Chondrocyte and Chondrosarcoma Cell Integrins with Affinity for Collagen Type II and Their Response to Mechanical Stress

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.