Mechanical stress is an important regulator of chondrocyte functions but the mechanisms by which chondrocytes sense mechanical signals are unknown. Receptors for matrix molecules are likely involved in the mechanical signaling. In the first part of this study we identified
integrins with affinity for the cartilage-specific
collagen type II. We report that the
collagen-binding
integrins alpha 1 beta 1 and alpha 2 beta 1 isolated from bovine chondrocytes or human
chondrosarcoma cells bound
collagen type II as judged from affinity chromatography. The
integrins alpha 3 beta 1 or alpha 9 beta 1 did not bind
collagen type II-
Sepharose. In the second part of the study we investigated the effect of mechanical stress on expression of matrix molecules and
integrin subunits. Chondrocytes and
chondrosarcoma cells, cultured on uncoated flexible
silicone membranes in the presence of serum, were exposed to mechanical stress by the Flexercell system. Dynamic stimulation of chondrocytes for 3 h increased the
mRNA expression of
collagen type II and
aggrecan as judged by Northern blotting, while the beta 1-integrin subunit was not changed. When
chondrosarcoma cells were exposed to mechanical stimulation under the same conditions,
mRNA expression of alpha 5 was found to increase while beta 1, alpha 2, and alpha v did not increase to significant levels. In another study the effect of mechanical stress on
integrins was investigated when the cells were cultured on
collagen type II-coated flex-dishes. Three hours of dynamic stress increased the
mRNA expression of alpha 2-integrin subunit while the level of
mRNA for
integrin subunits beta 1, alpha 1, alpha 5, and alpha v showed no or small changes, indicating that matrix components may modulate the expression of
integrins during mechanical stress.