Proteoglycan degradation by the ADAMTS family of proteinases

AbstractProteoglycans are key components of extracellular matrices, providing structural support as well as influencing cellular behaviour in physiological and pathological processes. The diversity of proteoglycan function reported in the literature is equally matched by diversity in proteoglycan structure. Members of the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin motifs) family of enzymes degrade proteoglycans and thereby have the potential to alter tissue architecture and regulate cellular function. In this review, we focus on ADAMTS enzymes that degrade the lectican and small leucine-rich repeat families of proteoglycans. We discuss the known ADAMTS cleavage sites and the consequences of cleavage at these sites. We illustrate our discussion with examples from the literature in which ADAMTS proteolysis of proteoglycans makes profound changes to tissue function

High-bandwidth AFM-based rheology is a sensitive indicator of early cartilage aggrecan degradation relevant to mouse models of osteoarthritis

Murine models of osteoarthritis (OA) and post-traumatic OA have been widely used to study the development and progression of these diseases using genetically engineered mouse strains along with surgical or biochemical interventions. However, due to the small size and thickness of murine cartilage, the relationship between mechanical properties, molecular structure and cartilage composition has not been well studied. We adapted a recently developed AFM-based nano-rheology system to probe the dynamic nanomechanical properties of murine cartilage over a wide frequency range of 1 Hz to 10 kHz, and studied the role of glycosaminoglycan (GAG) on the dynamic modulus and poroelastic properties of murine femoral cartilage. We showed that poroelastic properties, highlighting fluid–solid interactions, are more sensitive indicators of loss of mechanical function compared to equilibrium properties in which fluid flow is negligible. These fluid-flow-dependent properties include the hydraulic permeability (an indicator of the resistance of matrix to fluid flow) and the high frequency modulus, obtained at high rates of loading relevant to jumping and impact injury in vivo. Utilizing a fibril-reinforced finite element model, we estimated the poroelastic properties of mouse cartilage over a wide range of loading rates for the first time, and show that the hydraulic permeability increased by a factor ~16 from k[subscript normal] = 7.80 × 10[superscript −16] ± 1.3 × 10[superscript −16] m[superscript 4]/N s to k[subscript GAG-depleted] = 1.26 × 10[superscript −14] ± 6.73 × 10[superscript −15] m[superscript 4]/N s after GAG depletion. The high-frequency modulus, which is related to fluid pressurization and the fibrillar network, decreased significantly after GAG depletion. In contrast, the equilibrium modulus, which is fluid-flow independent, did not show a statistically significant alteration following GAG depletion.National Institutes of Health (U.S.) (Grant 060331)Whitaker Foundation (Health Sciences Fund Fellowship)Arthritis Australi

Evidence for lysosomal exocytosis and release of aggrecan-degrading hydrolases from hypertrophic chondrocytes, in vitro and in vivo

The abundant proteoglycan, aggrecan, is resorbed from growth plate cartilage during endochondral bone ossification, yet mice with genetically-ablated aggrecan-degrading activity have no defects in bone formation. To account for this apparent anomaly, we propose that lysosomal hydrolases degrade extracellular, hyaluronan-bound aggrecan aggregates in growth plate cartilage, and that lysosomal hydrolases are released from hypertrophic chondrocytes into growth plate cartilage via Ca2+-dependent lysosomal exocytosis. In this study we confirm that hypertrophic chondrocytes release hydrolases via lysosomal exocytosis in vitro and we show in vivo evidence for lysosomal exocytosis in hypertrophic chondrocytes during skeletal development. We show that lysosome-associated membrane protein 1 (LAMP1) is detected at the cell surface following in vitro treatment of epiphyseal chondrocytes with the calcium ionophore, ionomycin. Furthermore, we show that in addition to the lysosomal exocytosis markers, cathepsin D and beta-hexosaminidase, ionomycin induces release of aggrecan-and hyaluronan-degrading activity from cultured epiphyseal chondrocytes. We identify VAMP-8 and VAMP7 as v-SNARE proteins with potential roles in lysosomal exocytosis in hypertrophic chondrocytes, based on their colocalisation with LAMP1 at the cell surface in secondary ossification centers in mouse tibiae. We propose that resorbing growth plate cartilage involves release of destructive hydrolases from hypertrophic chondrocytes, via lysosomal exocytosis. (C) 2012. Published by The Company of Biologists Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Share Alike License (http://creativecommons.org/licenses/by-nc-sa/3.0)

Aggrecanase Cleavage in Juvenile Idiopathic Arthritis Patients Is Minimally Detected in the Aggrecan Interglobular Domain but Robust at the Aggrecan C-Terminus

OBJECTIVE: To understand aggrecan degradation in juvenile idiopathic arthritis (JIA), the pattern and abundance of aggrecan fragments in synovial fluid aspirates from JIA patients were analysed and compared with aggrecan fragments in synovial fluids from patients with other arthritides, juvenile knee injury and a knee-healthy reference group. METHODS: The concentration of sulphated glycosaminoglycans in synovial fluid was measured by the Alcian blue precipitation assay. Aggrecan fragments were purified by dissociative CsCl density gradient centrifugation, deglycosylated and analysed by Western blot using antibodies specific for either aggrecanase-derived ARGS, SELE and KEEE neoepitopes, or the aggrecan G3-domain. RESULTS: The concentration of sulphated glycosaminoglycans in JIA synovial fluids was significantly lower compared with the levels in fluids from OA (P<0.001), juvenile knee injury (P=0.006) and knee-healthy reference (P=0.022) groups. Western blot analysis detected KEEE, SELE, and G3 fragments generated by aggrecanase cleavage in the chondroitin sulphate-rich region of JIA aggrecan. The pattern of JIA aggrecan fragments was not identical to that in synovial fluids pooled from OA patients, although there were notable similarities. Surprisingly, aggrecanase-derived ARGS fragments were barely detectable in the JIA synovial fluids, in marked contrast to the levels of ARGS fragments in OA synovial fluids. CONCLUSIONS: Aggrecanases appear to cleave minimally in the interglobular domain of aggrecan in JIA patients despite robust levels of cleavage in aggrecan's chondroitin-sulphate rich region. The results suggest that unlike other arthritides, aggrecanase cleavage in the aggrecan interglobular domain might not be a major pathogenic event in JIA. © 2012 American College of Rheumatology