Stimulation of DNA Synthesis in Cultured Rat Alveolar Type II Cells

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Abstract
The effect of potential mitogens and culture substrata on DNA synthesis in rat alveolar type II cells in primary culture was studied to determine the factors involved in type II cell proliferation. Type II cells cultured in basal medium containing 10% fetal bovine serum (FBS) exhibited essentially no DNA synthesis. Factors that stimulated 3H-thymidine incorporation included cholera toxin, epidermal growth factor and rat serum. The greatest degree of stimulation was achieved by plating type II cells on an extracellular matrix prepared from bovine corneal endothelial cells and then by culturing the pneumocytes in medium containing rat serum, cholera toxin, insulin and epidermal growth factor. Under conditions of stimulation of 3H-thymidine incorporation there was an increased DNA content culture disk but no increase in cell number. The ability of various culture conditions to promote DNA synthesis in type II cells was verified by autoradiography. Type II cells were identified by the presence of cytoplasmic inclusions, which were visualized by tannic acid staining before autoradiography. The importance of soluble factors and culture substratum in stimulating DNA synthesis in rat alveolar type II cells in primary culture are demonstrated.