Transforming growth factor-β1 regulates basement membrane formation by alveolar epithelial cells in vitro

Immortalized alveolar type II epithelial (SV40-T2) cells formed a continuous, thin lamina densa when they were cultured on collagen fibrils with the supplement of 1.0ng/ml TGF-beta 1, Corresponding to lamina densa formation, immunohistochemical analysis of laminin, type IV collagen, perlecan, and entactin (nidogen) indicated integration of these components in a linear array beneath the SV40=T2 cells. Synthesis of these basement membrane constituents was significantly enhanced by TGF-beta 1 in a dose-dependent manner. On the other hand, TGF-beta 1 did not affect the synthesis of extracellular matrix-regulatory enzymes and their inhibitors, such as type II transglutaminase, matrix metalloproteinase-2, plasminogen activator inhibitor-1, or tissue inhibitor of matrix metalloproteinase-1, These results indicate that basement membrane formation in the presence of 1.0ng/ml TGF-beta 1 is attributable to enhanced synthesis of basement membrane constituents, However, formation of a continuous basement membrane was inhibited at a TGF-beta 1 concentration of 5.0 ngl ml, Synthesis of the basement membrane constituents was further enhanced at this concentration and the extracellular matrix-regulatory enzymes remained unchanged. The deposits of cellular fibronectin and type I collagen beneath SV40=T2 cells were significantly augmented. Thus excessive production of interstitial extracellular matrix components appears to obstruct the integration of basement membrane constituents into a continuous architecture, These results indicate that the basement membrane formation by SV40-T2 cells is achieved at the optimal TGF-beta 1 concentration.