Involvement of α5β1 Integrin in Matrix Interactions and Proliferation of Chondrocytes

Abstract

Integrins are cell surface receptors involved in cellular processes including adhesion, migration, and matrix assembly. In the present study, we analyzed the possible involvement of α5β1 integrin in the regulation of chondrocyte adhesion, spreading, and proliferation. We found that rabbit growth plate chondrocytes were able to attach to substrates coated with type I collagen, type II collagen, or fibronectin within 24 h of culture. During this time period, attachment to fibronectin appeared to be dependent on α5β1 integrin, whereas adhesion to collagens was not. By day 3 of culture, chondrocytes spread onto all the substrates tested. We found that regardless of the nature of the substrate, cell spreading was reversed by treatment with RGD peptide or antibodies against α5β1 or fibronectin, indicating that cell spreading involved α5β1 and fibronectin endogenously produced and deposited by the chondrocytes themselves. Colony formation by chondrocytes in soft agar was inhibited by treatment with RGD peptides or BIIG2, an antibody that interferes with α5β1 integrin–ligand interactions. Furthermore, DNA content was decreased by treatment with anti‐fibronectin antibody in micromass culture of chondrocytes. Immunohistochemical analysis on tissue sections revealed that the α5 subunit was particularly abundant in the proliferative and hypertrophic zones of growth plate. The results of the study indicate that α5β1 integrin plays multiple roles in chondrocyte behavior and function and appears to be involved in the regulation of both chondrocyte–matrix interactions and proliferation.