Proteoglycan Depletion Research Articles

ADAM-10 protein is present in human articular cartilage primarily in the membrane-bound form and is upregulated in osteoarthritis and in response to IL-1alpha in bovine nasal cartilage.

The objective of our study was to determine the tissue distribution and localization of ADAM-10 protein in human and bovine cartilage and the changes it undergoes with cartilage degeneration seen in osteoarthritis (OA) and under the influence of interleukin-1 (IL-1). Human normal and OA articular cartilage and bovine nasal cartilage cultured in the presence of IL-1alpha were processed for histology and immunohistochemistry. ADAM-10 protein was extracted from human cartilage and analyzed by Western blotting using anti-ADAM-10 antibodies. Fluor S Image analyzer and Quantity One software program were applied to quantify the total amount of ADAM-10. ADAM-10 protein was detected in both human and bovine cartilage. The strongest immunostaining was found in the cytoplasm and/or cell membranes of the superficial and upper middle layer of normal adult human cartilage, in the clusters and fibrillated areas of OA cartilage, and in IL-1alpha-stimulated bovine nasal cartilage. The distribution of ADAM-10 protein in bovine nasal cartilage was dependent on the length of exposure to IL-1alpha and corresponded to the areas of proteoglycan depletion. By Western blotting analysis of human cartilage, ADAM-10 was primarily detected in the membrane-enriched fraction and its levels were increased in degenerated and OA cartilage compared to normal cartilage. The results of this study suggest that ADAM-10 might be an important factor associated with cartilage degenerative processes. (J Histochem Cytochem 49:1165-1176, 2001)

Proteoglycan-induced changes in T1rho-relaxation of articular cartilage at 4T.

Proteoglycan (PG) depletion-induced changes in T1rho (spin-lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin-lock cluster pre-encoded fast spin echo sequence, T1rho maps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin-lock frequencies. Sequential PG depletion was induced by trypsinization of cartilage for varying amounts of time. Results demonstrated that over 50% depletion of PG from bovine articular cartilage resulted in average T1rho increases from 110-170 ms. Regression analysis of the data showed a strong correlation (R2 = 0.987) between changes in PG and T1rho. T1rho values were highest at the superficial zone and decreased gradually in the middle zone and again showed an increasing trend in the region near the subchondral bone. The potentials of this method in detecting early degenerative changes of cartilage are discussed. Also, T(1rho)-dispersion changes as a function of PG depletion are described.

An in situ calibration of an ultrasound transducer:: a potential application for an ultrasonic indentation test of articular cartilage

A change in mechanical properties of articular cartilage would be considered one of the most reliable signs of cartilage degeneration. While an indentation method has the potential to measure the cartilage properties in vivo, an accurate measurement of cartilage thickness in situ is technically difficult. An ultrasound transducer has often been used to measure the cartilage thickness. However, its accuracy is limited by the lack of an accurate measurement of the ultrasound speed of cartilage, for the ultrasound speed varies according to the pathological conditions of the tissue. Therefore, the objective of this study is to develop an in situ calibration method of predicting the true ultrasound speed of cartilage and thus allow the ultrasound transducer to measure the thickness of the tissue with great accuracy. By simultaneously implementing an indentation testing protocol using the ultrasound transducer as an indenter, this method can also provide an indentation stiffness measurement of cartilage. The feasibility of the proposed method was examined using normal and proteoglycan-depleted cartilage specimens. It was found that the true ultrasound speed measured by the in situ calibration method was sensitive to the proteoglycan depletion (1735±35 m/s for normal, and 1598±28 m/s for proteoglycan-depleted cartilage), and that the measured cartilage thickness was consistently accurate regardless of the tissue condition. The measured indentation stiffness of articular cartilage was also sensitive to the tissue condition. Thus, this study demonstrates that the proposed ultrasonic indentation technique can be used to accurately identify the abnormality of articular cartilage in situ.

Proteoglycan Depletion and Magnetic Resonance Parameters of Articular Cartilage

Calcium ions and various amounts of proteoglycans were removed from porcine articular cartilage explants using ethylenediaminetetraacetic acid or guanidinium chloride solutions. The water proton magnetic parameters such as T1 and T2 relaxation times, diffusion (D), and magnetization transfer (MS/M0) were then measured by 1D MR microscopy on native specimens, after incubation in the extracting solutions and after final reconditioning in a physiological saline. While the replacement of the interstitial fluid by the treating solutions strongly affected the various MR parameters, calcium depletion did not show any influence on the MRI appearance of the chondral tissue. Interestingly, only the longitudinal relaxation time T1 and the diffusion coefficient D were seen to be sensitive to an extensive proteoglycan depletion of the tissue. Our results indicate that a modest proteoglycan depletion, as it occurs in the early stage of a pathological cartilage degradation, has little relevance to the above MR parameters. Further MRI studies on the macromolecular components of cartilage are, therefore, necessary for a better understanding of the interaction mechanisms between water and extracellular matrix that might lead to the early diagnosis of the cartilage damage.

Effect of contact stress in bones of the distal interphalangeal joint on microscopic changes in articular cartilage and ligaments.

To examine articular cartilage of the distal interphalangeal (DIP) joint and distal sesamoidean impar ligament (DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive responses to contact stress. Specimens from 21 horses. Pressure-sensitive film was inserted between articular surfaces of the DIP joint. The digit was subjected to a load. Finite element models (FEM) were developed from the data. The navicular bone, distal phalanx, and distal attachments of the DSIL and DDFT were examined histologically. Analysis of pressure-sensitive film revealed significant increases in contact area and contact load at dorsiflexion in the joints between the distal phalanx and navicular bone and between the middle phalanx and navicular bone. The FEM results revealed compressive and shear stresses. Histologic evaluation revealed loss of proteoglycans in articular cartilage from older horses (7 to 27 years old). Tidemark advancement (up to 14 tidemarks) was observed in articular cartilage between the distal phalanx and navicular bone in older clinically normal horses. In 2 horses with navicular syndrome, more tidemarks were evident. Clinically normal horses had a progressive increase in proteoglycans in the DSIL and DDFT. Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.

Effects of strain level and proteoglycan depletion on preconditioning and viscoelastic responses of rat dorsal skin.

The mechanical response of rat dorsal skin was experimentally studied under cyclic uniaxial ramp stretches to various strain levels. Special emphasis was paid to the effects of the preconditioning protocol on the stress-strain relationship, and to the effects of ramp strain level and proteoglycan (PG) depletion, on viscoelasticity and preconditioning responses. The results show that preconditioning significantly reduced both the slope of the low strain stress-strain relationship, and the stress levels at consecutive stretch cycles. Following a short rest there was a significant partial recovery. Stress decay due to preconditioning was significant at all strain levels, and increased with strain. Stress relaxation was significant at all strain levels, but varied little with strain. Recovery following a 10 min rest was minor at all strain levels and varied little with strain. PG-depleted samples manifested similar response patterns. These results are consistent with the following notion: (1) skin consists of three mechanical components: elastin and proteoglycan which dominate the low strain response and are effected by preconditioning and (PG) depletion, and collagen which dominates the high strain response and is unaffected by preconditioning and PG depletion; (2) that the viscoelasticity of elastin and PG vs that of collagen are similar, so that rat dorsal skin can be regarded quasilinear viscoelastic.

Enhanced chondrocyte apoptosis leads to abnormal cartilage in rats and cats with glycosaminoglycan storage diseases

The mucopolysaccharidoses (MPS) are a family of glycosaminoglycan (GAG) storage diseases caused by the deficient activities of specific lysosomal enzymes. A major feature of the MPS disorders is abnormal cartilage and bone development leading to short stature, dysostosis multiplex, and degenerative joint disease. Ultrastructurally, the cytoplasm of affected MPS chondrocytes is filled with membrane bound vacuoles containing undegraded GAGs. Clusters of hypertrophic chondrocytes form in these disorders, leading to the disruption of the normal cartilage organization. To further investigate the cellular pathology of the MPS disorders, primary cultured chondrocytes and articular cartilage were examined from cats and rats with MPS typeVI (Maroteaux-Lamy disease). Markedly increased numbers of apoptotic chondrocytes were identified by TUNEL staining and immunohistochemically with anti-poly (ADP-ribose) polymerase antibodies in the MPS animals as compared to age-matched controls. The prevalence of apoptotic cells was correlated with increased levels of nitrite and tumor necrosis factor-α. Marked proteoglycan depletion also was observed in the MPS epiphyses by Safranin-O staining, and the presence of excess collagen type II was detected by immunostaining. A model of MPS endochondryl bone pathology is proposed in which an inflammatory response to mechanical trauma is caused by the deformed and irregular subchondral bone contours, leading to increased nitric oxide (NO) production in response to TNF-α, thereby inducing chondrocyte cell death. Novel treatment strategies for these disorders might, therefore, be considered to prevent inflammation or inhibit NO production as an alternative to providing the missing enzymatic activities.

Basal lamina heparan sulphate proteoglycan is involved in otic placode invagination in chick embryos.

Formation of the otocyst from the otic placode appears to differ from invagination of other cup-shaped organ primordia. It is known that the cellular cytoskeleton plays a limited role in otic placode invagination, whilst the extracellular matrix underlying the otic primordium intervenes in the folding process. In this study we have analysed the role of the basal lamina heparan sulphate proteoglycan in otic primordium invagination. At 10 H.H. stage, heparan sulphate proteoglycan immunomarking begins to appear on the otic placode basal lamina, increasing noticeably at 13 H.H. stage, coinciding with maximum folding of the otic epithelium, and is still present at later stages. Enzyme degradation of heparan sulphate proteoglycan in the otic primordium basal lamina, by means of microinjection with heparinase III prior to folding, significantly disrupts invagination of the otic placode, which remains practically flat, with a significant reduction in the depth of the otic pit and an increase in the diameter of the otic opening. The immunocytochemistry analysis revealed a notable depletion of basal lamina heparan sulphate proteoglycan in the otic primordia microinjected with heparinase, with no statistically significant differences observed in the volume or rate of cell proliferation in the otic epithelium relative to the control, which suggests that heparan sulphate proteoglycan disruption does not interfere with the epithelial growth. In addition, a study of apoptosis distribution by the TUNEL method confirmed that treatment with heparinase does not cause interference with cell survival in the otic epithelium. Our findings support the theory that otic primordium invagination may be regulated, at least in part, by the basal lamina components, which might contribute towards anchoring the otic epithelium to adjacent structures.

Differences in type II collagen degradation between peripheral and central cartilage of rat stifle joints after cranial cruciate ligament transection.

Type II collagen degradation is thought to be the key process in cartilage degradation during the development of osteoarthritis (OA). In this study, we investigated the kinetics of type II collagen degradation during surgically induced OA. Experimental OA was induced in male Wistar rats by transecting the cranial (anterior) cruciate ligament (CCL). Hematoxylin and eosin staining was used to study overall cartilage degradation, while immunostained sections were used to demonstrate denatured type II collagen (Col2-3/4m antibody) and the collagenase cleavage site in type II collagen (Col2-3/ 4Cshort antibody). During the first 3-4 weeks, cartilage destruction, associated with chondrocyte death, proteoglycan depletion, and a marked increase in the collagenase cleavage neoepitope, was mainly located at the margins of the cartilage. From weeks 3-4, the central part of the cartilage showed increased surface fibrillation and apparent chondrocyte death. In these areas, increased denatured type II collagen staining but little cleavage-site staining was present. These results indicate that cartilage degradation after CCL transection in the rat consists of 2 phases. An early phase located at the cartilage margins and a late phase located at the central part of the cartilage. In the early phase, collagenase-dependent cartilage damage occurred. During the late phase, the level of type II collagen denaturation increased.

Normal and pathological adaptations of articular cartilage to joint loading.

Joints are functional units that transmit mechanical loads between contacting bones during normal daily or specialized activities, e.g., sports. All components of the joint, i.e. articular cartilage, bone, muscles, ligaments/tendons and nerves, participate in load transmission. Failure in any of these components can cause joint malfunction, which, in turn, may lead to accumulation of damage in other joint components. Mechanical forces have great influence on the synthesis and rate of turnover of articular cartilage molecules, such as proteoglycans (PGs). Regular cyclic loading of the joint enhances PG synthesis and makes cartilage stiff. On the other hand, loading appears to have less evident effects on the articular cartilage collagen fibril network. Continuous compression of the cartilage diminishes PG synthesis and causes damage of the tissue through necrosis. The prevailing view is that osteoarthrosis (OA) starts from the cartilage surface through PG depletion and fibrillation of the superficial collagen network. It has also been suggested that the initial structural changes take place in the subchondral bone, especially when the joint is exposed to an impact type of loading. This in turn would create an altered stress pattern on joint surfaces, which leads to structural damage and mechanical failure of articular cartilage. The importance of the neuromuscular system to the initiation and progression of OA is still poorly understood. Many surgical extra- and intra-articular procedures have been used for the treatment of OA. Although some of the new methods, such as autologous chondrocyte transplantation and mosaicplasty, have given good clinical results, it is reasonable to emphasize that the methods still are experimental and more controlled studies are needed.

Sensitivity of MRI to proteoglycan depletion in cartilage: comparison of sodium and proton MRI

Objective The purpose of this work was to evaluate the results from sodium and proton magnetic resonance imaging (MRI) in detecting small changes in proteoglycan (PG) content in bovine articular cartilage specimens.Design Articular cartilage from 15 specimens of bovine patellae were subjected to partial PG depletion with different concentrations of trypsin for 30min. Sodium and proton MR images of the intact specimen were obtained on a 4T GE clinical MRI system. Two custom-built 7cm-diameter solenoid coils tuned to proton and sodium frequencies were employed. Fast gradient echo and spin echo imaging sequences were used to determine sodium density, proton density and proton relaxation times (T1and T2) of the specimens. Spectrophotometric assay was performed after MRI to determine PG concentrations of the cartilage specimens.Results The sodium signal change correlated well with the observed PG loss (R2=0.85, P< 0.01) whereas the proton signal change was inconsistent (R2=0.10, P< 0.8). The change in protonT1 and T2between the two regions did not correlate with PG loss (R2=0.07 and R2=0.06, respectively).Conclusions Results from these studies demonstrate that sodium MRI is both sensitive and specific in detecting small changes in PG concentration, whereas proton density and relaxation properties are not sensitive to small changes in PG content.

Role of Fc receptor gamma chain in inflammation and cartilage damage during experimental antigen-induced arthritis.

To study the role of Fc receptor (FcR) gamma chain in inflammation and cartilage destruction during antigen-induced arthritis (AIA). FcR gamma-/- mice and controls were immunized with methylated bovine serum albumin (mBSA) in Freund's complete adjuvant, followed by induction of arthritis by local injection of mBSA into the right knee joint. Joint inflammation was studied by 99mTc uptake and by histology. Breakdown of proteoglycans from the cartilage matrix was determined by loss of red staining in Safranin O-stained knee joint sections, and matrix metalloproteinase (MMP)-mediated aggrecan degradation was determined by immunolocalization using anti-VDIPEN antibodies. Chondrocyte death was measured by determining empty lacunae in hematoxylin-stained sections and with the TUNEL assay in cryostat sections. Erosion was detected as ruffling of the cartilage surface. Joint swelling, as measured by 99mTc uptake on days 1, 3, and 7, was significantly decreased in FcR gamma-/- mice compared with controls. On day 7 after AIA induction, sustained joint inflammation, as seen histologically, was not significantly lower in FcR gamma-/- deficient mice. In various cartilage layers (femur, tibia, patella) of central arthritic knee joints, marked depletion of proteoglycans (40-70%), chondrocyte death (25-50%), and mild surface erosion were found. In FcR gamma-/- knee joints, depletion of proteoglycans was comparable (40-70%). Strikingly, chondrocyte death and matrix erosion were absent. Furthermore, MMP-induced aggrecan neoepitopes, which were abundantly found in controls, were also absent in FcR gamma-/-. Nevertheless, latent MMPs were present in the cartilage matrix as seen in APMA-activated patellae. FcR gamma chain is involved in the severity of acute and sustained inflammation and is a crucial factor in cartilage erosion during AIA, probably by regulating activation of latent MMPs present in the cartilage matrix.

123I-antileukoproteinase scintigraphy reveals microscopic cartilage alterations in the contralateral knee joint of rats with "monarticular" antigen-induced arthritis.

To assess the involvement of the contralateral knee joint in monarticular antigen-induced arthritis (AIA) by scintigraphy with the cationic (pI >10), 123I-labeled, serine proteinase inhibitor antileukoproteinase (123I-ALP) and to compare the scintigraphic findings with those of radiography and high-resolution ex vivo magnetic resonance imaging (MRI). Lewis rats with chronic AIA were examined 2.5 months following arthritis induction (injection of 500 microg of methylated bovine serum albumin/saline into the ipsilateral [arthritic] knee joint and injection of phosphate buffered saline into the contralateral knee joint following systemic immunization). 123I-ALP was injected intravenously into normal rats (n = 4) or rats with AIA (n = 6). The ipsilateral and contralateral knee joints and both ankles were examined by scintigraphy and radiography. Joint cartilage was examined by high-resolution ex vivo MRI, histopathology, and measurement of tissue radioactivity. ALP accumulation (typically observed in normal articular cartilage) was lost in both the ipsilateral and the contralateral knee joints, but not in the clinically unaffected ankles of rats with AIA. In both knee joints, 123I-ALP target:background ratios and cartilage radioactivity correlated negatively with the loss of toluidine blue staining in cartilage, which documents the depletion of charged matrix molecules. Findings of histopathology confirmed mild alterations in the ipsilateral knee joint and even milder alterations in the contralateral knee joint, while the ankles were normal. Radiography and high-resolution ex vivo MRI failed to detect abnormalities in the contralateral knee joint. Loss of ALP accumulation appears to document proteoglycan depletion, even in the microscopically altered cartilage of the contralateral knee joint in AIA. These findings underscore the high sensitivity of 123I-ALP for in vivo detection of biochemical cartilage alterations in arthritis, and furthermore, question the use of the contralateral knee joint as a normal control in AIA.

Osteoarthritis-like changes in the murine knee joint resulting from intra-articular transforming growth factor-β injections

Objective To examine the impact of prolonged TGF-β exposure on cartilage and ligamentous joint structures in vivo, to investigate involvement of TGF-β in osteoarthritis pathology.Methods TGF-β was injected into murine knee joints once or repeatedly, whereafter articular cartilage proteoglycan (PG) synthesis and content, and histological changes in knee joints were studied over a 2-month period.Results A single injection of TGF-β stimulated patellar cartilage PG synthesis for 3 weeks and PG content for 2 weeks. Triple TGF-β injections prolonged the increase in PG content to 3 weeks. Patellar cartilage showed no histological abnormalities at 1 and 2 months after the last injection. In contrast, 2 months after triple TGF-β injections the superficial layer of tibial cartilage still had an increased proteoglycan content, while severe PG depletion was found in deeper layers of the posterior part of the lateral tibia in particular. Eventually, lesions occurred at the level of the tide-mark, exactly the site where cartilage is torn off in experimental and spontaneous osteoarthritis in mice. Additionally, multiple TGF-β injections induced formation of chondroid structures along the margins of articular cartilage. These chondroid structures were transformed into osteophytes via endochondral ossification. Formation of chondroid tissue was also observed in collateral ligaments.Conclusion Multiple intra-articular injections of TGF-β induce changes in articular cartilage and surrounding tissues that have strong resemblance to features of experimental and spontaneous osteoarthritis in mice, suggesting a role for TGF-β in the OA process.

Active Matrix Metalloproteinases Are Present in Cartilage During Immune Complex-Mediated Arthritis: A Pivotal Role for Stromelysin-1 in Cartilage Destruction

The involvement of immune complexes during experimental arthritis in induction of metalloproteinases (MMP)-induced neoepitopes in aggrecan in cartilage, as well as the role of stromelysin-1 (SLN-1) in the induction of this neoepitope, was investigated. Passive immune complex arthritis was induced, and generation of the MMP-specific cleavage product (VDIPEN) was studied by immunolocalization. The role of SLN-1 was studied with use of SLN-1-deficient (SLN-1KO) mice. VDIPEN expression was studied in vitro by exposing the cartilage to IL-1 and subsequent activation of latent MMPs. Immune complex arthritis was characterized by an acute inflammation, with influx of mainly polymorphonuclear cells into the joint cavity. Expression of VDIPEN neoepitopes was consistently found in areas extensively depleted from proteoglycans. SLN-1KO mice did not show expression of the VDIPEN neoepitope, although inflammation and proteoglycan depletion was comparable to wild-type mice. In addition, erosions of cartilage were absent in SLN-1KO mice, but were present in wild-type mice, suggesting an important role for SLN-1 in cartilage destruction. In vitro studies showed that SLN-1 is also pivotally involved in IL-1-induced MMP activity. Stimulated polymorphonuclear neutrophils were able to activate latent MMPs present in the cartilage. Neutrophil elastase was also capable of activating IL-1-induced latent MMPs, which identifies elastase as a possible activator for latent VDIPEN-inducing MMPs. This study suggests that IC are important in the activation of latent MMPs in cartilage, possibly through polymorphonuclear neutrophil activation on the cartilage edge. SLN-1 is a pivotal enzyme in overall MMP-activity in cartilage during immune complex-mediated arthritis.

Transforming and epidermal growth factors in degenerated intervertebral discs

We studied the presence of anabolic growth factors in human herniated intervertebral discs (IVD) using a reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. Messenger RNA (mRNA) was isolated from the nucleus pulposus using oligo (dT)25 superparamagnetic beads and probing with gene-specific primers in RT-PCR. mRNA coding for TGF-α (3/10), EGF (0/10), TGF-β1 (0/10) and TGF-β3 (2/10) or the EGF receptor (EGF-R; 0/10) and TGF-β type-II receptor (0/10) was found only occasionally. Beta-actin was always present and positive sample controls confirmed the validity of the RT-PCR assay. These RT-PCR findings were confirmed using immunohistochemical staining of EGF and TFG-β, whereas TGF-α protein was always found associated with discocytes. We conclude that the nucleus pulposus of the herniated IVD is vulnerable to proteolytic degradation and depletion of proteoglycans due to the lack and/or low production of anabolic growth factors/receptors which could increase the local synthesis of the extracellular matrix.

Transforming and epidermal growth factors in degenerated intervertebral discs

We studied the presence of anabolic growth factors in human herniated intervertebral discs (IVD) using a reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. Messenger RNA (mRNA) was isolated from the nucleus pulposus using oligo (dT)25 superparamagnetic beads and probing with gene-specific primers in RT-PCR. mRNA coding for TGF-alpha (3/10), EGF (0/10), TGF-beta1 (0/10) and TGF-beta3 (2/10) or the EGF receptor (EGF-R; 0/10) and TGF-beta type-II receptor (0/10) was found only occasionally. Beta-actin was always present and positive sample controls confirmed the validity of the RT-PCR assay. These RT-PCR findings were confirmed using immunohistochemical staining of EGF and TFG-beta, whereas TGF-alpha protein was always found associated with discocytes. We conclude that the nucleus pulposus of the herniated IVD is vulnerable to proteolytic degradation and depletion of proteoglycans due to the lack and/or low production of anabolic growth factors/receptors which could increase the local synthesis of the extracellular matrix.

Cleavage of aggrecan at the Asn341-Phe342 site coincides with the initiation of collagen damage in murine antigen-induced arthritis: a pivotal role for stromelysin 1 in matrix metalloproteinase activity.

The destruction of articular cartilage during arthritis is due to proteolytic cleavage of the extracellular matrix components. This study investigates the kinetic involvement of metalloproteinases (MMPs) in the degradation of the 2 major cartilage components, aggrecan and type II collagen, during murine antigen-induced arthritis (AIA). In addition, the role of stromelysin 1 (SLN-1) induction of MMP-induced neoepitopes was studied. VDIPEN neoepitopes in aggrecan and collagenase-induced COL2-3/4C neoepitopes in type II collagen were identified by immunolocalization. Stromelysin 1-deficient knockout (SLN1-KO) mice were used to study SLN-1 involvement. In AIA, the VDIPEN epitopes in aggrecan appeared after initial proteoglycan (PG) depletion. The collagenase-induced type II collagen neoepitopes colocalized with VDIPEN epitopes. Remarkably, cartilage from arthritic SLN1-KO mice showed neither the induction of VDIPEN nor collagen cleavage-site neoepitopes during AIA, suggesting that stromelysin is a pivotal mediator in this process. PG depletion, as measured by the loss of Safranin O staining, was similar in SLN1-KO mice and wild-type strains. Furthermore, in vitro induction of VDIPEN epitopes in aggrecan and COL2-3/4C epitopes in type II collagen, on exposure of cartilage to interleukin-1, could not be accomplished in SLN1-KO mice, whereas intense staining was achieved for both epitopes in cartilage of wild-type strains. This study emphasizes that SLN-1 is essential in the induction of MMP-specific aggrecan and collagen cleavage sites during AIA. It suggests that SLN-1 is not a dominant enzyme in PG breakdown, but that it activates procollagenases and is crucial in the initiation of collagen damage.

The role of relaxation times in monitoring proteoglycan depletion in articular cartilage.

Various proton relaxation times (T2, T1rho, and gadolinium-diethylene triamine pentaacetic acid [Gd-DTPA]-enhanced T1) were measured in articular cartilage in vitro at 3 T to assess their role in visualizing proteoglycan depletion. Cartilage-bone specimens were obtained from patients who underwent total joint replacement and got a double dose of Gd-DTPA 2 hours prior surgery. In these specimens, regions of mechanically undamaged cartilage having a decreased content of proteoglycans showed about 15% lower T1 values compared with apparently normal cartilaginous tissue. The expected increase of the T2 relaxation time was not observed in these regions. On the other hand, the T2 and, to a lower degree, T1 relaxation times were found to be increased in regions of cartilage fibrillation. The T1rho relaxation times obtained were slightly longer than the corresponding T2 values, but both parameters showed almost identical spatial distributions. J. Magn. Reson. Imaging 1999;10:497-502.

The role of relaxation times in monitoring proteoglycan depletion in articular cartilage

The role of relaxation times in monitoring proteoglycan depletion in articular cartilage