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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Externalization of calpain (calcium-dependent neutral cysteine proteinase) in human arthritic cartilage.

OBJECTIVE: Calcium-dependent neutral cysteine proteinase (calpain) was originally referred to as an intracellular enzyme. However, recently it has come to be considered as an extracellular matrix proteinase, as well having a degrading effect on cartilage proteoglycan. In the present study we sought to determine whether human articular cartilage chondrocytes themselves have the capability to produce and secrete this interesting proteinase. METHODS: Human articular cartilage tissue cultures from osteoarthritic (11 specimens from 7 patients) and rheumatoid arthritic (3 specimens from 2 patients) knee joints were established, and the m-calpain released into the culture medium was concentrated and detected by immunoelectrophoretic blotting. The presence of m-calpain in the arthritic cartilage was also examined by immunohistochemistry before and after culturing. RESULTS: M-calpain was detectable in all of the cartilage tissue culture supernatants (conditioned medium) by western blotting. Positive intracellular immunostaining of m-calpain in chondrocytes was observed in all samples. Furthermore, m-calpain was found to be present in the matrix and on the articular surface of the cartilage in half of the specimens. CONCLUSION: The findings of our experiment suggest that cartilage chondrocytes may actively take part in m-calpain production and that they may have the capacity to release it into the extracellular matrices.[1]


  1. Externalization of calpain (calcium-dependent neutral cysteine proteinase) in human arthritic cartilage. Szomor, Z., Shimizu, K., Yamamoto, S., Yasuda, T., Ishikawa, H., Nakamura, T. Clinical and experimental rheumatology. (1999) [Pubmed]
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