Increased type II collagen cleavage by cathepsin K and collagenase activities with aging and osteoarthritis in human articular cartilage

Valeria M Dejica,John S Mort,David J Zukor,Michael Tanzer,A Robin Poole,John Antoniou,Sheila Laverty

doi:10.1186/ar3839

Abstract

IntroductionThe intra-helical cleavage of type II collagen by proteases, including collagenases and cathepsin K, is increased with aging and osteoarthritis (OA) in cartilage as determined by immunochemical assays. The distinct sites of collagen cleavage generated by collagenases and cathepsin K in healthy and OA human femoral condylar cartilages were identified and compared.MethodsFixed frozen cartilage sections were examined immunohistochemically, using antibodies that react with the collagenase-generated cleavage neoepitopes, C2C and C1,2C, and the primary cleavage neoepitope (C2K) generated in type II collagen by the action of cathepsin K and possibly by other proteases, but not by any collagenases studied to date.ResultsIn most cases, the staining patterns for collagen cleavage were similar for all three epitopes: weak to moderate mainly pericellular staining in non-OA cartilage from younger individuals and stronger, more widespread staining in aging and OA cartilages that often extended from the superficial to the mid/deep zone of the tissue. In very degenerate OA specimens, with significant disruption of the articular surface, staining was distributed throughout most of the cartilage matrix.ConclusionsCleavage of collagen by proteases usually arises pericellularly around chondrocytes at and near the articular surface, subsequently becoming more intense and extending progressively deeper into the cartilage with aging and OA. The close correspondence between the distributions of these products suggests that both collagenases and cathepsin K, and other proteases that may generate this distinct cathepsin K cleavage site, are usually active in the same sites in the degradation of type II collagen.

Highlights

The intra-helical cleavage of type II collagen by proteases, including collagenases and cathepsin K, is increased with aging and osteoarthritis (OA) in cartilage as determined by immunochemical assays
Articular chondrocytes express collagenases (MMP-1, 8, 13 and 14) that belong to the matrix metalloproteinase (MMP) family and the cysteine protease cathepsin K, both of which are capable of cleaving the triple helical region of type II collagen at specific and distinct sites [8,12]
The monoclonal antibody is specific for type II collagen since it only recognizes the C2C neoepitope that resides at the Cterminus of the TCA fragment produced by cleavage of type II collagen a1 monomer by collagenases [14]; whereas, the polyclonal antibody recognizes the shorter neoepitope, which results from secondary cleavage generating the C1,2C epitope and is found in both type II and type I collagen [2]

Summary

Introduction

The intra-helical cleavage of type II collagen by proteases, including collagenases and cathepsin K, is increased with aging and osteoarthritis (OA) in cartilage as determined by immunochemical assays. Cathepsin K, on the other hand, is known to cleave Col II extrahelical regions (telopeptides), resulting in fibril depolymerization, and the triplehelical region, for example, at a site located 58 residues from the N-terminus of the triple helix [8] (Figure 1). This cleavage pattern is considered unique among other proteases and it does not depend on previous destabilization of the triple helix. Collagenases, such as MMP13, do not generate this cleavage [4]

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