Zoledronic acid protects against local and systemic bone loss in tumor necrosis factor–mediated arthritis

Objective

Increased osteoclast activity is a key factor in bone loss in rheumatoid arthritis (RA). This suggests that osteoclast‐targeted therapies could effectively prevent skeletal damage in patients with RA. Zoledronic acid (ZA) is one of the most potent agents for blocking osteoclast function. We therefore investigated whether ZA can inhibit the bone loss associated with chronic inflammatory conditions.

Methods

Human tumor necrosis factor (TNF)–transgenic (hTNFtg) mice, which develop severe destructive arthritis as well as osteoporosis, were treated with phosphate buffered saline, single or repeated doses of ZA, calcitonin, or anti‐TNF, at the onset of arthritis.

Results

Synovial inflammation was not affected by ZA. In contrast, bone erosion was retarded by a single dose of ZA (−60%) and was almost completely blocked by repeated administration of ZA (−95%). Cartilage damage was partly inhibited, and synovial osteoclast counts were significantly reduced with ZA treatment. Systemic bone mass dramatically increased in hTNFtg mice after administration of ZA, which was attributable to an increase in trabecular number and connectivity. In addition, bone resorption parameters were significantly lowered after administration of ZA. Calcitonin had no effect on synovial inflammation, bone erosion, cartilage damage, or systemic bone mass. Anti‐TNF entirely blocked synovial inflammation, bone erosion, synovial osteoclast formation, and cartilage damage but had only minor effects on systemic bone mass.

Conclusion

ZA appears to be an effective tool for protecting bone from arthritic damage. In addition to their role in antiinflammatory drug therapy, modern bisphosphonates are promising candidates for maintaining joint integrity and reversing systemic bone loss in patients with arthritis.

     

Targeting osteoclasts with zoledronic acid prevents bone destruction in collagen‐induced arthritis

Objective

To study the effect of zoledronic acid (ZA) on synovial inflammation, structural joint damage, and bone metabolism in rats during the effector phase of collagen‐induced arthritis (CIA).

Methods

CIA was induced in female dark agouti rats. At the clinical onset of CIA, rats were assigned to treatment with vehicle or single subcutaneous doses of ZA (1.0, 10, 50, or 100 μg/kg). Clinical signs in all 4 paws were scored on a daily basis. After 2 weeks, the joints in the hind paws were assessed using plain radiographs, microfocal computed tomography (micro‐CT), histologic scoring, and histomorphometry, and the serum levels of type I collagen crosslinks were measured by enzyme‐linked immunosorbent assay.

Results

Although ZA mildly exacerbated synovitis, it effectively suppressed structural joint damage. At doses of ≥10 μg/kg, ZA significantly reduced radiographic bone erosions, Larsen scores, and juxtaarticular trabecular bone loss as quantified by micro‐CT. ZA prevented increased type I collagen (bone) breakdown in CIA and diminished histologic scores of focal bone erosion by up to 80%. Increases in the percentage of eroded surface, osteoclast surface, and osteoclast numbers associated with CIA were prevented by ZA, even though synovitis scores were unchanged.

Conclusion

Single doses (≥10 μg/kg) of ZA strikingly reduced focal bone erosions and juxtaarticular trabecular bone loss, although synovitis was mildly exacerbated. Targeting osteoclasts with ZA may therefore be an effective strategy for preventing structural joint damage in rheumatoid arthritis.

     

Proteasome inhibition aggravates tumor necrosis factor–mediated bone resorption in a mouse model of inflammatory arthritis

Objective

The proteasome inhibitor bortezomib has potent anti‐myeloma and bone‐protective activity. Recently, bortezomib was shown to directly inhibit osteoclastogenesis. The aim of this study was to analyze the influence and therapeutic effect of bortezomib in a mouse model of inflammatory arthritis.

Methods

Heterozygous human tumor necrosis factor α (hTNFα)–transgenic mice and their wild‐type (WT) littermates were intravenously injected with 0.75 mg/kg of bortezomib or phosphate buffered saline twice weekly. The mice were assessed for clinical signs of arthritis. After 6 weeks of treatment, mice were analyzed for synovial inflammation, cartilage damage, bone erosions, and systemic bone changes. Osteoclast precursors from WT and hTNF‐transgenic mice were isolated from bone marrow, treated with bortezomib, and analyzed for osteoclast differentiation, bone resorption, and expression of osteoclast‐specific genes as well as apoptosis and ubiquitination.

Results

Bortezomib‐treated hTNF‐transgenic mice showed moderately increased inflammatory activity and dramatically enhanced bone erosions associated with a significant increase in the number of synovial osteoclasts. Interestingly, bortezomib did not alter systemic bone turnover in either hTNF‐transgenic mice or WT mice. In vitro, treatment with therapeutically relevant concentrations of bortezomib resulted in increased differentiation of monocytes into osteoclasts and more resorption pits. Molecularly, bortezomib increased the expression of TNF receptor−associated factor 6, c‐Fos, and nuclear factor of activated T cells c1 in osteoclast precursors.

Conclusion

In TNF‐mediated bone destruction, bortezomib treatment increased synovial osteoclastogenesis and bone destruction. Hence, proteasome inhibition may have a direct bone‐resorptive effect via stimulation of osteoclastogenesis during chronic arthritis.

     

Tumor necrosis factor–inhibiting therapy preferentially targets bone destruction but not synovial inflammation in a tumor necrosis factor–driven model of rheumatoid arthritis

Objective

To investigate how tumor necrosis factor (TNF)–inhibiting therapy affects bone destruction and inflammation in a TNF‐driven mouse model of rheumatoid arthritis.

Methods

In order to evaluate the influence of TNF on osteoclastogenesis in vitro, different concentrations of TNF were added to spleen cell–derived monocytes in the absence or presence of different concentrations of RANKL. In addition, the effects of TNF inhibition on osteoclast precursors as well as local bone destruction in vivo were assessed by treating TNF‐transgenic mice with different doses of adalimumab.

Results

TNF stimulated osteoclastogenesis mainly by increasing the number of osteoclast precursor cells in vitro. This TNF effect was independent of the presence of RANKL. In the hTNF‐transgenic mouse model of destructive arthritis, low‐dose TNF‐inhibiting therapy with adalimumab had no effect on synovial inflammation but significantly inhibited local bone destruction and the generation of osteoclasts. This inhibition was accompanied by a reduction in the number of c‐Fms–positive osteoclast precursor cells in the bone marrow and a reduction of the osteoclast precursor pools in the blood and inflamed synovial membrane of hTNF‐transgenic mice.

Conclusion

Low‐dose TNF‐inhibiting therapy significantly reduces bone erosions by reducing the number of circulating and joint‐invading osteoclast precursors. This effect is uncoupled from its antiinflammatory action.

     

Host metalloproteinases in Lyme arthritis

Objective

: To assess the role of matrix metalloproteinases (MMPs) in cartilage and bone erosions in Lyme arthritis

Methods

We examined synovial fluid from 10 patients with Lyme arthritis for the presence of MMP‐2, MMP‐3, MMP‐9, and “aggrecanase” activity using gelatinolytic zymography and immunoblot analysis. We developed an in vitro model of Lyme arthritis using cartilage explants and observed changes in cartilage degradation in the presence of Borrelia burgdorferi and/or various protease inhibitors.

Results

Synovial fluid from patients with Lyme arthritis was found to contain at least 3 MMPs: gelatinase A (MMP‐2), stromelysin (MMP‐3), and gelatinase B (MMP‐9). In addition, there was evidence in 2 patients of “aggrecanase” activity not accounted for by the above enzymes. Infection of cartilage explants with B burgdorferi resulted in induction of MMP‐3, MMP‐9, and “aggrecanase” activity. Increased induction of these enzymes by B burgdorferi alone was not sufficient to cause cartilage destruction in the explants as measured by glycosaminoglycan (GAG) and hydroxyproline release. However, addition of plasminogen, which can act as an MMP activator, to cultures resulted in significant GAG and hydroxyproline release in the presence of B burgdorferi. The MMP inhibitor batimastat significantly reduced the GAG release and completely inhibited the collagen degradation.

Conclusion

MMPs are found in synovial fluids from patients with Lyme arthritis and are induced from cartilage tissue by the presence of B burgdorferi. Inhibition of MMP activity prevents B burgdorferi–induced cartilage degradation in vitro.

     

Membrane type 1 matrix metalloproteinase is a crucial promoter of synovial invasion in human rheumatoid arthritis

Objective

A hallmark of rheumatoid arthritis (RA) is invasion of the synovial pannus into cartilage, and this process requires degradation of the collagen matrix. The aim of this study was to explore the role of one of the collagen‐degrading matrix metalloproteinases (MMPs), membrane type 1 MMP (MT1‐MMP), in synovial pannus invasiveness.

Methods

The expression and localization of MT1‐MMP in human RA pannus were investigated by Western blot analysis of primary synovial cells and immunohistochemical analysis of RA joint specimens. The functional role of MT1‐MMP was analyzed by 3‐dimensional (3‐D) collagen invasion assays and a cartilage invasion assay in the presence or absence of tissue inhibitor of metalloproteinases 1 (TIMP‐1), TIMP‐2, or GM6001. The effect of adenoviral expression of a dominant‐negative MT1‐MMP construct lacking a catalytic domain was also examined.

Results

MT1‐MMP was highly expressed at the pannus–cartilage junction in RA joints. Freshly isolated rheumatoid synovial tissue and isolated RA synovial fibroblasts invaded into a 3‐D collagen matrix in an MT1‐MMP–dependent manner. Invasion was blocked by TIMP‐2 and GM6001 but not by TIMP‐1. Invasion was also inhibited by the overexpression of a dominant‐negative MT1‐MMP, which inhibits collagenolytic activity and proMMP‐2 activation by MT1‐MMP on the cell surface. Synovial fibroblasts also invaded into cartilage in an MT1‐MMP–dependent manner. This process was further enhanced by removing aggrecan from the cartilage matrix.

Conclusion

MT1‐MMP serves as an essential collagen‐degrading proteinase during pannus invasion in human RA. Specific inhibition of MT1‐MMP–dependent invasion may represent a novel therapeutic strategy for RA.

     

Activation of p38 MAPK is a key step in tumor necrosis factor–mediated inflammatory bone destruction

Objective

To investigate whether activation of p38 MAPK is a crucial signaling factor in inflammatory bone destruction mediated by tumor necrosis factor (TNF). Mice overexpressing TNF were treated with 2 different inhibitors of p38 MAPK, and the effect of this treatment on joint inflammation and structural damage was assessed.

Methods

Human TNF‐transgenic mice received systemic treatment with 2 different p38 MAPK inhibitors (RO4399247 and AVE8677). Treatment was started at the time of symptom onset and lasted for 6 weeks. Mice were assessed for clinical signs of arthritis, bone erosion, and cartilage damage. In addition, the effect of these inhibitors on osteoclast generation in vitro and in vivo was assessed.

Results

Both p38 MAPK inhibitors significantly reduced clinical signs of TNF‐mediated arthritis. This was attributable to reducing synovial inflammation by 50% without affecting the cellular composition of the infiltrate. Synovial expression of interleukin‐1 and RANKL was reduced upon p38 MAPK blockade, and activation of the molecular target MAPK‐activated protein kinase 2 (MAPKAP‐2) was also inhibited. Proteoglycan loss of articular cartilage was reduced by 50%, although p38 MAPK inhibition did not change matrix molecule synthesis by cultivated chondrocytes. Importantly, bone loss was almost completely prevented by p38 MAPK inhibition. The numbers of synovial osteoclasts and precursors were dramatically reduced, and both p38 MAPK inhibitors also inhibited in vitro osteoclastogenesis at micromolar concentrations and blocked activation of MAPKAP‐2 as well as differentiation markers in cultured osteoclast precursors.

Conclusion

These results suggest the major importance of p38 MAPK for TNF‐mediated inflammatory bone destruction in arthritis and suggest that inhibition of p38 MAPK might be an important tool for reducing structural damage in rheumatoid arthritis.

     

Midkine,a heparin‐binding growth factor,is fundamentally involved in the pathogenesis of rheumatoid arthritis

Objective

Midkine (MK), a heparin‐binding growth factor, promotes growth, survival, and migration of various cells. The essential role of MK in migration of inflammatory cells has been shown using mice deficient in the MK gene (Mdk^−/− mice). We undertook this study to investigate the role of MK in the pathogenesis of rheumatoid arthritis (RA).

Methods

MK levels in specimens from patients were determined by enzyme‐linked immunosorbent assay, and localization of MK was revealed by immunohistochemical analysis. Susceptibility to antibody‐induced arthritis was compared between Mdk^−/− and wild‐type (WT) mice. Osteoclast differentiation was monitored using macrophage‐like cells isolated from human synovial tissue and macrophages from mouse bone marrow.

Results

MK levels in sera and synovial fluid were increased in most RA patients, indicating a strong correlation between MK expression and RA. MK was expressed in macrophage‐like cells and fibroblast‐like cells in synovial membranes from the patients. In antibody‐induced arthritis, Mdk^−/− mice seldom developed the disease, while most of the WT mice did. Administration of MK to the Mdk^−/− mice increased the frequency of antibody‐induced arthritis. Migration of inflammatory leukocytes to the synovial membranes in the disease model was suppressed in the Mdk^−/− mice. Furthermore, MK was found to promote the differentiation of osteoclasts from macrophages.

Conclusion

MK participates in each of the two distinct phases of RA development, namely, migration of inflammatory leukocytes and osteoclast differentiation, and is a key molecule in the pathogenesis of RA.

     

Reduced expression and proteolytic susceptibility of lubricin/superficial zone protein may explain early elevation in the coefficient of friction in the joints of rats with antigen‐induced arthritis

Objective

To investigate the effect of arthritis development and progression on the integrity and function of lubricin and the relationship of lubricin to cartilage damage in a rat antigen‐induced arthritis model.

Methods

Arthritis was induced in the right knee joints, using methylated bovine serum albumin and Freund's complete adjuvant. Whole joint friction measurements were performed ex vivo with a modified Stanton pendulum configuration, and coefficients of friction (μ) were determined. Levels of messenger RNA (mRNA) for lubricin, cathepsin B, and interleukin‐1β (IL‐1β) in synovial tissue from control and affected joints were determined by quantitative polymerase chain reaction. Lubricin staining in cartilage was performed using a lubricin‐specific monoclonal antibody.

Results

The μ values in excised right joints following arthritis induction were significantly (P < 0.001) higher than those in excised left joints. Lubricin mRNA expression levels in synovial tissue on days 4 and 7 after arthritis induction were significantly (P < 0.001) lower in the right joints compared with the left joints, whereas levels of cathepsin B and IL‐1β mRNA expression on days 4, 7, and 14 were significantly (P < 0.001) higher in the right joints than the left joints. Lubricin staining was diminished in cartilage from the right joints compared with the left joints.

Conclusion

Elevated coefficients of friction in arthritic joints occur concurrently with enhanced proteolytic degradation by up‐regulated cathepsin B and other proteases, as well as decreased lubricin synthesis by synovial fibroblasts and superficial zone chondrocytes. Loss of joint lubrication is an early event in inflammatory arthropathy. Restoring chondroprotection and preventing potential wear‐induced cartilage degradation may require lubricin supplementation in synovial fluid.

     

Tumor necrosis factor α and RANKL blockade cannot halt bony spur formation in experimental inflammatory arthritis

Objective

To investigate the kinetics of bony spur formation and the relationship of bony spur formation to synovial inflammation and bone erosion in 2 rat arthritis models, and to address whether bony spur formation depends on the expression of tumor necrosis factor α (TNFα) or RANKL.

Methods

Analysis of the kinetics of synovial inflammation, bone erosion, osteoclast formation, and growth of bony spurs was performed in rat collagen‐induced arthritis (CIA) and adjuvant‐induced arthritis (AIA). In addition, inhibition experiments were performed to assess whether inhibition of TNFα and RANKL by pegylated soluble TNF receptor type I (pegTNFRI) and osteoprotegerin (OPG), respectively, affected bony spur formation.

Results

Bony spurs emerged from the periosteal surface close to joints, and initial proliferation of mesenchymal cells was noted as early as 3 days and 5 days after onset of CIA and AIA, respectively. Initiation of bony spur formation occurred shortly after the onset of inflammation and bone erosion. Neither pegTNFRI nor OPG could significantly halt the osteophytic responses in CIA and AIA.

Conclusion

These results suggest that bony spur formation is triggered by inflammation and initial structural damage in these rat models of inflammatory arthritis. Moreover, emergence of bony spurs depends on periosteal proliferation and is not affected by inhibition of either TNFα or RANKL. Bony spur formation can thus be considered a process that occurs independent of TNFα and RANKL and is triggered by destructive arthritis.

     

Antiinflammatory effects of tumor necrosis factor on hematopoietic cells in a murine model of erosive arthritis

Objective

To investigate the mechanisms leading to the influx of inflammatory hematopoietic cells into the synovial membrane and the role of tumor necrosis factor receptor I (TNFRI) and TNFRII in this process in an animal model of rheumatoid arthritis (RA).

Methods

We performed bone marrow transplantations in human TNF–transgenic mice using hematopoietic cells from wild‐type, TNFRI^−/−, TNFRII^−/−, and TNFRI/II^−/− mice as donors and assessed the severity of arthritis histologically. Generation of osteoclasts from the different genotypes was analyzed in vitro and in vivo. Apoptosis was analyzed using annexin V staining as well as TUNEL assays.

Results

Despite lacking responsiveness to TNF in their hematopoietic compartment, mice not only developed full‐blown erosive arthritis but even showed increased joint destruction when compared with mice with a TNF‐responsive hematopoietic compartment. We demonstrated different roles of the 2 different TNFRs in the regulation of these processes. The absence of TNFRI on hematopoietic cells did not affect joint inflammation but markedly attenuated erosive bone destruction via reduced synovial accumulation of osteoclast precursors. In contrast, the absence of TNFRII on hematopoietic cells increased joint inflammation as well as erosive bone destruction via the regulation of osteoclast precursor apoptosis.

Conclusion

Our findings indicate that selective blockade of TNFRI, leaving the antiinflammatory effects of TNFRII unaltered instead of unselectively blocking TNF, might be advantageous in patients with RA.

     

Reduction of CpG‐induced arthritis by suppressive oligodeoxynucleotides

Objective

Bacterial DNA contains immunostimulatory CpG motifs that cause inflammation when injected into the knee joints of normal mice. We examined whether synthetic oligodeoxynucleotides (ODN) that suppress CpG‐induced immune responses prevent CpG‐induced arthritis.

Methods

CpG, suppressive, and/or control ODN were injected into the knees of BALB/c mice. Joint swelling and inflammation were evaluated by physical measurement, by histologic analysis of joint tissue, and by magnetic resonance imaging.

Results

Immunostimulatory CpG DNA induced local arthritis, characterized by swelling of the knee joints, the presence of inflammatory cell infiltrates, the perivascular accumulation of mononuclear cells, and hyperplasia of the synovial lining. Administering suppressive (but not control) ODN reduced the manifestations and severity of arthritis up to 80%.

Conclusion

Suppressive ODN may be useful for the prevention or treatment of arthritis induced by bacterial DNA.

     

Interleukin‐20 antibody is a potential therapeutic agent for experimental arthritis

Objective

Interleukin‐20 (IL‐20) is a proinflammatory cytokine involved in the pathogenesis of rheumatoid arthritis (RA). We investigated whether anti–IL‐20 antibody treatment would modulate the severity of the disease in a collagen‐induced arthritis (CIA) rat model.

Methods

We generated a CIA model by immunizing rats with bovine type II collagen. Rats with CIA were treated subcutaneously with anti–IL‐20 antibody 7E, with the tumor necrosis factor (TNF) blocker etanercept, or with 7E in combination with etanercept. Arthritis severity was determined according to the hind paw thickness, arthritis severity score, degree of cartilage damage, bone mineral density, and cytokine production, which were evaluated using radiologic scans, microfocal computed tomography, and enzyme‐linked immunosorbent assay. To analyze gene regulation by IL‐20, rat synovial fibroblasts (SFs) were isolated and analyzed for the expression of RANKL, IL‐17, and TNFα. We also used real‐time quantitative polymerase chain reaction analysis and flow cytometry to determine IL‐20–regulated RANKL in mouse osteoblastic MC3T3‐E1 cells and Th17 cells.

Results

In vivo, treatment with 7E alone or in combination with etanercept significantly reduced the severity of arthritis by decreasing the hind paw thickness and swelling, preventing cartilage damage and bone loss, and reducing the expression of IL‐20, IL‐1β, IL‐6, RANKL, and matrix metalloproteinases (MMPs) in synovial tissue. In vitro, IL‐20 induced TNFα expression in SFs from rats with CIA. IL‐20 markedly induced RANKL production in SFs, osteoblasts, and Th17 cells.

Conclusion

Selectively blocking IL‐20 inhibited inflammation and bone loss in rats with CIA. Treatment with 7E combined with etanercept protected rats from CIA better than treatment with etanercept alone. Our findings provide evidence that IL‐20 is a novel target and that 7E may be a potential therapeutic agent for RA.

     

Glucocorticoid‐induced leucine zipper is an endogenous antiinflammatory mediator in arthritis

Objective

Glucocorticoid‐induced leucine zipper (GILZ) is a glucocorticoid‐induced protein, the reported molecular interactions of which suggest that it functions to inhibit inflammation. However, the role of endogenous GILZ in the regulation of inflammation in vivo has not been established. This study was undertaken to examine the expression and function of GILZ in vivo in collagen‐induced arthritis (CIA), a murine model of rheumatoid arthritis (RA), and in RA synoviocytes.

Methods

GILZ expression was detected in mouse and human synovium by immunohistochemistry and in cultured cells by real‐time polymerase chain reaction and permeabilization flow cytometry. GILZ function was assessed in vivo by small interfering RNA (siRNA) silencing using cationic liposome–encapsulated GILZ or control nontargeting siRNA and was assessed in vitro using transient overexpression.

Results

GILZ was readily detectable in the synovium of mice with CIA and was up‐regulated by therapeutic doses of glucocorticoids. Depleting GILZ expression in vivo increased the clinical and histologic severity of CIA and increased synovial expression of tumor necrosis factor and interleukin‐1 (IL‐1), without affecting the levels of circulating cytokines or anticollagen antibodies. GILZ was highly expressed in the synovium of patients with active RA and in cultured RA synovial fibroblasts, and GILZ overexpression in synovial fibroblasts inhibited IL‐6 and IL‐8 release.

Conclusion

Our findings indicate that GILZ functions as an endogenous inhibitor of chronic inflammation via effects on cytokine expression and suggest that local modulation of GILZ expression could be a beneficial therapeutic strategy.

     

Formation of invadopodia‐like structures by synovial cells promotes cartilage breakdown in collagen‐induced arthritis: Involvement of the protein tyrosine kinase Src

Objective

Invasive synovial fibroblasts are suggested to be the major effectors of cartilage and bone destruction, and this aggressive phenotype can lead to irreversible damage. In cancer cells, invasion across tissue boundaries and metastasis have recently been shown to depend on the capacity of the cells to breach the basement membrane, a process that was linked to the formation of the actin‐rich cell protrusions called invadopodia. This study was undertaken to investigate whether arthritic synovial cells use invadopodia to invade and degrade cartilage components.

Methods

Fibroblast‐like synoviocytes (FLS) from control rats or rats with collagen‐induced arthritis (CIA) were cultured on fluorescent matrix in the presence of Src inhibitors or were transfected with wild‐type or variants of Src kinases. The in vivo effect of Src inhibition on cartilage degradation and invasion was studied in a rat model of CIA.

Results

FLS from rats with CIA produced more invadopodia‐like structures than did FLS from control rats, leading to increased extracellular matrix degradation. Furthermore, c‐Src activation was increased in synovial cells from rats with CIA, and Src activity was found to mediate the formation of invadopodia. Pharmacologic blockade of Src activity by PP2 or intraarticular expression of a c‐Src–specific short hairpin RNA in the CIA model reduced synovial membrane hyperplasia and cartilage degradation, an event linked to decreased invadopodia formation by synovial fibroblasts.

Conclusion

This study demonstrates that inhibition of invadopodia formation in arthritic synovial cells leads to a direct effect on extracellular matrix degradation in vitro and in vivo, making invadopodia a relevant therapeutic target for interfering with this process.

     

Stimulation of collagenase 3 expression in synovial fibroblasts of patients with rheumatoid arthritis by contact with a three‐dimensional collagen matrix or with normal cartilage when coimplanted in NOD/SCID mice

Objective

To study the expression of collagenase 3 (matrix metalloproteinase 13 [MMP‐13]) and collagenase 1 (MMP‐1) in synovial fibroblasts from patients with rheumatoid arthritis (RA) when cultured within 3‐dimensional collagen gels or coimplanted with normal cartilage in immunodeficient NOD/SCID mice.

Methods

Messenger RNA (mRNA) and protein expression of collagenase 3 and collagenase 1 were characterized in synovial and skin fibroblasts by Northern blot and Western blot analysis. The mRNA expression of both collagenases in cell–cartilage implants in NOD/SCID mice was investigated by in situ hybridization in combination with immunohistochemistry of human fibroblasts.

Results

Synovial fibroblasts coimplanted with normal cartilage in NOD/SCID mice deeply invaded adjacent cartilage tissue. In this in vivo system of cartilage destruction, collagenase 3 mRNA was induced in synovial fibroblasts at sites of cartilage erosion, while the expression of collagenase 1 mRNA could not be detected. Culture of synovial fibroblasts within 3‐dimensional collagen gels was a ssociated with a marked increase in collagenase 3 mRNA expression and proenzyme production. This stimulatory effect was 1 order of magnitude higher in comparison with a 2–4‐fold increase upon treatment with interleukin‐1 β or tumor necrosis factor α. In contrast, mRNA expression and proenzyme production of collagenase 1 were increased strongly, and to a similar extent, either by contact with 3‐dimensional collagen or by proinflammatory cytokines.

Conclusion

The expression of collagenase 3, in contrast to that of collagenase 1, is preferentially stimulated in synovial fibroblasts by 3‐dimensional collagen rather than by proinflammatory cytokines. The induction of collagenase 3 by cell–matrix interactions represents a potential mechanism contributing to the invasive phenotype of synovial fibroblasts at sites of synovial invasion into cartilage in RA.

     

Transforming growth factor β–transduced mesenchymal stem cells ameliorate experimental autoimmune arthritis through reciprocal regulation of Treg/Th17 cells and osteoclastogenesis

Objective

Bone marrow–derived mesenchymal stem cells (MSCs) can prevent various autoimmune diseases. We examined the therapeutic potential of transforming growth factor β (TGFβ)–transduced MSCs in experimental autoimmune arthritis, using an accepted animal model of collagen‐induced arthritis (CIA).

Methods

DBA/1J mice with CIA were treated with syngeneic TGFβ‐induced MSCs, whereas control mice received either vehicle or MSCs alone. Arthritis severity was assessed by clinical and histologic scoring. TGFβ‐transduced MSCs were tested for their immunosuppressive ability and differential regulation in mice with CIA. T cell responses to type II collagen were evaluated by determining proliferative capacity and cytokine levels. The effects of TGFβ‐transduced MSCs on osteoclast formation were analyzed in vitro and in vivo.

Results

Systemic infusion of syngeneic TGFβ‐transduced MSCs prevented arthritis development and reduced bone erosion and cartilage destruction. Treatment with TGFβ‐transduced MSCs potently suppressed type II collagen–specific T cell proliferation and down‐regulated proinflammatory cytokine production. These therapeutic effects were associated with an increase in type II collagen–specific CD4+FoxP3+ Treg cells and inhibition of Th17 cell formation in the peritoneal cavity and spleen. Furthermore, TGFβ‐transduced MSCs inhibited osteoclast differentiation.

Conclusion

TGFβ‐transduced MSCs suppressed the development of autoimmune arthritis and joint inflammation. These data suggest that enhancing the immunomodulatory activity of MSCs and modulating T cell–mediated immunity using gene‐modified MSCs may be a gateway for new therapeutic approaches to clinical rheumatoid arthritis.