Extracellular matrix receptors in the kidney cortex.

Extracellular matrix (ECM) receptors anchor cells to substratum and impart positional information to cells. Within the group of ECM receptors known as integrins, alpha-subunits of these alpha beta heterodimers define ligand specificity, whereas beta-subunits define the subclass. We used immunofluorescence with anti-ECM receptor antibodies to examine distribution within human kidney cortex of all known alpha-subunits in the beta 1 subclass of integrins as well as a non-integrin 67-kDa elastin/lamin receptor. The alpha 1-subunit (alpha 1 beta 1 defines a collagen receptor) was present in mesangium and base of all tubule epithelial cells; alpha 2 (collagen) was present in mesangium and in distal but not proximal tubule cells; alpha 3 (collagen, laminin, fibronectin) was diffusely distributed within glomeruli but tubule staining was less intense; alpha 4 (fibronectin) was absent; alpha 5 (fibronectin) was present in blood vessels; and alpha 6 (laminin) was present along basolateral aspect of all tubule cells but absent in glomeruli. The elastin/laminin receptor was present in all tubule epithelial cells, but staining was heavier in distal tubules, especially intercalated cells. Thus striking heterogeneity in ECM receptor distribution was noted. For collagen receptors, differences in tubule staining were pronounced. Despite the presence of laminin within both glomeruli and tubules, laminin receptors also showed marked differences in staining between these structures. Both differences in ECM structure and intrinsic differences among different cells may underlie these differences in ECM receptor distribution.