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.


CONCLUSIONS
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.
Szomor
Z
Z
Department of Orthopaedic Surgery, Faculty of Medicine, Kyoto University, Japan.
Shimizu
K
K
Yamamoto
S
S
Yasuda
T
T
Ishikawa
H
H
Nakamura
T
T
D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D002154:Calpain / Q000032:analysis* / Q000378:metabolism; D002358:Cartilage, Articular / Q000737:chemistry* / Q000201:enzymology; D019902:Chondrocytes / Q000201:enzymology; D006801:Humans; D015151:Immunoblotting; D007719:Knee Joint / Q000378:metabolism / Q000473:pathology; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology
D002154:Calpain