Cysteine proteinase activity in the development of arthritis in an adjuvant model of the rat

Disease status in human and experimental arthritis, and response to TNF blockade, is associated with MHC class II invariant chain (CD74) isoform expression

Splice variants of CD74 differentially modulate the activity of cathepsin L (CTSL). As CD74 and CTSL participate in the pathogenesis of inflammatory diseases such as rheumatoid arthritis (RA), we determined whether splice variants of CD74 could be biomarkers of disease activity. Gene expression was measured in mice with collagen-induced arthritis using quantitative PCR (qPCR). In vitro studies using murine macrophage/DC-lineage cells determined the relative influence of macrophage phenotype on isoform expression and the potential to produce CTSL in response to TNF. CD74 splice variants were measured in human RA synovium and RA patients' monocytes. In arthritic mice, the expression of the p41 CD74 isoform was significantly higher in severely affected paws compared with unaffected paws or the paws of naïve mice; the p41 isoform significantly correlated with the expression of TNF in arthritic paws. Compared with M2-like macrophages, M1-like macrophages expressed increased levels of CD74 and had higher expression, secretion and activity of CTSL. RA patients that responded to TNF blockade had significantly higher expression levels of CD74 in circulating monocytes after treatment, compared with non-responders. The expression of the human CD74 isoform a was significantly higher in RA synovia, compared with osteoarthritis synovia, and was associated with CSTL enzymatic activity. This study is the first to demonstrate differential expression of the CD74 p41 isoform in an auto-immune disorder and in response to therapy. The differential expression of CD74 splice variants indicates an association, and potentially a mechanistic role, in the pathogenesis of RA.

Cathepsin L splice variants in human breast cell lines

Transcripts of the lysosomal cysteine proteinase cathepsin L are spliced into five variants (L-A, L-A1, LA-2, LA-3 and L-B), which have similar stabilities but different translation efficiencies, thus potentially yielding diverse amounts of the protein. The aim of this study was to investigate whether the abnormally elevated expression of cathepsin L in invasive tumours is due to overexpression of L-A3, the splice variant translated most efficiently. The expression pattern of cathepsin L mRNA variants was measured by quantitative polymerase chain reaction (qPCR) in two panels of cell lines obtained from precancerous and cancerous breast tissue. In both panels, the cell line exhibiting the highest in vitro invasiveness also expressed the highest amount of L-A3. Although the pattern of expression varied, the expression of the L-B variant was always remarkably lower than for other variants. We propose that posttranscriptional regulation of cathepsin L expression is altered during breast tumour progression.

In vivo imaging of protease activity in arthritis: A novel approach for monitoring treatment response

OBJECTIVE

Sensitive noninvasive strategies for monitoring treatment response in rheumatoid arthritis (RA) would be valuable for facilitating appropriate therapy and dosing, evaluating clinical outcome, and developing more effective drugs. Because different proteases are highly up-regulated in RA and contribute significantly to joint destruction, in the present study we investigated whether such enzymes are suitable in vivo imaging biomarkers for early evaluation of treatment response in a murine model of RA.

METHODS

Using a protease-activated near-infrared fluorescence (NIRF) imaging "smart" probe, we examined the presence and distribution of fluorescence in arthritic joints of mice with collagen-induced arthritis by both noninvasive fluorescence imaging and histology. Proteases that target the Lys-Lys cleavage site, including cathepsin B, activate probe fluorescence. Treatment monitoring data were obtained following methotrexate (MTX) therapy.

RESULTS

Twenty-four hours after intravenous injection of the protease sensor, affected toes and paws of arthritic mice showed significantly higher fluorescence intensity than did toes and paws of healthy mice. Fluorescence from the protease probe and cathepsin B antibody histologic staining were localized in the vast majority of cells in the inflamed synovium. In arthritic animals treated with MTX (35 mg of MTX/kg 48 hours prior to probe injection), a significantly lower fluorescent signal (inflamed paws 50%, inflamed toes 70%) was observed as compared with untreated arthritic animals.

CONCLUSION

Protease-activated NIRF probes are sensitive means of imaging the presence of target enzymes in arthritic joints and can be used for early monitoring of treatment response to antirheumatic drugs such as MTX.

Early diagnosis of osteoarthritis using cathepsin B sensitive near-infrared fluorescent probes

OBJECTIVE

Osteoarthritis is currently diagnosed utilizing X-ray and MRI-techniques, both of which are based on the morphological changes of tissue. However, once changes are detected, the tissue has an irreversible defect. This study investigates early diagnosis of OA on a molecular basis using a recently developed cathepsin B sensitive near-infrared (NIR) fluorescent probe.

METHOD

Twelve male nude mice were induced osteoarthritis by intra-articular injection of collagenase (1.0%, w/v) into the right knee joint. The left knee joint served as the negative control. The cathepsin B NIR probe is activated by arthritis-associated cathepsin B, thus resulting in the emission of an intensive NIR fluorescence signal which can be detected in vivo. NIR fluorescence signals were acquired on an optical imaging system using an excitation wavelength of 610-650 nm and an emission wavelength of 680-720 nm.

RESULTS

Mild to moderate degenerative cartilage was observed 1 month after collagenase injection. NIR fluorescence imaging of mice showed approximately a 3-fold difference in signal intensity between osteoarthritic and normal joints 24 h after intravenous injection of the reporter probe. Immunohistochemical evaluation also revealed cathepsin B expression in the arthritic lesion of femorotibial joints, and not in the control contra-lateral knee joints.

CONCLUSION

As the cathepsin B activatable NIR fluorescent imaging showed a significant difference between the osteoarthritic and normal joints, the cathepsin B activatable NIR fluorescent probe thus offers a potential new imaging technology for early OA diagnosis.

Synovial tissue protease gene expression and joint erosions in early rheumatoid arthritis

OBJECTIVE

To relate the expression of proteases in the lining and sublining layers of the synovial membrane to the rate of joint damage during 1 year in patients with early inflammatory arthritis.

METHODS

Samples of synovial membrane were obtained by closed-needle biopsy or needle arthroscopy from inflamed knees of 20 patients with early inflammatory polyarthritis (mean disease duration 9.6 months, range 2 weeks to 18 months). Expression of matrix metalloproteinase 1 (MMP-1), cathepsin B (CB), and cathepsin L (CL) was examined using in situ hybridization. Immunohistochemistry was used to identify infiltrating mononuclear cell populations. Radiographs of the hands and feet, performed at presentation and after 1 year, were evaluated for the development of new erosions.

RESULTS

Twelve patients had rheumatoid arthritis (RA), 6 had psoriatic arthritis (PsA), 1 had gout, and 1 had an undifferentiated arthritis. Six patients had erosions at presentation. Eleven patients (10 with RA, 1 with PsA) demonstrated at least 1 new erosion after 1 year of followup. MMP-1, CB, and CL messenger RNA (mRNA) were expressed in the synovial membrane of all patients and were present throughout the lining layer, as well as in perivascular cellular infiltrates and endothelial cells in the sublining layer. In the lining layer, the mean percentages of protease mRNA-positive cells per high-power field were higher in those patients who developed new joint erosions than in those without evidence of joint damage. A similar pattern was observed in the sublining layer, where mean numbers of protease mRNA-positive cells were also greater in patients with new joint erosions. There were significant differences between the two groups in MMP-1 mRNA expression in both the lining and sublining layers (P = 0.0007 and P = 0.0027, respectively), as well as in sublining layer CL mRNA expression (P = 0.017), but not in CB mRNA expression. Numbers of lining layer CD68+ cells correlated positively with lining layer MMP-1 mRNA expression (P = 0.043) and with the development of new joint erosions (P = 0.002).

CONCLUSION

The detection of MMP-1, CB, and CL in the synovium soon after the onset of symptoms highlights the potential for early joint destruction in patients with RA. High levels of MMP-1 mRNA expression in the lining layer distinguished patients with more rapidly progressive erosive disease. This is the first study to demonstrate features of early synovial pathophysiology that may identify patients at increased risk of developing new joint erosions.

Cysteine protease activity is up-regulated in inflamed ankle joints of rats with adjuvant-induced arthritis and decreases with in vivo administration of a vinyl sulfone cysteine protease inhibitor

OBJECTIVE

Cysteine proteases are postulated to play a role in tissue destruction in the joints of animals with arthritis. The purpose of the present study was to confirm the concept that cysteine proteases are enzymes involved in the pathology of rheumatoid arthritis (RA).

METHODS

Arthritis was induced in Lewis rats by adjuvant injection (adjuvant-induced arthritis [AIA] model) and scored for inflammation. At necropsy, the rear paws were either fixed in formalin and assigned a histologic score (based on synovial cell proliferation, cartilage erosion, bone erosion, and fibroproliferative pannus) or frozen, cryosectioned, and assayed for enzyme activity either by in situ cytochemical staining with a post-azo-coupling method using a chromogenic substrate (Z-arg-arg-MNA) or by a novel assay placing the tissue section directly in a cuvette using the fluorogenic substrate Z-arg-arg-AMC.

RESULTS

Enzymatic activity, measured either in frozen sections in situ or in the cuvette assay, was positively correlated with joint destruction (r = 0.7) and inflammation (r = 0.8). Activity was not inhibited significantly by Pefabloc (a serine protease inhibitor), EDTA (a metalloprotease inhibitor), or pepstatin A (an aspartyl protease inhibitor) but was inhibited by E-64 and vinyl sulfone irreversible inhibitors of cysteine proteases. The effect of one of the vinyl sulfone cysteine protease inhibitors, Mu-Leu-HomoPhe-vinylsulfone, was tested in vivo by dietary administration at 2.2 mg/kg/day in the AIA model; this resulted in a significant decrease in inflammation and in the amount of cysteine protease activity measured in the joint tissue.

CONCLUSION

Cysteine protease activity levels increase in the diseased state and may be an important target for designing small molecule inhibitors to reduce the inflammation and tissue destruction associated with RA.

Expression of matrix metalloproteinase 9 (96-kd gelatinase B) in human rheumatoid arthritis

OBJECTIVE

To determine the expression of matrix metalloproteinase 9/gelatinase B (MMP-9) in synovial fluid (SF), plasma, and synovial tissue from individuals with rheumatoid arthritis (RA), inflammatory arthritis (IA), and osteoarthritis (OA), using specific monoclonal antibody reagents.

METHODS

Gelatinolytic activity in the SF and plasma of patients with RA, IA, and OA was assessed by gelatin zymography. A mouse monoclonal antiserum, 277.13, which selectively recognizes soluble latent forms of human MMP-9, was used to quantitate MMP-9 levels in patient synovial effusions, plasma, and synovial tissue with a capture sandwich enzyme-linked immunosorbent assay (ELISA). Fifty-one SF samples (31 RA, 9 OA, 11 IA) were analyzed. Immunolocalization of MMP-9 in RA, OA, and normal synovium was investigated using MMP-9-specific antisera.

RESULTS

MMP-9 antigen levels in synovial effusions were elevated 67-fold in RA samples compared with OA samples. In addition, although MMP-9 antigen levels in IA synovial effusions were 2.7-fold less than the values in RA samples, they were elevated 34-fold over the values in OA samples. These data indicate an association between increased MMP-9 levels and inflammatory arthritis. A predominant 92-kd gelatinolytic activity (specifically inhibited by EDTA) was evident in RA and IA samples, but no activity was observed in OA samples. Among 86 plasma samples (17 RA, 9 IA, 60 normal controls) analyzed for MMP-9 antigen levels by immunocapture ELISA, MMP-9 antigen levels were elevated 7-fold in RA plasma compared with normal plasma. RA synovial tissue extracts demonstrated elevated levels of MMP-9 antigen compared with OA synovial tissue. MMP-9 immunolocalization studies demonstrated expression in infiltrating leukocytes (neutrophils and macrophages), endothelial cells, and synovial fibroblasts in RA synovium.

CONCLUSION

Latent MMP-9 and/or MMP-9-tissue inhibitor of metalloproteinases 1 (TIMP-1) complexes are elevated in RA and IA SF compared with OA SF. In addition, MMP-9 is increased in RA plasma versus normal control plasma. Synovial tissue levels of MMP-9 antigen are also elevated in RA versus OA. The tissue distribution of MMP-9 within RA synovium is localized to sites of inflammation comprising surface synovial lining cells, endothelium, and leukocytes. Taken together, these observations suggest that connective tissue turnover occurs as a result of excessive MMP activity over TIMP action in the invading pannus, periarticular tissue, or SF. Further studies such as those used in the present investigation will help elucidate the role of a number of different enzymes and inhibitors in the destructive arthropathies.

Cathepsin B in gingival crevicular fluid of adult periodontitis patients: identification by immunological and enzymological methods

Cathepsin B (EC 3.4.22.1), a typical lysosomal cysteine proteinase was identified immunologically with anti-human cathepsin B antibody in inflammatory exudate, gingival crevicular fluid (GCF) of adult periodontitis patients. The sensitive enzyme immunoassay (EIA) system initially developed, was rarely influenced by the presence of endogenous cysteine proteinase inhibitors, cystatin(s), indicating that it is possible to quantify the gross amount of cathepsin B including free enzyme forms and enzyme-inhibitor complex forms using this EIA system. The cathepsin B levels in GCF as determined by EIA and the activity measured with Z-Arg-Arg-MCA showed positive and significant correlation with various clinical parameters. Immunoblotting analysis revealed that the molecular form was a 29 kDa mature enzyme. More than 95% of Z-Arg-Arg-MCA hydrolytic activity in each GCF sample was inhibited by CA-074, specific inhibitor of cathepsin B. These results strongly suggested that the gross amount of cathepsin B in GCF as well as its activity level is closely associated with the severity of the disease and that cathepsins B play an important role in the pathogenesis of periodontitis.

Arthritis in Lewis rats induced by the non-immunogenic adjuvant CP20961: an immunohistochemical analysis of the developing disease

OBJECTIVES

The role of lymphocytes and macrophages in developing adjuvant arthritis induced by an injection of CP20961 in inbred Lewis rats was studied over a 32 day period using a novel biotin-avidin immunoperoxidase histochemical technique.

METHODS

Fresh frozen sections of hind paws and spleens, as well as lymph nodes draining the site of the injected adjuvant were immunostained using a panel of monoclonal antibodies specific for subsets of lymphocytes and macrophages and for MHC Class II antigen.

RESULTS

An increase in the numbers of activated T-lymphocytes was detected early in the draining lymph nodes before hind paw swelling had begun. The presence of these cells in significant numbers was only observed in the vicinity of the joint after joint swelling and damage had begun. Macrophages were among the first cells to invade the swollen paws and later were found with T-lymphocytes and cells bearing the MHC class II antigen at the face of eroding and re-organising bone.

CONCLUSIONS

The activity of T-lymphocytes in initiating arthritis appeared to occur early in lymph nodes. Joint destruction was more closely associated with the arrival of macrophages but later arrival of T-lymphocytes may have contributed to the maintenance of chronic inflammation.