit articular chondrocytes were cultured in alginate beads for 14 days or as monolayers for 7 days. The effect of 2 ng/ml IL-1beta or TGFbeta1 during the last two days in culture was determined, after [35S]methionine labeling over the last 24 h. Cell-associated and further-removed matrix compartments were separated by centrifugation after sodium citrate/EDTA treatment of alginate beads whereas medium and cell-layer fractions were isolated from monolayer cultures. Total newly synthesized PGs were first isolated by anion-exchange chromatography and the small PGs were further separated from aggrecans by gel-filtration (Sepharose CL-4B) and analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Addition of TGFbeta1 resulted in an overall rise in neosynthesized small PG content in both culture systems. However, TGFbeta1 significantly increased to the same extent the percentage of small PGs laid down in the cell-associated and the further-removed matrix compartments of the beads culture (+60%) whereas it augmented the content of small PGs in the medium (+40%) and reduced that of the cell fraction (-35%) in the monolayer culture. By adding IL-1, the amount of total newly synthesized small PGs was decreased in monolayers while it increased in alginate beads. IL-1 was also shown to change the relative distribution of these molecules in the monolayer system in contrast to the alginate beads culture where the proportions were not significantly altered. Electrophoretic analysis of the 35S-labeled small PGs-containing fractions confirmed these effects at the level of the 45-50 kDa-related core proteins. This study demonstrates that TGFbeta and IL-1 differently influence small PG synthesis of rabbit articular chondrocytes depending on whether they are cultured in alginate beads or in monolayers. Moreover, the regulation of small PG expression appears to be different from that of high-molecular weight aggrecans. As these small molecules are playing major roles in matrix assembly and growth factor regulation, the data may have great relevance to the pathogenesis of osteoarthritis and repair of articular cartilage lesions.

The macromolecular characteristics of cartilage proteoglycans do not change when synthesis is up-regulated by link protein peptide

Previous studies have shown that a synthetic, unglycosylated analogue of the N-terminal peptide from link protein can function as a growth factor and up-regulate proteoglycan biosynthesis in explant cultures of normal human articular cartilage from a wide age range of subjects (McKenna et al., Arthritis Rheum. 41 (1998) 157-162). The present work further shows that link peptide increased proteoglycan synthesis by cartilage cultured in both the presence and absence of serum, suggesting that the mechanism of up-regulation may be different from that of insulin-like growth factors. The proteoglycans synthesised during stimulation with link peptide were of normal hydrodynamic size and the ratio of core protein to glycosaminoglycan side chains and the proportions of the large proteoglycan aggrecan to the small proteoglycans, decorin and biglycan, remained constant. Aggrecan molecules were equally capable of forming aggregates as those from control tissues and the relative proportions of decorin and biglycan were unchanged showing that both were co-ordinately up-regulated. These results confirmed that this novel peptide is a potent stimulator of proteoglycan synthesis by articular cartilage and showed that the newly synthesised proteoglycans were of normal composition.

Matrix proteoglycans: from molecular design to cellular function

The proteoglycan superfamily now contains more than 30 full-time molecules that fulfill a variety of biological functions. Proteoglycans act as tissue organizers, influence cell growth and the maturation of specialized tissues, play a role as biological filters and modulate growth-factor activities, regulate collagen fibrillogenesis and skin tensile strength, affect tumor cell growth and invasion, and influence corneal transparency and neurite outgrowth. Additional roles, derived from studies of mutant animals, indicate that certain proteoglycans are essential to life whereas others might be redundant. The review focuses on the most recent genetic and molecular biological studies of the matrix proteoglycans, broadly defined as proteoglycans secreted into the pericellular matrix. Special emphasis is placed on the molecular organization of the protein core, the utilization of protein modules, the gene structure and transcriptional control, and the functional roles of the various proteoglycans. When possible, proteoglycans have been grouped into distinct gene families and subfamilies offering a simplified nomenclature based on their protein core design. The structure-function relationship of some paradigmatic proteoglycans is discussed in depth and novel aspects of their biology are examined.

A contribution to the regulation of proteoglycan production: modulation by TGF alpha, TGF beta and IL-1 of glycosaminoglycan biosynthesis on beta-D-xyloside in chick embryo fibroblasts

In order to elucidate the mechanisms determining the variability in the proteoglycan structure and the factors involved in this determination, we treated chick embryo skin fibroblasts with beta-D-xyloside to obtain glycosaminoglycan chains deprived of core proteins, and with different cytokines (transforming growth factor alpha and beta, interleukin-1) to produce variability. The different cytokines specifically regulate both cellular and extracellular amount and composition of glycosaminoglycans. Beta-D-xyloside treatment does not change protein content and protein synthesis, whereas it increases overall extracellular sulphated glycosaminoglycan production, heparan sulphate and chondroitin sulphate content, and reduces that of dermatan sulphate. This indicates that the core protein regulates quantitative proteoglycan production, and probably directs (with appropriate signals) the core oligosaccharide bound to it to the right synthesizing enzymes. The modulatory action of the different cytokines on sulphated glycosaminoglycan production and classes remains, even though the core protein is absent. This indicates that the cytokines also act on the glycosyltransferases. Our results suggest that the proteoglycan production may be subject to a double control, one of which is at the level of the core protein and the other, mediated by environmental signals, at the level of glycosaminoglycan synthesizing enzymes.

Expression of decorin and biglycan by rabbit articular chondrocytes. Effects of cytokines and phenotypic modulation

In this study, the levels of mRNAs coding for aggrecan, decorin and biglycan in rabbit articular chondrocytes were investigated, using both monolayer and 3D-alginate cultures treated with TGF-beta 1 and IL-1 beta. The cells were shown to express higher amounts of proteoglycan messages, specially the aggrecan, in gels than in monolayers. TGF-beta 1 increased aggrecan mRNA in both systems, whereas biglycan message was elevated only in alginate. It markedly decreased decorin expression in monolayer, either in primary or passaged cultures. In contrast, IL-1 beta had a weak inhibitory effect on both decorin and biglycan expression. Subculturing induced a dramatic decrease of aggrecan mRNA, while that of decorin augmented. Biglycan expression transiently increased after two passages, whereas it declined in further subcultures. Passaged chondrocytes transferred to alginate re-expressed high levels of aggrecan, decorin and biglycan. The data point to the influence of morphology, proliferative state and environment of the articular chondrocytes on their biosynthetic responses to cytokines. Although these immature cells do not fully reflect the adult chondrocytes present in the cartilage, this study may help in understanding the behaviour of these cells in osteoarticular diseases, where the surrounding extracellular matrix is profoundly altered.

Regulation of cartilage oligomeric matrix protein synthesis in human synovial cells and articular chondrocytes

OBJECTIVE

Cartilage oligomeric matrix protein (COMP) is a component of the extracellular matrix of articular cartilage. Its increased presence in synovial fluid and serum has been associated with accelerated joint damage in patients with rheumatoid arthritis (RA) and osteoarthritis. To fully understand the reasons for fluctuations of COMP levels, we studied the biosynthesis of this molecule in cells derived from joint tissues.

METHODS

Synovial cells were derived from synovial tissues of patients with RA, and human articular chondrocytes were prepared from normal articular cartilage. Analysis by Northern blotting was used to evaluate steady-state levels of COMP messenger RNA (mRNA), while secretion of the protein into culture media was analyzed by Western blotting. Expression of COMP in synovial tissues was studied by reverse transcriptase-polymerase chain reaction analysis and by in situ hybridization.

RESULTS

COMP was synthesized and secreted by synovial cells as well as by articular chondrocytes in culture. The basal rate of synthesis was very low; however, COMP biosynthesis in both cell populations was induced very strongly by transforming growth factor beta1 (TGFbeta1). Interleukin-1beta counteracted COMP induction by TGF-beta1. COMP was not detected in culture media of skin or fetal lung fibroblasts, either in the absence or the presence of TGFbeta1. COMP mRNA was also present in fresh synovial tissue specimens obtained from patients with RA.

CONCLUSION

COMP is synthesized and secreted not only by articular chondrocytes, but also by synovial fibroblasts. The demonstration of COMP expression in surgical specimens of synovial tissues suggests that the inflamed synovium may provide an additional source for the elevated levels of COMP observed in arthritis. Thus, increased COMP levels in body fluids may be indicative of active synovitis as well as of accelerated joint erosion.

Leucine-rich repeat glycoproteins of the extracellular matrix

The extracellular matrix plays an integral role in the pivotal processes of development, tissue repair, and metastasis by regulating cell proliferation, differentiation, adhesion, and migration. This review is focused on a family of related glycoproteins represented by at least one member in all specialized extracellular matrices. This family currently comprises nine members grouped together on the basis of their presence in the extracellular matrix and by virtue of a leucine-rich repeat motif that dominates the structure of the core protein. It is likely that most, if not all the members of this group exist as proteoglycans in some tissues, and thus have been termed the Small Leucine-Rich Proteoglycan family, or SLRPs. The leucine-rich repeat (LRR) is usually present in tandem array and has been described in an increasing number of proteins, giving rise to a LRR-superfamily. The LRR domain of the SLRP family is unique within the superfamily in that it is flanked by cysteine clusters, and the 24 amino acid consensus for SLRP members is x-x-I/V/L-x-x-x-x-F/P/L-x-x-L/P-x-x-L-x-x-L/I-x-L-x-x-N-x-I/L, where x is any amino acid. Enormous progress has been made in describing the membership, structure and localization of this family, and recently new insight has emerged into the putative function of these molecules not just as modulators of matrix assembly but also on their intriguing role in regulating cell growth, adhesion, and migration. Determination of membership, structure and putative function of this fascinating class of molecules is summarized in this review.

Effects of interferon-gamma and tumor necrosis factor alpha on the expression of the genes encoding aggrecan, biglycan, and decorin core proteins in cultured human chondrocytes

OBJECTIVE

To determine the effects of interferon-gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha), alone or in combination, on the expression of aggrecan, biglycan, and decorin core protein genes in human chondrocytes.

METHODS

Isolated human chondrocytes were cultured on poly(2-hydroxyethyl methacrylate)-coated plastic dishes to prevent the loss of cartilage-specific phenotype, and the effects of IFN gamma and TNF alpha, alone or in combination, on aggrecan, biglycan, and decorin core protein gene transcription and steady-state messenger RNA (mRNA) levels were examined.

RESULTS

The addition of IFN gamma (1.5 pM) or TNF alpha (0.3 pM) caused a decrease in the steady-state level of aggrecan mRNA (-25% and -15%, respectively), and the combination of these low-concentration cytokines caused a potent inhibition (-66%). These effects were the result of a decrease (-50%) in the transcription rate of the corresponding gene. At the concentrations used, IFN gamma did not alter the levels of biglycan mRNA or the transcription rates of the biglycan core protein gene. In contrast, TNF alpha decreased biglycan steady-state mRNA levels (-62%) and the biglycan core protein gene transcription rate (-18%). The combination of IFN gamma and TNF alpha resulted in a potentiation of the inhibitory effects of TNF alpha on biglycan mRNA levels (-79%) and transcription rate of the biglycan core protein gene (-46%). IFN gamma produced a modest decrease in decorin mRNA levels (-23%) and decorin core protein gene transcription rate (-17%). In contrast, TNF alpha resulted in a marked increase in decorin mRNA levels (+260%) that was not the result of transcriptional regulation. Notably, the combination of IFN gamma and TNF alpha potentiated the inhibitory effects of IFN gamma on decorin mRNA (-80%) and on the transcription of the corresponding gene (-43%). Similar results were obtained in fetal and adult articular chondrocytes.

CONCLUSION

These data demonstrate that 1) the expression of the core protein genes encoding the cartilage proteoglycans aggrecan, biglycan, and decorin is differentially regulated by IFN gamma and TNF alpha; 2) these effects are mediated by transcriptional and posttranscriptional mechanisms; and 3) the combination of the 2 cytokines causes a potent inhibitory effect on the expression of the genes for the core proteins of these 3 proteoglycans, which occurs largely at the transcriptional level. The inhibition of aggrecan, decorin, and biglycan core protein gene expression by the combination of IFN gamma and TNF alpha may contribute to the cartilage destruction that is characteristic of inflammatory joint diseases.

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.

Age-related changes in the structure of the keratan sulphate chains attached to fibromodulin isolated from articular cartilage

Bovine articular cartilage fibromodulin has been isolated from animals aged 3 months to 8 years, and the attached keratan sulphate (KS) chains digested with keratanase II. The oligosaccharides generated have been reduced, examined by high-pH anion-exchange chromatography and their structures identified by comparison with standards. It has been shown that in fibromodulin from young articular cartilage, the KS chains do not possess either non-reducing terminal (alpha2-6)-linked N-acetylneuraminic acid or fucose (alpha1-3)-linked to sulphated N-acetylglucosamine residues. However, an age-related increase has been observed in the abundance of both (alpha2-6)-linked N-acetylneuraminic acid and (alpha1-3)-linked fucose, neither of which is found in KS isolated from non-articular cartilage, irrespective of the age of the source. Interestingly, the KS chain length remains constant as a function of age, which possibly relates to a role in collagen fibril assembly. In addition, no significant age-related changes were identified in levels of galactose sulphation.

Effects of interferon-gamma and tumor necrosis factor alpha on the expression of the genes encoding aggrecan, biglycan, and decorin core proteins in cultured human chondrocytes

OBJECTIVE

To determine the effects of interferon-gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha), alone or in combination, on the expression of aggrecan, biglycan, and decorin core protein genes in human chondrocytes.

METHODS

Isolated human chondrocytes were cultured on poly(2-hydroxyethyl methacrylate)-coated plastic dishes to prevent the loss of cartilage-specific phenotype, and the effects of IFN gamma and TNF alpha, alone or in combination, on aggrecan, biglycan, and decorin core protein gene transcription and steady-state messenger RNA (mRNA) levels were examined.

RESULTS

The addition of IFN gamma (1.5 pM) or TNF alpha (0.3 pM) caused a decrease in the steady-state level of aggrecan mRNA (-25% and -15%, respectively), and the combination of these low-concentration cytokines caused a potent inhibition (-66%). These effects were the result of a decrease (-50%) in the transcription rate of the corresponding gene. At the concentrations used, IFN gamma did not alter the levels of biglycan mRNA or the transcription rates of the biglycan core protein gene. In contrast, TNF alpha decreased biglycan steady-state mRNA levels (-62%) and the biglycan core protein gene transcription rate (-18%). The combination of IFN gamma and TNF alpha resulted in a potentiation of the inhibitory effects of TNF alpha on biglycan mRNA levels (-79%) and transcription rate of the biglycan core protein gene (-46%). IFN gamma produced a modest decrease in decorin mRNA levels (-23%) and decorin core protein gene transcription rate (-17%). In contrast, TNF alpha resulted in a marked increase in decorin mRNA levels (+260%) that was not the result of transcriptional regulation. Notably, the combination of IFN gamma and TNF alpha potentiated the inhibitory effects of IFN gamma on decorin mRNA (-80%) and on the transcription of the corresponding gene (-43%). Similar results were obtained in fetal and adult articular chondrocytes.

CONCLUSION

These data demonstrate that 1) the expression of the core protein genes encoding the cartilage proteoglycans aggrecan, biglycan, and decorin is differentially regulated by IFN gamma and TNF alpha; 2) these effects are mediated by transcriptional and posttranscriptional mechanisms; and 3) the combination of the 2 cytokines causes a potent inhibitory effect on the expression of the genes for the core proteins of these 3 proteoglycans, which occurs largely at the transcriptional level. The inhibition of aggrecan, decorin, and biglycan core protein gene expression by the combination of IFN gamma and TNF alpha may contribute to the cartilage destruction that is characteristic of inflammatory joint diseases.

Elevated synthesis of biglycan and decorin in an ovine annular lesion model of experimental disc degeneration

The aim of this study was to extend our earlier observations on the changes that occur in the proteoglycans (PGs) of discs subjected to experimental injury to the annulus fibrosus (AF). We employed the alginate bead culture method to examine the metabolism of the dermatan sulphate (DS) containing PGs by cells derived from different regions of ovine discs that had been subjected to experimental annular injury. This was compared with the metabolism of the DS-PGs by cells isolated from equivalent regions of normal sham-operated discs. Six months after induction of the annular lesion, AF cells isolated from the lesion produced significantly higher levels of decorin and biglycan in alginate bead culture than did cells from equivalent zones of the controls. Decorin and biglycan were identified in culture media samples by immunoblotting, using specific antibodies (6-B-6, LF-96), and also by positive identification of their de-glycosylated core proteins. The core protein of the DS-PGs has been shown to inhibit type I/II collagen fibrillogenesis, to negatively regulate the action of transforming growth factor-beta (TGF-beta) and to diminish cellular proliferation in vitro; events which may be detrimental to tissue repair. The findings are therefore consistent with our previous observation the annular lesions in the avascular inner annulus have no capacity to heal.

Human intervertebral disc cells from the annulus: three-dimensional culture in agarose or alginate and responsiveness to TGF-beta1

Cell culture procedures were developed for use with surgical and normal control specimens of the annulus of the human intervertebral disc. Cells were established in monolayer explant culture and seeded into three-dimensional growth environments of alginate or agarose; under these growth conditions cells assumed a rounded phenotype and formed colonies. A novel method of layering suspensions of cells onto cell well inserts proved technically much easier than the microbead culture method. Immunohistochemistry was utilized to demonstrate in vitro production of the following extracellular matrix components: types I, II, III, and VI collagen, 4-S-chondroitin sulfate, and keratan sulfate. Young and old age- and gender-matched cells grown in the presence of TGF-beta1 showed significant enhancement of proliferation after 4 days of exposure to TGF-beta with a lessened mitogenic response present after 10 days. Molecular studies of proteoglycan gene expression showed that at 4 days young normal cells had increased biglycan, but not decorin, message levels. Decorin expression was unchanged at Day 4 and decreased or shut off by Day 10. Results support the use of three-dimensional culture systems for in vitro evaluation of human disc cell function and expand our understanding of the in vitro behavior of these cells.

Age-related changes in effects of insulin-like growth factor I on human osteoblast-like cells

The role of insulin-like growth factor I (IGF-I) in extracellular matrix metabolism was studied in both proliferating and confluent human osteoblast-like cultures derived from donors of different ages. In proliferating cultures, recombinant human (rh)IGF-I was found to increase the incorporation of [3H]thymidine in a dose- and age-dependent manner. To study cell proliferation dynamically, continuous growth curves with and without rhIGF-I were modelled by a modified logistic function. Increasing doses of rhIGF-I decreased the lag time and maximal growth rates, whereas plateau values decreased only at the highest dose (100 ng/ml). In post-proliferative cell strains, rhIGF-I (0.1-100 ng/ml) increased levels of type I collagen, biglycan and decorin, and to a smaller extent fibronectin and thrombospondin, whereas it decreased the levels of hyaluronan and a versican-like proteoglycan when protein and proteoglycan metabolism were followed by steady-state radiolabelling with [3H]proline, [3H]glucosamine or [35S]sulphate. These responses to rhIGF-I were found to be age-dependent, with osteoblast-like cells derived from younger patients being more responsive to rhIGF-I. When extracellular matrix turnover was analysed by pulse-chase experiments, rhIGF-I had no effect. The steady-state levels of collagen, decorin, hyaluronan and a versican-like proteoglycan for bone cells treated with rhIGF-I on day 7 in culture were equivalent to levels of these matrix components in untreated osteoblasts grown for 14 days. These results are consistent with rhIGF-I's altering cellular proliferative capacity and matrix synthesis, causing a change in the osteoblast differentiated state.

Distribution of transforming growth factor beta1-binding proteins and low-affinity receptors during odontoblast differentiation in the mouse

Transforming growth factor-beta1 (TGF-beta1) was immunolocalized within differentiated odontoblasts and ameloblasts while LAP-beta1 was detected at the apicol pole of odonotoblasts and ameloblasts and in predentine. Anti-LAP-beta1 antibodies also stained the epithelial-mesenchymal junction (EMJ). Decorin was immunolocalized in young functional odonotoblasts and in both predentine and dentine. Biglycan was similarly distributed but absent from dentine. Immunostaining with anti-latent TGF-beta1 binding protein-1 (LTBP-1) showed fibrillar structures located at the EMJ and between predontoblasts and odontoblasts; at older states staining was restricted to the dental papilla and sac. Thus differentiated odonotoblasts express TGF-beta1 and in a more restricted manner decorin, biglycan and LAP-beta1; it can be assumed that TGF-beta1 is able to interact with the three molecules present in predentine. Earlier, LTBP-1 and LAP-beta1, both present at the EMJ, may contribute to odontoblast differentiation.