Transglutaminase activity in aging articular chondrocytes and articular cartilage vesicles

✍ Scribed by Ann K. Rosenthal; Beth A. Derfus; Lisa A. Henry

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 565 KB
• Volume: 40
• Category: Article
• ISSN: 0004-3591
• DOI: 10.1002/art.1780400526

✦ Synopsis

Transglutaminases (TGases) (E.C. 2.3.2.13) catalyze a posttranslational modification of proteins and are associated with biomineralization in growth plate cartilage. Type I1 TGase participates in the activation of latent transforming growth factor P (TGFP), a crucial factor for both normal cartilage mineralization and the pathologic mineralization that results in calcium pyrophosphate dihydrate (CPPD) crystal formation in aging articular cartilage. To explore a possible association between TGase levels and CPPD crystal formation in mature articular cartilage, TGase activity in articular chondrocytes from old and young pigs and in the articular cartilage vesicle (ACV) fraction of porcine articular cartilage was examined. In addition, the effects of TGase inhibitors on the production of inorganic pyrophosphate (PPi), a process uecessary for CPPD crystallogenesis, were determined.

Methods. TGase activity was measured with a radiometric assay in cultured articular chondrocytes from the knee joints of old (5-5 years old) and young (2-6 weeks old) pigs and in the ACVs. PPi levels were measured in chondrocyte-conditioned media in the presence of TGase inhibitors or control compounds.

Results. Levels of TGase activity in the cytosolic fraction of old chondrocytes were 7-fold higher than those in identically cultured young chondrocytes. The mean f SD activity level in the membrane fraction of lysed chondrocytes was 6.0 f 0.6 units/mg protein in old articular chondrocytes and was undetectable in young chondrocytes. In ACVs, the mean f SD TGase activity