Blocking aggrecanase cleavage in the aggrecan interglobular domain abrogates cartilage erosion and promotes cartilage repair
Christopher B. Little, … , Susan M. Smith, Amanda J. Fosang
Christopher B. Little, … , Susan M. Smith, Amanda J. Fosang
Published June 1, 2007
Citation Information: J Clin Invest. 2007;117(6):1627-1636. https://doi.org/10.1172/JCI30765.
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Blocking aggrecanase cleavage in the aggrecan interglobular domain abrogates cartilage erosion and promotes cartilage repair

Abstract

Aggrecan loss from cartilage in arthritis is mediated by aggrecanases. Aggrecanases cleave aggrecan preferentially in the chondroitin sulfate–2 (CS-2) domain and secondarily at the E373↓374A bond in the interglobular domain (IGD). However, IGD cleavage may be more deleterious for cartilage biomechanics because it releases the entire CS-containing portion of aggrecan. Recent studies identifying aggrecanase-2 (ADAMTS-5) as the predominant aggrecanase in mouse cartilage have not distinguished aggrecanolysis in the IGD from aggrecanolysis in the CS-2 domain. We generated aggrecan knockin mice with a mutation that rendered only the IGD resistant to aggrecanases in order to assess the contribution of this specific cleavage to cartilage pathology. The knockin mice were viable and fertile. Aggrecanase cleavage in the aggrecan IGD was not detected in knockin mouse cartilage in situ nor following digestion with ADAMTS-5 or treatment of cartilage explant cultures with IL-1α. Blocking cleavage in the IGD not only diminished aggrecan loss and cartilage erosion in surgically induced osteoarthritis and a model of inflammatory arthritis, but appeared to stimulate cartilage repair following acute inflammation. We conclude that blocking aggrecanolysis in the aggrecan IGD alone protects against cartilage erosion and may potentiate cartilage repair.

Authors

Christopher B. Little, Clare T. Meeker, Suzanne B. Golub, Kate E. Lawlor, Pamela J. Farmer, Susan M. Smith, Amanda J. Fosang

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Figure 2

G1 fragments in Jaffa and wild-type cartilage extracts.

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G1 fragments in Jaffa and wild-type cartilage extracts. (A) The domain s...
(A) The domain structure of the aggrecan core protein, with 2 N-terminal globular domains, G1 and G2, and a C-terminal G3 domain. The extended region between G2 and G3 is heavily substituted with CS chains (wavy lines). Aggrecanase and MMP cleavage site sequences in the mouse IGD and CS-2 domains are shown, and amino acids that are different in human aggrecan are shown above. Numbering corresponds with the mouse sequence. (B) Cartilage extracts from wild-type and Jaffa mice were analyzed for VTEGE373 or DIPEN341 neoepitopes. (C) Dialyzed extracts of equal cartilage wet weight from wild-type and Jaffa mice were digested with or without recombinant human ADAMTS-5 and analyzed for the VTEGE373 and 374ALGSV neoepitopes. Stripping and reprobing the membranes with monoclonal antibody 2B6 confirmed sample loading in each lane (data not shown).