Biological properties of recombinant human monocyte-derived interleukin 1 receptor antagonist

Human monocytes cultured on adherent IgG produce a specific IL-1 inhibitor that functions as a receptor antagonist (IL-1ra). This molecular has been purified, sequenced, cloned as a cDNA, and expressed in Escherichia coli. Recombinant IL-1ra has 17,000 mol wt and binds to IL-1 receptors on T lymphocytes, synovial cells, and chondrocytes with an affinity nearly equal to that of IL-1. These studies have examined some biological properties of purified recombinant human IL-1ra. This protein exhibits a dose-responsive inhibition of Il-1 alpha and Il-1 beta augmentation of PHA-induced murine thymocyte proliferation. The recombinant IL-1ra also blocks IL-1 alpha and IL-1 beta stimulation of PGE2 production in human synovial cells and rabbit articular chondrocytes, and of collagenase production by the synovial cells. A 50% inhibition of these IL-1-induced biological responses requires amounts of IL-1ra up to 100-fold in excess of the amounts of IL-1 alpha or IL-1 beta present. IL-1ra may play an important role in normal physiology or in pathophysiological states by functioning as a natural IL-1 receptor antagonist in the cell microenvironment.

Cell therapy using allogeneic bone marrow mesenchymal stem cells prevents tissue damage in collagen-induced arthritis

OBJECTIVE

Mesenchymal stem cells (MSCs) are precursors of tissue of mesenchymal origin, but they also have the capacity to regulate the immune response by suppressing T and B lymphocyte proliferation in a non-major histocompatibility complex-restricted manner. Use of MSCs as immunosuppressant agents in autoimmune diseases has been proposed and successfully tested in animal models. We explored the feasibility of using allogeneic MSCs as therapy for collagen-induced arthritis, a mouse model for human rheumatoid arthritis.

METHODS

DBA/1 mice were immunized with type II collagen in Freund's complete adjuvant, and some of the animals received an intraperitoneal injection of allogeneic MSCs.

RESULTS

A single injection of MSCs prevented the occurrence of severe, irreversible damage to bone and cartilage. MSCs induced hyporesponsiveness of T lymphocytes as evidenced by a reduction in active proliferation, and modulated the expression of inflammatory cytokines. In particular, the serum concentration of tumor necrosis factor alpha was significantly decreased. MSCs exerted their immunomodulatory function by educating antigen-specific Tregs.

CONCLUSION

Our results suggest an effective new therapeutic approach to target the pathogenic mechanism of autoimmune arthritis using allogeneic MSCs. However, further studies are required before these results can be translated to clinical settings.

Repair of partial-thickness defects in articular cartilage: cell recruitment from the synovial membrane

Partial-thickness defects evolving in mature articular cartilage do not heal spontaneously. This type of defect was created in the articular cartilage of adult rabbits and Yucatan minipigs, and the effects of chondroitinase ABC or trypsin, fibrin clots, and mitogenic growth factors on the healing process were examined histologically at intervals ranging from one to forty-eight weeks. The effect of chondroitinase ABC or trypsin was examined initially. Articular cartilage contains macromolecules, including proteoglycans, which render the surfaces of this tissue, and of partial-thickness defects within it, antiadhesive. Chondroitinase ABC digests the glycosaminoglycan chains of cartilage proteoglycans, and trypsin degrades their core proteins. To test the hypothesis that mesenchymal cells may be prevented from adhering to and migrating over the surfaces of partial-thickness defects by proteoglycans, we removed a superficial layer of these macromolecules from the surface of the defect with use of one of these enzymes. The treatment evoked an increase in the coverage of the defect surface with mesenchymal cells; when combined with the local application of a mitogenic growth factor (basic fibroblast growth factor, transforming growth factor-beta 1, epidermal growth factor, insulin-like growth factor-1, or growth hormone), the coverage was more extensive but mesenchymal cells did not extend into and completely fill the volume of the defect. When the surface of the defect was treated with chondroitinase ABC and the cavity of the defect was filled with a fibrin clot to furnish a matrix or scaffolding for the migration of cells therein, there was migration and proliferation of cells throughout the volume of the defect but at a low population density. Mesenchymal cells remodeled the deposited fibrin matrix, which was replaced by a loose fibrous connective tissue. When defects that had been treated with chondroitinase ABC were filled with a fibrin clot containing a mitogenic growth factor, mesenchymal cells filled the entire cavity of the defect, and the density of the cells was greatly increased, particularly when transforming growth factor-beta 1 was used. Histological studies revealed a continuous layer of mesenchymal cells extending from the synovial membrane across the superficial tangential zone of normal articular cartilage into the defect, indicating that the cells that were recruited for the repair process were of synovial origin. At forty-eight weeks, the entire cavity of the defect remained filled with a fibrous connective tissue.

Direct human cartilage repair using three-dimensional bioprinting technology

Current cartilage tissue engineering strategies cannot as yet fabricate new tissue that is indistinguishable from native cartilage with respect to zonal organization, extracellular matrix composition, and mechanical properties. Integration of implants with surrounding native tissues is crucial for long-term stability and enhanced functionality. In this study, we developed a bioprinting system with simultaneous photopolymerization capable for three-dimensional (3D) cartilage tissue engineering. Poly(ethylene glycol) dimethacrylate (PEGDMA) with human chondrocytes were printed to repair defects in osteochondral plugs (3D biopaper) in layer-by-layer assembly. Compressive modulus of printed PEGDMA was 395.73±80.40 kPa, which was close to the range of the properties of native human articular cartilage. Printed human chondrocytes maintained the initially deposited positions due to simultaneous photopolymerization of surrounded biomaterial scaffold, which is ideal in precise cell distribution for anatomic cartilage engineering. Viability of printed human chondrocytes increased 26% in simultaneous polymerization than polymerized after printing. Printed cartilage implant attached firmly with surrounding tissue and greater proteoglycan deposition was observed at the interface of implant and native cartilage in Safranin-O staining. This is consistent with the enhanced interface failure strength during the culture assessed by push-out testing. Printed cartilage in 3D biopaper had elevated glycosaminoglycan (GAG) content comparing to that without biopaper when normalized to DNA. These observations were consistent with gene expression results. This study indicates the importance of direct cartilage repair and promising anatomic cartilage engineering using 3D bioprinting technology.

Involvement of reactive oxygen species in cytokine and growth factor induction of c-fos expression in chondrocytes

The cytokine tumor necrosis factor alpha (TNF alpha) and the growth factor basic fibroblast growth factor (bFGF) are known to induce early response genes such as c-fos and c-jun in various cell types. Activation of AP-1, a heterodimeric complex of Fos and Jun proteins, is required for matrix metalloproteinase production and cell proliferation. However, the signaling pathways by which these two factors influence the expression and activities of AP-1 remain currently poorly characterized. Several studies have shown that cytokines induce reactive oxygen species (ROS) production, but growth factor induction of ROS has not been reported. In the present study we demonstrate that both TNF alpha and bFGF induce ROS production, and that this is a common signaling event involved in the stimulation of c-fos gene expression in chondrocytes. To our knowledge, this is the first report directly demonstrating ROS production upon stimulation with a growth factor. TNF alpha and bFGF induction of ROS production is mediated through flavonoid-containing enzymes such as NADPH oxidase. Moreover, the ROS nitric oxide is not responsible for the induction of c-fos expression by TNF alpha and bFGF. In addition, the inhibitory effects of antioxidants on c-fos expression may account for their protective roles against proliferative and inflammatory diseases such as cancer, cardiovascular diseases, and arthritis.

Aging and osteoarthritis: Central role of the extracellular matrix

Osteoarthritis (OA), is a major cause of severe joint pain, physical disability and quality of life impairment in the aging population across the developed and developing world. Increased catabolism in the extracellular matrix (ECM) of the articular cartilage is a key factor in the development and progression of OA. The molecular mechanisms leading to an impaired matrix turnover have not been fully clarified, however cellular senescence, increased expression of inflammatory mediators as well as oxidative stress in association with an inherently limited regenerative potential of the tissue, are all important contributors to OA development. All these factors are linked to and tend to be maximized by aging. Nonetheless the role of aging in compromising joint stability and function in OA has not been completely clarified yet. This review will systematically analyze cellular and structural changes taking place in the articular cartilage and bone in the pathogenesis of OA which are linked to aging. A particular emphasis will be placed on age-related changes in the phenotype of the articular chondrocytes.

Interleukin 1 induces leukocyte infiltration and cartilage proteoglycan degradation in the synovial joint

Interleukin 1 (IL-1) is a polypeptide released by activated macrophages and is thought to be a key mediator of host responses to infection and inflammation. The availability of highly purified and recombinant material has now permitted the evaluation of IL-1 as a mediator of chronic inflammatory processes in vivo. We have demonstrated that intraarticular injection of IL-1 into rabbit knee joints induces the accumulation of polymorphonuclear and mononuclear leukocytes in the joint space and the loss of proteoglycan from the articular cartilage. The effects on cartilage could not be explained solely by the presence of leukocytes, since injections of endotoxin also stimulated leukocyte accumulation in the joint but had no effect on proteoglycan loss. Responses to IL-1 were not associated with increased production of the icosanoids prostaglandin E2 or leukotriene B4 and were not reduced by an inhibitor of their synthesis. The pattern of leukocyte infiltration and cartilage breakdown 24 hr after IL-1 injection was similar to that seen in animals with antigen-induced arthritis of 1 week's duration. These observations support the hypothesis that IL-1 acts directly to mediate the erosive processes of chronic arthritis.

Crosslinking by advanced glycation end products increases the stiffness of the collagen network in human articular cartilage: a possible mechanism through which age is a risk factor for osteoarthritis

OBJECTIVE

Age is an important risk factor for osteoarthritis (OA). During aging, nonenzymatic glycation results in the accumulation of advanced glycation end products (AGEs) in cartilage collagen. We studied the effect of AGE crosslinking on the stiffness of the collagen network in human articular cartilage.

METHODS

To increase AGE levels, human adult articular cartilage was incubated with threose. The stiffness of the collagen network was measured as the instantaneous deformation (ID) of the cartilage and as the change in tensile stress in the collagen network as a function of hydration (osmotic stress technique). AGE levels in the collagen network were determined as: Nepsilon-(carboxy[m]ethyl)lysine, pentosidine, amino acid modification (loss of arginine and [hydroxy-]lysine), AGE fluorescence (360/460 nm), and digestibility by bacterial collagenase.

RESULTS

Incubation of cartilage with threose resulted in a dose-dependent increase in AGEs and a concomitant decrease in ID (r = -0.81, P < 0.001; up to a 40% decrease at 200 mM threose), i.e., increased stiffness, which was confirmed by results from the osmotic stress technique. The decreased ID strongly correlated with AGE levels (e.g., AGE fluorescence r = -0.81, P < 0.0001). Coincubation with arginine or lysine (glycation inhibitors) attenuated the threose-induced decrease in ID (P < 0.05).

CONCLUSION

Increasing cartilage AGE crosslinking by in vitro incubation with threose resulted in increased stiffness of the collagen network. Increased stiffness by AGE crosslinking may contribute to the age-related failure of the collagen network in human articular cartilage to resist damage. Thus, the age-related accumulation of AGE crosslinks presents a putative molecular mechanism whereby age is a predisposing factor for the development of OA.

Cartilage-specific deletion of mTOR upregulates autophagy and protects mice from osteoarthritis

OBJECTIVES

Mammalian target of rapamycin (mTOR) (a serine/threonine protein kinase) is a major repressor of autophagy, a cell survival mechanism. The specific in vivo mechanism of mTOR signalling in OA pathophysiology is not fully characterised. We determined the expression of mTOR and known autophagy genes in human OA cartilage as well as mouse and dog models of experimental OA. We created cartilage-specific mTOR knockout (KO) mice to determine the specific role of mTOR in OA pathophysiology and autophagy signalling in vivo.

METHODS

Inducible cartilage-specific mTOR KO mice were generated and subjected to mouse model of OA. Human OA chondrocytes were treated with rapamycin and transfected with Unc-51-like kinase 1 (ULK1) siRNA to determine mTOR signalling.

RESULTS

mTOR is overexpressed in human OA cartilage as well as mouse and dog experimental OA. Upregulation of mTOR expression co-relates with increased chondrocyte apoptosis and reduced expression of key autophagy genes during OA. Subsequently, we show for the first time that cartilage-specific ablation of mTOR results in increased autophagy signalling and a significant protection from destabilisation of medial meniscus (DMM)-induced OA associated with a significant reduction in the articular cartilage degradation, apoptosis and synovial fibrosis. Furthermore, we show that regulation of ULK1/adenosine monophosphate-activated protein kinase (AMPK) signalling pathway by mTOR may in part be responsible for regulating autophagy signalling and the balance between catabolic and anabolic factors in the articular cartilage.

CONCLUSIONS

This study provides a direct evidence of the role of mTOR and its downstream modulation of autophagy in articular cartilage homeostasis.

The chitinase 3-like protein human cartilage glycoprotein 39 (HC-gp39) stimulates proliferation of human connective-tissue cells and activates both extracellular signal-regulated kinase- and protein kinase B-mediated signalling pathways

Human cartilage glycoprotein 39 (HC-gp39) is a glycoprotein secreted by articular chondrocytes, synoviocytes and macrophages. Increased levels of HC-gp39 have been demonstrated in synovial fluids of patients with rheumatoid or osteoarthritis. The increased secretion of HC-gp39 under physiological and pathological conditions with elevated connective-tissue turnover suggests its involvement in the homoeostasis of these tissues. We report here that HC-gp39 promotes the growth of human synovial cells as well as skin and fetal lung fibroblasts. A dose-dependent growth stimulation was observed when each of the fibroblastic cell lines was exposed to HC-gp39 in a concentration range from 0.1 to 2 nM, which is similar to the effective dose of the well-characterized mitogen, insulin-like growth factor-1. At suboptimal concentrations, the two growth factors work in a synergistic fashion. The use of selective inhibitors of the mitogen-activated protein kinase and the protein kinase B (AKT) signalling pathways indicates that both are involved in mediating the mitogenic response to HC-gp39. Phosphorylation of both extracellular signal-regulated kinases 1/2 and AKT occurred in a dose- and time-dependent fashion upon addition of HC-gp39. Activation of these signalling pathways could also be demonstrated in human chondrocytes. Thus HC-gp39 initiates a signalling cascade in connective-tissue cells which leads to increased cell proliferation, suggesting that this protein could play a major role in the pathological conditions leading to tissue fibrosis.

Mono-iodoacetate-induced experimental osteoarthritis: a dose-response study of loss of mobility, morphology, and biochemistry

OBJECTIVE

To characterize the dose-responsiveness of morphologic and biochemical chondral changes relative to mobility in mono-iodoacetate (MIA)-induced osteoarthritis (OA) in rats.

METHODS

Rat mobility was assessed by biotelemetry. Articular lesions were characterized by macroscopic and histologic examinations. Cartilage proteoglycan metabolism was evaluated by the 1,9-dimethylmethylene blue dye binding assay and by radiosulfate incorporation in patellar cartilage.

RESULTS

Spontaneous locomotor activity was rapidly, transiently, and dose-dependently decreased after MIA injection into rat knees (primary response). Thereafter, only high doses (0.3 mg and 3.0 mg) led to a secondary progressive long-term loss of spontaneous mobility on day 15, when subchondral bone was exposed. These 2 doses resulted in significant changes in cartilage proteoglycan concentration at day 15 and a strong inhibition of anabolism in the peripheral patellae by day 2, contrasting with the effects of lower doses (0.01, 0.03, and 0.1 mg).

CONCLUSION

When a sufficient dose of MIA is used, this model can easily and quickly reproduce OA-like lesions and functional impairment in rats, similar to that observed in human disease. These parameters, as well as proteoglycan metabolism, could serve as indicators for studying chondroprotective drugs, or for evaluating the ability of imaging techniques to detect and evaluate chondral lesions.

Glucosamine inhibits IL-1beta-induced NFkappaB activation in human osteoarthritic chondrocytes

OBJECTIVE

Glucosamine sulfate (GS) is a commonly used drug for the treatment of osteoarthritis. The mechanism of the action of this drug does, however, remain to be elucidated. In human osteoarthritic chondrocytes (HOC) stimulated with a proinflammatory cytokine, we studied whether GS could modify the NFkappaB activity and the expression of COX-2, a NFkappaB-dependent gene.

METHODS

Using HOC in culture stimulated with interleukin-1 beta (IL-1beta), the effects of GS on NFkappaB activation, nuclear translocation of NFkappaB/Rel family members, COX-1 and COX-2 expressions and syntheses and prostaglandin E2 (PGE2) concentration were studied.

RESULTS

GS significantly inhibited NFkappaB activity in a dose-dependent manner, as well as the nuclear translocation of p50 and p65 proteins. Furthermore, GS-preincubated IL-1beta-stimulated HOC showed an increase in IkappaBalpha in the cell cytoplasm in comparison with HOC incubated with IL-1beta alone. GS also inhibited the gene expression and the protein synthesis of COX-2 induced by IL-1beta, while no effect on COX-1 synthesis was seen. GS also inhibited the release of PGE2 to conditioned media of HOC stimulated with IL-1beta.

CONCLUSIONS

GS inhibits the synthesis of proinflammatory mediators in HOC stimulated with IL-1beta through a NFkappaB-dependent mechanism. Our study further supports the role of GS as a symptom- and structure-modifying drug in the treatment of OA.

Plasticity of clonal populations of dedifferentiated adult human articular chondrocytes

OBJECTIVE

To investigate whether adult human articular chondrocytes (AHACs), dedifferentiated by monolayer expansion, can differentiate toward diverse mesenchymal lineages and, if so, whether this ability is regulated by growth factors during monolayer expansion.

METHODS

AHACs were expanded as multiclonal or clonal populations in medium without (control) or with factors enhancing cell dedifferentiation (transforming growth factor beta1, fibroblast growth factor 2, and platelet-derived growth factor type BB [TFP]). Cells were then cultured under conditions promoting chondrogenic, osteogenic, or adipogenic differentiation, and the acquired phenotypes were assessed histologically, biochemically, and by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

Multiclonal populations of both control- and TFP-expanded AHACs differentiated toward the chondrogenic, osteogenic, and adipogenic lineages. Compared with control-expanded AHACs, TFP-expanded cells displayed enhanced chondrogenic differentiation capacity (2.4-fold higher glycosaminoglycan/DNA content and 2,500-fold higher up-regulation of type II collagen) and osteogenic differentiation capacity (9.4-fold higher increase in alkaline phosphatase activity and 12.4-fold higher up-regulation of bone sialoprotein), but reduced formation of adipocytes (5.2-fold lower oil red O-positive cells/area). Clonal populations of AHACs could be efficiently expanded in TFP, but not in control medium. Most TFP-expanded clones were able to redifferentiate only into chondrocytes (7 of 20) or were unable to differentiate (6 of 20). However, some clones (2 of 20) differentiated toward all of the lineages investigated, thus displaying characteristics of mesenchymal progenitor cells.

CONCLUSION

Dedifferentiated AHACs exhibit differentiation plasticity, which is modulated by growth factors used during monolayer expansion and is highly heterogeneous across different clones. Clonal culture of AHACs in the presence of regulatory molecules could lead to the identification of AHAC subpopulations with enhanced cartilage repair capacity.

Role of interleukin-1, tumor necrosis factor alpha, and interleukin-6 in cartilage proteoglycan metabolism and destruction. Effect of in situ blocking in murine antigen- and zymosan-induced arthritis

OBJECTIVE

To determine the involvement of interleukin-1 (IL-1), tumor necrosis factor (TNF), and IL-6 in the cartilage pathology of murine antigen-induced arthritis (AIA) and zymosan-induced arthritis (ZIA).

METHODS

Arthritis was induced by intraarticular injection of zymosan in naive mice or by subcutaneous injection of methylated bovine serum albumin in sensitized animals. Mini-osmotic pumps releasing human recombinant IL-1 receptor antagonist (IL-1ra) protein were implanted intraperitoneally 2 days before arthritis induction, and neutralizing antibodies directed against murine IL-1 alpha, IL-1 beta, TNF alpha, or IL-6 were administered 1 day before. Proteoglycan (PG) synthesis and degradation were assessed in patellar cartilage.

RESULTS

Murine IL-1 alpha and IL-1 beta injected intraarticularly at doses of 0.1-100 ng suppressed chondrocyte PG synthesis. The highest dose of TNF tested (100 ng) decreased PG synthesis marginally. In contrast, the maximum dose of IL-6 (1 microgram) stimulated PG synthesis 2 days after injection. Treatment of AIA with neutralizing monoclonal antibodies against either TNF alpha or IL-6 did not reduce either the PG degradation or the suppression of its synthesis. However, treatment with anti-IL-1 (alpha + beta) polyclonal antibodies totally prevented PG suppression, although the initial breakdown of PG was unaffected. This effect was confirmed when IL-1ra was administered in high doses. Moreover, treatment of ZIA with anti-IL-1 (alpha + beta), but not with anti-TNF, resulted in normal PG synthesis, confirming the key role played by IL-1 in the inhibition of PG synthesis. Treatment of AIA with anti-IL-1 did not affect inflammation during the acute phase, but a significant reduction of ongoing inflammation was noted at day 7, and there was a marked reduction in the loss of cartilage PG.

CONCLUSION

The suppression of PG synthesis in both ZIA and AIA in mice is due to the combined local action of IL-1 (alpha + beta), and neither IL-6 nor TNF is involved. Moreover, the normalization of PG synthesis brought about by blocking of IL-1 ameliorates the cartilage damage associated with AIA.

Nitric oxide mediates suppression of cartilage proteoglycan synthesis by interleukin-1

Slices of rabbit articular cartilage synthesized large quantities of nitric oxide (NO) following exposure to human recombinant interleukin-1 beta (hrIL-1 beta) or rabbit synovial cytokines (CAF). Each of these stimuli also strongly suppressed the biosynthetic incorporation of 35SO4(2-) into the glycosaminoglycans (GAGs) of cartilage proteoglycans. Treatment of cartilage fragments with L-NG-monomethylarginine (L-NMA), a competitive inhibitor of NO synthase, both inhibited NO synthesis in response to IL-1 and CAF and restored proteoglycan synthesis. D-NMA was inactive in this regard, and L-arginine reversed the effects of L-NMA. S-nitrosylacetylpenicillamine (SNAP), an organic donor of NO, reversibly mimicked the effect of IL-1 and CAF on 35SO4(2-) incorporation. These data suggest that endogenously synthesized NO is the mediator which reduces cartilage proteoglycan synthesis in response to cytokines such as IL-1 and CAF. Antagonists of NO production may promote cartilage matrix synthesis and thus have potential as chondroprotective or chondroreparative agents.

Compression-induced changes in the shape and volume of the chondrocyte nucleus

Changes in cell shape and volume are believed to play a role in the process of mechanical signal transduction by chondrocytes in articular cartilage. One proposed pathway through which chondrocyte deformation may be transduced to an intracellular signal is through cytoskeletally mediated deformation of intracellular organelles, and more specifically, of the cell nucleus. In this study, confocal scanning laser microscopy was used to perform in situ three-dimensional morphometric analyses of the nuclei of viable chondrocytes during controlled compression of articular cartilage explants from the canine patellofemoral groove. Unconfined compression of the tissue to a 15% surface-to-surface strain resulted in a significant decrease of chondrocyte height and volume by 14.7 +/- 6.4 and 11.4 +/- 8.4%, respectively, and of nuclear height and volume by 8.8 +/- 6.2% and 9.8 +/- 8.8%, respectively. Disruption of the actin cytoskeleton using cytochalasin D altered the relationship between matrix deformation and changes in nuclear height and shape, but not volume. The morphology and deformation behavior of the chondrocytes were not affected by cytochalasin treatment. These results suggest that the actin cytoskeleton plays an important role in the link between compression of the extracellular matrix and deformation of the chondrocyte nuclei and imply that chondrocytes and their nuclei undergo significant changes in shape and volume in vivo.

Articular cartilage superficial zone protein (SZP) is homologous to megakaryocyte stimulating factor precursor and Is a multifunctional proteoglycan with potential growth-promoting, cytoprotective, and lubricating properties in cartilage metabolism

We have performed cDNA sequencing and homology analyses to elucidate the complete amino acid composition for a superficial zone protein (SZP) from human and bovine cartilage which has previously been shown to be a proteoglycan specifically synthesized by chondrocytes located at the surface of bovine articular cartilage and also some synovial lining cells. The results of this study indicate that cartilage SZP is homologous with a glycoprotein first described as the precursor protein of a megakaryocyte stimulating factor (MSF). Sequence comparisons and analyses indicate that (i) the amino acid composition of SZP is highly conserved between bovine and human species, (ii) SZP contains structural motifs at the N- and C-termini which are similar to those found in vitronectin and which may impart cell-proliferative and matrix-binding properties to the molecule, and (iii) SZP contains large and small mucin-like repeat domains composed of the sequences KEPAPTTT/P (76-78 repeats) and XXTTTX (6-8 repeats), respectively, which occur within a large central region of approximately 940 amino acids. The mucin-like domains are likely to be substituted with O-linked oligosaccharides which would impart lubricating properties to SZP which in part accumulates at the articular cartilage-synovial fluid interface. Additionally, we have shown that interleukin-1 inhibits the biosynthesis of chondrocyte SZP, while TGF-beta and IGF-1 increase its biosynthesis, and that in pathological (osteoarthritic) human articular cartilage SZP mRNA can be expressed as an alternatively spliced variant lacking exons 4 and 5 which encode a potential heparin binding domain. The occurrence of different SZP alternative splice variants and the differential expression of SZP in the presence of cytokines and growth factors suggest that SZP may play an important cytoprotective role by preventing cellular adhesion to the articular cartilage surface in normal cartilage metabolism. Modifications to the structure of SZP, coupled with inhibition of SZP synthesis during inflammation, may account for the attachment and invasion of pannus observed in inflammatory joint diseases.

IL-17 derived from juxta-articular bone and synovium contributes to joint degradation in rheumatoid arthritis

The origin and role of IL-17, a T-cell derived cytokine, in cartilage and bone destruction during rheumatoid arthritis (RA) remain to be clarified. In human ex vivo models, addition of IL-17 enhanced IL-6 production and collagen destruction, and inhibited collagen synthesis by RA synovium explants. On mouse cartilage, IL-17 enhanced cartilage proteoglycan loss and inhibited its synthesis. On human RA bone explants, IL-17 also increased bone resorption and decreased formation. Addition of IL-1 in these conditions increased the effect of IL-17. Blocking of bone-derived endogenous IL-17 with specific inhibitors resulted in a protective inhibition of bone destruction. Conversely, intra-articular administration of IL-17 into a normal mouse joint induced cartilage degradation. In conclusion, the contribution of IL-17 derived from synovium and bone marrow T cells to joint destruction suggests the control of IL-17 for the treatment of RA.

Fibroblast growth factor-18 stimulates chondrogenesis and cartilage repair in a rat model of injury-induced osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is the most common form of arthritis and a primary cause of disability, however, there are no treatments that can slow disease progression or repair damaged joint cartilage. Fibroblast growth factor-18 (FGF18) has been reported to have significant anabolic effects on cartilage. We therefore examined its effects on repair of cartilage damage in a rat meniscal tear model of OA.

DESIGN

Surgical damage to the meniscus in rats leads to joint instability and significant damage to the articular cartilage at 3 weeks post-surgery. At this time, animals received bi-weekly intra-articular injections of FGF18 for 3 weeks, and the knee joints were then harvested for histologic examination.

RESULTS

FGF18-induced dose-dependent increases in cartilage thickness of the tibial plateau, due to new cartilage formation at the articular surface and the joint periphery. The generation of new cartilage resulted in significant reductions in cartilage degeneration scores. The highest dose of FGF18 also induced an increase in chondrophyte size and increased remodeling of the subchondral bone.

CONCLUSIONS

The results of this study demonstrate that FGF18 can stimulate repair of damaged cartilage in a setting of rapidly progressive OA in rats.

Effect of Intra-Articular Sprifermin vs Placebo on Femorotibial Joint Cartilage Thickness in Patients With Osteoarthritis: The FORWARD Randomized Clinical Trial

IMPORTANCE

Sprifermin is under investigation as a disease-modifying osteoarthritis drug.

OBJECTIVE

To evaluate the effects of sprifermin on changes in total femorotibial joint cartilage thickness in the more symptomatic knee of patients with osteoarthritis.

DESIGN, SETTING, AND PARTICIPANTS

FORWARD (FGF-18 Osteoarthritis Randomized Trial with Administration of Repeated Doses) was a 5-year, dose-finding, multicenter randomized clinical trial conducted at 10 sites. Eligible participants were aged 40 to 85 years with symptomatic, radiographic knee osteoarthritis and Kellgren-Lawrence grade 2 or 3. Enrollment began in July 2013 and ended in May 2014; the last participant visit occurred on May 8, 2017. The primary outcome at 2 years and a follow-up analysis at 3 years are reported.

INTERVENTIONS

Participants were randomized to 1 of 5 groups: intra-articular injections of 100 μg of sprifermin administered every 6 months (n = 110) or every 12 months (n = 110), 30 μg of sprifermin every 6 months (n = 111) or every 12 months (n = 110), or placebo every 6 months (n = 108). Each treatment consisted of weekly injections over 3 weeks.

MAIN OUTCOMES AND MEASURES

The primary end point was change in total femorotibial joint cartilage thickness measured by quantitative magnetic resonance imaging at 2 years. The secondary end points (of 15 total) included 2-year change from baseline in total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. The minimal clinically important difference (MCID) is unknown for the primary outcome; for total WOMAC score in patients with hip and knee osteoarthritis, the absolute MCID is 7 U (95% CI, 4 to 10 U) and the percentage MCID is 14% (95% CI, 9% to 18%).

RESULTS

Among 549 participants (median age, 65.0 years; 379 female [69.0%]), 474 (86.3%) completed 2-year follow-up. Compared with placebo, the changes from baseline to 2 years in total femorotibial joint cartilage thickness were 0.05 mm (95% CI, 0.03 to 0.07 mm) for 100 μg of sprifermin administered every 6 months; 0.04 mm (95% CI, 0.02 to 0.06 mm) for 100 μg of sprifermin every 12 months; 0.02 mm (95% CI, -0.01 to 0.04 mm) for 30 μg of sprifermin every 6 months; and 0.01 mm (95% CI, -0.01 to 0.03 mm) for 30 μg of sprifermin every 12 months. Compared with placebo, there were no statistically significant differences in mean absolute change from baseline in total WOMAC scores for 100 μg of sprifermin administered every 6 months or every 12 months, or for 30 μg of sprifermin every 6 months or every 12 months. The most frequently reported treatment-emergent adverse event was arthralgia (placebo: n = 46 [43.0%]; 100 μg of sprifermin administered every 6 months: n = 45 [41.3%]; 100 μg of sprifermin every 12 months: n = 50 [45.0%]; 30 μg of sprifermin every 6 months: n = 40 [36.0%]; and 30 μg of sprifermin every 12 months: n = 48 [44.0%]).

CONCLUSIONS AND RELEVANCE

Among participants with symptomatic radiographic knee osteoarthritis, the intra-articular administration of 100 μg of sprifermin every 6 or 12 months vs placebo resulted in an improvement in total femorotibial joint cartilage thickness after 2 years that was statistically significant, but of uncertain clinical importance; there was no significant difference for 30 μg of sprifermin every 6 or 12 months vs placebo. Durability of response also was uncertain.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01919164.

Osteoarthritis

Osteoarthritis (OA), the syndrome of joint pain and dysfunction caused by joint degeneration, affects more people than any other joint disease. In most instances joint degeneration develops in the absence of an identifiable cause, but increasing age, excessive joint loading, and joint abnormalities and insults increase the risk of OA. Articular surface contact stress that causes tissue damage and compromises that ability of chondrocytes to maintain and restore the tissue has an important role in the development of joint degeneration Current methods of attempting to restore an articular surface in osteoarthritic joints include penetrating subchondral bone, altering joint loading, osteotomies and insertion of soft tissue grafts. Dramatic advances in the prevention and treatment of OA are likely to stem from better understanding of the role of mechanical forces in the initiation and progression of joint degeneration.

Regulation of MMP-13 expression by RUNX2 and FGF2 in osteoarthritic cartilage

OBJECTIVE

To understand the molecular mechanisms that lead to increased MMP-13 expression and cartilage degeneration during the progression of osteoarthritis (OA), we have investigated the expression of the transcription factor RUNX2 in OA cartilage and the regulation of MMP-13 expression by RUNX2 and FGF2 in articular chondrocytes.

DESIGN

RUNX2 and MMP-13 expression in human OA and control cartilage was analyzed by immunohistochemistry. The effects of RUNX2 over-expression, with or without FGF2 treatment, on MMP-13 promoter activity and enzyme accumulation were measured in articular chondrocytes. Inhibitors of MEK/ERK were assayed for their ability to block FGF2 and RUNX2 up-regulation of the MMP-13 promoter. We analyzed RUNX2 phosphorylation in response to FGF2.

RESULTS

Fibrillated OA cartilage exhibited increased RUNX2 immunoreactivity when compared to control cartilage. RUNX2 co-localized with MMP-13 in clusters of chondrocytes in fibrillated OA cartilage. RUNX2 over-expression in cultured chondrocytes increased their responsiveness to FGF2 treatment, which led to increased MMP-13 expression. Inhibitors of MEK/ERK signaling blocked up-regulation of the MMP-13 promoter by RUNX2 and FGF2, and also blocked the activation of RUNX2 by FGF2. FGF2 treatment of articular chondrocytes increased RUNX2 phosphorylation approximately 2-fold.

CONCLUSIONS

Increased expression of RUNX2 in OA cartilage may contribute to increased expression of MMP-13. FGF2, which is present in OA synovial fluid, activated RUNX2 via the MEK/ERK pathway and increased MMP-13 expression. However, it is unlikely that RUNX2 is a substrate of ERK1/2. RUNX2 expression and activation may be a significant step in the progression of OA by promoting changes in gene expression and chondrocyte differentiation.

Overview of MMP-13 as a Promising Target for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common degenerative disease characterized by the destruction of articular cartilage and chronic inflammation of surrounding tissues. Matrix metalloproteinase-13 (MMP-13) is the primary MMP involved in cartilage degradation through its particular ability to cleave type II collagen. Hence, it is an attractive target for the treatment of OA. However, the detailed molecular mechanisms of OA initiation and progression remain elusive, and, currently, there are no interventions available to restore degraded cartilage. This review fully illustrates the involvement of MMP-13 in the initiation and progression of OA through the regulation of MMP-13 activity at the molecular and epigenetic levels, as well as the strategies that have been employed against MMP-13. The aim of this review is to identify MMP-13 as an attractive target for inhibitor development in the treatment of OA.

Characterization of and osteoarthritis susceptibility in ADAMTS-4-knockout mice

OBJECTIVE

To determine the importance of the enzymatic activity of ADAMTS-4 in normal growth and development and to evaluate the role of ADAMTS-4 in the progression of osteoarthritis (OA).

METHODS

We generated catalytic domain-deleted ADAMTS-4-transgenic mice and performed extensive gross and histologic analyses of various organs. The mice were challenged by surgical induction of joint instability leading to OA, to determine the importance of the enzymatic activity of ADAMTS-4 in the progression of the disease. The response of wild-type (WT) and ADAMTS-4-knockout (ADAMTS-4-KO) articular cartilage to interleukin-1 and retinoic acid challenge in vitro was also evaluated.

RESULTS

ADAMTS-4-KO mice up to 1 year of age exhibited no gross or histologic abnormalities in 36 tissue sites examined. Despite evidence of ADAMTS-4 expression and activity in growth plates of WT mice, catalytic silencing of this proteinase caused no abnormalities in skeletal development, growth, or remodeling. There was no effect of ADAMTS-4 knockout on the progression or severity of OA 4 weeks or 8 weeks after surgical induction of joint instability. Enzymatic cleavage of aggrecan at the TEGE(373-374)ARGS site was clearly evident after exposure of articular cartilage from ADAMTS-4-KO mice to inflammatory cytokines.

CONCLUSION

Although expression of the ADAMTS-4 gene has been found in many tissues throughout the body, deletion of enzymatic activity did not appear to have any effect on normal growth and physiology. Our study provides evidence that ADAMTS-4 is the primary aggrecanase in murine growth plates; however, deletion of its enzymatic activity did not affect normal long bone remodeling. Our results also lead to the hypothesis that, in the mouse, ADAMTS-4 is not the primary enzyme responsible for aggrecan degradation at the TEGE(373-374)ARGS site. The elucidation of the relative importance of ADAMTS-4 in the pathologic process of human OA will require examination of human OA tissues and evidence of disease modification in patients following therapeutic intervention.