Integrin Expression in Human Bone

Integrins are a family of heterodimeric transmembrane glycoproteins that are known to mediate cell-cell and cell-matrix interactions. Members of the VLA (very late activation) family, which consists of beta 1 integrin in association with the VLA alpha chains (alpha 1-6), mediate adhesion of a wide range of cells to matrix proteins, such as fibronectin, collagen, and laminin, and may therefore be important for cell-matrix interactions in bone. Integrin expression in human bone was studied immunohistochemically using cryostat sections of fracture callus, tumor-associated reactive bone, and neonatal costochondral junctions, with a panel of well-characterized antibodies against beta 1-4 integrins, alpha 1-6 and alpha V integrins, and the alpha V beta 3 dimer (the classic vitronectin receptor). All cell types present in bone expressed beta 1 and alpha 5 integrins; a subpopulation of osteoblastic cells expressed alpha 4. The alpha V was uniformly expressed by osteoblasts but was heterogeneously expressed by osteocytes. Osteoclasts also expressed alpha 2, alpha V, and alpha V beta 3. These results demonstrate differential expression of a restricted range of integrins in bone. This supports the possibility that integrins may mediate the differing interactions of cells of the osteoblast and osteoclast lineages with the matrix of bone.