The transglutaminase (TGase) family includes seven different enzymes that catalyse a protein cross-linking reaction resulting in structural and functional alterations in substrate proteins. TGase activity is easily measureable in mature articular cartilage where it may contribute to CPPD deposition disease through its actions on growth factors, crystal components or extracellular matrix proteins. In contrast, low levels of TGase activity are found in chondrocytes from young animals. We previously demonstrated type II TGase protein in articular chondrocytes. Earlier work also suggested the presence of another form of TGase in chondrocytes. We sought to determine if articular chondrocytes contain the TGase, Factor XIIIA (FXIIIA).
Western blots with FXIIIA antibody were used to detect FXIIIA in young and old porcine articular chondrocytes and articular cartilage vesicles (ACVs). The presence of FXIIIA mRNA was confirmed by RT-PCR.
Old chondrocyte conditioned medium, cytosol, and membrane fractions contained FXIIIA protein on Western blots, while less FXIIIA was detectable in cell fractions or media from young chondrocytes. ACVs also contained FXIIIA. FXIIIA mRNA was demonstrated by PCR in old and young chondrocytes.
FXIIIA is present in articular chondrocytes. FXIIIA levels correlate with TGase activity in chondrocytes. The presence of two forms of TGase in articular chondrocytes suggest an important function for this enzyme family in articular cartilage.