Integrins are heterodimeric integral membrane proteins made up of α and β
subunits. At least eighteen α and eight β subunit genes have been described in
mammals. Integrin family members are plasma membrane receptors involved in
cell adhesion and active as intra- and extracellular signalling molecules in a variety
of processes including embryogenesis, hemostasis, tissue repair, immune response
and metastatic spread of tumour cells. Integrin beta 1 (β1-integrin), the protein
encoded by the ITGB1 gene (also known as CD29 and VLAB), is a multi-functional
protein involved in cell-matrix adhesion, cell signalling, cellular defense, cell adhesion,
protein binding, protein heterodimerisation and receptor-mediated activity. It
is highly expressed in the human body (17.4 times higher than the average gene in
the last updated revision of the human genome). The extracellular matrix (ECM) of
articular cartilage is a unique environment. Interactions between chondrocytes and
the ECM regulate many biological processes important to homeostasis and repair of
articular cartilage, including cell attachment, growth, differentiation and survival.
The β1-integrin family of cell surface receptors appears to play a major role in mediating
cell–matrix interactions that are important in regulating these fundamental
processes. Chondrocyte mechanoreceptors have been proposed to incorporate β1-
integrins and mechanosensitive ion channels which link with key ECM, cytoskeletal
and signalling proteins to maintain the chondrocyte phenotype, prevent chondrocyte
apoptosis and regulate chondrocyte-specific gene expression. This review
focuses on the expression and function of β1-integrins in articular chondrocytes,
its role in the unique biology of these cells and its distribution in cartilage.