Neutral Proteases and Cathepsin D in Human Articular Cartilage

Sapolsky, Asher I.; Howell, David S.; Woessner, Jeff

doi:10.1172/jci107641

Cited by 100 publications

(34 citation statements)

References 31 publications

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“…Methods have previously been published for the assay on a microscale of hemoglobin digestion by cathepsin D (3), and casein and histone digestion at neutral pH by cartilage extracts (6).…”

Section: Methodsmentioning

confidence: 99%

Metalloproteases of human articular cartilage that digest cartilage proteoglycan at neutral and acid pH.

Sapolsky¹,

Keiser²,

Howell³

et al. 1976

J. Clin. Invest.

151

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A B S T R A C T Extracts of human articular cartilage contain proteases capable of degrading the proteoglycan component of cartilage matrix at neutral and acid pH. These enzymes have been partially purified by ion exchange chromatography and characterized by disc electrophoresis, inhibition patterns, and action on proteoglycan. Three distinct metalloproteases are described. A neutral protease that digests proteoglycan subunit optimally at pH 7.25 has been purified up to 900-fold. It is strongly inhibited by o-phenanthroline, a-2-macroglobulin, and egg white, and to a lesser extent by D-penicillamine and EDTA. Inhibition by chelating agents is reversed by cobalt, zinc, and ferrous ions. Two acid metalloproteases, distinct from cathepsins Bi, D, and F, digest proteoglycan subunit at pH 4.5 and 5.5. Both are inhibited by o-phenanthroline and activity is restored by cobalt, zinc, or ferrous ions. With electron microscopy, it was found that cartilage slices were depleted of ruthenium red-staining matrix proteoglycan after incubation in vitro with a partially purified cartilage extract at neutral pH. Sedimentation, gel chromatography, sodium dodecyl sulfate-gel electrophoresis, and immunodiffusion studies of digests of isolated proteoglycan fraction produced by the partially purified cartilage extract at neutral and acid pH confirmed that the cartilage enzymes act only on the protein component of proteoglycan subunit, producing fragments with 5 to 12 chondroitin sulfate chains. The link proteins were not digested.

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“…Methods have previously been published for the assay on a microscale of hemoglobin digestion by cathepsin D (3), and casein and histone digestion at neutral pH by cartilage extracts (6).…”

Section: Methodsmentioning

confidence: 99%

Metalloproteases of human articular cartilage that digest cartilage proteoglycan at neutral and acid pH.

Sapolsky¹,

Keiser²,

Howell³

et al. 1976

J. Clin. Invest.

151

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show abstract

“…The effect of enzymes on articular cartilage has been widely studied. Neutral protease (3)(4)(5)(6)(7), acid protease (4,6,(8)(9)(10), lysozyme (1 l), and collagenase (12-14) have been implicated in the erosive process. Acid protease (cathepsin D) (15) has been shown to be present in increased amounts in rheumatoid articular cartilage.…”

mentioning

confidence: 99%

Surface Ultrastructure of Rheumatoid Articular Cartilage

Kimura

Tateishi

Ziff

1977

Arthritis & Rheumatism

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Six rheumatoid articular cartilage specimens, which appeared grossly normal and were shown to be free of pannus when examined under the light microscope, were examined electron microscopically. For comparison, normal‐appearing cartilage specimens from 2 patients with meniscus injury and 2 with degenerative joint disease (DJD) were also examined. In all cases the normal‐appearing joint surface of rheumatoid cartilage was abnormal. Amorphous‐appearing material was present to a depth varying between 6 and 25 m̈m. Some of this material had the appearance of fibrin deposited at the cartilage surface, but much appeared to represent breakdown products of the cartilage matrix, i.e. degraded collagen and proteoglycan. DJD cartilage did not show similar changes. The findings suggest that the surface of rheumatoid articular cartilage, even when grossly normal in appearance, is degraded by enzymes either present in the synovial fluid or released by polymorphonuclear cells in close contact with the cartilage surface.

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“…However the possibility that chondrocytes are involved in matrix degradation cannot be ruled o u t (25).…”

Section: Discussionmentioning

confidence: 99%

“…T h e pH of the inflamed synovial exudate was again found t o be neutral, and the function of cathepsin D remains obscure. It has been suggested that its action may be confined t o intracellular digestion (25).…”

Section: Discussionmentioning

confidence: 99%