Review The regulation of the ADAMTS4 and ADAMTS5 aggrecanases in osteoarthritis: a review J. Bondeson1, S. Wainwright2, C. Hughes2, B. Caterson2 1Department of Rheumatology, Cardiff ABSTRACT on aggrecan monomers, with the asso- University and 2Connective Tissue Destruction of articular cartilage is a ciated water molecules, is essential for Biology Laboratories, Cardiff School of key feature of a number of arthritides, the ability of articular cartilage to with- Biosciences, Cardiff University, Cardiff, osteoarthritis prominent among them. stand compressive deformation during UK. Aggrecan degradation, caused by joint articulation (1). The chondrocytes Jan Bondeson, MD PhD; increased activity of proteolytic en- synthetize and catabolize ECM mac- Shane Wainwright, PhD; Clare Hughes, PhD; zymes that degrade macromolecules romolecules, which in turn serve to Bruce Caterson PhD. in the cartilage extracellular matrix, maintain the homeostasis of the cel- This work has been supported by the is followed by irreversible collagen lular environment and the cartilage Arthritis Research Campaign (UK), degradation. The degradation of ag- structure. In diseases like rheumatoid grants no. W0596, 13172 and 14570. grecan is mediated by various matrix arthritis (RA) and osteoarthritis (OA), Please address correspondence to: proteinases, mainly the aggrecanases, degradation of ECM macromolecules Prof. Bruce Caterson, Connective Tissue multidomain metalloproteinases be- exceeds their synthesis, resulting in a Biology Laboratories, Cardiff School of longing to the ADAMTS (a disintegrin net decrease in the amount of cartilage Biosciences, Cardiff University, Museum and metalloproteinase with throm- matrix, eventually leading to total or Avenue, Cardiff CF10 3US, UK. bospondin motifs) family. There has partial erosion of the cartilage. The de- E-mail: [email protected] been much interest in the possible role pletion of aggrecan from articular car- Reprints will not be available from the of these aggrecanases, mainly AD- tilage, as evidenced by the release of authors. AMTS4 and ADAMTS5, as therapeutic aggrecan catabolites into the synovial Received on June 25, 2007; accepted in targets in osteoarthritis. There is still fl uid, is an essential early pathophysi- revised form on November 30, 2007. debate which of them is the major ag- ological event in OA (1-2). The aspect Clin Exp Rheumatol 2008; 26: 139-145. grecanase in osteoarthritis, however, most studied has been the proteolysis of © CopyrightCopyright CLINICAL AND as well as major issues concerning the interglobular domain of aggrecan EXPERIMENTAL RHEUMATOLOGY 2007.2007. how they are regulated, with possible with release of the glycosaminoglycan discrepancies between murine models (GAG)-attachment regions, since it ap- Key words: Aggrecanase, and results obtained using human oste- pears to be the most destructive to tissue interleukin-1, matrix metalloproteinase, oarthritis tissue. This review discusses function. NF-kappaB, osteoarthritis, tumour some recent data regarding the regula- It has been debated whether the prote- necrosis factor alpha. tion of ADAMTS4 and ADAMTS5 gene olysis of the interglobular domain of expression in osteoarthritis, with em- aggrecan is mediated by matrix met- phasis on the role of proinfl ammatory alloproteases (MMPs) or by aggreca- cytokines in driving these enzymes, and nases. The aggrecanases are members of the transcription factor NFκB inin of the family of disintegrin and metal- mediating their expression. loproteases with thrombospondin mo- tifs (ADAMTS) that were fi rst char- Introduction acterised for their ability to cleave the Cartilage consists of a relatively small Glu373-Ala374 bond in the interglobular amount of chondrocytes, embedded in domain of aggrecan (1). These enzymes abundant extracellular matrix (ECM) are regulated at multiple levels through that contains numerous macromol- control of gene expression, mRNA ecules, major constituents being col- splicing and protein processing, as lagen fi brils and the large aggregating well as regulation of the expression of proteoglycan aggrecan. Aggrecan fi lls various naturally occurring inhibitors the interstices of the collagen meshwork (3). Several ADAMTS aggrecanases by forming large aggregated complexes have been identifi ed, among them ag- interacting with hyaluronan and link grecanase-1 (ADAMTS4) and aggre- proteins. The high negative charge den- canase-2 (ADAMTS5). Recent studies Competing interests: none declared. sity of the glycosaminoglycan chains suggest that one or more aggrecanases 139 REVIEW Regulation of aggrecanases in osteoarthritis / J. Bondeson et al. are responsible for cleavage of the interglobular domain with destructive loss of GAG (4-5). ADAMTS4 and ADAMTS5 are multi-domain metallo- proteases secreted from the cell into the extracellular space as furin active pro- teases. They both consist of a catalytic metalloprotease domain and a series of other ancillary domains that play a role in regulating their activity and substrate specifi city (Fig. 1). For example, AD- AMTS4 activity for the interglobular domain cleavage site is increased when the C-terminal spacer domain is re- moved, and additional C-terminal trun- cation also leads to a preferred substrate specifi city for small leucine-rich prote- oglycans and other proteins (6). Another recent study suggests that blocking ag- grecanase cleavage in the interglobular domain of aggrecan diminished aggre- can loss and cartilage erosion in murine models of surgically induced osteoar- Fig. 1. The structure of ADAMTS4, its only known splice variant, and ADAMTS5. thritis and infl ammatory arthritis, and appeared to stimulate repair following AMTS4 gene expression could be up- We used a model to effectively and acute infl ammation (7). regulated through treatment with either specifi cally neutralise the endogenous It has long been debated which of the IL-1β, TNF-α or oncostatin M, there production of these cytokines from ADAMTSs is the main aggrecanase in was little effect on ADAMTS5 in ei- the OA synovial macrophages (18). OA. Due to observations of ADAMTS4 ther human chondrocytes or cultured Cultures were either left untreated, mRNA being inducible through in- human cartilage explants. In contrast, incubated with the p75 TNF soluble terleukin (IL)-1 in chondrocytes, this there was an additive effect of combi- receptor Ig fusion protein etanercept enzyme has attracted a good deal of at- nation treatment with oncostatin M and (Enbrel), incubated with a neutraliz- tention (8-10). But in models of murine either IL-1β or TNF-α in these sys- ing anti-IL-1β antibody, or incubated OA induced by antigen or surgical joint tems, leading to marked induction of with a combination of Enbrel and anti- destabilisation, ADAMTS4-null mice ADAMTS4 gene expression and also IL-1β. There was no effect of either did not show any protective effect on some induction of ADAMTS5 (15). In Enbrel or the neutralizing anti-IL-1β cartilage aggrecan loss compared with OA synovium or cartilage, aggrecanase antibody on ADAMTS5 expression, wild-type mice, whereas there was a activity and expression of ADAMTS4 nor was it at all affected by a combina- marked protective effect in ADAMTS5- and ADAMTS5 is present constitu- tion of these treatments (Fig. 2). Thus null mice (11-13). These studies sug- tively, without any requirement for any ADAMTS5 appears to be constitutive gest that in this model of murine degen- catabolic stimulation (15-16). in OA synovial cells. In contrast, AD- erative arthritis, ADAMTS5 plays a key To investigate the role of TNF-α, and AMTS4 was signifi cantly (p < 0.05) in- role in aggrecan degradation. The sig- IL-1 in driving ADAMTS4 and AD- hibited by Enbrel, and more potently (p nifi cance of this important fi nding for AMTS5 expression in the human OA < 0.01) inhibited by a combination of idiopathic human OA is not yet known. synovium, we used a model of cultures Enbrel and the neutralizing anti-IL-1β of synovial cells from digested OA syn- antibody (Fig. 2). This would indicate The role of proinfl ammatory ovium (17). These cells have the advan- that in the human OA synovium, the cytokines in the regulation of tage of spontaneously producing a vari- upregulation of ADAMTS4 is depend- ADAMTS4 and ADAMTS5 ety of both pro- and anti-infl ammatory ent on TNF-α and IL-1 produced by In models of cultured bovine and cytokines, including TNF-α, IL-1 and the synovial macrophages, whereas the porcine chondrocytes or cartilage IL-10, as well as the major MMPs and level of ADAMTS5 is not changed by explants, ADAMTS4 is induced fol- TIMPs. By means of specifi c neutrali- these cytokines (18). lowing stimulation with IL-1, tumour zation of macrophage-produced TNF-α In contrast to this wealth of data from necrosis factor (TNF)α, oncostatin M and IL-1, it was possible to assess the human, porcine and bovine models or transforming growth factor β, but contribution of these two proinfl amma- indicating that ADAMTS4 mRNA re- ADAMTS5 is not (8-10,14). A recent tory cytokines on ADAMTS4 and AD- sponds to IL-1, there are two recent study (15) indicated that although AD- AMTS5 gene expression. papers indicating that this is not the 140 Regulation of aggrecanases in osteoarthritis / J. Bondeson et al. REVIEW A ADAMTS5 gene expression has also ADAMTS4 become clearer. ADAMTS4, but not ADAMTS5, has several NFκB binding sites on its 5’ fl anking region that are ADAMTS5 conserved between species (22). In bo- Patient 1 vine chondrocytes, ADAMTS4, but not GAPDH ADAMTS5, could be upregulated by IL- 1 stimulation (Fig. 3A). Using a model of transfecting bovine chondrocytes with the 5’ fl anking region of the AD- ADAMTS4 AMTS4 or ADAMTS5 gene luciferase receptor vector, it was observed that the IL-1-induced upregulation of the AD- Patient 2 ADAMTS5 AMTS4 gene involved its 5’ fl anking GAPDH region, whereas the 5’ fl anking region of the ADAMTS5 gene played no part (Fig. 3B). Mutation of any one of the three identifi ed NFκB binding sites re- sulted in the loss of the IL-1 response to the ADAMTS4 gene luciferase reporter B vector (Fig.