ADAMTS-9 in Mouse Cartilage Has Aggrecanase Activity That Is Distinct from ADAMTS-4 and ADAMTS-5.

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5 are the principal aggrecanases in mice and humans; however, mice lacking the catalytic domain of both enzymes (TS-4/5∆cat) have no skeletal phenotype, suggesting there is an alternative aggrecanase for modulating normal growth and development in these mice. We previously identified aggrecanase activity that (a) cleaved at E↓G rather than E↓A bonds in the aggrecan core protein, and (b) was upregulated by retinoic acid but not IL-1α. The present study aimed to identify the alternative aggrecanase. Femoral head cartilage explants from TS-4/5∆cat mice were stimulated with IL-1α or retinoic acid and total RNA was analysed by microarray. In addition to ADAMTS-5 and matrix metalloproteinase (MMP)-13, which are not candidates for the novel aggrecanase, the microarray analyses identified MMP-11, calpain-5 and ADAMTS-9 as candidate aggrecanases upregulated by retinoic acid. When calpain-5 and MMP-11 failed to meet subsequent criteria, ADAMTS-9 emerged as the most likely candidate for the novel aggrecanase. Immunohistochemistry revealed ADAMTS-9 expression throughout the mouse growth plate and strong expression, particularly in the proliferative zone of the TS-4/5-∆cat mice. In conclusion, ADAMTS-9 has a novel specificity for aggrecan, cleaving primarily at E↓G rather than E↓A bonds in mouse cartilage. ADAMTS-9 might have more important roles in normal skeletal development compared with ADAMTS-4 and ADAMTS-5, which have key roles in joint pathology.

Mast cell-restricted, tetramer-forming tryptases induce aggrecanolysis in articular cartilage by activating matrix metalloproteinase-3 and -13 zymogens.

Mouse mast cell protease (mMCP)-6-null C57BL/6 mice lost less aggrecan proteoglycan from the extracellular matrix of their articular cartilage during inflammatory arthritis than wild-type (WT) C57BL/6 mice, suggesting that this mast cell (MC)-specific mouse tryptase plays prominent roles in articular cartilage catabolism. We used ex vivo mouse femoral head explants to determine how mMCP-6 and its human ortholog hTryptase-ß mediate aggrecanolysis. Exposure of the explants to recombinant hTryptase-ß, recombinant mMCP-6, or lysates harvested from WT mouse peritoneal MCs (PMCs) significantly increased the levels of enzymatically active matrix metalloproteinases (MMP) in cartilage and significantly induced aggrecan loss into the conditioned media, relative to replicate explants exposed to medium alone or lysates collected from mMCP-6-null PMCs. Treatment of cartilage explants with tetramer-forming tryptases generated aggrecan fragments that contained C-terminal DIPEN and N-terminal FFGVG neoepitopes, consistent with MMP-dependent aggrecanolysis. In support of these data, hTryptase-ß was unable to induce aggrecan release from the femoral head explants obtained from Chloe mice that resist MMP cleavage at the DIPEN↓FFGVG site in the interglobular domain of aggrecan. In addition, the abilities of mMCP-6-containing lysates from WT PMCs to induce aggrecanolysis were prevented by inhibitors of MMP-3 and MMP-13. Finally, recombinant hTryptase-ß was able to activate latent pro-MMP-3 and pro-MMP-13 in vitro. The accumulated data suggest that human and mouse tetramer-forming tryptases are MMP convertases that mediate cartilage damage and the proteolytic loss of aggrecan proteoglycans in arthritis, in part, by activating the zymogen forms of MMP-3 and MMP-13, which are constitutively present in articular cartilage.

Changes in versican and chondroitin sulfate proteoglycans during structural development of the lung.

We have examined whether changes in versican levels, or in the sulfation pattern of its chondroitin sulfate (CS) side chains, are associated with the reduction in perialveolar tissue volumes that characterize lung maturation in late-gestation fetal sheep. Lung tissue was collected from fetuses [90-142 days gestational age (GA)] and lambs (2 wk after term birth). The level and distribution of versican and CS glycosaminoglycans (GAG) were determined using immunohistochemistry, whereas fluorophore-assisted carbohydrate electrophoresis was used to determine changes in CS sulfation patterns. Versican was the predominant CS-containing proteoglycan in the lung and decreased from 19.9 +/- 2.7 arbitrary units at 90 days GA to 6.0 +/- 0.5 arbitrary units at 142 days GA, in close association (P < 0.05) with the reduction in tissue volumes (from 66.0 +/- 4.6 to 25.3 +/- 1.5% at 142 days); similar reductions occurred for both chondroitin-6-sulfate and chondroitin-4-sulfate CS side chains. Hyaluronic acid levels decreased from 3,168 +/- 641 pmol/microg GAG at 90 days GA to 126 +/- 9 pmol/microg GAG at 142 days GA, and the predominant sulfated disaccharide changed from Delta-di-6S at 90 days GA to Delta-di-4S at term. These data indicate that structural development of the lung is closely associated with marked changes in versican levels and the microstructure of CS side chains in perisaccular/alveolar lung tissue.

ADAMTS5 is the major aggrecanase in mouse cartilage in vivo and in vitro.

Aggrecan is the major proteoglycan in cartilage, endowing this tissue with the unique capacity to bear load and resist compression. In arthritic cartilage, aggrecan is degraded by one or more 'aggrecanases' from the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family of proteinases. ADAMTS1, 8 and 9 have weak aggrecan-degrading activity. However, they are not thought to be the primary aggrecanases because ADAMTS1 null mice are not protected from experimental arthritis, and cleavage by ADAMTS8 and 9 is highly inefficient. Although ADAMTS4 and 5 are expressed in joint tissues, and are known to be efficient aggrecanases in vitro, the exact contribution of these two enzymes to cartilage pathology is unknown. Here we show that ADAMTS5 is the major aggrecanase in mouse cartilage, both in vitro and in a mouse model of inflammatory arthritis. Our data suggest that ADAMTS5 may be a suitable target for the development of new drugs designed to inhibit cartilage destruction in arthritis, although further work will be required to determine whether ADAMTS5 is also the major aggrecanase in human arthritis.