Evidence that the inhibition of cartilage proteoglycan breakdown by mannosamine is not mediated via inhibition of glycosylphosphatidylinositol anchor formation.

The effect of mannosamine, an inhibitor of glycosylphosphatidylinositol (GPI) anchor formation, on chondrocyte-mediated cartilage proteoglycan breakdown was investigated using cartilage explant cultures. Mannosamine inhibited interleukin 1alpha-, tumour necrosis factor alpha- and retinoic acid-stimulated proteoglycan release from bovine nasal and articular cartilage, and retinoic acid-stimulated proteoglycan release from human cartilage. Its effects on two GPI-anchored proteins [the urokinase receptor, which binds urokinase-type plasminogen activator (uPA) to cell surfaces, and alkaline phosphatase] were also studied using bovine chondrocytes. Enzyme histochemistry and zymography demonstrated cell-associated uPA-like serine proteinase activity and PA activity respectively which was not reduced by treatment of chondrocytes with mannosamine at concentrations effective at inhibiting cartilage proteoglycan breakdown. Similarly, the activity of cell-associated alkaline phosphatase was not reduced, except at mannosamine concentrations much higher than those used to inhibit proteoglycan breakdown. These results demonstrate that inhibition of proteoglycan breakdown by mannosamine is too potent to be explained by an effect on GPI-anchor formation.

Retinoic acid-induced type II collagen degradation does not correlate with matrix metalloproteinase activity in cartilage explant cultures.

OBJECTIVE: To determine the role of matrix metalloproteinases (MMPs) in retinoic acid (RetA)-induced degradation of type II collagen in cartilage. METHODS: Bovine nasal cartilage explants were cultured with 1 microM RetA or in 3 nM interleukin-1alpha (IL-1alpha). Release of proteoglycan and type II collagen into the medium was measured by colorimetric assay and immunoassay, respectively. MMP activity in the medium was determined using a quenched fluorescent substrate assay, while specific collagenases were identified by Western immunoblotting. In some cases the effects of low molecular mass synthetic MMP inhibitors and serum on collagen degradation were studied. RESULTS: RetA promoted maximal breakdown of type II collagen after 4 or 5 weeks in culture, compared with 3 weeks in culture with IL-1alpha. In IL-1alpha-stimulated cultures, collagen degradation was coincident with a large increase in MMP activity in the culture medium, whereas in RetA-stimulated cultures, there was only a small increase. In Western immunoblots of culture media containing RetA, prointerstitial collagenase and active collagenase 3 were sometimes detected, but not in all experiments. In IL-1alpha cultures, active interstitial collagenase was always detected, and active collagenase 3 was detectable in some experiments. Neutrophil collagenase was not detected in any cultures. IL-1alpha-stimulated collagen degradation was effectively inhibited by a potent, broad-spectrum inhibitor of MMPs, whereas it was poorly inhibited by a weak MMP inhibitor. The same 2 compounds were both only weak inhibitors of RetA-induced collagen degradation. When fetal calf serum was included in cartilage cultures, MMP activity in the culture medium was reduced to low levels. This resulted in a marked inhibition of IL-1alpha-induced type II collagen degradation, whereas there was no inhibition of RetA-induced collagen degradation. CONCLUSION: Unlike IL-1alpha, RetA induces degradation of type II collagen in cartilage explants by a mechanism that is mainly independent of those MMPs that can be detected in the culture medium.

Stromelysin 1, neutrophil collagenase, and collagenase 3 do not play major roles in a model of chondrocyte mediated cartilage breakdown.

AIMS: To determine the collective roles of stromelysin 1, neutrophil collagenase, and collagenase 3 in chondrocyte mediated cartilage proteoglycan and type II collagen degradation in tissue culture model systems. METHODS: Bovine nasal cartilage explants were cultured with and without recombinant human interleukin 1 alpha (IL-1 alpha), recombinant human tumour necrosis factor alpha, or retinoic acid. Proteoglycan and type II collagen release were determined by colorimetric assay and immunoassay, respectively, in the absence and presence of matrixin inhibitors. Potential toxic effects of the inhibitors were assessed by measuring rates of glycolysis. RESULTS: Loss of proteoglycan and type II collagen from nasal cartilage was inhibited by batimastat, a broad spectrum matrixin inhibitor. BB-3437, a selective inhibitor of stromelysin, neutrophil collagenase, and collagenase 3, at the concentrations used in this study, showed a weak but dose dependent inhibitory effect on the IL-1 stimulated degradation of type II collagen, but had virtually no effect on proteoglycan breakdown. Neither inhibitor affected rates of glycolysis. CONCLUSIONS: Stromelysin 1, neutrophil collagenase, and collagenase 3 are unlikely to contribute to chondrocyte mediated proteoglycan degradation in our model system. The modest effect of a selective inhibitor of these enzymes on IL-1 stimulated collagen breakdown suggests a minor role for one or more of these proteinases; potent inhibition by an inhibitor of interstitial collagenase and the gelatinases suggests that these enzymes play a major role in IL-1 stimulated, chondrocyte mediated type II collagen breakdown from nasal cartilage.

Degradation of type II collagen, but not proteoglycan, correlates with matrix metalloproteinase activity in cartilage explant cultures.

OBJECTIVE: To determine the contribution of certain matrix metalloproteinases (MMPs) to the degradation of proteoglycan and type II collagen in cartilage. METHODS: Bovine nasal and articular cartilage explants were cultured with recombinant human interleukin-1 alpha (IL-1 alpha) for up to 4 weeks. Release of proteoglycan and type II collagen into the medium was determined by colorimetric assay and immunoassay, respectively. The activity of MMPs in the medium was assayed using a quenched fluorescent substrate, as well as with a collagen fibril assay, by zymography, and in Western immunoblots. In some experiments, the effects of specific MMP inhibitors on type II collagen degradation were studied. RESULTS: In cultures of nasal cartilage with IL-1 alpha, almost all the proteoglycan was released within the first week, whereas there was no detectable release of type II collagen for the first 2 weeks of culture. A rapid period of almost complete dissolution of the collagen occurred in the third or fourth week. MMP activity measured using a quenched fluorescent substrate was negligible during the first 2 weeks of culture but was substantially increased in the third week of culture, at the time of collagen degradation. Similarly, there was a large increase in collagenolytic activity (by collagen fibril assay) and gelatinolytic activity (by zymography) during the third week of culture. Articular cartilage cultured with IL-1 alpha lost proteoglycan progressively during the 4-week period; however, there was no loss of type II collagen from the matrix in that time and no significant increase in MMP activity. The loss of type II collagen from nasal cartilage stimulated with IL-1 alpha was inhibited by BB87, an inhibitor of both collagenases and gelatinases, and by BB3003, a selective inhibitor of gelatinase A. In Western immunoblots, procollagenase and active interstitial collagenase could be readily detected in nasal cartilage cultures. Some procollagenase 3 and active collagenase 3 was also shown to be present. CONCLUSION: MMP activity correlates with degradation of type II collagen, but not proteoglycan, in cartilage cultures. Interstitial collagenase, collagenase 3, and gelatinases are all likely to contribute to cleavage and removal of collagen from the cartilage matrix. The proteinase(s) responsible for aggrecan breakdown remains unclear.

Effects of growth factors and interleukin-1 alpha on proteoglycan and type II collagen turnover in bovine nasal and articular chondrocyte pellet cultures.

The aim of this study was to investigate the effects of insulin-like growth factor-I, transforming growth factor-beta (TGF-beta), and interluekin-1 alpha (IL-1 alpha) on the deposition and degradation of a cartilage-like matrix in high-density pellet cultures of adult bovine chondrocytes. Proteoglycan was determined by toluidine blue staining and colorimetric assay. Type II collagen was determined by immunohistochemical staining and its unwinding in situ by a recently developed immunoassay. Bovine nasal chondrocytes cultured as pellets deposited a well-organized extracellular matrix of proteoglycan and type II collagen. Insulin-like growth factor-I (2-10 ng/ml) increased the synthesis and incorporation into the matrix of both these proteins. TGF-beta (2-10 ng/ml) also increased proteoglycan synthesis. However it inhibited proteoglycan deposition, presumably through increased degradation of the molecule, as shown by increased release of aggrecan fragments into the tissue culture medium. TGF-beta had no effect on type II collagen deposition. In pellet cultures of bovine nasal or articular chondrocytes, 20 ng/ml IL-1 alpha induced a significant degradation of both proteoglycan and type II collagen. The effect on collagen clearly involved proteolytic cleavage of its triple helix because there was an increase in the proportion of unwound type II collagen in the matrix, as well as a loss of total type II collagen. In explant cultures of intact bovine articular cartilage, incubation with 50 ng/ml IL-1 alpha stimulated significant degradation of the proteoglycan but no degradation of the type II collagen. These results demonstrate that although the articular chondrocytes are capable of degrading type II collagen when isolated, they do not do so in situ, presumably because of some inherent property of the mature extracellular matrix. This study demonstrates the utility of pellet cultures when investigating chondrocyte-mediated turnover of cartilage matrix and its modulation by cytokines and growth factors.