Enhanced breakdown of bovine articular cartilage proteoglycans by conditioned synovial medium in vitro. The effect of glucocorticoids and protein synthesis inhibitors

Interleukin-1 stimulates the secretion of proteoglycan- and collagen-degrading proteases by rabbit articular chondrocytes

Supernatants from the P388D1 murine macrophage cell line as well as commercially prepared human interleukin-1 (IL-1) stimulated primary rabbit articular chondrocytes to produce collagen- and proteoglycan-degrading proteases. The P388D1-derived factor had a molecular weight of 16,000-20,000 and a pI of 4.5-5.0, and was sensitive to phenylglyoxal treatment. Human IL-1 and the P388D1 supernatants enhanced glycosaminoglycan (GAG) release from bovine nasal cartilage explants. The proteoglycan- and collagen-degrading proteases required Ca2+ for activity. Latent proteoglycanase and collagenase had molecular weights of 44,000-56,500 and 34,000-44,000, respectively. The activated proteases had molecular weights of 30,000-40,000 and 22,000-36,000, respectively. Heparin-Sepharose affinity chromatography yielded two latent proteoglycanase-degrading protease activities and a collagen-degrading peak. The two proteoglycanase peaks also degraded fibronectin, laminin, gelatin, and azocoll but not type I collagen. The collagenase peak also degraded proteoglycan, gelatin, fibronectin, laminin, and azocoll. The activity of the proteoglycan- and collagen-degrading peaks was inhibited by phenanthroline and alpha 2-macroglobulin but not by phenylmethylsulfonylfluoride (PMSF), tosyllysylchloromethylketone (TLCK), pepstatin, or alpha 1-antitrypsin. The control of factors which augment protease production may offer a novel therapeutic approach to arthritis.

Chondrocyte-mediated depletion of articular cartilage proteoglycans in vitro

The degradation of proteoglycan was examined in cultured slices of pig articular cartilage. Pig leucocyte catabolin (10 ng/ml) was used to stimulate the chondrocytes and induce a 4-fold increase in the rate of proteoglycan loss from the matrix for 4 days. Material in the medium of both control and depleted cultures was mostly a degradation product of the aggregating proteoglycan. It was recovered as a very large molecule slightly smaller than the monomers extracted with 4M-guanidinium chloride and lacked a functional hyaluronate binding region. The size and charge were consistent with a very limited cleavage or conformational change of the core protein near the hyaluronate binding region releasing the C-terminal portion of the molecule intact from the aggregate. The 'clipped' monomer diffuses very rapidly through the matrix into the medium. The amount of proteoglycan extracted with 4M-guanidinium chloride decreased during culture from both the controls and depleted cartilage, and the average size of the molecules initially remained the same. However, the proportion of molecules with a smaller average size increased with time and was predominant in explants that had lost more than 70% of their proteoglycan. All of this material was able to form aggregates when mixed with hyaluronate, and glycosaminoglycans were the same size and charge as normal, indicating either that the core protein had been cleaved in many places or that larger molecules were preferentially released. A large proportion of the easily extracted and non-extractable proteoglycan remained in the partially depleted cartilage and the molecules were the same size and charge as those found in the controls. There was no evidence of detectable glycosidase activity and only very limited sulphatase activity. A similar rate of breakdown and final distribution pattern was found for newly synthesized proteoglycan. Increased amounts of latent neutral metalloproteinases and acid proteinase activities were present in the medium of depleted cartilage. These were not thought to be involved in the breakdown of proteoglycan. Increased release of proteoglycan ceased within 24h of removal of the catabolin, indicating that the effect was reversible and persisted only while the stimulus was present.

Effect of indomethacin and hydrocortisone upon joint tissue in vitro. Incorporation of [35S]sulphate into chondrocyte proteoglycans

It has previously been shown that products from the synovial tissue influence the behaviour of the chondrocyte in such a way that, not only is the degradation enhanced, but the synthesis of cartilage proteoglycans too is inhibited. In the case of cartilage degradation, these cellular interactions within the joint tissues have been shown to be partly modulated by arachidonic acid metabolites. The experiments reported here show that these cellular interactions cannot be completely ruled out in the case of cartilage synthesis either. Conditioned medium from synovial tissue (control SM) reduced the incorporation of [35S]sulphate into the monolayer cultures of chondrocytes. This reduction was not affected with the simultaneous addition of indomethacin (1.4 X 10(-6) mol/l) to the chondrocyte cultures. However, conditioned synovial medium from synovial tissue that had been cultured with indomethacin (1.4 X 10(-5) mol/l) enhanced radiosulphate incorporation, somewhat, as compared with control SM. Control SM together with hydrocortisone (2.2 X 10(-8) mol/l, 2.2 X 10(-7) mol/l, 2.2 X 10(-6) mol/l) reduced radiosulphate incorporation into the chondrocyte cultures in a dose-dependent manner. Conditioned synovial medium from synovial tissue that had been cultured with hydrocortisone (2.2 X 10(-8) mol/l, 2.2 X 10(-7) mol/l, 2.2 X 10(-6) mol/l) enhanced radiosulphate incorporation, as compared with control SM.

Continuous mechanical pressure and joint tissue. Effect of synovial membrane products and indomethacin in vitro

We have previously reported that a continuous mechanical pressure of approximately 30 kgfcm-2 greatly inhibited the degradation of articular proteoglycans in calves. In the present report it is shown that indomethacin (5 micrograms/ml) failed to inhibit cartilage degradation caused by mechanical pressure. It is therefore suggested that prostaglandins do not mediate the inhibition of cartilage degradation exerted by continuous mechanical pressure. We have also reported previously that bovine-conditioned synovial medium (SM) greatly enhances the degradation of calf articular cartilage proteoglycans. We now show that the catabolic activity of SM was greatly (but not entirely) inhibited by the application of a continuous mechanical pressure. Simultaneous addition of indomethacin (5 micrograms/ml) to the cartilage cultures did not affect this result. However, the addition of indo-SM (SM from synovial tissue cultured in the presence of 5 micrograms/ml indomethacin) to cartilage cultures subjected to continuous mechanical pressure did not increase cartilage degradation, compared with the addition of DMEM alone. A hypothesis is proposed that continuous mechanical pressure may cause a change in the state of synovial factor receptors on the membranes of chondrocytes.