Expression of laminin α3, α4, and α5 chains by alveolar epithelial cells and fibroblasts

Laminins are principal components of basement membranes. Eleven laminin isoforms an known, each a heterotrimer composed of polypeptide chains designated alpha, beta, and gamma. Five alpha chains have been identified to date: alpha(1), alpha(2), alpha(3), alpha(4), and alpha(5). Recent studies of fetal and adult mouse lung show prominence of alpha(3), alpha(4), and alpha(5) in alveolar tissue, and point to differences in the cellular expression of these alpha chains in the developing alveolus. We examined isolated rat alveolar type II cells and lung fibroblasts for expression oflaminins alpha(3), alpha(4), and alpha(5). We found that laminin alpha(3) was expressed only by alveolar epithelial cells, that laminin alpha(4) was expressed only by lung fibroblasts, and that laminin alpha(5) was expressed primarily by alveolar epithelial cells. Metabolic labeling and immunoprecipitation confirmed the production of laminin alpha(4) by fibroblasts and laminin alpha(5) by alveolar epithelial cells in culture. These studies indicate that different alveolar cell types contribute different laminin alpha chains to the laminin isoforms in alveolar basement membranes. Immunohistochemistry showed colocalization of these laminin a chains with the laminin beta(1), beta(2), and gamma(1) chains, indicating the likelihood that laminins 6 to 11 an present in alveolar basement membranes.