α2-Macroglobulin Is a Novel Substrate for ADAMTS-4 and ADAMTS-5 and Represents an Endogenous Inhibitor of These Enzymes

Abstract

Osteoarthritis is characterized by the loss of aggrecan and collagen from the cartilage extracellular matrix. The proteinases responsible for the breakdown of cartilage aggrecan include ADAMTS-4 (aggrecanase 1) and ADAMTS-5 (aggrecanase 2). Post-translational inhibition of ADAMTS-4/-5 activity may be important for maintaining normal homeostasis of aggrecan metabolism, and thus, any disruption to this inhibition could lead to accelerated aggrecan breakdown. To date TIMP-3 (tissue inhibitor of matrix metalloproteinases-3) is the only endogenous inhibitor of ADAMTS-4/-5 that has been identified. In the present studies we identify Loss of aggrecan from the cartilage extracellular matrix is an early and sustained feature of osteoarthritis (OA).1 Aggrecan, the major proteoglycan in cartilage, consists of a protein backbone of 210 -250 kDa containing 3 globular domains referred to as G1 (located at the N terminus), followed by G2 and G3 (located at the C terminus) (1). Attached to the core protein between G2 and G3 are the glycosaminoglycans, chondroitin sulfate, and keratan sulfate. The chondroitin sulfate chains (100 -125 per monomer) are located in the C-terminal portion of the core protein, whereas the keratan sulfate chains (25-50 per monomer) are preferentially located toward the N terminus (2). Multiple aggrecan monomers interact with hyaluronic acid via their G1 domain to form aggregates of very high molecular weight. The negatively charged glycosaminoglycan chains are responsible for the extremely high osmotic swelling pressure of cartilage, which is counteracted by the resistance of type II collagen fibers (the other major macromolecule of cartilage). Thus, aggrecan provides cartilage with the ability to resist compressive forces, and its loss will have a severe effect upon the functionality of the cartilage.The cleavage of cartilage aggrecan in OA has been attributed primarily to aggrecanase 1 and 2 (3-9). These enzymes are metalloproteinases that belong to the a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family and have been designated ADAMTS-4 and ADAMTS-5, respectively. Both enzymes cleave the core protein of aggrecan after the amino acids Glu 373 , Glu 1545 , Glu 1714 , Glu 1819 , and Glu 1919(human sequence) (10, 11). Because of their preference for cleaving at the C terminus of glutamic acid, these enzymes have been referred to as glutamyl endopeptidases (12). In fact, it has been shown that ADAMTS-4 can cleave other chondroitin sulfate proteoglycans, including brevican and versican after Glu 393 and Glu 441 , respectively (13-15). Tight regulation of aggrecanase activity is critical for maintaining a fine balance between aggrecan anabolism and catabolism. In diseases such as OA the balance is disturbed in favor of catabolism, and this could be attributed to de novo synthesis of ADAMTS-4 (9, 16) and/or post-translational activation of 18). Another control mechanism for aggrecan catabolism may involve endogenous inhibitors of the aggrecanases. Recently it has been shown that t...

BEHAB/brevican requires ADAMTS-mediated proteolytic cleavage to promote glioma invasion

“…Current evidence strongly suggests ADAMTS-4 (aggrecanase-1) and ADAMTS-5 (aggrecanase-2) as the most likely candidates, which are also upregulated in gliomas [36,51,52]. These two proteases also cleave two other members of the lectican family, aggrecan [53] and versican [54], and have a restricted additional spectrum of ECM substrates [55][56][57]. Other members of the ADAMTS family have been shown or proposed to have aggrecanase activity (recently reviewed in [58]) but their expression in the CNS is low and there is currently no evidence for their role in B/b processing in gliomas [59][60][61][62][63].…”

Discovery and Characterization of a Novel, Widely Expressed Metalloprotease, ADAMTS10, and Its Proteolytic Activation

“…5C). Cleavage of ␣ 2 -M within its bait region results in the entrapment of the cleaving protease in an irreversible complex with this protease inhibitor (34). Thus, an apparent size shift of myc-tagged ADAMTS10 is observed under nonreducing conditions, indicating cleavage of the inhibitor and entrapment of the enzyme (Fig.…”

Increased serum ADAMTS-4 in knee osteoarthritis: a potential indicator for the diagnosis of osteoarthritis in early stages

“…Mice with a double-knockout of ADAMTS-4 and ADAMTS-5 were physiologically normal animals in which OA was prevented (Majumdar et al, 2007). a 2 -Macroglobulin is an endogenous inhibitor of ADAMTS-4 and ADAMTS-5 (Tortorella et al, 2004). Fibroblast growth factor 2 is an intrinsic chondroprotective agent that suppresses ADAMTS-5 and delays cartilage degradation in murine OA (Chia et al, 2009).…”