TGF beta inhibits expression of SP-A, SP-B, SP-C, but not SP-D in human alveolar type II cells.

TGF beta is a multifunctional cytokine that regulates alveolar epithelial cells as well as immune cells and fibroblasts. TGF beta inhibits surfactant protein A, B and C expression in fetal human lung and can inhibit type II cell proliferation induced by FGF7 (KGF). However, little is known about direct effects of TGF beta on adult human type II cells. We cultured alveolar type II cells under air/liquid interface conditions to maintain their state of differentiation with or without TGF beta. TGF beta markedly decreased expression of SP-A, SP-B, SP-C, fatty acid synthase, and the phospholipid transporter ABCA3. However, TGF beta increased protein levels of SP-D with little change in mRNA levels, indicating that it is regulated independently from other components of surfactant. TGF beta is a negative regulator of both the protein and the phospholipid components of surfactant. TGF beta did not induce EMT changes in highly differentiated human type II cells. SP-D is an important host defense molecule and regulated independently from the other surfactant proteins. Taken together these data are the first report of the effect of TGF beta on highly differentiated adult human type II cells. The effects on the surfactant system are likely important in the development of fibrotic lung diseases.